[svn-r14903] Undoing change committed in r14902.

45 files changed, 5634 insertions, 5936 deletions

diff --git a/src/H5Adeprec.c b/src/H5Adeprec.c
index 9f888c8..85cef2f 100644
--- a/src/H5Adeprec.c
+++ b/src/H5Adeprec.c
@@ -312,6 +312,8 @@ H5Aget_num_attrs(hid_t loc_id)
     H5TRACE1("Is", "i", loc_id);
 
     /* check arguments */
+    if(H5I_BADID == H5I_get_type(loc_id))
+	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "bad location ID")
     if(H5I_FILE == H5I_get_type(loc_id) || H5I_ATTR == H5I_get_type(loc_id))
 	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "location is not valid for an attribute")
     if(NULL == (obj = H5I_object(loc_id)))
diff --git a/src/H5B2int.c b/src/H5B2int.c
index 2625c63..eae1291 100644
--- a/src/H5B2int.c
+++ b/src/H5B2int.c
@@ -203,7 +203,7 @@ HDmemset(shared->page, 0, shared->node_size);
 
     /* Compute size to store # of records in each node */
     /* (uses leaf # of records because its the largest) */
-    shared->max_nrec_size = (H5V_log2_gen((uint64_t)shared->node_info[0].max_nrec) + 7) / 8;
+    shared->max_nrec_size = H5V_limit_enc_size((uint64_t)shared->node_info[0].max_nrec);
     HDassert(shared->max_nrec_size <= H5B2_SIZEOF_RECORDS_PER_NODE);
 
     /* Initialize internal node info */
@@ -217,7 +217,7 @@ HDmemset(shared->page, 0, shared->node_size);
 
             shared->node_info[u].cum_max_nrec = ((shared->node_info[u].max_nrec + 1) * 
                 shared->node_info[u - 1].cum_max_nrec) + shared->node_info[u].max_nrec;
-            shared->node_info[u].cum_max_nrec_size = (H5V_log2_gen((uint64_t)shared->node_info[u].cum_max_nrec) + 7) / 8;
+            shared->node_info[u].cum_max_nrec_size = H5V_limit_enc_size((uint64_t)shared->node_info[u].cum_max_nrec);
 
             if((shared->node_info[u].nat_rec_fac = H5FL_fac_init(shared->type->nrec_size * shared->node_info[u].max_nrec)) == NULL)
                 HGOTO_ERROR(H5E_RESOURCE, H5E_CANTINIT, FAIL, "can't create node native key block factory")
@@ -576,7 +576,7 @@ H5B2_split_root(H5F_t *f, hid_t dxpl_id, H5B2_t *bt2, unsigned *bt2_flags_ptr)
     shared->node_info[shared->depth].merge_nrec = (shared->node_info[shared->depth].max_nrec * shared->merge_percent) / 100;
     shared->node_info[shared->depth].cum_max_nrec = ((shared->node_info[shared->depth].max_nrec + 1) * 
         shared->node_info[shared->depth - 1].cum_max_nrec) + shared->node_info[shared->depth].max_nrec;
-    shared->node_info[shared->depth].cum_max_nrec_size = (H5V_log2_gen((uint64_t)shared->node_info[shared->depth].cum_max_nrec) + 7) / 8;
+    shared->node_info[shared->depth].cum_max_nrec_size = H5V_limit_enc_size((uint64_t)shared->node_info[shared->depth].cum_max_nrec);
     if((shared->node_info[shared->depth].nat_rec_fac = H5FL_fac_init(shared->type->nrec_size * shared->node_info[shared->depth].max_nrec)) == NULL)
 	HGOTO_ERROR(H5E_RESOURCE, H5E_CANTINIT, FAIL, "can't create node native key block factory")
     if((shared->node_info[shared->depth].node_ptr_fac = H5FL_fac_init(sizeof(H5B2_node_ptr_t) * (shared->node_info[shared->depth].max_nrec + 1))) == NULL)
diff --git a/src/H5D.c b/src/H5D.c
index 7153ea5..7fd03b3 100644
--- a/src/H5D.c
+++ b/src/H5D.c
@@ -625,7 +625,7 @@ H5Dget_create_plist(hid_t dset_id)
                 H5I_dec_ref(src_id);
                 H5I_dec_ref(dst_id);
                 if(bkg_buf)
-                    H5FL_BLK_FREE(type_conv, bkg_buf);
+                    (void)H5FL_BLK_FREE(type_conv, bkg_buf);
                 HGOTO_ERROR(H5E_DATASET, H5E_CANTCONVERT, FAIL, "datatype conversion failed")
             } /* end if */
 
@@ -633,7 +633,7 @@ H5Dget_create_plist(hid_t dset_id)
             H5I_dec_ref(src_id);
             H5I_dec_ref(dst_id);
             if(bkg_buf)
-                H5FL_BLK_FREE(type_conv, bkg_buf);
+                (void)H5FL_BLK_FREE(type_conv, bkg_buf);
         } /* end if */
     } /* end if */
 
diff --git a/src/H5Dchunk.c b/src/H5Dchunk.c
new file mode 100644
index 0000000..baaa5f1
--- /dev/null
+++ b/src/H5Dchunk.c
@@ -0,0 +1,1515 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * Copyright by the Board of Trustees of the University of Illinois.         *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the files COPYING and Copyright.html.  COPYING can be found at the root   *
+ * of the source code distribution tree; Copyright.html can be found at the  *
+ * root level of an installed copy of the electronic HDF5 document set and   *
+ * is linked from the top-level documents page.  It can also be found at     *
+ * http://hdfgroup.org/HDF5/doc/Copyright.html.  If you do not have          *
+ * access to either file, you may request a copy from help@hdfgroup.org.     *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/****************/
+/* Module Setup */
+/****************/
+
+#define H5D_PACKAGE		/*suppress error about including H5Dpkg	  */
+
+
+/***********/
+/* Headers */
+/***********/
+#include "H5private.h"		/* Generic Functions			*/
+#include "H5Dpkg.h"		/* Dataset functions			*/
+#include "H5Eprivate.h"		/* Error handling		  	*/
+#include "H5FLprivate.h"	/* Free Lists                           */
+#include "H5Iprivate.h"		/* IDs			  		*/
+#ifdef H5_HAVE_PARALLEL
+#include "H5MMprivate.h"	/* Memory management			*/
+#endif /* H5_HAVE_PARALLEL */
+#include "H5Vprivate.h"		/* Vector and array functions		*/
+
+
+/****************/
+/* Local Macros */
+/****************/
+
+/* Default skip list height for storing list of chunks */
+#define H5D_DEFAULT_SKIPLIST_HEIGHT     8
+
+/* Macros for iterating over chunks to operate on */
+#define H5D_CHUNK_GET_FIRST_NODE(map) (map->use_single ? (H5SL_node_t *)(1) : H5SL_first(map->sel_chunks))
+#define H5D_CHUNK_GET_NODE_INFO(map, node)  (map->use_single ? map->single_chunk_info : (H5D_chunk_info_t *)H5SL_item(node))
+#define H5D_CHUNK_GET_NEXT_NODE(map, node)  (map->use_single ? (H5SL_node_t *)NULL : H5SL_next(node))
+
+
+/******************/
+/* Local Typedefs */
+/******************/
+
+
+/********************/
+/* Local Prototypes */
+/********************/
+
+/* Chunked layout operation callbacks */
+static herr_t H5D_chunk_io_init(const H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, hsize_t nelmts, const H5S_t *file_space,
+    const H5S_t *mem_space, H5D_chunk_map_t *fm);
+static herr_t H5D_chunk_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *fm);
+static herr_t H5D_chunk_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *fm);
+static herr_t H5D_chunk_io_term(const H5D_chunk_map_t *fm);
+
+/* "Null" layout operation callbacks */
+static ssize_t H5D_null_readvv(const H5D_io_info_t *io_info,
+    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[]);
+
+/* Helper routines */
+static herr_t H5D_free_chunk_info(void *item, void *key, void *opdata);
+static herr_t H5D_create_chunk_map_single(H5D_chunk_map_t *fm,
+    const H5D_io_info_t *io_info);
+static herr_t H5D_create_chunk_file_map_hyper(H5D_chunk_map_t *fm,
+    const H5D_io_info_t *io_info);
+static herr_t H5D_create_chunk_mem_map_hyper(const H5D_chunk_map_t *fm);
+static herr_t H5D_chunk_file_cb(void *elem, hid_t type_id, unsigned ndims,
+    const hsize_t *coords, void *fm);
+static herr_t H5D_chunk_mem_cb(void *elem, hid_t type_id, unsigned ndims,
+    const hsize_t *coords, void *fm);
+
+
+
+/*********************/
+/* Package Variables */
+/*********************/
+
+/* Compact storage layout I/O ops */
+const H5D_layout_ops_t H5D_LOPS_CHUNK[1] = {{
+    H5D_chunk_io_init,
+    H5D_chunk_read,
+    H5D_chunk_write,
+#ifdef H5_HAVE_PARALLEL
+    H5D_chunk_collective_read,
+    H5D_chunk_collective_write,
+#endif /* H5_HAVE_PARALLEL */
+    NULL,
+    NULL,
+    H5D_chunk_io_term
+}};
+
+
+/*******************/
+/* Local Variables */
+/*******************/
+
+/* "null" storage layout I/O ops */
+const H5D_layout_ops_t H5D_LOPS_NULL[1] = {{
+    NULL,
+    NULL,
+    NULL,
+#ifdef H5_HAVE_PARALLEL
+    NULL,
+    NULL,
+#endif /* H5_HAVE_PARALLEL */
+    H5D_null_readvv,
+    NULL,
+    NULL
+}};
+
+/* Declare a free list to manage the H5D_chunk_info_t struct */
+H5FL_DEFINE(H5D_chunk_info_t);
+
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_io_init
+ *
+ * Purpose:	Performs initialization before any sort of I/O on the raw data
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Thursday, March 20, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_chunk_io_init(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *fm)
+{
+    H5D_t *dataset = io_info->dset;     /* Local pointer to dataset info */
+    const H5T_t *mem_type = type_info->mem_type;        /* Local pointer to memory datatype */
+    H5S_t *tmp_mspace = NULL;   /* Temporary memory dataspace */
+    hssize_t old_offset[H5O_LAYOUT_NDIMS];  /* Old selection offset */
+    htri_t file_space_normalized = FALSE;   /* File dataspace was normalized */
+    hid_t f_tid = (-1);           /* Temporary copy of file datatype for iteration */
+    hbool_t iter_init = FALSE;  /* Selection iteration info has been initialized */
+    unsigned f_ndims;           /* The number of dimensions of the file's dataspace */
+    int sm_ndims;               /* The number of dimensions of the memory buffer's dataspace (signed) */
+    H5SL_node_t *curr_node;     /* Current node in skip list */
+    H5S_sel_type fsel_type;     /* Selection type on disk */
+    char bogus;                 /* "bogus" buffer to pass to selection iterator */
+    unsigned u;                 /* Local index variable */
+    hbool_t sel_hyper_flag;
+    herr_t ret_value = SUCCEED;	/* Return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_io_init)
+
+    /* Get layout for dataset */
+    fm->layout = &(dataset->shared->layout);
+    fm->nelmts = nelmts;
+
+    /* Check if the memory space is scalar & make equivalent memory space */
+    if((sm_ndims = H5S_GET_EXTENT_NDIMS(mem_space)) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "unable to get dimension number")
+    /* Set the number of dimensions for the memory dataspace */
+    H5_ASSIGN_OVERFLOW(fm->m_ndims, sm_ndims, int, unsigned);
+
+    /* Get dim number and dimensionality for each dataspace */
+    fm->f_ndims = f_ndims = dataset->shared->layout.u.chunk.ndims - 1;
+    if(H5S_get_simple_extent_dims(file_space, fm->f_dims, NULL) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "unable to get dimensionality")
+
+    /* Normalize hyperslab selections by adjusting them by the offset */
+    /* (It might be worthwhile to normalize both the file and memory dataspaces
+     * before any (contiguous, chunked, etc) file I/O operation, in order to
+     * speed up hyperslab calculations by removing the extra checks and/or
+     * additions involving the offset and the hyperslab selection -QAK)
+     */
+    if((file_space_normalized = H5S_hyper_normalize_offset((H5S_t *)file_space, old_offset)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to normalize dataspace by offset")
+
+    /* Decide the number of chunks in each dimension*/
+    for(u=0; u<f_ndims; u++) {
+        /* Keep the size of the chunk dimensions as hsize_t for various routines */
+        fm->chunk_dim[u]=fm->layout->u.chunk.dim[u];
+
+        /* Round up to the next integer # of chunks, to accomodate partial chunks */
+        fm->chunks[u] = ((fm->f_dims[u]+dataset->shared->layout.u.chunk.dim[u])-1) / dataset->shared->layout.u.chunk.dim[u];
+    } /* end for */
+
+    /* Compute the "down" size of 'chunks' information */
+    if(H5V_array_down(f_ndims,fm->chunks,fm->down_chunks) < 0)
+        HGOTO_ERROR(H5E_INTERNAL, H5E_BADVALUE, FAIL, "can't compute 'down' sizes")
+
+#ifdef H5_HAVE_PARALLEL
+    /* Calculate total chunk in file map*/
+    fm->select_chunk = NULL;
+    fm->total_chunks = 1;
+    for(u = 0; u < fm->f_ndims; u++)
+       fm->total_chunks = fm->total_chunks * fm->chunks[u];
+    if(io_info->using_mpi_vfd) {
+        H5_CHECK_OVERFLOW(fm->total_chunks, hsize_t, size_t);
+        if(NULL == (fm->select_chunk = (H5D_chunk_info_t **)H5MM_calloc((size_t)fm->total_chunks * sizeof(H5D_chunk_info_t *))))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
+    } /* end if */
+#endif /* H5_HAVE_PARALLEL */
+
+
+    /* Initialize "last chunk" information */
+    fm->last_index = (hsize_t)-1;
+    fm->last_chunk_info = NULL;
+
+    /* Point at the dataspaces */
+    fm->file_space = file_space;
+    fm->mem_space = mem_space;
+
+    /* Special case for only one element in selection */
+    /* (usually appending a record) */
+    if(nelmts == 1
+#ifdef H5_HAVE_PARALLEL
+            && !(io_info->using_mpi_vfd)
+#endif /* H5_HAVE_PARALLEL */
+        ) {
+        /* Initialize skip list for chunk selections */
+        fm->sel_chunks = NULL;
+        fm->use_single = TRUE;
+
+        /* Initialize single chunk dataspace */
+        if(NULL == dataset->shared->cache.chunk.single_space) {
+            /* Make a copy of the dataspace for the dataset */
+            if((dataset->shared->cache.chunk.single_space = H5S_copy(file_space, TRUE, FALSE)) == NULL)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy file space")
+
+            /* Resize chunk's dataspace dimensions to size of chunk */
+            if(H5S_set_extent_real(dataset->shared->cache.chunk.single_space, fm->chunk_dim) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't adjust chunk dimensions")
+
+            /* Set the single chunk dataspace to 'all' selection */
+            if(H5S_select_all(dataset->shared->cache.chunk.single_space, TRUE) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTSELECT, FAIL, "unable to set all selection")
+        } /* end if */
+        fm->single_space = dataset->shared->cache.chunk.single_space;
+        HDassert(fm->single_space);
+
+        /* Allocate the single chunk information */
+        if(NULL == dataset->shared->cache.chunk.single_chunk_info) {
+            if(NULL == (dataset->shared->cache.chunk.single_chunk_info = H5FL_MALLOC(H5D_chunk_info_t)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
+        } /* end if */
+        fm->single_chunk_info = dataset->shared->cache.chunk.single_chunk_info;
+        HDassert(fm->single_chunk_info);
+
+        /* Reset chunk template information */
+        fm->mchunk_tmpl = NULL;
+
+        /* Set up chunk mapping for single element */
+        if(H5D_create_chunk_map_single(fm, io_info) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create chunk selections for single element")
+    } /* end if */
+    else {
+        /* Initialize skip list for chunk selections */
+        if(NULL == dataset->shared->cache.chunk.sel_chunks) {
+            if(NULL == (dataset->shared->cache.chunk.sel_chunks = H5SL_create(H5SL_TYPE_HSIZE, 0.5, (size_t)H5D_DEFAULT_SKIPLIST_HEIGHT)))
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTCREATE, FAIL, "can't create skip list for chunk selections")
+        } /* end if */
+        fm->sel_chunks = dataset->shared->cache.chunk.sel_chunks;
+        HDassert(fm->sel_chunks);
+
+        /* We are not using single element mode */
+        fm->use_single = FALSE;
+
+        /* Get type of selection on disk & in memory */
+        if((fsel_type = H5S_GET_SELECT_TYPE(file_space)) < H5S_SEL_NONE)
+            HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to get type of selection")
+        if((fm->msel_type = H5S_GET_SELECT_TYPE(mem_space)) < H5S_SEL_NONE)
+            HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to get type of selection")
+
+        /* If the selection is NONE or POINTS, set the flag to FALSE */
+        if(fsel_type == H5S_SEL_POINTS || fsel_type == H5S_SEL_NONE)
+            sel_hyper_flag = FALSE;
+        else
+            sel_hyper_flag = TRUE;
+
+        /* Check if file selection is a not a hyperslab selection */
+        if(sel_hyper_flag) {
+            /* Build the file selection for each chunk */
+            if(H5D_create_chunk_file_map_hyper(fm, io_info) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create file chunk selections")
+
+            /* Clean file chunks' hyperslab span "scratch" information */
+            curr_node = H5SL_first(fm->sel_chunks);
+            while(curr_node) {
+                H5D_chunk_info_t *chunk_info;   /* Pointer chunk information */
+
+                /* Get pointer to chunk's information */
+                chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
+                HDassert(chunk_info);
+
+                /* Clean hyperslab span's "scratch" information */
+                if(H5S_hyper_reset_scratch(chunk_info->fspace) < 0)
+                    HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "unable to reset span scratch info")
+
+                /* Get the next chunk node in the skip list */
+                curr_node = H5SL_next(curr_node);
+            } /* end while */
+        } /* end if */
+        else {
+            /* Create temporary datatypes for selection iteration */
+            if((f_tid = H5I_register(H5I_DATATYPE, H5T_copy(dataset->shared->type, H5T_COPY_ALL))) < 0)
+                HGOTO_ERROR(H5E_DATATYPE, H5E_CANTREGISTER, FAIL, "unable to register file datatype")
+
+            /* Spaces might not be the same shape, iterate over the file selection directly */
+            if(H5S_select_iterate(&bogus, f_tid, file_space,  H5D_chunk_file_cb, fm) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create file chunk selections")
+
+            /* Reset "last chunk" info */
+            fm->last_index = (hsize_t)-1;
+            fm->last_chunk_info = NULL;
+        } /* end else */
+
+        /* Build the memory selection for each chunk */
+        if(sel_hyper_flag && H5S_select_shape_same(file_space, mem_space) == TRUE) {
+            /* Reset chunk template information */
+            fm->mchunk_tmpl = NULL;
+
+            /* If the selections are the same shape, use the file chunk information
+             * to generate the memory chunk information quickly.
+             */
+            if(H5D_create_chunk_mem_map_hyper(fm) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create memory chunk selections")
+        } /* end if */
+        else {
+            size_t elmt_size;           /* Memory datatype size */
+
+            /* Make a copy of equivalent memory space */
+            if((tmp_mspace = H5S_copy(mem_space, TRUE, FALSE)) == NULL)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy memory space")
+
+            /* De-select the mem space copy */
+            if(H5S_select_none(tmp_mspace) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to de-select memory space")
+
+            /* Save chunk template information */
+            fm->mchunk_tmpl = tmp_mspace;
+
+            /* Create temporary datatypes for selection iteration */
+            if(f_tid < 0) {
+                if((f_tid = H5I_register(H5I_DATATYPE, H5T_copy(dataset->shared->type, H5T_COPY_ALL))) < 0)
+                    HGOTO_ERROR(H5E_DATATYPE, H5E_CANTREGISTER, FAIL, "unable to register file datatype")
+            } /* end if */
+
+            /* Create selection iterator for memory selection */
+            if(0 == (elmt_size = H5T_get_size(mem_type)))
+                HGOTO_ERROR(H5E_DATATYPE, H5E_BADSIZE, FAIL, "datatype size invalid")
+            if(H5S_select_iter_init(&(fm->mem_iter), mem_space, elmt_size) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
+            iter_init = TRUE;	/* Selection iteration info has been initialized */
+
+            /* Spaces aren't the same shape, iterate over the memory selection directly */
+            if(H5S_select_iterate(&bogus, f_tid, file_space, H5D_chunk_mem_cb, fm) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create memory chunk selections")
+
+            /* Clean up hyperslab stuff, if necessary */
+            if(fm->msel_type != H5S_SEL_POINTS) {
+                /* Clean memory chunks' hyperslab span "scratch" information */
+                curr_node = H5SL_first(fm->sel_chunks);
+                while(curr_node) {
+                    H5D_chunk_info_t *chunk_info;   /* Pointer chunk information */
+
+                    /* Get pointer to chunk's information */
+                    chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
+                    HDassert(chunk_info);
+
+                    /* Clean hyperslab span's "scratch" information */
+                    if(H5S_hyper_reset_scratch(chunk_info->mspace) < 0)
+                        HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "unable to reset span scratch info")
+
+                    /* Get the next chunk node in the skip list */
+                    curr_node = H5SL_next(curr_node);
+                } /* end while */
+            } /* end if */
+        } /* end else */
+    } /* end else */
+
+done:
+    /* Release the [potentially partially built] chunk mapping information if an error occurs */
+    if(ret_value < 0) {
+        if(tmp_mspace && !fm->mchunk_tmpl) {
+            if(H5S_close(tmp_mspace) < 0)
+                HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "can't release memory chunk dataspace template")
+        } /* end if */
+
+        if(H5D_chunk_io_term(fm) < 0)
+            HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release chunk mapping")
+    } /* end if */
+
+    /* Reset the global dataspace info */
+    fm->file_space = NULL;
+    fm->mem_space = NULL;
+
+    if(iter_init) {
+        if(H5S_SELECT_ITER_RELEASE(&(fm->mem_iter)) < 0)
+            HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
+    } /* end if */
+    if(f_tid!=(-1)) {
+        if(H5I_dec_ref(f_tid) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't decrement temporary datatype ID")
+    } /* end if */
+    if(file_space_normalized) {
+        if(H5S_hyper_denormalize_offset((H5S_t *)file_space, old_offset) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to normalize dataspace by offset")
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_io_init() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5D_free_chunk_info
+ PURPOSE
+    Internal routine to destroy a chunk info node
+ USAGE
+    void H5D_free_chunk_info(chunk_info)
+        void *chunk_info;    IN: Pointer to chunk info to destroy
+ RETURNS
+    No return value
+ DESCRIPTION
+    Releases all the memory for a chunk info node.  Called by H5SL_free
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5D_free_chunk_info(void *item, void UNUSED *key, void UNUSED *opdata)
+{
+    H5D_chunk_info_t *chunk_info = (H5D_chunk_info_t *)item;
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_free_chunk_info)
+
+    HDassert(chunk_info);
+
+    /* Close the chunk's file dataspace, if it's not shared */
+    if(!chunk_info->fspace_shared)
+        (void)H5S_close(chunk_info->fspace);
+    else
+        H5S_select_all(chunk_info->fspace, TRUE);
+
+    /* Close the chunk's memory dataspace, if it's not shared */
+    if(!chunk_info->mspace_shared)
+        (void)H5S_close(chunk_info->mspace);
+
+    /* Free the actual chunk info */
+    H5FL_FREE(H5D_chunk_info_t, chunk_info);
+
+    FUNC_LEAVE_NOAPI(0)
+}   /* H5D_free_chunk_info() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_create_chunk_map_single
+ *
+ * Purpose:	Create chunk selections when appending a single record
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Tuesday, November 20, 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_create_chunk_map_single(H5D_chunk_map_t *fm, const H5D_io_info_t
+#ifndef H5_HAVE_PARALLEL
+    UNUSED
+#endif /* H5_HAVE_PARALLEL */
+    *io_info)
+{
+    H5D_chunk_info_t *chunk_info;           /* Chunk information to insert into skip list */
+    hsize_t     sel_start[H5O_LAYOUT_NDIMS]; /* Offset of low bound of file selection */
+    hsize_t     sel_end[H5O_LAYOUT_NDIMS];  /* Offset of high bound of file selection */
+    unsigned    u;                          /* Local index variable */
+    herr_t	ret_value = SUCCEED;        /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_create_chunk_map_single)
+
+    /* Sanity check */
+    HDassert(fm->f_ndims > 0);
+
+    /* Get coordinate for selection */
+    if(H5S_SELECT_BOUNDS(fm->file_space, sel_start, sel_end) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
+
+    /* Initialize the 'single chunk' file & memory chunk information */
+    chunk_info = fm->single_chunk_info;
+    chunk_info->chunk_points = 1;
+
+    /* Set chunk location & hyperslab size */
+    for(u = 0; u < fm->f_ndims; u++) {
+        HDassert(sel_start[u] == sel_end[u]);
+        chunk_info->coords[u] = (sel_start[u] / fm->layout->u.chunk.dim[u]) * fm->layout->u.chunk.dim[u];
+    } /* end for */
+    chunk_info->coords[fm->f_ndims] = 0;
+
+    /* Calculate the index of this chunk */
+    if(H5V_chunk_index(fm->f_ndims, chunk_info->coords, fm->layout->u.chunk.dim, fm->down_chunks, &chunk_info->index) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
+
+    /* Copy selection for file's dataspace into chunk dataspace */
+    if(H5S_select_copy(fm->single_space, fm->file_space, FALSE) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy file selection")
+
+    /* Move selection back to have correct offset in chunk */
+    if(H5S_SELECT_ADJUST_U(fm->single_space, chunk_info->coords) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk selection")
+
+#ifdef H5_HAVE_PARALLEL
+    /* store chunk selection information */
+    if(io_info->using_mpi_vfd)
+        fm->select_chunk[chunk_info->index] = chunk_info;
+#endif /* H5_HAVE_PARALLEL */
+
+    /* Set the file dataspace for the chunk to the shared 'single' dataspace */
+    chunk_info->fspace = fm->single_space;
+
+    /* Indicate that the chunk's file dataspace is shared */
+    chunk_info->fspace_shared = TRUE;
+
+    /* Just point at the memory dataspace & selection */
+    /* (Casting away const OK -QAK) */
+    chunk_info->mspace = (H5S_t *)fm->mem_space;
+
+    /* Indicate that the chunk's memory dataspace is shared */
+    chunk_info->mspace_shared = TRUE;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_create_chunk_map_single() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_create_chunk_file_map_hyper
+ *
+ * Purpose:	Create all chunk selections in file.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Thursday, May 29, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_create_chunk_file_map_hyper(H5D_chunk_map_t *fm, const H5D_io_info_t
+#ifndef H5_HAVE_PARALLEL
+    UNUSED
+#endif /* H5_HAVE_PARALLEL */
+    *io_info)
+{
+    hsize_t     sel_start[H5O_LAYOUT_NDIMS];   /* Offset of low bound of file selection */
+    hsize_t     sel_end[H5O_LAYOUT_NDIMS];   /* Offset of high bound of file selection */
+    hsize_t     sel_points;                 /* Number of elements in file selection */
+    hsize_t     start_coords[H5O_LAYOUT_NDIMS];   /* Starting coordinates of selection */
+    hsize_t     coords[H5O_LAYOUT_NDIMS];   /* Current coordinates of chunk */
+    hsize_t     end[H5O_LAYOUT_NDIMS];      /* Current coordinates of chunk */
+    hsize_t     chunk_index;                /* Index of chunk */
+    int         curr_dim;                   /* Current dimension to increment */
+    unsigned    u;                          /* Local index variable */
+    herr_t	ret_value = SUCCEED;        /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_create_chunk_file_map_hyper)
+
+    /* Sanity check */
+    assert(fm->f_ndims>0);
+
+    /* Get number of elements selected in file */
+    sel_points = fm->nelmts;
+
+    /* Get bounding box for selection (to reduce the number of chunks to iterate over) */
+    if(H5S_SELECT_BOUNDS(fm->file_space, sel_start, sel_end) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
+
+    /* Set initial chunk location & hyperslab size */
+
+    for(u=0; u<fm->f_ndims; u++) {
+        start_coords[u]=(sel_start[u]/fm->layout->u.chunk.dim[u])*fm->layout->u.chunk.dim[u];
+        coords[u]=start_coords[u];
+        end[u]=(coords[u]+fm->chunk_dim[u])-1;
+    } /* end for */
+
+
+    /* Calculate the index of this chunk */
+    if(H5V_chunk_index(fm->f_ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
+
+    /* Iterate through each chunk in the dataset */
+    while(sel_points) {
+        /* Check for intersection of temporary chunk and file selection */
+        /* (Casting away const OK - QAK) */
+        if(H5S_hyper_intersect_block((H5S_t *)fm->file_space,coords,end)==TRUE) {
+            H5S_t *tmp_fchunk;                  /* Temporary file dataspace */
+            H5D_chunk_info_t *new_chunk_info;   /* chunk information to insert into skip list */
+            hssize_t    schunk_points;          /* Number of elements in chunk selection */
+
+            /* Create "temporary" chunk for selection operations (copy file space) */
+            if((tmp_fchunk = H5S_copy(fm->file_space, TRUE, FALSE)) == NULL)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy memory space")
+
+            /* Make certain selections are stored in span tree form (not "optimized hyperslab" or "all") */
+            if(H5S_hyper_convert(tmp_fchunk) < 0) {
+                (void)H5S_close(tmp_fchunk);
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to convert selection to span trees")
+            } /* end if */
+
+            /* "AND" temporary chunk and current chunk */
+            if(H5S_select_hyperslab(tmp_fchunk,H5S_SELECT_AND,coords,NULL,fm->chunk_dim,NULL) < 0) {
+                (void)H5S_close(tmp_fchunk);
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't create chunk selection")
+            } /* end if */
+
+            /* Resize chunk's dataspace dimensions to size of chunk */
+            if(H5S_set_extent_real(tmp_fchunk,fm->chunk_dim) < 0) {
+                (void)H5S_close(tmp_fchunk);
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk dimensions")
+            } /* end if */
+
+            /* Move selection back to have correct offset in chunk */
+            if(H5S_SELECT_ADJUST_U(tmp_fchunk, coords) < 0) {
+                (void)H5S_close(tmp_fchunk);
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk selection")
+            } /* end if */
+
+            /* Add temporary chunk to the list of chunks */
+
+            /* Allocate the file & memory chunk information */
+            if (NULL==(new_chunk_info = H5FL_MALLOC (H5D_chunk_info_t))) {
+                (void)H5S_close(tmp_fchunk);
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
+            } /* end if */
+
+            /* Initialize the chunk information */
+
+            /* Set the chunk index */
+            new_chunk_info->index=chunk_index;
+
+#ifdef H5_HAVE_PARALLEL
+            /* store chunk selection information */
+            if(io_info->using_mpi_vfd)
+                fm->select_chunk[chunk_index] = new_chunk_info;
+#endif /* H5_HAVE_PARALLEL */
+
+            /* Set the file chunk dataspace */
+            new_chunk_info->fspace = tmp_fchunk;
+            new_chunk_info->fspace_shared = FALSE;
+
+            /* Set the memory chunk dataspace */
+            new_chunk_info->mspace=NULL;
+            new_chunk_info->mspace_shared = FALSE;
+
+            /* Copy the chunk's coordinates */
+            for(u=0; u<fm->f_ndims; u++)
+                new_chunk_info->coords[u]=coords[u];
+            new_chunk_info->coords[fm->f_ndims]=0;
+
+            /* Insert the new chunk into the skip list */
+            if(H5SL_insert(fm->sel_chunks,new_chunk_info,&new_chunk_info->index) < 0) {
+                H5D_free_chunk_info(new_chunk_info,NULL,NULL);
+                HGOTO_ERROR(H5E_DATASPACE,H5E_CANTINSERT,FAIL,"can't insert chunk into skip list")
+            } /* end if */
+
+            /* Get number of elements selected in chunk */
+            if((schunk_points=H5S_GET_SELECT_NPOINTS(tmp_fchunk)) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection # of elements")
+            H5_ASSIGN_OVERFLOW(new_chunk_info->chunk_points,schunk_points,hssize_t,size_t);
+
+            /* Decrement # of points left in file selection */
+            sel_points-=(hsize_t)schunk_points;
+
+            /* Leave if we are done */
+            if(sel_points==0)
+                HGOTO_DONE(SUCCEED)
+            assert(sel_points>0);
+        } /* end if */
+
+        /* Increment chunk index */
+        chunk_index++;
+
+        /* Set current increment dimension */
+        curr_dim=(int)fm->f_ndims-1;
+
+        /* Increment chunk location in fastest changing dimension */
+        H5_CHECK_OVERFLOW(fm->chunk_dim[curr_dim],hsize_t,hssize_t);
+        coords[curr_dim]+=fm->chunk_dim[curr_dim];
+        end[curr_dim]+=fm->chunk_dim[curr_dim];
+
+        /* Bring chunk location back into bounds, if necessary */
+        if(coords[curr_dim]>sel_end[curr_dim]) {
+            do {
+                /* Reset current dimension's location to 0 */
+                coords[curr_dim]=start_coords[curr_dim]; /*lint !e771 The start_coords will always be initialized */
+                end[curr_dim]=(coords[curr_dim]+(hssize_t)fm->chunk_dim[curr_dim])-1;
+
+                /* Decrement current dimension */
+                curr_dim--;
+
+                /* Increment chunk location in current dimension */
+                coords[curr_dim]+=fm->chunk_dim[curr_dim];
+                end[curr_dim]=(coords[curr_dim]+fm->chunk_dim[curr_dim])-1;
+            } while(coords[curr_dim]>sel_end[curr_dim]);
+
+            /* Re-Calculate the index of this chunk */
+            if(H5V_chunk_index(fm->f_ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
+        } /* end if */
+    } /* end while */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_create_chunk_file_map_hyper() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_create_chunk_mem_map_hyper
+ *
+ * Purpose:	Create all chunk selections in memory by copying the file
+ *              chunk selections and adjusting their offsets to be correct
+ *              for the memory.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Thursday, May 29, 2003
+ *
+ * Assumptions: That the file and memory selections are the same shape.
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_create_chunk_mem_map_hyper(const H5D_chunk_map_t *fm)
+{
+    H5SL_node_t *curr_node;                 /* Current node in skip list */
+    hsize_t    file_sel_start[H5O_LAYOUT_NDIMS];    /* Offset of low bound of file selection */
+    hsize_t    file_sel_end[H5O_LAYOUT_NDIMS];  /* Offset of high bound of file selection */
+    hsize_t    mem_sel_start[H5O_LAYOUT_NDIMS]; /* Offset of low bound of file selection */
+    hsize_t    mem_sel_end[H5O_LAYOUT_NDIMS];   /* Offset of high bound of file selection */
+    hssize_t adjust[H5O_LAYOUT_NDIMS];      /* Adjustment to make to all file chunks */
+    hssize_t chunk_adjust[H5O_LAYOUT_NDIMS];  /* Adjustment to make to a particular chunk */
+    unsigned    u;                          /* Local index variable */
+    herr_t	ret_value = SUCCEED;        /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_create_chunk_mem_map_hyper)
+
+    /* Sanity check */
+    assert(fm->f_ndims>0);
+
+    /* Check for all I/O going to a single chunk */
+    if(H5SL_count(fm->sel_chunks)==1) {
+        H5D_chunk_info_t *chunk_info;   /* Pointer to chunk information */
+
+        /* Get the node */
+        curr_node=H5SL_first(fm->sel_chunks);
+
+        /* Get pointer to chunk's information */
+        chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
+        assert(chunk_info);
+
+        /* Just point at the memory dataspace & selection */
+        /* (Casting away const OK -QAK) */
+        chunk_info->mspace=(H5S_t *)fm->mem_space;
+
+        /* Indicate that the chunk's memory space is shared */
+        chunk_info->mspace_shared = TRUE;
+    } /* end if */
+    else {
+        /* Get bounding box for file selection */
+        if(H5S_SELECT_BOUNDS(fm->file_space, file_sel_start, file_sel_end) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
+
+        /* Get bounding box for memory selection */
+        if(H5S_SELECT_BOUNDS(fm->mem_space, mem_sel_start, mem_sel_end) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
+
+        /* Calculate the adjustment for memory selection from file selection */
+        assert(fm->m_ndims==fm->f_ndims);
+        for(u=0; u<fm->f_ndims; u++) {
+            H5_CHECK_OVERFLOW(file_sel_start[u],hsize_t,hssize_t);
+            H5_CHECK_OVERFLOW(mem_sel_start[u],hsize_t,hssize_t);
+            adjust[u]=(hssize_t)file_sel_start[u]-(hssize_t)mem_sel_start[u];
+        } /* end for */
+
+        /* Iterate over each chunk in the chunk list */
+        curr_node=H5SL_first(fm->sel_chunks);
+        while(curr_node) {
+            H5D_chunk_info_t *chunk_info;   /* Pointer to chunk information */
+
+            /* Get pointer to chunk's information */
+            chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
+            assert(chunk_info);
+
+            /* Copy the information */
+
+            /* Copy the memory dataspace */
+            if((chunk_info->mspace = H5S_copy(fm->mem_space, TRUE, FALSE)) == NULL)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy memory space")
+
+            /* Release the current selection */
+            if(H5S_SELECT_RELEASE(chunk_info->mspace) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection")
+
+            /* Copy the file chunk's selection */
+            if(H5S_select_copy(chunk_info->mspace,chunk_info->fspace,FALSE) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy selection")
+
+            /* Compensate for the chunk offset */
+            for(u=0; u<fm->f_ndims; u++) {
+                H5_CHECK_OVERFLOW(chunk_info->coords[u],hsize_t,hssize_t);
+                chunk_adjust[u]=adjust[u]-(hssize_t)chunk_info->coords[u]; /*lint !e771 The adjust array will always be initialized */
+            } /* end for */
+
+            /* Adjust the selection */
+            if(H5S_hyper_adjust_s(chunk_info->mspace,chunk_adjust) < 0) /*lint !e772 The chunk_adjust array will always be initialized */
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk selection")
+
+            /* Get the next chunk node in the skip list */
+            curr_node=H5SL_next(curr_node);
+        } /* end while */
+    } /* end else */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_create_chunk_mem_map_hyper() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_file_cb
+ *
+ * Purpose:	Callback routine for file selection iterator.  Used when
+ *              creating selections in file for each point selected.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Wednesday, July 23, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_chunk_file_cb(void UNUSED *elem, hid_t UNUSED type_id, unsigned ndims, const hsize_t *coords, void *_fm)
+{
+    H5D_chunk_map_t      *fm = (H5D_chunk_map_t *)_fm;  /* File<->memory chunk mapping info */
+    H5D_chunk_info_t *chunk_info;               /* Chunk information for current chunk */
+    hsize_t    coords_in_chunk[H5O_LAYOUT_NDIMS];        /* Coordinates of element in chunk */
+    hsize_t     chunk_index;                    /* Chunk index */
+    unsigned    u;                              /* Local index variable */
+    herr_t	ret_value = SUCCEED;            /* Return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_file_cb)
+
+    /* Calculate the index of this chunk */
+    if(H5V_chunk_index(ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
+
+    /* Find correct chunk in file & memory skip list */
+    if(chunk_index==fm->last_index) {
+        /* If the chunk index is the same as the last chunk index we used,
+         * get the cached info to operate on.
+         */
+        chunk_info=fm->last_chunk_info;
+    } /* end if */
+    else {
+        /* If the chunk index is not the same as the last chunk index we used,
+         * find the chunk in the skip list.
+         */
+        /* Get the chunk node from the skip list */
+        if(NULL == (chunk_info = (H5D_chunk_info_t *)H5SL_search(fm->sel_chunks, &chunk_index))) {
+            H5S_t *fspace;                      /* Memory chunk's dataspace */
+
+            /* Allocate the file & memory chunk information */
+            if (NULL==(chunk_info = H5FL_MALLOC (H5D_chunk_info_t)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
+
+            /* Initialize the chunk information */
+
+            /* Set the chunk index */
+            chunk_info->index=chunk_index;
+
+            /* Create a dataspace for the chunk */
+            if((fspace = H5S_create_simple(fm->f_ndims,fm->chunk_dim,NULL))==NULL) {
+                H5FL_FREE(H5D_chunk_info_t,chunk_info);
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCREATE, FAIL, "unable to create dataspace for chunk")
+            } /* end if */
+
+            /* De-select the chunk space */
+            if(H5S_select_none(fspace) < 0) {
+                (void)H5S_close(fspace);
+                H5FL_FREE(H5D_chunk_info_t,chunk_info);
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to de-select dataspace")
+            } /* end if */
+
+            /* Set the file chunk dataspace */
+            chunk_info->fspace = fspace;
+            chunk_info->fspace_shared = FALSE;
+
+            /* Set the memory chunk dataspace */
+            chunk_info->mspace=NULL;
+            chunk_info->mspace_shared = FALSE;
+
+            /* Set the number of selected elements in chunk to zero */
+            chunk_info->chunk_points=0;
+
+            /* Compute the chunk's coordinates */
+            for(u=0; u<fm->f_ndims; u++) {
+                H5_CHECK_OVERFLOW(fm->layout->u.chunk.dim[u],hsize_t,hssize_t);
+                chunk_info->coords[u]=(coords[u]/(hssize_t)fm->layout->u.chunk.dim[u])*(hssize_t)fm->layout->u.chunk.dim[u];
+            } /* end for */
+            chunk_info->coords[fm->f_ndims]=0;
+
+            /* Insert the new chunk into the skip list */
+            if(H5SL_insert(fm->sel_chunks,chunk_info,&chunk_info->index) < 0) {
+                H5D_free_chunk_info(chunk_info,NULL,NULL);
+                HGOTO_ERROR(H5E_DATASPACE,H5E_CANTINSERT,FAIL,"can't insert chunk into skip list")
+            } /* end if */
+        } /* end if */
+
+        /* Update the "last chunk seen" information */
+        fm->last_index=chunk_index;
+        fm->last_chunk_info=chunk_info;
+    } /* end else */
+
+    /* Get the coordinates of the element in the chunk */
+    for(u=0; u<fm->f_ndims; u++)
+        coords_in_chunk[u]=coords[u]%fm->layout->u.chunk.dim[u];
+
+    /* Add point to file selection for chunk */
+    if(H5S_select_elements(chunk_info->fspace, H5S_SELECT_APPEND, (size_t)1, coords_in_chunk) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "unable to select element")
+
+    /* Increment the number of elemented selected in chunk */
+    chunk_info->chunk_points++;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_file_cb() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_mem_cb
+ *
+ * Purpose:	Callback routine for file selection iterator.  Used when
+ *              creating selections in memory for each chunk.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Raymond Lu
+ *		Thursday, April 10, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+/* ARGSUSED */
+static herr_t
+H5D_chunk_mem_cb(void UNUSED *elem, hid_t UNUSED type_id, unsigned ndims, const hsize_t *coords, void *_fm)
+{
+    H5D_chunk_map_t      *fm = (H5D_chunk_map_t *)_fm;  /* File<->memory chunk mapping info */
+    H5D_chunk_info_t *chunk_info;               /* Chunk information for current chunk */
+    hsize_t    coords_in_mem[H5O_LAYOUT_NDIMS];        /* Coordinates of element in memory */
+    hsize_t     chunk_index;                    /* Chunk index */
+    herr_t	ret_value = SUCCEED;            /* Return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_mem_cb)
+
+    /* Calculate the index of this chunk */
+    if(H5V_chunk_index(ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
+
+    /* Find correct chunk in file & memory skip list */
+    if(chunk_index==fm->last_index) {
+        /* If the chunk index is the same as the last chunk index we used,
+         * get the cached spaces to operate on.
+         */
+        chunk_info=fm->last_chunk_info;
+    } /* end if */
+    else {
+        /* If the chunk index is not the same as the last chunk index we used,
+         * find the chunk in the skip list.
+         */
+        /* Get the chunk node from the skip list */
+        if(NULL == (chunk_info = (H5D_chunk_info_t *)H5SL_search(fm->sel_chunks, &chunk_index)))
+            HGOTO_ERROR(H5E_DATASPACE, H5E_NOTFOUND, FAIL, "can't locate chunk in skip list")
+
+        /* Check if the chunk already has a memory space */
+        if(chunk_info->mspace==NULL) {
+            /* Copy the template memory chunk dataspace */
+            if((chunk_info->mspace = H5S_copy(fm->mchunk_tmpl, FALSE, FALSE)) == NULL)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy file space")
+        } /* end else */
+
+        /* Update the "last chunk seen" information */
+        fm->last_index=chunk_index;
+        fm->last_chunk_info=chunk_info;
+    } /* end else */
+
+    /* Get coordinates of selection iterator for memory */
+    if(H5S_SELECT_ITER_COORDS(&fm->mem_iter,coords_in_mem) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "unable to get iterator coordinates")
+
+    /* Add point to memory selection for chunk */
+    if(fm->msel_type==H5S_SEL_POINTS) {
+        if(H5S_select_elements(chunk_info->mspace, H5S_SELECT_APPEND, (size_t)1, coords_in_mem) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "unable to select element")
+    } /* end if */
+    else {
+        if(H5S_hyper_add_span_element(chunk_info->mspace, fm->m_ndims, coords_in_mem) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "unable to select element")
+    } /* end else */
+
+    /* Move memory selection iterator to next element in selection */
+    if(H5S_SELECT_ITER_NEXT(&fm->mem_iter, (size_t)1) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTNEXT, FAIL, "unable to move to next iterator location")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_mem_cb() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_cacheable
+ *
+ * Purpose:	A small internal function to if it's possible to load the
+ *              chunk into cache.
+ *
+ * Return:	TRUE or FALSE
+ *
+ * Programmer:	Raymond Lu
+ *		17 July 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+hbool_t 
+H5D_chunk_cacheable(const H5D_io_info_t *io_info, haddr_t caddr)
+{
+    const H5D_t *dataset = io_info->dset;
+    hbool_t ret_value;
+ 
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_chunk_cacheable)
+
+    HDassert(io_info);
+    HDassert(dataset);
+
+    /* Must bring the whole chunk in if there are any filters */
+    if(dataset->shared->dcpl_cache.pline.nused > 0)
+        ret_value = TRUE;
+    else
+#ifdef H5_HAVE_PARALLEL
+         /* If MPI based VFD is used and the file is opened for write access, must
+          *         bypass the chunk-cache scheme because other MPI processes could
+          *         be writing to other elements in the same chunk.  Do a direct
+          *         write-through of only the elements requested.
+          */
+        if(io_info->using_mpi_vfd && (H5F_ACC_RDWR & H5F_INTENT(dataset->oloc.file)))
+            ret_value = FALSE;
+        else
+#endif /* H5_HAVE_PARALLEL */
+            /* If the chunk is too large to keep in the cache and if the address
+             * for the chunk has been defined, then don't load the chunk into the
+             * cache, just write the data to it directly.
+             */
+            if(dataset->shared->layout.u.chunk.size > dataset->shared->cache.chunk.nbytes
+                    && H5F_addr_defined(caddr))
+                ret_value = FALSE;
+            else
+                ret_value = TRUE;
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_cacheable() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_in_cache
+ *
+ * Purpose:	Check if a chunk is in the cache.
+ *
+ * Return:	TRUE or FALSE
+ *
+ * Programmer:	Quincey Koziol
+ *		1 April 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static hbool_t 
+H5D_chunk_in_cache(const H5D_io_info_t *io_info)
+{
+    H5D_rdcc_t	*rdcc = &(io_info->dset->shared->cache.chunk);/*raw data chunk cache*/
+    hbool_t	found = FALSE;		/*already in cache?	*/
+ 
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_chunk_in_cache)
+
+    HDassert(io_info);
+
+    /* Check if the chunk is in the cache (but hasn't been written to disk yet) */
+    if(rdcc->nslots > 0) {
+        unsigned idx = H5D_CHUNK_HASH(io_info->dset->shared, io_info->store->chunk.index); /* Cache entry index */
+        H5D_rdcc_ent_t	*ent = rdcc->slot[idx]; /* Cache entry */
+
+        /* Potential match... */
+        if(ent) {
+            size_t u;           /* Local index variable */
+
+            for(u = 0, found = TRUE; u < io_info->dset->shared->layout.u.chunk.ndims; u++) {
+                if(io_info->store->chunk.offset[u] != ent->offset[u]) {
+                    found = FALSE;
+                    break;
+                } /* end if */
+            } /* end for */
+        } /* end if */
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(found)
+} /* end H5D_chunk_in_cache() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_read
+ *
+ * Purpose:	Read from a chunked dataset.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Raymond Lu
+ *		Thursday, April 10, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_chunk_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t UNUSED nelmts, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space,
+    H5D_chunk_map_t *fm)
+{
+    H5SL_node_t *chunk_node;            /* Current node in chunk skip list */
+    H5D_io_info_t nul_io_info;          /* "null" I/O info object */
+    H5D_io_info_t ctg_io_info;          /* Contiguous I/O info object */
+    H5D_storage_t ctg_store;            /* Chunk storage information as contiguous dataset */
+    H5D_io_info_t cpt_io_info;          /* Compact I/O info object */
+    H5D_storage_t cpt_store;            /* Chunk storage information as compact dataset */
+    hbool_t     cpt_dirty;              /* Temporary placeholder for compact storage "dirty" flag */
+    size_t      src_accessed_bytes = 0; /* Total accessed size in a chunk */
+    hbool_t     skip_missing_chunks = FALSE;    /* Whether to skip missing chunks */
+    unsigned    idx_hint = 0;           /* Cache index hint      */
+    herr_t	ret_value = SUCCEED;	/*return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_read)
+
+    /* Sanity check */
+    HDassert(io_info);
+    HDassert(io_info->u.rbuf);
+    HDassert(type_info);
+    HDassert(fm);
+
+    /* Set up "null" I/O info object */
+    HDmemcpy(&nul_io_info, io_info, sizeof(nul_io_info));
+    nul_io_info.layout_ops = *H5D_LOPS_NULL;
+
+    /* Set up contiguous I/O info object */
+    HDmemcpy(&ctg_io_info, io_info, sizeof(ctg_io_info));
+    ctg_io_info.store = &ctg_store;
+    ctg_io_info.layout_ops = *H5D_LOPS_CONTIG;
+
+    /* Initialize temporary contiguous storage info */
+    ctg_store.contig.dset_size = (hsize_t)io_info->dset->shared->layout.u.chunk.size;
+
+    /* Set up compact I/O info object */
+    HDmemcpy(&cpt_io_info, io_info, sizeof(cpt_io_info));
+    cpt_io_info.store = &cpt_store;
+    cpt_io_info.layout_ops = *H5D_LOPS_COMPACT;
+
+    /* Initialize temporary compact storage info */
+    cpt_store.compact.dirty = &cpt_dirty;
+
+    {
+        const H5O_fill_t *fill = &(io_info->dset->shared->dcpl_cache.fill);    /* Fill value info */
+        H5D_fill_value_t fill_status;       /* Fill value status */
+
+        /* Check the fill value status */
+        if(H5P_is_fill_value_defined(fill, &fill_status) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't tell if fill value defined")
+
+        /* If we are never to return fill values, or if we would return them
+         * but they aren't set, set the flag to skip missing chunks.
+         */
+        if(fill->fill_time == H5D_FILL_TIME_NEVER ||
+                (fill->fill_time == H5D_FILL_TIME_IFSET && fill_status != H5D_FILL_VALUE_USER_DEFINED))
+            skip_missing_chunks = TRUE;
+    }
+
+    /* Iterate through nodes in chunk skip list */
+    chunk_node = H5D_CHUNK_GET_FIRST_NODE(fm);
+    while(chunk_node) {
+        H5D_chunk_info_t *chunk_info;   /* Chunk information */
+        H5D_io_info_t *chk_io_info;     /* Pointer to I/O info object for this chunk */
+        void *chunk;                    /* Pointer to locked chunk buffer */
+        haddr_t	chunk_addr;             /* Chunk address on disk */
+        H5D_istore_ud1_t udata;		/* B-tree pass-through	*/
+
+        /* Get the actual chunk information from the skip list node */
+        chunk_info = H5D_CHUNK_GET_NODE_INFO(fm, chunk_node);
+
+        /* Pass in chunk's coordinates in a union. */
+        io_info->store->chunk.offset = chunk_info->coords;
+        io_info->store->chunk.index = chunk_info->index;
+
+        /* Get the address of the chunk in the file */
+        chunk_addr = H5D_istore_get_addr(io_info, &udata);
+
+        /* Check for non-existant chunk & skip it if appropriate */
+        if(!H5F_addr_defined(chunk_addr) && !H5D_chunk_in_cache(io_info)
+                && skip_missing_chunks) {
+            /* No chunk cached */
+            chunk = NULL;
+
+            /* Point I/O info at "null" I/O info for this chunk */
+            chk_io_info = &nul_io_info;
+        } /* end if */
+        else {
+            /* Load the chunk into cache and lock it. */
+            if(H5D_chunk_cacheable(io_info, chunk_addr)) {
+                /* Compute # of bytes accessed in chunk */
+                src_accessed_bytes = chunk_info->chunk_points * type_info->src_type_size;
+
+                /* Lock the chunk into the cache */
+                if(NULL == (chunk = H5D_istore_lock(io_info, &udata, FALSE, &idx_hint)))
+                    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
+
+                /* Set up the storage buffer information for this chunk */
+                cpt_store.compact.buf = chunk;
+
+                /* Point I/O info at contiguous I/O info for this chunk */
+                chk_io_info = &cpt_io_info;
+            } /* end if */
+            else {
+                /* Sanity check */
+                HDassert(H5F_addr_defined(chunk_addr));
+
+                /* Set up the storage address information for this chunk */
+                ctg_store.contig.dset_addr = chunk_addr;
+
+                /* No chunk cached */
+                chunk = NULL;
+
+                /* Point I/O info at temporary I/O info for this chunk */
+                chk_io_info = &ctg_io_info;
+            } /* end else */
+        } /* end else */
+
+        /* Perform the actual read operation */
+        if((io_info->io_ops.single_read)(chk_io_info, type_info,
+                (hsize_t)chunk_info->chunk_points, chunk_info->fspace, chunk_info->mspace) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "chunked read failed")
+
+        /* Release the cache lock on the chunk. */
+        if(chunk && H5D_istore_unlock(io_info, FALSE, idx_hint, chunk, src_accessed_bytes) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
+
+        /* Advance to next chunk in list */
+        chunk_node = H5D_CHUNK_GET_NEXT_NODE(fm, chunk_node);
+    } /* end while */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5D_chunk_read() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_write
+ *
+ * Purpose:	Writes to a chunked dataset.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Raymond Lu
+ *		Thursday, April 10, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_chunk_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t UNUSED nelmts, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space,
+    H5D_chunk_map_t *fm)
+{
+    H5SL_node_t *chunk_node;            /* Current node in chunk skip list */
+    H5D_io_info_t ctg_io_info;          /* Contiguous I/O info object */
+    H5D_storage_t ctg_store;            /* Chunk storage information as contiguous dataset */
+    H5D_io_info_t cpt_io_info;          /* Compact I/O info object */
+    H5D_storage_t cpt_store;            /* Chunk storage information as compact dataset */
+    hbool_t     cpt_dirty;              /* Temporary placeholder for compact storage "dirty" flag */
+    size_t      dst_accessed_bytes = 0; /* Total accessed size in a chunk */
+    unsigned    idx_hint = 0;           /* Cache index hint      */
+    herr_t	ret_value = SUCCEED;	/* Return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_write)
+
+    /* Sanity check */
+    HDassert(io_info);
+    HDassert(io_info->u.wbuf);
+    HDassert(type_info);
+    HDassert(fm);
+
+    /* Set up contiguous I/O info object */
+    HDmemcpy(&ctg_io_info, io_info, sizeof(ctg_io_info));
+    ctg_io_info.store = &ctg_store;
+    ctg_io_info.layout_ops = *H5D_LOPS_CONTIG;
+
+    /* Initialize temporary contiguous storage info */
+    ctg_store.contig.dset_size = (hsize_t)io_info->dset->shared->layout.u.chunk.size;
+
+    /* Set up compact I/O info object */
+    HDmemcpy(&cpt_io_info, io_info, sizeof(cpt_io_info));
+    cpt_io_info.store = &cpt_store;
+    cpt_io_info.layout_ops = *H5D_LOPS_COMPACT;
+
+    /* Initialize temporary compact storage info */
+    cpt_store.compact.dirty = &cpt_dirty;
+
+    /* Iterate through nodes in chunk skip list */
+    chunk_node = H5D_CHUNK_GET_FIRST_NODE(fm);
+    while(chunk_node) {
+        H5D_chunk_info_t *chunk_info;   /* Chunk information */
+        H5D_io_info_t *chk_io_info;     /* Pointer to I/O info object for this chunk */
+        void *chunk;                    /* Pointer to locked chunk buffer */
+        haddr_t	chunk_addr;             /* Chunk address on disk */
+        H5D_istore_ud1_t udata;		/* B-tree pass-through	*/
+
+        /* Get the actual chunk information from the skip list node */
+        chunk_info = H5D_CHUNK_GET_NODE_INFO(fm, chunk_node);
+
+        /* Pass in chunk's coordinates in a union. */
+        io_info->store->chunk.offset = chunk_info->coords;
+        io_info->store->chunk.index = chunk_info->index;
+
+        /* Load the chunk into cache.  But if the whole chunk is written,
+         * simply allocate space instead of load the chunk. */
+        chunk_addr = H5D_istore_get_addr(io_info, &udata);
+        if(H5D_chunk_cacheable(io_info, chunk_addr)) {
+            hbool_t entire_chunk = TRUE;       /* Whether whole chunk is selected */
+
+            /* Compute # of bytes accessed in chunk */
+            dst_accessed_bytes = chunk_info->chunk_points * type_info->dst_type_size;
+
+            /* Determine if we will access all the data in the chunk */
+            if(dst_accessed_bytes != ctg_store.contig.dset_size ||
+                    (chunk_info->chunk_points * type_info->src_type_size) != ctg_store.contig.dset_size)
+                entire_chunk = FALSE;
+
+            /* Lock the chunk into the cache */
+            if(NULL == (chunk = H5D_istore_lock(io_info, &udata, entire_chunk, &idx_hint)))
+                HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
+
+            /* Set up the storage buffer information for this chunk */
+            cpt_store.compact.buf = chunk;
+
+            /* Point I/O info at main I/O info for this chunk */
+            chk_io_info = &cpt_io_info;
+        } /* end if */
+        else {
+            /* Sanity check */
+            HDassert(H5F_addr_defined(chunk_addr));
+
+            /* Set up the storage address information for this chunk */
+            ctg_store.contig.dset_addr = chunk_addr;
+
+            /* No chunk cached */
+            chunk = NULL;
+
+            /* Point I/O info at temporary I/O info for this chunk */
+            chk_io_info = &ctg_io_info;
+        } /* end else */
+
+        /* Perform the actual write operation */
+        if((io_info->io_ops.single_write)(chk_io_info, type_info,
+                (hsize_t)chunk_info->chunk_points, chunk_info->fspace, chunk_info->mspace) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "chunked write failed")
+
+        /* Release the cache lock on the chunk. */
+        if(chunk && H5D_istore_unlock(io_info, TRUE, idx_hint, chunk, dst_accessed_bytes) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
+
+        /* Advance to next chunk in list */
+        chunk_node = H5D_CHUNK_GET_NEXT_NODE(fm, chunk_node);
+    } /* end while */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5D_chunk_write() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_io_term
+ *
+ * Purpose:	Destroy I/O operation information.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Saturday, May 17, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_chunk_io_term(const H5D_chunk_map_t *fm)
+{
+    herr_t	ret_value = SUCCEED;	/*return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_io_term)
+
+    /* Single element I/O vs. multiple element I/O cleanup */
+    if(fm->use_single) {
+        /* Sanity checks */
+        HDassert(fm->sel_chunks == NULL);
+        HDassert(fm->single_chunk_info);
+        HDassert(fm->single_chunk_info->fspace_shared);
+        HDassert(fm->single_chunk_info->mspace_shared);
+
+        /* Reset the selection for the single element I/O */
+        H5S_select_all(fm->single_space, TRUE);
+    } /* end if */
+    else {
+        /* Release the nodes on the list of selected chunks */
+        if(fm->sel_chunks)
+            if(H5SL_free(fm->sel_chunks, H5D_free_chunk_info, NULL) < 0)
+                HGOTO_ERROR(H5E_PLIST, H5E_CANTNEXT, FAIL, "can't iterate over chunks")
+    } /* end else */
+
+    /* Free the memory chunk dataspace template */
+    if(fm->mchunk_tmpl)
+        if(H5S_close(fm->mchunk_tmpl) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "can't release memory chunk dataspace template")
+#ifdef H5_HAVE_PARALLEL
+    if(fm->select_chunk)
+        H5MM_xfree(fm->select_chunk);
+#endif /* H5_HAVE_PARALLEL */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_io_term() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_null_readvv
+ *
+ * Purpose:	Performs "no-op" I/O operation, advancing through two I/O
+ *              vectors, until one runs out.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Tuesday, April  1, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static ssize_t
+H5D_null_readvv(const H5D_io_info_t UNUSED *io_info,
+    size_t chunk_max_nseq, size_t *chunk_curr_seq, size_t chunk_len_arr[], hsize_t chunk_offset_arr[],
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[])
+{
+    size_t u, v;                /* Local index variables */
+    size_t size;                /* Size of sequence in bytes */
+    ssize_t bytes_processed = 0; /* Eventual return value */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_null_readvv)
+
+    /* Check args */
+    HDassert(chunk_len_arr);
+    HDassert(chunk_offset_arr);
+    HDassert(mem_len_arr);
+    HDassert(mem_offset_arr);
+
+    /* Work through all the sequences */
+    for(u = *mem_curr_seq, v = *chunk_curr_seq; u < mem_max_nseq && v < chunk_max_nseq; ) {
+        /* Choose smallest buffer to write */
+        if(chunk_len_arr[v] < mem_len_arr[u])
+            size = chunk_len_arr[v];
+        else
+            size = mem_len_arr[u];
+
+        /* Update source information */
+        chunk_len_arr[v] -= size;
+        chunk_offset_arr[v] += size;
+        if(chunk_len_arr[v] == 0)
+            v++;
+
+        /* Update destination information */
+        mem_len_arr[u] -= size;
+        mem_offset_arr[u] += size;
+        if(mem_len_arr[u] == 0)
+            u++;
+
+        /* Increment number of bytes copied */
+        bytes_processed += (ssize_t)size;
+    } /* end for */
+
+    /* Update current sequence vectors */
+    *mem_curr_seq = u;
+    *chunk_curr_seq = v;
+
+    FUNC_LEAVE_NOAPI(bytes_processed)
+} /* H5D_null_readvv() */
+
diff --git a/src/H5Dcompact.c b/src/H5Dcompact.c
index 2e4d3f7..c3abab6 100644
--- a/src/H5Dcompact.c
+++ b/src/H5Dcompact.c
@@ -41,22 +41,52 @@
 #include "H5Oprivate.h"		/* Object headers		  	*/
 #include "H5Vprivate.h"		/* Vector and array functions		*/
 
+
 /****************/
 /* Local Macros */
 /****************/
 
+
 /******************/
 /* Local Typedefs */
 /******************/
 
+
 /********************/
 /* Local Prototypes */
 /********************/
 
+/* Layout operation callbacks */
+static herr_t H5D_compact_io_init(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *cm);
+static ssize_t H5D_compact_readvv(const H5D_io_info_t *io_info,
+    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_size_arr[], hsize_t dset_offset_arr[],
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[]);
+static ssize_t H5D_compact_writevv(const H5D_io_info_t *io_info,
+    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_size_arr[], hsize_t dset_offset_arr[],
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[]);
+
+
 /*********************/
 /* Package Variables */
 /*********************/
 
+/* Compact storage layout I/O ops */
+const H5D_layout_ops_t H5D_LOPS_COMPACT[1] = {{
+    H5D_compact_io_init,
+    H5D_contig_read,
+    H5D_contig_write,
+#ifdef H5_HAVE_PARALLEL
+    NULL,
+    NULL,
+#endif /* H5_HAVE_PARALLEL */
+    H5D_compact_readvv,
+    H5D_compact_writevv,
+    NULL
+}};
+
+
 /*******************/
 /* Local Variables */
 /*******************/
@@ -64,6 +94,7 @@
 /* Declare extern the free list to manage blocks of type conversion data */
 H5FL_BLK_EXTERN(type_conv);
 
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_compact_fill
@@ -118,6 +149,32 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5D_compact_io_init
+ *
+ * Purpose:	Performs initialization before any sort of I/O on the raw data
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Thursday, March 20, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_compact_io_init(const H5D_io_info_t *io_info, const H5D_type_info_t UNUSED *type_info,
+    hsize_t UNUSED nelmts, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space,
+    H5D_chunk_map_t UNUSED *cm)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_compact_io_init)
+
+    io_info->store->compact.buf = io_info->dset->shared->layout.u.compact.buf;
+    io_info->store->compact.dirty = &io_info->dset->shared->layout.u.compact.dirty;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5D_compact_io_init() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5D_compact_readvv
  *
  * Purpose:     Reads some data vectors from a dataset into a buffer.
@@ -135,20 +192,19 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-ssize_t
+static ssize_t
 H5D_compact_readvv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_size_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED addr, void UNUSED *pointer/*in*/, void *buf)
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[])
 {
-    ssize_t ret_value;          /* Return value */
+    ssize_t ret_value;                  /* Return value */
 
-    FUNC_ENTER_NOAPI(H5D_compact_readvv, FAIL)
+    FUNC_ENTER_NOAPI_NOINIT(H5D_compact_readvv)
 
-    assert(io_info->dset);
+    HDassert(io_info);
 
     /* Use the vectorized memory copy routine to do actual work */
-    if((ret_value=H5V_memcpyvv(buf,mem_max_nseq,mem_curr_seq,mem_size_arr,mem_offset_arr,io_info->dset->shared->layout.u.compact.buf,dset_max_nseq,dset_curr_seq,dset_size_arr,dset_offset_arr))<0)
+    if((ret_value = H5V_memcpyvv(io_info->u.rbuf, mem_max_nseq, mem_curr_seq, mem_size_arr, mem_offset_arr, io_info->store->compact.buf, dset_max_nseq, dset_curr_seq, dset_size_arr, dset_offset_arr)) < 0)
         HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "vectorized memcpy failed")
 
 done:
@@ -177,24 +233,23 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-ssize_t
+static ssize_t
 H5D_compact_writevv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_size_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED addr, void UNUSED *pointer/*in*/, const void *buf)
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[])
 {
-    ssize_t ret_value;          /* Return value */
+    ssize_t ret_value;                  /* Return value */
 
-    FUNC_ENTER_NOAPI(H5D_compact_writevv, FAIL)
+    FUNC_ENTER_NOAPI_NOINIT(H5D_compact_writevv)
 
-    assert(io_info->dset);
+    HDassert(io_info);
 
     /* Use the vectorized memory copy routine to do actual work */
-    if((ret_value=H5V_memcpyvv(io_info->dset->shared->layout.u.compact.buf,dset_max_nseq,dset_curr_seq,dset_size_arr,dset_offset_arr,buf,mem_max_nseq,mem_curr_seq,mem_size_arr,mem_offset_arr))<0)
+    if((ret_value = H5V_memcpyvv(io_info->store->compact.buf, dset_max_nseq, dset_curr_seq, dset_size_arr, dset_offset_arr, io_info->u.wbuf, mem_max_nseq, mem_curr_seq, mem_size_arr, mem_offset_arr)) < 0)
         HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "vectorized memcpy failed")
 
     /* Mark the compact dataset's buffer as dirty */
-    io_info->dset->shared->layout.u.compact.dirty = TRUE;
+    *io_info->store->compact.dirty = TRUE;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -371,11 +426,11 @@ done:
         if(H5I_dec_ref(tid_mem) < 0)
             HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't decrement temporary datatype ID")
     if(buf)
-        H5FL_BLK_FREE(type_conv, buf);
+        (void)H5FL_BLK_FREE(type_conv, buf);
     if(reclaim_buf)
-        H5FL_BLK_FREE(type_conv, reclaim_buf);
+        (void)H5FL_BLK_FREE(type_conv, reclaim_buf);
     if(bkg)
-        H5FL_BLK_FREE(type_conv, bkg);
+        (void)H5FL_BLK_FREE(type_conv, bkg);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_compact_copy() */
diff --git a/src/H5Dcontig.c b/src/H5Dcontig.c
index bdb8294..1a3fda5 100644
--- a/src/H5Dcontig.c
+++ b/src/H5Dcontig.c
@@ -45,24 +45,50 @@
 #include "H5Pprivate.h"		/* Property lists			*/
 #include "H5Vprivate.h"		/* Vector and array functions		*/
 
+
 /****************/
 /* Local Macros */
 /****************/
 
+
 /******************/
 /* Local Typedefs */
 /******************/
 
+
 /********************/
 /* Local Prototypes */
 /********************/
-static herr_t H5D_contig_write(H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache,
-    hid_t dxpl_id, const H5D_storage_t *store, hsize_t offset, size_t size, const void *buf);
+
+/* Layout operation callbacks */
+static herr_t H5D_contig_io_init(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *cm);
+
+/* Helper routines */
+static herr_t H5D_contig_write_one(H5D_io_info_t *io_info, hsize_t offset,
+    size_t size);
+
 
 /*********************/
 /* Package Variables */
 /*********************/
 
+/* Contiguous storage layout I/O ops */
+const H5D_layout_ops_t H5D_LOPS_CONTIG[1] = {{
+    H5D_contig_io_init,
+    H5D_contig_read,
+    H5D_contig_write,
+#ifdef H5_HAVE_PARALLEL
+    H5D_contig_collective_read,
+    H5D_contig_collective_write,
+#endif /* H5_HAVE_PARALLEL */
+    H5D_contig_readvv,
+    H5D_contig_writevv,
+    NULL
+}};
+
+
 /*******************/
 /* Local Variables */
 /*******************/
@@ -73,6 +99,7 @@ H5FL_BLK_DEFINE(sieve_buf);
 /* Declare extern the free list to manage blocks of type conversion data */
 H5FL_BLK_EXTERN(type_conv);
 
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_contig_create
@@ -121,7 +148,8 @@ done:
 herr_t
 H5D_contig_fill(H5D_t *dset, hid_t dxpl_id)
 {
-    H5D_storage_t store;                /* Union of storage info for dataset */
+    H5D_io_info_t ioinfo;       /* Dataset I/O info */
+    H5D_storage_t store;        /* Union of storage info for dataset */
     H5D_dxpl_cache_t _dxpl_cache;       /* Data transfer property cache buffer */
     H5D_dxpl_cache_t *dxpl_cache = &_dxpl_cache;   /* Data transfer property cache */
     hssize_t    snpoints;       /* Number of points in space (for error checking) */
@@ -198,6 +226,9 @@ H5D_contig_fill(H5D_t *dset, hid_t dxpl_id)
     /* Start at the beginning of the dataset */
     offset = 0;
 
+    /* Simple setup for dataset I/O info struct */
+    H5D_BUILD_IO_INFO_WRT(&ioinfo, dset, dxpl_cache, my_dxpl_id, &store, fb_info.fill_buf);
+
     /*
      * Fill the entire current extent with the fill value.  We can do
      * this quite efficiently by making sure we copy the fill value
@@ -225,7 +256,7 @@ H5D_contig_fill(H5D_t *dset, hid_t dxpl_id)
                 /* Write the chunks out from only one process */
                 /* !! Use the internal "independent" DXPL!! -QAK */
                 if(H5_PAR_META_WRITE == mpi_rank)
-                    if(H5D_contig_write(dset, dxpl_cache, my_dxpl_id, &store, offset, size, fb_info.fill_buf) < 0)
+                    if(H5D_contig_write_one(&ioinfo, offset, size) < 0)
                         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to write fill value to dataset")
 
                 /* Indicate that blocks are being written */
@@ -234,7 +265,7 @@ H5D_contig_fill(H5D_t *dset, hid_t dxpl_id)
             else {
 #endif /* H5_HAVE_PARALLEL */
                 H5_CHECK_OVERFLOW(size, size_t, hsize_t);
-                if(H5D_contig_write(dset, dxpl_cache, my_dxpl_id, &store, offset, size, fb_info.fill_buf) < 0)
+                if(H5D_contig_write_one(&ioinfo, offset, size) < 0)
                     HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to write fill value to dataset")
 #ifdef H5_HAVE_PARALLEL
             } /* end else */
@@ -324,8 +355,108 @@ H5D_contig_get_addr(const H5D_t *dset)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5D_contig_io_init
+ *
+ * Purpose:	Performs initialization before any sort of I/O on the raw data
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Thursday, March 20, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_contig_io_init(const H5D_io_info_t *io_info, const H5D_type_info_t UNUSED *type_info,
+    hsize_t UNUSED nelmts, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space,
+    H5D_chunk_map_t UNUSED *cm)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_contig_io_init)
+
+    io_info->store->contig.dset_addr = io_info->dset->shared->layout.u.contig.addr;
+    io_info->store->contig.dset_size = io_info->dset->shared->layout.u.contig.size;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5D_contig_io_init() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_contig_read
+ *
+ * Purpose:	Read from a contiguous dataset.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Raymond Lu
+ *		Thursday, April 10, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_contig_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t UNUSED *fm)
+{
+    herr_t	ret_value = SUCCEED;	/*return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_contig_read)
+
+    /* Sanity check */
+    HDassert(io_info);
+    HDassert(io_info->u.rbuf);
+    HDassert(type_info);
+    HDassert(mem_space);
+    HDassert(file_space);
+
+    /* Read data */
+    if((io_info->io_ops.single_read)(io_info, type_info, nelmts, file_space, mem_space) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "contiguous read failed")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_contig_read() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5D_contig_write
  *
+ * Purpose:	Write to a contiguous dataset.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Raymond Lu
+ *		Thursday, April 10, 2003
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_contig_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t UNUSED *fm)
+{
+    herr_t	ret_value = SUCCEED;	/*return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_contig_write)
+
+    /* Sanity check */
+    HDassert(io_info);
+    HDassert(io_info->u.wbuf);
+    HDassert(type_info);
+    HDassert(mem_space);
+    HDassert(file_space);
+
+    /* Write data */
+    if((io_info->io_ops.single_write)(io_info, type_info, nelmts, file_space, mem_space) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "contiguous write failed")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_contig_write() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_contig_write_one
+ *
  * Purpose:	Writes some data from a dataset into a buffer.
  *		The data is contiguous.	 The address is relative to the base
  *		address for the file.
@@ -338,34 +469,27 @@ H5D_contig_get_addr(const H5D_t *dset)
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_contig_write(H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache,
-    hid_t dxpl_id, const H5D_storage_t *store,
-    hsize_t offset, size_t size, const void *buf)
+H5D_contig_write_one(H5D_io_info_t *io_info, hsize_t offset, size_t size)
 {
-    H5D_io_info_t io_info;      /* Dataset I/O info */
-    hsize_t dset_off=offset;    /* Offset in dataset */
-    size_t dset_len=size;       /* Length in dataset */
-    size_t dset_curr_seq=0;     /* "Current sequence" in dataset */
-    hsize_t mem_off=0;          /* Offset in memory */
-    size_t mem_len=size;        /* Length in memory */
-    size_t mem_curr_seq=0;      /* "Current sequence" in memory */
-    herr_t ret_value=SUCCEED;   /* Return value */
-
-    FUNC_ENTER_NOAPI(H5D_contig_write, FAIL)
-
-    assert (dset);
-    assert (dxpl_cache);
-    assert (store);
-    assert (buf);
-
-    H5D_BUILD_IO_INFO(&io_info,dset,dxpl_cache,dxpl_id,store);
-    if(H5D_contig_writevv(&io_info, (size_t)1, &dset_curr_seq, &dset_len, &dset_off, 
-            (size_t)1, &mem_curr_seq, &mem_len, &mem_off, (haddr_t)0, NULL, buf) < 0)
+    hsize_t dset_off = offset;  /* Offset in dataset */
+    size_t dset_len = size;     /* Length in dataset */
+    size_t dset_curr_seq = 0;   /* "Current sequence" in dataset */
+    hsize_t mem_off = 0;        /* Offset in memory */
+    size_t mem_len = size;      /* Length in memory */
+    size_t mem_curr_seq = 0;    /* "Current sequence" in memory */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_contig_write_one)
+
+    HDassert(io_info);
+
+    if(H5D_contig_writevv(io_info, (size_t)1, &dset_curr_seq, &dset_len, &dset_off, 
+            (size_t)1, &mem_curr_seq, &mem_len, &mem_off) < 0)
         HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "vector write failed")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-}   /* end H5D_contig_write() */
+}   /* end H5D_contig_write_one() */
 
 
 /*-------------------------------------------------------------------------
@@ -389,67 +513,76 @@ done:
 ssize_t
 H5D_contig_readvv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED address, void UNUSED *pointer, void *_buf)
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[])
 {
     H5F_t *file = io_info->dset->oloc.file;        /* File for dataset */
-    H5D_rdcdc_t *dset_contig=&(io_info->dset->shared->cache.contig); /* Cached information about contiguous data */
-    const H5D_contig_storage_t *store_contig=&(io_info->store->contig);    /* Contiguous storage info for this I/O operation */
-    unsigned char *buf=(unsigned char *)_buf;   /* Pointer to buffer to fill */
+    H5D_rdcdc_t *dset_contig = &(io_info->dset->shared->cache.contig); /* Cached information about contiguous data */
+    const H5D_contig_storage_t *store_contig = &(io_info->store->contig);    /* Contiguous storage info for this I/O operation */
+    unsigned char *buf = (unsigned char *)io_info->u.rbuf;   /* Pointer to buffer to fill */
     haddr_t addr;               /* Actual address to read */
-    size_t total_size=0;        /* Total size of sequence in bytes */
+    size_t total_size = 0;      /* Total size of sequence in bytes */
     size_t size;                /* Size of sequence in bytes */
     size_t u;                   /* Counting variable */
     size_t v;                   /* Counting variable */
     ssize_t ret_value;          /* Return value */
 
     FUNC_ENTER_NOAPI(H5D_contig_readvv, FAIL)
+#ifdef QAK
+HDfprintf(stderr, "%s: dset_max_nseq = %Zu\n", FUNC, dset_max_nseq);
+HDfprintf(stderr, "%s: mem_max_nseq = %Zu\n", FUNC, mem_max_nseq);
+HDfprintf(stderr, "%s: *dset_curr_seq= %Zu\n", FUNC, *dset_curr_seq);
+HDfprintf(stderr, "%s: *mem_curr_seq= %Zu\n", FUNC, *mem_curr_seq);
+for(u = 0; u < dset_max_nseq; u++)
+    HDfprintf(stderr, "%s: dset_len_arr[%Zu] = %Zu, dset_offset_arr[%Zu] = %Hu\n", FUNC, u, dset_len_arr[u], u, dset_offset_arr[u]);
+for(u = 0; u < mem_max_nseq; u++)
+    HDfprintf(stderr, "%s: mem_len_arr[%Zu] = %Zu, mem_offset_arr[%Zu] = %Hu\n", FUNC, u, mem_len_arr[u], u, mem_offset_arr[u]);
+#endif /* QAK */
 
     /* Check args */
-    assert(io_info);
-    assert(io_info->dset);
-    assert(io_info->store);
-    assert(buf);
+    HDassert(io_info);
+    HDassert(io_info->dset);
+    HDassert(io_info->store);
+    HDassert(buf);
 
     /* Check if data sieving is enabled */
-    if(H5F_HAS_FEATURE(file,H5FD_FEAT_DATA_SIEVE)) {
-        haddr_t sieve_start=HADDR_UNDEF, sieve_end=HADDR_UNDEF;     /* Start & end locations of sieve buffer */
+    if(H5F_HAS_FEATURE(file, H5FD_FEAT_DATA_SIEVE)) {
+        haddr_t sieve_start = HADDR_UNDEF, sieve_end = HADDR_UNDEF;     /* Start & end locations of sieve buffer */
         haddr_t contig_end;             /* End locations of block to write */
-        size_t sieve_size=(size_t)-1;   /* size of sieve buffer */
+        size_t sieve_size = (size_t)-1;   /* size of sieve buffer */
         haddr_t abs_eoa;	        /* Absolute end of file address		*/
         haddr_t rel_eoa;	        /* Relative end of file address		*/
         hsize_t max_data;               /* Actual maximum size of data to cache */
 
         /* Set offsets in sequence lists */
-        u=*dset_curr_seq;
-        v=*mem_curr_seq;
+        u = *dset_curr_seq;
+        v = *mem_curr_seq;
 
         /* Stash local copies of these value */
-        if(dset_contig->sieve_buf!=NULL) {
-            sieve_start=dset_contig->sieve_loc;
-            sieve_size=dset_contig->sieve_size;
-            sieve_end=sieve_start+sieve_size;
+        if(dset_contig->sieve_buf != NULL) {
+            sieve_start = dset_contig->sieve_loc;
+            sieve_size = dset_contig->sieve_size;
+            sieve_end = sieve_start+sieve_size;
         } /* end if */
 
         /* Works through sequences as fast as possible */
-        for(; u<dset_max_nseq && v<mem_max_nseq; ) {
+        for(; u < dset_max_nseq && v < mem_max_nseq; ) {
             /* Choose smallest buffer to write */
-            if(mem_len_arr[v]<dset_len_arr[u])
-                size=mem_len_arr[v];
+            if(mem_len_arr[v] < dset_len_arr[u])
+                size = mem_len_arr[v];
             else
-                size=dset_len_arr[u];
+                size = dset_len_arr[u];
 
             /* Compute offset on disk */
-            addr=store_contig->dset_addr+dset_offset_arr[u];
+            addr = store_contig->dset_addr + dset_offset_arr[u];
 
             /* Compute offset in memory */
-            buf = (unsigned char *)_buf + mem_offset_arr[v];
+            buf = (unsigned char *)io_info->u.rbuf + mem_offset_arr[v];
 
             /* Check if the sieve buffer is allocated yet */
-            if(dset_contig->sieve_buf==NULL) {
+            if(dset_contig->sieve_buf == NULL) {
                 /* Check if we can actually hold the I/O request in the sieve buffer */
                 if(size>dset_contig->sieve_buf_size) {
-                    if (H5F_block_read(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf)<0)
+                    if(H5F_block_read(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf) < 0)
                         HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "block read failed")
                 } /* end if */
                 else {
@@ -465,40 +598,40 @@ H5D_contig_readvv(const H5D_io_info_t *io_info,
                         HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to determine file size")
 
                     /* Adjust absolute EOA address to relative EOA address */
-                    rel_eoa=abs_eoa-H5F_get_base_addr(file);
+                    rel_eoa = abs_eoa - H5F_get_base_addr(file);
 
                     /* Set up the buffer parameters */
-                    max_data=store_contig->dset_size-dset_offset_arr[u];
+                    max_data = store_contig->dset_size-dset_offset_arr[u];
 
                     /* Compute the size of the sieve buffer */
-                    H5_ASSIGN_OVERFLOW(dset_contig->sieve_size,MIN3(rel_eoa-dset_contig->sieve_loc,max_data,dset_contig->sieve_buf_size),hsize_t,size_t);
+                    H5_ASSIGN_OVERFLOW(dset_contig->sieve_size, MIN3(rel_eoa-dset_contig->sieve_loc, max_data, dset_contig->sieve_buf_size), hsize_t, size_t);
 
                     /* Read the new sieve buffer */
-                    if (H5F_block_read(file, H5FD_MEM_DRAW, dset_contig->sieve_loc, dset_contig->sieve_size, io_info->dxpl_id, dset_contig->sieve_buf)<0)
+                    if(H5F_block_read(file, H5FD_MEM_DRAW, dset_contig->sieve_loc, dset_contig->sieve_size, io_info->dxpl_id, dset_contig->sieve_buf) < 0)
                         HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "block read failed")
 
                     /* Grab the data out of the buffer (must be first piece of data in buffer ) */
-                    HDmemcpy(buf,dset_contig->sieve_buf,size);
+                    HDmemcpy(buf, dset_contig->sieve_buf, size);
 
                     /* Reset sieve buffer dirty flag */
-                    dset_contig->sieve_dirty=0;
+                    dset_contig->sieve_dirty = 0;
 
                     /* Stash local copies of these value */
-                    sieve_start=dset_contig->sieve_loc;
-                    sieve_size=dset_contig->sieve_size;
-                    sieve_end=sieve_start+sieve_size;
+                    sieve_start = dset_contig->sieve_loc;
+                    sieve_size = dset_contig->sieve_size;
+                    sieve_end = sieve_start+sieve_size;
                 } /* end else */
             } /* end if */
             else {
                 /* Compute end of sequence to retrieve */
-                contig_end=addr+size-1;
+                contig_end = addr + size - 1;
 
                 /* If entire read is within the sieve buffer, read it from the buffer */
                 if(addr>=sieve_start && contig_end<sieve_end) {
                     unsigned char *base_sieve_buf=dset_contig->sieve_buf+(addr-sieve_start);
 
                     /* Grab the data out of the buffer */
-                    HDmemcpy(buf,base_sieve_buf,size);
+                    HDmemcpy(buf, base_sieve_buf, size);
                 } /* end if */
                 /* Entire request is not within this data sieve buffer */
                 else {
@@ -510,16 +643,16 @@ H5D_contig_readvv(const H5D_io_info_t *io_info,
                             /* Flush the sieve buffer, if it's dirty */
                             if(dset_contig->sieve_dirty) {
                                 /* Write to file */
-                                if (H5F_block_write(file, H5FD_MEM_DRAW, sieve_start, sieve_size, io_info->dxpl_id, dset_contig->sieve_buf)<0)
+                                if(H5F_block_write(file, H5FD_MEM_DRAW, sieve_start, sieve_size, io_info->dxpl_id, dset_contig->sieve_buf) < 0)
                                     HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "block write failed")
 
                                 /* Reset sieve buffer dirty flag */
-                                dset_contig->sieve_dirty=0;
+                                dset_contig->sieve_dirty = 0;
                             } /* end if */
                         } /* end if */
 
                         /* Read directly into the user's buffer */
-                        if (H5F_block_read(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf)<0)
+                        if(H5F_block_read(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf) < 0)
                             HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "block read failed")
                     } /* end if */
                     /* Element size fits within the buffer size */
@@ -561,72 +694,72 @@ H5D_contig_readvv(const H5D_io_info_t *io_info,
                             HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "block read failed")
 
                         /* Grab the data out of the buffer (must be first piece of data in buffer ) */
-                        HDmemcpy(buf,dset_contig->sieve_buf,size);
+                        HDmemcpy(buf, dset_contig->sieve_buf, size);
 
                         /* Reset sieve buffer dirty flag */
-                        dset_contig->sieve_dirty=0;
+                        dset_contig->sieve_dirty = 0;
                     } /* end else */
                 } /* end else */
             } /* end else */
 
             /* Update memory information */
-            mem_len_arr[v]-=size;
-            mem_offset_arr[v]+=size;
-            if(mem_len_arr[v]==0)
+            mem_len_arr[v] -= size;
+            mem_offset_arr[v] += size;
+            if(mem_len_arr[v] == 0)
                 v++;
 
             /* Update file information */
-            dset_len_arr[u]-=size;
-            dset_offset_arr[u]+=size;
-            if(dset_len_arr[u]==0)
+            dset_len_arr[u] -= size;
+            dset_offset_arr[u] += size;
+            if(dset_len_arr[u] == 0)
                 u++;
 
             /* Increment number of bytes copied */
-            total_size+=size;
+            total_size += size;
         } /* end for */
     } /* end if */
     else {
         /* Work through all the sequences */
-        for(u=*dset_curr_seq, v=*mem_curr_seq; u<dset_max_nseq && v<mem_max_nseq; ) {
+        for(u = *dset_curr_seq, v = *mem_curr_seq; u < dset_max_nseq && v < mem_max_nseq; ) {
             /* Choose smallest buffer to write */
-            if(mem_len_arr[v]<dset_len_arr[u])
-                size=mem_len_arr[v];
+            if(mem_len_arr[v] < dset_len_arr[u])
+                size = mem_len_arr[v];
             else
-                size=dset_len_arr[u];
+                size = dset_len_arr[u];
 
             /* Compute offset on disk */
-            addr=store_contig->dset_addr+dset_offset_arr[u];
+            addr = store_contig->dset_addr + dset_offset_arr[u];
 
             /* Compute offset in memory */
-            buf = (unsigned char *)_buf + mem_offset_arr[v];
+            buf = (unsigned char *)io_info->u.rbuf + mem_offset_arr[v];
 
             /* Write data */
-            if (H5F_block_read(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf)<0)
+            if(H5F_block_read(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf) < 0)
                 HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "block write failed")
 
             /* Update memory information */
-            mem_len_arr[v]-=size;
-            mem_offset_arr[v]+=size;
-            if(mem_len_arr[v]==0)
+            mem_len_arr[v] -= size;
+            mem_offset_arr[v] += size;
+            if(mem_len_arr[v] == 0)
                 v++;
 
             /* Update file information */
-            dset_len_arr[u]-=size;
-            dset_offset_arr[u]+=size;
-            if(dset_len_arr[u]==0)
+            dset_len_arr[u] -= size;
+            dset_offset_arr[u] += size;
+            if(dset_len_arr[u] == 0)
                 u++;
 
             /* Increment number of bytes copied */
-            total_size+=size;
+            total_size += size;
         } /* end for */
     } /* end else */
 
     /* Update current sequence vectors */
-    *dset_curr_seq=u;
-    *mem_curr_seq=v;
+    *dset_curr_seq = u;
+    *mem_curr_seq = v;
 
     /* Set return value */
-    H5_ASSIGN_OVERFLOW(ret_value,total_size,size_t,ssize_t);
+    H5_ASSIGN_OVERFLOW(ret_value, total_size, size_t, ssize_t);
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -654,15 +787,14 @@ done:
 ssize_t
 H5D_contig_writevv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED address, void UNUSED *pointer, const void *_buf)
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[])
 {
     H5F_t *file = io_info->dset->oloc.file;        /* File for dataset */
-    H5D_rdcdc_t *dset_contig=&(io_info->dset->shared->cache.contig); /* Cached information about contiguous data */
-    const H5D_contig_storage_t *store_contig=&(io_info->store->contig);    /* Contiguous storage info for this I/O operation */
-    const unsigned char *buf=(const unsigned char *)_buf;      /* Pointer to buffer to fill */
+    H5D_rdcdc_t *dset_contig = &(io_info->dset->shared->cache.contig); /* Cached information about contiguous data */
+    const H5D_contig_storage_t *store_contig = &(io_info->store->contig);    /* Contiguous storage info for this I/O operation */
+    const unsigned char *buf = (const unsigned char *)io_info->u.wbuf;      /* Pointer to buffer to fill */
     haddr_t addr;               /* Actual address to read */
-    size_t total_size=0;        /* Size of sequence in bytes */
+    size_t total_size = 0;      /* Size of sequence in bytes */
     size_t size;                /* Size of sequence in bytes */
     size_t u;                   /* Counting variable */
     size_t v;                   /* Counting variable */
@@ -671,10 +803,10 @@ H5D_contig_writevv(const H5D_io_info_t *io_info,
     FUNC_ENTER_NOAPI(H5D_contig_writevv, FAIL)
 
     /* Check args */
-    assert(io_info);
-    assert(io_info->dset);
-    assert(io_info->store);
-    assert(buf);
+    HDassert(io_info);
+    HDassert(io_info->dset);
+    HDassert(io_info->store);
+    HDassert(buf);
 
     /* Check if data sieving is enabled */
     if(H5F_HAS_FEATURE(file,H5FD_FEAT_DATA_SIEVE)) {
@@ -708,18 +840,18 @@ H5D_contig_writevv(const H5D_io_info_t *io_info,
             addr=store_contig->dset_addr+dset_offset_arr[u];
 
             /* Compute offset in memory */
-            buf = (const unsigned char *)_buf + mem_offset_arr[v];
+            buf = (const unsigned char *)io_info->u.wbuf + mem_offset_arr[v];
 
             /* No data sieve buffer yet, go allocate one */
             if(dset_contig->sieve_buf==NULL) {
                 /* Check if we can actually hold the I/O request in the sieve buffer */
                 if(size>dset_contig->sieve_buf_size) {
-                    if (H5F_block_write(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf)<0)
+                    if(H5F_block_write(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf) < 0)
                         HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "block write failed")
                 } /* end if */
                 else {
                     /* Allocate room for the data sieve buffer */
-                    if (NULL==(dset_contig->sieve_buf=H5FL_BLK_MALLOC(sieve_buf,dset_contig->sieve_buf_size)))
+                    if(NULL == (dset_contig->sieve_buf = H5FL_BLK_MALLOC(sieve_buf, dset_contig->sieve_buf_size)))
                         HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
 #ifdef H5_CLEAR_MEMORY
 if(dset_contig->sieve_size > size)
@@ -750,15 +882,15 @@ if(dset_contig->sieve_size > size)
                     } /* end if */
 
                     /* Grab the data out of the buffer (must be first piece of data in buffer ) */
-                    HDmemcpy(dset_contig->sieve_buf,buf,size);
+                    HDmemcpy(dset_contig->sieve_buf, buf, size);
 
                     /* Set sieve buffer dirty flag */
-                    dset_contig->sieve_dirty=1;
+                    dset_contig->sieve_dirty = 1;
 
                     /* Stash local copies of these values */
-                    sieve_start=dset_contig->sieve_loc;
-                    sieve_size=dset_contig->sieve_size;
-                    sieve_end=sieve_start+sieve_size;
+                    sieve_start = dset_contig->sieve_loc;
+                    sieve_size = dset_contig->sieve_size;
+                    sieve_end = sieve_start + sieve_size;
                 } /* end else */
             } /* end if */
             else {
@@ -767,13 +899,13 @@ if(dset_contig->sieve_size > size)
 
                 /* If entire write is within the sieve buffer, write it to the buffer */
                 if(addr>=sieve_start && contig_end<sieve_end) {
-                    unsigned char *base_sieve_buf=dset_contig->sieve_buf+(addr-sieve_start);
+                    unsigned char *base_sieve_buf = dset_contig->sieve_buf + (addr - sieve_start);
 
                     /* Put the data into the sieve buffer */
-                    HDmemcpy(base_sieve_buf,buf,size);
+                    HDmemcpy(base_sieve_buf, buf, size);
 
                     /* Set sieve buffer dirty flag */
-                    dset_contig->sieve_dirty=1;
+                    dset_contig->sieve_dirty = 1;
                 } /* end if */
                 /* Entire request is not within this data sieve buffer */
                 else {
@@ -798,7 +930,7 @@ if(dset_contig->sieve_size > size)
                         } /* end if */
 
                         /* Write directly from the user's buffer */
-                        if (H5F_block_write(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf)<0)
+                        if(H5F_block_write(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf) < 0)
                             HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "block write failed")
                     } /* end if */
                     /* Element size fits within the buffer size */
@@ -808,30 +940,30 @@ if(dset_contig->sieve_size > size)
                                 (size+sieve_size)<=dset_contig->sieve_buf_size &&
                                 dset_contig->sieve_dirty) {
                             /* Prepend to existing sieve buffer */
-                            if((addr+size)==sieve_start) {
+                            if((addr + size) == sieve_start) {
                                 /* Move existing sieve information to correct location */
-                                HDmemmove(dset_contig->sieve_buf+size,dset_contig->sieve_buf,dset_contig->sieve_size);
+                                HDmemmove(dset_contig->sieve_buf + size, dset_contig->sieve_buf, dset_contig->sieve_size);
 
                                 /* Copy in new information (must be first in sieve buffer) */
-                                HDmemcpy(dset_contig->sieve_buf,buf,size);
+                                HDmemcpy(dset_contig->sieve_buf, buf, size);
 
                                 /* Adjust sieve location */
-                                dset_contig->sieve_loc=addr;
+                                dset_contig->sieve_loc = addr;
 
                             } /* end if */
                             /* Append to existing sieve buffer */
                             else {
                                 /* Copy in new information */
-                                HDmemcpy(dset_contig->sieve_buf+sieve_size,buf,size);
+                                HDmemcpy(dset_contig->sieve_buf + sieve_size, buf, size);
                             } /* end else */
 
                             /* Adjust sieve size */
                             dset_contig->sieve_size += size;
 
                             /* Update local copies of sieve information */
-                            sieve_start=dset_contig->sieve_loc;
-                            sieve_size=dset_contig->sieve_size;
-                            sieve_end=sieve_start+sieve_size;
+                            sieve_start = dset_contig->sieve_loc;
+                            sieve_size = dset_contig->sieve_size;
+                            sieve_end = sieve_start + sieve_size;
                         } /* end if */
                         /* Can't add the new data onto the existing sieve buffer */
                         else {
@@ -875,73 +1007,73 @@ if(dset_contig->sieve_size > size)
                             } /* end if */
 
                             /* Grab the data out of the buffer (must be first piece of data in buffer ) */
-                            HDmemcpy(dset_contig->sieve_buf,buf,size);
+                            HDmemcpy(dset_contig->sieve_buf, buf, size);
 
                             /* Set sieve buffer dirty flag */
-                            dset_contig->sieve_dirty=1;
+                            dset_contig->sieve_dirty = 1;
                         } /* end else */
                     } /* end else */
                 } /* end else */
             } /* end else */
 
             /* Update memory information */
-            mem_len_arr[v]-=size;
-            mem_offset_arr[v]+=size;
-            if(mem_len_arr[v]==0)
+            mem_len_arr[v] -= size;
+            mem_offset_arr[v] += size;
+            if(mem_len_arr[v] == 0)
                 v++;
 
             /* Update file information */
-            dset_len_arr[u]-=size;
-            dset_offset_arr[u]+=size;
-            if(dset_len_arr[u]==0)
+            dset_len_arr[u] -= size;
+            dset_offset_arr[u] += size;
+            if(dset_len_arr[u] == 0)
                 u++;
 
             /* Increment number of bytes copied */
-            total_size+=size;
+            total_size += size;
         } /* end for */
     } /* end if */
     else {
         /* Work through all the sequences */
-        for(u=*dset_curr_seq, v=*mem_curr_seq; u<dset_max_nseq && v<mem_max_nseq; ) {
+        for(u = *dset_curr_seq, v = *mem_curr_seq; u < dset_max_nseq && v < mem_max_nseq; ) {
             /* Choose smallest buffer to write */
-            if(mem_len_arr[v]<dset_len_arr[u])
-                size=mem_len_arr[v];
+            if(mem_len_arr[v] < dset_len_arr[u])
+                size = mem_len_arr[v];
             else
-                size=dset_len_arr[u];
+                size = dset_len_arr[u];
 
             /* Compute offset on disk */
-            addr=store_contig->dset_addr+dset_offset_arr[u];
+            addr = store_contig->dset_addr + dset_offset_arr[u];
 
             /* Compute offset in memory */
-            buf = (const unsigned char *)_buf + mem_offset_arr[v];
+            buf = (const unsigned char *)io_info->u.wbuf + mem_offset_arr[v];
 
             /* Write data */
-            if (H5F_block_write(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf)<0)
+            if(H5F_block_write(file, H5FD_MEM_DRAW, addr, size, io_info->dxpl_id, buf) < 0)
                 HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "block write failed")
 
             /* Update memory information */
-            mem_len_arr[v]-=size;
-            mem_offset_arr[v]+=size;
-            if(mem_len_arr[v]==0)
+            mem_len_arr[v] -= size;
+            mem_offset_arr[v] += size;
+            if(mem_len_arr[v] == 0)
                 v++;
 
             /* Update file information */
-            dset_len_arr[u]-=size;
-            dset_offset_arr[u]+=size;
-            if(dset_len_arr[u]==0)
+            dset_len_arr[u] -= size;
+            dset_offset_arr[u] += size;
+            if(dset_len_arr[u] == 0)
                 u++;
 
             /* Increment number of bytes copied */
-            total_size+=size;
+            total_size += size;
         } /* end for */
     } /* end else */
 
     /* Update current sequence vectors */
-    *dset_curr_seq=u;
-    *mem_curr_seq=v;
+    *dset_curr_seq = u;
+    *mem_curr_seq = v;
 
     /* Set return value */
-    H5_ASSIGN_OVERFLOW(ret_value,total_size,size_t,ssize_t);
+    H5_ASSIGN_OVERFLOW(ret_value, total_size, size_t, ssize_t);
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5Ddeprec.c b/src/H5Ddeprec.c
index 8f8aa50..fd1d2e8 100644
--- a/src/H5Ddeprec.c
+++ b/src/H5Ddeprec.c
@@ -156,7 +156,7 @@ H5Dcreate1(hid_t loc_id, const char *name, hid_t type_id, hid_t space_id,
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no name")
     if(H5I_DATATYPE != H5I_get_type(type_id))
 	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a datatype ID")
-    if(NULL == (space = H5I_object_verify(space_id,H5I_DATASPACE)))
+    if(NULL == (space = (const H5S_t *)H5I_object_verify(space_id,H5I_DATASPACE)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataspace ID")
     if(H5P_DEFAULT == dcpl_id)
         dcpl_id = H5P_DATASET_CREATE_DEFAULT;
diff --git a/src/H5Defl.c b/src/H5Defl.c
index c8d1098..7dac29b 100644
--- a/src/H5Defl.c
+++ b/src/H5Defl.c
@@ -33,30 +33,88 @@
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5Fprivate.h"		/* Files				*/
 
+
 /****************/
 /* Local Macros */
 /****************/
 
+
 /******************/
 /* Local Typedefs */
 /******************/
 
+
 /********************/
 /* Local Prototypes */
 /********************/
-static herr_t H5D_efl_read (const H5O_efl_t *efl, haddr_t addr, size_t size,
+
+/* Layout operation callbacks */
+static herr_t H5D_efl_io_init(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *cm);
+static ssize_t H5D_efl_readvv(const H5D_io_info_t *io_info,
+    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[]);
+static ssize_t H5D_efl_writevv(const H5D_io_info_t *io_info,
+    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[]);
+
+/* Helper routines */
+static herr_t H5D_efl_read(const H5O_efl_t *efl, haddr_t addr, size_t size,
     uint8_t *buf);
 static herr_t H5D_efl_write(const H5O_efl_t *efl, haddr_t addr, size_t size,
     const uint8_t *buf);
 
+
 /*********************/
 /* Package Variables */
 /*********************/
 
+/* External File List (EFL) storage layout I/O ops */
+const H5D_layout_ops_t H5D_LOPS_EFL[1] = {{
+    H5D_efl_io_init,
+    H5D_contig_read,
+    H5D_contig_write,
+#ifdef H5_HAVE_PARALLEL
+    NULL,
+    NULL,
+#endif /* H5_HAVE_PARALLEL */
+    H5D_efl_readvv,
+    H5D_efl_writevv,
+    NULL
+}};
+
+
 /*******************/
 /* Local Variables */
 /*******************/
 
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_efl_io_init
+ *
+ * Purpose:	Performs initialization before any sort of I/O on the raw data
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Thursday, March 20, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_efl_io_init(const H5D_io_info_t *io_info, const H5D_type_info_t UNUSED *type_info,
+    hsize_t UNUSED nelmts, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space,
+    H5D_chunk_map_t UNUSED *cm)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_efl_io_init)
+
+    HDmemcpy(&io_info->store->efl, &(io_info->dset->shared->dcpl_cache.efl), sizeof(H5O_efl_t));
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5D_efl_io_init() */
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_efl_read
@@ -77,26 +135,26 @@ static herr_t H5D_efl_write(const H5O_efl_t *efl, haddr_t addr, size_t size,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_efl_read (const H5O_efl_t *efl, haddr_t addr, size_t size, uint8_t *buf)
+H5D_efl_read(const H5O_efl_t *efl, haddr_t addr, size_t size, uint8_t *buf)
 {
-    int		fd=-1;
+    int		fd = -1;
     size_t	to_read;
 #ifndef NDEBUG
     hsize_t     tempto_read;
 #endif /* NDEBUG */
-    hsize_t     skip=0;
+    hsize_t     skip = 0;
     haddr_t     cur;
     ssize_t	n;
     size_t      u;                      /* Local index variable */
-    herr_t      ret_value=SUCCEED;       /* Return value */
+    herr_t      ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_efl_read)
 
     /* Check args */
-    assert (efl && efl->nused>0);
-    assert (H5F_addr_defined (addr));
-    assert (size < SIZET_MAX);
-    assert (buf || 0==size);
+    HDassert(efl && efl->nused>0);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(size < SIZET_MAX);
+    HDassert(buf || 0 == size);
 
     /* Find the first efl member from which to read */
     for (u=0, cur=0; u<efl->nused; u++) {
@@ -109,7 +167,7 @@ H5D_efl_read (const H5O_efl_t *efl, haddr_t addr, size_t size, uint8_t *buf)
 
     /* Read the data */
     while (size) {
-        assert(buf);
+        HDassert(buf);
 	if (u>=efl->nused)
 	    HGOTO_ERROR (H5E_EFL, H5E_OVERFLOW, FAIL, "read past logical end of file")
 	if (H5F_OVERFLOW_HSIZET2OFFT (efl->slot[u].offset+skip))
@@ -165,25 +223,25 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_efl_write (const H5O_efl_t *efl, haddr_t addr, size_t size, const uint8_t *buf)
+H5D_efl_write(const H5O_efl_t *efl, haddr_t addr, size_t size, const uint8_t *buf)
 {
-    int		fd=-1;
+    int		fd = -1;
     size_t	to_write;
 #ifndef NDEBUG
     hsize_t	tempto_write;
 #endif /* NDEBUG */
     haddr_t     cur;
-    hsize_t     skip=0;
+    hsize_t     skip = 0;
     size_t	u;                      /* Local index variable */
-    herr_t      ret_value=SUCCEED;       /* Return value */
+    herr_t      ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_efl_write)
 
     /* Check args */
-    assert (efl && efl->nused>0);
-    assert (H5F_addr_defined (addr));
-    assert (size < SIZET_MAX);
-    assert (buf || 0==size);
+    HDassert(efl && efl->nused>0);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(size < SIZET_MAX);
+    HDassert(buf || 0 == size);
 
     /* Find the first efl member in which to write */
     for (u=0, cur=0; u<efl->nused; u++) {
@@ -248,71 +306,68 @@ done:
  * Programmer:	Quincey Koziol
  *              Wednesday, May  7, 2003
  *
- * Modifications:
- *
  *-------------------------------------------------------------------------
  */
-ssize_t
+static ssize_t
 H5D_efl_readvv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED address, void UNUSED *pointer/*in*/, void *_buf)
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[])
 {
-    const H5O_efl_t *efl=&(io_info->store->efl); /* Pointer to efl info */
+    const H5O_efl_t *efl = &(io_info->store->efl); /* Pointer to efl info */
     unsigned char *buf;         /* Pointer to buffer to write */
     haddr_t addr;               /* Actual address to read */
-    size_t total_size=0;        /* Total size of sequence in bytes */
+    size_t total_size = 0;      /* Total size of sequence in bytes */
     size_t size;                /* Size of sequence in bytes */
     size_t u;                   /* Counting variable */
     size_t v;                   /* Counting variable */
     ssize_t ret_value;          /* Return value */
 
-    FUNC_ENTER_NOAPI(H5D_efl_readvv, FAIL)
+    FUNC_ENTER_NOAPI_NOINIT(H5D_efl_readvv)
 
     /* Check args */
-    assert (efl && efl->nused>0);
-    assert (_buf);
+    HDassert(efl && efl->nused > 0);
+    HDassert(io_info->u.rbuf);
 
     /* Work through all the sequences */
-    for(u=*dset_curr_seq, v=*mem_curr_seq; u<dset_max_nseq && v<mem_max_nseq; ) {
+    for(u = *dset_curr_seq, v = *mem_curr_seq; u < dset_max_nseq && v < mem_max_nseq; ) {
         /* Choose smallest buffer to write */
-        if(mem_len_arr[v]<dset_len_arr[u])
-            size=mem_len_arr[v];
+        if(mem_len_arr[v] < dset_len_arr[u])
+            size = mem_len_arr[v];
         else
-            size=dset_len_arr[u];
+            size = dset_len_arr[u];
 
         /* Compute offset on disk */
-        addr=dset_offset_arr[u];
+        addr = dset_offset_arr[u];
 
         /* Compute offset in memory */
-        buf = (unsigned char *)_buf + mem_offset_arr[v];
+        buf = (unsigned char *)io_info->u.rbuf + mem_offset_arr[v];
 
         /* Read data */
-        if (H5D_efl_read(efl, addr, size, buf)<0)
+        if(H5D_efl_read(efl, addr, size, buf) < 0)
             HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "block write failed")
 
         /* Update memory information */
-        mem_len_arr[v]-=size;
-        mem_offset_arr[v]+=size;
-        if(mem_len_arr[v]==0)
+        mem_len_arr[v] -= size;
+        mem_offset_arr[v] += size;
+        if(mem_len_arr[v] == 0)
             v++;
 
         /* Update file information */
-        dset_len_arr[u]-=size;
-        dset_offset_arr[u]+=size;
-        if(dset_len_arr[u]==0)
+        dset_len_arr[u] -= size;
+        dset_offset_arr[u] += size;
+        if(dset_len_arr[u] == 0)
             u++;
 
         /* Increment number of bytes copied */
-        total_size+=size;
+        total_size += size;
     } /* end for */
 
     /* Update current sequence vectors */
-    *dset_curr_seq=u;
-    *mem_curr_seq=v;
+    *dset_curr_seq = u;
+    *mem_curr_seq = v;
 
     /* Set return value */
-    H5_ASSIGN_OVERFLOW(ret_value,total_size,size_t,ssize_t);
+    H5_ASSIGN_OVERFLOW(ret_value, total_size, size_t, ssize_t);
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -332,71 +387,68 @@ done:
  * Programmer:	Quincey Koziol
  *              Friday, May  2, 2003
  *
- * Modifications:
- *
  *-------------------------------------------------------------------------
  */
-ssize_t
+static ssize_t
 H5D_efl_writevv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED address, void UNUSED *pointer/*in*/, const void *_buf)
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[])
 {
-    const H5O_efl_t *efl=&(io_info->store->efl); /* Pointer to efl info */
+    const H5O_efl_t *efl = &(io_info->store->efl); /* Pointer to efl info */
     const unsigned char *buf;   /* Pointer to buffer to write */
     haddr_t addr;               /* Actual address to read */
-    size_t total_size=0;        /* Total size of sequence in bytes */
+    size_t total_size = 0;      /* Total size of sequence in bytes */
     size_t size;                /* Size of sequence in bytes */
     size_t u;                   /* Counting variable */
     size_t v;                   /* Counting variable */
     ssize_t ret_value;          /* Return value */
 
-    FUNC_ENTER_NOAPI(H5D_efl_writevv, FAIL)
+    FUNC_ENTER_NOAPI_NOINIT(H5D_efl_writevv)
 
     /* Check args */
-    assert (efl && efl->nused>0);
-    assert (_buf);
+    HDassert(efl && efl->nused > 0);
+    HDassert(io_info->u.wbuf);
 
     /* Work through all the sequences */
-    for(u=*dset_curr_seq, v=*mem_curr_seq; u<dset_max_nseq && v<mem_max_nseq; ) {
+    for(u = *dset_curr_seq, v = *mem_curr_seq; u < dset_max_nseq && v < mem_max_nseq; ) {
         /* Choose smallest buffer to write */
-        if(mem_len_arr[v]<dset_len_arr[u])
-            size=mem_len_arr[v];
+        if(mem_len_arr[v] < dset_len_arr[u])
+            size = mem_len_arr[v];
         else
-            size=dset_len_arr[u];
+            size = dset_len_arr[u];
 
         /* Compute offset on disk */
-        addr=dset_offset_arr[u];
+        addr = dset_offset_arr[u];
 
         /* Compute offset in memory */
-        buf = (const unsigned char *)_buf + mem_offset_arr[v];
+        buf = (const unsigned char *)io_info->u.wbuf + mem_offset_arr[v];
 
         /* Write data */
-        if (H5D_efl_write(efl, addr, size, buf)<0)
+        if(H5D_efl_write(efl, addr, size, buf) < 0)
             HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "block write failed")
 
         /* Update memory information */
-        mem_len_arr[v]-=size;
-        mem_offset_arr[v]+=size;
-        if(mem_len_arr[v]==0)
+        mem_len_arr[v] -= size;
+        mem_offset_arr[v] += size;
+        if(mem_len_arr[v] == 0)
             v++;
 
         /* Update file information */
-        dset_len_arr[u]-=size;
-        dset_offset_arr[u]+=size;
-        if(dset_len_arr[u]==0)
+        dset_len_arr[u] -= size;
+        dset_offset_arr[u] += size;
+        if(dset_len_arr[u] == 0)
             u++;
 
         /* Increment number of bytes copied */
-        total_size+=size;
+        total_size += size;
     } /* end for */
 
     /* Update current sequence vectors */
-    *dset_curr_seq=u;
-    *mem_curr_seq=v;
+    *dset_curr_seq = u;
+    *mem_curr_seq = v;
 
     /* Set return value */
-    H5_ASSIGN_OVERFLOW(ret_value,total_size,size_t,ssize_t);
+    H5_ASSIGN_OVERFLOW(ret_value, total_size, size_t, ssize_t);
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5Dfill.c b/src/H5Dfill.c
index bfb4354..4879f4d 100644
--- a/src/H5Dfill.c
+++ b/src/H5Dfill.c
@@ -275,7 +275,7 @@ H5D_fill(const void *fill, const H5T_t *fill_type, void *buf,
                 HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize memory selection information")
 
             /* Scatter the data into memory */
-            if(H5D_select_mscat(tmp_buf, space, &mem_iter, (size_t)nelmts, dxpl_cache, buf/*out*/) < 0) {
+            if(H5D_scatter_mem(tmp_buf, space, &mem_iter, (size_t)nelmts, dxpl_cache, buf/*out*/) < 0) {
                 H5S_SELECT_ITER_RELEASE(&mem_iter);
                 HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "scatter failed")
             } /* end if */
@@ -337,13 +337,13 @@ done:
     if(dst_id != (-1) && H5I_dec_ref(dst_id) < 0)
         HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't decrement temporary datatype ID")
     if(tmp_buf)
-        H5FL_BLK_FREE(type_conv, tmp_buf);
+        (void)H5FL_BLK_FREE(type_conv, tmp_buf);
     if(elem_wb && H5WB_unwrap(elem_wb) < 0)
         HDONE_ERROR(H5E_ATTR, H5E_CLOSEERROR, FAIL, "can't close wrapped buffer")
     if(bkg_elem_wb && H5WB_unwrap(bkg_elem_wb) < 0)
         HDONE_ERROR(H5E_ATTR, H5E_CLOSEERROR, FAIL, "can't close wrapped buffer")
     if(bkg_buf)
-        H5FL_BLK_FREE(type_conv, bkg_buf);
+        (void)H5FL_BLK_FREE(type_conv, bkg_buf);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5D_fill() */
@@ -636,9 +636,9 @@ H5D_fill_release(H5D_fill_buf_info_t *fb_info)
             fb_info->fill_free_func(fb_info->fill_buf, fb_info->fill_free_info);
         else {
             if(fb_info->fill->buf)
-                H5FL_BLK_FREE(non_zero_fill, fb_info->fill_buf);
+                (void)H5FL_BLK_FREE(non_zero_fill, fb_info->fill_buf);
             else
-                H5FL_BLK_FREE(zero_fill, fb_info->fill_buf);
+                (void)H5FL_BLK_FREE(zero_fill, fb_info->fill_buf);
         } /* end else */
         fb_info->fill_buf = NULL;
     } /* end if */
@@ -677,7 +677,7 @@ H5D_fill_term(H5D_fill_buf_info_t *fb_info)
         else if(fb_info->mem_type)
             H5T_close(fb_info->mem_type);
         if(fb_info->bkg_buf)
-            H5FL_BLK_FREE(type_conv, fb_info->bkg_buf);
+            (void)H5FL_BLK_FREE(type_conv, fb_info->bkg_buf);
     } /* end if */
 
     FUNC_LEAVE_NOAPI(SUCCEED)
diff --git a/src/H5Dint.c b/src/H5Dint.c
index a5ea398..acb95d2 100644
--- a/src/H5Dint.c
+++ b/src/H5Dint.c
@@ -59,10 +59,12 @@ typedef struct {
 
 /* General stuff */
 static herr_t H5D_init_storage(H5D_t *dataset, hbool_t full_overwrite, hid_t dxpl_id);
+static herr_t H5D_get_dxpl_cache_real(hid_t dxpl_id, H5D_dxpl_cache_t *cache);
 static H5D_shared_t *H5D_new(hid_t dcpl_id, hbool_t creating, hbool_t vl_type);
 static herr_t H5D_init_type(H5F_t *file, const H5D_t *dset, hid_t type_id,
     const H5T_t *type);
 static herr_t H5D_init_space(H5F_t *file, const H5D_t *dset, const H5S_t *space);
+static herr_t H5D_set_io_ops(H5D_t *dataset);
 static herr_t H5D_update_oh_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset);
 static herr_t H5D_open_oid(H5D_t *dataset, hid_t dxpl_id);
 static herr_t H5D_flush_real(H5D_t *dataset, hid_t dxpl_id, unsigned flags);
@@ -250,6 +252,133 @@ H5D_term_interface(void)
 } /* end H5D_term_interface() */
 
 
+/*--------------------------------------------------------------------------
+ NAME
+    H5D_get_dxpl_cache_real
+ PURPOSE
+    Get all the values for the DXPL cache.
+ USAGE
+    herr_t H5D_get_dxpl_cache_real(dxpl_id, cache)
+        hid_t dxpl_id;          IN: DXPL to query
+        H5D_dxpl_cache_t *cache;IN/OUT: DXPL cache to fill with values
+ RETURNS
+    Non-negative on success/Negative on failure.
+ DESCRIPTION
+    Query all the values from a DXPL that are needed by internal routines
+    within the library.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5D_get_dxpl_cache_real(hid_t dxpl_id, H5D_dxpl_cache_t *cache)
+{
+    H5P_genplist_t *dx_plist;   /* Data transfer property list */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_get_dxpl_cache_real)
+
+    /* Check args */
+    HDassert(cache);
+
+    /* Get the dataset transfer property list */
+    if(NULL == (dx_plist = (H5P_genplist_t *)H5I_object(dxpl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
+
+    /* Get maximum temporary buffer size */
+    if(H5P_get(dx_plist, H5D_XFER_MAX_TEMP_BUF_NAME, &cache->max_temp_buf) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve maximum temporary buffer size")
+
+    /* Get temporary buffer pointer */
+    if(H5P_get(dx_plist, H5D_XFER_TCONV_BUF_NAME, &cache->tconv_buf) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve temporary buffer pointer")
+
+    /* Get background buffer pointer */
+    if(H5P_get(dx_plist, H5D_XFER_BKGR_BUF_NAME, &cache->bkgr_buf) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve background buffer pointer")
+
+    /* Get background buffer type */
+    if(H5P_get(dx_plist, H5D_XFER_BKGR_BUF_TYPE_NAME, &cache->bkgr_buf_type) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve background buffer type")
+
+    /* Get B-tree split ratios */
+    if(H5P_get(dx_plist, H5D_XFER_BTREE_SPLIT_RATIO_NAME, &cache->btree_split_ratio) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve B-tree split ratios")
+
+    /* Get I/O vector size */
+    if(H5P_get(dx_plist, H5D_XFER_HYPER_VECTOR_SIZE_NAME, &cache->vec_size) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve I/O vector size")
+
+#ifdef H5_HAVE_PARALLEL
+    /* Collect Parallel I/O information for possible later use */
+    if(H5P_get(dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &cache->xfer_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve parallel transfer method")
+    if(H5P_get(dx_plist, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME, &cache->coll_opt_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve collective transfer option")
+#endif /* H5_HAVE_PARALLEL */
+
+    /* Get error detection properties */
+    if(H5P_get(dx_plist, H5D_XFER_EDC_NAME, &cache->err_detect) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve error detection info")
+
+    /* Get filter callback function */
+    if(H5P_get(dx_plist, H5D_XFER_FILTER_CB_NAME, &cache->filter_cb) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve filter callback function")
+
+    /* Get the data transform property */
+    if(H5P_get(dx_plist, H5D_XFER_XFORM_NAME, &cache->data_xform_prop) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve data transform info")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+}   /* H5D_get_dxpl_cache_real() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5D_get_dxpl_cache
+ PURPOSE
+    Get all the values for the DXPL cache.
+ USAGE
+    herr_t H5D_get_dxpl_cache(dxpl_id, cache)
+        hid_t dxpl_id;          IN: DXPL to query
+        H5D_dxpl_cache_t *cache;IN/OUT: DXPL cache to fill with values
+ RETURNS
+    Non-negative on success/Negative on failure.
+ DESCRIPTION
+    Query all the values from a DXPL that are needed by internal routines
+    within the library.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    The CACHE pointer should point at already allocated memory to place
+    non-default property list info.  If a default property list is used, the
+    CACHE pointer will be changed to point at the default information.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5D_get_dxpl_cache(hid_t dxpl_id, H5D_dxpl_cache_t **cache)
+{
+    herr_t ret_value=SUCCEED;   /* Return value */
+
+    FUNC_ENTER_NOAPI(H5D_get_dxpl_cache,FAIL)
+
+    /* Check args */
+    assert(cache);
+
+    /* Check for the default DXPL */
+    if(dxpl_id==H5P_DATASET_XFER_DEFAULT)
+        *cache=&H5D_def_dxpl_cache;
+    else
+        if(H5D_get_dxpl_cache_real(dxpl_id,*cache) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "Can't retrieve DXPL values")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+}   /* H5D_get_dxpl_cache() */
+
+
 /*-------------------------------------------------------------------------
  * Function:	H5D_create_named
  *
@@ -556,6 +685,54 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5D_set_io_ops
+ *
+ * Purpose:	Set the I/O operation function pointers for a dataset
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Thursday, March 20, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_set_io_ops(H5D_t *dataset)
+{
+    herr_t ret_value = SUCCEED;		/* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_set_io_ops)
+
+    /* check args */
+    HDassert(dataset);
+
+    /* Set the I/O functions for each layout type */
+    switch(dataset->shared->layout.type) {
+        case H5D_CONTIGUOUS:
+            if(dataset->shared->dcpl_cache.efl.nused > 0)
+                dataset->shared->layout_ops = H5D_LOPS_EFL;
+            else
+                dataset->shared->layout_ops = H5D_LOPS_CONTIG;
+            break;
+
+        case H5D_CHUNKED:
+            dataset->shared->layout_ops = H5D_LOPS_CHUNK;
+            break;
+
+        case H5D_COMPACT:
+            dataset->shared->layout_ops = H5D_LOPS_COMPACT;
+            break;
+
+        default:
+            HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "unknown storage method")
+    } /* end switch */ /*lint !e788 All appropriate cases are covered */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_set_io_ops() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5D_update_oh_info
  *
  * Purpose:	Create and fill object header for dataset
@@ -979,18 +1156,10 @@ H5D_create(H5F_t *file, hid_t type_id, const H5S_t *space, hid_t dcpl_id,
                     } else if(max_points * H5T_get_size(type) > max_storage) {
                         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "data space size exceeds external storage size")
                     }
-
-                    /* Set the I/O functions for this layout type */
-                    new_dset->shared->io_ops.readvv = H5D_efl_readvv;
-                    new_dset->shared->io_ops.writevv = H5D_efl_writevv;
                 } /* end if */
                 else {
                     if(ndims > 0 && max_dim[0] > dim[0])
                         HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, NULL, "extendible contiguous non-external dataset")
-
-                    /* Set the I/O functions for this layout type */
-                    new_dset->shared->io_ops.readvv = H5D_contig_readvv;
-                    new_dset->shared->io_ops.writevv = H5D_contig_writevv;
                 } /* end else */
 
                 /* Compute the total size of a chunk */
@@ -1042,10 +1211,6 @@ H5D_create(H5F_t *file, hid_t type_id, const H5S_t *space, hid_t dcpl_id,
                 for(u = 1, new_dset->shared->layout.u.chunk.size = new_dset->shared->layout.u.chunk.dim[0]; u < new_dset->shared->layout.u.chunk.ndims; u++)
                     new_dset->shared->layout.u.chunk.size *= new_dset->shared->layout.u.chunk.dim[u];
 
-                /* Set the I/O functions for this layout type */
-                new_dset->shared->io_ops.readvv = H5D_istore_readvv;
-                new_dset->shared->io_ops.writevv = H5D_istore_writevv;
-
                 /* Initialize the chunk cache for the dataset */
                 if(H5D_istore_init(file, new_dset) < 0)
                     HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "can't initialize chunk cache")
@@ -1073,10 +1238,6 @@ H5D_create(H5F_t *file, hid_t type_id, const H5S_t *space, hid_t dcpl_id,
                 comp_data_size = H5O_MESG_MAX_SIZE - H5O_layout_meta_size(file, &(new_dset->shared->layout));
                 if(new_dset->shared->layout.u.compact.size > comp_data_size)
                     HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "compact dataset size is bigger than header message maximum size")
-
-                /* Set the I/O functions for this layout type */
-                new_dset->shared->io_ops.readvv = H5D_compact_readvv;
-                new_dset->shared->io_ops.writevv = H5D_compact_writevv;
             } /* end case */
             break;
 
@@ -1084,6 +1245,10 @@ H5D_create(H5F_t *file, hid_t type_id, const H5S_t *space, hid_t dcpl_id,
             HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, NULL, "not implemented yet")
     } /* end switch */ /*lint !e788 All appropriate cases are covered */
 
+    /* Set the dataset's I/O operations */
+    if(H5D_set_io_ops(new_dset) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "unable to initialize I/O operations")
+
     /* Update the dataset's object header info. */
     if(H5D_update_oh_info(file, dxpl_id, new_dset) != SUCCEED)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "can't update the metadata cache")
@@ -1252,9 +1417,9 @@ static herr_t
 H5D_open_oid(H5D_t *dataset, hid_t dxpl_id)
 {
     H5P_genplist_t *plist;              /* Property list */
-    H5O_pline_t  *pline;                /* I/O pipeline information */
     H5O_fill_t *fill_prop;              /* Pointer to dataset's fill value info */
     unsigned alloc_time_state;          /* Allocation time state */
+    htri_t msg_exists;                  /* Whether a particular type of message exists */
     herr_t ret_value = SUCCEED;		/* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_open_oid)
@@ -1285,13 +1450,17 @@ H5D_open_oid(H5D_t *dataset, hid_t dxpl_id)
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "can't get dataset creation property list")
 
     /* Get the optional filters message */
-    pline = &dataset->shared->dcpl_cache.pline;
-    if(NULL != H5O_msg_read(&(dataset->oloc), H5O_PLINE_ID, pline, dxpl_id)) {
-        if(H5P_set(plist, H5D_CRT_DATA_PIPELINE_NAME, pline) < 0)
+    if((msg_exists = H5O_msg_exists(&(dataset->oloc), H5O_PLINE_ID, dxpl_id)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't check if message exists")
+    if(msg_exists) {
+        /* Retrieve the I/O pipeline message */
+        if(NULL == H5O_msg_read(&(dataset->oloc), H5O_PLINE_ID, &dataset->shared->dcpl_cache.pline, dxpl_id))
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't retrieve message")
+
+        /* Set the I/O pipeline info in the property list */
+        if(H5P_set(plist, H5D_CRT_DATA_PIPELINE_NAME, &dataset->shared->dcpl_cache.pline) < 0)
             HGOTO_ERROR(H5E_DATASET, H5E_CANTSET, FAIL, "can't set pipeline")
     } /* end if */
-    else
-        H5E_clear_stack(NULL);
 
     /*
      * Get the raw data layout info.  It's actually stored in two locations:
@@ -1316,10 +1485,6 @@ H5D_open_oid(H5D_t *dataset, hid_t dxpl_id)
                 H5_ASSIGN_OVERFLOW(dataset->shared->layout.u.contig.size, tmp_size, hssize_t, hsize_t);
             } /* end if */
 
-            /* Set the I/O functions for this layout type */
-            dataset->shared->io_ops.readvv = H5D_contig_readvv;
-            dataset->shared->io_ops.writevv = H5D_contig_writevv;
-
             /* Get the sieve buffer size for this dataset */
             dataset->shared->cache.contig.sieve_buf_size = H5F_SIEVE_BUF_SIZE(dataset->oloc.file);
             break;
@@ -1344,33 +1509,34 @@ H5D_open_oid(H5D_t *dataset, hid_t dxpl_id)
                 if(H5D_istore_init(dataset->oloc.file, dataset) < 0)
                     HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "can't initialize chunk cache")
             }
-
-            /* Set the I/O functions for this layout type */
-            dataset->shared->io_ops.readvv = H5D_istore_readvv;
-            dataset->shared->io_ops.writevv = H5D_istore_writevv;
             break;
 
         case H5D_COMPACT:
-            /* Set the I/O functions for this layout type */
-            dataset->shared->io_ops.readvv = H5D_compact_readvv;
-            dataset->shared->io_ops.writevv = H5D_compact_writevv;
             break;
 
         default:
-            HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "not implemented yet")
+            HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "unknown storage method")
     } /* end switch */ /*lint !e788 All appropriate cases are covered */
 
     /* Point at dataset's copy, to cache it for later */
     fill_prop = &dataset->shared->dcpl_cache.fill;
 
     /* Try to get the new fill value message from the object header */
-    if(NULL == H5O_msg_read(&(dataset->oloc), H5O_FILL_NEW_ID, fill_prop, dxpl_id)) {
-        H5E_clear_stack(NULL);
-
+    if((msg_exists = H5O_msg_exists(&(dataset->oloc), H5O_FILL_NEW_ID, dxpl_id)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't check if message exists")
+    if(msg_exists) {
+        if(NULL == H5O_msg_read(&(dataset->oloc), H5O_FILL_NEW_ID, fill_prop, dxpl_id))
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't retrieve message")
+    } /* end if */
+    else {
 	/* For backward compatibility, try to retrieve the old fill value message */
-        if(NULL == H5O_msg_read(&(dataset->oloc), H5O_FILL_ID, fill_prop, dxpl_id)) {
-            H5E_clear_stack(NULL);
-
+        if((msg_exists = H5O_msg_exists(&(dataset->oloc), H5O_FILL_ID, dxpl_id)) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't check if message exists")
+        if(msg_exists) {
+            if(NULL == H5O_msg_read(&(dataset->oloc), H5O_FILL_ID, fill_prop, dxpl_id))
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't retrieve message")
+        } /* end if */
+        else {
             /* Set the space allocation time appropriately, based on the type of dataset storage */
             switch(dataset->shared->layout.type) {
                 case H5D_COMPACT:
@@ -1388,7 +1554,7 @@ H5D_open_oid(H5D_t *dataset, hid_t dxpl_id)
                 default:
                     HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "not implemented yet")
             } /* end switch */ /*lint !e788 All appropriate cases are covered */
-        } /* end if */
+        } /* end else */
 
         /* If "old" fill value size is 0 (undefined), map it to -1 */
         if(fill_prop->size == 0)
@@ -1412,18 +1578,23 @@ H5D_open_oid(H5D_t *dataset, hid_t dxpl_id)
      * also undefined when space allocate time is H5D_ALLOC_TIME_LATE. */
     if((dataset->shared->layout.type == H5D_CONTIGUOUS && !H5F_addr_defined(dataset->shared->layout.u.contig.addr))
             || (dataset->shared->layout.type == H5D_CHUNKED && !H5F_addr_defined(dataset->shared->layout.u.chunk.addr))) {
-        if(NULL != H5O_msg_read(&(dataset->oloc), H5O_EFL_ID, &dataset->shared->dcpl_cache.efl, dxpl_id)) {
+        if((msg_exists = H5O_msg_exists(&(dataset->oloc), H5O_EFL_ID, dxpl_id)) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't check if message exists")
+        if(msg_exists) {
+            /* Retrieve the EFL  message */
+            if(NULL == H5O_msg_read(&(dataset->oloc), H5O_EFL_ID, &dataset->shared->dcpl_cache.efl, dxpl_id))
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't retrieve message")
+
+            /* Set the EFL info in the property list */
             if(H5P_set(plist, H5D_CRT_EXT_FILE_LIST_NAME, &dataset->shared->dcpl_cache.efl) < 0)
             	HGOTO_ERROR(H5E_DATASET, H5E_CANTSET, FAIL, "can't set external file list")
-
-            /* Override the I/O functions for this layout type */
-            dataset->shared->io_ops.readvv = H5D_efl_readvv;
-            dataset->shared->io_ops.writevv = H5D_efl_writevv;
         } /* end if */
-        else
-            H5E_clear_stack(NULL);
     } /* end if */
 
+    /* Set the dataset's I/O operations */
+    if(H5D_set_io_ops(dataset) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize I/O operations")
+
     /*
      * Make sure all storage is properly initialized.
      * This is important only for parallel I/O where the space must
@@ -2334,7 +2505,7 @@ H5D_set_extent(H5D_t *dset, const hsize_t *size, hid_t dxpl_id)
                 HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't fill dxpl cache")
 
             /* Construct dataset I/O info */
-            H5D_BUILD_IO_INFO(&io_info, dset, dxpl_cache, dxpl_id, NULL);
+            H5D_BUILD_IO_INFO_RD(&io_info, dset, dxpl_cache, dxpl_id, NULL, NULL);
 
             /* Remove excess chunks */
             if(H5D_istore_prune_by_extent(&io_info, curr_dims) < 0)
diff --git a/src/H5Dio.c b/src/H5Dio.c
index 8576464..17bab19 100644
--- a/src/H5Dio.c
+++ b/src/H5Dio.c
@@ -28,27 +28,17 @@
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5FLprivate.h"	/* Free Lists                           */
 #include "H5Iprivate.h"		/* IDs			  		*/
-#include "H5MMprivate.h"	/* Memory management			*/
-#include "H5Sprivate.h"		/* Dataspace functions			*/
-#include "H5SLprivate.h"	/* Skip lists				*/
-#include "H5Vprivate.h"		/* Vector and array functions		*/
 
 #ifdef H5_HAVE_PARALLEL
 /* Remove this if H5R_DATASET_REGION is no longer used in this file */
-#   include "H5Rpublic.h"
+#include "H5Rpublic.h"
 #endif /*H5_HAVE_PARALLEL*/
 
+
 /****************/
 /* Local Macros */
 /****************/
 
-#define H5D_DEFAULT_SKIPLIST_HEIGHT     8
-
-/* Macros for iterating over chunks to operate on */
-#define H5D_CHUNK_GET_FIRST_NODE(map) (map.use_single ? (H5SL_node_t *)(1) : H5SL_first(map.sel_chunks))
-#define H5D_CHUNK_GET_NODE_INFO(map, node)  (map.use_single ? map.single_chunk_info : (H5D_chunk_info_t *)H5SL_item(node))
-#define H5D_CHUNK_GET_NEXT_NODE(map, node)  (map.use_single ? (H5SL_node_t *)NULL : H5SL_next(node))
-
 
 /******************/
 /* Local Typedefs */
@@ -59,64 +49,36 @@
 /* Local Prototypes */
 /********************/
 
+/* Internal I/O routines */
 static herr_t H5D_read(H5D_t *dataset, hid_t mem_type_id,
-			const H5S_t *mem_space, const H5S_t *file_space,
-			hid_t dset_xfer_plist, void *buf/*out*/);
+    const H5S_t *mem_space, const H5S_t *file_space, hid_t dset_xfer_plist,
+    void *buf/*out*/);
 static herr_t H5D_write(H5D_t *dataset, hid_t mem_type_id,
-			 const H5S_t *mem_space, const H5S_t *file_space,
-			 hid_t dset_xfer_plist, const void *buf);
-static herr_t H5D_contig_read(H5D_io_info_t *io_info, hsize_t nelmts,
-            const H5T_t *mem_type, const H5S_t *mem_space,
-            const H5S_t *file_space, H5T_path_t *tpath,
-            hid_t src_id, hid_t dst_id,  void *buf/*out*/);
-static herr_t H5D_contig_write(H5D_io_info_t *io_info, hsize_t nelmts,
-            const H5T_t *mem_type, const H5S_t *mem_space,
-	    const H5S_t *file_space, H5T_path_t *tpath,
-            hid_t src_id, hid_t dst_id, const void *buf);
-static herr_t H5D_chunk_read(H5D_io_info_t *io_info, hsize_t nelmts,
-            const H5T_t *mem_type, const H5S_t *mem_space,
-            const H5S_t *file_space, H5T_path_t *tpath,
-            hid_t src_id, hid_t dst_id, void *buf/*out*/);
-static herr_t H5D_chunk_write(H5D_io_info_t *io_info, hsize_t nelmts,
-            const H5T_t *mem_type, const H5S_t *mem_space,
-	    const H5S_t *file_space, H5T_path_t *tpath,
-            hid_t src_id, hid_t dst_id, const void *buf);
-static herr_t H5D_compound_opt_read(size_t nelmts, const H5S_t *mem_space,
-            H5S_sel_iter_t *iter, const H5D_dxpl_cache_t *dxpl_cache, 
-            hid_t src_id, hid_t dst_id, H5T_subset_t subset, void *data_buf, 
-            void *user_buf/*out*/);
-static herr_t H5D_compound_opt_write(size_t nelmts, hid_t src_id, hid_t dst_id, 
-            void *data_buf);
+    const H5S_t *mem_space, const H5S_t *file_space, hid_t dset_xfer_plist,
+    const void *buf);
 
+/* Setup/teardown routines */
+static herr_t H5D_ioinfo_init(H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache,
+    hid_t dxpl_id, const H5D_type_info_t *type_info, H5D_storage_t *store,
+    H5D_io_info_t *io_info);
+static herr_t H5D_typeinfo_init(const H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache,
+    hid_t dxpl_id, hid_t mem_type_id, hbool_t do_write,
+    H5D_type_info_t *type_info);
 #ifdef H5_HAVE_PARALLEL
+static herr_t H5D_ioinfo_adjust(H5D_io_info_t *io_info, const H5D_t *dset,
+    const H5D_dxpl_cache_t *dxpl_cache, hid_t dxpl_id,
+    const H5S_t *file_space, const H5S_t *mem_space,
+    const H5D_type_info_t *type_info, const H5D_chunk_map_t *fm);
 static herr_t H5D_ioinfo_term(H5D_io_info_t *io_info);
 #endif /* H5_HAVE_PARALLEL */
+static herr_t H5D_typeinfo_term(const H5D_type_info_t *type_info);
 
-/* I/O info operations */
-static herr_t H5D_ioinfo_init(H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache,
-    hid_t dxpl_id, const H5S_t *mem_space, const H5S_t *file_space,
-    H5T_path_t *tpath, H5D_io_info_t *io_info);
-
-/* Chunk operations */
-static herr_t H5D_create_chunk_map(H5D_chunk_map_t *fm, const H5D_io_info_t *io_info,
-    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
-    const H5T_t *mem_type);
-static herr_t H5D_destroy_chunk_map(const H5D_chunk_map_t *fm);
-static herr_t H5D_free_chunk_info(void *item, void *key, void *opdata);
-static herr_t H5D_create_chunk_map_single(H5D_chunk_map_t *fm,
-    const H5D_io_info_t *io_info);
-static herr_t H5D_create_chunk_file_map_hyper(H5D_chunk_map_t *fm,
-    const H5D_io_info_t *io_info);
-static herr_t H5D_create_chunk_mem_map_hyper(const H5D_chunk_map_t *fm);
-static herr_t H5D_chunk_file_cb(void *elem, hid_t type_id, unsigned ndims,
-    const hsize_t *coords, void *fm);
-static herr_t H5D_chunk_mem_cb(void *elem, hid_t type_id, unsigned ndims,
-    const hsize_t *coords, void *fm);
 
 /*********************/
 /* Package Variables */
 /*********************/
 
+
 /*******************/
 /* Local Variables */
 /*******************/
@@ -124,142 +86,6 @@ static herr_t H5D_chunk_mem_cb(void *elem, hid_t type_id, unsigned ndims,
 /* Declare a free list to manage blocks of type conversion data */
 H5FL_BLK_DEFINE(type_conv);
 
-/* Declare a free list to manage the H5D_chunk_info_t struct */
-H5FL_DEFINE(H5D_chunk_info_t);
-
-/* Declare a free list to manage sequences of size_t */
-H5FL_SEQ_DEFINE_STATIC(size_t);
-
-/* Declare a free list to manage sequences of hsize_t */
-H5FL_SEQ_DEFINE_STATIC(hsize_t);
-
-
-
-/*--------------------------------------------------------------------------
- NAME
-    H5D_get_dxpl_cache_real
- PURPOSE
-    Get all the values for the DXPL cache.
- USAGE
-    herr_t H5D_get_dxpl_cache_real(dxpl_id, cache)
-        hid_t dxpl_id;          IN: DXPL to query
-        H5D_dxpl_cache_t *cache;IN/OUT: DXPL cache to fill with values
- RETURNS
-    Non-negative on success/Negative on failure.
- DESCRIPTION
-    Query all the values from a DXPL that are needed by internal routines
-    within the library.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-herr_t
-H5D_get_dxpl_cache_real(hid_t dxpl_id, H5D_dxpl_cache_t *cache)
-{
-    H5P_genplist_t *dx_plist;   /* Data transfer property list */
-    herr_t ret_value=SUCCEED;   /* Return value */
-
-    FUNC_ENTER_NOAPI(H5D_get_dxpl_cache_real,FAIL)
-
-    /* Check args */
-    assert(cache);
-
-    /* Get the dataset transfer property list */
-    if (NULL == (dx_plist = (H5P_genplist_t *)H5I_object(dxpl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
-
-    /* Get maximum temporary buffer size */
-    if(H5P_get(dx_plist, H5D_XFER_MAX_TEMP_BUF_NAME, &cache->max_temp_buf) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve maximum temporary buffer size")
-
-    /* Get temporary buffer pointer */
-    if(H5P_get(dx_plist, H5D_XFER_TCONV_BUF_NAME, &cache->tconv_buf) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve temporary buffer pointer")
-
-    /* Get background buffer pointer */
-    if(H5P_get(dx_plist, H5D_XFER_BKGR_BUF_NAME, &cache->bkgr_buf) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve background buffer pointer")
-
-    /* Get background buffer type */
-    if(H5P_get(dx_plist, H5D_XFER_BKGR_BUF_TYPE_NAME, &cache->bkgr_buf_type) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve background buffer type")
-
-    /* Get B-tree split ratios */
-    if(H5P_get(dx_plist, H5D_XFER_BTREE_SPLIT_RATIO_NAME, &cache->btree_split_ratio) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve B-tree split ratios")
-
-    /* Get I/O vector size */
-    if(H5P_get(dx_plist, H5D_XFER_HYPER_VECTOR_SIZE_NAME, &cache->vec_size) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve I/O vector size")
-
-#ifdef H5_HAVE_PARALLEL
-    /* Collect Parallel I/O information for possible later use */
-     if(H5P_get(dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &cache->xfer_mode) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve parallel transfer method")
-     if(H5P_get(dx_plist, H5D_XFER_IO_XFER_OPT_MODE_NAME, &cache->xfer_opt_mode) < 0)
-       HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve parallel transfer method")
-#endif /*H5_HAVE_PARALLEL*/
-
-    /* Get error detection properties */
-    if(H5P_get(dx_plist, H5D_XFER_EDC_NAME, &cache->err_detect) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve error detection info")
-
-    /* Get filter callback function */
-    if(H5P_get(dx_plist, H5D_XFER_FILTER_CB_NAME, &cache->filter_cb) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve filter callback function")
-
-    /* Get the data transform property */
-    if(H5P_get(dx_plist, H5D_XFER_XFORM_NAME, &cache->data_xform_prop) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve data transform info")
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-}   /* H5D_get_dxpl_cache_real() */
-
-
-/*--------------------------------------------------------------------------
- NAME
-    H5D_get_dxpl_cache
- PURPOSE
-    Get all the values for the DXPL cache.
- USAGE
-    herr_t H5D_get_dxpl_cache(dxpl_id, cache)
-        hid_t dxpl_id;          IN: DXPL to query
-        H5D_dxpl_cache_t *cache;IN/OUT: DXPL cache to fill with values
- RETURNS
-    Non-negative on success/Negative on failure.
- DESCRIPTION
-    Query all the values from a DXPL that are needed by internal routines
-    within the library.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
-    The CACHE pointer should point at already allocated memory to place
-    non-default property list info.  If a default property list is used, the
-    CACHE pointer will be changed to point at the default information.
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-herr_t
-H5D_get_dxpl_cache(hid_t dxpl_id, H5D_dxpl_cache_t **cache)
-{
-    herr_t ret_value=SUCCEED;   /* Return value */
-
-    FUNC_ENTER_NOAPI(H5D_get_dxpl_cache,FAIL)
-
-    /* Check args */
-    assert(cache);
-
-    /* Check for the default DXPL */
-    if(dxpl_id==H5P_DATASET_XFER_DEFAULT)
-        *cache=&H5D_def_dxpl_cache;
-    else
-        if(H5D_get_dxpl_cache_real(dxpl_id,*cache) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "Can't retrieve DXPL values")
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-}   /* H5D_get_dxpl_cache() */
 
 
 /*-------------------------------------------------------------------------
@@ -300,7 +126,7 @@ H5Dread(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
     const H5S_t		   *mem_space = NULL;
     const H5S_t		   *file_space = NULL;
     char                    fake_char;
-    herr_t                  ret_value=SUCCEED;  /* Return value */
+    herr_t                  ret_value = SUCCEED;  /* Return value */
 
     FUNC_ENTER_API(H5Dread, FAIL)
     H5TRACE6("e", "iiiiix", dset_id, mem_type_id, mem_space_id, file_space_id,
@@ -316,7 +142,7 @@ H5Dread(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
 	    HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data space")
 
 	/* Check for valid selection */
-	if(H5S_SELECT_VALID(mem_space)!=TRUE)
+	if(H5S_SELECT_VALID(mem_space) != TRUE)
 	    HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "selection+offset not within extent")
     } /* end if */
     if(H5S_ALL != file_space_id) {
@@ -324,33 +150,33 @@ H5Dread(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
 	    HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data space")
 
 	/* Check for valid selection */
-	if(H5S_SELECT_VALID(file_space)!=TRUE)
+	if(H5S_SELECT_VALID(file_space) != TRUE)
 	    HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "selection+offset not within extent")
-    }
+    } /* end if */
 
     /* Get the default dataset transfer property list if the user didn't provide one */
     if (H5P_DEFAULT == plist_id)
         plist_id= H5P_DATASET_XFER_DEFAULT;
     else
-        if (TRUE!=H5P_isa_class(plist_id,H5P_DATASET_XFER))
+        if(TRUE != H5P_isa_class(plist_id, H5P_DATASET_XFER))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms")
-    if (!buf && H5S_GET_SELECT_NPOINTS(file_space)!=0)
+    if(!buf && H5S_GET_SELECT_NPOINTS(file_space) != 0)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no output buffer")
 
     /* If the buffer is nil, and 0 element is selected, make a fake buffer.
      * This is for some MPI package like ChaMPIon on NCSA's tungsten which 
      * doesn't support this feature. 
      */ 
-    if (!buf)
+    if(!buf)
         buf = &fake_char;
 
     /* read raw data */
-    if (H5D_read(dset, mem_type_id, mem_space, file_space, plist_id, buf/*out*/) < 0)
+    if(H5D_read(dset, mem_type_id, mem_space, file_space, plist_id, buf/*out*/) < 0)
 	HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "can't read data")
 
 done:
     FUNC_LEAVE_API(ret_value)
-}
+} /* end H5Dread() */
 
 
 /*-------------------------------------------------------------------------
@@ -392,7 +218,7 @@ H5Dwrite(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
     const H5S_t		   *mem_space = NULL;
     const H5S_t		   *file_space = NULL;
     char                    fake_char;
-    herr_t                  ret_value=SUCCEED;  /* Return value */
+    herr_t                  ret_value = SUCCEED;  /* Return value */
 
     FUNC_ENTER_API(H5Dwrite, FAIL)
     H5TRACE6("e", "iiiii*x", dset_id, mem_type_id, mem_space_id, file_space_id,
@@ -408,7 +234,7 @@ H5Dwrite(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
 	    HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data space")
 
 	/* Check for valid selection */
-	if (H5S_SELECT_VALID(mem_space)!=TRUE)
+	if(H5S_SELECT_VALID(mem_space) != TRUE)
 	    HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "memory selection+offset not within extent")
     } /* end if */
     if(H5S_ALL != file_space_id) {
@@ -416,7 +242,7 @@ H5Dwrite(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
 	    HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data space")
 
 	/* Check for valid selection */
-	if(H5S_SELECT_VALID(file_space)!=TRUE)
+	if(H5S_SELECT_VALID(file_space) != TRUE)
 	    HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "file selection+offset not within extent")
     } /* end if */
 
@@ -424,16 +250,16 @@ H5Dwrite(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
     if(H5P_DEFAULT == plist_id)
         plist_id= H5P_DATASET_XFER_DEFAULT;
     else
-        if(TRUE!=H5P_isa_class(plist_id,H5P_DATASET_XFER))
+        if(TRUE != H5P_isa_class(plist_id, H5P_DATASET_XFER))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms")
-    if(!buf && H5S_GET_SELECT_NPOINTS(file_space)!=0)
+    if(!buf && H5S_GET_SELECT_NPOINTS(file_space) != 0)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no output buffer")
     
     /* If the buffer is nil, and 0 element is selected, make a fake buffer.
      * This is for some MPI package like ChaMPIon on NCSA's tungsten which 
      * doesn't support this feature. 
      */ 
-    if (!buf)
+    if(!buf)
         buf = &fake_char;
 
     /* write raw data */
@@ -442,7 +268,7 @@ H5Dwrite(hid_t dset_id, hid_t mem_type_id, hid_t mem_space_id,
 
 done:
     FUNC_LEAVE_API(ret_value)
-}
+} /* end H5Dwrite() */
 
 
 /*-------------------------------------------------------------------------
@@ -462,16 +288,18 @@ static herr_t
 H5D_read(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
 	 const H5S_t *file_space, hid_t dxpl_id, void *buf/*out*/)
 {
+    H5D_chunk_map_t fm;                 /* Chunk file<->memory mapping */
+    H5D_io_info_t io_info;              /* Dataset I/O info     */
+    H5D_type_info_t type_info;          /* Datatype info for operation */
+    H5D_storage_t store;                /*union of EFL and chunk pointer in file space */
     hssize_t	snelmts;                /*total number of elmts	(signed) */
     hsize_t	nelmts;                 /*total number of elmts	*/
-    H5T_path_t	*tpath = NULL;		/*type conversion info	*/
-    const H5T_t	*mem_type = NULL;       /* Memory datatype */
-    H5D_io_info_t io_info;              /* Dataset I/O info     */
 #ifdef H5_HAVE_PARALLEL
     hbool_t     io_info_init = FALSE;   /* Whether the I/O info has been initialized */
 #endif /*H5_HAVE_PARALLEL*/
+    hbool_t     io_op_init = FALSE;     /* Whether the I/O op has been initialized */
     H5D_dxpl_cache_t _dxpl_cache;       /* Data transfer property cache buffer */
-    H5D_dxpl_cache_t *dxpl_cache=&_dxpl_cache;   /* Data transfer property cache */
+    H5D_dxpl_cache_t *dxpl_cache = &_dxpl_cache;   /* Data transfer property cache */
     herr_t	ret_value = SUCCEED;	/* Return value	*/
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_read)
@@ -479,10 +307,6 @@ H5D_read(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
     /* check args */
     HDassert(dataset && dataset->oloc.file);
 
-    /* Get memory datatype */
-    if(NULL == (mem_type = (const H5T_t *)H5I_object_verify(mem_type_id, H5I_DATATYPE)))
-	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a datatype")
-
     if(!file_space)
         file_space = dataset->shared->space;
     if(!mem_space)
@@ -492,23 +316,27 @@ H5D_read(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
     H5_ASSIGN_OVERFLOW(nelmts,snelmts,hssize_t,hsize_t);
 
     /* Fill the DXPL cache values for later use */
-    if(H5D_get_dxpl_cache(dxpl_id,&dxpl_cache) < 0)
+    if(H5D_get_dxpl_cache(dxpl_id, &dxpl_cache) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't fill dxpl cache")
 
+    /* Set up datatype info for operation */
+    if(H5D_typeinfo_init(dataset, dxpl_cache, dxpl_id, mem_type_id, FALSE, &type_info) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to set up type info")
+
 #ifdef H5_HAVE_PARALLEL
     /* Collective access is not permissible without a MPI based VFD */
-    if (dxpl_cache->xfer_mode==H5FD_MPIO_COLLECTIVE && !IS_H5FD_MPI(dataset->oloc.file))
+    if(dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE && !IS_H5FD_MPI(dataset->oloc.file))
         HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "collective access for MPI-based drivers only")
 #endif /*H5_HAVE_PARALLEL*/
 
     /* Make certain that the number of elements in each selection is the same */
-    if (nelmts!=(hsize_t)H5S_GET_SELECT_NPOINTS(file_space))
+    if(nelmts != (hsize_t)H5S_GET_SELECT_NPOINTS(file_space))
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "src and dest data spaces have different sizes")
 
     /* Make sure that both selections have their extents set */
-    if( !(H5S_has_extent(file_space)) )
+    if(!(H5S_has_extent(file_space)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "file dataspace does not have extent set")
-    if( !(H5S_has_extent(mem_space)) )
+    if(!(H5S_has_extent(mem_space)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "memory dataspace does not have extent set")
 
     /* Retrieve dataset properties */
@@ -539,49 +367,56 @@ H5D_read(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
             HGOTO_DONE(SUCCEED)
 
         /* Go fill the user's selection with the dataset's fill value */
-        if(H5D_fill(dataset->shared->dcpl_cache.fill.buf, dataset->shared->type, buf, mem_type, mem_space, dxpl_id) < 0)
+        if(H5D_fill(dataset->shared->dcpl_cache.fill.buf, dataset->shared->type, buf, type_info.mem_type, mem_space, dxpl_id) < 0)
             HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "filling buf failed")
         else
             HGOTO_DONE(SUCCEED)
     } /* end if */
 
-    /*
-     * Locate the type conversion function and data space conversion
-     * functions, and set up the element numbering information. If a data
-     * type conversion is necessary then register datatype atoms. Data type
-     * conversion is necessary if the user has set the `need_bkg' to a high
-     * enough value in xfer_parms since turning off datatype conversion also
-     * turns off background preservation.
-     */
-    if (NULL==(tpath=H5T_path_find(dataset->shared->type, mem_type, NULL, NULL, dxpl_id, FALSE)))
-        HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "unable to convert between src and dest datatype")
-
     /* Set up I/O operation */
-    if(H5D_ioinfo_init(dataset,dxpl_cache,dxpl_id,mem_space,file_space,tpath,&io_info) < 0)
+    io_info.op_type = H5D_IO_OP_READ;
+    io_info.u.rbuf = buf;
+    if(H5D_ioinfo_init(dataset, dxpl_cache, dxpl_id, &type_info, &store, &io_info) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "unable to set up I/O operation")
 #ifdef H5_HAVE_PARALLEL
     io_info_init = TRUE;
 #endif /*H5_HAVE_PARALLEL*/
 
-    /* Determine correct I/O routine to invoke */
-    if(dataset->shared->layout.type!=H5D_CHUNKED) {
-        if(H5D_contig_read(&io_info, nelmts, mem_type, mem_space, file_space, tpath,
-                dataset->shared->type_id, mem_type_id, buf) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "can't read data")
-    } /* end if */
-    else {
-        if(H5D_chunk_read(&io_info, nelmts, mem_type, mem_space, file_space, tpath,
-                dataset->shared->type_id, mem_type_id, buf) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "can't read data")
-    } /* end else */
+    /* Sanity check that space is allocated, if there are elements */
+    if(nelmts > 0)
+        HDassert(((dataset->shared->layout.type == H5D_CONTIGUOUS && H5F_addr_defined(dataset->shared->layout.u.contig.addr))
+                || (dataset->shared->layout.type == H5D_CHUNKED && H5F_addr_defined(dataset->shared->layout.u.chunk.addr)))
+                || dataset->shared->dcpl_cache.efl.nused > 0
+                || dataset->shared->layout.type == H5D_COMPACT);
+
+    /* Call storage method's I/O initialization routine */
+    if(io_info.layout_ops.init && (*io_info.layout_ops.init)(&io_info, &type_info, nelmts, file_space, mem_space, &fm) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "can't initialize I/O info")
+    io_op_init = TRUE;
+
+#ifdef H5_HAVE_PARALLEL
+    /* Adjust I/O info for any parallel I/O */
+    if(H5D_ioinfo_adjust(&io_info, dataset, dxpl_cache, dxpl_id, file_space, mem_space, &type_info, &fm) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to adjust I/O info for parallel I/O")
+#endif /*H5_HAVE_PARALLEL*/
+
+    /* Invoke correct "high level" I/O routine */
+    if((*io_info.io_ops.multi_read)(&io_info, &type_info, nelmts, file_space, mem_space, &fm) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "can't read data")
 
 done:
+    /* Shut down the I/O op information */
+    if(io_op_init && io_info.layout_ops.term && (*io_info.layout_ops.term)(&fm) < 0)
+        HDONE_ERROR(H5E_DATASET, H5E_CANTCLOSEOBJ, FAIL, "unable to shut down I/O op info")
 #ifdef H5_HAVE_PARALLEL
     /* Shut down io_info struct */
-    if (io_info_init)
+    if(io_info_init)
         if(H5D_ioinfo_term(&io_info) < 0)
             HDONE_ERROR(H5E_DATASET, H5E_CANTCLOSEOBJ, FAIL, "can't shut down io_info")
 #endif /*H5_HAVE_PARALLEL*/
+    /* Shut down datatype info for operation */
+    if(H5D_typeinfo_term(&type_info) < 0)
+        HDONE_ERROR(H5E_DATASET, H5E_CANTCLOSEOBJ, FAIL, "unable to shut down type info")
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_read() */
@@ -604,16 +439,18 @@ static herr_t
 H5D_write(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
 	  const H5S_t *file_space, hid_t dxpl_id, const void *buf)
 {
+    H5D_chunk_map_t fm;                 /* Chunk file<->memory mapping */
+    H5D_io_info_t io_info;              /* Dataset I/O info     */
+    H5D_type_info_t type_info;          /* Datatype info for operation */
+    H5D_storage_t store;                /*union of EFL and chunk pointer in file space */
     hssize_t	snelmts;                /*total number of elmts	(signed) */
     hsize_t	nelmts;                 /*total number of elmts	*/
-    H5T_path_t	*tpath = NULL;		/*type conversion info	*/
-    const H5T_t	*mem_type = NULL;       /* Memory datatype */
-    H5D_io_info_t io_info;              /* Dataset I/O info     */
 #ifdef H5_HAVE_PARALLEL
     hbool_t     io_info_init = FALSE;   /* Whether the I/O info has been initialized */
 #endif /*H5_HAVE_PARALLEL*/
+    hbool_t     io_op_init = FALSE;     /* Whether the I/O op has been initialized */
     H5D_dxpl_cache_t _dxpl_cache;       /* Data transfer property cache buffer */
-    H5D_dxpl_cache_t *dxpl_cache=&_dxpl_cache;   /* Data transfer property cache */
+    H5D_dxpl_cache_t *dxpl_cache = &_dxpl_cache;   /* Data transfer property cache */
     herr_t	ret_value = SUCCEED;	/* Return value	*/
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_write)
@@ -621,33 +458,33 @@ H5D_write(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
     /* check args */
     HDassert(dataset && dataset->oloc.file);
 
-    /* Get the memory datatype */
-    if(NULL == (mem_type = (const H5T_t *)H5I_object_verify(mem_type_id, H5I_DATATYPE)))
-	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a datatype")
-
     /* All filters in the DCPL must have encoding enabled. */
     if(!dataset->shared->checked_filters) {
-        if(H5Z_can_apply(dataset->shared->dcpl_id, dataset->shared->type_id) <0)
+        if(H5Z_can_apply(dataset->shared->dcpl_id, dataset->shared->type_id) < 0)
             HGOTO_ERROR(H5E_PLINE, H5E_CANAPPLY, FAIL, "can't apply filters")
 
         dataset->shared->checked_filters = TRUE;
     } /* end if */
 
     /* Check if we are allowed to write to this file */
-    if(0==(H5F_get_intent(dataset->oloc.file) & H5F_ACC_RDWR))
+    if(0 == (H5F_INTENT(dataset->oloc.file) & H5F_ACC_RDWR))
 	HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "no write intent on file")
 
     /* Fill the DXPL cache values for later use */
-    if(H5D_get_dxpl_cache(dxpl_id,&dxpl_cache) < 0)
+    if(H5D_get_dxpl_cache(dxpl_id, &dxpl_cache) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't fill dxpl cache")
 
+    /* Set up datatype info for operation */
+    if(H5D_typeinfo_init(dataset, dxpl_cache, dxpl_id, mem_type_id, TRUE, &type_info) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to set up type info")
+
     /* Various MPI based checks */
 #ifdef H5_HAVE_PARALLEL
     if(IS_H5FD_MPI(dataset->oloc.file)) {
         /* If MPI based VFD is used, no VL datatype support yet. */
         /* This is because they use the global heap in the file and we don't */
         /* support parallel access of that yet */
-        if(H5T_detect_class(mem_type, H5T_VLEN)>0)
+        if(H5T_detect_class(type_info.mem_type, H5T_VLEN) > 0)
             HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "Parallel IO does not support writing VL datatypes yet")
 
         /* If MPI based VFD is used, no VL datatype support yet. */
@@ -656,42 +493,48 @@ H5D_write(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
         /* We should really use H5T_detect_class() here, but it will be difficult
          * to detect the type of the reference if it is nested... -QAK
          */
-        if (H5T_get_class(mem_type, TRUE)==H5T_REFERENCE &&
-                H5T_get_ref_type(mem_type)==H5R_DATASET_REGION)
+        if(H5T_get_class(type_info.mem_type, TRUE) == H5T_REFERENCE &&
+                H5T_get_ref_type(type_info.mem_type) == H5R_DATASET_REGION)
             HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "Parallel IO does not support writing region reference datatypes yet")
+
+        /* Can't write to chunked datasets with filters, in parallel */
+        if(dataset->shared->layout.type == H5D_CHUNKED &&
+                dataset->shared->dcpl_cache.pline.nused > 0)
+            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "cannot write to chunked storage with filters in parallel")
     } /* end if */
     else {
         /* Collective access is not permissible without a MPI based VFD */
-        if (dxpl_cache->xfer_mode==H5FD_MPIO_COLLECTIVE)
+        if(dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE)
             HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "collective access for MPI-based driver only")
     } /* end else */
 #endif /*H5_HAVE_PARALLEL*/
 
-    if (!file_space)
+    /* Initialize dataspace information */
+    if(!file_space)
         file_space = dataset->shared->space;
-    if (!mem_space)
+    if(!mem_space)
         mem_space = file_space;
     if((snelmts = H5S_GET_SELECT_NPOINTS(mem_space)) < 0)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "src dataspace has invalid selection")
-    H5_ASSIGN_OVERFLOW(nelmts,snelmts,hssize_t,hsize_t);
+    H5_ASSIGN_OVERFLOW(nelmts, snelmts, hssize_t, hsize_t);
 
     /* Make certain that the number of elements in each selection is the same */
-    if (nelmts!=(hsize_t)H5S_GET_SELECT_NPOINTS(file_space))
+    if(nelmts != (hsize_t)H5S_GET_SELECT_NPOINTS(file_space))
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "src and dest data spaces have different sizes")
 
     /* Make sure that both selections have their extents set */
-    if( !(H5S_has_extent(file_space)) )
+    if(!(H5S_has_extent(file_space)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "file dataspace does not have extent set")
-    if( !(H5S_has_extent(mem_space)) )
+    if(!(H5S_has_extent(mem_space)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "memory dataspace does not have extent set")
 
     /* Retrieve dataset properties */
     /* <none needed currently> */
 
     /* Allocate data space and initialize it if it hasn't been. */
-    if(nelmts > 0 && dataset->shared->dcpl_cache.efl.nused==0 &&
-            ((dataset->shared->layout.type==H5D_CONTIGUOUS && !H5F_addr_defined(dataset->shared->layout.u.contig.addr))
-                || (dataset->shared->layout.type==H5D_CHUNKED && !H5F_addr_defined(dataset->shared->layout.u.chunk.addr)))) {
+    if(nelmts > 0 && dataset->shared->dcpl_cache.efl.nused == 0 &&
+            ((dataset->shared->layout.type == H5D_CONTIGUOUS && !H5F_addr_defined(dataset->shared->layout.u.contig.addr))
+                || (dataset->shared->layout.type == H5D_CHUNKED && !H5F_addr_defined(dataset->shared->layout.u.chunk.addr)))) {
         hssize_t file_nelmts;   /* Number of elements in file dataset's dataspace */
         hbool_t full_overwrite; /* Whether we are over-writing all the elements */
 
@@ -703,42 +546,36 @@ H5D_write(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
         if(H5T_detect_class(dataset->shared->type, H5T_VLEN))
             full_overwrite = FALSE;
         else
-            full_overwrite = (hsize_t)file_nelmts==nelmts ? TRUE : FALSE;
+            full_overwrite = (hsize_t)file_nelmts == nelmts ? TRUE : FALSE;
 
  	/* Allocate storage */
         if(H5D_alloc_storage(dataset->oloc.file, dxpl_id, dataset, H5D_ALLOC_WRITE, full_overwrite) < 0)
             HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize storage")
     } /* end if */
 
-    /*
-     * Locate the type conversion function and data space conversion
-     * functions, and set up the element numbering information. If a data
-     * type conversion is necessary then register datatype atoms. Data type
-     * conversion is necessary if the user has set the `need_bkg' to a high
-     * enough value in xfer_parms since turning off datatype conversion also
-     * turns off background preservation.
-     */
-    if (NULL==(tpath=H5T_path_find(mem_type, dataset->shared->type, NULL, NULL, dxpl_id, FALSE)))
-	HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "unable to convert between src and dest datatype")
-
     /* Set up I/O operation */
-    if(H5D_ioinfo_init(dataset,dxpl_cache,dxpl_id,mem_space,file_space,tpath,&io_info) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "unable to set up I/O operation")
+    io_info.op_type = H5D_IO_OP_WRITE;
+    io_info.u.wbuf = buf;
+    if(H5D_ioinfo_init(dataset, dxpl_cache, dxpl_id, &type_info, &store, &io_info) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to set up I/O operation")
 #ifdef H5_HAVE_PARALLEL
     io_info_init = TRUE;
 #endif /*H5_HAVE_PARALLEL*/
 
-    /* Determine correct I/O routine to invoke */
-    if(dataset->shared->layout.type!=H5D_CHUNKED) {
-        if(H5D_contig_write(&io_info, nelmts, mem_type, mem_space, file_space, tpath,
-                mem_type_id, dataset->shared->type_id, buf) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "can't write data")
-    } /* end if */
-    else {
-        if(H5D_chunk_write(&io_info, nelmts, mem_type, mem_space, file_space, tpath,
-                mem_type_id, dataset->shared->type_id, buf) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "can't write data")
-    } /* end else */
+    /* Call storage method's I/O initialization routine */
+    if(io_info.layout_ops.init && (*io_info.layout_ops.init)(&io_info, &type_info, nelmts, file_space, mem_space, &fm) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "can't initialize I/O info")
+    io_op_init = TRUE;
+
+#ifdef H5_HAVE_PARALLEL
+    /* Adjust I/O info for any parallel I/O */
+    if(H5D_ioinfo_adjust(&io_info, dataset, dxpl_cache, dxpl_id, file_space, mem_space, &type_info, &fm) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to adjust I/O info for parallel I/O")
+#endif /*H5_HAVE_PARALLEL*/
+
+    /* Invoke correct "high level" I/O routine */
+    if((*io_info.io_ops.multi_write)(&io_info, &type_info, nelmts, file_space, mem_space, &fm) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "can't write data")
 
 #ifdef OLD_WAY
 /*
@@ -756,2667 +593,325 @@ H5D_write(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
 #endif /* OLD_WAY */
 
 done:
+    /* Shut down the I/O op information */
+    if(io_op_init && io_info.layout_ops.term && (*io_info.layout_ops.term)(&fm) < 0)
+        HDONE_ERROR(H5E_DATASET, H5E_CANTCLOSEOBJ, FAIL, "unable to shut down I/O op info")
 #ifdef H5_HAVE_PARALLEL
     /* Shut down io_info struct */
-    if (io_info_init)
-        if(H5D_ioinfo_term(&io_info) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTCLOSEOBJ, FAIL, "can't shut down io_info")
+    if(io_info_init && H5D_ioinfo_term(&io_info) < 0)
+        HDONE_ERROR(H5E_DATASET, H5E_CANTCLOSEOBJ, FAIL, "can't shut down io_info")
 #endif /*H5_HAVE_PARALLEL*/
+    /* Shut down datatype info for operation */
+    if(H5D_typeinfo_term(&type_info) < 0)
+        HDONE_ERROR(H5E_DATASET, H5E_CANTCLOSEOBJ, FAIL, "unable to shut down type info")
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_write() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_contig_read
+ * Function:	H5D_ioinfo_init
  *
- * Purpose:	Read from a contiguous dataset.
+ * Purpose:	Routine for determining correct I/O operations for
+ *              each I/O action.
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:	Raymond Lu
- *		Thursday, April 10, 2003
+ * Programmer:	Quincey Koziol
+ *		Thursday, September 30, 2004
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_contig_read(H5D_io_info_t *io_info, hsize_t nelmts,
-    const H5T_t *mem_type, const H5S_t *mem_space,
-    const H5S_t *file_space, H5T_path_t *tpath,
-    hid_t src_id, hid_t dst_id, void *buf/*out*/)
+H5D_ioinfo_init(H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache, hid_t dxpl_id,
+    const H5D_type_info_t *type_info, H5D_storage_t *store, H5D_io_info_t *io_info)
 {
-    H5D_t *dataset=io_info->dset;       /* Local pointer to dataset info */
-    const H5D_dxpl_cache_t *dxpl_cache=io_info->dxpl_cache;     /* Local pointer to dataset transfer info */
-    herr_t      status;                 /*function return status*/
-#ifdef H5S_DEBUG
-    H5_timer_t	timer;
-#endif
-    size_t	src_type_size;		/*size of source type	*/
-    size_t	dst_type_size;	        /*size of destination type*/
-    size_t	max_type_size;	        /* Size of largest source/destination type */
-    size_t	target_size;		/*desired buffer size	*/
-    size_t	request_nelmts;		/*requested strip mine	*/
-    H5S_sel_iter_t mem_iter;            /*memory selection iteration info*/
-    hbool_t	mem_iter_init=0;	/*memory selection iteration info has been initialized */
-    H5S_sel_iter_t bkg_iter;            /*background iteration info*/
-    hbool_t	bkg_iter_init=0;	/*background iteration info has been initialized */
-    H5S_sel_iter_t file_iter;           /*file selection iteration info*/
-    hbool_t	file_iter_init=0;	/*file selection iteration info has been initialized */
-    H5T_bkg_t	need_bkg;		/*type of background buf*/
-    uint8_t	*tconv_buf = NULL;	/*datatype conv buffer	*/
-    uint8_t	*bkg_buf = NULL;	/*background buffer	*/
-    hsize_t	smine_start;		/*strip mine start loc	*/
-    size_t	n, smine_nelmts;	/*elements per strip	*/
-    H5D_storage_t store;                /*union of storage info for dataset */
-
-
-    herr_t	ret_value = SUCCEED;	/*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_contig_read)
-
-    assert (buf);
-
-    /* Initialize storage info for this dataset */
-    if (dataset->shared->dcpl_cache.efl.nused > 0)
-        HDmemcpy(&store.efl, &(dataset->shared->dcpl_cache.efl), sizeof(H5O_efl_t));
-    else {
-        store.contig.dset_addr = dataset->shared->layout.u.contig.addr;
-        store.contig.dset_size = dataset->shared->layout.u.contig.size;
-    } /* end if */
-
-    /* Set dataset storage for I/O info */
-    io_info->store=&store;
-
-    /*
-     * If there is no type conversion then read directly into the
-     * application's buffer.  This saves at least one mem-to-mem copy.
-     */
-    if ( H5Z_xform_noop(dxpl_cache->data_xform_prop) && H5T_path_noop(tpath)) {
-#ifdef H5S_DEBUG
-	H5_timer_begin(&timer);
-#endif
-  	/* Sanity check dataset, then read it */
-        assert(((dataset->shared->layout.type == H5D_CONTIGUOUS && H5F_addr_defined(dataset->shared->layout.u.contig.addr))
-                || (dataset->shared->layout.type == H5D_CHUNKED && H5F_addr_defined(dataset->shared->layout.u.chunk.addr)))
-                || dataset->shared->dcpl_cache.efl.nused > 0 || 0 == nelmts
-                || dataset->shared->layout.type==H5D_COMPACT);
-        H5_CHECK_OVERFLOW(nelmts,hsize_t,size_t);
-
-#ifdef H5_HAVE_PARALLEL
-	if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
-	  if(H5D_contig_collective_io(io_info,file_space,mem_space,buf,FALSE) < 0)
-	    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "contiguous read failed in collective mode");
-	}
-	else
-#endif
-        {
-            if((io_info->ops.read)(io_info, (size_t)nelmts,
-                    H5T_get_size(dataset->shared->type), file_space, mem_space,
-                    (haddr_t)0, NULL, buf/*out*/) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "contiguous read failed ");
-	}
-
-#ifdef H5S_DEBUG
-        H5_timer_end(&(io_info->stats->stats[1].read_timer), &timer);
-        io_info->stats->stats[1].read_nbytes += nelmts * H5T_get_size(dataset->shared->type);
-        io_info->stats->stats[1].read_ncalls++;
-#endif
-
-            /* direct xfer accomplished successfully */
-            HGOTO_DONE(SUCCEED)
-    } /* end if */
-
-    /*
-     * This is the general case (type conversion, usually).
-     */
-    if(nelmts==0)
-        HGOTO_DONE(SUCCEED)
-
-    /* Compute element sizes and other parameters */
-    src_type_size = H5T_get_size(dataset->shared->type);
-    dst_type_size = H5T_get_size(mem_type);
-    max_type_size = MAX(src_type_size, dst_type_size);
-    target_size = dxpl_cache->max_temp_buf;
-    /* XXX: This could cause a problem if the user sets their buffer size
-     * to the same size as the default, and then the dataset elements are
-     * too large for the buffer... - QAK
-     */
-    if(target_size == H5D_TEMP_BUF_SIZE) {
-        /* If the buffer is too small to hold even one element, make it bigger */
-        if(target_size<max_type_size)
-            target_size = max_type_size;
-        /* If the buffer is too large to hold all the elements, make it smaller */
-        else if(target_size>(nelmts*max_type_size))
-            target_size=(size_t)(nelmts*max_type_size);
-    } /* end if */
-    request_nelmts = target_size / max_type_size;
-
-    /* Sanity check elements in temporary buffer */
-    if (request_nelmts==0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "temporary buffer max size is too small")
-
-    /* Figure out the strip mine size. */
-    if (H5S_select_iter_init(&file_iter, file_space, src_type_size) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize file selection information")
-    file_iter_init=1;	/*file selection iteration info has been initialized */
-    if (H5S_select_iter_init(&mem_iter, mem_space, dst_type_size) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize memory selection information")
-    mem_iter_init=1;	/*file selection iteration info has been initialized */
-    if (H5S_select_iter_init(&bkg_iter, mem_space, dst_type_size) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize background selection information")
-    bkg_iter_init=1;	/*file selection iteration info has been initialized */
-
-    /*
-     * Get a temporary buffer for type conversion unless the app has already
-     * supplied one through the xfer properties. Instead of allocating a
-     * buffer which is the exact size, we allocate the target size.  The
-     * malloc() is usually less resource-intensive if we allocate/free the
-     * same size over and over.
-     */
-    if (H5T_path_bkg(tpath)) {
-        H5T_bkg_t path_bkg;     /* Type conversion's background info */
-
-        /* Retrieve the bkgr buffer property */
-        need_bkg=dxpl_cache->bkgr_buf_type;
-        path_bkg = H5T_path_bkg(tpath);
-        need_bkg = MAX(path_bkg, need_bkg);
-    } else {
-        need_bkg = H5T_BKG_NO; /*never needed even if app says yes*/
-    } /* end else */
-    if(NULL == (tconv_buf = (uint8_t *)dxpl_cache->tconv_buf)) {
-        /* Allocate temporary buffer */
-        if(NULL == (tconv_buf = H5FL_BLK_MALLOC(type_conv, target_size)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for type conversion")
-    } /* end if */
-    if(need_bkg && NULL == (bkg_buf = (uint8_t *)dxpl_cache->bkgr_buf)) {
-        /* Allocate background buffer */
-        /* (Need calloc()-like call since memory needs to be initialized) */
-        if(NULL == (bkg_buf = H5FL_BLK_CALLOC(type_conv, (request_nelmts * dst_type_size))))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for background conversion")
-    } /* end if */
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_ioinfo_init)
 
-    /* Start strip mining... */
-    for (smine_start=0; smine_start<nelmts; smine_start+=smine_nelmts) {
-        /* Go figure out how many elements to read from the file */
-        assert(H5S_SELECT_ITER_NELMTS(&file_iter)==(nelmts-smine_start));
-        smine_nelmts = (size_t)MIN(request_nelmts, (nelmts-smine_start));
+    /* check args */
+    HDassert(dset);
+    HDassert(dset->oloc.file);
+    HDassert(type_info);
+    HDassert(type_info->tpath);
+    HDassert(io_info);
 
-        /*
-         * Gather the data from disk into the datatype conversion
-         * buffer. Also gather data from application to background buffer
-         * if necessary.
-         */
-#ifdef H5S_DEBUG
-	H5_timer_begin(&timer);
-#endif
-	/* Sanity check that space is allocated, then read data from it */
-        HDassert(((dataset->shared->layout.type == H5D_CONTIGUOUS && H5F_addr_defined(dataset->shared->layout.u.contig.addr))
-                || (dataset->shared->layout.type == H5D_CHUNKED && H5F_addr_defined(dataset->shared->layout.u.chunk.addr)))
-            || dataset->shared->dcpl_cache.efl.nused > 0 ||
-             dataset->shared->layout.type == H5D_COMPACT);
-        n = H5D_select_fgath(io_info, file_space, &file_iter, smine_nelmts, (haddr_t)0, NULL, tconv_buf/*out*/);
-
-#ifdef H5S_DEBUG
-	H5_timer_end(&(io_info->stats->stats[1].gath_timer), &timer);
-	io_info->stats->stats[1].gath_nbytes += n * src_type_size;
-	io_info->stats->stats[1].gath_ncalls++;
-#endif
-	if (n!=smine_nelmts)
-            HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "file gather failed")
-
-        /* If the source and destination are compound types and subset of each other
-         * and no conversion is needed, copy the data directly into user's buffer and 
-         * bypass the rest of steps.  This optimization is for Chicago company */
-        if(H5T_SUBSET_SRC==H5T_path_compound_subset(tpath)) {
-            if(H5D_compound_opt_read(smine_nelmts, mem_space, &mem_iter, dxpl_cache,
-                src_id, dst_id, H5T_SUBSET_SRC, tconv_buf, buf /*out*/)<0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-
-            continue;
-        } else if(H5T_SUBSET_DST==H5T_path_compound_subset(tpath)) {
-            if(H5D_compound_opt_read(smine_nelmts, mem_space, &mem_iter, dxpl_cache,
-                src_id, dst_id, H5T_SUBSET_DST, tconv_buf, buf /*out*/)<0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-
-            continue;
-        }
-
-        if (H5T_BKG_YES==need_bkg) {
-#ifdef H5S_DEBUG
-            H5_timer_begin(&timer);
-#endif
-            n = H5D_select_mgath(buf, mem_space, &bkg_iter,
-				 smine_nelmts, dxpl_cache, bkg_buf/*out*/);
-#ifdef H5S_DEBUG
-            H5_timer_end(&(io_info->stats->stats[1].bkg_timer), &timer);
-            io_info->stats->stats[1].bkg_nbytes += n * dst_type_size;
-            io_info->stats->stats[1].bkg_ncalls++;
-#endif
-            if (n!=smine_nelmts)
-                HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "mem gather failed")
-        } /* end if */
+    /* Set up "normal" I/O fields */
+    io_info->dset = dset;
+    io_info->dxpl_cache = dxpl_cache;
+    io_info->dxpl_id = dxpl_id;
+    io_info->store = store;
 
-	/*
-         * Perform datatype conversion.
-         */
-        if (H5T_convert(tpath, src_id, dst_id, smine_nelmts, (size_t)0, (size_t)0, tconv_buf, bkg_buf, io_info->dxpl_id) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
+    /* Set I/O operations to initial values */
+    io_info->layout_ops = *dset->shared->layout_ops;
 
-	/* Do the data transform after the conversion (since we're using type mem_type) */
-        if(!H5Z_xform_noop(dxpl_cache->data_xform_prop))
-             if( H5Z_xform_eval(dxpl_cache->data_xform_prop, tconv_buf, smine_nelmts, mem_type) < 0)
-		    HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "Error performing data transform")
+    /* Set the "high-level" I/O operations for the dataset */
+    io_info->io_ops.multi_read = dset->shared->layout_ops->ser_read;
+    io_info->io_ops.multi_write = dset->shared->layout_ops->ser_write;
 
+    /* Set the I/O operations for reading/writing single blocks on disk */
+    if(type_info->is_xform_noop && type_info->is_conv_noop) {
         /*
-         * Scatter the data into memory.
+         * If there is no data transform or type conversion then read directly into
+         *  the application's buffer.  This saves at least one mem-to-mem copy.
          */
-#ifdef H5S_DEBUG
-	H5_timer_begin(&timer);
-#endif
-        status = H5D_select_mscat(tconv_buf, mem_space,
-                          &mem_iter, smine_nelmts, dxpl_cache, buf/*out*/);
-#ifdef H5S_DEBUG
-	H5_timer_end(&(io_info->stats->stats[1].scat_timer), &timer);
-	io_info->stats->stats[1].scat_nbytes += smine_nelmts * dst_type_size;
-	io_info->stats->stats[1].scat_ncalls++;
-#endif
-	if (status<0)
-            HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "scatter failed")
-    } /* end for */
-
-done:
-    /* Release selection iterators */
-    if(file_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
+        io_info->io_ops.single_read = H5D_select_read;
+        io_info->io_ops.single_write = H5D_select_write;
     } /* end if */
-    if(mem_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-    if(bkg_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-
-    if (tconv_buf && NULL==dxpl_cache->tconv_buf)
-        (void)H5FL_BLK_FREE(type_conv,tconv_buf);
-    if (bkg_buf && NULL==dxpl_cache->bkgr_buf)
-        (void)H5FL_BLK_FREE(type_conv,bkg_buf);
-
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_contig_read() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_contig_write
- *
- * Purpose:	Write to a contiguous dataset.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Raymond Lu
- *		Thursday, April 10, 2003
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_contig_write(H5D_io_info_t *io_info, hsize_t nelmts,
-    const H5T_t *mem_type, const H5S_t *mem_space,
-    const H5S_t *file_space, H5T_path_t *tpath,
-    hid_t src_id, hid_t dst_id, const void *buf)
-{
-    H5D_t *dataset=io_info->dset;       /* Local pointer to dataset info */
-    const H5D_dxpl_cache_t *dxpl_cache=io_info->dxpl_cache;     /* Local pointer to dataset transfer info */
-    herr_t      status;                 /*function return status*/
-#ifdef H5S_DEBUG
-    H5_timer_t	timer;
-#endif
-    size_t	src_type_size;		/*size of source type	*/
-    size_t	dst_type_size;	        /*size of destination type*/
-    size_t	max_type_size;	        /* Size of largest source/destination type */
-    size_t	target_size;		/*desired buffer size	*/
-    size_t	request_nelmts;		/*requested strip mine	*/
-    H5S_sel_iter_t mem_iter;            /*memory selection iteration info*/
-    hbool_t	mem_iter_init=0;	/*memory selection iteration info has been initialized */
-    H5S_sel_iter_t bkg_iter;            /*background iteration info*/
-    hbool_t	bkg_iter_init=0;	/*background iteration info has been initialized */
-    H5S_sel_iter_t file_iter;           /*file selection iteration info*/
-    hbool_t	file_iter_init=0;	/*file selection iteration info has been initialized */
-    H5T_bkg_t	need_bkg;		/*type of background buf*/
-    uint8_t	*tconv_buf = NULL;	/*datatype conv buffer	*/
-    uint8_t	*bkg_buf = NULL;	/*background buffer	*/
-    hsize_t	smine_start;		/*strip mine start loc	*/
-    size_t	n, smine_nelmts;	/*elements per strip	*/
-    H5D_storage_t store;                /*union of storage info for dataset */
-
-    herr_t	ret_value = SUCCEED;	/*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_contig_write)
-
-    assert (buf);
-
-    /* Initialize storage info for this dataset */
-    if(dataset->shared->dcpl_cache.efl.nused > 0)
-        HDmemcpy(&store.efl, &(dataset->shared->dcpl_cache.efl), sizeof(H5O_efl_t));
     else {
-        store.contig.dset_addr = dataset->shared->layout.u.contig.addr;
-        store.contig.dset_size = dataset->shared->layout.u.contig.size;
-    } /* end if */
-
-    /* Set dataset storage for I/O info */
-    io_info->store = &store;
-
-    /*
-     * If there is no type conversion then write directly from the
-     * application's buffer.  This saves at least one mem-to-mem copy.
-     */
-    if(H5Z_xform_noop(dxpl_cache->data_xform_prop) && H5T_path_noop(tpath)) {
-#ifdef H5S_DEBUG
-	H5_timer_begin(&timer);
-#endif
-        H5_CHECK_OVERFLOW(nelmts,hsize_t,size_t);
-#ifdef H5_HAVE_PARALLEL
-	if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
-	  if(H5D_contig_collective_io(io_info, file_space, mem_space, buf, TRUE) < 0)
-	    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "contiguous write failed in collective mode")
-	}
-	else
-#endif
-        {
-            if((io_info->ops.write)(io_info, (size_t)nelmts,
-                    H5T_get_size(dataset->shared->type), file_space, mem_space,
-                    (haddr_t)0, NULL, buf/*out*/) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "contiguous write failed ")
-	}
-
-#ifdef H5S_DEBUG
-        H5_timer_end(&(io_info->stats->stats[0].write_timer), &timer);
-        io_info->stats->stats[0].write_nbytes += nelmts * H5T_get_size(mem_type);
-        io_info->stats->stats[0].write_ncalls++;
-#endif
-
-	    /* direct xfer accomplished successfully */
-	    HGOTO_DONE(SUCCEED)
-    } /* end if */
-
-    /*
-     * This is the general case.
-     */
-    if(nelmts==0)
-        HGOTO_DONE(SUCCEED)
-
-    /* Compute element sizes and other parameters */
-    src_type_size = H5T_get_size(mem_type);
-    dst_type_size = H5T_get_size(dataset->shared->type);
-    max_type_size = MAX(src_type_size, dst_type_size);
-    target_size = dxpl_cache->max_temp_buf;
-    /* XXX: This could cause a problem if the user sets their buffer size
-     * to the same size as the default, and then the dataset elements are
-     * too large for the buffer... - QAK
-     */
-    if(target_size == H5D_TEMP_BUF_SIZE) {
-        /* If the buffer is too small to hold even one element, make it bigger */
-        if(target_size<max_type_size)
-            target_size = max_type_size;
-        /* If the buffer is too large to hold all the elements, make it smaller */
-        else if(target_size>(nelmts*max_type_size))
-            target_size=(size_t)(nelmts*max_type_size);
-    } /* end if */
-    request_nelmts = target_size / max_type_size;
-
-    /* Sanity check elements in temporary buffer */
-    if (request_nelmts==0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "temporary buffer max size is too small")
-
-    /* Figure out the strip mine size. */
-    if (H5S_select_iter_init(&file_iter, file_space, dst_type_size) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize file selection information")
-    file_iter_init=1;	/*file selection iteration info has been initialized */
-    if (H5S_select_iter_init(&mem_iter, mem_space, src_type_size) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize memory selection information")
-    mem_iter_init=1;	/*file selection iteration info has been initialized */
-    if (H5S_select_iter_init(&bkg_iter, file_space, dst_type_size) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize background selection information")
-    bkg_iter_init=1;	/*file selection iteration info has been initialized */
-
-    /*
-     * Get a temporary buffer for type conversion unless the app has already
-     * supplied one through the xfer properties.  Instead of allocating a
-     * buffer which is the exact size, we allocate the target size. The
-     * malloc() is usually less resource-intensive if we allocate/free the
-     * same size over and over.
-     */
-    if(H5T_detect_class(dataset->shared->type, H5T_VLEN)) {
-	/* Old data is retrieved into background buffer for VL datatype.  The
-	 * data is used later for freeing heap objects. */
-        need_bkg = H5T_BKG_YES;
-    } else if (H5T_path_bkg(tpath)) {
-        H5T_bkg_t path_bkg;     /* Type conversion's background info */
-
-        /* Retrieve the bkgr buffer property */
-        need_bkg=dxpl_cache->bkgr_buf_type;
-        path_bkg = H5T_path_bkg(tpath);
-        need_bkg = MAX (path_bkg, need_bkg);
-    } else {
-        need_bkg = H5T_BKG_NO; /*never needed even if app says yes*/
-    } /* end else */
-    if(NULL == (tconv_buf = (uint8_t *)dxpl_cache->tconv_buf)) {
-        /* Allocate temporary buffer */
-        if(NULL == (tconv_buf = H5FL_BLK_MALLOC(type_conv, target_size)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for type conversion")
-    } /* end if */
-    if(need_bkg && NULL == (bkg_buf = (uint8_t *)dxpl_cache->bkgr_buf)) {
-        /* Allocate background buffer */
-        /* (Don't need calloc()-like call since file data is already initialized) */
-        if(NULL == (bkg_buf = H5FL_BLK_MALLOC(type_conv, (request_nelmts * dst_type_size))))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for background conversion")
-    } /* end if */
-
-    /* Start strip mining... */
-    for (smine_start=0; smine_start<nelmts; smine_start+=smine_nelmts) {
-        /* Go figure out how many elements to read from the file */
-        assert(H5S_SELECT_ITER_NELMTS(&file_iter)==(nelmts-smine_start));
-        smine_nelmts = (size_t)MIN(request_nelmts, (nelmts-smine_start));
-
-        /*
-         * Gather data from application buffer into the datatype conversion
-         * buffer. Also gather data from the file into the background buffer
-         * if necessary.
-         */
-#ifdef H5S_DEBUG
-	H5_timer_begin(&timer);
-#endif
-        n = H5D_select_mgath(buf, mem_space, &mem_iter,
-			     smine_nelmts, dxpl_cache, tconv_buf/*out*/);
-#ifdef H5S_DEBUG
-	H5_timer_end(&(io_info->stats->stats[0].gath_timer), &timer);
-	io_info->stats->stats[0].gath_nbytes += n * src_type_size;
-	io_info->stats->stats[0].gath_ncalls++;
-#endif
-        if (n!=smine_nelmts)
-            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "mem gather failed")
-
-        /* If the source and destination are compound types and the destination is
-         * is a subset of the source and no conversion is needed, copy the data 
-         * directly into user's buffer and bypass the rest of steps.  If the source
-         * is a subset of the destination, the optimization is done in conversion
-         * function H5T_conv_struct_opt to protect the background data.  This
-         * optimization is for Chicago company */
-        if(H5T_SUBSET_DST==H5T_path_compound_subset(tpath)) {
-            if(H5D_compound_opt_write(smine_nelmts, src_id, dst_id, tconv_buf)<0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-        } else {
-            if (H5T_BKG_YES==need_bkg) {
-#ifdef H5S_DEBUG
-                H5_timer_begin(&timer);
-#endif
-                n = H5D_select_fgath(io_info, file_space, &bkg_iter, smine_nelmts,
-                                    (haddr_t)0, NULL, bkg_buf/*out*/);
-
-#ifdef H5S_DEBUG
-                H5_timer_end(&(io_info->stats->stats[0].bkg_timer), &timer);
-                io_info->stats->stats[0].bkg_nbytes += n * dst_type_size;
-                io_info->stats->stats[0].bkg_ncalls++;
-#endif
-                if (n!=smine_nelmts)
-                    HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "file gather failed")
-            } /* end if */
-
-	    /*
-             * Perform datatype conversion.
-             */
-            if(H5T_convert(tpath, src_id, dst_id, smine_nelmts, (size_t)0, (size_t)0, tconv_buf, bkg_buf, io_info->dxpl_id) < 0)
-                 HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-
-	    /* Do the data transform after the type conversion (since we're using dataset->shared->type). */
-	    if(!H5Z_xform_noop(dxpl_cache->data_xform_prop))
-	        if( H5Z_xform_eval(dxpl_cache->data_xform_prop, tconv_buf, smine_nelmts, dataset->shared->type) < 0)
-		    HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "Error performing data transform")
-        }
-
         /*
-         * Scatter the data out to the file.
+         * This is the general case (type conversion, usually).
          */
-#ifdef H5S_DEBUG
-        H5_timer_begin(&timer);
-#endif
-	status = H5D_select_fscat(io_info, file_space, &file_iter, smine_nelmts,
-                    (haddr_t)0, NULL, tconv_buf);
-#ifdef H5S_DEBUG
-        H5_timer_end(&(io_info->stats->stats[0].scat_timer), &timer);
-        io_info->stats->stats[0].scat_nbytes += smine_nelmts * dst_type_size;
-        io_info->stats->stats[0].scat_ncalls++;
-#endif
-        if (status<0)
-            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "scatter failed")
-    } /* end for */
-
-done:
-    /* Release selection iterators */
-    if(file_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-    if(mem_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-    if(bkg_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-
-    if (tconv_buf && NULL==dxpl_cache->tconv_buf)
-        (void)H5FL_BLK_FREE(type_conv,tconv_buf);
-    if (bkg_buf && NULL==dxpl_cache->bkgr_buf)
-        (void)H5FL_BLK_FREE(type_conv,bkg_buf);
-
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_contig_write() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_chunk_read
- *
- * Purpose:	Read from a chunked dataset.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Raymond Lu
- *		Thursday, April 10, 2003
- *
- * Modification: 
- *              Raymond Lu
- *              20 July 2007
- *              Moved H5D_istore_lock and H5D_istore_unlock to this level
- *              from H5D_istore_readvv to avoid frequent lock and unlock
- *              and to improve performance.
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_chunk_read(H5D_io_info_t *io_info, hsize_t nelmts,
-    const H5T_t *mem_type, const H5S_t *mem_space,
-    const H5S_t *file_space, H5T_path_t *tpath,
-    hid_t src_id, hid_t dst_id, void *buf/*out*/)
-{
-    H5D_t *dataset=io_info->dset;       /* Local pointer to dataset info */
-    const H5D_dxpl_cache_t *dxpl_cache=io_info->dxpl_cache;     /* Local pointer to dataset transfer info */
-    H5D_chunk_map_t      fm;            /* File<->memory mapping */
-    H5SL_node_t *chunk_node;            /* Current node in chunk skip list */
-    herr_t      status;                 /*function return status*/
-#ifdef H5S_DEBUG
-    H5_timer_t	timer;
-#endif
-    size_t	src_type_size;		/*size of source type	*/
-    size_t	dst_type_size;	        /*size of destination type*/
-    size_t	max_type_size;	        /* Size of largest source/destination type */
-    size_t	target_size;		/*desired buffer size	*/
-    size_t	request_nelmts;		/*requested strip mine	*/
-    hsize_t     smine_start;            /*strip mine start loc  */
-    size_t      n, smine_nelmts;        /*elements per strip    */
-    size_t      accessed_bytes = 0;     /*total accessed size in a chunk */
-    H5S_sel_iter_t mem_iter;            /*memory selection iteration info*/
-    hbool_t	mem_iter_init = FALSE;	/*memory selection iteration info has been initialized */
-    H5S_sel_iter_t bkg_iter;            /*background iteration info*/
-    hbool_t	bkg_iter_init = FALSE;	/*background iteration info has been initialized */
-    H5S_sel_iter_t file_iter;           /*file selection iteration info*/
-    hbool_t	file_iter_init = FALSE;	/*file selection iteration info has been initialized */
-    H5T_bkg_t	need_bkg;		/*type of background buf*/
-    uint8_t	*tconv_buf = NULL;	/*datatype conv buffer	*/
-    uint8_t	*bkg_buf = NULL;	/*background buffer	*/
-    H5D_storage_t store;                /*union of EFL and chunk pointer in file space */
-    void        *chunk = NULL;
-    haddr_t	chunk_addr;             /* Chunk address on disk */
-    H5D_istore_ud1_t udata;		/*B-tree pass-through	*/
-    unsigned    idx_hint=0;             /* Cache index hint      */
-    herr_t	ret_value = SUCCEED;	/*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_read)
-
-    assert (buf);
-
-    /* Map elements between file and memory for each chunk*/
-    if(H5D_create_chunk_map(&fm, io_info, nelmts, file_space, mem_space, mem_type) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "can't build chunk mapping")
-
-    /* Set dataset storage for I/O info */
-    io_info->store=&store;
-
-    /* Compute element sizes */
-    src_type_size = H5T_get_size(dataset->shared->type);
-    dst_type_size = H5T_get_size(mem_type);
-    max_type_size = MAX(src_type_size, dst_type_size);
-
-    /*
-     * If there is no type conversion then read directly into the
-     * application's buffer.  This saves at least one mem-to-mem copy.
-     */
-    if ( H5Z_xform_noop(dxpl_cache->data_xform_prop) && H5T_path_noop(tpath)) {
-#ifdef H5S_DEBUG
-	H5_timer_begin(&timer);
-#endif
-  	/* Sanity check dataset, then read it */
-        HDassert(((dataset->shared->layout.type == H5D_CONTIGUOUS && H5F_addr_defined(dataset->shared->layout.u.contig.addr))
-                || (dataset->shared->layout.type == H5D_CHUNKED && H5F_addr_defined(dataset->shared->layout.u.chunk.addr)))
-                || dataset->shared->dcpl_cache.efl.nused > 0 || 0 == nelmts
-                || dataset->shared->layout.type == H5D_COMPACT);
-
-#ifdef H5_HAVE_PARALLEL
-        /* Check whether the collective mode can be turned off globally*/
-#ifndef H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS
-        if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
-            if(H5D_mpio_chunk_adjust_iomode(io_info ,&fm))
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't adjust collective I/O")
-        }
-#endif /* H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS */
-	/* Temporarily shut down collective IO for chunking */
-	if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
-            if(H5D_chunk_collective_io(io_info, &fm, buf, FALSE) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "chunked read failed in collective mode")
-	}
-	else {/* sequential or independent read */
-#endif
-            /* Get first node in chunk skip list */
-            chunk_node = H5D_CHUNK_GET_FIRST_NODE(fm);
-
-            while(chunk_node) {
-                H5D_chunk_info_t *chunk_info;   /* chunk information */
-
-                /* Get the actual chunk information from the skip list node */
-                chunk_info = H5D_CHUNK_GET_NODE_INFO(fm, chunk_node);
-
-                /* Pass in chunk's coordinates in a union. */
-                store.chunk.offset = chunk_info->coords;
-                store.chunk.index = chunk_info->index;
-
-                /* Load the chunk into cache and lock it. */
-		chunk_addr = H5D_istore_get_addr(io_info, &udata);
-                if(H5D_istore_if_load(io_info, chunk_addr)) {
-		    if(NULL == (chunk = H5D_istore_lock(io_info, &udata, FALSE, &idx_hint)))
-			HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
-		} else
-		    chunk = NULL;
-
-                /* Perform the actual read operation */
-                if((io_info->ops.read)(io_info, chunk_info->chunk_points,
-                        src_type_size, chunk_info->fspace,
-                        chunk_info->mspace, chunk_addr, chunk, buf) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, " chunked read failed")
-  
-                /* Release the cache lock on the chunk. */
-                if(chunk) {
-                    accessed_bytes = chunk_info->chunk_points * src_type_size;
-		    if(H5D_istore_unlock(io_info, FALSE, idx_hint, chunk, accessed_bytes) < 0)
-			HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
-		} /* end if */
-
-                /* Advance to next chunk in list */
-                chunk_node = H5D_CHUNK_GET_NEXT_NODE(fm, chunk_node);
-            } /* end while */
-#ifdef H5_HAVE_PARALLEL
-	}
-#endif
-
-
-#ifdef H5S_DEBUG
-        H5_timer_end(&(io_info->stats->stats[1].read_timer), &timer);
-        io_info->stats->stats[1].read_nbytes += nelmts * src_type_size;
-        io_info->stats->stats[1].read_ncalls++;
-#endif
-
-	/* direct xfer accomplished successfully */
-        HGOTO_DONE(SUCCEED)
-    } /* end if */
-
-    /*
-     * This is the general case (type conversion, usually).
-     */
-    if(nelmts==0)
-        HGOTO_DONE(SUCCEED)
-
-    /* Compute buffer  sizes and other parameters */
-    target_size = dxpl_cache->max_temp_buf;
-    /* XXX: This could cause a problem if the user sets their buffer size
-     * to the same size as the default, and then the dataset elements are
-     * too large for the buffer... - QAK
-     */
-    if(target_size == H5D_TEMP_BUF_SIZE) {
-        /* If the buffer is too small to hold even one element, make it bigger */
-        if(target_size<max_type_size)
-            target_size = max_type_size;
-        /* If the buffer is too large to hold all the elements, make it smaller */
-        else if(target_size>(nelmts*max_type_size))
-            target_size=(size_t)(nelmts*max_type_size);
-    } /* end if */
-    request_nelmts = target_size / max_type_size;
-
-    /* Sanity check elements in temporary buffer */
-    if (request_nelmts==0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "temporary buffer max size is too small")
-
-    /*
-     * Get a temporary buffer for type conversion unless the app has already
-     * supplied one through the xfer properties. Instead of allocating a
-     * buffer which is the exact size, we allocate the target size.  The
-     * malloc() is usually less resource-intensive if we allocate/free the
-     * same size over and over.
-     */
-    if (H5T_path_bkg(tpath)) {
-        H5T_bkg_t path_bkg;     /* Type conversion's background info */
-
-        /* Retrieve the bkgr buffer property */
-        need_bkg=dxpl_cache->bkgr_buf_type;
-        path_bkg = H5T_path_bkg(tpath);
-        need_bkg = MAX(path_bkg, need_bkg);
-    } else {
-        need_bkg = H5T_BKG_NO; /*never needed even if app says yes*/
+        io_info->io_ops.single_read = H5D_scatgath_read;
+        io_info->io_ops.single_write = H5D_scatgath_write;
     } /* end else */
-    if(NULL == (tconv_buf = (uint8_t *)dxpl_cache->tconv_buf)) {
-        /* Allocate temporary buffer */
-        if(NULL == (tconv_buf = H5FL_BLK_MALLOC(type_conv, target_size)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for type conversion")
-    } /* end if */
-    if(need_bkg && NULL == (bkg_buf = (uint8_t *)dxpl_cache->bkgr_buf)) {
-        /* Allocate background buffer */
-        /* (Need calloc()-like call since memory needs to be initialized) */
-        if(NULL == (bkg_buf = H5FL_BLK_CALLOC(type_conv, (request_nelmts * dst_type_size))))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for background conversion")
-    } /* end if */
-
-    /* Loop over all the chunks, performing I/O on each */
-
-    /* Get first node in chunk skip list */
-    chunk_node = H5D_CHUNK_GET_FIRST_NODE(fm);
-
-    /* Iterate through chunks to be operated on */
-    while(chunk_node) {
-        H5D_chunk_info_t *chunk_info;   /* chunk information */
-
-        /* Get the actual chunk information from the skip list nodes */
-        chunk_info = H5D_CHUNK_GET_NODE_INFO(fm, chunk_node);
-
-        /* initialize selection iterator */
-        if (H5S_select_iter_init(&file_iter, chunk_info->fspace, src_type_size) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize file selection information")
-        file_iter_init = TRUE;	/*file selection iteration info has been initialized */
-        if (H5S_select_iter_init(&mem_iter, chunk_info->mspace, dst_type_size) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize memory selection information")
-        mem_iter_init = TRUE;	/*file selection iteration info has been initialized */
-        if (H5S_select_iter_init(&bkg_iter, chunk_info->mspace, dst_type_size) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize background selection information")
-        bkg_iter_init = TRUE;	/*file selection iteration info has been initialized */
-
-        /* Pass in chunk's coordinates in a union*/
-        store.chunk.offset = chunk_info->coords;
-        store.chunk.index = chunk_info->index;
-
-        /* Load the chunk into cache and lock it. */
-        chunk_addr = H5D_istore_get_addr(io_info, &udata);
-
-        if(H5D_istore_if_load(io_info, chunk_addr)) {
-            if(NULL == (chunk = H5D_istore_lock(io_info, &udata, FALSE, &idx_hint)))
-                HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
-        } else
-            chunk = NULL;
-
-        for(smine_start=0; smine_start<chunk_info->chunk_points; smine_start+=smine_nelmts) {
-            /* Go figure out how many elements to read from the file */
-            assert(H5S_SELECT_ITER_NELMTS(&file_iter)==(chunk_info->chunk_points-smine_start));
-            smine_nelmts = (size_t)MIN(request_nelmts, (chunk_info->chunk_points-smine_start));
-
-            /*
-             * Gather the data from disk into the datatype conversion
-             * buffer. Also gather data from application to background buffer
-             * if necessary.
-             */
-#ifdef H5S_DEBUG
-            H5_timer_begin(&timer);
-#endif
-            /* Sanity check that space is allocated, then read data from it */
-            HDassert(((dataset->shared->layout.type == H5D_CONTIGUOUS && H5F_addr_defined(dataset->shared->layout.u.contig.addr))
-                    || (dataset->shared->layout.type == H5D_CHUNKED && H5F_addr_defined(dataset->shared->layout.u.chunk.addr)))
-                || dataset->shared->dcpl_cache.efl.nused > 0 || dataset->shared->layout.type == H5D_COMPACT);
-
-            if(chunk) {
-                n = H5D_select_mgath(chunk, chunk_info->fspace, &file_iter, 
-                                 smine_nelmts, dxpl_cache, tconv_buf/*out*/);
-            } else {
-                n = H5D_select_fgath(io_info, chunk_info->fspace, &file_iter, smine_nelmts, 
-                                 chunk_addr, NULL, tconv_buf/*out*/);
-            }
-
-#ifdef H5S_DEBUG
-            H5_timer_end(&(io_info->stats->stats[1].gath_timer), &timer);
-            io_info->stats->stats[1].gath_nbytes += n * src_type_size;
-            io_info->stats->stats[1].gath_ncalls++;
-#endif
-            if(n != smine_nelmts)
-                HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "file gather failed")
-
-            /* If the source and destination are compound types and subset of each other
-             * and no conversion is needed, copy the data directly into user's buffer and 
-             * bypass the rest of steps.  This optimization is for Chicago company */
-            if(H5T_SUBSET_SRC==H5T_path_compound_subset(tpath)) {
-                if(H5D_compound_opt_read(smine_nelmts, chunk_info->mspace, &mem_iter, dxpl_cache,
-                    src_id, dst_id, H5T_SUBSET_SRC, tconv_buf, buf /*out*/)<0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-
-                continue;
-            } else if(H5T_SUBSET_DST==H5T_path_compound_subset(tpath)) {
-                if(H5D_compound_opt_read(smine_nelmts, chunk_info->mspace, &mem_iter, dxpl_cache,
-                    src_id, dst_id, H5T_SUBSET_DST, tconv_buf, buf /*out*/)<0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-
-                continue;
-            }
-
-            if(H5T_BKG_YES == need_bkg) {
-#ifdef H5S_DEBUG
-                H5_timer_begin(&timer);
-#endif
-                n = H5D_select_mgath(buf, chunk_info->mspace, &bkg_iter, smine_nelmts, dxpl_cache, bkg_buf/*out*/);
-#ifdef H5S_DEBUG
-                H5_timer_end(&(io_info->stats->stats[1].bkg_timer), &timer);
-                io_info->stats->stats[1].bkg_nbytes += n * dst_type_size;
-                io_info->stats->stats[1].bkg_ncalls++;
-#endif
-                if(n != smine_nelmts)
-                    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "mem gather failed")
-            } /* end if */
-
-            /*
-             * Perform datatype conversion.
-             */
-            if(H5T_convert(tpath, src_id, dst_id, smine_nelmts, (size_t)0, (size_t)0, tconv_buf, bkg_buf, io_info->dxpl_id) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-
-           /* Do the data transform after the conversion (since we're using type mem_type) */
-            if(!H5Z_xform_noop(dxpl_cache->data_xform_prop))
-	        if(H5Z_xform_eval(dxpl_cache->data_xform_prop, tconv_buf, smine_nelmts, mem_type) < 0)
-                    HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "Error performing data transform")
-
-            /*
-             * Scatter the data into memory.
-             */
-#ifdef H5S_DEBUG
-            H5_timer_begin(&timer);
-#endif
-            status = H5D_select_mscat(tconv_buf, chunk_info->mspace, &mem_iter, smine_nelmts, dxpl_cache, buf/*out*/);
-#ifdef H5S_DEBUG
-            H5_timer_end(&(io_info->stats->stats[1].scat_timer), &timer);
-            io_info->stats->stats[1].scat_nbytes += smine_nelmts * dst_type_size;
-            io_info->stats->stats[1].scat_ncalls++;
-#endif
-            if(status < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "scatter failed")
-        } /* end for */
-
-        /* Release the cache lock on the chunk. */
-        if(chunk) {
-            accessed_bytes = chunk_info->chunk_points * src_type_size;
-            if(H5D_istore_unlock(io_info, FALSE, idx_hint, chunk, accessed_bytes) < 0)
-                HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
-        } /* end if */
-
-        /* Release selection iterators */
-        if(file_iter_init) {
-            if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-            file_iter_init = FALSE;
-        } /* end if */
-        if(mem_iter_init) {
-            if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-            mem_iter_init = FALSE;
-        } /* end if */
-        if(bkg_iter_init) {
-            if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-            bkg_iter_init = FALSE;
-        } /* end if */
-
-        /* Get the next chunk node in the skip list */
-        chunk_node = H5D_CHUNK_GET_NEXT_NODE(fm, chunk_node);
-    } /* end while */
-
-done:
-    /* Release selection iterators, if necessary */
-    if(file_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-    if(mem_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-    if(bkg_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-
-    if(tconv_buf && NULL == dxpl_cache->tconv_buf)
-        (void)H5FL_BLK_FREE(type_conv, tconv_buf);
-    if(bkg_buf && NULL == dxpl_cache->bkgr_buf)
-        (void)H5FL_BLK_FREE(type_conv, bkg_buf);
-
-    /* Release chunk mapping information */
-    if(H5D_destroy_chunk_map(&fm) < 0)
-        HDONE_ERROR(H5E_DATASET, H5E_CANTRELEASE, FAIL, "can't release chunk mapping")
-
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* H5D_chunk_read() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_chunk_write
- *
- * Purpose:	Writes to a chunked dataset.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Raymond Lu
- *		Thursday, April 10, 2003
- *
- * Modification: 
- *              Raymond Lu
- *              20 July 2007
- *              Moved H5D_istore_lock and H5D_istore_unlock to this level
- *              from H5D_istore_writevv to avoid frequent lock and unlock
- *              and to improve performance.
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_chunk_write(H5D_io_info_t *io_info, hsize_t nelmts,
-    const H5T_t *mem_type, const H5S_t *mem_space,
-    const H5S_t *file_space, H5T_path_t *tpath,
-    hid_t src_id, hid_t dst_id, const void *buf)
-{
-    H5D_t *dataset=io_info->dset;       /* Local pointer to dataset info */
-    const H5D_dxpl_cache_t *dxpl_cache=io_info->dxpl_cache;     /* Local pointer to dataset transfer info */
-    H5D_chunk_map_t      fm;            /* File<->memory mapping */
-    H5SL_node_t *chunk_node;            /* Current node in chunk skip list */
-    herr_t      status;                 /*function return status*/
-#ifdef H5S_DEBUG
-    H5_timer_t	timer;
-#endif
-    size_t	src_type_size;		/*size of source type	*/
-    size_t	dst_type_size;	        /*size of destination type*/
-    size_t	max_type_size;	        /* Size of largest source/destination type */
-    size_t	target_size;		/*desired buffer size	*/
-    size_t	request_nelmts;		/*requested strip mine	*/
-    size_t      accessed_bytes;         /*total accessed size in a chunk */
-    hsize_t     smine_start;            /*strip mine start loc  */
-    size_t      n, smine_nelmts;        /*elements per strip    */
-    H5S_sel_iter_t mem_iter;            /*memory selection iteration info*/
-    hbool_t	mem_iter_init=0;	/*memory selection iteration info has been initialized */
-    H5S_sel_iter_t bkg_iter;            /*background iteration info*/
-    hbool_t	bkg_iter_init=0;	/*background iteration info has been initialized */
-    H5S_sel_iter_t file_iter;           /*file selection iteration info*/
-    hbool_t	file_iter_init=0;	/*file selection iteration info has been initialized */
-    H5T_bkg_t	need_bkg;		/*type of background buf*/
-    uint8_t	*tconv_buf = NULL;	/*datatype conv buffer	*/
-    uint8_t	*bkg_buf = NULL;	/*background buffer	*/
-    H5D_storage_t store;                /*union of EFL and chunk pointer in file space */
-    void     *chunk = NULL;
-    haddr_t	chunk_addr;             /* Chunk address on disk */
-    H5D_istore_ud1_t udata;		/*B-tree pass-through	*/
-    unsigned    idx_hint=0;             /* Cache index hint      */
-    hbool_t     relax=TRUE;             /* Whether whole chunk is selected */
-    herr_t	ret_value = SUCCEED;	/*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_write)
-
-    assert (buf);
-
-    /* Map elements between file and memory for each chunk*/
-    if(H5D_create_chunk_map(&fm, io_info, nelmts, file_space, mem_space, mem_type) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "can't build chunk mapping")
-
-    /* Set dataset storage for I/O info */
-    io_info->store=&store;
-
-#ifdef H5_HAVE_PARALLEL
-    /* Additional sanity checks when operating in parallel */
-    if(io_info->using_mpi_vfd) {
-        if (chunk_addr==HADDR_UNDEF)
-            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "unable to locate raw data chunk")
-        if (dataset->shared->dcpl_cache.pline.nused>0)
-            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "cannot write to chunked storage with filters in parallel")
-    } /* end if */
-#endif /* H5_HAVE_PARALLEL */
-
-    /* Compute element sizes and other parameters */
-    src_type_size = H5T_get_size(mem_type);
-    dst_type_size = H5T_get_size(dataset->shared->type);
-    max_type_size = MAX(src_type_size, dst_type_size);
-
-    /*
-     * If there is no type conversion then write directly from the
-     * application's buffer.  This saves at least one mem-to-mem copy.
-     */
-    if ( H5Z_xform_noop(dxpl_cache->data_xform_prop) && H5T_path_noop(tpath)) {
-#ifdef H5S_DEBUG
-	H5_timer_begin(&timer);
-#endif
 
 #ifdef H5_HAVE_PARALLEL
-        /* Check whether the collective mode can be turned off globally*/
-#ifndef H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS
-        if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
-            if(H5D_mpio_chunk_adjust_iomode(io_info,&fm))
-                HGOTO_ERROR(H5E_DATASET,H5E_CANTGET,FAIL,"can't adjust collective I/O")
-        }
-#endif /* H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS */
-	/* Temporarily shut down collective IO for chunking */
-        if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
-            if(H5D_chunk_collective_io(io_info,&fm,buf,TRUE) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "chunked write failed in collective mode");
-	}
-	else {/* sequential or independent write */
+    /* Determine if the file was opened with an MPI VFD */
+    io_info->using_mpi_vfd = IS_H5FD_MPI(dset->oloc.file);
 #endif /* H5_HAVE_PARALLEL */
-            /* Get first node in chunk skip list */
-            chunk_node = H5D_CHUNK_GET_FIRST_NODE(fm);
-
-            while(chunk_node) {
-                H5D_chunk_info_t *chunk_info;       /* Chunk information */
-
-                /* Get the actual chunk information from the skip list node */
-                chunk_info = H5D_CHUNK_GET_NODE_INFO(fm, chunk_node);
-
-                /* Pass in chunk's coordinates in a union. */
-                store.chunk.offset = chunk_info->coords;
-                store.chunk.index = chunk_info->index;
-
-                /* Load the chunk into cache.  But if the whole chunk is written,
-                 * simply allocate space instead of load the chunk. */
-                chunk_addr = H5D_istore_get_addr(io_info, &udata);
-
-                if(H5D_istore_if_load(io_info, chunk_addr)) {
-                    accessed_bytes = chunk_info->chunk_points * dst_type_size;
-                    if(accessed_bytes != dataset->shared->layout.u.chunk.size)
-                        relax = FALSE;
-
-		    if(NULL == (chunk = H5D_istore_lock(io_info, &udata, relax, &idx_hint)))
-			HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
-		} else
-		    chunk = NULL;
-
-                /* Perform the actual read operation */
-                if((io_info->ops.write)(io_info, chunk_info->chunk_points,
-                        dst_type_size, chunk_info->fspace,
-                        chunk_info->mspace, chunk_addr, chunk, buf) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, " chunked write failed")
-
-                /* Release the cache lock on the chunk. */
-                if(chunk) {
-		    if(H5D_istore_unlock(io_info, TRUE, idx_hint, chunk, accessed_bytes) < 0)
-			HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
-		} /* end if */
-                relax = TRUE;
-
-                /* Advance to next chunk in list */
-                chunk_node = H5D_CHUNK_GET_NEXT_NODE(fm, chunk_node);
-            } /* end while */
-#ifdef H5_HAVE_PARALLEL
-	}
-#endif
-
-#ifdef H5S_DEBUG
-	H5_timer_end(&(io_info->stats->stats[0].write_timer), &timer);
-	io_info->stats->stats[0].write_nbytes += nelmts * src_type_size;
-	io_info->stats->stats[0].write_ncalls++;
-#endif
-
-	/* direct xfer accomplished successfully */
-	HGOTO_DONE(SUCCEED)
-    } /* end if */
-
-    /*
-     * This is the general case (type conversion, usually).
-     */
-    if(nelmts==0)
-        HGOTO_DONE(SUCCEED)
-
-    /* Compute buffer sizes and other parameters */
-    target_size = dxpl_cache->max_temp_buf;
-    /* XXX: This could cause a problem if the user sets their buffer size
-     * to the same size as the default, and then the dataset elements are
-     * too large for the buffer... - QAK
-     */
-    if(target_size == H5D_TEMP_BUF_SIZE) {
-        /* If the buffer is too small to hold even one element, make it bigger */
-        if(target_size<max_type_size)
-            target_size = max_type_size;
-        /* If the buffer is too large to hold all the elements, make it smaller */
-        else if(target_size>(nelmts*max_type_size))
-            target_size=(size_t)(nelmts*max_type_size);
-    } /* end if */
-    request_nelmts = target_size / max_type_size;
-
-    /* Sanity check elements in temporary buffer */
-    if (request_nelmts==0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "temporary buffer max size is too small")
 
-    /*
-     * Get a temporary buffer for type conversion unless the app has already
-     * supplied one through the xfer properties.  Instead of allocating a
-     * buffer which is the exact size, we allocate the target size. The
-     * malloc() is usually less resource-intensive if we allocate/free the
-     * same size over and over.
-     */
-    if(H5T_detect_class(dataset->shared->type, H5T_VLEN)) {
-	/* Old data is retrieved into background buffer for VL datatype.  The
-	 * data is used later for freeing heap objects. */
-        need_bkg = H5T_BKG_YES;
-    } else if (H5T_path_bkg(tpath)) {
-        H5T_bkg_t path_bkg;     /* Type conversion's background info */
-
-        /* Retrieve the bkgr buffer property */
-        need_bkg=dxpl_cache->bkgr_buf_type;
-        path_bkg = H5T_path_bkg(tpath);
-        need_bkg = MAX (path_bkg, need_bkg);
-    } else {
-        need_bkg = H5T_BKG_NO; /*never needed even if app says yes*/
-    } /* end else */
-    if(NULL == (tconv_buf = (uint8_t *)dxpl_cache->tconv_buf)) {
-        /* Allocate temporary buffer */
-        if(NULL == (tconv_buf = H5FL_BLK_MALLOC(type_conv, target_size)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for type conversion")
-    } /* end if */
-    if(need_bkg && NULL == (bkg_buf = (uint8_t *)dxpl_cache->bkgr_buf)) {
-        /* Allocate background buffer */
-        /* (Don't need calloc()-like call since file data is already initialized) */
-        if(NULL == (bkg_buf = H5FL_BLK_MALLOC(type_conv, (request_nelmts * dst_type_size))))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for background conversion")
-    } /* end if */
-
-    /* Loop over all the chunks, performing I/O on each */
-
-    /* Get first node in chunk skip list */
-    chunk_node = H5D_CHUNK_GET_FIRST_NODE(fm);
-
-    /* Iterate through chunks to be operated on */
-    while(chunk_node) {
-        H5D_chunk_info_t *chunk_info;   /* chunk information */
-
-        /* Get the actual chunk information from the skip list node */
-        chunk_info = H5D_CHUNK_GET_NODE_INFO(fm, chunk_node);
-
-        /* initialize selection iterator */
-        if (H5S_select_iter_init(&file_iter, chunk_info->fspace, dst_type_size) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize file selection information")
-        file_iter_init=1;	/*file selection iteration info has been initialized */
-        if (H5S_select_iter_init(&mem_iter, chunk_info->mspace, src_type_size) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize memory selection information")
-        mem_iter_init=1;	/*file selection iteration info has been initialized */
-        if (H5S_select_iter_init(&bkg_iter, chunk_info->fspace, dst_type_size) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize background selection information")
-        bkg_iter_init=1;	/*file selection iteration info has been initialized */
-
-        /*pass in chunk's coordinates in a union*/
-        store.chunk.offset = chunk_info->coords;
-        store.chunk.index = chunk_info->index;
-
-        /* Load the chunk into cache.  But if the whole chunk is written,
-         * simply allocate space instead of load the chunk. */
-        chunk_addr = H5D_istore_get_addr(io_info, &udata);
-
-        if(H5D_istore_if_load(io_info, chunk_addr)) {
-            accessed_bytes = chunk_info->chunk_points * dst_type_size;
-            if(accessed_bytes != dataset->shared->layout.u.chunk.size)
-                relax=FALSE;
-            if(relax) {
-                accessed_bytes = H5S_GET_SELECT_NPOINTS(chunk_info->mspace) * src_type_size;
-                if(accessed_bytes != dataset->shared->layout.u.chunk.size)
-                    relax = FALSE;
-            }
-
-	    if(NULL == (chunk = H5D_istore_lock(io_info, &udata, relax, &idx_hint)))
-		HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
-	} else
-	    chunk = NULL;
-
-        for(smine_start=0; smine_start<chunk_info->chunk_points; smine_start+=smine_nelmts) {
-            /* Go figure out how many elements to read from the file */
-            assert(H5S_SELECT_ITER_NELMTS(&file_iter)==(chunk_info->chunk_points-smine_start));
-            smine_nelmts = (size_t)MIN(request_nelmts, (chunk_info->chunk_points-smine_start));
-
-            /*
-             * Gather the data from disk into the datatype conversion
-             * buffer. Also gather data from application to background buffer
-             * if necessary.
-             */
-#ifdef H5S_DEBUG
-            H5_timer_begin(&timer);
-#endif
-            n = H5D_select_mgath(buf, chunk_info->mspace, &mem_iter,
-                                 smine_nelmts, dxpl_cache, tconv_buf/*out*/);
-
-#ifdef H5S_DEBUG
-            H5_timer_end(&(io_info->stats->stats[1].gath_timer), &timer);
-            io_info->stats->stats[1].gath_nbytes += n * src_type_size;
-            io_info->stats->stats[1].gath_ncalls++;
-#endif
-            if (n!=smine_nelmts)
-                HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "file gather failed")
-
-            /* If the source and destination are compound types and the destination is
-             * is a subset of the source and no conversion is needed, copy the data 
-             * directly into user's buffer and bypass the rest of steps.  If the source
-             * is a subset of the destination, the optimization is done in conversion
-             * function H5T_conv_struct_opt to protect the background data.  This
-             * optimization is for Chicago company */
-            if(H5T_SUBSET_DST==H5T_path_compound_subset(tpath)) {
-                if(H5D_compound_opt_write(smine_nelmts, src_id, dst_id, tconv_buf)<0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-            } else {
-                if (H5T_BKG_YES==need_bkg) {
-#ifdef H5S_DEBUG
-                    H5_timer_begin(&timer);
-#endif
-                    if(chunk) {
-                        n = H5D_select_mgath(chunk, chunk_info->fspace, &bkg_iter, 
-                                 smine_nelmts, dxpl_cache, bkg_buf/*out*/);
-                    } else {
-                        n = H5D_select_fgath(io_info, chunk_info->fspace, &bkg_iter, smine_nelmts, 
-                                 chunk_addr, NULL, bkg_buf/*out*/);
-                    }
-
-#ifdef H5S_DEBUG
-                    H5_timer_end(&(io_info->stats->stats[0].bkg_timer), &timer);
-                    io_info->stats->stats[0].bkg_nbytes += n * dst_type_size;
-                    io_info->stats->stats[0].bkg_ncalls++;
-#endif
-                    if (n!=smine_nelmts)
-                        HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "file gather failed")
-                } /* end if */
-
-	        /*
-                 * Perform datatype conversion.
-                 */
-                if(H5T_convert(tpath, src_id, dst_id, smine_nelmts, (size_t)0, (size_t)0, tconv_buf, bkg_buf, io_info->dxpl_id) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
-
- 	        /* Do the data transform after the type conversion (since we're using dataset->shared->type) */
-                if(!H5Z_xform_noop(dxpl_cache->data_xform_prop))
-	            if( H5Z_xform_eval(dxpl_cache->data_xform_prop, tconv_buf, smine_nelmts, dataset->shared->type) < 0)
-		        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "Error performing data transform")
-            }
-
-            /*
-             * Scatter the data out to the file.
-             */
-#ifdef H5S_DEBUG
-            H5_timer_begin(&timer);
-#endif
-            status = H5D_select_fscat(io_info,
-                chunk_info->fspace, &file_iter, smine_nelmts,
-                chunk_addr, chunk, tconv_buf);
-
-#ifdef H5S_DEBUG
-            H5_timer_end(&(io_info->stats->stats[0].scat_timer), &timer);
-            io_info->stats->stats[0].scat_nbytes += n * dst_type_size;
-            io_info->stats->stats[0].scat_ncalls++;
-#endif
-            if (status<0)
-                HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "scatter failed")
-        } /* end for */
-
-        /* Release the cache lock on the chunk. */
-        if(chunk) {
-            accessed_bytes = chunk_info->chunk_points * dst_type_size;
-	    if(H5D_istore_unlock(io_info, TRUE, idx_hint, chunk, accessed_bytes) < 0)
-		HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
-	} /* end if */
-        relax = TRUE;
-
-        /* Release selection iterators */
-        if(file_iter_init) {
-            if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-            file_iter_init=0;
-        } /* end if */
-        if(mem_iter_init) {
-            if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-            mem_iter_init=0;
-        } /* end if */
-        if(bkg_iter_init) {
-            if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-            bkg_iter_init=0;
-        } /* end if */
-
-        /* Get the next chunk node in the skip list */
-        chunk_node = H5D_CHUNK_GET_NEXT_NODE(fm, chunk_node);
-    } /* end while */
-
-done:
-    /* Release selection iterators, if necessary */
-    if(file_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-    if(mem_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-    if(bkg_iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
-    } /* end if */
-
-    if (tconv_buf && NULL==dxpl_cache->tconv_buf)
-        (void)H5FL_BLK_FREE(type_conv,tconv_buf);
-    if (bkg_buf && NULL==dxpl_cache->bkgr_buf)
-        (void)H5FL_BLK_FREE(type_conv,bkg_buf);
-
-    /* Release chunk mapping information */
-    if(H5D_destroy_chunk_map(&fm) < 0)
-        HDONE_ERROR(H5E_DATASET, H5E_CANTRELEASE, FAIL, "can't release chunk mapping")
-
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* H5D_chunk_write() */
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5D_ioinfo_init() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_compound_opt_read
+ * Function:	H5D_typeinfo_init
  *
- * Purpose:	A shortcut optimization for the Chicago company for 
- *              a special optimization case when the source and 
- *              destination members are a subset of each other, and 
- *              the order is the same, and no conversion is needed.  
- *              For example:
- *                  struct source {            struct destination {
- *                      TYPE1 A;      -->          TYPE1 A;
- *                      TYPE2 B;      -->          TYPE2 B;
- *                      TYPE3 C;      -->          TYPE3 C;
- *                  };                             TYPE4 D;
- *                                                 TYPE5 E;
- *                                             };
- *              or
- *                  struct destination {       struct source {
- *                      TYPE1 A;      <--          TYPE1 A;
- *                      TYPE2 B;      <--          TYPE2 B;
- *                      TYPE3 C;      <--          TYPE3 C;
- *                  };                             TYPE4 D;
- *                                                 TYPE5 E;
- *                                             };
- *              The optimization is simply moving data to the appropriate 
- *              places in the buffer.
+ * Purpose:	Routine for determining correct datatype information for
+ *              each I/O action.
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:	Raymond Lu
- *		11 June 2007
+ * Programmer:	Quincey Koziol
+ *		Tuesday, March  4, 2008
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_compound_opt_read(size_t nelmts, const H5S_t *space,
-    H5S_sel_iter_t *iter, const H5D_dxpl_cache_t *dxpl_cache,
-    hid_t src_id, hid_t dst_id, H5T_subset_t subset, 
-    void *data_buf, void *user_buf/*out*/)
+H5D_typeinfo_init(const H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache,
+    hid_t dxpl_id, hid_t mem_type_id, hbool_t do_write,
+    H5D_type_info_t *type_info)
 {
-    uint8_t    *dbuf = (uint8_t *)data_buf;    /*cast for pointer arithmetic	*/
-    uint8_t    *ubuf = (uint8_t *)user_buf;    /*cast for pointer arithmetic	*/
-    uint8_t    *xdbuf;
-    uint8_t    *xubuf;
-
-    hsize_t    _off[H5D_IO_VECTOR_SIZE];       /* Array to store sequence offsets */
-    hsize_t    *off=NULL;                      /* Pointer to sequence offsets */
-    size_t     _len[H5D_IO_VECTOR_SIZE];       /* Array to store sequence lengths */
-    size_t     *len=NULL;                      /* Pointer to sequence lengths */
-    size_t     nseq;                           /* Number of sequences generated */
-    size_t     curr_off;                       /* offset of bytes left to process in sequence */
-    size_t     curr_seq;                       /* Current sequence being processed */
-    size_t     curr_len;                       /* Length of bytes left to process in sequence */
-    size_t     curr_nelmts;		       /* number of elements to process in sequence   */
-    size_t     i;
-
-    H5T_t      *src, *dst;
-    size_t     src_stride, dst_stride, type_size = 0;
-    size_t     elmtno;			/*element counter		*/
-
-    herr_t     ret_value = SUCCEED;	       /*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_compound_opt_read)
-
-    /* Check args */
-    assert (data_buf);
-    assert (user_buf);
-    assert (space);
-    assert (iter);
-    assert (nelmts>0);
-
-    /* Allocate the vector I/O arrays */
-    if(dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if((len = H5FL_SEQ_MALLOC(size_t,dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array");
-        if((off = H5FL_SEQ_MALLOC(hsize_t,dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array");
-    } /* end if */
-    else {
-        len=_len;
-        off=_off;
-    } /* end else */
-
-    if (NULL == (src = (H5T_t *)H5I_object(src_id)) || NULL == (dst = (H5T_t *)H5I_object(dst_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data type");
-
-    src_stride = H5T_get_size(src);
-    dst_stride = H5T_get_size(dst);
-
-    if(H5T_SUBSET_SRC == subset)
-        type_size = src_stride;
-    else if(H5T_SUBSET_DST == subset)
-        type_size = dst_stride;
-
-    xdbuf = dbuf;
-
-    /* Loop until all elements are written */
-    while(nelmts>0) {
-        /* Get list of sequences for selection to write */
-        if(H5S_SELECT_GET_SEQ_LIST(space,0,iter,dxpl_cache->vec_size,nelmts,&nseq,&elmtno,off,len)<0)
-            HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed");
-
-        /* Loop, while sequences left to process */
-        for(curr_seq=0; curr_seq<nseq; curr_seq++) {
-            /* Get the number of bytes and offset in sequence */
-            curr_len=len[curr_seq];
-            curr_off=off[curr_seq];
-
-            /* Decide the number of elements and position in the buffer. */
-            curr_nelmts = curr_len/dst_stride;
-            xubuf = ubuf + curr_off;
+    const H5T_t	*src_type;              /* Source datatype */
+    const H5T_t	*dst_type;              /* Destination datatype */
+    herr_t	ret_value = SUCCEED;	/* Return value	*/
 
-            /* Copy the data into the right place. */
-            for(i=0; i<curr_nelmts; i++) {
-                HDmemmove(xubuf, xdbuf, type_size); 
+    FUNC_ENTER_NOAPI_NOINIT(H5D_typeinfo_init)
 
-                /* Update pointers */
-                xdbuf += src_stride;
-                xubuf += dst_stride;
-            }
+    /* check args */
+    HDassert(type_info);
+    HDassert(dset);
 
-        } /* end for */
+    /* Initialize type info safely */
+    HDmemset(type_info, 0, sizeof(H5D_type_info_t));
 
-        /* Decrement number of elements left to process */
-        nelmts -= elmtno;
-    } /* end while */
+    /* Get the memory & dataset datatypes */
+    if(NULL == (type_info->mem_type = (const H5T_t *)H5I_object_verify(mem_type_id, H5I_DATATYPE)))
+	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a datatype")
+    type_info->dset_type = dset->shared->type;
 
-done:
-    if(dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(len!=NULL)
-            H5FL_SEQ_FREE(size_t,len);
-        if(off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,off);
+    if(do_write) {
+        src_type = type_info->mem_type;
+        dst_type = dset->shared->type;
+        type_info->src_type_id = mem_type_id;
+        type_info->dst_type_id = dset->shared->type_id;
     } /* end if */
+    else {
+        src_type = dset->shared->type;
+        dst_type = type_info->mem_type;
+        type_info->src_type_id = dset->shared->type_id;
+        type_info->dst_type_id = mem_type_id;
+    } /* end else */
 
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_compound_opt_read() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_compound_opt_write
- *
- * Purpose:	A shortcut optimization for the Chicago company for 
- *              a special optimization case when the source and 
- *              destination members are a subset of each other, and 
- *              the order is the same, and no conversion is needed.  
- *              For example:
- *                  struct source {            struct destination {
- *                      TYPE1 A;      -->          TYPE1 A;
- *                      TYPE2 B;      -->          TYPE2 B;
- *                      TYPE3 C;      -->          TYPE3 C;
- *                  };                             TYPE4 D;
- *                                                 TYPE5 E;
- *                                             };
- *              or
- *                  struct destination {       struct source {
- *                      TYPE1 A;      <--          TYPE1 A;
- *                      TYPE2 B;      <--          TYPE2 B;
- *                      TYPE3 C;      <--          TYPE3 C;
- *                  };                             TYPE4 D;
- *                                                 TYPE5 E;
- *                                             };
- *              The optimization is simply moving data to the appropriate 
- *              places in the buffer.
- *
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Raymond Lu
- *		11 June 2007
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_compound_opt_write(size_t nelmts, hid_t src_id, hid_t dst_id, void *data_buf)
-{
-    uint8_t    *dbuf = (uint8_t *)data_buf;    /*cast for pointer arithmetic	*/
-    uint8_t    *xsbuf, *xdbuf;
-    size_t     i;
-    H5T_t      *src, *dst;
-    size_t     src_stride, dst_stride;
-    herr_t     ret_value = SUCCEED;	       /*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_compound_opt_write)
-
-    /* Check args */
-    assert (data_buf);
-    assert (nelmts>0);
-
-    if (NULL == (src = (H5T_t *)H5I_object(src_id)) || NULL == (dst = (H5T_t *)H5I_object(dst_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data type");
-
-    src_stride = H5T_get_size(src);
-    dst_stride = H5T_get_size(dst);
-
-    xsbuf = dbuf;
-    xdbuf = dbuf;
-
-    /* Loop until all elements are written */
-    for(i=0; i<nelmts; i++) {
-        HDmemmove(xdbuf, xsbuf, dst_stride); 
-
-        /* Update pointers */
-        xsbuf += src_stride;
-        xdbuf += dst_stride;
-    }
-
-done:
-
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_compound_opt_write() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_create_chunk_map
- *
- * Purpose:	Creates the mapping between elements selected in each chunk
- *              and the elements in the memory selection.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Raymond Lu
- *		Thursday, April 10, 2003
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_create_chunk_map(H5D_chunk_map_t *fm, const H5D_io_info_t *io_info,
-    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
-    const H5T_t *mem_type)
-{
-    H5D_t *dataset=io_info->dset;       /* Local pointer to dataset info */
-    H5S_t *tmp_mspace = NULL;     /* Temporary memory dataspace */
-    hssize_t old_offset[H5O_LAYOUT_NDIMS];  /* Old selection offset */
-    htri_t file_space_normalized = FALSE;   /* File dataspace was normalized */
-    hid_t f_tid = (-1);           /* Temporary copy of file datatype for iteration */
-    hbool_t iter_init = FALSE;  /* Selection iteration info has been initialized */
-    unsigned f_ndims;           /* The number of dimensions of the file's dataspace */
-    int sm_ndims;               /* The number of dimensions of the memory buffer's dataspace (signed) */
-    H5SL_node_t *curr_node;     /* Current node in skip list */
-    H5S_sel_type fsel_type;     /* Selection type on disk */
-    char bogus;                 /* "bogus" buffer to pass to selection iterator */
-    unsigned u;                 /* Local index variable */
-    hbool_t sel_hyper_flag;
-    herr_t ret_value = SUCCEED;	/* Return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_create_chunk_map)
-
-    /* Get layout for dataset */
-    fm->layout = &(dataset->shared->layout);
-    fm->nelmts = nelmts;
-
-    /* Check if the memory space is scalar & make equivalent memory space */
-    if((sm_ndims = H5S_GET_EXTENT_NDIMS(mem_space)) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "unable to get dimension number")
-    /* Set the number of dimensions for the memory dataspace */
-    H5_ASSIGN_OVERFLOW(fm->m_ndims, sm_ndims, int, unsigned);
-
-    /* Get dim number and dimensionality for each dataspace */
-    fm->f_ndims = f_ndims = dataset->shared->layout.u.chunk.ndims - 1;
-    if(H5S_get_simple_extent_dims(file_space, fm->f_dims, NULL) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "unable to get dimensionality")
-
-    /* Normalize hyperslab selections by adjusting them by the offset */
-    /* (It might be worthwhile to normalize both the file and memory dataspaces
-     * before any (contiguous, chunked, etc) file I/O operation, in order to
-     * speed up hyperslab calculations by removing the extra checks and/or
-     * additions involving the offset and the hyperslab selection -QAK)
+    /*
+     * Locate the type conversion function and data space conversion
+     * functions, and set up the element numbering information. If a data
+     * type conversion is necessary then register datatype atoms. Data type
+     * conversion is necessary if the user has set the `need_bkg' to a high
+     * enough value in xfer_parms since turning off datatype conversion also
+     * turns off background preservation.
      */
-    if((file_space_normalized = H5S_hyper_normalize_offset((H5S_t *)file_space, old_offset)) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to normalize dataspace by offset")
-
-    /* Decide the number of chunks in each dimension*/
-    for(u=0; u<f_ndims; u++) {
-        /* Keep the size of the chunk dimensions as hsize_t for various routines */
-        fm->chunk_dim[u]=fm->layout->u.chunk.dim[u];
-
-        /* Round up to the next integer # of chunks, to accomodate partial chunks */
-        fm->chunks[u] = ((fm->f_dims[u]+dataset->shared->layout.u.chunk.dim[u])-1) / dataset->shared->layout.u.chunk.dim[u];
-    } /* end for */
-
-    /* Compute the "down" size of 'chunks' information */
-    if(H5V_array_down(f_ndims,fm->chunks,fm->down_chunks) < 0)
-        HGOTO_ERROR(H5E_INTERNAL, H5E_BADVALUE, FAIL, "can't compute 'down' sizes")
-
-#ifdef H5_HAVE_PARALLEL
-    /* Calculate total chunk in file map*/
-    fm->select_chunk = NULL;
-    fm->total_chunks = 1;
-    for(u = 0; u < fm->f_ndims; u++)
-       fm->total_chunks = fm->total_chunks * fm->chunks[u];
-    if(io_info->using_mpi_vfd) {
-        H5_CHECK_OVERFLOW(fm->total_chunks, hsize_t, size_t);
-        if(NULL == (fm->select_chunk = (hbool_t *)H5MM_calloc((size_t)fm->total_chunks * sizeof(hbool_t))))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
-    } /* end if */
-#endif /* H5_HAVE_PARALLEL */
-
-
-    /* Initialize "last chunk" information */
-    fm->last_index = (hsize_t)-1;
-    fm->last_chunk_info = NULL;
-
-    /* Point at the dataspaces */
-    fm->file_space = file_space;
-    fm->mem_space = mem_space;
-
-    /* Special case for only one element in selection */
-    /* (usually appending a record) */
-    if(nelmts == 1
-#ifdef H5_HAVE_PARALLEL
-            && !(io_info->using_mpi_vfd)
-#endif /* H5_HAVE_PARALLEL */
-        ) {
-        /* Initialize skip list for chunk selections */
-        fm->sel_chunks = NULL;
-        fm->use_single = TRUE;
-
-        /* Initialize single chunk dataspace */
-        if(NULL == dataset->shared->cache.chunk.single_space) {
-            /* Make a copy of the dataspace for the dataset */
-            if((dataset->shared->cache.chunk.single_space = H5S_copy(file_space, TRUE, FALSE)) == NULL)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy file space")
-
-            /* Resize chunk's dataspace dimensions to size of chunk */
-            if(H5S_set_extent_real(dataset->shared->cache.chunk.single_space, fm->chunk_dim) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't adjust chunk dimensions")
-
-            /* Set the single chunk dataspace to 'all' selection */
-            if(H5S_select_all(dataset->shared->cache.chunk.single_space, TRUE) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTSELECT, FAIL, "unable to set all selection")
-        } /* end if */
-        fm->single_space = dataset->shared->cache.chunk.single_space;
-        HDassert(fm->single_space);
-
-        /* Allocate the single chunk information */
-        if(NULL == dataset->shared->cache.chunk.single_chunk_info) {
-            if(NULL == (dataset->shared->cache.chunk.single_chunk_info = H5FL_MALLOC(H5D_chunk_info_t)))
-                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
-        } /* end if */
-        fm->single_chunk_info = dataset->shared->cache.chunk.single_chunk_info;
-        HDassert(fm->single_chunk_info);
-
-        /* Reset chunk template information */
-        fm->mchunk_tmpl = NULL;
+    if(NULL == (type_info->tpath = H5T_path_find(src_type, dst_type, NULL, NULL, dxpl_id, FALSE)))
+	HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "unable to convert between src and dest datatype")
 
-        /* Set up chunk mapping for single element */
-        if(H5D_create_chunk_map_single(fm, io_info) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create chunk selections for single element")
+    /* Precompute some useful information */
+    type_info->src_type_size = H5T_get_size(src_type);
+    type_info->dst_type_size = H5T_get_size(dst_type);
+    type_info->max_type_size = MAX(type_info->src_type_size, type_info->dst_type_size);
+    type_info->is_conv_noop = H5T_path_noop(type_info->tpath);
+    type_info->is_xform_noop = H5Z_xform_noop(dxpl_cache->data_xform_prop);
+    if(type_info->is_xform_noop && type_info->is_conv_noop) {
+        type_info->cmpd_subset = H5T_SUBSET_FALSE;
+        type_info->need_bkg = H5T_BKG_NO;
     } /* end if */
     else {
-        /* Initialize skip list for chunk selections */
-        if(NULL == dataset->shared->cache.chunk.sel_chunks) {
-            if(NULL == (dataset->shared->cache.chunk.sel_chunks = H5SL_create(H5SL_TYPE_HSIZE, 0.5, (size_t)H5D_DEFAULT_SKIPLIST_HEIGHT)))
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTCREATE, FAIL, "can't create skip list for chunk selections")
-        } /* end if */
-        fm->sel_chunks = dataset->shared->cache.chunk.sel_chunks;
-        HDassert(fm->sel_chunks);
-
-        /* We are not using single element mode */
-        fm->use_single = FALSE;
+        size_t	target_size;		/* Desired buffer size	*/
 
-        /* Get type of selection on disk & in memory */
-        if((fsel_type = H5S_GET_SELECT_TYPE(file_space)) < H5S_SEL_NONE)
-            HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to get type of selection")
-        if((fm->msel_type = H5S_GET_SELECT_TYPE(mem_space)) < H5S_SEL_NONE)
-            HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to get type of selection")
+        /* Check if the datatypes are compound subsets of one another */
+        type_info->cmpd_subset = H5T_path_compound_subset(type_info->tpath);
 
-        /* If the selection is NONE or POINTS, set the flag to FALSE */
-        if(fsel_type == H5S_SEL_POINTS || fsel_type == H5S_SEL_NONE)
-            sel_hyper_flag = FALSE;
-        else
-            sel_hyper_flag = TRUE;
-
-        /* Check if file selection is a not a hyperslab selection */
-        if(sel_hyper_flag) {
-            /* Build the file selection for each chunk */
-            if(H5D_create_chunk_file_map_hyper(fm, io_info) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create file chunk selections")
-
-            /* Clean file chunks' hyperslab span "scratch" information */
-            curr_node=H5SL_first(fm->sel_chunks);
-            while(curr_node) {
-                H5D_chunk_info_t *chunk_info;   /* Pointer chunk information */
-
-                /* Get pointer to chunk's information */
-                chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
-                assert(chunk_info);
-
-                /* Clean hyperslab span's "scratch" information */
-                if(H5S_hyper_reset_scratch(chunk_info->fspace) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "unable to reset span scratch info")
-
-                /* Get the next chunk node in the skip list */
-                curr_node=H5SL_next(curr_node);
-            } /* end while */
-        } /* end if */
+        /* Check if we need a background buffer */
+        if(do_write && H5T_detect_class(dset->shared->type, H5T_VLEN))
+            type_info->need_bkg = H5T_BKG_YES;
         else {
-            /* Create temporary datatypes for selection iteration */
-            if((f_tid = H5I_register(H5I_DATATYPE, H5T_copy(dataset->shared->type, H5T_COPY_ALL))) < 0)
-                HGOTO_ERROR(H5E_DATATYPE, H5E_CANTREGISTER, FAIL, "unable to register file datatype")
-
-            /* Spaces might not be the same shape, iterate over the file selection directly */
-            if(H5S_select_iterate(&bogus, f_tid, file_space,  H5D_chunk_file_cb, fm) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create file chunk selections")
-
-            /* Reset "last chunk" info */
-            fm->last_index=(hsize_t)-1;
-            fm->last_chunk_info=NULL;
-        } /* end else */
-
-        /* Build the memory selection for each chunk */
-        if(sel_hyper_flag && H5S_select_shape_same(file_space, mem_space) == TRUE) {
-            /* Reset chunk template information */
-            fm->mchunk_tmpl = NULL;
-
-            /* If the selections are the same shape, use the file chunk information
-             * to generate the memory chunk information quickly.
-             */
-            if(H5D_create_chunk_mem_map_hyper(fm) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create memory chunk selections")
-        } /* end if */
-        else {
-            size_t elmt_size;           /* Memory datatype size */
-
-            /* Make a copy of equivalent memory space */
-            if((tmp_mspace = H5S_copy(mem_space, TRUE, FALSE)) == NULL)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy memory space")
-
-            /* De-select the mem space copy */
-            if(H5S_select_none(tmp_mspace) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to de-select memory space")
-
-            /* Save chunk template information */
-            fm->mchunk_tmpl=tmp_mspace;
+            H5T_bkg_t path_bkg;     /* Type conversion's background info */
 
-            /* Create temporary datatypes for selection iteration */
-            if(f_tid<0) {
-                if((f_tid = H5I_register(H5I_DATATYPE, H5T_copy(dataset->shared->type, H5T_COPY_ALL))) < 0)
-                    HGOTO_ERROR(H5E_DATATYPE, H5E_CANTREGISTER, FAIL, "unable to register file datatype")
-            } /* end if */
-
-            /* Create selection iterator for memory selection */
-            if((elmt_size=H5T_get_size(mem_type))==0)
-                HGOTO_ERROR(H5E_DATATYPE, H5E_BADSIZE, FAIL, "datatype size invalid")
-            if(H5S_select_iter_init(&(fm->mem_iter), mem_space, elmt_size) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
-            iter_init = TRUE;	/* Selection iteration info has been initialized */
-
-            /* Spaces aren't the same shape, iterate over the memory selection directly */
-            if(H5S_select_iterate(&bogus, f_tid, file_space,  H5D_chunk_mem_cb, fm) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create memory chunk selections")
-
-            /* Clean up hyperslab stuff, if necessary */
-            if(fm->msel_type != H5S_SEL_POINTS) {
-                /* Clean memory chunks' hyperslab span "scratch" information */
-                curr_node=H5SL_first(fm->sel_chunks);
-                while(curr_node) {
-                    H5D_chunk_info_t *chunk_info;   /* Pointer chunk information */
-
-                    /* Get pointer to chunk's information */
-                    chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
-                    assert(chunk_info);
-
-                    /* Clean hyperslab span's "scratch" information */
-                    if(H5S_hyper_reset_scratch(chunk_info->mspace) < 0)
-                        HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "unable to reset span scratch info")
-
-                    /* Get the next chunk node in the skip list */
-                    curr_node=H5SL_next(curr_node);
-                } /* end while */
+            if((path_bkg = H5T_path_bkg(type_info->tpath))) {
+                /* Retrieve the bkgr buffer property */
+                type_info->need_bkg = dxpl_cache->bkgr_buf_type;
+                type_info->need_bkg = MAX(path_bkg, type_info->need_bkg);
             } /* end if */
+            else
+                type_info->need_bkg = H5T_BKG_NO; /*never needed even if app says yes*/
         } /* end else */
-    } /* end else */
-
-done:
-    /* Release the [potentially partially built] chunk mapping information if an error occurs */
-    if(ret_value<0) {
-        if(tmp_mspace && !fm->mchunk_tmpl) {
-            if(H5S_close(tmp_mspace) < 0)
-                HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "can't release memory chunk dataspace template")
-        } /* end if */
-
-        if (H5D_destroy_chunk_map(fm) < 0)
-            HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release chunk mapping")
-    } /* end if */
-
-    /* Reset the global dataspace info */
-    fm->file_space = NULL;
-    fm->mem_space = NULL;
-
-    if(iter_init) {
-        if(H5S_SELECT_ITER_RELEASE(&(fm->mem_iter)) < 0)
-            HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
-    } /* end if */
-    if(f_tid!=(-1)) {
-        if(H5I_dec_ref(f_tid) < 0)
-            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't decrement temporary datatype ID")
-    } /* end if */
-    if(file_space_normalized) {
-        if(H5S_hyper_denormalize_offset((H5S_t *)file_space, old_offset) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "unable to normalize dataspace by offset")
-    } /* end if */
-
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_create_chunk_map() */
-
-
-/*--------------------------------------------------------------------------
- NAME
-    H5D_free_chunk_info
- PURPOSE
-    Internal routine to destroy a chunk info node
- USAGE
-    void H5D_free_chunk_info(chunk_info)
-        void *chunk_info;    IN: Pointer to chunk info to destroy
- RETURNS
-    No return value
- DESCRIPTION
-    Releases all the memory for a chunk info node.  Called by H5SL_free
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-static herr_t
-H5D_free_chunk_info(void *item, void UNUSED *key, void UNUSED *opdata)
-{
-    H5D_chunk_info_t *chunk_info = (H5D_chunk_info_t *)item;
-
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_free_chunk_info)
-
-    HDassert(chunk_info);
-
-    /* Close the chunk's file dataspace, if it's not shared */
-    if(!chunk_info->fspace_shared)
-        (void)H5S_close(chunk_info->fspace);
-    else
-        H5S_select_all(chunk_info->fspace, TRUE);
-
-    /* Close the chunk's memory dataspace, if it's not shared */
-    if(!chunk_info->mspace_shared)
-        (void)H5S_close(chunk_info->mspace);
-
-    /* Free the actual chunk info */
-    H5FL_FREE(H5D_chunk_info_t, chunk_info);
-
-    FUNC_LEAVE_NOAPI(0);
-}   /* H5D_free_chunk_info() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_destroy_chunk_map
- *
- * Purpose:	Destroy chunk mapping information.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Saturday, May 17, 2003
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_destroy_chunk_map(const H5D_chunk_map_t *fm)
-{
-    herr_t	ret_value = SUCCEED;	/*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_destroy_chunk_map)
-
-    /* Single element I/O vs. multiple element I/O cleanup */
-    if(fm->use_single) {
-        /* Sanity checks */
-        HDassert(fm->sel_chunks == NULL);
-        HDassert(fm->single_chunk_info);
-        HDassert(fm->single_chunk_info->fspace_shared);
-        HDassert(fm->single_chunk_info->mspace_shared);
-
-        /* Reset the selection for the single element I/O */
-        H5S_select_all(fm->single_space, TRUE);
-    } /* end if */
-    else {
-        /* Release the nodes on the list of selected chunks */
-        if(fm->sel_chunks)
-            if(H5SL_free(fm->sel_chunks, H5D_free_chunk_info, NULL) < 0)
-                HGOTO_ERROR(H5E_PLIST, H5E_CANTNEXT, FAIL, "can't iterate over chunks")
-    } /* end else */
-
-    /* Free the memory chunk dataspace template */
-    if(fm->mchunk_tmpl)
-        if(H5S_close(fm->mchunk_tmpl) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "can't release memory chunk dataspace template")
-#ifdef H5_HAVE_PARALLEL
-    if(fm->select_chunk)
-        H5MM_xfree(fm->select_chunk);
-#endif /* H5_HAVE_PARALLEL */
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_destroy_chunk_map() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_create_chunk_map_single
- *
- * Purpose:	Create chunk selections when appending a single record
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Tuesday, November 20, 2007
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_create_chunk_map_single(H5D_chunk_map_t *fm, const H5D_io_info_t
-#ifndef H5_HAVE_PARALLEL
-    UNUSED
-#endif /* H5_HAVE_PARALLEL */
-    *io_info)
-{
-    H5D_chunk_info_t *chunk_info;           /* Chunk information to insert into skip list */
-    hsize_t     sel_start[H5O_LAYOUT_NDIMS]; /* Offset of low bound of file selection */
-    hsize_t     sel_end[H5O_LAYOUT_NDIMS];  /* Offset of high bound of file selection */
-    unsigned    u;                          /* Local index variable */
-    herr_t	ret_value = SUCCEED;        /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5D_create_chunk_map_single)
+        /* Set up datatype conversion/background buffers */
 
-    /* Sanity check */
-    HDassert(fm->f_ndims > 0);
+        /* Get buffer size from DXPL */
+        target_size = dxpl_cache->max_temp_buf;
 
-    /* Get coordinate for selection */
-    if(H5S_SELECT_BOUNDS(fm->file_space, sel_start, sel_end) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
+        /* If the buffer is too small to hold even one element, try to make it bigger */
+        if(target_size < type_info->max_type_size) {
+            hbool_t default_buffer_info;    /* Whether the buffer information are the defaults */
 
-    /* Initialize the 'single chunk' file & memory chunk information */
-    chunk_info = fm->single_chunk_info;
-    chunk_info->chunk_points = 1;
+            /* Detect if we have all default settings for buffers */
+            default_buffer_info = (H5D_TEMP_BUF_SIZE == dxpl_cache->max_temp_buf)
+                    && (NULL == dxpl_cache->tconv_buf) && (NULL == dxpl_cache->bkgr_buf);
 
-    /* Set chunk location & hyperslab size */
-    for(u = 0; u < fm->f_ndims; u++) {
-        HDassert(sel_start[u] == sel_end[u]);
-        chunk_info->coords[u] = (sel_start[u] / fm->layout->u.chunk.dim[u]) * fm->layout->u.chunk.dim[u];
-    } /* end for */
-    chunk_info->coords[fm->f_ndims] = 0;
-
-    /* Calculate the index of this chunk */
-    if(H5V_chunk_index(fm->f_ndims, chunk_info->coords, fm->layout->u.chunk.dim, fm->down_chunks, &chunk_info->index) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
-
-    /* Copy selection for file's dataspace into chunk dataspace */
-    if(H5S_select_copy(fm->single_space, fm->file_space, FALSE) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy file selection")
-
-    /* Move selection back to have correct offset in chunk */
-    if(H5S_SELECT_ADJUST_U(fm->single_space, chunk_info->coords) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk selection")
-
-#ifdef H5_HAVE_PARALLEL
-    /* store chunk selection information */
-    if(io_info->using_mpi_vfd)
-        fm->select_chunk[chunk_info->index] = TRUE;
-#endif /* H5_HAVE_PARALLEL */
-
-    /* Set the file dataspace for the chunk to the shared 'single' dataspace */
-    chunk_info->fspace = fm->single_space;
-
-    /* Indicate that the chunk's file dataspace is shared */
-    chunk_info->fspace_shared = TRUE;
-
-    /* Just point at the memory dataspace & selection */
-    /* (Casting away const OK -QAK) */
-    chunk_info->mspace = (H5S_t *)fm->mem_space;
-
-    /* Indicate that the chunk's memory dataspace is shared */
-    chunk_info->mspace_shared = TRUE;
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_create_chunk_map_single() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_create_chunk_file_map_hyper
- *
- * Purpose:	Create all chunk selections in file.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Thursday, May 29, 2003
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_create_chunk_file_map_hyper(H5D_chunk_map_t *fm, const H5D_io_info_t
-#ifndef H5_HAVE_PARALLEL
-    UNUSED
-#endif /* H5_HAVE_PARALLEL */
-    *io_info)
-{
-    hsize_t     sel_start[H5O_LAYOUT_NDIMS];   /* Offset of low bound of file selection */
-    hsize_t     sel_end[H5O_LAYOUT_NDIMS];   /* Offset of high bound of file selection */
-    hsize_t     sel_points;                 /* Number of elements in file selection */
-    hsize_t     start_coords[H5O_LAYOUT_NDIMS];   /* Starting coordinates of selection */
-    hsize_t     coords[H5O_LAYOUT_NDIMS];   /* Current coordinates of chunk */
-    hsize_t     end[H5O_LAYOUT_NDIMS];      /* Current coordinates of chunk */
-    hsize_t     chunk_index;                /* Index of chunk */
-    int         curr_dim;                   /* Current dimension to increment */
-    unsigned    u;                          /* Local index variable */
-    herr_t	ret_value = SUCCEED;        /* Return value */
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_create_chunk_file_map_hyper)
-
-    /* Sanity check */
-    assert(fm->f_ndims>0);
-
-    /* Get number of elements selected in file */
-    sel_points = fm->nelmts;
-
-    /* Get bounding box for selection (to reduce the number of chunks to iterate over) */
-    if(H5S_SELECT_BOUNDS(fm->file_space, sel_start, sel_end) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
-
-    /* Set initial chunk location & hyperslab size */
-
-    for(u=0; u<fm->f_ndims; u++) {
-        start_coords[u]=(sel_start[u]/fm->layout->u.chunk.dim[u])*fm->layout->u.chunk.dim[u];
-        coords[u]=start_coords[u];
-        end[u]=(coords[u]+fm->chunk_dim[u])-1;
-    } /* end for */
-
-
-    /* Calculate the index of this chunk */
-    if(H5V_chunk_index(fm->f_ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
-
-    /* Iterate through each chunk in the dataset */
-    while(sel_points) {
-        /* Check for intersection of temporary chunk and file selection */
-        /* (Casting away const OK - QAK) */
-        if(H5S_hyper_intersect_block((H5S_t *)fm->file_space,coords,end)==TRUE) {
-            H5S_t *tmp_fchunk;                  /* Temporary file dataspace */
-            H5D_chunk_info_t *new_chunk_info;   /* chunk information to insert into skip list */
-            hssize_t    schunk_points;          /* Number of elements in chunk selection */
-
-            /* Create "temporary" chunk for selection operations (copy file space) */
-            if((tmp_fchunk = H5S_copy(fm->file_space, TRUE, FALSE)) == NULL)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy memory space")
-
-            /* Make certain selections are stored in span tree form (not "optimized hyperslab" or "all") */
-            if(H5S_hyper_convert(tmp_fchunk) < 0) {
-                (void)H5S_close(tmp_fchunk);
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to convert selection to span trees")
-            } /* end if */
-
-            /* "AND" temporary chunk and current chunk */
-            if(H5S_select_hyperslab(tmp_fchunk,H5S_SELECT_AND,coords,NULL,fm->chunk_dim,NULL) < 0) {
-                (void)H5S_close(tmp_fchunk);
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't create chunk selection")
-            } /* end if */
-
-            /* Resize chunk's dataspace dimensions to size of chunk */
-            if(H5S_set_extent_real(tmp_fchunk,fm->chunk_dim) < 0) {
-                (void)H5S_close(tmp_fchunk);
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk dimensions")
-            } /* end if */
-
-            /* Move selection back to have correct offset in chunk */
-            if(H5S_SELECT_ADJUST_U(tmp_fchunk, coords) < 0) {
-                (void)H5S_close(tmp_fchunk);
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk selection")
-            } /* end if */
-
-            /* Add temporary chunk to the list of chunks */
-
-            /* Allocate the file & memory chunk information */
-            if (NULL==(new_chunk_info = H5FL_MALLOC (H5D_chunk_info_t))) {
-                (void)H5S_close(tmp_fchunk);
-                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
-            } /* end if */
-
-            /* Initialize the chunk information */
-
-            /* Set the chunk index */
-            new_chunk_info->index=chunk_index;
-
-#ifdef H5_HAVE_PARALLEL
-            /* store chunk selection information */
-            if(io_info->using_mpi_vfd)
-                fm->select_chunk[chunk_index] = TRUE;
-#endif /* H5_HAVE_PARALLEL */
-
-            /* Set the file chunk dataspace */
-            new_chunk_info->fspace = tmp_fchunk;
-            new_chunk_info->fspace_shared = FALSE;
-
-            /* Set the memory chunk dataspace */
-            new_chunk_info->mspace=NULL;
-            new_chunk_info->mspace_shared = FALSE;
-
-            /* Copy the chunk's coordinates */
-            for(u=0; u<fm->f_ndims; u++)
-                new_chunk_info->coords[u]=coords[u];
-            new_chunk_info->coords[fm->f_ndims]=0;
-
-            /* Insert the new chunk into the skip list */
-            if(H5SL_insert(fm->sel_chunks,new_chunk_info,&new_chunk_info->index) < 0) {
-                H5D_free_chunk_info(new_chunk_info,NULL,NULL);
-                HGOTO_ERROR(H5E_DATASPACE,H5E_CANTINSERT,FAIL,"can't insert chunk into skip list")
-            } /* end if */
-
-            /* Get number of elements selected in chunk */
-            if((schunk_points=H5S_GET_SELECT_NPOINTS(tmp_fchunk)) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection # of elements")
-            H5_ASSIGN_OVERFLOW(new_chunk_info->chunk_points,schunk_points,hssize_t,size_t);
-
-            /* Decrement # of points left in file selection */
-            sel_points-=(hsize_t)schunk_points;
-
-            /* Leave if we are done */
-            if(sel_points==0)
-                HGOTO_DONE(SUCCEED)
-            assert(sel_points>0);
+            /* Check if we are using the default buffer info */
+            if(default_buffer_info)
+                /* OK to get bigger for library default settings */
+                target_size = type_info->max_type_size;
+            else
+                /* Don't get bigger than the application has requested */
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "temporary buffer max size is too small")
         } /* end if */
 
-        /* Increment chunk index */
-        chunk_index++;
-
-        /* Set current increment dimension */
-        curr_dim=(int)fm->f_ndims-1;
-
-        /* Increment chunk location in fastest changing dimension */
-        H5_CHECK_OVERFLOW(fm->chunk_dim[curr_dim],hsize_t,hssize_t);
-        coords[curr_dim]+=fm->chunk_dim[curr_dim];
-        end[curr_dim]+=fm->chunk_dim[curr_dim];
-
-        /* Bring chunk location back into bounds, if necessary */
-        if(coords[curr_dim]>sel_end[curr_dim]) {
-            do {
-                /* Reset current dimension's location to 0 */
-                coords[curr_dim]=start_coords[curr_dim]; /*lint !e771 The start_coords will always be initialized */
-                end[curr_dim]=(coords[curr_dim]+(hssize_t)fm->chunk_dim[curr_dim])-1;
-
-                /* Decrement current dimension */
-                curr_dim--;
-
-                /* Increment chunk location in current dimension */
-                coords[curr_dim]+=fm->chunk_dim[curr_dim];
-                end[curr_dim]=(coords[curr_dim]+fm->chunk_dim[curr_dim])-1;
-            } while(coords[curr_dim]>sel_end[curr_dim]);
-
-            /* Re-Calculate the index of this chunk */
-            if(H5V_chunk_index(fm->f_ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
-        } /* end if */
-    } /* end while */
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_create_chunk_file_map_hyper() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_create_chunk_mem_map_hyper
- *
- * Purpose:	Create all chunk selections in memory by copying the file
- *              chunk selections and adjusting their offsets to be correct
- *              for the memory.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Thursday, May 29, 2003
- *
- * Assumptions: That the file and memory selections are the same shape.
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_create_chunk_mem_map_hyper(const H5D_chunk_map_t *fm)
-{
-    H5SL_node_t *curr_node;                 /* Current node in skip list */
-    hsize_t    file_sel_start[H5O_LAYOUT_NDIMS];    /* Offset of low bound of file selection */
-    hsize_t    file_sel_end[H5O_LAYOUT_NDIMS];  /* Offset of high bound of file selection */
-    hsize_t    mem_sel_start[H5O_LAYOUT_NDIMS]; /* Offset of low bound of file selection */
-    hsize_t    mem_sel_end[H5O_LAYOUT_NDIMS];   /* Offset of high bound of file selection */
-    hssize_t adjust[H5O_LAYOUT_NDIMS];      /* Adjustment to make to all file chunks */
-    hssize_t chunk_adjust[H5O_LAYOUT_NDIMS];  /* Adjustment to make to a particular chunk */
-    unsigned    u;                          /* Local index variable */
-    herr_t	ret_value = SUCCEED;        /* Return value */
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_create_chunk_mem_map_hyper)
-
-    /* Sanity check */
-    assert(fm->f_ndims>0);
-
-    /* Check for all I/O going to a single chunk */
-    if(H5SL_count(fm->sel_chunks)==1) {
-        H5D_chunk_info_t *chunk_info;   /* Pointer to chunk information */
-
-        /* Get the node */
-        curr_node=H5SL_first(fm->sel_chunks);
-
-        /* Get pointer to chunk's information */
-        chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
-        assert(chunk_info);
-
-        /* Just point at the memory dataspace & selection */
-        /* (Casting away const OK -QAK) */
-        chunk_info->mspace=(H5S_t *)fm->mem_space;
-
-        /* Indicate that the chunk's memory space is shared */
-        chunk_info->mspace_shared = TRUE;
-    } /* end if */
-    else {
-        /* Get bounding box for file selection */
-        if(H5S_SELECT_BOUNDS(fm->file_space, file_sel_start, file_sel_end) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
-
-        /* Get bounding box for memory selection */
-        if(H5S_SELECT_BOUNDS(fm->mem_space, mem_sel_start, mem_sel_end) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get file selection bound info")
-
-        /* Calculate the adjustment for memory selection from file selection */
-        assert(fm->m_ndims==fm->f_ndims);
-        for(u=0; u<fm->f_ndims; u++) {
-            H5_CHECK_OVERFLOW(file_sel_start[u],hsize_t,hssize_t);
-            H5_CHECK_OVERFLOW(mem_sel_start[u],hsize_t,hssize_t);
-            adjust[u]=(hssize_t)file_sel_start[u]-(hssize_t)mem_sel_start[u];
-        } /* end for */
-
-        /* Iterate over each chunk in the chunk list */
-        curr_node=H5SL_first(fm->sel_chunks);
-        while(curr_node) {
-            H5D_chunk_info_t *chunk_info;   /* Pointer to chunk information */
-
-            /* Get pointer to chunk's information */
-            chunk_info = (H5D_chunk_info_t *)H5SL_item(curr_node);
-            assert(chunk_info);
-
-            /* Copy the information */
-
-            /* Copy the memory dataspace */
-            if((chunk_info->mspace = H5S_copy(fm->mem_space, TRUE, FALSE)) == NULL)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy memory space")
-
-            /* Release the current selection */
-            if(H5S_SELECT_RELEASE(chunk_info->mspace) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection")
-
-            /* Copy the file chunk's selection */
-            if(H5S_select_copy(chunk_info->mspace,chunk_info->fspace,FALSE) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy selection")
-
-            /* Compensate for the chunk offset */
-            for(u=0; u<fm->f_ndims; u++) {
-                H5_CHECK_OVERFLOW(chunk_info->coords[u],hsize_t,hssize_t);
-                chunk_adjust[u]=adjust[u]-(hssize_t)chunk_info->coords[u]; /*lint !e771 The adjust array will always be initialized */
-            } /* end for */
-
-            /* Adjust the selection */
-            if(H5S_hyper_adjust_s(chunk_info->mspace,chunk_adjust) < 0) /*lint !e772 The chunk_adjust array will always be initialized */
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't adjust chunk selection")
-
-            /* Get the next chunk node in the skip list */
-            curr_node=H5SL_next(curr_node);
-        } /* end while */
-    } /* end else */
+        /* Compute the number of elements that will fit into buffer */
+        type_info->request_nelmts = target_size / type_info->max_type_size;
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_create_chunk_mem_map_hyper() */
+        /* Sanity check elements in temporary buffer */
+        if(type_info->request_nelmts == 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "temporary buffer max size is too small")
 
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_chunk_file_cb
- *
- * Purpose:	Callback routine for file selection iterator.  Used when
- *              creating selections in file for each point selected.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Wednesday, July 23, 2003
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_chunk_file_cb(void UNUSED *elem, hid_t UNUSED type_id, unsigned ndims, const hsize_t *coords, void *_fm)
-{
-    H5D_chunk_map_t      *fm = (H5D_chunk_map_t *)_fm;  /* File<->memory chunk mapping info */
-    H5D_chunk_info_t *chunk_info;               /* Chunk information for current chunk */
-    hsize_t    coords_in_chunk[H5O_LAYOUT_NDIMS];        /* Coordinates of element in chunk */
-    hsize_t     chunk_index;                    /* Chunk index */
-    unsigned    u;                              /* Local index variable */
-    herr_t	ret_value = SUCCEED;            /* Return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_file_cb)
-
-    /* Calculate the index of this chunk */
-    if(H5V_chunk_index(ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
-
-    /* Find correct chunk in file & memory skip list */
-    if(chunk_index==fm->last_index) {
-        /* If the chunk index is the same as the last chunk index we used,
-         * get the cached info to operate on.
-         */
-        chunk_info=fm->last_chunk_info;
-    } /* end if */
-    else {
-        /* If the chunk index is not the same as the last chunk index we used,
-         * find the chunk in the skip list.
+        /*
+         * Get a temporary buffer for type conversion unless the app has already
+         * supplied one through the xfer properties. Instead of allocating a
+         * buffer which is the exact size, we allocate the target size.  The
+         * malloc() is usually less resource-intensive if we allocate/free the
+         * same size over and over.
          */
-        /* Get the chunk node from the skip list */
-        if(NULL == (chunk_info = (H5D_chunk_info_t *)H5SL_search(fm->sel_chunks, &chunk_index))) {
-            H5S_t *fspace;                      /* Memory chunk's dataspace */
-
-            /* Allocate the file & memory chunk information */
-            if (NULL==(chunk_info = H5FL_MALLOC (H5D_chunk_info_t)))
-                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate chunk info")
-
-            /* Initialize the chunk information */
-
-            /* Set the chunk index */
-            chunk_info->index=chunk_index;
-
-            /* Create a dataspace for the chunk */
-            if((fspace = H5S_create_simple(fm->f_ndims,fm->chunk_dim,NULL))==NULL) {
-                H5FL_FREE(H5D_chunk_info_t,chunk_info);
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCREATE, FAIL, "unable to create dataspace for chunk")
-            } /* end if */
-
-            /* De-select the chunk space */
-            if(H5S_select_none(fspace) < 0) {
-                (void)H5S_close(fspace);
-                H5FL_FREE(H5D_chunk_info_t,chunk_info);
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to de-select dataspace")
-            } /* end if */
-
-            /* Set the file chunk dataspace */
-            chunk_info->fspace = fspace;
-            chunk_info->fspace_shared = FALSE;
-
-            /* Set the memory chunk dataspace */
-            chunk_info->mspace=NULL;
-            chunk_info->mspace_shared = FALSE;
-
-            /* Set the number of selected elements in chunk to zero */
-            chunk_info->chunk_points=0;
-
-            /* Compute the chunk's coordinates */
-            for(u=0; u<fm->f_ndims; u++) {
-                H5_CHECK_OVERFLOW(fm->layout->u.chunk.dim[u],hsize_t,hssize_t);
-                chunk_info->coords[u]=(coords[u]/(hssize_t)fm->layout->u.chunk.dim[u])*(hssize_t)fm->layout->u.chunk.dim[u];
-            } /* end for */
-            chunk_info->coords[fm->f_ndims]=0;
-
-            /* Insert the new chunk into the skip list */
-            if(H5SL_insert(fm->sel_chunks,chunk_info,&chunk_info->index) < 0) {
-                H5D_free_chunk_info(chunk_info,NULL,NULL);
-                HGOTO_ERROR(H5E_DATASPACE,H5E_CANTINSERT,FAIL,"can't insert chunk into skip list")
-            } /* end if */
+        if(NULL == (type_info->tconv_buf = (uint8_t *)dxpl_cache->tconv_buf)) {
+            /* Allocate temporary buffer */
+            if(NULL == (type_info->tconv_buf = H5FL_BLK_MALLOC(type_conv, target_size)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for type conversion")
+            type_info->tconv_buf_allocated = TRUE;
+        } /* end if */
+        if(type_info->need_bkg && NULL == (type_info->bkg_buf = (uint8_t *)dxpl_cache->bkgr_buf)) {
+            size_t	bkg_size;		/* Desired background buffer size	*/
+
+            /* Compute the background buffer size */
+            /* (don't try to use buffers smaller than the default size) */
+            bkg_size = type_info->request_nelmts * type_info->dst_type_size;
+            if(bkg_size < dxpl_cache->max_temp_buf)
+                bkg_size = dxpl_cache->max_temp_buf;
+
+            /* Allocate background buffer */
+            /* (Need calloc()-like call since memory needs to be initialized) */
+            if(NULL == (type_info->bkg_buf = H5FL_BLK_CALLOC(type_conv, bkg_size)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for background conversion")
+            type_info->bkg_buf_allocated = TRUE;
         } /* end if */
-
-        /* Update the "last chunk seen" information */
-        fm->last_index=chunk_index;
-        fm->last_chunk_info=chunk_info;
-    } /* end else */
-
-    /* Get the coordinates of the element in the chunk */
-    for(u=0; u<fm->f_ndims; u++)
-        coords_in_chunk[u]=coords[u]%fm->layout->u.chunk.dim[u];
-
-    /* Add point to file selection for chunk */
-    if(H5S_select_elements(chunk_info->fspace, H5S_SELECT_APPEND, (size_t)1, coords_in_chunk) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "unable to select element")
-
-    /* Increment the number of elemented selected in chunk */
-    chunk_info->chunk_points++;
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_chunk_file_cb() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_chunk_mem_cb
- *
- * Purpose:	Callback routine for file selection iterator.  Used when
- *              creating selections in memory for each chunk.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Raymond Lu
- *		Thursday, April 10, 2003
- *
- *-------------------------------------------------------------------------
- */
-/* ARGSUSED */
-static herr_t
-H5D_chunk_mem_cb(void UNUSED *elem, hid_t UNUSED type_id, unsigned ndims, const hsize_t *coords, void *_fm)
-{
-    H5D_chunk_map_t      *fm = (H5D_chunk_map_t *)_fm;  /* File<->memory chunk mapping info */
-    H5D_chunk_info_t *chunk_info;               /* Chunk information for current chunk */
-    hsize_t    coords_in_mem[H5O_LAYOUT_NDIMS];        /* Coordinates of element in memory */
-    hsize_t     chunk_index;                    /* Chunk index */
-    herr_t	ret_value = SUCCEED;            /* Return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_mem_cb)
-
-    /* Calculate the index of this chunk */
-    if(H5V_chunk_index(ndims,coords,fm->layout->u.chunk.dim,fm->down_chunks,&chunk_index) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "can't get chunk index")
-
-    /* Find correct chunk in file & memory skip list */
-    if(chunk_index==fm->last_index) {
-        /* If the chunk index is the same as the last chunk index we used,
-         * get the cached spaces to operate on.
-         */
-        chunk_info=fm->last_chunk_info;
-    } /* end if */
-    else {
-        /* If the chunk index is not the same as the last chunk index we used,
-         * find the chunk in the skip list.
-         */
-        /* Get the chunk node from the skip list */
-        if(NULL == (chunk_info = (H5D_chunk_info_t *)H5SL_search(fm->sel_chunks, &chunk_index)))
-            HGOTO_ERROR(H5E_DATASPACE, H5E_NOTFOUND, FAIL, "can't locate chunk in skip list")
-
-        /* Check if the chunk already has a memory space */
-        if(chunk_info->mspace==NULL) {
-            /* Copy the template memory chunk dataspace */
-            if((chunk_info->mspace = H5S_copy(fm->mchunk_tmpl, FALSE, FALSE)) == NULL)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy file space")
-        } /* end else */
-
-        /* Update the "last chunk seen" information */
-        fm->last_index=chunk_index;
-        fm->last_chunk_info=chunk_info;
-    } /* end else */
-
-    /* Get coordinates of selection iterator for memory */
-    if(H5S_SELECT_ITER_COORDS(&fm->mem_iter,coords_in_mem) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "unable to get iterator coordinates")
-
-    /* Add point to memory selection for chunk */
-    if(fm->msel_type==H5S_SEL_POINTS) {
-        if(H5S_select_elements(chunk_info->mspace, H5S_SELECT_APPEND, (size_t)1, coords_in_mem) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "unable to select element")
-    } /* end if */
-    else {
-        if(H5S_hyper_add_span_element(chunk_info->mspace, fm->m_ndims, coords_in_mem) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "unable to select element")
     } /* end else */
 
-    /* Move memory selection iterator to next element in selection */
-    if(H5S_SELECT_ITER_NEXT(&fm->mem_iter, (size_t)1) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTNEXT, FAIL, "unable to move to next iterator location")
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_chunk_mem_cb() */
+} /* end H5D_typeinfo_init() */
 
+#ifdef H5_HAVE_PARALLEL
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_ioinfo_init
+ * Function:	H5D_ioinfo_adjust
  *
- * Purpose:	Routine for determining correct I/O operations for
- *              each I/O action.
+ * Purpose:	Adjust operation's I/O info for any parallel I/O
  *
  * Return:	Non-negative on success/Negative on failure
  *
  * Programmer:	Quincey Koziol
- *		Thursday, September 30, 2004
+ *		Thursday, March 27, 2008
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_ioinfo_init(H5D_t *dset, const H5D_dxpl_cache_t *dxpl_cache, hid_t dxpl_id,
-    const H5S_t
-#if !(defined H5_HAVE_PARALLEL || defined H5S_DEBUG)
-    UNUSED
-#endif /* H5_HAVE_PARALLEL */
-    *mem_space, const H5S_t
-#if !(defined H5_HAVE_PARALLEL || defined H5S_DEBUG)
-    UNUSED
-#endif /* H5_HAVE_PARALLEL */
-    *file_space, H5T_path_t
-#ifndef H5_HAVE_PARALLEL
-    UNUSED
-#endif /* H5_HAVE_PARALLEL */
-    *tpath,
-    H5D_io_info_t *io_info)
+H5D_ioinfo_adjust(H5D_io_info_t *io_info, const H5D_t *dset,
+    const H5D_dxpl_cache_t *dxpl_cache, hid_t dxpl_id,
+    const H5S_t *file_space, const H5S_t *mem_space,
+    const H5D_type_info_t *type_info, const H5D_chunk_map_t *fm)
 {
     herr_t	ret_value = SUCCEED;	/* Return value	*/
 
-#if defined H5_HAVE_PARALLEL || defined H5S_DEBUG
-    FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_init)
-#else /* defined H5_HAVE_PARALLEL || defined H5S_DEBUG */
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_ioinfo_init)
-#endif /* defined H5_HAVE_PARALLEL || defined H5S_DEBUG */
+    FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_adjust)
 
     /* check args */
     HDassert(dset);
     HDassert(dset->oloc.file);
     HDassert(mem_space);
     HDassert(file_space);
-    HDassert(tpath);
+    HDassert(type_info);
+    HDassert(type_info->tpath);
     HDassert(io_info);
 
-    /* Set up "normal" I/O fields */
-    io_info->dset=dset;
-    io_info->dxpl_cache=dxpl_cache;
-    io_info->dxpl_id=dxpl_id;
-    io_info->store=NULL;        /* Set later in I/O routine? */
-
-    /* Set I/O operations to initial values */
-    io_info->ops=dset->shared->io_ops;
-
-#ifdef H5_HAVE_PARALLEL
-    /* Start in the "not modified" xfer_mode state */
-    io_info->xfer_mode_changed = FALSE;
-    io_info->using_mpi_vfd = IS_H5FD_MPI(dset->oloc.file);
-
+    /* Make any parallel I/O adjustments */
     if(io_info->using_mpi_vfd) {
         htri_t opt;         /* Flag whether a selection is optimizable */
 
+        /* Record the original state of parallel I/O transfer options */
+        io_info->orig.xfer_mode = io_info->dxpl_cache->xfer_mode;
+        io_info->orig.coll_opt_mode = io_info->dxpl_cache->coll_opt_mode;
+        io_info->orig.io_ops.single_read = io_info->io_ops.single_read;
+        io_info->orig.io_ops.single_write = io_info->io_ops.single_write;
+
         /* Get MPI communicator */
-        if((io_info->comm = H5F_mpi_get_comm(dset->oloc.file)) == MPI_COMM_NULL)
+        if(MPI_COMM_NULL == (io_info->comm = H5F_mpi_get_comm(dset->oloc.file)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't retrieve MPI communicator")
 
-        /*
-         * Check if we can set direct MPI-IO read/write functions
-         */
-        opt=H5D_mpio_opt_possible(io_info, mem_space, file_space, tpath);
-        if(opt==FAIL)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "invalid check for direct IO dataspace ");
+        /* Check if we can set direct MPI-IO read/write functions */
+        if((opt = H5D_mpio_opt_possible(io_info, file_space, mem_space, type_info, fm)) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "invalid check for direct IO dataspace ")
 
         /* Check if we can use the optimized parallel I/O routines */
-        if(opt==TRUE) {
-            /* Set the pointers to the MPI-specific routines */
-            io_info->ops.read = H5D_mpio_select_read;
-            io_info->ops.write = H5D_mpio_select_write;
+        if(opt == TRUE) {
+            /* Override the I/O op pointers to the MPI-specific routines */
+            io_info->io_ops.multi_read = dset->shared->layout_ops->par_read;
+            io_info->io_ops.multi_write = dset->shared->layout_ops->par_write;
+            io_info->io_ops.single_read = H5D_mpio_select_read;
+            io_info->io_ops.single_write = H5D_mpio_select_write;
         } /* end if */
         else {
-            /* Set the pointers to the non-MPI-specific routines */
-            io_info->ops.read = H5D_select_read;
-            io_info->ops.write = H5D_select_write;
-
             /* If we won't be doing collective I/O, but the user asked for
              * collective I/O, change the request to use independent I/O, but
              * mark it so that we remember to revert the change.
              */
-            if(io_info->dxpl_cache->xfer_mode==H5FD_MPIO_COLLECTIVE) {
+            if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
                 H5P_genplist_t *dx_plist;           /* Data transer property list */
 
                 /* Get the dataset transfer property list */
-                if (NULL == (dx_plist = (H5P_genplist_t *)H5I_object(dxpl_id)))
+                if(NULL == (dx_plist = (H5P_genplist_t *)H5I_object(dxpl_id)))
                     HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset creation property list")
 
                 /* Change the xfer_mode to independent for handling the I/O */
                 io_info->dxpl_cache->xfer_mode = H5FD_MPIO_INDEPENDENT;
-                if(H5P_set (dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->dxpl_cache->xfer_mode) < 0)
+                if(H5P_set(dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->dxpl_cache->xfer_mode) < 0)
                     HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set transfer mode")
-
-                /* Indicate that the transfer mode should be restored before returning
-                 * to user.
-                 */
-                io_info->xfer_mode_changed = TRUE;
             } /* end if */
         } /* end else */
     } /* end if */
-    else {
-        /* Set the pointers to the non-MPI-specific routines */
-        io_info->ops.read = H5D_select_read;
-        io_info->ops.write = H5D_select_write;
-    } /* end else */
-#else /* H5_HAVE_PARALLEL */
-    io_info->ops.read = H5D_select_read;
-    io_info->ops.write = H5D_select_write;
-#endif /* H5_HAVE_PARALLEL */
-
-#ifdef H5S_DEBUG
-    /* Get the information for the I/O statistics */
-    if((io_info->stats=H5S_find(mem_space,file_space))==NULL)
-        HGOTO_ERROR(H5E_DATASET, H5E_BADSELECT, FAIL, "can't set up selection statistics");
-#endif /* H5S_DEBUG */
 
-#if defined H5_HAVE_PARALLEL || defined H5S_DEBUG
 done:
-#endif /* H5_HAVE_PARALLEL || H5S_DEBUG */
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_ioinfo_init() */
+} /* end H5D_ioinfo_adjust() */
 
-#ifdef H5_HAVE_PARALLEL
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_ioinfo_term
@@ -3438,23 +933,69 @@ H5D_ioinfo_term(H5D_io_info_t *io_info)
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_term)
 
-    /* Check if we need to revert the change to the xfer mode */
-    if (io_info->xfer_mode_changed) {
-        H5P_genplist_t *dx_plist;           /* Data transer property list */
+    /* Check if we used the MPI VFD for the I/O */
+    if(io_info->using_mpi_vfd) {
+        /* Check if we need to revert the change to the xfer mode */
+        if(io_info->orig.xfer_mode != io_info->dxpl_cache->xfer_mode) {
+            H5P_genplist_t *dx_plist;           /* Data transer property list */
 
-        /* Get the dataset transfer property list */
-        if (NULL == (dx_plist = (H5P_genplist_t *)H5I_object(io_info->dxpl_id)))
-            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
+            /* Get the dataset transfer property list */
+            if(NULL == (dx_plist = (H5P_genplist_t *)H5I_object(io_info->dxpl_id)))
+                HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
+
+            /* Restore the original parallel I/O mode */
+            if(H5P_set(dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->orig.xfer_mode) < 0)
+                HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set transfer mode")
+        } /* end if */
 
-        /* Restore the original parallel I/O mode */
-        io_info->dxpl_cache->xfer_mode = H5FD_MPIO_COLLECTIVE;
-        if(H5P_set (dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->dxpl_cache->xfer_mode) < 0)
-            HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set transfer mode")
+        /* Check if we need to revert the change to the collective opt mode */
+        if(io_info->orig.coll_opt_mode != io_info->dxpl_cache->coll_opt_mode) {
+            H5P_genplist_t *dx_plist;           /* Data transer property list */
+
+            /* Get the dataset transfer property list */
+            if(NULL == (dx_plist = (H5P_genplist_t *)H5I_object(io_info->dxpl_id)))
+                HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
+
+            /* Restore the original parallel I/O mode */
+            if(H5P_set(dx_plist, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME, &io_info->orig.coll_opt_mode) < 0)
+                HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set collective option mode")
+        } /* end if */
     } /* end if */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_ioinfo_term() */
 
-#endif
+#endif /* H5_HAVE_PARALLEL */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_typeinfo_term
+ *
+ * Purpose:	Common logic for terminating a type info object
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Thursday, March  6, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_typeinfo_term(const H5D_type_info_t *type_info)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_typeinfo_term)
+
+    /* Check for releasing datatype conversion & background buffers */
+    if(type_info->tconv_buf_allocated) {
+        HDassert(type_info->tconv_buf);
+        (void)H5FL_BLK_FREE(type_conv, type_info->tconv_buf);
+    } /* end if */
+    if(type_info->bkg_buf_allocated) {
+        HDassert(type_info->bkg_buf);
+        (void)H5FL_BLK_FREE(type_conv, type_info->bkg_buf);
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5D_typeinfo_term() */
 
diff --git a/src/H5Distore.c b/src/H5Distore.c
index 47e4cab..efab271 100644
--- a/src/H5Distore.c
+++ b/src/H5Distore.c
@@ -104,30 +104,12 @@
  */
 #define H5D_ISTORE_NDIMS(X)	(((X)->sizeof_rkey-8)/8)
 
-#define H5D_HASH(D,ADDR) H5F_addr_hash(ADDR,(D)->cache.chunk.nslots)
-
 #define H5D_ISTORE_DEFAULT_SKIPLIST_HEIGHT     8
 
 /******************/
 /* Local Typedefs */
 /******************/
 
-/* Raw data chunks are cached.  Each entry in the cache is: */
-typedef struct H5D_rdcc_ent_t {
-    hbool_t	locked;		/*entry is locked in cache		*/
-    hbool_t	dirty;		/*needs to be written to disk?		*/
-    hsize_t	offset[H5O_LAYOUT_NDIMS]; /*chunk name			*/
-    size_t	rd_count;	/*bytes remaining to be read		*/
-    size_t	wr_count;	/*bytes remaining to be written		*/
-    size_t	chunk_size;	/*size of a chunk			*/
-    size_t	alloc_size;	/*amount allocated for the chunk	*/
-    uint8_t	*chunk;		/*the unfiltered chunk data		*/
-    unsigned	idx;		/*index in hash table			*/
-    struct H5D_rdcc_ent_t *next;/*next item in doubly-linked list	*/
-    struct H5D_rdcc_ent_t *prev;/*previous item in doubly-linked list	*/
-} H5D_rdcc_ent_t;
-typedef H5D_rdcc_ent_t *H5D_rdcc_ent_ptr_t; /* For free lists */
-
 /*
  * Data exchange structure for indexed storage nodes.  This structure is
  * passed through the B-link tree layer to the methods for the objects
@@ -192,7 +174,7 @@ typedef struct H5D_istore_it_ud4_t {
 /* B-tree callback info for iteration to obtain chunk address and the index of the chunk for all chunks in the B-tree. */
 typedef struct H5D_istore_it_ud5_t {
     H5D_istore_bt_ud_common_t common;           /* Common info for B-tree user data (must be first) */
-    hsize_t             *down_chunks;
+    const hsize_t       *down_chunks;
     haddr_t             *chunk_addr;
 } H5D_istore_it_ud5_t;
 
@@ -1490,7 +1472,7 @@ H5D_istore_flush(H5D_t *dset, hid_t dxpl_id, unsigned flags)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't fill dxpl cache")
 
     /* Construct dataset I/O info */
-    H5D_BUILD_IO_INFO(&io_info, dset, dxpl_cache, dxpl_id, NULL);
+    H5D_BUILD_IO_INFO_WRT(&io_info, dset, dxpl_cache, dxpl_id, NULL, NULL);
 
     /* Loop over all entries in the chunk cache */
     for(ent = rdcc->head; ent; ent = next) {
@@ -1525,48 +1507,48 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_istore_dest (H5D_t *dset, hid_t dxpl_id)
+H5D_istore_dest(H5D_t *dset, hid_t dxpl_id)
 {
     H5D_io_info_t io_info;              /* Temporary I/O info object */
     H5D_dxpl_cache_t _dxpl_cache;       /* Data transfer property cache buffer */
-    H5D_dxpl_cache_t *dxpl_cache=&_dxpl_cache;   /* Data transfer property cache */
-    H5D_rdcc_t		*rdcc = &(dset->shared->cache.chunk);
-    int		nerrors=0;
-    H5D_rdcc_ent_t	*ent=NULL, *next=NULL;
-    herr_t      ret_value=SUCCEED;       /* Return value */
+    H5D_dxpl_cache_t *dxpl_cache = &_dxpl_cache;   /* Data transfer property cache */
+    H5D_rdcc_t	*rdcc = &(dset->shared->cache.chunk);
+    int		nerrors = 0;
+    H5D_rdcc_ent_t	*ent = NULL, *next = NULL;
+    herr_t      ret_value = SUCCEED;       /* Return value */
 
     FUNC_ENTER_NOAPI(H5D_istore_dest, FAIL)
 
-    assert(dset);
+    HDassert(dset);
 
     /* Fill the DXPL cache values for later use */
-    if (H5D_get_dxpl_cache(dxpl_id,&dxpl_cache)<0)
+    if(H5D_get_dxpl_cache(dxpl_id, &dxpl_cache) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't fill dxpl cache")
 
     /* Construct dataset I/O info */
-    H5D_BUILD_IO_INFO(&io_info,dset,dxpl_cache,dxpl_id,NULL);
+    H5D_BUILD_IO_INFO_WRT(&io_info, dset, dxpl_cache, dxpl_id, NULL, NULL);
 
     /* Flush all the cached chunks */
-    for (ent=rdcc->head; ent; ent=next) {
+    for(ent = rdcc->head; ent; ent = next) {
 #ifdef H5D_ISTORE_DEBUG
 	HDfputc('c', stderr);
 	HDfflush(stderr);
 #endif
 	next = ent->next;
-	if (H5D_istore_preempt(&io_info, ent, TRUE )<0)
+	if(H5D_istore_preempt(&io_info, ent, TRUE) < 0)
 	    nerrors++;
-    }
-    if (nerrors)
+    } /* end for */
+    if(nerrors)
 	HGOTO_ERROR(H5E_IO, H5E_CANTFLUSH, FAIL, "unable to flush one or more raw data chunks")
 
     if(rdcc->slot)
-        H5FL_SEQ_FREE (H5D_rdcc_ent_ptr_t,rdcc->slot);
-    HDmemset (rdcc, 0, sizeof(H5D_rdcc_t));
+        H5FL_SEQ_FREE(H5D_rdcc_ent_ptr_t, rdcc->slot);
+    HDmemset(rdcc, 0, sizeof(H5D_rdcc_t));
 
     /* Free the raw B-tree node buffer */
-    if(dset->shared->layout.u.chunk.btree_shared==NULL)
+    if(dset->shared->layout.u.chunk.btree_shared == NULL)
         HGOTO_ERROR(H5E_IO, H5E_CANTFREE, FAIL, "ref-counted page nil")
-    if(H5RC_DEC(dset->shared->layout.u.chunk.btree_shared)<0)
+    if(H5RC_DEC(dset->shared->layout.u.chunk.btree_shared) < 0)
 	HGOTO_ERROR(H5E_IO, H5E_CANTFREE, FAIL, "unable to decrement ref-counted page")
 
 done:
@@ -1835,7 +1817,7 @@ H5D_istore_lock(const H5D_io_info_t *io_info, H5D_istore_ud1_t *udata,
 
     /* Search for the chunk in the cache */
     if(rdcc->nslots > 0) {
-        idx = H5D_HASH(dset->shared,io_info->store->chunk.index);
+        idx = H5D_CHUNK_HASH(dset->shared, io_info->store->chunk.index);
         ent = rdcc->slot[idx];
 
         if(ent)
@@ -1950,10 +1932,8 @@ H5D_istore_lock(const H5D_io_info_t *io_info, H5D_istore_ud1_t *udata,
                     if(H5D_fill_refill_vl(&fb_info, fb_info.elmts_per_buf, io_info->dxpl_id) < 0)
                         HGOTO_ERROR(H5E_DATASET, H5E_CANTCONVERT, NULL, "can't refill fill value buffer")
             } /* end if */
-#ifdef H5_CLEAR_MEMORY
             else
                 HDmemset(chunk, 0, chunk_size);
-#endif /* H5_CLEAR_MEMORY */
 #ifdef H5D_ISTORE_DEBUG
             rdcc->ninits++;
 #endif /* H5D_ISTORE_DEBUG */
@@ -2154,339 +2134,6 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_istore_if_load
- *
- * Purpose:	A small internal function to if it's necessary to load the
- *              chunk into cache.
- *
- * Return:	TRUE or FALSE
- *
- * Programmer:	Raymond Lu
- *		17 July 2007
- *
- *-------------------------------------------------------------------------
- */
-hbool_t 
-H5D_istore_if_load(const H5D_io_info_t *io_info, haddr_t caddr)
-{
-    const H5D_t *dataset = io_info->dset;
-    hbool_t ret_value;
- 
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_istore_if_load)
-
-    HDassert(io_info);
-    HDassert(dataset);
-
-    /*
-     * If the chunk is too large to load into the cache and it has no
-     * filters in the pipeline (i.e. not compressed) and if the address
-     * for the chunk has been defined, then don't load the chunk into the
-     * cache, just write the data to it directly.
-     *
-     * If MPI based VFD is used, must bypass the
-     * chunk-cache scheme because other MPI processes could be
-     * writing to other elements in the same chunk.  Do a direct
-     * write-through of only the elements requested.
-     */
-    if(dataset->shared->dcpl_cache.pline.nused==0 &&
-            ((dataset->shared->layout.u.chunk.size > dataset->shared->cache.chunk.nbytes && caddr != HADDR_UNDEF)
-#ifdef H5_HAVE_PARALLEL
-            || (io_info->using_mpi_vfd && (H5F_ACC_RDWR & H5F_get_intent(dataset->oloc.file)))
-#endif /* H5_HAVE_PARALLEL */
-            )) {
-        ret_value = FALSE;
-    } else
-        ret_value = TRUE;
-
-    FUNC_LEAVE_NOAPI(ret_value)
-}
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_istore_readvv
- *
- * Purpose:	Reads a multi-dimensional buffer from (part of) an indexed raw
- *		storage array.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Wednesday, May  7, 2003
- *
- * Modification: 
- *              Raymond Lu
- *              20 July 2007
- *              Moved H5D_istore_lock and H5D_istore_unlock to H5D_chunk_read
- *              from this function to avoid frequent lock and unlock.
- *
- *-------------------------------------------------------------------------
- */
-ssize_t
-H5D_istore_readvv(const H5D_io_info_t *io_info,
-    size_t chunk_max_nseq, size_t *chunk_curr_seq, size_t chunk_len_arr[], hsize_t chunk_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t chunk_addr, void *chunk, void *buf)
-{
-    H5D_t *dset=io_info->dset;          /* Local pointer to the dataset info */
-    size_t		u;              /* Local index variables */
-    ssize_t             ret_value;      /* Return value */
-
-    FUNC_ENTER_NOAPI(H5D_istore_readvv, FAIL)
-
-    /* Check args */
-    HDassert(io_info);
-    HDassert(dset && H5D_CHUNKED==dset->shared->layout.type);
-    HDassert(dset->shared->layout.u.chunk.ndims>0 && dset->shared->layout.u.chunk.ndims<=H5O_LAYOUT_NDIMS);
-    HDassert(io_info->dxpl_cache);
-    HDassert(io_info->store);
-    HDassert(chunk_len_arr);
-    HDassert(chunk_offset_arr);
-    HDassert(mem_len_arr);
-    HDassert(mem_offset_arr);
-    HDassert(buf);
-
-    /* Get the address of this chunk on disk */
-#ifdef QAK
-HDfprintf(stderr,"%s: io_info->store->chunk.offset={",FUNC);
-for(u=0; u<dset->shared->layout.u.chunk.ndims; u++)
-    HDfprintf(stderr,"%Hd%s",io_info->store->chunk.offset[u],(u<(dset->shared->layout.u.chunk.ndims-1) ? ", " : "}\n"));
-
-HDfprintf(stderr,"%s: chunk_addr=%a, chunk_size=%Zu\n",FUNC,chunk_addr,dset->shared->layout.u.chunk.size);
-HDfprintf(stderr,"%s: chunk_len_arr[%Zu]=%Zu\n",FUNC,*chunk_curr_seq,chunk_len_arr[*chunk_curr_seq]);
-HDfprintf(stderr,"%s: chunk_offset_arr[%Zu]=%Hu\n",FUNC,*chunk_curr_seq,chunk_offset_arr[*chunk_curr_seq]);
-HDfprintf(stderr,"%s: mem_len_arr[%Zu]=%Zu\n",FUNC,*mem_curr_seq,mem_len_arr[*mem_curr_seq]);
-HDfprintf(stderr,"%s: mem_offset_arr[%Zu]=%Hu\n",FUNC,*mem_curr_seq,mem_offset_arr[*mem_curr_seq]);
-HDfprintf(stderr,"%s: buf=%p\n",FUNC,buf);
-#endif /* QAK */
-
-    /*
-     * If the chunk is too large to load into the cache and it has no
-     * filters in the pipeline (i.e. not compressed) and if the address
-     * for the chunk has been defined, then don't load the chunk into the
-     * cache, just read the data from it directly.
-     *
-     * If MPI based VFD is used, must bypass the
-     * chunk-cache scheme because other MPI processes could be
-     * writing to other elements in the same chunk.  Do a direct
-     * read-through of only the elements requested.
-     */
-    if(!H5D_istore_if_load(io_info, chunk_addr)) {
-        H5D_io_info_t chk_io_info;      /* Temporary I/O info object */
-        H5D_storage_t chk_store;        /* Chunk storage information */
-
-        /* Set up the storage information for the chunk */
-        chk_store.contig.dset_addr=chunk_addr;
-        chk_store.contig.dset_size=(hsize_t)dset->shared->layout.u.chunk.size;
-
-        /* Set up new dataset I/O info */
-        H5D_BUILD_IO_INFO(&chk_io_info,dset,io_info->dxpl_cache,io_info->dxpl_id,&chk_store);
-
-        /* Do I/O directly on chunk without reading it into the cache */
-        if ((ret_value=H5D_contig_readvv(&chk_io_info, chunk_max_nseq, chunk_curr_seq, chunk_len_arr, 
-                chunk_offset_arr, mem_max_nseq, mem_curr_seq, mem_len_arr, mem_offset_arr, (haddr_t)0, NULL, buf))<0)
-            HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data to file")
-    } /* end if */
-    else {
-        ssize_t         naccessed;      /* Number of bytes accessed in chunk */
-
-        /* If the chunk address is not defined, check if the fill value is
-         * undefined also.  If both situations hold, don't bother copying
-         * values to the destination buffer, since they will just be
-         * garbage.
-         *
-         * Ideally, this will eventually be checked at a higher level and
-         * the entire I/O operation on the chunk will be skipped.  -QAK
-         */
-        if(!H5F_addr_defined(chunk_addr)) {
-            H5D_rdcc_t		*rdcc = &(dset->shared->cache.chunk);/*raw data chunk cache*/
-            hbool_t		found = FALSE;		/*already in cache?	*/
-
-            /* Check if the chunk is in the cache (but hasn't been written to disk yet) */
-            if(rdcc->nslots>0) {
-                unsigned idx = H5D_HASH(dset->shared, io_info->store->chunk.index); /* Cache entry index */
-                H5D_rdcc_ent_t	*ent = rdcc->slot[idx]; /* Cache entry */
-
-                /* Potential match... */
-                if(ent) {
-                    for(u = 0, found = TRUE; u < dset->shared->layout.u.chunk.ndims; u++) {
-                        if(io_info->store->chunk.offset[u] != ent->offset[u]) {
-                            found = FALSE;
-                            break;
-                        } /* end if */
-                    } /* end for */
-                } /* end if */
-            } /* end if */
-
-            /* If the chunk is in the cache, then it must have valid data */
-            if(!found) {
-                const H5O_fill_t *fill = &(dset->shared->dcpl_cache.fill);    /* Fill value info */
-                H5D_fill_value_t fill_status;
-
-                /* Check if the fill value is defined */
-                if(H5P_is_fill_value_defined(fill, &fill_status) < 0)
-                    HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't tell if fill value defined")
-
-                /* If we are never to return fill values, or if we would return them
-                 * but they aren't set, process the entire set of I/O vectors and
-                 * get out now.
-                 */
-                if(fill->fill_time == H5D_FILL_TIME_NEVER ||
-                        (fill->fill_time == H5D_FILL_TIME_IFSET && fill_status!=H5D_FILL_VALUE_USER_DEFINED)) {
-                    size_t size;                /* Size of sequence in bytes */
-                    size_t v;                   /* Local index variable */
-                    ssize_t bytes_processed = 0;  /* Eventual return value */
-
-                    /* Work through all the sequences */
-                    for(u = *mem_curr_seq, v = *chunk_curr_seq; u < mem_max_nseq && v < chunk_max_nseq; ) {
-                        /* Choose smallest buffer to write */
-                        if(chunk_len_arr[v] < mem_len_arr[u])
-                            size = chunk_len_arr[v];
-                        else
-                            size = mem_len_arr[u];
-
-                        /* Update source information */
-                        chunk_len_arr[v] -= size;
-                        chunk_offset_arr[v] += size;
-                        if(chunk_len_arr[v] == 0)
-                            v++;
-
-                        /* Update destination information */
-                        mem_len_arr[u] -= size;
-                        mem_offset_arr[u] += size;
-                        if(mem_len_arr[u] == 0)
-                            u++;
-
-                        /* Increment number of bytes copied */
-                        bytes_processed += (ssize_t)size;
-                    } /* end for */
-
-                    /* Update current sequence vectors */
-                    *mem_curr_seq = u;
-                    *chunk_curr_seq = v;
-
-                    HGOTO_DONE(bytes_processed)
-                } /* end if */
-            } /* end if */
-        } /* end if */
-
-        /* Use the vectorized memory copy routine to do actual work */
-        if((naccessed = H5V_memcpyvv(buf, mem_max_nseq, mem_curr_seq, mem_len_arr, mem_offset_arr, chunk, chunk_max_nseq, chunk_curr_seq, chunk_len_arr, chunk_offset_arr)) < 0)
-            HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "vectorized memcpy failed")
-
-        H5_CHECK_OVERFLOW(naccessed, ssize_t, size_t);
-
-        /* Set return value */
-        ret_value = naccessed;
-    } /* end else */
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* H5D_istore_readvv() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_istore_writevv
- *
- * Purpose:	Writes a multi-dimensional buffer to (part of) an indexed raw
- *		storage array.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Friday, May  2, 2003
- *
- * Modification: 
- *              Raymond Lu
- *              20 July 2007
- *              Moved H5D_istore_lock and H5D_istore_unlock to H5D_chunk_write
- *              from this function to avoid frequent lock and unlock.
- *
- *-------------------------------------------------------------------------
- */
-ssize_t
-H5D_istore_writevv(const H5D_io_info_t *io_info,
-    size_t chunk_max_nseq, size_t *chunk_curr_seq, size_t chunk_len_arr[], hsize_t chunk_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t chunk_addr, void *chunk, const void *buf)
-{
-    H5D_t *dset = io_info->dset;          /* Local pointer to the dataset info */
-    ssize_t             ret_value;      /* Return value */
-
-    FUNC_ENTER_NOAPI(H5D_istore_writevv, FAIL)
-
-    /* Check args */
-    HDassert(io_info);
-    HDassert(dset && H5D_CHUNKED==dset->shared->layout.type);
-    HDassert(dset->shared->layout.u.chunk.ndims>0 && dset->shared->layout.u.chunk.ndims<=H5O_LAYOUT_NDIMS);
-    HDassert(io_info->dxpl_cache);
-    HDassert(io_info->store);
-    HDassert(chunk_len_arr);
-    HDassert(chunk_offset_arr);
-    HDassert(mem_len_arr);
-    HDassert(mem_offset_arr);
-    HDassert(buf);
-
-#ifdef QAK
-{
-size_t		u;              /* Local index variables */
-
-HDfprintf(stderr,"%s: io_info->store->chunk.offset={",FUNC);
-for(u=0; u<dset->shared->layout.u.chunk.ndims; u++)
-    HDfprintf(stderr,"%Hd%s",io_info->store->chunk.offset[u],(u<(dset->shared->layout.u.chunk.ndims-1) ? ", " : "}\n"));
-
-HDfprintf(stderr,"%s: chunk_addr=%a, chunk_size=%Zu\n",FUNC,chunk_addr,dset->shared->layout.u.chunk.size);
-HDfprintf(stderr,"%s: chunk_len_arr[%Zu]=%Zu\n",FUNC,*chunk_curr_seq,chunk_len_arr[*chunk_curr_seq]);
-HDfprintf(stderr,"%s: chunk_offset_arr[%Zu]=%Hu\n",FUNC,*chunk_curr_seq,chunk_offset_arr[*chunk_curr_seq]);
-HDfprintf(stderr,"%s: mem_len_arr[%Zu]=%Zu\n",FUNC,*mem_curr_seq,mem_len_arr[*mem_curr_seq]);
-HDfprintf(stderr,"%s: mem_offset_arr[%Zu]=%Hu\n",FUNC,*mem_curr_seq,mem_offset_arr[*mem_curr_seq]);
-}
-#endif /* QAK */
-
-    /*
-     * If the chunk is too large to load into the cache and it has no
-     * filters in the pipeline (i.e. not compressed) and if the address
-     * for the chunk has been defined, then don't load the chunk into the
-     * cache, just write the data to it directly.
-     *
-     * If MPI based VFD is used, must bypass the
-     * chunk-cache scheme because other MPI processes could be
-     * writing to other elements in the same chunk.  Do a direct
-     * write-through of only the elements requested.
-     */
-    if(!H5D_istore_if_load(io_info, chunk_addr)) {
-        H5D_io_info_t chk_io_info;      /* Temporary I/O info object */
-        H5D_storage_t chk_store;        /* Chunk storage information */
-
-        /* Set up the storage information for the chunk */
-        chk_store.contig.dset_addr=chunk_addr;
-        chk_store.contig.dset_size=(hsize_t)dset->shared->layout.u.chunk.size;
-
-        /* Set up new dataset I/O info */
-        H5D_BUILD_IO_INFO(&chk_io_info,dset,io_info->dxpl_cache,io_info->dxpl_id,&chk_store);
-
-        /* Do I/O directly on chunk without reading it into the cache */
-        if((ret_value = H5D_contig_writevv(&chk_io_info, chunk_max_nseq, chunk_curr_seq, chunk_len_arr, chunk_offset_arr, mem_max_nseq, mem_curr_seq, mem_len_arr, mem_offset_arr, (haddr_t)0, NULL, buf)) < 0)
-            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "unable to write raw data to file")
-    } /* end if */
-    else {
-        ssize_t         naccessed;      /* Number of bytes accessed in chunk */
-
-        /* Use the vectorized memory copy routine to do actual work */
-        if((naccessed=H5V_memcpyvv(chunk,chunk_max_nseq,chunk_curr_seq,chunk_len_arr,chunk_offset_arr,buf,mem_max_nseq,mem_curr_seq,mem_len_arr,mem_offset_arr))<0)
-            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "vectorized memcpy failed")
-
-        H5_CHECK_OVERFLOW(naccessed,ssize_t,size_t);
-
-        /* Set return value */
-        ret_value=naccessed;
-    } /* end else */
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* H5D_istore_writevv() */
-
-
-/*-------------------------------------------------------------------------
  * Function:	H5D_istore_create
  *
  * Purpose:	Creates a new indexed-storage B-tree and initializes the
@@ -2567,16 +2214,16 @@ H5D_istore_allocated(H5D_t *dset, hid_t dxpl_id)
     HDassert(dset);
 
     /* Fill the DXPL cache values for later use */
-    if (H5D_get_dxpl_cache(dxpl_id,&dxpl_cache)<0)
+    if(H5D_get_dxpl_cache(dxpl_id,&dxpl_cache) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, 0, "can't fill dxpl cache")
 
     /* Construct dataset I/O info */
-    H5D_BUILD_IO_INFO(&io_info,dset,dxpl_cache,dxpl_id,NULL);
+    H5D_BUILD_IO_INFO_WRT(&io_info, dset, dxpl_cache, dxpl_id, NULL, NULL);
 
     /* Search for cached chunks that haven't been written out */
     for(ent = rdcc->head; ent; ent = ent->next) {
         /* Flush the chunk out to disk, to make certain the size is correct later */
-        if (H5D_istore_flush_entry(&io_info, ent, FALSE)<0)
+        if (H5D_istore_flush_entry(&io_info, ent, FALSE) < 0)
             HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, 0, "cannot flush indexed storage buffer")
     } /* end for */
 
@@ -2609,7 +2256,7 @@ done:
  */
 herr_t
 H5D_istore_chunkmap(const H5D_io_info_t *io_info, haddr_t chunk_addr[],
-    hsize_t down_chunks[])
+    const hsize_t down_chunks[])
 {
     H5D_t *dset = io_info->dset;       /* Local pointer to dataset info */
     H5D_istore_it_ud5_t	udata;
@@ -2908,7 +2555,7 @@ H5D_istore_allocate(H5D_t *dset, hid_t dxpl_id, hbool_t full_overwrite)
 
     /* Set up dataset I/O info */
     store.chunk.offset = chunk_offset;
-    H5D_BUILD_IO_INFO(&io_info, dset, dxpl_cache, data_dxpl_id, &store);
+    H5D_BUILD_IO_INFO_WRT(&io_info, dset, dxpl_cache, data_dxpl_id, &store, NULL);
 
     /* Reset the chunk offset indices */
     HDmemset(chunk_offset, 0, (layout->u.chunk.ndims * sizeof(chunk_offset[0])));
@@ -3574,7 +3221,7 @@ H5D_istore_initialize_by_extent(H5D_io_info_t *io_info)
                 HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize chunk selection information")
 
             /* Scatter the data into memory */
-            if(H5D_select_mscat(fb_info.fill_buf, space_chunk, &chunk_iter, (size_t)nelmts, io_info->dxpl_cache, chunk/*out*/) < 0) {
+            if(H5D_scatter_mem(fb_info.fill_buf, space_chunk, &chunk_iter, (size_t)nelmts, io_info->dxpl_cache, chunk/*out*/) < 0) {
                 H5S_SELECT_ITER_RELEASE(&chunk_iter);
                 HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "scatter failed")
             } /* end if */
@@ -3728,7 +3375,7 @@ H5D_istore_update_cache(H5D_t *dset, hid_t dxpl_id)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't fill dxpl cache")
 
     /* Construct dataset I/O info */
-    H5D_BUILD_IO_INFO(&io_info, dset, dxpl_cache, dxpl_id, NULL);
+    H5D_BUILD_IO_INFO_WRT(&io_info, dset, dxpl_cache, dxpl_id, NULL, NULL);
 
     /* Recompute the index for each cached chunk that is in a dataset */
     for(ent = rdcc->head; ent; ent = next) {
@@ -3744,7 +3391,7 @@ H5D_istore_update_cache(H5D_t *dset, hid_t dxpl_id)
 
         /* Compute the index for the chunk entry */
         old_idx=ent->idx;   /* Save for later */
-        ent->idx=H5D_HASH(dset->shared,idx);
+        ent->idx=H5D_CHUNK_HASH(dset->shared, idx);
 
         if(old_idx != ent->idx) {
             /* Check if there is already a chunk at this chunk's new location */
diff --git a/src/H5Dmpio.c b/src/H5Dmpio.c
index 22f32ab..889fbce 100644
--- a/src/H5Dmpio.c
+++ b/src/H5Dmpio.c
@@ -34,12 +34,12 @@
 /* Headers */
 /***********/
 #include "H5private.h"		/* Generic Functions			*/
-#include "H5Iprivate.h"
 #include "H5Dpkg.h"		/* Datasets				*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5Fprivate.h"		/* File access				*/
 #include "H5FDprivate.h"	/* File drivers				*/
-#include "H5MMprivate.h"
+#include "H5Iprivate.h"		/* IDs			  		*/
+#include "H5MMprivate.h"	/* Memory management			*/
 #include "H5Oprivate.h"		/* Object headers		  	*/
 #include "H5Pprivate.h"         /* Property lists                       */
 #include "H5Sprivate.h"		/* Dataspaces 				*/
@@ -86,6 +86,7 @@
 #define H5D_CHUNK_SELECT_IRREG        2
 #define H5D_CHUNK_SELECT_NONE         0
 
+
 /******************/
 /* Local Typedefs */
 /******************/
@@ -95,66 +96,47 @@ typedef struct H5D_chunk_addr_info_t {
   H5D_chunk_info_t chunk_info;
 } H5D_chunk_addr_info_t;
 
-/* Combine all information that needs to know for collective MPI-IO of this selection. */
-typedef struct H5D_common_coll_info_t {
-  hbool_t mbt_is_derived;
-  hbool_t mft_is_derived;
-  size_t  mpi_buf_count;
-  haddr_t chunk_addr;
-} H5D_common_coll_info_t;
-  
 
 /********************/
 /* Local Prototypes */
 /********************/
-
-static herr_t 
-H5D_multi_chunk_collective_io(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,const void *buf, 
-			      hbool_t do_write);
-static herr_t
-H5D_multi_chunk_collective_io_no_opt(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,const void *buf,
-                              hbool_t do_write);
-
-static herr_t
-H5D_link_chunk_collective_io(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,const void *buf, 
-			     hbool_t do_write,int sum_chunk);
-
-static herr_t 
-H5D_inter_collective_io(H5D_io_info_t *io_info,const H5S_t *file_space,
-			const H5S_t *mem_space,haddr_t addr, 
-		        const void *buf, hbool_t do_write );
-
-static herr_t 
-H5D_final_collective_io(H5D_io_info_t *io_info,MPI_Datatype*mpi_file_type,
-			 MPI_Datatype *mpi_buf_type,
-			 H5D_common_coll_info_t* coll_info, 
-			 const void *buf, hbool_t do_write);
-static herr_t 
-H5D_sort_chunk(H5D_io_info_t * io_info,
-	       H5D_chunk_map_t *fm,
-	       H5D_chunk_addr_info_t chunk_addr_info_array[],
-	       int many_chunk_opt);
-
-static herr_t 
-H5D_obtain_mpio_mode(H5D_io_info_t* io_info, 
-		     H5D_chunk_map_t *fm,
-		     uint8_t assign_io_mode[],
-		     haddr_t chunk_addr[]);
-
-static herr_t H5D_ioinfo_make_ind(H5D_io_info_t *io_info);
-static herr_t H5D_ioinfo_make_coll_opt(H5D_io_info_t *io_info);
-static herr_t H5D_ioinfo_make_coll(H5D_io_info_t *io_info);
+static herr_t H5D_chunk_collective_io(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, H5D_chunk_map_t *fm);
+static herr_t H5D_multi_chunk_collective_io(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, H5D_chunk_map_t *fm,
+    H5P_genplist_t *dx_plist);
+static herr_t H5D_multi_chunk_collective_io_no_opt(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, H5D_chunk_map_t *fm, H5P_genplist_t *dx_plist);
+#ifdef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
+static herr_t H5D_link_chunk_collective_io(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, H5D_chunk_map_t *fm, int sum_chunk);
+#endif /* H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS */
+static herr_t H5D_inter_collective_io(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, const H5S_t *file_space,
+    const H5S_t *mem_space);
+static herr_t H5D_final_collective_io(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, size_t nelmts, MPI_Datatype *mpi_file_type,
+    MPI_Datatype *mpi_buf_type);
+static herr_t H5D_sort_chunk(H5D_io_info_t *io_info, const H5D_chunk_map_t *fm,
+    H5D_chunk_addr_info_t chunk_addr_info_array[], int many_chunk_opt);
+static herr_t H5D_obtain_mpio_mode(H5D_io_info_t *io_info, H5D_chunk_map_t *fm,
+    H5P_genplist_t *dx_plist, uint8_t assign_io_mode[], haddr_t chunk_addr[]);
+static herr_t H5D_ioinfo_xfer_mode(H5D_io_info_t *io_info, H5P_genplist_t *dx_plist,
+    H5FD_mpio_xfer_t xfer_mode);
+static herr_t H5D_ioinfo_coll_opt_mode(H5D_io_info_t *io_info, H5P_genplist_t *dx_plist,
+    H5FD_mpio_collective_opt_t coll_opt_mode);
 static herr_t H5D_mpio_get_min_chunk(const H5D_io_info_t *io_info,
     const H5D_chunk_map_t *fm, int *min_chunkf);
 static int H5D_cmp_chunk_addr(const void *addr1, const void *addr2);
 static herr_t H5D_mpio_get_sum_chunk(const H5D_io_info_t *io_info,
-		       const H5D_chunk_map_t *fm, int *sum_chunkf);
+    const H5D_chunk_map_t *fm, int *sum_chunkf);
 
 
 /*********************/
 /* Package Variables */
 /*********************/
 
+
 /*******************/
 /* Local Variables */
 /*******************/
@@ -175,64 +157,77 @@ static herr_t H5D_mpio_get_sum_chunk(const H5D_io_info_t *io_info,
  *-------------------------------------------------------------------------
  */
 htri_t
-H5D_mpio_opt_possible( const H5D_io_info_t *io_info,
-    const H5S_t *mem_space, const H5S_t *file_space, const H5T_path_t *tpath)
+H5D_mpio_opt_possible(const H5D_io_info_t *io_info, const H5S_t *file_space,
+    const H5S_t *mem_space, const H5D_type_info_t *type_info,
+    const H5D_chunk_map_t *fm)
 {
-    int         local_opinion = TRUE;   /* This process's idea of whether to perform collective I/O or not */
-    int         consensus;              /* Consensus opinion of all processes */
-    int         mpi_code;               /* MPI error code */
-    htri_t ret_value=TRUE;
+    int local_opinion = TRUE;   /* This process's idea of whether to perform collective I/O or not */
+    int consensus;              /* Consensus opinion of all processes */
+    int mpi_code;               /* MPI error code */
+    htri_t ret_value = TRUE;
 
-    FUNC_ENTER_NOAPI(H5D_mpio_opt_possible, FAIL);
+    FUNC_ENTER_NOAPI(H5D_mpio_opt_possible, FAIL)
 
     /* Check args */
-    assert(io_info);
-    assert(mem_space);
-    assert(file_space);
+    HDassert(io_info);
+    HDassert(mem_space);
+    HDassert(file_space);
+    HDassert(type_info);
 
     /* For independent I/O, get out quickly and don't try to form consensus */
-    if (io_info->dxpl_cache->xfer_mode==H5FD_MPIO_INDEPENDENT)
+    if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_INDEPENDENT)
         HGOTO_DONE(FALSE);
 
+    /* Don't allow collective operations if datatype conversions need to happen */
+    if(!type_info->is_conv_noop) {
+        local_opinion = FALSE;
+        goto broadcast;
+    } /* end if */
+
+    /* Don't allow collective operations if data transform operations should occur */
+    if(!type_info->is_xform_noop) {
+        local_opinion = FALSE;
+        goto broadcast;
+    } /* end if */
+
     /* Optimized MPI types flag must be set and it must be collective IO */
     /* (Don't allow parallel I/O for the MPI-posix driver, since it doesn't do real collective I/O) */
-    if (!(H5S_mpi_opt_types_g && io_info->dxpl_cache->xfer_mode==H5FD_MPIO_COLLECTIVE && !IS_H5FD_MPIPOSIX(io_info->dset->oloc.file))) {
+    if(!(H5S_mpi_opt_types_g && io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE
+            && !IS_H5FD_MPIPOSIX(io_info->dset->oloc.file))) {
         local_opinion = FALSE;
         goto broadcast;
     } /* end if */
 
     /* Check whether these are both simple or scalar dataspaces */
-    if (!((H5S_SIMPLE==H5S_GET_EXTENT_TYPE(mem_space) || H5S_SCALAR==H5S_GET_EXTENT_TYPE(mem_space))
-            && (H5S_SIMPLE==H5S_GET_EXTENT_TYPE(file_space) || H5S_SCALAR==H5S_GET_EXTENT_TYPE(file_space)))) {
+    if(!((H5S_SIMPLE == H5S_GET_EXTENT_TYPE(mem_space) || H5S_SCALAR == H5S_GET_EXTENT_TYPE(mem_space))
+            && (H5S_SIMPLE == H5S_GET_EXTENT_TYPE(file_space) || H5S_SCALAR == H5S_GET_EXTENT_TYPE(file_space)))) {
         local_opinion = FALSE;
         goto broadcast;
     } /* end if */
 
     /* Can't currently handle point selections */
-    if (H5S_SEL_POINTS==H5S_GET_SELECT_TYPE(mem_space) || H5S_SEL_POINTS==H5S_GET_SELECT_TYPE(file_space)) {
+    if(H5S_SEL_POINTS == H5S_GET_SELECT_TYPE(mem_space)
+            || H5S_SEL_POINTS == H5S_GET_SELECT_TYPE(file_space)) {
         local_opinion = FALSE;
         goto broadcast;
     } /* end if */
 
     /* Dataset storage must be contiguous or chunked */
-    if (!(io_info->dset->shared->layout.type == H5D_CONTIGUOUS ||
+    if(!(io_info->dset->shared->layout.type == H5D_CONTIGUOUS ||
             io_info->dset->shared->layout.type == H5D_CHUNKED)) {
         local_opinion = FALSE;
         goto broadcast;
     } /* end if */
 
-    /*    The handling of memory space is different for chunking
-	  and contiguous storage,
-	  For contigous storage, mem_space and file_space won't
-	  change when it it is doing disk IO.
-	  For chunking storage, mem_space will change for different
-	  chunks. So for chunking storage, whether we can use
-	  collective IO will defer until each chunk IO is reached.
-	  For contiguous storage, if we find MPI-IO cannot
-	  support complicated MPI derived data type and the shape
-          of data space is not regular, we will
-	  set use_par_opt_io = FALSE.
-	*/
+    /* The handling of memory space is different for chunking and contiguous
+     *  storage.  For contiguous storage, mem_space and file_space won't change
+     *  when it it is doing disk IO.  For chunking storage, mem_space will
+     *  change for different chunks. So for chunking storage, whether we can
+     *  use collective IO will defer until each chunk IO is reached.  For
+     *  contiguous storage, if we find MPI-IO cannot support complicated MPI
+     *  derived data type and the shape of data space is not regular, we will
+     *  set use_par_opt_io = FALSE.
+     */
 #ifndef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
     if(io_info->dset->shared->layout.type == H5D_CONTIGUOUS)
         if((H5S_SELECT_IS_REGULAR(file_space) != TRUE) ||
@@ -243,81 +238,43 @@ H5D_mpio_opt_possible( const H5D_io_info_t *io_info,
 #endif
 
     /* Don't allow collective operations if filters need to be applied */
-    if(io_info->dset->shared->layout.type == H5D_CHUNKED)
-        if(io_info->dset->shared->dcpl_cache.pline.nused>0) {
+    if(io_info->dset->shared->layout.type == H5D_CHUNKED) {
+        if(io_info->dset->shared->dcpl_cache.pline.nused > 0) {
             local_opinion = FALSE;
             goto broadcast;
         } /* end if */
 
-    /* Don't allow collective operations if datatype conversions need to happen */
-    if(!H5T_path_noop(tpath)) {
-        local_opinion = FALSE;
-        goto broadcast;
-    } /* end if */
-
-    /* Don't allow collective operations if data transform operations should occur */
-    if(!H5Z_xform_noop(io_info->dxpl_cache->data_xform_prop)) {
-        local_opinion = FALSE;
-        goto broadcast;
+/* If H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS and H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
+ *      are defined, the HDF5 library will do collective IO if the application
+ *      asks for it.
+ *
+ * If H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS is not defined and one or more
+ *      processes are not participating in the IO, then collective IO is not
+ *      assured. The library will check each process for the number of chunks
+ *      it involves. If any process involves zero chunks, the library will use
+ *      independent IO mode instead.
+ */
+#ifndef H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS
+        /* Check the number of chunks to perform I/O on */
+        if(0 == H5SL_count(fm->sel_chunks)) {
+            local_opinion = FALSE;
+            goto broadcast;
+         } /* end if */
+#endif /* H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS */
     } /* end if */
 
 broadcast:
     /* Form consensus opinion among all processes about whether to perform
-     * collective I/O */
-    if (MPI_SUCCESS != (mpi_code = MPI_Allreduce(&local_opinion, &consensus, 1, MPI_INT, MPI_LAND, io_info->comm)))
+     * collective I/O
+     */
+    if(MPI_SUCCESS != (mpi_code = MPI_Allreduce(&local_opinion, &consensus, 1, MPI_INT, MPI_LAND, io_info->comm)))
         HMPI_GOTO_ERROR(FAIL, "MPI_Allreduce failed", mpi_code)
 
     ret_value = consensus > 0 ? TRUE : FALSE;
 
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
-} /* H5D_mpio_opt_possible() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_mpio_chunk_adjust_iomode
- *
- * Decription:  If H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS and 
-                H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS are defined,
-                the HDF5 library will do collective IO if the application asks for it.
-
-                If H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS is not defined
-                and one or more processes are not participating in the IO,
-                then collective IO is not assured. The library will check 
-                each process for the 
-                number of chunks it involves. If any process involves zero chunks,
-                the library will use independent IO mode instead.
-                This function is only used for linked chunk IO.
- * Purpose:	Checks if it is possible to do collective IO 
- *
- * Return:	Success:        Non-negative: TRUE or FALSE
- *		Failure:	Negative
- *
- * Programmer:	Muqun Yang
- *              Monday, Feb. 13th, 2006
- *
- *-------------------------------------------------------------------------
- */
-#ifndef H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS
-herr_t
-H5D_mpio_chunk_adjust_iomode(H5D_io_info_t *io_info, const H5D_chunk_map_t *fm)
-{
-   int   min_chunk;
-   herr_t ret_value = SUCCEED;
-
-   FUNC_ENTER_NOAPI_NOINIT(H5D_mpio_chunk_adjust_iomode)
-
-    if(H5D_mpio_get_min_chunk(io_info,fm,&min_chunk) < 0)
-         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSWAP, FAIL, "unable to obtain the min chunk number of all processes"); 
-    if(min_chunk == 0) {                
-        /* Switch to independent I/O */
-        if(H5D_ioinfo_make_ind(io_info) < 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
-     } /* end if */
-done:
     FUNC_LEAVE_NOAPI(ret_value)
-}
-#endif
+} /* H5D_mpio_opt_possible() */
 
 
 /*-------------------------------------------------------------------------
@@ -332,23 +289,20 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_mpio_select_read(H5D_io_info_t *io_info,
-                     size_t mpi_buf_count, 
-                     const size_t UNUSED elmt_size,
-		     const H5S_t UNUSED *file_space, 
-		     const H5S_t UNUSED *mem_space,
-		     haddr_t addr,		     
-                     void UNUSED *pointer,
-		     void *buf/*out*/)
+H5D_mpio_select_read(const H5D_io_info_t *io_info, const H5D_type_info_t UNUSED *type_info,
+    hsize_t mpi_buf_count, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space)
 {
+    const H5D_contig_storage_t *store_contig = &(io_info->store->contig);    /* Contiguous storage info for this I/O operation */
     herr_t ret_value = SUCCEED;
 
-    FUNC_ENTER_NOAPI(H5D_mpio_select_read,FAIL);
+    FUNC_ENTER_NOAPI(H5D_mpio_select_read, FAIL)
+
+    H5_CHECK_OVERFLOW(mpi_buf_count, hsize_t, size_t);
+    if(H5F_block_read(io_info->dset->oloc.file, H5FD_MEM_DRAW, store_contig->dset_addr, (size_t)mpi_buf_count, io_info->dxpl_id, io_info->u.rbuf) < 0)
+	HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "can't finish collective parallel read")
 
-    if(H5F_block_read (io_info->dset->oloc.file, H5FD_MEM_DRAW, addr, mpi_buf_count, io_info->dxpl_id, buf) < 0)
-	HGOTO_ERROR(H5E_IO,H5E_READERROR,FAIL,"can't finish collective parallel read");
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_mpio_select_read() */
 
 
@@ -364,32 +318,28 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_mpio_select_write(H5D_io_info_t *io_info,
-		      size_t mpi_buf_count, 
-		      const size_t UNUSED elmt_size,
-		      const H5S_t UNUSED *file_space, 
-		      const H5S_t UNUSED *mem_space,
-		      haddr_t addr,
-                      void UNUSED *pointer,
-		      const void *buf)
+H5D_mpio_select_write(const H5D_io_info_t *io_info, const H5D_type_info_t UNUSED *type_info,
+    hsize_t mpi_buf_count, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space)
 {
+    const H5D_contig_storage_t *store_contig = &(io_info->store->contig);    /* Contiguous storage info for this I/O operation */
     herr_t ret_value = SUCCEED;
 
-    FUNC_ENTER_NOAPI(H5D_mpio_select_write,FAIL);
+    FUNC_ENTER_NOAPI(H5D_mpio_select_write, FAIL)
 
     /*OKAY: CAST DISCARDS CONST QUALIFIER*/
-    if(H5F_block_write (io_info->dset->oloc.file, H5FD_MEM_DRAW, addr, mpi_buf_count, io_info->dxpl_id, buf)<0)
-       HGOTO_ERROR(H5E_IO,H5E_WRITEERROR,FAIL,"can't finish collective parallel write");
+    H5_CHECK_OVERFLOW(mpi_buf_count, hsize_t, size_t);
+    if(H5F_block_write(io_info->dset->oloc.file, H5FD_MEM_DRAW, store_contig->dset_addr, (size_t)mpi_buf_count, io_info->dxpl_id, io_info->u.wbuf) < 0)
+       HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "can't finish collective parallel write")
 
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_mpio_select_write() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_ioinfo_make_ind
+ * Function:	H5D_ioinfo_xfer_mode
  *
- * Purpose:	Switch to MPI independent I/O
+ * Purpose:	Switch to between collective & independent MPI I/O
  *
  * Return:	Non-negative on success/Negative on failure
  *
@@ -399,42 +349,42 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_ioinfo_make_ind(H5D_io_info_t *io_info)
+H5D_ioinfo_xfer_mode(H5D_io_info_t *io_info, H5P_genplist_t *dx_plist,
+    H5FD_mpio_xfer_t xfer_mode)
 {
-    H5P_genplist_t *dx_plist;           /* Data transer property list */
     herr_t	ret_value = SUCCEED;	/*return value		*/
 
-    FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_make_ind)
-
-    /* Get the dataset transfer property list */
-    if (NULL == (dx_plist = H5I_object(io_info->dxpl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
+    FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_xfer_mode)
 
-    /* Change the xfer_mode to independent, handle the request,
-     * then set xfer_mode before return.
-     */
-    io_info->dxpl_cache->xfer_mode = H5FD_MPIO_INDEPENDENT;
-    if(H5P_set (dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->dxpl_cache->xfer_mode) < 0)
+    /* Change the xfer_mode */
+    io_info->dxpl_cache->xfer_mode = xfer_mode;
+    if(H5P_set(dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->dxpl_cache->xfer_mode) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set transfer mode")
 
-    /* Set the pointers to the non-MPI-specific routines */
-    io_info->ops.read = H5D_select_read;
-    io_info->ops.write = H5D_select_write;
+    /* Change the "single I/O" function pointers */
+    if(xfer_mode == H5FD_MPIO_INDEPENDENT) {
+        /* Set the pointers to the original, non-MPI-specific routines */
+        io_info->io_ops.single_read = io_info->orig.io_ops.single_read;
+        io_info->io_ops.single_write = io_info->orig.io_ops.single_write;
+    } /* end if */
+    else {
+        HDassert(xfer_mode == H5FD_MPIO_COLLECTIVE);
 
-    /* Indicate that the transfer mode should be restored before returning
-     * to user.
-     */
-    io_info->xfer_mode_changed=TRUE;
+        /* Set the pointers to the MPI-specific routines */
+        io_info->io_ops.single_read = H5D_mpio_select_read;
+        io_info->io_ops.single_write = H5D_mpio_select_write;
+    } /* end else */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_ioinfo_make_ind() */
+} /* end H5D_ioinfo_xfer_mode() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_ioinfo_make_coll_opt
+ * Function:	H5D_ioinfo_coll_opt_mode
  *
- * Purpose:	Switch to MPI independent I/O with file set view
+ * Purpose:	Switch between using collective & independent MPI I/O w/file
+ *              set view
  *
  * Return:	Non-negative on success/Negative on failure
  *
@@ -444,87 +394,21 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_ioinfo_make_coll_opt(H5D_io_info_t *io_info)
+H5D_ioinfo_coll_opt_mode(H5D_io_info_t *io_info, H5P_genplist_t *dx_plist,
+    H5FD_mpio_collective_opt_t coll_opt_mode)
 {
-    H5P_genplist_t *dx_plist;           /* Data transer property list */
     herr_t	ret_value = SUCCEED;	/*return value		*/
 
-    FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_make_coll_opt)
+    FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_coll_opt_mode)
 
-    /* Get the dataset transfer property list */
-    if (NULL == (dx_plist = H5I_object(io_info->dxpl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
-
-    /* Change the optimial xfer_mode to independent, handle the request,
-     * then set xfer_mode before return.
-     */
-    io_info->dxpl_cache->xfer_opt_mode = H5FD_MPIO_INDIVIDUAL_IO;
-    if(H5P_set (dx_plist, H5D_XFER_IO_XFER_OPT_MODE_NAME, &io_info->dxpl_cache->xfer_opt_mode) < 0)
+    /* Change the optimal xfer_mode */
+    io_info->dxpl_cache->coll_opt_mode = coll_opt_mode;
+    if(H5P_set(dx_plist, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME, &io_info->dxpl_cache->coll_opt_mode) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set transfer mode")
 
-    /* Set the pointers to the non-MPI-specific routines */
-    io_info->ops.read  = H5D_mpio_select_read;
-    io_info->ops.write = H5D_mpio_select_write;
-
-    /* Indicate that the transfer mode should be restored before returning
-     * to user.
-     */
-    io_info->xfer_opt_mode_changed = TRUE;
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_ioinfo_make_coll_opt() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_ioinfo_make_coll
- *
- * Purpose:	Switch to MPI collective I/O
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *		Friday, August 12, 2005
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5D_ioinfo_make_coll(H5D_io_info_t *io_info)
-{
-    H5P_genplist_t *dx_plist;           /* Data transer property list */
-    herr_t	ret_value = SUCCEED;	/*return value		*/
-
-    FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_make_coll)
-
-    /* Get the dataset transfer property list */
-    if (NULL == (dx_plist = H5I_object(io_info->dxpl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
-
-    /* Change the xfer_mode to independent, handle the request,
-     * then set xfer_mode before return.
-     */
-    io_info->dxpl_cache->xfer_mode = H5FD_MPIO_COLLECTIVE;
-    if(H5P_set (dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->dxpl_cache->xfer_mode) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set transfer mode")
-
-    io_info->dxpl_cache->xfer_opt_mode = H5FD_MPIO_COLLECTIVE_IO;
-    if(H5P_set (dx_plist, H5D_XFER_IO_XFER_OPT_MODE_NAME, &io_info->dxpl_cache->xfer_opt_mode) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set transfer mode")
-
-
-    /* Set the pointers to the MPI-specific routines */
-    io_info->ops.read = H5D_mpio_select_read;
-    io_info->ops.write = H5D_mpio_select_write;
-
-    /* Indicate that the transfer mode should _NOT_ be restored before returning
-     * to user.
-     */
-    io_info->xfer_mode_changed=FALSE;
-    io_info->xfer_opt_mode_changed=FALSE;
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_ioinfo_make_coll() */
+} /* end H5D_ioinfo_coll_opt_mode() */
 
 
 /*-------------------------------------------------------------------------
@@ -535,29 +419,30 @@ done:
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_mpio_get_min_chunk(const H5D_io_info_t *io_info,
-    const H5D_chunk_map_t *fm, int *min_chunkf)
+H5D_mpio_get_min_chunk(const H5D_io_info_t *io_info, const H5D_chunk_map_t *fm,
+    int *min_chunkf)
 {
     int num_chunkf;             /* Number of chunks to iterate over */
     int mpi_code;               /* MPI return code */
     herr_t ret_value = SUCCEED;
 
-    FUNC_ENTER_NOAPI_NOINIT(H5D_mpio_get_min_chunk);
+    FUNC_ENTER_NOAPI_NOINIT(H5D_mpio_get_min_chunk)
 
     /* Get the number of chunks to perform I/O on */
     num_chunkf = H5SL_count(fm->sel_chunks);
 
     /* Determine the minimum # of chunks for all processes */
-    if (MPI_SUCCESS != (mpi_code = MPI_Allreduce(&num_chunkf, min_chunkf, 1, MPI_INT, MPI_MIN, io_info->comm)))
+    if(MPI_SUCCESS != (mpi_code = MPI_Allreduce(&num_chunkf, min_chunkf, 1, MPI_INT, MPI_MIN, io_info->comm)))
         HMPI_GOTO_ERROR(FAIL, "MPI_Allreduce failed", mpi_code)
 
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_mpio_get_min_chunk() */
 
 
@@ -569,221 +454,252 @@ done:
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_mpio_get_sum_chunk(const H5D_io_info_t *io_info,
-                       const H5D_chunk_map_t *fm, int *sum_chunkf)
+H5D_mpio_get_sum_chunk(const H5D_io_info_t *io_info, const H5D_chunk_map_t *fm,
+    int *sum_chunkf)
 {
     int num_chunkf;             /* Number of chunks to iterate over */
     size_t ori_num_chunkf;
     int mpi_code;               /* MPI return code */
     herr_t ret_value = SUCCEED;
 
-    FUNC_ENTER_NOAPI_NOINIT(H5D_mpio_get_sum_chunk);
+    FUNC_ENTER_NOAPI_NOINIT(H5D_mpio_get_sum_chunk)
 
     /* Get the number of chunks to perform I/O on */
     num_chunkf = 0;
     ori_num_chunkf = H5SL_count(fm->sel_chunks);
-    H5_ASSIGN_OVERFLOW(num_chunkf,ori_num_chunkf,size_t,int);
+    H5_ASSIGN_OVERFLOW(num_chunkf, ori_num_chunkf, size_t, int);
 
     /* Determine the summation of number of chunks for all processes */
-    if (MPI_SUCCESS != (mpi_code = MPI_Allreduce(&num_chunkf, sum_chunkf, 1, MPI_INT, MPI_SUM, io_info->comm)))
+    if(MPI_SUCCESS != (mpi_code = MPI_Allreduce(&num_chunkf, sum_chunkf, 1, MPI_INT, MPI_SUM, io_info->comm)))
         HMPI_GOTO_ERROR(FAIL, "MPI_Allreduce failed", mpi_code)
 
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_mpio_get_sum_chunk() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_contig_collective_io
+ * Function:	H5D_contig_collective_read
  *
- * Purpose:	Wrapper Routine for H5D_inter_collective_io
-                The starting file address of contiguous layout
-                will be calculated and passed to H5D_inter_collective_io routine.
- *               
+ * Purpose:	Reads directly from contiguous data in file into application
+ *              memory using collective I/O.
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:
- *
- * Modifications:
+ * Programmer:	Quincey Koziol
+ *              Tuesday, March  4, 2008
  *
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_contig_collective_io(H5D_io_info_t *io_info, 
-			 const H5S_t *file_space,
-			 const H5S_t *mem_space,
-			 const void *buf,
-			 hbool_t do_write) 
+H5D_contig_collective_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t UNUSED nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t UNUSED *fm)
 {
+    herr_t ret_value = SUCCEED;         /* Return value */
 
+    FUNC_ENTER_NOAPI(H5D_contig_collective_read, FAIL)
 
-    haddr_t	 addr = HADDR_UNDEF;                  /* Address of dataset (or selection) within file */
-    herr_t       ret_value = SUCCEED;  /* return value */
+    /* Sanity check */
+    HDassert(IS_H5FD_MPIO(io_info->dset->oloc.file));
+    HDassert(TRUE == H5P_isa_class(io_info->dxpl_id, H5P_DATASET_XFER));
+
+    /* Call generic internal collective I/O routine */
+    if(H5D_inter_collective_io(io_info, type_info, file_space, mem_space) < 0)
+	HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "couldn't finish shared collective MPI-IO")
 
-    FUNC_ENTER_NOAPI_NOINIT(H5D_contig_collective_io)
-    assert (IS_H5FD_MPIO(io_info->dset->oloc.file));
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_contig_collective_read() */
 
-    /* Make certain we have the correct type of property list */
-    assert(TRUE==H5P_isa_class(io_info->dxpl_id,H5P_DATASET_XFER));
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_contig_collective_write
+ *
+ * Purpose:	Write directly to contiguous data in file from application
+ *              memory using collective I/O.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Tuesday, March  4, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_contig_collective_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t UNUSED nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t UNUSED *fm)
+{
+    herr_t ret_value = SUCCEED;         /* Return value */
 
-    /* Get the base address of the contiguous dataset */
-    if(io_info->dset->shared->layout.type == H5D_CONTIGUOUS)
-       addr = H5D_contig_get_addr(io_info->dset);
+    FUNC_ENTER_NOAPI(H5D_contig_collective_write, FAIL)
 
-    if(H5D_inter_collective_io(io_info,file_space,mem_space,addr,buf,do_write)<0)
-	HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-      
- done: 
+    /* Sanity check */
+    HDassert(IS_H5FD_MPIO(io_info->dset->oloc.file));
+    HDassert(TRUE == H5P_isa_class(io_info->dxpl_id, H5P_DATASET_XFER));
 
+    /* Call generic internal collective I/O routine */
+    if(H5D_inter_collective_io(io_info, type_info, file_space, mem_space) < 0)
+	HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "couldn't finish shared collective MPI-IO")
+
+done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_contig_collective_io */
+} /* end H5D_contig_collective_write() */
 
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_chunk_collective_io
  *
  * Purpose:	Routine for 
-                1) choose an IO option: 
-		      a) One collective IO defined by one MPI derived datatype to link through all chunks
-		or    b) multiple chunk IOs,to do MPI-IO for each chunk, the IO mode may be adjusted 
-                         due to the selection pattern for each chunk.
+ *              1) choose an IO option: 
+ *                    a) One collective IO defined by one MPI derived datatype to link through all chunks
+ *              or    b) multiple chunk IOs,to do MPI-IO for each chunk, the IO mode may be adjusted 
+ *                       due to the selection pattern for each chunk.
  *              For option a)
-			1. Sort the chunk address, obtain chunk info according to the sorted chunk address
-                        2. Build up MPI derived datatype for each chunk
-                        3. Build up the final MPI derived datatype
-                        4. Set up collective IO property list
-                        5. Do IO
+ *                      1. Sort the chunk address, obtain chunk info according to the sorted chunk address
+ *                      2. Build up MPI derived datatype for each chunk
+ *                      3. Build up the final MPI derived datatype
+ *                      4. Set up collective IO property list
+ *                      5. Do IO
  *             For option b)
-                        1. Use MPI_gather and MPI_Bcast to obtain information of *collective/independent/none*
-                           IO mode for each chunk of the selection
-                        2. Depending on whether the IO mode is collective or independent or none,
-                           Create either MPI derived datatype for each chunk to do collective IO or 
-                           just do independent IO or independent IO with file set view
-                        3. Set up collective IO property list for collective mode
-                        4. DO IO               
+ *                      1. Use MPI_gather and MPI_Bcast to obtain information of *collective/independent/none*
+ *                         IO mode for each chunk of the selection
+ *                      2. Depending on whether the IO mode is collective or independent or none,
+ *                         Create either MPI derived datatype for each chunk to do collective IO or 
+ *                         just do independent IO or independent IO with file set view
+ *                      3. Set up collective IO property list for collective mode
+ *                      4. DO IO               
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:
- *
- * Modifications:
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
-herr_t 
-H5D_chunk_collective_io(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,const void *buf, hbool_t do_write) 
+static herr_t 
+H5D_chunk_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    H5D_chunk_map_t *fm)
 {
-
-    int               io_option = H5D_MULTI_CHUNK_IO_MORE_OPT;
-    int               sum_chunk = 0,mpi_size;
-    unsigned          one_link_chunk_io_threshold;
-    H5P_genplist_t    *plist; 
+    H5P_genplist_t *dx_plist;           /* Pointer to DXPL */
     H5FD_mpio_chunk_opt_t chunk_opt_mode;
-
+    int         io_option = H5D_MULTI_CHUNK_IO_MORE_OPT;
+    int         sum_chunk = -1;
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
-    htri_t            check_prop,temp_not_link_io = FALSE;
-    int               new_value;
+    htri_t      temp_not_link_io = FALSE;
 #endif
-    herr_t            ret_value = SUCCEED;    
+    herr_t      ret_value = SUCCEED;    
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_chunk_collective_io)
 
-    assert (IS_H5FD_MPIO(io_info->dset->oloc.file));
+    /* Sanity checks */
+    HDassert(io_info);
+    HDassert(io_info->using_mpi_vfd);
+    HDassert(type_info);
+    HDassert(fm);
     
     /* Obtain the data transfer properties */
-    if(NULL == (plist = H5I_object(io_info->dxpl_id)))
+    if(NULL == (dx_plist = H5I_object(io_info->dxpl_id)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list")
-    
+
     /* Check the optional property list on what to do with collective chunk IO. */
-    chunk_opt_mode=(H5FD_mpio_chunk_opt_t)H5P_peek_unsigned(plist,H5D_XFER_MPIO_CHUNK_OPT_HARD_NAME);
-    
+    chunk_opt_mode = (H5FD_mpio_chunk_opt_t)H5P_peek_unsigned(dx_plist, H5D_XFER_MPIO_CHUNK_OPT_HARD_NAME);
     if(chunk_opt_mode == H5FD_MPIO_CHUNK_ONE_IO)
-        io_option = H5D_ONE_LINK_CHUNK_IO;/*no opt*/
+        io_option = H5D_ONE_LINK_CHUNK_IO;      /*no opt*/
     else if(chunk_opt_mode == H5FD_MPIO_CHUNK_MULTI_IO)
-        io_option = H5D_MULTI_CHUNK_IO;/*no opt */
+        io_option = H5D_MULTI_CHUNK_IO;         /*no opt */
     else {
-       if(H5D_mpio_get_sum_chunk(io_info,fm,&sum_chunk)<0)   
+        unsigned one_link_chunk_io_threshold;   /* Threshhold to use single collective I/O for all chunks */
+        int mpi_size;                   /* Number of processes in MPI job */
+
+        if(H5D_mpio_get_sum_chunk(io_info, fm, &sum_chunk) < 0)
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSWAP, FAIL, "unable to obtain the total chunk number of all processes"); 
-       if((mpi_size = H5F_mpi_get_size(io_info->dset->oloc.file))<0)
-	 HGOTO_ERROR (H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi size");
+        if((mpi_size = H5F_mpi_get_size(io_info->dset->oloc.file)) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi size")
     
-       if(NULL == (plist = H5I_object(io_info->dxpl_id)))
-         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list")
-
-       one_link_chunk_io_threshold =H5P_peek_unsigned(plist,H5D_XFER_MPIO_CHUNK_OPT_NUM_NAME);
+        one_link_chunk_io_threshold = H5P_peek_unsigned(dx_plist, H5D_XFER_MPIO_CHUNK_OPT_NUM_NAME);
 
-      /* step 1: choose an IO option */
-      /* If the average number of chunk per process is greater than a threshold, we will do one link chunked IO. */
-       if((unsigned)sum_chunk/mpi_size >= one_link_chunk_io_threshold)
+        /* step 1: choose an IO option */
+        /* If the average number of chunk per process is greater than a threshold, we will do one link chunked IO. */
+        if((unsigned)sum_chunk / mpi_size >= one_link_chunk_io_threshold)
             io_option = H5D_ONE_LINK_CHUNK_IO_MORE_OPT;
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
-       else
-           temp_not_link_io = TRUE;
+        else
+            temp_not_link_io = TRUE;
+#endif
+   } /* end else */
+
+#ifndef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
+    if(io_option == H5D_ONE_LINK_CHUNK_IO)
+        io_option = H5D_MULTI_CHUNK_IO; /* We can not do this with one chunk IO. */
+    if(io_option == H5D_ONE_LINK_CHUNK_IO_MORE_OPT)
+        io_option = H5D_MULTI_CHUNK_IO_MORE_OPT;
 #endif
-   }
 
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
+{
+    htri_t            check_prop;
+    int               new_value;
+
     /*** Test collective chunk user-input optimization APIs. ***/
-    check_prop = H5Pexist(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_LINK_HARD_NAME);
+    check_prop = H5Pexist(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_LINK_HARD_NAME);
     if(check_prop > 0) {
         if(io_option == H5D_ONE_LINK_CHUNK_IO) {
-          new_value = 0;
-          if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_LINK_HARD_NAME,&new_value)<0)
-            HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to get property value");
-        }
-    }
-    check_prop = H5Pexist(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_HARD_NAME);
+            new_value = 0;
+            if(H5Pset(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_LINK_HARD_NAME, &new_value) < 0)
+                HGOTO_ERROR(H5E_IO, H5E_CANTSET, FAIL, "unable to set property value")
+        } /* end if */
+    } /* end if */
+    check_prop = H5Pexist(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_MULTI_HARD_NAME);
     if(check_prop > 0) {
-      if(io_option == H5D_MULTI_CHUNK_IO) {
-         new_value = 0;
-         if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_HARD_NAME,&new_value)<0)
-            HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to get property value");
-      }
-    }
-    check_prop = H5Pexist(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_LINK_NUM_TRUE_NAME);
+        if(io_option == H5D_MULTI_CHUNK_IO) {
+            new_value = 0;
+            if(H5Pset(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_MULTI_HARD_NAME, &new_value) < 0)
+                HGOTO_ERROR(H5E_IO, H5E_CANTSET, FAIL, "unable to set property value")
+        } /* end if */
+    } /* end if */
+    check_prop = H5Pexist(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_LINK_NUM_TRUE_NAME);
     if(check_prop > 0) {
-      if(io_option == H5D_ONE_LINK_CHUNK_IO_MORE_OPT) {
-          new_value = 0;
-         if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_LINK_NUM_TRUE_NAME,&new_value)<0)
-            HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to get property value");
-      }
-    }
-    check_prop = H5Pexist(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_LINK_NUM_FALSE_NAME);
+        if(io_option == H5D_ONE_LINK_CHUNK_IO_MORE_OPT) {
+            new_value = 0;
+            if(H5Pset(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_LINK_NUM_TRUE_NAME, &new_value) < 0)
+                HGOTO_ERROR(H5E_IO, H5E_CANTSET, FAIL, "unable to set property value")
+        } /* end if */
+    } /* end if */
+    check_prop = H5Pexist(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_LINK_NUM_FALSE_NAME);
     if(check_prop > 0) {
-       if(temp_not_link_io){
-          new_value = 0;
-          if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_LINK_NUM_FALSE_NAME,&new_value)<0)
-              HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to get property value");
-          }
-    }
-#endif
-
-#ifndef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
-    if(io_option == H5D_ONE_LINK_CHUNK_IO )
-        io_option = H5D_MULTI_CHUNK_IO ;/* We can not do this with one chunk IO. */
-    if(io_option == H5D_ONE_LINK_CHUNK_IO_MORE_OPT)
-        io_option = H5D_MULTI_CHUNK_IO_MORE_OPT;
+        if(temp_not_link_io) {
+            new_value = 0;
+            if(H5Pset(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_LINK_NUM_FALSE_NAME, &new_value) < 0)
+                HGOTO_ERROR(H5E_IO, H5E_CANTSET, FAIL, "unable to set property value")
+        } /* end if */
+    } /* end if */
+}
 #endif
 
     /* step 2:  Go ahead to do IO.*/
+#ifdef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
     if(io_option == H5D_ONE_LINK_CHUNK_IO || io_option == H5D_ONE_LINK_CHUNK_IO_MORE_OPT) {
-      if(H5D_link_chunk_collective_io(io_info,fm,buf,do_write,sum_chunk)<0)
-	HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish linked chunk MPI-IO");
-    }
-    else if(io_option == H5D_MULTI_CHUNK_IO) {
-      if(H5D_multi_chunk_collective_io_no_opt(io_info,fm,buf,do_write)<0)
-        HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish multiple chunk MPI-IO");
-    }
+        if(H5D_link_chunk_collective_io(io_info, type_info, fm, sum_chunk) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish linked chunk MPI-IO")
+    } /* end if */
+    else
+#endif /* H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS */
+    if(io_option == H5D_MULTI_CHUNK_IO) {
+        if(H5D_multi_chunk_collective_io_no_opt(io_info, type_info, fm, dx_plist) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish multiple chunk MPI-IO")
+    } /* end if */
     else { /*multiple chunk IOs with opt */
-      if(H5D_multi_chunk_collective_io(io_info,fm,buf,do_write)<0)
-        HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish multiple chunk MPI-IO");
-    }
+        if(H5D_multi_chunk_collective_io(io_info, type_info, fm, dx_plist) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish optimized multiple chunk MPI-IO")
+    } /* end else */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -791,459 +707,583 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_link_chunk_collective_io
+ * Function:	H5D_chunk_collective_read
  *
- * Purpose:	Routine for one collective IO with one MPI derived datatype to link with all chunks
+ * Purpose:	Reads directly from chunks in file into application memory
+ *              using collective I/O.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Tuesday, March  4, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_chunk_collective_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t UNUSED nelmts, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space,
+    H5D_chunk_map_t *fm)
+{
+    herr_t ret_value = SUCCEED;         /* Return value */
 
-			1. Sort the chunk address and chunk info
-                        2. Build up MPI derived datatype for each chunk
-                        3. Build up the final MPI derived datatype
-			4. Use common collective IO routine to do MPI-IO 
+    FUNC_ENTER_NOAPI(H5D_chunk_collective_read, FAIL)
 
+    /* Call generic selection operation */
+    if(H5D_chunk_collective_io(io_info, type_info, fm) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_collective_read() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_chunk_collective_write
  *
- * Return:	Non-negative on success/Negative on failure
+ * Purpose:	Write directly to chunks in file from application memory
+ *              using collective I/O.
  *
- * Programmer:
+ * Return:	Non-negative on success/Negative on failure
  *
- * Modifications:
+ * Programmer:	Quincey Koziol
+ *              Tuesday, March  4, 2008
  *
  *-------------------------------------------------------------------------
  */
+herr_t
+H5D_chunk_collective_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t UNUSED nelmts, const H5S_t UNUSED *file_space, const H5S_t UNUSED *mem_space,
+    H5D_chunk_map_t *fm)
+{
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI(H5D_chunk_collective_write, FAIL)
+
+    /* Call generic selection operation */
+    if(H5D_chunk_collective_io(io_info, type_info, fm) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_collective_write() */
 
+#ifdef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_link_chunk_collective_io
+ *
+ * Purpose:	Routine for one collective IO with one MPI derived datatype to link with all chunks
+ *
+ *                      1. Sort the chunk address and chunk info
+ *                      2. Build up MPI derived datatype for each chunk
+ *                      3. Build up the final MPI derived datatype
+ *                      4. Use common collective IO routine to do MPI-IO 
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
+ *
+ *-------------------------------------------------------------------------
+ */
 static herr_t
-H5D_link_chunk_collective_io(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,const void *buf, hbool_t do_write,int sum_chunk)
+H5D_link_chunk_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    H5D_chunk_map_t *fm, int sum_chunk)
 {
-      size_t	       src_type_size;		/*size of source type	*/
-      size_t	       dst_type_size;	        /*size of destination type*/
-      hsize_t          mpi_buf_extra_offset;
-      hsize_t          mpi_file_extra_offset;
-      size_t           mpi_buf_count;
-      size_t           mpi_file_count;
-      hbool_t	       mbt_is_derived=0,      /* Whether the buffer (memory) type is derived and needs to be free'd */
-		       mft_is_derived=0;      /* Whether the file type is derived and needs to be free'd */  
-     
-      int              mpi_size,mpi_code;              /* MPI return code */ 
-
-      int               i,num_chunk=0,total_chunks;
-      size_t            ori_num_chunk;
-      hsize_t           ori_total_chunks;
-      haddr_t           chunk_base_addr;
-      haddr_t*          total_chunk_addr_array=NULL;
-      MPI_Datatype     *chunk_mtype=NULL;
-      MPI_Datatype     *chunk_ftype=NULL;
-      MPI_Datatype      chunk_final_mtype;
-      MPI_Datatype      chunk_final_ftype;
-      MPI_Aint         *chunk_disp_array=NULL;
-      MPI_Aint         *chunk_mem_disp_array=NULL;
-      int              *blocklen=NULL;
-      int               blocklen_value;
-      int               actual_bsearch_coll_chunk_threshold;
-      int               bsearch_coll_chunk_threshold;
-      int               many_chunk_opt = 0;
-
-      H5D_common_coll_info_t coll_info;
-      H5D_chunk_addr_info_t*  chunk_addr_info_array=NULL;
-
-      herr_t            ret_value = SUCCEED;    
-      
-      FUNC_ENTER_NOAPI_NOINIT(H5D_link_chunk_collective_io)
-      ori_total_chunks = fm->total_chunks;
-      H5_ASSIGN_OVERFLOW(total_chunks,ori_total_chunks,hsize_t,int);
-
-    /* Handle with a special case when only one chunk is covered by all processes */
-    if(total_chunks == 1){
-        H5SL_node_t *chunk_node;
-        H5D_chunk_info_t *chunk_info;
-        H5D_storage_t  store;
+    H5D_chunk_addr_info_t *chunk_addr_info_array = NULL;
+    hbool_t mbt_is_derived = FALSE;
+    hbool_t mft_is_derived = FALSE;
+    MPI_Datatype chunk_final_mtype;         /* Final memory MPI datatype for all chunks with seletion */
+    MPI_Datatype chunk_final_ftype;         /* Final file MPI datatype for all chunks with seletion */
+    H5D_storage_t ctg_store;                /* Storage info for "fake" contiguous dataset */
+    size_t              total_chunks;
+    haddr_t            *total_chunk_addr_array = NULL;
+    MPI_Datatype       *chunk_mtype = NULL;
+    MPI_Datatype       *chunk_ftype = NULL;
+    MPI_Aint           *chunk_disp_array = NULL;
+    MPI_Aint           *chunk_mem_disp_array = NULL;
+    int                *blocklen = NULL;
+    int                 mpi_code;           /* MPI return code */ 
+    herr_t              ret_value = SUCCEED;    
+    
+    FUNC_ENTER_NOAPI_NOINIT(H5D_link_chunk_collective_io)
+
+    /* Get the sum # of chunks, if not already available */
+    if(sum_chunk < 0) {
+        if(H5D_mpio_get_sum_chunk(io_info, fm, &sum_chunk) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSWAP, FAIL, "unable to obtain the total chunk number of all processes"); 
+    } /* end if */
+
+    /* Retrieve total # of chunks in dataset */
+    H5_ASSIGN_OVERFLOW(total_chunks, fm->total_chunks, hsize_t, size_t);
+
+    /* Handle special case when dataspace dimensions only allow one chunk in
+     *  the dataset.  [This sometimes is used by developers who want the
+     *  equivalent of compressed contiguous datasets - QAK]
+     */
+    if(total_chunks == 1) {
+        H5D_storage_t chk_store;        /* Temporary storage info for chunk address lookup */
+        hsize_t coords[H5O_LAYOUT_NDIMS];   /* Coordinates of chunk in file dataset's dataspace */
+        H5SL_node_t *chunk_node;        /* Pointer to chunk node for selection */
+        H5S_t *fspace;                  /* Dataspace describing chunk & selection in it */
+        H5S_t *mspace;                  /* Dataspace describing selection in memory corresponding to this chunk */
+
+        /* Initialize the chunk coordinates */
+        /* (must be all zero, since there's only one chunk) */
+        HDmemset(coords, 0, sizeof(coords));
+
+        /* Look up address of chunk */
+        io_info->store = &chk_store;
+        chk_store.chunk.offset = coords;
+        chk_store.chunk.index  = 0;
+        if(HADDR_UNDEF == (ctg_store.contig.dset_addr = H5D_istore_get_addr(io_info, NULL)))
+            HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL, "couldn't get chunk info from skipped list")
  
+        /* Check for this process having selection in this chunk */
         chunk_node = H5SL_first(fm->sel_chunks);
 	if(chunk_node == NULL) {
-            if(H5D_istore_chunkmap(io_info, &chunk_base_addr, fm->down_chunks) < 0)
-                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address");
-            if(H5D_inter_collective_io(io_info,NULL,NULL,chunk_base_addr,buf,do_write)<0)
-                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-	}
+            /* Set the dataspace info for I/O to NULL, this process doesn't have any I/O to perform */
+            fspace = mspace = NULL;
+	} /* end if */
 	else {
-            if(NULL ==(chunk_info = H5SL_item(chunk_node)))
-                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
-            io_info->store = &store;
-            store.chunk.offset = chunk_info->coords;
-            store.chunk.index  = chunk_info->index;
+            H5D_chunk_info_t *chunk_info;
+
+            /* Get the chunk info, for the selection in the chunk */
+            if(NULL == (chunk_info = H5SL_item(chunk_node)))
+                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL, "couldn't get chunk info from skipped list")
+
+            /* Set the dataspace info for I/O */
+            fspace = chunk_info->fspace;
+            mspace = chunk_info->mspace;
+	} /* end else */
+
+        /* Set up the base storage address for this chunk */
+        io_info->store = &ctg_store;
 
-            if(HADDR_UNDEF==(chunk_base_addr = H5D_istore_get_addr(io_info,NULL)))
-                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
-	
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-   HDfprintf(H5DEBUG(D),"before inter_collective_io for total chunk = 1 \n");
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D),"before inter_collective_io for total chunk = 1 \n");
 #endif
-            if(H5D_inter_collective_io(io_info,chunk_info->fspace,chunk_info->mspace,chunk_base_addr,buf,do_write)<0)
-                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-	}
-	goto done;
-      }
 
-      /* Allocate chunking information */
-      ori_num_chunk        = H5SL_count(fm->sel_chunks);
-      H5_ASSIGN_OVERFLOW(num_chunk,ori_num_chunk,size_t,int);
+        /* Perform I/O */
+        if(H5D_inter_collective_io(io_info, type_info, fspace, mspace) < 0)
+            HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL, "couldn't finish shared collective MPI-IO")
+    } /* end if */
+    else {
+        size_t mpi_buf_count;   /* Number of MPI types */
+        size_t num_chunk;       /* Number of chunks for this process */
+        size_t u;               /* Local index variable */
+
+        /* Get the number of chunks with a selection */
+        num_chunk = H5SL_count(fm->sel_chunks);
+        H5_CHECK_OVERFLOW(num_chunk, size_t, int);
 
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"total_chunks = %d\n",(int)total_chunks);
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D),"total_chunks = %Zu, num_chunk = %Zu\n", total_chunks, num_chunk);
 #endif
-         
-      if(num_chunk == 0)
-          total_chunk_addr_array = H5MM_malloc(sizeof(haddr_t)*total_chunks);
-      else
-      {
-	chunk_addr_info_array= H5MM_malloc(num_chunk*sizeof(H5D_chunk_addr_info_t));
-	chunk_mtype          = H5MM_malloc(num_chunk*sizeof(MPI_Datatype));
-	chunk_ftype          = H5MM_malloc(num_chunk*sizeof(MPI_Datatype));
-	chunk_disp_array     = H5MM_malloc(num_chunk*sizeof(MPI_Aint));
-	chunk_mem_disp_array = H5MM_calloc(num_chunk*sizeof(MPI_Aint));
-	blocklen             = H5MM_malloc(num_chunk*sizeof(int));
-      }
-
-      /* Obtain information to do collective IO,
-         in order to do collective IO, no datatype conversion should happen. */
-      if((src_type_size = H5T_get_size(io_info->dset->shared->type))==0)
-	HGOTO_ERROR(H5E_DATATYPE, H5E_BADSIZE, FAIL, "datatype size invalid");
-      dst_type_size = src_type_size;
-
-      bsearch_coll_chunk_threshold  = H5D_ALL_CHUNK_ADDR_THRES_COL;
-
-      if((mpi_size = H5F_mpi_get_size(io_info->dset->oloc.file))<0)
-	 HGOTO_ERROR (H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi size");
-
-      /* Calculate the actual threshold to obtain all chunk addresses collectively 
-         The bigger this number is, the more possible the use of obtaining chunk address collectively. */
-      /* For non-optimization one-link IO, 
-         actual bsearch threshold is always 0,
-         we would always want to obtain the chunk addresses individually
-         for each process. */
-      actual_bsearch_coll_chunk_threshold = sum_chunk*100/(total_chunks*mpi_size);
-
-      if((actual_bsearch_coll_chunk_threshold > bsearch_coll_chunk_threshold)
-         &&(sum_chunk/mpi_size >= H5D_ALL_CHUNK_ADDR_THRES_COL_NUM))
-	 many_chunk_opt = H5D_OBTAIN_ALL_CHUNK_ADDR_COL;
+             
+        /* Set up MPI datatype for chunks selected */
+        if(num_chunk) {
+            hsize_t mpi_mem_extra_offset;       /* Extra offset for memory MPI datatype */
+            hsize_t mpi_file_extra_offset;      /* Extra offset for file MPI datatype */
+            size_t mpi_mem_count;               /* Memory MPI datatype count */
+            size_t mpi_file_count;              /* File MPI datatype count */
+            hbool_t locl_mbt_is_derived = FALSE,     /* Whether the buffer (memory) type is derived and needs to be free'd */
+                    local_mft_is_derived = FALSE;     /* Whether the file type is derived and needs to be free'd */  
+            int blocklen_value;                 /* Placeholder for array fill */
+
+            /* Allocate chunking information */
+            chunk_addr_info_array= H5MM_malloc(num_chunk * sizeof(H5D_chunk_addr_info_t));
+            chunk_mtype          = H5MM_malloc(num_chunk * sizeof(MPI_Datatype));
+            chunk_ftype          = H5MM_malloc(num_chunk * sizeof(MPI_Datatype));
+            chunk_disp_array     = H5MM_malloc(num_chunk * sizeof(MPI_Aint));
+            chunk_mem_disp_array = H5MM_calloc(num_chunk * sizeof(MPI_Aint));
+            blocklen             = H5MM_malloc(num_chunk * sizeof(int));
 
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
+if(H5DEBUG(D))
     HDfprintf(H5DEBUG(D),"before sorting the chunk address \n");
 #endif
-
-      /* Sort the chunk address 
-         when chunk optimization selection is either H5D_OBTAIN_*/
-
-      if(num_chunk == 0){ /* special case: this process doesn't select anything */
-         if(H5D_istore_chunkmap(io_info, total_chunk_addr_array, fm->down_chunks)<0)
-             HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address");
-         chunk_base_addr = total_chunk_addr_array[0];
-      }
- 
-      else {
-         if(H5D_sort_chunk(io_info,fm,chunk_addr_info_array,many_chunk_opt)<0)
-        	 HGOTO_ERROR (H5E_DATASPACE, H5E_CANTSWAP, FAIL, "unable to sort chunk address");
-         chunk_base_addr = chunk_addr_info_array[0].chunk_addr;
-      }
+            /* Sort the chunk address */
+            if(H5D_sort_chunk(io_info, fm, chunk_addr_info_array, sum_chunk) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSWAP, FAIL, "unable to sort chunk address")
+            ctg_store.contig.dset_addr = chunk_addr_info_array[0].chunk_addr;
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
+if(H5DEBUG(D))
     HDfprintf(H5DEBUG(D),"after sorting the chunk address \n");
 #endif
-      
-      /* Obtain MPI derived datatype from all individual chunks */ 
-      for ( i = 0; i < num_chunk; i++) {
-	  /* Disk MPI derived datatype */
-          if(H5S_mpio_space_type(chunk_addr_info_array[i].chunk_info.fspace,src_type_size,&chunk_ftype[i],
-				    &mpi_file_count,&mpi_file_extra_offset,&mft_is_derived)<0)
-	       	HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't create MPI file type");
-
-	  /* Buffer MPI derived datatype */
-          if(H5S_mpio_space_type(chunk_addr_info_array[i].chunk_info.mspace,dst_type_size,&chunk_mtype[i],
-                                       &mpi_buf_count,&mpi_buf_extra_offset,&mbt_is_derived)<0)
-	       	HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't create MPI buf type");
-           
-          /* Chunk address relative to the first chunk */
-	  chunk_addr_info_array[i].chunk_addr -= chunk_base_addr;
-          H5_ASSIGN_OVERFLOW(chunk_disp_array[i],chunk_addr_info_array[i].chunk_addr,haddr_t,MPI_Aint);
-      }
-
-      blocklen_value = 1;
-      if(num_chunk){
-	
-        /* initialize the buffer with the constant value 1; this algo. is very fast. */
-	H5V_array_fill(blocklen,&blocklen_value,sizeof(int),(size_t)num_chunk);
-
-      /* Create final MPI derived datatype */
-	if(MPI_SUCCESS != (mpi_code = MPI_Type_struct(num_chunk,blocklen,chunk_disp_array,chunk_ftype,&chunk_final_ftype)))
-	   HMPI_GOTO_ERROR(FAIL, "MPI_Type_struct failed", mpi_code);
-	if(MPI_SUCCESS != (mpi_code = MPI_Type_commit(&chunk_final_ftype)))
-	   HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-
-	if(MPI_SUCCESS != (mpi_code = MPI_Type_struct(num_chunk,blocklen,chunk_mem_disp_array,chunk_mtype,&chunk_final_mtype)))
-	   HMPI_GOTO_ERROR(FAIL, "MPI_Type_struct failed", mpi_code);
-	if(MPI_SUCCESS != (mpi_code = MPI_Type_commit(&chunk_final_mtype)))
-	   HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-
-	for ( i = 0; i< num_chunk;i++){
-	  if (MPI_SUCCESS != (mpi_code= MPI_Type_free( chunk_mtype+i )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-
-	  if (MPI_SUCCESS != (mpi_code= MPI_Type_free( chunk_ftype+i )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-	}
-
-	/* buffer, file derived datatypes should be true */
-	coll_info.mbt_is_derived = 1;
-	coll_info.mft_is_derived = 1;
-	coll_info.mpi_buf_count  = 1;
-	coll_info.chunk_addr     = chunk_base_addr;
-
-      }
-
-      else {/* no selection at all for this process */
-	chunk_final_ftype = MPI_BYTE;
-	chunk_final_mtype = MPI_BYTE;
-	
-	/* buffer, file derived datatypes should be true */
-	coll_info.mbt_is_derived = 0;
-	coll_info.mft_is_derived = 0;
-	coll_info.mpi_buf_count  = 0;
-	coll_info.chunk_addr     = chunk_base_addr;
-      }
+
+            /* Obtain MPI derived datatype from all individual chunks */ 
+            for(u = 0; u < num_chunk; u++) {
+                /* Disk MPI derived datatype */
+                if(H5S_mpio_space_type(chunk_addr_info_array[u].chunk_info.fspace,
+                        type_info->src_type_size, &chunk_ftype[u], &mpi_file_count,
+                        &mpi_file_extra_offset, &local_mft_is_derived) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL, "couldn't create MPI file type")
+
+                /* Buffer MPI derived datatype */
+                if(H5S_mpio_space_type(chunk_addr_info_array[u].chunk_info.mspace,
+                        type_info->dst_type_size, &chunk_mtype[u], &mpi_mem_count,
+                        &mpi_mem_extra_offset, &locl_mbt_is_derived) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL, "couldn't create MPI buf type")
+                   
+                /* Chunk address relative to the first chunk */
+                chunk_addr_info_array[u].chunk_addr -= ctg_store.contig.dset_addr;
+                H5_ASSIGN_OVERFLOW(chunk_disp_array[u], chunk_addr_info_array[u].chunk_addr, haddr_t, MPI_Aint);
+            } /* end for */
+
+            /* Initialize the buffer with the constant value 1 */
+            blocklen_value = 1;
+            H5V_array_fill(blocklen, &blocklen_value, sizeof(int), num_chunk);
+
+            /* Create final MPI derived datatype for the file */
+            if(MPI_SUCCESS != (mpi_code = MPI_Type_struct((int)num_chunk, blocklen, chunk_disp_array, chunk_ftype, &chunk_final_ftype)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_Type_struct failed", mpi_code)
+            if(MPI_SUCCESS != (mpi_code = MPI_Type_commit(&chunk_final_ftype)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code)
+
+            /* Create final MPI derived datatype for memory */
+            if(MPI_SUCCESS != (mpi_code = MPI_Type_struct(num_chunk, blocklen, chunk_mem_disp_array, chunk_mtype, &chunk_final_mtype)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_Type_struct failed", mpi_code)
+            if(MPI_SUCCESS != (mpi_code = MPI_Type_commit(&chunk_final_mtype)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code)
+
+            /* Free the file & memory MPI datatypes for each chunk */
+            for(u = 0; u < num_chunk; u++) {
+                if(MPI_SUCCESS != (mpi_code = MPI_Type_free(chunk_mtype + u)))
+                    HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code)
+
+                if(MPI_SUCCESS != (mpi_code = MPI_Type_free(chunk_ftype + u)))
+                    HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code)
+            } /* end for */
+
+            /* buffer, file derived datatypes should be true */
+            mbt_is_derived = TRUE;
+            mft_is_derived = TRUE;
+            mpi_buf_count  = (size_t)1;
+        } /* end if */
+        else {      /* no selection at all for this process */
+            /* Allocate chunking information */
+            total_chunk_addr_array = H5MM_malloc(sizeof(haddr_t) * total_chunks);
+
+            /* Retrieve chunk address map */
+            if(H5D_istore_chunkmap(io_info, total_chunk_addr_array, fm->down_chunks) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address")
+
+            /* Get chunk with lowest address */
+            ctg_store.contig.dset_addr = HADDR_MAX;
+            for(u = 0; u < total_chunks; u++)
+                if(total_chunk_addr_array[u] < ctg_store.contig.dset_addr)
+                    ctg_store.contig.dset_addr = total_chunk_addr_array[u];
+            HDassert(ctg_store.contig.dset_addr != HADDR_MAX);
+
+            /* Set the MPI datatype */
+            chunk_final_ftype = MPI_BYTE;
+            chunk_final_mtype = MPI_BYTE;
+          
+            /* buffer, file derived datatypes should be true */
+            mpi_buf_count  = (size_t)0;
+        } /* end else */
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
+if(H5DEBUG(D))
     HDfprintf(H5DEBUG(D),"before coming to final collective IO\n");
 #endif
 
-      if(H5D_final_collective_io(io_info,&chunk_final_ftype,&chunk_final_mtype,&coll_info,buf,do_write)<0)
-	HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish MPI-IO");
+        /* Set up the base storage address for this chunk */
+        io_info->store = &ctg_store;
+
+        /* Perform final collective I/O operation */
+        if(H5D_final_collective_io(io_info, type_info, mpi_buf_count, &chunk_final_ftype, &chunk_final_mtype) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish MPI-IO")
+    } /* end else */
 
 done:
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"before freeing memory inside  H5D_link_collective_io ret_value = %d\n",ret_value);
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D),"before freeing memory inside H5D_link_collective_io ret_value = %d\n", ret_value);
 #endif
-     if (fm->total_chunks != 1) {
-       if(num_chunk == 0) HDfree(total_chunk_addr_array);
-       else {
-          HDfree(chunk_addr_info_array);
-	  HDfree(chunk_mtype);
-	  HDfree(chunk_ftype);
-	  HDfree(chunk_disp_array);
-	  HDfree(chunk_mem_disp_array);
-	  HDfree(blocklen);
-        }
-      }
-      FUNC_LEAVE_NOAPI(ret_value)
+    if(total_chunk_addr_array)
+        H5MM_xfree(total_chunk_addr_array);
+    if(chunk_addr_info_array)
+        H5MM_xfree(chunk_addr_info_array);
+    if(chunk_mtype)
+        H5MM_xfree(chunk_mtype);
+    if(chunk_ftype)
+        H5MM_xfree(chunk_ftype);
+    if(chunk_disp_array)
+        H5MM_xfree(chunk_disp_array);
+    if(chunk_mem_disp_array)
+        H5MM_xfree(chunk_mem_disp_array);
+    if(blocklen)
+        H5MM_xfree(blocklen);
+
+    /* Free the MPI buf and file types, if they were derived */
+    if(mbt_is_derived && MPI_SUCCESS != (mpi_code = MPI_Type_free(&chunk_final_mtype)))
+        HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code)
+    if(mft_is_derived && MPI_SUCCESS != (mpi_code = MPI_Type_free(&chunk_final_ftype)))
+        HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code)
+
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_link_chunk_collective_io */
+#endif /* H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS */
 
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_multi_chunk_collective_io
  *
  * Purpose:	To do IO per chunk according to IO mode(collective/independent/none)
-
-                1. Use MPI_gather and MPI_Bcast to obtain IO mode in each chunk(collective/independent/none)
-                2. Depending on whether the IO mode is collective or independent or none,
-                   Create either MPI derived datatype for each chunk or just do independent IO
-                3. Use common collective IO routine to do MPI-IO               
  *
- * Return:	Non-negative on success/Negative on failure
+ *              1. Use MPI_gather and MPI_Bcast to obtain IO mode in each chunk(collective/independent/none)
+ *              2. Depending on whether the IO mode is collective or independent or none,
+ *                 Create either MPI derived datatype for each chunk or just do independent IO
+ *              3. Use common collective IO routine to do MPI-IO               
  *
- * Programmer:
+ * Return:	Non-negative on success/Negative on failure
  *
- * Modifications:
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
 static herr_t 
-H5D_multi_chunk_collective_io(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,const void *buf, hbool_t do_write) 
+H5D_multi_chunk_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    H5D_chunk_map_t *fm, H5P_genplist_t *dx_plist)
 {
-      unsigned          i, total_chunk;
-      hsize_t           ori_total_chunk;
-      uint8_t          *chunk_io_option;
-
-      H5SL_node_t      *chunk_node;           /* Current node in chunk skip list */
-      H5D_chunk_info_t *chunk_info=NULL;
-      haddr_t          *chunk_addr;
-      H5D_storage_t     store;                /* union of EFL and chunk pointer in file space */
-      hbool_t           select_chunk;
-      hbool_t 	        last_io_mode_coll = TRUE;
-
-      void             *chunk = NULL;         /* Pointer to the data chunk in cache */
-      H5D_t            *dataset=io_info->dset;/* Local pointer to dataset info */
-      H5D_istore_ud1_t  udata;		      /*B-tree pass-through	*/
-      haddr_t           caddr;                /* Address of the cached chunk */
-      size_t            accessed_bytes;       /*total accessed size in a chunk */
-      unsigned          idx_hint=0;           /* Cache index hint      */
-      hbool_t           dirty = TRUE;         /* Flag for cache flushing */
-      hbool_t           relax=TRUE;           /* Whether whole chunk is selected */
-
-      herr_t            ret_value = SUCCEED;    
+    H5D_t              *dataset = io_info->dset;/* Local pointer to dataset info */
+    H5D_io_info_t       ctg_io_info;          /* Contiguous I/O info object */
+    H5D_storage_t       ctg_store;            /* Chunk storage information as contiguous dataset */
+    H5D_io_info_t       cpt_io_info;          /* Compact I/O info object */
+    H5D_storage_t       cpt_store;            /* Chunk storage information as compact dataset */
+    hbool_t             cpt_dirty;            /* Temporary placeholder for compact storage "dirty" flag */
+    uint8_t            *chunk_io_option = NULL;
+    haddr_t            *chunk_addr = NULL;
+    H5D_storage_t       store;                /* union of EFL and chunk pointer in file space */
+    H5FD_mpio_xfer_t    last_xfer_mode = H5FD_MPIO_COLLECTIVE; /* Last parallel transfer for this request (H5D_XFER_IO_XFER_MODE_NAME) */
+    H5FD_mpio_collective_opt_t last_coll_opt_mode = H5FD_MPIO_COLLECTIVE_IO; /* Last parallel transfer with independent IO or collective IO with this mode */
+    size_t              total_chunk;          /* Total # of chunks in dataset */
 #ifdef H5Dmpio_DEBUG
-      int mpi_rank;
+    int mpi_rank;
 #endif
+    size_t              u;                    /* Local index variable */
+    herr_t              ret_value = SUCCEED;    
 
-
-      FUNC_ENTER_NOAPI_NOINIT(H5D_multi_chunk_collective_io)
+    FUNC_ENTER_NOAPI_NOINIT(H5D_multi_chunk_collective_io)
 
 #ifdef H5Dmpio_DEBUG
-      mpi_rank = H5F_mpi_get_rank(io_info->dset->oloc.file);
+    mpi_rank = H5F_mpi_get_rank(io_info->dset->oloc.file);
 #endif
 
-      /* Allocate memories */
-      ori_total_chunk     = fm->total_chunks;
-      H5_ASSIGN_OVERFLOW(total_chunk,ori_total_chunk,hsize_t,unsigned);
-      HDassert(total_chunk!=0);
-      chunk_io_option = (uint8_t *)H5MM_calloc(total_chunk*sizeof(MPI_BYTE));
-      chunk_addr      = (haddr_t *)H5MM_calloc(total_chunk*sizeof(haddr_t));
+    /* Retrieve total # of chunks in dataset */
+    H5_ASSIGN_OVERFLOW(total_chunk, fm->total_chunks, hsize_t, size_t);
+    HDassert(total_chunk != 0);
+
+    /* Allocate memories */
+    chunk_io_option = (uint8_t *)H5MM_calloc(total_chunk);
+    chunk_addr      = (haddr_t *)H5MM_calloc(total_chunk * sizeof(haddr_t));
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"total_chunk %u\n",total_chunk);
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D), "total_chunk %Zu\n", total_chunk);
 #endif
 
-      /* obtain IO option for each chunk */
-      if(H5D_obtain_mpio_mode(io_info,fm,chunk_io_option,chunk_addr)<0) 
-	HGOTO_ERROR (H5E_DATASET, H5E_CANTRECV, FAIL, "unable to obtain MPIO mode");
+    /* Obtain IO option for each chunk */
+    if(H5D_obtain_mpio_mode(io_info, fm, dx_plist, chunk_io_option, chunk_addr) < 0) 
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTRECV, FAIL, "unable to obtain MPIO mode")
+
+    /* Set up contiguous I/O info object */
+    HDmemcpy(&ctg_io_info, io_info, sizeof(ctg_io_info));
+    ctg_io_info.store = &ctg_store;
+    ctg_io_info.layout_ops = *H5D_LOPS_CONTIG;
+
+    /* Initialize temporary contiguous storage info */
+    ctg_store.contig.dset_size = (hsize_t)io_info->dset->shared->layout.u.chunk.size;
+
+    /* Set up compact I/O info object */
+    HDmemcpy(&cpt_io_info, io_info, sizeof(cpt_io_info));
+    cpt_io_info.store = &cpt_store;
+    cpt_io_info.layout_ops = *H5D_LOPS_COMPACT;
+
+    /* Initialize temporary compact storage info */
+    cpt_store.compact.dirty = &cpt_dirty;
+
+    /* Set dataset storage for I/O info */
+    io_info->store = &store;
+
+    /* Loop over _all_ the chunks */
+    for(u = 0; u < total_chunk; u++) {
+        H5D_chunk_info_t *chunk_info;    /* Chunk info for current chunk */
+        H5S_t *fspace;              /* Dataspace describing chunk & selection in it */
+        H5S_t *mspace;              /* Dataspace describing selection in memory corresponding to this chunk */
 
-      for(i = 0; i < total_chunk; i++) {
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"mpi_rank = %d, chunk index = %u\n",mpi_rank,i);
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D),"mpi_rank = %d, chunk index = %Zu\n", mpi_rank, u);
 #endif
-	select_chunk = fm->select_chunk[i];
-	if(select_chunk == 1){/* Have selection elements in this chunk. Find the chunk info. */
-	   if(NULL ==(chunk_node = H5SL_first(fm->sel_chunks)))
-	    HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk node from skipped list");
-
-	    while(chunk_node){
-	      if(NULL ==(chunk_info = H5SL_item(chunk_node)))
-		HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
-	      if(chunk_info->index == i) {
-		/* Set dataset storage for I/O info */
-		io_info->store=&store;
-		/* Pass in chunk's coordinates in a union. */
-		store.chunk.offset  = chunk_info->coords;
-		store.chunk.index   = chunk_info->index;
-		break;
-	      }
-
-	      chunk_node = H5SL_next(chunk_node);
-            }
-	}
-
-        if(chunk_io_option[i] == 1){ /*collective IO for this chunk, 
-				       note: even there is no selection for this process,
-                                             the process still needs to contribute MPI NONE TYPE.*/
+        /* Get the chunk info for this chunk, if there are elements selected */
+        chunk_info = fm->select_chunk[u];
+
+        /* Set the storage information for chunks with selections */
+        if(chunk_info) {
+            HDassert(chunk_info->index == u);
+
+            /* Pass in chunk's coordinates in a union. */
+            store.chunk.offset  = chunk_info->coords;
+            store.chunk.index   = chunk_info->index;
+	} /* end if */
+
+        /* Collective IO for this chunk, 
+         * Note: even there is no selection for this process, the process still
+         *      needs to contribute MPI NONE TYPE.
+         */
+        if(chunk_io_option[u] == 1) {
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"inside collective chunk IO mpi_rank = %d, chunk index = %u\n",mpi_rank,i);
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D),"inside collective chunk IO mpi_rank = %d, chunk index = %Zu\n", mpi_rank, u);
 #endif
 	
-	  if(!last_io_mode_coll)
-	  /* Switch back to collective I/O */
-              if(H5D_ioinfo_make_coll(io_info) < 0)
-                 HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to collective I/O")
+            /* Set the file & memory dataspaces */
+            if(chunk_info) {
+                fspace = chunk_info->fspace;
+                mspace = chunk_info->mspace;
+	    } /* end if */
+	    else {
+                fspace = mspace = NULL;
+	    } /* end else */
+
+            /* Switch back to collective I/O */
+            if(last_xfer_mode != H5FD_MPIO_COLLECTIVE) {
+                if(H5D_ioinfo_xfer_mode(io_info, dx_plist, H5FD_MPIO_COLLECTIVE) < 0)
+                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to collective I/O")
+                last_xfer_mode = H5FD_MPIO_COLLECTIVE;
+            } /* end if */
+            if(last_coll_opt_mode != H5FD_MPIO_COLLECTIVE_IO) {
+                if(H5D_ioinfo_coll_opt_mode(io_info, dx_plist, H5FD_MPIO_COLLECTIVE_IO) < 0)
+                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to collective I/O")
+                last_coll_opt_mode = H5FD_MPIO_COLLECTIVE_IO;
+            } /* end if */
           
-	    if(select_chunk){
-	      if(H5D_inter_collective_io(io_info,chunk_info->fspace,chunk_info->mspace,
-			             chunk_addr[i],buf,do_write )<0)
-	        HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-	       
-	    }
-	    else{
-	     if(H5D_inter_collective_io(io_info,NULL,NULL,
-			             chunk_addr[i],buf,do_write )<0)
-	        HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-	       
-	    } 
-              last_io_mode_coll = TRUE;
-
-	}
-	else {/*possible independent IO for this chunk*/
+            /* Initialize temporary contiguous storage address */
+            ctg_store.contig.dset_addr = chunk_addr[u];
+
+            /* Perform the I/O */
+            if(H5D_inter_collective_io(&ctg_io_info, type_info, fspace, mspace) < 0)
+                HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish shared collective MPI-IO")
+	} /* end if */
+	else {  /* possible independent IO for this chunk */
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"inside independent IO mpi_rank = %d, chunk index = %u\n",mpi_rank,i);
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D),"inside independent IO mpi_rank = %d, chunk index = %Zu\n", mpi_rank, u);
 #endif
 	
-            HDassert(chunk_io_option[i] == 0);
+            HDassert(chunk_io_option[u] == 0);
 
 #if !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-            if(!select_chunk)
-                continue; /* this process has nothing to do with this chunk, continue! */
-            if(last_io_mode_coll)
+            /* Check if this process has somethign to do with this chunk */
+            if(chunk_info) {
+                H5D_io_info_t *chk_io_info;     /* Pointer to I/O info object for this chunk */
+                H5D_istore_ud1_t udata;         /* B-tree pass-through	*/
+                void *chunk;                    /* Pointer to the data chunk in cache */
+                size_t accessed_bytes;          /* Total accessed size in a chunk */
+                unsigned idx_hint = 0;          /* Cache index hint      */
+                haddr_t caddr;                  /* Address of the cached chunk */
+
                 /* Switch to independent I/O */
-                if(H5D_ioinfo_make_ind(io_info) < 0)
-                   HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
-
-            /* Load the chunk into cache.  But if the whole chunk is written,
-             * simply allocate space instead of load the chunk. */
-            if(HADDR_UNDEF==(caddr = H5D_istore_get_addr(io_info, &udata)))
-                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
-
-            if(H5D_istore_if_load(io_info, caddr)) {
-                accessed_bytes = chunk_info->chunk_points * H5T_get_size(dataset->shared->type);
-                if((do_write && (accessed_bytes != dataset->shared->layout.u.chunk.size)) || !do_write)
-                    relax=FALSE;
-
-	        if(NULL == (chunk = H5D_istore_lock(io_info, &udata, relax, &idx_hint)))
-		    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
-	    } else
-		chunk = NULL;
- 
-            if(do_write) {
-                if((io_info->ops.write)(io_info,
-                         chunk_info->chunk_points,H5T_get_size(io_info->dset->shared->type),
-                         chunk_info->fspace,chunk_info->mspace,caddr,chunk, buf) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "optimized write failed")
-            }
-            else {
-                 if((io_info->ops.read)(io_info,
-                          chunk_info->chunk_points,H5T_get_size(io_info->dset->shared->type),
-                          chunk_info->fspace,chunk_info->mspace,caddr,chunk, buf) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "optimized read failed")
-            }
+                if(last_xfer_mode != H5FD_MPIO_INDEPENDENT) {
+                    if(H5D_ioinfo_xfer_mode(io_info, dx_plist, H5FD_MPIO_INDEPENDENT) < 0)
+                        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
+                    last_xfer_mode = H5FD_MPIO_INDEPENDENT;
+                } /* end if */
 
-            /* Release the cache lock on the chunk. */
-            if(chunk) {
-                if(!do_write)
-                    dirty = FALSE;
+                /* Load the chunk into cache.  But if the whole chunk is written,
+                 * simply allocate space instead of load the chunk.
+                 */
+                if(HADDR_UNDEF == (caddr = H5D_istore_get_addr(io_info, &udata)))
+                    HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL, "couldn't get chunk info from skipped list")
 
-	        if(H5D_istore_unlock(io_info, dirty, idx_hint, chunk, accessed_bytes) < 0)
-		    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
-	    } /* end if */
-#else
-            if(!last_io_mode_coll)
-                /* using independent I/O with file setview.*/
-                if(H5D_ioinfo_make_coll_opt(io_info) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to collective I/O")
-            if(select_chunk){
-                if(H5D_inter_collective_io(io_info,chunk_info->fspace,chunk_info->mspace,
-                                     chunk_addr[i],buf,do_write )<0)
-                    HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-            }
+                /* Load the chunk into cache and lock it. */
+                if(H5D_chunk_cacheable(io_info, caddr)) {
+                    hbool_t entire_chunk = TRUE;         /* Whether whole chunk is selected */
+
+                    /* Compute # of bytes accessed in chunk */
+                    accessed_bytes = chunk_info->chunk_points * type_info->src_type_size;
+
+                    /* Determine if we will access all the data in the chunk */
+                    if(((io_info->op_type == H5D_IO_OP_WRITE) && (accessed_bytes != ctg_store.contig.dset_size))
+                            || (io_info->op_type != H5D_IO_OP_WRITE))
+                        entire_chunk = FALSE;
+
+                    /* Lock the chunk into the cache */
+                    if(NULL == (chunk = H5D_istore_lock(io_info, &udata, entire_chunk, &idx_hint)))
+                        HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
+
+                    /* Set up the storage buffer information for this chunk */
+                    cpt_store.compact.buf = chunk;
+
+                    /* Point I/O info at contiguous I/O info for this chunk */
+                    chk_io_info = &cpt_io_info;
+                } /* end if */
+                else {
+                    /* Set up the storage address information for this chunk */
+                    ctg_store.contig.dset_addr = caddr;
+
+                    /* No chunk cached */
+                    chunk = NULL;
+
+                    /* Point I/O info at temporary I/O info for this chunk */
+                    chk_io_info = &ctg_io_info;
+                } /* end else */
+
+                if(io_info->op_type == H5D_IO_OP_WRITE) {
+                    if((io_info->io_ops.single_write)(chk_io_info, type_info,
+                            (hsize_t)chunk_info->chunk_points, chunk_info->fspace, chunk_info->mspace) < 0)
+                        HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "optimized write failed")
+                } /* end if */
+                else {
+                    if((io_info->io_ops.single_read)(chk_io_info, type_info,
+                            (hsize_t)chunk_info->chunk_points, chunk_info->fspace, chunk_info->mspace) < 0)
+                        HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "optimized read failed")
+                } /* end else */
+
+                /* Release the cache lock on the chunk. */
+                if(chunk && H5D_istore_unlock(io_info, (io_info->op_type == H5D_IO_OP_WRITE), idx_hint, chunk, accessed_bytes) < 0)
+                    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
+            } /* end if */
+#else /* !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS) */
+            /* Set the file & memory dataspaces */
+            if(chunk_info) {
+                fspace = chunk_info->fspace;
+                mspace = chunk_info->mspace;
+            } /* end if */
             else {
-                if(H5D_inter_collective_io(io_info,NULL,NULL,
-                                     chunk_addr[i],buf,do_write )<0)
-                    HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-            }
+                fspace = mspace = NULL;
+            } /* end else */
+
+            /* Using independent I/O with file setview.*/
+            if(last_coll_opt_mode != H5FD_MPIO_INDIVIDUAL_IO) {
+                if(H5D_ioinfo_coll_opt_mode(io_info, dx_plist, H5FD_MPIO_INDIVIDUAL_IO) < 0)
+                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to individual I/O")
+                last_coll_opt_mode = H5FD_MPIO_INDIVIDUAL_IO;
+            } /* end if */
 
+            /* Initialize temporary contiguous storage address */
+            ctg_store.contig.dset_addr = chunk_addr[u];
+
+            /* Perform the I/O */
+            if(H5D_inter_collective_io(&ctg_io_info, type_info, fspace, mspace) < 0)
+                HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish shared collective MPI-IO")
 #ifdef H5D_DEBUG
   if(H5DEBUG(D))
     HDfprintf(H5DEBUG(D),"after inter collective IO\n");
 #endif
-#endif
-            last_io_mode_coll = FALSE;
-        }
-      }
-      if(!last_io_mode_coll)
-	  /* Switch back to collective I/O */
-              if(H5D_ioinfo_make_coll(io_info) < 0)
-                 HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to collective I/O")
+#endif /* !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS) */
+        } /* end else */
+    } /* end for */
+
 done:
-    HDfree(chunk_io_option);
-    HDfree(chunk_addr);
+    if(chunk_io_option)
+        H5MM_xfree(chunk_io_option);
+    if(chunk_addr)
+        H5MM_xfree(chunk_addr);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_multi_chunk_collective_io */
@@ -1257,90 +1297,105 @@ done:
  *              non-contiguous(or with holes) storage efficiently.
  *              Under this case, the one independent IO call may consist of
  *              many small disk IOs. So we may use independent IO with derived datatype
-                to replace the independent IO when we find this chunk is not good to
-                do collective IO. However, according to our performance study,
-                this approach may not overcome the overhead caused by MPI gather/scatter.
-                So we decide to leave the original collective IO per chunk approach as 
-                an option for users. NO MPI gather/scatter calls are used.
-                HDF5 will try to collective IO if possible.
-                If users choose to use 
-                H5Pset_dxpl_mpio_chunk_opt(dxpl_id,H5FD_MPIO_OPT_MULTI_IO),
-                this function will be called. 
-                The HDF5 library won't do any IO management but leave it to MPI-IO to figure 
-                out.  
+ *              to replace the independent IO when we find this chunk is not good to
+ *              do collective IO. However, according to our performance study,
+ *              this approach may not overcome the overhead caused by MPI gather/scatter.
+ *              So we decide to leave the original collective IO per chunk approach as 
+ *              an option for users. NO MPI gather/scatter calls are used.
+ *              HDF5 will try to collective IO if possible.
+ *              If users choose to use 
+ *              H5Pset_dxpl_mpio_chunk_opt(dxpl_id,H5FD_MPIO_OPT_MULTI_IO),
+ *              this function will be called. 
+ *              The HDF5 library won't do any IO management but leave it to MPI-IO to figure 
+ *              out.  
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:
- *
- * Modifications:
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
 static herr_t 
-H5D_multi_chunk_collective_io_no_opt(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,const void *buf, hbool_t do_write) 
+H5D_multi_chunk_collective_io_no_opt(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, H5D_chunk_map_t *fm, H5P_genplist_t *dx_plist)
 {
-      int               count_chunk,min_num_chunk;
-      haddr_t           chunk_addr;
-      H5SL_node_t      *chunk_node;           /* Current node in chunk skip list */
-      H5D_storage_t     store;                /* union of EFL and chunk pointer in file space */
-      H5D_chunk_info_t *chunk_info;           /* chunk information */
-      hbool_t make_ind, make_coll;            /* Flags to indicate that the MPI mode should change */
-
-      void             *chunk = NULL;         /* Pointer to the data chunk in cache */
-      H5D_t            *dataset=io_info->dset;/* Local pointer to dataset info */
-      H5D_istore_ud1_t  udata;		      /*B-tree pass-through	*/
-      size_t            accessed_bytes;       /*total accessed size in a chunk */
-      unsigned          idx_hint=0;           /* Cache index hint      */
-      hbool_t           dirty = TRUE;         /* Flag for cache flushing */
-      hbool_t           relax=TRUE;           /* Whether whole chunk is selected */
-      herr_t            ret_value = SUCCEED;    
-
-#ifdef H5Dmpio_DEBUG
-      int mpi_rank;
-#endif
+    H5D_t          *dataset = io_info->dset;/* Local pointer to dataset info */
+    H5SL_node_t    *chunk_node;           /* Current node in chunk skip list */
+    H5D_io_info_t   ctg_io_info;          /* Contiguous I/O info object */
+    H5D_storage_t   ctg_store;            /* Chunk storage information as contiguous dataset */
+    H5D_io_info_t   cpt_io_info;          /* Compact I/O info object */
+    H5D_storage_t   cpt_store;            /* Chunk storage information as compact dataset */
+    hbool_t         cpt_dirty;            /* Temporary placeholder for compact storage "dirty" flag */
+    int             min_chunk = -1;       /* Minimum # of chunks all processes will operate on */
+    int             count_chunk;          /* How many chunks have we operated on? */
+    H5D_storage_t   store;                /* union of EFL and chunk pointer in file space */
+    herr_t          ret_value = SUCCEED;    
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_multi_chunk_collective_io_no_opt)
 
-      FUNC_ENTER_NOAPI_NOINIT(H5D_multi_chunk_collective_io_no_opt)
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D)){ 
+if(H5DEBUG(D)) {
+    int mpi_rank;
+
     mpi_rank = H5F_mpi_get_rank(io_info->dset->oloc.file);
-    HDfprintf(H5DEBUG(D),"coming to multi_chunk_collective_io_no_opt\n");
-  }         
+    HDfprintf(H5DEBUG(D), "coming to multi_chunk_collective_io_no_opt\n");
+}         
 #endif
 
-      if(H5D_mpio_get_min_chunk(io_info,fm,&min_num_chunk)<0)
-         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get minimum number of chunk");
-      count_chunk = 0;
-  
-      /* Get first node in chunk skip list */
-      chunk_node=H5SL_first(fm->sel_chunks);
- 
-       /* Iterate through chunks to be operated on */
-      while(chunk_node) {
-           H5D_chunk_info_t *chunk_info;   /* chunk information */
-           hbool_t make_ind, make_coll;        /* Flags to indicate that the MPI mode should change */
-
-           /* Get the actual chunk information from the skip list node */
-           chunk_info=H5SL_item(chunk_node);
-
-           /* Set dataset storage for I/O info */
-          io_info->store=&store;
-
-           /* Pass in chunk's coordinates in a union. */
-           store.chunk.offset = chunk_info->coords;
-           store.chunk.index = chunk_info->index;
-
-           /* Reset flags for changing parallel I/O mode */
-           make_ind = make_coll = FALSE;
-            
-           count_chunk++;
-          /* If the number of chunk is greater than minimum number of chunk,
-                  Do independent read */
-           if(count_chunk > min_num_chunk) {
-              /* Switch to independent I/O (permanently) */
-               make_ind = TRUE;
-            }
+    /* Set up contiguous I/O info object */
+    HDmemcpy(&ctg_io_info, io_info, sizeof(ctg_io_info));
+    ctg_io_info.store = &ctg_store;
+    ctg_io_info.layout_ops = *H5D_LOPS_CONTIG;
+
+    /* Initialize temporary contiguous storage info */
+    ctg_store.contig.dset_size = (hsize_t)io_info->dset->shared->layout.u.chunk.size;
+
+    /* Set up compact I/O info object */
+    HDmemcpy(&cpt_io_info, io_info, sizeof(cpt_io_info));
+    cpt_io_info.store = &cpt_store;
+    cpt_io_info.layout_ops = *H5D_LOPS_COMPACT;
+
+    /* Initialize temporary compact storage info */
+    cpt_store.compact.dirty = &cpt_dirty;
+
+    /* Set dataset storage for I/O info */
+    io_info->store = &store;
+
+    /* Get the min. # of chunks */
+    if(H5D_mpio_get_min_chunk(io_info, fm, &min_chunk) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get minimum number of chunk")
+    HDassert(min_chunk >= 0);
+
+    /* Get first node in chunk skip list */
+    chunk_node = H5SL_first(fm->sel_chunks);
+    count_chunk = 0;
+
+     /* Iterate through chunks to be operated on */
+    while(chunk_node) {
+        H5D_chunk_info_t *chunk_info;   /* chunk information */
+        haddr_t chunk_addr;             /* Address of chunk in file */
+        H5D_istore_ud1_t udata;		/* B-tree pass-through	*/
+        hbool_t make_ind, make_coll;    /* Flags to indicate that the MPI mode should change */
 
+        /* Get the actual chunk information from the skip list node */
+        chunk_info = H5SL_item(chunk_node);
+
+        /* Pass in chunk's coordinates in a union. */
+        store.chunk.offset = chunk_info->coords;
+        store.chunk.index = chunk_info->index;
+
+        /* Reset flags for changing parallel I/O mode */
+        make_ind = make_coll = FALSE;
+          
+        count_chunk++;
+
+        /* If the number of chunk is greater than minimum number of chunk,
+         *      Do independent read.
+         */
+        if(count_chunk > min_chunk)
+            /* Switch to independent I/O (permanently) */
+            make_ind = TRUE;
 #ifndef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
 /* This case needs to be improved to check if the selected space
    is regular. If all selections are regular, collective IO can still be done.
@@ -1349,67 +1404,92 @@ H5D_multi_chunk_collective_io_no_opt(H5D_io_info_t *io_info,H5D_chunk_map_t *fm,
    we turn off this optimization but leave the following code
    for future optimization. Otherwise, the following else {} doesn't make sense.
    KY 2006/8/4/ */
-            else {
-                 /* Switch to independent I/O (temporarily) */
-                   make_ind = TRUE;
-                    make_coll = TRUE;
-             } /* end else */
+        else {
+            /* Switch to independent I/O (temporarily) */
+            make_ind = TRUE;
+            make_coll = TRUE;
+        } /* end else */
 #endif /* H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS */
 
+        /* Retrieve the chunk's address */
+        if(HADDR_UNDEF == (chunk_addr = H5D_istore_get_addr(io_info, &udata)))
+            HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list")
+
+        /* Independent I/O */
+        if(make_ind) {
+            void *chunk;                /* Pointer to the data chunk in cache */
+            H5D_io_info_t *chk_io_info;     /* Pointer to I/O info object for this chunk */
+            size_t accessed_bytes = 0;  /* Total accessed size in a chunk */
+            unsigned idx_hint = 0;      /* Cache index hint      */
+
             /* Switch to independent I/O */
-            if(make_ind)
-                if(H5D_ioinfo_make_ind(io_info) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
+            if(H5D_ioinfo_xfer_mode(io_info, dx_plist, H5FD_MPIO_INDEPENDENT) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
 
-            if(HADDR_UNDEF==(chunk_addr = H5D_istore_get_addr(io_info, &udata)))
-                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
+            /* Load the chunk into cache and lock it. */
+            if(H5D_chunk_cacheable(io_info, chunk_addr)) {
+                hbool_t entire_chunk = TRUE;         /* Whether whole chunk is selected */
 
-            if(make_ind) {/*independent I/O */
-                /* Load the chunk into cache.  But if the whole chunk is written,
-                 * simply allocate space instead of load the chunk. */
-                if(H5D_istore_if_load(io_info, chunk_addr)) {
-                    accessed_bytes = chunk_info->chunk_points * H5T_get_size(dataset->shared->type);
-                    if((do_write && (accessed_bytes != dataset->shared->layout.u.chunk.size)) || !do_write)
-                        relax=FALSE;
-
-		    if(NULL == (chunk = H5D_istore_lock(io_info, &udata, relax, &idx_hint)))
-		        HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
-		} else
-		    chunk = NULL;
- 
-                if(do_write) {
-                    if((io_info->ops.write)(io_info,
-                         chunk_info->chunk_points,H5T_get_size(io_info->dset->shared->type),
-                         chunk_info->fspace,chunk_info->mspace, chunk_addr, chunk, buf) < 0)
-                        HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "optimized write failed")
-                } else {
-                    if((io_info->ops.read)(io_info,
-                          chunk_info->chunk_points,H5T_get_size(io_info->dset->shared->type),
-                          chunk_info->fspace,chunk_info->mspace, chunk_addr, chunk, buf) < 0)
-                        HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "optimized read failed")
-                }
+                /* Compute # of bytes accessed in chunk */
+                accessed_bytes = chunk_info->chunk_points * type_info->src_type_size;
 
-                /* Release the cache lock on the chunk. */
-                if(chunk) {
-                    if(!do_write)
-                        dirty = FALSE;
+                /* Determine if we will access all the data in the chunk */
+                if(((io_info->op_type == H5D_IO_OP_WRITE) && (accessed_bytes != ctg_store.contig.dset_size))
+                        || (io_info->op_type != H5D_IO_OP_WRITE))
+                    entire_chunk = FALSE;
+
+                /* Lock the chunk into the cache */
+                if(NULL == (chunk = H5D_istore_lock(io_info, &udata, entire_chunk, &idx_hint)))
+                    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to read raw data chunk")
 
-		    if(H5D_istore_unlock(io_info, dirty, idx_hint, chunk, accessed_bytes) < 0)
-			HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
-		} /* end if */
+                /* Set up the storage buffer information for this chunk */
+                cpt_store.compact.buf = chunk;
+
+                /* Point I/O info at contiguous I/O info for this chunk */
+                chk_io_info = &cpt_io_info;
             } /* end if */
-            else { /*collective I/O */
-              if(H5D_inter_collective_io(io_info,chunk_info->fspace,chunk_info->mspace,
-                     chunk_addr,buf,do_write ) < 0)
-                HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO");
-            }
-
-            if(make_coll)
-              if(H5D_ioinfo_make_coll(io_info) < 0)
-                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
-          /* Get the next chunk node in the skip list */
-            chunk_node=H5SL_next(chunk_node);
-       } /* end while */
+            else {
+                /* Set up the storage address information for this chunk */
+                ctg_store.contig.dset_addr = chunk_addr;
+
+                /* No chunk cached */
+                chunk = NULL;
+
+                /* Point I/O info at temporary I/O info for this chunk */
+                chk_io_info = &ctg_io_info;
+            } /* end else */
+
+            if(io_info->op_type == H5D_IO_OP_WRITE) {
+                if((io_info->io_ops.single_write)(chk_io_info, type_info,
+                        (hsize_t)chunk_info->chunk_points, chunk_info->fspace, chunk_info->mspace) < 0)
+                    HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "optimized write failed")
+            } /* end if */
+            else {
+                if((io_info->io_ops.single_read)(chk_io_info, type_info,
+                        (hsize_t)chunk_info->chunk_points, chunk_info->fspace, chunk_info->mspace) < 0)
+                   HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "optimized read failed")
+            } /* end ese */
+
+            /* Release the cache lock on the chunk. */
+            if(chunk)
+                if(H5D_istore_unlock(io_info, (io_info->op_type == H5D_IO_OP_WRITE), idx_hint, chunk, accessed_bytes) < 0)
+                    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "unable to unlock raw data chunk")
+        } /* end if */
+        else { /*collective I/O */
+            /* Set up the storage address information for this chunk */
+            ctg_store.contig.dset_addr = chunk_addr;
+
+            if(H5D_inter_collective_io(&ctg_io_info, type_info, chunk_info->fspace, chunk_info->mspace) < 0)
+                HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO")
+        } /* end else */
+
+        if(make_coll)
+            if(H5D_ioinfo_xfer_mode(io_info, dx_plist, H5FD_MPIO_COLLECTIVE) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
+
+        /* Get the next chunk node in the skip list */
+        chunk_node = H5SL_next(chunk_node);
+    } /* end while */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1420,303 +1500,266 @@ done:
  * Function:	H5D_inter_collective_io
  *
  * Purpose:	Routine for the shared part of collective IO between multiple chunk
-                collective IO and contiguous collective IO
-		
+ *              collective IO and contiguous collective IO
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:
- *
- * Modifications:
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
 static herr_t 
-H5D_inter_collective_io(H5D_io_info_t *io_info,const H5S_t *file_space,const H5S_t *mem_space,
-			 haddr_t addr, const void *buf, hbool_t do_write ) 
+H5D_inter_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    const H5S_t *file_space, const H5S_t *mem_space)
 {
+    size_t mpi_buf_count;               /* # of MPI types */
+    hbool_t mbt_is_derived = FALSE;
+    hbool_t mft_is_derived = FALSE;
+    MPI_Datatype        mpi_file_type, mpi_buf_type;
+    int                 mpi_code;           /* MPI return code */ 
+    herr_t       ret_value = SUCCEED;  /* return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_inter_collective_io)
+
+    if((file_space != NULL) && (mem_space != NULL)) {
+        hsize_t	mpi_buf_offset, mpi_file_offset;   /* Offset within dataset where selection (ie. MPI type) begins */
+        size_t  mpi_file_count;         /* Number of file "objects" to transfer */
 
-      size_t	        mpi_buf_count, mpi_file_count;     /* Number of "objects" to transfer */
-      MPI_Datatype      mpi_file_type,mpi_buf_type;
-      hsize_t	        mpi_buf_offset, mpi_file_offset;   /* Offset within dataset where selection (ie. MPI type) begins */
-      hbool_t	        mbt_is_derived=0,      /* Whether the buffer (memory) type is derived and needs to be free'd */
-		        mft_is_derived=0;      /* Whether the file type is derived and needs to be free'd */  
-      H5D_common_coll_info_t coll_info;
-      herr_t       ret_value = SUCCEED;  /* return value */
-
-      FUNC_ENTER_NOAPI_NOINIT(H5D_inter_collective_io)
-      if((file_space!=NULL) &&  (mem_space != NULL)) {
-	/*Obtain disk and memory MPI derived datatype */
-	if(H5S_mpio_space_type(file_space,H5T_get_size(io_info->dset->shared->type),
-			       &mpi_file_type,&mpi_file_count,&mpi_file_offset,&mft_is_derived)<0)
-	       HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't create MPI file type");
-
-	if(H5S_mpio_space_type(mem_space,H5T_get_size(io_info->dset->shared->type),
-			       &mpi_buf_type,&mpi_buf_count,&mpi_buf_offset,&mbt_is_derived)<0)
-	       HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't create MPI buffer type");
-	    
-      }
-      else {
-	    /* For non-selection, participate with a none MPI derived datatype, the count is 0.  */
-	    mpi_buf_type   = MPI_BYTE;   
-	    mpi_file_type  = MPI_BYTE;
-	    mpi_file_count = 0;
-	    mpi_buf_count  = 0;
-      }
-
-      coll_info.mbt_is_derived = mbt_is_derived;
-      coll_info.mft_is_derived = mft_is_derived;
-      coll_info.mpi_buf_count  = mpi_buf_count;
-      coll_info.chunk_addr     = addr;
+        /* Obtain disk and memory MPI derived datatype */
+        if(H5S_mpio_space_type(file_space, type_info->src_type_size,
+                &mpi_file_type, &mpi_file_count, &mpi_file_offset, &mft_is_derived) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL, "couldn't create MPI file type")
+        if(H5S_mpio_space_type(mem_space, type_info->src_type_size,
+                &mpi_buf_type, &mpi_buf_count, &mpi_buf_offset, &mbt_is_derived) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL, "couldn't create MPI buffer type")
+    } /* end if */
+    else {
+        /* For non-selection, participate with a none MPI derived datatype, the count is 0.  */
+        mpi_buf_type   = MPI_BYTE;   
+        mpi_file_type  = MPI_BYTE;
+        mpi_buf_count  = (size_t)0;
+        mbt_is_derived = FALSE;
+        mft_is_derived = FALSE;
+    } /* end else */
 
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-   HDfprintf(H5DEBUG(D),"before final collective IO \n");
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D),"before final collective IO \n");
 #endif
 
-      if(H5D_final_collective_io(io_info,&mpi_file_type,&mpi_buf_type,&coll_info,buf,do_write)<0)
-	    HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish collective MPI-IO");
- done:
+    /* Perform final collective I/O operation */
+    if(H5D_final_collective_io(io_info, type_info, mpi_buf_count, &mpi_file_type, &mpi_buf_type) < 0)
+        HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish collective MPI-IO")
+
+done:
+    /* Free the MPI buf and file types, if they were derived */
+    if(mbt_is_derived && MPI_SUCCESS != (mpi_code = MPI_Type_free(&mpi_buf_type)))
+        HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code)
+    if(mft_is_derived && MPI_SUCCESS != (mpi_code = MPI_Type_free(&mpi_file_type)))
+        HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code)
+
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
+if(H5DEBUG(D))
     HDfprintf(H5DEBUG(D),"before leaving inter_collective_io ret_value = %d\n",ret_value);
 #endif
 
-      FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5D_inter_collective_io */
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_inter_collective_io() */
 
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_final_collective_io
  *
  * Purpose:	Routine for the common part of collective IO with different storages.
-		
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:
- *
- * Modifications:
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
 static herr_t 
-H5D_final_collective_io(H5D_io_info_t *io_info,MPI_Datatype*mpi_file_type,MPI_Datatype *mpi_buf_type,
-			 H5D_common_coll_info_t* coll_info, const void *buf, hbool_t do_write) 
+H5D_final_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    size_t mpi_buf_count, MPI_Datatype *mpi_file_type, MPI_Datatype *mpi_buf_type)
 {
-
-
-    int               mpi_code;              /* MPI return code */ 
-    hbool_t	      plist_is_setup=0;      /* Whether the dxpl has been customized */
-    herr_t            ret_value = SUCCEED;
-
+    int         mpi_code;               /* MPI return code */ 
+    hbool_t	plist_is_setup = FALSE; /* Whether the dxpl has been customized */
+    herr_t      ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_final_collective_io)
 
-     /*
-	  * Pass buf type, file type to the file driver.
-     */
-
-     if(H5FD_mpi_setup_collective(io_info->dxpl_id, *mpi_buf_type, *mpi_file_type)<0)
-	HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set MPI-I/O properties");
+    /* Pass buf type, file type to the file driver.  */
+    if(H5FD_mpi_setup_collective(io_info->dxpl_id, *mpi_buf_type, *mpi_file_type) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set MPI-I/O properties")
+    plist_is_setup = TRUE;
 
-     plist_is_setup=1;
-#ifdef H5D_DEBUG
-  if(H5DEBUG(D)){
-    HDfprintf(H5DEBUG(D),"chunk addr %Hu\n",coll_info->chunk_addr);
-    HDfprintf(H5DEBUG(D),"mpi_buf_count %d\n",coll_info->mpi_buf_count);
-  }
-
-#endif
-
-    if(do_write) {
-        if((io_info->ops.write)(io_info,
-		coll_info->mpi_buf_count,0,NULL,NULL,coll_info->chunk_addr,
-                NULL, buf) < 0)
+    if(io_info->op_type == H5D_IO_OP_WRITE) {
+        if((io_info->io_ops.single_write)(io_info, type_info,
+                (hsize_t)mpi_buf_count, NULL, NULL) < 0)
 	    HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "optimized write failed")
-    }
+    } /* end if */
     else {
-        if((io_info->ops.read)(io_info,
-	        coll_info->mpi_buf_count,0,NULL,NULL,coll_info->chunk_addr,
-                NULL, buf) < 0)
+        if((io_info->io_ops.single_read)(io_info, type_info,
+                (hsize_t)mpi_buf_count, NULL, NULL) < 0)
             HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "optimized read failed")
-    }
+    } /* end else */
 
 done:
-     /* Reset the dxpl settings */
-      if(plist_is_setup) {
-        if(H5FD_mpi_teardown_collective(io_info->dxpl_id)<0)
-    	    HDONE_ERROR(H5E_DATASPACE, H5E_CANTFREE, FAIL, "unable to reset dxpl values");
-      } /* end if */
-
-     /* free the MPI buf and file types */
-      if (coll_info->mbt_is_derived) {
-	if (MPI_SUCCESS != (mpi_code= MPI_Type_free( mpi_buf_type )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-      }
-      if (coll_info->mft_is_derived) {
-	if (MPI_SUCCESS != (mpi_code= MPI_Type_free( mpi_file_type )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-      }
+    /* Reset the dxpl settings */
+    if(plist_is_setup)
+        if(H5FD_mpi_teardown_collective(io_info->dxpl_id) < 0)
+            HDONE_ERROR(H5E_DATASPACE, H5E_CANTFREE, FAIL, "unable to reset dxpl values")
+
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D)) 
+if(H5DEBUG(D)) 
     HDfprintf(H5DEBUG(D),"ret_value before leaving final_collective_io=%d\n",ret_value);
 #endif
-
       FUNC_LEAVE_NOAPI(ret_value)
-}/* end H5D_final_collective_io */
+} /* end H5D_final_collective_io */
 
 
 /*-------------------------------------------------------------------------
  * Function:	H5D_sort_chunk
  *
  * Purpose:	Routine to sort chunks in increasing order of chunk address
-                Each chunk address is also obtained.
-
-   Description:
-                For most cases, the chunk address has already been sorted in increasing order.
-		The special sorting flag is used to optimize this common case.
-                quick sort is used for necessary sorting.
-   
-   Parameters:
-                Input: H5D_io_info_t* io_info,
-		       H5D_chunk_map_t *fm(global chunk map struct)
-		Input/Output:  H5D_chunk_addr_info_t chunk_addr_info_array[]   : array to store chunk address and information 
-                       many_chunk_opt                         : flag to optimize the way to obtain chunk addresses 
-                                                                for many chunks
+ *              Each chunk address is also obtained.
  *
- * Return:	Non-negative on success/Negative on failure
+ * Description:
+ *              For most cases, the chunk address has already been sorted in increasing order.
+ *              The special sorting flag is used to optimize this common case.
+ *              quick sort is used for necessary sorting.
  *
- * Programmer:
+ * Parameters:
+ *              Input: H5D_io_info_t* io_info,
+ *                      H5D_chunk_map_t *fm(global chunk map struct)
+ *              Input/Output:  H5D_chunk_addr_info_t chunk_addr_info_array[]   : array to store chunk address and information 
+ *                     many_chunk_opt                         : flag to optimize the way to obtain chunk addresses 
+ *                                                              for many chunks
  *
- * Modifications:
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
-
 static herr_t 
-H5D_sort_chunk(H5D_io_info_t * io_info,
-	       H5D_chunk_map_t *fm,
-	       H5D_chunk_addr_info_t chunk_addr_info_array[],
-	       int many_chunk_opt)
+H5D_sort_chunk(H5D_io_info_t *io_info, const H5D_chunk_map_t *fm,
+    H5D_chunk_addr_info_t chunk_addr_info_array[], int sum_chunk)
 {
-
-
-    H5SL_node_t      *chunk_node;         /* Current node in chunk skip list */
+    H5SL_node_t    *chunk_node;         /* Current node in chunk skip list */
     H5D_chunk_info_t *chunk_info;         /* Current chunking info. of this node. */
-    haddr_t           chunk_addr;         /* Current chunking address of this node */
-    haddr_t          *total_chunk_addr_array=NULL; /* The array of chunk address for the total number of chunk */
-    int               i,mpi_code;
-    int               total_chunks;
-    size_t            num_chunks;
-    int               mpi_type_cleanup    = 0;
-    int               tchunk_addr_cleanup = 0;
-    MPI_Datatype      chunk_addrtype;
-    H5D_storage_t     store;              /*union of EFL and chunk pointer in file space */
-    hbool_t           do_sort = FALSE;
-    herr_t	      ret_value = SUCCEED;	/*return value		*/
+    haddr_t         chunk_addr;         /* Current chunking address of this node */
+    haddr_t        *total_chunk_addr_array = NULL; /* The array of chunk address for the total number of chunk */
+    H5D_storage_t   store;              /*union of EFL and chunk pointer in file space */
+    hbool_t         do_sort = FALSE;    /* Whether the addresses need to be sorted */
+    int             bsearch_coll_chunk_threshold;
+    int             many_chunk_opt = H5D_OBTAIN_ONE_CHUNK_ADDR_IND;
+    int             mpi_size;                   /* Number of MPI processes */
+    int             mpi_code;                   /* MPI return code */
+    int             i;                          /* Local index variable */
+    herr_t	    ret_value = SUCCEED;        /* Return value		*/
   
     FUNC_ENTER_NOAPI_NOINIT(H5D_sort_chunk)
 
-    num_chunks =  H5SL_count(fm->sel_chunks);
+    /* Retrieve # of MPI processes */
+    if((mpi_size = H5F_mpi_get_size(io_info->dset->oloc.file)) < 0)
+        HGOTO_ERROR(H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi size")
+
+    /* Calculate the actual threshold to obtain all chunk addresses collectively 
+     *  The bigger this number is, the more possible the use of obtaining chunk
+     * address collectively.
+     */
+    /* For non-optimization one-link IO, actual bsearch threshold is always
+     *   0, we would always want to obtain the chunk addresses individually
+     *   for each process.
+     */
+    bsearch_coll_chunk_threshold = (sum_chunk * 100) / ((int)fm->total_chunks * mpi_size);
+    if((bsearch_coll_chunk_threshold > H5D_ALL_CHUNK_ADDR_THRES_COL)
+            && ((sum_chunk / mpi_size) >= H5D_ALL_CHUNK_ADDR_THRES_COL_NUM))
+        many_chunk_opt = H5D_OBTAIN_ALL_CHUNK_ADDR_COL;
+
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D)) 
-    HDfprintf(H5DEBUG(D),"many_chunk_opt= %d\n",many_chunk_opt);
+if(H5DEBUG(D)) 
+    HDfprintf(H5DEBUG(D), "many_chunk_opt= %d\n", many_chunk_opt);
 #endif
 
     /* If we need to optimize the way to obtain the chunk address */
-    if(many_chunk_opt != H5D_OBTAIN_ONE_CHUNK_ADDR_IND){
+    if(many_chunk_opt != H5D_OBTAIN_ONE_CHUNK_ADDR_IND) {
+        int mpi_rank;
 
-      int mpi_rank, root;
-      total_chunks = (int)fm->total_chunks;
-      total_chunk_addr_array = H5MM_malloc(sizeof(haddr_t)*total_chunks);
-      tchunk_addr_cleanup = 1;
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"Coming inside H5D_OBTAIN_ALL_CHUNK_ADDR_COL\n");
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D), "Coming inside H5D_OBTAIN_ALL_CHUNK_ADDR_COL\n");
 #endif
-	root = 0;
-	if((mpi_rank = H5F_mpi_get_rank(io_info->dset->oloc.file))<0)
-	 HGOTO_ERROR (H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi rank");
-
-	/*Create received  MPI derived datatype */
-	if(MPI_SUCCESS !=(mpi_code = MPI_Type_contiguous((int)(sizeof(haddr_t)*total_chunks), MPI_BYTE, &chunk_addrtype)))
-	  HMPI_GOTO_ERROR(FAIL, "MPI_Type_contiguous failed", mpi_code);
-	if(MPI_SUCCESS !=(mpi_code = MPI_Type_commit(&chunk_addrtype)))
-	  HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-
-	mpi_type_cleanup = 1;
-
-	if(mpi_rank == root) {
-	   if(H5D_istore_chunkmap(io_info, total_chunk_addr_array, fm->down_chunks)<0)
-	     HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address");
-	}
+        /* Allocate array for chunk addresses */
+        if(NULL == (total_chunk_addr_array = H5MM_malloc(sizeof(haddr_t) * (size_t)fm->total_chunks)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "unable to allocate memory chunk address array")
+
+        /* Retrieve all the chunk addresses with process 0 */
+        if((mpi_rank = H5F_mpi_get_rank(io_info->dset->oloc.file)) < 0)
+            HGOTO_ERROR(H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi rank")
+	if(mpi_rank == 0) {
+            if(H5D_istore_chunkmap(io_info, total_chunk_addr_array, fm->down_chunks) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address")
+	} /* end if */
+
 	/* Broadcasting the MPI_IO option info. and chunk address info. */
-	if(MPI_SUCCESS !=(mpi_code = MPI_Bcast(total_chunk_addr_array,1,chunk_addrtype,root,io_info->comm)))
-	   HMPI_GOTO_ERROR(FAIL, "MPI_BCast failed", mpi_code);
+	if(MPI_SUCCESS != (mpi_code = MPI_Bcast(total_chunk_addr_array, (int)(sizeof(haddr_t) * fm->total_chunks), MPI_BYTE, (int)0, io_info->comm)))
+	   HMPI_GOTO_ERROR(FAIL, "MPI_BCast failed", mpi_code)
     } /* end if */
 
-    /* Get first node in chunk skip list */
-    if(NULL ==(chunk_node = H5SL_first(fm->sel_chunks)))
-	  HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk node from skipped list");
     /* Set dataset storage for I/O info */
     io_info->store = &store;
-    if(NULL ==(chunk_info = H5SL_item(chunk_node)))
-	  HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
-    store.chunk.offset = chunk_info->coords;
-    store.chunk.index  = chunk_info->index;
+
+    /* Start at first node in chunk skip list */
     i = 0;
-    if(many_chunk_opt == H5D_OBTAIN_ONE_CHUNK_ADDR_IND){
-      if(HADDR_UNDEF==(chunk_addr = H5D_istore_get_addr(io_info,NULL)))
-	  HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
+    if(NULL == (chunk_node = H5SL_first(fm->sel_chunks)))
+        HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk node from skipped list")
 
-#ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"coming to obtain each chunk address individually \n");
-#endif
-    }
-    else 
-       chunk_addr = total_chunk_addr_array[chunk_info->index];
+    /* Iterate over all chunks for this process */
+    while(chunk_node) {
+        if(NULL == (chunk_info = H5SL_item(chunk_node)))
+            HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list")
+        
+        if(many_chunk_opt == H5D_OBTAIN_ONE_CHUNK_ADDR_IND) {
+            store.chunk.offset = chunk_info->coords;
+            store.chunk.index  = chunk_info->index;
+            if(HADDR_UNDEF == (chunk_addr = H5D_istore_get_addr(io_info, NULL)))
+                HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL, "couldn't get chunk info from skipped list")
+        } /* end if */
+        else 
+            chunk_addr = total_chunk_addr_array[chunk_info->index];
 
-    chunk_addr_info_array[i].chunk_addr  = chunk_addr;
-    chunk_addr_info_array[i].chunk_info  = *chunk_info;
+        /* Check if chunk addresses are not in increasing order in the file */
+        if(i > 0 && chunk_addr < chunk_addr_info_array[i - 1].chunk_addr)
+            do_sort = TRUE;
 
-    chunk_node = H5SL_next(chunk_node);
+        /* Set the address & info for this chunk */
+        chunk_addr_info_array[i].chunk_addr = chunk_addr;
+        chunk_addr_info_array[i].chunk_info = *chunk_info;
 
-    while(chunk_node) {
+        /* Advance to next chunk in list */
+        i++;
+        chunk_node = H5SL_next(chunk_node);
+    } /* end while */
 
-            chunk_info         = H5SL_item(chunk_node);
-            store.chunk.offset = chunk_info->coords;
-            store.chunk.index  = chunk_info->index;
-	    
-	    if(many_chunk_opt == H5D_OBTAIN_ONE_CHUNK_ADDR_IND){
-	      if(HADDR_UNDEF==(chunk_addr = H5D_istore_get_addr(io_info,NULL)))
-		HGOTO_ERROR(H5E_STORAGE, H5E_CANTGET, FAIL,"couldn't get chunk info from skipped list");
-	    }
-	    else 
-	      chunk_addr = total_chunk_addr_array[chunk_info->index];
-
-	    if(chunk_addr < chunk_addr_info_array[i].chunk_addr) do_sort = TRUE;
-	    chunk_addr_info_array[i+1].chunk_addr = chunk_addr;
-            chunk_addr_info_array[i+1].chunk_info =*chunk_info;
-            i++;
-            chunk_node = H5SL_next(chunk_node);
-    }
 #ifdef H5D_DEBUG
-  if(H5DEBUG(D))
-    HDfprintf(H5DEBUG(D),"before Qsort\n");
+if(H5DEBUG(D))
+    HDfprintf(H5DEBUG(D), "before Qsort\n");
 #endif
-    if(do_sort)
-	    HDqsort(chunk_addr_info_array,num_chunks,sizeof(chunk_addr_info_array),H5D_cmp_chunk_addr);
+    if(do_sort) {
+        size_t num_chunks = H5SL_count(fm->sel_chunks);
+
+        HDqsort(chunk_addr_info_array, num_chunks, sizeof(chunk_addr_info_array[0]), H5D_cmp_chunk_addr);
+    } /* end if */
 
 done:
+    if(total_chunk_addr_array)
+        H5MM_xfree(total_chunk_addr_array);
 
-    if(tchunk_addr_cleanup)
-       HDfree(total_chunk_addr_array);
-    if(mpi_type_cleanup) {
-      if (MPI_SUCCESS != (mpi_code= MPI_Type_free( &chunk_addrtype )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-    }
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_sort_chunk() */
     
@@ -1725,310 +1768,244 @@ done:
  * Function:	H5D_obtain_mpio_mode
  *
  * Purpose:	Routine to obtain each io mode(collective,independent or none) for each chunk;
-                Each chunk address is also obtained.
-
-   Description:
-
-                1) Each process provides two piece of information for all chunks having selection
-		   a) chunk index 
-                   b) wheather this chunk is regular(for MPI derived datatype not working case)
-
-                2) Gather all the information to the root process
-		
-		3) Root process will do the following:
-		   a) Obtain chunk addresses for all chunks in this data space
-		   b) With the consideration of the user option, calculate IO mode for each chunk
-		   c) Build MPI derived datatype to combine "chunk address" and "assign_io" information
-		      in order to do MPI Bcast only once
-                   d) MPI Bcast the IO mode and chunk address information for each chunk.
-		4) Each process then retrieves IO mode and chunk address information to assign_io_mode and chunk_addr.
- 
-   Parameters:
-
-                Input: H5D_io_info_t* io_info,
-		       H5D_chunk_map_t *fm,(global chunk map struct)
-		Output: uint8_t assign_io_mode[], : IO mode, collective, independent or none
-		        haddr_t chunk_addr[],     : chunk address array for each chunk
+ *              Each chunk address is also obtained.
  *
- * Return:	Non-negative on success/Negative on failure
+ * Description:
  *
- * Programmer:
+ *              1) Each process provides two piece of information for all chunks having selection
+ *                 a) chunk index 
+ *                 b) wheather this chunk is regular(for MPI derived datatype not working case)
+ *
+ *              2) Gather all the information to the root process
  *
- * Modifications:
+ *              3) Root process will do the following:
+ *                 a) Obtain chunk addresses for all chunks in this data space
+ *                 b) With the consideration of the user option, calculate IO mode for each chunk
+ *                 c) Build MPI derived datatype to combine "chunk address" and "assign_io" information
+ *                      in order to do MPI Bcast only once
+ *                 d) MPI Bcast the IO mode and chunk address information for each chunk.
+ *              4) Each process then retrieves IO mode and chunk address information to assign_io_mode and chunk_addr.
+ *
+ * Parameters:
+ *
+ *              Input: H5D_io_info_t* io_info,
+ *                      H5D_chunk_map_t *fm,(global chunk map struct)
+ *              Output: uint8_t assign_io_mode[], : IO mode, collective, independent or none
+ *                      haddr_t chunk_addr[],     : chunk address array for each chunk
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Muqun Yang
+ *              Monday, Feb. 13th, 2006
  *
  *-------------------------------------------------------------------------
  */
-
 static herr_t 
-H5D_obtain_mpio_mode(H5D_io_info_t* io_info, 
-		     H5D_chunk_map_t *fm,
-		     uint8_t assign_io_mode[],
-		     haddr_t chunk_addr[])
+H5D_obtain_mpio_mode(H5D_io_info_t* io_info, H5D_chunk_map_t *fm,
+    H5P_genplist_t *dx_plist, uint8_t assign_io_mode[], haddr_t chunk_addr[])
 {
-
-  int               total_chunks;
-  hsize_t           ori_total_chunks;
-  unsigned          percent_nproc_per_chunk,threshold_nproc_per_chunk;
-  H5FD_mpio_chunk_opt_t chunk_opt_mode;
-  uint8_t*          io_mode_info=NULL;
-  uint8_t*          recv_io_mode_info=NULL;
-  uint8_t*          mergebuf=NULL;
-  uint8_t*          tempbuf;
-
-  H5SL_node_t*      chunk_node;  
-  H5D_chunk_info_t* chunk_info;
-
-  MPI_Datatype      bastype[2];
-  MPI_Datatype      chunk_addrtype;
-  int               bascount;
-  int               basblock[2];
-  MPI_Aint          basdisp[2];
-  MPI_Datatype      rtype;
-  MPI_Datatype      stype;
-  int               mpi_size,mpi_rank;
-  MPI_Comm          comm;
-  int               ic,root;
-  int               mpi_code;
-  H5P_genplist_t    *plist;
-  int               mem_cleanup      = 0,
-                    mpi_type_cleanup = 0;
-
+    int               total_chunks;
+    unsigned          percent_nproc_per_chunk,threshold_nproc_per_chunk;
+    H5FD_mpio_chunk_opt_t chunk_opt_mode;
+    uint8_t*          io_mode_info=NULL;
+    uint8_t*          recv_io_mode_info=NULL;
+    uint8_t*          mergebuf=NULL;
+    uint8_t*          tempbuf;
+    H5SL_node_t*      chunk_node;  
+    H5D_chunk_info_t* chunk_info;
+    int               mpi_size,mpi_rank;
+    MPI_Comm          comm;
+    int               ic,root;
+    int               mpi_code;
+    int               mem_cleanup      = 0;
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
-  int new_value;
-  htri_t check_prop;
+    int new_value;
+    htri_t check_prop;
 #endif
+    herr_t            ret_value = SUCCEED;
 
-  herr_t            ret_value = SUCCEED;
-
-  FUNC_ENTER_NOAPI_NOINIT(H5D_obtain_mpio_mode)
+    FUNC_ENTER_NOAPI_NOINIT(H5D_obtain_mpio_mode)
 
-  /* Assign the rank 0 to the root */
-  root              = 0; 
-  comm              = io_info->comm;
+    /* Assign the rank 0 to the root */
+    root              = 0; 
+    comm              = io_info->comm;
 
-  /* Obtain the number of process and the current rank of the process */
-  if((mpi_rank = H5F_mpi_get_rank(io_info->dset->oloc.file))<0)
-	 HGOTO_ERROR (H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi rank");
-  if((mpi_size = H5F_mpi_get_size(io_info->dset->oloc.file))<0)
-	 HGOTO_ERROR (H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi size");
+    /* Obtain the number of process and the current rank of the process */
+    if((mpi_rank = H5F_mpi_get_rank(io_info->dset->oloc.file)) < 0)
+        HGOTO_ERROR(H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi rank")
+    if((mpi_size = H5F_mpi_get_size(io_info->dset->oloc.file)) < 0)
+        HGOTO_ERROR(H5E_IO, H5E_MPI, FAIL, "unable to obtain mpi size")
   
-   /* Allocate memory */
-  ori_total_chunks      = fm->total_chunks;
-  H5_ASSIGN_OVERFLOW(total_chunks,ori_total_chunks,hsize_t,int);
-
- /* Obtain the data transfer properties */
-  if(NULL == (plist = H5I_object(io_info->dxpl_id)))
-       HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list")
-  
-  percent_nproc_per_chunk=H5P_peek_unsigned(plist,H5D_XFER_MPIO_CHUNK_OPT_RATIO_NAME);
+    /* Setup parameters */
+    H5_ASSIGN_OVERFLOW(total_chunks, fm->total_chunks, hsize_t, int);
+    percent_nproc_per_chunk = H5P_peek_unsigned(dx_plist, H5D_XFER_MPIO_CHUNK_OPT_RATIO_NAME);
 #if defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) && defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-   
-  chunk_opt_mode=(H5FD_mpio_chunk_opt_t)H5P_peek_unsigned(plist,H5D_XFER_MPIO_CHUNK_OPT_HARD_NAME);
-
-  if((chunk_opt_mode == H5FD_MPIO_CHUNK_MULTI_IO) || (percent_nproc_per_chunk == 0)){
-    if(H5D_istore_chunkmap(io_info, chunk_addr, fm->down_chunks) < 0)
-       HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address");    
-    for(ic = 0; ic<total_chunks;ic++)
-       assign_io_mode[ic] = H5D_CHUNK_IO_MODE_COL;
-       goto done;
-  }
+    chunk_opt_mode = (H5FD_mpio_chunk_opt_t)H5P_peek_unsigned(dx_plist, H5D_XFER_MPIO_CHUNK_OPT_HARD_NAME);
+    if((chunk_opt_mode == H5FD_MPIO_CHUNK_MULTI_IO) || (percent_nproc_per_chunk == 0)) {
+        if(H5D_istore_chunkmap(io_info, chunk_addr, fm->down_chunks) < 0)
+           HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address");    
+        for(ic = 0; ic < total_chunks; ic++)
+           assign_io_mode[ic] = H5D_CHUNK_IO_MODE_COL;
+
+        HGOTO_DONE(SUCCEED)
+    } /* end if */
 #endif    
-  threshold_nproc_per_chunk = mpi_size * percent_nproc_per_chunk/100;
-
-  io_mode_info      = (uint8_t *)H5MM_calloc(total_chunks*sizeof(MPI_BYTE));
-  mergebuf          = H5MM_malloc((sizeof(haddr_t)+sizeof(MPI_BYTE))*total_chunks);
-  tempbuf           = mergebuf + sizeof(MPI_BYTE)*total_chunks;
-  if(mpi_rank == root) 
-     recv_io_mode_info = (uint8_t *)H5MM_malloc(total_chunks*sizeof(MPI_BYTE)*mpi_size);
+    threshold_nproc_per_chunk = mpi_size * percent_nproc_per_chunk/100;
+
+    /* Allocate memory */
+    io_mode_info      = (uint8_t *)H5MM_calloc(total_chunks);
+    mergebuf          = H5MM_malloc((sizeof(haddr_t) + 1) * total_chunks);
+    tempbuf           = mergebuf + total_chunks;
+    if(mpi_rank == root) 
+        recv_io_mode_info = (uint8_t *)H5MM_malloc(total_chunks * mpi_size);
   
-  mem_cleanup       = 1;
+    mem_cleanup       = 1;
 
-  chunk_node        = H5SL_first(fm->sel_chunks);
-
-  /*Obtain the regularity and selection information for all chunks in this process. */
-  while(chunk_node){
-
-      chunk_info    = H5SL_item(chunk_node);
+    /* Obtain the regularity and selection information for all chunks in this process. */
+    chunk_node        = H5SL_first(fm->sel_chunks);
+    while(chunk_node) {
+        chunk_info    = H5SL_item(chunk_node);
 
 #ifndef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
-      /* regularity information: 1, selection information: 2 */
-      if(H5S_SELECT_IS_REGULAR(chunk_info->fspace) == TRUE &&
-         H5S_SELECT_IS_REGULAR(chunk_info->mspace) == TRUE)
+        /* regularity information: 1, selection information: 2 */
+        if(H5S_SELECT_IS_REGULAR(chunk_info->fspace) == TRUE &&
+                H5S_SELECT_IS_REGULAR(chunk_info->mspace) == TRUE)
 #endif
-	io_mode_info[chunk_info->index] = H5D_CHUNK_SELECT_REG; /* this chunk is selected and is "regular" without defining H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS. */
+            io_mode_info[chunk_info->index] = H5D_CHUNK_SELECT_REG; /* this chunk is selected and is "regular" without defining H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS. */
 #ifndef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
-      else
-	io_mode_info[chunk_info->index] = H5D_CHUNK_SELECT_IRREG; /* this chunk is selected and is irregular*/
+        else
+            io_mode_info[chunk_info->index] = H5D_CHUNK_SELECT_IRREG; /* this chunk is selected and is irregular*/
 #endif
-
-      chunk_node = H5SL_next(chunk_node);
-  }
+        chunk_node = H5SL_next(chunk_node);
+    } /* end while */
   
-  /*Create sent MPI derived datatype */
-  if(MPI_SUCCESS !=(mpi_code = MPI_Type_contiguous(total_chunks,MPI_BYTE,&stype)))
-    HMPI_GOTO_ERROR(FAIL, "MPI_Comm_rank failed", mpi_code);
-  if(MPI_SUCCESS != (mpi_code = MPI_Type_commit(&stype)))
-    HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-
-  /*Create received basic MPI derived datatype */
-  bascount      = 2;
-  basblock[0]   = total_chunks;
-  basblock[1]   = total_chunks;
-  basdisp[0]    = 0;
-  basdisp[1]    = (MPI_Aint)(sizeof(MPI_BYTE)*total_chunks);/* may need to check overflow */
-  bastype[0]    = MPI_BYTE;
- 
-  if(MPI_SUCCESS !=(mpi_code = MPI_Type_contiguous(sizeof(haddr_t),MPI_BYTE,&chunk_addrtype)))
-    HMPI_GOTO_ERROR(FAIL, "MPI_Type_contiguous failed", mpi_code);
-  if(MPI_SUCCESS != (mpi_code = MPI_Type_commit(&chunk_addrtype)))
-    HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-  bastype[1]    = chunk_addrtype;
-
-  if(MPI_SUCCESS !=(mpi_code = MPI_Type_struct(bascount,basblock,basdisp,bastype,&rtype)))
-    HMPI_GOTO_ERROR(FAIL, "MPI_Type_struct failed", mpi_code);
-  if(MPI_SUCCESS !=(mpi_code = MPI_Type_commit(&rtype)))
-    HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-
-  /* Set up a flag to clean up the MPI derived datatype later */
-  mpi_type_cleanup = 1;
-
-  /*Gather all the information */
-  if(MPI_SUCCESS !=(mpi_code = MPI_Gather(io_mode_info,1,stype,recv_io_mode_info,1,stype,root,comm)))
-    HMPI_GOTO_ERROR(FAIL, "MPI_Gather failed", mpi_code);
-
-  /* Calculate the mode for IO(collective, independent or none) at root process */
-  if(mpi_rank == root) {
-
-    int               nproc;
-    int*              nproc_per_chunk;
+    /*Gather all the information */
+    if(MPI_SUCCESS != (mpi_code = MPI_Gather(io_mode_info, total_chunks, MPI_BYTE, recv_io_mode_info, total_chunks, MPI_BYTE, root, comm)))
+        HMPI_GOTO_ERROR(FAIL, "MPI_Gather failed", mpi_code)
+
+    /* Calculate the mode for IO(collective, independent or none) at root process */
+    if(mpi_rank == root) {
+        int               nproc;
+        int*              nproc_per_chunk;
 #if !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-    int*              ind_this_chunk;
+        int*              ind_this_chunk;
 #endif
 
-    /* pre-computing: calculate number of processes and 
-        regularity of the selection occupied in each chunk */
-    nproc_per_chunk = (int*)H5MM_calloc(total_chunks*sizeof(int));
+        /* pre-computing: calculate number of processes and 
+            regularity of the selection occupied in each chunk */
+        nproc_per_chunk = (int*)H5MM_calloc(total_chunks * sizeof(int));
 #if !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-    ind_this_chunk   = (int*)H5MM_calloc(total_chunks*sizeof(int));
+        ind_this_chunk   = (int*)H5MM_calloc(total_chunks * sizeof(int));
 #endif
 
-    /* calculating the chunk address */
-    if(H5D_istore_chunkmap(io_info, chunk_addr, fm->down_chunks)<0){
-      HDfree(nproc_per_chunk);
+        /* calculating the chunk address */
+        if(H5D_istore_chunkmap(io_info, chunk_addr, fm->down_chunks) < 0) {
+            HDfree(nproc_per_chunk);
 #if !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-      HDfree(ind_this_chunk);
+            HDfree(ind_this_chunk);
 #endif
-      HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address");
-    }
-
-    /* checking for number of process per chunk and regularity of the selection*/
-    for (nproc = 0;nproc <mpi_size;nproc++){
-	uint8_t *tmp_recv_io_mode_info = recv_io_mode_info + nproc*total_chunks;
-        /* calculate the number of process per chunk and adding irregular selection option */
-	for(ic = 0; ic < total_chunks; ic++, tmp_recv_io_mode_info++){
-		if(*tmp_recv_io_mode_info != 0) {
-           		nproc_per_chunk[ic]++;
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get chunk address")
+        } /* end if */
+
+        /* checking for number of process per chunk and regularity of the selection*/
+        for(nproc = 0; nproc < mpi_size; nproc++) {
+            uint8_t *tmp_recv_io_mode_info = recv_io_mode_info + (nproc * total_chunks);
+
+            /* Calculate the number of process per chunk and adding irregular selection option */
+            for(ic = 0; ic < total_chunks; ic++, tmp_recv_io_mode_info++) {
+                if(*tmp_recv_io_mode_info != 0) {
+                    nproc_per_chunk[ic]++;
 #ifndef H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS
-			if(*tmp_recv_io_mode_info == H5D_CHUNK_SELECT_IRREG)
-				ind_this_chunk[ic] = 1;
+                    if(*tmp_recv_io_mode_info == H5D_CHUNK_SELECT_IRREG)
+                        ind_this_chunk[ic] = 1;
 #endif
-                }
+                } /* end if */
 #ifndef H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS
                 else {
-                /*checking whether we have a selection in this chunk */
-		       ind_this_chunk[ic] = 1;
-        	}
+                    /*checking whether we have a selection in this chunk */
+                    ind_this_chunk[ic] = 1;
+                } /* end else */
 #endif
-         }
+            } /* end for */
+        } /* end for */
 
-    }
-
-    /* Calculating MPIO mode for each chunk (collective, independent, none) */
-    for(ic = 0; ic < total_chunks; ic++){
-	  if(nproc_per_chunk[ic]>MAX(1,threshold_nproc_per_chunk)){
+        /* Calculating MPIO mode for each chunk (collective, independent, none) */
+        for(ic = 0; ic < total_chunks; ic++) {
+            if(nproc_per_chunk[ic] > MAX(1, threshold_nproc_per_chunk)) {
 #if !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-	    if(!ind_this_chunk[ic]) assign_io_mode[ic] = H5D_CHUNK_IO_MODE_COL;
+                if(!ind_this_chunk[ic])
+                    assign_io_mode[ic] = H5D_CHUNK_IO_MODE_COL;
 #else
-	    assign_io_mode[ic] = H5D_CHUNK_IO_MODE_COL;
+                assign_io_mode[ic] = H5D_CHUNK_IO_MODE_COL;
 #endif
-	  }
-    }
+            } /* end if */
+        } /* end for */
 
 
-    /* merge buffer io_mode info and chunk addr into one */
-    HDmemcpy(mergebuf,assign_io_mode,sizeof(MPI_BYTE)*total_chunks);
-    HDmemcpy(tempbuf,chunk_addr,sizeof(haddr_t)*total_chunks);
+        /* merge buffer io_mode info and chunk addr into one */
+        HDmemcpy(mergebuf, assign_io_mode, total_chunks);
+        HDmemcpy(tempbuf, chunk_addr, sizeof(haddr_t) * total_chunks);
 
-    HDfree(nproc_per_chunk);
+        HDfree(nproc_per_chunk);
 #if !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-    HDfree(ind_this_chunk);
+        HDfree(ind_this_chunk);
 #endif
-  }
+    } /* end if */
 
-   /* Broadcasting the MPI_IO option info. and chunk address info. */
-   if(MPI_SUCCESS !=(mpi_code = MPI_Bcast(mergebuf,1,rtype,root,comm)))
-     HMPI_GOTO_ERROR(FAIL, "MPI_BCast failed", mpi_code);
+    /* Broadcasting the MPI_IO option info. and chunk address info. */
+    if(MPI_SUCCESS != (mpi_code = MPI_Bcast(mergebuf, ((sizeof(haddr_t) + 1) * total_chunks), MPI_BYTE, root, comm)))
+        HMPI_GOTO_ERROR(FAIL, "MPI_BCast failed", mpi_code)
 
-   HDmemcpy(assign_io_mode,mergebuf,sizeof(MPI_BYTE)*total_chunks);
-   HDmemcpy(chunk_addr,tempbuf,sizeof(haddr_t)*total_chunks);
+    HDmemcpy(assign_io_mode, mergebuf, total_chunks);
+    HDmemcpy(chunk_addr, tempbuf, sizeof(haddr_t) * total_chunks);
 
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
-    check_prop = H5Pexist(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_RATIO_COLL_NAME);
+    check_prop = H5Pexist(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_MULTI_RATIO_COLL_NAME);
     if(check_prop > 0) {
 #if !defined(H5_MPI_COMPLEX_DERIVED_DATATYPE_WORKS) || !defined(H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS)
-      new_value = 0;
-      if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_RATIO_COLL_NAME,&new_value)<0)
-              HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to set property value");
+        new_value = 0;
+        if(H5Pset(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_MULTI_RATIO_COLL_NAME, &new_value) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to set property value")
 #else 
-      for(ic = 0; ic < total_chunks; ic++){
-        if(assign_io_mode[ic] == H5D_CHUNK_IO_MODE_COL) {
-           new_value = 0;
-	   if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_RATIO_COLL_NAME,&new_value)<0)
-              HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to set property value");
-           break;
-        }
-      }
+        for(ic = 0; ic < total_chunks; ic++) {
+            if(assign_io_mode[ic] == H5D_CHUNK_IO_MODE_COL) {
+                new_value = 0;
+                if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_RATIO_COLL_NAME,&new_value) < 0)
+                    HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to set property value")
+                break;
+            } /* end if */
+        } /* end for */
 #endif
-    }
-   check_prop = H5Pexist(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_RATIO_IND_NAME);
-   if(check_prop > 0) {
-      int temp_count = 0;
-      for(ic = 0; ic < total_chunks; ic++){
-        if(assign_io_mode[ic] == H5D_CHUNK_IO_MODE_COL) {
-          temp_count++;
-          break;
-        }
-      }
-      if(temp_count==0){
-        new_value = 0;
-        if(H5Pset(io_info->dxpl_id,H5D_XFER_COLL_CHUNK_MULTI_RATIO_IND_NAME,&new_value)<0)
-          HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to set property value");
-      }
-   }
+    } /* end if */
+
+    check_prop = H5Pexist(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_MULTI_RATIO_IND_NAME);
+    if(check_prop > 0) {
+        int temp_count = 0;
+
+        for(ic = 0; ic < total_chunks; ic++) {
+            if(assign_io_mode[ic] == H5D_CHUNK_IO_MODE_COL) {
+                temp_count++;
+                break;
+            } /* end if */
+        } /* end for */
+        if(temp_count == 0) {
+            new_value = 0;
+            if(H5Pset(io_info->dxpl_id, H5D_XFER_COLL_CHUNK_MULTI_RATIO_IND_NAME, &new_value) < 0)
+                HGOTO_ERROR(H5E_PLIST, H5E_UNSUPPORTED, FAIL, "unable to set property value")
+        } /* end if */
+    } /* end if */
 #endif
  
 done:
-
-   if(mpi_type_cleanup) {
-     if (MPI_SUCCESS != (mpi_code= MPI_Type_free( &chunk_addrtype )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-
-     if (MPI_SUCCESS != (mpi_code= MPI_Type_free( &stype )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-
-     if (MPI_SUCCESS != (mpi_code= MPI_Type_free( &rtype )))
-            HMPI_DONE_ERROR(FAIL, "MPI_Type_free failed", mpi_code);
-   }
-
-   if(mem_cleanup){
-     HDfree(io_mode_info);
-     HDfree(mergebuf);
-     if(mpi_rank == root) 
-       HDfree(recv_io_mode_info);
-   }
+    if(mem_cleanup) {
+        HDfree(io_mode_info);
+        HDfree(mergebuf);
+        if(mpi_rank == root) 
+            HDfree(recv_io_mode_info);
+    } /* end if */
 
     FUNC_LEAVE_NOAPI(ret_value)
-}/* end H5D_obtain_mpio_mode*/
+} /* end H5D_obtain_mpio_mode() */
 
 static int
 H5D_cmp_chunk_addr(const void *chunk_addr_info1, const void *chunk_addr_info2)
@@ -2041,7 +2018,6 @@ H5D_cmp_chunk_addr(const void *chunk_addr_info1, const void *chunk_addr_info2)
    addr2 = ((const H5D_chunk_addr_info_t *)chunk_addr_info2)->chunk_addr;
 
    FUNC_LEAVE_NOAPI(H5F_addr_cmp(addr1, addr2))
-
 }
 #endif  /* H5_HAVE_PARALLEL */
 
diff --git a/src/H5Doh.c b/src/H5Doh.c
index 01447a3..37f011b 100644
--- a/src/H5Doh.c
+++ b/src/H5Doh.c
@@ -316,7 +316,7 @@ H5O_dset_get_oloc(hid_t obj_id)
     FUNC_ENTER_NOAPI_NOINIT(H5O_dset_get_oloc)
 
     /* Get the dataset */
-    if(NULL == (dset = H5I_object(obj_id)))
+    if(NULL == (dset = (H5D_t *)H5I_object(obj_id)))
         HGOTO_ERROR(H5E_OHDR, H5E_BADATOM, NULL, "couldn't get object from ID")
 
     /* Get the dataset's object header location */
diff --git a/src/H5Dpkg.h b/src/H5Dpkg.h
index aec5e19..97dcacf 100644
--- a/src/H5Dpkg.h
+++ b/src/H5Dpkg.h
@@ -49,74 +49,156 @@
 #define H5D_MINHDR_SIZE 256
 
 /* [Simple] Macro to construct a H5D_io_info_t from it's components */
-#define H5D_BUILD_IO_INFO(io_info,ds,dxpl_c,dxpl_i,str)                 \
-    (io_info)->dset=ds;                                                 \
-    (io_info)->dxpl_cache=dxpl_c;                                       \
-    (io_info)->dxpl_id=dxpl_i;                                          \
-    (io_info)->store=str
+#define H5D_BUILD_IO_INFO_WRT(io_info, ds, dxpl_c, dxpl_i, str, buf)    \
+    (io_info)->dset = ds;                                               \
+    (io_info)->dxpl_cache = dxpl_c;                                     \
+    (io_info)->dxpl_id = dxpl_i;                                        \
+    (io_info)->store = str;                                             \
+    (io_info)->op_type = H5D_IO_OP_WRITE;                               \
+    (io_info)->u.wbuf = buf
+#define H5D_BUILD_IO_INFO_RD(io_info, ds, dxpl_c, dxpl_i, str, buf)     \
+    (io_info)->dset = ds;                                               \
+    (io_info)->dxpl_cache = dxpl_c;                                     \
+    (io_info)->dxpl_id = dxpl_i;                                        \
+    (io_info)->store = str;                                             \
+    (io_info)->op_type = H5D_IO_OP_READ;                                \
+    (io_info)->u.rbuf = buf
+
+#define H5D_CHUNK_HASH(D, ADDR) H5F_addr_hash(ADDR, (D)->cache.chunk.nslots)
 
 
 /****************************/
 /* Package Private Typedefs */
 /****************************/
 
-/*
- * If there is no data type conversion then it might be possible to
- * transfer data points between application memory and the file in one
- * step without going through the data type conversion buffer.
- */
-
-/* Read from file to application w/o intermediate scratch buffer */
+/* Typedef for datatype information for raw data I/O operation */
+typedef struct H5D_type_info_t {
+    /* Initial values */
+    const H5T_t *mem_type;              /* Pointer to memory datatype */
+    const H5T_t *dset_type;             /* Pointer to dataset datatype */
+    H5T_path_t *tpath;                  /* Datatype conversion path */
+    hid_t src_type_id;                  /* Source datatype ID */
+    hid_t dst_type_id;                  /* Destination datatype ID */
+
+    /* Computed/derived values */
+    size_t src_type_size;		/* Size of source type	*/
+    size_t dst_type_size;	        /* Size of destination type*/
+    size_t max_type_size;	        /* Size of largest source/destination type */
+    hbool_t is_conv_noop;               /* Whether the type conversion is a NOOP */
+    hbool_t is_xform_noop;              /* Whether the data transform is a NOOP */
+    H5T_subset_t cmpd_subset;           /* Whether (and which) the source/destination datatypes are compound subsets of one another */
+    H5T_bkg_t need_bkg;		        /* Type of background buf needed */
+    size_t request_nelmts;		/* Requested strip mine	*/
+    uint8_t *tconv_buf;	                /* Datatype conv buffer	*/
+    hbool_t tconv_buf_allocated;        /* Whether the type conversion buffer was allocated */
+    uint8_t *bkg_buf;	                /* Background buffer	*/
+    hbool_t bkg_buf_allocated;          /* Whether the background buffer was allocated */
+} H5D_type_info_t;
+
+/* Forward declaration of structs used below */
 struct H5D_io_info_t;
-typedef herr_t (*H5D_io_read_func_t)(struct H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const H5S_t *file_space, const H5S_t *mem_space, haddr_t addr,
-    void *chunk, void *buf/*out*/);
-
-
-/* Write directly from app buffer to file */
-typedef herr_t (*H5D_io_write_func_t)(struct H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const H5S_t *file_space, const H5S_t *mem_space, haddr_t addr,
-    void *chunk, const void *buf);
+struct H5D_chunk_map_t;
 
 /* Function pointers for I/O on particular types of dataset layouts */
-typedef ssize_t (*H5D_io_readvv_func_t)(const struct H5D_io_info_t *io_info,
+typedef herr_t (*H5D_layout_init_func_t)(const struct H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    struct H5D_chunk_map_t *cm);
+typedef herr_t (*H5D_layout_read_func_t)(struct H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, hsize_t nelmts, const H5S_t *file_space,
+    const H5S_t *mem_space, struct H5D_chunk_map_t *fm);
+typedef herr_t (*H5D_layout_write_func_t)(struct H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, hsize_t nelmts, const H5S_t *file_space,
+    const H5S_t *mem_space, struct H5D_chunk_map_t *fm);
+typedef ssize_t (*H5D_layout_readvv_func_t)(const struct H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t chunk_addr, void *chunk, void *buf);
-typedef ssize_t (*H5D_io_writevv_func_t)(const struct H5D_io_info_t *io_info,
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[]);
+typedef ssize_t (*H5D_layout_writevv_func_t)(const struct H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t chunk_addr, void *chunk, const void *buf);
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[]);
+typedef herr_t (*H5D_layout_term_func_t)(const struct H5D_chunk_map_t *cm);
+
+/* Typedef for grouping layout I/O routines */
+typedef struct H5D_layout_ops_t {
+    H5D_layout_init_func_t init;        /* I/O initialization routine */
+    H5D_layout_read_func_t ser_read;    /* High-level I/O routine for reading data in serial */
+    H5D_layout_write_func_t ser_write;  /* High-level I/O routine for writing data in serial */
+#ifdef H5_HAVE_PARALLEL
+    H5D_layout_read_func_t par_read;    /* High-level I/O routine for reading data in parallel */
+    H5D_layout_write_func_t par_write;  /* High-level I/O routine for writing data in parallel */
+#endif /* H5_HAVE_PARALLEL */
+    H5D_layout_readvv_func_t readvv;    /* Low-level I/O routine for reading data */
+    H5D_layout_writevv_func_t writevv;  /* Low-level I/O routine for writing data */
+    H5D_layout_term_func_t term;        /* I/O shutdown routine */
+} H5D_layout_ops_t;
+
+/* Function pointers for either multiple or single block I/O access */
+typedef herr_t (*H5D_io_single_read_func_t)(const struct H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
+typedef herr_t (*H5D_io_single_write_func_t)(const struct H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
 
 /* Typedef for raw data I/O framework info */
 typedef struct H5D_io_ops_t {
-    H5D_io_read_func_t read;            /* Direct I/O routine for reading */
-    H5D_io_write_func_t write;          /* Direct I/O routine for writing */
-    H5D_io_readvv_func_t readvv;        /* I/O routine for reading data */
-    H5D_io_writevv_func_t writevv;      /* I/O routine for writing data */
+    H5D_layout_read_func_t multi_read;          /* High-level I/O routine for reading data */
+    H5D_layout_write_func_t multi_write;        /* High-level I/O routine for writing data */
+    H5D_io_single_read_func_t single_read;      /* I/O routine for reading single block */
+    H5D_io_single_write_func_t single_write;    /* I/O routine for writing single block */
 } H5D_io_ops_t;
 
+/* Typedefs for dataset storage information */
+typedef struct {
+    haddr_t dset_addr;      /* Address of dataset in file */
+    hsize_t dset_size;      /* Total size of dataset in file */
+} H5D_contig_storage_t;
+
+typedef struct {
+    hsize_t index;          /* "Index" of chunk in dataset (must be first for TBBT routines) */
+    hsize_t *offset;        /* Chunk's coordinates in elements */
+} H5D_chunk_storage_t;
+
+typedef struct {
+    void *buf;              /* Buffer for compact dataset */
+    hbool_t *dirty;         /* Pointer to dirty flag to mark */
+} H5D_compact_storage_t;
+
+typedef union H5D_storage_t {
+    H5D_contig_storage_t contig; /* Contiguous information for dataset */
+    H5D_chunk_storage_t chunk;  /* Chunk information for dataset */
+    H5D_compact_storage_t compact; /* Compact information for dataset */
+    H5O_efl_t   efl;            /* External file list information for dataset */
+} H5D_storage_t;
+
 /* Typedef for raw data I/O operation info */
 typedef struct H5D_io_info_t {
     H5D_t *dset;                /* Pointer to dataset being operated on */
 #ifndef H5_HAVE_PARALLEL
     const
 #endif /* H5_HAVE_PARALLEL */
-        H5D_dxpl_cache_t *dxpl_cache; /* Pointer to cache DXPL info */
+        H5D_dxpl_cache_t *dxpl_cache; /* Pointer to cached DXPL info */
     hid_t dxpl_id;              /* Original DXPL ID */
 #ifdef H5_HAVE_PARALLEL
     MPI_Comm comm;              /* MPI communicator for file */
-    hbool_t xfer_mode_changed;  /* Whether the transfer mode was changed */
-    hbool_t xfer_opt_mode_changed;
     hbool_t using_mpi_vfd;      /* Whether the file is using an MPI-based VFD */
+    struct {
+        H5FD_mpio_xfer_t xfer_mode; /* Parallel transfer for this request (H5D_XFER_IO_XFER_MODE_NAME) */
+        H5FD_mpio_collective_opt_t coll_opt_mode; /* Parallel transfer with independent IO or collective IO with this mode */
+        H5D_io_ops_t io_ops;    /* I/O operation function pointers */
+    } orig;                     
 #endif /* H5_HAVE_PARALLEL */
-    const H5D_storage_t *store; /* Dataset storage info */
-    H5D_io_ops_t ops;           /* I/O operation function pointers */
-#ifdef H5S_DEBUG
-    H5S_iostats_t *stats;       /* I/O statistics */
-#endif /* H5S_DEBUG */
+    H5D_storage_t *store;       /* Dataset storage info */
+    H5D_layout_ops_t layout_ops;    /* Dataset layout I/O operation function pointers */
+    H5D_io_ops_t io_ops;        /* I/O operation function pointers */
+    enum {
+        H5D_IO_OP_READ,         /* Read operation */
+        H5D_IO_OP_WRITE         /* Write operation */
+    } op_type;
+    union {
+        void *rbuf;             /* Pointer to buffer for read */
+        const void *wbuf;       /* Pointer to buffer to write */
+    } u;
 } H5D_io_info_t;
 
 /* Structure holding information about a chunk's selection for mapping */
@@ -183,8 +265,8 @@ typedef struct H5D_shared_t {
     hbool_t             layout_dirty;   /* Whether the layout info needs to be flushed to the file */
     hid_t               dcpl_id;        /* dataset creation property id */
     H5D_dcpl_cache_t    dcpl_cache;     /* Cached DCPL values */
-    H5D_io_ops_t        io_ops;         /* I/O operations */
     H5O_layout_t        layout;         /* data layout                  */
+    const H5D_layout_ops_t *layout_ops; /* Pointer to data layout I/O operations */
     hbool_t             checked_filters;/* TRUE if dataset passes can_apply check */
 
     /* Buffered/cached information for types of raw data storage*/
@@ -229,18 +311,21 @@ typedef struct H5D_chunk_map_t {
     H5S_sel_type msel_type;     /* Selection type in memory */
 
     H5SL_t *sel_chunks;         /* Skip list containing information for each chunk selected */
+
     H5S_t  *single_space;       /* Dataspace for single chunk */
     H5D_chunk_info_t *single_chunk_info;  /* Pointer to single chunk's info */
     hbool_t use_single;         /* Whether I/O is on a single element */
+
     hsize_t last_index;         /* Index of last chunk operated on */
     H5D_chunk_info_t *last_chunk_info;  /* Pointer to last chunk's info */
+
     hsize_t chunks[H5O_LAYOUT_NDIMS];   /* Number of chunks in each dimension */
     hsize_t chunk_dim[H5O_LAYOUT_NDIMS];    /* Size of chunk in each dimension */
     hsize_t down_chunks[H5O_LAYOUT_NDIMS];   /* "down" size of number of chunks in each dimension */
 
 #ifdef H5_HAVE_PARALLEL
-    hsize_t total_chunks;       /* Number of total chunks */
-    hbool_t *select_chunk;         /* store the information about whether this chunk is selected or not */
+    hsize_t total_chunks;       /* Number of chunks covered by dataspace */
+    H5D_chunk_info_t **select_chunk;    /* Store the information about whether this chunk is selected or not */
 #endif /* H5_HAVE_PARALLEL */
 } H5D_chunk_map_t;
 
@@ -332,12 +417,34 @@ typedef struct {
     hsize_t size;       /* Accumulated number of bytes for the selection */
 } H5D_vlen_bufsize_t;
 
+/* Raw data chunks are cached.  Each entry in the cache is: */
+typedef struct H5D_rdcc_ent_t {
+    hbool_t	locked;		/*entry is locked in cache		*/
+    hbool_t	dirty;		/*needs to be written to disk?		*/
+    hsize_t	offset[H5O_LAYOUT_NDIMS]; /*chunk name			*/
+    size_t	rd_count;	/*bytes remaining to be read		*/
+    size_t	wr_count;	/*bytes remaining to be written		*/
+    size_t	chunk_size;	/*size of a chunk			*/
+    size_t	alloc_size;	/*amount allocated for the chunk	*/
+    uint8_t	*chunk;		/*the unfiltered chunk data		*/
+    unsigned	idx;		/*index in hash table			*/
+    struct H5D_rdcc_ent_t *next;/*next item in doubly-linked list	*/
+    struct H5D_rdcc_ent_t *prev;/*previous item in doubly-linked list	*/
+} H5D_rdcc_ent_t;
+typedef H5D_rdcc_ent_t *H5D_rdcc_ent_ptr_t; /* For free lists */
+
 
 /*****************************/
 /* Package Private Variables */
 /*****************************/
 extern H5D_dxpl_cache_t H5D_def_dxpl_cache;
 
+/* Storage layout classes */
+H5_DLLVAR const H5D_layout_ops_t H5D_LOPS_CONTIG[1];
+H5_DLLVAR const H5D_layout_ops_t H5D_LOPS_EFL[1];
+H5_DLLVAR const H5D_layout_ops_t H5D_LOPS_COMPACT[1];
+H5_DLLVAR const H5D_layout_ops_t H5D_LOPS_CHUNK[1];
+
 
 /******************************/
 /* Package Private Prototypes */
@@ -361,54 +468,51 @@ H5_DLL herr_t H5D_vlen_get_buf_size(void *elem, hid_t type_id, unsigned ndim,
     const hsize_t *point, void *op_data);
 H5_DLL herr_t H5D_check_filters(H5D_t *dataset);
 H5_DLL herr_t H5D_set_extent(H5D_t *dataset, const hsize_t *size, hid_t dxpl_id);
-
-/* Functions that perform serial I/O operations */
-H5_DLL herr_t H5D_select_fscat(H5D_io_info_t *io_info,
-    const H5S_t *file_space, H5S_sel_iter_t *file_iter, size_t nelmts,
-    haddr_t chunk_addr, void *chunk, const void *_buf);
-H5_DLL size_t H5D_select_fgath(H5D_io_info_t *io_info,
-    const H5S_t *file_space, H5S_sel_iter_t *file_iter, size_t nelmts,
-    haddr_t chunk_addr, void *chunk, void *buf);
-H5_DLL herr_t H5D_select_mscat(const void *_tscat_buf,
+H5_DLL herr_t H5D_get_dxpl_cache(hid_t dxpl_id, H5D_dxpl_cache_t **cache);
+
+/* Functions that perform direct serial I/O operations */
+H5_DLL herr_t H5D_select_read(const H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
+H5_DLL herr_t H5D_select_write(const H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
+
+/* Functions that perform scatter-gather serial I/O operations */
+H5_DLL herr_t H5D_scatter_mem(const void *_tscat_buf,
     const H5S_t *space, H5S_sel_iter_t *iter, size_t nelmts,
-    const H5D_dxpl_cache_t *dxpl_cache, void *_buf/*out*/);
-H5_DLL size_t H5D_select_mgath(const void *_buf,
-    const H5S_t *space, H5S_sel_iter_t *iter, size_t nelmts,
-    const H5D_dxpl_cache_t *dxpl_cache, void *_tgath_buf/*out*/);
-H5_DLL herr_t H5D_select_read(H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const H5S_t *file_space, const H5S_t *mem_space,
-    haddr_t addr, void *chunk/*in*/, void *buf/*out*/);
-H5_DLL herr_t H5D_select_write(H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const H5S_t *file_space, const H5S_t *mem_space,
-    haddr_t addr, void *chunk/*in*/, const void *buf/*out*/);
+    const H5D_dxpl_cache_t *dxpl_cache, void *_buf);
+H5_DLL herr_t H5D_scatgath_read(const H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
+H5_DLL herr_t H5D_scatgath_write(const H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
 
 /* Functions that operate on contiguous storage */
 H5_DLL herr_t H5D_contig_create(H5F_t *f, hid_t dxpl_id, H5O_layout_t *layout);
 H5_DLL herr_t H5D_contig_fill(H5D_t *dset, hid_t dxpl_id);
 H5_DLL haddr_t H5D_contig_get_addr(const H5D_t *dset);
+H5_DLL herr_t H5D_contig_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *fm);
+H5_DLL herr_t H5D_contig_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space,
+    H5D_chunk_map_t *fm);
 H5_DLL ssize_t H5D_contig_readvv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED address, void UNUSED *pointer, void *buf);
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[]);
 H5_DLL ssize_t H5D_contig_writevv(const H5D_io_info_t *io_info,
     size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED address, void UNUSED *pointer, const void *buf);
+    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[]);
 H5_DLL herr_t H5D_contig_copy(H5F_t *f_src, const H5O_layout_t *layout_src, H5F_t *f_dst, 
     H5O_layout_t *layout_dst, H5T_t *src_dtype, H5O_copy_t *cpy_info, hid_t dxpl_id);
 
+/* Functions that operate on chunked dataset storage */
+H5_DLL hbool_t H5D_chunk_cacheable(const H5D_io_info_t *io_info, haddr_t caddr);
+
 /* Functions that operate on compact dataset storage */
 H5_DLL herr_t H5D_compact_fill(H5D_t *dset, hid_t dxpl_id);
-H5_DLL ssize_t H5D_compact_readvv(const H5D_io_info_t *io_info,
-    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_size_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED addr, void UNUSED *pointer/*in*/, void *buf);
-H5_DLL ssize_t H5D_compact_writevv(const H5D_io_info_t *io_info,
-    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_size_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_size_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED addr, void UNUSED *pointer/*in*/, const void *buf);
 H5_DLL herr_t H5D_compact_copy(H5F_t *f_src, H5O_layout_t *layout_src,
     H5F_t *f_dst, H5O_layout_t *layout_dst, H5T_t *src_dtype, H5O_copy_t *cpy_info, hid_t dxpl_id);
 
@@ -430,19 +534,11 @@ H5_DLL herr_t H5D_istore_initialize_by_extent(H5D_io_info_t *io_info);
 H5_DLL herr_t H5D_istore_update_cache(H5D_t *dset, hid_t dxpl_id);
 H5_DLL herr_t H5D_istore_dump_btree(H5F_t *f, hid_t dxpl_id, FILE *stream, unsigned ndims,
         haddr_t addr);
-H5_DLL herr_t H5D_istore_chunkmap(const H5D_io_info_t *io_info, haddr_t chunk_addr[],hsize_t down_chunks[] );
+H5_DLL herr_t H5D_istore_chunkmap(const H5D_io_info_t *io_info,
+    haddr_t chunk_addr[], const hsize_t down_chunks[]);
 #ifdef H5D_ISTORE_DEBUG
 H5_DLL herr_t H5D_istore_stats (H5D_t *dset, hbool_t headers);
 #endif /* H5D_ISTORE_DEBUG */
-H5_DLL ssize_t H5D_istore_readvv(const H5D_io_info_t *io_info,
-    size_t chunk_max_nseq, size_t *chunk_curr_seq, size_t chunk_len_arr[],
-    hsize_t chunk_offset_arr[], size_t mem_max_nseq, size_t *mem_curr_seq,
-    size_t mem_len_arr[], hsize_t mem_offset_arr[], haddr_t chunk_addr, void *chunk, void *buf);
-H5_DLL ssize_t H5D_istore_writevv(const H5D_io_info_t *io_info,
-    size_t chunk_max_nseq, size_t *chunk_curr_seq, size_t chunk_len_arr[],
-    hsize_t chunk_offset_arr[], size_t mem_max_nseq, size_t *mem_curr_seq,
-    size_t mem_len_arr[], hsize_t mem_offset_arr[], haddr_t chunk_addr, void *chunk, 
-    const void *buf);
 H5_DLL haddr_t H5D_istore_get_addr(const H5D_io_info_t *io_info,
     struct H5D_istore_ud1_t *_udata);
 H5_DLL herr_t H5D_istore_copy(H5F_t *f_src, H5O_layout_t *layout_src,
@@ -452,17 +548,6 @@ H5_DLL void * H5D_istore_lock(const H5D_io_info_t *io_info, H5D_istore_ud1_t *ud
     hbool_t relax, unsigned *idx_hint/*in,out*/);
 H5_DLL herr_t H5D_istore_unlock(const H5D_io_info_t *io_info,
     hbool_t dirty, unsigned idx_hint, void *chunk, size_t naccessed);
-H5_DLL hbool_t H5D_istore_if_load(const H5D_io_info_t *io_info, haddr_t caddr);
-
-/* Functions that operate on external file list (efl) storage */
-H5_DLL ssize_t H5D_efl_readvv(const H5D_io_info_t *io_info,
-    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED addr, void UNUSED *pointer/*in*/, void *buf);
-H5_DLL ssize_t H5D_efl_writevv(const H5D_io_info_t *io_info,
-    size_t dset_max_nseq, size_t *dset_curr_seq, size_t dset_len_arr[], hsize_t dset_offset_arr[],
-    size_t mem_max_nseq, size_t *mem_curr_seq, size_t mem_len_arr[], hsize_t mem_offset_arr[],
-    haddr_t UNUSED addr, void UNUSED *pointer/*in*/, const void *buf);
 
 /* Functions that perform fill value operations on datasets */
 H5_DLL herr_t H5D_fill(const void *fill, const H5T_t *fill_type, void *buf,
@@ -485,36 +570,37 @@ H5_DLL herr_t H5D_fill_term(H5D_fill_buf_info_t *fb_info);
 #define H5Dmpio_DEBUG
 #endif /*H5Dmpio_DEBUG*/
 #endif/*H5S_DEBUG*/
-/* MPI-IO function to read , it will select either regular or irregular read */
-H5_DLL herr_t H5D_mpio_select_read(H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const struct H5S_t *file_space, const struct H5S_t *mem_space,
-    haddr_t addr, void UNUSED *pointer/*in*/, void *buf/*out*/);
-
-/* MPI-IO function to read , it will select either regular or irregular read */
-H5_DLL herr_t H5D_mpio_select_write(H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const struct H5S_t *file_space, const struct H5S_t *mem_space,
-    haddr_t addr, void UNUSED *pointer/*in*/, const void *buf);
-
-/* MPI-IO function to handle contiguous collective IO */
-H5_DLL herr_t
-H5D_contig_collective_io(H5D_io_info_t *io_info,
-			 const H5S_t *file_space,const H5S_t *mem_space,
-			 const void *_buf,hbool_t do_write);
-
-/* MPI-IO function to handle chunked collective IO */
-H5_DLL herr_t
-H5D_chunk_collective_io(H5D_io_info_t * io_info, H5D_chunk_map_t *fm, const void*buf,
-			hbool_t do_write);
+/* MPI-IO function to read, it will select either regular or irregular read */
+H5_DLL herr_t H5D_mpio_select_read(const H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
+
+/* MPI-IO function to write, it will select either regular or irregular read */
+H5_DLL herr_t H5D_mpio_select_write(const H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space);
+
+/* MPI-IO functions to handle contiguous collective IO */
+H5_DLL herr_t H5D_contig_collective_read(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, hsize_t nelmts, const H5S_t *file_space,
+    const H5S_t *mem_space, H5D_chunk_map_t *fm);
+H5_DLL herr_t H5D_contig_collective_write(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, hsize_t nelmts, const H5S_t *file_space,
+    const H5S_t *mem_space, H5D_chunk_map_t *fm);
+
+/* MPI-IO functions to handle chunked collective IO */
+H5_DLL herr_t H5D_chunk_collective_read(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, hsize_t nelmts, const H5S_t *file_space,
+    const H5S_t *mem_space, H5D_chunk_map_t *fm);
+H5_DLL herr_t H5D_chunk_collective_write(H5D_io_info_t *io_info,
+    const H5D_type_info_t *type_info, hsize_t nelmts, const H5S_t *file_space,
+    const H5S_t *mem_space, H5D_chunk_map_t *fm);
+
 /* MPI-IO function to check if a direct I/O transfer is possible between
  * memory and the file */
-H5_DLL htri_t H5D_mpio_opt_possible(const H5D_io_info_t *io_info, const H5S_t *mem_space,
-    const H5S_t *file_space, const H5T_path_t *tpath);
-
-#ifndef H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS
-H5_DLL herr_t  H5D_mpio_chunk_adjust_iomode(H5D_io_info_t *io_info, const H5D_chunk_map_t *fm);
-#endif /* H5_MPI_SPECIAL_COLLECTIVE_IO_WORKS */
+H5_DLL htri_t H5D_mpio_opt_possible(const H5D_io_info_t *io_info,
+    const H5S_t *file_space, const H5S_t *mem_space,
+    const H5D_type_info_t *type_info, const H5D_chunk_map_t *fm);
 
 #endif /* H5_HAVE_PARALLEL */
 
diff --git a/src/H5Dprivate.h b/src/H5Dprivate.h
index 410dc43..8cf134f 100644
--- a/src/H5Dprivate.h
+++ b/src/H5Dprivate.h
@@ -65,7 +65,6 @@
 #define H5D_XFER_HYPER_VECTOR_SIZE_NAME "vec_size"      /* Hyperslab vector size */
 #ifdef H5_HAVE_PARALLEL
 #define H5D_XFER_IO_XFER_MODE_NAME      "io_xfer_mode"  /* I/O transfer mode */
-#define H5D_XFER_IO_XFER_OPT_MODE_NAME  "io_xfer_opt_mode" /* I/O optimization transfer mode (using MPI-IO independent IO with file set view) */
 #define H5D_XFER_MPIO_COLLECTIVE_OPT_NAME "mpio_collective_opt" /* Optimization of MPI-IO transfer mode */
 #define H5D_XFER_MPIO_CHUNK_OPT_HARD_NAME "mpio_chunk_opt_hard"
 #define H5D_XFER_MPIO_CHUNK_OPT_NUM_NAME "mpio_chunk_opt_num"
@@ -107,23 +106,6 @@
 /* Typedef for dataset in memory (defined in H5Dpkg.h) */
 typedef struct H5D_t H5D_t;
 
-/* Typedef for dataset storage information */
-typedef struct {
-    hsize_t index;          /* "Index" of chunk in dataset (must be first for TBBT routines) */
-    hsize_t *offset;        /* Chunk's coordinates in elements */
-} H5D_chunk_storage_t;
-
-typedef struct {
-    haddr_t dset_addr;      /* Address of dataset in file */
-    hsize_t dset_size;      /* Total size of dataset in file */
-} H5D_contig_storage_t;
-
-typedef union H5D_storage_t {
-    H5O_efl_t   efl;            /* External file list information for dataset */
-    H5D_chunk_storage_t chunk;  /* Chunk information for dataset */
-    H5D_contig_storage_t contig; /* Contiguous information for dataset */
-} H5D_storage_t;
-
 /* Typedef for cached dataset transfer property list information */
 typedef struct H5D_dxpl_cache_t {
     size_t max_temp_buf;        /* Maximum temporary buffer size (H5D_XFER_MAX_TEMP_BUF_NAME) */
@@ -135,7 +117,7 @@ typedef struct H5D_dxpl_cache_t {
     size_t vec_size;            /* Size of hyperslab vector (H5D_XFER_HYPER_VECTOR_SIZE_NAME) */
 #ifdef H5_HAVE_PARALLEL
     H5FD_mpio_xfer_t xfer_mode; /* Parallel transfer for this request (H5D_XFER_IO_XFER_MODE_NAME) */
-    H5FD_mpio_collective_opt_t xfer_opt_mode; /* Parallel transfer with independent IO or collective IO with this mode */
+    H5FD_mpio_collective_opt_t coll_opt_mode; /* Parallel transfer with independent IO or collective IO with this mode */
 #endif /*H5_HAVE_PARALLEL*/
     H5Z_cb_t filter_cb;         /* Filter callback function (H5D_XFER_FILTER_CB_NAME) */
     H5Z_data_xform_t *data_xform_prop; /* Data transform prop (H5D_XFER_XFORM_NAME) */
@@ -163,8 +145,6 @@ H5_DLL H5O_loc_t *H5D_oloc(H5D_t *dataset);
 H5_DLL H5G_name_t *H5D_nameof(H5D_t *dataset);
 H5_DLL H5T_t *H5D_typeof(const H5D_t *dset);
 H5_DLL herr_t H5D_flush(const H5F_t *f, hid_t dxpl_id, unsigned flags);
-H5_DLL herr_t H5D_get_dxpl_cache(hid_t dxpl_id, H5D_dxpl_cache_t **cache);
-H5_DLL herr_t H5D_get_dxpl_cache_real(hid_t dxpl_id, H5D_dxpl_cache_t *cache);
 
 /* Functions that operate on vlen data */
 H5_DLL herr_t H5D_vlen_reclaim(hid_t type_id, H5S_t *space, hid_t plist_id,
diff --git a/src/H5Dscatgath.c b/src/H5Dscatgath.c
new file mode 100644
index 0000000..3ea4c69
--- /dev/null
+++ b/src/H5Dscatgath.c
@@ -0,0 +1,899 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * Copyright by the Board of Trustees of the University of Illinois.         *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the files COPYING and Copyright.html.  COPYING can be found at the root   *
+ * of the source code distribution tree; Copyright.html can be found at the  *
+ * root level of an installed copy of the electronic HDF5 document set and   *
+ * is linked from the top-level documents page.  It can also be found at     *
+ * http://hdfgroup.org/HDF5/doc/Copyright.html.  If you do not have          *
+ * access to either file, you may request a copy from help@hdfgroup.org.     *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/****************/
+/* Module Setup */
+/****************/
+
+#define H5D_PACKAGE		/*suppress error about including H5Dpkg	  */
+
+
+/***********/
+/* Headers */
+/***********/
+#include "H5private.h"		/* Generic Functions			*/
+#include "H5Dpkg.h"		/* Dataset functions			*/
+#include "H5Eprivate.h"		/* Error handling		  	*/
+#include "H5FLprivate.h"	/* Free Lists                           */
+
+
+/****************/
+/* Local Macros */
+/****************/
+
+
+/******************/
+/* Local Typedefs */
+/******************/
+
+
+/********************/
+/* Local Prototypes */
+/********************/
+static size_t H5D_gather_file(const H5D_io_info_t *io_info,
+    const H5S_t *file_space, H5S_sel_iter_t *file_iter, size_t nelmts,
+    void *buf);
+static herr_t H5D_scatter_file(const H5D_io_info_t *io_info,
+    const H5S_t *file_space, H5S_sel_iter_t *file_iter, size_t nelmts,
+    const void *buf);
+static size_t H5D_gather_mem(const void *_buf,
+    const H5S_t *space, H5S_sel_iter_t *iter, size_t nelmts,
+    const H5D_dxpl_cache_t *dxpl_cache, void *_tgath_buf/*out*/);
+static herr_t H5D_compound_opt_read(size_t nelmts, const H5S_t *mem_space,
+    H5S_sel_iter_t *iter, const H5D_dxpl_cache_t *dxpl_cache,
+    const H5D_type_info_t *type_info, void *user_buf/*out*/);
+static herr_t H5D_compound_opt_write(size_t nelmts, const H5D_type_info_t *type_info);
+
+
+/*********************/
+/* Package Variables */
+/*********************/
+
+
+/*******************/
+/* Local Variables */
+/*******************/
+
+/* Declare a free list to manage sequences of size_t */
+H5FL_SEQ_EXTERN(size_t);
+
+/* Declare a free list to manage sequences of hsize_t */
+H5FL_SEQ_EXTERN(hsize_t);
+
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_scatter_file
+ *
+ * Purpose:	Scatters dataset elements from the type conversion buffer BUF
+ *		to the file F where the data points are arranged according to
+ *		the file dataspace FILE_SPACE and stored according to
+ *		LAYOUT and EFL. Each element is ELMT_SIZE bytes.
+ *		The caller is requesting that NELMTS elements are copied.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Thursday, June 20, 2002
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_scatter_file(const H5D_io_info_t *_io_info,
+    const H5S_t *space, H5S_sel_iter_t *iter, size_t nelmts,
+    const void *_buf)
+{
+    H5D_io_info_t tmp_io_info;     /* Temporary I/O info object */
+    hsize_t _off[H5D_IO_VECTOR_SIZE];             /* Array to store sequence offsets */
+    hsize_t *off = NULL;           /* Pointer to sequence offsets */
+    hsize_t mem_off;               /* Offset in memory */
+    size_t mem_curr_seq;           /* "Current sequence" in memory */
+    size_t dset_curr_seq;          /* "Current sequence" in dataset */
+    size_t _len[H5D_IO_VECTOR_SIZE];              /* Array to store sequence lengths */
+    size_t *len = NULL;            /* Array to store sequence lengths */
+    size_t orig_mem_len, mem_len;  /* Length of sequence in memory */
+    size_t  nseq;                  /* Number of sequences generated */
+    size_t  nelem;                 /* Number of elements used in sequences */
+    herr_t  ret_value = SUCCEED;   /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_scatter_file)
+
+    /* Check args */
+    HDassert(_io_info);
+    HDassert(space);
+    HDassert(iter);
+    HDassert(nelmts > 0);
+    HDassert(_buf);
+
+    /* Set up temporary I/O info object */
+    HDmemcpy(&tmp_io_info, _io_info, sizeof(*_io_info));
+    tmp_io_info.op_type = H5D_IO_OP_WRITE;
+    tmp_io_info.u.wbuf = _buf;
+
+    /* Allocate the vector I/O arrays */
+    if(tmp_io_info.dxpl_cache->vec_size > H5D_IO_VECTOR_SIZE) {
+        if(NULL == (len = H5FL_SEQ_MALLOC(size_t, tmp_io_info.dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array")
+        if(NULL == (off = H5FL_SEQ_MALLOC(hsize_t, tmp_io_info.dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array")
+    } /* end if */
+    else {
+        len = _len;
+        off = _off;
+    } /* end else */
+
+    /* Loop until all elements are written */
+    while(nelmts > 0) {
+        /* Get list of sequences for selection to write */
+        if(H5S_SELECT_GET_SEQ_LIST(space, H5S_GET_SEQ_LIST_SORTED, iter, tmp_io_info.dxpl_cache->vec_size, nelmts, &nseq, &nelem, off, len) < 0)
+            HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
+
+        /* Reset the current sequence information */
+        mem_curr_seq = dset_curr_seq = 0;
+        orig_mem_len = mem_len = nelem * iter->elmt_size;
+        mem_off = 0;
+
+        /* Write sequence list out */
+        if((*tmp_io_info.layout_ops.writevv)(&tmp_io_info, nseq, &dset_curr_seq,
+                len, off, (size_t)1, &mem_curr_seq, &mem_len, &mem_off) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
+
+        /* Update buffer */
+        tmp_io_info.u.wbuf = (const uint8_t *)tmp_io_info.u.wbuf + orig_mem_len;
+
+        /* Decrement number of elements left to process */
+        nelmts -= nelem;
+    } /* end while */
+
+done:
+    /* Release resources, if allocated */
+    if(len && len != _len)
+        H5FL_SEQ_FREE(size_t, len);
+    if(off && off != _off)
+        H5FL_SEQ_FREE(hsize_t, off);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5D_scatter_file() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_gather_file
+ *
+ * Purpose:	Gathers data points from file F and accumulates them in the
+ *		type conversion buffer BUF.  The LAYOUT argument describes
+ *		how the data is stored on disk and EFL describes how the data
+ *		is organized in external files.  ELMT_SIZE is the size in
+ *		bytes of a datum which this function treats as opaque.
+ *		FILE_SPACE describes the dataspace of the dataset on disk
+ *		and the elements that have been selected for reading (via
+ *		hyperslab, etc).  This function will copy at most NELMTS
+ *		elements.
+ *
+ * Return:	Success:	Number of elements copied.
+ *		Failure:	0
+ *
+ * Programmer:	Quincey Koziol
+ *              Monday, June 24, 2002
+ *
+ *-------------------------------------------------------------------------
+ */
+static size_t
+H5D_gather_file(const H5D_io_info_t *_io_info,
+    const H5S_t *space, H5S_sel_iter_t *iter, size_t nelmts,
+    void *_buf/*out*/)
+{
+    H5D_io_info_t tmp_io_info;  /* Temporary I/O info object */
+    hsize_t _off[H5D_IO_VECTOR_SIZE];   /* Array to store sequence offsets */
+    hsize_t *off = NULL;        /* Pointer to sequence offsets */
+    hsize_t mem_off;            /* Offset in memory */
+    size_t mem_curr_seq;        /* "Current sequence" in memory */
+    size_t dset_curr_seq;       /* "Current sequence" in dataset */
+    size_t _len[H5D_IO_VECTOR_SIZE];    /* Array to store sequence lengths */
+    size_t *len = NULL;         /* Pointer to sequence lengths */
+    size_t orig_mem_len, mem_len;       /* Length of sequence in memory */
+    size_t nseq;                /* Number of sequences generated */
+    size_t nelem;               /* Number of elements used in sequences */
+    size_t ret_value = nelmts;  /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_gather_file)
+
+    /* Check args */
+    HDassert(_io_info);
+    HDassert(_io_info->dset);
+    HDassert(_io_info->store);
+    HDassert(space);
+    HDassert(iter);
+    HDassert(nelmts > 0);
+    HDassert(_buf);
+
+    /* Set up temporary I/O info object */
+    HDmemcpy(&tmp_io_info, _io_info, sizeof(*_io_info));
+    tmp_io_info.op_type = H5D_IO_OP_READ;
+    tmp_io_info.u.rbuf = _buf;
+
+    /* Allocate the vector I/O arrays */
+    if(tmp_io_info.dxpl_cache->vec_size > H5D_IO_VECTOR_SIZE) {
+        if(NULL == (len = H5FL_SEQ_MALLOC(size_t, tmp_io_info.dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O length vector array")
+        if(NULL == (off = H5FL_SEQ_MALLOC(hsize_t, tmp_io_info.dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O offset vector array")
+    } /* end if */
+    else {
+        len = _len;
+        off = _off;
+    } /* end else */
+
+    /* Loop until all elements are read */
+    while(nelmts > 0) {
+        /* Get list of sequences for selection to read */
+        if(H5S_SELECT_GET_SEQ_LIST(space, H5S_GET_SEQ_LIST_SORTED, iter, tmp_io_info.dxpl_cache->vec_size, nelmts, &nseq, &nelem, off, len) < 0)
+            HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed")
+
+        /* Reset the current sequence information */
+        mem_curr_seq = dset_curr_seq = 0;
+        orig_mem_len = mem_len = nelem * iter->elmt_size;
+        mem_off = 0;
+
+        /* Read sequence list in */
+        if((*tmp_io_info.layout_ops.readvv)(&tmp_io_info, nseq, &dset_curr_seq,
+                len, off, (size_t)1, &mem_curr_seq, &mem_len, &mem_off) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, 0, "read error")
+
+        /* Update buffer */
+        tmp_io_info.u.rbuf = (uint8_t *)tmp_io_info.u.rbuf + orig_mem_len;
+
+        /* Decrement number of elements left to process */
+        nelmts -= nelem;
+    } /* end while */
+
+done:
+    /* Release resources, if allocated */
+    if(len && len != _len)
+        H5FL_SEQ_FREE(size_t, len);
+    if(off && off != _off)
+        H5FL_SEQ_FREE(hsize_t, off);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5D_gather_file() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_scatter_mem
+ *
+ * Purpose:	Scatters NELMTS data points from the scatter buffer
+ *		TSCAT_BUF to the application buffer BUF.  Each element is
+ *		ELMT_SIZE bytes and they are organized in application memory
+ *		according to SPACE.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Monday, July 8, 2002
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_scatter_mem (const void *_tscat_buf, const H5S_t *space,
+    H5S_sel_iter_t *iter, size_t nelmts, const H5D_dxpl_cache_t *dxpl_cache,
+    void *_buf/*out*/)
+{
+    uint8_t *buf = (uint8_t *)_buf;   /* Get local copies for address arithmetic */
+    const uint8_t *tscat_buf = (const uint8_t *)_tscat_buf;
+    hsize_t _off[H5D_IO_VECTOR_SIZE];          /* Array to store sequence offsets */
+    hsize_t *off = NULL;          /* Pointer to sequence offsets */
+    size_t _len[H5D_IO_VECTOR_SIZE];           /* Array to store sequence lengths */
+    size_t *len = NULL;           /* Pointer to sequence lengths */
+    size_t curr_len;            /* Length of bytes left to process in sequence */
+    size_t nseq;                /* Number of sequences generated */
+    size_t curr_seq;            /* Current sequence being processed */
+    size_t nelem;               /* Number of elements used in sequences */
+    herr_t ret_value = SUCCEED;   /* Number of elements scattered */
+
+    FUNC_ENTER_NOAPI(H5D_scatter_mem, FAIL)
+
+    /* Check args */
+    HDassert(tscat_buf);
+    HDassert(space);
+    HDassert(iter);
+    HDassert(nelmts > 0);
+    HDassert(buf);
+
+    /* Allocate the vector I/O arrays */
+    if(dxpl_cache->vec_size > H5D_IO_VECTOR_SIZE) {
+        if(NULL == (len = H5FL_SEQ_MALLOC(size_t, dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array")
+        if(NULL == (off = H5FL_SEQ_MALLOC(hsize_t, dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array")
+    } /* end if */
+    else {
+        len = _len;
+        off = _off;
+    } /* end else */
+
+    /* Loop until all elements are written */
+    while(nelmts > 0) {
+        /* Get list of sequences for selection to write */
+        if(H5S_SELECT_GET_SEQ_LIST(space, 0, iter, dxpl_cache->vec_size, nelmts, &nseq, &nelem, off, len) < 0)
+            HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed")
+
+        /* Loop, while sequences left to process */
+        for(curr_seq = 0; curr_seq < nseq; curr_seq++) {
+            /* Get the number of bytes in sequence */
+            curr_len = len[curr_seq];
+
+            HDmemcpy(buf + off[curr_seq], tscat_buf, curr_len);
+
+            /* Advance offset in destination buffer */
+            tscat_buf += curr_len;
+        } /* end for */
+
+        /* Decrement number of elements left to process */
+        nelmts -= nelem;
+    } /* end while */
+
+done:
+    /* Release resources, if allocated */
+    if(len && len != _len)
+        H5FL_SEQ_FREE(size_t, len);
+    if(off && off != _off)
+        H5FL_SEQ_FREE(hsize_t, off);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+}   /* H5D_scatter_mem() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_gather_mem
+ *
+ * Purpose:	Gathers dataset elements from application memory BUF and
+ *		copies them into the gather buffer TGATH_BUF.
+ *		Each element is ELMT_SIZE bytes and arranged in application
+ *		memory according to SPACE.
+ *		The caller is requesting that at most NELMTS be gathered.
+ *
+ * Return:	Success:	Number of elements copied.
+ *		Failure:	0
+ *
+ * Programmer:	Quincey Koziol
+ *              Monday, June 24, 2002
+ *
+ *-------------------------------------------------------------------------
+ */
+static size_t
+H5D_gather_mem(const void *_buf, const H5S_t *space,
+    H5S_sel_iter_t *iter, size_t nelmts, const H5D_dxpl_cache_t *dxpl_cache,
+    void *_tgath_buf/*out*/)
+{
+    const uint8_t *buf = (const uint8_t *)_buf;   /* Get local copies for address arithmetic */
+    uint8_t *tgath_buf = (uint8_t *)_tgath_buf;
+    hsize_t _off[H5D_IO_VECTOR_SIZE];          /* Array to store sequence offsets */
+    hsize_t *off = NULL;          /* Pointer to sequence offsets */
+    size_t _len[H5D_IO_VECTOR_SIZE];           /* Array to store sequence lengths */
+    size_t *len = NULL;           /* Pointer to sequence lengths */
+    size_t curr_len;            /* Length of bytes left to process in sequence */
+    size_t nseq;                /* Number of sequences generated */
+    size_t curr_seq;            /* Current sequence being processed */
+    size_t nelem;               /* Number of elements used in sequences */
+    size_t ret_value = nelmts;    /* Number of elements gathered */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_gather_mem)
+
+    /* Check args */
+    HDassert(buf);
+    HDassert(space);
+    HDassert(iter);
+    HDassert(nelmts > 0);
+    HDassert(tgath_buf);
+
+    /* Allocate the vector I/O arrays */
+    if(dxpl_cache->vec_size > H5D_IO_VECTOR_SIZE) {
+        if(NULL == (len = H5FL_SEQ_MALLOC(size_t, dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O length vector array")
+        if(NULL == (off = H5FL_SEQ_MALLOC(hsize_t, dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O offset vector array")
+    } /* end if */
+    else {
+        len = _len;
+        off = _off;
+    } /* end else */
+
+    /* Loop until all elements are written */
+    while(nelmts > 0) {
+        /* Get list of sequences for selection to write */
+        if(H5S_SELECT_GET_SEQ_LIST(space, 0, iter, dxpl_cache->vec_size, nelmts, &nseq, &nelem, off, len) < 0)
+            HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed")
+
+        /* Loop, while sequences left to process */
+        for(curr_seq = 0; curr_seq < nseq; curr_seq++) {
+            /* Get the number of bytes in sequence */
+            curr_len = len[curr_seq];
+
+            HDmemcpy(tgath_buf, buf + off[curr_seq], curr_len);
+
+            /* Advance offset in gather buffer */
+            tgath_buf += curr_len;
+        } /* end for */
+
+        /* Decrement number of elements left to process */
+        nelmts -= nelem;
+    } /* end while */
+
+done:
+    /* Release resources, if allocated */
+    if(len && len != _len)
+        H5FL_SEQ_FREE(size_t, len);
+    if(off && off != _off)
+        H5FL_SEQ_FREE(hsize_t, off);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+}   /* H5D_gather_mem() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_scatgath_read
+ *
+ * Purpose:	Perform scatter/gather ead from a contiguous [piece of a] dataset.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Thursday, March  6, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_scatgath_read(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space)
+{
+    const H5D_dxpl_cache_t *dxpl_cache = io_info->dxpl_cache;     /* Local pointer to dataset transfer info */
+    void        *buf = io_info->u.rbuf; /* Local pointer to application buffer */
+    H5S_sel_iter_t mem_iter;            /*memory selection iteration info*/
+    hbool_t	mem_iter_init = FALSE;	/*memory selection iteration info has been initialized */
+    H5S_sel_iter_t bkg_iter;            /*background iteration info*/
+    hbool_t	bkg_iter_init = FALSE;	/*background iteration info has been initialized */
+    H5S_sel_iter_t file_iter;           /*file selection iteration info*/
+    hbool_t	file_iter_init = FALSE;	/*file selection iteration info has been initialized */
+    hsize_t	smine_start;		/*strip mine start loc	*/
+    size_t	smine_nelmts;		/*elements per strip	*/
+    herr_t	ret_value = SUCCEED;	/*return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_scatgath_read)
+
+    /* Sanity check */
+    HDassert(io_info);
+    HDassert(type_info);
+    HDassert(mem_space);
+    HDassert(file_space);
+    HDassert(buf);
+
+    /* Check for NOOP read */
+    if(nelmts == 0)
+        HGOTO_DONE(SUCCEED)
+
+    /* Figure out the strip mine size. */
+    if(H5S_select_iter_init(&file_iter, file_space, type_info->src_type_size) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize file selection information")
+    file_iter_init = TRUE;	/*file selection iteration info has been initialized */
+    if(H5S_select_iter_init(&mem_iter, mem_space, type_info->dst_type_size) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize memory selection information")
+    mem_iter_init = TRUE;	/*file selection iteration info has been initialized */
+    if(H5S_select_iter_init(&bkg_iter, mem_space, type_info->dst_type_size) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize background selection information")
+    bkg_iter_init = TRUE;	/*file selection iteration info has been initialized */
+
+    /* Start strip mining... */
+    for(smine_start = 0; smine_start < nelmts; smine_start += smine_nelmts) {
+        size_t n;               /* Elements operated on */
+
+        /* Go figure out how many elements to read from the file */
+        HDassert(H5S_SELECT_ITER_NELMTS(&file_iter) == (nelmts - smine_start));
+        smine_nelmts = (size_t)MIN(type_info->request_nelmts, (nelmts - smine_start));
+
+        /*
+         * Gather the data from disk into the datatype conversion
+         * buffer. Also gather data from application to background buffer
+         * if necessary.
+         */
+
+	/* 
+         * Gather data
+         */
+        n = H5D_gather_file(io_info, file_space, &file_iter, smine_nelmts,
+                type_info->tconv_buf/*out*/);
+	if(n != smine_nelmts)
+            HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "file gather failed")
+
+        /* If the source and destination are compound types and subset of each other
+         * and no conversion is needed, copy the data directly into user's buffer and 
+         * bypass the rest of steps.
+         */
+        if(H5T_SUBSET_FALSE != type_info->cmpd_subset) {
+            if(H5D_compound_opt_read(smine_nelmts, mem_space, &mem_iter, dxpl_cache,
+                    type_info, buf /*out*/) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
+        } /* end if */
+        else {
+            if(H5T_BKG_YES == type_info->need_bkg) {
+                n = H5D_gather_mem(buf, mem_space, &bkg_iter, smine_nelmts,
+                        dxpl_cache, type_info->bkg_buf/*out*/);
+                if(n != smine_nelmts)
+                    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "mem gather failed")
+            } /* end if */
+
+            /*
+             * Perform datatype conversion.
+             */
+            if(H5T_convert(type_info->tpath, type_info->src_type_id, type_info->dst_type_id,
+                    smine_nelmts, (size_t)0, (size_t)0, type_info->tconv_buf,
+                    type_info->bkg_buf, io_info->dxpl_id) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTCONVERT, FAIL, "datatype conversion failed")
+
+            /* Do the data transform after the conversion (since we're using type mem_type) */
+            if(!type_info->is_xform_noop)
+                if(H5Z_xform_eval(dxpl_cache->data_xform_prop, type_info->tconv_buf, smine_nelmts, type_info->mem_type) < 0)
+                    HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "Error performing data transform")
+
+            /*
+             * Scatter the data into memory.
+             */
+            if(H5D_scatter_mem(type_info->tconv_buf, mem_space, &mem_iter,
+                    smine_nelmts, dxpl_cache, buf/*out*/) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "scatter failed")
+        } /* end else */
+    } /* end for */
+
+done:
+    /* Release selection iterators */
+    if(file_iter_init) {
+        if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
+    } /* end if */
+    if(mem_iter_init) {
+        if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
+    } /* end if */
+    if(bkg_iter_init) {
+        if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_scatgath_read() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_scatgath_write
+ *
+ * Purpose:	Perform scatter/gather write to a contiguous [piece of a] dataset.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Thursday, March  6, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_scatgath_write(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space)
+{
+    const H5D_dxpl_cache_t *dxpl_cache = io_info->dxpl_cache;     /* Local pointer to dataset transfer info */
+    const void  *buf = io_info->u.wbuf; /* Local pointer to application buffer */
+    H5S_sel_iter_t mem_iter;            /*memory selection iteration info*/
+    hbool_t	mem_iter_init = FALSE;	/*memory selection iteration info has been initialized */
+    H5S_sel_iter_t bkg_iter;            /*background iteration info*/
+    hbool_t	bkg_iter_init = FALSE;	/*background iteration info has been initialized */
+    H5S_sel_iter_t file_iter;           /*file selection iteration info*/
+    hbool_t	file_iter_init = FALSE;	/*file selection iteration info has been initialized */
+    hsize_t	smine_start;		/*strip mine start loc	*/
+    size_t	smine_nelmts;		/*elements per strip	*/
+    herr_t	ret_value = SUCCEED;	/*return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_scatgath_write)
+
+    /* Sanity check */
+    HDassert(io_info);
+    HDassert(type_info);
+    HDassert(mem_space);
+    HDassert(file_space);
+    HDassert(buf);
+
+    /* Check for NOOP write */
+    if(nelmts == 0)
+        HGOTO_DONE(SUCCEED)
+
+    /* Figure out the strip mine size. */
+    if(H5S_select_iter_init(&file_iter, file_space, type_info->dst_type_size) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize file selection information")
+    file_iter_init = TRUE;	/*file selection iteration info has been initialized */
+    if(H5S_select_iter_init(&mem_iter, mem_space, type_info->src_type_size) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize memory selection information")
+    mem_iter_init = TRUE;	/*file selection iteration info has been initialized */
+    if(H5S_select_iter_init(&bkg_iter, file_space, type_info->dst_type_size) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize background selection information")
+    bkg_iter_init = TRUE;	/*file selection iteration info has been initialized */
+
+    /* Start strip mining... */
+    for(smine_start = 0; smine_start < nelmts; smine_start += smine_nelmts) {
+        size_t n;               /* Elements operated on */
+
+        /* Go figure out how many elements to read from the file */
+        HDassert(H5S_SELECT_ITER_NELMTS(&file_iter) == (nelmts - smine_start));
+        smine_nelmts = (size_t)MIN(type_info->request_nelmts, (nelmts - smine_start));
+
+        /*
+         * Gather data from application buffer into the datatype conversion
+         * buffer. Also gather data from the file into the background buffer
+         * if necessary.
+         */
+        n = H5D_gather_mem(buf, mem_space, &mem_iter, smine_nelmts,
+                dxpl_cache, type_info->tconv_buf/*out*/);
+        if(n != smine_nelmts)
+            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "mem gather failed")
+
+        /* If the source and destination are compound types and the destination is
+         * is a subset of the source and no conversion is needed, copy the data 
+         * directly into user's buffer and bypass the rest of steps.  If the source
+         * is a subset of the destination, the optimization is done in conversion
+         * function H5T_conv_struct_opt to protect the background data.
+         */
+        if(H5T_SUBSET_DST == type_info->cmpd_subset) {
+            if(H5D_compound_opt_write(smine_nelmts, type_info) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "datatype conversion failed")
+        } /* end if */
+        else {
+            if(H5T_BKG_YES == type_info->need_bkg) {
+                n = H5D_gather_file(io_info, file_space, &bkg_iter, smine_nelmts,
+                        type_info->bkg_buf/*out*/);
+                if(n != smine_nelmts)
+                    HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "file gather failed")
+            } /* end if */
+
+            /*
+             * Perform datatype conversion.
+             */
+            if(H5T_convert(type_info->tpath, type_info->src_type_id, type_info->dst_type_id,
+                    smine_nelmts, (size_t)0, (size_t)0, type_info->tconv_buf,
+                    type_info->bkg_buf, io_info->dxpl_id) < 0)
+                 HGOTO_ERROR(H5E_DATASET, H5E_CANTCONVERT, FAIL, "datatype conversion failed")
+
+	    /* Do the data transform after the type conversion (since we're using dataset->shared->type). */
+	    if(!type_info->is_xform_noop)
+	        if(H5Z_xform_eval(dxpl_cache->data_xform_prop, type_info->tconv_buf, smine_nelmts, type_info->dset_type) < 0)
+		    HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "Error performing data transform")
+        } /* end else */
+
+        /*
+         * Scatter the data out to the file.
+         */
+        if(H5D_scatter_file(io_info, file_space, &file_iter, smine_nelmts,
+                type_info->tconv_buf) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "scatter failed")
+    } /* end for */
+
+done:
+    /* Release selection iterators */
+    if(file_iter_init) {
+        if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
+    } /* end if */
+    if(mem_iter_init) {
+        if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
+    } /* end if */
+    if(bkg_iter_init) {
+        if(H5S_SELECT_ITER_RELEASE(&bkg_iter) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "Can't release selection iterator")
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_scatgath_write() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_compound_opt_read
+ *
+ * Purpose:	A special optimization case when the source and 
+ *              destination members are a subset of each other, and 
+ *              the order is the same, and no conversion is needed.  
+ *              For example:
+ *                  struct source {            struct destination {
+ *                      TYPE1 A;      -->          TYPE1 A;
+ *                      TYPE2 B;      -->          TYPE2 B;
+ *                      TYPE3 C;      -->          TYPE3 C;
+ *                  };                             TYPE4 D;
+ *                                                 TYPE5 E;
+ *                                             };
+ *              or
+ *                  struct destination {       struct source {
+ *                      TYPE1 A;      <--          TYPE1 A;
+ *                      TYPE2 B;      <--          TYPE2 B;
+ *                      TYPE3 C;      <--          TYPE3 C;
+ *                  };                             TYPE4 D;
+ *                                                 TYPE5 E;
+ *                                             };
+ *              The optimization is simply moving data to the appropriate 
+ *              places in the buffer.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Raymond Lu
+ *		11 June 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_compound_opt_read(size_t nelmts, const H5S_t *space,
+    H5S_sel_iter_t *iter, const H5D_dxpl_cache_t *dxpl_cache,
+    const H5D_type_info_t *type_info, void *user_buf/*out*/)
+{
+    uint8_t    *ubuf = (uint8_t *)user_buf;     /* Cast for pointer arithmetic	*/
+    uint8_t    *xdbuf;                          /* Pointer into dataset buffer */
+    hsize_t    _off[H5D_IO_VECTOR_SIZE];        /* Array to store sequence offsets */
+    hsize_t    *off = NULL;                     /* Pointer to sequence offsets */
+    size_t     _len[H5D_IO_VECTOR_SIZE];        /* Array to store sequence lengths */
+    size_t     *len = NULL;                     /* Pointer to sequence lengths */
+    size_t     src_stride, dst_stride, type_size;
+    herr_t     ret_value = SUCCEED;	       /*return value		*/
+
+    FUNC_ENTER_NOAPI_NOINIT(H5D_compound_opt_read)
+
+    /* Check args */
+    HDassert(nelmts > 0);
+    HDassert(space);
+    HDassert(iter);
+    HDassert(dxpl_cache);
+    HDassert(type_info);
+    HDassert(user_buf);
+
+    /* Allocate the vector I/O arrays */
+    if(dxpl_cache->vec_size > H5D_IO_VECTOR_SIZE) {
+        if(NULL == (len = H5FL_SEQ_MALLOC(size_t, dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array")
+        if(NULL == (off = H5FL_SEQ_MALLOC(hsize_t, dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array")
+    } /* end if */
+    else {
+        len = _len;
+        off = _off;
+    } /* end else */
+
+    /* Get source & destination strides */
+    src_stride = type_info->src_type_size;
+    dst_stride = type_info->dst_type_size;
+
+    if(H5T_SUBSET_SRC == type_info->cmpd_subset)
+        type_size = src_stride;
+    else {
+        HDassert(H5T_SUBSET_DST == type_info->cmpd_subset);
+        type_size = dst_stride;
+    } /* end else */
+
+    /* Loop until all elements are written */
+    xdbuf = type_info->tconv_buf;
+    while(nelmts > 0) {
+        size_t     nseq;                /* Number of sequences generated */
+        size_t     curr_seq;            /* Current sequence being processed */
+        size_t     elmtno;		/* Element counter */
+
+        /* Get list of sequences for selection to write */
+        if(H5S_SELECT_GET_SEQ_LIST(space, 0, iter, dxpl_cache->vec_size, nelmts, &nseq, &elmtno, off, len) < 0)
+            HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed")
+
+        /* Loop, while sequences left to process */
+        for(curr_seq = 0; curr_seq < nseq; curr_seq++) {
+            size_t     curr_off;        /* Offset of bytes left to process in sequence */
+            size_t     curr_len;        /* Length of bytes left to process in sequence */
+            size_t     curr_nelmts;	/* Number of elements to process in sequence   */
+            uint8_t    *xubuf;
+            size_t     i;               /* Local index variable */
+
+            /* Get the number of bytes and offset in sequence */
+            curr_len = len[curr_seq];
+            curr_off = off[curr_seq];
+
+            /* Decide the number of elements and position in the buffer. */
+            curr_nelmts = curr_len / dst_stride;
+            xubuf = ubuf + curr_off;
+
+            /* Copy the data into the right place. */
+            for(i = 0; i < curr_nelmts; i++) {
+                HDmemmove(xubuf, xdbuf, type_size); 
+
+                /* Update pointers */
+                xdbuf += src_stride;
+                xubuf += dst_stride;
+            } /* end for */
+        } /* end for */
+
+        /* Decrement number of elements left to process */
+        nelmts -= elmtno;
+    } /* end while */
+
+done:
+    /* Release resources, if allocated */
+    if(len && len != _len)
+        H5FL_SEQ_FREE(size_t, len);
+    if(off && off != _off)
+        H5FL_SEQ_FREE(hsize_t, off);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_compound_opt_read() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_compound_opt_write
+ *
+ * Purpose:	A special optimization case when the source and 
+ *              destination members are a subset of each other, and 
+ *              the order is the same, and no conversion is needed.  
+ *              For example:
+ *                  struct source {            struct destination {
+ *                      TYPE1 A;      -->          TYPE1 A;
+ *                      TYPE2 B;      -->          TYPE2 B;
+ *                      TYPE3 C;      -->          TYPE3 C;
+ *                  };                             TYPE4 D;
+ *                                                 TYPE5 E;
+ *                                             };
+ *              or
+ *                  struct destination {       struct source {
+ *                      TYPE1 A;      <--          TYPE1 A;
+ *                      TYPE2 B;      <--          TYPE2 B;
+ *                      TYPE3 C;      <--          TYPE3 C;
+ *                  };                             TYPE4 D;
+ *                                                 TYPE5 E;
+ *                                             };
+ *              The optimization is simply moving data to the appropriate 
+ *              places in the buffer.
+ *
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Raymond Lu
+ *		11 June 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5D_compound_opt_write(size_t nelmts, const H5D_type_info_t *type_info)
+{
+    uint8_t    *xsbuf, *xdbuf;                  /* Source & destination pointers into dataset buffer */
+    size_t     src_stride, dst_stride;          /* Strides through source & destination datatypes */
+    size_t     i;                               /* Local index variable */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5D_compound_opt_write)
+
+    /* Check args */
+    HDassert(nelmts > 0);
+    HDassert(type_info);
+
+    /* Initialize values for loop */
+    src_stride = type_info->src_type_size;
+    dst_stride = type_info->dst_type_size;
+
+    /* Loop until all elements are written */
+    xsbuf = (uint8_t *)type_info->tconv_buf;
+    xdbuf = (uint8_t *)type_info->tconv_buf;
+    for(i = 0; i < nelmts; i++) {
+        HDmemmove(xdbuf, xsbuf, dst_stride); 
+
+        /* Update pointers */
+        xsbuf += src_stride;
+        xdbuf += dst_stride;
+    } /* end for */
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5D_compound_opt_write() */
+
diff --git a/src/H5Dselect.c b/src/H5Dselect.c
index f08672f..947c81e 100644
--- a/src/H5Dselect.c
+++ b/src/H5Dselect.c
@@ -34,400 +34,37 @@
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5FLprivate.h"	/* Free Lists                           */
 
+
 /****************/
 /* Local Macros */
 /****************/
 
+
 /******************/
 /* Local Typedefs */
 /******************/
 
+
 /********************/
 /* Local Prototypes */
 /********************/
 
-/* Struct for holding the vectorized I/O operation buffers "loosely" */
-typedef struct {
-    enum {
-        H5S_SELECT_READ,                /* Read selection */
-        H5S_SELECT_WRITE                /* Write selection */
-    } op_type;
-    union {
-        void *rbuf;                          /* Buffer for read */
-        const void *wbuf;                    /* Buffer to write */
-    } u;
-} H5D_select_buf_t;
 
 /*********************/
 /* Package Variables */
 /*********************/
 
+
 /*******************/
 /* Local Variables */
 /*******************/
 
 /* Declare a free list to manage sequences of size_t */
-H5FL_SEQ_DEFINE_STATIC(size_t);
+H5FL_SEQ_DEFINE(size_t);
 
 /* Declare a free list to manage sequences of hsize_t */
-H5FL_SEQ_DEFINE_STATIC(hsize_t);
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_select_fscat
- *
- * Purpose:	Scatters dataset elements from the type conversion buffer BUF
- *		to the file F where the data points are arranged according to
- *		the file dataspace FILE_SPACE and stored according to
- *		LAYOUT and EFL. Each element is ELMT_SIZE bytes.
- *		The caller is requesting that NELMTS elements are copied.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *              Thursday, June 20, 2002
- *
- *-------------------------------------------------------------------------
- */
-herr_t
-H5D_select_fscat (H5D_io_info_t *io_info,
-    const H5S_t *space, H5S_sel_iter_t *iter, size_t nelmts,
-    haddr_t chunk_addr, void *chunk/*in*/, const void *_buf)
-{
-    const uint8_t *buf=_buf;       /* Alias for pointer arithmetic */
-    hsize_t _off[H5D_IO_VECTOR_SIZE];             /* Array to store sequence offsets */
-    hsize_t *off=NULL;             /* Pointer to sequence offsets */
-    hsize_t mem_off;               /* Offset in memory */
-    size_t mem_curr_seq;           /* "Current sequence" in memory */
-    size_t dset_curr_seq;          /* "Current sequence" in dataset */
-    size_t _len[H5D_IO_VECTOR_SIZE];              /* Array to store sequence lengths */
-    size_t *len=NULL;              /* Array to store sequence lengths */
-    size_t orig_mem_len, mem_len;  /* Length of sequence in memory */
-    size_t  nseq;                  /* Number of sequences generated */
-    size_t  nelem;                 /* Number of elements used in sequences */
-    herr_t  ret_value=SUCCEED;     /* Return value */
-
-    FUNC_ENTER_NOAPI(H5D_select_fscat, FAIL);
-
-    /* Check args */
-    assert (io_info);
-    assert (space);
-    assert (iter);
-    assert (nelmts>0);
-    assert (_buf);
-    assert(TRUE==H5P_isa_class(io_info->dxpl_id,H5P_DATASET_XFER));
-
-    /* Allocate the vector I/O arrays */
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if((len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array");
-        if((off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array");
-    } /* end if */
-    else {
-        len=_len;
-        off=_off;
-    } /* end else */
-
-    /* Loop until all elements are written */
-    while(nelmts>0) {
-        /* Get list of sequences for selection to write */
-        if(H5S_SELECT_GET_SEQ_LIST(space,H5S_GET_SEQ_LIST_SORTED,iter,io_info->dxpl_cache->vec_size,nelmts,&nseq,&nelem,off,len)<0)
-            HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed");
-
-        /* Reset the current sequence information */
-        mem_curr_seq=dset_curr_seq=0;
-        orig_mem_len=mem_len=nelem*iter->elmt_size;
-        mem_off=0;
-
-        /* Write sequence list out */
-        if((*io_info->ops.writevv)(io_info, nseq, &dset_curr_seq, len, off, (size_t)1, &mem_curr_seq, &mem_len, &mem_off, chunk_addr, chunk, buf) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error");
-
-        /* Update buffer */
-        buf += orig_mem_len;
-
-        /* Decrement number of elements left to process */
-        nelmts -= nelem;
-    } /* end while */
-
-done:
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(len!=NULL)
-            H5FL_SEQ_FREE(size_t,len);
-        if(off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,off);
-    } /* end if */
-    FUNC_LEAVE_NOAPI(ret_value);
-} /* H5D_select_fscat() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_select_fgath
- *
- * Purpose:	Gathers data points from file F and accumulates them in the
- *		type conversion buffer BUF.  The LAYOUT argument describes
- *		how the data is stored on disk and EFL describes how the data
- *		is organized in external files.  ELMT_SIZE is the size in
- *		bytes of a datum which this function treats as opaque.
- *		FILE_SPACE describes the dataspace of the dataset on disk
- *		and the elements that have been selected for reading (via
- *		hyperslab, etc).  This function will copy at most NELMTS
- *		elements.
- *
- * Return:	Success:	Number of elements copied.
- *		Failure:	0
- *
- * Programmer:	Quincey Koziol
- *              Monday, June 24, 2002
- *
- *-------------------------------------------------------------------------
- */
-size_t
-H5D_select_fgath (H5D_io_info_t *io_info,
-    const H5S_t *space, H5S_sel_iter_t *iter, size_t nelmts,
-    haddr_t chunk_addr, void *chunk/*in*/, void *_buf/*out*/)
-{
-    uint8_t *buf=(uint8_t*)_buf;          /* Alias for pointer arithmetic */
-    hsize_t _off[H5D_IO_VECTOR_SIZE];          /* Array to store sequence offsets */
-    hsize_t *off=NULL;          /* Pointer to sequence offsets */
-    hsize_t mem_off;            /* Offset in memory */
-    size_t mem_curr_seq;        /* "Current sequence" in memory */
-    size_t dset_curr_seq;       /* "Current sequence" in dataset */
-    size_t _len[H5D_IO_VECTOR_SIZE];           /* Array to store sequence lengths */
-    size_t *len=NULL;           /* Pointer to sequence lengths */
-    size_t orig_mem_len, mem_len;       /* Length of sequence in memory */
-    size_t nseq;                /* Number of sequences generated */
-    size_t nelem;               /* Number of elements used in sequences */
-    size_t ret_value=nelmts;    /* Return value */
-
-    FUNC_ENTER_NOAPI(H5D_select_fgath, 0);
-
-    /* Check args */
-    assert (io_info);
-    assert (io_info->dset);
-    assert (io_info->store);
-    assert (space);
-    assert (iter);
-    assert (nelmts>0);
-    assert (_buf);
-
-    /* Allocate the vector I/O arrays */
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if((len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O length vector array");
-        if((off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O offset vector array");
-    } /* end if */
-    else {
-        len=_len;
-        off=_off;
-    } /* end else */
-
-    /* Loop until all elements are read */
-    while(nelmts>0) {
-        /* Get list of sequences for selection to read */
-        if(H5S_SELECT_GET_SEQ_LIST(space,H5S_GET_SEQ_LIST_SORTED,iter,io_info->dxpl_cache->vec_size,nelmts,&nseq,&nelem,off,len)<0)
-            HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed");
-
-        /* Reset the current sequence information */
-        mem_curr_seq=dset_curr_seq=0;
-        orig_mem_len=mem_len=nelem*iter->elmt_size;
-        mem_off=0;
-
-        /* Read sequence list in */
-        if((*io_info->ops.readvv)(io_info, nseq, &dset_curr_seq, len, off, (size_t)1, 
-                                  &mem_curr_seq, &mem_len, &mem_off, chunk_addr, chunk, buf) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, 0, "read error");
-
-        /* Update buffer */
-        buf += orig_mem_len;
-
-        /* Decrement number of elements left to process */
-        nelmts -= nelem;
-    } /* end while */
-
-done:
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(len!=NULL)
-            H5FL_SEQ_FREE(size_t,len);
-        if(off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,off);
-    } /* end if */
-    FUNC_LEAVE_NOAPI(ret_value);
-} /* H5D_select_fgath() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_select_mscat
- *
- * Purpose:	Scatters NELMTS data points from the scatter buffer
- *		TSCAT_BUF to the application buffer BUF.  Each element is
- *		ELMT_SIZE bytes and they are organized in application memory
- *		according to SPACE.
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *              Monday, July 8, 2002
- *
- *-------------------------------------------------------------------------
- */
-herr_t
-H5D_select_mscat (const void *_tscat_buf, const H5S_t *space,
-    H5S_sel_iter_t *iter, size_t nelmts, const H5D_dxpl_cache_t *dxpl_cache,
-    void *_buf/*out*/)
-{
-    uint8_t *buf=(uint8_t *)_buf;   /* Get local copies for address arithmetic */
-    const uint8_t *tscat_buf=(const uint8_t *)_tscat_buf;
-    hsize_t _off[H5D_IO_VECTOR_SIZE];          /* Array to store sequence offsets */
-    hsize_t *off=NULL;          /* Pointer to sequence offsets */
-    size_t _len[H5D_IO_VECTOR_SIZE];           /* Array to store sequence lengths */
-    size_t *len=NULL;           /* Pointer to sequence lengths */
-    size_t curr_len;            /* Length of bytes left to process in sequence */
-    size_t nseq;                /* Number of sequences generated */
-    size_t curr_seq;            /* Current sequence being processed */
-    size_t nelem;               /* Number of elements used in sequences */
-    herr_t ret_value=SUCCEED;   /* Number of elements scattered */
-
-    FUNC_ENTER_NOAPI(H5D_select_mscat, FAIL);
-
-    /* Check args */
-    assert (tscat_buf);
-    assert (space);
-    assert (iter);
-    assert (nelmts>0);
-    assert (buf);
-
-    /* Allocate the vector I/O arrays */
-    if(dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if((len = H5FL_SEQ_MALLOC(size_t,dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array");
-        if((off = H5FL_SEQ_MALLOC(hsize_t,dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array");
-    } /* end if */
-    else {
-        len=_len;
-        off=_off;
-    } /* end else */
-
-    /* Loop until all elements are written */
-    while(nelmts>0) {
-        /* Get list of sequences for selection to write */
-        if(H5S_SELECT_GET_SEQ_LIST(space,0,iter,dxpl_cache->vec_size,nelmts,&nseq,&nelem,off,len)<0)
-            HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed");
-
-        /* Loop, while sequences left to process */
-        for(curr_seq=0; curr_seq<nseq; curr_seq++) {
-            /* Get the number of bytes in sequence */
-            curr_len=len[curr_seq];
+H5FL_SEQ_DEFINE(hsize_t);
 
-            HDmemcpy(buf+off[curr_seq],tscat_buf,curr_len);
-
-            /* Advance offset in destination buffer */
-            tscat_buf+=curr_len;
-        } /* end for */
-
-        /* Decrement number of elements left to process */
-        nelmts -= nelem;
-    } /* end while */
-
-done:
-    if(dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(len!=NULL)
-            H5FL_SEQ_FREE(size_t,len);
-        if(off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,off);
-    } /* end if */
-    FUNC_LEAVE_NOAPI(ret_value);
-}   /* H5D_select_mscat() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5D_select_mgath
- *
- * Purpose:	Gathers dataset elements from application memory BUF and
- *		copies them into the gather buffer TGATH_BUF.
- *		Each element is ELMT_SIZE bytes and arranged in application
- *		memory according to SPACE.
- *		The caller is requesting that at most NELMTS be gathered.
- *
- * Return:	Success:	Number of elements copied.
- *		Failure:	0
- *
- * Programmer:	Quincey Koziol
- *              Monday, June 24, 2002
- *
- *-------------------------------------------------------------------------
- */
-size_t
-H5D_select_mgath (const void *_buf, const H5S_t *space,
-    H5S_sel_iter_t *iter, size_t nelmts, const H5D_dxpl_cache_t *dxpl_cache,
-    void *_tgath_buf/*out*/)
-{
-    const uint8_t *buf=(const uint8_t *)_buf;   /* Get local copies for address arithmetic */
-    uint8_t *tgath_buf=(uint8_t *)_tgath_buf;
-    hsize_t _off[H5D_IO_VECTOR_SIZE];          /* Array to store sequence offsets */
-    hsize_t *off=NULL;          /* Pointer to sequence offsets */
-    size_t _len[H5D_IO_VECTOR_SIZE];           /* Array to store sequence lengths */
-    size_t *len=NULL;           /* Pointer to sequence lengths */
-    size_t curr_len;            /* Length of bytes left to process in sequence */
-    size_t nseq;                /* Number of sequences generated */
-    size_t curr_seq;            /* Current sequence being processed */
-    size_t nelem;               /* Number of elements used in sequences */
-    size_t ret_value=nelmts;    /* Number of elements gathered */
-
-    FUNC_ENTER_NOAPI(H5D_select_mgath, 0);
-
-    /* Check args */
-    assert (buf);
-    assert (space);
-    assert (iter);
-    assert (nelmts>0);
-    assert (tgath_buf);
-
-    /* Allocate the vector I/O arrays */
-    if(dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if((len = H5FL_SEQ_MALLOC(size_t,dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O length vector array");
-        if((off = H5FL_SEQ_MALLOC(hsize_t,dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, 0, "can't allocate I/O offset vector array");
-    } /* end if */
-    else {
-        len=_len;
-        off=_off;
-    } /* end else */
-
-    /* Loop until all elements are written */
-    while(nelmts>0) {
-        /* Get list of sequences for selection to write */
-        if(H5S_SELECT_GET_SEQ_LIST(space,0,iter,dxpl_cache->vec_size,nelmts,&nseq,&nelem,off,len)<0)
-            HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, 0, "sequence length generation failed");
-
-        /* Loop, while sequences left to process */
-        for(curr_seq=0; curr_seq<nseq; curr_seq++) {
-            /* Get the number of bytes in sequence */
-            curr_len=len[curr_seq];
-
-            HDmemcpy(tgath_buf,buf+off[curr_seq],curr_len);
-
-            /* Advance offset in gather buffer */
-            tgath_buf+=curr_len;
-        } /* end for */
-
-        /* Decrement number of elements left to process */
-        nelmts -= nelem;
-    } /* end while */
-
-done:
-    if(dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(len!=NULL)
-            H5FL_SEQ_FREE(size_t,len);
-        if(off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,off);
-    } /* end if */
-    FUNC_LEAVE_NOAPI(ret_value);
-}   /* H5D_select_mgath() */
 
 
 /*-------------------------------------------------------------------------
@@ -443,11 +80,8 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5D_select_io(H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const H5S_t *file_space, const H5S_t *mem_space,
-    haddr_t addr, void *chunk/*in*/,
-    const H5D_select_buf_t *io_buf)
+H5D_select_io(const H5D_io_info_t *io_info, size_t elmt_size,
+    size_t nelmts, const H5S_t *file_space, const H5S_t *mem_space)
 {
     H5S_sel_iter_t mem_iter;    /* Memory selection iteration info */
     hbool_t mem_iter_init = 0;  /* Memory selection iteration info has been initialized */
@@ -475,10 +109,10 @@ H5D_select_io(H5D_io_info_t *io_info,
     HDassert(io_info->dset);
     HDassert(io_info->store);
     HDassert(TRUE == H5P_isa_class(io_info->dxpl_id, H5P_DATASET_XFER));
-    HDassert(io_buf->u.rbuf);
+    HDassert(io_info->u.rbuf);
 
     /* Allocate the vector I/O arrays */
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
+    if(io_info->dxpl_cache->vec_size > H5D_IO_VECTOR_SIZE) {
         if(NULL == (mem_len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size)))
             HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array")
         if(NULL == (mem_off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size)))
@@ -511,19 +145,17 @@ H5D_select_io(H5D_io_info_t *io_info,
         *file_len = *mem_len = elmt_size;
 
         /* Perform I/O on memory and file sequences */
-        if(io_buf->op_type == H5S_SELECT_READ) {
-            if((tmp_file_len = (*io_info->ops.readvv)(io_info,
+        if(io_info->op_type == H5D_IO_OP_READ) {
+            if((tmp_file_len = (*io_info->layout_ops.readvv)(io_info,
                     file_nseq, &curr_file_seq, file_len, file_off,
-                    mem_nseq, &curr_mem_seq, mem_len, mem_off,
-                    addr, chunk, io_buf->u.rbuf)) < 0)
+                    mem_nseq, &curr_mem_seq, mem_len, mem_off)) < 0)
                 HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
         } /* end if */
         else {
-            HDassert(io_buf->op_type == H5S_SELECT_WRITE);
-            if((tmp_file_len = (*io_info->ops.writevv)(io_info,
+            HDassert(io_info->op_type == H5D_IO_OP_WRITE);
+            if((tmp_file_len = (*io_info->layout_ops.writevv)(io_info,
                     file_nseq, &curr_file_seq, file_len, file_off,
-                    mem_nseq, &curr_mem_seq, mem_len, mem_off,
-                    addr, chunk, io_buf->u.wbuf)) < 0)
+                    mem_nseq, &curr_mem_seq, mem_len, mem_off)) < 0)
                 HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
         } /* end else */
 
@@ -571,19 +203,17 @@ H5D_select_io(H5D_io_info_t *io_info,
             } /* end if */
 
             /* Perform I/O on memory and file sequences */
-            if(io_buf->op_type == H5S_SELECT_READ) {
-                if((tmp_file_len = (*io_info->ops.readvv)(io_info,
+            if(io_info->op_type == H5D_IO_OP_READ) {
+                if((tmp_file_len = (*io_info->layout_ops.readvv)(io_info,
                         file_nseq, &curr_file_seq, file_len, file_off,
-                        mem_nseq, &curr_mem_seq, mem_len, mem_off,
-                        addr, chunk, io_buf->u.rbuf)) < 0)
+                        mem_nseq, &curr_mem_seq, mem_len, mem_off)) < 0)
                     HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
             } /* end if */
             else {
-                HDassert(io_buf->op_type == H5S_SELECT_WRITE);
-                if((tmp_file_len = (*io_info->ops.writevv)(io_info,
+                HDassert(io_info->op_type == H5D_IO_OP_WRITE);
+                if((tmp_file_len = (*io_info->layout_ops.writevv)(io_info,
                         file_nseq, &curr_file_seq, file_len, file_off,
-                        mem_nseq, &curr_mem_seq, mem_len, mem_off,
-                        addr, chunk, io_buf->u.wbuf)) < 0)
+                        mem_nseq, &curr_mem_seq, mem_len, mem_off)) < 0)
                     HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
             } /* end else */
 
@@ -604,17 +234,15 @@ done:
         if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
             HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
 
-    /* Free vector arrays */
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(file_len != NULL)
-            H5FL_SEQ_FREE(size_t, file_len);
-        if(file_off != NULL)
-            H5FL_SEQ_FREE(hsize_t, file_off);
-        if(mem_len != NULL)
-            H5FL_SEQ_FREE(size_t, mem_len);
-        if(mem_off != NULL)
-            H5FL_SEQ_FREE(hsize_t, mem_off);
-    } /* end if */
+    /* Release vector arrays, if allocated */
+    if(file_len && file_len != _file_len)
+        H5FL_SEQ_FREE(size_t, file_len);
+    if(file_off && file_off != _file_off)
+        H5FL_SEQ_FREE(hsize_t, file_off);
+    if(mem_len && mem_len != _mem_len)
+        H5FL_SEQ_FREE(size_t, mem_len);
+    if(mem_off && mem_off != _mem_off)
+        H5FL_SEQ_FREE(hsize_t, mem_off);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_select_io() */
@@ -633,23 +261,17 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_select_read(H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const H5S_t *file_space, const H5S_t *mem_space,
-    haddr_t addr, void *chunk/*in*/,
-    void *buf/*out*/)
+H5D_select_read(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space)
 {
-    H5D_select_buf_t io_buf;      /* Selection I/O operation to perform */
     herr_t ret_value = SUCCEED; /* Return value */
 
     FUNC_ENTER_NOAPI(H5D_select_read, FAIL)
 
-    /* Construct proper I/O operation */
-    io_buf.op_type = H5S_SELECT_READ;
-    io_buf.u.rbuf = buf;
-
     /* Call generic selection operation */
-    if(H5D_select_io(io_info, nelmts, elmt_size, file_space, mem_space, addr, chunk, &io_buf) < 0)
+    H5_CHECK_OVERFLOW(nelmts, hsize_t, size_t);
+    if(H5D_select_io(io_info, type_info->src_type_size, (size_t)nelmts,
+            file_space, mem_space) < 0)
         HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
 
 done:
@@ -670,23 +292,17 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_select_write(H5D_io_info_t *io_info,
-    size_t nelmts, size_t elmt_size,
-    const H5S_t *file_space, const H5S_t *mem_space,
-    haddr_t addr, void *chunk/*in*/,
-    const void *buf/*out*/)
+H5D_select_write(const H5D_io_info_t *io_info, const H5D_type_info_t *type_info,
+    hsize_t nelmts, const H5S_t *file_space, const H5S_t *mem_space)
 {
-    H5D_select_buf_t io_buf;      /* Selection I/O operation to perform */
     herr_t ret_value = SUCCEED; /* Return value */
 
     FUNC_ENTER_NOAPI(H5D_select_write, FAIL)
 
-    /* Construct proper I/O operation */
-    io_buf.op_type = H5S_SELECT_WRITE;
-    io_buf.u.wbuf = buf;
-
     /* Call generic selection operation */
-    if(H5D_select_io(io_info, nelmts, elmt_size, file_space, mem_space, addr, chunk, &io_buf) < 0)
+    H5_CHECK_OVERFLOW(nelmts, hsize_t, size_t);
+    if(H5D_select_io(io_info, type_info->dst_type_size, (size_t)nelmts,
+            file_space, mem_space) < 0)
         HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
 
 done:
diff --git a/src/H5F.c b/src/H5F.c
index cb9e3b8..80c28bc 100644
--- a/src/H5F.c
+++ b/src/H5F.c
@@ -978,6 +978,9 @@ done:
  * Programmer:	Robb Matzke
  *		matzke@llnl.gov
  *		Jul 18 1997
+ * Modifications:
+ *		Vailin Choi,  April 2, 2008
+ *		Free f->extpath
  *
  *-------------------------------------------------------------------------
  */
@@ -1068,6 +1071,7 @@ H5F_dest(H5F_t *f, hid_t dxpl_id)
 
     /* Free the non-shared part of the file */
     f->name = H5MM_xfree(f->name);
+    f->extpath = H5MM_xfree(f->extpath);
     f->mtab.child = H5MM_xfree(f->mtab.child);
     f->mtab.nalloc = 0;
     if(H5FO_top_dest(f) < 0)
@@ -1078,6 +1082,8 @@ H5F_dest(H5F_t *f, hid_t dxpl_id)
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5F_dest() */
 
+
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5F_open
@@ -1157,6 +1163,9 @@ H5F_dest(H5F_t *f, hid_t dxpl_id)
  *		Modified H5F_flush call to take one flag instead of
  *		multiple Boolean flags.
  *
+ *		Vailin Choi, 2008-04-02
+ *		To formulate path for later searching of target file for external link
+ *		via H5_build_extpath().
  *-------------------------------------------------------------------------
  */
 H5F_t *
@@ -1353,6 +1362,10 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t d
             HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "file close degree doesn't match")
     } /* end if */
 
+    /* formulate the absolute path for later search of target file for external link */
+    if (H5_build_extpath(name, &file->extpath) < 0)
+	HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to build extpath")
+    
     /* Success */
     ret_value = file;
 
@@ -2140,6 +2153,33 @@ H5F_get_intent(const H5F_t *f)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5F_get_extpath
+ *
+ * Purpose:	Retrieve the file's 'extpath' flags
+ *		This is used by H5L_extern_traverse() to retrieve the main file's location
+ *		when searching the target file.
+ *
+ * Return:	'extpath' on success/abort on failure (shouldn't fail)
+ * 
+ * Programmer:	Vailin Choi, April 2, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+char *
+H5F_get_extpath(const H5F_t *f)
+{
+    /* Use FUNC_ENTER_NOAPI_NOINIT_NOFUNC here to avoid performance issues */
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5F_get_extpath)
+
+    HDassert(f);
+
+    FUNC_LEAVE_NOAPI(f->extpath)
+} /* end H5F_get_extpath() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5F_sizeof_addr
  *
  * Purpose:	Quick and dirty routine to retrieve the size of the file's size_t
@@ -3618,4 +3658,3 @@ H5Fget_info(hid_t obj_id, H5F_info_t *finfo)
 done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Fget_info() */
-
diff --git a/src/H5FDmpi.h b/src/H5FDmpi.h
index 90aa0e2..0384018 100644
--- a/src/H5FDmpi.h
+++ b/src/H5FDmpi.h
@@ -42,14 +42,14 @@ typedef enum H5FD_mpio_xfer_t {
     H5FD_MPIO_COLLECTIVE
 } H5FD_mpio_xfer_t;
 
-/* Type of I/O for data transfer properties */
+/* Type of chunked dataset I/O */
 typedef enum H5FD_mpio_chunk_opt_t {
     H5FD_MPIO_CHUNK_DEFAULT = 0,
     H5FD_MPIO_CHUNK_ONE_IO,  		/*zero is the default*/
     H5FD_MPIO_CHUNK_MULTI_IO
 } H5FD_mpio_chunk_opt_t;
 
-/* Type of I/O for data transfer properties */
+/* Type of collective I/O */
 typedef enum H5FD_mpio_collective_opt_t {
     H5FD_MPIO_COLLECTIVE_IO = 0,
     H5FD_MPIO_INDIVIDUAL_IO  		/*zero is the default*/
diff --git a/src/H5FDmpio.c b/src/H5FDmpio.c
index c8087bb..89a8637 100644
--- a/src/H5FDmpio.c
+++ b/src/H5FDmpio.c
@@ -572,15 +572,15 @@ H5Pset_dxpl_mpio_collective_opt(hid_t dxpl_id, H5FD_mpio_collective_opt_t opt_mo
         HGOTO_ERROR(H5E_PLIST, H5E_BADTYPE, FAIL, "not a dxpl")
 
     /* Set the transfer mode */
-    if (H5P_set(plist,H5D_XFER_MPIO_COLLECTIVE_OPT_NAME,&opt_mode)<0)
+    if(H5P_set(plist, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME, &opt_mode) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set value")
 
     /* Initialize driver-specific properties */
-    ret_value= H5P_set_driver(plist, H5FD_MPIO, NULL);
+    ret_value = H5P_set_driver(plist, H5FD_MPIO, NULL);
 
 done:
     FUNC_LEAVE_API(ret_value)
-}
+} /* end H5Pset_dxpl_mpio_collective_opt() */
 
 
 /*-------------------------------------------------------------------------
@@ -1413,8 +1413,8 @@ H5FD_mpio_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id, haddr_t add
     int                         type_size;      /* MPI datatype used for I/O's size */
     int                         io_size;        /* Actual number of bytes requested */
     H5P_genplist_t              *plist;      /* Property list pointer */
-    unsigned			use_view_this_time=0;
-    herr_t              	ret_value=SUCCEED;
+    hbool_t			use_view_this_time = FALSE;
+    herr_t              	ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI(H5FD_mpio_read, FAIL)
 
@@ -1464,7 +1464,7 @@ H5FD_mpio_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id, haddr_t add
             MPI_Datatype		file_type;
 
             /* Remember that views are used */
-            use_view_this_time=TRUE;
+            use_view_this_time = TRUE;
 
             /* prepare for a full-blown xfer using btype, ftype, and disp */
             if(H5P_get(plist,H5FD_MPI_XFER_MEM_MPI_TYPE_NAME,&buf_type)<0)
@@ -1487,9 +1487,9 @@ H5FD_mpio_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id, haddr_t add
     } /* end if */
 
     /* Read the data. */
-    if (use_view_this_time) {
+    if(use_view_this_time) {
        H5FD_mpio_collective_opt_t coll_opt_mode;
-       H5FD_mpio_collective_opt_t xfer_opt_mode;
+
 #ifdef H5FDmpio_DEBUG
 	if (H5FD_mpio_Debug[(int)'t'])
 	    fprintf(stdout, "H5FD_mpio_read: using MPIO collective mode\n");
@@ -1497,28 +1497,23 @@ H5FD_mpio_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id, haddr_t add
         /* Peek the collective_opt property to check whether the application wants to do IO individually. */
         coll_opt_mode = (H5FD_mpio_collective_opt_t)H5P_peek_unsigned(plist, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME);
 
-       /* Peek the xfer_opt_mode property to check whether the application wants to do IO individually. */
-        xfer_opt_mode = (H5FD_mpio_collective_opt_t)H5P_peek_unsigned(plist, H5D_XFER_IO_XFER_OPT_MODE_NAME);
-     
-        if(coll_opt_mode == H5FD_MPIO_COLLECTIVE_IO && xfer_opt_mode == H5FD_MPIO_COLLECTIVE_IO) {
+        if(coll_opt_mode == H5FD_MPIO_COLLECTIVE_IO) {
 #ifdef H5FDmpio_DEBUG
-        if (H5FD_mpio_Debug[(int)'t'])
-            fprintf(stdout, "H5FD_mpio_read: doing MPI collective IO\n");
+            if(H5FD_mpio_Debug[(int)'t'])
+                fprintf(stdout, "H5FD_mpio_read: doing MPI collective IO\n");
 #endif
-/* Temporarily change to read_at_all 
-        if (MPI_SUCCESS!= (mpi_code=MPI_File_read_at_all(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat )))*/
-        if (MPI_SUCCESS!= (mpi_code=MPI_File_read_at_all(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat )))
-            HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at_all failed", mpi_code)
-        }
+            if(MPI_SUCCESS != (mpi_code = MPI_File_read_at_all(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at_all failed", mpi_code)
+        } /* end if */
         else {
 #ifdef H5FDmpio_DEBUG
-        if (H5FD_mpio_Debug[(int)'t'])
-            fprintf(stdout, "H5FD_mpio_read: doing MPI independent IO\n");
+            if(H5FD_mpio_Debug[(int)'t'])
+                fprintf(stdout, "H5FD_mpio_read: doing MPI independent IO\n");
 #endif
 
-        if (MPI_SUCCESS!= (mpi_code=MPI_File_read_at(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat )))
-            HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at failed", mpi_code)
-        }
+            if(MPI_SUCCESS != (mpi_code = MPI_File_read_at(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at failed", mpi_code)
+        } /* end else */
  
         /*
          * Reset the file view when we used MPI derived types
@@ -1700,7 +1695,7 @@ H5FD_mpio_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr,
     int         		size_i, bytes_written;
     int                         type_size;      /* MPI datatype used for I/O's size */
     int                         io_size;        /* Actual number of bytes requested */
-    unsigned			use_view_this_time=0;
+    hbool_t			use_view_this_time = FALSE;
     H5P_genplist_t              *plist;                 /* Property list pointer */
     herr_t              	ret_value=SUCCEED;
 
@@ -1718,26 +1713,25 @@ H5FD_mpio_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr,
     assert(buf);
 
     /* Portably initialize MPI status variable */
-    HDmemset(&mpi_stat,0,sizeof(MPI_Status));
+    HDmemset(&mpi_stat, 0, sizeof(MPI_Status));
 
     /* some numeric conversions */
-    if (H5FD_mpi_haddr_to_MPIOff(addr, &mpi_off)<0)
+    if(H5FD_mpi_haddr_to_MPIOff(addr, &mpi_off) < 0)
         HGOTO_ERROR(H5E_INTERNAL, H5E_BADRANGE, FAIL, "can't convert from haddr to MPI off")
     size_i = (int)size;
-    if ((hsize_t)size_i != size)
+    if((hsize_t)size_i != size)
         HGOTO_ERROR(H5E_INTERNAL, H5E_BADRANGE, FAIL, "can't convert from size to size_i")
 
 #ifdef H5FDmpio_DEBUG
-    if (H5FD_mpio_Debug[(int)'w'])
-        fprintf(stdout, "in H5FD_mpio_write  mpi_off=%ld  size_i=%d\n",
-                (long)mpi_off, size_i);
+    if(H5FD_mpio_Debug[(int)'w'])
+        fprintf(stdout, "in H5FD_mpio_write  mpi_off=%ld  size_i=%d\n", (long)mpi_off, size_i);
 #endif
 
     /* Obtain the data transfer properties */
     if(NULL == (plist = (H5P_genplist_t *)H5I_object(dxpl_id)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list")
 
-    if(type==H5FD_MEM_DRAW) {
+    if(type == H5FD_MEM_DRAW) {
         H5FD_mpio_xfer_t            xfer_mode;   /* I/O tranfer mode */
 
         /* Obtain the data transfer properties */
@@ -1749,114 +1743,71 @@ H5FD_mpio_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr,
          * us to test that btype=ftype=MPI_BYTE (or even MPI_TYPE_NULL, which
          * could mean "use MPI_BYTE" by convention).
          */
-        if(xfer_mode==H5FD_MPIO_COLLECTIVE) {
+        if(xfer_mode == H5FD_MPIO_COLLECTIVE) {
             MPI_Datatype		file_type;
 
             /* Remember that views are used */
-            use_view_this_time=TRUE;
+            use_view_this_time = TRUE;
 
             /* prepare for a full-blown xfer using btype, ftype, and disp */
-            if(H5P_get(plist,H5FD_MPI_XFER_MEM_MPI_TYPE_NAME,&buf_type)<0)
+            if(H5P_get(plist, H5FD_MPI_XFER_MEM_MPI_TYPE_NAME, &buf_type) < 0)
                 HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get MPI-I/O type property")
-            if(H5P_get(plist,H5FD_MPI_XFER_FILE_MPI_TYPE_NAME,&file_type)<0)
+            if(H5P_get(plist, H5FD_MPI_XFER_FILE_MPI_TYPE_NAME, &file_type) < 0)
                 HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get MPI-I/O type property")
 
             /*
              * Set the file view when we are using MPI derived types
              */
             /*OKAY: CAST DISCARDS CONST QUALIFIER*/
-            if (MPI_SUCCESS != (mpi_code=MPI_File_set_view(file->f, mpi_off, MPI_BYTE, file_type, H5FD_mpi_native_g, file->info)))
+            if(MPI_SUCCESS != (mpi_code = MPI_File_set_view(file->f, mpi_off, MPI_BYTE, file_type, H5FD_mpi_native_g, file->info)))
                 HMPI_GOTO_ERROR(FAIL, "MPI_File_set_view failed", mpi_code)
 
             /* When using types, use the address as the displacement for
              * MPI_File_set_view and reset the address for the read to zero
              */
-            mpi_off=0;
+            mpi_off = 0;
         } /* end if */
     } /* end if */
     else {
-        unsigned		        block_before_meta_write=0;      /* Whether to block before a metadata write */
-
-        /* Check if we need to syncronize all processes before attempting metadata write
-         * (Prevents race condition where the process writing the metadata goes ahead
-         * and writes the metadata to the file before all the processes have
-         * read the data, "transmitting" data from the "future" to the reading
-         * process. -QAK )
-         *
-         * The only time we don't want to block before a metadata write is when
-         * we are flushing out a bunch of metadata.  Then, we block before the
-         * first write and don't block for further writes in the sequence.
-         */
-        if(H5P_exist_plist(plist,H5AC_BLOCK_BEFORE_META_WRITE_NAME)>0)
-            if(H5P_get(plist,H5AC_BLOCK_BEFORE_META_WRITE_NAME,&block_before_meta_write)<0)
-                HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get H5AC property")
-
-#if 0 /* JRM */
-	/* The metadata cache now only writes from process 0, which makes
-	 * this synchronization incorrect.  I'm leaving this code commented
-	 * out instead of deleting it to remind us that we should re-write
-	 * this function so that a metadata write from any other process 
-	 * should flag an error.
-	 *                                  -- JRM 9/1/05
-	 */
-        if(block_before_meta_write)
-            if (MPI_SUCCESS!= (mpi_code=MPI_Barrier(file->comm)))
-                HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_code)
-#endif /* JRM */
-
-        /* Only one process will do the actual write if all procs in comm write same metadata */
-        if (file->mpi_rank != H5_PAR_META_WRITE) {
-#ifdef H5FDmpio_DEBUG
-            if (H5FD_mpio_Debug[(int)'w']) {
-                fprintf(stdout,
-                    "  proc %d: in H5FD_mpio_write (write omitted)\n",
-                    file->mpi_rank );
-            }
-#endif
+        /* Only one process can do the actual metadata write */
+        if(file->mpi_rank != H5_PAR_META_WRITE)
+#ifdef LATER
+            HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "can't write metadata from non-zero rank")
+#else /* LATER */
             HGOTO_DONE(SUCCEED) /* skip the actual write */
-        } /* end if */
+#endif /* LATER */
     } /* end if */
 
     /* Write the data. */
-    if (use_view_this_time) {
-       H5FD_mpio_collective_opt_t coll_opt_mode;
-       H5FD_mpio_collective_opt_t  xfer_opt_mode;
+    if(use_view_this_time) {
+        H5FD_mpio_collective_opt_t coll_opt_mode;
+
 #ifdef H5FDmpio_DEBUG
-        if (H5FD_mpio_Debug[(int)'t'])
+        if(H5FD_mpio_Debug[(int)'t'])
             fprintf(stdout, "H5FD_mpio_write: using MPIO collective mode\n");
 #endif
         /* Peek the collective_opt property to check whether the application wants to do IO individually. */
-        coll_opt_mode = (H5FD_mpio_collective_opt_t)H5P_peek_unsigned(plist,H5D_XFER_MPIO_COLLECTIVE_OPT_NAME);
-
-         /* Peek the xfer_opt_mode property to check whether the application wants to do IO individually. */
-        xfer_opt_mode = (H5FD_mpio_collective_opt_t)H5P_peek_unsigned(plist,H5D_XFER_IO_XFER_OPT_MODE_NAME);
+        coll_opt_mode = (H5FD_mpio_collective_opt_t)H5P_peek_unsigned(plist, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME);
 
         /*OKAY: CAST DISCARDS CONST QUALIFIER*/
-        if(coll_opt_mode == H5FD_MPIO_COLLECTIVE_IO && xfer_opt_mode == H5FD_MPIO_COLLECTIVE_IO ) {
+        if(coll_opt_mode == H5FD_MPIO_COLLECTIVE_IO) {
 #ifdef H5FDmpio_DEBUG
-        if (H5FD_mpio_Debug[(int)'t'])
-            fprintf(stdout, "H5FD_mpio_write: doing MPI collective IO\n");
+            if(H5FD_mpio_Debug[(int)'t'])
+                fprintf(stdout, "H5FD_mpio_write: doing MPI collective IO\n");
 #endif
-        /* Temporarily change to _at 
-if (MPI_SUCCESS != (mpi_code=MPI_File_write_at_all(file->f, mpi_off, (void*)buf, size_i, buf_type, &mpi_stat)))
-*/
-        if (MPI_SUCCESS != (mpi_code=MPI_File_write_at_all(file->f, mpi_off, (void*)buf, size_i, buf_type, &mpi_stat)))
-            HMPI_GOTO_ERROR(FAIL, "MPI_File_write_at_all failed", mpi_code)
-        }
+            if(MPI_SUCCESS != (mpi_code = MPI_File_write_at_all(file->f, mpi_off, (void*)buf, size_i, buf_type, &mpi_stat)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_File_write_at_all failed", mpi_code)
+        } /* end if */
         else {
 #ifdef H5FDmpio_DEBUG
-        if (H5FD_mpio_Debug[(int)'t'])
-            fprintf(stdout, "H5FD_mpio_write: doing MPI independent IO\n");
+            if(H5FD_mpio_Debug[(int)'t'])
+                fprintf(stdout, "H5FD_mpio_write: doing MPI independent IO\n");
 #endif
- 
-          if (MPI_SUCCESS != (mpi_code=MPI_File_write_at(file->f, mpi_off, (void*)buf, size_i, buf_type, &mpi_stat)))
-            HMPI_GOTO_ERROR(FAIL, "MPI_File_write_at failed", mpi_code)
-        }
-
+            if(MPI_SUCCESS != (mpi_code = MPI_File_write_at(file->f, mpi_off, (void*)buf, size_i, buf_type, &mpi_stat)))
+                HMPI_GOTO_ERROR(FAIL, "MPI_File_write_at failed", mpi_code)
+        } /* end else */
 
-       /*
-         * Reset the file view when we used MPI derived types
-         */
+        /* Reset the file view when we used MPI derived types */
         /*OKAY: CAST DISCARDS CONST QUALIFIER*/
         if(MPI_SUCCESS != (mpi_code = MPI_File_set_view(file->f, (MPI_Offset)0, MPI_BYTE, MPI_BYTE, H5FD_mpi_native_g,  file->info)))
             HMPI_GOTO_ERROR(FAIL, "MPI_File_set_view failed", mpi_code)
@@ -1872,48 +1823,31 @@ if (MPI_SUCCESS != (mpi_code=MPI_File_write_at_all(file->f, mpi_off, (void*)buf,
      *  datatype in this call though... (We aren't because using it causes
      *  the LANL "qsc" machine to dump core - 12/19/03) - QAK]
      */
-    if (MPI_SUCCESS != (mpi_code=MPI_Get_elements(&mpi_stat, MPI_BYTE, &bytes_written)))
+    if(MPI_SUCCESS != (mpi_code = MPI_Get_elements(&mpi_stat, MPI_BYTE, &bytes_written)))
         HMPI_GOTO_ERROR(FAIL, "MPI_Get_elements failed", mpi_code)
 
     /* Get the type's size */
-    if (MPI_SUCCESS != (mpi_code=MPI_Type_size(buf_type,&type_size)))
+    if(MPI_SUCCESS != (mpi_code = MPI_Type_size(buf_type, &type_size)))
         HMPI_GOTO_ERROR(FAIL, "MPI_Type_size failed", mpi_code)
 
     /* Compute the actual number of bytes requested */
-    io_size=type_size*size_i;
+    io_size = type_size * size_i;
 
     /* Check for write failure */
-    if (bytes_written != io_size)
+    if(bytes_written != io_size)
         HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "file write failed")
 
     /* Forget the EOF value (see H5FD_mpio_get_eof()) --rpm 1999-08-06 */
     file->eof = HADDR_UNDEF;
 
 done:
-
-#if 0 /* JRM */
-    /* Since metadata writes are now done by process 0 only, this broadcast
-     * is no longer needed.  I leave it in and commented out to remind us 
-     * that we need to re-work this function to reflect this reallity.
-     *
-     *                                          -- JRM 9/1/05
-     */
-    /* if only one process writes, need to broadcast the ret_value to 
-     * other processes 
-     */
-    if(type != H5FD_MEM_DRAW) {
-	if(MPI_SUCCESS != (mpi_code = MPI_Bcast(&ret_value, (int)sizeof(ret_value), MPI_BYTE, H5_PAR_META_WRITE, file->comm)))
-	    HMPI_DONE_ERROR(FAIL, "MPI_Bcast failed", mpi_code)
-    } /* end if */
-#endif /* JRM */
-
 #ifdef H5FDmpio_DEBUG
-    if (H5FD_mpio_Debug[(int)'t'])
+    if(H5FD_mpio_Debug[(int)'t'])
     	fprintf(stdout, "proc %d: Leaving H5FD_mpio_write with ret_value=%d\n",
 	    file->mpi_rank, ret_value );
 #endif
     FUNC_LEAVE_NOAPI(ret_value)
-}
+} /* end H5FD_mpio_write() */
 
 
 /*-------------------------------------------------------------------------
diff --git a/src/H5FScache.c b/src/H5FScache.c
index 74a9aab..8ad9631 100644
--- a/src/H5FScache.c
+++ b/src/H5FScache.c
@@ -606,7 +606,7 @@ HDfprintf(stderr, "%s: fspace->addr = %a, fs_addr = %a\n", FUNC, fspace->addr, f
         unsigned sect_cnt_size;         /* The size of the section size counts */
 
         /* Compute the size of the section counts */
-        sect_cnt_size = MAX(1, (H5V_log2_gen(fspace->serial_sect_count) + 7) / 8);
+        sect_cnt_size = H5V_limit_enc_size((uint64_t)fspace->serial_sect_count);
 #ifdef QAK
 HDfprintf(stderr, "%s: sect_cnt_size = %u\n", FUNC, sect_cnt_size);
 HDfprintf(stderr, "%s: fspace->sect_len_size = %u\n", FUNC, fspace->sect_len_size);
@@ -905,7 +905,7 @@ HDfprintf(stderr, "%s: sinfo->fspace->addr = %a\n", FUNC, sinfo->fspace->addr);
         /* Set up user data for iterator */
         udata.sinfo = sinfo;
         udata.p = &p;
-        udata.sect_cnt_size = MAX(1, (H5V_log2_gen(sinfo->fspace->serial_sect_count) + 7) / 8);
+        udata.sect_cnt_size = H5V_limit_enc_size((uint64_t)sinfo->fspace->serial_sect_count);
 #ifdef QAK
 HDfprintf(stderr, "%s: udata.sect_cnt_size = %u\n", FUNC, udata.sect_cnt_size);
 #endif /* QAK */
diff --git a/src/H5FSsection.c b/src/H5FSsection.c
index c589aa0..34da067 100644
--- a/src/H5FSsection.c
+++ b/src/H5FSsection.c
@@ -147,7 +147,7 @@ H5FS_sinfo_new(H5F_t *f, H5FS_t *fspace)
     sinfo->nbins = H5V_log2_gen(fspace->max_sect_size);
     sinfo->sect_prefix_size = H5FS_SINFO_PREFIX_SIZE(f);
     sinfo->sect_off_size = (fspace->max_sect_addr + 7) / 8;
-    sinfo->sect_len_size = (H5V_log2_gen(fspace->max_sect_size) + 7) / 8;
+    sinfo->sect_len_size = H5V_limit_enc_size((uint64_t)fspace->max_sect_size);
     sinfo->fspace = fspace;
 #ifdef QAK
 HDfprintf(stderr, "%s: sinfo->nbins = %u\n", FUNC, sinfo->nbins);
@@ -1300,7 +1300,7 @@ HDfprintf(stderr, "%s: fspace->sinfo->serial_size_count = %Zu\n", FUNC, fspace->
 HDfprintf(stderr, "%s: fspace->sinfo->serial_size_count = %Zu\n", FUNC, fspace->sinfo->serial_size_count);
 HDfprintf(stderr, "%s: fspace->serial_sect_count = %Hu\n", FUNC, fspace->serial_sect_count);
 #endif /* QAK */
-        sect_buf_size += fspace->sinfo->serial_size_count * MAX(1, ((H5V_log2_gen(fspace->serial_sect_count) + 7) / 8));
+        sect_buf_size += fspace->sinfo->serial_size_count * H5V_limit_enc_size((uint64_t)fspace->serial_sect_count);
 
         /* Size for each differently sized serializable section */
         sect_buf_size += fspace->sinfo->serial_size_count * fspace->sinfo->sect_len_size;
diff --git a/src/H5Fpkg.h b/src/H5Fpkg.h
index 3f10e1a..288ef8a 100644
--- a/src/H5Fpkg.h
+++ b/src/H5Fpkg.h
@@ -142,6 +142,7 @@ typedef struct H5F_mtab_t {
 struct H5F_t {
     unsigned		intent;		/* The flags passed to H5F_open()*/
     char		*name;		/* Name used to open file	*/
+    char               	*extpath;       /* Path for searching target external link file */
     H5F_file_t		*shared;	/* The shared file info		*/
     unsigned		nopen_objs;	/* Number of open object headers*/
     H5FO_t              *obj_count;     /* # of time each object is opened through top file structure */
diff --git a/src/H5Fprivate.h b/src/H5Fprivate.h
index 1044b14..27b45f2 100644
--- a/src/H5Fprivate.h
+++ b/src/H5Fprivate.h
@@ -265,6 +265,7 @@ typedef struct H5F_t H5F_t;
 #define H5F_GC_REF(F)           ((F)->shared->gc_ref)
 #define H5F_USE_LATEST_FORMAT(F) ((F)->shared->latest_format)
 #define H5F_INTENT(F)           ((F)->intent)
+#define H5F_EXTPATH(F)          ((F)->extpath)
 #define H5F_GET_FC_DEGREE(F)    ((F)->shared->fc_degree)
 #define H5F_STORE_MSG_CRT_IDX(F)    ((F)->shared->store_msg_crt_idx)
 #define H5F_GET_FILENO(F,FILENUM) ((FILENUM) = (F)->shared->lf->fileno)
@@ -284,6 +285,7 @@ typedef struct H5F_t H5F_t;
 #define H5F_GC_REF(F)           (H5F_gc_ref(F))
 #define H5F_USE_LATEST_FORMAT(F) (H5F_use_latest_format(F))
 #define H5F_INTENT(F)           (H5F_get_intent(F))
+#define H5F_EXTPATH(F)          (H5F_get_extpath(F))
 #define H5F_GET_FC_DEGREE(F)    (H5F_get_fc_degree(F))
 #define H5F_STORE_MSG_CRT_IDX(F)    (H5F_store_msg_crt_idx(F))
 #define H5F_GET_FILENO(F,FILENUM) (H5F_get_filenum((F), &(FILENUM)))
@@ -417,6 +419,7 @@ H5_DLL herr_t H5F_try_close(H5F_t *f);
 H5_DLL hid_t H5F_get_driver_id(const H5F_t *f);
 H5_DLL hid_t H5F_get_access_plist(H5F_t *f);
 H5_DLL unsigned H5F_get_intent(const H5F_t *f);
+H5_DLL char *H5F_get_extpath(const H5F_t *f);
 H5_DLL herr_t H5F_get_fileno(const H5F_t *f, unsigned long *filenum);
 H5_DLL hid_t H5F_get_id(H5F_t *file);
 H5_DLL unsigned H5F_get_obj_count(const H5F_t *f, unsigned types);
diff --git a/src/H5HFhdr.c b/src/H5HFhdr.c
index c1b856b..60d5002 100644
--- a/src/H5HFhdr.c
+++ b/src/H5HFhdr.c
@@ -225,7 +225,7 @@ H5HF_hdr_finish_init_phase1(H5HF_hdr_t *hdr)
 
     /* Set the size of heap IDs */
     hdr->heap_len_size = MIN(hdr->man_dtable.max_dir_blk_off_size,
-            ((H5V_log2_gen((uint64_t)hdr->max_man_size) + 7) / 8));
+            H5V_limit_enc_size((uint64_t)hdr->max_man_size));
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5HFiblock.c b/src/H5HFiblock.c
index 70133aa..7fedc48 100644
--- a/src/H5HFiblock.c
+++ b/src/H5HFiblock.c
@@ -1591,7 +1591,7 @@ done:
  */
 herr_t
 H5HF_man_iblock_size(H5F_t *f, hid_t dxpl_id, H5HF_hdr_t *hdr, haddr_t iblock_addr,
-    unsigned nrows, hsize_t *heap_size)
+    unsigned nrows, H5HF_indirect_t *par_iblock, unsigned par_entry, hsize_t *heap_size)
 {
     H5HF_indirect_t     *iblock = NULL;         /* Pointer to indirect block */
     hbool_t             did_protect;            /* Whether we protected the indirect block or not */
@@ -1608,7 +1608,7 @@ H5HF_man_iblock_size(H5F_t *f, hid_t dxpl_id, H5HF_hdr_t *hdr, haddr_t iblock_ad
     HDassert(heap_size);
 
     /* Protect the indirect block */
-    if(NULL == (iblock = H5HF_man_iblock_protect(hdr, dxpl_id, iblock_addr, nrows, NULL, 0, FALSE, H5AC_READ, &did_protect)))
+    if(NULL == (iblock = H5HF_man_iblock_protect(hdr, dxpl_id, iblock_addr, nrows, par_iblock, par_entry, FALSE, H5AC_READ, &did_protect)))
         HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, FAIL, "unable to load fractal heap indirect block")
 
     /* Accumulate size of this indirect block */
@@ -1624,13 +1624,14 @@ H5HF_man_iblock_size(H5F_t *f, hid_t dxpl_id, H5HF_hdr_t *hdr, haddr_t iblock_ad
         entry = hdr->man_dtable.max_direct_rows * hdr->man_dtable.cparam.width;
 	first_row_bits = H5V_log2_of2((uint32_t)hdr->man_dtable.cparam.start_block_size) +
 			    H5V_log2_of2(hdr->man_dtable.cparam.width);
-        num_indirect_rows = (H5V_log2_gen(hdr->man_dtable.row_block_size[u]) - first_row_bits) + 1;
+        num_indirect_rows = 
+	    (H5V_log2_gen(hdr->man_dtable.row_block_size[hdr->man_dtable.max_direct_rows]) - first_row_bits) + 1;
         for(u = hdr->man_dtable.max_direct_rows; u < iblock->nrows; u++, num_indirect_rows++) {
             size_t      v;                      /* Local index variable */
 
 	    for(v = 0; v < hdr->man_dtable.cparam.width; v++, entry++)
 		if(H5F_addr_defined(iblock->ents[entry].addr))
-		    if(H5HF_man_iblock_size(f, dxpl_id, hdr, iblock->ents[entry].addr, num_indirect_rows, heap_size) < 0)
+		    if(H5HF_man_iblock_size(f, dxpl_id, hdr, iblock->ents[entry].addr, num_indirect_rows, iblock, entry, heap_size) < 0)
 			HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, FAIL, "unable to get fractal heap storage info for indirect block")
         } /* end for */
     } /* end if */
@@ -1639,6 +1640,7 @@ done:
     /* Release the indirect block */
     if(iblock && H5HF_man_iblock_unprotect(iblock, dxpl_id, H5AC__NO_FLAGS_SET, did_protect) < 0)
 	HGOTO_ERROR(H5E_HEAP, H5E_CANTUNPROTECT, FAIL, "unable to release fractal heap indirect block")
+    iblock = NULL;
 
    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5HF_man_iblock_size() */
diff --git a/src/H5HFpkg.h b/src/H5HFpkg.h
index 702ce08..fd332e5 100644
--- a/src/H5HFpkg.h
+++ b/src/H5HFpkg.h
@@ -601,7 +601,7 @@ H5_DLL herr_t H5HF_man_iblock_delete(H5HF_hdr_t *hdr, hid_t dxpl_id,
     haddr_t iblock_addr, unsigned iblock_nrows, H5HF_indirect_t *par_iblock,
     unsigned par_entry);
 H5_DLL herr_t H5HF_man_iblock_size(H5F_t *f, hid_t dxpl_id, H5HF_hdr_t *hdr,
-    haddr_t iblock_addr, unsigned nrows, hsize_t *heap_size/*out*/);
+    haddr_t iblock_addr, unsigned nrows, H5HF_indirect_t *par_iblock, unsigned par_entry, hsize_t *heap_size/*out*/);
 
 /* Direct block routines */
 H5_DLL herr_t H5HF_man_dblock_new(H5HF_hdr_t *fh, hid_t dxpl_id, size_t request,
diff --git a/src/H5HFstat.c b/src/H5HFstat.c
index 2e3e189..d151b47 100644
--- a/src/H5HFstat.c
+++ b/src/H5HFstat.c
@@ -128,6 +128,7 @@ H5HF_size(const H5HF_t *fh, hid_t dxpl_id, hsize_t *heap_size)
 {
     H5HF_hdr_t *hdr;                            /* Fractal heap header */
     herr_t      ret_value = SUCCEED;            /* Return value */
+    hsize_t	meta_size = 0;			/* free space storage size */
 
     FUNC_ENTER_NOAPI(H5HF_size, FAIL)
 
@@ -147,7 +148,7 @@ H5HF_size(const H5HF_t *fh, hid_t dxpl_id, hsize_t *heap_size)
 
     /* Check for indirect blocks for managed objects */
     if(H5F_addr_defined(hdr->man_dtable.table_addr) && hdr->man_dtable.curr_root_rows != 0)
-        if(H5HF_man_iblock_size(hdr->f, dxpl_id, hdr, hdr->man_dtable.table_addr, hdr->man_dtable.curr_root_rows, heap_size) < 0)
+        if(H5HF_man_iblock_size(hdr->f, dxpl_id, hdr, hdr->man_dtable.table_addr, hdr->man_dtable.curr_root_rows, NULL, 0, heap_size) < 0)
             HGOTO_ERROR(H5E_HEAP, H5E_CANTGET, FAIL, "unable to get fractal heap storage info for indirect block")
 
     /* Get B-tree storage for huge objects in fractal heap */
@@ -172,9 +173,11 @@ H5HF_size(const H5HF_t *fh, hid_t dxpl_id, hsize_t *heap_size)
     } /* end if */
 
     /* Get storage for free-space tracking info */
-    if(H5F_addr_defined(hdr->fs_addr))
-        if(H5HF_space_size(hdr, dxpl_id, heap_size) < 0)
+    if(H5F_addr_defined(hdr->fs_addr)) {
+        if(H5HF_space_size(hdr, dxpl_id, &meta_size) < 0)
             HGOTO_ERROR(H5E_FSPACE, H5E_CANTGET, FAIL, "can't retrieve FS meta storage info")
+	*heap_size += meta_size;
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5Lexternal.c b/src/H5Lexternal.c
index 5a8eb33..4e355bb 100644
--- a/src/H5Lexternal.c
+++ b/src/H5Lexternal.c
@@ -76,6 +76,81 @@ H5L_init_extern_interface(void)
 } /* H5L_init_extern_interface() */
 
 
+
+/*--------------------------------------------------------------------------
+ * Function: H5L_getenv_prefix_name --
+ *
+ * Purpose:  Get the first pathname in the list of pathnames stored in ENV_PREFIX,
+ *           which is separated by the environment delimiter.
+ *           ENV_PREFIX is modified to point to the remaining pathnames
+ *           in the list.
+ *
+ * Return:   A pointer to a pathname
+ *
+ * Programmer:	Vailin Choi, April 2, 2008
+ *
+--------------------------------------------------------------------------*/
+static char *
+H5L_getenv_prefix_name(char **env_prefix/*in,out*/)
+{
+    char        *retptr=NULL;
+    char        *strret=NULL;
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5L_getenv_prefix_name)
+
+    strret = HDstrchr(*env_prefix, COLON_SEPC);
+    if (strret == NULL) {
+        retptr = *env_prefix;
+        *env_prefix = strret;
+    } else {
+        retptr = *env_prefix;
+        *env_prefix = strret + 1;
+        *strret = '\0';
+    }
+    return(retptr);
+    FUNC_LEAVE_NOAPI(retptr)
+}
+
+
+/*--------------------------------------------------------------------------
+ * Function: H5L_build_name
+ *
+ * Purpose:  Prepend PREFIX to FILE_NAME and store in FULL_NAME
+ *
+ * Return:   Non-negative on success/Negative on failure
+ *
+ * Programmer:	Vailin Choi, April 2, 2008
+ *
+--------------------------------------------------------------------------*/
+static herr_t
+H5L_build_name(char *prefix, char *file_name, char **full_name/*out*/)
+{
+    size_t      prefix_len;             /* length of prefix */
+    size_t      fname_len;              /* Length of external link file name */
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5L_build_name)
+
+    prefix_len = HDstrlen(prefix);
+    fname_len = HDstrlen(file_name);
+
+    /* Allocate a buffer to hold the filename + prefix + possibly the delimiter + terminating null byte */
+    if(NULL == (*full_name = H5MM_malloc(prefix_len + fname_len + 2)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "unable to allocate filename buffer")
+
+    /* Copy the prefix into the buffer */
+    HDstrcpy(*full_name, prefix);
+    if (!CHECK_DELIMITER(prefix[prefix_len-1]))
+        HDstrcat(*full_name, DIR_SEPS);
+
+    /* Add the external link's filename to the prefix supplied */
+    HDstrcat(*full_name, file_name);
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5L_build_name() */
+
+
 /*-------------------------------------------------------------------------
  * Function:	H5L_extern_traverse
  *
@@ -92,6 +167,10 @@ H5L_init_extern_interface(void)
  *
  * Programmer:	James Laird
  *              Monday, July 10, 2006
+ * Modifications:
+ *		Vailin Choi, April 2, 2008
+ *		Add handling to search for the target file 
+ *		See description in RM: H5Lcreate_external
  *
  *-------------------------------------------------------------------------
  */
@@ -114,6 +193,11 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
     hid_t       ext_obj = -1;           /* ID for external link's object */
     hid_t       ret_value;              /* Return value */
 
+    char        *tempname=NULL, *ptr=NULL, *extpath=NULL;
+    char        *env_prefix=NULL, *tmp_env_prefix=NULL;
+    char        *out_prefix_name=NULL, *pp=NULL;
+
+
     FUNC_ENTER_NOAPI(H5L_extern_traverse, FAIL)
 
     /* Sanity checks */
@@ -135,28 +219,6 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
     if(NULL == (plist = H5P_object_verify(lapl_id, H5P_LINK_ACCESS)))
         HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
 
-    /* Get the current prefix */
-    if(H5P_get(plist, H5L_ACS_ELINK_PREFIX_NAME, &my_prefix) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get external link prefix")
-
-    /* Check for prefix being set, if so, prepend it to the filename */
-    if(my_prefix) {
-        size_t prefix_len = HDstrlen(my_prefix);
-
-        /* Allocate a buffer to hold the filename plus prefix */
-        if(NULL == (full_name = H5MM_malloc(prefix_len + fname_len + 1)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "unable to allocate filename buffer")
-
-        /* Copy the prefix into the buffer */
-        HDstrcpy(full_name, my_prefix);
-
-        /* Add the external link's filename to the prefix supplied */
-        HDstrcat(full_name, (const char *)p);
-
-        /* Point to name w/prefix */
-        file_name = full_name;
-    } /* end if */
-
     /* Get the location for the group holding the external link */
     if(H5G_loc(cur_group, &loc) < 0)
         HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't get object location")
@@ -183,10 +245,92 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
             HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set file close degree")
     } /* end if */
 
-    /* Open the external file */
-    /* (extra work with file intent to mask off inappropriate flags) */
-    if(NULL == (ext_file = H5F_open(file_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY), H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)))
-	HGOTO_ERROR(H5E_LINK, H5E_CANTOPENFILE, FAIL, "unable to open external file")
+    /*
+     * Start searching for the target file
+     */
+    if ((tempname=H5MM_strdup(file_name)) == NULL)
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    /* target file_name is an absolute pathname: see RM for detailed description */
+    if (CHECK_ABSOLUTE(file_name) || CHECK_ABS_PATH(file_name)) {
+        if(NULL == (ext_file = H5F_open(file_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                                H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id))) {
+            H5E_clear_stack(NULL);
+            /* get last component of file_name */
+	    GET_LAST_DELIMITER(file_name, ptr)
+	    HDassert(ptr);
+	    HDstrcpy(tempname, ++ptr);
+        }
+    } else if (CHECK_ABS_DRIVE(file_name)) {
+        if(NULL == (ext_file = H5F_open(file_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                                H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id))) {
+            H5E_clear_stack(NULL);
+	    /* strip "<drive-letter>:" */
+	    HDstrcpy(tempname, &file_name[2]);
+	}
+    }
+    
+    /* try searching from paths set in the environment variable */
+    if ((ext_file == NULL) && (env_prefix=HDgetenv("HDF5_EXT_PREFIX"))) {
+
+        tmp_env_prefix = H5MM_strdup(env_prefix);
+	pp = tmp_env_prefix;
+
+        while ((tmp_env_prefix) && (*tmp_env_prefix)) {
+            out_prefix_name = H5L_getenv_prefix_name(&tmp_env_prefix/*in,out*/);
+            if ((out_prefix_name) && (*out_prefix_name)) {
+
+                if (H5L_build_name(out_prefix_name, tempname, &full_name/*out*/) < 0)
+                    HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't prepend prefix to filename")
+
+                ext_file = H5F_open(full_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                            H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id);
+                if (full_name)
+                    H5MM_xfree(full_name);
+                if (ext_file != NULL)
+                    break;
+                H5E_clear_stack(NULL);
+            }
+        } /* end while */
+        if (pp)
+            H5MM_xfree(pp);
+    }
+    
+    /* try searching from property list */
+    if (ext_file == NULL) {
+        if(H5P_get(plist, H5L_ACS_ELINK_PREFIX_NAME, &my_prefix) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get external link prefix")
+        if (my_prefix) {
+            if (H5L_build_name(my_prefix, tempname, &full_name/*out*/) < 0)
+                HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't prepend prefix to filename")
+            if ((ext_file=H5F_open(full_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                        H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
+                H5E_clear_stack(NULL);
+            if (full_name)
+                H5MM_xfree(full_name);
+        }
+    }
+
+    /* try searching from main file's "extpath":see description in H5F_open() & H5_build_extpath() */
+    if ((ext_file == NULL) && (extpath=H5F_EXTPATH(loc.oloc->file))) {
+        if (H5L_build_name(extpath, tempname, &full_name/*out*/) < 0)
+            HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't prepend prefix to filename")
+        if ((ext_file = H5F_open(full_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                    H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
+            H5E_clear_stack(NULL);
+        if (full_name)
+            H5MM_xfree(full_name);
+    }
+
+    /* try the relative file_name stored in tempname */
+    if (ext_file == NULL) {
+        if ((ext_file=H5F_open(tempname, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                        H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
+            HGOTO_ERROR(H5E_LINK, H5E_CANTOPENFILE, FAIL, "unable to open external file")
+    }
+
+    if (tempname)
+        H5MM_xfree(tempname);
 
     /* Increment the number of open objects, to hold the file open */
     H5F_incr_nopen_objs(ext_file);
@@ -219,10 +363,6 @@ done:
     if(ext_file && H5F_try_close(ext_file) < 0)
         HDONE_ERROR(H5E_LINK, H5E_CANTCLOSEFILE, FAIL, "problem closing external file")
 
-    /* Free full_name if it's been allocated */
-    if(full_name)
-        H5MM_xfree(full_name);
-
     /* Close object if it's open and something failed */
     if(ret_value < 0 && ext_obj >= 0 && H5I_dec_ref(ext_obj) < 0)
         HDONE_ERROR(H5E_ATOM, H5E_CANTRELEASE, FAIL, "unable to close atom for external object")
diff --git a/src/H5Odtype.c b/src/H5Odtype.c
index ac07edf..ba343bc 100644
--- a/src/H5Odtype.c
+++ b/src/H5Odtype.c
@@ -232,10 +232,11 @@ H5O_dtype_decode_helper(H5F_t *f, const uint8_t **pp, H5T_t *dt)
         case H5T_COMPOUND:
             {
                 unsigned offset_nbytes;         /* Size needed to encode member offsets */
+                size_t max_memb_pos = 0;        /* Maximum member covered, so far */
                 unsigned j;
 
                 /* Compute the # of bytes required to store a member offset */
-                offset_nbytes = (H5V_log2_gen((uint64_t)dt->shared->size) + 7) / 8;
+                offset_nbytes = H5V_limit_enc_size((uint64_t)dt->shared->size);
 
                 /*
                  * Compound datatypes...
@@ -336,6 +337,18 @@ H5O_dtype_decode_helper(H5F_t *f, const uint8_t **pp, H5T_t *dt)
                     /* Set the field datatype (finally :-) */
                     dt->shared->u.compnd.memb[i].type = temp_type;
 
+                    /* Check if this field overlaps with a prior field */
+                    /* (probably indicates that the file is corrupt) */
+                    if(i > 0 && dt->shared->u.compnd.memb[i].offset < max_memb_pos) {
+                        for(j = 0; j < i; j++)
+                            if(dt->shared->u.compnd.memb[i].offset >= dt->shared->u.compnd.memb[j].offset
+                                    && dt->shared->u.compnd.memb[i].offset < (dt->shared->u.compnd.memb[j].offset + dt->shared->u.compnd.memb[j].size))
+                                HGOTO_ERROR(H5E_DATATYPE, H5E_CANTDECODE, FAIL, "member overlaps with previous member")
+                    } /* end if */
+
+                    /* Update the maximum member position covered */
+                    max_memb_pos = MAX(max_memb_pos, (dt->shared->u.compnd.memb[i].offset + dt->shared->u.compnd.memb[i].size));
+
                     /* Check if the datatype stayed packed */
                     if(dt->shared->u.compnd.packed) {
                         /* Check if the member type is packed */
@@ -734,7 +747,7 @@ H5O_dtype_encode_helper(const H5F_t *f, uint8_t **pp, const H5T_t *dt)
                 unsigned offset_nbytes;         /* Size needed to encode member offsets */
 
                 /* Compute the # of bytes required to store a member offset */
-                offset_nbytes = (H5V_log2_gen((uint64_t)dt->shared->size) + 7) / 8;
+                offset_nbytes = H5V_limit_enc_size((uint64_t)dt->shared->size);
 
                 /*
                  * Compound datatypes...
@@ -1097,7 +1110,7 @@ H5O_dtype_size(const H5F_t *f, const void *_mesg)
                 unsigned offset_nbytes;         /* Size needed to encode member offsets */
 
                 /* Compute the # of bytes required to store a member offset */
-                offset_nbytes = (H5V_log2_gen((uint64_t)dt->shared->size) + 7) / 8;
+                offset_nbytes = H5V_limit_enc_size((uint64_t)dt->shared->size);
 
                 /* Compute the total size needed to encode compound datatype */
                 for(u = 0; u < dt->shared->u.compnd.nmembs; u++) {
diff --git a/src/H5Pdxpl.c b/src/H5Pdxpl.c
index 6affcad..8bc263a 100644
--- a/src/H5Pdxpl.c
+++ b/src/H5Pdxpl.c
@@ -90,9 +90,6 @@
 /* Definitions for I/O transfer mode property */
 #define H5D_XFER_IO_XFER_MODE_SIZE       sizeof(H5FD_mpio_xfer_t)
 #define H5D_XFER_IO_XFER_MODE_DEF        H5FD_MPIO_INDEPENDENT
-/* Definitions for I/O optimization transfer mode property(using MPI-IO independent IO with file set view) */
-#define H5D_XFER_IO_XFER_OPT_MODE_SIZE    sizeof(H5FD_mpio_collective_opt_t)
-#define H5D_XFER_IO_XFER_OPT_MODE_DEF         H5FD_MPIO_COLLECTIVE_IO
 /* Definitions for optimization of MPI-IO transfer mode property */
 #define H5D_XFER_MPIO_COLLECTIVE_OPT_SIZE       sizeof(H5FD_mpio_collective_opt_t)
 #define H5D_XFER_MPIO_COLLECTIVE_OPT_DEF        H5FD_MPIO_COLLECTIVE_IO
@@ -199,7 +196,6 @@ H5P_dxfr_reg_prop(H5P_genclass_t *pclass)
     size_t def_hyp_vec_size = H5D_XFER_HYPER_VECTOR_SIZE_DEF;   /* Default value for vector size */
 #ifdef H5_HAVE_PARALLEL
     H5FD_mpio_xfer_t def_io_xfer_mode = H5D_XFER_IO_XFER_MODE_DEF;      /* Default value for I/O transfer mode */
-    H5FD_mpio_collective_opt_t def_io_xfer_opt_mode = H5D_XFER_IO_XFER_OPT_MODE_DEF;
     H5FD_mpio_chunk_opt_t def_mpio_chunk_opt_mode = H5D_XFER_MPIO_CHUNK_OPT_HARD_DEF;
     H5FD_mpio_collective_opt_t def_mpio_collective_opt_mode = H5D_XFER_MPIO_COLLECTIVE_OPT_DEF;
     unsigned def_mpio_chunk_opt_num = H5D_XFER_MPIO_CHUNK_OPT_NUM_DEF;
@@ -265,8 +261,6 @@ H5P_dxfr_reg_prop(H5P_genclass_t *pclass)
     /* Register the I/O transfer mode property */
     if(H5P_register(pclass, H5D_XFER_IO_XFER_MODE_NAME, H5D_XFER_IO_XFER_MODE_SIZE, &def_io_xfer_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
-    if(H5P_register(pclass, H5D_XFER_IO_XFER_OPT_MODE_NAME, H5D_XFER_IO_XFER_OPT_MODE_SIZE, &def_io_xfer_opt_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
     if(H5P_register(pclass, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME, H5D_XFER_MPIO_COLLECTIVE_OPT_SIZE, &def_mpio_collective_opt_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
     if(H5P_register(pclass, H5D_XFER_MPIO_CHUNK_OPT_HARD_NAME, H5D_XFER_MPIO_CHUNK_OPT_HARD_SIZE, &def_mpio_chunk_opt_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
diff --git a/src/H5S.c b/src/H5S.c
index 8a58cba..4996f1f 100644
--- a/src/H5S.c
+++ b/src/H5S.c
@@ -45,18 +45,6 @@ static herr_t H5S_encode(H5S_t *obj, unsigned char *buf, size_t *nalloc);
 static H5S_t *H5S_decode(const unsigned char *buf);
 static htri_t H5S_extent_equal(const H5S_t *ds1, const H5S_t *ds2);
 
-#ifdef H5S_DEBUG
-/* Names of the selection names, for debugging */
-static const char *H5S_sel_names[]={
-    "none", "point", "hyperslab", "all"
-};
-
-/* The path table, variable length */
-static H5S_iostats_t		**H5S_iostats_g = NULL;
-static size_t			H5S_aiostats_g = 0;	/*entries allocated*/
-static size_t			H5S_niostats_g = 0;	/*entries used*/
-#endif /* H5S_DEBUG */
-
 #ifdef H5_HAVE_PARALLEL
 /* Global vars whose value can be set from environment variable also */
 hbool_t H5S_mpi_opt_types_g = TRUE;
@@ -87,9 +75,9 @@ DESCRIPTION
 static herr_t
 H5S_init_interface(void)
 {
-    herr_t ret_value=SUCCEED;   /* Return value */
+    herr_t ret_value = SUCCEED;   /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5S_init_interface);
+    FUNC_ENTER_NOAPI_NOINIT(H5S_init_interface)
 
     /* Initialize the atom group for the file IDs */
     if(H5I_register_type(H5I_DATASPACE, (size_t)H5I_DATASPACEID_HASHSIZE, H5S_RESERVED_ATOMS, (H5I_free_t)H5S_close) < 0)
@@ -105,8 +93,8 @@ H5S_init_interface(void)
 #endif /* H5_HAVE_PARALLEL */
 
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
-}
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S_init_interface() */
 
 
 /*--------------------------------------------------------------------------
@@ -129,156 +117,26 @@ done:
 int
 H5S_term_interface(void)
 {
-    int	n=0;
-#ifdef H5S_DEBUG
-    size_t	i;
-    int		j, nprints=0;
-    H5S_iostats_t	*path=NULL;
-    char	buf[256];
-#endif /* H5S_DEBUG */
-
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5S_term_interface);
-
-    if (H5_interface_initialize_g) {
-	if ((n=H5I_nmembers(H5I_DATASPACE))) {
-	    H5I_clear_type(H5I_DATASPACE, FALSE);
-	} else {
-#ifdef H5S_DEBUG
-	    /*
-	     * Print statistics about each conversion path.
-	     */
-	    if (H5DEBUG(S)) {
-		for (i=0; i<H5S_niostats_g; i++) {
-		    path = H5S_iostats_g[i];
-		    for (j=0; j<2; j++) {
-			if (0==path->stats[j].gath_ncalls &&
-			    0==path->stats[j].scat_ncalls &&
-			    0==path->stats[j].bkg_ncalls &&
-			    0==path->stats[j].read_ncalls &&
-			    0==path->stats[j].write_ncalls) {
-			    continue;
-			}
-			if (0==nprints++) {
-			    fprintf(H5DEBUG(S), "H5S: data space conversion "
-				    "statistics:\n");
-			    fprintf(H5DEBUG(S),
-				    "   %-16s %10s %10s %8s %8s %8s %10s\n",
-				    "Memory <> File", "Bytes", "Calls",
-				    "User", "System", "Elapsed", "Bandwidth");
-			    fprintf(H5DEBUG(S),
-				    "   %-16s %10s %10s %8s %8s %8s %10s\n",
-				    "--------------", "-----", "-----",
-				    "----", "------", "-------", "---------");
-			}
-
-			/* Summary */
-			sprintf(buf, "%s %c %s",
-				H5S_sel_names[path->mtype], 0==j?'>':'<', H5S_sel_names[path->ftype]);
-			fprintf(H5DEBUG(S), "   %-16s\n", buf);
-
-			/* Gather */
-			if (path->stats[j].gath_ncalls) {
-			    H5_bandwidth(buf,
-					 (double)(path->stats[j].gath_nbytes),
-					 path->stats[j].gath_timer.etime);
-			    HDfprintf(H5DEBUG(S),
-				      "   %16s %10Hu %10Hu %8.2f %8.2f %8.2f "
-				      "%10s\n", "gather",
-				      path->stats[j].gath_nbytes,
-				      path->stats[j].gath_ncalls,
-				      path->stats[j].gath_timer.utime,
-				      path->stats[j].gath_timer.stime,
-				      path->stats[j].gath_timer.etime,
-				      buf);
-			}
-
-			/* Scatter */
-			if (path->stats[j].scat_ncalls) {
-			    H5_bandwidth(buf,
-					 (double)(path->stats[j].scat_nbytes),
-					 path->stats[j].scat_timer.etime);
-			    HDfprintf(H5DEBUG(S),
-				      "   %16s %10Hu %10Hu %8.2f %8.2f %8.2f "
-				      "%10s\n", "scatter",
-				      path->stats[j].scat_nbytes,
-				      path->stats[j].scat_ncalls,
-				      path->stats[j].scat_timer.utime,
-				      path->stats[j].scat_timer.stime,
-				      path->stats[j].scat_timer.etime,
-				      buf);
-			}
-
-			/* Background */
-			if (path->stats[j].bkg_ncalls) {
-			    H5_bandwidth(buf,
-					 (double)(path->stats[j].bkg_nbytes),
-					 path->stats[j].bkg_timer.etime);
-			    HDfprintf(H5DEBUG(S),
-				      "   %16s %10Hu %10Hu %8.2f %8.2f %8.2f "
-				      "%10s\n", "background",
-				      path->stats[j].bkg_nbytes,
-				      path->stats[j].bkg_ncalls,
-				      path->stats[j].bkg_timer.utime,
-				      path->stats[j].bkg_timer.stime,
-				      path->stats[j].bkg_timer.etime,
-				      buf);
-			}
-
-			/* Read */
-			if (path->stats[j].read_ncalls) {
-			    H5_bandwidth(buf,
-					 (double)(path->stats[j].read_nbytes),
-					 path->stats[j].read_timer.etime);
-			    HDfprintf(H5DEBUG(S),
-				      "   %16s %10Hu %10Hu %8.2f %8.2f %8.2f "
-				      "%10s\n", "read",
-				      path->stats[j].read_nbytes,
-				      path->stats[j].read_ncalls,
-				      path->stats[j].read_timer.utime,
-				      path->stats[j].read_timer.stime,
-				      path->stats[j].read_timer.etime,
-				      buf);
-			}
-
-			/* Write */
-			if (path->stats[j].write_ncalls) {
-			    H5_bandwidth(buf,
-					 (double)(path->stats[j].write_nbytes),
-					 path->stats[j].write_timer.etime);
-			    HDfprintf(H5DEBUG(S),
-				      "   %16s %10Hu %10Hu %8.2f %8.2f %8.2f "
-				      "%10s\n", "write",
-				      path->stats[j].write_nbytes,
-				      path->stats[j].write_ncalls,
-				      path->stats[j].write_timer.utime,
-				      path->stats[j].write_timer.stime,
-				      path->stats[j].write_timer.etime,
-				      buf);
-			}
-		    }
-		}
-	    }
-#endif /* H5S_DEBUG */
+    int	n = 0;
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5S_term_interface)
 
+    if(H5_interface_initialize_g) {
+	if((n = H5I_nmembers(H5I_DATASPACE))) {
+	    H5I_clear_type(H5I_DATASPACE, FALSE);
+	} /* end if */
+        else {
 	    /* Free data types */
 	    H5I_dec_type_ref(H5I_DATASPACE);
 
-#ifdef H5S_DEBUG
-	    /* Clear/free conversion table */
-	    for (i=0; i<H5S_niostats_g; i++)
-                H5MM_xfree(H5S_iostats_g[i]);
-	    H5S_iostats_g = H5MM_xfree(H5S_iostats_g);
-	    H5S_niostats_g = H5S_aiostats_g = 0;
-#endif /* H5S_DEBUG */
-
 	    /* Shut down interface */
 	    H5_interface_initialize_g = 0;
 	    n = 1; /*H5I*/
-	}
-    }
+	} /* end else */
+    } /* end if */
 
-    FUNC_LEAVE_NOAPI(n);
-}
+    FUNC_LEAVE_NOAPI(n)
+} /* end H5S_term_interface() */
 
 
 /*--------------------------------------------------------------------------
@@ -1384,105 +1242,6 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5S_set_extent_simple() */
 
-#ifdef H5S_DEBUG
-
-/*-------------------------------------------------------------------------
- * Function:	H5S_find
- *
- * Purpose:	Given two data spaces (MEM_SPACE and FILE_SPACE) this
- *		function returns a pointer to the conversion path information,
- *		creating a new conversion path entry if necessary.
- *
- * Return:	Success:	Ptr to a conversion path entry
- *
- *		Failure:	NULL
- *
- * Programmer:	Robb Matzke
- *		Wednesday, January 21, 1998
- *
- * Modifications:
- *
- * 	Quincey Koziol
- *	Instead of returning a point into the data space conversion table we
- *	copy all the information into a user-supplied CONV buffer and return
- *	non-negative on success or negative on failure.
- *
- * 	Robb Matzke, 11 Aug 1998
- *	Returns a pointer into the conversion path table.  A path entry
- *	contains pointers to the memory and file half of the conversion (the
- *	pointers registered in the H5S_fconv_g[] and H5S_mconv_g[] tables)
- *	along with other data whose scope is the conversion path (like path
- *	statistics).
- *
- *	John Mainzer, 8/30/04
- *	Modified code to check with all other processes that have the
- *	file open before OKing collective I/O.
- *
- *-------------------------------------------------------------------------
- */
-H5S_iostats_t *
-H5S_find (const H5S_t *mem_space, const H5S_t *file_space)
-{
-    H5S_iostats_t	*path=NULL;  /* Space conversion path */
-    size_t	u;      /* Index variable */
-    H5S_iostats_t *ret_value;   /* Return value */
-
-    FUNC_ENTER_NOAPI(H5S_find, NULL);
-
-    /* Check args */
-    assert (mem_space && (H5S_SIMPLE==H5S_GET_EXTENT_TYPE(mem_space) ||
-                          H5S_NULL==H5S_GET_EXTENT_TYPE(mem_space) ||
-			  H5S_SCALAR==H5S_GET_EXTENT_TYPE(mem_space)));
-    assert (file_space && (H5S_SIMPLE==H5S_GET_EXTENT_TYPE(file_space) ||
-                           H5S_NULL==H5S_GET_EXTENT_TYPE(file_space) ||
-			   H5S_SCALAR==H5S_GET_EXTENT_TYPE(file_space)));
-
-    /*
-     * Is this path already present in the data space conversion path table?
-     * If so then return a pointer to that entry.
-     */
-    for (u=0; u<H5S_niostats_g; u++)
-        if (H5S_iostats_g[u]->ftype==H5S_GET_SELECT_TYPE(file_space) &&
-                H5S_iostats_g[u]->mtype==H5S_GET_SELECT_TYPE(mem_space))
-            HGOTO_DONE(H5S_iostats_g[u]);
-
-    /*
-     * The path wasn't found.  Create a new path.
-     */
-    if (NULL==(path = H5MM_calloc(sizeof(*path))))
-        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed for data space conversion path")
-
-    /* Initialize file & memory conversion functions */
-    path->ftype = H5S_GET_SELECT_TYPE(file_space);
-    path->mtype = H5S_GET_SELECT_TYPE(mem_space);
-
-    /*
-     * Add the new path to the table.
-     */
-    if (H5S_niostats_g>=H5S_aiostats_g) {
-        size_t n = MAX(10, 2*H5S_aiostats_g);
-        H5S_iostats_t **p = H5MM_realloc(H5S_iostats_g, n*sizeof(H5S_iostats_g[0]));
-
-        if (NULL==p)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed for data space conversion path table")
-        H5S_aiostats_g = n;
-        H5S_iostats_g = p;
-    } /* end if */
-    H5S_iostats_g[H5S_niostats_g++] = path;
-
-    /* Set the return value */
-    ret_value=path;
-
-done:
-    if(ret_value==NULL) {
-        if(path!=NULL)
-            H5MM_xfree(path);
-    } /* end if */
-
-    FUNC_LEAVE_NOAPI(ret_value);
-} /* end H5S_find() */
-#endif /* H5S_DEBUG */
-
 
 /*-------------------------------------------------------------------------
  * Function:	H5Screate_simple
diff --git a/src/H5Smpio.c b/src/H5Smpio.c
index cc89b49..725b8fc 100644
--- a/src/H5Smpio.c
+++ b/src/H5Smpio.c
@@ -123,7 +123,7 @@ H5S_mpio_all_type( const H5S_t *space, size_t elmt_size,
     *new_type = MPI_BYTE;
     H5_ASSIGN_OVERFLOW(*count, total_bytes, hsize_t, size_t);
     *extra_offset = 0;
-    *is_derived_type = 0;
+    *is_derived_type = FALSE;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value);
@@ -163,7 +163,7 @@ H5S_mpio_none_type( const H5S_t UNUSED *space, size_t UNUSED elmt_size,
     *new_type = MPI_BYTE;
     *count = 0;
     *extra_offset = 0;
-    *is_derived_type = 0;
+    *is_derived_type = FALSE;
 
     FUNC_LEAVE_NOAPI(SUCCEED);
 } /* H5S_mpio_none_type() */
@@ -456,7 +456,7 @@ H5S_mpio_hyper_type( const H5S_t *space, size_t elmt_size,
     /* fill in the remaining return values */
     *count = 1;			/* only have to move one of these suckers! */
     *extra_offset = 0;
-    *is_derived_type = 1;
+    *is_derived_type = TRUE;
     HGOTO_DONE(SUCCEED);
 
 empty:
@@ -464,7 +464,7 @@ empty:
     *new_type = MPI_BYTE;
     *count = 0;
     *extra_offset = 0;
-    *is_derived_type = 0;
+    *is_derived_type = FALSE;
 
 done:
     /* Release selection iterator */
@@ -475,7 +475,7 @@ done:
 
 #ifdef H5S_DEBUG
   if(H5DEBUG(S)){
-    HDfprintf(H5DEBUG(S), "Leave %s, count=%ld  is_derived_type=%d\n",
+    HDfprintf(H5DEBUG(S), "Leave %s, count=%ld  is_derived_type=%t\n",
 		FUNC, *count, *is_derived_type );
   }
 #endif
@@ -556,7 +556,7 @@ H5S_mpio_span_hyper_type( const           H5S_t *space,
     /* fill in the remaining return values */
     *count = 1;
     *extra_offset = 0;
-    *is_derived_type = 1;
+    *is_derived_type = TRUE;
 
     HGOTO_DONE(SUCCEED);
 
@@ -565,7 +565,7 @@ empty:
     *new_type        = MPI_BYTE;
     *count           = 0;
     *extra_offset    = 0;
-    *is_derived_type = 0;
+    *is_derived_type = FALSE;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value);
diff --git a/src/H5Sprivate.h b/src/H5Sprivate.h
index bd27f09..8744872 100644
--- a/src/H5Sprivate.h
+++ b/src/H5Sprivate.h
@@ -115,31 +115,6 @@ typedef struct H5S_sel_iter_t {
     } u;
 } H5S_sel_iter_t;
 
-#ifdef H5S_DEBUG
-typedef struct H5S_iostats_t {
-    H5S_sel_type	ftype;
-    H5S_sel_type	mtype;
-
-    struct {
-	H5_timer_t	scat_timer;		/*time spent scattering	*/
-	hsize_t		scat_nbytes;		/*scatter throughput	*/
-	hsize_t		scat_ncalls;		/*number of calls	*/
-	H5_timer_t	gath_timer;		/*time spent gathering	*/
-	hsize_t		gath_nbytes;		/*gather throughput	*/
-	hsize_t		gath_ncalls;		/*number of calls	*/
-	H5_timer_t	bkg_timer;		/*time for background	*/
-	hsize_t		bkg_nbytes;		/*background throughput	*/
-	hsize_t		bkg_ncalls;		/*number of calls	*/
-	H5_timer_t	read_timer;		/*time for read calls	*/
-	hsize_t		read_nbytes;		/*total bytes read	*/
-	hsize_t		read_ncalls;		/*number of calls	*/
-	H5_timer_t	write_timer;		/*time for write calls	*/
-	hsize_t		write_nbytes;		/*total bytes written	*/
-	hsize_t		write_ncalls;		/*number of calls	*/
-    } stats[2];		/* 0=output, 1=input */
-} H5S_iostats_t;
-#endif
-
 /* If the module using this macro is allowed access to the private variables, access them directly */
 #ifdef H5S_PACKAGE
 #define H5S_GET_EXTENT_TYPE(S)          ((S)->extent.type)
@@ -198,9 +173,6 @@ typedef struct H5S_iostats_t {
 /* Operations on dataspaces */
 H5_DLL H5S_t *H5S_copy(const H5S_t *src, hbool_t share_selection, hbool_t copy_max);
 H5_DLL herr_t H5S_close(H5S_t *ds);
-#ifdef H5S_DEBUG
-H5_DLL H5S_iostats_t *H5S_find(const H5S_t *mem_space, const H5S_t *file_space);
-#endif /* H5S_DEBUG */
 H5_DLL H5S_class_t H5S_get_simple_extent_type(const H5S_t *ds);
 H5_DLL hssize_t H5S_get_simple_extent_npoints(const H5S_t *ds);
 H5_DLL hsize_t H5S_get_npoints_max(const H5S_t *ds);
diff --git a/src/H5T.c b/src/H5T.c
index 04d6c0b..c726e5c 100644
--- a/src/H5T.c
+++ b/src/H5T.c
@@ -4552,7 +4552,7 @@ H5T_path_compound_subset(const H5T_path_t *p)
 
     FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5T_path_compound_subset);
 
-    assert(p);
+    HDassert(p);
 
     if(p->are_compounds)
         ret_value = H5T_conv_struct_subset(&(p->cdata));
diff --git a/src/H5Tconv.c b/src/H5Tconv.c
index 0da4d53..7803d07 100644
--- a/src/H5Tconv.c
+++ b/src/H5Tconv.c
@@ -1890,17 +1890,15 @@ H5T_subset_t
 H5T_conv_struct_subset(const H5T_cdata_t *cdata)
 {
     H5T_conv_struct_t	*priv;
-    H5T_subset_t        ret_value;       /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5T_conv_struct_subset)
 
     HDassert(cdata);
     HDassert(cdata->priv);
 
-    priv = (H5T_conv_struct_t*)(cdata->priv);
-    ret_value = priv->smembs_subset;
+    priv = (H5T_conv_struct_t *)(cdata->priv);
 
-    FUNC_LEAVE_NOAPI(ret_value)
+    FUNC_LEAVE_NOAPI(priv->smembs_subset)
 } /* end H5T_conv_struct_subset() */
 
 
diff --git a/src/H5Tprivate.h b/src/H5Tprivate.h
index dfe2367..2fe4c3a 100644
--- a/src/H5Tprivate.h
+++ b/src/H5Tprivate.h
@@ -69,7 +69,7 @@ typedef struct H5T_conv_cb_t {
 
 /* Values for the optimization of compound data reading and writing.  They indicate
  * whether the fields of the source and destination are subset of each other and
- * there is no conversion needed.  It's for the Chicago company.
+ * there is no conversion needed.
  */
 typedef enum {
     H5T_SUBSET_BADVALUE = -1,   /* Invalid value */
diff --git a/src/H5Vprivate.h b/src/H5Vprivate.h
index 94b3699..b92266c 100644
--- a/src/H5Vprivate.h
+++ b/src/H5Vprivate.h
@@ -410,5 +410,25 @@ H5V_log2_of2(uint32_t n)
     return(MultiplyDeBruijnBitPosition[(n * (uint32_t)0x077CB531UL) >> 27]);
 } /* H5V_log2_of2() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5V_limit_enc_size
+ *
+ * Purpose:     Determine the # of bytes needed to encode values within a
+ *              range from 0 to a given limit
+ *
+ * Return:      Number of bytes needed
+ *
+ * Programmer:  Quincey Koziol
+ *              Thursday, March 13, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static H5_inline unsigned UNUSED
+H5V_limit_enc_size(uint64_t limit)
+{
+    return (H5V_log2_gen(limit) / 8) + 1;
+} /* end H5V_limit_enc_size() */
+
 #endif /* H5Vprivate_H */
 
diff --git a/src/H5config.h.in b/src/H5config.h.in
index 5c767ef..77a3b23 100644
--- a/src/H5config.h.in
+++ b/src/H5config.h.in
@@ -368,6 +368,9 @@
 /* Define to 1 if you have the `waitpid' function. */
 #undef HAVE_WAITPID
 
+/* Define if your system has window style path name. */
+#undef HAVE_WINDOW_PATH
+
 /* Define to 1 if you have the <winsock.h> header file. */
 #undef HAVE_WINSOCK_H
 
diff --git a/src/H5private.h b/src/H5private.h
index 11f3037..b60c50a 100644
--- a/src/H5private.h
+++ b/src/H5private.h
@@ -638,7 +638,15 @@ H5_DLL int HDfprintf (FILE *stream, const char *fmt, ...);
 #define HDfwrite(M,Z,N,F)	fwrite(M,Z,N,F)
 #define HDgetc(F)		getc(F)
 #define HDgetchar()		getchar()
+#ifdef _WIN32
+#define HDgetcwd(S,Z)		_getcwd(S,Z)
+#define HDgetdcwd(D,S,Z)	_getdcwd(D,S,Z)
+#define HDgetdrive()		_getdrive()
+#else
 #define HDgetcwd(S,Z)		getcwd(S,Z)
+#define HDgetdcwd(D,S,Z)	getcwd(S,Z)
+#define HDgetdrive()		0
+#endif
 #define HDgetegid()		getegid()
 #define HDgetenv(S)		getenv(S)
 #define HDgeteuid()		geteuid()
@@ -911,6 +919,42 @@ extern char *strdup(const char *s);
 
 #endif /* _WIN32 */
 
+#ifdef H5_HAVE_WINDOW_PATH
+
+/* directory delimiter for Windows: slash and backslash are acceptable on Windows */
+#define	DIR_SLASH_SEPC 		'/'
+#define	DIR_SEPC 		'\\'
+#define	DIR_SEPS 		"\\"
+#define CHECK_DELIMITER(SS)     ((SS == DIR_SEPC)||(SS == DIR_SLASH_SEPC))
+#define CHECK_ABSOLUTE(NAME)    ((isalpha(NAME[0])) && (NAME[1] == ':') && (CHECK_DELIMITER(NAME[2])))
+#define CHECK_ABS_DRIVE(NAME)   ((isalpha(NAME[0])) && (NAME[1] == ':'))
+#define CHECK_ABS_PATH(NAME)    (CHECK_DELIMITER(NAME[0]))
+
+#define GET_LAST_DELIMITER(NAME, ptr) {                 \
+    char        *slash, *backslash;                     \
+    slash = strrchr(NAME, DIR_SLASH_SEPC);              \
+    backslash = strrchr(NAME, DIR_SEPC);                \
+    if (backslash > slash)                              \
+        (ptr = backslash);                              \
+    else                                                \
+        (ptr = slash);                                  \
+}
+
+#else
+
+#define		DIR_SEPC	'/'
+#define		DIR_SEPS	"/"
+#define         CHECK_DELIMITER(SS)             (SS == DIR_SEPC)
+#define         CHECK_ABSOLUTE(NAME)            (CHECK_DELIMITER(*NAME))
+#define 	CHECK_ABS_DRIVE(NAME)   	(0)
+#define 	CHECK_ABS_PATH(NAME)    	(0)
+#define         GET_LAST_DELIMITER(NAME, ptr)   ptr = strrchr(NAME, DIR_SEPC);
+
+#endif
+
+#define 	COLON_SEPC	':'
+H5_DLL herr_t   H5_build_extpath(const char *, char ** /*out*/ );
+
 
 /*
  * These macros check whether debugging has been requested for a certain
diff --git a/src/H5public.h b/src/H5public.h
index 06060dd..5606171 100644
--- a/src/H5public.h
+++ b/src/H5public.h
@@ -70,11 +70,11 @@ extern "C" {
 
 /* Version numbers */
 #define H5_VERS_MAJOR	1	/* For major interface/format changes  	     */
-#define H5_VERS_MINOR	8	/* For minor interface/format changes  	     */
-#define H5_VERS_RELEASE	0	/* For tweaks, bug-fixes, or development     */
+#define H5_VERS_MINOR	9	/* For minor interface/format changes  	     */
+#define H5_VERS_RELEASE	5	/* For tweaks, bug-fixes, or development     */
 #define H5_VERS_SUBRELEASE ""	/* For pre-releases like snap0       */
 				/* Empty string for real releases.           */
-#define H5_VERS_INFO    "HDF5 library version: 1.8.0"      /* Full version string */
+#define H5_VERS_INFO    "HDF5 library version: 1.9.5"      /* Full version string */
 
 #define H5check()	H5check_version(H5_VERS_MAJOR,H5_VERS_MINOR,	      \
 				        H5_VERS_RELEASE)
diff --git a/src/H5system.c b/src/H5system.c
index 5eae11d..4a49d71 100644
--- a/src/H5system.c
+++ b/src/H5system.c
@@ -35,6 +35,8 @@
 #include "H5private.h"		/* Generic Functions			*/
 #include "H5Fprivate.h"		/* File access				*/
 #include "H5MMprivate.h"	/* Memory management			*/
+#include "H5Eprivate.h"
+
 
 
 /****************/
@@ -578,4 +580,100 @@ HDremove_all(const char *fname)
 }
 #endif
 
+
+/*
+ *-------------------------------------------------------------------------
+ *
+ * Function: H5_build_extpath
+ *
+ * Purpose:  To build the path for later searching of target file for external link.
+ *   	     This path can be either:
+ *                      1. The absolute path of NAME
+ *                      or
+ *                      2. The current working directory + relative path of NAME
+ *
+ * Return:	Success:        0
+ *		Failure:	-1
+ *
+ * Programmer:	Vailin Choi
+ *		April 2, 2008
+ *-------------------------------------------------------------------------
+ */
+#define MAX_PATH_LEN     1024
+
+herr_t
+H5_build_extpath(const char *name, char **extpath/*out*/)
+{
+    char        *full_path=NULL, *ptr=NULL;
+    char        *retcwd=NULL, *cwdpath=NULL, *new_name=NULL;
+    int         drive;
+    size_t      cwdlen, path_len;
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5_build_extpath)
+
+    *extpath = NULL;
+
+    /* 
+     * Unix: name[0] is a "/"
+     * Windows: name[0-2] is "<drive letter>:\" or "<drive-letter>:/"
+     */
+    if (CHECK_ABSOLUTE(name)) {
+        if ((full_path=H5MM_strdup(name)) == NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+    } else { /* relative pathname */
+        if ((cwdpath=H5MM_malloc(MAX_PATH_LEN)) == NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+        if ((new_name=H5MM_strdup(name)) == NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+	/* 
+	 * Windows: name[0-1] is "<drive-letter>:"
+	 * 	Get current working directory on the drive specified in NAME 
+	 * Unix: does not apply
+	 */
+        if (CHECK_ABS_DRIVE(name)) {
+            drive = name[0] - 'A' + 1;
+            retcwd = HDgetdcwd(drive, cwdpath, MAX_PATH_LEN);
+            HDstrcpy(new_name, &name[2]);
+	/* 
+	 * Windows: name[0] is a '/' or '\' 
+	 *	Get current drive
+	 * Unix: does not apply
+	 */
+        } else if (CHECK_ABS_PATH(name) && (drive=HDgetdrive())) {
+            sprintf(cwdpath, "%c:%c", (drive+'A'-1), name[0]);
+            retcwd = cwdpath;
+            HDstrcpy(new_name, &name[1]);
+        } else /* totally relative for both Unix and Windows: get current working directory  */
+            retcwd = HDgetcwd(cwdpath, MAX_PATH_LEN);
+
+        if (retcwd != NULL) {
+            cwdlen = HDstrlen(cwdpath);
+            HDassert(cwdlen);
+            path_len = cwdlen + HDstrlen(new_name) + 2;
+            if ((full_path=H5MM_malloc(path_len)) == NULL)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+            HDstrcpy(full_path, cwdpath);
+            if (!CHECK_DELIMITER(cwdpath[cwdlen-1]))
+                HDstrcat(full_path, DIR_SEPS);
+            HDstrcat(full_path, new_name);
+        }
+    }
+
+    /* strip out the last component (the file name itself) from the path */
+    if (full_path) {
+        GET_LAST_DELIMITER(full_path, ptr)
+        HDassert(ptr);
+        *++ptr = '\0';
+        *extpath = full_path;
+    }
 
+done:
+    if (cwdpath)
+	H5MM_xfree(cwdpath);
+    if (new_name)
+	H5MM_xfree(new_name);
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5_build_extpath() */
diff --git a/src/Makefile.am b/src/Makefile.am
index 0e5030b..fcb47e2 100755
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -46,10 +46,10 @@ libhdf5_la_SOURCES= H5.c H5checksum.c H5dbg.c H5system.c H5timer.c H5trace.c \
         H5AC.c H5B.c H5Bcache.c \
         H5B2.c H5B2cache.c H5B2dbg.c H5B2int.c H5B2stat.c H5B2test.c \
         H5C.c H5CS.c \
-        H5D.c H5Dcompact.c H5Dcontig.c H5Ddbg.c \
+        H5D.c H5Dchunk.c H5Dcompact.c H5Dcontig.c H5Ddbg.c \
         H5Ddeprec.c H5Defl.c H5Dfill.c H5Dint.c \
         H5Dio.c \
-        H5Distore.c H5Dmpio.c H5Doh.c H5Dselect.c H5Dtest.c \
+        H5Distore.c H5Dmpio.c H5Doh.c H5Dscatgath.c H5Dselect.c H5Dtest.c \
         H5E.c H5Edeprec.c H5Eint.c \
         H5F.c H5Fdbg.c H5Ffake.c H5Fmount.c H5Fsfile.c H5Fsuper.c H5Ftest.c \
         H5FD.c H5FDcore.c  \
diff --git a/src/Makefile.in b/src/Makefile.in
index 085bf96..8e8f339 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -82,19 +82,20 @@ am_libhdf5_la_OBJECTS = H5.lo H5checksum.lo H5dbg.lo H5system.lo \
 	H5timer.lo H5trace.lo H5A.lo H5Abtree2.lo H5Adense.lo \
 	H5Adeprec.lo H5Aint.lo H5Atest.lo H5AC.lo H5B.lo H5Bcache.lo \
 	H5B2.lo H5B2cache.lo H5B2dbg.lo H5B2int.lo H5B2stat.lo \
-	H5B2test.lo H5C.lo H5CS.lo H5D.lo H5Dcompact.lo H5Dcontig.lo \
-	H5Ddbg.lo H5Ddeprec.lo H5Defl.lo H5Dfill.lo H5Dint.lo H5Dio.lo \
-	H5Distore.lo H5Dmpio.lo H5Doh.lo H5Dselect.lo H5Dtest.lo \
-	H5E.lo H5Edeprec.lo H5Eint.lo H5F.lo H5Fdbg.lo H5Ffake.lo \
-	H5Fmount.lo H5Fsfile.lo H5Fsuper.lo H5Ftest.lo H5FD.lo \
-	H5FDcore.lo H5FDdirect.lo H5FDfamily.lo H5FDlog.lo H5FDmpi.lo \
-	H5FDmpio.lo H5FDmpiposix.lo H5FDmulti.lo H5FDsec2.lo \
-	H5FDspace.lo H5FDstdio.lo H5FL.lo H5FO.lo H5FS.lo H5FScache.lo \
-	H5FSdbg.lo H5FSsection.lo H5G.lo H5Gbtree2.lo H5Gcompact.lo \
-	H5Gdense.lo H5Gdeprec.lo H5Gent.lo H5Gint.lo H5Glink.lo \
-	H5Gloc.lo H5Gname.lo H5Gnode.lo H5Gobj.lo H5Goh.lo H5Gstab.lo \
-	H5Gtest.lo H5Gtraverse.lo H5HF.lo H5HFbtree2.lo H5HFcache.lo \
-	H5HFdbg.lo H5HFdblock.lo H5HFdtable.lo H5HFhdr.lo H5HFhuge.lo \
+	H5B2test.lo H5C.lo H5CS.lo H5D.lo H5Dchunk.lo H5Dcompact.lo \
+	H5Dcontig.lo H5Ddbg.lo H5Ddeprec.lo H5Defl.lo H5Dfill.lo \
+	H5Dint.lo H5Dio.lo H5Distore.lo H5Dmpio.lo H5Doh.lo \
+	H5Dscatgath.lo H5Dselect.lo H5Dtest.lo H5E.lo H5Edeprec.lo \
+	H5Eint.lo H5F.lo H5Fdbg.lo H5Ffake.lo H5Fmount.lo H5Fsfile.lo \
+	H5Fsuper.lo H5Ftest.lo H5FD.lo H5FDcore.lo H5FDdirect.lo \
+	H5FDfamily.lo H5FDlog.lo H5FDmpi.lo H5FDmpio.lo \
+	H5FDmpiposix.lo H5FDmulti.lo H5FDsec2.lo H5FDspace.lo \
+	H5FDstdio.lo H5FL.lo H5FO.lo H5FS.lo H5FScache.lo H5FSdbg.lo \
+	H5FSsection.lo H5G.lo H5Gbtree2.lo H5Gcompact.lo H5Gdense.lo \
+	H5Gdeprec.lo H5Gent.lo H5Gint.lo H5Glink.lo H5Gloc.lo \
+	H5Gname.lo H5Gnode.lo H5Gobj.lo H5Goh.lo H5Gstab.lo H5Gtest.lo \
+	H5Gtraverse.lo H5HF.lo H5HFbtree2.lo H5HFcache.lo H5HFdbg.lo \
+	H5HFdblock.lo H5HFdtable.lo H5HFhdr.lo H5HFhuge.lo \
 	H5HFiblock.lo H5HFiter.lo H5HFman.lo H5HFsection.lo \
 	H5HFspace.lo H5HFstat.lo H5HFtest.lo H5HFtiny.lo H5HG.lo \
 	H5HGdbg.lo H5HL.lo H5HLdbg.lo H5HP.lo H5I.lo H5L.lo \
@@ -383,7 +384,7 @@ CHECK_CLEANFILES = *.chkexe *.chklog *.clog
 # Add libtool shared library version numbers to the HDF5 library
 # See libtool versioning documentation online.
 LT_VERS_INTERFACE = 5
-LT_VERS_REVISION = 0
+LT_VERS_REVISION = 6
 LT_VERS_AGE = 0
 H5detect_CFLAGS = -g
 
@@ -404,10 +405,10 @@ libhdf5_la_SOURCES = H5.c H5checksum.c H5dbg.c H5system.c H5timer.c H5trace.c \
         H5AC.c H5B.c H5Bcache.c \
         H5B2.c H5B2cache.c H5B2dbg.c H5B2int.c H5B2stat.c H5B2test.c \
         H5C.c H5CS.c \
-        H5D.c H5Dcompact.c H5Dcontig.c H5Ddbg.c \
+        H5D.c H5Dchunk.c H5Dcompact.c H5Dcontig.c H5Ddbg.c \
         H5Ddeprec.c H5Defl.c H5Dfill.c H5Dint.c \
         H5Dio.c \
-        H5Distore.c H5Dmpio.c H5Doh.c H5Dselect.c H5Dtest.c \
+        H5Distore.c H5Dmpio.c H5Doh.c H5Dscatgath.c H5Dselect.c H5Dtest.c \
         H5E.c H5Edeprec.c H5Eint.c \
         H5F.c H5Fdbg.c H5Ffake.c H5Fmount.c H5Fsfile.c H5Fsuper.c H5Ftest.c \
         H5FD.c H5FDcore.c  \
@@ -602,6 +603,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5C.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5CS.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5D.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Dchunk.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Dcompact.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Dcontig.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Ddbg.Plo@am__quote@
@@ -613,6 +615,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Distore.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Dmpio.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Doh.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Dscatgath.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Dselect.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Dtest.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5E.Plo@am__quote@