[svn-r19890] Add initial implementation for H5Ocompare and usage in h5diff. Currentlyinactive/h5ocompare

incomplete/experimental.  Note that if 2 datasets are not comparable by direct
binary comparison, H5Ocompare (and h5diff!) will report that they are different.
Do not use in production.

Tested: Fedora, jam

14 files changed, 1467 insertions, 8 deletions

diff --git a/src/H5Dchunk.c b/src/H5Dchunk.c
index e7a5bf1..34c7e1a 100644
--- a/src/H5Dchunk.c
+++ b/src/H5Dchunk.c
@@ -186,6 +186,9 @@ static herr_t H5D_chunk_write(H5D_io_info_t *io_info, const H5D_type_info_t *typ
     H5D_chunk_map_t *fm);
 static herr_t H5D_chunk_flush(H5D_t *dset, hid_t dxpl_id);
 static herr_t H5D_chunk_io_term(const H5D_chunk_map_t *fm);
+static htri_t H5D_chunk_compare(const H5F_t *f1, const H5F_t *f2,
+    const H5O_layout_t *layout1, const H5O_layout_t *layout2, hid_t dxpl1_id,
+    hid_t dxpl2_id, H5D_cmp_ud_t *udata);
 
 /* "Nonexistent" layout operation callback */
 static ssize_t
@@ -237,7 +240,8 @@ const H5D_layout_ops_t H5D_LOPS_CHUNK[1] = {{
     NULL,
     NULL,
     H5D_chunk_flush,
-    H5D_chunk_io_term
+    H5D_chunk_io_term,
+    H5D_chunk_compare
 }};
 
 
@@ -260,6 +264,7 @@ const H5D_layout_ops_t H5D_LOPS_NONEXISTENT[1] = {{
     H5D_nonexistent_readvv,
     NULL,
     NULL,
+    NULL,
     NULL
 }};
 
@@ -5045,3 +5050,194 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5D_nonexistent_readvv() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5D_chunk_compare
+ *
+ * Purpose:     fnord
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Friday, December 3, 2010
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5D_chunk_compare(const H5F_t *f1, const H5F_t *f2,
+    const H5O_layout_t *layout1, const H5O_layout_t *layout2, hid_t dxpl1_id,
+    hid_t dxpl2_id, H5D_cmp_ud_t *udata)
+{
+    void        *buf1 = NULL;
+    void        *buf2 = NULL;
+    size_t      buf_size = 0;
+    H5D_chk_idx_info_t idx_info1;       /* Chunked index info */
+    H5D_chk_idx_info_t idx_info2;       /* Chunked index info */
+    hbool_t     idx_info1_init = FALSE;
+    hbool_t     idx_info2_init = FALSE;
+    H5D_chunk_ud_t chk_udata1;
+    H5D_chunk_ud_t chk_udata2;
+    int         space_ndims;            /* Dataset's space rank */
+    hsize_t     space_dim[H5O_LAYOUT_NDIMS]; /* Current dataspace dimensions */
+    hsize_t     chunk_offset[H5O_LAYOUT_NDIMS]; /* Offset of current chunk */
+    hbool_t     carry = FALSE;          /* Flag to indicate that chunk increment carries to higher dimension (sorta) */
+    int         i;
+    htri_t      ret_value = FALSE;      /* Return value */
+
+    FUNC_ENTER_NOAPI(H5D_chunk_compare, FAIL)
+
+    /* Sanity check */
+    HDassert(f1);
+    HDassert(f2);
+    HDassert(layout1);
+    HDassert(layout2);
+    HDassert(udata);
+
+    if(H5F_addr_defined(layout1->storage.u.chunk.idx_addr)) {
+        if(H5F_addr_defined(layout2->storage.u.chunk.idx_addr)) {
+            /* Both have space allocated.  Read both datasets into memory and
+             * compare, chunk by chunk. */
+            /* Go get the rank & dimensions */
+            if((space_ndims = H5S_get_simple_extent_dims(udata->space,
+                    space_dim, NULL)) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get dataset dimensions")
+
+            /* Create index info structs */
+            idx_info1.f = f1;
+            idx_info1.dxpl_id = dxpl1_id;
+            idx_info1.pline = udata->pline1;
+            idx_info1.layout = &layout1->u.chunk;
+            idx_info1.storage = &layout1->storage.u.chunk;
+            if((layout1->storage.u.chunk.ops->init)(&idx_info1, udata->space,
+                    udata->addr1) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "can't init index info")
+            idx_info1_init = TRUE;
+
+            idx_info2.f = f2;
+            idx_info2.dxpl_id = dxpl2_id;
+            idx_info2.pline = udata->pline2;
+            idx_info2.layout = &layout2->u.chunk;
+            idx_info2.storage = &(layout2->storage.u.chunk);
+            if((layout2->storage.u.chunk.ops->init)(&idx_info2, udata->space,
+                    udata->addr2) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "can't init index info")
+            idx_info2_init = TRUE;
+
+            /* Initialize chunk udatas */
+            chk_udata1.common.layout = &(layout1->u.chunk);
+            chk_udata1.common.storage = &(layout1->storage.u.chunk);
+            chk_udata1.common.offset = chunk_offset;
+            chk_udata1.common.rdcc = NULL;
+            chk_udata1.idx_hint = UINT_MAX;
+
+            chk_udata2.common.layout = &(layout2->u.chunk);
+            chk_udata2.common.storage = &(layout2->storage.u.chunk);
+            chk_udata2.common.offset = chunk_offset;
+            chk_udata2.common.rdcc = NULL;
+            chk_udata2.idx_hint = UINT_MAX;
+
+            /* Loop over all chunks logically according to offset */
+            HDmemset(chunk_offset, 0, sizeof(chunk_offset));
+            while(!carry) {
+                /* Lookup chunk 1 */
+                chk_udata1.nbytes = 0;
+                chk_udata1.filter_mask = 0;
+                chk_udata1.addr = HADDR_UNDEF;
+                if((layout1->storage.u.chunk.ops->get_addr)(&idx_info1,
+                        &chk_udata1) < 0)
+                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't query chunk address")
+
+                /* Lookup chunk 2 */
+                chk_udata2.nbytes = 0;
+                chk_udata2.filter_mask = 0;
+                chk_udata2.addr = HADDR_UNDEF;
+                if((layout2->storage.u.chunk.ops->get_addr)(&idx_info2,
+                        &chk_udata2) < 0)
+                    HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't query chunk address")
+
+                if(H5F_addr_defined(chk_udata1.addr)) {
+                    if(H5F_addr_defined(chk_udata2.addr)) {
+                        /* Both chunks exist, read from disk and compare */
+                        /* Check that the sizes are identical */
+                        if(chk_udata1.nbytes != chk_udata2.nbytes)
+                            HGOTO_DONE(TRUE)
+
+                        /* Allocate new buffer, if necessary */
+                        if(chk_udata1.nbytes > buf_size) {
+                            buf_size = chk_udata1.nbytes;
+                            if(NULL == (buf1 = H5MM_realloc(buf1, buf_size)))
+                                HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "unable to allocate memory")
+                            if(NULL == (buf2 = H5MM_realloc(buf2, buf_size)))
+                                HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "unable to allocate memory")
+                        } /* end if */
+
+                        /* Read chunks */
+                        if(H5F_block_read(f1, H5FD_MEM_DRAW, chk_udata1.addr,
+                                chk_udata1.nbytes, dxpl1_id, buf1) < 0)
+                            HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "block read failed")
+                        if(H5F_block_read(f2, H5FD_MEM_DRAW, chk_udata2.addr,
+                                chk_udata1.nbytes, dxpl2_id, buf2) < 0)
+                            HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "block read failed")
+
+                        /* Compare */
+                        if(HDmemcmp(buf1, buf2, chk_udata1.nbytes))
+                            HGOTO_DONE(TRUE)
+                    } /* end if */
+                    else
+                        /* One chunk exists and the other doesn't.  Assume they
+                         * are different.  Eventually should check data in 1
+                         * against fill value in 2. */
+                        HGOTO_DONE(TRUE)
+                } /* end if */
+                else
+                    if(H5F_addr_defined(chk_udata2.addr))
+                        /* One chunk exists and the other doesn't.  Assume they
+                         * are different.  Eventually should check data in 2
+                         * against fill value in 1. */
+                        HGOTO_DONE(TRUE)
+                    else
+                        /* Neither chunk exists.  If their fill values are not
+                         * identical, they are different. */
+                        if(!udata->fill_identical)
+                            HGOTO_DONE(TRUE)
+
+                /* Increment indices */
+                carry = TRUE;
+                for(i = space_ndims - 1; i >= 0; --i) {
+                    chunk_offset[i] += layout1->u.chunk.dim[i];
+                    if(chunk_offset[i] >= space_dim[i])
+                        chunk_offset[i] = 0;
+                    else {
+                        carry = FALSE;
+                        break;
+                    } /* end else */
+                } /* end for */
+            } /* end while */
+        } /* end if */
+        else
+            /* One has space allocated and the other doesn't.  Assume they are
+             * different.  Eventually should check data in 1 against fill value
+             * in 2. */
+            HGOTO_DONE(TRUE)
+    } /* end if */
+    else
+        if(H5F_addr_defined(layout2->storage.u.chunk.idx_addr))
+            /* One has space allocated and the other doesn't.  Assume they are
+             * different.  Eventually should check data in 2 against fill value
+             * in 1. */
+            HGOTO_DONE(TRUE)
+        else
+            /* Neither has space allocated.  If their fill values are not
+             * identical, they are different. */
+            if(!udata->fill_identical)
+                HGOTO_DONE(TRUE)
+
+done:
+    if(idx_info1_init && (layout1->storage.u.chunk.ops->dest)(&idx_info1) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "can't destroy index info")
+    if(idx_info2_init && (layout2->storage.u.chunk.ops->dest)(&idx_info2) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "can't destroy index info")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_chunk_compare() */
+
diff --git a/src/H5Dcompact.c b/src/H5Dcompact.c
index b98f2cb..dc9bdba 100644
--- a/src/H5Dcompact.c
+++ b/src/H5Dcompact.c
@@ -70,6 +70,9 @@ 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[]);
 static herr_t H5D_compact_flush(H5D_t *dset, hid_t dxpl_id);
+static htri_t H5D_compact_compare(const H5F_t *f1, const H5F_t *f2,
+    const H5O_layout_t *layout1, const H5O_layout_t *layout2, hid_t dxpl1_id,
+    hid_t dxpl2_id, H5D_cmp_ud_t *udata);
 
 
 /*********************/
@@ -91,7 +94,8 @@ const H5D_layout_ops_t H5D_LOPS_COMPACT[1] = {{
     H5D_compact_readvv,
     H5D_compact_writevv,
     H5D_compact_flush,
-    NULL
+    NULL,
+    H5D_compact_compare
 }};
 
 
@@ -576,3 +580,44 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_compact_copy() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5D_compact_compare
+ *
+ * Purpose:     fnord
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Tuesday, November 30, 2010
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5D_compact_compare(const H5F_t UNUSED *f1, const H5F_t UNUSED *f2,
+    const H5O_layout_t *layout1, const H5O_layout_t *layout2,
+    hid_t UNUSED dxpl1_id, hid_t UNUSED dxpl2_id, H5D_cmp_ud_t UNUSED *udata)
+{
+    htri_t ret_value = FALSE;           /* Return value */
+
+    FUNC_ENTER_NOAPI_NOFUNC(H5D_compact_compare)
+
+    /* Sanity check */
+    HDassert(f1);
+    HDassert(f2);
+    HDassert(layout1);
+    HDassert(layout2);
+    HDassert(layout1->storage.u.compact.buf);
+    HDassert(layout2->storage.u.compact.buf);
+    HDassert(layout1->storage.u.compact.size
+            == layout2->storage.u.compact.size);
+
+    /* Compare the two datasets */
+    if(HDmemcmp(layout1->storage.u.compact.buf, layout2->storage.u.compact.buf,
+            layout1->storage.u.compact.size))
+        HGOTO_DONE(TRUE)
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_compact_compare() */
+
diff --git a/src/H5Dcontig.c b/src/H5Dcontig.c
index 9a6e08f..c6d9318 100644
--- a/src/H5Dcontig.c
+++ b/src/H5Dcontig.c
@@ -41,6 +41,7 @@
 #include "H5FLprivate.h"	/* Free Lists                           */
 #include "H5Iprivate.h"		/* IDs			  		*/
 #include "H5MFprivate.h"	/* File memory management		*/
+#include "H5MMprivate.h"        /* Memory management                    */
 #include "H5Oprivate.h"		/* Object headers		  	*/
 #include "H5Pprivate.h"		/* Property lists			*/
 #include "H5Vprivate.h"		/* Vector and array functions		*/
@@ -106,6 +107,9 @@ static 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[]);
 static herr_t H5D_contig_flush(H5D_t *dset, hid_t dxpl_id);
+static htri_t H5D_contig_compare(const H5F_t *f1, const H5F_t *f2,
+    const H5O_layout_t *layout1, const H5O_layout_t *layout2, hid_t dxpl1_id,
+    hid_t dxpl2_id, H5D_cmp_ud_t *udata);
 
 /* Helper routines */
 static herr_t H5D_contig_write_one(H5D_io_info_t *io_info, hsize_t offset,
@@ -131,7 +135,8 @@ const H5D_layout_ops_t H5D_LOPS_CONTIG[1] = {{
     H5D_contig_readvv,
     H5D_contig_writevv,
     H5D_contig_flush,
-    NULL
+    NULL,
+    H5D_contig_compare
 }};
 
 
@@ -1525,3 +1530,81 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_contig_copy() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5D_contig_compare
+ *
+ * Purpose:     fnord
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Tuesday, November 30, 2010
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5D_contig_compare(const H5F_t *f1, const H5F_t *f2,
+    const H5O_layout_t *layout1, const H5O_layout_t *layout2, hid_t dxpl1_id,
+    hid_t dxpl2_id, H5D_cmp_ud_t *udata)
+{
+    void *buf1 = NULL;
+    void *buf2 = NULL;
+    htri_t ret_value = FALSE;           /* Return value */
+
+    FUNC_ENTER_NOAPI(H5D_contig_compare, FAIL)
+
+    /* Sanity check */
+    HDassert(f1);
+    HDassert(f2);
+    HDassert(layout1);
+    HDassert(layout2);
+    HDassert(udata);
+
+    if(H5F_addr_defined(layout1->storage.u.contig.addr)) {
+        if(H5F_addr_defined(layout2->storage.u.contig.addr)) {
+            /* Both have space allocated.  Read both datasets into memory and
+             * compare.  Will eventually want to use a buffer with a
+             * user-configurable size so we don't alloc something too big. */
+            HDassert(layout1->storage.u.contig.size
+                    == layout2->storage.u.contig.size);
+            if(NULL == (buf1 = H5MM_malloc(layout1->storage.u.contig.size)))
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "unable to allocate memory")
+            if(NULL == (buf2 = H5MM_malloc(layout1->storage.u.contig.size)))
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "unable to allocate memory")
+
+            if(H5F_block_read(f1, H5FD_MEM_DRAW, layout1->storage.u.contig.addr,
+                    layout1->storage.u.contig.size, dxpl1_id, buf1) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "block read failed")
+            if(H5F_block_read(f2, H5FD_MEM_DRAW, layout2->storage.u.contig.addr,
+                    layout1->storage.u.contig.size, dxpl2_id, buf2) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_READERROR, FAIL, "block read failed")
+
+            if(HDmemcmp(buf1, buf2, layout1->storage.u.contig.size))
+                HGOTO_DONE(TRUE)
+        } /* end if */
+        else
+            /* One has space allocated and the other doesn't.  Assume they are
+             * different.  Eventually should check data in 1 against fill value
+             * in 2. */
+            HGOTO_DONE(TRUE)
+    } /* end if */
+    else
+        if(H5F_addr_defined(layout2->storage.u.contig.addr))
+            /* One has space allocated and the other doesn't.  Assume they are
+             * different.  Eventually should check data in 2 against fill value
+             * in 1. */
+            HGOTO_DONE(TRUE)
+        else
+            /* Neither has space allocated.  If their fill values are not
+             * identical, they are different. */
+            if(!udata->fill_identical)
+                HGOTO_DONE(TRUE)
+
+done:
+    buf1 = H5MM_xfree(buf1);
+    buf2 = H5MM_xfree(buf2);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_contig_compare() */
+
diff --git a/src/H5Doh.c b/src/H5Doh.c
index 8de28ce..278bc71 100644
--- a/src/H5Doh.c
+++ b/src/H5Doh.c
@@ -55,6 +55,9 @@ static void *H5O_dset_create(H5F_t *f, void *_crt_info, H5G_loc_t *obj_loc,
 static H5O_loc_t *H5O_dset_get_oloc(hid_t obj_id);
 static herr_t H5O_dset_bh_info(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
     H5_ih_info_t *bh_info);
+static htri_t H5O_dset_compare(const H5F_t *f1, const H5F_t *f2,
+    const H5O_t *oh1, const H5O_t *oh2, haddr_t addr1, haddr_t addr2,
+    hid_t dxpl1_id, hid_t dxpl2_id, H5O_cmp_t *cmp_info);
 
 
 /*********************/
@@ -81,7 +84,8 @@ const H5O_obj_class_t H5O_OBJ_DATASET[1] = {{
     H5O_dset_open, 		/* open an object of this class */
     H5O_dset_create, 		/* create an object of this class */
     H5O_dset_get_oloc, 		/* get an object header location for an object */
-    H5O_dset_bh_info 		/* get the index & heap info for an object */
+    H5O_dset_bh_info,		/* get the index & heap info for an object */
+    H5O_dset_compare            /* compare two datasets */
 }};
 
 /* Declare a free list to manage the H5D_copy_file_ud_t struct */
@@ -431,3 +435,300 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_dset_bh_info() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_dset_compare
+ *
+ * Purpose:     fnord
+ *
+ * Return:      Success:        0 (equal) or 1 (not equal)
+ *              Failure:        negative
+ *
+ * Programmer:  Neil Fortner
+ *              October 27, 2010
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5O_dset_compare(const H5F_t *f1, const H5F_t *f2, const H5O_t *oh1,
+    const H5O_t *oh2, haddr_t addr1, haddr_t addr2, hid_t dxpl1_id,
+    hid_t dxpl2_id, H5O_cmp_t UNUSED *cmp_info)
+{
+    H5S_t               *space1;                /* Dataspace message */
+    H5S_t               *space2;                /* Dataspace message */
+    H5O_layout_t        layout1;                /* Data storage layout message */
+    H5O_layout_t        layout2;                /* Data storage layout message */
+    H5O_pline_t         pline1 = H5O_CRT_PIPELINE_DEF; /* I/O pipeline message */
+    H5O_pline_t         pline2 = H5O_CRT_PIPELINE_DEF; /* I/O pipeline message */
+    H5T_t               *dtype1;                /* Datatype message */
+    H5T_t               *dtype2;                /* Datatype message */
+    H5O_fill_t          fill1;                  /* Fill value message */
+    H5O_fill_t          fill2;                  /* Fill value message */
+    hbool_t             space_read = FALSE;     /* Whether the dataspace messages were read */
+    hbool_t             layout_read = FALSE;    /* Whether the layout messages were read */
+    hbool_t             pline_read = FALSE;     /* Whether the I/O pipeline messages were read */
+    hbool_t             dtype_read = FALSE;     /* Whether the datatype messages were read */
+    hbool_t             fill1_read = FALSE;     /* Whether the fill value message was read */
+    hbool_t             fill2_read = FALSE;     /* Whether the fill value message was read */
+    int                 ndims1;
+    int                 ndims2;
+    hsize_t             dims1[H5O_LAYOUT_NDIMS];
+    hsize_t             dims2[H5O_LAYOUT_NDIMS];
+    H5D_cmp_ud_t        udata;
+    htri_t              tri_ret;                /* htri_t return value */
+    unsigned            i;
+    htri_t              ret_value;              /* Return value */
+
+    FUNC_ENTER_NOAPI(H5O_dset_compare, FAIL)
+
+    /* Sanity check */
+    HDassert(f1);
+    HDassert(f2);
+    HDassert(oh1);
+    HDassert(oh2);
+
+    /* Save the dset oh addresses in udata */
+    udata.addr1 = addr1;
+    udata.addr2 = addr2;
+
+    /* Get the dataspace messages */
+    if(NULL == (space1 = H5S_read_oh(f1, oh1, dxpl1_id)))
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't read dataspace message")
+    if(NULL == (space2 = H5S_read_oh(f2, oh2, dxpl2_id))) {
+        if(H5S_close(space1) < 0)
+            HERROR(H5E_DATASET, H5E_CANTFREE, "can't close dataspace");
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't read dataspace message")
+    } /* end if */
+    space_read = TRUE;
+
+    /* Check if the dataspace extents are identical */
+    if((ndims1 = H5S_get_simple_extent_dims(space1, dims1, NULL)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get dataspace dimensions")
+    if((ndims2 = H5S_get_simple_extent_dims(space2, dims2, NULL)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get dataspace dimensions")
+    if(ndims1 != ndims2 || HDmemcmp(dims1, dims2, (size_t)ndims1 * sizeof(dims1[0])))
+        HGOTO_DONE(TRUE)
+
+    /* Save the dataspace in udata */
+    udata.space = space1;
+
+    /* Get the layout messages */
+    if(NULL == H5O_msg_read_oh(f1, dxpl1_id, oh1, H5O_LAYOUT_ID, &layout1))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't find layout message")
+    if(NULL == H5O_msg_read_oh(f2, dxpl2_id, oh2, H5O_LAYOUT_ID, &layout2)) {
+        if(H5O_msg_reset(H5O_LAYOUT_ID, &layout1) < 0)
+            HERROR(H5E_DATASET, H5E_CANTRESET, "unable to reset data storage layout message");
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't find layout message")
+    } /* end if */
+    layout_read = TRUE;
+
+    /* Check if the layout messages are identical */
+    /* Will eventually want to check if they are compatible, even if not
+     * identical -NAF */
+    /*FIXME fnord Note we do not handle external datasets! */
+    if(layout1.type != layout2.type)
+        HGOTO_DONE(TRUE)
+    else if(layout1.type == H5D_CHUNKED) {
+        if(layout1.u.chunk.ndims != layout2.u.chunk.ndims ||
+                HDmemcmp(layout1.u.chunk.dim, layout2.u.chunk.dim,
+                layout1.u.chunk.ndims * sizeof(layout1.u.chunk.dim[0])))
+            HGOTO_DONE(TRUE)
+        HDassert(layout1.u.chunk.size == layout2.u.chunk.size);
+        HDassert(layout1.u.chunk.nchunks == layout2.u.chunk.nchunks);
+        HDassert(!HDmemcmp(layout1.u.chunk.chunks, layout2.u.chunk.chunks,
+                layout1.u.chunk.ndims * sizeof(layout1.u.chunk.dim[0])));
+        HDassert(!HDmemcmp(layout1.u.chunk.down_chunks,
+                layout2.u.chunk.down_chunks, layout1.u.chunk.ndims
+                * sizeof(layout1.u.chunk.dim[0])));
+    } /* end if */
+
+    /* Get the pipeline messages */
+    if((tri_ret = H5O_msg_exists_oh(oh1, H5O_PLINE_ID)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to read object header")
+    if(tri_ret) {
+        /* Make sure both objects have a pipeline - mix/match not supported yet
+         */
+        if((tri_ret = H5O_msg_exists_oh(oh2 , H5O_PLINE_ID)) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to read object header")
+        if(!tri_ret)
+            HGOTO_DONE(TRUE)
+
+        if(NULL == H5O_msg_read_oh(f1, dxpl1_id, oh1, H5O_PLINE_ID, &pline1))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't find pipeline message")
+        if(NULL == H5O_msg_read_oh(f2, dxpl2_id, oh2, H5O_PLINE_ID, &pline2)) {
+            if(H5O_msg_reset(H5O_PLINE_ID, &pline1) < 0)
+                HERROR(H5E_DATASET, H5E_CANTRESET, "unable to reset pipeline message");
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't find pipeline message")
+        } /* end if */
+        pline_read = TRUE;
+
+        /* Check if the pipeline messages are identical */
+        /* Will eventually want to handle different pipelines */
+        if(pline1.nused != pline2.nused)
+            HGOTO_DONE(TRUE)
+        else
+            for(i=0; i<pline1.nused; i++)
+                if(pline1.filter[i].id != pline2.filter[i].id
+                        || pline1.filter[i].cd_nelmts != pline2.filter[i].cd_nelmts
+                        || HDmemcmp(pline1.filter[i].cd_values,
+                        pline2.filter[i].cd_values, pline1.filter[i].cd_nelmts
+                        * sizeof(pline1.filter[i].cd_values[0])))
+                    HGOTO_DONE(TRUE)
+    } /* end if */
+    else {
+        /* Make sure object 2 doesn't have a pipeline */
+        if((tri_ret = H5O_msg_exists_oh(oh2 , H5O_PLINE_ID)) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to read object header")
+        if(tri_ret)
+            HGOTO_DONE(TRUE)
+    } /* end else */
+
+    /* Save the plines in udata */
+    udata.pline1 = &pline1;
+    udata.pline2 = &pline2;
+
+    /* Get the datatype messages */
+    if(NULL == (dtype1 = (H5T_t *)H5O_msg_read_oh(f1, dxpl1_id, oh1,
+            H5O_DTYPE_ID, NULL)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't find datatype message")
+    if(NULL == (dtype2 = (H5T_t *)H5O_msg_read_oh(f2, dxpl2_id, oh2,
+            H5O_DTYPE_ID, NULL)))
+            {
+        (void)H5O_msg_free(H5O_DTYPE_ID, dtype1);
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't find datatype message")
+    } /* end if */
+    dtype_read = TRUE;
+
+    /* Check if the datatypes are identical */
+    if(H5T_cmp(dtype1, dtype2, FALSE))
+        HGOTO_DONE(TRUE)
+
+    /* Check for vlen or reference types - not supported currently */
+    if(H5T_detect_class(dtype1, H5T_VLEN, FALSE))
+        HGOTO_DONE(TRUE)
+    if(H5T_detect_class(dtype1, H5T_REFERENCE, FALSE))
+        HGOTO_DONE(TRUE)
+
+    /* Get the fill value messages */
+    if((tri_ret = H5O_msg_exists_oh(oh1, H5O_FILL_NEW_ID)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to read object header")
+    if(tri_ret) {
+        if(NULL == H5O_msg_read_oh(f1, dxpl1_id, oh1, H5O_FILL_NEW_ID, &fill1))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read fill message")
+        fill1_read = TRUE;
+    } /* end if */
+    else {
+        if((tri_ret = H5O_msg_exists_oh(oh1, H5O_FILL_ID)) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to read object header")
+        if(tri_ret) {
+            if(NULL == H5O_msg_read_oh(f1, dxpl1_id, oh1, H5O_FILL_ID, &fill1))
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read fill message")
+            fill1_read = TRUE;
+        } else {
+            fill1.fill_time = H5D_FILL_TIME_NEVER;
+            fill1.fill_defined = FALSE;
+        } /* end else */
+    } /* end else */
+    if((tri_ret = H5O_msg_exists_oh(oh2, H5O_FILL_NEW_ID)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to read object header")
+    if(tri_ret) {
+        if(NULL == H5O_msg_read_oh(f2, dxpl2_id, oh2, H5O_FILL_NEW_ID, &fill2))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read fill message")
+        fill2_read = TRUE;
+    } /* end if */
+    else {
+        if((tri_ret = H5O_msg_exists_oh(oh2, H5O_FILL_ID)) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to read object header")
+        if(tri_ret) {
+            if(NULL == H5O_msg_read_oh(f2, dxpl2_id, oh2, H5O_FILL_ID, &fill2))
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, FAIL, "can't read fill message")
+            fill2_read = TRUE;
+        } else {
+            fill2.fill_time = H5D_FILL_TIME_NEVER;
+            fill2.fill_defined = FALSE;
+        } /* end else */
+    } /* end else */
+
+    /* Check if fill values are identical */
+    if(fill1.fill_defined && (fill1.fill_time == H5D_FILL_TIME_IFSET
+            || fill1.fill_time == H5D_FILL_TIME_ALLOC)) {
+        if(fill2.fill_defined && (fill2.fill_time == H5D_FILL_TIME_IFSET
+                || fill2.fill_time == H5D_FILL_TIME_ALLOC)) {
+            /* Both fill values are defined */
+            HDassert(fill1.size == fill2.size);
+            if(HDmemcmp(fill1.buf, fill2.buf, (size_t)fill1.size))
+                udata.fill_identical = FALSE;
+            else
+                udata.fill_identical = TRUE;
+        } /* end if */
+        else {
+            /* fill1 is defined but fill2 isn't */
+            /* Check for a non-zero character in fill1 (is there an ISO C
+             * function that does this?) */
+            udata.fill_identical = TRUE;
+            for(i=0; i<fill1.size; i++)
+                if(((uint8_t *)fill1.buf)[i] != (uint8_t)0) {
+                    udata.fill_identical = FALSE;
+                    break;
+                } /* end if */
+        } /* end else */
+    } /* end if */
+    else {
+        if(fill2.fill_defined && (fill2.fill_time == H5D_FILL_TIME_IFSET
+                || fill2.fill_time == H5D_FILL_TIME_ALLOC)) {
+            /* fill2 is defined but fill1 isn't */
+            /* Check for a non-zero character in fill2 (is there an ISO C
+             * function that does this?) */
+            udata.fill_identical = TRUE;
+            for(i=0; i<fill2.size; i++)
+                if(((uint8_t *)fill2.buf)[i] != (uint8_t)0) {
+                    udata.fill_identical = FALSE;
+                    break;
+                } /* end if */
+        } /* end if */
+        else
+            /* Both fill1 and fill2 are undefined */
+            udata.fill_identical = TRUE;
+    } /* end else */
+
+    /* Perform the comparison */
+    HDassert(layout1.ops->compare);
+    if((ret_value = layout1.ops->compare(f1, f2, &layout1, &layout2, dxpl1_id,
+            dxpl2_id, &udata)) < 0)
+        HGOTO_ERROR(H5E_DATASET, H5E_CANTCOMPARE, FAIL, "unable to compare datasets")
+
+done:
+    /* Free messages, if they've been read in */
+    if(space_read) {
+        if(H5S_close(space1) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "can't close dataspace")
+        if(H5S_close(space2) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTFREE, FAIL, "can't close dataspace")
+    } /* end if */
+    if(layout_read) {
+        if(H5O_msg_reset(H5O_LAYOUT_ID, &layout1) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTRESET, FAIL, "unable to reset data storage layout message")
+        if(H5O_msg_reset(H5O_LAYOUT_ID, &layout2) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTRESET, FAIL, "unable to reset data storage layout message")
+    } /* end if */
+    if(pline_read) {
+        if(H5O_msg_reset(H5O_PLINE_ID, &pline1) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTRESET, FAIL, "unable to reset I/O pipeline message")
+        if(H5O_msg_reset(H5O_PLINE_ID, &pline2) < 0)
+            HDONE_ERROR(H5E_DATASET, H5E_CANTRESET, FAIL, "unable to reset I/O pipeline message")
+    } /* end if */
+    if(dtype_read) {
+        (void)H5O_msg_free(H5O_DTYPE_ID, dtype1);
+        (void)H5O_msg_free(H5O_DTYPE_ID, dtype2);
+    } /* end if */
+    /* Note that we take advantage of the fact that both versions of the fill
+     * message use the same reset routine.  If this changes, we will have to
+     * change this to pass the correct message ID. */
+    if(fill1_read)
+        (void)H5O_msg_reset(H5O_FILL_NEW_ID, &fill1);
+    if(fill2_read)
+        (void)H5O_msg_reset(H5O_FILL_NEW_ID, &fill2);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_dset_compare() */
+
diff --git a/src/H5Dpkg.h b/src/H5Dpkg.h
index 44b44d9..d03335f 100644
--- a/src/H5Dpkg.h
+++ b/src/H5Dpkg.h
@@ -94,6 +94,16 @@ typedef struct H5D_type_info_t {
     hbool_t bkg_buf_allocated;          /* Whether the background buffer was allocated */
 } H5D_type_info_t;
 
+/* Typedef for udata struct shared between functions when comparing datasets */
+typedef struct H5D_cmp_ud_t {
+    hbool_t fill_identical;     /* Whether the fill values are identical */
+    const H5O_pline_t *pline1;  /* Pipeline for dataset "1" */
+    const H5O_pline_t *pline2;  /* Pipeline for dataset "2" */
+    H5S_t *space;               /* Dataspace (must be the same for datasets 1 and 2) */
+    haddr_t addr1;              /* Address for dataset 1 */
+    haddr_t addr2;              /* Address for dataset 2 */
+} H5D_cmp_ud_t;
+
 /* Forward declaration of structs used below */
 struct H5D_io_info_t;
 struct H5D_chunk_map_t;
@@ -121,6 +131,9 @@ typedef ssize_t (*H5D_layout_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 herr_t (*H5D_layout_flush_func_t)(H5D_t *dataset, hid_t dxpl_id);
 typedef herr_t (*H5D_layout_io_term_func_t)(const struct H5D_chunk_map_t *cm);
+typedef htri_t (*H5D_layout_compare_func_t)(const H5F_t *f1, const H5F_t *f2,
+    const H5O_layout_t *layout1, const H5O_layout_t *layout2,
+    hid_t dxpl1_id, hid_t dxpl2_id, H5D_cmp_ud_t *udata);
 
 /* Typedef for grouping layout I/O routines */
 typedef struct H5D_layout_ops_t {
@@ -138,6 +151,7 @@ typedef struct H5D_layout_ops_t {
     H5D_layout_writevv_func_t writevv;  /* Low-level I/O routine for writing data */
     H5D_layout_flush_func_t flush;      /* Low-level I/O routine for flushing raw data */
     H5D_layout_io_term_func_t io_term;  /* I/O shutdown routine */
+    H5D_layout_compare_func_t compare;  /* Data comparison routine */
 } H5D_layout_ops_t;
 
 /* Function pointers for either multiple or single block I/O access */
diff --git a/src/H5Ocompare.c b/src/H5Ocompare.c
new file mode 100644
index 0000000..c45e689
--- /dev/null
+++ b/src/H5Ocompare.c
@@ -0,0 +1,749 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * 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.     *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*-------------------------------------------------------------------------
+ *
+ * Created:		H5Ocompare.c
+ *			Oct 12 2010
+ *			Neil Fortner <nfortne2@hdfgroup.org>
+ *
+ * Purpose:		Object comparison routines.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/****************/
+/* Module Setup */
+/****************/
+
+#define H5O_PACKAGE		/*suppress error about including H5Opkg	  */
+
+/***********/
+/* Headers */
+/***********/
+#include "H5private.h"		/* Generic Functions			*/
+#include "H5Eprivate.h"		/* Error handling		  	*/
+#include "H5Iprivate.h"		/* IDs			  		*/
+#include "H5MMprivate.h"	/* Memory management			*/
+#include "H5Opkg.h"             /* Object headers			*/
+#include "H5Pprivate.h"         /* Property lists                       */
+
+
+/****************/
+/* Local Macros */
+/****************/
+
+
+/******************/
+/* Local Typedefs */
+/******************/
+
+
+/********************/
+/* Package Typedefs */
+/********************/
+
+
+/********************/
+/* Local Prototypes */
+/********************/
+
+static herr_t H5O_compare_obj(const H5O_loc_t *oloc1, const H5O_loc_t *oloc2,
+    hid_t ocmppl_id);
+
+/*********************/
+/* Package Variables */
+/*********************/
+
+
+/*****************************/
+/* Library Private Variables */
+/*****************************/
+
+
+/*******************/
+/* Local Variables */
+/*******************/
+
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Ocompare
+ *
+ * Purpose:     fnord
+ *
+ * Usage:       fnord
+ *
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              October 12, 2010
+ *
+ *-------------------------------------------------------------------------
+ */
+htri_t
+H5Ocompare(hid_t loc1_id, const char *name1, hid_t loc2_id, const char *name2,
+    hid_t ocmppl_id)
+{
+    H5G_loc_t	base_loc1;              /* Base location for object 1 */
+    H5G_loc_t	base_loc2;              /* Base location for object 2 */
+    H5G_loc_t	loc1;                   /* Object location for object 1 */
+    H5G_loc_t   loc2;                   /* Object location for object 2 */
+
+    /* for opening the objects */
+    H5G_name_t  path1;                  /* Opened object 1 hier. path */
+    H5G_name_t  path2;                  /* Opened object 2 hier. path */
+    H5O_loc_t   oloc1;                  /* Opened object 1 object location */
+    H5O_loc_t   oloc2;                  /* Opened object 2 object location */
+    hbool_t     loc1_found = FALSE;     /* Location at 'name1' found */
+    hbool_t     loc2_found = FALSE;     /* Location at 'name2' found */
+    hbool_t     obj1_open = FALSE;      /* Entry at 'name1' found */
+    hbool_t     obj2_open = FALSE;      /* Entry at 'name2' found */
+
+    htri_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_API(H5Ocompare, FAIL)
+
+    /* Check arguments */
+    if(H5G_loc(loc1_id, &base_loc1) < 0)
+	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "loc1_id not a location")
+    if(H5G_loc(loc2_id, &base_loc2) < 0)
+	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "loc2_id not a location")
+    if(!name1 || !*name2)
+	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no name specified for object 1")
+    if(!name2 || !*name2)
+	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no name specified for object 2")
+
+    /* Set up opened group locations to fill in */
+    loc1.oloc = &oloc1;
+    loc1.path = &path1;
+    H5G_loc_reset(&loc1);
+    loc2.oloc = &oloc2;
+    loc2.path = &path2;
+    H5G_loc_reset(&loc2);
+
+    /* Find the objects to compare */
+    if(H5G_loc_find(&base_loc1, name1, &loc1/*out*/, H5P_DEFAULT, H5AC_dxpl_id) < 0)
+        HGOTO_ERROR(H5E_SYM, H5E_NOTFOUND, FAIL, "object 1 not found")
+    loc1_found = TRUE;
+    if(H5G_loc_find(&base_loc2, name2, &loc2/*out*/, H5P_DEFAULT, H5AC_dxpl_id) < 0)
+        HGOTO_ERROR(H5E_SYM, H5E_NOTFOUND, FAIL, "object 2 not found")
+    loc2_found = TRUE;
+
+    /* Open the objects' object headers */
+    if(H5O_open(&oloc1) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTOPENOBJ, FAIL, "unable to open object 1")
+    obj1_open = TRUE;
+    if(H5O_open(&oloc2) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTOPENOBJ, FAIL, "unable to open object 2")
+    obj2_open = TRUE;
+#if 0
+    /* Get correct property lists */
+    if(H5P_DEFAULT == lcpl_id) {
+        if((lcpl_id = H5L_get_default_lcpl()) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTINIT, FAIL, "unable to get default lcpl")
+    } /* end if */
+    else
+        if(TRUE != H5P_isa_class(lcpl_id, H5P_LINK_CREATE))
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not link creation property list")
+
+    /* Get object copy property list */
+    if(H5P_DEFAULT == ocpypl_id)
+        ocpypl_id = H5P_OBJECT_COPY_DEFAULT;
+    else
+        if(TRUE != H5P_isa_class(ocpypl_id, H5P_OBJECT_COPY))
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not object copy property list")
+#endif
+    /* Do the actual copying of the object */
+    if((ret_value = H5O_compare_obj(&oloc1, &oloc2, ocmppl_id)) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTCOMPARE, FAIL, "unable to compare object")
+
+done:
+    if(loc1_found && H5G_loc_free(&loc1) < 0)
+        HDONE_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "can't free location 1")
+    if(loc2_found && H5G_loc_free(&loc2) < 0)
+        HDONE_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "can't free location 2")
+    if(obj1_open)
+        H5O_close(&oloc1);
+    if(obj2_open)
+        H5O_close(&oloc2);
+
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Ocompare() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_compare_obj
+ *
+ * Purpose:     fnord
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Novermeber 23, 2010
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5O_compare_obj(const H5O_loc_t *oloc1, const H5O_loc_t *oloc2, hid_t ocmppl_id)
+{
+    H5O_t                  *oh1 = NULL;             /* Object header for object 1 */
+    H5O_t                  *oh2 = NULL;             /* Object header for object 2 */
+    const H5O_obj_class_t  *obj1_class = NULL;      /* Type of object 1 */
+    const H5O_obj_class_t  *obj2_class = NULL;      /* Type of object 2 */
+    hid_t                  dxpl1_id = H5AC_dxpl_id;
+    hid_t                  dxpl2_id = -1;
+    H5P_genplist_t         *dxpl = NULL;
+    haddr_t                prev_tag1 = HADDR_UNDEF;
+    haddr_t                prev_tag2 = HADDR_UNDEF;
+    htri_t                 ret_value = SUCCEED;
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_compare_obj)
+
+    HDassert(oloc1);
+    HDassert(oloc1->file);
+    HDassert(H5F_addr_defined(oloc1->addr));
+    HDassert(oloc2);
+    HDassert(oloc2->file);
+    HDassert(H5F_addr_defined(oloc2->addr));
+
+    /* Copy dxpl1 to dxpl2 */
+    if(NULL == (dxpl = (H5P_genplist_t *)H5I_object_verify(dxpl1_id, H5I_GENPROP_LST)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list")
+    if((dxpl2_id = H5P_copy_plist((H5P_genplist_t *)dxpl, FALSE)) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTCOPY, FAIL, "can't copy property list");
+
+    /* Set up metadata tagging */
+    if(H5AC_tag(dxpl1_id, oloc1->addr, &prev_tag1) < 0)
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTTAG, FAIL, "unable to apply metadata tag")
+    if(H5AC_tag(dxpl2_id, oloc2->addr, &prev_tag2) < 0)
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTTAG, FAIL, "unable to apply metadata tag")
+
+    /* Get object headers */
+    /*FIXME fnord Set up tagging here? */
+    if(NULL == (oh1 = H5O_protect(oloc1, dxpl1_id, H5AC_READ)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTPROTECT, FAIL, "unable to load object header")
+    if(NULL == (oh2 = H5O_protect(oloc2, dxpl2_id, H5AC_READ)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTPROTECT, FAIL, "unable to load object header")
+
+    /* Get pointer to object class for objects */
+    if(NULL == (obj1_class = H5O_obj_class_real(oh1)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to determine object type")
+    if(NULL == (obj2_class = H5O_obj_class_real(oh1)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to determine object type")
+    if(obj1_class->type != obj2_class->type)
+        HGOTO_DONE(TRUE)
+
+    /* Do the comparison */
+    HDassert(obj1_class->compare);
+    if((ret_value = obj1_class->compare(oloc1->file, oloc2->file, oh1, oh2,
+            oloc1->addr, oloc2->addr, dxpl1_id, dxpl2_id, NULL)) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTCOMPARE, FAIL, "unable to compare objects")
+
+done:
+    /* Release pointer to object headers and their derived objects */
+    if(oh1 && H5O_unprotect(oloc1, dxpl1_id, oh1, H5AC__NO_FLAGS_SET) < 0)
+        HDONE_ERROR(H5E_OHDR, H5E_CANTUNPROTECT, FAIL, "unable to release object header")
+    if(oh2 && H5O_unprotect(oloc2, dxpl2_id, oh2, H5AC__NO_FLAGS_SET) < 0)
+        HDONE_ERROR(H5E_OHDR, H5E_CANTUNPROTECT, FAIL, "unable to release object header")
+
+    if(H5AC_tag(dxpl1_id, prev_tag1, NULL) < 0)
+        HDONE_ERROR(H5E_CACHE, H5E_CANTTAG, FAIL, "unable to apply metadata tag")
+    if(H5AC_tag(dxpl2_id, prev_tag2, NULL) < 0)
+        HDONE_ERROR(H5E_CACHE, H5E_CANTTAG, FAIL, "unable to apply metadata tag")
+
+    if(dxpl2_id >= 0 && H5I_dec_ref(dxpl2_id) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTDEC, FAIL, "can't decrement ID ref count")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_compare_obj() */
+
+#if 0
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_header_map
+ *
+ * Purpose:     Copy header object from one location to another, detecting
+ *              already mapped objects, etc.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Quincey Koziol
+ *              November 1, 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5O_copy_header_map(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
+    hid_t dxpl_id, H5O_copy_t *cpy_info, hbool_t inc_depth,
+    H5O_type_t *obj_type, void **udata)
+{
+    H5O_addr_map_t      *addr_map = NULL;       /* Address mapping of object copied */
+    H5_obj_t            src_obj_pos;            /* Position of source object */
+    hbool_t             inc_link;               /* Whether to increment the link count for the object */
+    herr_t              ret_value = SUCCEED;
+
+    FUNC_ENTER_NOAPI(H5O_copy_header_map, FAIL)
+
+    /* Sanity check */
+    HDassert(oloc_src);
+    HDassert(oloc_src->file);
+    HDassert(oloc_dst);
+    HDassert(oloc_dst->file);
+    HDassert(cpy_info);
+
+    /* Create object "position" struct */
+    H5F_GET_FILENO(oloc_src->file, src_obj_pos.fileno);
+    src_obj_pos.addr = oloc_src->addr;
+
+    /* Search for the object in the skip list of copied objects */
+    addr_map = (H5O_addr_map_t *)H5SL_search(cpy_info->map_list,
+            &src_obj_pos);
+
+    /* Check if address is already in list of objects copied */
+    if(addr_map == NULL) {
+        /* Copy object for the first time */
+
+        /* Check for incrementing the depth of copy */
+        /* (Can't do this for all copies, since committed datatypes should always be copied) */
+        if(inc_depth)
+            cpy_info->curr_depth++;
+
+        /* Copy object referred to */
+        if(H5O_copy_header_real(oloc_src, oloc_dst, dxpl_id, cpy_info, obj_type,
+                udata) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object")
+
+        /* Check for incrementing the depth of copy */
+        if(inc_depth)
+            cpy_info->curr_depth--;
+
+        /* When an object is copied for the first time, increment it's link */
+        inc_link = TRUE;
+
+        /* indicate that a new object is created */
+        ret_value++;
+    } /* end if */
+    else {
+        /* Object has already been copied, set its address in destination file */
+        oloc_dst->addr = addr_map->dst_addr;
+
+        /* Return saved obj_type and udata, if requested */
+        if(obj_type) {
+            HDassert(udata);
+            *obj_type = addr_map->obj_class->type;
+            *udata = addr_map->udata;
+        } /* end if */
+
+        /* If the object is locked currently (because we are copying a group
+         * hierarchy and this is a link to a group higher in the hierarchy),
+         * increment it's deferred reference count instead of incrementing the
+         * reference count now.
+         */
+        if(addr_map->is_locked) {
+            addr_map->inc_ref_count++;
+            inc_link = FALSE;
+        } /* end if */
+        else
+            inc_link = TRUE;
+    } /* end else */
+
+    /* Increment destination object's link count, if allowed */
+    if(inc_link)
+        if(H5O_link(oloc_dst, 1, dxpl_id) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to increment object link count")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_header_map() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5O_copy_free_addrmap_cb
+ PURPOSE
+    Internal routine to free address maps from the skip list for copying objects
+ USAGE
+    herr_t H5O_copy_free_addrmap_cb(item, key, op_data)
+        void *item;             IN/OUT: Pointer to addr
+        void *key;              IN/OUT: (unused)
+        void *op_data;          IN: (unused)
+ RETURNS
+    Returns zero on success, negative on failure.
+ DESCRIPTION
+        Releases the memory for the address.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5O_copy_free_addrmap_cb(void *_item, void UNUSED *key, void UNUSED *op_data)
+{
+    H5O_addr_map_t *item = (H5O_addr_map_t *)_item;
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_copy_free_addrmap_cb)
+
+    HDassert(item);
+
+    /* Release user data for particular type of object */
+    if(item->udata) {
+        HDassert(item->obj_class);
+        HDassert(item->obj_class->free_copy_file_udata);
+        (item->obj_class->free_copy_file_udata)(item->udata);
+    } /* end if */
+
+    /* Release the item */
+    item = H5FL_FREE(H5O_addr_map_t, item);
+
+    FUNC_LEAVE_NOAPI(0)
+}   /* H5O_copy_free_addrmap_cb() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_header
+ *
+ * Purpose:     copy header object from one location to another.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Peter Cao
+ *              May 30, 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_header(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
+    hid_t dxpl_id, unsigned cpy_option)
+{
+    H5O_copy_t  cpy_info;               /* Information for copying object */
+    herr_t      ret_value = SUCCEED;
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_copy_header)
+
+    HDassert(oloc_src);
+    HDassert(oloc_src->file);
+    HDassert(H5F_addr_defined(oloc_src->addr));
+    HDassert(oloc_dst->file);
+
+    /* Convert copy flags into copy struct */
+    HDmemset(&cpy_info, 0, sizeof(H5O_copy_t));
+    if((cpy_option & H5O_COPY_SHALLOW_HIERARCHY_FLAG) > 0) {
+        cpy_info.copy_shallow = TRUE;
+        cpy_info.max_depth = 1;
+    } /* end if */
+    else
+        cpy_info.max_depth = -1;        /* Current default is for full, recursive hier. copy */
+    cpy_info.curr_depth = 0;
+    if((cpy_option & H5O_COPY_EXPAND_SOFT_LINK_FLAG) > 0)
+        cpy_info.expand_soft_link = TRUE;
+    if((cpy_option & H5O_COPY_EXPAND_EXT_LINK_FLAG) > 0)
+        cpy_info.expand_ext_link = TRUE;
+    if((cpy_option & H5O_COPY_EXPAND_REFERENCE_FLAG) > 0)
+        cpy_info.expand_ref = TRUE;
+    if((cpy_option & H5O_COPY_WITHOUT_ATTR_FLAG) > 0)
+        cpy_info.copy_without_attr = TRUE;
+    if((cpy_option & H5O_COPY_PRESERVE_NULL_FLAG) > 0)
+        cpy_info.preserve_null = TRUE;
+
+    /* Create a skip list to keep track of which objects are copied */
+    if((cpy_info.map_list = H5SL_create(H5SL_TYPE_OBJ)) == NULL)
+        HGOTO_ERROR(H5E_SLIST, H5E_CANTCREATE, FAIL, "cannot make skip list")
+
+    /* copy the object from the source file to the destination file */
+    if(H5O_copy_header_real(oloc_src, oloc_dst, dxpl_id, &cpy_info, NULL, NULL)
+            < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object")
+
+done:
+    if(cpy_info.map_list)
+        H5SL_destroy(cpy_info.map_list, H5O_copy_free_addrmap_cb, NULL);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_header() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_obj
+ *
+ * Purpose:     Copy an object to destination location
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Peter Cao
+ *              June 4, 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_obj(H5G_loc_t *src_loc, H5G_loc_t *dst_loc, const char *dst_name,
+    hid_t ocpypl_id, hid_t lcpl_id)
+{
+    H5P_genplist_t  *ocpy_plist=NULL;           /* Object copy property list created */
+    hid_t           dxpl_id=H5AC_dxpl_id;
+    H5G_name_t      new_path;                   /* Copied object group hier. path */
+    H5O_loc_t       new_oloc;                   /* Copied object object location */
+    H5G_loc_t       new_loc;                    /* Group location of object copied */
+    H5F_t           *cached_dst_file;           /* Cached destination file */
+    hbool_t         entry_inserted=FALSE;       /* Flag to indicate that the new entry was inserted into a group */
+    unsigned        cpy_option = 0;             /* Copy options */
+    herr_t          ret_value = SUCCEED;        /* Return value */
+
+    FUNC_ENTER_NOAPI(H5O_copy_obj, FAIL)
+
+    HDassert(src_loc);
+    HDassert(src_loc->oloc->file);
+    HDassert(dst_loc);
+    HDassert(dst_loc->oloc->file);
+    HDassert(dst_name);
+
+    /* Get the copy property list */
+    if(NULL == (ocpy_plist = (H5P_genplist_t *)H5I_object(ocpypl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list")
+
+    /* Retrieve the copy parameters */
+    if(H5P_get(ocpy_plist, H5O_CPY_OPTION_NAME, &cpy_option) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get object copy flag")
+
+    /* Set up copied object location to fill in */
+    new_loc.oloc = &new_oloc;
+    new_loc.path = &new_path;
+    H5G_loc_reset(&new_loc);
+    new_oloc.file = dst_loc->oloc->file;
+
+    /* Make a copy of the destination file, in case the original is changed by
+     * H5O_copy_header.  If and when oloc's point to the shared file struct,
+     * this will no longer be necessary, so this code can be removed. */
+    cached_dst_file = dst_loc->oloc->file;
+
+    /* Copy the object from the source file to the destination file */
+    if(H5O_copy_header(src_loc->oloc, &new_oloc, dxpl_id, cpy_option) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object")
+
+    /* Patch dst_loc.  Again, this can be removed once oloc's point to shared
+     * file structs. */
+    dst_loc->oloc->file = cached_dst_file;
+
+    /* Insert the new object in the destination file's group */
+    if(H5L_link(dst_loc, dst_name, &new_loc, lcpl_id, H5P_DEFAULT, dxpl_id) < 0)
+	HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "unable to insert link")
+    entry_inserted = TRUE;
+
+done:
+    /* Free the ID to name buffers */
+    if(entry_inserted)
+        H5G_loc_free(&new_loc);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_obj() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_copy_obj_by_ref
+ *
+ * Purpose:     Copy the object pointed by _src_ref.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  Peter Cao
+ *              Aug 7 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_copy_obj_by_ref(H5O_loc_t *src_oloc, hid_t dxpl_id, H5O_loc_t *dst_oloc,
+    H5G_loc_t *dst_root_loc, H5O_copy_t *cpy_info)
+{
+    herr_t  ret_value = SUCCEED;
+
+    FUNC_ENTER_NOAPI(H5O_copy_obj_by_ref, FAIL)
+
+    HDassert(src_oloc);
+    HDassert(dst_oloc);
+
+    /* Perform the copy, or look up existing copy */
+    if((ret_value = H5O_copy_header_map(src_oloc, dst_oloc, dxpl_id, cpy_info,
+            FALSE, NULL, NULL)) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object")
+
+    /* Check if a new valid object is copied to the destination */
+    if(H5F_addr_defined(dst_oloc->addr) && (ret_value > SUCCEED)) {
+        char    tmp_obj_name[80];
+        H5G_name_t      new_path;
+        H5O_loc_t       new_oloc;
+        H5G_loc_t       new_loc;
+
+        /* Set up group location for new object */
+        new_loc.oloc = &new_oloc;
+        new_loc.path = &new_path;
+        H5G_loc_reset(&new_loc);
+        new_oloc.file = dst_oloc->file;
+        new_oloc.addr = dst_oloc->addr;
+
+        /* Pick a default name for the new object */
+        sprintf(tmp_obj_name, "~obj_pointed_by_%llu", (unsigned long long)dst_oloc->addr);
+
+        /* Create a link to the newly copied object */
+        /* Note: since H5O_copy_header_map actually copied the target object, it
+         * must exist either in cache or on disk, therefore it is is safe to not
+         * pass the obj_type and udata fields returned by H5O_copy_header_map.
+         * This could be changed in the future to slightly improve performance
+         * --NAF */
+        if(H5L_link(dst_root_loc, tmp_obj_name, &new_loc, H5P_DEFAULT, H5P_DEFAULT, dxpl_id) < 0)
+            HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "unable to insert link")
+
+        H5G_loc_free(&new_loc);
+    } /* if (H5F_addr_defined(dst_oloc.addr)) */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_obj_by_ref() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_copy_expand_ref
+ *
+ * Purpose:	Copy the object pointed by _src_ref.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:  Peter Cao
+ *		Aug 7 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5O_copy_expand_ref(H5F_t *file_src, void *_src_ref, hid_t dxpl_id,
+    H5F_t *file_dst, void *_dst_ref, size_t ref_count, H5R_type_t ref_type,
+    H5O_copy_t *cpy_info)
+{
+    H5O_loc_t 	dst_oloc;         	/* Copied object object location */
+    H5O_loc_t	src_oloc;          	/* Temporary object location for source object */
+    H5G_loc_t   dst_root_loc;           /* The location of root group of the destination file */
+    uint8_t     *p;                     /* Pointer to OID to store */
+    size_t      i;                      /* Local index variable */
+    herr_t	ret_value = SUCCEED;
+
+    FUNC_ENTER_NOAPI(H5O_copy_expand_ref, FAIL)
+
+    /* Sanity checks */
+    HDassert(file_src);
+    HDassert(_src_ref);
+    HDassert(file_dst);
+    HDassert(_dst_ref);
+    HDassert(ref_count);
+    HDassert(cpy_info);
+
+    /* Initialize object locations */
+    H5O_loc_reset(&src_oloc);
+    H5O_loc_reset(&dst_oloc);
+    src_oloc.file = file_src;
+    dst_oloc.file = file_dst;
+
+    /* Set up the root group in the destination file */
+    if(NULL == (dst_root_loc.oloc = H5G_oloc(H5G_rootof(file_dst))))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "unable to get object location for root group")
+    if(NULL == (dst_root_loc.path = H5G_nameof(H5G_rootof(file_dst))))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "unable to get path for root group")
+
+    /* Copy object references */
+    if(H5R_OBJECT == ref_type) {
+        hobj_ref_t *src_ref = (hobj_ref_t *)_src_ref;
+        hobj_ref_t *dst_ref = (hobj_ref_t *)_dst_ref;
+
+        /* Making equivalent references in the destination file */
+        for(i = 0; i < ref_count; i++) {
+            /* Set up for the object copy for the reference */
+            p = (uint8_t *)(&src_ref[i]);
+            H5F_addr_decode(src_oloc.file, (const uint8_t **)&p, &(src_oloc.addr));
+            dst_oloc.addr = HADDR_UNDEF;
+
+            /* Attempt to copy object from source to destination file */
+            if(src_oloc.addr != (haddr_t)0) {
+                if(H5O_copy_obj_by_ref(&src_oloc, dxpl_id, &dst_oloc, &dst_root_loc, cpy_info) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object")
+            } /* end if */
+            else
+                /* Set parameters so the reference is written as all 0's */
+                HDmemset(&dst_oloc.addr, 0, sizeof(dst_oloc.addr));
+
+            /* Set the object reference info for the destination file */
+            p = (uint8_t *)(&dst_ref[i]);
+            H5F_addr_encode(dst_oloc.file, &p, dst_oloc.addr);
+	} /* end for */
+    }  /* end if */
+    /* Copy region references */
+    else if(H5R_DATASET_REGION == ref_type) {
+        hdset_reg_ref_t *src_ref = (hdset_reg_ref_t *)_src_ref;
+        hdset_reg_ref_t *dst_ref = (hdset_reg_ref_t *)_dst_ref;
+        uint8_t *buf = NULL;    /* Buffer to store serialized selection in */
+        H5HG_t hobjid;          /* Heap object ID */
+        size_t buf_size;        /* Length of object in heap */
+
+        /* Making equivalent references in the destination file */
+        for(i = 0; i < ref_count; i++) {
+            /* Get the heap ID for the dataset region */
+            p = (uint8_t *)(&src_ref[i]);
+            H5F_addr_decode(src_oloc.file, (const uint8_t **)&p, &(hobjid.addr));
+            INT32DECODE(p, hobjid.idx);
+
+            if(hobjid.addr != (haddr_t)0) {
+                /* Get the dataset region from the heap (allocate inside routine) */
+                if((buf = (uint8_t *)H5HG_read(src_oloc.file, dxpl_id, &hobjid, NULL, &buf_size)) == NULL)
+                    HGOTO_ERROR(H5E_REFERENCE, H5E_READERROR, FAIL, "Unable to read dataset region information")
+
+                /* Get the object oid for the dataset */
+                p = (uint8_t *)buf;
+                H5F_addr_decode(src_oloc.file, (const uint8_t **)&p, &(src_oloc.addr));
+                dst_oloc.addr = HADDR_UNDEF;
+
+                /* copy the object pointed by the ref to the destination */
+                if(H5O_copy_obj_by_ref(&src_oloc, dxpl_id, &dst_oloc, &dst_root_loc, cpy_info) < 0) {
+                    H5MM_xfree(buf);
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "unable to copy object")
+                } /* end if */
+
+                /* Serialize object ID */
+                p = (uint8_t *)buf;
+                H5F_addr_encode(dst_oloc.file, &p, dst_oloc.addr);
+
+                /* Save the serialized buffer to the destination */
+                if(H5HG_insert(dst_oloc.file, dxpl_id, buf_size, buf, &hobjid) < 0) {
+                    H5MM_xfree(buf);
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTCOPY, FAIL, "Unable to write dataset region information")
+                } /* end if */
+            } /* end if */
+            else
+                /* Set parameters so the reference is written as all 0's */
+                HDmemset(&hobjid, 0, sizeof(hobjid));
+
+            /* Set the dataset region reference info for the destination file */
+            p = (uint8_t *)(&dst_ref[i]);
+            H5F_addr_encode(dst_oloc.file, &p, hobjid.addr);
+            INT32ENCODE(p, hobjid.idx);
+
+            /* Free the buffer allocated in H5HG_read() */
+            H5MM_xfree(buf);
+        } /* end for */
+    } /* end if */
+    else
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid reference type")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_copy_expand_ref() */
+#endif
+
diff --git a/src/H5Opkg.h b/src/H5Opkg.h
index 54e7233..2931381 100644
--- a/src/H5Opkg.h
+++ b/src/H5Opkg.h
@@ -325,6 +325,9 @@ typedef struct H5O_obj_class_t {
     void	*(*create)(H5F_t *, void *, H5G_loc_t *, hid_t );	/*create an object of this class */
     H5O_loc_t	*(*get_oloc)(hid_t );		/*get the object header location for an object */
     herr_t      (*bh_info)(H5F_t *f, hid_t dxpl_id, H5O_t *oh, H5_ih_info_t *bh_info); /*get the index & heap info for an object */
+    htri_t      (*compare)(const H5F_t *f1, const H5F_t *f2, const H5O_t *oh1,
+            const H5O_t *oh2, haddr_t addr1, haddr_t addr2, hid_t dxpl1_id,
+            hid_t dxpl2_id, H5O_cmp_t *cmp_info); /*compare two objects of this class */
 } H5O_obj_class_t;
 
 /* Node in skip list to map addresses from one file to another during object header copy */
diff --git a/src/H5Oprivate.h b/src/H5Oprivate.h
index 56901f3..5ca93b4 100644
--- a/src/H5Oprivate.h
+++ b/src/H5Oprivate.h
@@ -145,6 +145,10 @@ typedef struct H5O_copy_t {
     H5O_t   *oh_dst;                    /* The destination object header */
 } H5O_copy_t;
 
+/* Settings/flags for comparing objects */
+/* Empty for now */
+typedef void H5O_cmp_t;
+
 /* Header message IDs */
 #define H5O_NULL_ID	0x0000          /* Null Message.  */
 #define H5O_SDSPACE_ID	0x0001          /* Dataspace Message. */
diff --git a/src/H5Opublic.h b/src/H5Opublic.h
index c5ae3c1..2334bd5 100644
--- a/src/H5Opublic.h
+++ b/src/H5Opublic.h
@@ -172,6 +172,8 @@ H5_DLL herr_t H5Ovisit(hid_t obj_id, H5_index_t idx_type, H5_iter_order_t order,
 H5_DLL herr_t H5Ovisit_by_name(hid_t loc_id, const char *obj_name,
     H5_index_t idx_type, H5_iter_order_t order, H5O_iterate_t op,
     void *op_data, hid_t lapl_id);
+H5_DLL htri_t H5Ocompare(hid_t loc1_id, const char *name1, hid_t loc2_id,
+    const char *name2, hid_t ocmppl_id);
 H5_DLL herr_t H5Oclose(hid_t object_id);
 
 /* Symbols defined for compatibility with previous versions of the HDF5 API.
diff --git a/src/H5S.c b/src/H5S.c
index e7cac9d..c92df45 100644
--- a/src/H5S.c
+++ b/src/H5S.c
@@ -1063,6 +1063,54 @@ done:
 } /* end H5S_read() */
 
 
+/*-------------------------------------------------------------------------
+ * Function:    H5S_read_oh
+ *
+ * Purpose:     Reads the dataspace from an object header.
+ *
+ * Return:      Success:        Pointer to a new dataspace.
+ *
+ *              Failure:        NULL
+ *
+ * Programmer:  Robb Matzke
+ *              Tuesday, December  9, 1997
+ *
+ *-------------------------------------------------------------------------
+ */
+H5S_t *
+H5S_read_oh(const H5F_t *f, const H5O_t *oh, hid_t dxpl_id)
+{
+    H5S_t          *ds = NULL;          /* Dataspace to return */
+    H5S_t          *ret_value;          /* Return value */
+
+    FUNC_ENTER_NOAPI(H5S_read_oh, NULL)
+
+    /* check args */
+    HDassert(oh);
+
+    if(NULL == (ds = H5FL_CALLOC(H5S_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")
+
+    if(H5O_msg_read_oh(f, dxpl_id, oh, H5O_SDSPACE_ID, &(ds->extent)) == NULL)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, NULL, "unable to load dataspace info from dataset header")
+
+    /* Default to entire dataspace being selected */
+    if(H5S_select_all(ds, FALSE) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, NULL, "unable to set all selection")
+
+    /* Set the value for successful return */
+    ret_value = ds;
+
+done:
+    if(ret_value == NULL) {
+        if(ds != NULL)
+            ds = H5FL_FREE(H5S_t, ds);
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S_read_oh() */
+
+
 /*--------------------------------------------------------------------------
  NAME
     H5S_is_simple
diff --git a/src/H5Sprivate.h b/src/H5Sprivate.h
index 0e67af1..eb97a4d 100644
--- a/src/H5Sprivate.h
+++ b/src/H5Sprivate.h
@@ -188,6 +188,7 @@ H5_DLL herr_t H5S_write(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned update_flag
     H5S_t *ds);
 H5_DLL herr_t H5S_append(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh, H5S_t *ds);
 H5_DLL H5S_t *H5S_read(const struct H5O_loc_t *loc, hid_t dxpl_id);
+H5_DLL H5S_t *H5S_read_oh(const H5F_t *f, const H5O_t *oh, hid_t dxpl_id);
 H5_DLL htri_t H5S_set_extent(H5S_t *space, const hsize_t *size);
 H5_DLL herr_t H5S_set_extent_real(H5S_t *space, const hsize_t *size);
 H5_DLL H5S_t *H5S_create(H5S_class_t type);
diff --git a/src/Makefile.am b/src/Makefile.am
index dc0edb3..f0e1614 100755
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -77,8 +77,8 @@ libhdf5_la_SOURCES= H5.c H5checksum.c H5dbg.c H5system.c H5timer.c H5trace.c \
         H5MM.c H5MP.c H5MPtest.c \
         H5O.c H5Oainfo.c H5Oalloc.c H5Oattr.c \
         H5Oattribute.c H5Obogus.c H5Obtreek.c H5Ocache.c H5Ochunk.c \
-        H5Ocont.c H5Ocopy.c H5Odbg.c H5Odrvinfo.c H5Odtype.c H5Oefl.c \
-        H5Ofill.c H5Ofsinfo.c H5Oginfo.c \
+        H5Ocompare.c H5Ocont.c H5Ocopy.c H5Odbg.c H5Odrvinfo.c H5Odtype.c \
+        H5Oefl.c H5Ofill.c H5Ofsinfo.c H5Oginfo.c \
         H5Olayout.c \
         H5Olinfo.c H5Olink.c H5Omessage.c H5Omtime.c \
         H5Oname.c H5Onull.c H5Opline.c H5Orefcount.c \
diff --git a/src/Makefile.in b/src/Makefile.in
index 55e52ae..0700f23 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -126,7 +126,7 @@ am_libhdf5_la_OBJECTS = H5.lo H5checksum.lo H5dbg.lo H5system.lo \
 	H5L.lo H5Lexternal.lo H5lib_settings.lo H5MF.lo H5MFaggr.lo \
 	H5MFdbg.lo H5MFsection.lo H5MM.lo H5MP.lo H5MPtest.lo H5O.lo \
 	H5Oainfo.lo H5Oalloc.lo H5Oattr.lo H5Oattribute.lo H5Obogus.lo \
-	H5Obtreek.lo H5Ocache.lo H5Ochunk.lo H5Ocont.lo H5Ocopy.lo \
+	H5Obtreek.lo H5Ocache.lo H5Ochunk.lo H5Ocompare.lo H5Ocont.lo H5Ocopy.lo \
 	H5Odbg.lo H5Odrvinfo.lo H5Odtype.lo H5Oefl.lo H5Ofill.lo \
 	H5Ofsinfo.lo H5Oginfo.lo H5Olayout.lo H5Olinfo.lo H5Olink.lo \
 	H5Omessage.lo H5Omtime.lo H5Oname.lo H5Onull.lo H5Opline.lo \
@@ -510,7 +510,7 @@ libhdf5_la_SOURCES = H5.c H5checksum.c H5dbg.c H5system.c H5timer.c H5trace.c \
         H5MM.c H5MP.c H5MPtest.c \
         H5O.c H5Oainfo.c H5Oalloc.c H5Oattr.c \
         H5Oattribute.c H5Obogus.c H5Obtreek.c H5Ocache.c H5Ochunk.c \
-        H5Ocont.c H5Ocopy.c H5Odbg.c H5Odrvinfo.c H5Odtype.c H5Oefl.c \
+        H5Ocompare.c H5Ocont.c H5Ocopy.c H5Odbg.c H5Odrvinfo.c H5Odtype.c H5Oefl.c \
         H5Ofill.c H5Ofsinfo.c H5Oginfo.c \
         H5Olayout.c \
         H5Olinfo.c H5Olink.c H5Omessage.c H5Omtime.c \
@@ -835,6 +835,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Obtreek.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Ocache.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Ochunk.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Ocompare.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Ocont.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Ocopy.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Odbg.Plo@am__quote@
diff --git a/tools/lib/h5diff_dset.c b/tools/lib/h5diff_dset.c
index 8e25b6d..905cbbc 100644
--- a/tools/lib/h5diff_dset.c
+++ b/tools/lib/h5diff_dset.c
@@ -44,7 +44,16 @@ hsize_t diff_dataset( hid_t file1_id,
     hid_t   dcpl1 = -1;
     hid_t   dcpl2 = -1;
     hsize_t nfound = 0;
+    htri_t  tri_ret;
 
+    /* Do the comparison */
+    if((tri_ret = H5Ocompare(file1_id, obj1_name, file2_id, obj2_name, H5P_DEFAULT)) < 0)
+        goto error;
+
+    if(tri_ret)
+        nfound = 1;
+
+#if 0
     /*-------------------------------------------------------------------------
     * open the handles
     *-------------------------------------------------------------------------
@@ -102,12 +111,14 @@ hsize_t diff_dataset( hid_t file1_id,
         H5Dclose(did2);
         /* enable error reporting */
     } H5E_END_TRY;
+#endif
 
 
     return nfound;
 
 error:
     options->err_stat=1;
+#if 0
     /* disable error reporting */
     H5E_BEGIN_TRY {
         H5Pclose(dcpl1);
@@ -116,6 +127,7 @@ error:
         H5Dclose(did2);
         /* enable error reporting */
     } H5E_END_TRY;
+#endif
 
     return nfound;
 }