[svn-r12938] Description:

    Add src/H5Oalloc.c file forgotten in previous object header checkin

    Break out more object header routines into separate file (debugging routines
this time).

    Fix "//" style comment in recent ISOHM source changes.

    Fix 'size_t' vs. 'unsigned' problem (visible in 64-bit testing) in recent
ISOHM test changes.

Tested on:
    FreeBSD/32 4.11 (sleipnir)
    Linux/32 2.4 (heping)
    Linux/64 2.4 (mir)

1 files changed, 1489 insertions, 0 deletions

diff --git a/src/H5Oalloc.c b/src/H5Oalloc.c
new file mode 100644
index 0000000..3d728ce
--- /dev/null
+++ b/src/H5Oalloc.c
@@ -0,0 +1,1489 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * 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://hdf.ncsa.uiuc.edu/HDF5/doc/Copyright.html.  If you do not have     *
+ * access to either file, you may request a copy from hdfhelp@ncsa.uiuc.edu. *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*-------------------------------------------------------------------------
+ *
+ * Created:		H5Oalloc.c
+ *			Nov 17 2006
+ *			Quincey Koziol <koziol@hdfgroup.org>
+ *
+ * Purpose:		Object header allocation routines.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/****************/
+/* Module Setup */
+/****************/
+
+#define H5O_PACKAGE		/*suppress error about including H5Opkg	  */
+
+/***********/
+/* Headers */
+/***********/
+#include "H5private.h"		/* Generic Functions			*/
+#include "H5Eprivate.h"		/* Error handling		  	*/
+#include "H5FLprivate.h"	/* Free lists                           */
+#include "H5MFprivate.h"	/* File memory management		*/
+#include "H5Opkg.h"             /* Object headers			*/
+
+/****************/
+/* Local Macros */
+/****************/
+
+
+/******************/
+/* Local Typedefs */
+/******************/
+
+
+/********************/
+/* Package Typedefs */
+/********************/
+
+
+/********************/
+/* Local Prototypes */
+/********************/
+
+static herr_t H5O_add_gap(H5O_t *oh, unsigned chunkno, unsigned idx,
+    uint8_t *new_gap_loc, size_t new_gap_size);
+static herr_t H5O_eliminate_gap(H5O_t *oh, H5O_mesg_t *mesg,
+    uint8_t *new_gap_loc, size_t new_gap_size);
+static herr_t H5O_alloc_null(H5O_t *oh, unsigned null_idx,
+    const H5O_msg_class_t *new_type, void *new_native, size_t new_size);
+static herr_t H5O_alloc_msgs(H5O_t *oh, size_t min_alloc);
+static htri_t H5O_alloc_extend_chunk(H5F_t *f, H5O_t *oh, unsigned chunkno,
+    size_t size, unsigned * msg_idx);
+static unsigned H5O_alloc_new_chunk(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
+    size_t size);
+static htri_t H5O_move_msgs_forward(H5O_t *oh);
+static htri_t H5O_merge_null(H5O_t *oh);
+static htri_t H5O_remove_empty_chunks(H5F_t *f, H5O_t *oh, hid_t dxpl_id);
+
+
+/*********************/
+/* Package Variables */
+/*********************/
+
+/* Declare extern the free list for H5O_cont_t's */
+H5FL_EXTERN(H5O_cont_t);
+
+
+/*****************************/
+/* Library Private Variables */
+/*****************************/
+
+
+/*******************/
+/* Local Variables */
+/*******************/
+
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_add_gap
+ *
+ * Purpose:     Add a gap to a chunk
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:  Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              Oct 17 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_add_gap(H5O_t *oh, unsigned chunkno, unsigned idx,
+    uint8_t *new_gap_loc, size_t new_gap_size)
+{
+    hbool_t merged_with_null;           /* Whether the gap was merged with a null message */
+    unsigned u;                         /* Local index variable */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_add_gap)
+
+    /* check args */
+    HDassert(oh);
+    HDassert(oh->version > H5O_VERSION_1);
+    HDassert(new_gap_loc);
+    HDassert(new_gap_size);
+
+    /* Check for existing null message in chunk */
+    merged_with_null = FALSE;
+    for(u = 0; u < oh->nmesgs && !merged_with_null; u++) {
+        /* Find a null message in the chunk with the new gap */
+        /* (a null message that's not the one we are eliminating) */
+        if(H5O_NULL_ID == oh->mesg[u].type->id && oh->mesg[u].chunkno == chunkno
+                && u != idx) {
+            /* Sanity check - chunks with null messages shouldn't have a gap */
+            HDassert(oh->chunk[chunkno].gap == 0);
+
+            /* Eliminate the gap in the chunk */
+            if(H5O_eliminate_gap(oh, &oh->mesg[u], new_gap_loc, new_gap_size) < 0)
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't eliminate gap in chunk")
+
+            /* Set flag to indicate that the gap was handled */
+            merged_with_null = TRUE;
+        } /* end if */
+    } /* end for */
+
+    /* If we couldn't find a null message in the chunk, move the gap to the end */
+    if(!merged_with_null) {
+        /* Adjust message offsets after new gap forward in chunk */
+        for(u = 0; u < oh->nmesgs; u++)
+            if(oh->mesg[u].chunkno == chunkno && oh->mesg[u].raw > new_gap_loc)
+                oh->mesg[u].raw -= new_gap_size;
+
+        /* Slide raw message info forward in chunk image */
+        HDmemmove(new_gap_loc, new_gap_loc + new_gap_size, 
+                (size_t)((oh->chunk[chunkno].image + (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM_OH(oh))) - (new_gap_loc + new_gap_size)));
+
+        /* Add existing gap size to new gap size */
+        new_gap_size += oh->chunk[chunkno].gap;
+
+        /* Merging with existing gap will allow for a new null message */
+        if(new_gap_size >= (size_t)H5O_SIZEOF_MSGHDR_OH(oh)) {
+            H5O_mesg_t *null_msg;       /* Pointer to new null message */
+
+            /* Check if we need to extend message table to hold the new null message */
+            if(oh->nmesgs >= oh->alloc_nmesgs)
+                if(H5O_alloc_msgs(oh, (size_t)1) < 0)
+                    HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, UFAIL, "can't allocate more space for messages")
+
+            /* Increment new gap size */
+            oh->chunk[chunkno].gap += new_gap_size;
+
+            /* Create new null message, with the tail of the previous null message */
+            null_msg = &(oh->mesg[oh->nmesgs++]);
+            null_msg->type = H5O_MSG_NULL;
+            null_msg->dirty = TRUE;
+            null_msg->native = NULL;
+            null_msg->raw_size = new_gap_size - H5O_SIZEOF_MSGHDR_OH(oh);
+            null_msg->raw = (oh->chunk[chunkno].image + oh->chunk[chunkno].size)
+                    - (H5O_SIZEOF_CHKSUM_OH(oh) + null_msg->raw_size);
+            null_msg->chunkno = chunkno;
+
+            /* Zero out new null message's raw data */
+            if(null_msg->raw_size)
+                HDmemset(null_msg->raw, 0, null_msg->raw_size);
+
+            /* Reset size of gap in chunk */
+            oh->chunk[chunkno].gap = 0;
+        } /* end if */
+        else
+            oh->chunk[chunkno].gap = new_gap_size;
+    } /* end if */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_add_gap() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_eliminate_gap
+ *
+ * Purpose:     Eliminate a gap in a chunk with a null message
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:  Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              Oct 17 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_eliminate_gap(H5O_t *oh, H5O_mesg_t *mesg, uint8_t *gap_loc, size_t gap_size)
+{
+    uint8_t *move_start, *move_end;     /* Pointers to area of messages to move */
+    hbool_t null_before_gap;    /* Flag whether the null message is before the gap or not */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_eliminate_gap)
+
+    /* check args */
+    HDassert(oh);
+    HDassert(oh->version > H5O_VERSION_1);
+    HDassert(mesg);
+    HDassert(gap_loc);
+    HDassert(gap_size);
+
+    /* Check if the null message is before or after the gap produced */
+    null_before_gap = (hbool_t)(mesg->raw < gap_loc);
+
+    /* Set up information about region of messages to move */
+    if(null_before_gap) {
+        move_start = mesg->raw + mesg->raw_size;
+        move_end = gap_loc;
+    } /* end if */
+    else {
+        move_start = gap_loc + gap_size;
+        move_end = mesg->raw - H5O_SIZEOF_MSGHDR_OH(oh);
+    } /* end else */
+
+    /* Check for messages between null message and gap */
+    if(move_end > move_start) {
+        unsigned u;                 /* Local index variable */
+
+        /* Look for messages that need to move, to adjust raw pointers in chunk */
+        for(u = 0; u < oh->nmesgs; u++) {
+            uint8_t *msg_start;     /* Start of encoded message in chunk */
+
+            msg_start = oh->mesg[u].raw - H5O_SIZEOF_MSGHDR_OH(oh);
+            if(oh->mesg[u].chunkno == mesg->chunkno
+                    && (msg_start >= move_start && msg_start < move_end)) {
+                /* Move message's raw pointer in appropriate direction */
+                if(null_before_gap)
+                    oh->mesg[u].raw += gap_size;
+                else
+                    oh->mesg[u].raw -= gap_size;
+            } /* end if */
+        } /* end for */
+
+        /* Slide raw message info in chunk image */
+        if(null_before_gap)
+            /* Slide messages down */
+            HDmemmove(move_start + gap_size, move_start, (size_t)(move_end - move_start));
+        else {
+            /* Slide messages up */
+            HDmemmove(move_start - gap_size, move_start, (size_t)(move_end - move_start));
+
+            /* Adjust start of null message */
+            mesg->raw -= gap_size;
+        } /* end else */
+    } /* end if */
+
+    /* Zero out addition to null message */
+    HDmemset(mesg->raw + mesg->raw_size, 0, gap_size);
+
+    /* Adjust size of null message */
+    mesg->raw_size += gap_size;
+
+    /* Mark null message as dirty */
+    mesg->dirty = TRUE;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* H5O_eliminate_gap() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_alloc_null
+ *
+ * Purpose:     Allocate room for a new message from a null message
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Oct 22 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_alloc_null(H5O_t *oh, unsigned null_idx, const H5O_msg_class_t *new_type,
+    void *new_native, size_t new_size)
+{
+    H5O_mesg_t *alloc_msg;              /* Pointer to null message to allocate out of */
+    herr_t ret_value = SUCCEED; 	/* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_alloc_null)
+
+    /* check args */
+    HDassert(oh);
+    HDassert(new_type);
+    HDassert(new_size);
+
+    /* Point to null message to allocate out of */
+    alloc_msg = &oh->mesg[null_idx];
+
+    /* Check if there's a need to split the null message */
+    if(alloc_msg->raw_size > new_size) {
+        /* Check for producing a gap in the chunk */
+        if((alloc_msg->raw_size - new_size) < (size_t)H5O_SIZEOF_MSGHDR_OH(oh)) {
+            size_t gap_size = alloc_msg->raw_size - new_size;     /* Size of gap produced */
+
+            /* Adjust the size of the null message being eliminated */
+            alloc_msg->raw_size = new_size;
+
+            /* Add the gap to the chunk */
+            if(H5O_add_gap(oh, alloc_msg->chunkno, null_idx, alloc_msg->raw + alloc_msg->raw_size, gap_size) < 0)
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, UFAIL, "can't insert gap in chunk")
+        } /* end if */
+        else {
+            size_t  new_mesg_size = new_size + H5O_SIZEOF_MSGHDR_OH(oh); /* Total size of newly allocated message */
+            H5O_mesg_t *null_msg;       /* Pointer to new null message */
+
+            /* Check if we need to extend message table to hold the new null message */
+            if(oh->nmesgs >= oh->alloc_nmesgs) {
+                if(H5O_alloc_msgs(oh, (size_t)1) < 0)
+                    HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, UFAIL, "can't allocate more space for messages")
+
+                /* "Retarget" 'alloc_msg' pointer into newly re-allocated array of messages */
+                alloc_msg = &oh->mesg[null_idx];
+            } /* end if */
+
+            /* Create new null message, with the tail of the previous null message */
+            null_msg = &(oh->mesg[oh->nmesgs++]);
+            null_msg->type = H5O_MSG_NULL;
+            null_msg->dirty = TRUE;
+            null_msg->native = NULL;
+            null_msg->raw = alloc_msg->raw + new_mesg_size;
+            null_msg->raw_size = alloc_msg->raw_size - new_mesg_size;
+            null_msg->chunkno = alloc_msg->chunkno;
+
+            /* Check for gap in new null message's chunk */
+            if(oh->chunk[null_msg->chunkno].gap > 0) {
+                unsigned null_chunkno = null_msg->chunkno;   /* Chunk w/gap */
+
+                /* Eliminate the gap in the chunk */
+                if(H5O_eliminate_gap(oh, null_msg,
+                        ((oh->chunk[null_chunkno].image + oh->chunk[null_chunkno].size) - (H5O_SIZEOF_CHKSUM_OH(oh) + oh->chunk[null_chunkno].gap)),
+                        oh->chunk[null_chunkno].gap) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTREMOVE, UFAIL, "can't eliminate gap in chunk")
+
+                /* Set the gap size to zero for the chunk */
+                oh->chunk[null_chunkno].gap = 0;
+            } /* end if */
+
+            /* Set the size of the new "real" message */
+            alloc_msg->raw_size = new_size;
+        } /* end else */
+    } /* end if */
+
+    /* Initialize the new message */
+    alloc_msg->type = new_type;
+    alloc_msg->dirty = TRUE;
+    alloc_msg->native = new_native;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_alloc_null() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_alloc_msgs
+ *
+ * Purpose:     Allocate more messages for a header
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Nov 21 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_alloc_msgs(H5O_t *oh, size_t min_alloc)
+{
+    size_t old_alloc;                   /* Old number of messages allocated */
+    size_t na;                          /* New number of messages allocated */
+    H5O_mesg_t *new_mesg;               /* Pointer to new message array */
+    herr_t ret_value = SUCCEED; 	/* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_alloc_msgs)
+
+    /* check args */
+    HDassert(oh);
+
+    /* Initialize number of messages information */
+    old_alloc = oh->alloc_nmesgs;
+    na = oh->alloc_nmesgs + MAX(oh->alloc_nmesgs, min_alloc);
+
+    /* Attempt to allocate more memory */
+    if(NULL == (new_mesg = H5FL_SEQ_REALLOC(H5O_mesg_t, oh->mesg, na)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    /* Update ohdr information */
+    oh->alloc_nmesgs = na;
+    oh->mesg = new_mesg;
+
+    /* Set new object header info to zeros */
+    HDmemset(&oh->mesg[old_alloc], 0, (oh->alloc_nmesgs - old_alloc) * sizeof(H5O_mesg_t));
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_alloc_msgs() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_alloc_extend_chunk
+ *
+ * Purpose:     Attempt to extend a chunk that is allocated on disk.
+ *
+ *              If the extension is successful, and if the last message
+ *		of the chunk is the null message, then that message will
+ *		be extended with the chunk.  Otherwise a new null message
+ *		is created.
+ *
+ *              f is the file in which the chunk will be written.  It is
+ *              included to ensure that there is enough space to extend
+ *              this chunk.
+ *
+ * Return:      TRUE:		The chunk has been extended, and *msg_idx
+ *				contains the message index for null message
+ *				which is large enough to hold size bytes.
+ *
+ *		FALSE:		The chunk cannot be extended, and *msg_idx
+ *				is undefined.
+ *
+ *		FAIL:		Some internal error has been detected.
+ *
+ * Programmer:  John Mainzer -- 8/16/05
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5O_alloc_extend_chunk(H5F_t *f,
+                       H5O_t *oh,
+                       unsigned chunkno,
+                       size_t size,
+                       unsigned * msg_idx)
+{
+    size_t      delta;          /* Change in chunk's size */
+    size_t      aligned_size = H5O_ALIGN_OH(oh, size);
+    uint8_t     *old_image;     /* Old address of chunk's image in memory */
+    size_t      old_size;       /* Old size of chunk */
+    htri_t      tri_result;     /* Result from checking if chunk can be extended */
+    int         extend_msg = -1;/* Index of null message to extend */
+    unsigned    u;              /* Local index variable */
+    htri_t      ret_value = TRUE; 	/* return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_alloc_extend_chunk)
+
+    /* check args */
+    HDassert(f != NULL);
+    HDassert(oh != NULL);
+    HDassert(chunkno < oh->nchunks);
+    HDassert(size > 0);
+    HDassert(msg_idx != NULL);
+    HDassert(H5F_addr_defined(oh->chunk[chunkno].addr));
+
+    /* Test to see if the specified chunk ends with a null messages.
+     * If successful, set the index of the the null message in extend_msg.
+     */
+    for(u = 0; u < oh->nmesgs; u++) {
+        /* Check for null message at end of proper chunk */
+        /* (account for possible checksum at end of chunk) */
+        if(oh->mesg[u].chunkno == chunkno && H5O_NULL_ID == oh->mesg[u].type->id &&
+                ((oh->mesg[u].raw + oh->mesg[u].raw_size)
+                == ((oh->chunk[chunkno].image + oh->chunk[chunkno].size) -
+                    (oh->chunk[chunkno].gap + H5O_SIZEOF_CHKSUM_OH(oh))))) {
+
+            extend_msg = u;
+            break;
+        } /* end if */
+    } /* end for */
+
+    /* If we can extend an existing null message, adjust the delta appropriately */
+    if(extend_msg >= 0) {
+        HDassert(oh->chunk[chunkno].gap == 0);
+        delta = aligned_size - oh->mesg[extend_msg].raw_size;
+    } /* end if */
+    else
+        delta = (aligned_size + H5O_SIZEOF_MSGHDR_OH(oh)) - oh->chunk[chunkno].gap;
+    delta = H5O_ALIGN_OH(oh, delta);
+
+    /* Determine whether the chunk can be extended */
+    tri_result = H5MF_can_extend(f, H5FD_MEM_OHDR, oh->chunk[chunkno].addr,
+                                 (hsize_t)(oh->chunk[chunkno].size), (hsize_t)delta);
+    if(tri_result == FALSE)     /* can't extend -- we are done */
+        HGOTO_DONE(FALSE)
+    else if(tri_result < 0) /* error */
+        HGOTO_ERROR(H5E_RESOURCE, H5E_SYSTEM, FAIL, "can't tell if we can extend chunk")
+
+    /* If we get this far, we should be able to extend the chunk */
+    if(H5MF_extend(f, H5FD_MEM_OHDR, oh->chunk[chunkno].addr, (hsize_t)(oh->chunk[chunkno].size), (hsize_t)delta) < 0 )
+        HGOTO_ERROR(H5E_RESOURCE, H5E_SYSTEM, FAIL, "can't extend chunk")
+
+    /* If we can extend an existing null message, take care of that */
+    if(extend_msg >= 0) {
+        /* Adjust message size of existing null message */
+        oh->mesg[extend_msg].dirty = TRUE;
+        oh->mesg[extend_msg].raw_size += delta;
+    } /* end if */
+    /* Create new null message for end of chunk */
+    else {
+        /* Create a new null message */
+        if(oh->nmesgs >= oh->alloc_nmesgs)
+            if(H5O_alloc_msgs(oh, (size_t)1) < 0)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate more space for messages")
+
+        /* Set extension message */
+        extend_msg = oh->nmesgs++;
+
+        /* Initialize new null message */
+        oh->mesg[extend_msg].type = H5O_MSG_NULL;
+        oh->mesg[extend_msg].dirty = TRUE;
+        oh->mesg[extend_msg].native = NULL;
+        oh->mesg[extend_msg].raw = ((oh->chunk[chunkno].image + oh->chunk[chunkno].size)
+                - (H5O_SIZEOF_CHKSUM_OH(oh) + oh->chunk[chunkno].gap))
+                + H5O_SIZEOF_MSGHDR_OH(oh);
+        oh->mesg[extend_msg].raw_size = (delta + oh->chunk[chunkno].gap) - H5O_SIZEOF_MSGHDR_OH(oh);
+        oh->mesg[extend_msg].chunkno = chunkno;
+    } /* end else */
+
+    /* Allocate more memory space for chunk's image */
+    old_image = oh->chunk[chunkno].image;
+    old_size = oh->chunk[chunkno].size;
+    oh->chunk[chunkno].size += delta;
+    oh->chunk[chunkno].image = H5FL_BLK_REALLOC(chunk_image, old_image, oh->chunk[chunkno].size);
+    oh->chunk[chunkno].gap = 0;
+    oh->chunk[chunkno].dirty = TRUE;
+    if(NULL == oh->chunk[chunkno].image)
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    /* Wipe new space for chunk */
+    HDmemset(oh->chunk[chunkno].image + old_size, 0, oh->chunk[chunkno].size - old_size);
+
+    /* Spin through existing messages, adjusting them */
+    for(u = 0; u < oh->nmesgs; u++) {
+        /* Adjust raw addresses for messages in this chunk to reflect new 'image' address */
+        if(oh->mesg[u].chunkno == chunkno)
+            oh->mesg[u].raw = oh->chunk[chunkno].image + (oh->mesg[u].raw - old_image);
+
+        /* Find continuation message which points to this chunk and adjust chunk's size */
+        /* (Chunk 0 doesn't have a continuation message that points to it and
+         * it's size is directly encoded in the object header) */
+        if(chunkno > 0 && (H5O_CONT_ID == oh->mesg[u].type->id) &&
+                (((H5O_cont_t *)(oh->mesg[u].native))->chunkno == chunkno)) {
+            /* Adjust size of continuation message */
+            HDassert(((H5O_cont_t *)(oh->mesg[u].native))->size == old_size);
+            ((H5O_cont_t *)(oh->mesg[u].native))->size = oh->chunk[chunkno].size;
+
+            /* Flag continuation message as dirty */
+            oh->mesg[u].dirty = TRUE;
+        } /* end if */
+    } /* end for */
+
+    /* Set return value */
+    *msg_idx = extend_msg;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_alloc_extend_chunk() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_alloc_new_chunk
+ *
+ * Purpose:     Allocates a new chunk for the object header, including
+ *		file space.
+ *
+ *              One of the other chunks will get an object continuation
+ *		message.  If there isn't room in any other chunk for the
+ *		object continuation message, then some message from
+ *		another chunk is moved into this chunk to make room.
+ *
+ *              SIZE need not be aligned.
+ *
+ * Return:      Success:        Index number of the null message for the
+ *                              new chunk.  The null message will be at
+ *                              least SIZE bytes not counting the message
+ *                              ID or size fields.
+ *
+ *              Failure:        Negative
+ *
+ * Programmer:  Robb Matzke
+ *              matzke@llnl.gov
+ *              Aug  7 1997
+ *
+ *-------------------------------------------------------------------------
+ */
+static unsigned
+H5O_alloc_new_chunk(H5F_t *f,
+                    hid_t dxpl_id,
+                    H5O_t *oh,
+                    size_t size)
+{
+    size_t      cont_size;              /*continuation message size     */
+    int         found_null = (-1);      /*best fit null message         */
+    int         found_attr = (-1);      /*best fit attribute message    */
+    int         found_link = (-1);      /*best fit link message         */
+    int         found_other = (-1);     /*best fit other message        */
+    unsigned    idx;                    /*message number */
+    uint8_t     *p = NULL;              /*ptr into new chunk            */
+    H5O_cont_t  *cont = NULL;           /*native continuation message   */
+    unsigned    chunkno;                /* Chunk allocated */
+    haddr_t	new_chunk_addr;
+    unsigned    u;                      /* Local index variable */
+    unsigned    ret_value;              /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_alloc_new_chunk)
+
+    /* check args */
+    HDassert(oh);
+    HDassert(size > 0);
+    size = H5O_ALIGN_OH(oh, size);
+
+    /*
+     * Find the smallest null message that will hold an object
+     * continuation message.  Failing that, find the smallest message
+     * that could be moved to make room for the continuation message.
+     *
+     * Don't ever move continuation message from one chunk to another.
+     * Prioritize link messages moving to later chunks, instead of
+     * more "important" messages.
+     * Avoid moving attributes when possible to preserve their
+     * ordering (although ordering is *not* guaranteed!).
+     *
+     */
+    cont_size = H5O_ALIGN_OH(oh, H5F_SIZEOF_ADDR(f) + H5F_SIZEOF_SIZE(f));
+    for(u = 0; u < oh->nmesgs; u++) {
+        int msg_id = oh->mesg[u].type->id;      /* Temp. copy of message type ID */
+
+	if(H5O_NULL_ID == msg_id) {
+	    if(cont_size == oh->mesg[u].raw_size) {
+		found_null = u;
+		break;
+	    } else if(oh->mesg[u].raw_size >= cont_size &&
+                   (found_null < 0 ||
+                    oh->mesg[u].raw_size < oh->mesg[found_null].raw_size)) {
+		found_null = u;
+	    }
+	} else if(H5O_CONT_ID == msg_id) {
+	    /*don't consider continuation messages */
+	} else if(H5O_ATTR_ID == msg_id) {
+            if(oh->mesg[u].raw_size >= cont_size &&
+                   (found_attr < 0 ||
+                    oh->mesg[u].raw_size < oh->mesg[found_attr].raw_size))
+                found_attr = u;
+	} else if(H5O_LINK_ID == msg_id) {
+            if(oh->mesg[u].raw_size >= cont_size &&
+                   (found_link < 0 ||
+                    oh->mesg[u].raw_size < oh->mesg[found_link].raw_size))
+                found_link = u;
+	} else {
+            if(oh->mesg[u].raw_size >= cont_size &&
+                   (found_other < 0 ||
+                    oh->mesg[u].raw_size < oh->mesg[found_other].raw_size))
+                found_other = u;
+	} /* end else */
+    } /* end for */
+    HDassert(found_null >= 0 || found_attr >= 0 || found_link >= 0 || found_other >= 0);
+
+    /*
+     * If we must move some other message to make room for the null
+     * message, then make sure the new chunk has enough room for that
+     * other message.
+     *
+     * Move link messages first, then other messages, and attributes
+     * only as a last resort.
+     *
+     */
+    if(found_null < 0) {
+        if(found_link >= 0)
+            found_other = found_link;
+
+        if(found_other < 0)
+            found_other = found_attr;
+
+        HDassert(found_other >= 0);
+        size += H5O_SIZEOF_MSGHDR_OH(oh) + oh->mesg[found_other].raw_size;
+    } /* end if */
+
+    /*
+     * The total chunk size must include enough space for the checksum
+     * on the chunk and the continuation chunk magic #. (which are only present
+     * in later versions of the object header)
+     */
+    size +=  H5O_SIZEOF_CHKHDR_OH(oh);
+
+    /*
+     * The total chunk size must include the requested space plus enough
+     * for the message header.  This must be at least some minimum and a
+     * multiple of the alignment size.
+     */
+    size = MAX(H5O_MIN_SIZE, size + H5O_SIZEOF_MSGHDR_OH(oh));
+    HDassert(size == H5O_ALIGN_OH(oh, size));
+
+    /* allocate space in file to hold the new chunk */
+    new_chunk_addr = H5MF_alloc(f, H5FD_MEM_OHDR, dxpl_id, (hsize_t)size);
+    if(HADDR_UNDEF == new_chunk_addr)
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, UFAIL, "unable to allocate space for new chunk")
+
+    /*
+     * Create the new chunk giving it a file address.
+     */
+    if(oh->nchunks >= oh->alloc_nchunks) {
+        unsigned na = MAX(H5O_NCHUNKS, oh->alloc_nchunks * 2);        /* Double # of chunks allocated */
+        H5O_chunk_t *x = H5FL_SEQ_REALLOC(H5O_chunk_t, oh->chunk, (size_t)na);
+
+        if(!x)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, UFAIL, "memory allocation failed")
+        oh->alloc_nchunks = na;
+        oh->chunk = x;
+    } /* end if */
+
+    chunkno = oh->nchunks++;
+    oh->chunk[chunkno].dirty = TRUE;
+    oh->chunk[chunkno].addr = new_chunk_addr;
+    oh->chunk[chunkno].size = size;
+    oh->chunk[chunkno].gap = 0;
+    if(NULL == (oh->chunk[chunkno].image = p = H5FL_BLK_CALLOC(chunk_image, size)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, UFAIL, "memory allocation failed")
+
+    /* If this is a later version of the object header format, put the magic
+     *  # at the beginning of the chunk image.
+     */
+    if(oh->version > H5O_VERSION_1) {
+        HDmemcpy(p, H5O_CHK_MAGIC, (size_t)H5O_SIZEOF_MAGIC);
+        p += H5O_SIZEOF_MAGIC;
+    } /* end if */
+
+    /*
+     * Make sure we have enough space for all possible new messages
+     * that could be generated below.
+     */
+    if(oh->nmesgs + 3 > oh->alloc_nmesgs)
+        if(H5O_alloc_msgs(oh, (size_t)3) < 0)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, UFAIL, "can't allocate more space for messages")
+
+    /* Move message (that will be replaced with continuation message) 
+     *  to new chunk, if necessary.
+     */
+    if(found_null < 0) {
+        H5O_mesg_t *null_msg;       /* Pointer to new null message */
+
+        /* Create null message for space that message to copy currently occupies */
+        found_null = oh->nmesgs++;
+        null_msg = &(oh->mesg[found_null]);
+        null_msg->type = H5O_MSG_NULL;
+        null_msg->dirty = TRUE;
+        null_msg->native = NULL;
+        null_msg->raw = oh->mesg[found_other].raw;
+        null_msg->raw_size = oh->mesg[found_other].raw_size;
+        null_msg->chunkno = oh->mesg[found_other].chunkno;
+
+        /* Copy the message to move to its new location */
+        /* (Chunk is already dirty, no need to mark it) */
+        HDmemcpy(p, oh->mesg[found_other].raw - H5O_SIZEOF_MSGHDR_OH(oh),
+                 oh->mesg[found_other].raw_size + H5O_SIZEOF_MSGHDR_OH(oh));
+
+        /* Switch message to point to new location */
+        oh->mesg[found_other].raw = p + H5O_SIZEOF_MSGHDR_OH(oh);
+        oh->mesg[found_other].chunkno = chunkno;
+
+        /* Account for copied message in new chunk */
+        p += H5O_SIZEOF_MSGHDR_OH(oh) + oh->mesg[found_other].raw_size;
+        size -= H5O_SIZEOF_MSGHDR_OH(oh) + oh->mesg[found_other].raw_size;
+    } /* end if */
+    HDassert(found_null >= 0);
+
+    /* Create null message for [rest of] space in new chunk */
+    /* (account for chunk's magic # & checksum) */
+    idx = oh->nmesgs++;
+    oh->mesg[idx].type = H5O_MSG_NULL;
+    oh->mesg[idx].dirty = TRUE;
+    oh->mesg[idx].native = NULL;
+    oh->mesg[idx].raw = p + H5O_SIZEOF_MSGHDR_OH(oh);
+    oh->mesg[idx].raw_size = size -
+                (H5O_SIZEOF_CHKHDR_OH(oh) + H5O_SIZEOF_MSGHDR_OH(oh));
+    oh->mesg[idx].chunkno = chunkno;
+
+    /* Initialize the continuation information */
+    if(NULL == (cont = H5FL_MALLOC(H5O_cont_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, UFAIL, "memory allocation failed")
+    cont->addr = oh->chunk[chunkno].addr;
+    cont->size = oh->chunk[chunkno].size;
+    cont->chunkno = chunkno;
+
+    /* Split the null message and point at continuation message */
+    if(H5O_alloc_null(oh, (unsigned)found_null, H5O_MSG_CONT, cont, cont_size) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, UFAIL, "can't split null message")
+
+    /* Set return value */
+    ret_value = idx;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_alloc_new_chunk() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_alloc
+ *
+ * Purpose:     Allocate enough space in the object header for this message.
+ *
+ * Return:      Success:        Index of message
+ *
+ *              Failure:        Negative
+ *
+ * Programmer:  Robb Matzke
+ *              matzke@llnl.gov
+ *              Aug  6 1997
+ *
+ *-------------------------------------------------------------------------
+ */
+unsigned
+H5O_alloc(H5F_t *f,
+          hid_t dxpl_id,
+          H5O_t *oh,
+          const H5O_msg_class_t *type,
+          size_t size,
+          unsigned * oh_flags_ptr)
+{
+    size_t      aligned_size = H5O_ALIGN_OH(oh, size);
+    unsigned    idx;            /* Index of message which fits allocation */
+    unsigned    ret_value;      /* Return value */
+
+    FUNC_ENTER_NOAPI(H5O_alloc, UFAIL)
+
+    /* check args */
+    HDassert(oh);
+    HDassert(type);
+    HDassert(oh_flags_ptr);
+
+    /* look for a null message which is large enough */
+    for(idx = 0; idx < oh->nmesgs; idx++)
+        if(H5O_NULL_ID == oh->mesg[idx].type->id && oh->mesg[idx].raw_size >= aligned_size)
+            break;
+
+    /* if we didn't find one, then allocate more header space */
+    if(idx >= oh->nmesgs) {
+        unsigned        chunkno;
+
+        /* check to see if we can extend one of the chunks.  If we can,
+         * do so.  Otherwise, we will have to allocate a new chunk.
+         *
+         * Note that in this new version of this function, all chunks
+         * must have file space allocated to them.
+         */
+        for(chunkno = 0; chunkno < oh->nchunks; chunkno++) {
+            htri_t	tri_result;
+
+            HDassert(H5F_addr_defined(oh->chunk[chunkno].addr));
+
+            tri_result = H5O_alloc_extend_chunk(f, oh, chunkno, size, &idx);
+            if(tri_result == TRUE)
+		break;
+            else if(tri_result == FALSE)
+                idx = UFAIL;
+            else
+                HGOTO_ERROR(H5E_OHDR, H5E_SYSTEM, UFAIL, "H5O_alloc_extend_chunk failed unexpectedly")
+        } /* end for */
+
+        /* If idx is still UFAIL, we were not able to extend a chunk,
+         *      create a new one.
+         */
+        if(idx == UFAIL)
+            if((idx = H5O_alloc_new_chunk(f, dxpl_id, oh, size)) == UFAIL)
+                HGOTO_ERROR(H5E_OHDR, H5E_NOSPACE, UFAIL, "unable to create a new object header data chunk")
+    } /* end if */
+
+    /* Split the null message and point at continuation message */
+    if(H5O_alloc_null(oh, idx, type, NULL, aligned_size) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, UFAIL, "can't split null message")
+
+    /* Mark the object header as modified */
+    *oh_flags_ptr |= H5AC__DIRTIED_FLAG;
+
+#ifdef H5O_DEBUG
+H5O_assert(oh);
+#endif /* H5O_DEBUG */
+    /* Set return value */
+    ret_value = idx;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_alloc() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_release_mesg
+ *
+ * Purpose:     Convert a message into a null message
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Oct 22 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5O_release_mesg(H5F_t *f, hid_t dxpl_id, H5O_t *oh, H5O_mesg_t *mesg,
+    hbool_t delete_mesg, hbool_t adj_link)
+{
+    herr_t ret_value = SUCCEED; 	                /* Return value */
+
+    FUNC_ENTER_NOAPI(H5O_release_mesg, FAIL)
+
+    /* check args */
+    HDassert(f);
+    HDassert(oh);
+    HDassert(mesg);
+
+    /* Check if we should operate on the message */
+    if(delete_mesg) {
+        /* Free any space referred to in the file from this message */
+        if(H5O_delete_mesg(f, dxpl_id, mesg, adj_link) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTDELETE, FAIL, "unable to delete file space for object header message")
+
+        /* Free any native information */
+        H5O_free_mesg(mesg);
+    } /* end if */
+
+    /* Change message type to nil and zero it */
+    mesg->type = H5O_MSG_NULL;
+    HDassert(mesg->raw + mesg->raw_size <= (oh->chunk[mesg->chunkno].image + oh->chunk[mesg->chunkno].size) - (H5O_SIZEOF_CHKSUM_OH(oh) + oh->chunk[mesg->chunkno].gap));
+    HDmemset(mesg->raw, 0, mesg->raw_size);
+
+    /* Clear message flags */
+    mesg->flags = 0;
+
+    /* Indicate that the message was modified */
+    mesg->dirty = TRUE;
+
+    /* Check if chunk has a gap currently */
+    if(oh->chunk[mesg->chunkno].gap) {
+        /* Eliminate the gap in the chunk */
+        if(H5O_eliminate_gap(oh, mesg, 
+                ((oh->chunk[mesg->chunkno].image + oh->chunk[mesg->chunkno].size) - (H5O_SIZEOF_CHKSUM_OH(oh) + oh->chunk[mesg->chunkno].gap)),
+                oh->chunk[mesg->chunkno].gap) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTREMOVE, FAIL, "can't eliminate gap in chunk")
+
+        /* Set the gap size to zero for the chunk */
+        oh->chunk[mesg->chunkno].gap = 0;
+    } /* end if */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_release_mesg() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_move_msgs_forward
+ *
+ * Purpose:     Move messages toward first chunk
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Oct 17 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5O_move_msgs_forward(H5O_t *oh)
+{
+    hbool_t packed_msg;                 /* Flag to indicate that messages were packed */
+    hbool_t did_packing = FALSE;        /* Whether any messages were packed */
+    htri_t ret_value; 	                /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_move_msgs_forward)
+
+    /* check args */
+    HDassert(oh);
+
+    /* Loop until no messages packed */
+    /* (Double loop is not very efficient, but it would be some extra work to
+     *      add a list of messages to each chunk -QAK)
+     */
+    do {
+        H5O_mesg_t *curr_msg;       /* Pointer to current message to operate on */
+        unsigned	u;              /* Local index variable */
+
+        /* Reset packed messages flag */
+        packed_msg = FALSE;
+
+        /* Scan through messages for messages that can be moved earlier in chunks */
+        for(u = 0, curr_msg = &oh->mesg[0]; u < oh->nmesgs; u++, curr_msg++) {
+            if(H5O_NULL_ID == curr_msg->type->id) {
+                H5O_chunk_t *chunk;     /* Pointer to chunk that null message is in */
+
+                /* Check if null message is not last in chunk */
+                chunk = &(oh->chunk[curr_msg->chunkno]);
+                if((curr_msg->raw + curr_msg->raw_size) 
+                        != ((chunk->image + chunk->size) - (H5O_SIZEOF_CHKSUM_OH(oh) + chunk->gap))) {
+                    H5O_mesg_t *nonnull_msg;       /* Pointer to current message to operate on */
+                    unsigned	v;              /* Local index variable */
+
+                    /* Loop over messages again, looking for the message in the chunk after the null message */
+                    for(v = 0, nonnull_msg = &oh->mesg[0]; v < oh->nmesgs; v++, nonnull_msg++) {
+                        /* Locate message that is immediately after the null message */
+                        if((curr_msg->chunkno == nonnull_msg->chunkno) &&
+                                ((curr_msg->raw + curr_msg->raw_size) == (nonnull_msg->raw - H5O_SIZEOF_MSGHDR_OH(oh)))) {
+                            /* Don't swap messages if the second message is also a null message */
+                            /* (We'll merge them together later, in another routine) */
+                            if(H5O_NULL_ID != nonnull_msg->type->id) {
+                                /* Copy raw data for non-null message to new location */
+                                HDmemmove(curr_msg->raw - H5O_SIZEOF_MSGHDR_OH(oh),
+                                    nonnull_msg->raw - H5O_SIZEOF_MSGHDR_OH(oh), nonnull_msg->raw_size + H5O_SIZEOF_MSGHDR_OH(oh));
+
+                                /* Adjust non-null message's offset in chunk */
+                                nonnull_msg->raw = curr_msg->raw;
+
+                                /* Adjust null message's offset in chunk */
+                                curr_msg->raw = nonnull_msg->raw +
+                                        nonnull_msg->raw_size + H5O_SIZEOF_MSGHDR_OH(oh);
+
+                                /* Mark null message dirty */
+                                /* (since we need to re-encode its message header) */
+                                /* (also, marking this message dirty means we
+                                 *  don't have to mark chunk as dirty)
+                                 */
+                                curr_msg->dirty = TRUE;
+
+                                /* Set the flag to indicate that the null message
+                                 * was packed - if its not at the end its chunk,
+                                 * we'll move it again on the next pass.
+                                 */
+                                packed_msg = TRUE;
+                            } /* end if */
+
+                            /* Break out of loop */
+                            break;
+                        } /* end if */
+                    } /* end for */
+                    /* Should have been message after null message */
+                    HDassert(v < oh->nmesgs);
+                } /* end if */
+            } /* end if */
+            else {
+                H5O_mesg_t *null_msg;       /* Pointer to current message to operate on */
+                unsigned	v;              /* Local index variable */
+
+                /* Loop over messages again, looking for large enough null message in earlier chunk */
+                for(v = 0, null_msg = &oh->mesg[0]; v < oh->nmesgs; v++, null_msg++) {
+                    if(H5O_NULL_ID == null_msg->type->id && curr_msg->chunkno > null_msg->chunkno
+                            && curr_msg->raw_size <= null_msg->raw_size) {
+                        unsigned old_chunkno;   /* Old message information */
+                        uint8_t *old_raw;
+
+                        /* Keep old information about non-null message */
+                        old_chunkno = curr_msg->chunkno;
+                        old_raw = curr_msg->raw;
+
+                        /* Copy raw data for non-null message to new chunk */
+                        HDmemcpy(null_msg->raw - H5O_SIZEOF_MSGHDR_OH(oh), curr_msg->raw - H5O_SIZEOF_MSGHDR_OH(oh), curr_msg->raw_size + H5O_SIZEOF_MSGHDR_OH(oh));
+
+                        /* Mark null message's chunk as dirty, since the raw data image changed */
+                        oh->chunk[null_msg->chunkno].dirty = TRUE;
+
+                        /* Point non-null message at null message's space */
+                        curr_msg->chunkno = null_msg->chunkno;
+                        curr_msg->raw = null_msg->raw;
+
+                        /* Change information for null message */
+                        if(curr_msg->raw_size == null_msg->raw_size) {
+                            /* Point null message at old non-null space */
+                            /* (Instead of freeing it and allocating new message) */
+                            null_msg->chunkno = old_chunkno;
+                            null_msg->raw = old_raw;
+
+                            /* Mark null message dirty */
+                            null_msg->dirty = TRUE;
+                        } /* end if */
+                        else {
+                            unsigned new_null_msg;          /* Message index for new null message */
+
+                            /* Check if null message is large enough to still exist */
+                            if((null_msg->raw_size - curr_msg->raw_size) < (size_t)H5O_SIZEOF_MSGHDR_OH(oh)) {
+                                size_t gap_size = null_msg->raw_size - curr_msg->raw_size;     /* Size of gap produced */
+
+                                /* Adjust the size of the null message being eliminated */
+                                null_msg->raw_size = curr_msg->raw_size;
+
+                                /* Add the gap to the chunk */
+                                if(H5O_add_gap(oh, null_msg->chunkno, v, null_msg->raw + null_msg->raw_size, gap_size) < 0)
+                                    HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, FAIL, "can't insert gap in chunk")
+
+                                /* Re-use message # for new null message taking place of non-null message */
+                                new_null_msg = v;
+                            } /* end if */
+                            else {
+                                /* Adjust null message's size & offset */
+                                null_msg->raw += curr_msg->raw_size + H5O_SIZEOF_MSGHDR_OH(oh);
+                                null_msg->raw_size -= curr_msg->raw_size + H5O_SIZEOF_MSGHDR_OH(oh);
+
+                                /* Mark null message dirty */
+                                null_msg->dirty = TRUE;
+
+                                /* Create new null message for previous location of non-null message */
+                                if(oh->nmesgs >= oh->alloc_nmesgs) {
+                                    if(H5O_alloc_msgs(oh, (size_t)1) < 0)
+                                        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate more space for messages")
+
+                                    /* "Retarget" 'curr_msg' pointer into newly re-allocated array of messages */
+                                    curr_msg = &oh->mesg[u];
+                                } /* end if */
+
+                                /* Get message # for new null message */
+                                new_null_msg = oh->nmesgs++;
+                            } /* end else */
+
+                            /* Initialize new null message to take over non-null message's location */
+                            oh->mesg[new_null_msg].type = H5O_MSG_NULL;
+                            oh->mesg[new_null_msg].dirty = TRUE;
+                            oh->mesg[new_null_msg].native = NULL;
+                            oh->mesg[new_null_msg].raw = old_raw;
+                            oh->mesg[new_null_msg].raw_size = curr_msg->raw_size;
+                            oh->mesg[new_null_msg].chunkno = old_chunkno;
+
+                            /* Check for gap in new null message's chunk */
+                            if(oh->chunk[old_chunkno].gap > 0) {
+                                /* Eliminate the gap in the chunk */
+                                if(H5O_eliminate_gap(oh, &oh->mesg[new_null_msg], 
+                                        ((oh->chunk[old_chunkno].image + oh->chunk[old_chunkno].size) - (H5O_SIZEOF_CHKSUM_OH(oh) + oh->chunk[old_chunkno].gap)),
+                                        oh->chunk[old_chunkno].gap) < 0)
+                                    HGOTO_ERROR(H5E_OHDR, H5E_CANTREMOVE, FAIL, "can't eliminate gap in chunk")
+
+                                /* Set the gap size to zero for the chunk */
+                                oh->chunk[old_chunkno].gap = 0;
+                            } /* end if */
+                        } /* end else */
+
+                        /* Indicate that we packed messages */
+                        packed_msg = TRUE;
+
+                        /* Break out of loop */
+                        /* (If it's possible to move message to even earlier chunk
+                         *      we'll get it on the next pass - QAK)
+                         */
+                        break;
+                    } /* end if */
+                } /* end for */
+
+                /* If we packed messages, get out of loop and start over */
+                /* (Don't know if this has any benefit one way or the other -QAK) */
+                if(packed_msg)
+                    break;
+            } /* end else */
+        } /* end for */
+
+        /* If we did any packing, remember that */
+        if(packed_msg)
+            did_packing = TRUE;
+    } while(packed_msg);
+
+    /* Set return value */
+    ret_value = did_packing;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_move_msgs_forward() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_merge_null
+ *
+ * Purpose:     Merge neighboring null messages in an object header
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Oct 10 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5O_merge_null(H5O_t *oh)
+{
+    hbool_t merged_msg;                 /* Flag to indicate that messages were merged */
+    hbool_t did_merging = FALSE;        /* Whether any messages were merged */
+    htri_t ret_value; 	                /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_merge_null)
+
+    /* check args */
+    HDassert(oh != NULL);
+
+    /* Loop until no messages merged */
+    /* (Double loop is not very efficient, but it would be some extra work to add
+     *      a list of messages to each chunk -QAK)
+     */
+    do {
+        H5O_mesg_t *curr_msg;       /* Pointer to current message to operate on */
+        unsigned	u;              /* Local index variable */
+
+        /* Reset merged messages flag */
+        merged_msg = FALSE;
+
+        /* Scan messages for adjacent null messages & merge them */
+        for(u = 0, curr_msg = &oh->mesg[0]; u < oh->nmesgs; u++, curr_msg++) {
+            if(H5O_NULL_ID == curr_msg->type->id) {
+                H5O_mesg_t *curr_msg2;       /* Pointer to current message to operate on */
+                unsigned	v;              /* Local index variable */
+
+                /* Should be no gaps in chunk with null message */
+                HDassert(oh->chunk[curr_msg->chunkno].gap == 0);
+
+                /* Loop over messages again, looking for null message in same chunk */
+                for(v = 0, curr_msg2 = &oh->mesg[0]; v < oh->nmesgs; v++, curr_msg2++) {
+                    if(u != v && H5O_NULL_ID == curr_msg2->type->id && curr_msg->chunkno == curr_msg2->chunkno) {
+
+                        /* Check for second message after first message */
+                        if((curr_msg->raw + curr_msg->raw_size) == (curr_msg2->raw - H5O_SIZEOF_MSGHDR_OH(oh))) {
+                            /* Extend first null message length to cover second null message */
+                            curr_msg->raw_size += (H5O_SIZEOF_MSGHDR_OH(oh) + curr_msg2->raw_size);
+
+                            /* Message has been merged */
+                            merged_msg = TRUE;
+                        } /* end if */
+                        /* Check for second message before first message */
+                        else if((curr_msg->raw - H5O_SIZEOF_MSGHDR_OH(oh)) == (curr_msg2->raw + curr_msg2->raw_size)) {
+                            /* Adjust first message address and extend length to cover second message */
+                            curr_msg->raw -= (H5O_SIZEOF_MSGHDR_OH(oh) + curr_msg2->raw_size);
+                            curr_msg->raw_size += (H5O_SIZEOF_MSGHDR_OH(oh) + curr_msg2->raw_size);
+
+                            /* Message has been merged */
+                            merged_msg = TRUE;
+                        } /* end if */
+
+                        /* Second message has been merged, delete it */
+                        if(merged_msg) {
+                            /* Release any information/memory for second message */
+                            H5O_free_mesg(curr_msg2);
+
+                            /* Mark first message as dirty */
+                            curr_msg->dirty = TRUE;
+
+                            /* Remove second message from list of messages */
+                            if(v < (oh->nmesgs - 1))
+                                HDmemmove(&oh->mesg[v], &oh->mesg[v + 1], ((oh->nmesgs - 1) - v) * sizeof(H5O_mesg_t));
+
+                            /* Decrement # of messages */
+                            /* (Don't bother reducing size of message array for now -QAK) */
+                            oh->nmesgs--;
+
+                            /* Get out of loop */
+                            break;
+                        } /* end if */
+                    } /* end if */
+                } /* end for */
+
+                /* Get out of loop if we merged messages */
+                if(merged_msg)
+                    break;
+            } /* end if */
+        } /* end for */
+
+        /* If we did any merging, remember that */
+        if(merged_msg)
+            did_merging = TRUE;
+    } while(merged_msg);
+
+    /* Set return value */
+    ret_value = did_merging;
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_merge_null() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_remove_empty_chunks
+ *
+ * Purpose:     Attempt to eliminate empty chunks from object header.
+ *
+ *              This examines a chunk to see if it's empty
+ *              and removes it (and the continuation message that points to it)
+ *              from the object header.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Oct 17 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+static htri_t
+H5O_remove_empty_chunks(H5F_t *f, H5O_t *oh, hid_t dxpl_id)
+{
+    hbool_t deleted_chunk;              /* Whether to a chunk was deleted */
+    hbool_t did_deleting = FALSE;       /* Whether any chunks were deleted */
+    htri_t ret_value; 	                /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_remove_empty_chunks)
+
+    /* check args */
+    HDassert(oh != NULL);
+
+    /* Loop until no chunks are freed */
+    do {
+        H5O_mesg_t *null_msg;       /* Pointer to null message found */
+        H5O_mesg_t *cont_msg;       /* Pointer to continuation message found */
+        unsigned	u, v;       /* Local index variables */
+
+        /* Reset 'chunk deleted' flag */
+        deleted_chunk = FALSE;
+
+        /* Scan messages for null messages that fill an entire chunk */
+        for(u = 0, null_msg = &oh->mesg[0]; u < oh->nmesgs; u++, null_msg++) {
+            /* If a null message takes up an entire object header chunk (and
+             * its not the "base" chunk), delete that chunk from object header
+             */
+            if(H5O_NULL_ID == null_msg->type->id && null_msg->chunkno > 0 &&
+                    (H5O_SIZEOF_MSGHDR_OH(oh) + null_msg->raw_size)
+                         == (oh->chunk[null_msg->chunkno].size - H5O_SIZEOF_CHKHDR_OH(oh))) {
+                H5O_mesg_t *curr_msg;           /* Pointer to current message to operate on */
+                unsigned null_msg_no;           /* Message # for null message */
+                unsigned deleted_chunkno;       /* Chunk # to delete */
+
+                /* Locate continuation message that points to chunk */
+                for(v = 0, cont_msg = &oh->mesg[0]; v < oh->nmesgs; v++, cont_msg++) {
+                    if(H5O_CONT_ID == cont_msg->type->id) {
+                        /* Decode current continuation message if necessary */
+                        if(NULL == cont_msg->native) {
+                            HDassert(H5O_MSG_CONT->decode);
+                            cont_msg->native = (H5O_MSG_CONT->decode)(f, dxpl_id, cont_msg->raw);
+                            if(NULL == cont_msg->native)
+                                HGOTO_ERROR(H5E_OHDR, H5E_CANTDECODE, FAIL, "unable to decode message")
+                        } /* end if */
+
+                        /* Check for correct chunk to delete */
+                        if(oh->chunk[null_msg->chunkno].addr == ((H5O_cont_t *)(cont_msg->native))->addr)
+                            break;
+                    } /* end if */
+                } /* end for */
+                /* Must be a continuation message that points to chunk containing null message */
+                HDassert(v < oh->nmesgs);
+                HDassert(cont_msg);
+
+                /* Initialize information about null message */
+                null_msg_no = u;
+                deleted_chunkno = null_msg->chunkno;
+
+                /* Convert continuation message into a null message */
+                if(H5O_release_mesg(f, dxpl_id, oh, cont_msg, TRUE, TRUE) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTDELETE, FAIL, "unable to convert into null message")
+
+                /*
+                 * Remove chunk from object header's data structure
+                 */
+
+                /* Free memory for chunk image */
+                H5FL_BLK_FREE(chunk_image, oh->chunk[null_msg->chunkno].image);
+
+                /* Remove chunk from list of chunks */
+                if(null_msg->chunkno < (oh->nchunks - 1))
+                    HDmemmove(&oh->chunk[null_msg->chunkno], &oh->chunk[null_msg->chunkno + 1], ((oh->nchunks - 1) - null_msg->chunkno) * sizeof(H5O_chunk_t));
+
+                /* Decrement # of chunks */
+                /* (Don't bother reducing size of chunk array for now -QAK) */
+                oh->nchunks--;
+
+                /*
+                 * Delete null message (in empty chunk that was be freed) from list of messages
+                 */
+
+                /* Release any information/memory for message */
+                H5O_free_mesg(null_msg);
+
+                /* Remove null message from list of messages */
+                if(null_msg_no < (oh->nmesgs - 1))
+                    HDmemmove(&oh->mesg[null_msg_no], &oh->mesg[null_msg_no + 1], ((oh->nmesgs - 1) - null_msg_no) * sizeof(H5O_mesg_t));
+
+                /* Decrement # of messages */
+                /* (Don't bother reducing size of message array for now -QAK) */
+                oh->nmesgs--;
+
+                /* Adjust chunk # for messages in chunks after deleted chunk */
+                for(u = 0, curr_msg = &oh->mesg[0]; u < oh->nmesgs; u++, curr_msg++) {
+                    HDassert(curr_msg->chunkno != deleted_chunkno);
+                    if(curr_msg->chunkno > deleted_chunkno)
+                        curr_msg->chunkno--;
+                } /* end for */
+
+                /* Found chunk to delete */
+                deleted_chunk = TRUE;
+                break;
+            } /* end if */
+        } /* end for */
+
+        /* If we deleted any chunks, remember that */
+        if(deleted_chunk)
+            did_deleting = TRUE;
+    } while(deleted_chunk);
+
+    /* Set return value */
+    ret_value = did_deleting;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_remove_empty_chunks() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5O_condense_header
+ *
+ * Purpose:     Attempt to eliminate empty chunks from object header.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Oct  4 2005
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5O_condense_header(H5F_t *f, H5O_t *oh, hid_t dxpl_id)
+{
+    hbool_t rescan_header;              /* Whether to rescan header */
+    htri_t result;                      /* Result from packing/merging/etc */
+    herr_t ret_value = SUCCEED; 	/* return value */
+
+    FUNC_ENTER_NOAPI(H5O_condense_header, FAIL)
+
+    /* check args */
+    HDassert(oh != NULL);
+
+    /* Loop until no changed to the object header messages & chunks */
+    do {
+        /* Reset 'rescan chunks' flag */
+        rescan_header = FALSE;
+
+        /* Scan for messages that can be moved earlier in chunks */
+        result = H5O_move_msgs_forward(oh);
+        if(result < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTPACK, FAIL, "can't move header messages forward")
+        if(result > 0)
+            rescan_header = TRUE;
+
+        /* Scan for adjacent null messages & merge them */
+        result = H5O_merge_null(oh);
+        if(result < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTPACK, FAIL, "can't pack null header messages")
+        if(result > 0)
+            rescan_header = TRUE;
+
+        /* Scan for empty chunks to remove */
+        result = H5O_remove_empty_chunks(f, oh, dxpl_id);
+        if(result < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTPACK, FAIL, "can't remove empty chunk")
+        if(result > 0)
+            rescan_header = TRUE;
+    } while(rescan_header);
+#ifdef H5O_DEBUG
+H5O_assert(oh);
+#endif /* H5O_DEBUG */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_condense_header() */
+