[svn-r18574] Description:

	Bring r18571 from trunk to 1.8 branch:

	Bring r18542 from metadata journaling "merging" branch to trunk:

	Bring new object header pin/unpin & protect/unprotect routines and
split-out object header chunk proxy changes from metadata_journaling branch to
"merging" branch, along with some other minor tweaks to clean up compiler
warnings, etc.

	Also: clean up chunk protect/unprotect calls when allocating or freeing
space in a chunk, optimize metadata accumulator code to avoid some re-reading
of information from the file, refactor H5O_pin/H5O_unpin from way they are done
on the merging branch back to way they were previously done on trunk, other
minor code cleanups, etc.

Tested on:
        FreeBSD/32 6.3 (duty) in debug mode
        FreeBSD/64 6.3 (liberty) w/C++ & FORTRAN, in debug mode
        Linux/64-amd64 2.6 (abe) w/parallel, w/FORTRAN, in production mode
	(h5committested on trunk)

1 files changed, 867 insertions, 443 deletions

diff --git a/src/H5Ocache.c b/src/H5Ocache.c
index d3e736e..8fe3cf5 100644
--- a/src/H5Ocache.c
+++ b/src/H5Ocache.c
@@ -39,6 +39,7 @@
 #include "H5FLprivate.h"	/* Free lists                           */
 #include "H5MFprivate.h"	/* File memory management		*/
 #include "H5Opkg.h"             /* Object headers			*/
+#include "H5WBprivate.h"        /* Wrapped Buffers                      */
 
 
 /****************/
@@ -74,33 +75,69 @@ static herr_t H5O_dest(H5F_t *f, H5O_t *oh);
 static herr_t H5O_clear(H5F_t *f, H5O_t *oh, hbool_t destroy);
 static herr_t H5O_size(const H5F_t *f, const H5O_t *oh, size_t *size_ptr);
 
+static H5O_chunk_proxy_t *H5O_cache_chk_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void *_udata1,
+		       void *_udata2);
+static herr_t H5O_cache_chk_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5O_chunk_proxy_t *chk_proxy, unsigned UNUSED * flags_ptr);
+static herr_t H5O_cache_chk_dest(H5F_t *f, H5O_chunk_proxy_t *chk_proxy);
+static herr_t H5O_cache_chk_clear(H5F_t *f, H5O_chunk_proxy_t *chk_proxy, hbool_t destroy);
+static herr_t H5O_cache_chk_size(const H5F_t *f, const H5O_chunk_proxy_t *chk_proxy, size_t *size_ptr);
+
+/* Chunk proxy routines */
+static herr_t H5O_chunk_proxy_dest(H5O_chunk_proxy_t *chunk_proxy);
+
+/* Chunk routines */
+static herr_t H5O_chunk_deserialize(H5O_t *oh, haddr_t addr, size_t len,
+    const uint8_t *image, H5O_common_cache_ud_t *udata, hbool_t *dirty);
+static herr_t H5O_chunk_serialize(const H5F_t *f, H5O_t *oh, unsigned chunkno);
+
+/* Misc. routines */
+static herr_t H5O_add_cont_msg(H5O_cont_msgs_t *cont_msg_info,
+    const H5O_cont_t *cont);
+
 
 /*********************/
 /* Package Variables */
 /*********************/
 
+/* H5O object header prefix inherits cache-like properties from H5AC */
+const H5AC_class_t H5AC_OHDR[1] = {{
+    H5AC_OHDR_ID,
+    (H5AC_load_func_t)H5O_load,
+    (H5AC_flush_func_t)H5O_flush,
+    (H5AC_dest_func_t)H5O_dest,
+    (H5AC_clear_func_t)H5O_clear,
+    (H5AC_size_func_t)H5O_size,
+}};
+
+/* H5O object header chunk inherits cache-like properties from H5AC */
+const H5AC_class_t H5AC_OHDR_CHK[1] = {{
+    H5AC_OHDR_CHK_ID,
+    (H5AC_load_func_t)H5O_cache_chk_load,
+    (H5AC_flush_func_t)H5O_cache_chk_flush,
+    (H5AC_dest_func_t)H5O_cache_chk_dest,
+    (H5AC_clear_func_t)H5O_cache_chk_clear,
+    (H5AC_size_func_t)H5O_cache_chk_size,
+}};
+
+/* Declare external the free list for H5O_unknown_t's */
+H5FL_EXTERN(H5O_unknown_t);
+
+/* Declare extern the free list for H5O_chunk_proxy_t's */
+H5FL_EXTERN(H5O_chunk_proxy_t);
+
+/* Declare the free list for H5O_cont_t sequences */
+H5FL_SEQ_DEFINE(H5O_cont_t);
+
 
 /*****************************/
 /* Library Private Variables */
 /*****************************/
 
-/* Declare external the free list for H5O_unknown_t's */
-H5FL_EXTERN(H5O_unknown_t);
-
 
 /*******************/
 /* Local Variables */
 /*******************/
 
-/* H5O inherits cache-like properties from H5AC */
-const H5AC_class_t H5AC_OHDR[1] = {{
-    H5AC_OHDR_ID,
-    (H5AC_load_func_t)H5O_load,
-    (H5AC_flush_func_t)H5O_flush,
-    (H5AC_dest_func_t)H5O_dest,
-    (H5AC_clear_func_t)H5O_clear,
-    (H5AC_size_func_t)H5O_size,
-}};
 
 
 /*-------------------------------------------------------------------------
@@ -120,18 +157,17 @@ const H5AC_class_t H5AC_OHDR[1] = {{
  */
 static H5O_t *
 H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
-	 void UNUSED * _udata2)
+	 void *_udata2)
 {
     H5O_t	*oh = NULL;     /* Object header read in */
+    H5O_cache_ud_t *udata = (H5O_cache_ud_t *)_udata2;       /* User data for callback */
+    H5WB_t      *wb = NULL;     /* Wrapped buffer for prefix data */
     uint8_t     read_buf[H5O_SPEC_READ_SIZE];       /* Buffer for speculative read */
     const uint8_t *p;           /* Pointer into buffer to decode */
+    uint8_t     *buf;           /* Buffer to decode */
     size_t	spec_read_size; /* Size of buffer to speculatively read in */
     size_t	prefix_size;    /* Size of object header prefix */
-    unsigned	nmesgs;         /* Total # of messages in this object header */
-    unsigned	curmesg = 0;    /* Current message being decoded in object header */
-    unsigned    merged_null_msgs = 0;   /* Number of null messages merged together */
-    haddr_t	chunk_addr;     /* Address of first chunk */
-    size_t	chunk_size;     /* Size of first chunk */
+    size_t	buf_size;       /* Size of prefix+chunk #0 buffer */
     haddr_t     eoa;		/* Relative end of file address	*/
     H5O_t	*ret_value;     /* Return value */
 
@@ -141,7 +177,9 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
     HDassert(f);
     HDassert(H5F_addr_defined(addr));
     HDassert(!_udata1);
-    HDassert(!_udata2);
+    HDassert(udata);
+    HDassert(udata->common.f);
+    HDassert(udata->common.cont_msg_info);
 
     /* Make certain we don't speculatively read off the end of the file */
     if(HADDR_UNDEF == (eoa = H5F_get_eoa(f, H5FD_MEM_OHDR)))
@@ -160,8 +198,8 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
 	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")
 
     /* File-specific, non-stored information */
-    oh->sizeof_size = H5F_SIZEOF_SIZE(f);
-    oh->sizeof_addr = H5F_SIZEOF_ADDR(f);
+    oh->sizeof_size = H5F_SIZEOF_SIZE(udata->common.f);
+    oh->sizeof_addr = H5F_SIZEOF_ADDR(udata->common.f);
 
     /* Check for presence of magic number */
     /* (indicates version 2 or later) */
@@ -179,9 +217,6 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
         if(oh->flags & ~H5O_HDR_ALL_FLAGS)
             HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "unknown object header status flag(s)")
 
-        /* Number of messages (to allocate initially) */
-        nmesgs = 1;
-
         /* Number of links to object (unless overridden by refcount message) */
         oh->nlink = 1;
 
@@ -206,7 +241,7 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
             UINT16DECODE(p, oh->max_compact);
             UINT16DECODE(p, oh->min_dense);
             if(oh->max_compact < oh->min_dense)
-                HGOTO_ERROR(H5E_OHDR, H5E_VERSION, NULL, "bad object header attribute phase change values")
+                HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad object header attribute phase change values")
         } /* end if */
         else {
             oh->max_compact = H5O_CRT_ATTR_MAX_COMPACT_DEF;
@@ -216,26 +251,26 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
         /* First chunk size */
         switch(oh->flags & H5O_HDR_CHUNK0_SIZE) {
             case 0:     /* 1 byte size */
-                chunk_size = *p++;
+                oh->chunk0_size = *p++;
                 break;
 
             case 1:     /* 2 byte size */
-                UINT16DECODE(p, chunk_size);
+                UINT16DECODE(p, oh->chunk0_size);
                 break;
 
             case 2:     /* 4 byte size */
-                UINT32DECODE(p, chunk_size);
+                UINT32DECODE(p, oh->chunk0_size);
                 break;
 
             case 3:     /* 8 byte size */
-                UINT64DECODE(p, chunk_size);
+                UINT64DECODE(p, oh->chunk0_size);
                 break;
 
             default:
                 HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad size for chunk 0")
         } /* end switch */
-        if(chunk_size > 0 && chunk_size < H5O_SIZEOF_MSGHDR_OH(oh))
-            HGOTO_ERROR(H5E_OHDR, H5E_VERSION, NULL, "bad object header chunk size")
+        if(oh->chunk0_size > 0 && oh->chunk0_size < H5O_SIZEOF_MSGHDR_OH(oh))
+            HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad object header chunk size")
     } /* end if */
     else {
         /* Version */
@@ -250,7 +285,7 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
         p++;
 
         /* Number of messages */
-        UINT16DECODE(p, nmesgs);
+        UINT16DECODE(p, udata->v1_pfx_nmesgs);
 
         /* Link count */
         UINT32DECODE(p, oh->nlink);
@@ -263,10 +298,10 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
         oh->min_dense = 0;
 
         /* First chunk size */
-        UINT32DECODE(p, chunk_size);
-        if((nmesgs > 0 && chunk_size < H5O_SIZEOF_MSGHDR_OH(oh)) ||
-                (nmesgs == 0 && chunk_size > 0))
-            HGOTO_ERROR(H5E_OHDR, H5E_VERSION, NULL, "bad object header chunk size")
+        UINT32DECODE(p, oh->chunk0_size);
+        if((udata->v1_pfx_nmesgs > 0 && oh->chunk0_size < H5O_SIZEOF_MSGHDR_OH(oh)) ||
+                (udata->v1_pfx_nmesgs == 0 && oh->chunk0_size > 0))
+            HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad object header chunk size")
 
         /* Reserved, in version 1 (for 8-byte alignment padding) */
         p += 4;
@@ -276,356 +311,44 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
     prefix_size = (size_t)(p - (const uint8_t *)read_buf);
     HDassert((size_t)prefix_size == (size_t)(H5O_SIZEOF_HDR(oh) - H5O_SIZEOF_CHKSUM_OH(oh)));
 
-    /* Compute first chunk address */
-    chunk_addr = addr + (hsize_t)prefix_size;
-
-    /* Allocate the message array */
-    oh->alloc_nmesgs = (nmesgs > 0) ? nmesgs : 1;
-    if(NULL == (oh->mesg = H5FL_SEQ_MALLOC(H5O_mesg_t, oh->alloc_nmesgs)))
-	HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, NULL, "memory allocation failed")
-
-    /* Read each chunk from disk */
-    while(H5F_addr_defined(chunk_addr)) {
-        unsigned chunkno;       /* Current chunk's index */
-#ifndef NDEBUG
-        unsigned nullcnt;       /* Count of null messages (for sanity checking gaps in chunks) */
-#endif /* NDEBUG */
-        uint8_t *eom_ptr;       /* Pointer to end of messages for a chunk */
-
-	/* Increase chunk array size, if necessary */
-	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_OHDR, H5E_CANTALLOC, NULL, "memory allocation failed")
-	    oh->alloc_nchunks = na;
-	    oh->chunk = x;
-	} /* end if */
-
-	/* Init the chunk data info */
-	chunkno = oh->nchunks++;
-	oh->chunk[chunkno].dirty = FALSE;
-	oh->chunk[chunkno].gap = 0;
-        if(chunkno == 0) {
-            /* First chunk's 'image' includes room for the object header prefix */
-            oh->chunk[0].addr = addr;
-            oh->chunk[0].size = chunk_size + H5O_SIZEOF_HDR(oh);
-        } /* end if */
-        else {
-            oh->chunk[chunkno].addr = chunk_addr;
-            oh->chunk[chunkno].size = chunk_size;
-        } /* end else */
-	if(NULL == (oh->chunk[chunkno].image = H5FL_BLK_MALLOC(chunk_image, oh->chunk[chunkno].size)))
-	    HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, NULL, "memory allocation failed")
-
-        /* Handle chunk 0 as special case */
-        if(chunkno == 0) {
-            /* Check for speculative read of first chunk containing all the data needed */
-            if(spec_read_size >= oh->chunk[0].size)
-                HDmemcpy(oh->chunk[0].image, read_buf, oh->chunk[0].size);
-            else {
-                /* Copy the object header prefix into chunk 0's image */
-                HDmemcpy(oh->chunk[0].image, read_buf, prefix_size);
-
-                /* Read the chunk raw data */
-                /* (probably re-reads some data we already retrieved, but since
-                 *      we have to do the I/O operation anyway, we might as
-                 *      well avoid memcpy()ing the data in our buffer already)
-                 */
-                if(H5F_block_read(f, H5FD_MEM_OHDR, chunk_addr, (oh->chunk[0].size - prefix_size),
-                        dxpl_id, (oh->chunk[0].image + prefix_size)) < 0)
-                    HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to read object header data")
-            } /* end else */
-
-            /* Point into chunk image to decode */
-            p = oh->chunk[0].image + prefix_size;
-        } /* end if */
-        else {
-            /* Read the chunk raw data */
-            if(H5F_block_read(f, H5FD_MEM_OHDR, chunk_addr, chunk_size, dxpl_id, oh->chunk[chunkno].image) < 0)
-                HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to read object header data")
-
-            /* Point into chunk image to decode */
-            p = oh->chunk[chunkno].image;
-        } /* end else */
-
-        /* Check for magic # on chunks > 0 in later versions of the format */
-        if(chunkno > 0 && oh->version > H5O_VERSION_1) {
-            /* Magic number */
-            if(HDmemcmp(p, H5O_CHK_MAGIC, (size_t)H5_SIZEOF_MAGIC))
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "wrong object header chunk signature")
-            p += H5_SIZEOF_MAGIC;
-        } /* end if */
-
-	/* Decode messages from this chunk */
-        eom_ptr = oh->chunk[chunkno].image + (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM_OH(oh));
-#ifndef NDEBUG
-        nullcnt = 0;
-#endif /* NDEBUG */
-	while(p < eom_ptr) {
-            unsigned    mesgno;         /* Current message to operate on */
-            size_t	mesg_size;      /* Size of message read in */
-            unsigned	id;             /* ID (type) of current message */
-            uint8_t	flags;          /* Flags for current message */
-            H5O_msg_crt_idx_t crt_idx = 0;  /* Creation index for current message */
-
-            /* Decode message prefix info */
-
-            /* Version # */
-            if(oh->version == H5O_VERSION_1)
-                UINT16DECODE(p, id)
-            else
-                id = *p++;
-
-            /* Check for unknown message ID getting encoded in file */
-            if(id == H5O_UNKNOWN_ID)
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "'unknown' message ID encoded in file?!?")
-
-            /* Message size */
-	    UINT16DECODE(p, mesg_size);
-	    HDassert(mesg_size == H5O_ALIGN_OH(oh, mesg_size));
-
-            /* Message flags */
-	    flags = *p++;
-            if(flags & ~H5O_MSG_FLAG_BITS)
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "unknown flag for message")
-            if((flags & H5O_MSG_FLAG_SHARED) && (flags & H5O_MSG_FLAG_DONTSHARE))
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "bad flag combination for message")
-            if((flags & H5O_MSG_FLAG_WAS_UNKNOWN) && (flags & H5O_MSG_FLAG_FAIL_IF_UNKNOWN))
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "bad flag combination for message")
-            if((flags & H5O_MSG_FLAG_WAS_UNKNOWN) && !(flags & H5O_MSG_FLAG_MARK_IF_UNKNOWN))
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "bad flag combination for message")
-
-            /* Reserved bytes/creation index */
-            if(oh->version == H5O_VERSION_1)
-                p += 3; /*reserved*/
-            else {
-                /* Only decode creation index if they are being tracked */
-                if(oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED)
-                    UINT16DECODE(p, crt_idx);
-            } /* end else */
-
-            /* Try to detect invalidly formatted object header message that
-             *  extends past end of chunk.
-             */
-	    if(p + mesg_size > eom_ptr)
-		HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "corrupt object header")
-
-#ifndef NDEBUG
-            /* Increment count of null messages */
-            if(H5O_NULL_ID == id)
-                nullcnt++;
-#endif /* NDEBUG */
-
-            /* Check for combining two adjacent 'null' messages */
-            if((H5F_INTENT(f) & H5F_ACC_RDWR) &&
-                    H5O_NULL_ID == id && oh->nmesgs > 0 &&
-                    H5O_NULL_ID == oh->mesg[oh->nmesgs - 1].type->id &&
-                    oh->mesg[oh->nmesgs - 1].chunkno == chunkno) {
-
-                /* Combine adjacent null messages */
-                mesgno = oh->nmesgs - 1;
-                oh->mesg[mesgno].raw_size += H5O_SIZEOF_MSGHDR_OH(oh) + mesg_size;
-                oh->mesg[mesgno].dirty = TRUE;
-                merged_null_msgs++;
-            } /* end if */
-            else {
-                /* Check if we need to extend message table to hold the new message */
-                if(oh->nmesgs >= oh->alloc_nmesgs)
-                    if(H5O_alloc_msgs(oh, (size_t)1) < 0)
-                        HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, NULL, "can't allocate more space for messages")
-
-                /* Get index for message */
-                mesgno = oh->nmesgs++;
-
-                /* Initialize information about message */
-                oh->mesg[mesgno].dirty = FALSE;
-                oh->mesg[mesgno].flags = flags;
-                oh->mesg[mesgno].crt_idx = crt_idx;
-                oh->mesg[mesgno].native = NULL;
-                oh->mesg[mesgno].raw = (uint8_t *)p;        /* Casting away const OK - QAK */
-                oh->mesg[mesgno].raw_size = mesg_size;
-                oh->mesg[mesgno].chunkno = chunkno;
-
-                /* Point unknown messages at 'unknown' message class */
-                /* (Usually from future versions of the library) */
-                if(id >= NELMTS(H5O_msg_class_g) || NULL == H5O_msg_class_g[id]) {
-                    H5O_unknown_t *unknown;     /* Pointer to "unknown" message info */
-
-                    /* Allocate "unknown" message info */
-                    if(NULL == (unknown = H5FL_MALLOC(H5O_unknown_t)))
-                        HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, NULL, "memory allocation failed")
-
-                    /* Save the original message type ID */
-                    *unknown = id;
-
-                    /* Save 'native' form of unknown message */
-                    oh->mesg[mesgno].native = unknown;
-
-                    /* Set message to "unknown" class */
-                    oh->mesg[mesgno].type = H5O_msg_class_g[H5O_UNKNOWN_ID];
-
-                    /* Check for "fail if unknown" message flag */
-                    if(flags & H5O_MSG_FLAG_FAIL_IF_UNKNOWN)
-                        HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, NULL, "unknown message with 'fail if unknown' flag found")
-                    /* Check for "mark if unknown" message flag, etc. */
-                    else if((flags & H5O_MSG_FLAG_MARK_IF_UNKNOWN) &&
-                            !(flags & H5O_MSG_FLAG_WAS_UNKNOWN) &&
-                            (H5F_INTENT(f) & H5F_ACC_RDWR)) {
-
-                        /* Mark the message as "unknown" */
-                        /* This is a bit aggressive, since the application may
-                         * never change anything about the object (metadata or
-                         * raw data), but we can sort out the finer details
-                         * when/if we start using the flag - QAK
-                         */
-                        /* Also, it's possible that this functionality may not
-                         * get invoked if the object header is brought into
-                         * the metadata cache in some other "weird" way, like
-                         * using H5Ocopy() - QAK
-                         */
-                        oh->mesg[mesgno].flags |= H5O_MSG_FLAG_WAS_UNKNOWN;
-
-                        /* Mark the message and object header as dirty */
-                        oh->mesg[mesgno].dirty = TRUE;
-                        oh->cache_info.is_dirty = TRUE;
-                    } /* end if */
-                } /* end if */
-                else
-                    /* Set message class for "known" messages */
-                    oh->mesg[mesgno].type = H5O_msg_class_g[id];
-            } /* end else */
-
-            /* Advance decode pointer past message */
-            p += mesg_size;
+    /* Compute the size of the buffer used */
+    buf_size = oh->chunk0_size + (size_t)H5O_SIZEOF_HDR(oh);
 
-            /* Check for 'gap' at end of chunk */
-            if((eom_ptr - p) > 0 && (eom_ptr - p) < H5O_SIZEOF_MSGHDR_OH(oh)) {
-                /* Gaps can only occur in later versions of the format */
-                HDassert(oh->version > H5O_VERSION_1);
+    /* Check if the speculative read was large enough to parse the first chunk */
+    if(spec_read_size < buf_size) {
+        /* Wrap the local buffer for serialized header info */
+        if(NULL == (wb = H5WB_wrap(read_buf, sizeof(read_buf))))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't wrap buffer")
 
-                /* Gaps should only occur in chunks with no null messages */
-                HDassert(nullcnt == 0);
+        /* Get a pointer to a buffer that's large enough for serialized header */
+        if(NULL == (buf = (uint8_t *)H5WB_actual(wb, buf_size)))
+            HGOTO_ERROR(H5E_OHDR, H5E_NOSPACE, NULL, "can't get actual buffer")
 
-                /* Set gap information for chunk */
-                oh->chunk[chunkno].gap = (size_t)(eom_ptr - p);
+        /* Copy existing raw data into new buffer */
+        HDmemcpy(buf, read_buf, spec_read_size);
 
-                /* Increment location in chunk */
-                p += oh->chunk[chunkno].gap;
-            } /* end if */
-	} /* end while */
-
-        /* Check for correct checksum on chunks, in later versions of the format */
-        if(oh->version > H5O_VERSION_1) {
-            uint32_t stored_chksum;     /* Checksum from file */
-            uint32_t computed_chksum;   /* Checksum computed in memory */
-
-            /* Metadata checksum */
-            UINT32DECODE(p, stored_chksum);
-
-            /* Compute checksum on chunk */
-            computed_chksum = H5_checksum_metadata(oh->chunk[chunkno].image, (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM), 0);
-
-            /* Verify checksum */
-            if(stored_chksum != computed_chksum)
-                HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "incorrect metadata checksum for object header chunk")
-        } /* end if */
-
-        /* Sanity check */
-        HDassert(p == oh->chunk[chunkno].image + oh->chunk[chunkno].size);
-
-        /* Check for another chunk to read in & parse */
-        for(chunk_addr = HADDR_UNDEF; !H5F_addr_defined(chunk_addr) && curmesg < oh->nmesgs; ++curmesg) {
-            /* Check if next message to examine is a continuation message */
-            if(H5O_CONT_ID == oh->mesg[curmesg].type->id) {
-                H5O_cont_t *cont;
-                unsigned ioflags = 0;   /* Flags for decode routine */
-
-                /* Decode continuation message */
-                cont = (H5O_cont_t *)(H5O_MSG_CONT->decode)(f, dxpl_id, NULL, 0, &ioflags, oh->mesg[curmesg].raw);
-                cont->chunkno = oh->nchunks;	/*the next chunk to allocate */
-
-                /* Save 'native' form of continuation message */
-                oh->mesg[curmesg].native = cont;
-
-                /* Set up to read in next chunk */
-                chunk_addr = cont->addr;
-                chunk_size = cont->size;
-
-                /* Mark the object header as dirty if the message was changed by decoding */
-                if((ioflags & H5O_DECODEIO_DIRTY) && (H5F_get_intent(f) & H5F_ACC_RDWR)) {
-                    oh->mesg[curmesg].dirty = TRUE;
-                    oh->cache_info.is_dirty = TRUE;
-	            }
-            } /* end if */
-            /* Check if next message to examine is a ref. count message */
-            else if(H5O_REFCOUNT_ID == oh->mesg[curmesg].type->id) {
-                H5O_refcount_t *refcount;
-                unsigned ioflags = 0;   /* Flags for decode routine */
-
-                /* Decode ref. count message */
-                HDassert(oh->version > H5O_VERSION_1);
-                refcount = (H5O_refcount_t *)(H5O_MSG_REFCOUNT->decode)(f, dxpl_id, NULL, 0, &ioflags, oh->mesg[curmesg].raw);
-
-                /* Save 'native' form of ref. count message */
-                oh->mesg[curmesg].native = refcount;
-
-                /* Set object header values */
-                oh->has_refcount_msg = TRUE;
-                oh->nlink = *refcount;
-
-                /* Mark the object header as dirty if the message was changed by decoding */
-                if((ioflags & H5O_DECODEIO_DIRTY) && (H5F_get_intent(f) & H5F_ACC_RDWR)) {
-                    oh->mesg[curmesg].dirty = TRUE;
-                    oh->cache_info.is_dirty = TRUE;
-	            }
-            } /* end if */
-            /* Check if next message to examine is a link message */
-            else if(H5O_LINK_ID == oh->mesg[curmesg].type->id) {
-                /* Increment the count of link messages */
-                oh->link_msgs_seen++;
-            } /* end if */
-            /* Check if next message to examine is an attribute message */
-            else if(H5O_ATTR_ID == oh->mesg[curmesg].type->id) {
-                /* Increment the count of attribute messages */
-                oh->attr_msgs_seen++;
-            } /* end if */
-        } /* end for */
-    } /* end while */
-
-    /* Mark the object header dirty if we've merged a message */
-    if(merged_null_msgs)
-	oh->cache_info.is_dirty = TRUE;
+        /* Read rest of the raw data */
+        if(H5F_block_read(f, H5FD_MEM_OHDR, (addr + spec_read_size), (buf_size - spec_read_size), dxpl_id, (buf + spec_read_size)) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to read object header data")
+    } /* end if */
+    else
+        buf = read_buf;
 
-/* Don't check for the incorrect # of object header messages bug unless we've
- * enabled strict format checking.  This allows for older files, created with
- * a version of the library that had a bug in tracking the correct # of header
- * messages to be read in without the library fussing about things. -QAK
- */
-#ifdef H5_STRICT_FORMAT_CHECKS
-    /* Sanity check for the correct # of messages in object header */
-    if(oh->version == H5O_VERSION_1)
-        if((oh->nmesgs + merged_null_msgs) != nmesgs)
-            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "corrupt object header - too few messages")
-#else /* H5_STRICT_FORMAT_CHECKS */
-    /* Check for incorrect # of messages in object header and if we have write
-     * access on the file, flag the object header as dirty, so it gets fixed.
-     */
-    if(oh->version == H5O_VERSION_1)
-        if((oh->nmesgs + merged_null_msgs) != nmesgs &&
-                (H5F_get_intent(f) & H5F_ACC_RDWR))
-            oh->cache_info.is_dirty = TRUE;
-#endif /* H5_STRICT_FORMAT_CHECKS */
+    /* Parse the first chunk */
+    if(H5O_chunk_deserialize(oh, addr, oh->chunk0_size, buf, &(udata->common), &oh->cache_info.is_dirty) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't deserialize first object header chunk")
 
-#ifdef H5O_DEBUG
-H5O_assert(oh);
-#endif /* H5O_DEBUG */
+    /* Note that we've loaded the object header from the file */
+    udata->made_attempt = TRUE;
 
     /* Set return value */
     ret_value = oh;
 
 done:
+    /* Release resources */
+    if(wb && H5WB_unwrap(wb) < 0)
+        HDONE_ERROR(H5E_OHDR, H5E_CLOSEERROR, NULL, "can't close wrapped buffer")
+
     /* Release the [possibly partially initialized] object header on errors */
     if(!ret_value && oh)
         if(H5O_free(oh) < 0)
@@ -663,7 +386,6 @@ H5O_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t UNUSED addr, H5O_t *
     /* flush */
     if(oh->cache_info.is_dirty) {
         uint8_t	*p;             /* Pointer to object header prefix buffer */
-        unsigned u;             /* Local index variable */
 
 #ifdef H5O_DEBUG
 H5O_assert(oh);
@@ -677,7 +399,10 @@ H5O_assert(oh);
          * on the entire block of memory needs to be updated if anything is
          * modified */
         if(oh->version > H5O_VERSION_1) {
-            uint64_t chunk0_size = oh->chunk[0].size - H5O_SIZEOF_HDR(oh);  /* Size of chunk 0's data */
+            uint64_t chunk0_size;       /* Size of chunk 0's data */
+
+            HDassert(oh->chunk[0].size >= (size_t)H5O_SIZEOF_HDR(oh));
+            chunk0_size = oh->chunk[0].size - (size_t)H5O_SIZEOF_HDR(oh);
 
             /* Verify magic number */
             HDassert(!HDmemcmp(p, H5O_HDR_MAGIC, H5_SIZEOF_MAGIC));
@@ -748,7 +473,7 @@ H5O_assert(oh);
             UINT32ENCODE(p, oh->nlink);
 
             /* First chunk size */
-            UINT32ENCODE(p, (oh->chunk[0].size - H5O_SIZEOF_HDR(oh)));
+            UINT32ENCODE(p, (oh->chunk[0].size - (size_t)H5O_SIZEOF_HDR(oh)));
 
             /* Zero to alignment */
             HDmemset(p, 0, (size_t)(H5O_SIZEOF_HDR(oh) - 12));
@@ -756,57 +481,14 @@ H5O_assert(oh);
         } /* end else */
         HDassert((size_t)(p - oh->chunk[0].image) == (size_t)(H5O_SIZEOF_HDR(oh) - H5O_SIZEOF_CHKSUM_OH(oh)));
 
-        /* Mark chunk 0 as dirty, since the object header prefix has been updated */
-        /* (this could be more sophisticated and track whether any prefix fields
-         *      have been changed, which could save I/O accesses if the
-         *      messages in chunk 0 haven't changed - QAK)
-         */
-        HDassert(H5F_addr_eq(addr, oh->chunk[0].addr));
-        oh->chunk[0].dirty = TRUE;
-
-	/* Encode any dirty messages */
-        if(H5O_flush_msgs(f, oh) < 0)
-            HGOTO_ERROR(H5E_OHDR, H5E_CANTFLUSH, FAIL, "unable to flush object header messages")
-
-	/* Write each chunk to disk, if it's dirty */
-	for(u = 0; u < oh->nchunks; u++) {
-            /* Sanity checks */
-            if(oh->version > H5O_VERSION_1)
-                /* Make certain the magic # is present */
-                HDassert(!HDmemcmp(oh->chunk[u].image, (u == 0 ? H5O_HDR_MAGIC : H5O_CHK_MAGIC), H5_SIZEOF_MAGIC));
-            else
-                /* Gaps should never occur in version 1 of the format */
-                HDassert(oh->chunk[u].gap == 0);
-
-            /* Write out chunk, if it's dirty */
-	    if(oh->chunk[u].dirty) {
-                /* Extra work, for later versions of the format */
-                if(oh->version > H5O_VERSION_1) {
-                    uint32_t metadata_chksum;   /* Computed metadata checksum value */
-
-                    /* Check for gap in chunk & zero it out */
-                    if(oh->chunk[u].gap)
-                        HDmemset((oh->chunk[u].image + oh->chunk[u].size) -
-                            (H5O_SIZEOF_CHKSUM + oh->chunk[u].gap), 0, oh->chunk[u].gap);
-
-                    /* Compute metadata checksum */
-                    metadata_chksum = H5_checksum_metadata(oh->chunk[u].image, (oh->chunk[u].size - H5O_SIZEOF_CHKSUM), 0);
-
-                    /* Metadata checksum */
-                    p = oh->chunk[u].image + (oh->chunk[u].size - H5O_SIZEOF_CHKSUM);
-                    UINT32ENCODE(p, metadata_chksum);
-                } /* end if */
-
-                /* Write the chunk out */
-                HDassert(H5F_addr_defined(oh->chunk[u].addr));
-                if(H5F_block_write(f, H5FD_MEM_OHDR, oh->chunk[u].addr,
-                            oh->chunk[u].size, dxpl_id, oh->chunk[u].image) < 0)
-                    HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to write object header chunk to disk")
+        /* Serialize messages for this chunk */
+        if(H5O_chunk_serialize(f, oh, (unsigned)0) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTSERIALIZE, FAIL, "unable to serialize first object header chunk")
 
-                /* Mark chunk as clean now */
-                oh->chunk[u].dirty = FALSE;
-	    } /* end if */
-	} /* end for */
+        /* Write the chunk out */
+        HDassert(H5F_addr_defined(oh->chunk[0].addr));
+        if(H5F_block_write(f, H5FD_MEM_OHDR, oh->chunk[0].addr, oh->chunk[0].size, dxpl_id, oh->chunk[0].image) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to write object header chunk to disk")
 
         /* Mark object header as clean now */
 	oh->cache_info.is_dirty = FALSE;
@@ -844,6 +526,7 @@ H5O_dest(H5F_t *f, H5O_t *oh)
 
     /* check args */
     HDassert(oh);
+    HDassert(oh->rc == 0);
 
     /* Verify that node is clean */
     HDassert(!oh->cache_info.is_dirty);
@@ -892,17 +575,13 @@ H5O_clear(H5F_t *f, H5O_t *oh, hbool_t destroy)
     /* check args */
     HDassert(oh);
 
-    /* Mark chunks as clean */
-    for(u = 0; u < oh->nchunks; u++)
-        oh->chunk[u].dirty = FALSE;
-
     /* Mark messages as clean */
     for(u = 0; u < oh->nmesgs; u++)
         oh->mesg[u].dirty = FALSE;
 
 #ifndef NDEBUG
-        /* Reset the number of messages dirtied by decoding */
-        oh->ndecode_dirtied = 0;
+    /* Reset the number of messages dirtied by decoding */
+    oh->ndecode_dirtied = 0;
 #endif /* NDEBUG */
 
     /* Mark whole header as clean */
@@ -934,22 +613,767 @@ done:
 static herr_t
 H5O_size(const H5F_t UNUSED *f, const H5O_t *oh, size_t *size_ptr)
 {
-    size_t	size;           /* Running sum of the object header's size */
-    unsigned	u;              /* Local index variable */
-
     FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_size)
 
     /* check args */
     HDassert(oh);
     HDassert(size_ptr);
 
-    /* Add sizes of all the chunks */
-    /* (includes size of prefix, in chunk 0) */
-    for(u = 0, size = 0; u < oh->nchunks; u++)
-        size += oh->chunk[u].size;
-
-    *size_ptr = size;
+    /* Report the object header's prefix+first chunk length */
+    *size_ptr = (size_t)H5O_SIZEOF_HDR(oh) + oh->chunk0_size;
 
     FUNC_LEAVE_NOAPI(SUCCEED)
 } /* H5O_size() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_cache_chk_load
+ *
+ * Purpose:	Loads an object header continuation chunk from disk.
+ *
+ * Return:	Success:	Pointer to the new object header chunk proxy.
+ *		Failure:	NULL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Jul 12 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static H5O_chunk_proxy_t *
+H5O_cache_chk_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
+    void *_udata2)
+{
+    H5O_chunk_proxy_t	*chk_proxy = NULL;     /* Chunk proxy object */
+    H5O_chk_cache_ud_t *udata = (H5O_chk_cache_ud_t *)_udata2;       /* User data for callback */
+    H5WB_t      *wb = NULL;             /* Wrapped buffer for prefix data */
+    uint8_t     chunk_buf[H5O_SPEC_READ_SIZE];       /* Buffer for speculative read */
+    uint8_t     *buf;                   /* Buffer to decode */
+    H5O_chunk_proxy_t	*ret_value;     /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_cache_chk_load)
+
+    /* Check arguments */
+    HDassert(f);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(udata);
+    HDassert(udata->oh);
+
+    /* Allocate space for the object header data structure */
+    if(NULL == (chk_proxy = H5FL_CALLOC(H5O_chunk_proxy_t)))
+	HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, NULL, "memory allocation failed")
+
+    /* Wrap the local buffer for serialized header info */
+    if(NULL == (wb = H5WB_wrap(chunk_buf, sizeof(chunk_buf))))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't wrap buffer")
+
+    /* Get a pointer to a buffer that's large enough for serialized header */
+    if(NULL == (buf = (uint8_t *)H5WB_actual(wb, udata->chunk_size)))
+        HGOTO_ERROR(H5E_OHDR, H5E_NOSPACE, NULL, "can't get actual buffer")
+
+    /* Read rest of the raw data */
+    if(H5F_block_read(f, H5FD_MEM_OHDR, addr, udata->chunk_size, dxpl_id, buf) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to read object header continuation chunk")
+
+    /* Check if we are still decoding the object header */
+    /* (as opposed to bringing a piece of it back from the file) */
+    if(udata->decoding) {
+        /* Sanity check */
+        HDassert(udata->common.f);
+        HDassert(udata->common.cont_msg_info);
+
+        /* Parse the chunk */
+        if(H5O_chunk_deserialize(udata->oh, addr, udata->chunk_size, buf, &(udata->common), &chk_proxy->cache_info.is_dirty) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't deserialize object header chunk")
+
+        /* Set the fields for the chunk proxy */
+        chk_proxy->oh = udata->oh;
+        chk_proxy->chunkno = udata->oh->nchunks - 1;
+    } /* end if */
+    else {
+        /* Sanity check */
+        HDassert(udata->chunkno < udata->oh->nchunks);
+
+        /* Set the fields for the chunk proxy */
+        chk_proxy->oh = udata->oh;
+        chk_proxy->chunkno = udata->chunkno;
+
+        /* Sanity check that the chunk representation we have in memory is the same
+         *      as the one being brought in from disk.
+         */
+        HDassert(0 == HDmemcmp(buf, chk_proxy->oh->chunk[chk_proxy->chunkno].image, chk_proxy->oh->chunk[chk_proxy->chunkno].size));
+    } /* end else */
+
+    /* Increment reference count of object header */
+    if(H5O_inc_rc(udata->oh) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTINC, NULL, "can't increment reference count on object header")
+
+    /* Set return value */
+    ret_value = chk_proxy;
+
+done:
+    /* Release resources */
+    if(wb && H5WB_unwrap(wb) < 0)
+        HDONE_ERROR(H5E_OHDR, H5E_CLOSEERROR, NULL, "can't close wrapped buffer")
+
+    /* Release the [possibly partially initialized] object header on errors */
+    if(!ret_value && chk_proxy)
+        if(H5O_chunk_proxy_dest(chk_proxy) < 0)
+	    HDONE_ERROR(H5E_OHDR, H5E_CANTRELEASE, NULL, "unable to destroy object header chunk proxy")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_cache_chk_load() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_cache_chk_flush
+ *
+ * Purpose:	Flushes (and destroys) an object header continuation chunk.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Jul 12 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_cache_chk_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr,
+    H5O_chunk_proxy_t *chk_proxy, unsigned UNUSED * flags_ptr)
+{
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_cache_chk_flush)
+
+    /* flush */
+    if(chk_proxy->cache_info.is_dirty) {
+        /* Serialize messages for this chunk */
+        if(H5O_chunk_serialize(f, chk_proxy->oh, chk_proxy->chunkno) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTSERIALIZE, FAIL, "unable to serialize object header continuation chunk")
+
+        /* Write the chunk out */
+        HDassert(H5F_addr_defined(chk_proxy->oh->chunk[chk_proxy->chunkno].addr));
+        HDassert(H5F_addr_eq(addr, chk_proxy->oh->chunk[chk_proxy->chunkno].addr));
+        if(H5F_block_write(f, H5FD_MEM_OHDR, addr, chk_proxy->oh->chunk[chk_proxy->chunkno].size, dxpl_id, chk_proxy->oh->chunk[chk_proxy->chunkno].image) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to write object header continuation chunk to disk")
+
+        /* Mark object header as clean now */
+	chk_proxy->cache_info.is_dirty = FALSE;
+    } /* end if */
+
+    /* Destroy the object header, if requested */
+    if(destroy)
+        if(H5O_cache_chk_dest(f, chk_proxy) < 0)
+	    HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to destroy object header continuation chunk data")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_cache_chk_flush() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_cache_chk_dest
+ *
+ * Purpose:	Destroys an object header continuation chunk.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              July 12, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_cache_chk_dest(H5F_t *f, H5O_chunk_proxy_t *chk_proxy)
+{
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_cache_chk_dest)
+
+    /* Check arguments */
+    HDassert(chk_proxy);
+    HDassert(chk_proxy->chunkno > 0);
+
+    /* Verify that node is clean */
+    HDassert(chk_proxy->cache_info.is_dirty == FALSE);
+
+    /* If we're going to free the space on disk, the address must be valid */
+    HDassert(!chk_proxy->cache_info.free_file_space_on_destroy || H5F_addr_defined(chk_proxy->cache_info.addr));
+
+    /* Check for releasing file space for object header */
+    if(chk_proxy->cache_info.free_file_space_on_destroy) {
+        /* Release the space on disk */
+        /* (XXX: Nasty usage of internal DXPL value! -QAK) */
+        if(H5MF_xfree(f, H5FD_MEM_OHDR, H5AC_dxpl_id, chk_proxy->oh->chunk[chk_proxy->chunkno].addr, (hsize_t)chk_proxy->oh->chunk[chk_proxy->chunkno].size) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to free object header continuation chunk")
+    } /* end if */
+
+    /* Destroy object header chunk proxy */
+    if(H5O_chunk_proxy_dest(chk_proxy) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTRELEASE, FAIL, "unable to destroy object header chunk proxy")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_cache_chk_dest() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_cache_chk_clear
+ *
+ * Purpose:	Mark a object header continuation chunk in memory as non-dirty.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              July 12, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_cache_chk_clear(H5F_t *f, H5O_chunk_proxy_t *chk_proxy, hbool_t destroy)
+{
+    unsigned	u;      /* Local index variable */
+    herr_t ret_value = SUCCEED;
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_cache_chk_clear)
+
+    /* check args */
+    HDassert(chk_proxy);
+
+    /* Mark messages in chunk as clean */
+    for(u = 0; u < chk_proxy->oh->nmesgs; u++)
+        if(chk_proxy->oh->mesg[u].chunkno == chk_proxy->chunkno)
+            chk_proxy->oh->mesg[u].dirty = FALSE;
+
+    /* Mark as clean */
+    chk_proxy->cache_info.is_dirty = FALSE;
+
+    if(destroy)
+        if(H5O_cache_chk_dest(f, chk_proxy) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to destroy object header continuation chunk data")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_cache_chk_clear() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_cache_chk_size
+ *
+ * Purpose:	Compute the size in bytes of the specified instance of
+ *              an object header continuation chunk on disk, and return it in
+ *              *len_ptr.  On failure, the value of *len_ptr is undefined.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              July 12, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_cache_chk_size(const H5F_t UNUSED *f, const H5O_chunk_proxy_t *chk_proxy, size_t *size_ptr)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_cache_chk_size)
+
+    /* check args */
+    HDassert(chk_proxy);
+    HDassert(size_ptr);
+
+    /* Report the object header continuation chunk's length */
+    *size_ptr = chk_proxy->oh->chunk[chk_proxy->chunkno].size;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* H5O_cache_chk_size() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_add_cont_msg
+ *
+ * Purpose:	Add information from a continuation message to the list of
+ *              continuation messages in the object header
+ *
+ * Return:	Success: SUCCEED
+ *              Failure: FAIL
+ *
+ * Programmer:	Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              July 12, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_add_cont_msg(H5O_cont_msgs_t *cont_msg_info, const H5O_cont_t *cont)
+{
+    unsigned contno;            /* Continuation message index */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_add_cont_msg)
+
+    /* Check arguments */
+    HDassert(cont_msg_info);
+    HDassert(cont);
+
+    /* Increase chunk array size, if necessary */
+    if(cont_msg_info->nmsgs >= cont_msg_info->alloc_nmsgs) {
+        unsigned na = MAX(H5O_NCHUNKS, cont_msg_info->alloc_nmsgs * 2);        /* Double # of messages allocated */
+        H5O_cont_t *x = H5FL_SEQ_REALLOC(H5O_cont_t, cont_msg_info->msgs, (size_t)na);
+
+        if(!x)
+            HGOTO_ERROR(H5E_OHDR, H5E_NOSPACE, FAIL, "memory allocation failed")
+        cont_msg_info->alloc_nmsgs = na;
+        cont_msg_info->msgs = x;
+    } /* end if */
+
+    /* Init the continuation message info */
+    contno = cont_msg_info->nmsgs++;
+    cont_msg_info->msgs[contno].addr = cont->addr;
+    cont_msg_info->msgs[contno].size = cont->size;
+    cont_msg_info->msgs[contno].chunkno = cont->chunkno;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_add_cont_msg() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_chunk_deserialize
+ *
+ * Purpose:	Deserialize a chunk for an object header
+ *
+ * Return:	Success: SUCCEED
+ *              Failure: FAIL
+ *
+ * Programmer:	Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              July 12, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_chunk_deserialize(H5O_t *oh, haddr_t addr, size_t len, const uint8_t *image,
+    H5O_common_cache_ud_t *udata, hbool_t *dirty)
+{
+    const uint8_t *p;           /* Pointer into buffer to decode */
+    uint8_t *eom_ptr;           /* Pointer to end of messages for a chunk */
+    unsigned curmesg;           /* Current message being decoded in object header */
+    unsigned merged_null_msgs = 0;  /* Number of null messages merged together */
+    unsigned chunkno;           /* Current chunk's index */
+#ifndef NDEBUG
+    unsigned nullcnt;           /* Count of null messages (for sanity checking gaps in chunks) */
+#endif /* NDEBUG */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_chunk_deserialize)
+
+    /* Check arguments */
+    HDassert(oh);
+    HDassert(image);
+    HDassert(udata->f);
+    HDassert(udata->cont_msg_info);
+
+    /* Increase chunk array size, if necessary */
+    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_OHDR, H5E_CANTALLOC, FAIL, "memory allocation failed")
+        oh->alloc_nchunks = na;
+        oh->chunk = x;
+    } /* end if */
+
+    /* Init the chunk data info */
+    chunkno = oh->nchunks++;
+    oh->chunk[chunkno].gap = 0;
+    if(chunkno == 0) {
+        /* First chunk's 'image' includes room for the object header prefix */
+        oh->chunk[0].addr = addr;
+        oh->chunk[0].size = len + (size_t)H5O_SIZEOF_HDR(oh);
+    } /* end if */
+    else {
+        oh->chunk[chunkno].addr = addr;
+        oh->chunk[chunkno].size = len;
+    } /* end else */
+    if(NULL == (oh->chunk[chunkno].image = H5FL_BLK_MALLOC(chunk_image, oh->chunk[chunkno].size)))
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, FAIL, "memory allocation failed")
+
+    /* Copy disk image into chunk's image */
+    HDmemcpy(oh->chunk[chunkno].image, image, oh->chunk[chunkno].size);
+
+    /* Point into chunk image to decode */
+    p = oh->chunk[chunkno].image;
+
+    /* Handle chunk 0 as special case */
+    if(chunkno == 0)
+        /* Skip over [already decoded] prefix */
+        p += (size_t)(H5O_SIZEOF_HDR(oh) - H5O_SIZEOF_CHKSUM_OH(oh));
+    /* Check for magic # on chunks > 0 in later versions of the format */
+    else if(chunkno > 0 && oh->version > H5O_VERSION_1) {
+        /* Magic number */
+        if(HDmemcmp(p, H5O_CHK_MAGIC, (size_t)H5_SIZEOF_MAGIC))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "wrong object header chunk signature")
+        p += H5_SIZEOF_MAGIC;
+    } /* end if */
+
+    /* Save # of messages already inspected */
+    curmesg = oh->nmesgs;
+
+    /* Decode messages from this chunk */
+    eom_ptr = oh->chunk[chunkno].image + (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM_OH(oh));
+#ifndef NDEBUG
+    nullcnt = 0;
+#endif /* NDEBUG */
+    while(p < eom_ptr) {
+        unsigned mesgno;        /* Current message to operate on */
+        size_t mesg_size;       /* Size of message read in */
+        unsigned id;            /* ID (type) of current message */
+        uint8_t	flags;          /* Flags for current message */
+        H5O_msg_crt_idx_t crt_idx = 0;  /* Creation index for current message */
+
+        /* Decode message prefix info */
+
+        /* Version # */
+        if(oh->version == H5O_VERSION_1)
+            UINT16DECODE(p, id)
+        else
+            id = *p++;
+
+        /* Check for unknown message ID getting encoded in file */
+        if(id == H5O_UNKNOWN_ID)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "'unknown' message ID encoded in file?!?")
+
+        /* Message size */
+        UINT16DECODE(p, mesg_size);
+        HDassert(mesg_size == H5O_ALIGN_OH(oh, mesg_size));
+
+        /* Message flags */
+        flags = *p++;
+        if(flags & ~H5O_MSG_FLAG_BITS)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unknown flag for message")
+        if((flags & H5O_MSG_FLAG_SHARED) && (flags & H5O_MSG_FLAG_DONTSHARE))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")
+        if((flags & H5O_MSG_FLAG_WAS_UNKNOWN) && (flags & H5O_MSG_FLAG_FAIL_IF_UNKNOWN))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")
+        if((flags & H5O_MSG_FLAG_WAS_UNKNOWN) && !(flags & H5O_MSG_FLAG_MARK_IF_UNKNOWN))
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")
+
+        /* Reserved bytes/creation index */
+        if(oh->version == H5O_VERSION_1)
+            p += 3; /*reserved*/
+        else {
+            /* Only decode creation index if they are being tracked */
+            if(oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED)
+                UINT16DECODE(p, crt_idx);
+        } /* end else */
+
+        /* Try to detect invalidly formatted object header message that
+         *  extends past end of chunk.
+         */
+        if(p + mesg_size > eom_ptr)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "corrupt object header")
+
+#ifndef NDEBUG
+        /* Increment count of null messages */
+        if(H5O_NULL_ID == id)
+            nullcnt++;
+#endif /* NDEBUG */
+
+        /* Check for combining two adjacent 'null' messages */
+        if((udata->file_intent & H5F_ACC_RDWR) &&
+                H5O_NULL_ID == id && oh->nmesgs > 0 &&
+                H5O_NULL_ID == oh->mesg[oh->nmesgs - 1].type->id &&
+                oh->mesg[oh->nmesgs - 1].chunkno == chunkno) {
+
+            /* Combine adjacent null messages */
+            mesgno = oh->nmesgs - 1;
+            oh->mesg[mesgno].raw_size += H5O_SIZEOF_MSGHDR_OH(oh) + mesg_size;
+            oh->mesg[mesgno].dirty = TRUE;
+            merged_null_msgs++;
+            udata->merged_null_msgs++;
+        } /* end if */
+        else {
+            /* Check if we need to extend message table to hold the new message */
+            if(oh->nmesgs >= oh->alloc_nmesgs)
+                if(H5O_alloc_msgs(oh, (size_t)1) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, FAIL, "can't allocate more space for messages")
+
+            /* Get index for message */
+            mesgno = oh->nmesgs++;
+
+            /* Initialize information about message */
+            oh->mesg[mesgno].dirty = FALSE;
+            oh->mesg[mesgno].flags = flags;
+            oh->mesg[mesgno].crt_idx = crt_idx;
+            oh->mesg[mesgno].native = NULL;
+            oh->mesg[mesgno].raw = (uint8_t *)p;        /* Casting away const OK - QAK */
+            oh->mesg[mesgno].raw_size = mesg_size;
+            oh->mesg[mesgno].chunkno = chunkno;
+
+            /* Point unknown messages at 'unknown' message class */
+            /* (Usually from future versions of the library) */
+            if(id >= NELMTS(H5O_msg_class_g) || NULL == H5O_msg_class_g[id]) {
+                H5O_unknown_t *unknown;     /* Pointer to "unknown" message info */
+
+                /* Allocate "unknown" message info */
+                if(NULL == (unknown = H5FL_MALLOC(H5O_unknown_t)))
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, FAIL, "memory allocation failed")
+
+                /* Save the original message type ID */
+                *unknown = id;
+
+                /* Save 'native' form of unknown message */
+                oh->mesg[mesgno].native = unknown;
+
+                /* Set message to "unknown" class */
+                oh->mesg[mesgno].type = H5O_msg_class_g[H5O_UNKNOWN_ID];
+
+                /* Check for "fail if unknown" message flag */
+                if(flags & H5O_MSG_FLAG_FAIL_IF_UNKNOWN)
+                    HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, FAIL, "unknown message with 'fail if unknown' flag found")
+                /* Check for "mark if unknown" message flag, etc. */
+                else if((flags & H5O_MSG_FLAG_MARK_IF_UNKNOWN) &&
+                        !(flags & H5O_MSG_FLAG_WAS_UNKNOWN) &&
+                        (udata->file_intent & H5F_ACC_RDWR)) {
+
+                    /* Mark the message as "unknown" */
+                    /* This is a bit aggressive, since the application may
+                     * never change anything about the object (metadata or
+                     * raw data), but we can sort out the finer details
+                     * when/if we start using the flag - QAK
+                     */
+                    /* Also, it's possible that this functionality may not
+                     * get invoked if the object header is brought into
+                     * the metadata cache in some other "weird" way, like
+                     * using H5Ocopy() - QAK
+                     */
+                    oh->mesg[mesgno].flags |= H5O_MSG_FLAG_WAS_UNKNOWN;
+
+                    /* Mark the message and chunk as dirty */
+                    oh->mesg[mesgno].dirty = TRUE;
+                    udata->mesgs_modified = TRUE;
+                    *dirty = TRUE;
+                } /* end if */
+            } /* end if */
+            else
+                /* Set message class for "known" messages */
+                oh->mesg[mesgno].type = H5O_msg_class_g[id];
+        } /* end else */
+
+        /* Advance decode pointer past message */
+        p += mesg_size;
+
+        /* Check for 'gap' at end of chunk */
+        if((eom_ptr - p) > 0 && (eom_ptr - p) < H5O_SIZEOF_MSGHDR_OH(oh)) {
+            /* Gaps can only occur in later versions of the format */
+            HDassert(oh->version > H5O_VERSION_1);
+
+            /* Gaps should only occur in chunks with no null messages */
+            HDassert(nullcnt == 0);
+
+            /* Set gap information for chunk */
+            oh->chunk[chunkno].gap = (size_t)(eom_ptr - p);
+
+            /* Increment location in chunk */
+            p += oh->chunk[chunkno].gap;
+        } /* end if */
+    } /* end while */
+
+    /* Check for correct checksum on chunks, in later versions of the format */
+    if(oh->version > H5O_VERSION_1) {
+        uint32_t stored_chksum;     /* Checksum from file */
+        uint32_t computed_chksum;   /* Checksum computed in memory */
+
+        /* Metadata checksum */
+        UINT32DECODE(p, stored_chksum);
+
+        /* Compute checksum on chunk */
+        computed_chksum = H5_checksum_metadata(oh->chunk[chunkno].image, (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM), 0);
+
+        /* Verify checksum */
+        if(stored_chksum != computed_chksum)
+            HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, FAIL, "incorrect metadata checksum for object header chunk")
+    } /* end if */
+
+    /* Sanity check */
+    HDassert(p == oh->chunk[chunkno].image + oh->chunk[chunkno].size);
+
+    /* Do some inspection/interpretation of new messages from this chunk */
+    /* (detect continuation messages, ref. count messages, etc.) */
+    while(curmesg < oh->nmesgs) {
+        /* Check if next message to examine is a continuation message */
+        if(H5O_CONT_ID == oh->mesg[curmesg].type->id) {
+            H5O_cont_t *cont;
+            unsigned ioflags = 0;   /* Flags for decode routine */
+
+            /* Decode continuation message */
+            cont = (H5O_cont_t *)(H5O_MSG_CONT->decode)(udata->f, udata->dxpl_id, NULL, 0, &ioflags, oh->mesg[curmesg].raw);
+            cont->chunkno = udata->cont_msg_info->nmsgs + 1;	/*the next continuation message/chunk */
+
+            /* Save 'native' form of continuation message */
+            oh->mesg[curmesg].native = cont;
+
+            /* Add to continuation messages left to interpret */
+            if(H5O_add_cont_msg(udata->cont_msg_info, cont) < 0)
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTSET, FAIL, "can't add continuation message")
+
+            /* Mark the message & chunk as dirty if the message was changed by decoding */
+            if((ioflags & H5O_DECODEIO_DIRTY) && (udata->file_intent & H5F_ACC_RDWR)) {
+                oh->mesg[curmesg].dirty = TRUE;
+                udata->mesgs_modified = TRUE;
+                *dirty = TRUE;
+            } /* end if */
+        } /* end if */
+        /* Check if next message to examine is a ref. count message */
+        else if(H5O_REFCOUNT_ID == oh->mesg[curmesg].type->id) {
+            H5O_refcount_t *refcount;
+            unsigned ioflags = 0;   /* Flags for decode routine */
+
+            /* Decode ref. count message */
+            HDassert(oh->version > H5O_VERSION_1);
+            refcount = (H5O_refcount_t *)(H5O_MSG_REFCOUNT->decode)(udata->f, udata->dxpl_id, NULL, 0, &ioflags, oh->mesg[curmesg].raw);
+
+            /* Save 'native' form of ref. count message */
+            oh->mesg[curmesg].native = refcount;
+
+            /* Set object header values */
+            oh->has_refcount_msg = TRUE;
+            oh->nlink = *refcount;
+
+            /* Mark the message & chunk as dirty if the message was changed by decoding */
+            if((ioflags & H5O_DECODEIO_DIRTY) && (udata->file_intent & H5F_ACC_RDWR)) {
+                oh->mesg[curmesg].dirty = TRUE;
+                udata->mesgs_modified = TRUE;
+                *dirty = TRUE;
+            } /* end if */
+        } /* end if */
+        /* Check if next message to examine is a link message */
+        else if(H5O_LINK_ID == oh->mesg[curmesg].type->id) {
+            /* Increment the count of link messages */
+            oh->link_msgs_seen++;
+        } /* end if */
+        /* Check if next message to examine is an attribute message */
+        else if(H5O_ATTR_ID == oh->mesg[curmesg].type->id) {
+            /* Increment the count of attribute messages */
+            oh->attr_msgs_seen++;
+        } /* end if */
+
+        /* Advance to next message */
+        curmesg++;
+    } /* end while */
+
+    /* Mark the chunk dirty if we've merged null messages */
+    if(merged_null_msgs) {
+        udata->mesgs_modified = TRUE;
+	*dirty = TRUE;
+    } /* end if */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_chunk_deserialize() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_chunk_serialize
+ *
+ * Purpose:	Serialize a chunk for an object header
+ *
+ * Return:	Success: SUCCEED
+ *              Failure: FAIL
+ *
+ * Programmer:	Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              July 12, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_chunk_serialize(const H5F_t *f, H5O_t *oh, unsigned chunkno)
+{
+    H5O_mesg_t *curr_msg;       /* Pointer to current message being operated on */
+    unsigned	u;              /* Local index variable */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_chunk_serialize)
+
+    /* Check arguments */
+    HDassert(f);
+    HDassert(oh);
+
+    /* Encode any dirty messages in this chunk */
+    for(u = 0, curr_msg = &oh->mesg[0]; u < oh->nmesgs; u++, curr_msg++)
+        if(curr_msg->dirty && curr_msg->chunkno == chunkno)
+            /* Casting away const OK -QAK */
+            if(H5O_msg_flush((H5F_t *)f, oh, curr_msg) < 0)
+                HGOTO_ERROR(H5E_OHDR, H5E_CANTENCODE, FAIL, "unable to encode object header message")
+
+    /* Sanity checks */
+    if(oh->version > H5O_VERSION_1)
+        /* Make certain the magic # is present */
+        HDassert(!HDmemcmp(oh->chunk[chunkno].image, (chunkno == 0 ? H5O_HDR_MAGIC : H5O_CHK_MAGIC), H5_SIZEOF_MAGIC));
+    else
+        /* Gaps should never occur in version 1 of the format */
+        HDassert(oh->chunk[chunkno].gap == 0);
+
+    /* Extra work, for later versions of the format */
+    if(oh->version > H5O_VERSION_1) {
+        uint32_t metadata_chksum;   /* Computed metadata checksum value */
+        uint8_t	*p;                 /* Pointer into object header chunk */
+
+        /* Check for gap in chunk & zero it out */
+        if(oh->chunk[chunkno].gap)
+            HDmemset((oh->chunk[chunkno].image + oh->chunk[chunkno].size) -
+                (H5O_SIZEOF_CHKSUM + oh->chunk[chunkno].gap), 0, oh->chunk[chunkno].gap);
+
+        /* Compute metadata checksum */
+        metadata_chksum = H5_checksum_metadata(oh->chunk[chunkno].image, (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM), 0);
+
+        /* Metadata checksum */
+        p = oh->chunk[chunkno].image + (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM);
+        UINT32ENCODE(p, metadata_chksum);
+    } /* end if */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_chunk_serialize() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_chunk_proxy_dest
+ *
+ * Purpose:	Destroy a chunk proxy object
+ *
+ * Return:	Success: SUCCEED
+ *              Failure: FAIL
+ *
+ * Programmer:	Quincey Koziol
+ *              koziol@hdfgroup.org
+ *              July 13, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_chunk_proxy_dest(H5O_chunk_proxy_t *chk_proxy)
+{
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_chunk_proxy_dest)
+
+    /* Check arguments */
+    HDassert(chk_proxy);
+
+    /* Decrement reference count of object header */
+    if(H5O_dec_rc(chk_proxy->oh) < 0)
+        HGOTO_ERROR(H5E_OHDR, H5E_CANTDEC, FAIL, "can't decrement reference count on object header")
+
+    /* Release the chunk proxy object */
+    chk_proxy = H5FL_FREE(H5O_chunk_proxy_t, chk_proxy);
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_chunk_proxy_dest() */
+