path: root/src/H5O.c

/*-------------------------------------------------------------------------
 * Copyright (C) 1997	National Center for Supercomputing Applications.
 *			All rights reserved.
 *
 *-------------------------------------------------------------------------
 *
 * Created:		H5O.c
 *			Aug  5 1997
 *			Robb Matzke <matzke@llnl.gov>
 *
 * Purpose:		Object header virtual functions.
 *
 * Modifications:	
 *
 *-------------------------------------------------------------------------
 */
#include <H5private.h>
#include <H5ACprivate.h>
#include <H5Eprivate.h>
#include <H5Fprivate.h>
#include <H5MFprivate.h>
#include <H5MMprivate.h>
#include <H5Oprivate.h>

#define PABLO_MASK	H5O_mask

/* PRIVATE PROTOTYPES */
static herr_t H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr,
			H5O_t *oh);
static H5O_t *H5O_load(H5F_t *f, const haddr_t *addr, const void *_udata1,
		       void *_udata2);
static intn H5O_find_in_ohdr(H5F_t *f, const haddr_t *addr,
			     const H5O_class_t **type_p, intn sequence);
static intn H5O_alloc(H5F_t *f, H5O_t *oh, const H5O_class_t *type,
		      size_t size);
static intn H5O_alloc_extend_chunk(H5O_t *oh, intn chunkno, size_t size);
static intn H5O_alloc_new_chunk(H5F_t *f, H5O_t *oh, size_t size);

/* H5O inherits cache-like properties from H5AC */
static const H5AC_class_t H5AC_OHDR[1] = {{
    H5AC_OHDR_ID,
    (void *(*)(H5F_t *, const haddr_t *, const void *, void *)) H5O_load,
    (herr_t (*)(H5F_t *, hbool_t, const haddr_t *, void *)) H5O_flush,
}};

/* Interface initialization */
static intn interface_initialize_g = FALSE;
#define INTERFACE_INIT	H5O_init_interface
static herr_t H5O_init_interface(void);

/* ID to type mapping */
static const H5O_class_t *const message_type_g[] = {
    H5O_NULL,		/*0x0000 Null					*/
    H5O_SDSPACE,	/*0x0001 Simple Dimensionality			*/
    NULL,		/*0x0002 Data space (fiber bundle?)		*/
    H5O_DTYPE,		/*0x0003 Data Type				*/
    NULL,		/*0x0004 Not assigned				*/
    NULL,		/*0x0005 Not assigned				*/
    NULL,		/*0x0006 Data storage -- compact object		*/
    H5O_EFL,		/*0x0007 Data storage -- external data files	*/
    H5O_LAYOUT,		/*0x0008 Data Layout				*/
    NULL,		/*0x0009 Not assigned				*/
    NULL,		/*0x000A Not assigned				*/
    NULL,		/*0x000B Data storage -- compressed object	*/
    NULL,		/*0x000C Attribute list				*/
    H5O_NAME,		/*0x000D Object name				*/
    NULL,		/*0x000E Object modification date and time	*/
    NULL,		/*0x000F Shared header message			*/
    H5O_CONT,		/*0x0010 Object header continuation		*/
    H5O_STAB,		/*0x0011 Symbol table				*/
};

/*
 * An array of functions indexed by symbol table entry cache type
 * (H5G_type_t) that are called to retrieve constant messages cached in the
 * symbol table entry.
 */
static void *(*H5O_fast_g[H5G_NCACHED]) (const H5G_cache_t *,
					 const H5O_class_t *,
					 void *);

/*-------------------------------------------------------------------------
 * Function:	H5O_init_interface
 *
 * Purpose:	Initialize the H5O interface.
 *
 * Return:	Success:	SUCCEED
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		Tuesday, January  6, 1998
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_init_interface(void)
{
    FUNC_ENTER(H5O_init_interface, FAIL);

    /*
     * Initialize functions that decode messages from symbol table entries.
     */
    H5O_fast_g[H5G_CACHED_STAB] = H5O_stab_fast;

    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_create
 *
 * Purpose:	Creates a new object header, sets the link count
 *		to 0, and caches the header.  The object header is opened for
 *		write access and should eventually be closed by calling
 *		H5O_close().
 *
 * Return:	Success:	SUCCEED, the ENT argument contains
 *				information about the object header,
 *				including its address.
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  5 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5O_create(H5F_t *f, size_t size_hint, H5G_entry_t *ent/*out*/)
{
    size_t	size;	/*total size of object header	*/
    H5O_t	*oh = NULL;
    haddr_t	tmp_addr;

    FUNC_ENTER(H5O_create, FAIL);

    /* check args */
    assert(f);
    assert(ent);
    HDmemset(ent, 0, sizeof(H5G_entry_t));
    size_hint = H5O_ALIGN (MAX (H5O_MIN_SIZE, size_hint));

    /* allocate disk space for header and first chunk */
    size = H5O_SIZEOF_HDR(f) + size_hint;
    ent->file = f;
    if (H5MF_alloc(f, H5MF_META, size, &(ent->header)/*out*/) < 0) {
	HRETURN_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
		      "unable to allocate file space for object header hdr");
    }
    
    /* allocate the object header and fill in header fields */
    oh = H5MM_xcalloc(1, sizeof(H5O_t));
    oh->dirty = TRUE;
    oh->version = H5O_VERSION;
    oh->nlink = 0;

    /* create the chunk list and initialize the first chunk */
    oh->nchunks = 1;
    oh->alloc_nchunks = H5O_NCHUNKS;
    oh->chunk = H5MM_xmalloc(oh->alloc_nchunks * sizeof(H5O_chunk_t));

    tmp_addr = ent->header;
    H5F_addr_inc(&tmp_addr, H5O_SIZEOF_HDR(f));
    oh->chunk[0].dirty = TRUE;
    oh->chunk[0].addr = tmp_addr;
    oh->chunk[0].size = size_hint;
    oh->chunk[0].image = H5MM_xcalloc(1, size_hint);

    /* create the message list and initialize the first message */
    oh->nmesgs = 1;
    oh->alloc_nmesgs = H5O_NMESGS;
    oh->mesg = H5MM_xcalloc(oh->alloc_nmesgs, sizeof(H5O_mesg_t));

    oh->mesg[0].type = H5O_NULL;
    oh->mesg[0].dirty = TRUE;
    oh->mesg[0].native = NULL;
    oh->mesg[0].raw = oh->chunk[0].image + H5O_SIZEOF_MSGHDR(f);
    oh->mesg[0].raw_size = size_hint - H5O_SIZEOF_MSGHDR(f);
    oh->mesg[0].chunkno = 0;

    /* cache it */
    if (H5AC_set(f, H5AC_OHDR, &(ent->header), oh) < 0) {
	H5MM_xfree(oh);
	HRETURN_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
		      "unable to cache object header");
    }

    /* open it */
    if (H5O_open(ent) < 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_CANTOPENOBJ, FAIL,
		      "unable to open object header");
    }
    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_open
 *
 * Purpose:	Opens an object header which is described by the symbol table
 *		entry OBJ_ENT.
 *
 * Return:	Success:	SUCCEED
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		Monday, January	 5, 1998
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5O_open(H5G_entry_t *obj_ent)
{
    FUNC_ENTER(H5O_open, FAIL);

    /* Check args */
    assert(obj_ent);
    assert(obj_ent->file);

#ifdef H5O_DEBUG
    fprintf(stderr, ">");
    H5F_addr_print(stderr, &(obj_ent->header));
    fprintf(stderr, "\n");
#endif

    /* Increment open-lock counters */
    obj_ent->file->nopen++;
    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_close
 *
 * Purpose:	Closes an object header that was previously open.
 *
 * Return:	Success:	SUCCEED
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		Monday, January	 5, 1998
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5O_close(H5G_entry_t *obj_ent)
{
    FUNC_ENTER(H5O_close, FAIL);

    /* Check args */
    assert(obj_ent);
    assert(obj_ent->file);
    assert(obj_ent->file->nopen > 0);

    /* Decrement open-lock counters */
    --obj_ent->file->nopen;

    /*
     * If the file open-lock count has reached zero and the file has a close
     * pending then close the file.
     */
    if (0 == obj_ent->file->nopen && obj_ent->file->close_pending) {
	H5F_close(obj_ent->file);
    }
#ifdef H5O_DEBUG
    fprintf(stderr, "<");
    H5F_addr_print(stderr, &(obj_ent->header));
    fprintf(stderr, "\n");
#endif

    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_load
 *
 * Purpose:	Loads an object header from disk.
 *
 * Return:	Success:	Pointer to the new object header.
 *
 *		Failure:	NULL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  5 1997
 *
 * Modifications:
 *
 *	Robb Matzke, 30 Aug 1997
 *	Plugged memory leaks that occur during error handling.
 *
 *	Robb Matzke, 7 Jan 1998
 *	Able to distinguish between constant and variable messages.
 *
 *-------------------------------------------------------------------------
 */
static H5O_t *
H5O_load(H5F_t *f, const haddr_t *addr, const void *_udata1, void *_udata2)
{
    H5O_t	*oh = NULL;
    H5O_t	*ret_value = NULL;
    uint8	buf[16], *p;
    size_t	hdr_size, mesg_size;
    uintn	id;
    intn	mesgno, chunkno, curmesg = 0, nmesgs;
    haddr_t	chunk_addr;
    size_t	chunk_size;
    H5O_cont_t	*cont = NULL;
    uint8	flags;

    FUNC_ENTER(H5O_load, NULL);

    /* check args */
    assert(f);
    assert(addr && H5F_addr_defined(addr));
    assert(!_udata1);
    assert(!_udata2);

    /* allocate ohdr and init chunk list */
    oh = H5MM_xcalloc(1, sizeof(H5O_t));

    /* read fixed-lenth part of object header */
    hdr_size = H5O_SIZEOF_HDR(f);
    if (H5F_block_read(f, addr, hdr_size, buf) < 0) {
	HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL,
		    "unable to read object header");
    }
    p = buf;

    /* decode version */
    oh->version = *p++;
    if (H5O_VERSION != oh->version) {
	HGOTO_ERROR(H5E_OHDR, H5E_VERSION, NULL,
		    "bad object header version number");
    }
    
    /* reserved */
    p++;
    
    /* decode number of messages */
    UINT16DECODE(p, nmesgs);

    /* decode link count */
    UINT32DECODE(p, oh->nlink);

    /* decode first chunk info */
    chunk_addr = *addr;
    H5F_addr_inc(&chunk_addr, H5O_SIZEOF_HDR(f));
    UINT32DECODE(p, chunk_size);

    /* build the message array */
    oh->alloc_nmesgs = MAX(H5O_NMESGS, nmesgs);
    oh->mesg = H5MM_xcalloc(oh->alloc_nmesgs, sizeof(H5O_mesg_t));

    /* read each chunk from disk */
    while (H5F_addr_defined(&chunk_addr)) {

	/* increase chunk array size */
	if (oh->nchunks >= oh->alloc_nchunks) {
	    oh->alloc_nchunks += H5O_NCHUNKS;
	    oh->chunk = H5MM_xrealloc(oh->chunk,
				   oh->alloc_nchunks * sizeof(H5O_chunk_t));
	}
	
	/* read the chunk raw data */
	chunkno = oh->nchunks++;
	oh->chunk[chunkno].dirty = FALSE;
	oh->chunk[chunkno].addr = chunk_addr;
	oh->chunk[chunkno].size = chunk_size;
	oh->chunk[chunkno].image = H5MM_xmalloc(chunk_size);
	if (H5F_block_read(f, &chunk_addr, chunk_size,
			   oh->chunk[chunkno].image) < 0) {
	    HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL,
			"unable to read object header data");
	}
	
	/* load messages from this chunk */
	for (p = oh->chunk[chunkno].image;
	     p < oh->chunk[chunkno].image + chunk_size;
	     p += mesg_size) {
	    UINT16DECODE(p, id);
	    UINT16DECODE(p, mesg_size);
	    assert (mesg_size==H5O_ALIGN (mesg_size));
	    flags = *p++;
	    p += 3; /*reserved*/

	    if (id >= NELMTS(message_type_g) || NULL == message_type_g[id]) {
		HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, NULL,
			    "corrupt object header");
	    }
	    if (p + mesg_size > oh->chunk[chunkno].image + chunk_size) {
		HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL,
			    "corrupt object header");
	    }
	    if (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(f) + mesg_size;
	    } else {
		/* new message */
		if (oh->nmesgs >= nmesgs) {
		    HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL,
				"corrupt object header");
		}
		mesgno = oh->nmesgs++;
		oh->mesg[mesgno].type = message_type_g[id];
		oh->mesg[mesgno].dirty = FALSE;
		oh->mesg[mesgno].flags = flags;
		oh->mesg[mesgno].native = NULL;
		oh->mesg[mesgno].raw = p;
		oh->mesg[mesgno].raw_size = mesg_size;
		oh->mesg[mesgno].chunkno = chunkno;
	    }
	}
	assert(p == oh->chunk[chunkno].image + chunk_size);

	/* decode next object header continuation message */
	for (H5F_addr_undef(&chunk_addr);
	     !H5F_addr_defined(&chunk_addr) && curmesg < oh->nmesgs;
	     curmesg++) {
	    if (H5O_CONT_ID == oh->mesg[curmesg].type->id) {
		uint8 *p2 = oh->mesg[curmesg].raw;
		cont = (H5O_CONT->decode) (f, p2, NULL);
		oh->mesg[curmesg].native = cont;
		chunk_addr = cont->addr;
		chunk_size = cont->size;
		cont->chunkno = oh->nchunks;	/*the next chunk to allocate */
	    }
	}
    }
    ret_value = oh;

  done:
    if (!ret_value && oh) {
	/*
	 * Free resources.
	 */
	int i;
	for (i = 0; i < oh->nchunks; i++) {
	    oh->chunk[i].image = H5MM_xfree(oh->chunk[i].image);
	}
	oh->chunk = H5MM_xfree(oh->chunk);
	oh->mesg = H5MM_xfree(oh->mesg);
	oh = H5MM_xfree(oh);
    }
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_flush
 *
 * Purpose:	Flushes (and destroys) an object header.
 *
 * Return:	Success:	SUCCESS
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  5 1997
 *
 * Modifications:
 *
 *	Robb Matzke, 7 Jan 1998
 *	Handles constant vs non-constant messages.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr, H5O_t *oh)
{
    uint8	buf[16], *p;
    intn	i, id;
    H5O_cont_t	*cont = NULL;
    herr_t	(*encode)(H5F_t*, uint8*, const void*) = NULL;

    FUNC_ENTER(H5O_flush, FAIL);

    /* check args */
    assert(f);
    assert(addr && H5F_addr_defined(addr));
    assert(oh);

    /* flush */
    if (oh->dirty) {
	p = buf;

	/* encode version */
	*p++ = oh->version;

	/* reserved */
	*p++ = 0;

	/* encode number of messages */
	UINT16ENCODE(p, oh->nmesgs);

	/* encode link count */
	UINT32ENCODE(p, oh->nlink);

	/* encode body size */
	UINT32ENCODE(p, oh->chunk[0].size);

	/* zero to alignment */
	HDmemset (p, 0, H5O_SIZEOF_HDR(f)-12);

	/* write the object header header */
	if (H5F_block_write(f, addr, H5O_SIZEOF_HDR(f), buf) < 0) {
	    HRETURN_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL,
			  "unable to write object header hdr to disk");
	}
	
	/* encode messages */
	for (i = 0; i < oh->nmesgs; i++) {
	    if (oh->mesg[i].dirty) {
		p = oh->mesg[i].raw - H5O_SIZEOF_MSGHDR(f);

		id = oh->mesg[i].type->id;
		UINT16ENCODE(p, id);
		UINT16ENCODE(p, oh->mesg[i].raw_size);
		*p++ = oh->mesg[i].flags;
		*p++ = 0; /*reserved*/
		*p++ = 0; /*reserved*/
		*p++ = 0; /*reserved*/
		
		if (oh->mesg[i].native) {
		    assert(oh->mesg[i].type->encode);

		    /* allocate file space for chunks that have none yet */
		    if (H5O_CONT_ID == oh->mesg[i].type->id &&
			!H5F_addr_defined(&(((H5O_cont_t *)
					     (oh->mesg[i].native))->addr))) {
			cont = (H5O_cont_t *) (oh->mesg[i].native);
			assert(cont->chunkno >= 0);
			assert(cont->chunkno < oh->nchunks);
			assert(!H5F_addr_defined(&(oh->chunk[cont->chunkno].addr)));
			cont->size = oh->chunk[cont->chunkno].size;
			if (H5MF_alloc(f, H5MF_META, cont->size,
				       &(cont->addr)/*out*/) < 0) {
			    HRETURN_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
				      "unable to allocate space for object "
					  "header data");
			}
			oh->chunk[cont->chunkno].addr = cont->addr;
		    }
		    
		    /*
		     * Encode the message.  If the message is shared then we
		     * encode a Shared Object message instead of the object
		     * which is being shared.
		     */
		    assert(oh->mesg[i].raw >=
			   oh->chunk[oh->mesg[i].chunkno].image);
		    assert (oh->mesg[i].raw_size ==
			    H5O_ALIGN (oh->mesg[i].raw_size));
		    assert(oh->mesg[i].raw + oh->mesg[i].raw_size <=
			   oh->chunk[oh->mesg[i].chunkno].image +
			   oh->chunk[oh->mesg[i].chunkno].size);
		    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
			encode = H5O_SHARED->encode;
		    } else {
			encode = oh->mesg[i].type->encode;
		    }
		    if ((encode)(f, oh->mesg[i].raw, oh->mesg[i].native)<0) {
			HRETURN_ERROR(H5E_OHDR, H5E_CANTENCODE, FAIL,
				  "unable to encode object header message");
		    }
		}
		oh->mesg[i].dirty = FALSE;
		oh->chunk[oh->mesg[i].chunkno].dirty = TRUE;
	    }
	}

	/* write each chunk to disk */
	for (i = 0; i < oh->nchunks; i++) {
	    if (oh->chunk[i].dirty) {
		assert(H5F_addr_defined(&(oh->chunk[i].addr)));
		if (H5F_block_write(f, &(oh->chunk[i].addr), oh->chunk[i].size,
				    oh->chunk[i].image) < 0) {
		    HRETURN_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL,
			      "unable to write object header data to disk");
		}
		oh->chunk[i].dirty = FALSE;
	    }
	}
	oh->dirty = FALSE;
    }

    if (destroy) {
	/* destroy chunks */
	for (i = 0; i < oh->nchunks; i++) {
	    oh->chunk[i].image = H5MM_xfree(oh->chunk[i].image);
	}
	oh->chunk = H5MM_xfree(oh->chunk);

	/* destroy messages */
	for (i = 0; i < oh->nmesgs; i++) {
	    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
		H5O_reset (H5O_SHARED, oh->mesg[i].native);
	    } else {
		H5O_reset(oh->mesg[i].type, oh->mesg[i].native);
	    }
	    oh->mesg[i].native = H5MM_xfree(oh->mesg[i].native);
	}
	oh->mesg = H5MM_xfree(oh->mesg);

	/* destroy object header */
	H5MM_xfree(oh);
    }
    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_reset
 *
 * Purpose:	Some message data structures have internal fields that
 *		need to be freed.  This function does that if appropriate
 *		but doesn't free NATIVE.
 *
 * Return:	Success:	SUCCEED
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug 12 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5O_reset(const H5O_class_t *type, void *native)
{
    FUNC_ENTER(H5O_reset, FAIL);

    if (native) {
	if (type->reset) {
	    if ((type->reset) (native) < 0) {
		HRETURN_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
			      "reset method failed");
	    }
	} else {
	    HDmemset(native, 0, type->native_size);
	}
    }
    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_link
 *
 * Purpose:	Adjust the link count for an object header by adding
 *		ADJUST to the link count.
 *
 * Return:	Success:	New link count
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  5 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
intn
H5O_link(H5G_entry_t *ent, intn adjust)
{
    H5O_t	*oh = NULL;
    intn	ret_value = FAIL;

    FUNC_ENTER(H5O_link, FAIL);

    /* check args */
    assert(ent);
    assert(ent->file);
    assert(H5F_addr_defined(&(ent->header)));
    if (0==(ent->file->intent & H5F_ACC_RDWR)) {
	HGOTO_ERROR (H5E_OHDR, H5E_WRITEERROR, FAIL,
		     "no write intent on file");
    }

    /* get header */
    if (NULL == (oh = H5AC_protect(ent->file, H5AC_OHDR, &(ent->header),
				   NULL, NULL))) {
	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL,
		    "unable to load object header");
    }

    /* adjust link count */
    if (adjust < 0) {
	if (oh->nlink + adjust < 0) {
	    HGOTO_ERROR(H5E_OHDR, H5E_LINKCOUNT, FAIL,
			"link count would be negative");
	}
	oh->nlink += adjust;
    } else {
	oh->nlink += adjust;
    }

    oh->dirty = TRUE;
    ret_value = oh->nlink;

  done:
    if (oh && H5AC_unprotect(ent->file, H5AC_OHDR, &(ent->header), oh) < 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_PROTECT, FAIL,
		      "unable to release object header");
    }
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_read
 *
 * Purpose:	Reads a message from an object header and returns a pointer
 *		to it.	The caller will usually supply the memory through
 *		MESG and the return value will be MESG.	 But if MESG is
 *		the null pointer, then this function will malloc() memory
 *		to hold the result and return its pointer instead.
 *
 * Return:	Success:	Ptr to message in native format.
 *
 *		Failure:	NULL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  6 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
void *
H5O_read(H5G_entry_t *ent, const H5O_class_t *type, intn sequence, void *mesg)
{
    H5O_t		*oh = NULL;
    void		*ret_value = NULL;
    intn		idx;
    H5G_cache_t		*cache = NULL;
    H5G_type_t		cache_type;

    FUNC_ENTER(H5O_read, NULL);

    /* check args */
    assert(ent);
    assert(ent->file);
    assert(H5F_addr_defined(&(ent->header)));
    assert(type);
    assert(sequence >= 0);

    /* can we get it from the symbol table entry? */
    cache = H5G_ent_cache(ent, &cache_type);
    if (H5O_fast_g[cache_type]) {
	ret_value = (H5O_fast_g[cache_type]) (cache, type, mesg);
	if (ret_value)
	    HRETURN(ret_value);
	H5E_clear(); /*don't care, try reading from header */
    }

    /* can we get it from the object header? */
    if ((idx = H5O_find_in_ohdr(ent->file, &(ent->header), &type,
				sequence)) < 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_NOTFOUND, NULL,
		      "unable to find message in object header");
    }

    /* copy the message to the user-supplied buffer */
    if (NULL == (oh = H5AC_protect(ent->file, H5AC_OHDR, &(ent->header),
				   NULL, NULL))) {
	HRETURN_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL,
		      "unable to load object header");
    }
    if (oh->mesg[idx].flags & H5O_FLAG_SHARED) {
	/*
	 * If the message is shared then then the native pointer points to an
	 * H5O_SHARED message.  We use that information to look up the real
	 * message in the global heap.
	 */
	H5O_shared_t *shared;
	void *tmp_buf, *tmp_mesg;

	shared = (H5O_shared_t *)(oh->mesg[idx].native);
	if (NULL==(tmp_buf = H5HG_read (ent->file, shared, NULL))) {
	    HGOTO_ERROR (H5E_OHDR, H5E_CANTLOAD, NULL,
			 "unable to read shared message from global heap");
	}
	tmp_mesg = (type->decode)(ent->file, tmp_buf, shared);
	if (!tmp_mesg) {
	    H5MM_xfree (tmp_buf);
	    HGOTO_ERROR (H5E_OHDR, H5E_CANTLOAD, NULL,
			 "unable to decode object header shared message");
	}
	if (mesg) {
	    HDmemcpy (mesg, tmp_mesg, type->native_size);
	    H5MM_xfree (tmp_mesg);
	} else {
	    ret_value = tmp_mesg;
	}
    } else {
	/*
	 * The message is not shared, but rather exists in the object
	 * header.  The object header caches the native message (along with
	 * the raw message) so we must copy the native message before
	 * returning.
	 */
	if (NULL==(ret_value = (type->copy) (oh->mesg[idx].native, mesg))) {
	    HGOTO_ERROR (H5E_OHDR, H5E_CANTINIT, NULL,
			 "unable to copy message to user space");
	}
    }

 done:
    if (H5AC_unprotect(ent->file, H5AC_OHDR, &(ent->header), oh) < 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_PROTECT, NULL,
		      "unable to release object header");
    }
    oh = NULL;
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_find_in_ohdr
 *
 * Purpose:	Find a message in the object header without consulting
 *		a symbol table entry.
 *
 * Return:	Success:	Index number of message.
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  6 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static intn
H5O_find_in_ohdr(H5F_t *f, const haddr_t *addr, const H5O_class_t **type_p,
		 intn sequence)
{
    H5O_t		*oh = NULL;
    int			i;
    const H5O_class_t	*type = NULL;

    FUNC_ENTER(H5O_find_in_ohdr, FAIL);

    /* Check args */
    assert(f);
    assert(addr && H5F_addr_defined(addr));
    assert(type_p);

    /* Load the object header */
    if (NULL == (oh = H5AC_find(f, H5AC_OHDR, addr, NULL, NULL))) {
	HRETURN_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL,
		      "unable to load object header");
    }

    /* Scan through the messages looking for the right one */
    for (i = 0; i < oh->nmesgs; i++) {
	if (*type_p && (*type_p)->id != oh->mesg[i].type->id) continue;
	if (--sequence < 0) break;
    }
    if (sequence >= 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_NOTFOUND, FAIL,
		      "unable to find object header message");
    }

    /*
     * Decode the message if necessary.  If the message is shared then decode
     * a shared message, ignoring the message type.
     */
    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
	type = H5O_SHARED;
    } else {
	type = oh->mesg[i].type;
    }
    if (NULL == oh->mesg[i].native) {
	assert(type->decode);
	oh->mesg[i].native = (type->decode) (f, oh->mesg[i].raw, NULL);
	if (NULL == oh->mesg[i].native) {
	    HRETURN_ERROR(H5E_OHDR, H5E_CANTDECODE, FAIL,
			  "unable to decode message");
	}
    }

    /*
     * Return the message type. If this is a shared message then return the
     * pointed-to type.
     */
    *type_p = oh->mesg[i].type;
    FUNC_LEAVE(i);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_modify
 *
 * Purpose:	Modifies an existing message or creates a new message.
 *		The cache fields in that symbol table entry ENT are *not*
 *		updated, you must do that separately because they often
 *		depend on multiple object header messages.  Besides, we
 *		don't know which messages will be constant and which will
 *		not.
 *
 *		The OVERWRITE argument is either a sequence number of a
 *		message to overwrite (usually zero) or the constant
 *		H5O_NEW_MESSAGE (-1) to indicate that a new message is to
 *		be created.  If the message to overwrite doesn't exist then
 *		it is created (but only if it can be inserted so its sequence
 *		number is OVERWRITE; that is, you can create a message with
 *		the sequence number 5 if there is no message with sequence
 *		number 4).
 *
 * Return:	Success:	The sequence number of the message that
 *				was modified or created.
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  6 1997
 *
 * Modifications:
 *
 *	Robb Matzke, 7 Jan 1998
 *	Handles constant vs non-constant messages.  Once a message is made
 *	constant it can never become non-constant.  Constant messages cannot
 *	be modified.
 *
 *-------------------------------------------------------------------------
 */
intn
H5O_modify(H5G_entry_t *ent, const H5O_class_t *type, intn overwrite,
	   uintn flags, const void *mesg)
{
    H5O_t		*oh = NULL;
    intn		idx, sequence;
    intn		ret_value = FAIL;
    size_t		size = 0;
    H5O_shared_t	*sh_mesg = NULL;

    FUNC_ENTER(H5O_modify, FAIL);

    /* check args */
    assert(ent);
    assert(ent->file);
    assert(H5F_addr_defined(&(ent->header)));
    assert(type);
    assert(mesg);
    assert (0==(flags & ~H5O_FLAG_BITS));
    if (0==(ent->file->intent & H5F_ACC_RDWR)) {
	HGOTO_ERROR (H5E_OHDR, H5E_WRITEERROR, FAIL,
		     "no write intent on file");
    }

    if (NULL == (oh = H5AC_protect(ent->file, H5AC_OHDR, &(ent->header),
				   NULL, NULL))) {
	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL,
		    "unable to load object header");
    }

    /* Count similar messages */
    for (idx = 0, sequence = -1; idx < oh->nmesgs; idx++) {
	if (type->id != oh->mesg[idx].type->id) continue;
	if (++sequence == overwrite) break;
    }

    /* Was the right message found? */
    if (overwrite >= 0 &&
	(idx >= oh->nmesgs || sequence != overwrite)) {

	/* But can we insert a new one with this sequence number? */
	if (overwrite == sequence + 1) {
	    overwrite = -1;
	} else {
	    HGOTO_ERROR(H5E_OHDR, H5E_NOTFOUND, FAIL, "message not found");
	}
    }
    if (overwrite < 0) {
	/* Allocate space for the new message */
	if (flags & H5O_FLAG_SHARED) {
	    if (NULL==type->share) {
		HGOTO_ERROR (H5E_OHDR, H5E_UNSUPPORTED, FAIL,
			     "message class is not sharable");
	    }
	    sh_mesg = H5MM_xcalloc (1, sizeof *sh_mesg);
	    if ((type->share)(ent->file, mesg, sh_mesg/*out*/)<0) {
		/*
		 * If the message isn't shared then turn of the shared bit
		 * and treat it as an unshared message.
		 */
		H5E_clear ();
		flags &= ~H5O_FLAG_SHARED;
	    } else {
		if (H5HG_link (ent->file, sh_mesg, 1)<0) {
		    HGOTO_ERROR (H5E_OHDR, H5E_LINK, FAIL,
				 "unable to adjust shared object link count");
		}
		size = (H5O_SHARED->raw_size)(ent->file, sh_mesg);
	    }
	}
	if (0==(flags & H5O_FLAG_SHARED)) {
	    size = (type->raw_size) (ent->file, mesg);
	}
	size = H5O_ALIGN(size);
	idx = H5O_alloc(ent->file, oh, type, size);
	if (idx < 0) {
	    HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
			"unable to allocate space for message");
	}
	sequence++;
	    
    } else if (oh->mesg[idx].flags & H5O_FLAG_CONSTANT) {
	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL,
		    "unable to modify constant message");
    } else if (oh->mesg[idx].flags & H5O_FLAG_SHARED) {
	HGOTO_ERROR (H5E_OHDR, H5E_WRITEERROR, FAIL,
		     "unable to modify shared (constant) message");
    }
    

    /* Copy the native value into the object header */
    if (flags & H5O_FLAG_SHARED) {
	oh->mesg[idx].native = sh_mesg;
    } else {
	oh->mesg[idx].native = (type->copy) (mesg, oh->mesg[idx].native);
	if (NULL == oh->mesg[idx].native) {
	    HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
			"unable to copy message to object header");
	}
    }
    
    oh->mesg[idx].flags = flags;
    oh->mesg[idx].dirty = TRUE;
    oh->dirty = TRUE;
    ret_value = sequence;

  done:
    if (oh && H5AC_unprotect(ent->file, H5AC_OHDR, &(ent->header), oh) < 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_PROTECT, FAIL,
		      "unable to release object header");
    }
    
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_remove
 *
 * Purpose:	Removes the specified message from the object header.
 *		If sequence is H5O_ALL (-1) then all messages of the
 *		specified type are removed.  Removing a message causes
 *		the sequence numbers to change for subsequent messages of
 *		the same type.
 *
 *		No attempt is made to join adjacent free areas of the
 *		object header into a single larger free area.
 *
 * Return:	Success:	SUCCEED
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug 28 1997
 *
 * Modifications:
 *
 *	Robb Matzke, 7 Jan 1998
 *	Does not remove constant messages.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5O_remove(H5G_entry_t *ent, const H5O_class_t *type, intn sequence)
{
    H5O_t		*oh = NULL;
    intn		i, seq, nfailed = 0;
    herr_t		ret_value = FAIL;
    H5O_shared_t	*sh_mesg = NULL;

    FUNC_ENTER(H5O_remove, FAIL);

    /* check args */
    assert(ent);
    assert(ent->file);
    assert(H5F_addr_defined(&(ent->header)));
    assert(type);
    if (0==(ent->file->intent & H5F_ACC_RDWR)) {
	HRETURN_ERROR (H5E_HEAP, H5E_WRITEERROR, FAIL,
		       "no write intent on file");
    }

    /* load the object header */
    if (NULL == (oh = H5AC_protect(ent->file, H5AC_OHDR, &(ent->header),
				   NULL, NULL))) {
	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL,
		    "unable to load object header");
    }
    
    for (i = seq = 0; i < oh->nmesgs; i++) {
	if (type->id != oh->mesg[i].type->id) continue;
	if (seq++ == sequence || H5O_ALL == sequence) {
	    /*
	     * Keep track of how many times we failed trying to remove constant
	     * messages.
	     */
	    if (oh->mesg[i].flags & H5O_FLAG_CONSTANT) {
		nfailed++;
		continue;
	    }

	    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
		if (NULL==oh->mesg[i].native) {
		    sh_mesg = (H5O_SHARED->decode)(ent->file, oh->mesg[i].raw,
						   NULL);
		    if (NULL==(oh->mesg[i].native = sh_mesg)) {
			HGOTO_ERROR (H5E_OHDR, H5E_CANTDECODE, FAIL,
				     "unable to decode shared message info");
		    }
		}
		if (H5HG_link (ent->file, sh_mesg, -1)<0) {
		    HGOTO_ERROR (H5E_OHDR, H5E_LINK, FAIL,
				 "unable to decrement link count on shared "
				 "message");
		}
	    }

	    /* change message type to nil and zero it */
	    oh->mesg[i].type = H5O_NULL;
	    HDmemset(oh->mesg[i].raw, 0, oh->mesg[i].raw_size);
	    H5O_reset(type, oh->mesg[i].native);
	    oh->mesg[i].native = H5MM_xfree(oh->mesg[i].native);

	    oh->mesg[i].dirty = TRUE;
	    oh->dirty = TRUE;
	}
    }

    /* Fail if we tried to remove any constant messages */
    if (nfailed) {
	HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
		    "unable to remove constant message(s)");
    }
    ret_value = SUCCEED;

  done:
    if (oh && H5AC_unprotect(ent->file, H5AC_OHDR, &(ent->header), oh) < 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_PROTECT, FAIL,
		      "unable to release object header");
    }
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_alloc_extend_chunk
 *
 * Purpose:	Extends a chunk which hasn't been allocated on disk yet
 *		to make the chunk large enough to contain a message whose
 *		data size is at least SIZE bytes.
 *
 *		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.
 *
 * Return:	Success:	Message index for null message which
 *				is large enough to hold SIZE bytes.
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  7 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static intn
H5O_alloc_extend_chunk(H5O_t *oh, intn chunkno, size_t size)
{
    intn	idx, i;
    size_t	delta;
    uint8	*old_addr;

    FUNC_ENTER(H5O_alloc_extend_chunk, FAIL);

    /* check args */
    assert(oh);
    assert(chunkno >= 0 && chunkno < oh->nchunks);
    assert(size > 0);
    assert (size==H5O_ALIGN (size));

    if (H5F_addr_defined(&(oh->chunk[chunkno].addr))) {
	HRETURN_ERROR(H5E_OHDR, H5E_NOSPACE, FAIL, "chunk is on disk");
    }

    /* try to extend a null message */
    for (idx=0; idx<oh->nmesgs; idx++) {
	if (H5O_NULL_ID == oh->mesg[idx].type->id &&
	    (oh->mesg[idx].raw + oh->mesg[idx].raw_size ==
	     oh->chunk[chunkno].image + oh->chunk[chunkno].size)) {

	    delta = MAX (H5O_MIN_SIZE, size - oh->mesg[idx].raw_size);
	    assert (delta=H5O_ALIGN (delta));
	    oh->mesg[idx].dirty = TRUE;
	    oh->mesg[idx].raw_size += delta;

	    old_addr = oh->chunk[chunkno].image;

	    /* Be careful not to indroduce garbage */
	    oh->chunk[chunkno].image = H5MM_xrealloc(old_addr,
						     (oh->chunk[chunkno].size +
						      delta));
	    HDmemset(oh->chunk[chunkno].image + oh->chunk[chunkno].size,
		     0, delta);
	    oh->chunk[chunkno].size += delta;

	    /* adjust raw addresses for messages of this chunk */
	    if (old_addr != oh->chunk[chunkno].image) {
		for (i = 0; i < oh->nmesgs; i++) {
		    if (oh->mesg[i].chunkno == chunkno) {
			oh->mesg[i].raw = oh->chunk[chunkno].image +
					  (oh->mesg[i].raw - old_addr);
		    }
		}
	    }
	    HRETURN(idx);
	}
    }

    /* create a new null message */
    if (oh->nmesgs >= oh->alloc_nmesgs) {
	oh->alloc_nmesgs += H5O_NMESGS;
	oh->mesg = H5MM_xrealloc(oh->mesg,
				 oh->alloc_nmesgs * sizeof(H5O_mesg_t));
    }
    delta = MAX(H5O_MIN_SIZE, size+H5O_SIZEOF_MSGHDR(f));
    delta = H5O_ALIGN(delta);
    idx = oh->nmesgs++;
    oh->mesg[idx].type = H5O_NULL;
    oh->mesg[idx].dirty = TRUE;
    oh->mesg[idx].native = NULL;
    oh->mesg[idx].raw = oh->chunk[chunkno].image +
			oh->chunk[chunkno].size +
			H5O_SIZEOF_MSGHDR(f);
    oh->mesg[idx].raw_size = delta - H5O_SIZEOF_MSGHDR(f);
    oh->mesg[idx].chunkno = chunkno;

    old_addr = oh->chunk[chunkno].image;
    oh->chunk[chunkno].size += delta;
    oh->chunk[chunkno].image = H5MM_xrealloc(old_addr,
					     oh->chunk[chunkno].size);

    /* adjust raw addresses for messages of this chunk */
    if (old_addr != oh->chunk[chunkno].image) {
	for (i = 0; i < oh->nmesgs; i++) {
	    if (oh->mesg[i].chunkno == chunkno) {
		oh->mesg[i].raw = oh->chunk[chunkno].image +
		    (oh->mesg[i].raw - old_addr);
	    }
	}
    }
    FUNC_LEAVE(idx);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_alloc_new_chunk
 *
 * Purpose:	Allocates a new chunk for the object header but doen't
 *		give the new chunk a file address yet.	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.
 *
 * 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:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  7 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static intn
H5O_alloc_new_chunk(H5F_t *f, H5O_t *oh, size_t size)
{
    size_t	cont_size;		/*continuation message size	*/
    intn	found_null = (-1);	/*best fit null message		*/
    intn	found_other = (-1);	/*best fit other message	*/
    intn	idx = FAIL;		/*message number return value	*/
    uint8	*p = NULL;		/*ptr into new chunk		*/
    H5O_cont_t	*cont = NULL;		/*native continuation message	*/
    intn	i, chunkno;

    FUNC_ENTER(H5O_alloc_new_chunk, FAIL);

    /* check args */
    assert (oh);
    assert (size > 0);
    assert (size == H5O_ALIGN (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.
     */
    cont_size = H5O_ALIGN (H5F_SIZEOF_ADDR(f) + H5F_SIZEOF_SIZE(f));
    for (i=0; i<oh->nmesgs; i++) {
	if (H5O_NULL_ID == oh->mesg[i].type->id) {
	    if (cont_size == oh->mesg[i].raw_size) {
		found_null = i;
		break;
	    } else if (oh->mesg[i].raw_size >= cont_size &&
		       (found_null < 0 ||
			(oh->mesg[i].raw_size <
			 oh->mesg[found_null].raw_size))) {
		found_null = i;
	    }
	} else if (H5O_CONT_ID == oh->mesg[i].type->id) {
	    /*don't consider continuation messages */
	} else if (oh->mesg[i].raw_size >= cont_size &&
		   (found_other < 0 ||
		    oh->mesg[i].raw_size < oh->mesg[found_other].raw_size)) {
	    found_other = i;
	}
    }
    assert(found_null >= 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.
     */
    if (found_null < 0)
	size += H5O_SIZEOF_MSGHDR(f) + oh->mesg[found_other].raw_size;

    /*
     * 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(f));
    assert (size == H5O_ALIGN (size));

    /*
     * Create the new chunk without giving it a file address.
     */
    if (oh->nchunks >= oh->alloc_nchunks) {
	oh->alloc_nchunks += H5O_NCHUNKS;
	oh->chunk = H5MM_xrealloc(oh->chunk,
				  oh->alloc_nchunks * sizeof(H5O_chunk_t));
    }
    chunkno = oh->nchunks++;
    oh->chunk[chunkno].dirty = TRUE;
    H5F_addr_undef(&(oh->chunk[chunkno].addr));
    oh->chunk[chunkno].size = size;
    oh->chunk[chunkno].image = p = H5MM_xcalloc(1, size);

    /*
     * Make sure we have enough space for all possible new messages
     * that could be generated below.
     */
    if (oh->nmesgs + 3 > oh->alloc_nmesgs) {
	oh->alloc_nmesgs += MAX(H5O_NMESGS, 3);
	oh->mesg = H5MM_xrealloc(oh->mesg,
				 oh->alloc_nmesgs * sizeof(H5O_mesg_t));
    }

    /*
     * Describe the messages of the new chunk.
     */
    if (found_null < 0) {
	found_null = i = oh->nmesgs++;
	oh->mesg[i].type = H5O_NULL;
	oh->mesg[i].dirty = TRUE;
	oh->mesg[i].native = NULL;
	oh->mesg[i].raw = oh->mesg[found_other].raw;
	oh->mesg[i].raw_size = oh->mesg[found_other].raw_size;
	oh->mesg[i].chunkno = oh->mesg[found_other].chunkno;

	oh->mesg[found_other].dirty = TRUE;
	oh->mesg[found_other].raw = p + H5O_SIZEOF_MSGHDR(f);
	oh->mesg[found_other].chunkno = chunkno;
	p += H5O_SIZEOF_MSGHDR(f) + oh->mesg[found_other].raw_size;
	size -= H5O_SIZEOF_MSGHDR(f) + oh->mesg[found_other].raw_size;
    }
    idx = oh->nmesgs++;
    oh->mesg[idx].type = H5O_NULL;
    oh->mesg[idx].dirty = TRUE;
    oh->mesg[idx].native = NULL;
    oh->mesg[idx].raw = p + H5O_SIZEOF_MSGHDR(f);
    oh->mesg[idx].raw_size = size - H5O_SIZEOF_MSGHDR(f);
    oh->mesg[idx].chunkno = chunkno;

    /*
     * If the null message that will receive the continuation message
     * is larger than the continuation message, then split it into
     * two null messages.
     */
    if (oh->mesg[found_null].raw_size > cont_size) {
	i = oh->nmesgs++;
	oh->mesg[i].type = H5O_NULL;
	oh->mesg[i].dirty = TRUE;
	oh->mesg[i].native = NULL;
	oh->mesg[i].raw = oh->mesg[found_null].raw +
			  cont_size +
			  H5O_SIZEOF_MSGHDR(f);
	oh->mesg[i].raw_size = oh->mesg[found_null].raw_size -
			       (cont_size + H5O_SIZEOF_MSGHDR(f));
	oh->mesg[i].chunkno = oh->mesg[found_null].chunkno;

	oh->mesg[found_null].dirty = TRUE;
	oh->mesg[found_null].raw_size = cont_size;
    }

    /*
     * Initialize the continuation message.
     */
    oh->mesg[found_null].type = H5O_CONT;
    oh->mesg[found_null].dirty = TRUE;
    cont = H5MM_xcalloc(1, sizeof(H5O_cont_t));
    H5F_addr_undef(&(cont->addr));
    cont->size = 0;
    cont->chunkno = chunkno;
    oh->mesg[found_null].native = cont;

    FUNC_LEAVE(idx);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_alloc
 *
 * Purpose:	Allocate enough space in the object header for this message.
 *
 * Return:	Success:	Index of message
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  6 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static intn
H5O_alloc(H5F_t *f, H5O_t *oh, const H5O_class_t *type, size_t size)
{
    intn	chunkno;
    intn	idx;
    intn	null_idx;

    FUNC_ENTER(H5O_alloc, FAIL);

    /* check args */
    assert (oh);
    assert (type);
    assert (size == H5O_ALIGN (size));

    /* 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 >= size)
	    break;
    }

#ifdef LATER
    /*
     * Perhaps if we join adjacent null messages we could make one
     * large enough... we leave this as an exercise for future
     * programmers :-)	This isn't a high priority because when an
     * object header is read from disk the null messages are combined
     * anyway.
     */
#endif

    /* if we didn't find one, then allocate more header space */
    if (idx >= oh->nmesgs) {
	/*
	 * Look for a chunk which hasn't had disk space allocated yet
	 * since we can just increase the size of that chunk.
	 */
	for (chunkno = 0; chunkno < oh->nchunks; chunkno++) {
	    if ((idx = H5O_alloc_extend_chunk(oh, chunkno, size)) >= 0) {
		break;
	    }
	    H5E_clear();
	}

	/*
	 * Create a new chunk
	 */
	if (idx < 0) {
	    if ((idx = H5O_alloc_new_chunk(f, oh, size)) < 0) {
		HRETURN_ERROR(H5E_OHDR, H5E_NOSPACE, FAIL,
			 "unable to create a new object header data chunk");
	    }
	}
    }

    /* do we need to split the null message? */
    if (oh->mesg[idx].raw_size > size) {
	assert(oh->mesg[idx].raw_size - size >= H5O_SIZEOF_MSGHDR(f));

	if (oh->nmesgs >= oh->alloc_nmesgs) {
	    oh->alloc_nmesgs += H5O_NMESGS;
	    oh->mesg = H5MM_xrealloc(oh->mesg,
				     oh->alloc_nmesgs * sizeof(H5O_mesg_t));
	}
	null_idx = oh->nmesgs++;
	oh->mesg[null_idx].type = H5O_NULL;
	oh->mesg[null_idx].dirty = TRUE;
	oh->mesg[null_idx].native = NULL;
	oh->mesg[null_idx].raw = oh->mesg[idx].raw +
				 size +
				 H5O_SIZEOF_MSGHDR(f);
	oh->mesg[null_idx].raw_size = oh->mesg[idx].raw_size -
				      (size + H5O_SIZEOF_MSGHDR(f));
	oh->mesg[null_idx].chunkno = oh->mesg[idx].chunkno;
	oh->mesg[idx].raw_size = size;
    }
    /* initialize the new message */
    oh->mesg[idx].type = type;
    oh->mesg[idx].dirty = TRUE;
    oh->mesg[idx].native = NULL;

    oh->dirty = TRUE;
    FUNC_LEAVE(idx);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_share
 *
 * Purpose:	Writes a message to the global heap.
 *
 * Return:	Success:	SUCCEED, and HOBJ describes the global heap
 *				object.
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *              Thursday, April  2, 1998
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5O_share (H5F_t *f, const H5O_class_t *type, const void *mesg,
	   H5HG_t *hobj/*out*/)
{
    size_t	size;
    void	*buf = NULL;
    herr_t	ret_value = FAIL;
    
    FUNC_ENTER (H5O_share, FAIL);

    /* Check args */
    assert (f);
    assert (type);
    assert (mesg);
    assert (hobj);

    /* Encode the message put it in the global heap */
    if ((size = (type->raw_size)(f, mesg))>0) {
	buf = H5MM_xmalloc (size);
	if ((type->encode)(f, buf, mesg)<0) {
	    HGOTO_ERROR (H5E_OHDR, H5E_CANTENCODE, FAIL,
			 "unable to encode message");
	}
	if (H5HG_insert (f, size, buf, hobj)<0) {
	    HGOTO_ERROR (H5E_OHDR, H5E_CANTINIT, FAIL,
			 "unable to store message in global heap");
	}
    }
    ret_value = SUCCEED;

 done:
    H5MM_xfree (buf);
    FUNC_LEAVE (ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5O_debug
 *
 * Purpose:	Prints debugging info about an object header.
 *
 * Return:	Success:	SUCCEED
 *
 *		Failure:	FAIL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  6 1997
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5O_debug(H5F_t *f, const haddr_t *addr, FILE * stream, intn indent,
	  intn fwidth)
{
    H5O_t	*oh = NULL;
    intn	i, chunkno;
    size_t	mesg_total = 0, chunk_total = 0;
    int		*sequence;
    haddr_t	tmp_addr;
    herr_t	ret_value = FAIL;
    void	*(*decode)(H5F_t*, const uint8*, H5HG_t*);
    herr_t      (*debug)(H5F_t*, const void*, FILE*, intn, intn)=NULL;

    FUNC_ENTER(H5O_debug, FAIL);

    /* check args */
    assert(f);
    assert(addr && H5F_addr_defined(addr));
    assert(stream);
    assert(indent >= 0);
    assert(fwidth >= 0);

    if (NULL == (oh = H5AC_protect(f, H5AC_OHDR, addr, NULL, NULL))) {
	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL,
		    "unable to load object header");
    }

    /* debug */
    fprintf(stream, "%*sObject Header...\n", indent, "");

    fprintf(stream, "%*s%-*s %d\n", indent, "", fwidth,
	    "Dirty:",
	    (int) (oh->dirty));
    fprintf(stream, "%*s%-*s %d\n", indent, "", fwidth,
	    "Version:",
	    (int) (oh->version));
    fprintf(stream, "%*s%-*s %d\n", indent, "", fwidth,
	    "Number of links:",
	    (int) (oh->nlink));
    fprintf(stream, "%*s%-*s %d (%d)\n", indent, "", fwidth,
	    "Number of messages (allocated):",
	    (int) (oh->nmesgs), (int) (oh->alloc_nmesgs));
    fprintf(stream, "%*s%-*s %d (%d)\n", indent, "", fwidth,
	    "Number of chunks (allocated):",
	    (int) (oh->nchunks), (int) (oh->alloc_nchunks));

    /* debug each chunk */
    for (i=0, chunk_total=0; i<oh->nchunks; i++) {
	chunk_total += oh->chunk[i].size;
	fprintf(stream, "%*sChunk %d...\n", indent, "", i);

	fprintf(stream, "%*s%-*s %d\n", indent + 3, "", MAX(0, fwidth - 3),
		"Dirty:",
		(int) (oh->chunk[i].dirty));

	fprintf(stream, "%*s%-*s ", indent + 3, "", MAX(0, fwidth - 3),
		"Address:");
	H5F_addr_print(stream, &(oh->chunk[i].addr));
	fprintf(stream, "\n");

	tmp_addr = *addr;
	H5F_addr_inc(&tmp_addr, H5O_SIZEOF_HDR(f));
	if (0 == i && H5F_addr_ne(&(oh->chunk[i].addr), &tmp_addr)) {
	    fprintf(stream, "*** WRONG ADDRESS!\n");
	}
	fprintf(stream, "%*s%-*s %lu\n", indent + 3, "", MAX(0, fwidth - 3),
		"Size in bytes:",
		(unsigned long) (oh->chunk[i].size));
    }

    /* debug each message */
    sequence = H5MM_xcalloc(NELMTS(message_type_g), sizeof(int));
    for (i=0, mesg_total=0; i<oh->nmesgs; i++) {
	mesg_total += H5O_SIZEOF_MSGHDR(f) + oh->mesg[i].raw_size;
	fprintf(stream, "%*sMessage %d...\n", indent, "", i);

	/* check for bad message id */
	if (oh->mesg[i].type->id < 0 ||
	    oh->mesg[i].type->id >= NELMTS(message_type_g)) {
	    fprintf(stream, "*** BAD MESSAGE ID 0x%04x\n",
		    oh->mesg[i].type->id);
	    continue;
	}

	/* message name and size */
	fprintf(stream, "%*s%-*s 0x%04x %s(%d)\n",
		indent + 3, "", MAX(0, fwidth - 3),
		"Message ID:",
		(unsigned) (oh->mesg[i].type->id),
		oh->mesg[i].type->name,
		sequence[oh->mesg[i].type->id]++);
	fprintf (stream, "%*s%-*s %s\n", indent+3, "", MAX (0, fwidth-3),
		 "Shared message:",
		 (oh->mesg[i].flags & H5O_FLAG_SHARED) ? "Yes" : "No");
	fprintf(stream, "%*s%-*s %s\n", indent + 3, "", MAX(0, fwidth - 3),
		"Constant:",
		(oh->mesg[i].flags & H5O_FLAG_CONSTANT) ? "Yes" : "No");
	if (oh->mesg[i].flags & ~H5O_FLAG_BITS) {
	    fprintf (stream, "%*s%-*s 0x%02x\n", indent+3,"",MAX(0,fwidth-3), 
		     "*** ADDITIONAL UNKNOWN FLAGS --->",
		     oh->mesg[i].flags & ~H5O_FLAG_BITS);
	}
	fprintf(stream, "%*s%-*s %lu bytes\n", indent+3, "", MAX(0,fwidth-3),
		"Raw size in obj header:",
		(unsigned long) (oh->mesg[i].raw_size));
	fprintf(stream, "%*s%-*s %d\n", indent + 3, "", MAX(0, fwidth - 3),
		"Chunk number:",
		(int) (oh->mesg[i].chunkno));
	chunkno = oh->mesg[i].chunkno;
	if (chunkno < 0 || chunkno >= oh->nchunks) {
	    fprintf(stream, "*** BAD CHUNK NUMBER\n");
	}
	
	/* check the size */
	if ((oh->mesg[i].raw + oh->mesg[i].raw_size >
	     oh->chunk[chunkno].image + oh->chunk[chunkno].size) ||
	    (oh->mesg[i].raw < oh->chunk[chunkno].image)) {
	    fprintf(stream, "*** BAD MESSAGE RAW ADDRESS\n");
	}
	
	/* decode the message */
	if (NULL == oh->mesg[i].native && oh->mesg[i].type->decode) {
	    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
		decode = H5O_SHARED->decode;
		debug = H5O_SHARED->debug;
	    } else {
		decode = oh->mesg[i].type->decode;
		debug = oh->mesg[i].type->debug;
	    }
	    oh->mesg[i].native = (decode)(f, oh->mesg[i].raw, NULL);
	} else {
	    debug = NULL;
	}
	
	/* print the message */
	if (debug) {
	    (debug)(f, oh->mesg[i].native, stream, indent+3, MAX(0, fwidth-3));
	} else {
	    fprintf(stream, "%*sNo info for this message.\n", indent + 3, "");
	}

	/* If the message is shared then also print the pointed-to message */
	if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
	    void *p = H5HG_read (f, oh->mesg[i].native, NULL);
	    void *mesg = (oh->mesg[i].type->decode)(f, p, oh->mesg[i].native);
	    if (oh->mesg[i].type->debug) {
		(oh->mesg[i].type->debug)(f, mesg, stream, indent+3,
					  MAX (0, fwidth-3));
	    }
	    H5O_reset (oh->mesg[i].type, mesg);
	    H5MM_xfree (mesg);
	    H5MM_xfree (p);
	}
    }
    sequence = H5MM_xfree(sequence);

    if (mesg_total != chunk_total) {
	fprintf(stream, "*** TOTAL SIZE DOES NOT MATCH ALLOCATED SIZE!\n");
    }
    ret_value = SUCCEED;

  done:
    if (oh && H5AC_unprotect(f, H5AC_OHDR, addr, oh) < 0) {
	HRETURN_ERROR(H5E_OHDR, H5E_PROTECT, FAIL,
		      "unable to release object header");
    }
    FUNC_LEAVE(ret_value);
}