[svn-r13012] Description:

    Refactor object header code to separate process of creating an object
header message from the process of writing to an existing one.

    Start renaming operations that deal with object header messages to have
"H5O_msg_" prefix...

Tested on:
    Mac OS X/32 10.4.8 (amazon)
    FreeBSD/32 4.11 (sleipnir)
    Linux/32 2.4 (heping)
    AIX/32 5.? (copper)

15 files changed, 237 insertions, 200 deletions

diff --git a/src/H5A.c b/src/H5A.c
index 135f88e..06ab7eb 100644
--- a/src/H5A.c
+++ b/src/H5A.c
@@ -417,7 +417,7 @@ H5A_create(const H5G_loc_t *loc, const char *name, const H5T_t *type,
     attr->obj_opened = TRUE;
 
     /* Create the attribute message and save the attribute index */
-    if(H5O_modify(&(attr->oloc), H5O_ATTR_ID, H5O_NEW_MESG, 0, H5O_UPDATE_TIME, attr, dxpl_id) < 0)
+    if(H5O_msg_create(&(attr->oloc), H5O_ATTR_ID, 0, H5O_UPDATE_TIME, attr, dxpl_id) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to update attribute header messages")
 
     /* Register the new attribute and get an ID for it */
@@ -828,7 +828,7 @@ H5A_write(H5A_t *attr, const H5T_t *mem_type, const void *buf, hid_t dxpl_id)
             HGOTO_ERROR(H5E_ATTR, H5E_BADVALUE, FAIL, "attribute not found")
 
         /* Modify the attribute data */
-        if(H5O_modify(&(attr->oloc), H5O_ATTR_ID, idx, 0, H5O_UPDATE_DATA_ONLY|H5O_UPDATE_TIME, attr, dxpl_id) < 0)
+        if(H5O_write(&(attr->oloc), H5O_ATTR_ID, idx, 0, H5O_UPDATE_DATA_ONLY|H5O_UPDATE_TIME, attr, dxpl_id) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to update attribute header messages")
     } /* end if */
 
@@ -1380,7 +1380,7 @@ H5A_rename(H5O_loc_t *loc, const char *old_name, const char *new_name, hid_t dxp
     found_attr.initialized = TRUE;
 
     /* Modify the attribute message */
-    if(H5O_modify(loc, H5O_ATTR_ID, idx, 0, H5O_UPDATE_TIME, &found_attr, dxpl_id) < 0)
+    if(H5O_write(loc, H5O_ATTR_ID, idx, 0, H5O_UPDATE_TIME, &found_attr, dxpl_id) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to update attribute header messages")
 
     /* Close the attribute */
diff --git a/src/H5D.c b/src/H5D.c
index a1dfce5..76b7a9c 100644
--- a/src/H5D.c
+++ b/src/H5D.c
@@ -1302,7 +1302,7 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to protect dataset object header")
 
     /* Write new fill value message */
-    if(H5O_append(file, dxpl_id, oh, H5O_FILL_NEW_ID, H5O_MSG_FLAG_CONSTANT, &fill, &oh_flags) < 0)
+    if(H5O_append(file, dxpl_id, oh, H5O_FILL_NEW_ID, H5O_MSG_FLAG_CONSTANT, 0, &fill, &oh_flags) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update fill value header message")
 
     /* If there is valid information for the old fill value struct, update it */
@@ -1317,7 +1317,7 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
             HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT,FAIL,"unable to copy fill value")
 
         /* Write old fill value */
-        if(fill_prop->buf && H5O_append(file, dxpl_id, oh, H5O_FILL_ID, H5O_MSG_FLAG_CONSTANT, fill_prop, &oh_flags) < 0)
+        if(fill_prop->buf && H5O_append(file, dxpl_id, oh, H5O_FILL_ID, H5O_MSG_FLAG_CONSTANT, 0, fill_prop, &oh_flags) < 0)
             HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update fill value header message")
 
         /* Update dataset creation property */
@@ -1327,7 +1327,7 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
     } /* end if */
 
     /* Update the type and space header messages */
-    if(H5O_append(file, dxpl_id, oh, H5O_DTYPE_ID, H5O_MSG_FLAG_CONSTANT | H5O_MSG_FLAG_SHARED, type, &oh_flags) < 0 ||
+    if(H5O_append(file, dxpl_id, oh, H5O_DTYPE_ID, H5O_MSG_FLAG_CONSTANT | H5O_MSG_FLAG_SHARED, 0, type, &oh_flags) < 0 ||
             H5S_append(file, dxpl_id, oh, dset->shared->space, &oh_flags) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update type or space header messages")
 
@@ -1338,7 +1338,7 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
         if(H5P_get(dc_plist, H5D_CRT_DATA_PIPELINE_NAME, &pline) < 0)
             HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "Can't retrieve pipeline filter")
 
-        if(pline.nused > 0 && H5O_append(file, dxpl_id, oh, H5O_PLINE_ID, H5O_MSG_FLAG_CONSTANT, &pline, &oh_flags) < 0)
+        if(pline.nused > 0 && H5O_append(file, dxpl_id, oh, H5O_PLINE_ID, H5O_MSG_FLAG_CONSTANT, 0, &pline, &oh_flags) < 0)
             HGOTO_ERROR (H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update filter header message")
     } /* end if */
 
@@ -1351,7 +1351,7 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
             HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to initialize storage")
 
     /* Update external storage message */
-    if (efl->nused > 0) {
+    if(efl->nused > 0) {
         size_t heap_size = H5HL_ALIGN(1);
         size_t u;
 
@@ -1362,7 +1362,7 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
                 H5HL_insert(file, dxpl_id, efl->heap_addr, (size_t)1, "") == (size_t)(-1))
             HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to create external file list name heap")
 
-        for (u = 0; u < efl->nused; ++u) {
+        for(u = 0; u < efl->nused; ++u) {
             size_t offset = H5HL_insert(file, dxpl_id, efl->heap_addr,
                         HDstrlen(efl->slot[u].name) + 1, efl->slot[u].name);
 
@@ -1372,16 +1372,16 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
                 HGOTO_ERROR(H5E_EFL, H5E_CANTINIT, FAIL, "unable to insert URL into name heap")
 
             efl->slot[u].name_offset = offset;
-        }
+        } /* end for */
 
-        if (H5O_append(file, dxpl_id, oh, H5O_EFL_ID, H5O_MSG_FLAG_CONSTANT, efl, &oh_flags) < 0)
+        if(H5O_append(file, dxpl_id, oh, H5O_EFL_ID, H5O_MSG_FLAG_CONSTANT, 0, efl, &oh_flags) < 0)
             HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update external file list message")
-    }
+    } /* end if */
 
-    /* Update layout message */
+    /* Create layout message */
     /* (Don't make layout message constant unless allocation time is early, since space may not be allocated) */
-    /* Note: this is relying on H5D_alloc_storage not calling H5O_modify during dataset creation */
-    if (H5D_COMPACT != layout->type && H5O_append(file, dxpl_id, oh, H5O_LAYOUT_ID, (alloc_time == H5D_ALLOC_TIME_EARLY ? H5O_MSG_FLAG_CONSTANT : 0), layout, &oh_flags) < 0)
+    /* Note: this is relying on H5D_alloc_storage not calling H5O_write during dataset creation */
+    if(H5O_append(file, dxpl_id, oh, H5O_LAYOUT_ID, ((alloc_time == H5D_ALLOC_TIME_EARLY && H5D_COMPACT != layout->type) ? H5O_MSG_FLAG_CONSTANT : 0), 0, layout, &oh_flags) < 0)
          HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update layout")
 
 #ifdef H5O_ENABLE_BOGUS
@@ -1393,7 +1393,7 @@ H5D_update_entry_info(H5F_t *file, hid_t dxpl_id, H5D_t *dset)
 #endif /* H5O_ENABLE_BOGUS */
 
     /* Add a modification time message. */
-    if (H5O_touch_oh(file, dxpl_id, oh, TRUE, &oh_flags) < 0)
+    if(H5O_touch_oh(file, dxpl_id, oh, TRUE, &oh_flags) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update modification time message")
 
 done:
@@ -2170,7 +2170,7 @@ H5D_close(H5D_t *dataset)
             case H5D_COMPACT:
                 /* Update header message of layout for compact dataset. */
                 if(dataset->shared->layout.u.compact.dirty) {
-                    if(H5O_modify(&(dataset->oloc), H5O_LAYOUT_ID, 0, 0, H5O_UPDATE_TIME, &(dataset->shared->layout), H5AC_dxpl_id)<0)
+                    if(H5O_write(&(dataset->oloc), H5O_LAYOUT_ID, 0, 0, H5O_UPDATE_TIME, &(dataset->shared->layout), H5AC_dxpl_id) < 0)
                         HGOTO_ERROR(H5E_DATASET, H5E_CANTRELEASE, FAIL, "unable to update layout message")
                     dataset->shared->layout.u.compact.dirty = FALSE;
                 } /* end if */
@@ -2305,7 +2305,7 @@ H5D_extend (H5D_t *dataset, const hsize_t *size, hid_t dxpl_id)
 
     if (changed>0){
 	/* Save the new dataspace in the file if necessary */
-	if(H5S_modify (&(dataset->oloc), space, TRUE, dxpl_id) < 0)
+	if(H5S_write(&(dataset->oloc), space, TRUE, dxpl_id) < 0)
 	    HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "unable to update file with new dataspace")
 
         /* Update the index values for the cached chunks for this dataset */
@@ -2438,7 +2438,7 @@ H5D_get_file (const H5D_t *dset)
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_alloc_storage (H5F_t *f, hid_t dxpl_id, H5D_t *dset/*in,out*/, H5D_time_alloc_t time_alloc,
+H5D_alloc_storage(H5F_t *f, hid_t dxpl_id, H5D_t *dset/*in,out*/, H5D_time_alloc_t time_alloc,
     hbool_t update_time, hbool_t full_overwrite)
 {
     struct H5O_layout_t *layout;        /* The dataset's layout information */
@@ -2563,7 +2563,7 @@ H5D_alloc_storage (H5F_t *f, hid_t dxpl_id, H5D_t *dset/*in,out*/, H5D_time_allo
          * set the address.  (this is improves forward compatibility).
          */
         if(time_alloc != H5D_ALLOC_CREATE && addr_set)
-            if(H5O_modify(&(dset->oloc), H5O_LAYOUT_ID, 0, H5O_MSG_FLAG_CONSTANT, update_time, &(dset->shared->layout), dxpl_id) < 0)
+            if(H5O_write(&(dset->oloc), H5O_LAYOUT_ID, 0, H5O_MSG_FLAG_CONSTANT, update_time, &(dset->shared->layout), dxpl_id) < 0)
                 HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to update layout message")
     } /* end if */
 
@@ -3353,7 +3353,7 @@ H5D_set_extent(H5D_t *dset, const hsize_t *size, hid_t dxpl_id)
       *-------------------------------------------------------------------------
       */
         /* Save the new dataspace in the file if necessary */
-        if(H5S_modify(&(dset->oloc), space, TRUE, dxpl_id) < 0)
+        if(H5S_write(&(dset->oloc), space, TRUE, dxpl_id) < 0)
             HGOTO_ERROR(H5E_DATASET, H5E_WRITEERROR, FAIL, "unable to update file with new dataspace")
 
         /* Update the index values for the cached chunks for this dataset */
@@ -3468,7 +3468,7 @@ H5D_flush(const H5F_t *f, hid_t dxpl_id, unsigned flags)
 
                 case H5D_COMPACT:
                     if(dataset->shared->layout.u.compact.dirty) {
-                        if(H5O_modify(&(dataset->oloc), H5O_LAYOUT_ID, 0, 0, H5O_UPDATE_TIME, &(dataset->shared->layout), dxpl_id)<0)
+                        if(H5O_write(&(dataset->oloc), H5O_LAYOUT_ID, 0, 0, H5O_UPDATE_TIME, &(dataset->shared->layout), dxpl_id)<0)
                             HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "unable to update layout message")
                         dataset->shared->layout.u.compact.dirty = FALSE;
                     } /* end if */
diff --git a/src/H5Gcompact.c b/src/H5Gcompact.c
index 7e7266a..e321155 100644
--- a/src/H5Gcompact.c
+++ b/src/H5Gcompact.c
@@ -194,7 +194,7 @@ H5G_compact_insert(H5O_loc_t *grp_oloc, H5O_link_t *obj_lnk,
     HDassert(obj_lnk);
 
     /* Insert link message into group */
-    if(H5O_modify(grp_oloc, H5O_LINK_ID, H5O_NEW_MESG, 0, H5O_UPDATE_TIME, obj_lnk, dxpl_id) < 0)
+    if(H5O_msg_create(grp_oloc, H5O_LINK_ID, 0, H5O_UPDATE_TIME, obj_lnk, dxpl_id) < 0)
         HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "can't create message")
 
 done:
diff --git a/src/H5Gdeprec.c b/src/H5Gdeprec.c
index 3be71a8..5163748 100644
--- a/src/H5Gdeprec.c
+++ b/src/H5Gdeprec.c
@@ -619,7 +619,7 @@ H5G_set_comment(H5G_loc_t *loc, const char *name, const char *buf, hid_t dxpl_id
     if(buf && *buf) {
         /* Casting away const OK -QAK */
 	comment.s = (char *)buf;
-	if(H5O_modify(obj_loc.oloc, H5O_NAME_ID, H5O_NEW_MESG, 0, H5O_UPDATE_TIME, &comment, dxpl_id) < 0)
+	if(H5O_msg_create(obj_loc.oloc, H5O_NAME_ID, 0, H5O_UPDATE_TIME, &comment, dxpl_id) < 0)
 	    HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to set comment object header message")
     } /* end if */
 
diff --git a/src/H5Gobj.c b/src/H5Gobj.c
index 32febfc..8a223a7 100644
--- a/src/H5Gobj.c
+++ b/src/H5Gobj.c
@@ -194,11 +194,11 @@ H5G_obj_create(H5F_t *f, hid_t dxpl_id, const H5O_ginfo_t *ginfo,
     /* Check for format of group to create */
     if(use_latest_format) {
         /* Insert link info message */
-        if(H5O_modify(oloc, H5O_LINFO_ID, H5O_NEW_MESG, 0, 0, linfo, dxpl_id) < 0)
+        if(H5O_msg_create(oloc, H5O_LINFO_ID, 0, 0, linfo, dxpl_id) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "can't create message")
 
         /* Insert group info message */
-        if(H5O_modify(oloc, H5O_GINFO_ID, H5O_NEW_MESG, H5O_MSG_FLAG_CONSTANT, H5O_UPDATE_TIME, ginfo, dxpl_id) < 0)
+        if(H5O_msg_create(oloc, H5O_GINFO_ID, H5O_MSG_FLAG_CONSTANT, H5O_UPDATE_TIME, ginfo, dxpl_id) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "can't create message")
     } /* end if */
     else {
@@ -482,11 +482,11 @@ H5G_obj_insert(H5O_loc_t *grp_oloc, const char *name, H5O_link_t *obj_lnk,
             /* Convert group to "new format" group, in order to hold the information */
 
             /* Insert link info message */
-            if(H5O_modify(grp_oloc, H5O_LINFO_ID, H5O_NEW_MESG, 0, 0, &new_linfo, dxpl_id) < 0)
+            if(H5O_msg_create(grp_oloc, H5O_LINFO_ID, 0, 0, &new_linfo, dxpl_id) < 0)
                 HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "can't create message")
 
             /* Insert group info message */
-            if(H5O_modify(grp_oloc, H5O_GINFO_ID, H5O_NEW_MESG, H5O_MSG_FLAG_CONSTANT, 0, &new_ginfo, dxpl_id) < 0)
+            if(H5O_msg_create(grp_oloc, H5O_GINFO_ID, H5O_MSG_FLAG_CONSTANT, H5O_UPDATE_TIME, &new_ginfo, dxpl_id) < 0)
                 HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "can't create message")
 
             /* Set up user data for iteration */
@@ -541,7 +541,7 @@ H5G_obj_insert(H5O_loc_t *grp_oloc, const char *name, H5O_link_t *obj_lnk,
     /* Increment the number of objects in this group */
     if(!use_old_format) {
         linfo.nlinks++;
-        if(H5O_modify(grp_oloc, H5O_LINFO_ID, 0, 0, H5O_UPDATE_TIME, &linfo, dxpl_id) < 0)
+        if(H5O_write(grp_oloc, H5O_LINFO_ID, 0, 0, H5O_UPDATE_TIME, &linfo, dxpl_id) < 0)
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "can't update link info message")
     } /* end if */
 
@@ -906,10 +906,26 @@ H5G_obj_remove_update_linfo(H5O_loc_t *oloc, H5O_linfo_t *linfo, hid_t dxpl_id)
 
                 /* If ok, insert links as link messages */
                 if(can_convert) {
+                    struct H5O_t *oh = NULL;      /* Pointer to group's object header */
+                    unsigned oh_flags = H5AC__DIRTIED_FLAG;
+
+                    /* Get a pointer to the object header itself */
+                    if((oh = H5O_protect(oloc, dxpl_id)) == NULL)
+                        HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to protect dataset object header")
+
                     /* Insert link messages into group */
                     for(u = 0; u < linfo->nlinks; u++)
-                        if(H5O_modify(oloc, H5O_LINK_ID, H5O_NEW_MESG, 0, H5O_UPDATE_TIME, &(ltable.lnks[u]), dxpl_id) < 0)
+                        if(H5O_append(oloc->file, dxpl_id, oh, H5O_LINK_ID, 0, H5O_UPDATE_TIME, &(ltable.lnks[u]), &oh_flags) < 0) {
+                            /* Release object header */
+                            if(H5O_unprotect(oloc, oh, dxpl_id, oh_flags) < 0)
+                                HDONE_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to unprotect dataset object header")
+
                             HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "can't create message")
+                        } /* end if */
+
+                    /* Release object header */
+                    if(H5O_unprotect(oloc, oh, dxpl_id, oh_flags) < 0)
+                        HDONE_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to unprotect dataset object header")
 
                     /* Remove the dense storage */
                     if(H5G_dense_delete(oloc->file, dxpl_id, linfo, FALSE) < 0)
@@ -924,7 +940,7 @@ H5G_obj_remove_update_linfo(H5O_loc_t *oloc, H5O_linfo_t *linfo, hid_t dxpl_id)
     } /* end if */
 
     /* Update link info in the object header */
-    if(H5O_modify(oloc, H5O_LINFO_ID, 0, 0, H5O_UPDATE_TIME, linfo, dxpl_id) < 0)
+    if(H5O_write(oloc, H5O_LINFO_ID, 0, 0, H5O_UPDATE_TIME, linfo, dxpl_id) < 0)
         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "can't update link info message")
 
 done:
diff --git a/src/H5Gstab.c b/src/H5Gstab.c
index c617d6e..2e41dc5 100644
--- a/src/H5Gstab.c
+++ b/src/H5Gstab.c
@@ -186,7 +186,7 @@ H5G_stab_create(H5O_loc_t *grp_oloc, hid_t dxpl_id, const H5O_ginfo_t *ginfo,
      * Insert the symbol table message into the object header and the symbol
      * table entry.
      */
-    if(H5O_modify(grp_oloc, H5O_STAB_ID, H5O_NEW_MESG, 0, H5O_UPDATE_TIME, stab, dxpl_id) < 0)
+    if(H5O_msg_create(grp_oloc, H5O_STAB_ID, 0, H5O_UPDATE_TIME, stab, dxpl_id) < 0)
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "can't create message")
 
 done:
diff --git a/src/H5O.c b/src/H5O.c
index 253e535..00fc201 100644
--- a/src/H5O.c
+++ b/src/H5O.c
@@ -54,7 +54,7 @@
         const H5O_msg_class_t	*decode_type;                                 \
                                                                               \
         /* Check for shared message */                                        \
-        if ((MSG)->flags & H5O_MSG_FLAG_SHARED)                                   \
+        if((MSG)->flags & H5O_MSG_FLAG_SHARED)                                \
             decode_type = H5O_MSG_SHARED;                                     \
         else                                                                  \
             decode_type = (MSG)->type;                                        \
@@ -123,12 +123,12 @@ static void *H5O_read_real(H5F_t *f, H5O_t *oh, unsigned type_id, int sequence,
     void *mesg, hid_t dxpl_id);
 static unsigned H5O_find_in_ohdr(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
                                  const H5O_msg_class_t **type_p, int sequence);
-static int H5O_modify_real(H5O_loc_t *loc, const H5O_msg_class_t *type,
-    int overwrite, unsigned flags, unsigned update_flags, const void *mesg,
+static herr_t H5O_write_real(H5O_loc_t *loc, const H5O_msg_class_t *type,
+    unsigned overwrite, unsigned flags, unsigned update_flags, const void *mesg,
     hid_t dxpl_id);
-static int H5O_append_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
-    const H5O_msg_class_t *type, unsigned flags, const void *mesg,
-    unsigned * oh_flags_ptr);
+static herr_t H5O_append_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
+    const H5O_msg_class_t *type, unsigned mesg_flags, unsigned update_flags,
+    const void *mesg, unsigned * oh_flags_ptr);
 static herr_t H5O_remove_real(const H5O_loc_t *loc, const H5O_msg_class_t *type,
     int sequence, H5O_operator_t op, void *op_data, hbool_t adj_link, hid_t dxpl_id);
 static herr_t H5O_delete_oh(H5F_t *f, hid_t dxpl_id, H5O_t *oh);
@@ -136,9 +136,9 @@ static unsigned H5O_new_mesg(H5F_t *f, H5O_t *oh, unsigned *flags,
     const H5O_msg_class_t *orig_type, const void *orig_mesg, H5O_shared_t *sh_mesg,
     const H5O_msg_class_t **new_type, const void **new_mesg, hid_t dxpl_id,
     unsigned * oh_flags_ptr);
-static herr_t H5O_write_mesg(H5O_t *oh, unsigned idx, const H5O_msg_class_t *type,
-    const void *mesg, unsigned flags, unsigned update_flags,
-    unsigned * oh_flags_ptr);
+static herr_t H5O_write_mesg(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned idx,
+    const H5O_msg_class_t *type, const void *mesg, unsigned flags,
+    unsigned update_flags, unsigned * oh_flags_ptr);
 static herr_t H5O_iterate_real(const H5O_loc_t *loc, const H5O_msg_class_t *type,
     H5AC_protect_t prot, hbool_t internal, H5O_mesg_operator_t op, void *op_data, hid_t dxpl_id);
 static const H5O_obj_class_t *H5O_obj_class(H5O_loc_t *loc, hid_t dxpl_id);
@@ -1724,30 +1724,21 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5O_modify
+ * Function:	H5O_write
  *
  * 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_MESG (-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).
- *
- *              The UPDATE_TIME argument is a boolean that allows the caller
- *              to skip updating the modification time.  This is useful when
- *              several calls to H5O_modify will be made in a sequence.
  *
- * Return:	Success:	The sequence number of the message that
- *				was modified or created.
+ *		The OVERWRITE argument is a sequence number of a
+ *		message to overwrite (usually zero).
+ *		If the message to overwrite doesn't exist then this routine
+ *              fails.
+ *
+ *              The UPDATE_FLAGS argument are flags that allow the caller
+ *              to skip updating the modification time or reseting the message
+ *              data.  This is useful when several calls to H5O_write will be
+ *              made in a sequence.
+ *
+ * Return:	Success:	Non-negative
  *
  *		Failure:	Negative
  *
@@ -1759,15 +1750,15 @@ done:
  */
 /* JAMES: this will probably get put through its paces when extending shared
  * dataspaces */
-int
-H5O_modify(H5O_loc_t *loc, unsigned type_id, int overwrite,
+herr_t
+H5O_write(H5O_loc_t *loc, unsigned type_id, unsigned overwrite,
    unsigned mesg_flags, unsigned update_flags, void *mesg, hid_t dxpl_id)
 {
-    const H5O_msg_class_t *type;            /* Actual H5O class type for the ID */
-    htri_t shared_mess;
-    int	ret_value;              /* Return value */
+    const H5O_msg_class_t *type;        /* Actual H5O class type for the ID */
+    htri_t shared_mesg;                 /* Whether the message should be shared */
+    herr_t ret_value = SUCCEED;         /* Return value */
 
-    FUNC_ENTER_NOAPI(H5O_modify, FAIL)
+    FUNC_ENTER_NOAPI(H5O_write, FAIL)
 
     /* check args */
     HDassert(loc);
@@ -1780,48 +1771,37 @@ H5O_modify(H5O_loc_t *loc, unsigned type_id, int overwrite,
     HDassert(0 == (mesg_flags & ~H5O_MSG_FLAG_BITS));
 
     /* Should this message be written as a SOHM? */
-    if((shared_mess = H5SM_try_share(loc->file, dxpl_id, type_id, mesg)) >0)
-    {
+    if((shared_mesg = H5SM_try_share(loc->file, dxpl_id, type_id, mesg)) > 0)
         /* Mark the message as shared */
         mesg_flags |= H5O_MSG_FLAG_SHARED;
-
-    } else if(shared_mess < 0)
+    else if(shared_mesg < 0)
 	HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, FAIL, "error while trying to share message");
 
     /* Call the "real" modify routine */
-    if((ret_value = H5O_modify_real(loc, type, overwrite, mesg_flags, update_flags, mesg, dxpl_id)) < 0)
+    if(H5O_write_real(loc, type, overwrite, mesg_flags, update_flags, mesg, dxpl_id) < 0)
 	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to write object header message")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5O_modify() */
+} /* end H5O_write() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5O_modify_real
+ * Function:	H5O_write_real
  *
  * 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_MESG (-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).
- *
- *              The UPDATE_TIME argument is a boolean that allows the caller
- *              to skip updating the modification time.  This is useful when
- *              several calls to H5O_modify will be made in a sequence.
  *
- * Return:	Success:	The sequence number of the message that
- *				was modified or created.
+ *		The OVERWRITE argument is a sequence number of a
+ *		message to overwrite (usually zero).
+ *		If the message to overwrite doesn't exist then this routine
+ *              fails.
+ *
+ *              The UPDATE_FLAGS argument are flags that allow the caller
+ *              to skip updating the modification time or reseting the message
+ *              data.  This is useful when several calls to H5O_write will be
+ *              made in a sequence.
+ *
+ * Return:	Success:	Non-negative
  *
  *		Failure:	Negative
  *
@@ -1831,21 +1811,21 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-static int
-H5O_modify_real(H5O_loc_t *loc, const H5O_msg_class_t *type, int overwrite,
+static herr_t
+H5O_write_real(H5O_loc_t *loc, const H5O_msg_class_t *type, unsigned overwrite,
    unsigned mesg_flags, unsigned update_flags, const void *mesg, hid_t dxpl_id)
 {
     H5O_t		*oh = NULL;
     unsigned		oh_flags = H5AC__NO_FLAGS_SET;
-    int		        sequence;
+    int	        	sequence;       /* Sequence # of message type to modify */
     unsigned		idx;            /* Index of message to modify */
     H5O_mesg_t         *idx_msg;        /* Pointer to message to modify */
     H5O_shared_t	sh_mesg;
-    const H5O_msg_class_t *write_type = type;    /* Type of message to be written */
-    const void          *write_mesg = mesg;    /* Actual message being written */
-    int		        ret_value;
+    const H5O_msg_class_t *write_type = type;   /* Type of message to be written */
+    const void          *write_mesg = mesg;     /* Actual message being written */
+    herr_t	        ret_value = SUCCEED;    /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5O_modify_real)
+    FUNC_ENTER_NOAPI_NOINIT(H5O_write_real)
 
     /* check args */
     HDassert(loc);
@@ -1864,33 +1844,19 @@ H5O_modify_real(H5O_loc_t *loc, const H5O_msg_class_t *type, int overwrite,
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
     /* Count similar messages */
-    for(idx = 0, sequence = -1, idx_msg=&oh->mesg[0]; idx < oh->nmesgs; idx++, idx_msg++) {
+    for(idx = 0, sequence = -1, idx_msg = &oh->mesg[0]; idx < oh->nmesgs; idx++, idx_msg++) {
 	if(type->id != idx_msg->type->id)
             continue;
-	if(++sequence == overwrite)
+	if(++sequence == (int)overwrite)
             break;
     } /* end for */
 
     /* Was the right message found? */
-    if(overwrite >= 0 && (idx >= oh->nmesgs || sequence != overwrite)) {
-	/* No, 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")
-    } /* end if */
+    if(sequence != (int)overwrite)
+        HGOTO_ERROR(H5E_OHDR, H5E_NOTFOUND, FAIL, "message not found")
 
-    /* Check for creating new message */
-    if(overwrite < 0) {
-        /* Create a new message */
-        /* JAMES: why is sh_mesg passed in here?  Is it ever used? */
-        if((idx = H5O_new_mesg(loc->file, oh, &mesg_flags, type, mesg, &sh_mesg, &write_type, &write_mesg, dxpl_id, &oh_flags)) == UFAIL)
-	    HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to create new message")
-
-        /* Set the correct sequence number for the message created */
-	sequence++;
-
-    } else if(oh->mesg[idx].flags & H5O_MSG_FLAG_CONSTANT) {
+    /* Check for modifying a constant message */
+    if(oh->mesg[idx].flags & H5O_MSG_FLAG_CONSTANT) {
 	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to modify constant message")
     } else if(oh->mesg[idx].flags & H5O_MSG_FLAG_SHARED) {
         /* This message is shared, but it's being modified.  This is valid if
@@ -1898,54 +1864,97 @@ H5O_modify_real(H5O_loc_t *loc, const H5O_msg_class_t *type, int overwrite,
          * First, make sure it's not a committed message; these can't ever
          * be modified.
          */
-        if(((H5O_shared_t*) oh->mesg[idx].native)->flags & H5O_COMMITTED_FLAG)
+        if(((H5O_shared_t*)oh->mesg[idx].native)->flags & H5O_COMMITTED_FLAG)
             HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to modify committed message")
 
         /* Remove the old message from the SOHM index */
         if(H5SM_try_delete(loc->file, dxpl_id, oh->mesg[idx].type->id, oh->mesg[idx].native) < 0)
             HGOTO_ERROR (H5E_OHDR, H5E_CANTFREE, FAIL, "unable to delete message from SOHM table")
 
-        /* Now this message is no longer shared and we can safely overwrite
-         * it.
+        /* Now this message is no longer shared and we can safely overwrite it.
          * We need to make sure that the message we're writing is shared,
          * though, and that the library doesn't try to reset the current
          * message like it would in a normal overwrite (this message is
-         * realy a shared pointer, not a real
-         * message).
+         * realy a shared pointer, not a real message).
          * JAMES: will this break if a shared message is overwritten with a larger
          * non-shared message?
          */
         HDassert(H5O_is_shared(type->id, mesg) > 0); /* JAMES: this should work with
                                                       * replacement messages that aren't shared, too. */
 
-        if(H5O_get_share(type->id, loc->file, mesg, &sh_mesg)<0)
+        if(H5O_get_share(type->id, loc->file, mesg, &sh_mesg) < 0)
               HGOTO_ERROR (H5E_OHDR, H5E_BADMESG, FAIL, "can't get shared message")
 
         /* Instead of writing the original message, write a shared message */
-        write_type = H5O_msg_class_g[H5O_SHARED_ID];
+        write_type = H5O_MSG_SHARED;
         write_mesg = &sh_mesg;
-    }
+    } /* end if */
 
     /* Write the information to the message */
-    if(H5O_write_mesg(oh, idx, write_type, write_mesg, mesg_flags, update_flags, &oh_flags) < 0)
+    if(H5O_write_mesg(loc->file, dxpl_id, oh, idx, write_type, write_mesg, mesg_flags, update_flags, &oh_flags) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to write message")
-
-    /* Update the modification time message if any */
-    if(update_flags & H5O_UPDATE_TIME)
-        H5O_touch_oh(loc->file, dxpl_id, oh, FALSE, &oh_flags);
 #ifdef H5O_DEBUG
 H5O_assert(oh);
 #endif /* H5O_DEBUG */
 
-    /* Set return value */
-    ret_value = sequence;
+done:
+    if(oh && H5AC_unprotect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, oh, oh_flags) < 0)
+	HDONE_ERROR(H5E_OHDR, H5E_PROTECT, FAIL, "unable to release object header")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_write_real() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_msg_create
+ *
+ * Purpose:	Create a new object header message
+ *
+ * Return:	Success:	The sequence number of the message that
+ *				was created.
+ *
+ *		Failure:	Negative
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@hdfgroup.org
+ *		Dec  1 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5O_msg_create(H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
+    unsigned update_flags, void *mesg, hid_t dxpl_id)
+{
+    H5O_t *oh = NULL;                   /* Object header */
+    unsigned oh_flags = H5AC__NO_FLAGS_SET;     /* Metadata cache flags for object header */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI(H5O_msg_create, FAIL)
+
+    /* check args */
+    HDassert(loc);
+    HDassert(type_id < NELMTS(H5O_msg_class_g));
+    HDassert(0 == (mesg_flags & ~H5O_MSG_FLAG_BITS));
+    HDassert(mesg);
+
+    /* Check for write access on the file */
+    if(0 == (loc->file->intent & H5F_ACC_RDWR))
+	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "no write intent on file")
+
+    /* Protect the object header */
+    if(NULL == (oh = H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_WRITE)))
+	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unable to load object header")
+
+    /* Go append message to object header */
+    if(H5O_append(loc->file, dxpl_id, oh, type_id, mesg_flags, update_flags, mesg, &oh_flags) < 0)
+	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to append to object header")
 
 done:
     if(oh && H5AC_unprotect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, oh, oh_flags) < 0)
 	HDONE_ERROR(H5E_OHDR, H5E_PROTECT, FAIL, "unable to release object header")
 
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5O_modify_real() */
+} /* end H5O_msg_create() */
 
 
 /*-------------------------------------------------------------------------
@@ -2033,8 +2042,9 @@ done:
 /*-------------------------------------------------------------------------
  * Function:	H5O_append
  *
- * Purpose:	Simplified version of H5O_modify, used when creating a new
- *              object header message (usually during object creation)
+ * Purpose:	Simplified version of H5O_msg_create, used when creating a new
+ *              object header message (usually during object creation) and
+ *              several messages will be added to the object header at once.
  *
  * Return:	Success:	The sequence number of the message that
  *				was created.
@@ -2047,13 +2057,13 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-int
+herr_t
 H5O_append(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned type_id, unsigned mesg_flags,
-    void *mesg, unsigned * oh_flags_ptr)
+    unsigned update_flags, void *mesg, unsigned * oh_flags_ptr)
 {
     const H5O_msg_class_t *type;        /* Actual H5O class type for the ID */
-    htri_t shared_mess;              /* Should this message be stored in the Shared Message table? */
-    int	ret_value;                      /* Return value */
+    htri_t shared_mesg;                 /* Should this message be stored in the Shared Message table? */
+    herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI(H5O_append, FAIL)
 
@@ -2068,15 +2078,13 @@ H5O_append(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned type_id, unsigned mesg_f
     HDassert(oh_flags_ptr);
 
     /* Should this message be written as a SOHM? */
-    if((shared_mess = H5SM_try_share(f, dxpl_id, type_id, mesg)) >0)
-    {
+    if((shared_mesg = H5SM_try_share(f, dxpl_id, type_id, mesg)) > 0)
         /* Mark the message as shared */
         mesg_flags |= H5O_MSG_FLAG_SHARED;
-    }
-    else if(shared_mess < 0)
+    else if(shared_mesg < 0)
 	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "error determining if message should be shared");
 
-    if((ret_value = H5O_append_real( f, dxpl_id, oh, type, mesg_flags, mesg, oh_flags_ptr)) < 0)
+    if(H5O_append_real(f, dxpl_id, oh, type, mesg_flags, update_flags, mesg, oh_flags_ptr) < 0)
 	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to append to object header")
 
 done:
@@ -2087,8 +2095,9 @@ done:
 /*-------------------------------------------------------------------------
  * Function:	H5O_append_real
  *
- * Purpose:	Simplified version of H5O_modify, used when creating a new
- *              object header message (usually during object creation)
+ * Purpose:	Simplified version of H5O_msg_create, used when creating a new
+ *              object header message (usually during object creation) and
+ *              several messages will be added to the object header at once.
  *
  * Return:	Success:	The sequence number of the message that
  *				was created.
@@ -2101,13 +2110,13 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-static int
+static herr_t
 H5O_append_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh, const H5O_msg_class_t *type,
-    unsigned mesg_flags, const void *mesg, unsigned * oh_flags_ptr)
+    unsigned mesg_flags, unsigned update_flags, const void *mesg, unsigned * oh_flags_ptr)
 {
     unsigned		idx;            /* Index of message to modify */
     H5O_shared_t	sh_mesg;
-    int		        ret_value;
+    herr_t	        ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5O_append_real)
 
@@ -2124,15 +2133,12 @@ H5O_append_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh, const H5O_msg_class_t *type,
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to create new message")
 
     /* Write the information to the message */
-    if(H5O_write_mesg(oh, idx, type, mesg, mesg_flags, 0, oh_flags_ptr) < 0)
+    if(H5O_write_mesg(f, dxpl_id, oh, idx, type, mesg, mesg_flags, update_flags, oh_flags_ptr) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to write message")
 #ifdef H5O_DEBUG
 H5O_assert(oh);
 #endif /* H5O_DEBUG */
 
-    /* Set return value */
-    ret_value = idx;
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_append_real () */
@@ -2175,20 +2181,21 @@ H5O_new_mesg(H5F_t *f, H5O_t *oh, unsigned *mesg_flags, const H5O_msg_class_t *o
 
     /* Check for shared message */
     if(*mesg_flags & H5O_MSG_FLAG_SHARED) {
-        HDmemset(sh_mesg, 0, sizeof(H5O_shared_t));
-
-        if ((NULL == orig_type->is_shared) || (NULL == orig_type->get_share))
-            HGOTO_ERROR(H5E_OHDR, H5E_UNSUPPORTED, UFAIL, "message class is not sharable");
-        if ((is_shared = (orig_type->is_shared)(orig_mesg)) == FALSE) {
+        if((NULL == orig_type->is_shared) || (NULL == orig_type->get_share))
+            HGOTO_ERROR(H5E_OHDR, H5E_UNSUPPORTED, UFAIL, "message class is not sharable")
+        if((is_shared = (orig_type->is_shared)(orig_mesg)) == FALSE) {
             /*
              * If the message isn't shared then turn off the shared bit
              * and treat it as an unshared message.
              */
             *mesg_flags &= ~H5O_MSG_FLAG_SHARED;
+            *new_type = orig_type;
+            *new_mesg = orig_mesg;
         } else if(is_shared > 0) {
             /* Message is shared. Get shared message, change message type,
              * and use shared information */
-            if ((orig_type->get_share)(f, orig_mesg, sh_mesg/*out*/) < 0)
+            HDmemset(sh_mesg, 0, sizeof(H5O_shared_t));
+            if((orig_type->get_share)(f, orig_mesg, sh_mesg/*out*/) < 0)
                 HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, UFAIL, "can't get shared message")
 
             *new_type = H5O_MSG_SHARED;
@@ -2232,9 +2239,9 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_write_mesg(H5O_t *oh, unsigned idx, const H5O_msg_class_t *type,
-    const void *mesg, unsigned mesg_flags, unsigned update_flags,
-    unsigned * oh_flags_ptr)
+H5O_write_mesg(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned idx,
+    const H5O_msg_class_t *type, const void *mesg, unsigned mesg_flags,
+    unsigned update_flags, unsigned *oh_flags_ptr)
 {
     H5O_mesg_t         *idx_msg;        /* Pointer to message to modify */
     herr_t      ret_value = SUCCEED;    /* Return value */
@@ -2242,6 +2249,7 @@ H5O_write_mesg(H5O_t *oh, unsigned idx, const H5O_msg_class_t *type,
     FUNC_ENTER_NOAPI_NOINIT(H5O_write_mesg)
 
     /* check args */
+    HDassert(f);
     HDassert(oh);
     HDassert(type);
     HDassert(mesg);
@@ -2258,8 +2266,15 @@ H5O_write_mesg(H5O_t *oh, unsigned idx, const H5O_msg_class_t *type,
     if(NULL == (idx_msg->native = (type->copy)(mesg, idx_msg->native, update_flags)))
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to copy message to object header")
 
+    /* Update the message flags and mark the message as modified */
     idx_msg->flags = mesg_flags;
     idx_msg->dirty = TRUE;
+
+    /* Update the modification time message if any */
+    if(update_flags & H5O_UPDATE_TIME)
+        H5O_touch_oh(f, dxpl_id, oh, FALSE, oh_flags_ptr);
+
+    /* Mark the object header as modified */
     *oh_flags_ptr |= H5AC__DIRTIED_FLAG;
 
 done:
@@ -2613,7 +2628,7 @@ done:
  */
 static herr_t
 H5O_remove_cb(H5O_t *oh, H5O_mesg_t *mesg/*in,out*/, 
-    unsigned sequence, unsigned * oh_flags_ptr, void *_udata/*in,out*/)
+    unsigned sequence, unsigned *oh_flags_ptr, void *_udata/*in,out*/)
 {
     H5O_iter_ud1_t *udata = (H5O_iter_ud1_t *)_udata;   /* Operator user data */
     htri_t try_remove = FALSE;         /* Whether to try removing a message */
diff --git a/src/H5Odtype.c b/src/H5Odtype.c
index 1a3fd4c..feae7e7 100644
--- a/src/H5Odtype.c
+++ b/src/H5Odtype.c
@@ -33,11 +33,9 @@ static void *H5O_dtype_copy(const void *_mesg, void *_dest, unsigned update_flag
 static size_t H5O_dtype_size(const H5F_t *f, const void *_mesg);
 static herr_t H5O_dtype_reset(void *_mesg);
 static herr_t H5O_dtype_free(void *_mesg);
-static herr_t H5O_dtype_get_share(H5F_t *f, const void *_mesg,
-    H5O_shared_t *sh);
-static herr_t H5O_dtype_set_share(H5F_t *f, void *_mesg,
-    const H5O_shared_t *sh);
-static herr_t H5O_dtype_is_shared (const void *_mesg);
+static herr_t H5O_dtype_get_share(H5F_t *f, const void *_mesg, H5O_shared_t *sh);
+static herr_t H5O_dtype_set_share(H5F_t *f, void *_mesg, const H5O_shared_t *sh);
+static herr_t H5O_dtype_is_shared(const void *_mesg);
 static herr_t H5O_dtype_pre_copy_file(H5F_t *file_src, const H5O_msg_class_t *type,
     const void *mesg_src, hbool_t *deleted, const H5O_copy_t *cpy_info, void *_udata);
 static herr_t H5O_dtype_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
diff --git a/src/H5Olayout.c b/src/H5Olayout.c
index 88a41e7..f8ec192 100644
--- a/src/H5Olayout.c
+++ b/src/H5Olayout.c
@@ -315,8 +315,11 @@ H5O_layout_encode(H5F_t *f, uint8_t *p, const void *_mesg)
             UINT16ENCODE(p, mesg->u.compact.size);
 
             /* Raw data */
-            if(mesg->u.compact.size > 0 && mesg->u.compact.buf) {
-                HDmemcpy(p, mesg->u.compact.buf, mesg->u.compact.size);
+            if(mesg->u.compact.size > 0) {
+                if(mesg->u.compact.buf)
+                    HDmemcpy(p, mesg->u.compact.buf, mesg->u.compact.size);
+                else
+                    HDmemset(p, 0, mesg->u.compact.size);
                 p += mesg->u.compact.size;
             } /* end if */
             break;
diff --git a/src/H5Oprivate.h b/src/H5Oprivate.h
index dcddfa2..acb291f 100644
--- a/src/H5Oprivate.h
+++ b/src/H5Oprivate.h
@@ -63,7 +63,6 @@ typedef uint64_t H5SM_fheap_id_t;
 
 /* Object header macros */
 #define H5O_MESG_MAX_SIZE	65536	/*max obj header message size	     */
-#define H5O_NEW_MESG	(-1)		/*new message			     */
 #define H5O_ALL		(-1)		/* Operate on all messages of type   */
 #define H5O_FIRST	(-2)		/* Operate on first message of type  */
 
@@ -389,15 +388,18 @@ H5_DLL int H5O_count(H5O_loc_t *loc, unsigned type_id, hid_t dxpl_id);
 H5_DLL htri_t H5O_exists(H5O_loc_t *loc, unsigned type_id, int sequence,
     hid_t dxpl_id);
 H5_DLL htri_t H5O_exists_oh(struct H5O_t *oh, unsigned type_id, int sequence);
+H5_DLL herr_t H5O_msg_create(H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
+    unsigned update_flags, void *mesg, hid_t dxpl_id);
 H5_DLL void *H5O_read(const H5O_loc_t *loc, unsigned type_id, int sequence,
     void *mesg, hid_t dxpl_id);
-H5_DLL int H5O_modify(H5O_loc_t *loc, unsigned type_id,
-    int overwrite, unsigned flags, unsigned update_flags, void *mesg, hid_t dxpl_id);
+H5_DLL herr_t H5O_write(H5O_loc_t *loc, unsigned type_id, unsigned overwrite,
+    unsigned flags, unsigned update_flags, void *mesg, hid_t dxpl_id);
 H5_DLL struct H5O_t *H5O_protect(H5O_loc_t *loc, hid_t dxpl_id);
 H5_DLL herr_t H5O_unprotect(H5O_loc_t *loc, struct H5O_t *oh, hid_t dxpl_id,
     unsigned oh_flags);
-H5_DLL int H5O_append(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh, unsigned type_id,
-    unsigned flags, void *mesg, unsigned * oh_flags_ptr);
+H5_DLL herr_t H5O_append(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh, unsigned type_id,
+    unsigned mesg_flags, unsigned update_flags, void *mesg,
+    unsigned *oh_flags_ptr);
 H5_DLL herr_t H5O_touch(H5O_loc_t *loc, hbool_t force, hid_t dxpl_id);
 H5_DLL herr_t H5O_touch_oh(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh,
     hbool_t force, unsigned *oh_flags_ptr);
diff --git a/src/H5Oshared.c b/src/H5Oshared.c
index 032e2b0..108e74e 100644
--- a/src/H5Oshared.c
+++ b/src/H5Oshared.c
@@ -531,7 +531,7 @@ H5O_shared_delete(H5F_t *f, hid_t dxpl_id, const void *_mesg,
      * are written (in H5O_shared_link) and decrement it here.
      * SOHMs in the heap behave differently; their refcount is incremented
      * during H5SM_share when they are going to be written (in H5O_append
-     * or H5O_modify). Their refcount in the SOHM indexes still needs to
+     * or H5O_write). Their refcount in the SOHM indexes still needs to
      * be decremented when they're deleted (in H5O_shared_link_adj).
      */
 
diff --git a/src/H5S.c b/src/H5S.c
index 0fbb7fa..7cd960a 100644
--- a/src/H5S.c
+++ b/src/H5S.c
@@ -1029,7 +1029,7 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5S_modify
+ * Function:	H5S_write
  *
  * Purpose:	Updates a data space by writing a message to an object
  *		header.
@@ -1042,11 +1042,11 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5S_modify(H5O_loc_t *loc, const H5S_t *ds, hbool_t update_time, hid_t dxpl_id)
+H5S_write(H5O_loc_t *loc, const H5S_t *ds, hbool_t update_time, hid_t dxpl_id)
 {
     herr_t ret_value = SUCCEED;   /* Return value */
 
-    FUNC_ENTER_NOAPI(H5S_modify, FAIL)
+    FUNC_ENTER_NOAPI(H5S_write, FAIL)
 
     HDassert(loc);
     HDassert(ds);
@@ -1055,7 +1055,7 @@ H5S_modify(H5O_loc_t *loc, const H5S_t *ds, hbool_t update_time, hid_t dxpl_id)
         case H5S_NULL:
         case H5S_SCALAR:
         case H5S_SIMPLE:
-            if(H5O_modify(loc, H5O_SDSPACE_ID, 0, 0, update_time, &(ds->extent), dxpl_id) < 0)
+            if(H5O_write(loc, H5O_SDSPACE_ID, 0, 0, update_time, &(ds->extent), dxpl_id) < 0)
                 HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "can't update simple dataspace message")
             break;
 
@@ -1066,7 +1066,7 @@ H5S_modify(H5O_loc_t *loc, const H5S_t *ds, hbool_t update_time, hid_t dxpl_id)
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S_modify() */
+} /* end H5S_write() */
 
 
 /*-------------------------------------------------------------------------
@@ -1091,23 +1091,23 @@ done:
  */
 herr_t
 H5S_append(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh, const H5S_t *ds,
-           unsigned * oh_flags_ptr)
+           unsigned *oh_flags_ptr)
 {
-    herr_t ret_value=SUCCEED;   /* Return value */
+    herr_t ret_value = SUCCEED;   /* Return value */
 
-    FUNC_ENTER_NOAPI(H5S_append, FAIL);
+    FUNC_ENTER_NOAPI(H5S_append, FAIL)
 
-    assert(f);
-    assert(oh);
-    assert(ds);
-    assert(oh_flags_ptr);
+    HDassert(f);
+    HDassert(oh);
+    HDassert(ds);
+    HDassert(oh_flags_ptr);
 
     switch (H5S_GET_EXTENT_TYPE(ds)) {
         case H5S_NULL:
         case H5S_SCALAR:
         case H5S_SIMPLE:
-            if (H5O_append(f, dxpl_id, oh, H5O_SDSPACE_ID, 0, &(ds->extent), oh_flags_ptr)<0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "can't update simple data space message");
+            if(H5O_append(f, dxpl_id, oh, H5O_SDSPACE_ID, 0, 0, &(ds->extent), oh_flags_ptr) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "can't update simple data space message")
             break;
 
         default:
@@ -1116,7 +1116,7 @@ H5S_append(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh, const H5S_t *ds,
     }
 
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S_append() */
 
 
diff --git a/src/H5SM.c b/src/H5SM.c
index 7ab2f59..38b8c75 100755
--- a/src/H5SM.c
+++ b/src/H5SM.c
@@ -519,6 +519,9 @@ H5SM_try_share(H5F_t *f, hid_t dxpl_id, unsigned type_id, void *mesg)
 
     /* Type-specific checks */
     /* JAMES: should this go here? Should there be a "can share" callback? */
+    /* QAK: Yes, a "can share" callback would be very good here, this chunk of
+     *          code is really violating the encapsulation of the datatype class
+     */
     if(type_id == H5O_DTYPE_ID)
     {
         /* Don't share immutable datatypes */
@@ -573,12 +576,12 @@ H5SM_try_share(H5F_t *f, hid_t dxpl_id, unsigned type_id, void *mesg)
 done:
     /* Release the master SOHM table */
     if (table && H5AC_unprotect(f, dxpl_id, H5AC_SOHM_TABLE, f->shared->sohm_addr, table, cache_flags) < 0)
-	HGOTO_ERROR(H5E_CACHE, H5E_CANTRELEASE, FAIL, "unable to close SOHM master table")
+	HDONE_ERROR(H5E_CACHE, H5E_CANTRELEASE, FAIL, "unable to close SOHM master table")
 
     FUNC_LEAVE_NOAPI(ret_value)
 }
-
 
+
 /*-------------------------------------------------------------------------
  * Function:    H5SM_write_mesg
  *
diff --git a/src/H5Sprivate.h b/src/H5Sprivate.h
index bdcd60a..7538cbd 100644
--- a/src/H5Sprivate.h
+++ b/src/H5Sprivate.h
@@ -202,7 +202,7 @@ H5_DLL hbool_t H5S_has_extent(const H5S_t *ds);
 H5_DLL int H5S_get_simple_extent_ndims(const H5S_t *ds);
 H5_DLL int H5S_get_simple_extent_dims(const H5S_t *ds, hsize_t dims[]/*out*/,
 					hsize_t max_dims[]/*out*/);
-H5_DLL herr_t H5S_modify(struct H5O_loc_t *loc, const H5S_t *space,
+H5_DLL herr_t H5S_write(struct H5O_loc_t *loc, const H5S_t *space,
     hbool_t update_time, hid_t dxpl_id);
 H5_DLL herr_t H5S_append(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh,
                          const H5S_t *ds, unsigned * oh_flags_ptr);
diff --git a/src/H5Tcommit.c b/src/H5Tcommit.c
index 025aca3..efe1d92 100644
--- a/src/H5Tcommit.c
+++ b/src/H5Tcommit.c
@@ -281,7 +281,7 @@ H5T_commit(H5F_t *file, H5T_t *type, hid_t dxpl_id, hid_t tcpl_id, hid_t UNUSED
      */
     if(H5O_create(file, dxpl_id, dtype_size, tcpl_id, &temp_oloc) < 0)
 	HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "unable to create datatype object header")
-    if(H5O_modify(&temp_oloc, H5O_DTYPE_ID, 0, H5O_MSG_FLAG_CONSTANT | H5O_MSG_FLAG_DONTSOHM, H5O_UPDATE_TIME, type, dxpl_id) < 0)
+    if(H5O_msg_create(&temp_oloc, H5O_DTYPE_ID, H5O_MSG_FLAG_CONSTANT | H5O_MSG_FLAG_DONTSOHM, H5O_UPDATE_TIME, type, dxpl_id) < 0)
 	HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "unable to update type header message")
 
     /* Copy the new object header's location into the datatype, taking ownership of it */