[svn-r13486] Description:

	Move attribute tracking information out of object header prefix and
make it into a message that is inserted only when attributes are present on
the object.

Tested on:
	FreeBSD/32 6.2 (duty)

15 files changed, 687 insertions, 512 deletions

diff --git a/src/H5Adense.c b/src/H5Adense.c
index a1f9587..5a4f256 100644
--- a/src/H5Adense.c
+++ b/src/H5Adense.c
@@ -185,7 +185,7 @@ H5FL_BLK_DEFINE(ser_attr);
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_create(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
+H5A_dense_create(H5F_t *f, hid_t dxpl_id, H5O_ainfo_t *ainfo)
 {
     H5HF_create_t fheap_cparam;         /* Fractal heap creation parameters */
     H5HF_t *fheap;                      /* Fractal heap handle */
@@ -198,7 +198,7 @@ H5A_dense_create(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
 
     /* Set fractal heap creation parameters */
 /* XXX: Give some control of these to applications? */
@@ -216,10 +216,10 @@ H5A_dense_create(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to create fractal heap")
 
     /* Retrieve the heap's address in the file */
-    if(H5HF_get_heap_addr(fheap, &(oh->attr_fheap_addr)) < 0)
+    if(H5HF_get_heap_addr(fheap, &ainfo->fheap_addr) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTGETSIZE, FAIL, "can't get fractal heap address")
 #ifdef QAK
-HDfprintf(stderr, "%s: oh->attr_fheap_addr = %a\n", FUNC, oh->attr_fheap_addr);
+HDfprintf(stderr, "%s: ainfo->fheap_addr = %a\n", FUNC, ainfo->fheap_addr);
 #endif /* QAK */
 
 #ifndef NDEBUG
@@ -248,14 +248,14 @@ HDfprintf(stderr, "%s: fheap_id_len = %Zu\n", FUNC, fheap_id_len);
     if(H5B2_create(f, dxpl_id, H5A_BT2_NAME,
             (size_t)H5A_NAME_BT2_NODE_SIZE, bt2_rrec_size,
             H5A_NAME_BT2_SPLIT_PERC, H5A_NAME_BT2_MERGE_PERC,
-            &(oh->name_bt2_addr)) < 0)
+            &ainfo->name_bt2_addr) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to create v2 B-tree for name index")
 #ifdef QAK
-HDfprintf(stderr, "%s: oh->name_bt2_addr = %a\n", FUNC, oh->name_bt2_addr);
+HDfprintf(stderr, "%s: ainfo->name_bt2_addr = %a\n", FUNC, ainfo->name_bt2_addr);
 #endif /* QAK */
 
     /* Check if we should create a creation order index v2 B-tree */
-    if(oh->flags & H5P_CRT_ORDER_INDEXED) {
+    if(ainfo->index_corder) {
         /* Create the creation order index v2 B-tree */
         bt2_rrec_size = 4 +             /* Creation order index */
                 1 +                     /* Message flags */
@@ -263,10 +263,10 @@ HDfprintf(stderr, "%s: oh->name_bt2_addr = %a\n", FUNC, oh->name_bt2_addr);
         if(H5B2_create(f, dxpl_id, H5A_BT2_CORDER,
                 (size_t)H5A_CORDER_BT2_NODE_SIZE, bt2_rrec_size,
                 H5A_CORDER_BT2_SPLIT_PERC, H5A_CORDER_BT2_MERGE_PERC,
-                &(oh->corder_bt2_addr)) < 0)
+                &ainfo->corder_bt2_addr) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to create v2 B-tree for name index")
 #ifdef QAK
-HDfprintf(stderr, "%s: oh->corder_bt2_addr = %a\n", FUNC, oh->corder_bt2_addr);
+HDfprintf(stderr, "%s: ainfo->corder_bt2_addr = %a\n", FUNC, ainfo->corder_bt2_addr);
 #endif /* QAK */
     } /* end if */
 
@@ -323,7 +323,7 @@ H5A_dense_fnd_cb(const H5A_t *attr, hbool_t *took_ownership, void *_user_attr)
  *-------------------------------------------------------------------------
  */
 H5A_t *
-H5A_dense_open(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
+H5A_dense_open(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo, const char *name)
 {
     H5A_bt2_ud_common_t udata;          /* User data for v2 B-tree modify */
     H5HF_t *fheap = NULL;               /* Fractal heap handle */
@@ -337,11 +337,11 @@ H5A_dense_open(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
     HDassert(name);
 
     /* Open the fractal heap */
-    if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+    if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
         HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, NULL, "unable to open fractal heap")
 
     /* Check if attributes are shared in this file */
@@ -377,7 +377,7 @@ H5A_dense_open(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
     udata.found_op_data = &ret_value;
 
     /* Find & copy the attribute in the 'name' index */
-    if(H5B2_find(f, dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &udata, NULL, NULL) < 0)
+    if(H5B2_find(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, &udata, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_NOTFOUND, NULL, "can't locate attribute in name index")
 
 done:
@@ -405,7 +405,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_insert(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
+H5A_dense_insert(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo, H5A_t *attr)
 {
     H5A_bt2_ud_ins_t udata;             /* User data for v2 B-tree insertion */
     H5HF_t *fheap = NULL;               /* Fractal heap handle for attributes */
@@ -422,7 +422,7 @@ H5A_dense_insert(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
     HDassert(attr);
 
     /* Check if attributes are shared in this file */
@@ -462,7 +462,7 @@ H5A_dense_insert(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
     } /* end if */
 
     /* Open the fractal heap */
-    if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+    if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
         HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
     /* Check for inserting shared attribute */
@@ -512,14 +512,14 @@ H5A_dense_insert(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
     /* udata.id already set */
 
     /* Insert attribute into 'name' tracking v2 B-tree */
-    if(H5B2_insert(f, dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &udata) < 0)
+    if(H5B2_insert(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, &udata) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINSERT, FAIL, "unable to insert record into v2 B-tree")
 
     /* Check if we should create a creation order index v2 B-tree record */
-    if(oh->flags & H5P_CRT_ORDER_INDEXED) {
+    if(ainfo->index_corder) {
         /* Insert the record into the creation order index v2 B-tree */
-        HDassert(H5F_addr_defined(oh->corder_bt2_addr));
-        if(H5B2_insert(f, dxpl_id, H5A_BT2_CORDER, oh->corder_bt2_addr, &udata) < 0)
+        HDassert(H5F_addr_defined(ainfo->corder_bt2_addr));
+        if(H5B2_insert(f, dxpl_id, H5A_BT2_CORDER, ainfo->corder_bt2_addr, &udata) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTINSERT, FAIL, "unable to insert record into v2 B-tree")
     } /* end if */
 
@@ -695,7 +695,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_write(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
+H5A_dense_write(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo, H5A_t *attr)
 {
     H5A_bt2_ud_common_t udata;          /* User data for v2 B-tree modify */
     H5A_bt2_od_wrt_t op_data;           /* "Op data" for v2 B-tree modify */
@@ -710,7 +710,9 @@ H5A_dense_write(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
+    HDassert(H5F_addr_defined(ainfo->fheap_addr));
+    HDassert(H5F_addr_defined(ainfo->name_bt2_addr));
     HDassert(attr);
 
     /* Check if attributes are shared in this file */
@@ -734,7 +736,7 @@ H5A_dense_write(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
     } /* end if */
 
     /* Open the fractal heap */
-    if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+    if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
         HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
     /* Create the "udata" information for v2 B-tree record modify */
@@ -755,10 +757,10 @@ H5A_dense_write(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, H5A_t *attr)
     op_data.fheap = fheap;
     op_data.shared_fheap = shared_fheap;
     op_data.attr = attr;
-    op_data.corder_bt2_addr = oh->corder_bt2_addr;
+    op_data.corder_bt2_addr = ainfo->corder_bt2_addr;
 
     /* Modify attribute through 'name' tracking v2 B-tree */
-    if(H5B2_modify(f, dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &udata, H5A_dense_write_bt2_cb, &op_data) < 0)
+    if(H5B2_modify(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, &udata, H5A_dense_write_bt2_cb, &op_data) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINSERT, FAIL, "unable to modify record in v2 B-tree")
 
 done:
@@ -830,7 +832,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *old_name,
+H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo, const char *old_name,
     const char *new_name)
 {
     H5A_bt2_ud_common_t udata;          /* User data for v2 B-tree modify */
@@ -847,7 +849,7 @@ H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *old_name,
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
     HDassert(old_name);
     HDassert(new_name);
 
@@ -872,7 +874,7 @@ H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *old_name,
     } /* end if */
 
     /* Open the fractal heap */
-    if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+    if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
         HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
     /* Create the "udata" information for v2 B-tree record modify */
@@ -888,7 +890,7 @@ H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *old_name,
     udata.found_op_data = &attr_copy;
 
     /* Get copy of attribute through 'name' tracking v2 B-tree */
-    if(H5B2_find(f, dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &udata, NULL, NULL) < 0)
+    if(H5B2_find(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, &udata, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINSERT, FAIL, "unable to find record in v2 B-tree")
     HDassert(attr_copy);
 
@@ -907,7 +909,7 @@ H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *old_name,
 
     /* Insert renamed attribute back into dense storage */
     /* (Possibly making it shared) */
-    if(H5A_dense_insert(f, dxpl_id, oh, attr_copy) < 0)
+    if(H5A_dense_insert(f, dxpl_id, ainfo, attr_copy) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTINSERT, FAIL, "unable to add to dense storage")
 
     /* Was this attribute shared? */
@@ -941,7 +943,7 @@ H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *old_name,
 	HGOTO_ERROR(H5E_ATTR, H5E_WRITEERROR, FAIL, "error determining if message should be shared")
 
     /* Delete old attribute from dense storage */
-    if(H5A_dense_remove(f, dxpl_id, oh, old_name) < 0)
+    if(H5A_dense_remove(f, dxpl_id, ainfo, old_name) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete attribute in dense storage")
 
 done:
@@ -1059,9 +1061,8 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id, haddr_t attr_fheap_addr,
-    haddr_t name_bt2_addr, haddr_t corder_bt2_addr, H5_index_t idx_type,
-    H5_iter_order_t order, hsize_t skip, hsize_t *last_attr,
+H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id, const H5O_ainfo_t *ainfo,
+    H5_index_t idx_type, H5_iter_order_t order, hsize_t skip, hsize_t *last_attr,
     const H5A_attr_iter_op_t *attr_op, void *op_data)
 {
     H5HF_t *fheap = NULL;               /* Fractal heap handle */
@@ -1077,8 +1078,9 @@ H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id, haddr_t attr_fheap_addr
      * Check arguments.
      */
     HDassert(f);
-    HDassert(H5F_addr_defined(attr_fheap_addr));
-    HDassert(H5F_addr_defined(name_bt2_addr));
+    HDassert(ainfo);
+    HDassert(H5F_addr_defined(ainfo->fheap_addr));
+    HDassert(H5F_addr_defined(ainfo->name_bt2_addr));
     HDassert(attr_op);
 
     /* Determine the address of the index to use */
@@ -1088,8 +1090,8 @@ H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id, haddr_t attr_fheap_addr
          *      table and sorting it.
          */
         if(order == H5_ITER_NATIVE) {
-            HDassert(H5F_addr_defined(name_bt2_addr));
-            bt2_addr = name_bt2_addr;
+            HDassert(H5F_addr_defined(ainfo->name_bt2_addr));
+            bt2_addr = ainfo->name_bt2_addr;
             bt2_class = H5A_BT2_NAME;
         } /* end if */
         else
@@ -1102,7 +1104,7 @@ H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id, haddr_t attr_fheap_addr
          *      there's no index on it.  If there's no v2 B-tree that indexes
          *      the links, a table will be built.
          */
-        bt2_addr = corder_bt2_addr;
+        bt2_addr = ainfo->corder_bt2_addr;
         bt2_class = H5A_BT2_CORDER;
     } /* end else */
 
@@ -1112,7 +1114,7 @@ H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id, haddr_t attr_fheap_addr
         htri_t attr_sharable;               /* Flag indicating attributes are sharable */
 
         /* Open the fractal heap */
-        if(NULL == (fheap = H5HF_open(f, dxpl_id, attr_fheap_addr)))
+        if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
             HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
         /* Check if attributes are shared in this file */
@@ -1158,7 +1160,7 @@ H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id, haddr_t attr_fheap_addr
     else {
         /* Build the table of attributes for this object */
         /* (build table using the name index, but sort according to idx_type) */
-        if(H5A_dense_build_table(f, dxpl_id, attr_fheap_addr, name_bt2_addr, idx_type, order, &atable) < 0)
+        if(H5A_dense_build_table(f, dxpl_id, ainfo, idx_type, order, &atable) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTGET, FAIL, "error building table of attributes")
 
         /* Iterate over attributes in table */
@@ -1248,7 +1250,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_remove(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
+H5A_dense_remove(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo, const char *name)
 {
     H5A_bt2_ud_rm_t udata;              /* User data for v2 B-tree record removal */
     H5HF_t *fheap = NULL;               /* Fractal heap handle */
@@ -1263,11 +1265,11 @@ H5A_dense_remove(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
     HDassert(name && *name);
 
     /* Open the fractal heap */
-    if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+    if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
         HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
     /* Check if attributes are shared in this file */
@@ -1299,10 +1301,10 @@ H5A_dense_remove(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
     udata.common.name_hash = H5_checksum_lookup3(name, HDstrlen(name), 0);
     udata.common.found_op = H5A_dense_fnd_cb;       /* v2 B-tree comparison callback */
     udata.common.found_op_data = &attr_copy;
-    udata.corder_bt2_addr = oh->corder_bt2_addr;
+    udata.corder_bt2_addr = ainfo->corder_bt2_addr;
 
     /* Remove the record from the name index v2 B-tree */
-    if(H5B2_remove(f, dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &udata, H5A_dense_remove_bt2_cb, &udata) < 0)
+    if(H5B2_remove(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, &udata, H5A_dense_remove_bt2_cb, &udata) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTREMOVE, FAIL, "unable to remove attribute from name index v2 B-tree")
 
 done:
@@ -1437,7 +1439,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, 
+H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo, 
     H5_index_t idx_type, H5_iter_order_t order, hsize_t n)
 {
     H5HF_t *fheap = NULL;               /* Fractal heap handle */
@@ -1453,7 +1455,7 @@ H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
 
     /* Determine the address of the index to use */
     if(idx_type == H5_INDEX_NAME) {
@@ -1462,7 +1464,7 @@ H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
          *      table and sorting it.
          */
         if(order == H5_ITER_NATIVE) {
-            bt2_addr = oh->name_bt2_addr;
+            bt2_addr = ainfo->name_bt2_addr;
             bt2_class = H5A_BT2_NAME;
             HDassert(H5F_addr_defined(bt2_addr));
         } /* end if */
@@ -1476,7 +1478,7 @@ H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
          *      there's no index on it.  If there's no v2 B-tree that indexes
          *      the links, a table will be built.
          */
-        bt2_addr = oh->corder_bt2_addr;
+        bt2_addr = ainfo->corder_bt2_addr;
         bt2_class = H5A_BT2_CORDER;
     } /* end else */
 
@@ -1486,7 +1488,7 @@ H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
         htri_t attr_sharable;           /* Flag indicating attributes are sharable */
 
         /* Open the fractal heap */
-        if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+        if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
             HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
         /* Check if attributes are shared in this file */
@@ -1515,7 +1517,7 @@ H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
         udata.fheap = fheap;
         udata.shared_fheap = shared_fheap;
         udata.idx_type = idx_type;
-        udata.other_bt2_addr = idx_type == H5_INDEX_NAME ? oh->corder_bt2_addr : oh->name_bt2_addr;
+        udata.other_bt2_addr = idx_type == H5_INDEX_NAME ? ainfo->corder_bt2_addr : ainfo->name_bt2_addr;
 
         /* Remove the record from the name index v2 B-tree */
         if(H5B2_remove_by_idx(f, dxpl_id, bt2_class, bt2_addr, order, n, H5A_dense_remove_by_idx_bt2_cb, &udata) < 0)
@@ -1524,7 +1526,7 @@ H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
     else {
         /* Build the table of attributes for this object */
         /* (build table using the name index, but sort according to idx_type) */
-        if(H5A_dense_build_table(f, dxpl_id, oh->attr_fheap_addr, oh->name_bt2_addr, idx_type, order, &atable) < 0)
+        if(H5A_dense_build_table(f, dxpl_id, ainfo, idx_type, order, &atable) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTGET, FAIL, "error building table of attributes")
 
         /* Check for skipping too many attributes */
@@ -1532,7 +1534,7 @@ H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
             HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid index specified")
 
         /* Delete appropriate attribute from dense storage */
-        if(H5A_dense_remove(f, dxpl_id, oh, atable.attrs[n].name) < 0)
+        if(H5A_dense_remove(f, dxpl_id, ainfo, atable.attrs[n].name) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete attribute in dense storage")
     } /* end else */
 
@@ -1564,7 +1566,7 @@ done:
  *-------------------------------------------------------------------------
  */
 htri_t
-H5A_dense_exists(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
+H5A_dense_exists(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo, const char *name)
 {
     H5A_bt2_ud_common_t udata;          /* User data for v2 B-tree modify */
     H5HF_t *fheap = NULL;               /* Fractal heap handle */
@@ -1578,11 +1580,11 @@ H5A_dense_exists(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
     HDassert(name);
 
     /* Open the fractal heap */
-    if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+    if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
         HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
     /* Check if attributes are shared in this file */
@@ -1618,7 +1620,7 @@ H5A_dense_exists(H5F_t *f, hid_t dxpl_id, const H5O_t *oh, const char *name)
     udata.found_op_data = NULL;
 
     /* Find the attribute in the 'name' index */
-    if(H5B2_find(f, dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &udata, NULL, NULL) < 0) {
+    if(H5B2_find(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, &udata, NULL, NULL) < 0) {
         /* Assume that the failure was just not finding the attribute & clear stack */
         H5E_clear_stack(NULL);
 
@@ -1715,7 +1717,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_delete(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
+H5A_dense_delete(H5F_t *f, hid_t dxpl_id, H5O_ainfo_t *ainfo)
 {
     H5A_bt2_ud_common_t udata;          /* v2 B-tree user data for deleting attributes */
     H5HF_t *fheap = NULL;               /* Fractal heap handle */
@@ -1727,10 +1729,10 @@ H5A_dense_delete(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
      * Check arguments.
      */
     HDassert(f);
-    HDassert(oh);
+    HDassert(ainfo);
 
     /* Open the fractal heap */
-    if(NULL == (fheap = H5HF_open(f, dxpl_id, oh->attr_fheap_addr)))
+    if(NULL == (fheap = H5HF_open(f, dxpl_id, ainfo->fheap_addr)))
         HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "unable to open fractal heap")
 
     /* Create the "udata" information for v2 B-tree 'delete' */
@@ -1746,9 +1748,9 @@ H5A_dense_delete(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
     udata.found_op_data = NULL;
 
     /* Delete name index v2 B-tree */
-    if(H5B2_delete(f, dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, H5A_dense_delete_bt2_cb, &udata) < 0)
+    if(H5B2_delete(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, H5A_dense_delete_bt2_cb, &udata) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete v2 B-tree for name index")
-    oh->name_bt2_addr = HADDR_UNDEF;
+    ainfo->name_bt2_addr = HADDR_UNDEF;
 
     /* Release resources */
     if(H5HF_close(fheap, dxpl_id) < 0)
@@ -1756,17 +1758,17 @@ H5A_dense_delete(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
     fheap = NULL;
 
     /* Check if we should delete the creation order index v2 B-tree */
-    if(H5F_addr_defined(oh->corder_bt2_addr)) {
+    if(H5F_addr_defined(ainfo->corder_bt2_addr)) {
         /* Delete the creation order index, without adjusting the ref. count on the attributes  */
-        if(H5B2_delete(f, dxpl_id, H5A_BT2_CORDER, oh->corder_bt2_addr, NULL, NULL) < 0)
+        if(H5B2_delete(f, dxpl_id, H5A_BT2_CORDER, ainfo->corder_bt2_addr, NULL, NULL) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTDELETE, FAIL, "unable to delete v2 B-tree for creation order index")
-        oh->corder_bt2_addr = HADDR_UNDEF;
+        ainfo->corder_bt2_addr = HADDR_UNDEF;
     } /* end if */
 
     /* Delete fractal heap */
-    if(H5HF_delete(f, dxpl_id, oh->attr_fheap_addr) < 0)
+    if(H5HF_delete(f, dxpl_id, ainfo->fheap_addr) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete fractal heap")
-    oh->attr_fheap_addr = HADDR_UNDEF;
+    ainfo->fheap_addr = HADDR_UNDEF;
 
 done:
     /* Release resources */
diff --git a/src/H5Aint.c b/src/H5Aint.c
index 953dda2..18b49f8 100644
--- a/src/H5Aint.c
+++ b/src/H5Aint.c
@@ -274,9 +274,8 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5A_dense_build_table(H5F_t *f, hid_t dxpl_id, haddr_t attr_fheap_addr,
-    haddr_t name_bt2_addr, H5_index_t idx_type, H5_iter_order_t order,
-    H5A_attr_table_t *atable)
+H5A_dense_build_table(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
+    H5_index_t idx_type, H5_iter_order_t order, H5A_attr_table_t *atable)
 {
     hsize_t nrec;                       /* # of records in v2 B-tree */
     herr_t ret_value = SUCCEED;         /* Return value */
@@ -285,13 +284,14 @@ H5A_dense_build_table(H5F_t *f, hid_t dxpl_id, haddr_t attr_fheap_addr,
 
     /* Sanity check */
     HDassert(f);
-    HDassert(H5F_addr_defined(attr_fheap_addr));
-    HDassert(H5F_addr_defined(name_bt2_addr));
+    HDassert(ainfo);
+    HDassert(H5F_addr_defined(ainfo->fheap_addr));
+    HDassert(H5F_addr_defined(ainfo->name_bt2_addr));
     HDassert(atable);
 
     /* Retrieve # of records in "name" B-tree */
     /* (should be same # of records in all indices) */
-    if(H5B2_get_nrec(f, dxpl_id, H5A_BT2_NAME, name_bt2_addr, &nrec) < 0)
+    if(H5B2_get_nrec(f, dxpl_id, H5A_BT2_NAME, ainfo->name_bt2_addr, &nrec) < 0)
         HGOTO_ERROR(H5E_ATTR, H5E_CANTGET, FAIL, "can't retrieve # of records in index")
 
     /* Set size of table */
@@ -316,9 +316,8 @@ H5A_dense_build_table(H5F_t *f, hid_t dxpl_id, haddr_t attr_fheap_addr,
         attr_op.u.lib_op = H5A_dense_build_table_cb;
 
         /* Iterate over the links in the group, building a table of the link messages */
-        if(H5A_dense_iterate(f, dxpl_id, (hid_t)0, attr_fheap_addr, name_bt2_addr,
-                HADDR_UNDEF, H5_INDEX_NAME, H5_ITER_NATIVE, (hsize_t)0, NULL,
-                &attr_op, &udata) < 0)
+        if(H5A_dense_iterate(f, dxpl_id, (hid_t)0, ainfo, H5_INDEX_NAME,
+                H5_ITER_NATIVE, (hsize_t)0, NULL, &attr_op, &udata) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "error building attribute table")
 
         /* Sort attribute table in correct iteration order */
diff --git a/src/H5Apkg.h b/src/H5Apkg.h
index f5d843b..c3fe261 100644
--- a/src/H5Apkg.h
+++ b/src/H5Apkg.h
@@ -186,32 +186,34 @@ H5_DLL herr_t H5A_free(H5A_t *attr);
 H5_DLL herr_t H5A_close(H5A_t *attr);
 
 /* Attribute "dense" storage routines */
-H5_DLL herr_t H5A_dense_create(H5F_t *f, hid_t dxpl_id, H5O_t *oh);
-H5_DLL H5A_t *H5A_dense_open(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
+H5_DLL herr_t H5A_dense_create(H5F_t *f, hid_t dxpl_id, H5O_ainfo_t *ainfo);
+H5_DLL H5A_t *H5A_dense_open(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
     const char *name);
-H5_DLL herr_t H5A_dense_insert(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
+H5_DLL herr_t H5A_dense_insert(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
     H5A_t *attr);
-H5_DLL herr_t H5A_dense_write(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
+H5_DLL herr_t H5A_dense_write(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
     H5A_t *attr);
-H5_DLL herr_t H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
+H5_DLL herr_t H5A_dense_rename(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
     const char *old_name, const char *new_name);
 H5_DLL herr_t H5A_dense_iterate(H5F_t *f, hid_t dxpl_id, hid_t loc_id,
-    haddr_t attr_fheap_addr, haddr_t name_bt2_addr, haddr_t corder_bt2_addr,
-    H5_index_t idx_type, H5_iter_order_t order, hsize_t skip,
-    hsize_t *last_attr, const H5A_attr_iter_op_t *attr_op, void *op_data);
-H5_DLL herr_t H5A_dense_remove(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
+    const H5O_ainfo_t *ainfo, H5_index_t idx_type, H5_iter_order_t order,
+    hsize_t skip, hsize_t *last_attr, const H5A_attr_iter_op_t *attr_op,
+    void *op_data);
+H5_DLL herr_t H5A_dense_remove(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
     const char *name);
-H5_DLL herr_t H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
+H5_DLL herr_t H5A_dense_remove_by_idx(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
     H5_index_t idx_type, H5_iter_order_t order, hsize_t n);
-H5_DLL htri_t H5A_dense_exists(H5F_t *f, hid_t dxpl_id, const H5O_t *oh,
+H5_DLL htri_t H5A_dense_exists(H5F_t *f, hid_t dxpl_id, const H5O_ainfo_t *ainfo,
     const char *name);
+H5_DLL herr_t H5A_dense_delete(H5F_t *f, hid_t dxpl_id, H5O_ainfo_t *ainfo);
+
 
 /* Attribute table operations */
 H5_DLL herr_t H5A_compact_build_table(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
     H5_index_t idx_type, H5_iter_order_t order, H5A_attr_table_t *atable);
 H5_DLL herr_t H5A_dense_build_table(H5F_t *f, hid_t dxpl_id,
-    haddr_t attr_fheap_addr, haddr_t name_bt2_addr, H5_index_t idx_type,
-    H5_iter_order_t order, H5A_attr_table_t *atable);
+    const H5O_ainfo_t *ainfo, H5_index_t idx_type, H5_iter_order_t order,
+    H5A_attr_table_t *atable);
 H5_DLL herr_t H5A_attr_iterate_table(const H5A_attr_table_t *atable,
     hsize_t skip, hsize_t *last_attr, hid_t loc_id,
     const H5A_attr_iter_op_t *attr_op, void *op_data);
diff --git a/src/H5Aprivate.h b/src/H5Aprivate.h
index 75a2884..d46e46b 100644
--- a/src/H5Aprivate.h
+++ b/src/H5Aprivate.h
@@ -48,14 +48,10 @@ typedef struct H5A_attr_iter_op_t H5A_attr_iter_op_t;
 /***************************************/
 /* Library-private Function Prototypes */
 /***************************************/
-struct H5O_t; /*forward decl*/
 
 /* General attribute routines */
 H5_DLL struct H5O_loc_t *H5A_oloc(H5A_t *attr);
 H5_DLL H5G_name_t *H5A_nameof(H5A_t *attr);
 
-/* Attribute "dense" storage routines */
-H5_DLL herr_t H5A_dense_delete(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh);
-
 #endif /* _H5Aprivate_H */
 
diff --git a/src/H5O.c b/src/H5O.c
index 0741621..cd961cd 100644
--- a/src/H5O.c
+++ b/src/H5O.c
@@ -38,7 +38,6 @@
 /* Headers */
 /***********/
 #include "H5private.h"		/* Generic Functions			*/
-#include "H5Aprivate.h"		/* Attributes			  	*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5Fpkg.h"		/* File access				*/
 #include "H5FLprivate.h"	/* Free lists                           */
@@ -693,11 +692,6 @@ H5O_create(H5F_t *f, hid_t dxpl_id, size_t size_hint, hid_t ocpl_id,
         if(H5P_get(oc_plist, H5O_CRT_ATTR_MIN_DENSE_NAME, &oh->min_dense) < 0)
             HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get min. # of dense attributes")
 
-        /* Set starting values for dense attribute storage info */
-        oh->attr_fheap_addr = HADDR_UNDEF;
-        oh->name_bt2_addr = HADDR_UNDEF;
-        oh->corder_bt2_addr = HADDR_UNDEF;
-
         /* Check for non-default attribute storage phase change values */
         if(oh->max_compact != H5O_CRT_ATTR_MAX_COMPACT_DEF || oh->min_dense != H5O_CRT_ATTR_MIN_DENSE_DEF)
             oh->flags |= H5O_HDR_ATTR_STORE_PHASE_CHANGE;
@@ -708,11 +702,6 @@ H5O_create(H5F_t *f, hid_t dxpl_id, size_t size_hint, hid_t ocpl_id,
 
         /* Reset unused time fields */
         oh->atime = oh->mtime = oh->ctime = oh->btime = 0;
-
-        /* Reset unused attribute fields */
-        oh->attr_fheap_addr = HADDR_UNDEF;
-        oh->name_bt2_addr = HADDR_UNDEF;
-        oh->corder_bt2_addr = HADDR_UNDEF;
     } /* end else */
 
     /* Compute total size of initial object header */
@@ -1467,12 +1456,6 @@ H5O_delete_oh(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
             HGOTO_ERROR(H5E_OHDR, H5E_CANTDELETE, FAIL, "unable to delete file space for object header message")
     } /* end for */
 
-    /* Check for dense attribute storage & delete it if necessary */
-    if(oh->version > H5O_VERSION_1 && H5F_addr_defined(oh->attr_fheap_addr)) {
-        if(H5A_dense_delete(f, dxpl_id, oh) < 0)
-            HGOTO_ERROR(H5E_OHDR, H5E_CANTDELETE, FAIL, "unable to delete dense attribute storage")
-    } /* end if */
-
     /* Free main (first) object header "chunk" */
     if(H5MF_xfree(f, H5FD_MEM_OHDR, dxpl_id, oh->chunk[0].addr, (hsize_t)oh->chunk[0].size) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to free object header")
@@ -1920,7 +1903,6 @@ H5O_get_info(H5O_loc_t *oloc, H5O_info_t *oinfo, hid_t dxpl_id)
     oinfo->hdr.flags = oh->flags;
 
     /* Iterate over all the messages, accumulating message size & type information */
-    oinfo->num_attrs = 0;
     oinfo->hdr.space.meta = H5O_SIZEOF_HDR(oh) + (H5O_SIZEOF_CHKHDR_OH(oh) * (oh->nchunks - 1));
     oinfo->hdr.space.mesg = 0;
     oinfo->hdr.space.free = 0;
@@ -1929,10 +1911,6 @@ H5O_get_info(H5O_loc_t *oloc, H5O_info_t *oinfo, hid_t dxpl_id)
     for(u = 0, curr_msg = &oh->mesg[0]; u < oh->nmesgs; u++, curr_msg++) {
         uint64_t type_flag;             /* Flag for message type */
 
-        /* Check for attribute message */
-	if(H5O_ATTR_ID == curr_msg->type->id)
-            oinfo->num_attrs++;
-
         /* Accumulate space usage information, based on the type of message */
 	if(H5O_NULL_ID == curr_msg->type->id)
             oinfo->hdr.space.free += H5O_SIZEOF_MSGHDR_OH(oh) + curr_msg->raw_size;
@@ -1952,15 +1930,8 @@ H5O_get_info(H5O_loc_t *oloc, H5O_info_t *oinfo, hid_t dxpl_id)
             oinfo->hdr.mesg.shared |= type_flag;
     } /* end for */
 
-    /* Sanity checking, etc. for # of attributes */
-    if(oh->version > H5O_VERSION_1) {
-        if(H5F_addr_defined(oh->attr_fheap_addr)) {
-            HDassert(oinfo->num_attrs == 0);
-            oinfo->num_attrs = oh->nattrs;
-        } /* end if */
-        else
-            HDassert(oh->nattrs == oinfo->num_attrs);
-    } /* end if */
+    /* Retrieve # of attributes */
+    oinfo->num_attrs = H5O_attr_count_real(oloc->file, dxpl_id, oh);
 
     /* Iterate over all the chunks, adding any gaps to the free space */
     oinfo->hdr.space.total = 0;
diff --git a/src/H5Oainfo.c b/src/H5Oainfo.c
index 514d451..7c3183a 100644
--- a/src/H5Oainfo.c
+++ b/src/H5Oainfo.c
@@ -24,9 +24,11 @@
  *-------------------------------------------------------------------------
  */
 
+#define H5A_PACKAGE		/*suppress error about including H5Apkg	  */
 #define H5O_PACKAGE		/*suppress error about including H5Opkg	  */
 
 #include "H5private.h"		/* Generic Functions			*/
+#include "H5Apkg.h"             /* Attributes				*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5FLprivate.h"	/* Free lists                           */
 #include "H5Opkg.h"             /* Object headers			*/
@@ -39,6 +41,10 @@ static void *H5O_ainfo_copy(const void *_mesg, void *_dest);
 static size_t H5O_ainfo_size(const H5F_t *f, hbool_t disable_shared, const void *_mesg);
 static herr_t H5O_ainfo_free(void *_mesg);
 static herr_t H5O_ainfo_delete(H5F_t *f, hid_t dxpl_id, const void *_mesg);
+static herr_t H5O_ainfo_pre_copy_file(H5F_t *file_src, const void *mesg_src,
+    hbool_t *deleted, const H5O_copy_t *cpy_info, void *udata);
+static void *H5O_ainfo_copy_file(H5F_t *file_src, void *mesg_src,
+    H5F_t *file_dst, hid_t dxpl_id, H5O_copy_t *cpy_info, void *udata);
 static herr_t H5O_ainfo_debug(H5F_t *f, hid_t dxpl_id, const void *_mesg,
 			     FILE * stream, int indent, int fwidth);
 
@@ -58,8 +64,8 @@ const H5O_msg_class_t H5O_MSG_AINFO[1] = {{
     NULL,			/* link method			*/
     NULL, 			/*set share method		*/
     NULL,		    	/*can share method		*/
-    NULL,			/* pre copy native value to file */
-    NULL,			/* copy native value to file    */
+    H5O_ainfo_pre_copy_file,	/* pre copy native value to file */
+    H5O_ainfo_copy_file,	/* copy native value to file    */
     NULL,			/* post copy native value to file */
     NULL,			/* get creation index		*/
     NULL,			/* set creation index		*/
@@ -69,10 +75,11 @@ const H5O_msg_class_t H5O_MSG_AINFO[1] = {{
 /* Current version of attribute info information */
 #define H5O_AINFO_VERSION 	0
 
-/* Flags for attribute info index flag encoding */
+/* Flags for attribute info flag encoding */
 #define H5O_AINFO_INDEX_NAME            0x01
-#define H5O_AINFO_INDEX_CORDER          0x02
-#define H5O_AINFO_ALL_FLAGS             (H5O_AINFO_INDEX_NAME | H5O_AINFO_INDEX_CORDER)
+#define H5O_AINFO_TRACK_CORDER          0x02
+#define H5O_AINFO_INDEX_CORDER          0x04
+#define H5O_AINFO_ALL_FLAGS             (H5O_AINFO_INDEX_NAME | H5O_AINFO_TRACK_CORDER | H5O_AINFO_INDEX_CORDER)
 
 /* Declare a free list to manage the H5O_ainfo_t struct */
 H5FL_DEFINE_STATIC(H5O_ainfo_t);
@@ -97,7 +104,7 @@ H5O_ainfo_decode(H5F_t *f, hid_t UNUSED dxpl_id, unsigned UNUSED mesg_flags,
     const uint8_t *p)
 {
     H5O_ainfo_t	*ainfo = NULL;  /* Attribute info */
-    unsigned char index_flags;  /* Flags for encoding link index info */
+    unsigned char flags;        /* Flags for encoding attribute info */
     void        *ret_value;     /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5O_ainfo_decode)
@@ -114,18 +121,22 @@ H5O_ainfo_decode(H5F_t *f, hid_t UNUSED dxpl_id, unsigned UNUSED mesg_flags,
     if(NULL == (ainfo = H5FL_MALLOC(H5O_ainfo_t)))
 	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")
 
-    /* Get the index flags for the object */
-    index_flags = *p++;
-    HDassert(index_flags & H5O_AINFO_INDEX_NAME);
-    if(index_flags & ~H5O_AINFO_ALL_FLAGS)
+    /* Get the flags for the message */
+    flags = *p++;
+    HDassert(flags & H5O_AINFO_INDEX_NAME);
+    if(flags & ~H5O_AINFO_ALL_FLAGS)
         HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "bad flag value for message")
-    ainfo->index_corder = (index_flags & H5O_AINFO_INDEX_CORDER) ? TRUE : FALSE;
+    ainfo->track_corder = (flags & H5O_AINFO_TRACK_CORDER) ? TRUE : FALSE;
+    ainfo->index_corder = (flags & H5O_AINFO_INDEX_CORDER) ? TRUE : FALSE;
 
     /* Number of attributes on the object */
     H5F_DECODE_LENGTH(f, p, ainfo->nattrs)
 
     /* Max. creation order value for the object */
-    UINT16DECODE(p, ainfo->max_crt_idx);
+    if(ainfo->track_corder)
+        UINT16DECODE(p, ainfo->max_crt_idx)
+    else
+        ainfo->max_crt_idx = H5O_MAX_CRT_ORDER_IDX;
 
     /* Address of fractal heap to store "dense" attributes */
     H5F_addr_decode(f, &p, &(ainfo->fheap_addr));
@@ -143,9 +154,8 @@ H5O_ainfo_decode(H5F_t *f, hid_t UNUSED dxpl_id, unsigned UNUSED mesg_flags,
     ret_value = ainfo;
 
 done:
-    if(ret_value == NULL)
-        if(ainfo != NULL)
-            H5FL_FREE(H5O_ainfo_t, ainfo);
+    if(ret_value == NULL && ainfo != NULL)
+        H5FL_FREE(H5O_ainfo_t, ainfo);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_ainfo_decode() */
@@ -168,7 +178,7 @@ static herr_t
 H5O_ainfo_encode(H5F_t *f, hbool_t UNUSED disable_shared, uint8_t *p, const void *_mesg)
 {
     const H5O_ainfo_t   *ainfo = (const H5O_ainfo_t *)_mesg;
-    unsigned char       index_flags;          /* Flags for encoding attribute index info */
+    unsigned char       flags;          /* Flags for encoding attribute info */
 
     FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_ainfo_encode)
 
@@ -181,15 +191,17 @@ H5O_ainfo_encode(H5F_t *f, hbool_t UNUSED disable_shared, uint8_t *p, const void
     *p++ = H5O_AINFO_VERSION;
 
     /* The flags for the attribute indices */
-    index_flags = H5O_AINFO_INDEX_NAME;       /* Names are always indexed */
-    index_flags |= ainfo->index_corder ? H5O_AINFO_INDEX_CORDER : 0;
-    *p++ = index_flags;
+    flags = H5O_AINFO_INDEX_NAME;       /* Names are always indexed */
+    flags |= ainfo->track_corder ? H5O_AINFO_TRACK_CORDER : 0;
+    flags |= ainfo->index_corder ? H5O_AINFO_INDEX_CORDER : 0;
+    *p++ = flags;
 
     /* Number of attributes on the object */
     H5F_ENCODE_LENGTH(f, p, ainfo->nattrs)
 
     /* Max. creation order value for the object */
-    UINT16ENCODE(p, ainfo->max_crt_idx);
+    if(ainfo->track_corder)
+        UINT16ENCODE(p, ainfo->max_crt_idx);
 
     /* Address of fractal heap to store "dense" attributes */
     H5F_addr_encode(f, &p, ainfo->fheap_addr);
@@ -275,7 +287,7 @@ H5O_ainfo_size(const H5F_t *f, hbool_t UNUSED disable_shared, const void *_mesg)
     ret_value = 1                       /* Version */
                 + 1                     /* Index flags */
                 + H5F_SIZEOF_SIZE(f)    /* Number of attributes */
-                + 2                     /* Curr. max. creation order value */
+                + (ainfo->track_corder ? 2 : 0) /* Curr. max. creation order value */
                 + H5F_SIZEOF_ADDR(f)    /* Address of fractal heap to store "dense" attributes */
                 + H5F_SIZEOF_ADDR(f)    /* Address of v2 B-tree for indexing names of attributes */
                 + (ainfo->index_corder ? H5F_SIZEOF_ADDR(f) : 0);   /* Address of v2 B-tree for indexing creation order values of attributes */
@@ -334,11 +346,9 @@ H5O_ainfo_delete(H5F_t *f, hid_t dxpl_id, const void *_mesg)
     HDassert(ainfo);
 
     /* If the object is using "dense" attribute storage, delete it */
-#ifdef NOT_YET
     if(H5F_addr_defined(ainfo->fheap_addr))
-        if(H5G_dense_delete(f, dxpl_id, (H5O_linfo_t *)linfo, TRUE) < 0)   /* Casting away const OK - QAK */
-            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to free dense link storage")
-#endif /* NOT_YET */
+        if(H5A_dense_delete(f, dxpl_id, (H5O_ainfo_t *)ainfo) < 0)   /* Casting away const OK - QAK */
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to free dense attribute storage")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -346,6 +356,94 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:    H5O_ainfo_pre_copy_file
+ *
+ * Purpose:     Perform any necessary actions before copying message between
+ *              files.
+ *
+ * Return:      Success:        Non-negative
+ *              Failure:        Negative
+ *
+ * Programmer:  Quincey Koziol
+ *              Friday, March  9, 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_ainfo_pre_copy_file(H5F_t UNUSED *file_src, const void UNUSED *native_src,
+    hbool_t *deleted, const H5O_copy_t *cpy_info, void UNUSED *udata)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_ainfo_pre_copy_file)
+
+    /* check args */
+    HDassert(deleted);
+    HDassert(cpy_info);
+
+    /* If we are not copying attributes into the destination file, indicate
+     *  that this message should be deleted.
+     */
+    if(cpy_info->copy_without_attr)
+        *deleted = TRUE;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5O_ainfo_pre_copy_file() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5O_ainfo_copy_file
+ *
+ * Purpose:     Copies a message from _MESG to _DEST in file
+ *
+ * Return:      Success:        Ptr to _DEST
+ *              Failure:        NULL
+ *
+ * Programmer:  Quincey Koziol
+ *              March 9, 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+static void *
+H5O_ainfo_copy_file(H5F_t UNUSED *file_src, void *mesg_src,
+    H5F_t UNUSED *file_dst, hid_t UNUSED dxpl_id, H5O_copy_t UNUSED *cpy_info,
+    void UNUSED *udata)
+{
+    H5O_ainfo_t *ainfo_src = (H5O_ainfo_t *)mesg_src;
+    H5O_ainfo_t *ainfo_dst = NULL;
+    void        *ret_value;             /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5O_ainfo_copy_file)
+
+    /* check args */
+    HDassert(file_src);
+    HDassert(ainfo_src);
+    HDassert(file_dst);
+    HDassert(cpy_info);
+    HDassert(!cpy_info->copy_without_attr);
+
+/* XXX: Bail out for now, if the source object has densely stored attributes */
+    if(H5F_addr_defined(ainfo_src->fheap_addr))
+        HGOTO_ERROR(H5E_OHDR, H5E_UNSUPPORTED, NULL, "densely stored attributes not supported yet")
+
+    /* Allocate space for the destination message */
+    if(NULL == (ainfo_dst = H5FL_MALLOC(H5O_ainfo_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")
+
+    /* Copy the top level of the information */
+    *ainfo_dst = *ainfo_src;
+
+    /* Set return value */
+    ret_value = ainfo_dst;
+
+done:
+    /* Release destination attribute information on failure */
+    if(ret_value == NULL && ainfo_dst != NULL)
+        H5FL_FREE(H5O_ainfo_t, ainfo_dst);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5O_ainfo_copy_file() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5O_ainfo_debug
  *
  * Purpose:     Prints debugging info for a message.
@@ -373,10 +471,12 @@ H5O_ainfo_debug(H5F_t UNUSED *f, hid_t UNUSED dxpl_id, const void *_mesg, FILE *
     HDassert(indent >= 0);
     HDassert(fwidth >= 0);
 
-    HDfprintf(stream, "%*s%-*s %t\n", indent, "", fwidth,
-	      "Index creation order of links:", ainfo->index_corder);
     HDfprintf(stream, "%*s%-*s %Hu\n", indent, "", fwidth,
 	      "Number of attributes:", ainfo->nattrs);
+    HDfprintf(stream, "%*s%-*s %t\n", indent, "", fwidth,
+	      "Track creation order of attributes:", ainfo->track_corder);
+    HDfprintf(stream, "%*s%-*s %t\n", indent, "", fwidth,
+	      "Index creation order of attributes:", ainfo->index_corder);
     HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
 	      "Max. creation index value:", (unsigned)ainfo->max_crt_idx);
     HDfprintf(stream, "%*s%-*s %a\n", indent, "", fwidth,
diff --git a/src/H5Oattr.c b/src/H5Oattr.c
index 0db28fa..20af30c 100644
--- a/src/H5Oattr.c
+++ b/src/H5Oattr.c
@@ -711,7 +711,7 @@ H5O_attr_pre_copy_file(H5F_t UNUSED *file_src, const void UNUSED *native_src,
  *-------------------------------------------------------------------------
  */
 static void *
-H5O_attr_copy_file(H5F_t *file_src, const H5O_msg_class_t UNUSED *mesg_type,
+H5O_attr_copy_file(H5F_t UNUSED *file_src, const H5O_msg_class_t UNUSED *mesg_type,
     void *native_src, H5F_t *file_dst, hid_t dxpl_id,
     H5O_copy_t *cpy_info, void UNUSED *udata)
 {
@@ -970,10 +970,10 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_attr_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src, H5O_loc_t *dst_oloc,
-    void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info)
+H5O_attr_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src,
+    H5O_loc_t *dst_oloc, void *mesg_dst, hid_t dxpl_id, H5O_copy_t *cpy_info)
 {
-    H5A_t  *attr_src = (H5A_t *)mesg_src;
+    const H5A_t  *attr_src = (const H5A_t *)mesg_src;
     H5A_t  *attr_dst = (H5A_t *)mesg_dst;
     H5F_t  *file_src = src_oloc->file;
     H5F_t  *file_dst = dst_oloc->file;
@@ -988,30 +988,33 @@ H5O_attr_post_copy_file(const H5O_loc_t *src_oloc, const void *mesg_src, H5O_loc
     HDassert(attr_dst);
     HDassert(file_dst);
 
-    /* only need to fix reference attribute */
-    if ( (NULL == attr_src->data) ||
-         (H5T_get_class(attr_src->dt, FALSE) != H5T_REFERENCE) ||
-         (file_src == file_dst) )
-        HGOTO_DONE(SUCCEED)
-
-    /* copy object pointed by reference. The current implementation does not deal with
-       nested reference such as reference in a compound structure */
-
-    /* Check for expanding references */
-    if(cpy_info->expand_ref) {
-        size_t ref_count;
+    /* Only need to fix reference attribute with real data being copied to
+     *  another file.
+     */
+    if((NULL != attr_src->data) &&
+            (H5T_get_class(attr_src->dt, FALSE) == H5T_REFERENCE) &&
+            (file_src != file_dst)) {
 
-        /* Determine # of reference elements to copy */
-        ref_count = attr_dst->data_size / H5T_get_size(attr_dst->dt);
+        /* copy object pointed by reference. The current implementation does not
+         *  deal with nested reference such as reference in a compound structure
+         */
 
-        /* Copy objects referenced in source buffer to destination file and set destination elements */
-        if(H5O_copy_expand_ref(file_src, attr_src->data, dxpl_id,
-                file_dst, attr_dst->data, ref_count, H5T_get_ref_type(attr_src->dt), cpy_info) < 0)
-            HGOTO_ERROR(H5E_ATTR, H5E_CANTCOPY, FAIL, "unable to copy reference attribute")
+        /* Check for expanding references */
+        if(cpy_info->expand_ref) {
+            size_t ref_count;
+
+            /* Determine # of reference elements to copy */
+            ref_count = attr_dst->data_size / H5T_get_size(attr_dst->dt);
+
+            /* Copy objects referenced in source buffer to destination file and set destination elements */
+            if(H5O_copy_expand_ref(file_src, attr_src->data, dxpl_id,
+                    file_dst, attr_dst->data, ref_count, H5T_get_ref_type(attr_src->dt), cpy_info) < 0)
+                HGOTO_ERROR(H5E_ATTR, H5E_CANTCOPY, FAIL, "unable to copy reference attribute")
+        } /* end if */
+        else
+            /* Reset value to zero */
+            HDmemset(attr_dst->data, 0, attr_dst->data_size);
     } /* end if */
-    else
-        /* Reset value to zero */
-        HDmemset(attr_dst->data, 0, attr_dst->data_size);
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5Oattribute.c b/src/H5Oattribute.c
index 3e97862..f824ad9 100644
--- a/src/H5Oattribute.c
+++ b/src/H5Oattribute.c
@@ -55,6 +55,7 @@
 typedef struct {
     H5F_t      *f;              /* Pointer to file for insertion */
     hid_t dxpl_id;              /* DXPL during iteration */
+    H5O_ainfo_t *ainfo;         /* Attribute info struct */
 } H5O_iter_cvt_t;
 
 /* User data for iteration when opening an attribute */
@@ -173,9 +174,13 @@ H5O_attr_to_dense_cb(H5O_t *oh, H5O_mesg_t *mesg/*in,out*/,
     /* check args */
     HDassert(oh);
     HDassert(mesg);
+    HDassert(udata);
+    HDassert(udata->f);
+    HDassert(udata->ainfo);
+    HDassert(attr);
 
     /* Insert attribute into dense storage */
-    if(H5A_dense_insert(udata->f, udata->dxpl_id, oh, attr) < 0)
+    if(H5A_dense_insert(udata->f, udata->dxpl_id, udata->ainfo, attr) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_CANTINSERT, H5_ITER_ERROR, "unable to add to dense storage")
 
     /* Convert message into a null message in the header */
@@ -207,6 +212,7 @@ herr_t
 H5O_attr_create(const H5O_loc_t *loc, hid_t dxpl_id, H5A_t *attr)
 {
     H5O_t *oh = NULL;                   /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;                  /* Attribute information for object */
     unsigned oh_flags = H5AC__NO_FLAGS_SET;     /* Metadata cache flags for object header */
     htri_t shared_mesg;                 /* Should this message be stored in the Shared Message table? */
     herr_t ret_value = SUCCEED;         /* Return value */
@@ -221,59 +227,107 @@ H5O_attr_create(const H5O_loc_t *loc, hid_t dxpl_id, H5A_t *attr)
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_WRITE)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
-    /* Check if switching to "dense" attribute storage is possible */
-    if(oh->version > H5O_VERSION_1 && !H5F_addr_defined(oh->attr_fheap_addr)) {
-        htri_t sharable;        /* Whether the attribute will be shared */
-        size_t raw_size = 0;    /* Raw size of message */
-
-        /* Check for attribute being sharable */
-        if((sharable = H5SM_can_share(loc->file, dxpl_id, NULL, NULL, H5O_ATTR_ID, attr)) < 0)
-            HGOTO_ERROR(H5E_ATTR, H5E_BADMESG, FAIL, "can't determine attribute sharing status")
-        else if(sharable == FALSE) {
-            /* Compute the size needed to encode the attribute */
-            raw_size = (H5O_MSG_ATTR->raw_size)(loc->file, FALSE, attr);
+    /* Check if this object already has attribute information */
+    if(oh->version > H5O_VERSION_1) {
+        hbool_t new_ainfo = FALSE;          /* Flag to indicate that the attribute information is new */
+
+        if(NULL == H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo)) {
+            /* Clear error stack from not finding attribute info */
+            H5E_clear_stack(NULL);
+
+            /* Initialize attribute information */
+            ainfo.track_corder = (oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED) ? TRUE : FALSE;
+            ainfo.index_corder = (oh->flags & H5O_HDR_ATTR_CRT_ORDER_INDEXED) ? TRUE : FALSE;
+            ainfo.max_crt_idx = 0;
+            ainfo.corder_bt2_addr = HADDR_UNDEF;
+            ainfo.nattrs = 0;
+            ainfo.fheap_addr = HADDR_UNDEF;
+            ainfo.name_bt2_addr = HADDR_UNDEF;
+
+            /* Set flag to add attribute information to object header */
+            new_ainfo = TRUE;
         } /* end if */
+        else {
+            /* Sanity check attribute info read in */
+            HDassert(ainfo.nattrs > 0);
+            HDassert(ainfo.track_corder == ((oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED) > 0));
+            HDassert(ainfo.index_corder == ((oh->flags & H5O_HDR_ATTR_CRT_ORDER_INDEXED) > 0));
+        } /* end else */
 
-        /* Check for condititions for switching to "dense" attribute storage are met */
-        if(oh->nattrs == oh->max_compact || (!sharable && raw_size >= H5O_MESG_MAX_SIZE)) {
-            H5O_iter_cvt_t udata;           /* User data for callback */
-            H5O_mesg_operator_t op;         /* Wrapper for operator */
-
-            /* Create dense storage for attributes */
-            if(H5A_dense_create(loc->file, dxpl_id, oh) < 0)
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to create dense storage for attributes")
-
-            /* Set up user data for callback */
-            udata.f = loc->file;
-            udata.dxpl_id = dxpl_id;
+        /* Check if switching to "dense" attribute storage is possible */
+        if(!H5F_addr_defined(ainfo.fheap_addr)) {
+            htri_t sharable;        /* Whether the attribute will be shared */
+            size_t raw_size = 0;    /* Raw size of message */
+
+            /* Check for attribute being sharable */
+            if((sharable = H5SM_can_share(loc->file, dxpl_id, NULL, NULL, H5O_ATTR_ID, attr)) < 0)
+                HGOTO_ERROR(H5E_ATTR, H5E_BADMESG, FAIL, "can't determine attribute sharing status")
+            else if(sharable == FALSE) {
+                /* Compute the size needed to encode the attribute */
+                raw_size = (H5O_MSG_ATTR->raw_size)(loc->file, FALSE, attr);
+            } /* end if */
 
-            /* Iterate over existing attributes, moving them to dense storage */
-            op.op_type = H5O_MESG_OP_LIB;
-            op.u.lib_op = H5O_attr_to_dense_cb;
-            if(H5O_msg_iterate_real(loc->file, oh, H5O_MSG_ATTR, &op, &udata, dxpl_id) < 0)
-                HGOTO_ERROR(H5E_ATTR, H5E_CANTCONVERT, FAIL, "error converting attributes to dense storage")
+            /* Check for condititions for switching to "dense" attribute storage are met */
+            if(ainfo.nattrs == oh->max_compact || (!sharable && raw_size >= H5O_MESG_MAX_SIZE)) {
+                H5O_iter_cvt_t udata;           /* User data for callback */
+                H5O_mesg_operator_t op;         /* Wrapper for operator */
+
+                /* Create dense storage for attributes */
+                if(H5A_dense_create(loc->file, dxpl_id, &ainfo) < 0)
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to create dense storage for attributes")
+
+                /* Set up user data for callback */
+                udata.f = loc->file;
+                udata.dxpl_id = dxpl_id;
+                udata.ainfo = &ainfo;
+
+                /* Iterate over existing attributes, moving them to dense storage */
+                op.op_type = H5O_MESG_OP_LIB;
+                op.u.lib_op = H5O_attr_to_dense_cb;
+                if(H5O_msg_iterate_real(loc->file, oh, H5O_MSG_ATTR, &op, &udata, dxpl_id) < 0)
+                    HGOTO_ERROR(H5E_ATTR, H5E_CANTCONVERT, FAIL, "error converting attributes to dense storage")
+            } /* end if */
         } /* end if */
-    } /* end if */
 
-    /* Increment attribute count on object */
-    oh->nattrs++;
+        /* Increment attribute count on object */
+        ainfo.nattrs++;
 
-    /* Later versions of the object header track the creation index on attributes */
-    if(oh->version > H5O_VERSION_1 && (oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED)) {
-        /* Check for attribute creation order index on the object wrapping around */
-        if(oh->max_attr_crt_idx == H5O_MAX_CRT_ORDER_IDX)
-            HGOTO_ERROR(H5E_ATTR, H5E_CANTINC, FAIL, "attribute creation index can't be incremented")
+        /* Check whether we're tracking the creation index on attributes */
+        if(ainfo.track_corder) {
+            /* Check for attribute creation order index on the object wrapping around */
+            if(ainfo.max_crt_idx == H5O_MAX_CRT_ORDER_IDX)
+                HGOTO_ERROR(H5E_ATTR, H5E_CANTINC, FAIL, "attribute creation index can't be incremented")
 
-        /* Set the creation order index on the attribute & incr. creation order index */
-        attr->crt_idx = oh->max_attr_crt_idx++;
+            /* Set the creation order index on the attribute & incr. creation order index */
+            attr->crt_idx = ainfo.max_crt_idx++;
+        } /* end if */
+        else
+            /* Set "bogus" creation index for attribute */
+            attr->crt_idx = H5O_MAX_CRT_ORDER_IDX;
+
+        /* Add the attribute information message, if one is needed */
+        if(new_ainfo) {
+            if(H5O_msg_append_real(loc->file, dxpl_id, oh, H5O_MSG_AINFO, H5O_MSG_FLAG_DONTSHARE, 0, &ainfo) < 0)
+                HGOTO_ERROR(H5E_ATTR, H5E_CANTINSERT, FAIL, "unable to create new attribute info message")
+        } /* end if */
+        /* Otherwise, update existing message */
+        else {
+            if(H5O_msg_write_real(loc->file, dxpl_id, oh, H5O_MSG_AINFO, H5O_MSG_FLAG_DONTSHARE, 0, &ainfo) < 0)
+                HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "unable to update attribute info message")
+        } /* end else */
     } /* end if */
-    else
+    else {
+        /* Set "bogus" creation index for attribute */
         attr->crt_idx = H5O_MAX_CRT_ORDER_IDX;
 
+        /* Set attribute info value to get attribute into object header */
+        ainfo.fheap_addr = HADDR_UNDEF;
+    } /* end else */
+
     /* Check for storing attribute with dense storage */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Insert attribute into dense storage */
-        if(H5A_dense_insert(loc->file, dxpl_id, oh, attr) < 0)
+        if(H5A_dense_insert(loc->file, dxpl_id, &ainfo, attr) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTINSERT, FAIL, "unable to add to dense storage")
     } /* end if */
     else {
@@ -399,6 +453,7 @@ H5A_t *
 H5O_attr_open_by_name(const H5O_loc_t *loc, const char *name, hid_t dxpl_id)
 {
     H5O_t *oh = NULL;                   /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;                  /* Attribute information for object */
     H5A_t *ret_value;                   /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5O_attr_open_by_name)
@@ -411,10 +466,16 @@ H5O_attr_open_by_name(const H5O_loc_t *loc, const char *name, hid_t dxpl_id)
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, NULL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check for opening attribute with dense storage */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Open attribute in dense storage */
-        if(NULL == (ret_value = H5A_dense_open(loc->file, dxpl_id, oh, name)))
+        if(NULL == (ret_value = H5A_dense_open(loc->file, dxpl_id, &ainfo, name)))
             HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, NULL, "can't open attribute")
     } /* end if */
     else {
@@ -671,6 +732,7 @@ herr_t
 H5O_attr_write(const H5O_loc_t *loc, hid_t dxpl_id, H5A_t *attr)
 {
     H5O_t *oh = NULL;                   /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;                  /* Attribute information for object */
     unsigned oh_flags = H5AC__NO_FLAGS_SET;     /* Metadata cache flags for object header */
     herr_t ret_value = SUCCEED;         /* Return value */
 
@@ -684,10 +746,16 @@ H5O_attr_write(const H5O_loc_t *loc, hid_t dxpl_id, H5A_t *attr)
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_WRITE)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check for attributes stored densely */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Modify the attribute data in dense storage */
-        if(H5A_dense_write(loc->file, dxpl_id, oh, attr) < 0)
+        if(H5A_dense_write(loc->file, dxpl_id, &ainfo, attr) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "error updating attribute")
     } /* end if */
     else {
@@ -836,13 +904,6 @@ H5O_attr_rename_mod_cb(H5O_t *oh, H5O_mesg_t *mesg/*in,out*/,
                 attr = (H5A_t *)mesg->native;
                 mesg->native = NULL;
 
-                /* If the later version of the object header format, decrement attribute */
-                /* (must be decremented before call to H5O_release_mesg(),
-                 *      so that the sanity checks pass - QAK)
-                 */
-                if(oh->version > H5O_VERSION_1)
-                    oh->nattrs--;
-
                 /* Delete old attribute */
                 /* (doesn't decrement the link count on shared components becuase
                  *      the "native" pointer has been reset)
@@ -850,13 +911,6 @@ H5O_attr_rename_mod_cb(H5O_t *oh, H5O_mesg_t *mesg/*in,out*/,
                 if(H5O_release_mesg(udata->f, udata->dxpl_id, oh, mesg, FALSE) < 0)
                     HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, H5_ITER_ERROR, "unable to release previous attribute")
 
-                /* Increment attribute count */
-                /* (must be incremented before call to H5O_msg_append_real(),
-                 *      so that the sanity checks pass - QAK)
-                 */
-                if(oh->version > H5O_VERSION_1)
-                    oh->nattrs++;
-
                 /* Append renamed attribute to object header */
                 /* (Don't let it become shared) */
                 if(H5O_msg_append_real(udata->f, udata->dxpl_id, oh, H5O_MSG_ATTR, (mesg->flags | H5O_MSG_FLAG_DONTSHARE), 0, attr) < 0)
@@ -902,6 +956,7 @@ H5O_attr_rename(const H5O_loc_t *loc, hid_t dxpl_id, const char *old_name,
     const char *new_name)
 {
     H5O_t *oh = NULL;                   /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;                  /* Attribute information for object */
     unsigned oh_flags = H5AC__NO_FLAGS_SET;     /* Metadata cache flags for object header */
     herr_t ret_value = SUCCEED;         /* Return value */
 
@@ -916,10 +971,16 @@ H5O_attr_rename(const H5O_loc_t *loc, hid_t dxpl_id, const char *old_name,
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_WRITE)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check for attributes stored densely */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Rename the attribute data in dense storage */
-        if(H5A_dense_rename(loc->file, dxpl_id, oh, old_name, new_name) < 0)
+        if(H5A_dense_rename(loc->file, dxpl_id, &ainfo, old_name, new_name) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "error updating attribute")
     } /* end if */
     else {
@@ -987,6 +1048,7 @@ H5O_attr_iterate_real(hid_t loc_id, const H5O_loc_t *loc, hid_t dxpl_id,
     hsize_t *last_attr, const H5A_attr_iter_op_t *attr_op, void *op_data)
 {
     H5O_t *oh = NULL;                   /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;                  /* Attribute information for object */
     H5A_attr_table_t atable = {0, NULL};        /* Table of attributes */
     herr_t ret_value;                   /* Return value */
 
@@ -1002,30 +1064,26 @@ H5O_attr_iterate_real(hid_t loc_id, const H5O_loc_t *loc, hid_t dxpl_id,
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
-    /* Check for attributes stored densely */
-    if(oh->version > H5O_VERSION_1 && H5F_addr_defined(oh->attr_fheap_addr)) {
-        haddr_t attr_fheap_addr;            /* Address of fractal heap for dense attribute storage */
-        haddr_t name_bt2_addr;              /* Address of v2 B-tree for name index on dense attribute storage */
-        haddr_t corder_bt2_addr;            /* Address of v2 B-tree for creation order index on dense attribute storage */
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
 
+    /* Check for attributes stored densely */
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Check for skipping too many attributes */
-        if(skip > 0 && skip >= oh->nattrs)
+        if(skip > 0 && skip >= ainfo.nattrs)
             HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid index specified")
 
-        /* Retrieve the information about dense attribute storage */
-        attr_fheap_addr = oh->attr_fheap_addr;
-        name_bt2_addr = oh->name_bt2_addr;
-        corder_bt2_addr = oh->corder_bt2_addr;
-
         /* Release the object header */
         if(H5AC_unprotect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, oh, H5AC__NO_FLAGS_SET) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_PROTECT, FAIL, "unable to release object header")
         oh = NULL;
 
         /* Iterate over attributes in dense storage */
-        if((ret_value = H5A_dense_iterate(loc->file, dxpl_id, loc_id, attr_fheap_addr,
-                name_bt2_addr, corder_bt2_addr, idx_type, order, skip,
-                last_attr, attr_op, op_data)) < 0)
+        if((ret_value = H5A_dense_iterate(loc->file, dxpl_id, loc_id, &ainfo,
+                idx_type, order, skip, last_attr, attr_op, op_data)) < 0)
             HERROR(H5E_ATTR, H5E_BADITER, "error iterating over attributes");
     } /* end if */
     else {
@@ -1109,85 +1167,90 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_attr_remove_update(const H5O_loc_t *loc, H5O_t *oh, hid_t dxpl_id)
+H5O_attr_remove_update(const H5O_loc_t *loc, H5O_t *oh, H5O_ainfo_t *ainfo,
+    hid_t dxpl_id)
 {
-    herr_t ret_value = SUCCEED;         /* Return value */
+    H5A_attr_table_t atable = {0, NULL};        /* Table of attributes */
+    herr_t ret_value = SUCCEED;                 /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5O_attr_remove_update)
 
     /* Check arguments */
     HDassert(loc);
     HDassert(oh);
+    HDassert(ainfo);
 
-    /* Reset the creation order min/max if there's no more attributes on the object */
-    if(oh->nattrs == 0)
-        oh->max_attr_crt_idx = 0;
+    /* Decrement the number of attributes on the object */
+    ainfo->nattrs--;
 
     /* Check for shifting from dense storage back to compact storage */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
-        /* Check if there's no more attributes */
-        if(oh->nattrs == 0) {
-            /* Delete the dense storage */
-            if(H5A_dense_delete(loc->file, dxpl_id, oh) < 0)
-                HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete dense attribute storage")
-        } /* end if */
-        else if(oh->nattrs < oh->min_dense) {
-            H5A_attr_table_t atable = {0, NULL};        /* Table of attributes */
-            hbool_t can_convert = TRUE;     /* Whether converting to attribute messages is possible */
-            size_t u;                       /* Local index */
-
-            /* Build the table of attributes for this object */
-            if(H5A_dense_build_table(loc->file, dxpl_id, oh->attr_fheap_addr, oh->name_bt2_addr, H5_INDEX_NAME, H5_ITER_NATIVE, &atable) < 0)
-                HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "error building attribute table")
-
-            /* Inspect attributes in table for ones that can't be converted back
-             * into attribute message form (currently only attributes which
-             * can't fit into an object header message)
-             */
-            for(u = 0; u < oh->nattrs; u++)
-                if(H5O_msg_size_oh(loc->file, oh, H5O_ATTR_ID, &(atable.attrs[u]), (size_t)0) >= H5O_MESG_MAX_SIZE) {
-                    can_convert = FALSE;
-                    break;
-                } /* end if */
+    if(H5F_addr_defined(ainfo->fheap_addr) && ainfo->nattrs < oh->min_dense) {
+        hbool_t can_convert = TRUE;     /* Whether converting to attribute messages is possible */
+        size_t u;                       /* Local index */
+
+        /* Build the table of attributes for this object */
+        if(H5A_dense_build_table(loc->file, dxpl_id, ainfo, H5_INDEX_NAME, H5_ITER_NATIVE, &atable) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "error building attribute table")
 
-            /* If ok, insert attributes as object header messages */
-            if(can_convert) {
-                /* Iterate over attributes, to put them into header */
-                for(u = 0; u < oh->nattrs; u++) {
-                    htri_t shared_mesg;             /* Should this message be stored in the Shared Message table? */
-
-                    /* Check if attribute is shared */
-                    if((shared_mesg = H5O_msg_is_shared(H5O_ATTR_ID, &(atable.attrs[u]))) < 0)
-                        HGOTO_ERROR(H5E_ATTR, H5E_CANTGET, FAIL, "error determining if message is shared")
-                    else if(shared_mesg == 0) {
-                        /* Increment reference count on attribute components */
-                        /* (so that they aren't deleted when the dense attribute storage is deleted) */
-                        if(H5O_attr_link(loc->file, dxpl_id, &(atable.attrs[u])) < 0)
-                            HGOTO_ERROR(H5E_ATTR, H5E_LINKCOUNT, FAIL, "unable to adjust attribute link count")
-                    } /* end if */
-                    else {
-                        /* Reset 'shared' status, so attributes will be shared again */
-                        atable.attrs[u].sh_loc.flags = 0;
-                    } /* end else */
-
-                    /* Insert attribute message into object header */
-                    /* (Will increment reference count on shared attributes) */
-                    if(H5O_msg_append_real(loc->file, dxpl_id, oh, H5O_MSG_ATTR, 0, 0, &(atable.attrs[u])) < 0)
-                        HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "can't create message")
-                } /* end for */
-
-                /* Remove the dense storage */
-                if(H5A_dense_delete(loc->file, dxpl_id, oh) < 0)
-                    HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete dense attribute storage")
+        /* Inspect attributes in table for ones that can't be converted back
+         * into attribute message form (currently only attributes which
+         * can't fit into an object header message)
+         */
+        for(u = 0; u < ainfo->nattrs; u++)
+            if(H5O_msg_size_oh(loc->file, oh, H5O_ATTR_ID, &(atable.attrs[u]), (size_t)0) >= H5O_MESG_MAX_SIZE) {
+                can_convert = FALSE;
+                break;
             } /* end if */
 
-            /* Free attribute table information */
-            if(H5A_attr_release_table(&atable) < 0)
-                HGOTO_ERROR(H5E_ATTR, H5E_CANTFREE, FAIL, "unable to release attribute table")
-        } /* end else */
+        /* If ok, insert attributes as object header messages */
+        if(can_convert) {
+            /* Iterate over attributes, to put them into header */
+            for(u = 0; u < ainfo->nattrs; u++) {
+                htri_t shared_mesg;             /* Should this message be stored in the Shared Message table? */
+
+                /* Check if attribute is shared */
+                if((shared_mesg = H5O_msg_is_shared(H5O_ATTR_ID, &(atable.attrs[u]))) < 0)
+                    HGOTO_ERROR(H5E_ATTR, H5E_CANTGET, FAIL, "error determining if message is shared")
+                else if(shared_mesg == 0) {
+                    /* Increment reference count on attribute components */
+                    /* (so that they aren't deleted when the dense attribute storage is deleted) */
+                    if(H5O_attr_link(loc->file, dxpl_id, &(atable.attrs[u])) < 0)
+                        HGOTO_ERROR(H5E_ATTR, H5E_LINKCOUNT, FAIL, "unable to adjust attribute link count")
+                } /* end if */
+                else {
+                    /* Reset 'shared' status, so attributes will be shared again */
+                    atable.attrs[u].sh_loc.flags = 0;
+                } /* end else */
+
+                /* Insert attribute message into object header */
+                /* (Will increment reference count on shared attributes) */
+                if(H5O_msg_append_real(loc->file, dxpl_id, oh, H5O_MSG_ATTR, 0, 0, &(atable.attrs[u])) < 0)
+                    HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "can't create message")
+            } /* end for */
+
+            /* Remove the dense storage */
+            if(H5A_dense_delete(loc->file, dxpl_id, ainfo) < 0)
+                HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete dense attribute storage")
+        } /* end if */
     } /* end if */
 
+    /* Check if we have deleted all the attributes and the attribute info
+     *  message should be deleted itself.
+     */
+    if(ainfo->nattrs == 0) {
+        if(H5O_msg_remove_real(loc->file, oh, H5O_MSG_AINFO, H5O_ALL, NULL, NULL, TRUE, dxpl_id) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete attribute info")
+    } /* end if */
+    else {
+        if(H5O_msg_write_real(loc->file, dxpl_id, oh, H5O_MSG_AINFO, H5O_MSG_FLAG_DONTSHARE, 0, ainfo) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "unable to update attribute info message")
+    } /* end else */
+
 done:
+    /* Release resources */
+    if(atable.attrs && H5A_attr_release_table(&atable) < 0)
+        HDONE_ERROR(H5E_ATTR, H5E_CANTFREE, FAIL, "unable to release attribute table")
+
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_attr_remove_update() */
 
@@ -1222,13 +1285,6 @@ H5O_attr_remove_cb(H5O_t *oh, H5O_mesg_t *mesg/*in,out*/,
 
     /* Check for correct attribute message to modify */
     if(HDstrcmp(((H5A_t *)mesg->native)->name, udata->name) == 0) {
-        /* If the later version of the object header format, decrement attribute */
-        /* (must be decremented before call to H5O_release_mesg(), in order for
-         *      sanity checks to pass - QAK)
-         */
-        if(oh->version > H5O_VERSION_1)
-            oh->nattrs--;
-
         /* Convert message into a null message (i.e. delete it) */
         if(H5O_release_mesg(udata->f, udata->dxpl_id, oh, mesg, TRUE) < 0)
             HGOTO_ERROR(H5E_OHDR, H5E_CANTDELETE, H5_ITER_ERROR, "unable to convert into null message")
@@ -1264,6 +1320,8 @@ herr_t
 H5O_attr_remove(const H5O_loc_t *loc, const char *name, hid_t dxpl_id)
 {
     H5O_t *oh = NULL;                   /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;                  /* Attribute information for object */
+    H5O_ainfo_t *ainfo_ptr = NULL;      /* Pointer to attribute information for object */
     unsigned oh_flags = H5AC__NO_FLAGS_SET;     /* Metadata cache flags for object header */
     herr_t ret_value = SUCCEED;         /* Return value */
 
@@ -1277,14 +1335,17 @@ H5O_attr_remove(const H5O_loc_t *loc, const char *name, hid_t dxpl_id)
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_WRITE)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == (ainfo_ptr = H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo)))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check for attributes stored densely */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Delete attribute from dense storage */
-        if(H5A_dense_remove(loc->file, dxpl_id, oh, name) < 0)
+        if(H5A_dense_remove(loc->file, dxpl_id, &ainfo, name) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete attribute in dense storage")
-
-        /* Decrement # of attributes on object */
-        oh->nattrs--;
     } /* end if */
     else {
         H5O_iter_rm_t udata;            /* User data for callback */
@@ -1307,9 +1368,10 @@ H5O_attr_remove(const H5O_loc_t *loc, const char *name, hid_t dxpl_id)
             HGOTO_ERROR(H5E_ATTR, H5E_NOTFOUND, FAIL, "can't locate attribute")
     } /* end else */
 
-    /* Update the object header information after removing an attribute */
-    if(H5O_attr_remove_update(loc, oh, dxpl_id) < 0)
-        HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "unable to update attribute info")
+    /* Update the attribute information after removing an attribute */
+    if(ainfo_ptr)
+        if(H5O_attr_remove_update(loc, oh, &ainfo, dxpl_id) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "unable to update attribute info")
 
     /* Update the modification time, if any */
     if(H5O_touch_oh(loc->file, dxpl_id, oh, FALSE) < 0)
@@ -1344,6 +1406,8 @@ H5O_attr_remove_by_idx(const H5O_loc_t *loc, H5_index_t idx_type,
     H5_iter_order_t order, hsize_t n, hid_t dxpl_id)
 {
     H5O_t *oh = NULL;                   /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;                  /* Attribute information for object */
+    H5O_ainfo_t *ainfo_ptr = NULL;      /* Pointer to attribute information for object */
     unsigned oh_flags = H5AC__NO_FLAGS_SET;     /* Metadata cache flags for object header */
     H5A_attr_table_t atable = {0, NULL};        /* Table of attributes */
     herr_t ret_value = SUCCEED;         /* Return value */
@@ -1357,14 +1421,17 @@ H5O_attr_remove_by_idx(const H5O_loc_t *loc, H5_index_t idx_type,
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_WRITE)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == (ainfo_ptr = H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo)))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check for attributes stored densely */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Delete attribute from dense storage */
-        if(H5A_dense_remove_by_idx(loc->file, dxpl_id, oh, idx_type, order, n) < 0)
+        if(H5A_dense_remove_by_idx(loc->file, dxpl_id, &ainfo, idx_type, order, n) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete attribute in dense storage")
-
-        /* Decrement # of attributes on object */
-        oh->nattrs--;
     } /* end if */
     else {
         H5O_iter_rm_t udata;            /* User data for callback */
@@ -1395,9 +1462,10 @@ H5O_attr_remove_by_idx(const H5O_loc_t *loc, H5_index_t idx_type,
             HGOTO_ERROR(H5E_ATTR, H5E_NOTFOUND, FAIL, "can't locate attribute")
     } /* end else */
 
-    /* Update the object header information after removing an attribute */
-    if(H5O_attr_remove_update(loc, oh, dxpl_id) < 0)
-        HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "unable to update attribute info")
+    /* Update the attribute information after removing an attribute */
+    if(ainfo_ptr)
+        if(H5O_attr_remove_update(loc, oh, &ainfo, dxpl_id) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTUPDATE, FAIL, "unable to update attribute info")
 
     /* Update the modification time, if any */
     if(H5O_touch_oh(loc->file, dxpl_id, oh, FALSE) < 0)
@@ -1417,6 +1485,56 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5O_attr_count_real
+ *
+ * Purpose:	Determine the # of attributes on an object
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		Thursday, March  9, 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+hsize_t
+H5O_attr_count_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh)
+{
+    hsize_t ret_value;          /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5O_attr_count_real)
+
+    /* Check arguments */
+    HDassert(f);
+    HDassert(oh);
+
+    /* Check for attributes stored densely */
+    if(oh->version > H5O_VERSION_1) {
+        H5O_ainfo_t ainfo;                  /* Attribute information for object */
+
+        /* Attempt to get the attribute information from the object header */
+        if(H5O_msg_read_real(f, dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+            ret_value = ainfo.nattrs;
+        else {
+            /* Clear error stack from not finding attribute info */
+            H5E_clear_stack(NULL);
+
+            ret_value = 0;
+        } /* end else */
+    } /* end if */
+    else {
+        unsigned u;             /* Local index variable */
+
+        /* Loop over all messages, counting the attributes */
+        for(u = ret_value = 0; u < oh->nmesgs; u++)
+            if(oh->mesg[u].type == H5O_MSG_ATTR)
+                ret_value++;
+    } /* end else */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5O_attr_count_real */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5O_attr_count
  *
  * Purpose:	Determine the # of attributes on an object
@@ -1443,17 +1561,8 @@ H5O_attr_count(const H5O_loc_t *loc, hid_t dxpl_id)
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
-    /* Check for attributes stored densely */
-    if(oh->version > H5O_VERSION_1)
-        ret_value = (int)oh->nattrs;
-    else {
-        unsigned u;             /* Local index variable */
-
-        /* Loop over all messages, counting the attributes */
-        for(u = ret_value = 0; u < oh->nmesgs; u++)
-            if(oh->mesg[u].type == H5O_MSG_ATTR)
-                ret_value++;
-    } /* end else */
+    /* Retrieve # of attributes on object */
+    ret_value = (int)H5O_attr_count_real(loc->file, dxpl_id, oh);
 
 done:
     if(oh && H5AC_unprotect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, oh, H5AC__NO_FLAGS_SET) < 0)
@@ -1519,6 +1628,7 @@ htri_t
 H5O_attr_exists(const H5O_loc_t *loc, const char *name, hid_t dxpl_id)
 {
     H5O_t *oh = NULL;           /* Pointer to actual object header */
+    H5O_ainfo_t ainfo;          /* Attribute information for object */
     htri_t ret_value;           /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5O_attr_exists)
@@ -1531,10 +1641,16 @@ H5O_attr_exists(const H5O_loc_t *loc, const char *name, hid_t dxpl_id)
     if(NULL == (oh = (H5O_t *)H5AC_protect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_ATTR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(loc->file, dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check for attributes stored densely */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Check if attribute exists in dense storage */
-        if((ret_value = H5A_dense_exists(loc->file, dxpl_id, oh, name)) < 0)
+        if((ret_value = H5A_dense_exists(loc->file, dxpl_id, &ainfo, name)) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_BADITER, FAIL, "error checking for existence of attribute")
     } /* end if */
     else {
diff --git a/src/H5Ocache.c b/src/H5Ocache.c
index 7000e9e..786d1d3 100644
--- a/src/H5Ocache.c
+++ b/src/H5Ocache.c
@@ -48,9 +48,6 @@
  *      extra I/O operations) */
 #define H5O_SPEC_READ_SIZE 512
 
-/* All the object header status flags that this version of the library knows about */
-#define H5O_HDR_ALL_FLAGS       (H5O_HDR_ATTR_CRT_ORDER_TRACKED | H5O_HDR_ATTR_CRT_ORDER_INDEXED | H5O_HDR_ATTR_STORE_PHASE_CHANGE | H5O_HDR_STORE_TIMES)
-
 
 /******************/
 /* Local Typedefs */
@@ -324,16 +321,6 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
             oh->max_compact = H5O_CRT_ATTR_MAX_COMPACT_DEF;
             oh->min_dense = H5O_CRT_ATTR_MIN_DENSE_DEF;
         } /* end else */
-        H5F_DECODE_LENGTH(f, p, oh->nattrs);
-        H5F_addr_decode(f, &p, &(oh->attr_fheap_addr));
-        H5F_addr_decode(f, &p, &(oh->name_bt2_addr));
-        H5F_addr_decode(f, &p, &(oh->corder_bt2_addr));
-
-        /* Only encode max. creation index if they are being tracked */
-        if(oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED)
-            UINT16DECODE(p, oh->max_attr_crt_idx)
-        else
-            oh->max_attr_crt_idx = 0;
     } /* end if */
     else {
         /* Reset unused time fields */
@@ -342,11 +329,6 @@ H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED * _udata1,
         /* Reset unused attribute fields */
         oh->max_compact = 0;
         oh->min_dense = 0;
-        oh->nattrs = 0;
-        oh->attr_fheap_addr = HADDR_UNDEF;
-        oh->name_bt2_addr = HADDR_UNDEF;
-        oh->corder_bt2_addr = HADDR_UNDEF;
-        oh->max_attr_crt_idx = 0;
     } /* end else */
 
     /* First chunk size */
@@ -689,14 +671,6 @@ H5O_assert(oh);
                 UINT16ENCODE(p, oh->max_compact);
                 UINT16ENCODE(p, oh->min_dense);
             } /* end if */
-            H5F_ENCODE_LENGTH(f, p, oh->nattrs);
-            H5F_addr_encode(f, &p, oh->attr_fheap_addr);
-            H5F_addr_encode(f, &p, oh->name_bt2_addr);
-            H5F_addr_encode(f, &p, oh->corder_bt2_addr);
-
-            /* Only encode max. creation index if they are being tracked */
-            if(oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED)
-                UINT16ENCODE(p, oh->max_attr_crt_idx);
 
             /* Chunk size */
             UINT32ENCODE(p, (oh->chunk[0].size - H5O_SIZEOF_HDR(oh)));
diff --git a/src/H5Ocopy.c b/src/H5Ocopy.c
index 6a01355..55ba9bf 100644
--- a/src/H5Ocopy.c
+++ b/src/H5Ocopy.c
@@ -348,28 +348,9 @@ H5O_copy_header_real(const H5O_loc_t *oloc_src, H5O_loc_t *oloc_dst /*out */,
     oh_dst->ctime = oh_src->ctime;
     oh_dst->btime = oh_src->btime;
 
-    /* Copy attribute information */
+    /* Copy attribute storage information */
     oh_dst->max_compact = oh_src->max_compact;
     oh_dst->min_dense = oh_src->min_dense;
-    if(cpy_info->copy_without_attr) {
-        oh_dst->nattrs = 0;
-        oh_dst->attr_fheap_addr = HADDR_UNDEF;
-        oh_dst->name_bt2_addr = HADDR_UNDEF;
-        oh_dst->corder_bt2_addr = HADDR_UNDEF;
-    } /* end if */
-    else {
-        oh_dst->nattrs = oh_src->nattrs;
-/* XXX: Bail out for now, if the source object has densely stored attributes */
-        if(H5F_addr_defined(oh_src->attr_fheap_addr))
-            HGOTO_ERROR(H5E_OHDR, H5E_UNSUPPORTED, FAIL, "densely stored attributes not supported yet")
-        else {
-            HDassert(!H5F_addr_defined(oh_src->name_bt2_addr));
-            oh_dst->attr_fheap_addr = HADDR_UNDEF;
-            oh_dst->name_bt2_addr = HADDR_UNDEF;
-            oh_dst->corder_bt2_addr = HADDR_UNDEF;
-        } /* end else */
-    } /* end else */
-    
 
     /* Initialize size of chunk array.  The destination always has only one
      * chunk.
diff --git a/src/H5Odbg.c b/src/H5Odbg.c
index de706c7..a5428c1 100644
--- a/src/H5Odbg.c
+++ b/src/H5Odbg.c
@@ -94,7 +94,6 @@ H5O_assert(const H5O_t *oh)
 {
     H5O_mesg_t *curr_msg;               /* Pointer to current message to examine */
     H5O_mesg_t *tmp_msg;                /* Pointer to temporary message to examine */
-    hsize_t num_attrs;                  /* Number of attributes on object */
     size_t meta_space;                  /* Size of header metadata */
     size_t mesg_space;                  /* Size of message raw data */
     size_t free_space;                  /* Size of free space in header */
@@ -108,7 +107,6 @@ H5O_assert(const H5O_t *oh)
     meta_space = H5O_SIZEOF_HDR(oh) + (H5O_SIZEOF_CHKHDR_OH(oh) * (oh->nchunks - 1));
     mesg_space = 0;
     free_space = 0;
-    num_attrs = 0;
 
     /* Loop over all chunks in object header */
     for(u = 0; u < oh->nchunks; u++) {
@@ -140,10 +138,6 @@ H5O_assert(const H5O_t *oh)
 
     /* Loop over all messages in object header */
     for(u = 0, curr_msg = &oh->mesg[0]; u < oh->nmesgs; u++, curr_msg++) {
-        /* Check for attribute message */
-	if(H5O_ATTR_ID == curr_msg->type->id)
-            num_attrs++;
-
         /* Accumulate information, based on the type of message */
 	if(H5O_NULL_ID == curr_msg->type->id)
             free_space += H5O_SIZEOF_MSGHDR_OH(oh) + curr_msg->raw_size;
@@ -175,8 +169,6 @@ H5O_assert(const H5O_t *oh)
                 HDassert(!(tmp_msg->raw >= curr_msg->raw && tmp_msg->raw < (curr_msg->raw + curr_msg->raw_size)));
         } /* end for */
     } /* end for */
-    if(oh->version > H5O_VERSION_1 && !H5F_addr_defined(oh->attr_fheap_addr))
-        HDassert(oh->nattrs == num_attrs);
 
     /* Sanity check that all the bytes are accounted for */
     HDassert(hdr_size == (free_space + meta_space + mesg_space + oh->skipped_mesg_size));
@@ -276,54 +268,59 @@ H5O_debug_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh, haddr_t addr, FILE *stream, i
     HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
 	      "Number of links:",
 	      oh->nlink);
+
     /* Extra information for later versions */
     if(oh->version > H5O_VERSION_1) {
-        struct tm *tm;          /* Time structure */
-        char buf[128];          /* Buffer for formatting time info */
-
-        /* Time fields */
-        tm = HDlocaltime(&oh->atime);
-        HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
-        HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
-                "Access Time:", buf);
-        tm = HDlocaltime(&oh->mtime);
-        HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
-        HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
-                "Modification Time:", buf);
-        tm = HDlocaltime(&oh->ctime);
-        HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
-        HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
-                "Change Time:", buf);
-        tm = HDlocaltime(&oh->btime);
-        HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
-        HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
-                "Birth Time:", buf);
-
-        /* Attribute tracking fields */
+        /* Display object's status flags */
 	HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
 		   "Attribute creation order tracked:",
 		   (oh->flags & H5P_CRT_ORDER_TRACKED) ? "Yes" : "No");
 	HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
 		   "Attribute creation order indexed:",
 		   (oh->flags & H5P_CRT_ORDER_INDEXED) ? "Yes" : "No");
-        HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
-                  "Max. compact attributes:",
-                  (unsigned)oh->max_compact);
-        HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
-                  "Min. dense attributes:",
-                  (unsigned)oh->min_dense);
-        HDfprintf(stream, "%*s%-*s %Hu\n", indent, "", fwidth,
-                  "Number of attributes:",
-                  oh->nattrs);
-        HDfprintf(stream, "%*s%-*s %a\n", indent, "", fwidth,
-                  "Attribute heap address:",
-                  oh->attr_fheap_addr);
-        HDfprintf(stream, "%*s%-*s %a\n", indent, "", fwidth,
-                  "Attribute name index address:",
-                  oh->name_bt2_addr);
-        HDfprintf(stream, "%*s%-*s %a\n", indent, "", fwidth,
-                  "Attribute creation order index address:",
-                  oh->corder_bt2_addr);
+	HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
+		   "Attribute storage phase change values:",
+		   (oh->flags & H5O_HDR_ATTR_STORE_PHASE_CHANGE) ? "Non-default" : "Default");
+	HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
+		   "Timestamps:",
+		   (oh->flags & H5O_HDR_STORE_TIMES) ? "Enabled" : "Disabled");
+        if(oh->flags & ~H5O_HDR_ALL_FLAGS)
+            HDfprintf(stream, "*** UNKNOWN OBJECT HEADER STATUS FLAG: %02x!\n",
+                (unsigned)oh->flags);
+
+        /* Only dump times, if they are tracked */
+        if(oh->flags & H5O_HDR_STORE_TIMES) {
+            struct tm *tm;          /* Time structure */
+            char buf[128];          /* Buffer for formatting time info */
+
+            /* Time fields */
+            tm = HDlocaltime(&oh->atime);
+            HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
+            HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
+                    "Access Time:", buf);
+            tm = HDlocaltime(&oh->mtime);
+            HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
+            HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
+                    "Modification Time:", buf);
+            tm = HDlocaltime(&oh->ctime);
+            HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
+            HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
+                    "Change Time:", buf);
+            tm = HDlocaltime(&oh->btime);
+            HDstrftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", tm);
+            HDfprintf(stream, "%*s%-*s %s\n", indent, "", fwidth,
+                    "Birth Time:", buf);
+        } /* end if */
+
+        /* Attribute tracking fields */
+        if(oh->flags & H5O_HDR_ATTR_STORE_PHASE_CHANGE) {
+            HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
+                      "Max. compact attributes:",
+                      (unsigned)oh->max_compact);
+            HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
+                      "Min. dense attributes:",
+                      (unsigned)oh->min_dense);
+        } /* end if */
     } /* end if */
 
     HDfprintf(stream, "%*s%-*s %Zu (%Zu)\n", indent, "", fwidth,
diff --git a/src/H5Omessage.c b/src/H5Omessage.c
index bf0d0b0..651cd64 100644
--- a/src/H5Omessage.c
+++ b/src/H5Omessage.c
@@ -73,12 +73,7 @@ typedef struct {
 /* Local Prototypes */
 /********************/
 
-static herr_t H5O_msg_write_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
-    const H5O_msg_class_t *type, unsigned mesg_flags, unsigned update_flags,
-    void *mesg);
 static herr_t H5O_msg_reset_real(const H5O_msg_class_t *type, void *native);
-static herr_t H5O_msg_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_msg_remove_cb(H5O_t *oh, H5O_mesg_t *mesg/*in,out*/, 
     unsigned sequence, hbool_t *oh_modified, void *_udata/*in,out*/);
 static herr_t H5O_copy_mesg(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned idx,
@@ -325,7 +320,7 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-static herr_t
+herr_t
 H5O_msg_write_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh, const H5O_msg_class_t *type,
     unsigned mesg_flags, unsigned update_flags, void *mesg)
 {
@@ -339,10 +334,11 @@ H5O_msg_write_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh, const H5O_msg_class_t *ty
     HDassert(f);
     HDassert(oh);
     HDassert(type);
+    HDassert(type != H5O_MSG_ATTR);
     HDassert(mesg);
     HDassert(0 == (mesg_flags & ~H5O_MSG_FLAG_BITS));
 
-    /* Count similar messages */
+    /* Locate message of correct type */
     for(idx = 0, idx_msg = &oh->mesg[0]; idx < oh->nmesgs; idx++, idx_msg++)
 	if(type->id == idx_msg->type->id)
             break;
@@ -433,7 +429,7 @@ H5O_msg_read(const H5O_loc_t *loc, unsigned type_id, void *mesg,
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL, "unable to load object header")
 
     /* Call the "real" read routine */
-    if((ret_value = H5O_msg_read_real(loc->file, dxpl_id, oh, type_id, mesg)) == NULL)
+    if(NULL == (ret_value = H5O_msg_read_real(loc->file, dxpl_id, oh, type_id, mesg)))
 	HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to load object header")
 
 done:
@@ -915,6 +911,7 @@ herr_t
 H5O_msg_remove(H5O_loc_t *loc, unsigned type_id, int sequence, hbool_t adj_link,
     hid_t dxpl_id)
 {
+    H5O_t *oh = NULL;                   /* Pointer to actual object header */
     const H5O_msg_class_t *type;            /* Actual H5O class type for the ID */
     herr_t      ret_value;              /* Return value */
 
@@ -929,11 +926,18 @@ H5O_msg_remove(H5O_loc_t *loc, unsigned type_id, int sequence, hbool_t adj_link,
     type = H5O_msg_class_g[type_id];    /* map the type ID to the actual type object */
     HDassert(type);
 
+    /* Protect the object header to iterate over */
+    if(NULL == (oh = (H5O_t *)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")
+
     /* Call the "real" remove routine */
-    if((ret_value = H5O_msg_remove_real(loc, type, sequence, NULL, NULL, adj_link, dxpl_id)) < 0)
+    if((ret_value = H5O_msg_remove_real(loc->file, oh, type, sequence, NULL, NULL, adj_link, dxpl_id)) < 0)
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTDELETE, FAIL, "unable to remove object header message")
 
 done:
+    if(oh && H5AC_unprotect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, oh, H5AC__NO_FLAGS_SET) < 0)
+        HDONE_ERROR(H5E_OHDR, H5E_PROTECT, FAIL, "unable to release object header")
+
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_msg_remove() */
 
@@ -959,6 +963,7 @@ herr_t
 H5O_msg_remove_op(const H5O_loc_t *loc, unsigned type_id, int sequence,
     H5O_operator_t op, void *op_data, hbool_t adj_link, hid_t dxpl_id)
 {
+    H5O_t *oh = NULL;                   /* Pointer to actual object header */
     const H5O_msg_class_t *type;            /* Actual H5O class type for the ID */
     herr_t      ret_value;              /* Return value */
 
@@ -973,11 +978,18 @@ H5O_msg_remove_op(const H5O_loc_t *loc, unsigned type_id, int sequence,
     type = H5O_msg_class_g[type_id];    /* map the type ID to the actual type object */
     HDassert(type);
 
+    /* Protect the object header to iterate over */
+    if(NULL == (oh = (H5O_t *)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")
+
     /* Call the "real" remove routine */
-    if((ret_value = H5O_msg_remove_real(loc, type, sequence, op, op_data, adj_link, dxpl_id)) < 0)
+    if((ret_value = H5O_msg_remove_real(loc->file, oh, type, sequence, op, op_data, adj_link, dxpl_id)) < 0)
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTDELETE, FAIL, "unable to remove object header message")
 
 done:
+    if(oh && H5AC_unprotect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, oh, H5AC__NO_FLAGS_SET) < 0)
+        HDONE_ERROR(H5E_OHDR, H5E_PROTECT, FAIL, "unable to release object header")
+
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_msg_remove_op() */
 
@@ -1058,9 +1070,6 @@ done:
  *		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:	Non-negative on success/Negative on failure
  *
  * Programmer:	Robb Matzke
@@ -1069,28 +1078,28 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-static herr_t
-H5O_msg_remove_real(const H5O_loc_t *loc, const H5O_msg_class_t *type, int sequence,
-    H5O_operator_t app_op, void *op_data, hbool_t adj_link, hid_t dxpl_id)
+herr_t
+H5O_msg_remove_real(H5F_t *f, H5O_t *oh, const H5O_msg_class_t *type,
+    int sequence, H5O_operator_t app_op, void *op_data, hbool_t adj_link,
+    hid_t dxpl_id)
 {
-    H5O_t *oh = NULL;                   /* Pointer to actual object header */
     H5O_iter_rm_t udata;                /* User data for iterator */
     H5O_mesg_operator_t op;             /* Wrapper for operator */
     herr_t ret_value = SUCCEED;         /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5O_msg_remove_real)
+    FUNC_ENTER_NOAPI(H5O_msg_remove_real, FAIL)
 
     /* check args */
-    HDassert(loc);
-    HDassert(loc->file);
+    HDassert(f);
+    HDassert(oh);
     HDassert(type);
 
     /* Make certain we are allowed to modify the file */
-    if(0 == (H5F_INTENT(loc->file) & H5F_ACC_RDWR))
-	HGOTO_ERROR(H5E_HEAP, H5E_WRITEERROR, FAIL, "no write intent on file")
+    if(0 == (H5F_INTENT(f) & H5F_ACC_RDWR))
+	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "no write intent on file")
 
     /* Set up iterator operator data */
-    udata.f = loc->file;
+    udata.f = f;
     udata.dxpl_id = dxpl_id;
     udata.sequence = sequence;
     udata.nfailed = 0;
@@ -1098,14 +1107,10 @@ H5O_msg_remove_real(const H5O_loc_t *loc, const H5O_msg_class_t *type, int seque
     udata.op_data = op_data;
     udata.adj_link = adj_link;
 
-    /* Protect the object header to iterate over */
-    if(NULL == (oh = (H5O_t *)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")
-
     /* Iterate over the messages, deleting appropriate one(s) */
     op.op_type = H5O_MESG_OP_LIB;
     op.u.lib_op = H5O_msg_remove_cb;
-    if(H5O_msg_iterate_real(loc->file, oh, type, &op, &udata, dxpl_id) < 0)
+    if(H5O_msg_iterate_real(f, oh, type, &op, &udata, dxpl_id) < 0)
         HGOTO_ERROR(H5E_OHDR, H5E_NOTFOUND, FAIL, "error iterating over messages")
 
     /* Fail if we tried to remove any constant messages */
@@ -1113,9 +1118,6 @@ H5O_msg_remove_real(const H5O_loc_t *loc, const H5O_msg_class_t *type, int seque
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "unable to remove constant message(s)")
 
 done:
-    if(oh && H5AC_unprotect(loc->file, dxpl_id, H5AC_OHDR, loc->addr, oh, H5AC__NO_FLAGS_SET) < 0)
-        HDONE_ERROR(H5E_OHDR, H5E_PROTECT, FAIL, "unable to release object header")
-
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_msg_remove_real() */
 
diff --git a/src/H5Opkg.h b/src/H5Opkg.h
index 68066cf..bd92478 100644
--- a/src/H5Opkg.h
+++ b/src/H5Opkg.h
@@ -24,7 +24,6 @@
 #include "H5Oprivate.h"		/* Object headers		  	*/
 
 /* Other private headers needed by this file */
-#include "H5Aprivate.h"		/* Attributes				*/
 #include "H5ACprivate.h"	/* Metadata cache			*/
 
 /* Object header macros */
@@ -116,13 +115,6 @@
                   2 +		/*max compact attributes */		      \
                   2		/*min dense attributes	*/		      \
                 ) : 0) +						      \
-                (O)->sizeof_size + /*# of attributes	*/		      \
-                (O)->sizeof_addr + /*addr of attribute heap */		      \
-                (O)->sizeof_addr + /*addr of attribute name index */	      \
-                (O)->sizeof_addr + /*addr of attribute creation order index */ \
-                (((O)->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED) ? (	      \
-                  2		/*max attr. creation index */		      \
-                ) : 0) +						      \
                 4 +		/*chunk data size	*/		      \
                 H5O_SIZEOF_CHKSUM) /*checksum size	*/		      \
     )
@@ -197,6 +189,9 @@
         } /* end if */							      \
     } /* end if */
 
+/* All the object header status flags that this version of the library knows about */
+#define H5O_HDR_ALL_FLAGS       (H5O_HDR_ATTR_CRT_ORDER_TRACKED | H5O_HDR_ATTR_CRT_ORDER_INDEXED | H5O_HDR_ATTR_STORE_PHASE_CHANGE | H5O_HDR_STORE_TIMES)
+
 
 /* The "message class" type */
 struct H5O_msg_class_t {
@@ -263,11 +258,6 @@ struct H5O_t {
     /* Attribute information (stored, for versions > 1) */
     unsigned	max_compact;		/* Maximum # of compact attributes   */
     unsigned	min_dense;		/* Minimum # of "dense" attributes   */
-    hsize_t     nattrs;                 /* Number of attributes on the object */
-    haddr_t     attr_fheap_addr;        /* Address of fractal heap for storing "dense" attributes */
-    haddr_t     name_bt2_addr;          /* Address of v2 B-tree for indexing names of attributes */
-    haddr_t     corder_bt2_addr;        /* Address of v2 B-tree for indexing creation order of attributes */
-    H5O_msg_crt_idx_t max_attr_crt_idx; /* Maximum attribute creation index used */
 
     /* Message management (stored, encoded in chunks) */
     size_t	nmesgs;			/*number of messages		     */
@@ -469,12 +459,17 @@ H5_DLL unsigned H5O_msg_alloc(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
 H5_DLL herr_t H5O_msg_append_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
     const H5O_msg_class_t *type, unsigned mesg_flags, unsigned update_flags,
     void *mesg);
+H5_DLL herr_t H5O_msg_write_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
+    const H5O_msg_class_t *type, unsigned mesg_flags, unsigned update_flags,
+    void *mesg);
 H5_DLL void *H5O_msg_read_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh,
     unsigned type_id, void *mesg);
 H5_DLL void *H5O_msg_free_real(const H5O_msg_class_t *type, void *mesg);
 H5_DLL herr_t H5O_msg_free_mesg(H5O_mesg_t *mesg);
 H5_DLL unsigned H5O_msg_count_real(const H5O_t *oh, const H5O_msg_class_t *type);
 H5_DLL htri_t H5O_msg_exists_oh(const H5O_t *oh, unsigned type_id);
+H5_DLL herr_t H5O_msg_remove_real(H5F_t *f, H5O_t *oh, const H5O_msg_class_t *type,
+    int sequence, H5O_operator_t op, void *op_data, hbool_t adj_link, hid_t dxpl_id);
 H5_DLL void *H5O_msg_copy_file(const H5O_msg_class_t *type, H5F_t *file_src,
     void *mesg_src, H5F_t *file_dst, hid_t dxpl_id, hbool_t *shared,
     H5O_copy_t *cpy_info, void *udata);
@@ -502,7 +497,7 @@ H5_DLL herr_t H5O_shared_copy_file(H5F_t *file_src, H5F_t *file_dst, hid_t dxpl_
 H5_DLL herr_t H5O_shared_debug(const H5O_shared_t *mesg, FILE *stream,
     int indent, int fwidth);
 
-/* Attribute operators */
+/* Attribute message operators */
 H5_DLL herr_t H5O_attr_reset(void *_mesg);
 H5_DLL herr_t H5O_attr_delete(H5F_t *f, hid_t dxpl_id, const void *_mesg);
 H5_DLL herr_t H5O_attr_link(H5F_t *f, hid_t dxpl_id, const void *_mesg);
diff --git a/src/H5Oprivate.h b/src/H5Oprivate.h
index 5349827..c916f7e 100644
--- a/src/H5Oprivate.h
+++ b/src/H5Oprivate.h
@@ -415,6 +415,7 @@ typedef struct H5O_drvinfo_t {
  */
 typedef struct H5O_ainfo_t {
     /* (creation order info) */
+    hbool_t     track_corder;           /* Are creation order values tracked on attributes? */
     hbool_t     index_corder;           /* Are creation order values indexed on attributes? */
     H5O_msg_crt_idx_t max_crt_idx;      /* Maximum attribute creation index used */
     haddr_t     corder_bt2_addr;        /* Address of v2 B-tree for indexing creation order values of "dense" attributes */
@@ -525,5 +526,8 @@ H5_DLL herr_t H5O_link_delete(H5F_t *f, hid_t dxpl_id, const void *_mesg);
 /* Shared message operators */
 H5_DLL herr_t H5O_shared_copy(void *dst, const H5O_shared_t *src);
 
+/* Attribute operators */
+H5_DLL hsize_t H5O_attr_count_real(H5F_t *f, hid_t dxpl_id, H5O_t *oh);
+
 #endif /* _H5Oprivate_H */
 
diff --git a/src/H5Otest.c b/src/H5Otest.c
index ac444e5..dc516c6 100644
--- a/src/H5Otest.c
+++ b/src/H5Otest.c
@@ -96,6 +96,7 @@ htri_t
 H5O_is_attr_dense_test(hid_t oid)
 {
     H5O_t *oh = NULL;           /* Object header */
+    H5O_ainfo_t ainfo;          /* Attribute information for object */
     H5O_loc_t *oloc;            /* Pointer to object's location */
     htri_t ret_value;           /* Return value */
 
@@ -109,8 +110,14 @@ H5O_is_attr_dense_test(hid_t oid)
     if(NULL == (oh = H5AC_protect(oloc->file, H5AC_ind_dxpl_id, H5AC_OHDR, oloc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(oloc->file, H5AC_ind_dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check if dense storage is being used */
-    if(H5F_addr_defined(oh->attr_fheap_addr)) {
+    if(H5F_addr_defined(ainfo.fheap_addr)) {
         /* Check for any messages in object header */
         HDassert(H5O_msg_count_real(oh, H5O_MSG_ATTR) == 0);
 
@@ -149,6 +156,8 @@ htri_t
 H5O_is_attr_empty_test(hid_t oid)
 {
     H5O_t *oh = NULL;           /* Object header */
+    H5O_ainfo_t ainfo;          /* Attribute information for object */
+    H5O_ainfo_t *ainfo_ptr = NULL;      /* Pointer to attribute information for object */
     H5O_loc_t *oloc;            /* Pointer to object's location */
     hsize_t nattrs;             /* Number of attributes */
     htri_t ret_value;           /* Return value */
@@ -163,23 +172,33 @@ H5O_is_attr_empty_test(hid_t oid)
     if(NULL == (oh = H5AC_protect(oloc->file, H5AC_ind_dxpl_id, H5AC_OHDR, oloc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == (ainfo_ptr = H5O_msg_read_real(oloc->file, H5AC_ind_dxpl_id, oh, H5O_AINFO_ID, &ainfo)))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Retrieve the number of attribute messages in header */
     nattrs = H5O_msg_count_real(oh, H5O_MSG_ATTR);
 
-    /* Check for later version of object header format */
+    /* Check for later version of object header format & attribute info available */
     if(oh->version > H5O_VERSION_1) {
-        /* Check for using dense storage */
-        if(H5F_addr_defined(oh->attr_fheap_addr)) {
-            /* Check for any messages in object header */
-            HDassert(nattrs == 0);
-
-            /* Retrieve # of records in name index */
-            if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &nattrs) < 0)
-                HGOTO_ERROR(H5E_SYM, H5E_CANTCOUNT, FAIL, "unable to retrieve # of records from name index")
+        if(ainfo_ptr) {
+            /* Check for using dense storage */
+            if(H5F_addr_defined(ainfo.fheap_addr)) {
+                /* Check for any messages in object header */
+                HDassert(nattrs == 0);
+
+                /* Retrieve # of records in name index */
+                if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_NAME, ainfo.name_bt2_addr, &nattrs) < 0)
+                    HGOTO_ERROR(H5E_SYM, H5E_CANTCOUNT, FAIL, "unable to retrieve # of records from name index")
+            } /* end if */
+
+            /* Verify that attribute count in object header is correct */
+            HDassert(nattrs == ainfo.nattrs);
         } /* end if */
-
-        /* Verify that attribute count in object header is correct */
-        HDassert(nattrs == oh->nattrs);
+        else
+            HDassert(nattrs == 0);
     } /* end if */
 
     /* Set the return value */
@@ -216,6 +235,7 @@ herr_t
 H5O_num_attrs_test(hid_t oid, hsize_t *nattrs)
 {
     H5O_t *oh = NULL;           /* Object header */
+    H5O_ainfo_t ainfo;          /* Attribute information for object */
     H5O_loc_t *oloc;            /* Pointer to object's location */
     hsize_t obj_nattrs;         /* Number of attributes */
     herr_t ret_value = SUCCEED; /* Return value */
@@ -230,23 +250,29 @@ H5O_num_attrs_test(hid_t oid, hsize_t *nattrs)
     if(NULL == (oh = H5AC_protect(oloc->file, H5AC_ind_dxpl_id, H5AC_OHDR, oloc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(oloc->file, H5AC_ind_dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Retrieve the number of attribute messages in header */
     obj_nattrs = H5O_msg_count_real(oh, H5O_MSG_ATTR);
 
     /* Check for later version of object header format */
     if(oh->version > H5O_VERSION_1) {
         /* Check for using dense storage */
-        if(H5F_addr_defined(oh->attr_fheap_addr)) {
+        if(H5F_addr_defined(ainfo.fheap_addr)) {
             /* Check for any messages in object header */
             HDassert(obj_nattrs == 0);
 
             /* Retrieve # of records in name index */
-            if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, &obj_nattrs) < 0)
+            if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_NAME, ainfo.name_bt2_addr, &obj_nattrs) < 0)
                 HGOTO_ERROR(H5E_SYM, H5E_CANTCOUNT, FAIL, "unable to retrieve # of records from name index")
         } /* end if */
 
         /* Verify that attribute count in object header is correct */
-        HDassert(obj_nattrs == oh->nattrs);
+        HDassert(obj_nattrs == ainfo.nattrs);
     } /* end if */
 
     /* Set the number of attributes */
@@ -285,6 +311,7 @@ herr_t
 H5O_attr_dense_info_test(hid_t oid, hsize_t *name_count, hsize_t *corder_count)
 {
     H5O_t *oh = NULL;           /* Object header */
+    H5O_ainfo_t ainfo;          /* Attribute information for object */
     H5O_loc_t *oloc;            /* Pointer to object's location */
     herr_t ret_value = SUCCEED; /* Return value */
 
@@ -298,20 +325,26 @@ H5O_attr_dense_info_test(hid_t oid, hsize_t *name_count, hsize_t *corder_count)
     if(NULL == (oh = H5AC_protect(oloc->file, H5AC_ind_dxpl_id, H5AC_OHDR, oloc->addr, NULL, NULL, H5AC_READ)))
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unable to load object header")
 
+    /* Check for attribute info stored */
+    ainfo.fheap_addr = HADDR_UNDEF;
+    if(oh->version > H5O_VERSION_1 && NULL == H5O_msg_read_real(oloc->file, H5AC_ind_dxpl_id, oh, H5O_AINFO_ID, &ainfo))
+        /* Clear error stack from not finding attribute info */
+        H5E_clear_stack(NULL);
+
     /* Check for 'dense' attribute storage file addresses being defined */
-    if(!H5F_addr_defined(oh->attr_fheap_addr))
+    if(!H5F_addr_defined(ainfo.fheap_addr))
         HGOTO_DONE(FAIL)
-    if(!H5F_addr_defined(oh->name_bt2_addr))
+    if(!H5F_addr_defined(ainfo.name_bt2_addr))
         HGOTO_DONE(FAIL)
 
     /* Retrieve # of records in name index */
-    if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_NAME, oh->name_bt2_addr, name_count) < 0)
+    if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_NAME, ainfo.name_bt2_addr, name_count) < 0)
         HGOTO_ERROR(H5E_SYM, H5E_CANTCOUNT, FAIL, "unable to retrieve # of records from name index")
 
     /* Check if there is a creation order index */
-    if(H5F_addr_defined(oh->corder_bt2_addr)) {
+    if(H5F_addr_defined(ainfo.corder_bt2_addr)) {
         /* Retrieve # of records in creation order index */
-        if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_CORDER, oh->corder_bt2_addr, corder_count) < 0)
+        if(H5B2_get_nrec(oloc->file, H5AC_ind_dxpl_id, H5A_BT2_CORDER, ainfo.corder_bt2_addr, corder_count) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTCOUNT, FAIL, "unable to retrieve # of records from creation order index")
     } /* end if */
     else