[svn-r13375] Description:

	Straighten out some of the code for handling superblocks, in preparation
for revising the format of the latest version of the superblock before the
beta release.

Tested on:
	Mac OS X/32 10.4.8 (amazon)
	FreeBSD/32 6.2 (duty)

8 files changed, 308 insertions, 324 deletions

diff --git a/src/H5F.c b/src/H5F.c
index 236c07d..36e1053 100644
--- a/src/H5F.c
+++ b/src/H5F.c
@@ -946,9 +946,8 @@ H5F_new(H5F_file_t *shared, hid_t fcpl_id, hid_t fapl_id, H5FD_t *lf)
          * and set the version # of the superblock to 1 if it is a non-default
          * value.
          */
-        if(f->shared->btree_k[H5B_ISTORE_ID]!=HDF5_BTREE_ISTORE_IK_DEF) {
-            super_vers= HDF5_SUPERBLOCK_VERSION_1 ; /* Super block version 1 */
-        }
+        if(f->shared->btree_k[H5B_ISTORE_ID] != HDF5_BTREE_ISTORE_IK_DEF)
+            super_vers = HDF5_SUPERBLOCK_VERSION_1; /* Super block version 1 */
 
         /* The shared object header message table gets created later, but if
          * it is present we should use version 2 of the superblock.
@@ -958,9 +957,9 @@ H5F_new(H5F_file_t *shared, hid_t fcpl_id, hid_t fapl_id, H5FD_t *lf)
         HDassert(sohm_indexes < 255);
         f->shared->sohm_nindexes = sohm_indexes;
 
-        if(sohm_indexes > 0) {
-            super_vers= HDF5_SUPERBLOCK_VERSION_2; /* Super block version 2 */
-        }
+        /* Bump superblock version to hold SOHM info */
+        if(sohm_indexes > 0)
+            super_vers = HDF5_SUPERBLOCK_VERSION_2; /* Super block version 2 */
 
         if(NULL == (plist = H5I_object(fapl_id)))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not file access property list")
@@ -1377,80 +1376,56 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t d
      * empty or not.
      */
     if(0 == H5FD_get_eof(lf) && (flags & H5F_ACC_RDWR)) {
+        H5O_loc_t ext_loc;      /* Superblock extension location */
+
         /*
          * We've just opened a fresh new file (or truncated one). We need
          * to create & write the superblock.
          */
+
         /* Initialize information about the superblock and allocate space for it */
-        if(H5F_init_superblock(file, dxpl_id) == 0)
+        if(H5F_init_superblock(file, &ext_loc, dxpl_id) < 0)
             HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to allocate file superblock")
 
-        /* Create the Shared Object Header Message table and register it with the
-         * metadata cache, if this file supports shared messages */
+        /* Create the Shared Object Header Message table and register it with
+         *      the metadata cache, if this file supports shared messages.
+         */
         if(file->shared->sohm_nindexes > 0) {
             H5P_genplist_t     *c_plist;            /*file creation property list     */
-            if(NULL == (c_plist = H5P_object_verify(fcpl_id,H5P_FILE_CREATE)))
+
+            /* Get the file's creation property list */
+            if(NULL == (c_plist = H5P_object_verify(fcpl_id, H5P_FILE_CREATE)))
                 HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, NULL, "can't find object for ID");
 
-            if(H5SM_init(file, c_plist, dxpl_id) <0)
+            /* Initialize the shared message code */
+            if(H5SM_init(file, c_plist, &ext_loc, dxpl_id) < 0)
                 HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to create SOHM table")
-        }
-
-        /* Create and open the root group */
-        /* (This must be after the space for the superblock is allocated in
-         *      the file and after the SOHM table has been created)
-         */
-        if(H5G_mkroot(file, dxpl_id, NULL) < 0)
-            HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to create/open root group")
+        } /* end if */
 
-        /* Create the superblock extension and write "extra" superblock data.
-         * Currently, the extension is only needed if Shared Object Header
-         * Messages are enabled.
-         */
-        if(file->shared->sohm_nindexes > 0) {
-            H5O_loc_t ext_loc;                      /* Superblock extension location */
-            H5O_shmesg_table_t sohm_table;
-
-            /* The superblock extension isn't actually a group, but the
-             * default group creation list should work fine.
-             * If we don't supply a size for the object header, HDF5 will
-             * allocate H5O_MIN_SIZE by default.  This is currently
-             * big enough to hold the biggest possible extension, but should
-             * be tuned if more information is added to the superblock
-             * extension.
+        /* Close the superblock extension, if it was opened */
+        if(H5F_addr_defined(file->shared->extension_addr)) {
+            /* Twiddle the number of open objects to avoid closing the file
+             * (since this will be the only open object currently).
              */
-            H5O_loc_reset(&ext_loc);
-            if(H5O_create(file, dxpl_id, 0, H5P_GROUP_CREATE_DEFAULT, &ext_loc) < 0)
-                HGOTO_ERROR(H5E_OHDR, H5E_CANTCREATE, NULL, "unable to create superblock extension")
-
-            /* Record this address */
-            file->shared->extension_addr = ext_loc.addr;
-
-            /* Write shared message information to the extension */
-            sohm_table.addr = file->shared->sohm_addr;
-            sohm_table.version = file->shared->sohm_vers;
-            sohm_table.nindexes = file->shared->sohm_nindexes;
-
-            if(H5O_msg_create(&ext_loc, H5O_SHMESG_ID, H5O_MSG_FLAG_CONSTANT | H5O_MSG_FLAG_DONTSHARE, H5O_UPDATE_TIME, &sohm_table, dxpl_id) < 0)
-	        HGOTO_ERROR(H5E_DATATYPE, H5E_CANTINIT, NULL, "unable to update type header message")
-
-            /* Close the extension.  Bump the version number to avoid closing the
-            * file (since this will be the only open object).
-            */
             file->nopen_objs++;
             if(H5O_close(&ext_loc) < 0)
                 HGOTO_ERROR(H5E_OHDR, H5E_CANTRELEASE, NULL, "unable to close superblock extension")
             file->nopen_objs--;
-        }
+        } /* end if */
 
+        /* Create and open the root group */
+        /* (This must be after the space for the superblock is allocated in
+         *      the file and after the SOHM table has been created)
+         */
+        if(H5G_mkroot(file, dxpl_id, NULL) < 0)
+            HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to create/open root group")
 
-         /* Write the superblock to the file */
+        /* Write the superblock to the file */
         /* (This must be after the root group is created, since the root
          *      group's symbol table entry is part of the superblock)
          */
         if(H5F_write_superblock(file, dxpl_id) < 0)
             HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to write file superblock")
-
     } else if (1 == shared->nrefs) {
         H5G_loc_t           root_loc;           /*root location                 */
         H5O_loc_t           root_oloc;          /*root object location          */
@@ -1462,7 +1437,7 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t d
         H5G_loc_reset(&root_loc);
 
 	/* Read the superblock if it hasn't been read before. */
-        if(H5F_read_superblock(file, dxpl_id, &root_loc, HADDR_UNDEF, NULL, (size_t)0) < 0)
+        if(H5F_read_superblock(file, dxpl_id, &root_loc) < 0)
 	    HGOTO_ERROR(H5E_FILE, H5E_READERROR, NULL, "unable to read superblock")
 
 	/* Open the root group */
diff --git a/src/H5Fpkg.h b/src/H5Fpkg.h
index b6d6a38..c699485 100644
--- a/src/H5Fpkg.h
+++ b/src/H5Fpkg.h
@@ -43,16 +43,6 @@
 #include "H5RCprivate.h"	/* Reference counted object functions	*/
 
 /*
- * Feature: Define this constant to be non-zero if you want to enable code
- *	    that minimizes the number of calls to lseek().  This has a huge
- *	    performance benefit on some systems.  Set this constant to zero
- *	    on the compiler command line to disable that optimization.
- */
-#ifndef H5F_OPT_SEEK
-#  define H5F_OPT_SEEK 1
-#endif
-
-/*
  * Feature: Define this constant on the compiler command-line if you want to
  *	    see some debugging messages on the debug stream.
  */
@@ -60,59 +50,6 @@
 #  undef H5F_DEBUG
 #endif
 
-/* Superblock sizes for various versions */
-/* Checksum size in the file */
-#define H5F_SIZEOF_CHKSUM 4
-
-/* Fixed-size portion at the beginning of all superblocks */
-#define H5F_SUPERBLOCK_FIXED_SIZE ( H5F_SIGNATURE_LEN                   \
-        + 3 /* superblock, freespace, and root group versions */        \
-        + 1 /* reserved */                                              \
-        + 3 /* shared header vers, size of address, size of lengths */  \
-        + 1 /* reserved */                                              \
-        + 4 /* group leaf k, group internal k */                        \
-        + 4) /* consistency flags */
-
-#define H5F_SUPERBLOCK_VARLEN_SIZE_V0(f)                                \
-        ( H5F_SIZEOF_ADDR(f) /* base address */                         \
-        + H5F_SIZEOF_ADDR(f) /* free space address */                   \
-        + H5F_SIZEOF_ADDR(f) /* EOF address */                          \
-        + H5F_SIZEOF_ADDR(f) /* driver block address */                 \
-        + H5G_SIZEOF_ENTRY(f)) /* root group ptr */
-
-#define H5F_SUPERBLOCK_VARLEN_SIZE_V1(f)                                \
-        ( 2 /* indexed B-tree internal k */                             \
-        + 2 /* reserved */                                              \
-        + H5F_SIZEOF_ADDR(f) /* base address */                         \
-        + H5F_SIZEOF_ADDR(f) /* free space address */                   \
-        + H5F_SIZEOF_ADDR(f) /* EOF address */                          \
-        + H5F_SIZEOF_ADDR(f) /* driver block address */                 \
-        + H5G_SIZEOF_ENTRY(f)) /* root group ptr */
-
-#define H5F_SUPERBLOCK_VARLEN_SIZE_V2(f)                                \
-        ( 2 /* indexed B-tree internal k */                             \
-        + H5F_SIZEOF_ADDR(f) /* base address */                         \
-        + H5F_SIZEOF_ADDR(f) /* free space address */                   \
-/*        + H5F_SIZEOF_ADDR(f) */ /* shared message table address */         \
-/* JAMES        + 2 */ /* shared message version and number of indexes */          \
-        + H5F_SIZEOF_ADDR(f) /* EOF address */                          \
-        + H5F_SIZEOF_ADDR(f) /* driver block address */                 \
-        + H5G_SIZEOF_ENTRY(f) /* root group ptr */                      \
-        + H5F_SIZEOF_CHKSUM)
-
-#define H5F_SUPERBLOCK_SIZE(v, f) ( H5F_SUPERBLOCK_FIXED_SIZE           \
-        + (v == 0 ? H5F_SUPERBLOCK_VARLEN_SIZE_V0(f) : 0)               \
-        + (v == 1 ? H5F_SUPERBLOCK_VARLEN_SIZE_V1(f) : 0)               \
-        + (v == 2 ? H5F_SUPERBLOCK_VARLEN_SIZE_V2(f) : 0))
-
-
-#define H5F_DRVINFOBLOCK_HDR_SIZE 16
-#define H5F_DRVINFO_CHKSUM(v) (v == 0 ? 0 : H5F_SIZEOF_CHKSUM)
-
-/* Maximum size of super-block buffers */
-#define H5F_MAX_SUPERBLOCK_SIZE  134
-#define H5F_MAX_DRVINFOBLOCK_SIZE  1024
-
 /* Define the HDF5 file signature */
 #define H5F_SIGNATURE	  "\211HDF\r\n\032\n"
 #define H5F_SIGNATURE_LEN 8
@@ -224,7 +161,6 @@ H5FL_EXTERN(H5F_file_t);
 /* Package Private Prototypes */
 /******************************/
 
-
 /* General routines */
 H5_DLL herr_t H5F_init(void);
 H5_DLL herr_t H5F_try_close(H5F_t *f);
@@ -236,9 +172,9 @@ H5_DLL int H5F_term_unmount_cb(void *obj_ptr, hid_t obj_id, void *key);
 H5_DLL herr_t H5F_mount_count_ids(H5F_t *f, unsigned *nopen_files, unsigned *nopen_objs);
 
 /* Superblock related routines */
-H5_DLL hsize_t H5F_init_superblock(const H5F_t *f, hid_t dxpl_id);
+H5_DLL herr_t H5F_init_superblock(H5F_t *f, H5O_loc_t *ext_loc, hid_t dxpl_id);
 H5_DLL herr_t H5F_write_superblock(H5F_t *f, hid_t dxpl_id);
-H5_DLL herr_t H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr, uint8_t *buf, size_t buf_size);
+H5_DLL herr_t H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc);
 
 /* Shared file list related routines */
 H5_DLL herr_t H5F_sfile_add(H5F_file_t *shared);
diff --git a/src/H5Fsuper.c b/src/H5Fsuper.c
index dc31a97..ffb101f 100644
--- a/src/H5Fsuper.c
+++ b/src/H5Fsuper.c
@@ -13,13 +13,19 @@
  * access to either file, you may request a copy from help@hdfgroup.org.     *
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
+/****************/
+/* Module Setup */
+/****************/
+
 #define H5F_PACKAGE		/*suppress error about including H5Fpkg	  */
 
 /* Interface initialization */
 #define H5_INTERFACE_INIT_FUNC	H5F_init_super_interface
 
 
-/* Packages needed by this file... */
+/***********/
+/* Headers */
+/***********/
 #include "H5private.h"		/* Generic Functions			*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5Fpkg.h"             /* File access				*/
@@ -28,7 +34,92 @@
 #include "H5Pprivate.h"		/* Property lists			*/
 #include "H5SMprivate.h"        /* Shared Object Header Messages        */
 
-/* PRIVATE PROTOTYPES */
+
+/****************/
+/* Local Macros */
+/****************/
+
+/* Superblock sizes for various versions */
+#define H5F_SIZEOF_CHKSUM 4     /* Checksum size in the file */
+
+/* Fixed-size portion at the beginning of all superblocks */
+#define H5F_SUPERBLOCK_FIXED_SIZE ( H5F_SIGNATURE_LEN                   \
+        + 3 /* superblock, freespace, and root group versions */        \
+        + 1 /* reserved */                                              \
+        + 3 /* shared header vers, size of address, size of lengths */  \
+        + 1 /* reserved */                                              \
+        + 4 /* group leaf k, group internal k */                        \
+        + 4) /* consistency flags */
+
+/* Macros for computing variable-size superblock size */
+#define H5F_SUPERBLOCK_VARLEN_SIZE_V0(f)                                \
+        ( H5F_SIZEOF_ADDR(f) /* base address */                         \
+        + H5F_SIZEOF_ADDR(f) /* free space address */                   \
+        + H5F_SIZEOF_ADDR(f) /* EOF address */                          \
+        + H5F_SIZEOF_ADDR(f) /* driver block address */                 \
+        + H5G_SIZEOF_ENTRY(f)) /* root group ptr */
+#define H5F_SUPERBLOCK_VARLEN_SIZE_V1(f)                                \
+        ( 2 /* indexed B-tree internal k */                             \
+        + 2 /* reserved */                                              \
+        + H5F_SIZEOF_ADDR(f) /* base address */                         \
+        + H5F_SIZEOF_ADDR(f) /* free space address */                   \
+        + H5F_SIZEOF_ADDR(f) /* EOF address */                          \
+        + H5F_SIZEOF_ADDR(f) /* driver block address */                 \
+        + H5G_SIZEOF_ENTRY(f)) /* root group ptr */
+#define H5F_SUPERBLOCK_VARLEN_SIZE_V2(f)                                \
+        ( 2 /* indexed B-tree internal k */                             \
+        + H5F_SIZEOF_ADDR(f) /* base address */                         \
+        + H5F_SIZEOF_ADDR(f) /* free space address */                   \
+        + H5F_SIZEOF_ADDR(f) /* EOF address */                          \
+        + H5F_SIZEOF_ADDR(f) /* driver block address */                 \
+        + H5G_SIZEOF_ENTRY(f) /* root group ptr */                      \
+        + H5F_SIZEOF_CHKSUM)
+#define H5F_SUPERBLOCK_VARLEN_SIZE(v, f) (				\
+        (v == 0 ? H5F_SUPERBLOCK_VARLEN_SIZE_V0(f) : 0)			\
+        + (v == 1 ? H5F_SUPERBLOCK_VARLEN_SIZE_V1(f) : 0)               \
+        + (v == 2 ? H5F_SUPERBLOCK_VARLEN_SIZE_V2(f) : 0))
+
+/* Total size of superblock, depends on superblock version */
+#define H5F_SUPERBLOCK_SIZE(v, f) ( H5F_SUPERBLOCK_FIXED_SIZE           \
+        + H5F_SUPERBLOCK_VARLEN_SIZE(v, f))
+
+/* Driver info block macros */
+#define H5F_DRVINFOBLOCK_HDR_SIZE 16
+#define H5F_DRVINFO_CHKSUM(v) (v == 0 ? 0 : H5F_SIZEOF_CHKSUM)
+
+/* Maximum size of super-block buffers */
+#define H5F_MAX_SUPERBLOCK_SIZE  134
+#define H5F_MAX_DRVINFOBLOCK_SIZE  1024
+
+
+/******************/
+/* Local Typedefs */
+/******************/
+
+
+/********************/
+/* Package Typedefs */
+/********************/
+
+
+/********************/
+/* Local Prototypes */
+/********************/
+
+
+/*********************/
+/* Package Variables */
+/*********************/
+
+
+/*****************************/
+/* Library Private Variables */
+/*****************************/
+
+
+/*******************/
+/* Local Variables */
+/*******************/
 
 
 /*--------------------------------------------------------------------------
@@ -71,7 +162,7 @@ H5F_init_super_interface(void)
  *-------------------------------------------------------------------------
  */
 herr_t
-H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr, uint8_t *buf, size_t buf_size)
+H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc)
 {
     haddr_t             stored_eoa;         /*relative end-of-addr in file  */
     haddr_t             eof;                /*end of file address           */
@@ -84,16 +175,16 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
     H5F_file_t         *shared = NULL;      /* shared part of `file'        */
     H5FD_t             *lf = NULL;          /* file driver part of `shared' */
     uint8_t            *p;                  /* Temporary pointer into encoding buffers */
-    uint8_t            *start_p;            /* Start of encoding buffers    */
     uint32_t            read_chksum;        /* Checksum read from file  */
     uint32_t            computed_chksum;    /* Computed checksum  */
     size_t              driver_size;        /* Size of driver info block, in bytes */
     char                driver_name[9];     /* Name of driver, for driver info block */
-    unsigned            super_vers;         /* Super block version          */
+    unsigned            super_vers;         /* Superblock version          */
     unsigned            freespace_vers;     /* Freespace info version       */
     unsigned            obj_dir_vers;       /* Object header info version   */
     unsigned            share_head_vers;    /* Shared header info version   */
     uint8_t             sbuf[H5F_MAX_SUPERBLOCK_SIZE];     /* Local buffer                 */
+    size_t              buf_size = sizeof(sbuf);        /* Size of superblock buffer */
     unsigned            nindexes;           /* Number of shared message indexes */
     H5P_genplist_t     *c_plist;            /* File creation property list  */
     herr_t              ret_value = SUCCEED;
@@ -108,47 +199,39 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
     if (NULL == (c_plist = H5I_object(shared->fcpl_id)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "can't get property list")
 
-    /* Read the superblock if it hasn't been read before. */
-    if (addr == HADDR_UNDEF) {
-        if (HADDR_UNDEF == (shared->super_addr=H5F_locate_signature(lf,dxpl_id)))
-            HGOTO_ERROR(H5E_FILE, H5E_NOTHDF5, FAIL, "unable to find file signature")
-    } else {
-        shared->super_addr = addr;
-    }
-
-    if (!buf) {
-        start_p = p = sbuf;
-        buf_size=sizeof(sbuf);
+    /* Read the superblock */
+    if(HADDR_UNDEF == (shared->super_addr = H5F_locate_signature(lf, dxpl_id)))
+        HGOTO_ERROR(H5E_FILE, H5E_NOTHDF5, FAIL, "unable to find file signature")
 
-        if (H5FD_set_eoa(lf, H5FD_MEM_SUPER, shared->super_addr + fixed_size) < 0 ||
-                H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, shared->super_addr, fixed_size, p) < 0)
-            HGOTO_ERROR(H5E_FILE, H5E_READERROR, FAIL, "unable to read superblock")
-    } else {
-        start_p = p = buf;
-    }
+    /* Read fixed-size portion of the superblock */
+    p = sbuf;
+    if(H5FD_set_eoa(lf, H5FD_MEM_SUPER, shared->super_addr + fixed_size) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "set end of space allocation request failed")
+    if(H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, shared->super_addr, fixed_size, p) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_READERROR, FAIL, "unable to read superblock")
 
     /* Signature, already checked */
     p += H5F_SIGNATURE_LEN;
 
     /* Superblock version */
     super_vers = *p++;
-    if (super_vers > HDF5_SUPERBLOCK_VERSION_MAX)
+    if(super_vers > HDF5_SUPERBLOCK_VERSION_MAX)
         HGOTO_ERROR(H5E_FILE, H5E_BADVALUE, FAIL, "bad superblock version number")
-    if (H5P_set(c_plist, H5F_CRT_SUPER_VERS_NAME, &super_vers) < 0)
+    if(H5P_set(c_plist, H5F_CRT_SUPER_VERS_NAME, &super_vers) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set superblock version")
 
     /* Freespace version */
     freespace_vers = *p++;
-    if (HDF5_FREESPACE_VERSION != freespace_vers)
+    if(HDF5_FREESPACE_VERSION != freespace_vers)
         HGOTO_ERROR(H5E_FILE, H5E_BADVALUE, FAIL, "bad free space version number")
-    if (H5P_set(c_plist, H5F_CRT_FREESPACE_VERS_NAME, &freespace_vers) < 0)
+    if(H5P_set(c_plist, H5F_CRT_FREESPACE_VERS_NAME, &freespace_vers) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set free space version")
 
     /* Root group version number */
     obj_dir_vers = *p++;
-    if (HDF5_OBJECTDIR_VERSION != obj_dir_vers)
+    if(HDF5_OBJECTDIR_VERSION != obj_dir_vers)
         HGOTO_ERROR(H5E_FILE, H5E_BADVALUE, FAIL, "bad object directory version number")
-    if (H5P_set(c_plist, H5F_CRT_OBJ_DIR_VERS_NAME, &obj_dir_vers) < 0)
+    if(H5P_set(c_plist, H5F_CRT_OBJ_DIR_VERS_NAME, &obj_dir_vers) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set object directory version")
 
     /* Skip over reserved byte */
@@ -156,26 +239,26 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
 
     /* Shared header version number */
     share_head_vers = *p++;
-    if (HDF5_SHAREDHEADER_VERSION != share_head_vers)
+    if(HDF5_SHAREDHEADER_VERSION != share_head_vers)
         HGOTO_ERROR(H5E_FILE, H5E_BADVALUE, FAIL, "bad shared-header format version number")
-    if (H5P_set(c_plist, H5F_CRT_SHARE_HEAD_VERS_NAME, &share_head_vers) < 0)
+    if(H5P_set(c_plist, H5F_CRT_SHARE_HEAD_VERS_NAME, &share_head_vers) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set shared-header format version")
 
     /* Size of file addresses */
     sizeof_addr = *p++;
-    if (sizeof_addr != 2 && sizeof_addr != 4 &&
+    if(sizeof_addr != 2 && sizeof_addr != 4 &&
             sizeof_addr != 8 && sizeof_addr != 16 && sizeof_addr != 32)
         HGOTO_ERROR(H5E_FILE, H5E_BADVALUE, FAIL, "bad byte number in an address")
-    if (H5P_set(c_plist, H5F_CRT_ADDR_BYTE_NUM_NAME,&sizeof_addr) < 0)
+    if(H5P_set(c_plist, H5F_CRT_ADDR_BYTE_NUM_NAME,&sizeof_addr) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set byte number in an address")
     shared->sizeof_addr = sizeof_addr;  /* Keep a local copy also */
 
     /* Size of file sizes */
     sizeof_size = *p++;
-    if (sizeof_size != 2 && sizeof_size != 4 &&
+    if(sizeof_size != 2 && sizeof_size != 4 &&
             sizeof_size != 8 && sizeof_size != 16 && sizeof_size != 32)
         HGOTO_ERROR(H5E_FILE, H5E_BADVALUE, FAIL, "bad byte number for object size")
-    if (H5P_set(c_plist, H5F_CRT_OBJ_BYTE_NUM_NAME, &sizeof_size) < 0)
+    if(H5P_set(c_plist, H5F_CRT_OBJ_BYTE_NUM_NAME, &sizeof_size) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set byte number for object size")
     shared->sizeof_size = sizeof_size;  /* Keep a local copy also */
 
@@ -184,17 +267,17 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
 
     /* Various B-tree sizes */
     UINT16DECODE(p, sym_leaf_k);
-    if (sym_leaf_k == 0)
+    if(sym_leaf_k == 0)
         HGOTO_ERROR(H5E_FILE, H5E_BADRANGE, FAIL, "bad symbol table leaf node 1/2 rank")
-    if (H5P_set(c_plist, H5F_CRT_SYM_LEAF_NAME, &sym_leaf_k) < 0)
+    if(H5P_set(c_plist, H5F_CRT_SYM_LEAF_NAME, &sym_leaf_k) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set rank for symbol table leaf nodes")
     shared->sym_leaf_k = sym_leaf_k;    /* Keep a local copy also */
 
     /* Need 'get' call to set other array values */
-    if (H5P_get(c_plist, H5F_CRT_BTREE_RANK_NAME, btree_k) < 0)
+    if(H5P_get(c_plist, H5F_CRT_BTREE_RANK_NAME, btree_k) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get rank for btree internal nodes")
     UINT16DECODE(p, btree_k[H5B_SNODE_ID]);
-    if (btree_k[H5B_SNODE_ID] == 0)
+    if(btree_k[H5B_SNODE_ID] == 0)
         HGOTO_ERROR(H5E_FILE, H5E_BADRANGE, FAIL, "bad 1/2 rank for btree internal nodes")
     /*
      * Delay setting the value in the property list until we've checked
@@ -203,57 +286,48 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
 
     /* File consistency flags. Not really used yet */
     UINT32DECODE(p, shared->consist_flags);
-    assert(((size_t)(p - start_p)) == fixed_size);
-
-    /* Decode the variable-length part of the superblock... */
-    if(super_vers == HDF5_SUPERBLOCK_VERSION_DEF)
-        variable_size = H5F_SUPERBLOCK_VARLEN_SIZE_V0(f);
-    else if (super_vers == HDF5_SUPERBLOCK_VERSION_1)
-        variable_size = H5F_SUPERBLOCK_VARLEN_SIZE_V1(f);
-    else
-        variable_size = H5F_SUPERBLOCK_VARLEN_SIZE_V2(f);
+    HDassert(((size_t)(p - sbuf)) == fixed_size);
 
-    assert(fixed_size + variable_size <= buf_size);
+    /* Determine the size of the variable-length part of the superblock */
+    variable_size = H5F_SUPERBLOCK_VARLEN_SIZE(super_vers, f);
+    HDassert(variable_size > 0);
+    HDassert(fixed_size + variable_size <= buf_size);
 
-    /* The buffer (buf) is either passed in or the "local_buf" variable now */
-    if(!buf) {
-        if (H5FD_set_eoa(lf, H5FD_MEM_SUPER, shared->super_addr + fixed_size+variable_size) < 0 ||
-                H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, shared->super_addr + fixed_size,
-                          variable_size, p) < 0)
-            HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to read superblock")
-    } /* end if */
+    /* Read in variable-sized portion of superblock */
+    if(H5FD_set_eoa(lf, H5FD_MEM_SUPER, shared->super_addr + fixed_size + variable_size) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "set end of space allocation request failed")
+    if(H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, shared->super_addr + fixed_size, variable_size, p) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to read superblock")
 
     /*
      * If the superblock version # is greater than 0, read in the indexed
      * storage B-tree internal 'K' value
      */
-    if (super_vers > HDF5_SUPERBLOCK_VERSION_DEF) {
+    if(super_vers > HDF5_SUPERBLOCK_VERSION_DEF) {
         UINT16DECODE(p, btree_k[H5B_ISTORE_ID]);
         /* Reserved bytes are present only in version 1 */
-        if(super_vers == HDF5_SUPERBLOCK_VERSION_1) {
+        if(super_vers == HDF5_SUPERBLOCK_VERSION_1)
             p += 2;   /* reserved */
-        }
-    }
+    } /* end if */
     else
         btree_k[H5B_ISTORE_ID] = HDF5_BTREE_ISTORE_IK_DEF;
 
     /* Set the B-tree internal node values, etc */
-    if (H5P_set(c_plist, H5F_CRT_BTREE_RANK_NAME, btree_k) < 0)
+    if(H5P_set(c_plist, H5F_CRT_BTREE_RANK_NAME, btree_k) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set rank for btree internal nodes")
     HDmemcpy(shared->btree_k, btree_k, sizeof(unsigned) * (size_t)H5B_NUM_BTREE_ID);    /* Keep a local copy also */
 
     H5F_addr_decode(f, (const uint8_t **)&p, &shared->base_addr/*out*/);
-    H5F_addr_decode(f, (const uint8_t **)&p, &(shared->extension_addr)/*out*/);
-
+    H5F_addr_decode(f, (const uint8_t **)&p, &shared->extension_addr/*out*/);
     H5F_addr_decode(f, (const uint8_t **)&p, &stored_eoa/*out*/);
     H5F_addr_decode(f, (const uint8_t **)&p, &shared->driver_addr/*out*/);
     if(H5G_obj_ent_decode(f, (const uint8_t **)&p, root_loc->oloc/*out*/) < 0)
         HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to read root symbol entry")
 
-    /* Compute super block checksum for versions greater than 1 */
+    /* Compute superblock checksum for versions greater than 1 */
     if(super_vers >= HDF5_SUPERBLOCK_VERSION_2) {
         computed_chksum = H5_checksum_metadata(sbuf, (unsigned) (p - sbuf), 0);
-        /* Read stored super block checksum */
+        /* Read stored superblock checksum */
         UINT32DECODE(p, read_chksum);
 
         if(read_chksum != computed_chksum)
@@ -266,9 +340,9 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
      * Check if superblock address is different from base address and
      * adjust base address and "end of address" address if so.
      */
-    if (!H5F_addr_eq(shared->super_addr,shared->base_addr)) {
+    if(!H5F_addr_eq(shared->super_addr, shared->base_addr)) {
         /* Check if the superblock moved earlier in the file */
-        if (H5F_addr_lt(shared->super_addr, shared->base_addr))
+        if(H5F_addr_lt(shared->super_addr, shared->base_addr))
             stored_eoa -= (shared->base_addr - shared->super_addr);
         else
             /* The superblock moved later in the file */
@@ -286,30 +360,22 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
         shared->driver_addr = HADDR_UNDEF;
 
     /* Decode the optional driver information block */
-    if (H5F_addr_defined(shared->driver_addr)) {
+    if(H5F_addr_defined(shared->driver_addr)) {
         unsigned drv_vers;
         haddr_t drv_addr = shared->base_addr + shared->driver_addr;
         uint8_t dbuf[H5F_MAX_DRVINFOBLOCK_SIZE];     /* Local buffer                 */
-        size_t dbuf_size;               /* Size available for driver info */
-        const uint8_t *driver_p;        /* Remember beginning of driver info block */
-
+        size_t dbuf_size = sizeof(dbuf);        /* Size available for driver info */
 
-        if(!buf) {
-            driver_p = p = dbuf;
-            dbuf_size=sizeof(dbuf);
-
-            if (H5FD_set_eoa(lf, H5FD_MEM_SUPER, drv_addr + H5F_DRVINFOBLOCK_HDR_SIZE) < 0 ||
-                    H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, drv_addr, (size_t)H5F_DRVINFOBLOCK_HDR_SIZE, p) < 0)
-                HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to read driver information block")
-        } /* end if */
-        else {
-            driver_p = p;
-            dbuf_size=buf_size-(p-start_p);
-        } /* end else */
+        /* Read in fixed-sized portion of driver info block */
+        p = dbuf;
+        if(H5FD_set_eoa(lf, H5FD_MEM_SUPER, drv_addr + H5F_DRVINFOBLOCK_HDR_SIZE) < 0)
+            HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "set end of space allocation request failed")
+        if(H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, drv_addr, (size_t)H5F_DRVINFOBLOCK_HDR_SIZE, p) < 0)
+            HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to read driver information block")
 
         /* Version number */
         drv_vers = *p++;
-        if (drv_vers > HDF5_DRIVERINFO_VERSION_MAX)
+        if(drv_vers > HDF5_DRIVERINFO_VERSION_MAX)
             HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "bad driver information block version number")
 
         p += 3; /* reserved bytes */
@@ -327,11 +393,11 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
         /* Read driver information */
         HDassert((driver_size + H5F_DRVINFOBLOCK_HDR_SIZE + H5F_DRVINFO_CHKSUM(drv_vers)) <= dbuf_size);
 
-        if(!buf) {
-            if (H5FD_set_eoa(lf, H5FD_MEM_SUPER, drv_addr + H5F_DRVINFOBLOCK_HDR_SIZE + driver_size + H5F_DRVINFO_CHKSUM(drv_vers)) < 0 ||
-                    H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, drv_addr+H5F_DRVINFOBLOCK_HDR_SIZE, driver_size, p) < 0)
-                HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to read file driver information")
-        } /* end if */
+        /* Read in variable-sized portion of driver info block */
+        if(H5FD_set_eoa(lf, H5FD_MEM_SUPER, drv_addr + H5F_DRVINFOBLOCK_HDR_SIZE + driver_size + H5F_DRVINFO_CHKSUM(drv_vers)) < 0)
+            HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "set end of space allocation request failed")
+        if(H5FD_read(lf, H5FD_MEM_SUPER, dxpl_id, drv_addr + H5F_DRVINFOBLOCK_HDR_SIZE, driver_size, p) < 0)
+            HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to read file driver information")
 
         /* Decode driver information */
         /* Check if driver matches driver information saved. Unfortunately, we can't push this
@@ -341,12 +407,13 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
         if(!HDstrncmp(driver_name, "NCSAmult", (size_t)8) && HDstrcmp(lf->cls->name, "multi"))
             HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "multi driver should be used")
 
-        if (H5FD_sb_decode(lf, driver_name, p) < 0)
+        /* Decode the driver-specific driver info block information */
+        if(H5FD_sb_decode(lf, driver_name, p) < 0)
             HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to decode driver information")
 
         p += driver_size;
 
-        /* Compute checksum for versions > 0*/
+        /* Compute checksum for versions > 0 */
         if(drv_vers >= HDF5_DRIVERINFO_VERSION_1) {
             computed_chksum = H5_checksum_metadata(dbuf, (H5F_DRVINFOBLOCK_HDR_SIZE + driver_size), 0);
             /* Read checksum */
@@ -354,7 +421,7 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
 
             if(read_chksum != computed_chksum)
                 HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "bad checksum on driver information block")
-        }
+        } /* end if */
  
         HDassert((unsigned) (p - dbuf) == driver_size + H5F_DRVINFOBLOCK_HDR_SIZE + H5F_DRVINFO_CHKSUM(drv_vers));
     } /* end if */
@@ -363,25 +430,24 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
      * The user-defined data is the area of the file before the base
      * address.
      */
-    if (H5P_set(c_plist, H5F_CRT_USER_BLOCK_NAME, &shared->base_addr) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set usr block size")
+    if(H5P_set(c_plist, H5F_CRT_USER_BLOCK_NAME, &shared->base_addr) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "unable to set user block size")
 
     /*
      * Make sure that the data is not truncated. One case where this is
      * possible is if the first file of a family of files was opened
      * individually.
      */
-    if (HADDR_UNDEF == (eof = H5FD_get_eof(lf)))
+    if(HADDR_UNDEF == (eof = H5FD_get_eof(lf)))
         HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to determine file size")
-
-    if (eof < stored_eoa)
+    if(eof < stored_eoa)
         HGOTO_ERROR(H5E_FILE, H5E_TRUNCATED, FAIL, "truncated file")
 
     /*
      * Tell the file driver how much address space has already been
      * allocated so that it knows how to allocate additional memory.
      */
-    if (H5FD_set_eoa(lf, H5FD_MEM_SUPER, stored_eoa) < 0)
+    if(H5FD_set_eoa(lf, H5FD_MEM_SUPER, stored_eoa) < 0)
         HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, FAIL, "unable to set end-of-address marker for file")
 
     /* Read the file's superblock extension, if there is one. */
@@ -415,12 +481,10 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
         if(H5O_close(&ext_loc) < 0)
             HGOTO_ERROR(H5E_OHDR, H5E_CANTOPENFILE, FAIL, "unable to close superblock extension")
         f->nopen_objs--;
-    }
+    } /* end if */
 
-    /* Decode shared object header message information and store it in the
-     * fcpl */
-    if(shared->sohm_addr != HADDR_UNDEF)
-    {
+    /* Decode shared object header message information and store it in the FCPL */
+    if(shared->sohm_addr != HADDR_UNDEF) {
         unsigned index_flags[H5O_SHMESG_MAX_NINDEXES] = {0};
         unsigned minsizes[H5O_SHMESG_MAX_NINDEXES] = {0};
         unsigned sohm_l2b;           /* SOHM list-to-btree cutoff    */
@@ -443,14 +507,13 @@ H5F_read_superblock(H5F_t *f, hid_t dxpl_id, H5G_loc_t *root_loc, haddr_t addr,
             HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set SOHM cutoff in property list");
         if(H5P_set(c_plist, H5F_CRT_SHMSG_BTREE_MIN_NAME, &sohm_b2l) < 0)
             HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set SOHM cutoff in property list");
-    }
-    else
-    {
+    } /* end if */
+    else {
         /* Shared object header messages are disabled */
         nindexes = 0;
         if(H5P_set(c_plist, H5F_CRT_SHMSG_NINDEXES_NAME, &nindexes) < 0)
             HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set number of SOHM indexes");
-    }
+    } /* end else */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -471,26 +534,24 @@ done:
  *              koziol@ncsa.uiuc.edu
  *              Sept 15, 2003
  *
- * Modifications:
- *
  *-------------------------------------------------------------------------
  */
-hsize_t
-H5F_init_superblock(const H5F_t *f, hid_t dxpl_id)
+herr_t
+H5F_init_superblock(H5F_t *f, H5O_loc_t *ext_loc, hid_t dxpl_id)
 {
     hsize_t         userblock_size = 0;         /* Size of userblock, in bytes */
     size_t          superblock_size;            /* Size of superblock, in bytes     */
     size_t          driver_size;                /* Size of driver info block (bytes)*/
-    unsigned        super_vers;                 /* Super block version              */
+    unsigned        super_vers;                 /* Superblock version              */
     haddr_t         addr;                       /* Address of superblock            */
     H5P_genplist_t *plist;                      /* Property list                    */
-    hsize_t         ret_value;
+    herr_t          ret_value = SUCCEED;
 
-    FUNC_ENTER_NOAPI(H5F_init_superblock, UFAIL)
+    FUNC_ENTER_NOAPI(H5F_init_superblock, FAIL)
 
     /* Get the shared file creation property list */
-    if (NULL == (plist = H5I_object(f->shared->fcpl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, UFAIL, "not a property list")
+    if(NULL == (plist = H5I_object(f->shared->fcpl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list")
 
     /*
      * The superblock starts immediately after the user-defined
@@ -499,36 +560,35 @@ H5F_init_superblock(const H5F_t *f, hid_t dxpl_id)
      * now.
      */
     if(H5P_get(plist, H5F_CRT_USER_BLOCK_NAME, &userblock_size) < 0)
-        HGOTO_ERROR(H5E_FILE, H5E_CANTGET, UFAIL, "unable to get user block size")
+        HGOTO_ERROR(H5E_FILE, H5E_CANTGET, FAIL, "unable to get user block size")
     f->shared->super_addr = userblock_size;
     f->shared->base_addr = f->shared->super_addr;
     f->shared->consist_flags = 0x03;
 
     /* Grab superblock version from property list */
-    if (H5P_get(plist, H5F_CRT_SUPER_VERS_NAME, &super_vers) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, UFAIL, "unable to get super block version")
+    if(H5P_get(plist, H5F_CRT_SUPER_VERS_NAME, &super_vers) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get superblock version")
 
     /* Compute the size of the superblock */
-    superblock_size=H5F_SUPERBLOCK_FIXED_SIZE;
-
-    if(super_vers==HDF5_SUPERBLOCK_VERSION_DEF)
-        superblock_size += H5F_SUPERBLOCK_VARLEN_SIZE_V0(f);
-    else if (super_vers == HDF5_SUPERBLOCK_VERSION_1)
-        superblock_size += H5F_SUPERBLOCK_VARLEN_SIZE_V1(f);
-    else if (super_vers == HDF5_SUPERBLOCK_VERSION_2)
-        superblock_size += H5F_SUPERBLOCK_VARLEN_SIZE_V2(f);
+    superblock_size = H5F_SUPERBLOCK_SIZE(super_vers, f);
 
     /* Compute the size of the driver information block. Use driver block
-     * version 1 if the superblock is at least version 2 */
+     * version 1 if the superblock is at least version 2
+     */
     H5_ASSIGN_OVERFLOW(driver_size, H5FD_sb_size(f->shared->lf), hsize_t, size_t);
-    if (driver_size > 0)
-    {
+    if(driver_size > 0) {
         driver_size += H5F_DRVINFOBLOCK_HDR_SIZE;
         if(super_vers > HDF5_SUPERBLOCK_VERSION_1)
             driver_size += H5F_DRVINFO_CHKSUM(1);
         else
             driver_size += H5F_DRVINFO_CHKSUM(0);
-    }
+
+        /*
+         * The file driver information block begins immediately after the
+         * superblock.
+         */
+        f->shared->driver_addr = superblock_size;
+    } /* end if */
 
     /*
      * Allocate space for the userblock, superblock, driver info
@@ -538,28 +598,34 @@ H5F_init_superblock(const H5F_t *f, hid_t dxpl_id)
      * allocation request is required to return memory at format 
      * address zero.
      */
-
     H5_CHECK_OVERFLOW(f->shared->base_addr, haddr_t, hsize_t);
     addr = H5FD_alloc(f->shared->lf, H5FD_MEM_SUPER, dxpl_id,
                       ((hsize_t)f->shared->base_addr + superblock_size + driver_size));
-
-    if (HADDR_UNDEF == addr)
-        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, UFAIL,
-                    "unable to allocate file space for userblock and/or superblock")
-
-    if (0 != addr)
-        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, UFAIL,
-                    "file driver failed to allocate userblock and/or superblock at address zero")
-
-    /*
-     * The file driver information block begins immediately after the
-     * superblock.
+    if(HADDR_UNDEF == addr)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "unable to allocate file space for userblock and/or superblock")
+    if(0 != addr)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "file driver failed to allocate userblock and/or superblock at address zero")
+
+    /* Create the superblock extension for "extra" superblock data, if necessary.
+     * (Currently, the extension is only needed if Shared Object Header
+     *  Messages are enabled)
      */
-    if (driver_size > 0)
-        f->shared->driver_addr = superblock_size;
+    if(f->shared->sohm_nindexes > 0) {
+        /* The superblock extension isn't actually a group, but the
+         * default group creation list should work fine.
+         * If we don't supply a size for the object header, HDF5 will
+         * allocate H5O_MIN_SIZE by default.  This is currently
+         * big enough to hold the biggest possible extension, but should
+         * be tuned if more information is added to the superblock
+         * extension.
+         */
+        H5O_loc_reset(ext_loc);
+        if(H5O_create(f, dxpl_id, 0, H5P_GROUP_CREATE_DEFAULT, ext_loc) < 0)
+            HGOTO_ERROR(H5E_OHDR, H5E_CANTCREATE, FAIL, "unable to create superblock extension")
 
-    /* Return the size of the super block+driver info block */
-    ret_value=superblock_size+driver_size;
+        /* Record this address */
+        f->shared->extension_addr = ext_loc->addr;
+    } /* end if */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -594,7 +660,7 @@ H5F_write_superblock(H5F_t *f, hid_t dxpl_id)
     size_t          superblock_size;            /* Size of superblock, in bytes     */
     size_t          driver_size;                /* Size of driver info block (bytes)*/
     char            driver_name[9];             /* Name of driver, for driver info block */
-    unsigned        super_vers;                 /* Super block version              */
+    unsigned        super_vers;                 /* Superblock version              */
     unsigned        freespace_vers;             /* Freespace info version           */
     unsigned        obj_dir_vers;               /* Object header info version       */
     unsigned        share_head_vers;            /* Shared header info version       */
@@ -604,20 +670,20 @@ H5F_write_superblock(H5F_t *f, hid_t dxpl_id)
     FUNC_ENTER_NOAPI(H5F_write_superblock, FAIL)
 
     /* Get the shared file creation property list */
-    if (NULL == (plist = H5I_object(f->shared->fcpl_id)))
+    if(NULL == (plist = H5I_object(f->shared->fcpl_id)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list")
 
     /* Grab values from property list */
-    if (H5P_get(plist, H5F_CRT_SUPER_VERS_NAME, &super_vers) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get super block version")
-    if (H5P_get(plist, H5F_CRT_FREESPACE_VERS_NAME, &freespace_vers) < 0)
+    if(H5P_get(plist, H5F_CRT_SUPER_VERS_NAME, &super_vers) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get superblock version")
+    if(H5P_get(plist, H5F_CRT_FREESPACE_VERS_NAME, &freespace_vers) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get free space version")
-    if (H5P_get(plist, H5F_CRT_OBJ_DIR_VERS_NAME, &obj_dir_vers) < 0)
+    if(H5P_get(plist, H5F_CRT_OBJ_DIR_VERS_NAME, &obj_dir_vers) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get object directory version")
-    if (H5P_get(plist, H5F_CRT_SHARE_HEAD_VERS_NAME, &share_head_vers) < 0)
+    if(H5P_get(plist, H5F_CRT_SHARE_HEAD_VERS_NAME, &share_head_vers) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get shared-header format version")
 
-    /* Encode the file super block */
+    /* Encode the file superblock */
     p = sbuf;
     HDmemcpy(p, H5F_SIGNATURE, (size_t)H5F_SIGNATURE_LEN);
     p += H5F_SIGNATURE_LEN;
@@ -641,27 +707,26 @@ H5F_write_superblock(H5F_t *f, hid_t dxpl_id)
      * Versions of the superblock >0 have the indexed storage B-tree
      * internal 'K' value stored
      */
-    if (super_vers > HDF5_SUPERBLOCK_VERSION_DEF) {
+    if(super_vers > HDF5_SUPERBLOCK_VERSION_DEF) {
         UINT16ENCODE(p, f->shared->btree_k[H5B_ISTORE_ID]);
-        if (super_vers < HDF5_SUPERBLOCK_VERSION_2) {
+        if(super_vers < HDF5_SUPERBLOCK_VERSION_2) {
             *p++ = 0;   /*reserved */
             *p++ = 0;   /*reserved */
-        }
-    }
+        } /* end if */
+    } /* end if */
 
     H5F_addr_encode(f, &p, f->shared->base_addr);
     H5F_addr_encode(f, &p, f->shared->extension_addr);
-
     H5F_addr_encode(f, &p, H5FD_get_eoa(f->shared->lf, H5FD_MEM_SUPER));
     H5F_addr_encode(f, &p, f->shared->driver_addr);
     if(H5G_obj_ent_encode(f, &p, H5G_oloc(f->shared->root_grp))<0)
         HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "unable to encode root group information")
 
-    /* Compute super block checksum */
+    /* Compute superblock checksum */
     if(super_vers >= HDF5_SUPERBLOCK_VERSION_2) {
         chksum = H5_checksum_metadata(sbuf, H5F_SUPERBLOCK_SIZE(super_vers, f) - H5F_SIZEOF_CHKSUM, 0);
         UINT32ENCODE(p, chksum);
-    }
+    } /* end if */
 
     /* Double check we didn't overrun the block (unlikely) */
     H5_ASSIGN_OVERFLOW(superblock_size, p - sbuf, int, size_t);
@@ -671,23 +736,19 @@ H5F_write_superblock(H5F_t *f, hid_t dxpl_id)
     HDassert(superblock_size == (H5F_SUPERBLOCK_SIZE(super_vers, f)));
 
     /* Write superblock */
-    if (H5FD_write(f->shared->lf, H5FD_MEM_SUPER, dxpl_id,
-                    f->shared->super_addr, superblock_size, sbuf) < 0)
+    if(H5FD_write(f->shared->lf, H5FD_MEM_SUPER, dxpl_id, f->shared->super_addr, superblock_size, sbuf) < 0)
         HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "unable to write superblock")
 
-
     /* Encode the driver information block. */
     H5_ASSIGN_OVERFLOW(driver_size, H5FD_sb_size(f->shared->lf), hsize_t, size_t);
-
-    if (driver_size > 0) {
+    if(driver_size > 0) {
         unsigned driver_vers;
 
         /* Use driver info block version 1 on superblock version >= 2 */
-        if(super_vers > HDF5_SUPERBLOCK_VERSION_1) {
+        if(super_vers > HDF5_SUPERBLOCK_VERSION_1)
             driver_vers = HDF5_DRIVERINFO_VERSION_1;
-        } else {
+        else
             driver_vers = HDF5_DRIVERINFO_VERSION_0;
-        }
 
         driver_size += H5F_DRVINFOBLOCK_HDR_SIZE + H5F_DRVINFO_CHKSUM(driver_vers);
 
@@ -706,7 +767,7 @@ H5F_write_superblock(H5F_t *f, hid_t dxpl_id)
 	UINT32ENCODE(p, driver_size - H5F_DRVINFOBLOCK_HDR_SIZE - H5F_DRVINFO_CHKSUM(driver_vers));
 
 	/* Encode driver-specific data */
-	if (H5FD_sb_encode(f->shared->lf, driver_name, dbuf + H5F_DRVINFOBLOCK_HDR_SIZE) < 0)
+	if(H5FD_sb_encode(f->shared->lf, driver_name, dbuf + H5F_DRVINFOBLOCK_HDR_SIZE) < 0)
 	    HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "unable to encode driver information")
 
 	/* Driver name */
@@ -716,13 +777,13 @@ H5F_write_superblock(H5F_t *f, hid_t dxpl_id)
         if(driver_vers > HDF5_DRIVERINFO_VERSION_0) {
             chksum = H5_checksum_metadata(dbuf, (driver_size - H5F_SIZEOF_CHKSUM), 0);
             UINT32ENCODE(p, chksum);
-        }
+        } /* end if */
 
         /* Write driver information block */
-        if (H5FD_write(f->shared->lf, H5FD_MEM_SUPER, dxpl_id,
-                        f->shared->base_addr + f->shared->driver_addr, driver_size, dbuf) < 0)
+        if(H5FD_write(f->shared->lf, H5FD_MEM_SUPER, dxpl_id, f->shared->base_addr + f->shared->driver_addr, driver_size, dbuf) < 0)
             HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "unable to write driver information block")
     } /* end if */
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5F_write_superblock() */
diff --git a/src/H5G.c b/src/H5G.c
index 4159bf2..86b446e 100644
--- a/src/H5G.c
+++ b/src/H5G.c
@@ -987,6 +987,8 @@ H5G_mkroot(H5F_t *f, hid_t dxpl_id, H5G_loc_t *loc)
 
     /* check args */
     HDassert(f);
+
+    /* Check if the root group is already initialized */
     if(f->shared->root_grp)
         HGOTO_DONE(SUCCEED)
 
@@ -996,9 +998,9 @@ H5G_mkroot(H5F_t *f, hid_t dxpl_id, H5G_loc_t *loc)
 
     /*
      * If there is no root object then create one. The root group always starts
-     * with a hard link count of one since it's pointed to by the boot block.
+     * with a hard link count of one since it's pointed to by the superblock.
      */
-    if (loc == NULL) {
+    if(loc == NULL) {
         H5P_genplist_t *fc_plist;       /* File creation property list */
         H5O_ginfo_t     ginfo;          /* Group info parameters */
         H5O_linfo_t     linfo;          /* Link info parameters */
@@ -1022,11 +1024,13 @@ H5G_mkroot(H5F_t *f, hid_t dxpl_id, H5G_loc_t *loc)
         H5G_loc_reset(&new_root_loc);
         loc = &new_root_loc;
 
+        /* Create root group */
 	if(H5G_obj_create(f, dxpl_id, &ginfo, &linfo, f->shared->fcpl_id, loc->oloc/*out*/) < 0)
 	    HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to create group entry")
 	if(1 != H5O_link(loc->oloc, 1, dxpl_id))
 	    HGOTO_ERROR(H5E_SYM, H5E_LINKCOUNT, FAIL, "internal error (wrong link count)")
-    } else {
+    } /* end if */
+    else {
 	/*
 	 * Open the root object as a group.
 	 */
diff --git a/src/H5Omessage.c b/src/H5Omessage.c
index 8307b49..a7ecb63 100644
--- a/src/H5Omessage.c
+++ b/src/H5Omessage.c
@@ -117,7 +117,7 @@ static herr_t H5O_copy_mesg(H5F_t *f, hid_t dxpl_id, H5O_t *oh, unsigned idx,
  *-------------------------------------------------------------------------
  */
 herr_t
-H5O_msg_create(H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
+H5O_msg_create(const H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
     unsigned update_flags, void *mesg, hid_t dxpl_id)
 {
     H5O_t *oh = NULL;                   /* Object header */
@@ -268,7 +268,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5O_msg_write(H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
+H5O_msg_write(const H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
     unsigned update_flags, void *mesg, hid_t dxpl_id)
 {
     H5O_t *oh = NULL;                   /* Object header to use */
diff --git a/src/H5Oprivate.h b/src/H5Oprivate.h
index ef18518..883f262 100644
--- a/src/H5Oprivate.h
+++ b/src/H5Oprivate.h
@@ -417,12 +417,12 @@ H5_DLL herr_t H5O_obj_type(const H5O_loc_t *loc, H5O_type_t *obj_type, hid_t dxp
 H5_DLL herr_t H5O_get_create_plist(const H5O_loc_t *loc, hid_t dxpl_id, struct H5P_genplist_t *oc_plist);
 
 /* Object header message routines */
-H5_DLL herr_t H5O_msg_create(H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
+H5_DLL herr_t H5O_msg_create(const H5O_loc_t *loc, unsigned type_id, unsigned mesg_flags,
     unsigned update_flags, void *mesg, hid_t dxpl_id);
 H5_DLL herr_t H5O_msg_append(H5F_t *f, hid_t dxpl_id, struct H5O_t *oh, unsigned type_id,
     unsigned mesg_flags, unsigned update_flags, void *mesg,
     unsigned *oh_flags_ptr);
-H5_DLL herr_t H5O_msg_write(H5O_loc_t *loc, unsigned type_id, unsigned flags,
+H5_DLL herr_t H5O_msg_write(const H5O_loc_t *loc, unsigned type_id, unsigned flags,
     unsigned update_flags, void *mesg, hid_t dxpl_id);
 H5_DLL void *H5O_msg_read(const H5O_loc_t *loc, unsigned type_id, void *mesg,
     hid_t dxpl_id);
diff --git a/src/H5SM.c b/src/H5SM.c
index 3f2d9f7..c2e2534 100755
--- a/src/H5SM.c
+++ b/src/H5SM.c
@@ -99,18 +99,19 @@ H5FL_ARR_DEFINE(H5SM_sohm_t, H5O_SHMESG_MAX_LIST_SIZE);
  *-------------------------------------------------------------------------
  */
 herr_t
-H5SM_init(H5F_t *f, H5P_genplist_t * fc_plist, hid_t dxpl_id)
+H5SM_init(H5F_t *f, H5P_genplist_t * fc_plist, const H5O_loc_t *ext_loc, hid_t dxpl_id)
 {
-    H5SM_master_table_t *table = NULL;
-    haddr_t table_addr = HADDR_UNDEF;
-    unsigned num_indexes;
-    unsigned list_max, btree_min;
-    unsigned index_type_flags[H5O_SHMESG_MAX_NINDEXES];
-    unsigned minsizes[H5O_SHMESG_MAX_NINDEXES];
-    unsigned type_flags_used;
-    unsigned x;
-    hsize_t table_size;
-    herr_t ret_value=SUCCEED;
+    H5O_shmesg_table_t sohm_table;      /* SOHM message for superblock extension */
+    H5SM_master_table_t *table = NULL;  /* SOHM master table for file */
+    haddr_t table_addr = HADDR_UNDEF;   /* Address of SOHM master table in file */
+    unsigned num_indexes;               /* Number of SOHM indices */
+    unsigned list_max, btree_min;       /* Phase change limits for SOHM indices */
+    unsigned index_type_flags[H5O_SHMESG_MAX_NINDEXES]; /* Messages types stored in each index */
+    unsigned minsizes[H5O_SHMESG_MAX_NINDEXES]; /* Message size sharing threshhold for each index */
+    unsigned type_flags_used;           /* Message type flags used, for sanity checking */
+    hsize_t table_size;                 /* Size of SOHM master table in file */
+    unsigned x;                         /* Local index variable */
+    herr_t ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI(H5SM_init, NULL)
 
@@ -144,7 +145,7 @@ H5SM_init(H5F_t *f, H5P_genplist_t * fc_plist, hid_t dxpl_id)
         if(index_type_flags[x] & type_flags_used)
             HGOTO_ERROR(H5E_PLIST, H5E_BADVALUE, FAIL, "the same shared message type flag is assigned to more than one index")
         type_flags_used |= index_type_flags[x];
-    }
+    } /* end for */
 
     /* Set version and number of indexes in table and in superblock.
      * Right now we just use one byte to hold the number of indexes.
@@ -167,7 +168,7 @@ H5SM_init(H5F_t *f, H5P_genplist_t * fc_plist, hid_t dxpl_id)
     /* Initialize all of the indexes, but don't allocate space for them to
      * hold messages until we actually need to write to them.
      */
-    for(x=0; x<table->num_indexes; x++)
+    for(x = 0; x < table->num_indexes; x++)
     {
         table->indexes[x].btree_min = btree_min;
         table->indexes[x].list_max = list_max;
@@ -176,12 +177,12 @@ H5SM_init(H5F_t *f, H5P_genplist_t * fc_plist, hid_t dxpl_id)
         table->indexes[x].index_addr = HADDR_UNDEF;
         table->indexes[x].heap_addr = HADDR_UNDEF;
         table->indexes[x].num_messages = 0;
+
         /* Indexes start as lists unless the list-to-btree threshold is zero */
-        if(table->indexes[x].list_max > 0) {
+        if(table->indexes[x].list_max > 0)
             table->indexes[x].index_type = H5SM_LIST;
-        } else {
+        else
             table->indexes[x].index_type = H5SM_BTREE;
-        }
     } /* end for */
 
     /* Allocate space for the table on disk */
@@ -191,19 +192,25 @@ H5SM_init(H5F_t *f, H5P_genplist_t * fc_plist, hid_t dxpl_id)
 
     /* Cache the new table */
     if(H5AC_set(f, dxpl_id, H5AC_SOHM_TABLE, table_addr, table, H5AC__NO_FLAGS_SET) < 0)
-	HGOTO_ERROR(H5E_CACHE, H5E_CANTLOAD, FAIL, "can't add SOHM table to cache")
+	HGOTO_ERROR(H5E_CACHE, H5E_CANTINS, FAIL, "can't add SOHM table to cache")
 
     /* Record the address of the master table in the file */
     f->shared->sohm_addr = table_addr;
 
+    /* Write shared message information to the superblock extension */
+    sohm_table.addr = f->shared->sohm_addr;
+    sohm_table.version = f->shared->sohm_vers;
+    sohm_table.nindexes = f->shared->sohm_nindexes;
+    if(H5O_msg_create(ext_loc, H5O_SHMESG_ID, H5O_MSG_FLAG_CONSTANT | H5O_MSG_FLAG_DONTSHARE, H5O_UPDATE_TIME, &sohm_table, dxpl_id) < 0)
+        HGOTO_ERROR(H5E_SOHM, H5E_CANTINIT, FAIL, "unable to update SOHM header message")
+
 done:
-    if(ret_value < 0)
-    {
+    if(ret_value < 0) {
         if(table_addr != HADDR_UNDEF)
             H5MF_xfree(f, H5FD_MEM_SOHM_TABLE, dxpl_id, table_addr, (hsize_t)H5SM_TABLE_SIZE(f));
         if(table != NULL)
             H5FL_FREE(H5SM_master_table_t, table);
-    }
+    } /* end if */
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5SM_init() */
diff --git a/src/H5SMprivate.h b/src/H5SMprivate.h
index 49d0916..5c56602 100755
--- a/src/H5SMprivate.h
+++ b/src/H5SMprivate.h
@@ -39,7 +39,8 @@ typedef struct H5SM_master_table_t H5SM_master_table_t;
 /******************************/
 
 /* Generally useful shared message routines */
-H5_DLL herr_t H5SM_init(H5F_t *f, H5P_genplist_t *fc_plist, hid_t dxpl_id);
+H5_DLL herr_t H5SM_init(H5F_t *f, H5P_genplist_t *fc_plist,
+    const H5O_loc_t *ext_loc, hid_t dxpl_id);
 H5_DLL htri_t H5SM_can_share(H5F_t *f, hid_t dxpl_id, H5SM_master_table_t *table,
     ssize_t *sohm_index_num, unsigned type_id, const void *mesg);
 H5_DLL htri_t H5SM_try_share(H5F_t *f, hid_t dxpl_id, unsigned type_id,