[svn-r22452] - remove nrefs param

- create a struct to hold parameters for object locations instead of calling into VOL to lookup and free object:
  * update the implementation for H5Oopen(_by_name/idx/ref)
  * H5Rderefence
  * H5Aopen(_by_name), H5Arename(_by_name)
  * other routines coming later

19 files changed, 400 insertions, 287 deletions

diff --git a/src/H5A.c b/src/H5A.c
index ca35078..a41340b 100644
--- a/src/H5A.c
+++ b/src/H5A.c
@@ -218,7 +218,7 @@ H5Acreate2(hid_t loc_id, const char *attr_name, hid_t type_id, hid_t space_id,
     hid_t acpl_id, hid_t UNUSED aapl_id)
 {
     H5P_genplist_t      *plist;            /* Property list pointer */
-    void *location = NULL;
+    H5VL_loc_params_t loc_params;
     hid_t		ret_value;              /* Return value */
 
     FUNC_ENTER_API(FAIL)
@@ -234,6 +234,9 @@ H5Acreate2(hid_t loc_id, const char *attr_name, hid_t type_id, hid_t space_id,
     if(H5P_DEFAULT == acpl_id)
         acpl_id = H5P_ATTRIBUTE_CREATE_DEFAULT;
 
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_ID;
+    loc_params.loc_data.loc_by_id.id = loc_id;
+
     /* Get the plist structure */
     if(NULL == (plist = (H5P_genplist_t *)H5I_object(acpl_id)))
         HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
@@ -243,7 +246,7 @@ H5Acreate2(hid_t loc_id, const char *attr_name, hid_t type_id, hid_t space_id,
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for datatype id")
     if(H5P_set(plist, H5VL_ATTR_SPACE_ID, &space_id) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for space id")
-    if(H5P_set(plist, H5VL_ATTR_LOCATION, &location) < 0)
+    if(H5P_set(plist, H5VL_ATTR_LOC_PARAMS, &loc_params) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for location")
 
     /* Create the attribute through the VOL */
@@ -288,13 +291,12 @@ done:
 /* ARGSUSED */
 hid_t
 H5Acreate_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
-    hid_t type_id, hid_t space_id, hid_t acpl_id, hid_t UNUSED aapl_id,
+    hid_t type_id, hid_t space_id, hid_t acpl_id, hid_t aapl_id,
     hid_t lapl_id)
 {
     H5P_genplist_t      *plist;            /* Property list pointer */
-    void                *location = NULL;  /* a pointer to VOL specific token that indicates 
-                                              the location of the object */
-    hid_t		ret_value;              /* Return value */
+    H5VL_loc_params_t    loc_params;
+    hid_t		 ret_value;        /* Return value */
 
     FUNC_ENTER_API(FAIL)
     H5TRACE8("i", "i*s*siiiii", loc_id, obj_name, attr_name, type_id, space_id,
@@ -308,14 +310,14 @@ H5Acreate_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
     if(!attr_name || !*attr_name)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no attribute name")
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup(loc_id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, H5_REQUEST_NULL, obj_name, lapl_id) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
-
     /* Get correct property list */
     if(H5P_DEFAULT == acpl_id)
         acpl_id = H5P_ATTRIBUTE_CREATE_DEFAULT;
 
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+    loc_params.loc_data.loc_by_name.name = obj_name;
+    loc_params.loc_data.loc_by_name.lapl_id = lapl_id;
+
     /* Get the plist structure */
     if(NULL == (plist = (H5P_genplist_t *)H5I_object(acpl_id)))
         HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
@@ -325,7 +327,7 @@ H5Acreate_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for datatype id")
     if(H5P_set(plist, H5VL_ATTR_SPACE_ID, &space_id) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for space id")
-    if(H5P_set(plist, H5VL_ATTR_LOCATION, &location) < 0)
+    if(H5P_set(plist, H5VL_ATTR_LOC_PARAMS, &loc_params) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for location")
 
     /* Create the attribute through the VOL */
@@ -333,11 +335,6 @@ H5Acreate_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to create attribute")
 
 done:
-    if (NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 } /* H5Acreate_by_name() */
 
@@ -533,6 +530,7 @@ done:
 hid_t
 H5Aopen(hid_t loc_id, const char *attr_name, hid_t aapl_id)
 {
+    H5VL_loc_params_t loc_params; 
     hid_t		ret_value;
 
     FUNC_ENTER_API(FAIL)
@@ -544,9 +542,12 @@ H5Aopen(hid_t loc_id, const char *attr_name, hid_t aapl_id)
     if(!attr_name || !*attr_name)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no attribute name")
 
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_ID;
+    loc_params.loc_data.loc_by_id.id = loc_id;
+
     /* Open the attribute through the VOL */
-    if((ret_value = H5VL_attr_open(loc_id, NULL, attr_name, aapl_id, H5_REQUEST_NULL)) < 0)
-	HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to open attribute")
+    if((ret_value = H5VL_attr_open(loc_id, loc_params, attr_name, aapl_id, H5_REQUEST_NULL)) < 0)
+	HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to open attribute")
 
 done:
     FUNC_LEAVE_API(ret_value)
@@ -576,10 +577,9 @@ done:
 --------------------------------------------------------------------------*/
 hid_t
 H5Aopen_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
-    hid_t UNUSED aapl_id, hid_t lapl_id)
+    hid_t aapl_id, hid_t lapl_id)
 {
-    void                *location = NULL;  /* a pointer to VOL specific token that indicates 
-                                              the location of the object */
+    H5VL_loc_params_t   loc_params;
     hid_t		ret_value;
 
     FUNC_ENTER_API(FAIL)
@@ -598,20 +598,15 @@ H5Aopen_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
         if(TRUE != H5P_isa_class(lapl_id, H5P_LINK_ACCESS))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not link access property list ID")
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup(loc_id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, H5_REQUEST_NULL, obj_name, lapl_id) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+    loc_params.loc_data.loc_by_name.name = obj_name;
+    loc_params.loc_data.loc_by_name.lapl_id = lapl_id;
 
     /* Open the attribute through the VOL */
-    if((ret_value = H5VL_attr_open(loc_id, location, attr_name, aapl_id, H5_REQUEST_NULL)) < 0)
-	HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to open attribute")
+    if((ret_value = H5VL_attr_open(loc_id, loc_params, attr_name, aapl_id, H5_REQUEST_NULL)) < 0)
+	HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to open attribute")
 
 done:
-    if (NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 } /* H5Aopen_by_name() */
 
@@ -1643,9 +1638,8 @@ herr_t
 H5Aget_info_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
     H5A_info_t *ainfo, hid_t lapl_id)
 {
+    H5VL_loc_params_t   loc_params;
     hid_t attr_id = -1;
-    void        *location = NULL;  /* a pointer to VOL specific token that indicates 
-                                      the location of the object */
     herr_t	ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_API(FAIL)
@@ -1665,23 +1659,14 @@ H5Aget_info_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
     else
         if(TRUE != H5P_isa_class(lapl_id, H5P_LINK_ACCESS))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not link access property list ID")
-#if 0
-    /* Open the attribute on the object header */
-    if(NULL == (attr = H5A_open_by_name(&loc, obj_name, attr_name, lapl_id, H5AC_ind_dxpl_id)))
-        HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "can't open attribute")
-
-    /* Get the attribute information */
-    if(H5A_get_info(attr, ainfo) < 0)
-	HGOTO_ERROR(H5E_ATTR, H5E_CANTGET, FAIL, "unable to get attribute info")
-#endif
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup(loc_id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, H5_REQUEST_NULL, obj_name, lapl_id) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+    loc_params.loc_data.loc_by_name.name = obj_name;
+    loc_params.loc_data.loc_by_name.lapl_id = lapl_id;
 
     /* Open the attribute through the VOL */
-    if((attr_id = H5VL_attr_open(loc_id, location, attr_name, H5P_DEFAULT, H5_REQUEST_NULL)) < 0)
-	HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to open attribute")
+    if((attr_id = H5VL_attr_open(loc_id, loc_params, attr_name, H5P_DEFAULT, H5_REQUEST_NULL)) < 0)
+	HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to open attribute")
 
     /* get the attribute info through the VOL */
     if(H5VL_attr_get(attr_id, H5VL_ATTR_GET_INFO, H5_REQUEST_NULL, ainfo) < 0)
@@ -1691,11 +1676,6 @@ done:
     if(attr_id > 0 && H5VL_attr_close(attr_id, H5_REQUEST_NULL) < 0)
         HDONE_ERROR(H5E_ATTR, H5E_CANTFREE, FAIL, "can't close attribute")
 
-    if(NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 } /* end H5Aget_info_by_name() */
 
@@ -1840,11 +1820,16 @@ H5Arename(hid_t loc_id, const char *old_name, const char *new_name)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "location is not valid for an attribute")
 
     /* Avoid thrashing things if the names are the same */
-    if(HDstrcmp(old_name, new_name))
+    if(HDstrcmp(old_name, new_name)) {
+        H5VL_loc_params_t loc_params;
+
+        loc_params.type = H5VL_OBJECT_LOOKUP_BY_ID;
+        loc_params.loc_data.loc_by_id.id = loc_id;
+
         /* rename the attribute info through the VOL */
-        if(H5VL_object_misc(loc_id, H5VL_ATTR_RENAME, H5_REQUEST_NULL, NULL, old_name, new_name) < 0)
+        if(H5VL_object_misc(loc_id, H5VL_ATTR_RENAME, H5_REQUEST_NULL, loc_params, old_name, new_name) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTRENAME, FAIL, "can't rename attribute")
-
+    }
 done:
     FUNC_LEAVE_API(ret_value)
 } /* H5Arename() */
@@ -1890,21 +1875,15 @@ H5Arename_by_name(hid_t loc_id, const char *obj_name, const char *old_attr_name,
 
     /* Avoid thrashing things if the names are the same */
     if(HDstrcmp(old_attr_name, new_attr_name)) {
-        void *location = NULL;
+        H5VL_loc_params_t loc_params;
 
-        /* Get the token for the Object location through the VOL */
-        if(H5VL_object_lookup(loc_id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, H5_REQUEST_NULL, obj_name, lapl_id) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+        loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+        loc_params.loc_data.loc_by_name.name = obj_name;
+        loc_params.loc_data.loc_by_name.lapl_id = lapl_id;
 
         /* get the attribute info through the VOL */
-        if(H5VL_object_misc(loc_id, H5VL_ATTR_RENAME, H5_REQUEST_NULL, location, old_attr_name, new_attr_name) < 0)
+        if(H5VL_object_misc(loc_id, H5VL_ATTR_RENAME, H5_REQUEST_NULL, loc_params, old_attr_name, new_attr_name) < 0)
             HGOTO_ERROR(H5E_INTERNAL, H5E_CANTGET, FAIL, "unable to get attribute info")
-
-        if(NULL != location) {
-            /* free the location token through the VOL */
-            if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-                HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-        }
     } /* end if */
 
 done:
@@ -2039,11 +2018,11 @@ H5Aiterate_by_name(hid_t loc_id, const char *obj_name, H5_index_t idx_type,
     H5_iter_order_t order, hsize_t *idx, H5A_operator2_t op, void *op_data,
     hid_t lapl_id)
 {
-    void *location = NULL;
     hid_t       obj_loc_id = (-1);      /* ID for object located */
     H5A_attr_iter_op_t attr_op; /* Attribute operator */
     hsize_t	start_idx;      /* Index of attribute to start iterating at */
     hsize_t	last_attr;      /* Index of last attribute examined */
+    H5VL_loc_params_t loc_params;
     herr_t	ret_value;      /* Return value */
 
     FUNC_ENTER_API(FAIL)
@@ -2065,12 +2044,11 @@ H5Aiterate_by_name(hid_t loc_id, const char *obj_name, H5_index_t idx_type,
         if(TRUE != H5P_isa_class(lapl_id, H5P_LINK_ACCESS))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not link access property list ID")
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup (loc_id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, H5_REQUEST_NULL, obj_name, lapl_id) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+    loc_params.loc_data.loc_by_name.name = obj_name;
 
     /* Open the object through the VOL */
-    if((obj_loc_id = H5VL_object_open_by_loc(loc_id, location, lapl_id, H5_REQUEST_NULL)) < 0)
+    if((obj_loc_id = H5VL_object_open(loc_id, loc_params, lapl_id, H5_REQUEST_NULL)) < 0)
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
 
     /* Build attribute operator info */
@@ -2093,11 +2071,6 @@ done:
             HDONE_ERROR(H5E_ATTR, H5E_CANTDEC, FAIL, "unable to close temporary object")
     } /* end if */
 
-    if(NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 } /* H5Aiterate_by_name() */
 
@@ -2132,7 +2105,7 @@ H5Adelete(hid_t loc_id, const char *name)
 
     /* Open the attribute through the VOL */
     if(H5VL_attr_remove(loc_id, NULL, name, H5_REQUEST_NULL) < 0)
-	HGOTO_ERROR(H5E_DATASET, H5E_CANTDELETE, FAIL, "unable to delete attribute")
+	HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete attribute")
 
 done:
     FUNC_LEAVE_API(ret_value)
@@ -2184,7 +2157,7 @@ H5Adelete_by_name(hid_t loc_id, const char *obj_name, const char *attr_name,
 
     /* Open the attribute through the VOL */
     if(H5VL_attr_remove(loc_id, location, attr_name, H5_REQUEST_NULL) < 0)
-	HGOTO_ERROR(H5E_DATASET, H5E_CANTDELETE, FAIL, "unable to delete attribute")
+	HGOTO_ERROR(H5E_ATTR, H5E_CANTDELETE, FAIL, "unable to delete attribute")
 
 done:
     if(NULL != location) {
@@ -2288,7 +2261,7 @@ H5Aclose(hid_t attr_id)
 
     /* Close the attribute through the VOL */
     if((ret_value = H5VL_attr_close(attr_id, H5_REQUEST_NULL)) < 0)
-	HGOTO_ERROR(H5E_DATASET, H5E_CANTRELEASE, FAIL, "unable to close attribute")
+	HGOTO_ERROR(H5E_ATTR, H5E_CANTRELEASE, FAIL, "unable to close attribute")
 
 done:
     FUNC_LEAVE_API(ret_value)
diff --git a/src/H5Adeprec.c b/src/H5Adeprec.c
index 50f2cf1..6f6388c 100644
--- a/src/H5Adeprec.c
+++ b/src/H5Adeprec.c
@@ -139,7 +139,7 @@ hid_t
 H5Acreate1(hid_t loc_id, const char *name, hid_t type_id, hid_t space_id,
 	  hid_t plist_id)
 {
-    void *location = NULL;
+    H5VL_loc_params_t   loc_params;
     H5P_genplist_t      *plist;            /* Property list pointer */
     hid_t		ret_value;              /* Return value */
 
@@ -156,6 +156,9 @@ H5Acreate1(hid_t loc_id, const char *name, hid_t type_id, hid_t space_id,
     if(H5P_DEFAULT == plist_id)
         plist_id = H5P_ATTRIBUTE_CREATE_DEFAULT;
 
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_ID;
+    loc_params.loc_data.loc_by_id.id = loc_id;
+
     /* Get the plist structure */
     if(NULL == (plist = (H5P_genplist_t *)H5I_object(plist_id)))
         HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
@@ -165,7 +168,7 @@ H5Acreate1(hid_t loc_id, const char *name, hid_t type_id, hid_t space_id,
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for datatype id")
     if(H5P_set(plist, H5VL_ATTR_SPACE_ID, &space_id) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for space id")
-    if(H5P_set(plist, H5VL_ATTR_LOCATION, &location) < 0)
+    if(H5P_set(plist, H5VL_ATTR_LOC_PARAMS, &loc_params) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't set property value for location")
 
     /* Create the attribute through the VOL */
@@ -202,6 +205,7 @@ done:
 hid_t
 H5Aopen_name(hid_t loc_id, const char *name)
 {
+    H5VL_loc_params_t loc_params; 
     hid_t		ret_value;
 
     FUNC_ENTER_API(FAIL)
@@ -213,9 +217,12 @@ H5Aopen_name(hid_t loc_id, const char *name)
     if(!name || !*name)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no name")
 
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_ID;
+    loc_params.loc_data.loc_by_id.id = loc_id;
+
     /* Open the attribute through the VOL */
-    if((ret_value = H5VL_attr_open(loc_id, NULL, name, H5P_DEFAULT, H5_REQUEST_NULL)) < 0)
-	HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to open attribute")
+    if((ret_value = H5VL_attr_open(loc_id, loc_params, name, H5P_DEFAULT, H5_REQUEST_NULL)) < 0)
+	HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to open attribute")
 
 done:
     FUNC_LEAVE_API(ret_value)
diff --git a/src/H5Aint.c b/src/H5Aint.c
index 74c5590..1bbbd31 100644
--- a/src/H5Aint.c
+++ b/src/H5Aint.c
@@ -1259,3 +1259,53 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5A_dense_post_copy_file_all */
 
+
+/*-------------------------------------------------------------------------
+ * Function:	H5A_rename_by_name
+ *
+ * Purpose:     Private version of H5Arename_by_name
+ *
+ * Return:	Success:             Non-negative
+ *		Failure:             Negative
+ *
+ * Programmer:	Quincey Koziol
+ *              February 20, 2007
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5A_rename_by_name(H5G_loc_t loc, const char *obj_name, const char *old_attr_name,
+                   const char *new_attr_name, hid_t lapl_id)
+{
+    H5G_loc_t   obj_loc;                /* Location used to open group */
+    H5G_name_t  obj_path;            	/* Opened object group hier. path */
+    H5O_loc_t   obj_oloc;            	/* Opened object object location */
+    hbool_t     loc_found = FALSE;      /* Entry at 'obj_name' found */
+    herr_t	ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Avoid thrashing things if the names are the same */
+    if(HDstrcmp(old_attr_name, new_attr_name)) {
+        /* Set up opened group location to fill in */
+        obj_loc.oloc = &obj_oloc;
+        obj_loc.path = &obj_path;
+        H5G_loc_reset(&obj_loc);
+
+        /* Find the object's location */
+        if(H5G_loc_find(&loc, obj_name, &obj_loc/*out*/, lapl_id, H5AC_ind_dxpl_id) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_NOTFOUND, FAIL, "object not found")
+        loc_found = TRUE;
+
+        /* Call attribute rename routine */
+        if(H5O_attr_rename(obj_loc.oloc, H5AC_dxpl_id, old_attr_name, new_attr_name) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTRENAME, FAIL, "can't rename attribute")
+    } /* end if */
+
+done:
+    /* Release resources */
+    if(loc_found && H5G_loc_free(&obj_loc) < 0)
+        HDONE_ERROR(H5E_ATTR, H5E_CANTRELEASE, FAIL, "can't free location")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5A_rename_by_name() */
diff --git a/src/H5Aprivate.h b/src/H5Aprivate.h
index 448ece5..9e2cbb2 100644
--- a/src/H5Aprivate.h
+++ b/src/H5Aprivate.h
@@ -82,6 +82,7 @@ H5_DLL herr_t H5O_attr_iterate_real(hid_t loc_id, const H5O_loc_t *loc,
 H5_DLL herr_t H5O_attr_iterate(hid_t loc_id, hid_t dxpl_id, H5_index_t idx_type,
     H5_iter_order_t order, hsize_t skip, hsize_t *last_attr,
     const H5A_attr_iter_op_t *op, void *op_data);
-
+H5_DLL herr_t H5A_rename_by_name(H5G_loc_t loc, const char *obj_name, const char *old_attr_name,
+                                 const char *new_attr_name, hid_t lapl_id);
 #endif /* _H5Aprivate_H */
 
diff --git a/src/H5F.c b/src/H5F.c
index 724477c..af71d09 100644
--- a/src/H5F.c
+++ b/src/H5F.c
@@ -338,7 +338,6 @@ H5F_get_access_plist(H5F_t *f, hbool_t app_ref)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set file driver ID")
 
     /* Increment the reference count on the VOL struct and insert it into the property list */
-    f->vol_cls->nrefs ++;
     if(H5P_set(new_plist, H5F_ACS_VOL_NAME, &(f->vol_cls)) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set file VOL plugin")
 
@@ -2157,7 +2156,6 @@ H5F_get_id(H5F_t *file, hbool_t app_ref)
         /* attach VOL information to the ID */
         if (H5I_register_aux(file->file_id, file->vol_cls, (H5I_free_t)H5VL_close) < 0)
             HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-        file->vol_cls->nrefs++;
     } else {
         /* Increment reference count on atom. */
         if(H5I_inc_ref(file->file_id, app_ref) < 0)
diff --git a/src/H5Gint.c b/src/H5Gint.c
index 1e204d8..5e220ed 100644
--- a/src/H5Gint.c
+++ b/src/H5Gint.c
@@ -839,7 +839,6 @@ H5G_iterate(hid_t loc_id, const char *group_name,
     vol_plugin = H5F_get_vol_cls(loc.oloc->file);
     if (H5I_register_aux(gid, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
     /* Set up user data for callback */
     udata.gid = gid;
@@ -1119,7 +1118,6 @@ H5G_visit(hid_t loc_id, const char *group_name, H5_index_t idx_type,
     vol_plugin = H5F_get_vol_cls(loc.oloc->file);
     if (H5I_register_aux(gid, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
     /* Set up user data */
     udata.gid = gid;
diff --git a/src/H5Gtraverse.c b/src/H5Gtraverse.c
index 2ff5477..44362b2 100644
--- a/src/H5Gtraverse.c
+++ b/src/H5Gtraverse.c
@@ -215,7 +215,6 @@ H5G_traverse_ud(const H5G_loc_t *grp_loc/*in,out*/, const H5O_link_t *lnk,
     vol_plugin = H5F_get_vol_cls(grp_loc->oloc->file);
     if (H5I_register_aux(cur_grp, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
     /* Check for generic default property list and use link access default if so */
     if(_lapl_id == H5P_DEFAULT) {
diff --git a/src/H5I.c b/src/H5I.c
index f4b308f..51823f3 100644
--- a/src/H5I.c
+++ b/src/H5I.c
@@ -2299,10 +2299,12 @@ H5I_register_aux(hid_t id, void *aux_ptr, H5I_free_t free_func)
 
     FUNC_ENTER_NOAPI_NOINIT
 
-    if(NULL != (id_ptr = H5I_find_id(id))) {
-        id_ptr->aux_ptr = aux_ptr;
-        id_ptr->free_aux = free_func;
-    }
+    if(NULL == (id_ptr = H5I_find_id(id)))
+        HGOTO_ERROR(H5E_ATOM, H5E_CANTGET, FAIL, "Invalid ID")
+
+    id_ptr->aux_ptr = aux_ptr;
+    id_ptr->free_aux = free_func;
+
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5L.c b/src/H5L.c
index 97116ea..ec88fd5 100644
--- a/src/H5L.c
+++ b/src/H5L.c
@@ -1711,7 +1711,6 @@ H5L_link_cb(H5G_loc_t *grp_loc/*in*/, const char *name, const H5O_link_t UNUSED
             vol_plugin = H5F_get_vol_cls(grp_loc->oloc->file);
             if (H5I_register_aux(grp_id, vol_plugin, (H5I_free_t)H5VL_close) < 0)
                 HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-            vol_plugin->nrefs++;
 
             /* Make callback */
             if((link_class->create_func)(name, grp_id, udata->lnk->u.ud.udata, udata->lnk->u.ud.size, H5P_DEFAULT) < 0)
diff --git a/src/H5O.c b/src/H5O.c
index 2f09b6f..4df3970 100644
--- a/src/H5O.c
+++ b/src/H5O.c
@@ -227,9 +227,8 @@ H5O_init_interface(void)
 hid_t
 H5Oopen(hid_t loc_id, const char *name, hid_t lapl_id)
 {
+    H5VL_loc_params_t loc_params;
     hid_t       ret_value = FAIL;
-    void       *location = NULL; /* a pointer to VOL specific token that indicates 
-                                    the location of the object */
 
     FUNC_ENTER_API(FAIL)
     H5TRACE3("i", "i*si", loc_id, name, lapl_id);
@@ -237,21 +236,14 @@ H5Oopen(hid_t loc_id, const char *name, hid_t lapl_id)
     if(!name || !*name)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no name")
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup (loc_id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, H5_REQUEST_NULL, name, lapl_id) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+    loc_params.loc_data.loc_by_name.name = name;
 
     /* Open the object through the VOL */
-    if((ret_value = H5VL_object_open_by_loc(loc_id, location, lapl_id, H5_REQUEST_NULL)) < 0)
+    if((ret_value = H5VL_object_open(loc_id, loc_params, lapl_id, H5_REQUEST_NULL)) < 0)
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
 
 done:
-    if (NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
-
     FUNC_LEAVE_API(ret_value)
 } /* end H5Oopen() */
 
@@ -283,7 +275,7 @@ hid_t
 H5Oopen_by_idx(hid_t loc_id, const char *group_name, H5_index_t idx_type,
     H5_iter_order_t order, hsize_t n, hid_t lapl_id)
 {
-    void       *location = NULL;
+    H5VL_loc_params_t loc_params;
     hid_t       ret_value = FAIL;
 
     FUNC_ENTER_API(FAIL)
@@ -302,21 +294,17 @@ H5Oopen_by_idx(hid_t loc_id, const char *group_name, H5_index_t idx_type,
         if(TRUE != H5P_isa_class(lapl_id, H5P_LINK_ACCESS))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not link access property list ID")
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup(loc_id, H5VL_OBJECT_LOOKUP_BY_IDX, &location, H5_REQUEST_NULL, group_name,
-                          idx_type, order, n, lapl_id) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_IDX;
+    loc_params.loc_data.loc_by_idx.name = group_name;
+    loc_params.loc_data.loc_by_idx.idx_type = idx_type;
+    loc_params.loc_data.loc_by_idx.order = order;
+    loc_params.loc_data.loc_by_idx.n = n;
 
     /* Open the object through the VOL */
-    if((ret_value = H5VL_object_open_by_loc(loc_id, location, lapl_id, H5_REQUEST_NULL)) < 0)
+    if((ret_value = H5VL_object_open(loc_id, loc_params, lapl_id, H5_REQUEST_NULL)) < 0)
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
 
 done:
-    if (NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 } /* end H5Oopen_by_idx() */
 
@@ -360,26 +348,20 @@ hid_t
 H5Oopen_by_addr(hid_t loc_id, haddr_t addr)
 {
     hid_t       lapl_id = H5P_LINK_ACCESS_DEFAULT; /* lapl to use to open this object */
-    void       *location = NULL;
+    H5VL_loc_params_t loc_params;
     hid_t       ret_value = FAIL;
 
     FUNC_ENTER_API(FAIL)
     H5TRACE2("i", "ia", loc_id, addr);
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup (loc_id, H5VL_OBJECT_LOOKUP_BY_ADDR, &location, H5_REQUEST_NULL, addr) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_ADDR;
+    loc_params.loc_data.loc_by_addr.addr = addr;
 
     /* Open the object through the VOL */
-    if((ret_value = H5VL_object_open_by_loc(loc_id, location, lapl_id, H5_REQUEST_NULL)) < 0)
+    if((ret_value = H5VL_object_open(loc_id, loc_params, lapl_id, H5_REQUEST_NULL)) < 0)
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
 
 done:
-    if (NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (loc_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 } /* end H5Oopen_by_addr() */
 
diff --git a/src/H5Pacpl.c b/src/H5Pacpl.c
index 04ab1b9..e73ef21 100644
--- a/src/H5Pacpl.c
+++ b/src/H5Pacpl.c
@@ -44,8 +44,8 @@
 /****************/
 
 /* Definitions for UDATA */
-#define H5A_CRT_LOCATION_SIZE   sizeof(void *)
-#define H5A_CRT_LOCATION_DEF    NULL
+#define H5A_CRT_LOCATION_SIZE   sizeof(H5VL_loc_params_t)
+#define H5A_CRT_LOCATION_DEF {H5VL_OBJECT_LOOKUP_BY_ID, {{FAIL}}}
 
 /******************/
 /* Local Typedefs */
@@ -105,7 +105,7 @@ H5P_acrt_reg_prop(H5P_genclass_t *pclass)
 {
     hid_t type_id = FAIL;
     hid_t space_id = FAIL;
-    void *location = H5A_CRT_LOCATION_DEF;
+    H5VL_loc_params_t loc_params = H5A_CRT_LOCATION_DEF;
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT
@@ -121,7 +121,7 @@ H5P_acrt_reg_prop(H5P_genclass_t *pclass)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
     /* Register the lcpl ID property */
-    if(H5P_register_real(pclass, H5VL_ATTR_LOCATION, H5A_CRT_LOCATION_SIZE, &location, 
+    if(H5P_register_real(pclass, H5VL_ATTR_LOC_PARAMS, H5A_CRT_LOCATION_SIZE, &loc_params, 
                          NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
diff --git a/src/H5R.c b/src/H5R.c
index bfead4a..4ce37da 100644
--- a/src/H5R.c
+++ b/src/H5R.c
@@ -511,8 +511,7 @@ done:
 hid_t
 H5Rdereference2(hid_t obj_id, hid_t oapl_id, H5R_type_t ref_type, const void *_ref)
 {
-    void       *location = NULL; /* a pointer to VOL specific token that indicates 
-                                    the location of the object */
+    H5VL_loc_params_t loc_params;
     hid_t ret_value;
 
     FUNC_ENTER_API(FAIL)
@@ -526,15 +525,14 @@ H5Rdereference2(hid_t obj_id, hid_t oapl_id, H5R_type_t ref_type, const void *_r
     if(_ref == NULL)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid reference pointer")
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup (obj_id, H5VL_OBJECT_LOOKUP_BY_REF, &location, H5_REQUEST_NULL, 
-                           ref_type, _ref) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
-
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_REF;
+    loc_params.loc_data.loc_by_ref.ref_type = ref_type;
+    loc_params.loc_data.loc_by_ref._ref = _ref;
 
     /* Open the object through the VOL */
-    if((ret_value = H5VL_object_open_by_loc(obj_id, location, oapl_id, H5_REQUEST_NULL)) < 0)
+    if((ret_value = H5VL_object_open(obj_id, loc_params, oapl_id, H5_REQUEST_NULL)) < 0)
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
+
 #if 0
     /* Create reference */
     if((ret_value = H5R_dereference(file, oapl_id, H5AC_dxpl_id, ref_type, _ref, TRUE)) < 0)
@@ -542,11 +540,6 @@ H5Rdereference2(hid_t obj_id, hid_t oapl_id, H5R_type_t ref_type, const void *_r
 #endif
 
 done:
-    if (NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (obj_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 }   /* end H5Rdereference2() */
 
diff --git a/src/H5Rdeprec.c b/src/H5Rdeprec.c
index e6d8d21..a595c90 100644
--- a/src/H5Rdeprec.c
+++ b/src/H5Rdeprec.c
@@ -182,8 +182,7 @@ done:
 hid_t
 H5Rdereference1(hid_t obj_id, H5R_type_t ref_type, const void *_ref)
 {
-    void       *location = NULL; /* a pointer to VOL specific token that indicates 
-                                    the location of the object */
+    H5VL_loc_params_t loc_params;
     hid_t ret_value;
 
     FUNC_ENTER_API(FAIL)
@@ -195,21 +194,15 @@ H5Rdereference1(hid_t obj_id, H5R_type_t ref_type, const void *_ref)
     if(_ref == NULL)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid reference pointer")
 
-    /* Get the token for the Object location through the VOL */
-    if(H5VL_object_lookup (obj_id, H5VL_OBJECT_LOOKUP_BY_REF, &location, H5_REQUEST_NULL,
-                           ref_type, _ref) < 0)
-	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+    loc_params.type = H5VL_OBJECT_LOOKUP_BY_REF;
+    loc_params.loc_data.loc_by_ref.ref_type = ref_type;
+    loc_params.loc_data.loc_by_ref._ref = _ref;
 
     /* Open the object through the VOL */
-    if((ret_value = H5VL_object_open_by_loc(obj_id, location, H5P_DATASET_ACCESS_DEFAULT, H5_REQUEST_NULL)) < 0)
+    if((ret_value = H5VL_object_open(obj_id, loc_params, H5P_DATASET_ACCESS_DEFAULT, H5_REQUEST_NULL)) < 0)
 	HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
 
 done:
-    if (NULL != location) {
-        /* free the location token through the VOL */
-        if(H5VL_object_free_loc (obj_id, location, H5_REQUEST_NULL) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-    }
     FUNC_LEAVE_API(ret_value)
 }   /* end H5Rdereference1() */
 
diff --git a/src/H5VL.c b/src/H5VL.c
index f4412d2..2d7823f 100644
--- a/src/H5VL.c
+++ b/src/H5VL.c
@@ -268,6 +268,37 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5VLis_registered
+ *
+ * Purpose:	Tests whether a VOL class has been registered or not
+ *
+ * Return:	Positive if the VOL class has been registered
+ *              Zero if it is unregistered
+ *              Negative on error (if the class is not a valid class ID)
+ *
+ * Programmer:	Mohamad Chaarawi
+ *              June 2012
+ *
+ *-------------------------------------------------------------------------
+ */
+htri_t
+H5VLis_registered(hid_t id)
+{
+    htri_t ret_value = FALSE;     /* Return value */
+
+    FUNC_ENTER_API(FAIL)
+    H5TRACE1("t", "Ll", id);
+
+    /* Check arguments */
+    if(NULL != H5I_object_verify(id, H5I_VOL))
+        ret_value = TRUE;
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5VLis_registered() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5VLget_plugin_name
  *
  * Purpose:	Returns the plugin name for the VOL associated with the 
diff --git a/src/H5VLdummy.c b/src/H5VLdummy.c
index 7be5825..22d2500 100644
--- a/src/H5VLdummy.c
+++ b/src/H5VLdummy.c
@@ -55,21 +55,20 @@ static hid_t H5VL_DUMMY_g = 0;
 
 /* Prototypes */
 static herr_t H5VL_dummy_term(void);
-static hid_t  H5VL_dummy_file_open(const char *name, unsigned flags, hid_t fapl_id);
-static herr_t H5VL_dummy_file_close(hid_t fid);
-static hid_t  H5VL_dummy_file_create(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id);
+static hid_t  H5VL_dummy_file_open(const char *name, unsigned flags, hid_t fapl_id, hid_t req);
+static herr_t H5VL_dummy_file_close(hid_t fid, hid_t req);
+static hid_t  H5VL_dummy_file_create(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t req);
 
 H5VL_class_t H5VL_dummy_g = {
     "dummy",					/* name */
-    0,                                          /* nrefs */
-    H5VL_dummy_init,
+    NULL,
     H5VL_dummy_term,                           /*terminate */
     {                                           /* attribute_cls */
         NULL,                                   /* create */
         NULL,                                   /* open */
         NULL,                                   /* read */
         NULL,                                   /* write */
-        NULL,                                   /* delete */
+        NULL,                                   /* get */
         NULL,                                   /* delete */
         NULL                                    /* close */
     },
@@ -93,6 +92,7 @@ H5VL_class_t H5VL_dummy_g = {
         NULL,
         NULL,
         NULL,
+        NULL,
         H5VL_dummy_file_close                   /* close */
     },
     {                                           /* group_cls */
@@ -105,6 +105,7 @@ H5VL_class_t H5VL_dummy_g = {
         NULL,                                   /* create */
         NULL,                                   /* delete */
         NULL,                                   /* move */
+        NULL,
         NULL
     },
     {                                           /* object_cls */
@@ -112,6 +113,10 @@ H5VL_class_t H5VL_dummy_g = {
         NULL,                                   /* copy */
         NULL,
         NULL,
+        NULL,
+        NULL,
+        NULL,
+        NULL,
         NULL
     }
 };
@@ -162,7 +167,6 @@ H5VL_dummy_init(void)
 
     /* Set return value */
     ret_value = &H5VL_dummy_g;
-    ret_value->nrefs ++;
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5VL_dummy_init() */
@@ -187,7 +191,6 @@ H5VL_dummy_term(void)
 
     /* Reset VOL ID */
     H5VL_DUMMY_g = 0;
-    H5VL_dummy_g.nrefs = 0;
 
     FUNC_LEAVE_NOAPI(SUCCEED)
 } /* end H5VL_dummy_term() */
@@ -239,7 +242,7 @@ done:
  *-------------------------------------------------------------------------
  */
 static hid_t
-H5VL_dummy_file_open(const char *name, unsigned flags, hid_t fapl_id)
+H5VL_dummy_file_open(const char *name, unsigned flags, hid_t fapl_id, hid_t req)
 {
     FUNC_ENTER_NOAPI_NOINIT_NOERR
 
@@ -263,7 +266,7 @@ H5VL_dummy_file_open(const char *name, unsigned flags, hid_t fapl_id)
  *-------------------------------------------------------------------------
  */
 static hid_t
-H5VL_dummy_file_create(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id)
+H5VL_dummy_file_create(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t req)
 {
     FUNC_ENTER_NOAPI_NOINIT_NOERR
 
@@ -287,7 +290,7 @@ H5VL_dummy_file_create(const char *name, unsigned flags, hid_t fcpl_id, hid_t fa
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_dummy_file_close(hid_t file_id)
+H5VL_dummy_file_close(hid_t file_id, hid_t req)
 {
     FUNC_ENTER_NOAPI_NOINIT_NOERR
 
diff --git a/src/H5VLint.c b/src/H5VLint.c
index 00e64c8..6371ef3 100644
--- a/src/H5VLint.c
+++ b/src/H5VLint.c
@@ -189,9 +189,6 @@ H5VL_fapl_open(H5P_genplist_t *plist, H5VL_class_t *vol_cls)
 
     FUNC_ENTER_NOAPI(FAIL)
 
-    /* Increment the reference count on vol and copy vol info */
-    vol_cls->nrefs++;
-
     /* Set the vol properties for the list */
     if(H5P_set(plist, H5F_ACS_VOL_NAME, &vol_cls) < 0)
         HGOTO_ERROR(H5E_FILE, H5E_CANTSET, FAIL, "can't set vol ID")
@@ -223,10 +220,6 @@ H5VL_fapl_close(H5VL_class_t *vol_cls)
 
     FUNC_ENTER_NOAPI(FAIL)
 
-    if(NULL != vol_cls) {
-        vol_cls->nrefs--;
-    }
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5VL_fapl_close() */
@@ -252,8 +245,6 @@ H5VL_close(H5VL_class_t *vol_plugin)
 
     FUNC_ENTER_NOAPI(FAIL)
 
-    vol_plugin->nrefs--;
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5VL_close() */
@@ -336,7 +327,6 @@ H5VL_attr_create(hid_t id, const char *name, hid_t acpl_id, hid_t aapl_id, hid_t
     /* attach VOL information to the ID */
     if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -358,7 +348,7 @@ done:
  *-------------------------------------------------------------------------
  */
 hid_t
-H5VL_attr_open(hid_t id, void *location, const char *name, hid_t aapl_id, hid_t req)
+H5VL_attr_open(hid_t id, H5VL_loc_params_t loc_params, const char *name, hid_t aapl_id, hid_t req)
 {
     H5VL_class_t       *vol_plugin;            /* VOL structure attached to id */
     hid_t		ret_value;             /* Return value */
@@ -374,13 +364,12 @@ H5VL_attr_open(hid_t id, void *location, const char *name, hid_t aapl_id, hid_t
     }
 
     /* call the corresponding VOL open callback */
-    if((ret_value = (vol_plugin->attr_cls.open) (id, location, name, aapl_id, req)) < 0)
+    if((ret_value = (vol_plugin->attr_cls.open) (id, loc_params, name, aapl_id, req)) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "open failed")
 
     /* attach VOL information to the ID */
     if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -500,7 +489,6 @@ H5VL_attr_get(hid_t id, H5VL_attr_get_t get_type, hid_t req, ...)
             /* attach VOL information to the ID */
             if (H5I_register_aux(*ret_id, vol_plugin, (H5I_free_t)H5VL_close) < 0)
                 HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-            vol_plugin->nrefs++;
         }
         va_end (arguments);
     }
@@ -620,7 +608,6 @@ H5VL_datatype_commit(hid_t id, const char *name, hid_t type_id, hid_t lcpl_id,
 
     if (H5I_register_aux(type_id, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -651,24 +638,17 @@ H5VL_datatype_open(hid_t id, const char *name, hid_t tapl_id, hid_t req)
 
     if (NULL == (vol_plugin = (H5VL_class_t *)H5I_get_aux(id)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "ID does not contain VOL information")
+
     /* check if the type specific corresponding VOL open callback exists */
     if(NULL == vol_plugin->datatype_cls.open) {
-        void       *location = NULL; /* a pointer to VOL specific token that indicates 
-                                        the location of the object */
+        H5VL_loc_params_t loc_params;
 
-        /* Get the token for the Object location through the VOL */
-        if(H5VL_object_lookup (id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, req, name, tapl_id) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+        loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+        loc_params.loc_data.loc_by_name.name = name;
 
-        /* Open the object through the VOL */
-        if((ret_value = H5VL_object_open_by_loc(id, location, tapl_id, req)) < 0)
+        /* Open the object class */
+        if((ret_value = H5VL_object_open(id, loc_params, tapl_id, H5_REQUEST_NULL)) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
-
-        if (NULL != location) {
-            /* free the location token through the VOL */
-            if(H5VL_object_free_loc (id, location, H5_REQUEST_NULL) < 0)
-                HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-        }
     }
     else {
         /* call the corresponding VOL open callback */
@@ -678,7 +658,6 @@ H5VL_datatype_open(hid_t id, const char *name, hid_t tapl_id, hid_t req)
         /* attach VOL information to the ID */
         if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
             HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-        vol_plugin->nrefs++;
     }
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -758,7 +737,6 @@ H5VL_dataset_create(hid_t id, const char *name, hid_t dcpl_id, hid_t dapl_id, hi
     /* attach VOL information to the ID */
     if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -792,22 +770,14 @@ H5VL_dataset_open(hid_t id, const char *name, hid_t dapl_id, hid_t req)
 
     /* check if the type specific corresponding VOL open callback exists */
     if(NULL == vol_plugin->dataset_cls.open) {
-        void       *location = NULL; /* a pointer to VOL specific token that indicates 
-                                        the location of the object */
+        H5VL_loc_params_t loc_params;
 
-        /* Get the token for the Object location through the VOL */
-        if(H5VL_object_lookup (id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, req, name, dapl_id) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+        loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+        loc_params.loc_data.loc_by_name.name = name;
 
-        /* Open the object through the VOL */
-        if((ret_value = H5VL_object_open_by_loc(id, location, dapl_id, req)) < 0)
+        /* Open the object class */
+        if((ret_value = H5VL_object_open(id, loc_params, dapl_id, H5_REQUEST_NULL)) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
-
-        if (NULL != location) {
-            /* free the location token through the VOL */
-            if(H5VL_object_free_loc (id, location, H5_REQUEST_NULL) < 0)
-                HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-        }
     }
     else {
         /* call the corresponding VOL open callback */
@@ -817,7 +787,6 @@ H5VL_dataset_open(hid_t id, const char *name, hid_t dapl_id, hid_t req)
         /* attach VOL information to the ID */
         if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
             HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-        vol_plugin->nrefs++;
     }
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -978,7 +947,6 @@ H5VL_dataset_get(hid_t id, H5VL_dataset_get_t get_type, hid_t req, ...)
             /* attach VOL information to the ID */
             if (H5I_register_aux(*ret_id, vol_plugin, (H5I_free_t)H5VL_close) < 0)
                 HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-            vol_plugin->nrefs++;
         }
         va_end (arguments);
     }
@@ -1067,7 +1035,6 @@ H5VL_file_open(const char *name, unsigned flags, hid_t fapl_id, hid_t req)
     /* attach VOL information to the ID */
     if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1113,7 +1080,6 @@ H5VL_file_create(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id,
     /* attach VOL information to the ID */
     if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1275,7 +1241,6 @@ H5VL_file_optional(hid_t id, H5VL_file_optional_t optional_type, hid_t req, ...)
         /* attach VOL information to the ID */
         if (H5I_register_aux(*ret_id, vol_plugin, (H5I_free_t)H5VL_close) < 0)
             HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-        vol_plugin->nrefs++;
         va_end (arguments);
     }
 
@@ -1355,7 +1320,6 @@ H5VL_group_create(hid_t id, const char *name, hid_t gcpl_id, hid_t gapl_id, hid_
     /* attach VOL information to the ID */
     if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1389,22 +1353,14 @@ H5VL_group_open(hid_t id, const char *name, hid_t gapl_id, hid_t req)
 
     /* check if the type specific corresponding VOL open callback exists */
     if(NULL == vol_plugin->group_cls.open) {
-        void       *location = NULL; /* a pointer to VOL specific token that indicates 
-                                        the location of the object */
+        H5VL_loc_params_t loc_params;
 
-        /* Get the token for the Object location through the VOL */
-        if(H5VL_object_lookup (id, H5VL_OBJECT_LOOKUP_BY_NAME, &location, req, name, gapl_id) < 0)
-            HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to locate object")
+        loc_params.type = H5VL_OBJECT_LOOKUP_BY_NAME;
+        loc_params.loc_data.loc_by_name.name = name;
 
-        /* Open the object through the VOL */
-        if((ret_value = H5VL_object_open_by_loc(id, location, gapl_id, req)) < 0)
+        /* Open the object class */
+        if((ret_value = H5VL_object_open(id, loc_params, gapl_id, H5_REQUEST_NULL)) < 0)
             HGOTO_ERROR(H5E_SYM, H5E_CANTINIT, FAIL, "unable to open object")
-
-        if (NULL != location) {
-            /* free the location token through the VOL */
-            if(H5VL_object_free_loc (id, location, H5_REQUEST_NULL) < 0)
-                HGOTO_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "unable to free location token")
-        }
     }
     else {
         /* call the corresponding VOL open callback */
@@ -1414,7 +1370,6 @@ H5VL_group_open(hid_t id, const char *name, hid_t gapl_id, hid_t req)
         /* attach VOL information to the ID */
         if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
             HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-        vol_plugin->nrefs++;
     }
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1718,7 +1673,7 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5VL_object_open_by_loc
+ * Function:	H5VL_object_open
  *
  * Purpose:	Opens a object through the VOL
  *
@@ -1732,7 +1687,7 @@ done:
  *-------------------------------------------------------------------------
  */
 hid_t
-H5VL_object_open_by_loc(hid_t id, void *obj_loc, hid_t lapl_id, hid_t req)
+H5VL_object_open(hid_t id, H5VL_loc_params_t params, hid_t lapl_id, hid_t req)
 {
     H5VL_class_t       *vol_plugin;            /* VOL structure attached to id */
     hid_t		ret_value;              /* Return value */
@@ -1747,17 +1702,16 @@ H5VL_object_open_by_loc(hid_t id, void *obj_loc, hid_t lapl_id, hid_t req)
 	HGOTO_ERROR(H5E_VOL, H5E_UNSUPPORTED, FAIL, "vol plugin has no `object open' method")
 
     /* call the corresponding VOL open callback */
-    if((ret_value = (vol_plugin->object_cls.open)(obj_loc, lapl_id, req)) < 0)
+    if((ret_value = (vol_plugin->object_cls.open)(id, params, lapl_id, req)) < 0)
 	HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "open failed")
 
     /* attach VOL information to the ID */
     if (H5I_register_aux(ret_value, vol_plugin, (H5I_free_t)H5VL_close) < 0)
         HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-    vol_plugin->nrefs++;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5VL_object_open_by_loc() */
+} /* end H5VL_object_open() */
 
 
 /*-------------------------------------------------------------------------
@@ -1988,12 +1942,9 @@ H5VL_object_misc(hid_t id, H5VL_object_misc_t misc_type, hid_t req, ...)
 
         va_start (arguments, req);
         ret_id = va_arg (arguments, hid_t *);
-
         /* attach VOL information to the ID */
         if (H5I_register_aux(*ret_id, vol_plugin, (H5I_free_t)H5VL_close) < 0)
             HGOTO_ERROR(H5E_VOL, H5E_CANTINIT, FAIL, "can't attach vol info to ID")
-        vol_plugin->nrefs++;
-
         va_end (arguments);
     }
 done:
diff --git a/src/H5VLnative.c b/src/H5VLnative.c
index 1ef7b09..db9c0ab 100644
--- a/src/H5VLnative.c
+++ b/src/H5VLnative.c
@@ -65,7 +65,7 @@ static hid_t H5VL_NATIVE_g = 0;
 static herr_t H5VL_native_term(void);
 
 static hid_t H5VL_native_attr_create(hid_t loc_id, const char *attr_name, hid_t acpl_id, hid_t aapl_id, hid_t req);
-static hid_t H5VL_native_attr_open(hid_t loc_id, void *location, const char *attr_name, hid_t aapl_id, hid_t req);
+static hid_t H5VL_native_attr_open(hid_t loc_id, H5VL_loc_params_t loc_params, const char *attr_name, hid_t aapl_id, hid_t req);
 static herr_t H5VL_native_attr_read(hid_t attr_id, hid_t dtype_id, void *buf, hid_t req);
 static herr_t H5VL_native_attr_write(hid_t attr_id, hid_t dtype_id, const void *buf, hid_t req);
 static herr_t H5VL_native_attr_get(hid_t id, H5VL_attr_get_t get_type, hid_t req, va_list arguments);
@@ -109,7 +109,7 @@ static herr_t H5VL_native_link_iterate(hid_t loc_id, const char *name, hbool_t r
 static herr_t H5VL_native_link_get(hid_t loc_id, H5VL_link_get_t get_type, hid_t req, va_list arguments);
 static herr_t H5VL_native_link_remove(hid_t loc_id, const char *name, void *udata, hid_t lapl_id, hid_t req);
 
-static hid_t H5VL_native_object_open(void *location, hid_t lapl_id, hid_t req);
+static hid_t H5VL_native_object_open(hid_t loc_id, H5VL_loc_params_t params, hid_t lapl_id, hid_t req);
 static herr_t H5VL_native_object_copy(hid_t src_loc_id, const char *src_name, hid_t dst_loc_id, 
                                       const char *dst_name, hid_t ocpypl_id, hid_t lcpl_id, hid_t req);
 static herr_t H5VL_native_object_visit(hid_t loc_id, const char *obj_name, H5_index_t idx_type,
@@ -124,7 +124,6 @@ static herr_t H5VL_native_object_close(hid_t object_id, hid_t req);
 
 static H5VL_class_t H5VL_native_g = {
     "native",					/* name */
-    0,                                          /* nrefs */
     NULL,                           /* initialize */
     H5VL_native_term,                           /* terminate */
     {                                           /* attribute_cls */
@@ -231,7 +230,6 @@ H5VL_native_init(void)
 
     /* Set return value */
     ret_value = &H5VL_native_g;
-    ret_value->nrefs ++;
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5VL_native_init() */
@@ -256,7 +254,6 @@ H5VL_native_term(void)
 
     /* Reset VOL ID */
     H5VL_NATIVE_g = 0;
-    H5VL_native_g.nrefs = 0;
 
     FUNC_LEAVE_NOAPI(SUCCEED)
 } /* end H5VL_native_term() */
@@ -311,11 +308,13 @@ static hid_t
 H5VL_native_attr_create(hid_t loc_id, const char *attr_name, hid_t acpl_id, hid_t UNUSED aapl_id, hid_t UNUSED req)
 {
     H5G_loc_t       loc;                /* Object location */
+    H5G_loc_t       obj_loc;            /* Location used to open group */
+    hbool_t         loc_found = FALSE;  
     H5P_genplist_t  *plist;             /* Property list pointer */
     hid_t           type_id, space_id;
     H5T_t	    *type;              /* Datatype to use for attribute */
     H5S_t	    *space;             /* Dataspace to use for attribute */
-    void            *location = NULL;
+    H5VL_loc_params_t loc_params;
     hid_t           ret_value;
 
     FUNC_ENTER_NOAPI_NOINIT
@@ -329,7 +328,7 @@ H5VL_native_attr_create(hid_t loc_id, const char *attr_name, hid_t acpl_id, hid_
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get property value for datatype id")
     if(H5P_get(plist, H5VL_ATTR_SPACE_ID, &space_id) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get property value for space id")
-    if(H5P_get(plist, H5VL_ATTR_LOCATION, &location) < 0)
+    if(H5P_get(plist, H5VL_ATTR_LOC_PARAMS, &loc_params) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get property value for lcpl id")
 
     if(H5G_loc(loc_id, &loc) < 0)
@@ -341,21 +340,38 @@ H5VL_native_attr_create(hid_t loc_id, const char *attr_name, hid_t acpl_id, hid_
     if(NULL == (space = (H5S_t *)H5I_object_verify(space_id, H5I_DATASPACE)))
 	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data space")
 
-    if(NULL == location) { /* H5Acreate */
+    if(loc_params.type == H5VL_OBJECT_LOOKUP_BY_ID) { /* H5Acreate */
         /* Go do the real work for attaching the attribute to the dataset */
         if((ret_value = H5A_create(&loc, attr_name, type, space, acpl_id, H5AC_dxpl_id)) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to create attribute")
     }
-    else { /* H5Acreate_by_name */
-        H5G_loc_t   *obj_loc = (H5G_loc_t *)location;
+    else if (loc_params.type == H5VL_OBJECT_LOOKUP_BY_NAME) { /* H5Acreate_by_name */
+        H5G_name_t          obj_path;            	/* Opened object group hier. path */
+        H5O_loc_t           obj_oloc;            	/* Opened object object location */
+
+        /* Set up opened group location to fill in */
+        obj_loc.oloc = &obj_oloc;
+        obj_loc.path = &obj_path;
+        H5G_loc_reset(&obj_loc);
+
+        /* Find the object's location */
+        if(H5G_loc_find(&loc, loc_params.loc_data.loc_by_name.name, &obj_loc/*out*/, 
+                        loc_params.loc_data.loc_by_name.lapl_id, H5AC_ind_dxpl_id) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_NOTFOUND, FAIL, "object not found")
+        loc_found = TRUE;
 
         /* Go do the real work for attaching the attribute to the dataset */
-        if((ret_value = H5A_create(obj_loc, attr_name, type, space, acpl_id, H5AC_dxpl_id)) < 0)
+        if((ret_value = H5A_create(&obj_loc, attr_name, type, space, acpl_id, H5AC_dxpl_id)) < 0)
             HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to create attribute")
     }
-
+    else {
+        HGOTO_ERROR(H5E_VOL, H5E_UNSUPPORTED, FAIL, "unknown attribute create parameters")
+    }
 done:
-    FUNC_LEAVE_NOAPI(ret_value)
+    /* Release resources */
+    if(loc_found && H5G_loc_free(&obj_loc) < 0)
+        HDONE_ERROR(H5E_ATTR, H5E_CANTRELEASE, FAIL, "can't free location") 
+   FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5VL_native_attr_create() */
 
 
@@ -373,7 +389,8 @@ done:
  *-------------------------------------------------------------------------
  */
 static hid_t
-H5VL_native_attr_open(hid_t loc_id, void *location, const char *attr_name, hid_t UNUSED aapl_id, hid_t UNUSED req)
+H5VL_native_attr_open(hid_t loc_id, H5VL_loc_params_t loc_params, const char *attr_name, 
+                      hid_t UNUSED aapl_id, hid_t UNUSED req)
 {
     H5G_loc_t    loc;             /* Object location */
     H5A_t        *attr = NULL;    /* Attribute opened */
@@ -387,22 +404,28 @@ H5VL_native_attr_open(hid_t loc_id, void *location, const char *attr_name, hid_t
     if(H5G_loc(loc_id, &loc) < 0)
 	HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a location")
 
-    if(NULL != location) { /* H5Aopen_by_name */
-        H5G_loc_t   *obj_loc = (H5G_loc_t *)location;
-
-        /* Read in attribute from object header */
-        if(NULL == (attr = H5O_attr_open_by_name(obj_loc->oloc, attr_name, H5AC_ind_dxpl_id)))
-            HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to load attribute info from object header")
-    }
-    else { /* H5Aopen */
+    if(loc_params.type == H5VL_OBJECT_LOOKUP_BY_ID) { /* H5Aopen */
         /* Read in attribute from object header */
         if(NULL == (attr = H5O_attr_open_by_name(loc.oloc, attr_name, H5AC_ind_dxpl_id)))
             HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to load attribute info from object header for attribute: '%s'", attr_name)
+        /* Finish initializing attribute */
+        if(H5A_open_common(&loc, attr) < 0)
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to initialize attribute")
+    }
+    else if(loc_params.type == H5VL_OBJECT_LOOKUP_BY_NAME) { /* H5Aopen_by_name */
+        H5G_loc_t   obj_loc;                /* Location used to open group */
+        H5G_name_t  obj_path;            	/* Opened object group hier. path */
+        H5O_loc_t   obj_oloc;            	/* Opened object object location */
+        hbool_t     loc_found = FALSE;      /* Entry at 'obj_name' found */
+
+        /* Open the attribute on the object header */
+        if(NULL == (attr = H5A_open_by_name(&loc, loc_params.loc_data.loc_by_name.name, attr_name, 
+                                            loc_params.loc_data.loc_by_name.lapl_id, H5AC_ind_dxpl_id)))
+            HGOTO_ERROR(H5E_ATTR, H5E_CANTOPENOBJ, FAIL, "can't open attribute")
+    }
+    else {
+        HGOTO_ERROR(H5E_VOL, H5E_UNSUPPORTED, FAIL, "unknown attribute open parameters")
     }
-
-    /* Finish initializing attribute */
-    if(H5A_open_common(&loc, attr) < 0)
-        HGOTO_ERROR(H5E_ATTR, H5E_CANTINIT, FAIL, "unable to initialize attribute")
 
     /* Register the attribute and get an ID for it */
     if((ret_value = H5I_register(H5I_ATTR, attr, TRUE)) < 0)
@@ -2596,22 +2619,91 @@ done:
  *-------------------------------------------------------------------------
  */
 static hid_t
-H5VL_native_object_open(void *location, hid_t lapl_id, hid_t UNUSED req)
+H5VL_native_object_open(hid_t loc_id, H5VL_loc_params_t params, hid_t lapl_id, hid_t UNUSED req)
 {
-    H5G_loc_t   *obj_loc = (H5G_loc_t *)location;
+    H5G_loc_t   loc;
+    H5G_loc_t   obj_loc;                /* Location used to open group */
+    H5G_name_t  obj_path;            	/* Opened object group hier. path */
+    H5O_loc_t   obj_oloc;            	/* Opened object object location */
+    hbool_t     loc_found = FALSE;      /* Entry at 'name' found */
     hid_t       ret_value = FAIL;
 
     FUNC_ENTER_NOAPI_NOINIT
 
-    /* Check args */
-    if(!H5F_addr_defined(obj_loc->oloc->addr))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no address supplied")
+    if(H5G_loc(loc_id, &loc) < 0)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a location")
 
-    /* Open the object */
-    if((ret_value = H5O_open_by_loc(obj_loc, lapl_id, H5AC_dxpl_id, TRUE)) < 0)
-        HGOTO_ERROR(H5E_SYM, H5E_CANTOPENOBJ, FAIL, "unable to open object")
+    switch (params.type) {
+        case H5VL_OBJECT_LOOKUP_BY_NAME:
+            {
+                /* Open the object */
+                if((ret_value = H5O_open_name(&loc, params.loc_data.loc_by_name.name, lapl_id, 
+                                              TRUE)) < 0)
+                    HGOTO_ERROR(H5E_SYM, H5E_CANTOPENOBJ, FAIL, "unable to open object")
+                break;
+            }
+        case H5VL_OBJECT_LOOKUP_BY_IDX:
+            {
+                /* Set up opened group location to fill in */
+                obj_loc.oloc = &obj_oloc;
+                obj_loc.path = &obj_path;
+                H5G_loc_reset(&obj_loc);
+
+                /* Find the object's location, according to the order in the index */
+                if(H5G_loc_find_by_idx(&loc, params.loc_data.loc_by_idx.name, 
+                                       params.loc_data.loc_by_idx.idx_type, 
+                                       params.loc_data.loc_by_idx.order, params.loc_data.loc_by_idx.n, 
+                                       &obj_loc/*out*/, lapl_id, H5AC_dxpl_id) < 0)
+                    HGOTO_ERROR(H5E_SYM, H5E_NOTFOUND, FAIL, "group not found")
+                loc_found = TRUE;
+
+                /* Open the object */
+                if((ret_value = H5O_open_by_loc(&obj_loc, lapl_id, H5AC_dxpl_id, TRUE)) < 0)
+                    HGOTO_ERROR(H5E_SYM, H5E_CANTOPENOBJ, FAIL, "unable to open object")
+                break;
+            }
+        case H5VL_OBJECT_LOOKUP_BY_ADDR:
+            {
+                if(!H5F_addr_defined(params.loc_data.loc_by_addr.addr))
+                    HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no address supplied")
+
+                /* Set up opened group location to fill in */
+                obj_loc.oloc = &obj_oloc;
+                obj_loc.path = &obj_path;
+                H5G_loc_reset(&obj_loc);
+                obj_loc.oloc->addr = params.loc_data.loc_by_addr.addr;
+                obj_loc.oloc->file = loc.oloc->file;
+                H5G_name_reset(obj_loc.path);       /* objects opened through this routine don't have a path name */
+
+                /* Open the object */
+                if((ret_value = H5O_open_by_loc(&obj_loc, lapl_id, H5AC_dxpl_id, TRUE)) < 0)
+                    HGOTO_ERROR(H5E_SYM, H5E_CANTOPENOBJ, FAIL, "unable to open object")
+                break;
+            }
+        case H5VL_OBJECT_LOOKUP_BY_REF:
+            {
+                H5F_t *file = NULL;
+
+                /* Get the file pointer from the entry */
+                file = loc.oloc->file;
+
+                /* Create reference */
+                if((ret_value = H5R_dereference(file, lapl_id, H5AC_dxpl_id, 
+                                                params.loc_data.loc_by_ref.ref_type, 
+                                                params.loc_data.loc_by_ref._ref, 
+                                                TRUE)) < 0)
+                    HGOTO_ERROR(H5E_REFERENCE, H5E_CANTINIT, FAIL, "unable to dereference object")
+                break;
+            }
+        default:
+            HGOTO_ERROR(H5E_VOL, H5E_UNSUPPORTED, FAIL, "unknown open parameters")
+    }
 
 done:
+    /* Release the object location if we failed after copying it */
+    if(ret_value < 0 && loc_found)
+        if(H5G_loc_free(&obj_loc) < 0)
+            HDONE_ERROR(H5E_SYM, H5E_CANTRELEASE, FAIL, "can't free location")
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5VL_native_object_open() */
 
@@ -2926,26 +3018,28 @@ H5VL_native_object_misc(hid_t loc_id, H5VL_object_misc_t misc_type, hid_t UNUSED
         /* H5Arename/rename_by_name */
         case H5VL_ATTR_RENAME:
             {
-                void    *location  = va_arg (arguments, void *);
-                char    *old_name  = va_arg (arguments, char *);
-                char    *new_name  = va_arg (arguments, char *);
+                H5VL_loc_params_t loc_params  = va_arg (arguments, H5VL_loc_params_t);
+                const char    *old_name  = va_arg (arguments, const char *);
+                const char    *new_name  = va_arg (arguments, const char *);
                 H5G_loc_t   loc;
 
                 if(H5G_loc(loc_id, &loc) < 0)
                     HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a location")
 
-                if(NULL == location) { /* H5Arename */
+                if(loc_params.type == H5VL_OBJECT_LOOKUP_BY_ID) { /* H5Arename */
                     /* Call attribute rename routine */
                     if(H5O_attr_rename(loc.oloc, H5AC_dxpl_id, old_name, new_name) < 0)
                         HGOTO_ERROR(H5E_ATTR, H5E_CANTRENAME, FAIL, "can't rename attribute")
                 }
-                else {
-                    H5G_loc_t   *obj_loc = (H5G_loc_t *)location;
-
+                else if(loc_params.type == H5VL_OBJECT_LOOKUP_BY_NAME) { /* H5Arename_by_name */
                     /* Call attribute rename routine */
-                    if(H5O_attr_rename(obj_loc->oloc, H5AC_dxpl_id, old_name, new_name) < 0)
+                    if(H5A_rename_by_name(loc, loc_params.loc_data.loc_by_name.name, old_name,
+                                          new_name, loc_params.loc_data.loc_by_name.lapl_id) < 0)
                         HGOTO_ERROR(H5E_ATTR, H5E_CANTRENAME, FAIL, "can't rename attribute")
                 }
+                else {
+                    HGOTO_ERROR(H5E_VOL, H5E_UNSUPPORTED, FAIL, "unknown attribute rename parameters")
+                }
                 break;
             }
         /* H5Oincr_refcount / H5Odecr_refcount */
diff --git a/src/H5VLprivate.h b/src/H5VLprivate.h
index 01754ca..eeb4b3c 100644
--- a/src/H5VLprivate.h
+++ b/src/H5VLprivate.h
@@ -50,7 +50,7 @@ H5_DLL ssize_t H5VL_get_plugin_name(hid_t id, char *name/*out*/, size_t size);
 H5_DLL herr_t H5VL_close(H5VL_class_t *vol_plugin);
 
 H5_DLL hid_t H5VL_attr_create(hid_t loc_id, const char *attr_name, hid_t acpl_id, hid_t aapl_id, hid_t req);
-H5_DLL hid_t H5VL_attr_open(hid_t loc_id, void *location, const char *name, hid_t aapl_id, hid_t req);
+H5_DLL hid_t H5VL_attr_open(hid_t loc_id, H5VL_loc_params_t loc_params, const char *name, hid_t aapl_id, hid_t req);
 H5_DLL herr_t H5VL_attr_read(hid_t attr_id, hid_t dtype_id, void *buf, hid_t req);
 H5_DLL herr_t H5VL_attr_write(hid_t attr_id, hid_t dtype_id, const void *buf, hid_t req);
 H5_DLL herr_t H5VL_attr_get(hid_t id, H5VL_attr_get_t get_type, hid_t req, ...);
@@ -92,7 +92,7 @@ H5_DLL herr_t H5VL_link_iterate(hid_t loc_id, const char *name, hbool_t recursiv
 H5_DLL herr_t H5VL_link_get(hid_t loc_id, H5VL_link_get_t get_type, hid_t req, ...);
 H5_DLL herr_t H5VL_link_remove(hid_t loc_id, const char *name, void *udata, hid_t lapl_id, hid_t req);
 
-H5_DLL hid_t H5VL_object_open_by_loc(hid_t loc_id, void *obj_loc, hid_t lapl_id, hid_t req);
+H5_DLL hid_t H5VL_object_open(hid_t loc_id, H5VL_loc_params_t params, hid_t lapl_id, hid_t req);
 H5_DLL herr_t H5VL_object_copy(hid_t src_loc_id, const char *src_name, hid_t dst_loc_id, 
                                const char *dst_name, hid_t ocpypl_id, hid_t lcpl_id, hid_t req);
 H5_DLL herr_t H5VL_object_visit(hid_t loc_id, const char *obj_name, H5_index_t idx_type,
diff --git a/src/H5VLpublic.h b/src/H5VLpublic.h
index 388debc..4e433e5 100644
--- a/src/H5VLpublic.h
+++ b/src/H5VLpublic.h
@@ -26,6 +26,7 @@
 #include "H5Fpublic.h"
 #include "H5Lpublic.h"
 #include "H5Opublic.h"
+#include "H5Rpublic.h"
 
 /* Dataset creation property names */
 #define H5VL_DSET_TYPE_ID        "dataset_type_id"
@@ -35,7 +36,7 @@
 /* Attribute creation property names */
 #define H5VL_ATTR_TYPE_ID        "attr_type_id"
 #define H5VL_ATTR_SPACE_ID       "attr_space_id"
-#define H5VL_ATTR_LOCATION       "attr_location"
+#define H5VL_ATTR_LOC_PARAMS       "attr_location"
 
 /* Link creation property names */
 #define H5VL_LINK_TARGET_ID      "target location id"
@@ -158,12 +159,50 @@ typedef enum H5VL_object_lookup_t {
     H5VL_OBJECT_LOOKUP_BY_REF       = 4
 } H5VL_object_lookup_t;
 
+struct H5VL_loc_by_id {
+    hid_t id;
+};
+
+struct H5VL_loc_by_name {
+    const char *name;
+    hid_t lapl_id;
+};
+
+struct H5VL_loc_by_idx {
+    const char *name;
+    H5_index_t idx_type;
+    H5_iter_order_t order;
+    hsize_t n;
+    hid_t lapl_id;
+};
+
+struct H5VL_loc_by_addr {
+    haddr_t addr;
+};
+
+struct H5VL_loc_by_ref {
+    H5R_type_t ref_type;
+    const void *_ref;
+};
+
+/* Structure to hold parameters for object location */
+typedef struct H5VL_loc_params_t {
+    H5VL_object_lookup_t type;
+    union{
+        struct H5VL_loc_by_id   loc_by_id;
+        struct H5VL_loc_by_name loc_by_name;
+        struct H5VL_loc_by_idx  loc_by_idx;
+        struct H5VL_loc_by_addr loc_by_addr;
+        struct H5VL_loc_by_ref  loc_by_ref;
+    }loc_data;
+} H5VL_loc_params_t;
+
 #define H5VL_VOL_DEFAULT 0   /* Default VOL plugin value */
 
 /* H5A routines */
 typedef struct H5VL_attr_class_t {
     hid_t  (*create)(hid_t loc_id, const char *attr_name, hid_t acpl_id, hid_t aapl_id, hid_t req);
-    hid_t  (*open)  (hid_t loc_id, void *location, const char *attr_name, hid_t aapl_id, hid_t req);
+    hid_t  (*open)  (hid_t loc_id, H5VL_loc_params_t loc_params, const char *attr_name, hid_t aapl_id, hid_t req);
     herr_t (*read)  (hid_t attr_id, hid_t mem_type_id, void *buf, hid_t req);
     herr_t (*write) (hid_t attr_id, hid_t mem_type_id, const void *buf, hid_t req);
     herr_t (*get)   (hid_t loc_id, H5VL_attr_get_t get_type, hid_t req, va_list arguments);
@@ -226,7 +265,7 @@ typedef struct H5VL_link_class_t {
 
 /* H5O routines */
 typedef struct H5VL_object_class_t {
-    hid_t  (*open)  (void *obj_loc, hid_t lapl_id, hid_t req);
+    hid_t  (*open)  (hid_t id, H5VL_loc_params_t params, hid_t lapl_id, hid_t req);
     herr_t (*copy)  (hid_t src_loc_id, const char *src_name, hid_t dst_loc_id, const char *dst_name,
                      hid_t ocpypl_id, hid_t lcpl_id, hid_t req);
     herr_t (*visit) (hid_t loc_id, const char *obj_name, H5_index_t idx_type, H5_iter_order_t order, 
@@ -242,7 +281,6 @@ typedef struct H5VL_object_class_t {
 /* Class information for each VOL driver */
 typedef struct H5VL_class_t {
     const char *name;
-    unsigned	nrefs;		/* Ref count for times struct is pointed to */
     herr_t  (*initialize)(void);
     herr_t  (*terminate)(void);
     H5VL_attr_class_t          attr_cls;
@@ -260,7 +298,8 @@ extern "C" {
 
 /* Function prototypes */
 H5_DLL hid_t H5VLregister(const H5VL_class_t *cls);
-H5_DLL herr_t H5VLunregister(hid_t driver_id);
+H5_DLL herr_t H5VLunregister(hid_t plugin_id);
+H5_DLL htri_t H5VLis_registered(hid_t id);
 H5_DLL ssize_t H5VLget_plugin_name(hid_t id, char *name/*out*/, size_t size);
 
 #ifdef __cplusplus