Merge pull request #1600 in HDFFV/hdf5 from ~SONGYULU/hdf5_ray:HDFFV-10658-performance-drop-from-1-8 to develop

* commit 'b5ef82a1786605ae86502bc82086047720b7d4ca': (21 commits)
  Moving the handling of null prefix into H5_combine_path.
  Changing the prefix of external file and VDS from empty string to null for performance improvement.
  Improving the condition checking of empty string.
  Replacing string operation strdup with assignment for empty string.
  Adding back links_env.out which I accidentally removed in my previous commit.
  Taking out two unnecessary diff output files.
  Taking out unnecessary diff files for output.
  Adding some comments.
  Some coding style changes.
  Adding the standard output files for the external_env.c and vds_env.c tests.
  Small correction for my previous commit.
  Forgot to add external_common.c and external_common.h.
  Updated CMake for the splitting of external.c and vds.c.
  Minor fix: removal of unnecessary enum values.
  Minor fixes: updating the test vds_env.c according to the set up of vds.c.
  Left out this file in previous commit.
  HDFFV-10658 - setting and getting properties in API context: 1. switched to use the existing H5F_prefix_open_t for enum type; 2. put the common private function used by external.c and external_env.c into external_common.c
  This commit basically has the following changes: 1. restored the datatype, dataspace, and LCPL of the dataset for VOL connector back to the properties. 2. splitted external.c and vds.c because they called HDsetenv in the program, instead using shell scripts to set the environment variables. 3. changed H5CX_get_vds_prefix and H5CX_get_ext_file_prefix to use H5P_peek instead of H5P_get.
  HDFFV-10658: I left out this file in my previous commit.
  HDFFV-10658: 1. moving HDgetenv to dataset initialization stage to reduce the overhead; 2. restoring the retrieval of three vol properties to H5P_get instead of using API context to prepare for Quincey's upcoming refactoring work.
  ...

21 files changed, 1220 insertions, 480 deletions

diff --git a/MANIFEST b/MANIFEST
index aa4c008..41edffb 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -992,6 +992,9 @@
 ./test/evict_on_close.c
 ./test/extend.c
 ./test/external.c
+./test/external_common.c
+./test/external_common.h
+./test/external_env.c
 ./test/error_test.c
 ./test/err_compat.c
 ./test/filter_error.h5
@@ -1116,6 +1119,7 @@
 ./test/tcoords.c
 ./test/testabort_fail.sh.in
 ./test/testcheck_version.sh.in
+./test/testexternal_env.sh.in
 ./test/testerror.sh.in
 ./test/testlinks_env.sh.in
 ./test/test_filter_plugin.sh.in
@@ -1131,6 +1135,7 @@
 ./test/testmeta.c
 ./test/testswmr.sh.in
 ./test/testvdsswmr.sh.in
+./test/testvds_env.sh.in
 ./test/tfile.c
 ./test/tgenprop.c
 ./test/th5o.c
@@ -1170,6 +1175,7 @@
 ./test/use_disable_mdc_flushes.c
 ./test/use.h
 ./test/vds.c
+./test/vds_env.c
 ./test/vds_swmr.h
 ./test/vds_swmr_gen.c
 ./test/vds_swmr_reader.c
diff --git a/configure.ac b/configure.ac
index 3bf138e..0d0e0df 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3477,10 +3477,12 @@ AC_CONFIG_FILES([src/libhdf5.settings
                  test/testabort_fail.sh
                  test/testcheck_version.sh
                  test/testerror.sh
+                 test/testexternal_env.sh
                  test/testflushrefresh.sh
                  test/testlibinfo.sh
                  test/testlinks_env.sh
                  test/testswmr.sh
+                 test/testvds_env.sh
                  test/testvdsswmr.sh
                  test/test_filter_plugin.sh
                  test/test_usecases.sh
diff --git a/src/H5CX.c b/src/H5CX.c
index c57e65d..5474b63 100644
--- a/src/H5CX.c
+++ b/src/H5CX.c
@@ -189,6 +189,10 @@ typedef struct H5CX_t {
     hid_t dcpl_id;              /* DCPL ID for API operation */
     H5P_genplist_t *dcpl;       /* Dataset Creation Property List */
 
+    /* DAPL */
+    hid_t dapl_id;              /* DAPL ID for API operation */
+    H5P_genplist_t *dapl;       /* Dataset Access Property List */
+
     /* FAPL */
     hid_t fapl_id;              /* FAPL ID for API operation */
     H5P_genplist_t *fapl;       /* File Access Property List */
@@ -279,8 +283,14 @@ typedef struct H5CX_t {
     hbool_t nlinks_valid;       /* Whether number of soft / UD links to traverse is valid */
 
     /* Cached DCPL properties */
-    hbool_t do_min_dset_ohdr;   /* Whether to minimize dataset object header */
-    hbool_t do_min_dset_ohdr_valid;   /* Whether minimize dataset object header flag is valid */
+    hbool_t   do_min_dset_ohdr;   /* Whether to minimize dataset object header */
+    hbool_t   do_min_dset_ohdr_valid;   /* Whether minimize dataset object header flag is valid */
+
+    /* Cached DAPL properties */
+    char *extfile_prefix;               /* Prefix for external file                      */
+    hbool_t extfile_prefix_valid;       /* Whether the prefix for external file is valid */
+    char *vds_prefix;                   /* Prefix for VDS                                */
+    hbool_t vds_prefix_valid;           /* Whether the prefix for VDS is valid           */
 
     /* Cached FAPL properties */
     H5F_libver_t low_bound;     /* low_bound property for H5Pset_libver_bounds() */
@@ -348,6 +358,13 @@ typedef struct H5CX_dcpl_cache_t {
     hbool_t do_min_dset_ohdr;   /* Whether to minimize dataset object header */
 } H5CX_dcpl_cache_t;
 
+/* Typedef for cached default dataset access property list information */
+/* (Same as the cached DXPL struct, above, except for the default DXPL) */
+typedef struct H5CX_dapl_cache_t {
+    char *extfile_prefix;       /* Prefix for external file */
+    char *vds_prefix;           /* Prefix for VDS           */
+} H5CX_dapl_cache_t;
+
 /* Typedef for cached default file access property list information */
 /* (Same as the cached DXPL struct, above, except for the default DCPL) */
 typedef struct H5CX_fapl_cache_t {
@@ -355,7 +372,6 @@ typedef struct H5CX_fapl_cache_t {
     H5F_libver_t high_bound;    /* high_bound property for H5Pset_libver_bounds */
 } H5CX_fapl_cache_t;
 
-
 /********************/
 /* Local Prototypes */
 /********************/
@@ -391,6 +407,9 @@ static H5CX_lapl_cache_t H5CX_def_lapl_cache;
 /* Define a "default" dataset creation property list cache structure to use for default DCPLs */
 static H5CX_dcpl_cache_t H5CX_def_dcpl_cache;
 
+/* Define a "default" dataset access property list cache structure to use for default DAPLs */
+static H5CX_dapl_cache_t H5CX_def_dapl_cache;
+
 /* Define a "default" file access property list cache structure to use for default FAPLs */
 static H5CX_fapl_cache_t H5CX_def_fapl_cache;
 
@@ -418,6 +437,7 @@ H5CX__init_package(void)
     H5P_genplist_t *dx_plist;           /* Data transfer property list */
     H5P_genplist_t *la_plist;           /* Link access property list */
     H5P_genplist_t *dc_plist;           /* Dataset creation property list */
+    H5P_genplist_t *da_plist;           /* Dataset access property list */
     H5P_genplist_t *fa_plist;           /* File access property list */
     herr_t ret_value = SUCCEED;         /* Return value */
 
@@ -532,6 +552,23 @@ H5CX__init_package(void)
     if(H5P_get(dc_plist, H5D_CRT_MIN_DSET_HDR_SIZE_NAME, &H5CX_def_dcpl_cache.do_min_dset_ohdr) < 0)
         HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve dataset minimize flag")
 
+    /* Reset the "default DAPL cache" information */
+    HDmemset(&H5CX_def_dapl_cache, 0, sizeof(H5CX_dapl_cache_t));
+
+    /* Get the default DAPL cache information */
+
+    /* Get the default dataset access property list */
+    if(NULL == (da_plist = (H5P_genplist_t *)H5I_object(H5P_DATASET_ACCESS_DEFAULT)))
+        HGOTO_ERROR(H5E_CONTEXT, H5E_BADTYPE, FAIL, "not a dataset create property list")
+
+    /* Get the prefix for the external file */
+    if(H5P_peek(da_plist, H5D_ACS_EFILE_PREFIX_NAME, &H5CX_def_dapl_cache.extfile_prefix) < 0)
+        HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve prefix for external file")
+
+    /* Get the prefix for the VDS file */
+    if(H5P_peek(da_plist, H5D_ACS_VDS_PREFIX_NAME, &H5CX_def_dapl_cache.vds_prefix) < 0)
+        HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve prefix for VDS")
+
     /* Reset the "default FAPL cache" information */
     HDmemset(&H5CX_def_fapl_cache, 0, sizeof(H5CX_fapl_cache_t));
 
@@ -548,7 +585,6 @@ H5CX__init_package(void)
     if(H5P_get(fa_plist, H5F_ACS_LIBVER_HIGH_BOUND_NAME, &H5CX_def_fapl_cache.high_bound) < 0)
         HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve dataset minimize flag")
 
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5CX__init_package() */
@@ -672,6 +708,8 @@ H5CX__push_common(H5CX_node_t *cnode)
 
     /* Set non-zero context info */
     cnode->ctx.dxpl_id = H5P_DATASET_XFER_DEFAULT;
+    cnode->ctx.dcpl_id = H5P_DATASET_CREATE_DEFAULT;
+    cnode->ctx.dapl_id = H5P_DATASET_ACCESS_DEFAULT;
     cnode->ctx.lapl_id = H5P_LINK_ACCESS_DEFAULT;
     cnode->ctx.fapl_id = H5P_FILE_ACCESS_DEFAULT;
     cnode->ctx.tag = H5AC__INVALID_TAG;
@@ -1158,6 +1196,7 @@ H5CX_set_apl(hid_t *acspl_id, const H5P_libclass_t *libclass,
         *acspl_id = *libclass->def_plist_id;
     else {
         htri_t is_lapl;         /* Whether the access property list is (or is derived from) a link access property list */
+        htri_t is_dapl;         /* Whether the access property list is (or is derived from) a dataset access property list */
         htri_t is_fapl;         /* Whether the access property list is (or is derived from) a file access property list */
 
 #ifdef H5CX_DEBUG
@@ -1172,6 +1211,12 @@ H5CX_set_apl(hid_t *acspl_id, const H5P_libclass_t *libclass,
         else if(is_lapl)
             (*head)->ctx.lapl_id = *acspl_id;
 
+        /* Check for dataset access property and set API context if so */
+        if((is_dapl = H5P_class_isa(*libclass->pclass, *H5P_CLS_DACC->pclass)) < 0)
+            HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "can't check for dataset access class")
+        else if(is_dapl)
+            (*head)->ctx.dapl_id = *acspl_id;
+
         /* Check for file access property and set API context if so */
         if((is_fapl = H5P_class_isa(*libclass->pclass, *H5P_CLS_FACC->pclass)) < 0)
             HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "can't check for file access class")
@@ -2443,6 +2488,120 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:    H5CX_get_ext_file_prefix
+ *
+ * Purpose:     Retrieves the prefix for external file
+ *
+ * Return:      Non-negative on success / Negative on failure
+ *
+ * Programmer:  Raymond Lu
+ *              March 6, 2019
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5CX_get_ext_file_prefix(char **extfile_prefix)
+{
+    H5CX_node_t **head = H5CX_get_my_context();  /* Get the pointer to the head of the API context, for this thread */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity check */
+    HDassert(extfile_prefix);
+    HDassert(head && *head);
+    HDassert(H5P_DEFAULT != (*head)->ctx.dapl_id);
+
+    /* Check if the value has been retrieved already */
+    if(!(*head)->ctx.extfile_prefix_valid) {
+        /* Check for default DAPL */
+        if((*head)->ctx.dapl_id == H5P_DATASET_ACCESS_DEFAULT)
+            (*head)->ctx.extfile_prefix = H5CX_def_dapl_cache.extfile_prefix;
+        else {
+            /* Check if the property list is already available */
+            if(NULL == (*head)->ctx.dapl)
+                /* Get the dataset access property list pointer */
+                if(NULL == ((*head)->ctx.dapl = (H5P_genplist_t *)H5I_object((*head)->ctx.dapl_id)))
+                    HGOTO_ERROR(H5E_CONTEXT, H5E_BADTYPE, FAIL, "can't get default dataset access property list")
+
+            /* Get the prefix for the external file */
+            /* (Note: 'peek', not 'get' - if this turns out to be a problem, we may need
+             *          to copy it and free this in the H5CX pop routine. -QAK)
+             */
+            if(H5P_peek((*head)->ctx.dapl, H5D_ACS_EFILE_PREFIX_NAME, &(*head)->ctx.extfile_prefix) < 0)
+                HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve external file prefix")
+        } /* end else */
+
+        /* Mark the value as valid */
+        (*head)->ctx.extfile_prefix_valid = TRUE;
+    } /* end if */
+
+    /* Get the value */
+    *extfile_prefix = (*head)->ctx.extfile_prefix;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5CX_get_ext_file_prefix() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5CX_get_vds_prefix
+ *
+ * Purpose:     Retrieves the prefix for VDS
+ *
+ * Return:      Non-negative on success / Negative on failure
+ *
+ * Programmer:  Raymond Lu
+ *              March 6, 2019
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5CX_get_vds_prefix(char **vds_prefix)
+{
+    H5CX_node_t **head = H5CX_get_my_context();  /* Get the pointer to the head of the API context, for this thread */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity check */
+    HDassert(vds_prefix);
+    HDassert(head && *head);
+    HDassert(H5P_DEFAULT != (*head)->ctx.dapl_id);
+
+    /* Check if the value has been retrieved already */
+    if(!(*head)->ctx.vds_prefix_valid) {
+        /* Check for default DAPL */
+        if((*head)->ctx.dapl_id == H5P_DATASET_ACCESS_DEFAULT)
+            (*head)->ctx.vds_prefix = H5CX_def_dapl_cache.vds_prefix;
+        else {
+            /* Check if the property list is already available */
+            if(NULL == (*head)->ctx.dapl)
+                /* Get the dataset access property list pointer */
+                if(NULL == ((*head)->ctx.dapl = (H5P_genplist_t *)H5I_object((*head)->ctx.dapl_id)))
+                    HGOTO_ERROR(H5E_CONTEXT, H5E_BADTYPE, FAIL, "can't get default dataset access property list")
+
+            /* Get the prefix for the VDS */
+            /* (Note: 'peek', not 'get' - if this turns out to be a problem, we may need
+             *          to copy it and free this in the H5CX pop routine. -QAK)
+             */
+            if(H5P_peek((*head)->ctx.dapl, H5D_ACS_VDS_PREFIX_NAME, &(*head)->ctx.vds_prefix) < 0)
+                HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve VDS prefix")
+        } /* end else */
+
+        /* Mark the value as valid */
+        (*head)->ctx.vds_prefix_valid = TRUE;
+    } /* end if */
+
+    /* Get the value */
+    *vds_prefix = (*head)->ctx.vds_prefix;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5CX_get_vds_prefix() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5CX_set_tag
  *
  * Purpose:     Sets the object tag for the current API call context.
diff --git a/src/H5CXprivate.h b/src/H5CXprivate.h
index 4270155..638c32a 100644
--- a/src/H5CXprivate.h
+++ b/src/H5CXprivate.h
@@ -128,6 +128,10 @@ H5_DLL herr_t H5CX_get_nlinks(size_t *nlinks);
 /* "Getter" routines for DCPL properties cached in API context */
 H5_DLL herr_t H5CX_get_dset_min_ohdr_flag(hbool_t *dset_min_ohdr_flag);
 
+/* "Getter" routines for DAPL properties cached in API context */
+H5_DLL herr_t H5CX_get_ext_file_prefix(char **prefix_extfile);
+H5_DLL herr_t H5CX_get_vds_prefix(char **prefix_vds);
+
 /* "Getter" routines for FAPL properties cached in API context */
 H5_DLL herr_t H5CX_get_libver_bounds(H5F_libver_t *low_bound, H5F_libver_t *high_bound);
 
diff --git a/src/H5D.c b/src/H5D.c
index fc350f2..413be37 100644
--- a/src/H5D.c
+++ b/src/H5D.c
@@ -135,6 +135,9 @@ H5Dcreate2(hid_t loc_id, const char *name, hid_t type_id, hid_t space_id,
         if(TRUE != H5P_isa_class(dcpl_id, H5P_DATASET_CREATE))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, H5I_INVALID_HID, "dcpl_id is not a dataset create property list ID")
 
+    /* Set the DCPL for the API context */
+    H5CX_set_dcpl(dcpl_id);
+
     /* Verify access property list and set up collective metadata if appropriate */
     if(H5CX_set_apl(&dapl_id, H5P_CLS_DACC, loc_id, TRUE) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTSET, H5I_INVALID_HID, "can't set access property list info")
@@ -228,6 +231,9 @@ H5Dcreate_anon(hid_t loc_id, hid_t type_id, hid_t space_id, hid_t dcpl_id,
         if(TRUE != H5P_isa_class(dcpl_id, H5P_DATASET_CREATE))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, H5I_INVALID_HID, "not dataset create property list ID")
 
+    /* Set the DCPL for the API context */
+    H5CX_set_dcpl(dcpl_id);
+
     /* Verify access property list and set up collective metadata if appropriate */
     if(H5CX_set_apl(&dapl_id, H5P_CLS_DACC, loc_id, TRUE) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTSET, H5I_INVALID_HID, "can't set access property list info")
diff --git a/src/H5Ddeprec.c b/src/H5Ddeprec.c
index 76827b4..85371ae 100644
--- a/src/H5Ddeprec.c
+++ b/src/H5Ddeprec.c
@@ -136,6 +136,9 @@ H5Dcreate1(hid_t loc_id, const char *name, hid_t type_id, hid_t space_id,
         if(TRUE != H5P_isa_class(dcpl_id, H5P_DATASET_CREATE))
             HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, H5I_INVALID_HID, "not dataset create property list ID")
 
+    /* Set the DCPL for the API context */
+    H5CX_set_dcpl(dcpl_id);
+
     /* Verify access property list and set up collective metadata if appropriate */
     if(H5CX_set_apl(&dapl_id, H5P_CLS_DACC, loc_id, TRUE) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTSET, H5I_INVALID_HID, "can't set access property list info")
diff --git a/src/H5Defl.c b/src/H5Defl.c
index 19f3a00..91caa61 100644
--- a/src/H5Defl.c
+++ b/src/H5Defl.c
@@ -477,7 +477,6 @@ H5D__efl_readvv(const H5D_io_info_t *io_info,
     HDassert(io_info->u.rbuf);
     HDassert(io_info->dset);
     HDassert(io_info->dset->shared);
-    HDassert(io_info->dset->shared->extfile_prefix);
     HDassert(dset_curr_seq);
     HDassert(dset_len_arr);
     HDassert(dset_off_arr);
@@ -561,7 +560,6 @@ H5D__efl_writevv(const H5D_io_info_t *io_info,
     HDassert(io_info->u.wbuf);
     HDassert(io_info->dset);
     HDassert(io_info->dset->shared);
-    HDassert(io_info->dset->shared->extfile_prefix);
     HDassert(dset_curr_seq);
     HDassert(dset_len_arr);
     HDassert(dset_off_arr);
diff --git a/src/H5Dint.c b/src/H5Dint.c
index 280d07e..220f026 100644
--- a/src/H5Dint.c
+++ b/src/H5Dint.c
@@ -54,7 +54,7 @@ static herr_t H5D__init_type(H5F_t *file, const H5D_t *dset, hid_t type_id, cons
 static herr_t H5D__cache_dataspace_info(const H5D_t *dset);
 static herr_t H5D__init_space(H5F_t *file, const H5D_t *dset, const H5S_t *space);
 static herr_t H5D__update_oh_info(H5F_t *file, H5D_t *dset, hid_t dapl_id);
-static herr_t H5D__build_file_prefix(const H5D_t *dset, hid_t dapl_id, const char *prefix_type, char **file_prefix);
+static herr_t H5D__build_file_prefix(const H5D_t *dset, H5F_prefix_open_t prefix_type, char **file_prefix);
 static herr_t H5D__open_oid(H5D_t *dataset, hid_t dapl_id);
 static herr_t H5D__init_storage(const H5D_io_info_t *io_info, hbool_t full_overwrite,
         hsize_t old_dim[]);
@@ -112,6 +112,10 @@ static const H5I_class_t H5I_DATASET_CLS[1] = {{
 /* Flag indicating "top" of interface has been initialized */
 static hbool_t H5D_top_package_initialize_s = FALSE;
 
+/* Prefixes of VDS and external file from the environment variables
+ * HDF5_EXTFILE_PREFIX and HDF5_VDS_PREFIX */ 
+const static char *H5D_prefix_ext_env = NULL;
+const static char *H5D_prefix_vds_env = NULL;
 
 
 /*-------------------------------------------------------------------------
@@ -188,6 +192,10 @@ H5D__init_package(void)
     /* Mark "top" of interface as initialized, too */
     H5D_top_package_initialize_s = TRUE;
 
+    /* Retrieve the prefixes of VDS and external file from the environment variable */
+    H5D_prefix_vds_env = HDgetenv("HDF5_VDS_PREFIX");
+    H5D_prefix_ext_env = HDgetenv("HDF5_EXTFILE_PREFIX");
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D__init_package() */
@@ -488,9 +496,6 @@ H5D__new(hid_t dcpl_id, hbool_t creating, hbool_t vl_type)
         new_dset->dcpl_id = H5P_copy_plist(plist, FALSE);
     } /* end else */
 
-    /* Set the DCPL for the API context */
-    H5CX_set_dcpl(new_dset->dcpl_id);
-
     /* Set return value */
     ret_value = new_dset;
 
@@ -1083,8 +1088,7 @@ done:
  *--------------------------------------------------------------------------
  */
 static herr_t
-H5D__build_file_prefix(const H5D_t *dset, hid_t dapl_id, const char *prefix_type,
-    char **file_prefix /*out*/)
+H5D__build_file_prefix(const H5D_t *dset, H5F_prefix_open_t prefix_type, char **file_prefix /*out*/)
 {
     char            *prefix = NULL;       /* prefix used to look for the file               */
     char            *filepath = NULL;     /* absolute path of directory the HDF5 file is in */
@@ -1105,20 +1109,22 @@ H5D__build_file_prefix(const H5D_t *dset, hid_t dapl_id, const char *prefix_type
     /* XXX: Future thread-safety note - getenv is not required
      *      to be reentrant.
      */
-    if(HDstrcmp(prefix_type, H5D_ACS_VDS_PREFIX_NAME) == 0)
-        prefix = HDgetenv("HDF5_VDS_PREFIX");
-    else if(HDstrcmp(prefix_type, H5D_ACS_EFILE_PREFIX_NAME) == 0)
-        prefix = HDgetenv("HDF5_EXTFILE_PREFIX");
-    else
-        HGOTO_ERROR(H5E_PLIST, H5E_BADTYPE, FAIL, "prefix name is not sensible")
-
-    if(prefix == NULL || *prefix == '\0') {
-        /* Set prefix to value of prefix_type property */
-        if(NULL == (plist = H5P_object_verify(dapl_id, H5P_DATASET_ACCESS)))
-            HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
-        if(H5P_peek(plist, prefix_type, &prefix) < 0)
-            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get file prefix")
-    } /* end if */
+    if(H5F_PREFIX_VDS == prefix_type) {
+        prefix = (char *)H5D_prefix_vds_env;
+
+        if(prefix == NULL || *prefix == '\0') {
+            if(H5CX_get_vds_prefix(&prefix) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get the prefix for vds file")
+        }
+    } else if(H5F_PREFIX_EFILE == prefix_type) {
+        prefix = (char *)H5D_prefix_ext_env;
+
+        if(prefix == NULL || *prefix == '\0') {
+            if(H5CX_get_ext_file_prefix(&prefix) < 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get the prefix for the external file")
+        }
+    } else
+        HGOTO_ERROR(H5E_DATASET, H5E_BADTYPE, FAIL, "prefix name is not sensible")
 
     /* Prefix has to be checked for NULL / empty string again because the
      * code above might have updated it.
@@ -1127,8 +1133,7 @@ H5D__build_file_prefix(const H5D_t *dset, hid_t dapl_id, const char *prefix_type
         /* filename is interpreted as relative to the current directory,
          * does not need to be expanded
          */
-        if(NULL == (*file_prefix = (char *)H5MM_strdup("")))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+        *file_prefix = NULL;
     } /* end if */
     else {
         if(HDstrncmp(prefix, "${ORIGIN}", HDstrlen("${ORIGIN}")) == 0) {
@@ -1326,11 +1331,11 @@ H5D__create(H5F_t *file, hid_t type_id, const H5S_t *space, hid_t dcpl_id,
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "unable to set up flush append property")
 
     /* Set the external file prefix */
-    if(H5D__build_file_prefix(new_dset, dapl_id, H5D_ACS_EFILE_PREFIX_NAME, &new_dset->shared->extfile_prefix) < 0)
+    if(H5D__build_file_prefix(new_dset, H5F_PREFIX_EFILE, &new_dset->shared->extfile_prefix) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "unable to initialize external file prefix")
 
     /* Set the VDS file prefix */
-    if(H5D__build_file_prefix(new_dset, dapl_id, H5D_ACS_VDS_PREFIX_NAME, &new_dset->shared->vds_prefix) < 0)
+    if(H5D__build_file_prefix(new_dset, H5F_PREFIX_VDS, &new_dset->shared->vds_prefix) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "unable to initialize VDS prefix")
 
     /* Add the dataset to the list of opened objects in the file */
@@ -1485,11 +1490,11 @@ H5D_open(const H5G_loc_t *loc, hid_t dapl_id)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTCOPY, NULL, "can't copy path")
 
     /* Get the external file prefix */
-    if(H5D__build_file_prefix(dataset, dapl_id, H5D_ACS_EFILE_PREFIX_NAME, &extfile_prefix) < 0)
+    if(H5D__build_file_prefix(dataset, H5F_PREFIX_EFILE, &extfile_prefix) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "unable to initialize external file prefix")
 
     /* Get the VDS prefix */
-    if(H5D__build_file_prefix(dataset, dapl_id, H5D_ACS_VDS_PREFIX_NAME, &vds_prefix) < 0)
+    if(H5D__build_file_prefix(dataset, H5F_PREFIX_VDS, &vds_prefix) < 0)
         HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL, "unable to initialize VDS prefix")
 
     /* Check if dataset was already open */
@@ -1533,8 +1538,13 @@ H5D_open(const H5G_loc_t *loc, hid_t dapl_id)
         /* Check whether the external file prefix of the already open dataset
          * matches the new external file prefix
          */
-        if(HDstrcmp(extfile_prefix, dataset->shared->extfile_prefix) != 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_CANTOPENOBJ, NULL, "new external file prefix does not match external file prefix of already open dataset")
+        if(extfile_prefix && dataset->shared->extfile_prefix) {
+            if(HDstrcmp(extfile_prefix, dataset->shared->extfile_prefix) != 0)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTOPENOBJ, NULL, "new external file prefix does not match external file prefix of already open dataset")
+        } else {
+            if(extfile_prefix || dataset->shared->extfile_prefix)
+                HGOTO_ERROR(H5E_DATASET, H5E_CANTOPENOBJ, NULL, "new external file prefix does not match external file prefix of already open dataset")
+        }
 
         /* Check if the object has been opened through the top file yet */
         if(H5FO_top_count(dataset->oloc.file, dataset->oloc.addr) == 0) {
diff --git a/src/H5Fprivate.h b/src/H5Fprivate.h
index e3860a0..0fa2214 100644
--- a/src/H5Fprivate.h
+++ b/src/H5Fprivate.h
@@ -702,8 +702,9 @@ typedef enum H5F_mem_page_t {
 
 /* Type of prefix for opening prefixed files */
 typedef enum H5F_prefix_open_t {
-    H5F_PREFIX_VDS,             /* Virtual dataset prefix */
-    H5F_PREFIX_ELINK            /* External link prefix */
+    H5F_PREFIX_VDS   = 0,           /* Virtual dataset prefix */
+    H5F_PREFIX_ELINK = 1,           /* External link prefix   */
+    H5F_PREFIX_EFILE = 2            /* External file prefix   */
 } H5F_prefix_open_t;
 
 
diff --git a/src/H5system.c b/src/H5system.c
index 2ddc29a..35123db 100644
--- a/src/H5system.c
+++ b/src/H5system.c
@@ -1256,13 +1256,13 @@ H5_combine_path(const char* path1, const char* path2, char **full_name /*out*/)
 
     FUNC_ENTER_NOAPI_NOINIT
 
-    HDassert(path1);
     HDassert(path2);
 
-    path1_len = HDstrlen(path1);
+    if(path1)
+        path1_len = HDstrlen(path1);
     path2_len = HDstrlen(path2);
 
-    if(*path1 == '\0' || H5_CHECK_ABSOLUTE(path2)) {
+    if(path1 == NULL || *path1 == '\0' || H5_CHECK_ABSOLUTE(path2)) {
 
         /* If path1 is empty or path2 is absolute, simply use path2 */
         if(NULL == (*full_name = (char *)H5MM_strdup(path2)))
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 772f790..8437e72 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -14,12 +14,14 @@ set (TEST_LIB_SOURCES
     ${HDF5_TEST_SOURCE_DIR}/h5test.c
     ${HDF5_TEST_SOURCE_DIR}/testframe.c
     ${HDF5_TEST_SOURCE_DIR}/cache_common.c
+    ${HDF5_TEST_SOURCE_DIR}/external_common.c
     ${HDF5_TEST_SOURCE_DIR}/swmr_common.c
 )
 
 set (TEST_LIB_HEADERS
     ${HDF5_TEST_SOURCE_DIR}/h5test.h
     ${HDF5_TEST_SOURCE_DIR}/cache_common.h
+    ${HDF5_TEST_SOURCE_DIR}/external_common.h
     ${HDF5_TEST_SOURCE_DIR}/swmr_common.h
 )
 
@@ -236,6 +238,7 @@ set (H5_TESTS
     extend
     direct_chunk # compression lib link
     external
+    external_env
     efc
     objcopy
     links
@@ -255,6 +258,7 @@ set (H5_TESTS
     enc_dec_plist_cross_platform
     getname
     vfd
+    vfd_env
     ntypes
     dangle
     dtransform
diff --git a/test/CMakeTests.cmake b/test/CMakeTests.cmake
index 2ae6fec..470feef 100644
--- a/test/CMakeTests.cmake
+++ b/test/CMakeTests.cmake
@@ -542,8 +542,10 @@ set (H5TEST_SEPARATE_TESTS
     testhdf5
     cache
     cache_image
+    external_env
     flush1
     flush2
+    vds_env
 )
 foreach (h5_test ${H5_TESTS})
   if (NOT h5_test IN_LIST H5TEST_SEPARATE_TESTS)
@@ -679,6 +681,71 @@ set_tests_properties (H5TEST-cache_image PROPERTIES
 )
 endif ()
 
+#-- Adding test for external_env
+add_test (
+    NAME H5TEST-clear-external_env-objects
+    COMMAND    ${CMAKE_COMMAND}
+        -D "TEST_PROGRAM=$<TARGET_FILE:external_env>"
+        -D "TEST_ARGS:STRING="
+        -D "TEST_ENV_VAR:STRING=HDF5_EXTFILE_PREFIX"
+        -D "TEST_ENV_VALUE:STRING=\${ORIGIN}"
+        -D "TEST_EXPECT=0"
+        -D "TEST_OUTPUT=external_env.txt"
+        -D "TEST_REFERENCE=external_env.out"
+        -D "TEST_FOLDER=${PROJECT_BINARY_DIR}/H5TEST"
+        -P "${HDF_RESOURCES_EXT_DIR}/runTest.cmake"
+        -E remove
+        extern_1r.raw
+        extern_2r.raw
+        extern_3r.raw
+        extern_4r.raw
+        extern_1w.raw
+        extern_2w.raw
+        extern_3w.raw
+        extern_4w.raw
+        external_env.txt
+        external_env.out
+    WORKING_DIRECTORY
+        ${HDF5_TEST_BINARY_DIR}/H5TEST
+)
+set_tests_properties (H5TEST-clear-external_env-objects PROPERTIES FIXTURES_SETUP external_env_clear_objects)
+add_test (NAME H5TEST-external_env COMMAND $<TARGET_FILE:external_env>)
+set_tests_properties (H5TEST-external_env PROPERTIES
+    FIXTURES_REQUIRED external_env_clear_objects
+    ENVIRONMENT "srcdir=${HDF5_TEST_BINARY_DIR}/H5TEST;HDF5TestExpress=${HDF_TEST_EXPRESS}"
+    WORKING_DIRECTORY ${HDF5_TEST_BINARY_DIR}/H5TEST
+)
+
+#-- Adding test for vds_env
+add_test (
+    NAME H5TEST-clear-vds_env-objects
+    COMMAND    ${CMAKE_COMMAND}
+        -D "TEST_PROGRAM=$<TARGET_FILE:vds_env>"
+        -D "TEST_ARGS:STRING="
+        -D "TEST_ENV_VAR:STRING=HDF5_VDS_PREFIX"
+        -D "TEST_ENV_VALUE:STRING=\${ORIGIN}/tmp"
+        -D "TEST_EXPECT=0"
+        -D "TEST_OUTPUT=vds_env.txt"
+        -D "TEST_REFERENCE=vds_env.out"
+        -D "TEST_FOLDER=${PROJECT_BINARY_DIR}/H5TEST"
+        -P "${HDF_RESOURCES_EXT_DIR}/runTest.cmake"
+        -E remove
+        vds_virt_0.h5
+        vds_virt_3.h5
+        vds_src_2.h5
+        vds_env.txt
+        vds_env.out
+    WORKING_DIRECTORY
+        ${HDF5_TEST_BINARY_DIR}/H5TEST
+)
+set_tests_properties (H5TEST-clear-vds_env-objects PROPERTIES FIXTURES_SETUP vds_env_clear_objects)
+add_test (NAME H5TEST-vds_env COMMAND $<TARGET_FILE:vds_env>)
+set_tests_properties (H5TEST-vds_env PROPERTIES
+    FIXTURES_REQUIRED vds_env_clear_objects
+    ENVIRONMENT "srcdir=${HDF5_TEST_BINARY_DIR}/H5TEST;HDF5TestExpress=${HDF_TEST_EXPRESS}"
+    WORKING_DIRECTORY ${HDF5_TEST_BINARY_DIR}/H5TEST
+)
+
 if (BUILD_SHARED_LIBS)
   #-- Adding test for cache
   if (NOT CYGWIN AND NOT WIN32)
@@ -1045,6 +1112,67 @@ if (BUILD_SHARED_LIBS)
       WORKING_DIRECTORY ${HDF5_TEST_BINARY_DIR}/H5TEST-shared
   )
 
+  #-- Adding test for external_env
+  add_test (NAME H5TEST-shared-clear-external_env-objects
+      COMMAND    ${CMAKE_COMMAND}
+          -E remove
+          extern_1r.raw
+          extern_2r.raw
+          extern_3r.raw
+          extern_4r.raw
+          extern_1w.raw
+          extern_2w.raw
+          extern_3w.raw
+          extern_4w.raw
+      WORKING_DIRECTORY
+          ${HDF5_TEST_BINARY_DIR}/H5TEST-shared
+  )
+  set_tests_properties (H5TEST-shared-clear-external_env-objects PROPERTIES FIXTURES_SETUP shared_external_env_clear_objects)
+  add_test (NAME H5TEST-shared-external_env COMMAND "${CMAKE_COMMAND}"
+      -D "TEST_PROGRAM=$<TARGET_FILE:external_env-shared>"
+      -D "TEST_ARGS:STRING="
+      -D "TEST_ENV_VAR:STRING=HDF5_EXTFILE_PREFIX"
+      -D "TEST_ENV_VALUE:STRING=\${ORIGIN}"
+      -D "TEST_EXPECT=0"
+      -D "TEST_OUTPUT=external_env.txt"
+      -D "TEST_REFERENCE=external_env.out"
+      -D "TEST_FOLDER=${PROJECT_BINARY_DIR}/H5TEST-shared"
+      -P "${HDF_RESOURCES_EXT_DIR}/runTest.cmake"
+  )
+  set_tests_properties (H5TEST-shared-external_env PROPERTIES
+      FIXTURES_REQUIRED shared_external_env_clear_objects
+      ENVIRONMENT "srcdir=${HDF5_TEST_BINARY_DIR}/H5TEST-shared"
+      WORKING_DIRECTORY ${HDF5_TEST_BINARY_DIR}/H5TEST-shared
+  )
+
+  #-- Adding test for vds_env
+  add_test (NAME H5TEST-shared-clear-vds_env-objects
+      COMMAND    ${CMAKE_COMMAND}
+          -E remove
+          vds_virt_0.h5
+          vds_virt_3.h5
+          vds_src_2.h5
+      WORKING_DIRECTORY
+          ${HDF5_TEST_BINARY_DIR}/H5TEST-shared
+  )
+  set_tests_properties (H5TEST-shared-clear-vds_env-objects PROPERTIES FIXTURES_SETUP shared_vds_env_clear_objects)
+  add_test (NAME H5TEST-shared-vds_env COMMAND "${CMAKE_COMMAND}"
+      -D "TEST_PROGRAM=$<TARGET_FILE:vds_env-shared>"
+      -D "TEST_ARGS:STRING="
+      -D "TEST_ENV_VAR:STRING=HDF5_VDS_PREFIX"
+      -D "TEST_ENV_VALUE:STRING=\${ORIGIN}/tmp"
+      -D "TEST_EXPECT=0"
+      -D "TEST_OUTPUT=vds_env.txt"
+      -D "TEST_REFERENCE=vds_env.out"
+      -D "TEST_FOLDER=${PROJECT_BINARY_DIR}/H5TEST-shared"
+      -P "${HDF_RESOURCES_EXT_DIR}/runTest.cmake"
+  )
+  set_tests_properties (H5TEST-shared-vds_env PROPERTIES
+      FIXTURES_REQUIRED shared_vds_env_clear_objects
+      ENVIRONMENT "srcdir=${HDF5_TEST_BINARY_DIR}/H5TEST-shared"
+      WORKING_DIRECTORY ${HDF5_TEST_BINARY_DIR}/H5TEST-shared
+  )
+
   #-- Adding test for libinfo
   add_test (NAME H5TEST-shared-testlibinfo
       COMMAND ${CMAKE_COMMAND} -D "TEST_PROGRAM=$<TARGET_FILE:${HDF5_LIBSH_TARGET}>" -P "${GREP_RUNNER}"
diff --git a/test/Makefile.am b/test/Makefile.am
index 88dc542..1b82aa4 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -26,21 +26,23 @@ AM_CPPFLAGS+=-I$(top_srcdir)/src -I$(top_builddir)/src
 #       testlibinfo.sh:
 #       testcheck_version.sh: tcheck_version
 #       testlinks_env.sh: links_env
+#       testexternal_env.sh: external_env
 #       testflushrefresh.sh: flushrefresh
+#       testvds_env.sh: vds_env
 #       testswmr.sh: swmr*
 #       testvdsswmr.sh: vds_swmr*
 #       testabort_fail.sh: filenotclosed.c and del_many_dense_attrs.c
 #       test_filter_plugin.sh: filter_plugin.c
 #       test_usecases.sh: use_append_chunk, use_append_mchunks, use_disable_mdc_flushes
-TEST_SCRIPT = testerror.sh testlibinfo.sh testcheck_version.sh testlinks_env.sh \
-    testswmr.sh testvdsswmr.sh testflushrefresh.sh test_usecases.sh testabort_fail.sh
+TEST_SCRIPT = testerror.sh testlibinfo.sh testcheck_version.sh testlinks_env.sh testexternal_env.sh \
+    testswmr.sh testvds_env.sh testvdsswmr.sh testflushrefresh.sh test_usecases.sh testabort_fail.sh
 SCRIPT_DEPEND = error_test$(EXEEXT) err_compat$(EXEEXT) links_env$(EXEEXT) \
-    filenotclosed$(EXEEXT) del_many_dense_attrs$(EXEEXT) \
+    external_env$(EXEEXT) filenotclosed$(EXEEXT) del_many_dense_attrs$(EXEEXT) \
     flushrefresh$(EXEEXT) use_append_chunk$(EXEEXT) use_append_mchunks$(EXEEXT) use_disable_mdc_flushes$(EXEEXT) \
     swmr_generator$(EXEEXT) swmr_reader$(EXEEXT) swmr_writer$(EXEEXT) \
     swmr_remove_reader$(EXEEXT) swmr_remove_writer$(EXEEXT) swmr_addrem_writer$(EXEEXT) \
     swmr_sparse_reader$(EXEEXT) swmr_sparse_writer$(EXEEXT) swmr_start_write$(EXEEXT) \
-    vds_swmr_gen$(EXEEXT) vds_swmr_reader$(EXEEXT) vds_swmr_writer$(EXEEXT)
+    vds_env$(EXEEXT) vds_swmr_gen$(EXEEXT) vds_swmr_reader$(EXEEXT) vds_swmr_writer$(EXEEXT)
 if HAVE_SHARED_CONDITIONAL
   TEST_SCRIPT += test_filter_plugin.sh test_vol_plugin.sh
   SCRIPT_DEPEND += filter_plugin$(EXEEXT) vol_plugin$(EXEEXT)
@@ -69,21 +71,23 @@ TEST_PROG= testhdf5 \
 # accum_swmr_reader is used by accum.c.
 # atomic_writer and atomic_reader are standalone programs.
 # links_env is used by testlinks_env.sh
+# external_env is used by testexternal_env.sh
 # filenotclosed and del_many_dense_attrs are used by testabort_fail.sh
 # flushrefresh is used by testflushrefresh.sh.
 # use_append_chunk, use_append_mchunks and use_disable_mdc_flushes are used by test_usecases.sh
 # swmr_* files (besides swmr.c) are used by testswmr.sh.
 # vds_swmr_* files are used by testvdsswmr.sh
+# vds_env is used by testvds_env.sh
 # 'make check' doesn't run them directly, so they are not included in TEST_PROG.
 # Also build testmeta, which is used for timings test.  It builds quickly,
 # and this lets automake keep all its test programs in one place.
 check_PROGRAMS=$(TEST_PROG) error_test err_compat tcheck_version \
-    testmeta accum_swmr_reader atomic_writer atomic_reader \
+    testmeta accum_swmr_reader atomic_writer atomic_reader external_env \
     links_env filenotclosed del_many_dense_attrs flushrefresh \
     use_append_chunk use_append_mchunks use_disable_mdc_flushes \
     swmr_generator swmr_start_write swmr_reader swmr_writer swmr_remove_reader \
     swmr_remove_writer swmr_addrem_writer swmr_sparse_reader swmr_sparse_writer \
-    swmr_check_compat_vfd vds_swmr_gen vds_swmr_reader vds_swmr_writer
+    swmr_check_compat_vfd vds_env vds_swmr_gen vds_swmr_reader vds_swmr_writer
 if HAVE_SHARED_CONDITIONAL
   check_PROGRAMS+= filter_plugin vol_plugin
 endif
@@ -131,7 +135,7 @@ else
   noinst_LTLIBRARIES=libh5test.la
 endif
 
-libh5test_la_SOURCES=h5test.c testframe.c cache_common.c swmr_common.c
+libh5test_la_SOURCES=h5test.c testframe.c cache_common.c swmr_common.c external_common.c
 
 # Use libhd5test.la to compile all of the tests
 LDADD=libh5test.la $(LIBHDF5)
@@ -223,7 +227,7 @@ use_disable_mdc_flushes_SOURCES=use_disable_mdc_flushes.c
 
 # Temporary files.
 DISTCLEANFILES=testerror.sh testlibinfo.sh testcheck_version.sh testlinks_env.sh test_filter_plugin.sh \
-    testswmr.sh testvdsswmr.sh test_usecases.sh testflushrefresh.sh testabort_fail.sh \
+    testexternal_env.sh testswmr.sh testvds_env.sh testvdsswmr.sh test_usecases.sh testflushrefresh.sh testabort_fail.sh \
 	test_vol_plugin.sh
 
 include $(top_srcdir)/config/conclude.am
diff --git a/test/external.c b/test/external.c
index 20a9ed8..af45445 100644
--- a/test/external.c
+++ b/test/external.c
@@ -17,25 +17,7 @@
  *
  * Purpose:	Tests datasets stored in external raw files.
  */
-#include "h5test.h"
-
-const char *FILENAME[] = {
-    "extern_1",
-    "extern_2",
-    "extern_3",
-    "extern_4",
-    "extern_dir/file_1",
-    "extern_5",
-    NULL
-};
-
-/* A similar collection of files is used for the tests that
- * perform file I/O.
- */
-#define N_EXT_FILES         4
-#define PART_SIZE           25
-#define TOTAL_SIZE          100
-#define GARBAGE_PER_FILE    10
+#include "external_common.h"
 
 
 /*-------------------------------------------------------------------------
@@ -99,106 +81,6 @@ out:
 
 
 /*-------------------------------------------------------------------------
- * Function:    reset_raw_data_files
- *
- * Purpose:     Resets the data in the raw data files for tests that
- *              perform dataset I/O on a set of files.
- *
- * Return:      SUCCEED/FAIL
- *
- * Programmer:  Dana Robinson
- *              February 2016
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-reset_raw_data_files(void)
-{
-    int		    fd = 0;             /* external file descriptor             */
-    size_t	    i, j;               /* iterators                            */
-    hssize_t	n;                  /* bytes of I/O                         */
-    char	    filename[1024];     /* file name                            */
-    int		    data[PART_SIZE];    /* raw data buffer                      */
-    uint8_t     *garbage = NULL;    /* buffer of garbage data               */
-    size_t      garbage_count;      /* size of garbage buffer               */
-    size_t      garbage_bytes;      /* # of garbage bytes written to file   */
-
-    /* Set up garbage buffer */
-    garbage_count = N_EXT_FILES * GARBAGE_PER_FILE;
-    if(NULL == (garbage = (uint8_t *)HDcalloc(garbage_count, sizeof(uint8_t))))
-        goto error;
-    for(i = 0; i < garbage_count; i++)
-        garbage[i] = 0xFF;
-
-    /* The *r files are pre-filled with data and are used to
-     * verify that read operations work correctly.
-     */
-    for(i = 0; i < N_EXT_FILES; i++) {
-
-        /* Open file */
-        HDsprintf(filename, "extern_%lur.raw", (unsigned long)i + 1);
-        if((fd = HDopen(filename, O_RDWR|O_CREAT|O_TRUNC, H5_POSIX_CREATE_MODE_RW)) < 0)
-            goto error;
-        
-        /* Write garbage data to the file. This allows us to test the
-         * the ability to set an offset in the raw data file.
-         */
-        garbage_bytes = i * 10;
-        n = HDwrite(fd, garbage, garbage_bytes);
-        if(n < 0 || (size_t)n != garbage_bytes)
-            goto error;
-
-        /* Fill array with data */
-        for(j = 0; j < PART_SIZE; j++) {
-            data[j] = (int)(i * 25 + j);
-        } /* end for */
-
-        /* Write raw data to the file. */
-        n = HDwrite(fd, data, sizeof(data));
-        if(n != sizeof(data))
-            goto error;
-
-        /* Close this file */
-        HDclose(fd);
-
-    } /* end for */
-
-    /* The *w files are only pre-filled with the garbage data and are
-     * used to verify that write operations work correctly. The individual
-     * tests fill in the actual data.
-     */
-    for(i = 0; i < N_EXT_FILES; i++) {
-
-        /* Open file */
-        HDsprintf(filename, "extern_%luw.raw", (unsigned long)i + 1);
-        if((fd = HDopen(filename, O_RDWR|O_CREAT|O_TRUNC, H5_POSIX_CREATE_MODE_RW)) < 0)
-            goto error;
-        
-        /* Write garbage data to the file. This allows us to test the
-         * the ability to set an offset in the raw data file.
-         */
-        garbage_bytes = i * 10;
-        n = HDwrite(fd, garbage, garbage_bytes);
-        if(n < 0 || (size_t)n != garbage_bytes)
-            goto error;
-
-        /* Close this file */
-        HDclose(fd);
-
-    } /* end for */
-    HDfree(garbage);
-    return SUCCEED;
-
-error:
-    if(fd)
-        HDclose(fd);
-    if(garbage)
-        HDfree(garbage);
-    return FAIL;
-} /* end reset_raw_data_files() */
-
-
-/*-------------------------------------------------------------------------
  * Function:    test_non_extendible
  *
  * Purpose:     Tests a non-extendible dataset with a single external file.
@@ -760,7 +642,7 @@ test_read_file_set(hid_t fapl)
      * debugging to be emitted before we start playing games with what the
      * output looks like.
      */
-    h5_fixname(FILENAME[1], fapl, filename, sizeof(filename));
+    h5_fixname(EXT_FNAME[1], fapl, filename, sizeof(filename));
     if((file = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
         FAIL_STACK_ERROR
     if((grp = H5Gcreate2(file, "emit-diagnostics", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0)
@@ -871,7 +753,7 @@ test_write_file_set(hid_t fapl)
         TEST_ERROR
 
     /* Create another file */
-    h5_fixname(FILENAME[2], fapl, filename, sizeof(filename));
+    h5_fixname(EXT_FNAME[2], fapl, filename, sizeof(filename));
     if((file = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
         FAIL_STACK_ERROR
 
@@ -989,7 +871,7 @@ test_path_absolute(hid_t fapl)
 
     TESTING("absolute filenames for external file");
 
-    h5_fixname(FILENAME[3], fapl, filename, sizeof(filename));
+    h5_fixname(EXT_FNAME[3], fapl, filename, sizeof(filename));
     if((file = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
         FAIL_STACK_ERROR
 
@@ -1085,7 +967,7 @@ test_path_relative(hid_t fapl)
     if (HDmkdir("extern_dir", (mode_t)0755) < 0 && errno != EEXIST)
         TEST_ERROR;
 
-    h5_fixname(FILENAME[4], fapl, filename, sizeof(filename));
+    h5_fixname(EXT_FNAME[4], fapl, filename, sizeof(filename));
     if((file = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
         FAIL_STACK_ERROR;
 
@@ -1180,7 +1062,7 @@ test_path_relative_cwd(hid_t fapl)
     if(HDmkdir("extern_dir", (mode_t)0755) < 0 && errno != EEXIST)
         TEST_ERROR;
 
-    h5_fixname(FILENAME[4], fapl, filename, sizeof(filename));
+    h5_fixname(EXT_FNAME[4], fapl, filename, sizeof(filename));
     if((file = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
         FAIL_STACK_ERROR;
 
@@ -1297,116 +1179,6 @@ error:
 
 
 /*-------------------------------------------------------------------------
- * Function:    test_path_env
- *
- * Purpose:     Test whether the value of HDF5_EXTFILE_PREFIX will overwrite
- *              the efile_prefix dataset access property.
- *              This will create an HDF5 file in a subdirectory which will
- *              refer to ../extern_*a.raw
- *              The files are then accessed by setting the HDF5_EXTFILE_PREFIX
- *              environment variable to "${ORIGIN}".
- *              The efile_prefix dataset access property is set to "someprefix",
- *              which will cause an error if the value is not overwritten by
- *              the environment variable.
- *
- * Return:      Success:    0
- *              Failure:    1
- *
- * Programmer:  Steffen Kiess
- *              March 10, 2015
- *
- *-------------------------------------------------------------------------
- */
-static int
-test_path_env(hid_t fapl)
-{
-    hid_t	file = -1;          /* file to write to                     */
-    hid_t	dcpl = -1;          /* dataset creation properties          */
-    hid_t	space = -1;         /* data space                           */
-    hid_t	dapl = -1;          /* dataset access property list         */
-    hid_t	dset = -1;          /* dataset                              */
-    size_t	i;                  /* miscellaneous counters               */
-    char	cwdpath[1024];		/* working directory                    */
-    char	filename[1024];		/* file name                            */
-    int	    part[PART_SIZE];    /* raw data buffer (partial)            */
-    int     whole[TOTAL_SIZE];  /* raw data buffer (total)              */
-    hsize_t	cur_size;           /* current data space size              */
-    char	buffer[1024];       /* buffer to read efile_prefix          */
-
-    TESTING("prefix in HDF5_EXTFILE_PREFIX");
-
-    if(HDsetenv("HDF5_EXTFILE_PREFIX", "${ORIGIN}", 1))
-        TEST_ERROR
-
-    if(HDmkdir("extern_dir", (mode_t)0755) < 0 && errno != EEXIST)
-        TEST_ERROR;
-
-    h5_fixname(FILENAME[4], fapl, filename, sizeof(filename));
-    if((file = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
-        FAIL_STACK_ERROR
-
-    /* Reset the raw data files */
-    if(reset_raw_data_files() < 0)
-        TEST_ERROR
-
-    /* Create the dataset */
-    if((dcpl = H5Pcreate(H5P_DATASET_CREATE)) < 0)
-        FAIL_STACK_ERROR
-    if(NULL == HDgetcwd(cwdpath, sizeof(cwdpath)))
-        TEST_ERROR
-    for(i = 0; i < N_EXT_FILES; i++) {
-        HDsnprintf(filename, sizeof(filename), "..%sextern_%dr.raw", H5_DIR_SEPS, (int) i + 1);
-        if(H5Pset_external(dcpl, filename, (off_t)(i * GARBAGE_PER_FILE), (hsize_t)sizeof(part)) < 0)
-            FAIL_STACK_ERROR
-    } /* end for */
-
-    cur_size = TOTAL_SIZE;
-    if((space = H5Screate_simple(1, &cur_size, NULL)) < 0)
-        FAIL_STACK_ERROR
-    if((dapl = H5Pcreate(H5P_DATASET_ACCESS)) < 0)
-        FAIL_STACK_ERROR
-
-    /* Set prefix to a nonexistent directory, will be overwritten by environment variable */
-    if(H5Pset_efile_prefix(dapl, "someprefix") < 0)
-        FAIL_STACK_ERROR
-    if(H5Pget_efile_prefix(dapl, buffer, sizeof(buffer)) < 0)
-        FAIL_STACK_ERROR
-    if(HDstrcmp(buffer, "someprefix") != 0)
-        FAIL_PUTS_ERROR("efile prefix not set correctly");
-
-    /* Create dataset */
-    if((dset = H5Dcreate2(file, "dset1", H5T_NATIVE_INT, space, H5P_DEFAULT, dcpl, dapl)) < 0)
-        FAIL_STACK_ERROR
-
-    /* Read the entire dataset and compare with the original */
-    HDmemset(whole, 0, sizeof(whole));
-    if(H5Dread(dset, H5T_NATIVE_INT, space, space, H5P_DEFAULT, whole) < 0)
-        FAIL_STACK_ERROR
-    for(i = 0; i < TOTAL_SIZE; i++)
-        if(whole[i] != (signed)i)
-            FAIL_PUTS_ERROR("Incorrect value(s) read.");
-
-    if(H5Dclose(dset) < 0) FAIL_STACK_ERROR
-    if(H5Pclose(dapl) < 0) FAIL_STACK_ERROR
-    if(H5Pclose(dcpl) < 0) FAIL_STACK_ERROR
-    if(H5Sclose(space) < 0) FAIL_STACK_ERROR
-    if(H5Fclose(file) < 0) FAIL_STACK_ERROR
-    PASSED();
-    return 0;
-
-error:
-    H5E_BEGIN_TRY {
-        H5Pclose(dapl);
-        H5Dclose(dset);
-        H5Pclose(dcpl);
-        H5Sclose(space);
-        H5Fclose(file);
-    } H5E_END_TRY;
-    return 1;
-} /* end test_path_env() */
-
-
-/*-------------------------------------------------------------------------
  * Function:    test_h5d_get_access_plist
  *
  * Purpose:     Ensure that H5Dget_access_plist returns correct values.
@@ -1441,7 +1213,7 @@ test_h5d_get_access_plist(hid_t fapl_id)
         TEST_ERROR
 
     /* Create the file */
-    h5_fixname(FILENAME[5], fapl_id, filename, sizeof(filename));
+    h5_fixname(EXT_FNAME[5], fapl_id, filename, sizeof(filename));
     if((fid = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl_id)) < 0)
         FAIL_STACK_ERROR
 
@@ -1532,7 +1304,7 @@ main(void)
 
     /* Get a fapl for the old (default) file format */
     fapl_id_old = h5_fileaccess();
-    h5_fixname(FILENAME[0], fapl_id_old, filename, sizeof(filename));
+    h5_fixname(EXT_FNAME[0], fapl_id_old, filename, sizeof(filename));
 
     /* Copy and set up a fapl for the latest file format */
     if((fapl_id_new = H5Pcopy(fapl_id_old)) < 0)
@@ -1585,10 +1357,9 @@ main(void)
         nerrors += test_path_absolute(current_fapl_id);
         nerrors += test_path_relative(current_fapl_id);
         nerrors += test_path_relative_cwd(current_fapl_id);
-        nerrors += test_path_env(current_fapl_id);
  
         /* Verify symbol table messages are cached */
-        nerrors += (h5_verify_cached_stabs(FILENAME, current_fapl_id) < 0 ? 1 : 0);
+        nerrors += (h5_verify_cached_stabs(EXT_FNAME, current_fapl_id) < 0 ? 1 : 0);
 
         /* Close the common file */
         if(H5Fclose(fid) < 0) FAIL_STACK_ERROR
@@ -1603,7 +1374,7 @@ main(void)
     HDputs("All external storage tests passed.");
 
     /* Clean up files used by file set tests */
-    if(h5_cleanup(FILENAME, fapl_id_old)) {
+    if(h5_cleanup(EXT_FNAME, fapl_id_old)) {
         HDremove("extern_1r.raw");
         HDremove("extern_2r.raw");
         HDremove("extern_3r.raw");
@@ -1630,4 +1401,3 @@ error:
     printf("%d TEST%s FAILED.\n", nerrors, 1 == nerrors ? "" : "s");
     return EXIT_FAILURE;
 } /* end main() */
-
diff --git a/test/external_common.c b/test/external_common.c
new file mode 100644
index 0000000..e43a713
--- /dev/null
+++ b/test/external_common.c
@@ -0,0 +1,121 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * Copyright by the Board of Trustees of the University of Illinois.         *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the COPYING file, which can be found at the root of the source code       *
+ * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
+ * If you do not have access to either file, you may request a copy from     *
+ * help@hdfgroup.org.                                                        *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*
+ * Programmer:  Raymond Lu <songyulu@hdfgroup.org>
+ *              April, 2019
+ *
+ * Purpose:     Private function for external.c and external_env.c
+ */
+
+#include "external_common.h"
+
+
+/*-------------------------------------------------------------------------
+ * Function:    reset_raw_data_files
+ *
+ * Purpose:     Resets the data in the raw data files for tests that
+ *              perform dataset I/O on a set of files.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ * Programmer:  Dana Robinson
+ *              February 2016
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+reset_raw_data_files(void)
+{
+    int		    fd = 0;             /* external file descriptor             */
+    size_t	    i, j;               /* iterators                            */
+    hssize_t	n;                  /* bytes of I/O                         */
+    char	    filename[1024];     /* file name                            */
+    int		    data[PART_SIZE];    /* raw data buffer                      */
+    uint8_t     *garbage = NULL;    /* buffer of garbage data               */
+    size_t      garbage_count;      /* size of garbage buffer               */
+    size_t      garbage_bytes;      /* # of garbage bytes written to file   */
+
+    /* Set up garbage buffer */
+    garbage_count = N_EXT_FILES * GARBAGE_PER_FILE;
+    if(NULL == (garbage = (uint8_t *)HDcalloc(garbage_count, sizeof(uint8_t))))
+        goto error;
+    for(i = 0; i < garbage_count; i++)
+        garbage[i] = 0xFF;
+
+    /* The *r files are pre-filled with data and are used to
+     * verify that read operations work correctly.
+     */
+    for(i = 0; i < N_EXT_FILES; i++) {
+
+        /* Open file */
+        HDsprintf(filename, "extern_%lur.raw", (unsigned long)i + 1);
+        if((fd = HDopen(filename, O_RDWR|O_CREAT|O_TRUNC, H5_POSIX_CREATE_MODE_RW)) < 0)
+            goto error;
+        
+        /* Write garbage data to the file. This allows us to test the
+         * the ability to set an offset in the raw data file.
+         */
+        garbage_bytes = i * 10;
+        n = HDwrite(fd, garbage, garbage_bytes);
+        if(n < 0 || (size_t)n != garbage_bytes)
+            goto error;
+
+        /* Fill array with data */
+        for(j = 0; j < PART_SIZE; j++) {
+            data[j] = (int)(i * 25 + j);
+        } /* end for */
+
+        /* Write raw data to the file. */
+        n = HDwrite(fd, data, sizeof(data));
+        if(n != sizeof(data))
+            goto error;
+
+        /* Close this file */
+        HDclose(fd);
+
+    } /* end for */
+
+    /* The *w files are only pre-filled with the garbage data and are
+     * used to verify that write operations work correctly. The individual
+     * tests fill in the actual data.
+     */
+    for(i = 0; i < N_EXT_FILES; i++) {
+
+        /* Open file */
+        HDsprintf(filename, "extern_%luw.raw", (unsigned long)i + 1);
+        if((fd = HDopen(filename, O_RDWR|O_CREAT|O_TRUNC, H5_POSIX_CREATE_MODE_RW)) < 0)
+            goto error;
+        
+        /* Write garbage data to the file. This allows us to test the
+         * the ability to set an offset in the raw data file.
+         */
+        garbage_bytes = i * 10;
+        n = HDwrite(fd, garbage, garbage_bytes);
+        if(n < 0 || (size_t)n != garbage_bytes)
+            goto error;
+
+        /* Close this file */
+        HDclose(fd);
+
+    } /* end for */
+    HDfree(garbage);
+    return SUCCEED;
+
+error:
+    if(fd)
+        HDclose(fd);
+    if(garbage)
+        HDfree(garbage);
+    return FAIL;
+}
diff --git a/test/external_common.h b/test/external_common.h
new file mode 100644
index 0000000..f1a15b5
--- /dev/null
+++ b/test/external_common.h
@@ -0,0 +1,45 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * Copyright by the Board of Trustees of the University of Illinois.         *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the COPYING file, which can be found at the root of the source code       *
+ * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
+ * If you do not have access to either file, you may request a copy from     *
+ * help@hdfgroup.org.                                                        *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*
+ * Programmer:  Raymond Lu <songyulu@hdfgroup.org>
+ *              April, 2019
+ *
+ * Purpose:     Private function for external.c and external_env.c
+ */
+#ifndef _EXTERNAL_COMMON_H
+#define _EXTERNAL_COMMON_H
+
+/* Include test header files */
+#include "h5test.h"
+
+static const char *EXT_FNAME[] = {
+    "extern_1",
+    "extern_2",
+    "extern_3",
+    "extern_4",
+    "extern_dir/file_1",
+    "extern_5",
+    NULL
+};
+
+/* A similar collection of files is used for the tests that
+ * perform file I/O.
+ */
+#define N_EXT_FILES         4
+#define PART_SIZE           25
+#define TOTAL_SIZE          100
+#define GARBAGE_PER_FILE    10
+
+herr_t reset_raw_data_files(void);
+#endif /* _EXTERNAL_COMMON_H */
diff --git a/test/external_env.c b/test/external_env.c
new file mode 100644
index 0000000..0f8c9ec
--- /dev/null
+++ b/test/external_env.c
@@ -0,0 +1,215 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * Copyright by the Board of Trustees of the University of Illinois.         *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the COPYING file, which can be found at the root of the source code       *
+ * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
+ * If you do not have access to either file, you may request a copy from     *
+ * help@hdfgroup.org.                                                        *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*
+ * Purpose:	Tests datasets stored in external raw files.
+ */
+#include "external_common.h"
+
+
+/*-------------------------------------------------------------------------
+ * Function:    test_path_env
+ *
+ * Purpose:     Test whether the value of HDF5_EXTFILE_PREFIX will overwrite
+ *              the efile_prefix dataset access property.
+ *              This will create an HDF5 file in a subdirectory which will
+ *              refer to ../extern_*a.raw
+ *              The files are then accessed by setting the HDF5_EXTFILE_PREFIX
+ *              environment variable to "${ORIGIN}".
+ *              The efile_prefix dataset access property is set to "someprefix",
+ *              which will cause an error if the value is not overwritten by
+ *              the environment variable.
+ *
+ * Return:      Success:    0
+ *              Failure:    1
+ *
+ * Programmer:  Steffen Kiess
+ *              March 10, 2015
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+test_path_env(hid_t fapl)
+{
+    hid_t	file = -1;          /* file to write to                     */
+    hid_t	dcpl = -1;          /* dataset creation properties          */
+    hid_t	space = -1;         /* data space                           */
+    hid_t	dapl = -1;          /* dataset access property list         */
+    hid_t	dset = -1;          /* dataset                              */
+    size_t	i;                  /* miscellaneous counters               */
+    char	cwdpath[1024];		/* working directory                    */
+    char	filename[1024];		/* file name                            */
+    int	    part[PART_SIZE];    /* raw data buffer (partial)            */
+    int     whole[TOTAL_SIZE];  /* raw data buffer (total)              */
+    hsize_t	cur_size;           /* current data space size              */
+    char	buffer[1024];       /* buffer to read efile_prefix          */
+
+    TESTING("prefix in HDF5_EXTFILE_PREFIX");
+
+    if(HDmkdir("extern_dir", (mode_t)0755) < 0 && errno != EEXIST)
+        TEST_ERROR;
+
+    h5_fixname(EXT_FNAME[4], fapl, filename, sizeof(filename));
+    if((file = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
+        FAIL_STACK_ERROR
+
+    /* Reset the raw data files */
+    if(reset_raw_data_files() < 0)
+        TEST_ERROR
+
+    /* Create the dataset */
+    if((dcpl = H5Pcreate(H5P_DATASET_CREATE)) < 0)
+        FAIL_STACK_ERROR
+    if(NULL == HDgetcwd(cwdpath, sizeof(cwdpath)))
+        TEST_ERROR
+    for(i = 0; i < N_EXT_FILES; i++) {
+        HDsnprintf(filename, sizeof(filename), "..%sextern_%dr.raw", H5_DIR_SEPS, (int) i + 1);
+        if(H5Pset_external(dcpl, filename, (off_t)(i * GARBAGE_PER_FILE), (hsize_t)sizeof(part)) < 0)
+            FAIL_STACK_ERROR
+    } /* end for */
+
+    cur_size = TOTAL_SIZE;
+    if((space = H5Screate_simple(1, &cur_size, NULL)) < 0)
+        FAIL_STACK_ERROR
+    if((dapl = H5Pcreate(H5P_DATASET_ACCESS)) < 0)
+        FAIL_STACK_ERROR
+
+    /* Set prefix to a nonexistent directory, will be overwritten by environment variable */
+    if(H5Pset_efile_prefix(dapl, "someprefix") < 0)
+        FAIL_STACK_ERROR
+    if(H5Pget_efile_prefix(dapl, buffer, sizeof(buffer)) < 0)
+        FAIL_STACK_ERROR
+    if(HDstrcmp(buffer, "someprefix") != 0)
+        FAIL_PUTS_ERROR("efile prefix not set correctly");
+
+    /* Create dataset */
+    if((dset = H5Dcreate2(file, "dset1", H5T_NATIVE_INT, space, H5P_DEFAULT, dcpl, dapl)) < 0)
+        FAIL_STACK_ERROR
+
+    /* Read the entire dataset and compare with the original */
+    HDmemset(whole, 0, sizeof(whole));
+    if(H5Dread(dset, H5T_NATIVE_INT, space, space, H5P_DEFAULT, whole) < 0)
+        FAIL_STACK_ERROR
+    for(i = 0; i < TOTAL_SIZE; i++)
+        if(whole[i] != (signed)i)
+            FAIL_PUTS_ERROR("Incorrect value(s) read.");
+
+    if(H5Dclose(dset) < 0) FAIL_STACK_ERROR
+    if(H5Pclose(dapl) < 0) FAIL_STACK_ERROR
+    if(H5Pclose(dcpl) < 0) FAIL_STACK_ERROR
+    if(H5Sclose(space) < 0) FAIL_STACK_ERROR
+    if(H5Fclose(file) < 0) FAIL_STACK_ERROR
+
+    PASSED();
+    return 0;
+
+error:
+    H5E_BEGIN_TRY {
+        H5Pclose(dapl);
+        H5Dclose(dset);
+        H5Pclose(dcpl);
+        H5Sclose(space);
+        H5Fclose(file);
+    } H5E_END_TRY;
+    return 1;
+} /* end test_path_env() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    main
+ *
+ * Purpose:     Runs external dataset tests.
+ *
+ * Return:      EXIT_SUCCESS/EXIT_FAILURE
+ *
+ * Programmer:	Robb Matzke
+ *              Tuesday, March  3, 1998
+ *
+ *-------------------------------------------------------------------------
+ */
+int
+main(void)
+{
+    hid_t	fapl_id_old = -1;   /* file access properties (old format)  */
+    hid_t	fapl_id_new = -1;   /* file access properties (new format)  */
+    hid_t	fid = -1;           /* file for test_1* functions           */
+    hid_t	gid = -1;           /* group to emit diagnostics            */
+    char	filename[1024];     /* file name for test_1* funcs          */
+    unsigned latest_format;     /* default or latest file format        */
+    int		nerrors = 0;        /* number of errors                     */
+
+    h5_reset();
+
+    /* Get a fapl for the old (default) file format */
+    fapl_id_old = h5_fileaccess();
+    h5_fixname(EXT_FNAME[0], fapl_id_old, filename, sizeof(filename));
+
+    /* Copy and set up a fapl for the latest file format */
+    if((fapl_id_new = H5Pcopy(fapl_id_old)) < 0)
+        FAIL_STACK_ERROR
+    if(H5Pset_libver_bounds(fapl_id_new, H5F_LIBVER_LATEST, H5F_LIBVER_LATEST) < 0)
+        FAIL_STACK_ERROR
+
+    /* Test with old & new format groups */
+    for(latest_format = FALSE; latest_format <= TRUE; latest_format++) {
+        hid_t current_fapl_id = -1;
+
+        /* Set the fapl for different file formats */
+        if(latest_format) {
+            HDputs("\nTesting with the latest file format:");
+            current_fapl_id = fapl_id_new;
+        } /* end if */
+        else {
+            HDputs("Testing with the default file format:");
+            current_fapl_id = fapl_id_old;
+        } /* end else */
+
+        nerrors += test_path_env(current_fapl_id);
+    } /* end for */
+
+    if(nerrors > 0) goto error;
+
+    /* Close the new ff fapl. h5_cleanup will take care of the old ff fapl */
+    if(H5Pclose(fapl_id_new) < 0) FAIL_STACK_ERROR
+
+    HDputs("All external storage tests passed.");
+
+    /* Clean up files used by file set tests */
+    if(h5_cleanup(EXT_FNAME, fapl_id_old)) {
+        HDremove("extern_1r.raw");
+        HDremove("extern_2r.raw");
+        HDremove("extern_3r.raw");
+        HDremove("extern_4r.raw");
+
+        HDremove("extern_1w.raw");
+        HDremove("extern_2w.raw");
+        HDremove("extern_3w.raw");
+        HDremove("extern_4w.raw");
+
+        HDrmdir("extern_dir");
+    } /* end if */
+
+    return EXIT_SUCCESS;
+
+error:
+    H5E_BEGIN_TRY {
+        H5Fclose(fid);
+        H5Pclose(fapl_id_old);
+        H5Pclose(fapl_id_new);
+        H5Gclose(gid);
+    } H5E_END_TRY;
+    nerrors = MAX(1, nerrors);
+    printf("%d TEST%s FAILED.\n", nerrors, 1 == nerrors ? "" : "s");
+    return EXIT_FAILURE;
+} /* end main() */
+
diff --git a/test/testexternal_env.sh.in b/test/testexternal_env.sh.in
new file mode 100644
index 0000000..3cc140d
--- /dev/null
+++ b/test/testexternal_env.sh.in
@@ -0,0 +1,42 @@
+#! /bin/sh
+#
+# Copyright by The HDF Group.
+# Copyright by the Board of Trustees of the University of Illinois.
+# All rights reserved.
+#
+# This file is part of HDF5.  The full HDF5 copyright notice, including
+# terms governing use, modification, and redistribution, is contained in
+# the COPYING file, which can be found at the root of the source code
+# distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.
+# If you do not have access to either file, you may request a copy from
+# help@hdfgroup.org.
+#
+# Test for external file with environment variable: HDF5_EXTFILE_PREFIX
+
+srcdir=@srcdir@
+
+nerrors=0
+
+##############################################################################
+##############################################################################
+###			  T H E   T E S T S                                ###
+##############################################################################
+##############################################################################
+
+# test for external file with HDF5_EXTFILE_PREFIX
+echo "Testing external file with HDF5_EXTFILE_PREFIX"
+TEST_NAME=external_env                         # The test name
+TEST_BIN=`pwd`/$TEST_NAME                      # The path of the test binary
+ENVCMD="env HDF5_EXTFILE_PREFIX=\${ORIGIN}"    # The environment variable & value
+#
+# Run the test
+# echo "$ENVCMD $RUNSERIAL $TEST_BIN"
+$ENVCMD $RUNSERIAL $TEST_BIN
+exitcode=$?
+if [ $exitcode -eq 0 ]; then
+        echo "Test prefix for HDF5_EXTFILE_PREFIX PASSED"
+    else
+ 	nerrors="`expr $nerrors + 1`"
+	echo "***Error encountered for HDF5_EXTFILE_PREFIX test***"
+fi
+exit $nerrors
diff --git a/test/testvds_env.sh.in b/test/testvds_env.sh.in
new file mode 100644
index 0000000..894e52e
--- /dev/null
+++ b/test/testvds_env.sh.in
@@ -0,0 +1,44 @@
+#! /bin/sh
+#
+# Copyright by The HDF Group.
+# Copyright by the Board of Trustees of the University of Illinois.
+# All rights reserved.
+#
+# This file is part of HDF5.  The full HDF5 copyright notice, including
+# terms governing use, modification, and redistribution, is contained in
+# the COPYING file, which can be found at the root of the source code
+# distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.
+# If you do not have access to either file, you may request a copy from
+# help@hdfgroup.org.
+#
+# Test for external file with environment variable: HDF5_VDS_PREFIX
+
+srcdir=@srcdir@
+
+nerrors=0
+
+##############################################################################
+##############################################################################
+###			  T H E   T E S T S                                ###
+##############################################################################
+##############################################################################
+
+# test for VDS with HDF5_VDS_PREFIX
+echo "Testing basic virtual dataset I/O via H5Pset_vds_prefix(): all selection with ENV prefix"
+TEST_NAME=vds_env                               # The test name
+TEST_BIN=`pwd`/$TEST_NAME                       # The path of the test binary
+ENVCMD="env HDF5_VDS_PREFIX=\${ORIGIN}/tmp"     # Set the environment variable & value
+UNENVCMD="unset HDF5_VDS_PREFIX"                # Unset the environment variable & value
+#
+# Run the test
+# echo "$ENVCMD $RUNSERIAL $TEST_BIN"
+$ENVCMD $RUNSERIAL $TEST_BIN
+exitcode=$?
+if [ $exitcode -eq 0 ]; then
+        echo "Test prefix for HDF5_VDS_PREFIX PASSED"
+    else
+ 	nerrors="`expr $nerrors + 1`"
+	echo "***Error encountered for HDF5_VDS_PREFIX test***"
+fi
+$UNENVCMD
+exit $nerrors
diff --git a/test/vds.c b/test/vds.c
index db01b2b..c3b6181 100644
--- a/test/vds.c
+++ b/test/vds.c
@@ -1121,7 +1121,7 @@ error:
 } /* end test_api() */
 
 /*-------------------------------------------------------------------------
- * Function:    vds_link_prefix
+ * Function:    test_vds_prefix_first
  *
  * Purpose:     Set up vds link prefix via H5Pset_virtual_prefix() to be "tmp"
  *        Should be able to access the target source files in tmp directory via the prefix set
@@ -1132,18 +1132,16 @@ error:
  *-------------------------------------------------------------------------
  */
 static int
-test_vds_prefix(unsigned config, hid_t fapl)
+test_vds_prefix_first(unsigned config, hid_t fapl)
 {
     char        srcfilename[FILENAME_BUF_SIZE];
     char        srcfilename_map[FILENAME_BUF_SIZE];
     char        vfilename[FILENAME_BUF_SIZE];
-    char        vfilename2[FILENAME_BUF_SIZE];
     char        srcfilenamepct[FILENAME_BUF_SIZE];
     char        srcfilenamepct_map[FILENAME_BUF_SIZE];
     const char *srcfilenamepct_map_orig = "vds%%%%_src";
     hid_t       srcfile[4] = {-1, -1, -1, -1}; /* Files with source dsets */
     hid_t       vfile = -1;     /* File with virtual dset */
-    hid_t       vfile2 = -1;    /* File with copied virtual dset */
     hid_t       dcpl = -1;      /* Dataset creation property list */
     hid_t       dapl = -1;      /* Dataset access property list */
     hid_t       srcspace[4] = {-1, -1, -1, -1}; /* Source dataspaces */
@@ -1158,10 +1156,9 @@ test_vds_prefix(unsigned config, hid_t fapl)
     int         i, j;
     char        buffer[1024];   /* buffer to read vds_prefix       */
 
-    TESTING("basic virtual dataset I/O via H5Pset_vds_prefix()")
+    TESTING("basic virtual dataset I/O via H5Pset_vds_prefix(): all selection")
 
     h5_fixname(FILENAME[0], fapl, vfilename, sizeof vfilename);
-    h5_fixname(FILENAME[7], fapl, vfilename2, sizeof vfilename2);
     h5_fixname(FILENAME[8], fapl, srcfilename, sizeof srcfilename);
     h5_fixname_printf(FILENAME[8], fapl, srcfilename_map, sizeof srcfilename_map);
     h5_fixname(FILENAME[10], fapl, srcfilenamepct, sizeof srcfilenamepct);
@@ -1191,9 +1188,6 @@ test_vds_prefix(unsigned config, hid_t fapl)
     if(HDstrcmp(buffer, TMPDIR) != 0)
         FAIL_PUTS_ERROR("vds prefix not set correctly");
 
-    /*
-     * Test 1: All - all selection
-     */
     /* Create source dataspace */
     if((srcspace[0] = H5Screate_simple(2, dims, NULL)) < 0)
         TEST_ERROR
@@ -1346,187 +1340,6 @@ test_vds_prefix(unsigned config, hid_t fapl)
         TEST_ERROR
     dcpl = -1;
 
-    /*
-     * Test 2: All - all selection with ENV prefix
-     */
-    if(HDsetenv("HDF5_VDS_PREFIX", "${ORIGIN}/tmp", 1))
-        TEST_ERROR
-
-    /* Create DCPL */
-    if((dcpl = H5Pcreate(H5P_DATASET_CREATE)) < 0)
-        TEST_ERROR
-
-    /* Set fill value */
-    if(H5Pset_fill_value(dcpl, H5T_NATIVE_INT, &fill) < 0)
-        TEST_ERROR
-
-    /* Set prefix to a nonexistent directory, will be overwritten by environment variable */
-    if((dapl = H5Pcreate(H5P_DATASET_ACCESS)) < 0)
-        TEST_ERROR
-
-    if(H5Pset_virtual_prefix(dapl, "someprefix") < 0)
-        TEST_ERROR
-    if(H5Pget_virtual_prefix(dapl, buffer, sizeof(buffer)) < 0)
-        TEST_ERROR
-
-    if(HDstrcmp(buffer, "someprefix") != 0)
-        FAIL_PUTS_ERROR("vds prefix not set correctly");
-
-    /* Create source dataspace */
-    if((srcspace[0] = H5Screate_simple(2, dims, NULL)) < 0)
-        TEST_ERROR
-
-    /* Create virtual dataspace */
-    if((vspace[0] = H5Screate_simple(2, dims, NULL)) < 0)
-        TEST_ERROR
-
-    /* Select all (should not be necessary, but just to be sure) */
-    if(H5Sselect_all(srcspace[0]) < 0)
-        TEST_ERROR
-    if(H5Sselect_all(vspace[0]) < 0)
-        TEST_ERROR
-
-    /* Add virtual layout mapping */
-    if(H5Pset_virtual(dcpl, vspace[0], config & TEST_IO_DIFFERENT_FILE ? srcfilename_map : ".", "src_dset", srcspace[0]) < 0)
-        TEST_ERROR
-
-    /* Create virtual file */
-    if((vfile = H5Fcreate(vfilename2, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
-        TEST_ERROR
-
-    /* Create source file if requested */
-    if(config & TEST_IO_DIFFERENT_FILE) {
-        HDgetcwd(buffer, 1024);
-        HDchdir(TMPDIR);
-        if((srcfile[0] = H5Fcreate(srcfilename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
-            TEST_ERROR
-        HDchdir(buffer);
-    }
-    else {
-        srcfile[0] = vfile;
-        if(H5Iinc_ref(srcfile[0]) < 0)
-            TEST_ERROR
-    }
-
-    /* Create source dataset */
-    if((srcdset[0] = H5Dcreate2(srcfile[0], "src_dset", H5T_NATIVE_INT, srcspace[0], H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0)
-        TEST_ERROR
-
-    /* Create virtual dataset */
-    if((vdset = H5Dcreate2(vfile, "v_dset", H5T_NATIVE_INT, vspace[0], H5P_DEFAULT, dcpl, dapl)) < 0)
-        TEST_ERROR
-
-    /* Populate write buffer */
-    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++)
-        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
-            buf[i][j] = (i * (int)(sizeof(buf[0]) / sizeof(buf[0][0]))) + j;
-
-    /* Write data directly to source dataset */
-    if(H5Dwrite(srcdset[0], H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, buf[0]) < 0)
-        TEST_ERROR
-
-    /* Close srcdset and srcfile if config option specified */
-    if(config & TEST_IO_CLOSE_SRC) {
-        if(H5Dclose(srcdset[0]) < 0)
-            TEST_ERROR
-        srcdset[0] = -1;
-
-        if(config & TEST_IO_DIFFERENT_FILE) {
-            if(H5Fclose(srcfile[0]) < 0)
-                TEST_ERROR
-            srcfile[0] = -1;
-        }
-    }
-
-    /* Reopen virtual dataset and file if config option specified */
-    if(config & TEST_IO_REOPEN_VIRT) {
-        if(H5Dclose(vdset) < 0)
-            TEST_ERROR
-        vdset = -1;
-        if(H5Fclose(vfile) < 0)
-            TEST_ERROR
-        vfile = -1;
-        if((vfile = H5Fopen(vfilename2, H5F_ACC_RDWR, fapl)) < 0)
-            TEST_ERROR
-        if((vdset = H5Dopen2(vfile, "v_dset", dapl)) < 0)
-            TEST_ERROR
-    }
-
-    /* Read data through virtual dataset */
-    HDmemset(rbuf[0], 0, sizeof(rbuf));
-    if(H5Dread(vdset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, rbuf[0]) < 0)
-        TEST_ERROR
-
-    /* Verify read data */
-    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++) {
-        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
-            if(rbuf[i][j] != buf[i][j]) {
-                TEST_ERROR
-            }
-    }
-
-    /* Adjust write buffer */
-    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++)
-        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
-            buf[i][j] += (int)(sizeof(buf) / sizeof(buf[0][0]));
-
-    /* Write data through virtual dataset */
-    if(H5Dwrite(vdset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, buf[0]) < 0)
-        TEST_ERROR
-
-    /* Reopen srcdset and srcfile if config option specified */
-    if(config & TEST_IO_CLOSE_SRC) {
-        if(config & TEST_IO_DIFFERENT_FILE) {
-            HDgetcwd(buffer, 1024);
-            HDchdir(TMPDIR);
-            if((srcfile[0] = H5Fopen(srcfilename, H5F_ACC_RDONLY, fapl)) < 0)
-                TEST_ERROR
-            HDchdir(buffer);
-        }
-        if((srcdset[0] = H5Dopen2(srcfile[0], "src_dset", H5P_DEFAULT)) < 0)
-            TEST_ERROR
-    }
-
-    /* Read data directly from source dataset */
-    HDmemset(rbuf[0], 0, sizeof(rbuf));
-    if(H5Dread(srcdset[0], H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, rbuf[0]) < 0)
-        TEST_ERROR
-
-    /* Verify read data */
-    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++)
-        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
-            if(rbuf[i][j] != buf[i][j])
-                TEST_ERROR
-
-    /* Close */
-    if(H5Dclose(vdset) < 0)
-        TEST_ERROR
-    vdset = -1;
-    if(H5Dclose(srcdset[0]) < 0)
-        TEST_ERROR
-    srcdset[0] = -1;
-    if(H5Fclose(srcfile[0]) < 0)
-        TEST_ERROR
-    srcfile[0] = -1;
-    if(H5Fclose(vfile) < 0)
-        TEST_ERROR
-    vfile = -1;
-    if(H5Sclose(srcspace[0]) < 0)
-        TEST_ERROR
-    srcspace[0] = -1;
-    if(H5Sclose(vspace[0]) < 0)
-        TEST_ERROR
-    vspace[0] = -1;
-    if(H5Pclose(dapl) < 0)
-        TEST_ERROR
-    dapl = -1;
-    if(H5Pclose(dcpl) < 0)
-        TEST_ERROR
-    dcpl = -1;
-
-    if(HDsetenv("HDF5_VDS_PREFIX", "", 1) < 0)
-        TEST_ERROR
-
     PASSED();
     return 0;
 
@@ -1538,7 +1351,6 @@ test_vds_prefix(unsigned config, hid_t fapl)
         for(i = 0; i < (int)(sizeof(srcfile) / sizeof(srcfile[0])); i++)
             H5Fclose(srcfile[i]);
         H5Fclose(vfile);
-        H5Fclose(vfile2);
         for(i = 0; i < (int)(sizeof(srcspace) / sizeof(srcspace[0])); i++)
             H5Sclose(srcspace[i]);
         for(i = 0; i < (int)(sizeof(vspace) / sizeof(vspace[0])); i++)
@@ -1552,7 +1364,7 @@ test_vds_prefix(unsigned config, hid_t fapl)
         TEST_ERROR
 
     return 1;
-} /* end vds_link_prefix() */
+} /* end test_vds_prefix */
 
 
 /*-------------------------------------------------------------------------
@@ -11663,7 +11475,7 @@ main(void)
             for(bit_config = 0; bit_config < TEST_IO_NTESTS; bit_config++) {
                 HDprintf("Config: %s%s%s\n", bit_config & TEST_IO_CLOSE_SRC ? "closed source dataset, " : "", bit_config & TEST_IO_DIFFERENT_FILE ? "different source file" : "same source file", bit_config & TEST_IO_REOPEN_VIRT ? ", reopen virtual file" : "");
                 nerrors += test_basic_io(bit_config, my_fapl);
-                nerrors += test_vds_prefix(bit_config, my_fapl);
+                nerrors += test_vds_prefix_first(bit_config, my_fapl);
                 nerrors += test_unlim(bit_config, my_fapl);
                 nerrors += test_printf(bit_config, my_fapl);
                 nerrors += test_all(bit_config, my_fapl);
diff --git a/test/vds_env.c b/test/vds_env.c
new file mode 100644
index 0000000..55e4c85
--- /dev/null
+++ b/test/vds_env.c
@@ -0,0 +1,366 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the COPYING file, which can be found at the root of the source code       *
+ * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
+ * If you do not have access to either file, you may request a copy from     *
+ * help@hdfgroup.org.                                                        *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*
+ * Programmer:  Neil Fortner <nfortne2@hdfgroup.org>
+ *              Monday, February 16, 2015
+ *
+ * Purpose:     Tests datasets with virtual layout.
+ */
+#include "h5test.h"
+
+const char *FILENAME[] = {
+    "vds_virt_0",
+    "vds_virt_3",
+    "vds_src_2",
+    "vds%%_src2",
+    NULL
+};
+
+/* I/O test config flags */
+#define TEST_IO_CLOSE_SRC       0x01u
+#define TEST_IO_DIFFERENT_FILE  0x02u
+#define TEST_IO_REOPEN_VIRT     0x04u
+#define TEST_IO_NTESTS          0x08u
+
+#define FILENAME_BUF_SIZE       1024
+
+#define TMPDIR          "tmp/"
+
+/*-------------------------------------------------------------------------
+ * Function:    test_vds_prefix_second
+ *
+ * Purpose:     Set up vds link prefix via H5Pset_virtual_prefix() to be "tmp"
+ *        Should be able to access the target source files in tmp directory via the prefix set
+ *        by H5Pset_virtual_prefix()
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *-------------------------------------------------------------------------
+ */
+static int
+test_vds_prefix_second(unsigned config, hid_t fapl)
+{
+    char        srcfilename[FILENAME_BUF_SIZE];
+    char        srcfilename_map[FILENAME_BUF_SIZE];
+    char        vfilename[FILENAME_BUF_SIZE];
+    char        vfilename2[FILENAME_BUF_SIZE];
+    char        srcfilenamepct[FILENAME_BUF_SIZE];
+    char        srcfilenamepct_map[FILENAME_BUF_SIZE];
+    const char *srcfilenamepct_map_orig = "vds%%%%_src";
+    hid_t       srcfile[4] = {-1, -1, -1, -1}; /* Files with source dsets */
+    hid_t       vfile = -1;     /* File with virtual dset */
+    hid_t       dcpl = -1;      /* Dataset creation property list */
+    hid_t       dapl = -1;      /* Dataset access property list */
+    hid_t       srcspace[4] = {-1, -1, -1, -1}; /* Source dataspaces */
+    hid_t       vspace[4] = {-1, -1, -1, -1}; /* Virtual dset dataspaces */
+    hid_t       memspace = -1;  /* Memory dataspace */
+    hid_t       srcdset[4] = {-1, -1, -1, -1}; /* Source datsets */
+    hid_t       vdset = -1;     /* Virtual dataset */
+    hsize_t     dims[4] = {10, 26, 0, 0}; /* Data space current size */
+    int         buf[10][26];    /* Write and expected read buffer */
+    int         rbuf[10][26];   /* Read buffer */
+    int         fill = -1;      /* Fill value */
+    int         i, j;
+    char        buffer[1024];   /* buffer to read vds_prefix       */
+
+    TESTING("basic virtual dataset I/O via H5Pset_vds_prefix(): all selection with ENV prefix")
+
+    h5_fixname(FILENAME[0], fapl, vfilename, sizeof vfilename);
+    h5_fixname(FILENAME[1], fapl, vfilename2, sizeof vfilename2);
+    h5_fixname(FILENAME[2], fapl, srcfilename, sizeof srcfilename);
+    h5_fixname_printf(FILENAME[2], fapl, srcfilename_map, sizeof srcfilename_map);
+    h5_fixname(FILENAME[3], fapl, srcfilenamepct, sizeof srcfilenamepct);
+    h5_fixname_printf(srcfilenamepct_map_orig, fapl, srcfilenamepct_map, sizeof srcfilenamepct_map);
+
+    /* create tmp directory and get current working directory path */
+    if (HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST)
+        TEST_ERROR
+
+    /* Create DCPL */
+    if((dcpl = H5Pcreate(H5P_DATASET_CREATE)) < 0)
+        TEST_ERROR
+
+    /* Set fill value */
+    if(H5Pset_fill_value(dcpl, H5T_NATIVE_INT, &fill) < 0)
+        TEST_ERROR
+
+    /* Set prefix to a nonexistent directory, will be overwritten by environment variable */
+    if((dapl = H5Pcreate(H5P_DATASET_ACCESS)) < 0)
+        TEST_ERROR
+
+    if(H5Pset_virtual_prefix(dapl, "someprefix") < 0)
+        TEST_ERROR
+    if(H5Pget_virtual_prefix(dapl, buffer, sizeof(buffer)) < 0)
+        TEST_ERROR
+
+    if(HDstrcmp(buffer, "someprefix") != 0)
+        FAIL_PUTS_ERROR("vds prefix not set correctly");
+
+    /* Create source dataspace */
+    if((srcspace[0] = H5Screate_simple(2, dims, NULL)) < 0)
+        TEST_ERROR
+
+    /* Create virtual dataspace */
+    if((vspace[0] = H5Screate_simple(2, dims, NULL)) < 0)
+        TEST_ERROR
+
+    /* Select all (should not be necessary, but just to be sure) */
+    if(H5Sselect_all(srcspace[0]) < 0)
+        TEST_ERROR
+    if(H5Sselect_all(vspace[0]) < 0)
+        TEST_ERROR
+
+    /* Add virtual layout mapping */
+    if(H5Pset_virtual(dcpl, vspace[0], config & TEST_IO_DIFFERENT_FILE ? srcfilename_map : ".", "src_dset", srcspace[0]) < 0)
+        TEST_ERROR
+
+    /* Create virtual file */
+    if((vfile = H5Fcreate(vfilename2, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
+        TEST_ERROR
+
+    /* Create source file if requested */
+    if(config & TEST_IO_DIFFERENT_FILE) {
+        HDgetcwd(buffer, 1024);
+        HDchdir(TMPDIR);
+        if((srcfile[0] = H5Fcreate(srcfilename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
+            TEST_ERROR
+        HDchdir(buffer);
+    }
+    else {
+        srcfile[0] = vfile;
+        if(H5Iinc_ref(srcfile[0]) < 0)
+            TEST_ERROR
+    }
+
+    /* Create source dataset */
+    if((srcdset[0] = H5Dcreate2(srcfile[0], "src_dset", H5T_NATIVE_INT, srcspace[0], H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0)
+        TEST_ERROR
+
+    /* Create virtual dataset */
+    if((vdset = H5Dcreate2(vfile, "v_dset", H5T_NATIVE_INT, vspace[0], H5P_DEFAULT, dcpl, dapl)) < 0)
+        TEST_ERROR
+
+    /* Populate write buffer */
+    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++)
+        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
+            buf[i][j] = (i * (int)(sizeof(buf[0]) / sizeof(buf[0][0]))) + j;
+
+    /* Write data directly to source dataset */
+    if(H5Dwrite(srcdset[0], H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, buf[0]) < 0)
+        TEST_ERROR
+
+    /* Close srcdset and srcfile if config option specified */
+    if(config & TEST_IO_CLOSE_SRC) {
+        if(H5Dclose(srcdset[0]) < 0)
+            TEST_ERROR
+        srcdset[0] = -1;
+
+        if(config & TEST_IO_DIFFERENT_FILE) {
+            if(H5Fclose(srcfile[0]) < 0)
+                TEST_ERROR
+            srcfile[0] = -1;
+        }
+    }
+
+    /* Reopen virtual dataset and file if config option specified */
+    if(config & TEST_IO_REOPEN_VIRT) {
+        if(H5Dclose(vdset) < 0)
+            TEST_ERROR
+        vdset = -1;
+        if(H5Fclose(vfile) < 0)
+            TEST_ERROR
+        vfile = -1;
+        if((vfile = H5Fopen(vfilename2, H5F_ACC_RDWR, fapl)) < 0)
+            TEST_ERROR
+        if((vdset = H5Dopen2(vfile, "v_dset", dapl)) < 0)
+            TEST_ERROR
+    }
+
+    /* Read data through virtual dataset */
+    HDmemset(rbuf[0], 0, sizeof(rbuf));
+    if(H5Dread(vdset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, rbuf[0]) < 0)
+        TEST_ERROR
+
+    /* Verify read data */
+    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++) {
+        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
+            if(rbuf[i][j] != buf[i][j]) {
+                TEST_ERROR
+            }
+    }
+
+    /* Adjust write buffer */
+    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++)
+        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
+            buf[i][j] += (int)(sizeof(buf) / sizeof(buf[0][0]));
+
+    /* Write data through virtual dataset */
+    if(H5Dwrite(vdset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, buf[0]) < 0)
+        TEST_ERROR
+
+    /* Reopen srcdset and srcfile if config option specified */
+    if(config & TEST_IO_CLOSE_SRC) {
+        if(config & TEST_IO_DIFFERENT_FILE) {
+            HDgetcwd(buffer, 1024);
+            HDchdir(TMPDIR);
+            if((srcfile[0] = H5Fopen(srcfilename, H5F_ACC_RDONLY, fapl)) < 0)
+                TEST_ERROR
+            HDchdir(buffer);
+        }
+        if((srcdset[0] = H5Dopen2(srcfile[0], "src_dset", H5P_DEFAULT)) < 0)
+            TEST_ERROR
+    }
+
+    /* Read data directly from source dataset */
+    HDmemset(rbuf[0], 0, sizeof(rbuf));
+    if(H5Dread(srcdset[0], H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, rbuf[0]) < 0)
+        TEST_ERROR
+
+    /* Verify read data */
+    for(i = 0; i < (int)(sizeof(buf) / sizeof(buf[0])); i++)
+        for(j = 0; j < (int)(sizeof(buf[0]) / sizeof(buf[0][0])); j++)
+            if(rbuf[i][j] != buf[i][j])
+                TEST_ERROR
+
+    /* Close */
+    if(H5Dclose(vdset) < 0)
+        TEST_ERROR
+    vdset = -1;
+    if(H5Dclose(srcdset[0]) < 0)
+        TEST_ERROR
+    srcdset[0] = -1;
+    if(H5Fclose(srcfile[0]) < 0)
+        TEST_ERROR
+    srcfile[0] = -1;
+    if(H5Fclose(vfile) < 0)
+        TEST_ERROR
+    vfile = -1;
+    if(H5Sclose(srcspace[0]) < 0)
+        TEST_ERROR
+    srcspace[0] = -1;
+    if(H5Sclose(vspace[0]) < 0)
+        TEST_ERROR
+    vspace[0] = -1;
+    if(H5Pclose(dapl) < 0)
+        TEST_ERROR
+    dapl = -1;
+    if(H5Pclose(dcpl) < 0)
+        TEST_ERROR
+    dcpl = -1;
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+        for(i = 0; i < (int)(sizeof(srcdset) / sizeof(srcdset[0])); i++)
+            H5Dclose(srcdset[i]);
+        H5Dclose(vdset);
+        for(i = 0; i < (int)(sizeof(srcfile) / sizeof(srcfile[0])); i++)
+            H5Fclose(srcfile[i]);
+        H5Fclose(vfile);
+        for(i = 0; i < (int)(sizeof(srcspace) / sizeof(srcspace[0])); i++)
+            H5Sclose(srcspace[i]);
+        for(i = 0; i < (int)(sizeof(vspace) / sizeof(vspace[0])); i++)
+            H5Sclose(vspace[i]);
+        H5Sclose(memspace);
+        H5Pclose(dapl);
+        H5Pclose(dcpl);
+    } H5E_END_TRY;
+
+    return 1;
+} /* end test_vds_prefix2 */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    main
+ *
+ * Purpose:     Tests datasets with virtual layout
+ *
+ * Return:      EXIT_SUCCESS/EXIT_FAILURE
+ *-------------------------------------------------------------------------
+ */
+int
+main(void)
+{
+    char filename[FILENAME_BUF_SIZE];
+    hid_t fapl, my_fapl;
+    int test_api_config;
+    unsigned bit_config;
+    H5F_libver_t low, high;     /* Low and high bounds */
+    unsigned latest = FALSE;    /* Using the latest library version bound */
+    int nerrors = 0;
+
+    /* Testing setup */
+    h5_reset();
+    fapl = h5_fileaccess();
+
+    /* Set to use the latest file format */
+    if((my_fapl = H5Pcopy(fapl)) < 0) TEST_ERROR
+
+     /* Loop through all the combinations of low/high version bounds */
+    for(low = H5F_LIBVER_EARLIEST; low < H5F_LIBVER_NBOUNDS; H5_INC_ENUM(H5F_libver_t, low)) {
+        for(high = H5F_LIBVER_EARLIEST; high < H5F_LIBVER_NBOUNDS; H5_INC_ENUM(H5F_libver_t, high)) {
+            char msg[80];       /* Message for file version bounds */
+            char *low_string;   /* The low bound string */
+            char *high_string;  /* The high bound string */
+
+            /* Invalid combinations, just continue */
+            if(high == H5F_LIBVER_EARLIEST || high < low)
+                continue;
+
+            /* Test virtual dataset only for V110 and above */
+            if(high < H5F_LIBVER_V110)
+                continue;
+
+            /* Whether to use latest hyperslab/point selection version */
+            if(low >= H5F_LIBVER_V112)
+                latest = TRUE;
+
+            /* Set the low/high version bounds */
+            if(H5Pset_libver_bounds(my_fapl, low, high) < 0)
+                TEST_ERROR
+
+            /* Display testing info */
+            low_string = h5_get_version_string(low);
+            high_string = h5_get_version_string(high);
+            HDsprintf(msg, "Testing virtual dataset with file version bounds: (%s, %s):", low_string, high_string);
+            HDputs(msg);
+
+            for(bit_config = 0; bit_config < TEST_IO_NTESTS; bit_config++) {
+                HDprintf("Config: %s%s%s\n", bit_config & TEST_IO_CLOSE_SRC ? "closed source dataset, " : "", bit_config & TEST_IO_DIFFERENT_FILE ? "different source file" : "same source file", bit_config & TEST_IO_REOPEN_VIRT ? ", reopen virtual file" : "");
+                nerrors += test_vds_prefix_second(bit_config, fapl);
+            }
+
+            /* Verify symbol table messages are cached */
+            nerrors += (h5_verify_cached_stabs(FILENAME, my_fapl) < 0 ? 1 : 0);
+
+       } /* end for high */
+    } /* end for low */
+
+    if(H5Pclose(my_fapl) < 0)
+        TEST_ERROR
+
+    if(nerrors)
+        goto error;
+    HDprintf("All virtual dataset tests passed.\n");
+    h5_cleanup(FILENAME, fapl);
+
+    return EXIT_SUCCESS;
+
+error:
+    nerrors = MAX(1, nerrors);
+    HDprintf("***** %d VIRTUAL DATASET TEST%s FAILED! *****\n",
+            nerrors, 1 == nerrors ? "" : "S");
+    return EXIT_FAILURE;
+} /* end main() */