Merge pull request #15 in ~VCHOI/my_third_fork from hdf5_1_10 to bugfix/110_HDFFV-10808-h5pset_file_space_strategy

* commit '3049d2c140b06d5b2b419562c3d4d1d1c66612e3':
  A minor bug fix.
  Updated the command for external_env and vds_env to the most recent changes.
  1. Updated the commands for compiling two new tests (external_env.c and vds_env.c). 2. Changed the data file names for external.c and external_env.c to avoid potential name conflict.
  HDFFV-10658: setting and getting properties in API context.  Porting the changes to the develop branch into the 1.10 branch: mainly the external file prefix and VDS prefix.

6 files changed, 208 insertions, 33 deletions

diff --git a/src/H5CX.c b/src/H5CX.c
index 7cf283a..01962a1 100644
--- a/src/H5CX.c
+++ b/src/H5CX.c
@@ -186,6 +186,10 @@ typedef struct H5CX_t {
     hid_t lapl_id;              /* LAPL ID for API operation */
     H5P_genplist_t *lapl;       /* Link Access 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 */
@@ -275,6 +279,12 @@ typedef struct H5CX_t {
     size_t nlinks;              /* Number of soft / UD links to traverse (H5L_ACS_NLINKS_NAME) */
     hbool_t nlinks_valid;       /* Whether number of soft / UD links to traverse 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() */
     hbool_t low_bound_valid;    /* Whether low_bound property is valid */
@@ -329,6 +339,13 @@ typedef struct H5CX_lapl_cache_t {
     size_t nlinks;                  /* Number of soft / UD links to traverse (H5L_ACS_NLINKS_NAME) */
 } H5CX_lapl_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 {
@@ -367,6 +384,9 @@ static H5CX_dxpl_cache_t H5CX_def_dxpl_cache;
 /* Define a "default" link access property list cache structure to use for default LAPLs */
 static H5CX_lapl_cache_t H5CX_def_lapl_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;
 
@@ -390,6 +410,7 @@ 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 *da_plist;           /* Dataset access property list */
     H5P_genplist_t *fa_plist;           /* File access property list */
     herr_t ret_value = SUCCEED;         /* Return value */
 
@@ -490,6 +511,23 @@ H5CX__init_package(void)
     if(H5P_get(la_plist, H5L_ACS_NLINKS_NAME, &H5CX_def_lapl_cache.nlinks) < 0)
         HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve number of soft / UD links to traverse")
 
+    /* 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));
 
@@ -630,6 +668,7 @@ H5CX__push_common(H5CX_node_t *cnode)
     /* Set non-zero context info */
     cnode->ctx.dxpl_id = H5P_DATASET_XFER_DEFAULT;
     cnode->ctx.lapl_id = H5P_LINK_ACCESS_DEFAULT;
+    cnode->ctx.dapl_id = H5P_DATASET_ACCESS_DEFAULT;
     cnode->ctx.fapl_id = H5P_FILE_ACCESS_DEFAULT;
     cnode->ctx.tag = H5AC__INVALID_TAG;
     cnode->ctx.ring = H5AC_RING_USER;
@@ -867,6 +906,7 @@ 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
@@ -881,6 +921,12 @@ 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")
@@ -1971,6 +2017,119 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5CX_get_libver_bounds() */
 
+/*-------------------------------------------------------------------------
+ * 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
diff --git a/src/H5CXprivate.h b/src/H5CXprivate.h
index 6c01119..d67f226 100644
--- a/src/H5CXprivate.h
+++ b/src/H5CXprivate.h
@@ -102,6 +102,10 @@ H5_DLL herr_t H5CX_get_dt_conv_cb(H5T_conv_cb_t *cb_struct);
 /* "Getter" routines for LAPL properties cached in API context */
 H5_DLL herr_t H5CX_get_nlinks(size_t *nlinks);
 
+/* "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/H5Defl.c b/src/H5Defl.c
index 42b3947..ce0bb80 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 d3cad8f..a54333f 100644
--- a/src/H5Dint.c
+++ b/src/H5Dint.c
@@ -54,8 +54,8 @@ static herr_t H5D__init_type(H5F_t *file, const H5D_t *dset, hid_t type_id,
 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() */
@@ -1045,8 +1053,7 @@ 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 */
@@ -1067,20 +1074,22 @@ 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.
@@ -1089,8 +1098,7 @@ 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) {
@@ -1285,11 +1293,11 @@ 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 */
@@ -1444,11 +1452,11 @@ 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 */
@@ -1492,8 +1500,13 @@ 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 d60c08f..5e78d9e 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 186d8fa..41e2a48 100644
--- a/src/H5system.c
+++ b/src/H5system.c
@@ -1125,13 +1125,13 @@ 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)))