[svn-r17971] Description:

    Allow the core VFD to properly support opening backing store files through
symbolic links and have the external links in the file be treated in the same
way as for the sec2 driver.

Tested on:
    FreeBSD/32 6.3 (duty) in debug mode
    FreeBSD/64 6.3 (liberty) w/C++ & FORTRAN, in debug mode
    Linux/32 2.6 (jam) w/PGI compilers, w/default API=1.8.x,
        w/C++ & FORTRAN, w/threadsafe, in debug mode
    Linux/64-amd64 2.6 (smirom) w/Intel compilers, w/default API=1.6.x,
        w/C++ & FORTRAN, in production mode
    Solaris/32 2.10 (linew) w/deprecated symbols disabled, w/C++ & FORTRAN,
        w/szip filter, in production mode
    Linux/64-ia64 2.6 (cobalt) w/Intel compilers, w/C++ & FORTRAN,
        in production mode
    Linux/64-ia64 2.4 (tg-login3) w/parallel, w/FORTRAN, in debug mode
    Linux/64-amd64 2.6 (abe) w/parallel, w/FORTRAN, in production mode
    Mac OS X/32 10.6.2 (amazon) in debug mode
    Mac OS X/32 10.6.2 (amazon) w/C++ & FORTRAN, w/threadsafe,
        in production mode

8 files changed, 119 insertions, 58 deletions

diff --git a/src/H5F.c b/src/H5F.c
index 7e9a32e..4a20825 100644
--- a/src/H5F.c
+++ b/src/H5F.c
@@ -69,6 +69,8 @@ static size_t H5F_get_objects(const H5F_t *f, unsigned types, size_t max_objs, h
 static int H5F_get_objects_cb(void *obj_ptr, hid_t obj_id, void *key);
 static H5F_t *H5F_new(H5F_file_t *shared, hid_t fcpl_id, hid_t fapl_id,
                       H5FD_t *lf);
+static herr_t H5F_build_actual_name(const H5F_t *f, const H5P_genplist_t *fapl,
+    const char *name, char ** /*out*/ actual_name);
 static herr_t H5F_dest(H5F_t *f, hid_t dxpl_id);
 static herr_t H5F_close(H5F_t *f);
 
@@ -1142,7 +1144,8 @@ H5F_dest(H5F_t *f, hid_t dxpl_id)
  *-------------------------------------------------------------------------
  */
 H5F_t *
-H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t dxpl_id)
+H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id,
+    hid_t dxpl_id)
 {
     H5F_t              *file = NULL;        /*the success return value      */
     H5F_file_t         *shared = NULL;      /*shared part of `file'         */
@@ -1312,7 +1315,7 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id, hid_t d
 	HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to build extpath")
 
     /* Formulate the actual file name, after following symlinks, etc. */
-    if(H5F_build_actual_name(file, name, &file->actual_name) < 0)
+    if(H5F_build_actual_name(file, a_plist, name, &file->actual_name) < 0)
 	HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to build actual name")
 
     /* Success */
@@ -2147,15 +2150,18 @@ H5F_decr_nopen_objs(H5F_t *f)
  *
  *-------------------------------------------------------------------------
  */
-herr_t
-H5F_build_actual_name(const H5F_t *f, const char *name, char **actual_name/*out*/)
+static herr_t
+H5F_build_actual_name(const H5F_t *f, const H5P_genplist_t *fapl, const char *name,
+    char **actual_name/*out*/)
 {
+    hid_t       new_fapl_id = -1;       /* ID for duplicated FAPL */
     herr_t      ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5F_build_actual_name)
 
     /* Sanity check */
     HDassert(f);
+    HDassert(fapl);
     HDassert(name);
     HDassert(actual_name);
 
@@ -2176,10 +2182,12 @@ H5F_build_actual_name(const H5F_t *f, const char *name, char **actual_name/*out*
 
         /* Check for symbolic link */
         if(S_IFLNK == (lst.st_mode & S_IFMT)) {
+            H5P_genplist_t *new_fapl;   /* Duplicated FAPL */
             int *fd;                    /* POSIX I/O file descriptor */
             h5_stat_t st;               /* Stat info from stat() call */
             h5_stat_t fst;              /* Stat info from fstat() call */
             char realname[PATH_MAX];    /* Fully resolved path name of file */
+            hbool_t want_posix_fd;      /* Flag for retrieving file descriptor from VFD */
 
             /* Perform a sanity check that the file or link wasn't switched
              * between when we opened it and when we called lstat().  This is
@@ -2187,8 +2195,19 @@ H5F_build_actual_name(const H5F_t *f, const char *name, char **actual_name/*out*
              * here: https://www.securecoding.cert.org/confluence/display/seccode/POS35-C.+Avoid+race+conditions+while+checking+for+the+existence+of+a+symbolic+link
              */
 
+            /* Copy the FAPL object to modify */
+            if((new_fapl_id = H5P_copy_plist(fapl, FALSE)) < 0)
+                HGOTO_ERROR(H5E_FILE, H5E_CANTCOPY, FAIL, "unable to copy file access property list")
+            if(NULL == (new_fapl = (H5P_genplist_t *)H5I_object(new_fapl_id)))
+                HGOTO_ERROR(H5E_FILE, H5E_CANTCREATE, FAIL, "can't get property list")
+
+            /* Set the character encoding on the new property list */
+            want_posix_fd = TRUE;
+            if(H5P_set(new_fapl, H5F_ACS_WANT_POSIX_FD_NAME, &want_posix_fd) < 0)
+                HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set character encoding")
+
             /* Retrieve the file handle */
-            if(H5F_get_vfd_handle(f, H5P_DEFAULT, (void **)&fd) < 0)
+            if(H5F_get_vfd_handle(f, new_fapl_id, (void **)&fd) < 0)
                 HGOTO_ERROR(H5E_FILE, H5E_CANTGET, FAIL, "can't retrieve POSIX file descriptor")
 
             /* Stat the filename we're resolving */
@@ -2222,6 +2241,9 @@ H5F_build_actual_name(const H5F_t *f, const char *name, char **actual_name/*out*
     } /* end else */
 
 done:
+    if(new_fapl_id > 0 && H5Pclose(new_fapl_id) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTCLOSEOBJ, FAIL, "can't close duplicated FAPL")
+
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5F_build_actual_name() */
 
diff --git a/src/H5FDcore.c b/src/H5FDcore.c
index a08abdd..2d754f5 100644
--- a/src/H5FDcore.c
+++ b/src/H5FDcore.c
@@ -398,29 +398,29 @@ H5FD_core_open(const char *name, unsigned flags, hid_t fapl_id,
     FUNC_ENTER_NOAPI(H5FD_core_open, NULL)
 
     /* Check arguments */
-    if (!name || !*name)
+    if(!name || !*name)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, NULL, "invalid file name")
-    if (0==maxaddr || HADDR_UNDEF==maxaddr)
+    if(0 == maxaddr || HADDR_UNDEF == maxaddr)
         HGOTO_ERROR(H5E_ARGS, H5E_BADRANGE, NULL, "bogus maxaddr")
     if(ADDR_OVERFLOW(maxaddr))
         HGOTO_ERROR(H5E_ARGS, H5E_OVERFLOW, NULL, "maxaddr overflow")
-    assert(H5P_DEFAULT != fapl_id);
-	if(NULL == (plist = (H5P_genplist_t *)H5I_object(fapl_id)))
-		HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not a file access property list")
-	fa = (H5FD_core_fapl_t *)H5P_get_driver_info(plist);
+    HDassert(H5P_DEFAULT != fapl_id);
+    if(NULL == (plist = (H5P_genplist_t *)H5I_object(fapl_id)))
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not a file access property list")
+    fa = (H5FD_core_fapl_t *)H5P_get_driver_info(plist);
 
     /* Build the open flags */
     o_flags = (H5F_ACC_RDWR & flags) ? O_RDWR : O_RDONLY;
-    if (H5F_ACC_TRUNC & flags) o_flags |= O_TRUNC;
-    if (H5F_ACC_CREAT & flags) o_flags |= O_CREAT;
-    if (H5F_ACC_EXCL & flags) o_flags |= O_EXCL;
+    if(H5F_ACC_TRUNC & flags) o_flags |= O_TRUNC;
+    if(H5F_ACC_CREAT & flags) o_flags |= O_CREAT;
+    if(H5F_ACC_EXCL & flags) o_flags |= O_EXCL;
 
     /* Open backing store.  The only case that backing store is off is when
      * the backing_store flag is off and H5F_ACC_CREAT is on. */
     if(fa->backing_store || !(H5F_ACC_CREAT & flags)) {
-        if (fa && (fd=HDopen(name, o_flags, 0666))<0)
+        if(fa && (fd = HDopen(name, o_flags, 0666)) < 0)
             HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, NULL, "unable to open file")
-    }
+    } /* end if */
 
     /* Create the new file struct */
     if(NULL == (file = (H5FD_core_t *)H5MM_calloc(sizeof(H5FD_core_t))))
@@ -441,35 +441,34 @@ H5FD_core_open(const char *name, unsigned flags, hid_t fapl_id,
 
     /* If an existing file is opened, load the whole file into memory. */
     if(!(H5F_ACC_CREAT & flags)) {
-        unsigned char *x=NULL;
         size_t size;
 
-        if (HDfstat(file->fd, &sb)<0)
+        /* stat() file to retrieve its size */
+        if(HDfstat(file->fd, &sb) < 0)
             HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, NULL, "unable to fstat file")
-
 	size = (size_t)sb.st_size;
 
+        /* Check if we should allocate the memory buffer and read in existing data */
         if(size) {
-            if (NULL==file->mem)
-                x = (unsigned char*)H5MM_malloc(size);
-
-            if (!x)
+            /* Allocate memory for the file's data */
+            if(NULL == (file->mem = (unsigned char*)H5MM_malloc(size)))
                 HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "unable to allocate memory block")
 
-            file->mem = x;
+            /* Set up data structures */
             file->eof = size;
 
-            if(HDread(file->fd, file->mem, size)<0)
+            /* Read in existing data */
+            if(HDread(file->fd, file->mem, size) < 0)
                 HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, NULL, "unable to read file")
-        }
-    }
+        } /* end if */
+    } /* end if */
 
     /* Set return value */
-    ret_value=(H5FD_t *)file;
+    ret_value = (H5FD_t *)file;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-}
+} /* end H5FD_core_open() */
 
 
 /*-------------------------------------------------------------------------
@@ -576,13 +575,12 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-/* ARGSUSED */
 static herr_t
-H5FD_core_query(const H5FD_t UNUSED * _f, unsigned long *flags /* out */)
+H5FD_core_query(const H5FD_t * _file, unsigned long *flags /* out */)
 {
-    herr_t ret_value = SUCCEED;         /* Return value */
+    const H5FD_core_t	*file = (const H5FD_core_t*)_file;
 
-    FUNC_ENTER_NOAPI(H5FD_core_query, FAIL)
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5FD_core_query)
 
     /* Set the VFL feature flags that this driver supports */
     if(flags) {
@@ -591,10 +589,13 @@ H5FD_core_query(const H5FD_t UNUSED * _f, unsigned long *flags /* out */)
         *flags |= H5FD_FEAT_ACCUMULATE_METADATA; /* OK to accumulate metadata for faster writes */
         *flags |= H5FD_FEAT_DATA_SIEVE;       /* OK to perform data sieving for faster raw data reads & writes */
         *flags |= H5FD_FEAT_AGGREGATE_SMALLDATA; /* OK to aggregate "small" raw data allocations */
+
+        /* If the backing store is open, a POSIX file handle is available */
+        if(file->fd >= 0 && file->backing_store)
+            *flags |= H5FD_FEAT_POSIX_COMPAT_HANDLE; /* VFD handle is POSIX I/O call compatible */
     } /* end if */
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
+    FUNC_LEAVE_NOAPI(SUCCEED)
 } /* end H5FD_core_query() */
 
 
@@ -622,9 +623,8 @@ done:
 static haddr_t
 H5FD_core_get_eoa(const H5FD_t *_file, H5FD_mem_t UNUSED type)
 {
-    haddr_t ret_value;   /* Return value */
-
     const H5FD_core_t	*file = (const H5FD_core_t*)_file;
+    haddr_t ret_value;   /* Return value */
 
     FUNC_ENTER_NOAPI(H5FD_core_get_eoa, HADDR_UNDEF)
 
@@ -726,23 +726,52 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-/* ARGSUSED */
 static herr_t
-H5FD_core_get_handle(H5FD_t *_file, hid_t UNUSED fapl, void** file_handle)
+H5FD_core_get_handle(H5FD_t *_file, hid_t fapl, void** file_handle)
 {
-    H5FD_core_t         *file = (H5FD_core_t *)_file;
-    herr_t              ret_value = SUCCEED;
+    H5FD_core_t *file = (H5FD_core_t *)_file;   /* core VFD info */
+    herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI(H5FD_core_get_handle, FAIL)
 
+    /* Check args */
     if(!file_handle)
          HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "file handle not valid")
 
-    *file_handle = &(file->mem);
+    /* Check for non-default FAPL */
+    if(H5P_FILE_ACCESS_DEFAULT != fapl && H5P_DEFAULT != fapl) {
+        H5P_genplist_t *plist;  /* Property list pointer */
+
+        /* Get the FAPL */
+        if(NULL == (plist = (H5P_genplist_t *)H5I_object(fapl)))
+            HGOTO_ERROR(H5E_VFL, H5E_BADTYPE, FAIL, "not a file access property list")
+
+        /* Check if private property for retrieving the backing store POSIX
+         * file descriptor is set.  (This should not be set except within the
+         * library)  QAK - 2009/12/04
+         */
+        if(H5P_exist_plist(plist, H5F_ACS_WANT_POSIX_FD_NAME) > 0) {
+            hbool_t want_posix_fd;  /* Setting for retrieving file descriptor from core VFD */
+
+            /* Get property */
+            if(H5P_get(plist, H5F_ACS_WANT_POSIX_FD_NAME, &want_posix_fd) < 0)
+                HGOTO_ERROR(H5E_VFL, H5E_CANTGET, NULL, "can't get property of retrieving file descriptor")
+
+            /* If property is set, pass back the file descriptor instead of the memory address */
+            if(want_posix_fd)
+                *file_handle = &(file->fd);
+            else
+                *file_handle = &(file->mem);
+        } /* end if */
+        else
+            *file_handle = &(file->mem);
+    } /* end if */
+    else
+        *file_handle = &(file->mem);
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-}
+} /* end H5FD_core_get_handle() */
 
 
 /*-------------------------------------------------------------------------
diff --git a/src/H5FDsec2.c b/src/H5FDsec2.c
index a030934..c715aae 100644
--- a/src/H5FDsec2.c
+++ b/src/H5FDsec2.c
@@ -328,19 +328,18 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-/* ARGSUSED */
 static H5FD_t *
 H5FD_sec2_open(const char *name, unsigned flags, hid_t fapl_id, haddr_t maxaddr)
 {
-    int	o_flags;
-    int		fd=(-1);
-    H5FD_sec2_t	*file=NULL;
+    H5FD_sec2_t	*file = NULL;   /* sec2 VFD info */
+    int	fd = (-1);              /* File descriptor */
+    int	o_flags;                /* Flags for open() call */
 #ifdef _WIN32
     HFILE filehandle;
     struct _BY_HANDLE_FILE_INFORMATION fileinfo;
 #endif
     h5_stat_t	sb;
-    H5FD_t	*ret_value;
+    H5FD_t	*ret_value;     /* Return value */
 
     FUNC_ENTER_NOAPI(H5FD_sec2_open, NULL)
 
diff --git a/src/H5Fprivate.h b/src/H5Fprivate.h
index c55c616..f7df7f7 100644
--- a/src/H5Fprivate.h
+++ b/src/H5Fprivate.h
@@ -380,6 +380,7 @@ typedef struct H5F_blk_aggr_t H5F_blk_aggr_t;
 #define H5F_ACS_FAMILY_TO_SEC2_NAME             "family_to_sec2" /* Whether to convert family to sec2 driver.  (private property only used by h5repart) */
 #define H5F_ACS_MULTI_TYPE_NAME                 "multi_type"    /* Data type in multi file driver */
 #define H5F_ACS_LATEST_FORMAT_NAME              "latest_format" /* 'Use latest format version' flag */
+#define H5F_ACS_WANT_POSIX_FD_NAME              "want_posix_fd" /* Internal: query the file descriptor from the core VFD, instead of the memory address */
 
 /* ======================== File Mount properties ====================*/
 #define H5F_MNT_SYM_LOCAL_NAME 		"local"                 /* Whether absolute symlinks local to file. */
@@ -475,8 +476,6 @@ H5_DLL H5F_t *H5F_open(const char *name, unsigned flags, hid_t fcpl_id,
 H5_DLL herr_t H5F_try_close(H5F_t *f);
 H5_DLL unsigned H5F_incr_nopen_objs(H5F_t *f);
 H5_DLL unsigned H5F_decr_nopen_objs(H5F_t *f);
-H5_DLL herr_t H5F_build_actual_name(const H5F_t *f, const char *,
-    char ** /*out*/ );
 
 /* Functions than retrieve values from the file struct */
 H5_DLL unsigned H5F_get_intent(const H5F_t *f);
diff --git a/src/H5Pfapl.c b/src/H5Pfapl.c
index e082e9c..486bda3 100644
--- a/src/H5Pfapl.c
+++ b/src/H5Pfapl.c
@@ -101,18 +101,23 @@
 #define H5F_ACS_FAMILY_OFFSET_DEF               0
 /* Definition for new member size of family driver. It's private
  * property only used by h5repart */
-#define H5F_ACS_FAMILY_NEWSIZE_SIZE            sizeof(hsize_t)
-#define H5F_ACS_FAMILY_NEWSIZE_DEF             0
+#define H5F_ACS_FAMILY_NEWSIZE_SIZE             sizeof(hsize_t)
+#define H5F_ACS_FAMILY_NEWSIZE_DEF              0
 /* Definition for whether to convert family to sec2 driver. It's private
  * property only used by h5repart */
-#define H5F_ACS_FAMILY_TO_SEC2_SIZE            sizeof(hbool_t)
-#define H5F_ACS_FAMILY_TO_SEC2_DEF             FALSE
+#define H5F_ACS_FAMILY_TO_SEC2_SIZE             sizeof(hbool_t)
+#define H5F_ACS_FAMILY_TO_SEC2_DEF              FALSE
 /* Definition for data type in multi file driver */
 #define H5F_ACS_MULTI_TYPE_SIZE                 sizeof(H5FD_mem_t)
 #define H5F_ACS_MULTI_TYPE_DEF                  H5FD_MEM_DEFAULT
 /* Definition for 'use latest format version' flag */
 #define H5F_ACS_LATEST_FORMAT_SIZE              sizeof(hbool_t)
 #define H5F_ACS_LATEST_FORMAT_DEF               FALSE
+/* Definition for whether to query the file descriptor from the core VFD
+ * instead of the memory address.  (Private to library)
+ */
+#define H5F_ACS_WANT_POSIX_FD_SIZE              sizeof(hbool_t)
+#define H5F_ACS_WANT_POSIX_FD_DEF               FALSE
 
 
 /******************/
@@ -204,6 +209,7 @@ H5P_facc_reg_prop(H5P_genclass_t *pclass)
     hbool_t family_to_sec2 = H5F_ACS_FAMILY_TO_SEC2_DEF;        /* Default ?? for family VFD */
     H5FD_mem_t mem_type = H5F_ACS_MULTI_TYPE_DEF;               /* Default file space type for multi VFD */
     hbool_t latest_format = H5F_ACS_LATEST_FORMAT_DEF;          /* Default setting for "use the latest version of the format" flag */
+    hbool_t want_posix_fd = H5F_ACS_WANT_POSIX_FD_DEF;          /* Default setting for retrieving 'handle' from core VFD */
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5P_facc_reg_prop)
@@ -280,6 +286,11 @@ H5P_facc_reg_prop(H5P_genclass_t *pclass)
     if(H5P_register(pclass, H5F_ACS_LATEST_FORMAT_NAME, H5F_ACS_LATEST_FORMAT_SIZE, &latest_format, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
          HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
+    /* Register the private property of whether to retrieve the file descriptor from the core VFD */
+    /* (used internally to the library only) */
+    if(H5P_register(pclass, H5F_ACS_WANT_POSIX_FD_NAME, H5F_ACS_WANT_POSIX_FD_SIZE, &want_posix_fd, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
+         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5P_facc_reg_prop() */
diff --git a/src/H5Pint.c b/src/H5Pint.c
index 4da7f09..7111cba 100644
--- a/src/H5Pint.c
+++ b/src/H5Pint.c
@@ -619,7 +619,7 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 hid_t
-H5P_copy_plist(H5P_genplist_t *old_plist, hbool_t app_ref)
+H5P_copy_plist(const H5P_genplist_t *old_plist, hbool_t app_ref)
 {
     H5P_genclass_t *tclass;     /* Temporary class pointer */
     H5P_genplist_t *new_plist=NULL;  /* New property list generated from copy */
diff --git a/src/H5Pprivate.h b/src/H5Pprivate.h
index 0b37938..f544dbc 100644
--- a/src/H5Pprivate.h
+++ b/src/H5Pprivate.h
@@ -58,7 +58,7 @@ H5_DLL herr_t H5P_init(void);
 /* Internal versions of API routines */
 H5_DLL herr_t H5P_close(void *_plist);
 H5_DLL hid_t H5P_create_id(H5P_genclass_t *pclass, hbool_t app_ref);
-H5_DLL hid_t H5P_copy_plist(H5P_genplist_t *old_plist, hbool_t app_ref);
+H5_DLL hid_t H5P_copy_plist(const H5P_genplist_t *old_plist, hbool_t app_ref);
 H5_DLL herr_t H5P_get(const H5P_genplist_t *plist, const char *name, void *value);
 H5_DLL herr_t H5P_set(H5P_genplist_t *plist, const char *name, const void *value);
 H5_DLL herr_t H5P_insert(H5P_genplist_t *plist, const char *name, size_t size,
diff --git a/test/links.c b/test/links.c
index 84d2542..deae5ef 100644
--- a/test/links.c
+++ b/test/links.c
@@ -6434,10 +6434,11 @@ external_symlink(const char *env_h5_drvr, hid_t fapl, hbool_t new_format)
         TESTING("external links w/symlink files")
 
 #ifdef H5_HAVE_SYMLINK
-    /* Skip test when using VFDs that have their own 'alloc' callback, which
-     *  don't push mis-aligned space fragments on the file free space list
+    /* Skip test when using VFDs that can't provide a POSIX compatible file
+     *  descriptor.
      */
     have_posix_compat_vfd = (hbool_t)(!HDstrcmp(env_h5_drvr, "sec2")
+            || !HDstrcmp(env_h5_drvr, "core")
             || !HDstrcmp(env_h5_drvr, "nomatch"));
     if(have_posix_compat_vfd) {
         /* set up name for main file: "extlinks21A" */