[svn-r14789] Add handling for external link:

1. src/H5F.c, src/H5system.c: formulate path for mainfile
2. src/H5Lexternal.c: add search for target file
3. configure.in: add H5_HAVE_WINDOW_PATH
4. test/links.c: add tests for external link

11 files changed, 1268 insertions, 43 deletions

diff --git a/configure.in b/configure.in
index 2a4c06c..67f881c 100644
--- a/configure.in
+++ b/configure.in
@@ -2814,6 +2814,24 @@ else
   AC_MSG_RESULT([false])
 fi
 
+dnl ----------------------------------------------------------------------
+dnl Set the flag to indicate that the machine has window style pathname,
+dnl that is, "drive-letter:\" (e.g. "C:") or "drive-letter:/" (e.g. "C:/").
+dnl (This flag should be _unset_ for all machines, except for Windows, where
+dnl it's set in the custom Windows H5pubconf.h file)
+dnl
+AC_MSG_CHECKING([if the machine has window style path name])
+AC_CACHE_VAL([hdf5_have_window_path], [hdf5_have_window_path=no])
+
+if test ${hdf5_have_window_path} = "yes"; then
+  AC_DEFINE([HAVE_WINDOW_PATH], [1],
+            [Define if your system has window style path name.])
+  AC_MSG_RESULT([true])
+else
+  AC_MSG_RESULT([false])
+fi
+
+
 dnl -----------------------------------------------------------------------
 dnl Set flag to indicate that the machine can handle conversion from 
 dnl long double to integers accurately.  This flag should be set "yes" for 
diff --git a/src/H5F.c b/src/H5F.c
index cb9e3b8..80c28bc 100644
--- a/src/H5F.c
+++ b/src/H5F.c
@@ -978,6 +978,9 @@ done:
  * Programmer:	Robb Matzke
  *		matzke@llnl.gov
  *		Jul 18 1997
+ * Modifications:
+ *		Vailin Choi,  April 2, 2008
+ *		Free f->extpath
  *
  *-------------------------------------------------------------------------
  */
@@ -1068,6 +1071,7 @@ H5F_dest(H5F_t *f, hid_t dxpl_id)
 
     /* Free the non-shared part of the file */
     f->name = H5MM_xfree(f->name);
+    f->extpath = H5MM_xfree(f->extpath);
     f->mtab.child = H5MM_xfree(f->mtab.child);
     f->mtab.nalloc = 0;
     if(H5FO_top_dest(f) < 0)
@@ -1078,6 +1082,8 @@ H5F_dest(H5F_t *f, hid_t dxpl_id)
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5F_dest() */
 
+
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5F_open
@@ -1157,6 +1163,9 @@ H5F_dest(H5F_t *f, hid_t dxpl_id)
  *		Modified H5F_flush call to take one flag instead of
  *		multiple Boolean flags.
  *
+ *		Vailin Choi, 2008-04-02
+ *		To formulate path for later searching of target file for external link
+ *		via H5_build_extpath().
  *-------------------------------------------------------------------------
  */
 H5F_t *
@@ -1353,6 +1362,10 @@ 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, "file close degree doesn't match")
     } /* end if */
 
+    /* formulate the absolute path for later search of target file for external link */
+    if (H5_build_extpath(name, &file->extpath) < 0)
+	HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, NULL, "unable to build extpath")
+    
     /* Success */
     ret_value = file;
 
@@ -2140,6 +2153,33 @@ H5F_get_intent(const H5F_t *f)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5F_get_extpath
+ *
+ * Purpose:	Retrieve the file's 'extpath' flags
+ *		This is used by H5L_extern_traverse() to retrieve the main file's location
+ *		when searching the target file.
+ *
+ * Return:	'extpath' on success/abort on failure (shouldn't fail)
+ * 
+ * Programmer:	Vailin Choi, April 2, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+char *
+H5F_get_extpath(const H5F_t *f)
+{
+    /* Use FUNC_ENTER_NOAPI_NOINIT_NOFUNC here to avoid performance issues */
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5F_get_extpath)
+
+    HDassert(f);
+
+    FUNC_LEAVE_NOAPI(f->extpath)
+} /* end H5F_get_extpath() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5F_sizeof_addr
  *
  * Purpose:	Quick and dirty routine to retrieve the size of the file's size_t
@@ -3618,4 +3658,3 @@ H5Fget_info(hid_t obj_id, H5F_info_t *finfo)
 done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Fget_info() */
-
diff --git a/src/H5Fpkg.h b/src/H5Fpkg.h
index 3f10e1a..288ef8a 100644
--- a/src/H5Fpkg.h
+++ b/src/H5Fpkg.h
@@ -142,6 +142,7 @@ typedef struct H5F_mtab_t {
 struct H5F_t {
     unsigned		intent;		/* The flags passed to H5F_open()*/
     char		*name;		/* Name used to open file	*/
+    char               	*extpath;       /* Path for searching target external link file */
     H5F_file_t		*shared;	/* The shared file info		*/
     unsigned		nopen_objs;	/* Number of open object headers*/
     H5FO_t              *obj_count;     /* # of time each object is opened through top file structure */
diff --git a/src/H5Fprivate.h b/src/H5Fprivate.h
index 1044b14..27b45f2 100644
--- a/src/H5Fprivate.h
+++ b/src/H5Fprivate.h
@@ -265,6 +265,7 @@ typedef struct H5F_t H5F_t;
 #define H5F_GC_REF(F)           ((F)->shared->gc_ref)
 #define H5F_USE_LATEST_FORMAT(F) ((F)->shared->latest_format)
 #define H5F_INTENT(F)           ((F)->intent)
+#define H5F_EXTPATH(F)          ((F)->extpath)
 #define H5F_GET_FC_DEGREE(F)    ((F)->shared->fc_degree)
 #define H5F_STORE_MSG_CRT_IDX(F)    ((F)->shared->store_msg_crt_idx)
 #define H5F_GET_FILENO(F,FILENUM) ((FILENUM) = (F)->shared->lf->fileno)
@@ -284,6 +285,7 @@ typedef struct H5F_t H5F_t;
 #define H5F_GC_REF(F)           (H5F_gc_ref(F))
 #define H5F_USE_LATEST_FORMAT(F) (H5F_use_latest_format(F))
 #define H5F_INTENT(F)           (H5F_get_intent(F))
+#define H5F_EXTPATH(F)          (H5F_get_extpath(F))
 #define H5F_GET_FC_DEGREE(F)    (H5F_get_fc_degree(F))
 #define H5F_STORE_MSG_CRT_IDX(F)    (H5F_store_msg_crt_idx(F))
 #define H5F_GET_FILENO(F,FILENUM) (H5F_get_filenum((F), &(FILENUM)))
@@ -417,6 +419,7 @@ H5_DLL herr_t H5F_try_close(H5F_t *f);
 H5_DLL hid_t H5F_get_driver_id(const H5F_t *f);
 H5_DLL hid_t H5F_get_access_plist(H5F_t *f);
 H5_DLL unsigned H5F_get_intent(const H5F_t *f);
+H5_DLL char *H5F_get_extpath(const H5F_t *f);
 H5_DLL herr_t H5F_get_fileno(const H5F_t *f, unsigned long *filenum);
 H5_DLL hid_t H5F_get_id(H5F_t *file);
 H5_DLL unsigned H5F_get_obj_count(const H5F_t *f, unsigned types);
diff --git a/src/H5Lexternal.c b/src/H5Lexternal.c
index 5a8eb33..4e355bb 100644
--- a/src/H5Lexternal.c
+++ b/src/H5Lexternal.c
@@ -76,6 +76,81 @@ H5L_init_extern_interface(void)
 } /* H5L_init_extern_interface() */
 
 
+
+/*--------------------------------------------------------------------------
+ * Function: H5L_getenv_prefix_name --
+ *
+ * Purpose:  Get the first pathname in the list of pathnames stored in ENV_PREFIX,
+ *           which is separated by the environment delimiter.
+ *           ENV_PREFIX is modified to point to the remaining pathnames
+ *           in the list.
+ *
+ * Return:   A pointer to a pathname
+ *
+ * Programmer:	Vailin Choi, April 2, 2008
+ *
+--------------------------------------------------------------------------*/
+static char *
+H5L_getenv_prefix_name(char **env_prefix/*in,out*/)
+{
+    char        *retptr=NULL;
+    char        *strret=NULL;
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5L_getenv_prefix_name)
+
+    strret = HDstrchr(*env_prefix, COLON_SEPC);
+    if (strret == NULL) {
+        retptr = *env_prefix;
+        *env_prefix = strret;
+    } else {
+        retptr = *env_prefix;
+        *env_prefix = strret + 1;
+        *strret = '\0';
+    }
+    return(retptr);
+    FUNC_LEAVE_NOAPI(retptr)
+}
+
+
+/*--------------------------------------------------------------------------
+ * Function: H5L_build_name
+ *
+ * Purpose:  Prepend PREFIX to FILE_NAME and store in FULL_NAME
+ *
+ * Return:   Non-negative on success/Negative on failure
+ *
+ * Programmer:	Vailin Choi, April 2, 2008
+ *
+--------------------------------------------------------------------------*/
+static herr_t
+H5L_build_name(char *prefix, char *file_name, char **full_name/*out*/)
+{
+    size_t      prefix_len;             /* length of prefix */
+    size_t      fname_len;              /* Length of external link file name */
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5L_build_name)
+
+    prefix_len = HDstrlen(prefix);
+    fname_len = HDstrlen(file_name);
+
+    /* Allocate a buffer to hold the filename + prefix + possibly the delimiter + terminating null byte */
+    if(NULL == (*full_name = H5MM_malloc(prefix_len + fname_len + 2)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "unable to allocate filename buffer")
+
+    /* Copy the prefix into the buffer */
+    HDstrcpy(*full_name, prefix);
+    if (!CHECK_DELIMITER(prefix[prefix_len-1]))
+        HDstrcat(*full_name, DIR_SEPS);
+
+    /* Add the external link's filename to the prefix supplied */
+    HDstrcat(*full_name, file_name);
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5L_build_name() */
+
+
 /*-------------------------------------------------------------------------
  * Function:	H5L_extern_traverse
  *
@@ -92,6 +167,10 @@ H5L_init_extern_interface(void)
  *
  * Programmer:	James Laird
  *              Monday, July 10, 2006
+ * Modifications:
+ *		Vailin Choi, April 2, 2008
+ *		Add handling to search for the target file 
+ *		See description in RM: H5Lcreate_external
  *
  *-------------------------------------------------------------------------
  */
@@ -114,6 +193,11 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
     hid_t       ext_obj = -1;           /* ID for external link's object */
     hid_t       ret_value;              /* Return value */
 
+    char        *tempname=NULL, *ptr=NULL, *extpath=NULL;
+    char        *env_prefix=NULL, *tmp_env_prefix=NULL;
+    char        *out_prefix_name=NULL, *pp=NULL;
+
+
     FUNC_ENTER_NOAPI(H5L_extern_traverse, FAIL)
 
     /* Sanity checks */
@@ -135,28 +219,6 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
     if(NULL == (plist = H5P_object_verify(lapl_id, H5P_LINK_ACCESS)))
         HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
 
-    /* Get the current prefix */
-    if(H5P_get(plist, H5L_ACS_ELINK_PREFIX_NAME, &my_prefix) < 0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get external link prefix")
-
-    /* Check for prefix being set, if so, prepend it to the filename */
-    if(my_prefix) {
-        size_t prefix_len = HDstrlen(my_prefix);
-
-        /* Allocate a buffer to hold the filename plus prefix */
-        if(NULL == (full_name = H5MM_malloc(prefix_len + fname_len + 1)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "unable to allocate filename buffer")
-
-        /* Copy the prefix into the buffer */
-        HDstrcpy(full_name, my_prefix);
-
-        /* Add the external link's filename to the prefix supplied */
-        HDstrcat(full_name, (const char *)p);
-
-        /* Point to name w/prefix */
-        file_name = full_name;
-    } /* end if */
-
     /* Get the location for the group holding the external link */
     if(H5G_loc(cur_group, &loc) < 0)
         HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't get object location")
@@ -183,10 +245,92 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
             HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set file close degree")
     } /* end if */
 
-    /* Open the external file */
-    /* (extra work with file intent to mask off inappropriate flags) */
-    if(NULL == (ext_file = H5F_open(file_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY), H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)))
-	HGOTO_ERROR(H5E_LINK, H5E_CANTOPENFILE, FAIL, "unable to open external file")
+    /*
+     * Start searching for the target file
+     */
+    if ((tempname=H5MM_strdup(file_name)) == NULL)
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    /* target file_name is an absolute pathname: see RM for detailed description */
+    if (CHECK_ABSOLUTE(file_name) || CHECK_ABS_PATH(file_name)) {
+        if(NULL == (ext_file = H5F_open(file_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                                H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id))) {
+            H5E_clear_stack(NULL);
+            /* get last component of file_name */
+	    GET_LAST_DELIMITER(file_name, ptr)
+	    HDassert(ptr);
+	    HDstrcpy(tempname, ++ptr);
+        }
+    } else if (CHECK_ABS_DRIVE(file_name)) {
+        if(NULL == (ext_file = H5F_open(file_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                                H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id))) {
+            H5E_clear_stack(NULL);
+	    /* strip "<drive-letter>:" */
+	    HDstrcpy(tempname, &file_name[2]);
+	}
+    }
+    
+    /* try searching from paths set in the environment variable */
+    if ((ext_file == NULL) && (env_prefix=HDgetenv("HDF5_EXT_PREFIX"))) {
+
+        tmp_env_prefix = H5MM_strdup(env_prefix);
+	pp = tmp_env_prefix;
+
+        while ((tmp_env_prefix) && (*tmp_env_prefix)) {
+            out_prefix_name = H5L_getenv_prefix_name(&tmp_env_prefix/*in,out*/);
+            if ((out_prefix_name) && (*out_prefix_name)) {
+
+                if (H5L_build_name(out_prefix_name, tempname, &full_name/*out*/) < 0)
+                    HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't prepend prefix to filename")
+
+                ext_file = H5F_open(full_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                            H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id);
+                if (full_name)
+                    H5MM_xfree(full_name);
+                if (ext_file != NULL)
+                    break;
+                H5E_clear_stack(NULL);
+            }
+        } /* end while */
+        if (pp)
+            H5MM_xfree(pp);
+    }
+    
+    /* try searching from property list */
+    if (ext_file == NULL) {
+        if(H5P_get(plist, H5L_ACS_ELINK_PREFIX_NAME, &my_prefix) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get external link prefix")
+        if (my_prefix) {
+            if (H5L_build_name(my_prefix, tempname, &full_name/*out*/) < 0)
+                HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't prepend prefix to filename")
+            if ((ext_file=H5F_open(full_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                        H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
+                H5E_clear_stack(NULL);
+            if (full_name)
+                H5MM_xfree(full_name);
+        }
+    }
+
+    /* try searching from main file's "extpath":see description in H5F_open() & H5_build_extpath() */
+    if ((ext_file == NULL) && (extpath=H5F_EXTPATH(loc.oloc->file))) {
+        if (H5L_build_name(extpath, tempname, &full_name/*out*/) < 0)
+            HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't prepend prefix to filename")
+        if ((ext_file = H5F_open(full_name, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                    H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
+            H5E_clear_stack(NULL);
+        if (full_name)
+            H5MM_xfree(full_name);
+    }
+
+    /* try the relative file_name stored in tempname */
+    if (ext_file == NULL) {
+        if ((ext_file=H5F_open(tempname, ((intent & H5F_ACC_RDWR) ? H5F_ACC_RDWR : H5F_ACC_RDONLY),
+                        H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
+            HGOTO_ERROR(H5E_LINK, H5E_CANTOPENFILE, FAIL, "unable to open external file")
+    }
+
+    if (tempname)
+        H5MM_xfree(tempname);
 
     /* Increment the number of open objects, to hold the file open */
     H5F_incr_nopen_objs(ext_file);
@@ -219,10 +363,6 @@ done:
     if(ext_file && H5F_try_close(ext_file) < 0)
         HDONE_ERROR(H5E_LINK, H5E_CANTCLOSEFILE, FAIL, "problem closing external file")
 
-    /* Free full_name if it's been allocated */
-    if(full_name)
-        H5MM_xfree(full_name);
-
     /* Close object if it's open and something failed */
     if(ret_value < 0 && ext_obj >= 0 && H5I_dec_ref(ext_obj) < 0)
         HDONE_ERROR(H5E_ATOM, H5E_CANTRELEASE, FAIL, "unable to close atom for external object")
diff --git a/src/H5config.h.in b/src/H5config.h.in
index 5c767ef..77a3b23 100644
--- a/src/H5config.h.in
+++ b/src/H5config.h.in
@@ -368,6 +368,9 @@
 /* Define to 1 if you have the `waitpid' function. */
 #undef HAVE_WAITPID
 
+/* Define if your system has window style path name. */
+#undef HAVE_WINDOW_PATH
+
 /* Define to 1 if you have the <winsock.h> header file. */
 #undef HAVE_WINSOCK_H
 
diff --git a/src/H5private.h b/src/H5private.h
index 11f3037..734290d 100644
--- a/src/H5private.h
+++ b/src/H5private.h
@@ -638,9 +638,19 @@ H5_DLL int HDfprintf (FILE *stream, const char *fmt, ...);
 #define HDfwrite(M,Z,N,F)	fwrite(M,Z,N,F)
 #define HDgetc(F)		getc(F)
 #define HDgetchar()		getchar()
+#ifdef _WIN32
+#define HDgetcwd(S,Z)		_getcwd(S,Z)
+#define HDgetdcwd(D,S,Z)	_getdcwd(D,S,Z)
+#define HDgetdrive()		_getdrive()
+#else
 #define HDgetcwd(S,Z)		getcwd(S,Z)
+#define HDgetdcwd(D,S,Z)	getcwd(S,Z)
+#define HDgetdrive()		0
+#endif
 #define HDgetegid()		getegid()
 #define HDgetenv(S)		getenv(S)
+#define HDsetenv(S,V,O)		setenv(S,V,O)
+#define HDunsetenv(S)		unsetenv(S)
 #define HDgeteuid()		geteuid()
 #define HDgetgid()		getgid()
 #define HDgetgrgid(G)		getgrgid(G)
@@ -911,6 +921,43 @@ extern char *strdup(const char *s);
 
 #endif /* _WIN32 */
 
+#ifdef H5_HAVE_WINDOW_PATH
+
+/* directory delimiter for Windows: slash and backslash are acceptable on Windows */
+#define	DIR_SLASH_SEPC 		'/'
+#define	DIR_SEPC 		'\\'
+#define	DIR_SEPS 		"\\"
+#define CHECK_DELIMITER(SS)     ((SS == DIR_SEPC)||(SS == DIR_SLASH_SEPC))
+#define CHECK_ABSOLUTE(NAME)    (((isalpha(NAME[0])) && (NAME[1] == ':') && CHECK_DELIMITER(NAME[2]))
+#define CHECK_ABS_DRIVE(NAME)   ((isalpha(NAME[0])) && (NAME[1] == ':'))
+#define CHECK_ABS_PATH(NAME)    (CHECK_DELIMITER(NAME[0]))
+
+#define GET_LAST_DELIMITER(NAME, ptr) {                 \
+    char        *slash, *backslash;                     \
+    slash = strrchr(NAME, DIR_SLASH_SEPC);              \
+    backslash = strrchr(NAME, DIR_SEPC);                \
+    if (backslash > slash)                              \
+        (ptr = backslash);                              \
+    else                                                \
+        (ptr = slash);                                  \
+}
+
+
+#else
+
+#define		DIR_SEPC	'/'
+#define		DIR_SEPS	"/"
+#define         CHECK_DELIMITER(SS)             (SS == DIR_SEPC)
+#define         CHECK_ABSOLUTE(NAME)            (CHECK_DELIMITER(*NAME))
+#define 	CHECK_ABS_DRIVE(NAME)   	(0)
+#define 	CHECK_ABS_PATH(NAME)    	(0)
+#define         GET_LAST_DELIMITER(NAME, ptr)   ptr = strrchr(NAME, DIR_SEPC);
+
+#endif
+
+#define 	COLON_SEPC	':'
+H5_DLL herr_t 	H5_build_extpath(const char *, char **/*out*/);
+
 
 /*
  * These macros check whether debugging has been requested for a certain
diff --git a/src/H5system.c b/src/H5system.c
index 5eae11d..d65103a 100644
--- a/src/H5system.c
+++ b/src/H5system.c
@@ -35,6 +35,8 @@
 #include "H5private.h"		/* Generic Functions			*/
 #include "H5Fprivate.h"		/* File access				*/
 #include "H5MMprivate.h"	/* Memory management			*/
+#include "H5Eprivate.h"
+
 
 
 /****************/
@@ -578,4 +580,98 @@ HDremove_all(const char *fname)
 }
 #endif
 
+
+/*
+ *
+ * Function: H5_build_extpath
+ *
+ * Purpose:  To build the path for later searching of target file for external link.
+ *   	     This path can be either:
+ *                      1. The absolute path of NAME
+ *                      or
+ *                      2. The current working directory + relative path of NAME
+ *
+ * Return:	Success:        0
+ *		Failure:	-1
+ *
+ * Programmer:	Vailin Choi
+ *		April 2, 2008
+ */
+#define MAX_PATH_LEN     1024
+
+herr_t
+H5_build_extpath(const char *name, char **extpath/*out*/)
+{
+    char        *full_path=NULL, *ptr=NULL;
+    char        *retcwd=NULL, *cwdpath=NULL, *new_name=NULL;
+    int         drive;
+    size_t      cwdlen, path_len;
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5_build_extpath)
+
+    *extpath = NULL;
+
+    /* 
+     * Unix: name[0] is a "/"
+     * Windows: name[0-2] is "<drive letter>:\" or "<drive-letter>:/"
+     */
+    if (CHECK_ABSOLUTE(name)) {
+        if ((full_path=H5MM_strdup(name)) == NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+    } else { /* relative pathname */
+        if ((cwdpath=H5MM_malloc(MAX_PATH_LEN)) == NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+        if ((new_name=H5MM_strdup(name)) == NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+	/* 
+	 * Windows: name[0-1] is "<drive-letter>:"
+	 * 	Get current working directory on the drive specified in NAME 
+	 * Unix: does not apply
+	 */
+        if (CHECK_ABS_DRIVE(name)) {
+            drive = name[0] - 'A' + 1;
+            retcwd = HDgetdcwd(drive, cwdpath, MAX_PATH_LEN);
+            HDstrcpy(new_name, &name[2]);
+	/* 
+	 * Windows: name[0] is a '/' or '\' 
+	 *	Get current drive
+	 * Unix: does not apply
+	 */
+        } else if (CHECK_ABS_PATH(name) && (drive=HDgetdrive())) {
+            sprintf(cwdpath, "%c:%c", (drive+'A'-1), name[0]);
+            retcwd = cwdpath;
+            HDstrcpy(new_name, &name[1]);
+        } else /* totally relative for both Unix and Windows: get current working directory  */
+            retcwd = HDgetcwd(cwdpath, MAX_PATH_LEN);
+
+        if (retcwd != NULL) {
+            cwdlen = HDstrlen(cwdpath);
+            HDassert(cwdlen);
+            path_len = cwdlen + HDstrlen(new_name) + 2;
+            if ((full_path=H5MM_malloc(path_len)) == NULL)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+            HDstrcpy(full_path, cwdpath);
+            if (!CHECK_DELIMITER(cwdpath[cwdlen-1]))
+                HDstrcat(full_path, DIR_SEPS);
+            HDstrcat(full_path, new_name);
+        }
+    }
+
+    /* strip out the last component (the file name itself) from the path */
+    if (full_path) {
+        GET_LAST_DELIMITER(full_path, ptr)
+        HDassert(ptr);
+        *++ptr = '\0';
+        *extpath = full_path;
+    }
 
+done:
+    if (cwdpath)
+	H5MM_xfree(cwdpath);
+    if (new_name)
+	H5MM_xfree(new_name);
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5_build_extpath() */
diff --git a/test/Makefile.am b/test/Makefile.am
index 53df8bb..191e999 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -105,7 +105,8 @@ flush2.chkexe_: flush1.chkexe_
 CHECK_CLEANFILES+=cmpd_dset.h5 compact_dataset.h5 dataset.h5 extend.h5 istore.h5\
             tfile[1-4].h5 th5s[1-3].h5 lheap.h5 fheap.h5 ohdr.h5 stab.h5 \
             extern_[1-3].h5 extern_[1-4][ab].raw gheap[0-4].h5 dt_arith[1-2]\
-            links.h5 links[0-6]*.h5 big.data big[0-9][0-9][0-9][0-9][0-9].h5  \
+            links.h5 links[0-6]*.h5 extlinks[0-9].h5 tmp \
+	    big.data big[0-9][0-9][0-9][0-9][0-9].h5  \
             stdio.h5 sec2.h5 dtypes[1-8].h5 dt_arith[1-2].h5 tattr.h5        \
             tselect.h5 mtime.h5 unlink.h5 unicode.h5 coord.h5 \
             fillval_[0-9].h5 fillval.raw mount_[0-9].h5 testmeta.h5 ttime.h5 \
diff --git a/test/Makefile.in b/test/Makefile.in
index 7e47249..1297a44 100644
--- a/test/Makefile.in
+++ b/test/Makefile.in
@@ -595,8 +595,8 @@ CHECK_CLEANFILES = *.chkexe *.chklog *.clog cmpd_dset.h5 \
 	compact_dataset.h5 dataset.h5 extend.h5 istore.h5 \
 	tfile[1-4].h5 th5s[1-3].h5 lheap.h5 fheap.h5 ohdr.h5 stab.h5 \
 	extern_[1-3].h5 extern_[1-4][ab].raw gheap[0-4].h5 \
-	dt_arith[1-2] links.h5 links[0-6]*.h5 big.data \
-	big[0-9][0-9][0-9][0-9][0-9].h5 stdio.h5 sec2.h5 \
+	dt_arith[1-2] links.h5 links[0-6]*.h5 extlinks[0-9].h5 tmp \
+	big.data big[0-9][0-9][0-9][0-9][0-9].h5 stdio.h5 sec2.h5 \
 	dtypes[1-8].h5 dt_arith[1-2].h5 tattr.h5 tselect.h5 mtime.h5 \
 	unlink.h5 unicode.h5 coord.h5 fillval_[0-9].h5 fillval.raw \
 	mount_[0-9].h5 testmeta.h5 ttime.h5 trefer[1-3].h5 tvltypes.h5 \
diff --git a/test/links.c b/test/links.c
index 1bff4c6..d517b4d 100644
--- a/test/links.c
+++ b/test/links.c
@@ -40,15 +40,38 @@ const char *FILENAME[] = {
     "links1",
     "links2",
     "links3",
-    "links4a",
-    "links4b",
-    "links4c",
-    "links4d",
-    "links5",
-    "links6",
+    "links4a", /* 4 */
+    "links4b", /* 5 */
+    "links4c", /* 6 */
+    "links4d", /* 7 */
+    "links5",  /* 8 */
+    "links6",  /* 9 */
+    "links7",  /* 10 */
+    "links8",  /* 11 */
+    "extlinks0",  	/* 12: main files */
+    "tmp/extlinks0",  	/* 13: */
+    "extlinks1",  	/* 14: target files */
+    "tmp/extlinks1",  	/* 15: */
+    "extlinks2",	/* 16: */
+    "tmp/extlinks2",	/* 17: */
+    "extlinks3",	/* 18: */
+    "tmp/extlinks3",	/* 19: */
+    "extlinks4",	/* 20: */
+    "tmp/extlinks4",	/* 21: */
+    "extlinks5",	/* 22: */
+    "tmp/extlinks6",	/* 23: */
+    "extlinks7",	/* 24: */
+    "tmp/extlinks7",	/* 25: */
+    "tmp/extlinks8",	/* 26: */
+    "extlinks9",	/* 27: */
+    "tmp/extlinks9",	/* 28: */
     NULL
 };
 
+#define TMPDIR		"tmp"
+/* do not do check_all_closed() for "ext*" files and "tmp/ext*" */
+#define EXTSTOP		12
+
 #define LINK_BUF_SIZE   1024
 #define NAME_BUF_SIZE   1024
 #define MAX_NAME_LEN    ((64*1024)+1024)
@@ -2552,6 +2575,844 @@ external_link_dangling(hid_t fapl, hbool_t new_format)
     return -1;
 } /* end external_link_dangling() */
 
+
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_env: test 1
+ *
+ * Purpose:     1. Create target file in tmp directory ("tmp/extlinks1")
+ *		2. Create main file in current directory ("extlinks0")
+*		3. Create external link to target file ("extlinks1")
+ * 		4. Set up environment variable "HDF5_EXT_PREFIX" to be ".:tmp"
+ *		Should be able to access the target file in tmp directory through searching 
+ *		the pathnames set in HDF5_EXT_PREFIX 
+ *		
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb. 20, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_env(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	*envval=NULL;
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+    		filename3[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via environment variable (w/new group format)")
+    else
+        TESTING("external links via environment variable")
+
+
+    /* set up name for main file:"extlinks0" */
+    h5_fixname(FILENAME[12], fapl, filename1, sizeof filename1);
+    /* set up name for external linked target file: "extlinks1" */
+    h5_fixname(FILENAME[14], fapl, filename2, sizeof filename2);
+
+    if (HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST)
+	TEST_ERROR
+
+    /* set up name for target file: "tmp/extlinks1" */
+    h5_fixname(FILENAME[15], fapl, filename3, sizeof filename3);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename3, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* get original value for the HDF library environment variable for external link if set */
+    envval = HDgetenv("HDF5_EXT_PREFIX");
+    setenv("HDF5_EXT_PREFIX", ".:tmp", 1);
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    /* restore value for the environment variable as needed */
+    if (envval)
+	HDsetenv("HDF5_EXT_PREFIX", envval, 1);
+    else
+	HDunsetenv("HDF5_EXT_PREFIX");
+	
+    /* should be able to find the target file from pathnames set via environment variable */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in tmp directory.");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_env() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_prefix: test 2
+ *
+ * Purpose:     1. Create the target file in tmp directory ("tmp/extlinks2")
+ *		2. Create the main file in current directory ("extlinks0")
+*		3. Create external link to target file ("extlinks2")
+ * 		4. Set up external link prefix via H5Pset_elink_prefix() to be "tmp"
+ *		Should be able to access the target file in tmp directory via the prefix set 
+ *		by H5Pset_elink_prefix()
+ *		
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb 19, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_prefix(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    hid_t	gapl_id = (-1);
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+    		filename3[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via H5Pset_elink_prefix()(w/new group format)")
+    else
+        TESTING("external links via H5Pset_elink_prefix()")
+
+    /* set up name for main file: "extlinks0" */
+    h5_fixname(FILENAME[12], fapl, filename1, sizeof filename1);
+    /* set up name for external linked target file: "extlinks2" */
+    h5_fixname(FILENAME[16], fapl, filename2, sizeof filename2);
+
+    /* create tmp directory and get current working directory path */
+    if (HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST)
+	TEST_ERROR
+
+    /* set up name for target file: "tmp/extlinks2" */
+    h5_fixname(FILENAME[17], fapl, filename3, sizeof filename3);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename3, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file (without the absolute path) */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* set up prefix for external link */
+    if((gapl_id = H5Pcreate(H5P_GROUP_ACCESS)) < 0) TEST_ERROR
+    if(H5Pset_elink_prefix(gapl_id, TMPDIR) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", gapl_id);
+    } H5E_END_TRY;
+
+    /* should be able to find the target file from pathnames set via H5Pset_elink_prefix() */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in tmp directory.");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_prefix() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_abs_mainpath: test 3
+ *
+ * Purpose:     1. Create target file in tmp directory ("tmp/extlinks3")
+ *		2. Create main file (with absolute pathname) in tmp directory ("/CWD/tmp/extlinks0")
+ *		3. Create external link to target file without absolute path ("extlinks3")
+ *		Should be able to access the target file via the main file's
+ *		absolute pathname ("/CWD/tmp")
+ *		
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb 19, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_abs_mainpath(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+    		filename3[NAME_BUF_SIZE],
+    		tmpname[NAME_BUF_SIZE],
+    		cwdpath[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via main file's absolute path (w/new group format)")
+    else
+        TESTING("external links via main file's absolute path")
+
+    /* set up name for external linked target file: "extlinks3" */
+    h5_fixname(FILENAME[18], fapl, filename2, sizeof filename2);
+    /* set up name for target file: "tmp/extlinks3" */
+    h5_fixname(FILENAME[19], fapl, filename3, sizeof filename3); 
+
+    /* create tmp directory and get current working directory path */
+    if ((HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST) || (HDgetcwd(cwdpath, NAME_BUF_SIZE)==NULL))
+        TEST_ERROR
+
+     /* set up name for main file: "/CWD/tmp/extlinks0" */
+    HDstrcpy(tmpname, cwdpath);
+    HDstrcat(tmpname, "/");
+    HDstrcat(tmpname, FILENAME[13]);
+    h5_fixname(tmpname, fapl, filename1, sizeof filename1);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename3, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    /* should be able to find the target file from absolute path set for main file */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in tmp directory.");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_abs_mainpath() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_rel_mainpath: test 4
+ *
+ * Purpose: 	1. Create target file in tmp directory ("tmp/extlinks4")
+ * Purpose:     2. Create main file (with relative pathname) in tmp directory ("tmp/extlinks0")
+ *		3. Create external link to target file without the absolute pathname ("extlinks4")
+ *		Should be able to access the target file via the main file's
+ *		CWD+relative path ("/CWD/tmp")
+ *		
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb 19, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_rel_mainpath(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+    		filename3[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via main file's CWD + relative path(w/new group format)")
+    else
+        TESTING("external links via main file's CWD + relative path")
+
+    /* set up name for external linked target file: "extlinks4" */
+    h5_fixname(FILENAME[20], fapl, filename2, sizeof filename2);
+
+    if (HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST)
+        TEST_ERROR
+
+     /* set up name for main file: "tmp/extlinks0" */
+    h5_fixname(FILENAME[13], fapl, filename1, sizeof filename1);
+    /* set up name for target file: "tmp/extlinks4" */
+    h5_fixname(FILENAME[21], fapl, filename3, sizeof filename3);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename3, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    /* should be able to find the target file from the main file's relative pathname */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in current working directory");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_rel_mainpath() */
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_cwd: test 5
+ *
+ * Purpose:     1. Create main file (with absolute path) in tmp directory ("/CWD/tmp/extlinks0")
+ * 		2. Create target file in current working directory ("extlinks5")
+ *		3. Create external link to target file (without the absolute path) ("extlinks5")
+ *		Should be able to access the target file in the current working directory
+ *		
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb 19, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_cwd(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+		tmpname[NAME_BUF_SIZE],
+                cwdpath[NAME_BUF_SIZE];
+
+
+    if(new_format)
+        TESTING("external links via current working directory(w/new group format)")
+    else
+        TESTING("external links via current working directory")
+
+    /* set up name for external linked target file: "extlinks5"  */
+    /* set up name for target file: "extlinks5" */
+    h5_fixname(FILENAME[22], fapl, filename2, sizeof filename2);
+
+    if ((HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST) || (HDgetcwd(cwdpath, NAME_BUF_SIZE)==NULL))
+        TEST_ERROR
+ 
+    /* set up name for main file: "/CWD/tmp/extlinks0"  */
+    HDstrcpy(tmpname, cwdpath);
+    HDstrcat(tmpname, "/");
+    HDstrcat(tmpname, FILENAME[13]);
+    h5_fixname(tmpname, fapl, filename1, sizeof filename1);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename2, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    /* should be able to find the target file from the current working directory */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in current working directory");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_cwd() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_abstar: test 6
+ *
+ * Purpose:     1. Create target file in tmp directory (with absolute path) ("tmp/extlinks6")
+ *		2. Create main file in current directory ("extlinks0")
+ *		3. Create external link to target file (with absolute path) ("/CWD/tmp/extlinks6")
+ *		Should be able to access the target file (with absolute path) directly 
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb. 20, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_abstar(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+    		filename3[NAME_BUF_SIZE],
+		tmpname[NAME_BUF_SIZE],
+                cwdpath[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via target's absolute path (w/new group format)")
+    else
+        TESTING("external links via target's absolute path")
+
+    /* set up name for main file: "extlinks0" */
+    h5_fixname(FILENAME[12], fapl, filename1, sizeof filename1);
+
+     /* create tmp directory and get current working directory path */
+    if ((HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST) || (HDgetcwd(cwdpath, NAME_BUF_SIZE)==NULL))
+        TEST_ERROR 
+    
+    /* set up name for external linked target file: "/CWD/tmp/extlinks6" */
+    HDstrcpy(tmpname, cwdpath);
+    HDstrcat(tmpname, "/");
+    HDstrcat(tmpname, FILENAME[23]);
+    h5_fixname(tmpname, fapl, filename2, sizeof filename2);
+
+    /* set up name for target file: "tmp/extlinks6" */
+    h5_fixname(FILENAME[23], fapl, filename3, sizeof filename3);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename3, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    /* should be able to find the target file with abolute path */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in tmp directory.");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_abstar() */
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_abstar_cur: test 7
+ *
+ * Purpose:     1. Create target file in current working directory "extlinks7"
+ *		2. Create main file in current working directory "extlinks0"
+ *		3. Create external link to target file (with absolute path
+ *		   that does not exist in that directory) ("/CWD/tmp/extlinks7")
+ *		Should be able to access the target file via the main file's CWD.
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb. 20, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_abstar_cur(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+    		filename3[NAME_BUF_SIZE],
+    		tmpname[NAME_BUF_SIZE],
+    		cwdpath[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via main file's CWD (w/new group format)")
+    else
+        TESTING("external links via main file's CWD")
+
+    /* set up name for main file: "extlinks0" */
+    h5_fixname(FILENAME[12], fapl, filename1, sizeof filename1);
+
+    /* set up name for target file name: "extlinks7" */
+    h5_fixname(FILENAME[24], fapl, filename3, sizeof filename3);
+
+    /* create tmp directory and get current working directory path */
+    if ((HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST) || (HDgetcwd(cwdpath, NAME_BUF_SIZE)==NULL))
+        TEST_ERROR
+
+     /* set up name for external linked target file: "/CWD/tmp/extlinks7" */
+    HDstrcpy(tmpname, cwdpath);
+    HDstrcat(tmpname, "/");
+    HDstrcat(tmpname, FILENAME[25]);
+    h5_fixname(tmpname, fapl, filename2, sizeof filename2);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename3, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    /* should be able to find the target file from main file's current working directory */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in current working directory.");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_abstar_cur() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_reltar: test 8
+ *
+ * Purpose:     1. Create target file in tmp directory ("tmp/extlinks8")
+ *		2. Create main file in current working directory ("extlinks0")
+ *		3. Create external link to target file with relative path ("tmp/extlinks8")
+ *		Should be able to access the target file via the main file's 
+ *		relative pathname (CWD + relative path of targetfile: "/CWD/tmp/extlinks8")
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb. 20, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_reltar(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via main file's CWD + target's relative path(w/new group format)")
+    else
+        TESTING("external links via main file's CWD + target's relative path")
+
+    /* set up name for main file: "extlinks0" */
+    h5_fixname(FILENAME[12], fapl, filename1, sizeof filename1);
+
+    /* create tmp directory */
+    if (HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST)
+        TEST_ERROR
+
+    /* set up name for target file name: "tmp/extlinks8" */
+    /* set up name for external linked target file: "tmp/extlinks8" */
+    h5_fixname(FILENAME[26], fapl, filename2, sizeof filename2);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename2, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    /* 
+     * Should be able to find the target file from:
+     * main file's current working directory + pathname of external linked targetfile 
+     */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in tmp directory.");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_reltar() */
+
+/*-------------------------------------------------------------------------
+ * Function:    external_link_chdir: test 9
+ *
+ * Purpose:     1. Create target file in tmp directory ("tmp/extlinks9")
+ *		2. Create main file in current working directory ("extlinks0")
+ *		3. chdir "tmp"
+ *		3. Create external link to target file ("extlinks9")
+ *		Should be able to access the target file in current working directory
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Vailin Choi
+ *              Feb. 20, 2008
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_link_chdir(hid_t fapl, hbool_t new_format)
+{
+    hid_t	fid = (-1);     		/* File ID */
+    hid_t	gid = (-1);	                /* Group IDs */
+    char	filename1[NAME_BUF_SIZE],
+    		filename2[NAME_BUF_SIZE],
+    		filename3[NAME_BUF_SIZE];
+
+    if(new_format)
+        TESTING("external links via chdir and found in current working directory (w/new group format)")
+    else
+        TESTING("external links via chdir and found in current working directory")
+
+    /* set up name for main file: "extlinks0" */
+    h5_fixname(FILENAME[12], fapl, filename1, sizeof filename1);
+    /* set up name for external linked target file ("extlinks9") */
+    h5_fixname(FILENAME[27], fapl, filename2, sizeof filename2);
+
+    /* create tmp directory */
+    if (HDmkdir(TMPDIR, (mode_t)0755) < 0 && errno != EEXIST)
+        TEST_ERROR
+
+    /* set up name for target file name ("tmp/extlinks9") */
+    h5_fixname(FILENAME[28], fapl, filename3, sizeof filename3);
+
+    /* Create the target file */
+    if((fid=H5Fcreate(filename3, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if((gid=H5Gcreate2(fid, "A", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+
+    /* closing for target file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+
+    /* Create the main file */
+    if((fid=H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+
+    /* Create external link to target file */
+    if(H5Lcreate_external(filename2, "/A", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+
+    if (HDchdir(TMPDIR) < 0) TEST_ERROR
+
+    /* Open object through external link */
+    H5E_BEGIN_TRY {
+        gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT);
+    } H5E_END_TRY;
+
+    if (HDchdir("..") < 0) TEST_ERROR
+    
+    /* 
+     * Should be able to find the target file from:
+     * main file's current working directory + pathname of external linked targetfile
+     */
+    if (gid < 0) {
+	H5_FAILED();
+	puts("    Should have found the file in tmp directory.");
+	goto error;
+    }
+
+    /* closing for main file */
+    if(H5Gclose(gid) < 0) TEST_ERROR
+    if(H5Fclose(fid) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+	H5Gclose (gid);
+	H5Fclose (fid);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_link_chdir() */
 
 /*-------------------------------------------------------------------------
  * Function:    external_link_recursive
@@ -5284,7 +6145,7 @@ linkinfo(hid_t fapl, hbool_t new_format)
  *-------------------------------------------------------------------------
  */
 static int
-check_all_closed(hid_t fapl, hbool_t new_format)
+check_all_closed(hid_t fapl, hbool_t new_format, int stopat)
 {
     hid_t fid=-1;
     char filename[NAME_BUF_SIZE];
@@ -5300,7 +6161,7 @@ check_all_closed(hid_t fapl, hbool_t new_format)
      * To check this, try to create every file used in this test.  If
      * a file is already open, creating it will fail.
      */
-    for(x=0; FILENAME[x] != NULL; x++)
+    for(x=0; FILENAME[x] != NULL && x < stopat; x++)
     {
         h5_fixname(FILENAME[x], fapl, filename, sizeof filename);
 
@@ -10225,6 +11086,8 @@ main(void)
                 my_fapl = fapl;
 
             /* General tests... (on both old & new format groups */
+
+
             nerrors += mklinks(my_fapl, new_format) < 0 ? 1 : 0;
             nerrors += cklinks(my_fapl, new_format) < 0 ? 1 : 0;
             nerrors += new_links(my_fapl, new_format) < 0 ? 1 : 0;
@@ -10263,6 +11126,17 @@ main(void)
             nerrors += external_link_endian(my_fapl, new_format) < 0 ? 1 : 0;
             nerrors += external_link_strong(my_fapl, new_format) < 0 ? 1 : 0;
 
+	    /* tests for external link */
+            nerrors += external_link_env(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_prefix(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_abs_mainpath(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_rel_mainpath(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_cwd(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_abstar(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_abstar_cur(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_reltar(my_fapl, new_format) < 0 ? 1 : 0;
+            nerrors += external_link_chdir(my_fapl, new_format) < 0 ? 1 : 0;
+
             /* These tests assume that external links are a form of UD links,
              * so assume that everything that passed for external links
              * above has already been tested for UD links.
@@ -10284,7 +11158,8 @@ main(void)
             nerrors += obj_visit_by_name(my_fapl, new_format) < 0 ? 1 : 0;
 
             /* Keep this test last, it's testing files that are used above */
-            nerrors += check_all_closed(my_fapl, new_format) < 0 ? 1 : 0;
+	    /* do not do this for files used by external link tests */
+            nerrors += check_all_closed(my_fapl, new_format, EXTSTOP) < 0 ? 1 : 0;
         } /* end for */
 
         /* New group revision feature tests */
@@ -10324,6 +11199,8 @@ main(void)
 	}
 	printf("All link tests passed.\n");
 	h5_cleanup(FILENAME, fapl);
+	/* clean up tmp directory created by external link tests */
+	HDrmdir(TMPDIR);
     }
     else
         puts("All link tests skipped - Incompatible with current Virtual File Driver");