[svn-r16281] Purpose: Add functions to allow more flexible traversal of external links.

Description: Added H5Pset/get_elink_cb to allow the user to specify a callback
function to be called whenever an external link is traversed.  Added
H5Pset/get_elink_acc_flags to allow the user to specify the file access flags
to use to open the target file of an external link.  All these properties are set on a LAPL.

Tested: jam, linew, smirom (h5committest)

15 files changed, 606 insertions, 26 deletions

diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index bfb30f8..b2a5bee 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -51,12 +51,18 @@ New Features
 
     Library:
     --------
+    - Added H5Pset_elink_cb and H5Pget_elink_cb functions to support a
+      user-defined callback function for external link traversal.
+      (NAF - 2009/01/08)
+    - Added H5Pset_elink_acc_flags and H5Pget_elink_acc_flags functions to
+      allow the user to specify the file access flags used to open the target
+      file of an external link. (NAF - 2009/01/08)
     - Added H5Pset_chunk_cache() and H5Pget_chunk_cache() functions to allow
-        individual rdcc configuration for each dataset.  Added
-        H5Dget_access_plist() function to retrieve a dataset access property
-        list form a dataset. (NAF - 2008/11/12)
+      individual rdcc configuration for each dataset.  Added
+      H5Dget_access_plist() function to retrieve a dataset access property
+      list from a dataset. (NAF - 2008/11/12)
     - Added H5Iis_valid() function to check if an id is valid without producing
-        an error message. (NAF - 2008/11/5)
+      an error message. (NAF - 2008/11/5)
     - Added two new public routines: H5Pget_elink_fapl() and
       H5Pset_elink_fapl(). (see bug #1247) (VC - 2008/10/13)
     - Improved free space tracking in file to be faster. (QAK - 2008/10/06)
diff --git a/src/H5Fprivate.h b/src/H5Fprivate.h
index fb28c4e..e717b99 100644
--- a/src/H5Fprivate.h
+++ b/src/H5Fprivate.h
@@ -259,6 +259,7 @@ typedef struct H5F_blk_aggr_t H5F_blk_aggr_t;
 #define H5F_GC_REF(F)           ((F)->shared->gc_ref)
 #define H5F_USE_LATEST_FORMAT(F) ((F)->shared->latest_format)
 #define H5F_EXTPATH(F)          ((F)->extpath)
+#define H5F_NAME(F)             ((F)->name)
 #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_HAS_FEATURE(F,FL)   ((F)->shared->lf->feature_flags & (FL))
@@ -280,6 +281,7 @@ typedef struct H5F_blk_aggr_t H5F_blk_aggr_t;
 #define H5F_GC_REF(F)           (H5F_gc_ref(F))
 #define H5F_USE_LATEST_FORMAT(F) (H5F_use_latest_format(F))
 #define H5F_EXTPATH(F)          (H5F_get_extpath(F))
+#define H5F_NAME(F)             (H5F_get_name(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_HAS_FEATURE(F,FL)   (H5F_has_feature(F,FL))
@@ -466,6 +468,7 @@ H5_DLL unsigned H5F_decr_nopen_objs(H5F_t *f);
 H5_DLL unsigned H5F_get_intent(const H5F_t *f);
 H5_DLL hid_t H5F_get_access_plist(H5F_t *f, hbool_t app_ref);
 H5_DLL char *H5F_get_extpath(const H5F_t *f);
+H5_DLL char *H5F_get_name(const H5F_t *f);
 H5_DLL hid_t H5F_get_id(H5F_t *file, hbool_t app_ref);
 H5_DLL size_t H5F_get_obj_count(const H5F_t *f, unsigned types, hbool_t app_ref);
 H5_DLL size_t H5F_get_obj_ids(const H5F_t *f, unsigned types, size_t max_objs, hid_t *obj_id_list, hbool_t app_ref);
diff --git a/src/H5Fpublic.h b/src/H5Fpublic.h
index 312d92e..287e9b5 100644
--- a/src/H5Fpublic.h
+++ b/src/H5Fpublic.h
@@ -50,6 +50,10 @@
 #define H5F_ACC_DEBUG	(H5CHECK 0x0008u)	/*print debug info	     */
 #define H5F_ACC_CREAT	(H5CHECK 0x0010u)	/*create non-existing files  */
 
+/* Value passed to H5Pset_elink_acc_flags to cause flags to be taken from the
+ * parent file. */
+#define H5F_ACC_DEFAULT (H5CHECK 0xffffu)	/*ignore setting on lapl     */
+
 /* Flags for H5Fget_obj_count() & H5Fget_obj_ids() calls */
 #define H5F_OBJ_FILE	(0x0001u)       /* File objects */
 #define H5F_OBJ_DATASET	(0x0002u)       /* Dataset objects */
diff --git a/src/H5Fquery.c b/src/H5Fquery.c
index 550a507..275061d 100644
--- a/src/H5Fquery.c
+++ b/src/H5Fquery.c
@@ -130,6 +130,32 @@ H5F_get_extpath(const H5F_t *f)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5F_get_name
+ *
+ * Purpose:	Retrieve the name of a file.
+ *
+ * Return:	Success:	The name of the file.
+ *
+ * 		Failure:	? (should not happen)
+ *
+ * Programmer:	Neil Fortner
+ *		December 15 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+char *
+H5F_get_name(const H5F_t *f)
+{
+    /* Use FUNC_ENTER_NOAPI_NOINIT_NOFUNC here to avoid performance issues */
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5F_get_name)
+
+    HDassert(f);
+
+    FUNC_LEAVE_NOAPI(f->name)
+} /* end H5F_get_name() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5F_get_fcpl
  *
  * Purpose:	Retrieve the value of a file's FCPL.
diff --git a/src/H5Glink.c b/src/H5Glink.c
index 9527521..7051453 100644
--- a/src/H5Glink.c
+++ b/src/H5Glink.c
@@ -41,6 +41,7 @@
 #include "H5Iprivate.h"         /* IDs                                  */
 #include "H5Lprivate.h"		/* Links                                */
 #include "H5MMprivate.h"	/* Memory management			*/
+#include "H5Ppublic.h"		/* Property Lists                       */
 
 
 /****************/
diff --git a/src/H5Gnode.c b/src/H5Gnode.c
index 9468302..6b16544 100644
--- a/src/H5Gnode.c
+++ b/src/H5Gnode.c
@@ -39,6 +39,7 @@
 #include "H5HLprivate.h"	/* Local Heaps				*/
 #include "H5MFprivate.h"	/* File memory management		*/
 #include "H5MMprivate.h"	/* Memory management			*/
+#include "H5Ppublic.h"		/* Property Lists                       */
 
 /* Private typedefs */
 
diff --git a/src/H5Lexternal.c b/src/H5Lexternal.c
index 46ed467..2c6b3a3 100644
--- a/src/H5Lexternal.c
+++ b/src/H5Lexternal.c
@@ -197,6 +197,9 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
     const char  *obj_name;              /* Name external link's object */
     size_t      fname_len;              /* Length of external link file name */
     unsigned    intent;                 /* File access permissions */
+    H5L_elink_cb_t cb_info;             /* Callback info struct */
+    const char  *parent_file_name = NULL; /* Parent file name */
+    const char  *parent_group_name = NULL; /* Parent group name */
     hid_t       fapl_id = -1;           /* File access property list for external link's file */
     hid_t       ext_obj = -1;           /* ID for external link's object */
     hid_t       ret_value;              /* Return value */
@@ -237,15 +240,68 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
     if(H5G_loc(cur_group, &loc) < 0)
         HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't get object location")
 
-    /* get the file access mode flags for the parent file */
-    intent = H5F_INTENT(loc.oloc->file);
+    /* get the access flags set for lapl_id if any */
+    if(H5P_get(plist, H5L_ACS_ELINK_FLAGS_NAME, &intent) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get elink file access flags")
 
-    if ((fapl_id == H5P_DEFAULT) && ((fapl_id = H5F_get_access_plist(loc.oloc->file, FALSE)) < 0))
+    /* get the file access mode flags for the parent file, if they were not set
+     * on lapl_id */
+    if(intent == H5F_ACC_DEFAULT)
+        intent = H5F_INTENT(loc.oloc->file);
+
+    if((fapl_id == H5P_DEFAULT) && ((fapl_id = H5F_get_access_plist(loc.oloc->file, FALSE)) < 0))
 	HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "can't get parent's file access property list")
 
-    /* Set file close degree for new file to "weak" */
+    /* Get callback_info */
+    if(H5P_get(plist, H5L_ACS_ELINK_CB_NAME, &cb_info)<0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get elink callback info")
+
+    /* Get file access property list */
     if(NULL == (fa_plist = H5P_object_verify(fapl_id, H5P_FILE_ACCESS)))
 	HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Make callback if it exists */
+    if(cb_info.func) {
+        /* Get parent file name */
+        parent_file_name = H5F_NAME(loc.oloc->file);
+
+        /* Get parent group name */
+        if(loc.path->user_path_r != NULL && loc.path->obj_hidden == 0)
+            /* Use user_path_r if possible */
+            parent_group_name = H5RS_get_str(loc.path->user_path_r);
+        else {
+            /* Otherwise use H5G_get_name */
+            ssize_t group_name_len; /* Length of parent group name */
+
+            /* Get length of parent group name */
+            if((group_name_len = H5G_get_name(cur_group, NULL, (size_t) 0, lapl_id, H5AC_ind_dxpl_id)) < 0)
+                HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "unable to retrieve length of group name")
+
+            /* account for null terminator */
+            group_name_len++;
+
+            /* Copy parent group name */
+            if(NULL == (tempname = (char *) H5MM_malloc((size_t) group_name_len)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+            if(H5G_get_name(cur_group, tempname, (size_t) group_name_len, lapl_id, H5AC_ind_dxpl_id) < 0)
+                HGOTO_ERROR(H5E_LINK, H5E_CANTGET, FAIL, "unable to retrieve group name")
+            parent_group_name = tempname;
+        } /* end else */
+
+        /* Make callback */
+        if((cb_info.func)(parent_file_name, parent_group_name, file_name, obj_name,
+                &intent, fapl_id, cb_info.user_data) < 0)
+            HGOTO_ERROR(H5E_LINK, H5E_CALLBACK, FAIL, "traversal operator failed")
+
+        /* Free tempname */
+        tempname = (char *)H5MM_xfree(tempname);
+
+        /* Check access flags */
+        if((intent & H5F_ACC_TRUNC) || (intent & H5F_ACC_EXCL))
+            HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid file open flags")
+    } /* end if */
+
+    /* Set file close degree for new file to "weak" */
     if(H5P_set(fa_plist, H5F_ACS_CLOSE_DEGREE_NAME, &fc_degree) < 0)
 	HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set file close degree")
 
@@ -277,7 +333,8 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
     /* 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);
+        if ((tmp_env_prefix = H5MM_strdup(env_prefix)) == NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
 	pp = tmp_env_prefix;
 
         while ((tmp_env_prefix) && (*tmp_env_prefix)) {
@@ -290,14 +347,13 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
                 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);
+                    H5MM_free(full_name);
                 if (ext_file != NULL)
                     break;
                 H5E_clear_stack(NULL);
             }
         } /* end while */
-        if (pp)
-            H5MM_xfree(pp);
+        pp = (char *)H5MM_xfree(pp);
     }
 
     /* try searching from property list */
@@ -311,7 +367,7 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
                         H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
                 H5E_clear_stack(NULL);
             if (full_name)
-                H5MM_xfree(full_name);
+                H5MM_free(full_name);
         }
     }
 
@@ -323,7 +379,7 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
                     H5P_FILE_CREATE_DEFAULT, fapl_id, H5AC_dxpl_id)) == NULL)
             H5E_clear_stack(NULL);
         if (full_name)
-            H5MM_xfree(full_name);
+            H5MM_free(full_name);
     }
 
     /* try the relative file_name stored in tempname */
@@ -333,8 +389,7 @@ H5L_extern_traverse(const char UNUSED *link_name, hid_t cur_group,
             HGOTO_ERROR(H5E_LINK, H5E_CANTOPENFILE, FAIL, "unable to open external file")
     }
 
-    if (tempname)
-        H5MM_xfree(tempname);
+    tempname = (char *)H5MM_xfree(tempname);
 
     /* Increment the number of open objects, to hold the file open */
     H5F_incr_nopen_objs(ext_file);
@@ -367,9 +422,14 @@ done:
     if(ext_file && H5F_try_close(ext_file) < 0)
         HDONE_ERROR(H5E_LINK, H5E_CANTCLOSEFILE, FAIL, "problem closing external file")
 
-    /* Close object if it's open and something failed */
-    if(ret_value < 0 && ext_obj >= 0 && H5I_dec_ref(ext_obj, FALSE) < 0)
-        HDONE_ERROR(H5E_ATOM, H5E_CANTRELEASE, FAIL, "unable to close atom for external object")
+    if(ret_value < 0) {
+        H5MM_xfree(tempname);
+        H5MM_xfree(pp);
+
+        /* Close object if it's open and something failed */
+        if(ext_obj >= 0 && H5I_dec_ref(ext_obj, FALSE) < 0)
+            HDONE_ERROR(H5E_ATOM, H5E_CANTRELEASE, FAIL, "unable to close atom for external object")
+    } /* end if */
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5L_extern_traverse() */
diff --git a/src/H5Lprivate.h b/src/H5Lprivate.h
index cd17a87..f3079bc 100644
--- a/src/H5Lprivate.h
+++ b/src/H5Lprivate.h
@@ -39,15 +39,23 @@
 #define H5L_CRT_INTERMEDIATE_GROUP_NAME         "intermediate_group" /* Create intermediate groups flag */
 
 /* ========  Link access property names ======== */
-#define H5L_ACS_NLINKS_NAME        "max soft links"        /* Number of soft links to traverse */
-#define H5L_ACS_ELINK_PREFIX_NAME  "external link prefix"  /* External link prefix */
-#define H5L_ACS_ELINK_FAPL_NAME    "external link fapl"      /* file access property list for external link access */
+#define H5L_ACS_NLINKS_NAME        "max soft links"         /* Number of soft links to traverse */
+#define H5L_ACS_ELINK_PREFIX_NAME  "external link prefix"   /* External link prefix */
+#define H5L_ACS_ELINK_FAPL_NAME    "external link fapl"     /* file access property list for external link access */
+#define H5L_ACS_ELINK_FLAGS_NAME   "external link flags"    /* file access flags for external link traversal */
+#define H5L_ACS_ELINK_CB_NAME      "external link callback" /*  callback function for external link traversal */
 
 
 /****************************/
 /* Library Private Typedefs */
 /****************************/
 
+/* Structure for external link traversal callback property */
+typedef struct H5L_elink_cb_t {
+    H5L_elink_traverse_t      func;
+    void                      *user_data;
+} H5L_elink_cb_t;
+
 
 /*****************************/
 /* Library Private Variables */
diff --git a/src/H5Lpublic.h b/src/H5Lpublic.h
index eba09b2..620d2e9 100644
--- a/src/H5Lpublic.h
+++ b/src/H5Lpublic.h
@@ -29,7 +29,6 @@
 /* Public headers needed by this file */
 #include "H5public.h"		/* Generic Functions			*/
 #include "H5Ipublic.h"		/* IDs			  		*/
-#include "H5Ppublic.h"		/* Property lists                       */
 #include "H5Tpublic.h"		/* Datatypes				*/
 
 /*****************/
@@ -131,6 +130,12 @@ typedef struct {
 typedef herr_t (*H5L_iterate_t)(hid_t group, const char *name, const H5L_info_t *info,
     void *op_data);
 
+/* Callback for external link traversal */
+typedef herr_t (*H5L_elink_traverse_t)(const char *parent_file_name,
+    const char *parent_group_name, const char *child_file_name,
+    const char *child_object_name, unsigned *acc_flags, hid_t fapl_id,
+    void *op_data);
+
 
 /********************/
 /* Public Variables */
diff --git a/src/H5Odbg.c b/src/H5Odbg.c
index 7a49f75..8a8b783 100644
--- a/src/H5Odbg.c
+++ b/src/H5Odbg.c
@@ -37,6 +37,7 @@
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5MMprivate.h"	/* Memory management			*/
 #include "H5Opkg.h"             /* Object headers			*/
+#include "H5Ppublic.h"		/* Property Lists			*/
 
 /****************/
 /* Local Macros */
diff --git a/src/H5Plapl.c b/src/H5Plapl.c
index e7b4381..664dab2 100644
--- a/src/H5Plapl.c
+++ b/src/H5Plapl.c
@@ -62,6 +62,14 @@
 #define H5L_ACS_ELINK_FAPL_COPY        	H5P_lacc_elink_fapl_copy
 #define H5L_ACS_ELINK_FAPL_CLOSE       	H5P_lacc_elink_fapl_close
 
+/* Definitions for file access flags for external link traversal */
+#define H5L_ACS_ELINK_FLAGS_SIZE        sizeof(unsigned)
+#define H5L_ACS_ELINK_FLAGS_DEF         H5F_ACC_DEFAULT
+
+/* Definitions for callback function for external link traversal */
+#define H5L_ACS_ELINK_CB_SIZE           sizeof(H5L_elink_cb_t)
+#define H5L_ACS_ELINK_CB_DEF            {NULL,NULL}
+
 /******************/
 /* Local Typedefs */
 /******************/
@@ -142,6 +150,9 @@ H5P_lacc_reg_prop(H5P_genclass_t *pclass)
     size_t nlinks = H5L_ACS_NLINKS_DEF; 	   /* Default number of soft links to traverse */
     char *elink_prefix = H5L_ACS_ELINK_PREFIX_DEF; /* Default external link prefix string */
     hid_t def_fapl_id = H5L_ACS_ELINK_FAPL_DEF;    /* Default fapl for external link access */
+    unsigned elink_flags = H5L_ACS_ELINK_FLAGS_DEF; /* Default file access flags for external link traversal */
+    H5L_elink_cb_t elink_cb = H5L_ACS_ELINK_CB_DEF; /* Default external link traversal callback */
+
     herr_t ret_value = SUCCEED;         	   /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT(H5P_lacc_reg_prop)
@@ -160,6 +171,16 @@ H5P_lacc_reg_prop(H5P_genclass_t *pclass)
     if(H5P_register(pclass, H5L_ACS_ELINK_FAPL_NAME, H5L_ACS_ELINK_FAPL_SIZE, &def_fapl_id, NULL, NULL, NULL, H5L_ACS_ELINK_FAPL_DEL, H5L_ACS_ELINK_FAPL_COPY, NULL, H5L_ACS_ELINK_FAPL_CLOSE) < 0)
          HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
+    /* Register property for external link file access flags */
+    if(H5P_register(pclass, H5L_ACS_ELINK_FLAGS_NAME, H5L_ACS_ELINK_FLAGS_SIZE,
+             &elink_flags, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
+         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
+    /* Register property for external link file traversal callback */
+    if(H5P_register(pclass, H5L_ACS_ELINK_CB_NAME, H5L_ACS_ELINK_CB_SIZE,
+             &elink_cb, 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_lacc_reg_prop() */
@@ -634,3 +655,163 @@ done:
     FUNC_LEAVE_API(ret_value);
 } /* end H5Pget_elink_fapl() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pset_elink_acc_flags
+ *
+ * Purpose:     Sets the file access flags to be used when traversing an
+ *              external link.  This should be either H5F_ACC_RDONLY or
+ *              H5F_ACC_RDWR, or H5F_ACC_DEFAULT to unset the value.
+ *
+ * Return:  Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Tuesday, December 9, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pset_elink_acc_flags(hid_t lapl_id, unsigned flags)
+{
+    H5P_genplist_t *plist;              /* Property list pointer */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_API(H5Pset_elink_acc_flags, FAIL)
+
+    /* Check that flags are valid */
+    if((flags != H5F_ACC_RDWR) && (flags != H5F_ACC_RDONLY) && (flags != H5F_ACC_DEFAULT))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid file open flags")
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(lapl_id, H5P_LINK_ACCESS)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Set flags */
+    if(H5P_set(plist, H5L_ACS_ELINK_FLAGS_NAME, &flags) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set access flags")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pset_elink_acc_flags() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pget_elink_acc_flags
+ *
+ * Purpose:     Gets the file access flags to be used when traversing an
+ *              external link.
+ *
+ * Return:  Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Tuesday, December 9, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_elink_acc_flags(hid_t lapl_id, unsigned *flags)
+{
+    H5P_genplist_t *plist;              /* Property list pointer */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_API(H5Pget_elink_acc_flags, FAIL)
+
+    /* Get the plist structure */
+    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 flags */
+    if (flags)
+        if(H5P_get(plist, H5L_ACS_ELINK_FLAGS_NAME, flags)<0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, 0, "can't get access flags")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_elink_acc_flags() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pset_elink_cb
+ *
+ * Purpose:     Sets the file access flags to be used when traversing an
+ *              external link.  This should be either H5F_ACC_RDONLY or
+ *              H5F_ACC_RDWR.
+ *
+ * Return:  Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Tuesday, December 15, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pset_elink_cb(hid_t lapl_id, H5L_elink_traverse_t func, void *op_data)
+{
+    H5P_genplist_t  *plist;                 /* Property list pointer */
+    H5L_elink_cb_t  cb_info;                /* Callback info struct */
+    herr_t          ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_API(H5Pset_elink_cb, FAIL)
+
+    /* Check if the callback function is NULL and the user data is non-NULL.
+     * This is almost certainly an error as the user data will not be used. */
+    if(!func && op_data)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "callback is NULL while user data is not")
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(lapl_id, H5P_LINK_ACCESS)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Populate the callback info struct */
+    cb_info.func = func;
+    cb_info.user_data = op_data;
+
+    /* Set callback info */
+    if(H5P_set(plist, H5L_ACS_ELINK_CB_NAME, &cb_info) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set callback info")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pset_elink_acc_flags() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pget_elink_cb
+ *
+ * Purpose:     Gets the file access flags to be used when traversing an
+ *              external link.
+ *
+ * Return:  Non-negative on success/Negative on failure
+ *
+ * Programmer:  Neil Fortner
+ *              Tuesday, December 15, 2008
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_elink_cb(hid_t lapl_id, H5L_elink_traverse_t *func, void **op_data)
+{
+    H5P_genplist_t  *plist;                 /* Property list pointer */
+    H5L_elink_cb_t  cb_info;                /* Callback info struct */
+    herr_t          ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_API(H5Pget_elink_cb, FAIL)
+
+    /* Get the plist structure */
+    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 callback_info */
+    if(H5P_get(plist, H5L_ACS_ELINK_CB_NAME, &cb_info)<0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get callback info")
+
+    if(func)
+        *func = cb_info.func;
+
+    if(op_data)
+        *op_data = cb_info.user_data;
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_elink_cb() */
+
diff --git a/src/H5Ppublic.h b/src/H5Ppublic.h
index 498eecc..a67ea71 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -29,6 +29,7 @@
 #include "H5Fpublic.h"
 #include "H5FDpublic.h"
 #include "H5Ipublic.h"
+#include "H5Lpublic.h"
 #include "H5MMpublic.h"
 #include "H5Tpublic.h"
 #include "H5Zpublic.h"
@@ -46,9 +47,6 @@
 #define H5OPEN
 #endif  /* _H5private_H */
 
-/* Default value for all property list classes */
-#define H5P_DEFAULT     0
-
 /*
  * The library's property list classes
  */
@@ -384,6 +382,10 @@ H5_DLL herr_t H5Pset_elink_prefix(hid_t plist_id, const char *prefix);
 H5_DLL ssize_t H5Pget_elink_prefix(hid_t plist_id, char *prefix, size_t size);
 H5_DLL hid_t H5Pget_elink_fapl(hid_t lapl_id);
 H5_DLL herr_t H5Pset_elink_fapl(hid_t lapl_id, hid_t fapl_id);
+H5_DLL herr_t H5Pset_elink_acc_flags(hid_t lapl_id, unsigned flags);
+H5_DLL herr_t H5Pget_elink_acc_flags(hid_t lapl_id, unsigned *flags);
+H5_DLL herr_t H5Pset_elink_cb(hid_t lapl_id, H5L_elink_traverse_t func, void *op_data);
+H5_DLL herr_t H5Pget_elink_cb(hid_t lapl_id, H5L_elink_traverse_t *func, void **op_data);
 
 /* Object copy property list (OCPYPL) routines */
 H5_DLL herr_t H5Pset_copy_object(hid_t plist_id, unsigned crt_intmd);
diff --git a/src/H5Tdeprec.c b/src/H5Tdeprec.c
index df6238c..0314a38 100644
--- a/src/H5Tdeprec.c
+++ b/src/H5Tdeprec.c
@@ -44,6 +44,7 @@
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5FOprivate.h"	/* File objects				*/
 #include "H5Iprivate.h"		/* IDs					*/
+#include "H5Ppublic.h"		/* Property Lists			*/
 #include "H5Tpkg.h"		/* Datatypes				*/
 
 
diff --git a/src/H5public.h b/src/H5public.h
index e926473..cf9ff14 100644
--- a/src/H5public.h
+++ b/src/H5public.h
@@ -264,6 +264,9 @@ typedef signed long_long	hssize_t;
 #   error "nothing appropriate for uint64_t"
 #endif
 
+/* Default value for all property list classes */
+#define H5P_DEFAULT     0
+
 /* Common iteration orders */
 typedef enum {
     H5_ITER_UNKNOWN = -1,       /* Unknown order */
diff --git a/test/links.c b/test/links.c
index 433e9f8..cab5f6e 100644
--- a/test/links.c
+++ b/test/links.c
@@ -76,6 +76,10 @@ const char *FILENAME[] = {
     "extlinks16A",	/* 37: */ /* TESTS for H5P_set_elink_fapl */
     "extlinks16B",	/* 38: */
     "extlinks17",	/* 39: */
+    "extlinks18A",	/* 40: */
+    "extlinks18B",	/* 41: */
+    "extlinks19A",	/* 42: */
+    "extlinks19B",	/* 43: */
     NULL
 };
 
@@ -3947,6 +3951,278 @@ external_set_elink_fapl3(hbool_t new_format)
 } /* end external_set_elink_fapl3() */
 
 
+/*-------------------------------------------------------------------------
+ * Function:    external_set_elink_acc_flags
+ *
+ * Purpose:     Verify functionality of H5P_set/get_elink_acc_flags
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Neil Fortner
+ *              Jan. 5, 2009
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+external_set_elink_acc_flags(hid_t fapl, hbool_t new_format)
+{
+    hid_t       file1, file2, group, subgroup, gapl;
+    char        filename1[NAME_BUF_SIZE],
+                filename2[NAME_BUF_SIZE];
+    unsigned    flags;
+
+    if(new_format)
+        TESTING("H5Pset/get_elink_acc_flags() (w/new group format)")
+    else
+        TESTING("H5Pset/get_elink_acc_flags()")
+
+    /* Create parent and target files, and external link */
+    h5_fixname(FILENAME[40], fapl, filename1, sizeof filename1);
+    h5_fixname(FILENAME[41], fapl, filename2, sizeof filename2);
+    if ((file1 = H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if ((file2 = H5Fcreate(filename2, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if (H5Lcreate_external(filename2, "/", file1, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Close file2, leave file1 open (should be read-write) */
+    if (H5Fclose(file2) < 0) TEST_ERROR
+
+    /* Create new gapl, and set elink access flags to be H5F_ACC_RDONLY */
+    if ((gapl = H5Pcreate(H5P_GROUP_ACCESS)) < 0) TEST_ERROR
+    if (H5Pset_elink_acc_flags(gapl, H5F_ACC_RDONLY) < 0) TEST_ERROR
+
+    /* Verify "get" routine functionality */
+    if (H5Pget_elink_acc_flags(gapl, &flags) < 0) TEST_ERROR
+    if (flags != H5F_ACC_RDONLY) TEST_ERROR
+
+    /* Attempt to create a group through the external link using gapl (should fail) */
+    H5E_BEGIN_TRY {
+        group = H5Gcreate2(file1, "/ext_link/group", H5P_DEFAULT, H5P_DEFAULT, gapl);
+    } H5E_END_TRY;
+    if (group != FAIL) TEST_ERROR
+
+    /* Close file1 and reopen with read only access */
+    if (H5Fclose(file1) < 0) TEST_ERROR
+    if ((file1 = H5Fopen(filename1, H5F_ACC_RDONLY, fapl)) < 0) TEST_ERROR
+
+    /* Set elink access flags on gapl to be H5F_ACC_RDWR */
+    if (H5Pset_elink_acc_flags(gapl, H5F_ACC_RDWR) < 0) TEST_ERROR
+
+    /* Create a group through the external link using gapl (should succeed) */
+    if ((group = H5Gcreate2(file1, "/ext_link/group", H5P_DEFAULT, H5P_DEFAULT, gapl)) < 0) TEST_ERROR
+
+    /* Unset elink access flags on gapl */
+    if (H5Pset_elink_acc_flags(gapl, H5F_ACC_DEFAULT) < 0) TEST_ERROR
+
+    /* Attempt to create a group through the external link using gapl (should fail) */
+    H5E_BEGIN_TRY {
+        subgroup = H5Gcreate2(file1, "/ext_link/group/subgroup", H5P_DEFAULT, H5P_DEFAULT, gapl);
+    } H5E_END_TRY;
+    if (subgroup != FAIL) TEST_ERROR
+
+    /* Close file1 and group */
+    if (H5Gclose(group) < 0) TEST_ERROR
+    if (H5Fclose(file1) < 0) TEST_ERROR
+
+    /* Verify that H5Fcreate and H5Fopen reject H5F_ACC_DEFAULT */
+    H5E_BEGIN_TRY {
+        file1 = H5Fcreate(filename1, H5F_ACC_DEFAULT, H5P_DEFAULT, fapl);
+    } H5E_END_TRY;
+    if (file1 != FAIL) TEST_ERROR
+    H5E_BEGIN_TRY {
+        file1 = H5Fcreate(filename1, H5F_ACC_TRUNC | H5F_ACC_DEFAULT, H5P_DEFAULT, fapl);
+    } H5E_END_TRY;
+    if (file1 != FAIL) TEST_ERROR
+    H5E_BEGIN_TRY {
+        file1 = H5Fopen(filename1, H5F_ACC_DEFAULT, fapl);
+    } H5E_END_TRY;
+    if (file1 != FAIL) TEST_ERROR
+    H5E_BEGIN_TRY {
+        file1 = H5Fopen(filename1, H5F_ACC_RDWR | H5F_ACC_DEFAULT, fapl);
+    } H5E_END_TRY;
+    if (file1 != FAIL) TEST_ERROR
+
+    /* Close gapl */
+    if (H5Pclose(gapl) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+        H5Gclose(group);
+        H5Gclose(subgroup);
+        H5Fclose(file1);
+        H5Fclose(file2);
+        H5Pclose(gapl);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_set_elink_acc_flags() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    external_set_elink_cb
+ *
+ * Purpose:     Verify functionality of H5P_set/get_elink_cb
+ *
+ * Return:      Success:        0
+ *              Failure:        -1
+ *
+ * Programmer:  Neil Fortner
+ *              Jan. 5, 2009
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+typedef struct {
+    const char  *parent_file;
+    const char  *target_file;
+    hid_t       fapl;
+} set_elink_cb_t;
+
+/* Callback function */
+static herr_t
+external_set_elink_cb_cb(const char *parent_file, const char *parent_group,
+    const char *target_file, const char *target_obj, unsigned *flags,
+    hid_t fapl, void *_op_data)
+{
+    set_elink_cb_t  *op_data = (set_elink_cb_t *)_op_data;
+    hid_t           driver;
+    const void      *driver_info;
+
+    /* Codes to cause an invalid condition (and verify that an error is issued */
+    if (op_data->fapl == -1) return FAIL;
+    if (op_data->fapl == -2) {
+        *flags = H5F_ACC_DEFAULT;
+        return 0;
+    } /* end if */
+
+    /* Verify file and object names are correct */
+    if (HDstrcmp(parent_file, op_data->parent_file)) return FAIL;
+    if (HDstrcmp(parent_group, "/group1")) return FAIL;
+    if (HDstrcmp(target_file, op_data->target_file)) return FAIL;
+    if (HDstrcmp(target_obj, "/")) return FAIL;
+
+    /* Set flags to be read-write */
+    *flags = (*flags & ~H5F_ACC_RDONLY) | H5F_ACC_RDWR;
+
+    /* Copy driver info from op_data->fapl to fapl */
+    driver = H5Pget_driver(op_data->fapl);
+    driver_info = H5Pget_driver_info(op_data->fapl);
+    if (H5Pset_driver(fapl, driver, driver_info) < 0) return FAIL;
+
+    return 0;
+}
+
+/* Main test function */
+static int
+external_set_elink_cb(hid_t fapl, hbool_t new_format)
+{
+    hid_t       file1, file2, group, gapl, fam_fapl, ret_fapl;
+    set_elink_cb_t op_data,
+                *op_data_p;
+    H5L_elink_traverse_t cb;
+    char        filename1[NAME_BUF_SIZE],
+                filename2[NAME_BUF_SIZE];
+    unsigned    flags;
+
+    if(new_format)
+        TESTING("H5Pset/get_elink_cb() (w/new group format)")
+    else
+        TESTING("H5Pset/get_elink_cb()")
+
+    /* Create family fapl */
+    if ((fam_fapl = H5Pcopy(fapl)) < 0) TEST_ERROR
+    if (H5Pset_fapl_family(fam_fapl, (hsize_t) 100, fapl) < 0) TEST_ERROR
+
+    /* Create parent and target files, group, and external link */
+    h5_fixname(FILENAME[40], fapl, filename1, sizeof filename1);
+    h5_fixname(FILENAME[41], fam_fapl, filename2, sizeof filename2);
+    if ((file1 = H5Fcreate(filename1, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0) TEST_ERROR
+    if ((file2 = H5Fcreate(filename2, H5F_ACC_TRUNC, H5P_DEFAULT, fam_fapl)) < 0) TEST_ERROR
+    if ((group = H5Gcreate2(file1, "group1",H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0) TEST_ERROR
+    if (H5Lcreate_external(filename2, "/", group, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0) TEST_ERROR
+
+    /* Close files and group */
+    if (H5Fclose(file1) < 0) TEST_ERROR
+    if (H5Fclose(file2) < 0) TEST_ERROR
+    if (H5Gclose(group) < 0) TEST_ERROR
+
+    /* Build user data for callback */
+    op_data.parent_file = filename1;
+    op_data.target_file = filename2;
+    op_data.fapl = fam_fapl;
+
+    /* Create new gapl, and set elink callback */
+    if ((gapl = H5Pcreate(H5P_GROUP_ACCESS)) < 0) TEST_ERROR
+    if (H5Pset_elink_cb(gapl, external_set_elink_cb_cb, &op_data) < 0) TEST_ERROR
+
+    /* Verify "get" routine functionality */
+    if (H5Pget_elink_cb(gapl, &cb, (void **) &op_data_p) < 0) TEST_ERROR
+    if (cb != external_set_elink_cb_cb) TEST_ERROR
+    if (op_data_p != &op_data) TEST_ERROR
+
+    /* Open file1 with read only access */
+    if ((file1 = H5Fopen(filename1, H5F_ACC_RDONLY, fapl)) < 0) TEST_ERROR
+
+    /* Create a group through the external link using gapl */
+    if ((group = H5Gcreate2(file1, "/group1/ext_link/group2", H5P_DEFAULT, H5P_DEFAULT, gapl)) < 0) TEST_ERROR
+
+    /* Verify that the correct parameters have been set on file2 (somewhat
+     * redundant as the library would be unable to create the group otherwise)
+     */
+    if ((file2 = H5Iget_file_id(group)) < 0) TEST_ERROR
+    if (H5Fget_intent(file2, &flags) < 0) TEST_ERROR
+    if (!(flags & H5F_ACC_RDWR)) TEST_ERROR
+    if ((ret_fapl = H5Fget_access_plist(file2)) < 0) TEST_ERROR
+    if (H5FD_FAMILY != H5Pget_driver(ret_fapl)) TEST_ERROR
+
+    if (H5Gclose(group) < 0) TEST_ERROR
+    if (H5Fclose(file2) < 0) TEST_ERROR
+    if (H5Pclose(ret_fapl) < 0) TEST_ERROR
+    if (H5Pclose(fam_fapl) < 0) TEST_ERROR
+
+    /* Modify the user data structure to cause the callback to fail next time */
+    op_data.fapl = -1;
+
+    /* Attempt to reopen group2 (should fail) */
+    H5E_BEGIN_TRY {
+        group = H5Gopen2(file1, "/group1/ext_link/group2", gapl);
+    } H5E_END_TRY;
+    if (group != FAIL) TEST_ERROR
+
+    /* Modify the user data structure to cause the callback to return invalid flags */
+    op_data.fapl = -2;
+
+    /* Attempt to reopen group2 (should fail) */
+    H5E_BEGIN_TRY {
+        group = H5Gopen2(file1, "/group1/ext_link/group2", gapl);
+    } H5E_END_TRY;
+    if (group != FAIL) TEST_ERROR
+
+    /* Close */
+    if (H5Fclose(file1) < 0) TEST_ERROR
+    if (H5Pclose(gapl) < 0) TEST_ERROR
+
+    PASSED();
+    return 0;
+
+ error:
+    H5E_BEGIN_TRY {
+        H5Gclose(group);
+        H5Fclose(file1);
+        H5Fclose(file2);
+        H5Pclose(gapl);
+        H5Pclose(ret_fapl);
+        H5Pclose(fam_fapl);
+    } H5E_END_TRY;
+    return -1;
+} /* end external_set_elink_cb() */
+
+
 #ifdef H5_HAVE_WINDOW_PATH
 
 /*-------------------------------------------------------------------------
@@ -12342,6 +12618,8 @@ main(void)
         nerrors += external_set_elink_fapl1(my_fapl, new_format) < 0 ? 1 : 0;
         nerrors += external_set_elink_fapl2(my_fapl, new_format) < 0 ? 1 : 0;
         nerrors += external_set_elink_fapl3(new_format) < 0 ? 1 : 0;
+        nerrors += external_set_elink_acc_flags(my_fapl, new_format) < 0 ? 1 : 0;
+        nerrors += external_set_elink_cb(my_fapl, new_format) < 0 ? 1 : 0;
 
 #ifdef H5_HAVE_WINDOW_PATH
         nerrors += external_link_win1(my_fapl, new_format) < 0 ? 1 : 0;