Add an 'unwrap' VOL callback, so that connectors can unwrap an underlying

object without closing it.  (Especially needed for pass-through connectors)

8 files changed, 213 insertions, 60 deletions

diff --git a/src/H5Dvirtual.c b/src/H5Dvirtual.c
index d38df1b..e3e0aa5 100644
--- a/src/H5Dvirtual.c
+++ b/src/H5Dvirtual.c
@@ -3035,7 +3035,7 @@ H5D__virtual_refresh_source_dset(H5D_t **dset)
     /* Discard the identifier & replace the dataset */
     if(NULL == (vol_obj = (H5VL_object_t *)H5I_remove(temp_id)))
         HGOTO_ERROR(H5E_DATASET, H5E_CANTREMOVE, FAIL, "can't unregister source dataset ID")
-    if(NULL == (*dset = (H5D_t *)H5VL_object_data(vol_obj)))
+    if(NULL == (*dset = (H5D_t *)H5VL_object_unwrap(vol_obj)))
         HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't retrieve library object from VOL object")
     vol_obj->data = NULL;
 
diff --git a/src/H5I.c b/src/H5I.c
index 345c010..2edea9b 100644
--- a/src/H5I.c
+++ b/src/H5I.c
@@ -1134,7 +1134,7 @@ done:
  *
  *-------------------------------------------------------------------------
  */
-void *
+static void *
 H5I__remove_verify(hid_t id, H5I_type_t id_type)
 {
     void * ret_value = NULL;	/*return value			*/
diff --git a/src/H5VLcallback.c b/src/H5VLcallback.c
index 03828fa..b785747 100644
--- a/src/H5VLcallback.c
+++ b/src/H5VLcallback.c
@@ -740,84 +740,89 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:    H5VL_free_wrap_ctx
+ * Function:    H5VL_wrap_object
  *
- * Purpose:     Free object wrapping context for a connector
+ * Purpose:     Wrap an object with connector
  *
- * Return:      Success:    Non-negative
- *              Failure:    Negative
+ * Return:      Success:    Non-NULL
+ *              Failure:    NULL
  *
  *-------------------------------------------------------------------------
  */
-herr_t
-H5VL_free_wrap_ctx(const H5VL_class_t *connector, void *wrap_ctx)
+void *
+H5VL_wrap_object(const H5VL_class_t *connector, void *wrap_ctx, void *obj,
+    H5I_type_t obj_type)
 {
-    herr_t ret_value = SUCCEED;   /* Return value */
+    void *ret_value;            /* Return value */
 
-    FUNC_ENTER_NOAPI(FAIL)
+    FUNC_ENTER_NOAPI(NULL)
 
     /* Sanity checks */
     HDassert(connector);
+    HDassert(obj);
 
-    /* Only free wrap context, if it's non-NULL */
+    /* Only wrap object if there's a wrap context */
     if(wrap_ctx) {
-        /* Free the connector's object wrapping context */
-        if((connector->wrap_cls.free_wrap_ctx)(wrap_ctx) < 0)
-            HGOTO_ERROR(H5E_VOL, H5E_CANTRELEASE, FAIL, "connector wrap context free request failed")
+        /* Ask the connector to wrap the object */
+        if(NULL == (ret_value = (connector->wrap_cls.wrap_object)(obj, obj_type, wrap_ctx)))
+            HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "can't wrap object")
     } /* end if */
+    else
+        ret_value = obj;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5VL_free_wrap_ctx() */
+} /* end H5VL_wrap_object() */
 
 
 /*---------------------------------------------------------------------------
- * Function:    H5VLfree_wrap_ctx
+ * Function:    H5VLwrap_object
  *
- * Purpose:     Release a VOL connector's object wrapping context
+ * Purpose:     Asks a connector to wrap an underlying object.
  *
- * Return:      Success:    Non-negative
- *              Failure:    Negative
+ * Return:      Success:    Non-NULL
+ *              Failure:    NULL
  *
  *---------------------------------------------------------------------------
  */
-herr_t
-H5VLfree_wrap_ctx(void *wrap_ctx, hid_t connector_id)
+void *
+H5VLwrap_object(void *obj, H5I_type_t obj_type, hid_t connector_id, void *wrap_ctx)
 {
-    H5VL_class_t *cls;                  /* VOL connector's class struct */
-    herr_t ret_value = SUCCEED;         /* Return value */
+    H5VL_class_t *cls;          /* VOL connector's class struct */
+    void *ret_value = NULL;     /* Return value */
 
     FUNC_ENTER_API_NOINIT
-    H5TRACE2("e", "*xi", wrap_ctx, connector_id);
+    H5TRACE4("*x", "*xIti*x", obj, obj_type, connector_id, wrap_ctx);
 
     /* Check args and get class pointer */
+    if(NULL == obj)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, NULL, "invalid object")
     if(NULL == (cls = (H5VL_class_t *)H5I_object_verify(connector_id, H5I_VOL)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a VOL connector ID")
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not a VOL connector ID")
 
-    /* Release the VOL connector's object wrapper */
-    if(H5VL_free_wrap_ctx(cls, wrap_ctx) < 0)
-        HGOTO_ERROR(H5E_VOL, H5E_CANTRELEASE, FAIL, "unable to release VOL connector object wrap context")
+    /* Wrap the object */
+    if(NULL == (ret_value = H5VL_wrap_object(cls, wrap_ctx, obj, obj_type)))
+        HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "unable to wrap object")
 
 done:
     FUNC_LEAVE_API_NOINIT(ret_value)
-} /* H5VLfree_wrap_ctx() */
+} /* H5VLwrap_object */
 
 
 /*-------------------------------------------------------------------------
- * Function:    H5VL_wrap_object
+ * Function:    H5VL_unwrap_object
  *
- * Purpose:     Wrap an object with connector
+ * Purpose:     Unwrap an object from connector
  *
- * Return:      Success:    Non-negative
- *              Failure:    Negative
+ * Return:      Success:    Non-NULL
+ *              Failure:    NULL
  *
  *-------------------------------------------------------------------------
  */
 void *
-H5VL_wrap_object(const H5VL_class_t *connector, void *wrap_ctx, void *obj,
-    H5I_type_t obj_type)
+H5VL_unwrap_object(const H5VL_class_t *connector, void *obj)
 {
-    void *ret_value = SUCCEED;   /* Return value */
+    void *ret_value;            /* Return value */
 
     FUNC_ENTER_NOAPI(NULL)
 
@@ -825,24 +830,24 @@ H5VL_wrap_object(const H5VL_class_t *connector, void *wrap_ctx, void *obj,
     HDassert(connector);
     HDassert(obj);
 
-    /* Only wrap object if there's a wrap context */
-    if(wrap_ctx) {
-        /* Ask the connector to wrap the object */
-        if(NULL == (ret_value = (connector->wrap_cls.wrap_object)(obj, obj_type, wrap_ctx)))
-            HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "can't wrap object")
+    /* Only unwrap object if there's an unwrap callback */
+    if(connector->wrap_cls.wrap_object) {
+        /* Ask the connector to unwrap the object */
+        if(NULL == (ret_value = (connector->wrap_cls.unwrap_object)(obj)))
+            HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "can't unwrap object")
     } /* end if */
     else
         ret_value = obj;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5VL_wrap_object() */
+} /* end H5VL_unwrap_object() */
 
 
 /*---------------------------------------------------------------------------
- * Function:    H5VLwrap_object
+ * Function:    H5VLunwrap_object
  *
- * Purpose:     Asks a connector to wrap an underlying object.
+ * Purpose:     Unwrap an object from connector
  *
  * Return:      Success:    Non-NULL
  *              Failure:    NULL
@@ -850,13 +855,13 @@ done:
  *---------------------------------------------------------------------------
  */
 void *
-H5VLwrap_object(void *obj, H5I_type_t obj_type, hid_t connector_id, void *wrap_ctx)
+H5VLunwrap_object(void *obj, hid_t connector_id)
 {
     H5VL_class_t *cls;          /* VOL connector's class struct */
     void *ret_value = NULL;     /* Return value */
 
     FUNC_ENTER_API_NOINIT
-    H5TRACE4("*x", "*xIti*x", obj, obj_type, connector_id, wrap_ctx);
+    H5TRACE2("*x", "*xi", obj, connector_id);
 
     /* Check args and get class pointer */
     if(NULL == obj)
@@ -864,13 +869,77 @@ H5VLwrap_object(void *obj, H5I_type_t obj_type, hid_t connector_id, void *wrap_c
     if(NULL == (cls = (H5VL_class_t *)H5I_object_verify(connector_id, H5I_VOL)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not a VOL connector ID")
 
-    /* Wrap the object */
-    if(NULL == (ret_value = H5VL_wrap_object(cls, wrap_ctx, obj, obj_type)))
-        HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "unable to wrap object")
+    /* Unwrap the object */
+    if(NULL == (ret_value = H5VL_unwrap_object(cls, obj)))
+        HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "unable to unwrap object")
 
 done:
     FUNC_LEAVE_API_NOINIT(ret_value)
-} /* H5VLwrap_object */
+} /* H5VLunwrap_object */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5VL_free_wrap_ctx
+ *
+ * Purpose:     Free object wrapping context for a connector
+ *
+ * Return:      Success:    Non-negative
+ *              Failure:    Negative
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5VL_free_wrap_ctx(const H5VL_class_t *connector, void *wrap_ctx)
+{
+    herr_t ret_value = SUCCEED;   /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity checks */
+    HDassert(connector);
+
+    /* Only free wrap context, if it's non-NULL */
+    if(wrap_ctx) {
+        /* Free the connector's object wrapping context */
+        if((connector->wrap_cls.free_wrap_ctx)(wrap_ctx) < 0)
+            HGOTO_ERROR(H5E_VOL, H5E_CANTRELEASE, FAIL, "connector wrap context free request failed")
+    } /* end if */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5VL_free_wrap_ctx() */
+
+
+/*---------------------------------------------------------------------------
+ * Function:    H5VLfree_wrap_ctx
+ *
+ * Purpose:     Release a VOL connector's object wrapping context
+ *
+ * Return:      Success:    Non-negative
+ *              Failure:    Negative
+ *
+ *---------------------------------------------------------------------------
+ */
+herr_t
+H5VLfree_wrap_ctx(void *wrap_ctx, hid_t connector_id)
+{
+    H5VL_class_t *cls;                  /* VOL connector's class struct */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_API_NOINIT
+    H5TRACE2("e", "*xi", wrap_ctx, connector_id);
+
+    /* Check args and get class pointer */
+    if(NULL == (cls = (H5VL_class_t *)H5I_object_verify(connector_id, H5I_VOL)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a VOL connector ID")
+
+    /* Release the VOL connector's object wrapper */
+    if(H5VL_free_wrap_ctx(cls, wrap_ctx) < 0)
+        HGOTO_ERROR(H5E_VOL, H5E_CANTRELEASE, FAIL, "unable to release VOL connector object wrap context")
+
+done:
+    FUNC_LEAVE_API_NOINIT(ret_value)
+} /* H5VLfree_wrap_ctx() */
 
 
 /*-------------------------------------------------------------------------
diff --git a/src/H5VLint.c b/src/H5VLint.c
index fda4443..1b735f5 100644
--- a/src/H5VLint.c
+++ b/src/H5VLint.c
@@ -1358,6 +1358,32 @@ H5VL_object_data(const H5VL_object_t *vol_obj)
 
 
 /*-------------------------------------------------------------------------
+ * Function:    H5VL_object_unwrap
+ *
+ * Purpose:     Correctly unwrap the 'data' field for a VOL object (H5VL_object),
+ *              even for nested / stacked VOL connectors.
+ *
+ * Return:      Success:        Object pointer
+ *              Failure:        NULL
+ *
+ *-------------------------------------------------------------------------
+ */
+void *
+H5VL_object_unwrap(const H5VL_object_t *vol_obj)
+{
+    void *ret_value = NULL;
+
+    FUNC_ENTER_NOAPI(NULL)
+
+    if(NULL == (ret_value = H5VL_unwrap_object(vol_obj->connector->cls, vol_obj->data)))
+        HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "can't unwrap object")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5VL_object_unwrap() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5VL__object
  *
  * Purpose:     Internal function to return the VOL object pointer associated
@@ -1444,7 +1470,7 @@ H5VL_object(hid_t id)
 
     /* Get the underlying object */
     if(NULL == (ret_value = H5VL__object(id, H5I_get_type(id))))
-        HGOTO_ERROR(H5E_ARGS, H5E_CANTGET, NULL, "can't retrieve object for ID")
+        HGOTO_ERROR(H5E_VOL, H5E_CANTGET, NULL, "can't retrieve object for ID")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5VLnative.c b/src/H5VLnative.c
index f4f3b5f..7848c5d 100644
--- a/src/H5VLnative.c
+++ b/src/H5VLnative.c
@@ -50,6 +50,7 @@ static H5VL_class_t H5VL_native_cls_g = {
         NULL,                                       /* get_object   */
         NULL,                                       /* get_wrap_ctx */
         NULL,                                       /* wrap_object  */
+        NULL,                                       /* unwrap_object */
         NULL                                        /* free_wrap_ctx */
     },
     {   /* attribute_cls */
diff --git a/src/H5VLpassthru.c b/src/H5VLpassthru.c
index a4c85cc..85a9346 100644
--- a/src/H5VLpassthru.c
+++ b/src/H5VLpassthru.c
@@ -98,9 +98,10 @@ static herr_t H5VL_pass_through_str_to_info(const char *str, void **info);
 /* VOL object wrap / retrieval callbacks */
 static void *H5VL_pass_through_get_object(const void *obj);
 static herr_t H5VL_pass_through_get_wrap_ctx(const void *obj, void **wrap_ctx);
-static herr_t H5VL_pass_through_free_wrap_ctx(void *obj);
 static void *H5VL_pass_through_wrap_object(void *obj, H5I_type_t obj_type,
     void *wrap_ctx);
+static void *H5VL_pass_through_unwrap_object(void *obj);
+static herr_t H5VL_pass_through_free_wrap_ctx(void *obj);
 
 /* Attribute callbacks */
 static void *H5VL_pass_through_attr_create(void *obj, const H5VL_loc_params_t *loc_params, const char *name, hid_t acpl_id, hid_t aapl_id, hid_t dxpl_id, void **req);
@@ -194,6 +195,7 @@ static const H5VL_class_t H5VL_pass_through_g = {
         H5VL_pass_through_get_object,               /* get_object   */
         H5VL_pass_through_get_wrap_ctx,             /* get_wrap_ctx */
         H5VL_pass_through_wrap_object,              /* wrap_object  */
+        H5VL_pass_through_unwrap_object,            /* unwrap_object */
         H5VL_pass_through_free_wrap_ctx,            /* free_wrap_ctx */
     },
     {                                           /* attribute_cls */
@@ -683,8 +685,8 @@ H5VL_pass_through_get_wrap_ctx(const void *obj, void **wrap_ctx)
  *
  * Purpose:     Use a "wrapper context" to wrap a data object
  *
- * Return:      Success:    0
- *              Failure:    -1
+ * Return:      Success:    Pointer to wrapped object
+ *              Failure:    NULL
  *
  *---------------------------------------------------------------------------
  */
@@ -711,6 +713,37 @@ H5VL_pass_through_wrap_object(void *obj, H5I_type_t obj_type, void *_wrap_ctx)
 
 
 /*---------------------------------------------------------------------------
+ * Function:    H5VL_pass_through_unwrap_object
+ *
+ * Purpose:     Unwrap a wrapped object, discarding the wrapper, but returning
+ *		underlying object.
+ *
+ * Return:      Success:    Pointer to unwrapped object
+ *              Failure:    NULL
+ *
+ *---------------------------------------------------------------------------
+ */
+static void *
+H5VL_pass_through_unwrap_object(void *obj)
+{
+    H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
+    void *under;
+
+#ifdef ENABLE_PASSTHRU_LOGGING
+    printf("------- PASS THROUGH VOL UNWRAP Object\n");
+#endif
+
+    /* Unrap the object with the underlying VOL */
+    under = H5VLunwrap_object(o->under_object, o->under_vol_id);
+
+    if(under)
+        H5VL_pass_through_free_obj(o);
+
+    return under;
+} /* end H5VL_pass_through_unwrap_object() */
+
+
+/*---------------------------------------------------------------------------
  * Function:    H5VL_pass_through_free_wrap_ctx
  *
  * Purpose:     Release a "wrapper context" for an object
@@ -1194,17 +1227,22 @@ H5VL_pass_through_dataset_specific(void *obj, H5VL_dataset_specific_t specific_t
     hid_t dxpl_id, void **req, va_list arguments)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
+    hid_t under_vol_id;
     herr_t ret_value;
 
 #ifdef ENABLE_PASSTHRU_LOGGING 
     printf("------- PASS THROUGH VOL H5Dspecific\n");
 #endif
 
+    // Save copy of underlying VOL connector ID and prov helper, in case of
+    // refresh destroying the current object
+    under_vol_id = o->under_vol_id;
+
     ret_value = H5VLdataset_specific(o->under_object, o->under_vol_id, specific_type, dxpl_id, req, arguments);
 
     /* Check for async request */
     if(req && *req)
-        *req = H5VL_pass_through_new_obj(*req, o->under_vol_id);
+        *req = H5VL_pass_through_new_obj(*req, under_vol_id);
 
     return ret_value;
 } /* end H5VL_pass_through_dataset_specific() */
@@ -1396,17 +1434,22 @@ H5VL_pass_through_datatype_specific(void *obj, H5VL_datatype_specific_t specific
     hid_t dxpl_id, void **req, va_list arguments)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
+    hid_t under_vol_id;
     herr_t ret_value;
 
 #ifdef ENABLE_PASSTHRU_LOGGING 
     printf("------- PASS THROUGH VOL DATATYPE Specific\n");
 #endif
 
+    // Save copy of underlying VOL connector ID and prov helper, in case of
+    // refresh destroying the current object
+    under_vol_id = o->under_vol_id;
+
     ret_value = H5VLdatatype_specific(o->under_object, o->under_vol_id, specific_type, dxpl_id, req, arguments);
 
     /* Check for async request */
     if(req && *req)
-        *req = H5VL_pass_through_new_obj(*req, o->under_vol_id);
+        *req = H5VL_pass_through_new_obj(*req, under_vol_id);
 
     return ret_value;
 } /* end H5VL_pass_through_datatype_specific() */
@@ -1936,17 +1979,22 @@ H5VL_pass_through_group_specific(void *obj, H5VL_group_specific_t specific_type,
     hid_t dxpl_id, void **req, va_list arguments)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
+    hid_t under_vol_id;
     herr_t ret_value;
 
 #ifdef ENABLE_PASSTHRU_LOGGING 
     printf("------- PASS THROUGH VOL GROUP Specific\n");
 #endif
 
+    // Save copy of underlying VOL connector ID and prov helper, in case of
+    // refresh destroying the current object
+    under_vol_id = o->under_vol_id;
+
     ret_value = H5VLgroup_specific(o->under_object, o->under_vol_id, specific_type, dxpl_id, req, arguments);
 
     /* Check for async request */
     if(req && *req)
-        *req = H5VL_pass_through_new_obj(*req, o->under_vol_id);
+        *req = H5VL_pass_through_new_obj(*req, under_vol_id);
 
     return ret_value;
 } /* end H5VL_pass_through_group_specific() */
@@ -2372,17 +2420,22 @@ H5VL_pass_through_object_specific(void *obj, const H5VL_loc_params_t *loc_params
     va_list arguments)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
+    hid_t under_vol_id;
     herr_t ret_value;
 
 #ifdef ENABLE_PASSTHRU_LOGGING 
     printf("------- PASS THROUGH VOL OBJECT Specific\n");
 #endif
 
+    // Save copy of underlying VOL connector ID and prov helper, in case of
+    // refresh destroying the current object
+    under_vol_id = o->under_vol_id;
+
     ret_value = H5VLobject_specific(o->under_object, loc_params, o->under_vol_id, specific_type, dxpl_id, req, arguments);
 
     /* Check for async request */
     if(req && *req)
-        *req = H5VL_pass_through_new_obj(*req, o->under_vol_id);
+        *req = H5VL_pass_through_new_obj(*req, under_vol_id);
 
     return ret_value;
 } /* end H5VL_pass_through_object_specific() */
diff --git a/src/H5VLprivate.h b/src/H5VLprivate.h
index dc4f9c5..04cc982 100644
--- a/src/H5VLprivate.h
+++ b/src/H5VLprivate.h
@@ -86,6 +86,7 @@ H5_DLL hid_t H5VL_register_connector(const void *cls, hbool_t app_ref, hid_t vip
 /* Functions that manipulate VOL objects */
 H5_DLL void *H5VL_object(hid_t id);
 H5_DLL void *H5VL_object_data(const H5VL_object_t *vol_obj);
+H5_DLL void *H5VL_object_unwrap(const H5VL_object_t *vol_obj);
 H5_DLL void *H5VL_object_verify(hid_t id, H5I_type_t obj_type);
 H5_DLL H5VL_object_t *H5VL_vol_object(hid_t id);
 H5_DLL herr_t H5VL_free_object(H5VL_object_t *obj);
@@ -93,13 +94,14 @@ H5_DLL herr_t H5VL_free_object(H5VL_object_t *obj);
 /* Functions that wrap / unwrap VOL objects */
 H5_DLL herr_t H5VL_get_wrap_ctx(const H5VL_class_t *connector, void *obj,
     void **wrap_ctx);
+H5_DLL void * H5VL_wrap_object(const H5VL_class_t *connector, void *wrap_ctx,
+    void *obj, H5I_type_t obj_type);
+H5_DLL void * H5VL_unwrap_object(const H5VL_class_t *connector, void *obj);
 H5_DLL herr_t H5VL_free_wrap_ctx(const H5VL_class_t *connector, void *wrap_ctx);
 H5_DLL herr_t H5VL_set_vol_wrapper(void *obj, H5VL_t *vol_connector);
 H5_DLL herr_t H5VL_inc_vol_wrapper(void *vol_wrap_ctx);
 H5_DLL herr_t H5VL_dec_vol_wrapper(void *vol_wrap_ctx);
 H5_DLL herr_t H5VL_reset_vol_wrapper(void);
-H5_DLL void * H5VL_wrap_object(const H5VL_class_t *connector, void *wrap_ctx,
-    void *obj, H5I_type_t obj_type);
 
 /* Library state functions */
 H5_DLL herr_t H5VL_retrieve_lib_state(void **state);
diff --git a/src/H5VLpublic.h b/src/H5VLpublic.h
index da31a97..56e703c 100644
--- a/src/H5VLpublic.h
+++ b/src/H5VLpublic.h
@@ -253,6 +253,7 @@ typedef struct H5VL_wrap_class_t {
     void * (*get_object)(const void *obj);          /* Callback to retrieve underlying object       */
     herr_t (*get_wrap_ctx)(const void *obj, void **wrap_ctx); /* Callback to retrieve the object wrapping context for the connector */
     void * (*wrap_object)(void *obj, H5I_type_t obj_type, void *wrap_ctx); /* Callback to wrap a library object */
+    void * (*unwrap_object)(void *obj);             /* Callback to unwrap a library object */
     herr_t (*free_wrap_ctx)(void *wrap_ctx);        /* Callback to release the object wrapping context for the connector */
 } H5VL_wrap_class_t;
 
@@ -472,6 +473,7 @@ H5_DLL void *H5VLget_object(void *obj, hid_t connector_id);
 H5_DLL herr_t H5VLget_wrap_ctx(void *obj, hid_t connector_id, void **wrap_ctx);
 H5_DLL void *H5VLwrap_object(void *obj, H5I_type_t obj_type, hid_t connector_id,
     void *wrap_ctx);
+H5_DLL void *H5VLunwrap_object(void *obj, hid_t connector_id);
 H5_DLL herr_t H5VLfree_wrap_ctx(void *wrap_ctx, hid_t connector_id);
 
 /* Public wrappers for attribute callbacks */