block: More detailed syntax error reporting for JSON filenames

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <1488317230-26248-14-git-send-email-armbru@redhat.com>

block.c

@@ -1262,9 +1262,14 @@ static QDict *parse_json_filename(const char *filename, Error **errp)
     ret = strstart(filename, "json:", &filename);
     assert(ret);
 
-    options_obj = qobject_from_json(filename, NULL);
+    options_obj = qobject_from_json(filename, errp);
     if (!options_obj) {
-        error_setg(errp, "Could not parse the JSON options");
+        /* Work around qobject_from_json() lossage TODO fix that */
+        if (errp && !*errp) {
+            error_setg(errp, "Could not parse the JSON options");
+            return NULL;
+        }
+        error_prepend(errp, "Could not parse the JSON options: ");
         return NULL;
     }