block: Use CAFs in bdrv_refresh_filename()

bdrv_refresh_filename() and the kind of related bdrv_dirname() should
look to the primary child when they wish to copy the underlying file's
filename.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -6822,6 +6822,7 @@ void bdrv_refresh_filename(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
     BdrvChild *child;
+    BlockDriverState *primary_child_bs;
     QDict *opts;
     bool backing_overridden;
     bool generate_json_filename; /* Whether our default implementation should
@@ -6891,20 +6892,30 @@ void bdrv_refresh_filename(BlockDriverState *bs)
     qobject_unref(bs->full_open_options);
     bs->full_open_options = opts;
 
+    primary_child_bs = bdrv_primary_bs(bs);
+
     if (drv->bdrv_refresh_filename) {
         /* Obsolete information is of no use here, so drop the old file name
          * information before refreshing it */
         bs->exact_filename[0] = '\0';
 
         drv->bdrv_refresh_filename(bs);
-    } else if (bs->file) {
+    } else if (primary_child_bs) {
-        /* Try to reconstruct valid information from the underlying file */
+        /*
+         * Try to reconstruct valid information from the underlying
+         * file -- this only works for format nodes (filter nodes
+         * cannot be probed and as such must be selected by the user
+         * either through an options dict, or through a special
+         * filename which the filter driver must construct in its
+         * .bdrv_refresh_filename() implementation).
+         */
 
         bs->exact_filename[0] = '\0';
 
         /*
          * We can use the underlying file's filename if:
          * - it has a filename,
+         * - the current BDS is not a filter,
          * - the file is a protocol BDS, and
          * - opening that file (as this BDS's format) will automatically create
          *   the BDS tree we have right now, that is:
@@ -6913,11 +6924,11 @@ void bdrv_refresh_filename(BlockDriverState *bs)
          *   - no non-file child of this BDS has been overridden by the user
          *   Both of these conditions are represented by generate_json_filename.
          */
-        if (bs->file->bs->exact_filename[0] &&
+        if (primary_child_bs->exact_filename[0] &&
-            bs->file->bs->drv->bdrv_file_open &&
+            primary_child_bs->drv->bdrv_file_open &&
-            !generate_json_filename)
+            !drv->is_filter && !generate_json_filename)
         {
-            strcpy(bs->exact_filename, bs->file->bs->exact_filename);
+            strcpy(bs->exact_filename, primary_child_bs->exact_filename);
         }
     }
 
@@ -6937,6 +6948,7 @@ void bdrv_refresh_filename(BlockDriverState *bs)
 char *bdrv_dirname(BlockDriverState *bs, Error **errp)
 {
     BlockDriver *drv = bs->drv;
+    BlockDriverState *child_bs;
 
     if (!drv) {
         error_setg(errp, "Node '%s' is ejected", bs->node_name);
@@ -6947,8 +6959,9 @@ char *bdrv_dirname(BlockDriverState *bs, Error **errp)
         return drv->bdrv_dirname(bs, errp);
     }
 
-    if (bs->file) {
+    child_bs = bdrv_primary_bs(bs);
-        return bdrv_dirname(bs->file->bs, errp);
+    if (child_bs) {
+        return bdrv_dirname(child_bs, errp);
     }
 
     bdrv_refresh_filename(bs);