1 files changed, 16 insertions, 37 deletions

diff --git a/block.c b/block.c
index 6472866283..d047cae43c 100644
--- a/block.c
+++ b/block.c
@@ -4237,7 +4237,7 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
                                      Error **errp)
 {
     BlockDriverState *bs = reopen_state->bs;
-    BlockDriverState *overlay_bs, *below_bs, *new_backing_bs;
+    BlockDriverState *new_backing_bs;
     QObject *value;
     const char *str;
 
@@ -4266,6 +4266,18 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
         g_assert_not_reached();
     }
 
+    if (bs->backing) {
+        if (bdrv_skip_implicit_filters(bs->backing->bs) == new_backing_bs) {
+            return 0;
+        }
+
+        if (bs->backing->bs->implicit) {
+            error_setg(errp, "Cannot change backing link if '%s' has "
+                       "an implicit backing file", bs->node_name);
+            return -EPERM;
+        }
+    }
+
     /*
      * Ensure that @bs can really handle backing files, because we are
      * about to give it one (or swap the existing one)
@@ -4283,42 +4295,9 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
         return -EINVAL;
     }
 
-    /*
-     * Find the "actual" backing file by skipping all links that point
-     * to an implicit node, if any (e.g. a commit filter node).
-     * We cannot use any of the bdrv_skip_*() functions here because
-     * those return the first explicit node, while we are looking for
-     * its overlay here.
-     */
-    overlay_bs = bs;
-    for (below_bs = bdrv_filter_or_cow_bs(overlay_bs);
-         below_bs && below_bs->implicit;
-         below_bs = bdrv_filter_or_cow_bs(overlay_bs))
-    {
-        overlay_bs = below_bs;
-    }
-
-    /* If we want to replace the backing file we need some extra checks */
-    if (new_backing_bs != bdrv_filter_or_cow_bs(overlay_bs)) {
-        int ret;
-
-        /* Check for implicit nodes between bs and its backing file */
-        if (bs != overlay_bs) {
-            error_setg(errp, "Cannot change backing link if '%s' has "
-                       "an implicit backing file", bs->node_name);
-            return -EPERM;
-        }
-
-        reopen_state->replace_backing_bs = true;
-        reopen_state->old_backing_bs = bs->backing ? bs->backing->bs : NULL;
-        ret = bdrv_set_backing_noperm(bs, new_backing_bs, set_backings_tran,
-                                      errp);
-        if (ret < 0) {
-            return ret;
-        }
-    }
-
-    return 0;
+    reopen_state->replace_backing_bs = true;
+    reopen_state->old_backing_bs = bs->backing ? bs->backing->bs : NULL;
+    return bdrv_set_backing_noperm(bs, new_backing_bs, set_backings_tran, errp);
 }
 
 /*