block: introduce bdrv_remove_file_or_backing_child()

To be used for reopen in future commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210610120537.196183-2-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -4795,17 +4795,16 @@ static TransactionActionDrv bdrv_remove_filter_or_cow_child_drv = {
 };
 
 /*
- * A function to remove backing-chain child of @bs if exists: cow child for
- * format nodes (always .backing) and filter child for filters (may be .file or
- * .backing)
- *
+ * A function to remove backing or file child of @bs.
  * Function doesn't update permissions, caller is responsible for this.
  */
-static void bdrv_remove_filter_or_cow_child(BlockDriverState *bs,
-                                            Transaction *tran)
+static void bdrv_remove_file_or_backing_child(BlockDriverState *bs,
+                                              BdrvChild *child,
+                                              Transaction *tran)
 {
     BdrvRemoveFilterOrCowChild *s;
-    BdrvChild *child = bdrv_filter_or_cow_child(bs);
+
+    assert(child == bs->backing || child == bs->file);
 
     if (!child) {
         return;
@@ -4830,6 +4829,17 @@ static void bdrv_remove_filter_or_cow_child(BlockDriverState *bs,
     }
 }
 
+/*
+ * A function to remove backing-chain child of @bs if exists: cow child for
+ * format nodes (always .backing) and filter child for filters (may be .file or
+ * .backing)
+ */
+static void bdrv_remove_filter_or_cow_child(BlockDriverState *bs,
+                                            Transaction *tran)
+{
+    bdrv_remove_file_or_backing_child(bs, bdrv_filter_or_cow_child(bs), tran);
+}
+
 static int bdrv_replace_node_noperm(BlockDriverState *from,
                                     BlockDriverState *to,
                                     bool auto_skip, Transaction *tran,