The commit and mirror block nodes are filters, so they should be marked
as such.  (Strictly speaking, BDS.is_filter's documentation states that
a filter's child must be bs->file.  The following patch will relax this
restriction, however.)

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/commit.c | 2 ++
 block/mirror.c | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/block/commit.c b/block/commit.c
index 408ae15389..19915603ae 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -254,6 +254,8 @@ static BlockDriver bdrv_commit_top = {
     .bdrv_co_block_status       = bdrv_co_block_status_from_backing,
     .bdrv_refresh_filename      = bdrv_commit_top_refresh_filename,
     .bdrv_child_perm            = bdrv_commit_top_child_perm,
+
+    .is_filter                  = true,
 };
 
 void commit_start(const char *job_id, BlockDriverState *bs,
diff --git a/block/mirror.c b/block/mirror.c
index 2b870683f1..a8f2d7a305 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1507,6 +1507,8 @@ static BlockDriver bdrv_mirror_top = {
     .bdrv_refresh_filename      = bdrv_mirror_top_refresh_filename,
     .bdrv_child_perm            = bdrv_mirror_top_child_perm,
     .bdrv_refresh_limits        = bdrv_mirror_top_refresh_limits,
+
+    .is_filter                  = true,
 };
 
 static BlockJob *mirror_start_job(
-- 
2.21.0