block: Mark commit, mirror, blkreplay as filters

The commit, mirror, and blkreplay block nodes are filters, so they should
be marked as such.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200513110544.176672-2-mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/blkreplay.c

@@ -135,6 +135,7 @@ static int blkreplay_snapshot_goto(BlockDriverState *bs,
 static BlockDriver bdrv_blkreplay = {
     .format_name            = "blkreplay",
     .instance_size          = 0,
+    .is_filter              = true,
 
     .bdrv_open              = blkreplay_open,
     .bdrv_child_perm        = bdrv_filter_default_perms,

block/commit.c

@@ -240,6 +240,8 @@ 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,

block/mirror.c

@@ -1530,6 +1530,8 @@ static BlockDriver bdrv_mirror_top = {
     .bdrv_co_block_status       = bdrv_co_block_status_from_backing,
     .bdrv_refresh_filename      = bdrv_mirror_top_refresh_filename,
     .bdrv_child_perm            = bdrv_mirror_top_child_perm,
+
+    .is_filter                  = true,
 };
 
 static BlockJob *mirror_start_job(