[PATCH v2 1/5] block: Mark commit and mirror as filter drivers

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

From: Max Reitz <mreitz@redhat.com>

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

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
   [squash comment fix from another Max's patch and adjust commit msg]
---
 include/block/block_int.h | 8 +++++---
 block/commit.c            | 2 ++
 block/mirror.c            | 2 ++
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index dd033d0b37..964ce58481 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -89,9 +89,11 @@ struct BlockDriver {
     int instance_size;
 
     /* set to true if the BlockDriver is a block filter. Block filters pass
-     * certain callbacks that refer to data (see block.c) to their bs->file if
-     * the driver doesn't implement them. Drivers that do not wish to forward
-     * must implement them and return -ENOTSUP.
+     * certain callbacks that refer to data (see block.c) to their bs->file
+     * or bs->backing (whichever one exists) if the driver doesn't implement
+     * them. Drivers that do not wish to forward must implement them and return
+     * -ENOTSUP.
+     * Note that filters are not allowed to modify data.
      */
     bool is_filter;
     /* for snapshots block filter like Quorum can implement the
diff --git a/block/commit.c b/block/commit.c
index 23c90b3b91..9b455c4285 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -253,6 +253,8 @@ 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 f0f2d9dff1..8cbbe1e065 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1505,6 +1505,8 @@ 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(
-- 
2.21.0