block: Introduce BDS.file_child

Store the BdrvChild for bs->file. At this point, bs->file_child->bs just
duplicates the bs->file pointer. Later, it will completely replace it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 14ad4c334b..d0dd93e5af 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -381,6 +381,7 @@ struct BlockDriverState {
     BlockDriverState *backing_hd;
     BdrvChild *backing_child;
     BlockDriverState *file;
+    BdrvChild *file_child;
 
     NotifierList close_notifiers;