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>

2 files changed, 10 insertions, 3 deletions

diff --git a/block.c b/block.c
index 1f90b47..75afed1 100644
--- a/block.c
+++ b/block.c
@@ -1487,11 +1487,17 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename,
 
         assert(file == NULL);
         bs->open_flags = flags;
-        ret = bdrv_open_image(&file, filename, options, "file",
-                              bs, &child_file, true, &local_err);
-        if (ret < 0) {
+
+        bs->file_child = bdrv_open_child(filename, options, "file", bs,
+                                         &child_file, true, &local_err);
+        if (local_err) {
+            ret = -EINVAL;
             goto fail;
         }
+
+        if (bs->file_child) {
+            file = bs->file_child->bs;
+        }
     }
 
     /* Image format probing */
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 14ad4c3..d0dd93e 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;