block: Introduce bdrv_open_child()

It is the same as bdrv_open_image(), except that it doesn't only return
success or failure, but the newly created BdrvChild object for the new
child node.

As the BdrvChild object already contains a BlockDriverState pointer (and
this is supposed to become the only pointer so that bdrv_append() and
friends can just change a single pointer in BdrvChild), the pbs
parameter is removed for bdrv_open_child().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

2 files changed, 8 insertions, 2 deletions

diff --git a/include/block/block.h b/include/block/block.h
index 06e4137008..50487726f5 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -12,6 +12,7 @@
 /* block.c */
 typedef struct BlockDriver BlockDriver;
 typedef struct BlockJob BlockJob;
+typedef struct BdrvChild BdrvChild;
 typedef struct BdrvChildRole BdrvChildRole;
 
 typedef struct BlockDriverInfo {
@@ -208,6 +209,11 @@ int bdrv_open_image(BlockDriverState **pbs, const char *filename,
                     QDict *options, const char *bdref_key,
                     BlockDriverState* parent, const BdrvChildRole *child_role,
                     bool allow_none, Error **errp);
+BdrvChild *bdrv_open_child(const char *filename,
+                           QDict *options, const char *bdref_key,
+                           BlockDriverState* parent,
+                           const BdrvChildRole *child_role,
+                           bool allow_none, Error **errp);
 void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd);
 int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp);
 int bdrv_append_temp_snapshot(BlockDriverState *bs, int flags, Error **errp);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 8996baf2f0..ec244b5d06 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -335,11 +335,11 @@ struct BdrvChildRole {
 extern const BdrvChildRole child_file;
 extern const BdrvChildRole child_format;
 
-typedef struct BdrvChild {
+struct BdrvChild {
     BlockDriverState *bs;
     const BdrvChildRole *role;
     QLIST_ENTRY(BdrvChild) next;
-} BdrvChild;
+};
 
 /*
  * Note: the function bdrv_append() copies and swaps contents of