block: Fix reconfiguring graph with drained nodes

When changing the BlockDriverState that a BdrvChild points to while the
node is currently drained, we must call the .drained_end() parent
callback. Conversely, when this means attaching a new node that is
already drained, we need to call .drained_begin().

bdrv_root_attach_child() takes now an opaque parameter, which is needed
because the callbacks must also be called if we're attaching a new child
to the BlockBackend when the root node is already drained, and they need
a way to identify the BlockBackend. Previously, child->opaque was set
too late and the callbacks would still see it as NULL.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/block/block_int.h b/include/block/block_int.h
index b6f4755725..30a97178c8 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -719,7 +719,8 @@ void hmp_drive_add_node(Monitor *mon, const char *optstr);
 
 BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
                                   const char *child_name,
-                                  const BdrvChildRole *child_role);
+                                  const BdrvChildRole *child_role,
+                                  void *opaque);
 void bdrv_root_unref_child(BdrvChild *child);
 
 const char *bdrv_get_parent_name(const BlockDriverState *bs);