block: throttle-groups: Use BlockBackend pointers internally

As a first step towards moving I/O throttling to the BlockBackend level,
this patch changes all pointers in struct ThrottleGroup from referencing
a BlockDriverState to referencing a BlockBackend.

This change is valid because we made sure that throttling can only be
enabled on BDSes which have a BB attached.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index a771603bd0..1dcd70e2ca 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -63,7 +63,10 @@ typedef struct BlockDevOps {
  * fields that must be public. This is in particular for QLIST_ENTRY() and
  * friends so that BlockBackends can be kept in lists outside block-backend.c */
 typedef struct BlockBackendPublic {
-    int dummy; /* empty structs are illegal */
+    /* I/O throttling */
+    /* The following fields are protected by the ThrottleGroup lock.
+     * See the ThrottleGroup documentation for details. */
+    QLIST_ENTRY(BlockBackendPublic) round_robin;
 } BlockBackendPublic;
 
 BlockBackend *blk_new(Error **errp);