block: Manage backing file references in bdrv_set_backing_hd()

This simplifies the code somewhat, especially when dropping whole
backing file subchains.

The exception is the mirroring code that does adventurous things with
bdrv_swap() and in order to keep it working, I had to duplicate most of
bdrv_set_backing_hd() locally. We'll get rid again of this ugliness
shortly.

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

1 files changed, 12 insertions, 4 deletions

diff --git a/block/mirror.c b/block/mirror.c
index 5d3b8bbd9c..6247b27612 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -370,10 +370,18 @@ static void mirror_exit(BlockJob *job, void *opaque)
         bdrv_swap(s->target, to_replace);
         if (s->common.driver->job_type == BLOCK_JOB_TYPE_COMMIT) {
             /* drop the bs loop chain formed by the swap: break the loop then
-             * trigger the unref from the top one */
-            BlockDriverState *p = backing_bs(s->base);
-            bdrv_set_backing_hd(s->base, NULL);
-            bdrv_unref(p);
+             * trigger the unref */
+            /* FIXME This duplicates bdrv_set_backing_hd(), except for the
+             * actual detach/unref so that the loop can be broken. When
+             * bdrv_swap() gets replaced, this will become sane again. */
+            BlockDriverState *backing = s->base->backing->bs;
+            assert(s->base->backing_blocker);
+            bdrv_op_unblock_all(backing, s->base->backing_blocker);
+            error_free(s->base->backing_blocker);
+            s->base->backing_blocker = NULL;
+            bdrv_detach_child(s->base->backing);
+            s->base->backing = NULL;
+            bdrv_unref(backing);
         }
     }
     if (s->to_replace) {