mirror: Fix permissions for removing mirror_top_bs

mirror_top_bs takes write permissions on its backing file, which can
make it impossible to attach that backing file node to another parent.
However, this is exactly what needs to be done in order to remove
mirror_top_bs from the backing chain. So give up the write permission
first.

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

diff --git a/block/mirror.c b/block/mirror.c
index c9185b38a8f59866a1467737bacba8b953041a18..001b5f0a15a3f1d4e81dea85793e4ce1ab3fe965 100644 (file)
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -566,8 +566,10 @@ static void mirror_exit(BlockJob *job, void *opaque)
 
     /* Remove the mirror filter driver from the graph. Before this, get rid of
      * the blockers on the intermediate nodes so that the resulting state is
-     * valid. */
+     * valid. Also give up permissions on mirror_top_bs->backing, which might
+     * block the removal. */
     block_job_remove_all_bdrv(job);
+    bdrv_child_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL);
     bdrv_replace_in_backing_chain(mirror_top_bs, backing_bs(mirror_top_bs));
 
     /* We just changed the BDS the job BB refers to (with either or both of the
@@ -1234,6 +1236,7 @@ fail:
         block_job_unref(&s->common);
     }
 
+    bdrv_child_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL);
     bdrv_replace_in_backing_chain(mirror_top_bs, backing_bs(mirror_top_bs));
 }