block: Use bdrv_set_backing_hd everywhere We need to handle the coming backing_blocker properly, so don't open code the assignment, instead, call bdrv_set_backing_hd to change backing_hd. Signed-off-by: Fam Zheng <famz@redhat.com> Reviewed-by: Jeff Cody <jcody@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/block.c b/block.c
index 911ba68..1271dd2 100644
--- a/block.c
+++ b/block.c

@@ -2652,13 +2652,11 @@
     if (ret) {
         goto exit;
     }
-    new_top_bs->backing_hd = base_bs;
-
-    bdrv_refresh_limits(new_top_bs);
+    bdrv_set_backing_hd(new_top_bs, base_bs);
 
     QSIMPLEQ_FOREACH_SAFE(intermediate_state, &states_to_delete, entry, next) {
         /* so that bdrv_close() does not recursively close the chain */
-        intermediate_state->bs->backing_hd = NULL;
+        bdrv_set_backing_hd(intermediate_state->bs, NULL);
         bdrv_unref(intermediate_state->bs);
     }
     ret = 0;

diff --git a/block/stream.c b/block/stream.c
index dd0b4ac..91d18a2 100644
--- a/block/stream.c
+++ b/block/stream.c

@@ -60,7 +60,7 @@
     /* Must assign before bdrv_delete() to prevent traversing dangling pointer
      * while we delete backing image instances.
      */
-    top->backing_hd = base;
+    bdrv_set_backing_hd(top, base);
 
     while (intermediate) {
         BlockDriverState *unused;
@@ -72,7 +72,7 @@
 
         unused = intermediate;
         intermediate = intermediate->backing_hd;
-        unused->backing_hd = NULL;
+        bdrv_set_backing_hd(unused, NULL);
         bdrv_unref(unused);
     }
 

diff --git a/block/vvfat.c b/block/vvfat.c
index c3af7ff..417e96f 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c

@@ -2947,7 +2947,7 @@
     unlink(s->qcow_filename);
 #endif
 
-    s->bs->backing_hd = bdrv_new("", &error_abort);
+    bdrv_set_backing_hd(s->bs, bdrv_new("", &error_abort));
     s->bs->backing_hd->drv = &vvfat_write_target;
     s->bs->backing_hd->opaque = g_malloc(sizeof(void*));
     *(void**)s->bs->backing_hd->opaque = s;