bdrv_has_zero_init() and the related bdrv_unallocated_blocks_are_zero()
should use bdrv_filtered_cow_child() if they want to check whether the
given BDS has a COW backing file.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index bfa5e27850..486c75d847 100644
--- a/block.c
+++ b/block.c
@@ -5063,7 +5063,7 @@ int bdrv_has_zero_init(BlockDriverState *bs)
 
     /* If BS is a copy on write image, it is initialized to
        the contents of the base image, which may not be zeroes.  */
-    if (bs->backing) {
+    if (bdrv_filtered_cow_child(bs)) {
         return 0;
     }
     if (bs->drv->bdrv_has_zero_init) {
@@ -5081,7 +5081,7 @@ bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs)
 {
     BlockDriverInfo bdi;
 
-    if (bs->backing) {
+    if (bdrv_filtered_cow_child(bs)) {
         return false;
     }
 
-- 
2.21.0