block: Use BDRV_O_NO_BACKING where appropriate

If you open an image temporarily just because you want to check its size
or get it flushed, there's no real reason to open the whole backing file
chain.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/block.c b/block.c
index 08dd7f2294..3d78581c63 100644
--- a/block.c
+++ b/block.c
@@ -1061,7 +1061,8 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
         /* Get the required size from the image */
         bs1 = bdrv_new("");
         QINCREF(options);
-        ret = bdrv_open(bs1, filename, options, 0, drv, &local_err);
+        ret = bdrv_open(bs1, filename, options, BDRV_O_NO_BACKING,
+                        drv, &local_err);
         if (ret < 0) {
             bdrv_unref(bs1);
             goto fail;