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: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NBenoit Canet <benoit@irqsave.net>

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;

block/qcow2.c

@@ -1588,7 +1588,8 @@ static int qcow2_create2(const char *filename, int64_t total_size,
 
     /* Reopen the image without BDRV_O_NO_FLUSH to flush it before returning */
     ret = bdrv_open(bs, filename, NULL,
-                    BDRV_O_RDWR | BDRV_O_CACHE_WB, drv, &local_err);
+                    BDRV_O_RDWR | BDRV_O_CACHE_WB | BDRV_O_NO_BACKING,
+                    drv, &local_err);
     if (error_is_set(&local_err)) {
         error_propagate(errp, local_err);
         goto out;

block/vmdk.c

@@ -1690,7 +1690,7 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options,
     }
     if (backing_file) {
         BlockDriverState *bs = bdrv_new("");
-        ret = bdrv_open(bs, backing_file, NULL, 0, NULL, errp);
+        ret = bdrv_open(bs, backing_file, NULL, BDRV_O_NO_BACKING, NULL, errp);
         if (ret != 0) {
             bdrv_unref(bs);
             return ret;