block/stream: Don't stream unbacked devices

If a block device is unbacked, a streaming blockjob should immediately
finish instead of beginning to try to stream, then noticing the backing
file does not contain even the first sector (since it does not exist)
and then finishing normally.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/stream.c b/block/stream.c
index 694fd42..46bec7d 100644 (file)
--- a/block/stream.c
+++ b/block/stream.c
@@ -88,6 +88,11 @@ static void coroutine_fn stream_run(void *opaque)
     int n = 0;
     void *buf;
 
+    if (!bs->backing_hd) {
+        block_job_completed(&s->common, 0);
+        return;
+    }
+
     s->common.len = bdrv_getlength(bs);
     if (s->common.len < 0) {
         block_job_completed(&s->common, s->common.len);