block: complete all IOs before resizing a device

this patch ensures that all pending IOs are completed
before a device is resized. this is especially important
if a device is shrinked as it the bdrv_check_request()
result is invalidated.

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

diff --git a/blockdev.c b/blockdev.c
index 09f76b7..6f2b759 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1127,6 +1127,9 @@
         return;
     }
 
+    /* complete all in-flight operations before resizing the device */
+    bdrv_drain_all();
+
     switch (bdrv_truncate(bs, size)) {
     case 0:
         break;