block: Prepare for NULL BDS

blk_bs() will not necessarily return a non-NULL value any more (unless
blk_is_available() is true or it can be assumed to otherwise, e.g.
because it is called immediately after a successful blk_new_with_bs() or
blk_new_open()).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/monitor.c b/monitor.c
index 4f1ba2f666..301a143ffa 100644
--- a/monitor.c
+++ b/monitor.c
@@ -4145,6 +4145,10 @@ int monitor_read_block_device_key(Monitor *mon, const char *device,
         monitor_printf(mon, "Device not found %s\n", device);
         return -1;
     }
+    if (!blk_bs(blk)) {
+        monitor_printf(mon, "Device '%s' has no medium\n", device);
+        return -1;
+    }
 
     bdrv_add_key(blk_bs(blk), NULL, &err);
     if (err) {