block/qdev: Let 'drive' property fall back to node name

If a qdev block device is created with an anonymous BlockBackend (i.e.
a node name rather than a BB name was given for the drive property),
qdev used to return an empty string when the property was read. This
patch fixes it to return the node name instead.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

hw/core/qdev-properties-system.c

@@ -126,7 +126,16 @@ static void release_drive(Object *obj, const char *name, void *opaque)
 
 static char *print_drive(void *ptr)
 {
-    return g_strdup(blk_name(ptr));
+    const char *name;
+
+    name = blk_name(ptr);
+    if (!*name) {
+        BlockDriverState *bs = blk_bs(ptr);
+        if (bs) {
+            name = bdrv_get_node_name(bs);
+        }
+    }
+    return g_strdup(name);
 }
 
 static void get_drive(Object *obj, Visitor *v, const char *name, void *opaque,