When BDSs are created by qemu itself (e.g. as filters in block jobs),
they may not have a "driver" option in their options QDict.  When
generating a json:{} filename, however, it must always be present.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
---
 block.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/block.c b/block.c
index c9a6cf0440..d496debda4 100644
--- a/block.c
+++ b/block.c
@@ -5557,6 +5557,12 @@ static bool append_strong_runtime_options(QDict *d, BlockDriverState *bs)
         }
     }
 
+    if (!qdict_haskey(d, "driver")) {
+        /* Drivers created with bdrv_new_open_driver() may not have a
+         * @driver option.  Add it here. */
+        qdict_put_str(d, "driver", bs->drv->format_name);
+    }
+
     return found_any;
 }
 
-- 
2.20.1