[Qemu-block] [PATCH] block: don't add 'driver' to options when refering to backing via node name

[Peter Krempa]

When refering to a backing file of an image via node name
bdrv_open_backing_file would add the 'driver' option to the option list
filling it with the backing format driver. This breaks construction of
the backing chain via -blockdev, as bdrv_open_inherit reports an error
if both 'reference' and 'options' are provided.

Signed-off-by: Peter Krempa <address@hidden>
---
 block.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 46eb1728da..684cb018da 100644
--- a/block.c
+++ b/block.c
@@ -2245,7 +2245,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict 
*parent_options,
         goto free_exit;
     }

-    if (bs->backing_format[0] != '\0' && !qdict_haskey(options, "driver")) {
+    if (!reference &&
+        bs->backing_format[0] != '\0' && !qdict_haskey(options, "driver")) {
         qdict_put_str(options, "driver", bs->backing_format);
     }

-- 
2.14.1