[Qemu-devel] [PATCH 5/7] block: pass new base image format to bdrv_change_backing_file

[Paolo Bonzini <pbonzini@redhat.com>]

The format was not written to the image, only the file name.

This will overwrite an auto-probe image with the right format.
Format probing is unsafe and we want to avoid it whenever possible.
An alternative would be to look out the backing file from the image
above base.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/stream.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/stream.c b/block/stream.c
index 54f2b39..2b492d5 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -240,11 +240,14 @@ retry:
     }
 
     if (!block_job_is_cancelled(&s->common) && sector_num == end && ret == 0) {
-        const char *base_id = NULL;
+        const char *base_id = NULL, *base_fmt = NULL;
         if (base) {
             base_id = s->backing_file_id;
+            if (base->drv) {
+                base_fmt = base->drv->format_name;
+            }
         }
-        ret = bdrv_change_backing_file(bs, base_id, NULL);
+        ret = bdrv_change_backing_file(bs, base_id, base_fmt);
         close_unused_images(bs, base, base_id);
     }
 
-- 
1.7.9.3