[Qemu-devel] [PATCH v2] block: Close backing file early in bdrv_img_create

[Max Reitz <mreitz@redhat.com>]

Leaving the backing file open although it is not needed anymore can
cause problems if it is opened through a block driver which allows
exclusive access only and if the create function of the block driver
used for the top image (the one being created) tries to close and reopen
the image file (which will include opening the backing file a second
time).

In particular, this will happen with a backing file opened through
qemu-nbd and using qcow2 as the top image file format (which reopens the
image to flush it to disk).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
v2:
 - Minimizing the changes prevents introducing a leak of the
   BlockDriverState in case of an error in bdrv_open() (thanks, Kevin).
---
 block.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block.c b/block.c
index 382ea71..6d571ad 100644
--- a/block.c
+++ b/block.c
@@ -4608,6 +4608,9 @@ void bdrv_img_create(const char *filename, const char *fmt,
 
             snprintf(buf, sizeof(buf), "%" PRId64, size);
             set_option_parameter(param, BLOCK_OPT_SIZE, buf);
+
+            bdrv_unref(bs);
+            bs = NULL;
         } else {
             error_setg(errp, "Image creation needs a size parameter");
             goto out;
-- 
1.8.4.2