qcow: fix a reference leak

Since 42a3e1ab367cdf38cce093de24eb406b99a4ef96 qemu asserts when using the
vvfat driver:

git clone git://qemu.org/qemu.git
cd qemu
./configure --target-list=ppc-softmmu --enable-debug
make -j8
mkdir foo
touch foo/hello
./ppc-softmmu/qemu-system-ppc -M prep --nographic --monitor null             \
                              -hda fat:rw:./foo

"Ctrl-C"

qemu-system-ppc: block.c:3368: bdrv_close_all: Assertion                     \
   `((&all_bdrv_states)->tqh_first == ((void *)0))' failed.

This is because we reference bs twice in qcow_co_create(..) one time in
bdrv_open_blockdev_ref(..) and in blk_insert_bs(..) but we unref it only once
in blk_unref which leads to the reference leak.

Note that I didn't tested much QCOW after this change as I don't use it much.

Signed-off-by: KONRAD Frederic <frederic.konrad@adacore.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/block/qcow.c b/block/qcow.c
index 102d058d1c..385d935258 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -938,6 +938,7 @@ static int coroutine_fn qcow_co_create(BlockdevCreateOptions *opts,
     ret = 0;
 exit:
     blk_unref(qcow_blk);
+    bdrv_unref(bs);
     qcrypto_block_free(crypto);
     return ret;
 }