This is a little simpler than the commit block job because it's
synchronous and only commits into the immediate backing file, but
otherwise doing more or less the same.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Acked-by: NFam Zheng <famz@redhat.com>