First, we can downsize vl.c, make it simpler by
little and little. Second, I can maintain those code
and make some improvement.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>