/* Insert a new entry before the specified head. This is useful for implementing queues.  */
void llist_add_tail(llist_head *p, llist_head *head)
/* Insert a new entry before the specified head. This is useful for implementing queues.  */
void llist_add_tail(llist_head *p, llist_head *head)
{
    __llist_add(p, head->prev, head);
}