XBD_Q_FREE
xbd_initq_cm(sc, XBD_Q_FREE);
xbd_enqueue_cm(cm, XBD_Q_FREE);
if ((cm = xbd_dequeue_cm(sc, XBD_Q_FREE)) == NULL) {
xbd_enqueue_cm(cm, XBD_Q_FREE);
xbd_enqueue_cm(cm, XBD_Q_FREE);
cm = xbd_dequeue_cm(sc, XBD_Q_FREE);