CCB_DONE_EMPTY
np->ccb_done[j] = (struct ccb *)CCB_DONE_EMPTY;
np->ccb_done[i] = (struct ccb *)CCB_DONE_EMPTY;
#define CCB_DONE_VALID(cp) (((u_long) cp) != CCB_DONE_EMPTY)
(((u_long) cp) & 0xfffffffful) != CCB_DONE_EMPTY)