struct sptf_queue {
	TAILQ_HEAD(sptfq, buf) queue;
	daddr_t	lastpos;
	int t_lastpos;
};

#define sptf_init(q)       do { \
	TAILQ_INIT(&(q)->queue); \
	(q)->lastpos = 0; \
	(q)->t_lastpos = 0; \
} while(0)

#define sptf_enqueue(q,bp) TAILQ_INSERT_TAIL(&(q)->queue, (bp), b_act)
#define sptf_dequeue(q,bp) do { \
	TAILQ_REMOVE(&(q)->queue, (bp), b_act); \
	(q)->lastpos = (bp)->b_pblkno; \
} while(0)

#define sptf_iodone(q,bp)  do { \
	(q)->lastpos = (bp)->b_pblkno; \
	(q)->t_lastpos = NOW; \
} while(0)

#define sptf_dist(q,bp) (postime((bp)->b_pblkno - (q)->lastpos))

struct buf *sptf_select(struct sptf_queue *q)
{
	struct buf *bp, *bq = 0;
	int t0 = INT_MAX, t;
	quad_t now __attribute__ ((unused)) = ll_microtime();

	asptf_switch = 1;
	TAILQ_FOREACH(bp, &q->queue, b_act) {
#ifdef ASPTF_BOUND
		if (now - bp->b_t_enqueue > ASPTF_BOUND * 1000LL) return bp;
#endif
		t = sptf_dist(q,bp);
		if (!bq || t < t0) t0 = t, bq = bp;
	}
	asptf_switch = 0;
	return bq;
}

#define sptf_foreach(q,bp) TAILQ_FOREACH(bp, &(q)->queue, b_act)