[linux-2.6-block.git] / block / blk-merge.c

/*
 * Functions related to segment and merge handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/scatterlist.h>

#include "blk.h"

void blk_recalc_rq_sectors(struct request *rq, int nsect)
{
	if (blk_fs_request(rq) || blk_discard_rq(rq)) {
		rq->hard_sector += nsect;
		rq->hard_nr_sectors -= nsect;

		/*
		 * Move the I/O submission pointers ahead if required.
		 */
		if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
		    (rq->sector <= rq->hard_sector)) {
			rq->sector = rq->hard_sector;
			rq->nr_sectors = rq->hard_nr_sectors;
			rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
			rq->current_nr_sectors = rq->hard_cur_sectors;
			rq->buffer = bio_data(rq->bio);
		}

		/*
		 * if total number of sectors is less than the first segment
		 * size, something has gone terribly wrong
		 */
		if (rq->nr_sectors < rq->current_nr_sectors) {
			printk(KERN_ERR "blk: request botched\n");
			rq->nr_sectors = rq->current_nr_sectors;
		}
	}
}

void blk_recalc_rq_segments(struct request *rq)
{
	int nr_phys_segs;
	unsigned int phys_size;
	struct bio_vec *bv, *bvprv = NULL;
	int seg_size;
	int cluster;
	struct req_iterator iter;
	int high, highprv = 1;
	struct request_queue *q = rq->q;

	if (!rq->bio)
		return;

	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
	seg_size = 0;
	phys_size = nr_phys_segs = 0;
	rq_for_each_segment(bv, rq, iter) {
		/*
		 * the trick here is making sure that a high page is never
		 * considered part of another segment, since that might
		 * change with the bounce page.
		 */
		high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
		if (high || highprv)
			goto new_segment;
		if (cluster) {
			if (seg_size + bv->bv_len > q->max_segment_size)
				goto new_segment;
			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
				goto new_segment;
			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
				goto new_segment;

			seg_size += bv->bv_len;
			bvprv = bv;
			continue;
		}
new_segment:
		if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
			rq->bio->bi_seg_front_size = seg_size;

		nr_phys_segs++;
		bvprv = bv;
		seg_size = bv->bv_len;
		highprv = high;
	}

	if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
		rq->bio->bi_seg_front_size = seg_size;
	if (seg_size > rq->biotail->bi_seg_back_size)
		rq->biotail->bi_seg_back_size = seg_size;

	rq->nr_phys_segments = nr_phys_segs;
}

void blk_recount_segments(struct request_queue *q, struct bio *bio)
{
	struct request rq;
	struct bio *nxt = bio->bi_next;
	rq.q = q;
	rq.bio = rq.biotail = bio;
	bio->bi_next = NULL;
	blk_recalc_rq_segments(&rq);
	bio->bi_next = nxt;
	bio->bi_phys_segments = rq.nr_phys_segments;
	bio->bi_flags |= (1 << BIO_SEG_VALID);
}
EXPORT_SYMBOL(blk_recount_segments);

static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
				   struct bio *nxt)
{
	if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
		return 0;

	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
	    q->max_segment_size)
		return 0;

	if (!bio_has_data(bio))
		return 1;

	if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
		return 0;

	/*
	 * bio and nxt are contiguous in memory; check if the queue allows
	 * these two to be merged into one
	 */
	if (BIO_SEG_BOUNDARY(q, bio, nxt))
		return 1;

	return 0;
}

/*
 * map a request to scatterlist, return number of sg entries setup. Caller
 * must make sure sg can hold rq->nr_phys_segments entries
 */
int blk_rq_map_sg(struct request_queue *q, struct request *rq,
		  struct scatterlist *sglist)
{
	struct bio_vec *bvec, *bvprv;
	struct req_iterator iter;
	struct scatterlist *sg;
	int nsegs, cluster;

	nsegs = 0;
	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);

	/*
	 * for each bio in rq
	 */
	bvprv = NULL;
	sg = NULL;
	rq_for_each_segment(bvec, rq, iter) {
		int nbytes = bvec->bv_len;

		if (bvprv && cluster) {
			if (sg->length + nbytes > q->max_segment_size)
				goto new_segment;

			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
				goto new_segment;
			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
				goto new_segment;

			sg->length += nbytes;
		} else {
new_segment:
			if (!sg)
				sg = sglist;
			else {
				/*
				 * If the driver previously mapped a shorter
				 * list, we could see a termination bit
				 * prematurely unless it fully inits the sg
				 * table on each mapping. We KNOW that there
				 * must be more entries here or the driver
				 * would be buggy, so force clear the
				 * termination bit to avoid doing a full
				 * sg_init_table() in drivers for each command.
				 */
				sg->page_link &= ~0x02;
				sg = sg_next(sg);
			}

			sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
			nsegs++;
		}
		bvprv = bvec;
	} /* segments in rq */


	if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
	    (rq->data_len & q->dma_pad_mask)) {
		unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;

		sg->length += pad_len;
		rq->extra_len += pad_len;
	}

	if (q->dma_drain_size && q->dma_drain_needed(rq)) {
		if (rq->cmd_flags & REQ_RW)
			memset(q->dma_drain_buffer, 0, q->dma_drain_size);

		sg->page_link &= ~0x02;
		sg = sg_next(sg);
		sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
			    q->dma_drain_size,
			    ((unsigned long)q->dma_drain_buffer) &
			    (PAGE_SIZE - 1));
		nsegs++;
		rq->extra_len += q->dma_drain_size;
	}

	if (sg)
		sg_mark_end(sg);

	return nsegs;
}
EXPORT_SYMBOL(blk_rq_map_sg);

static inline int ll_new_hw_segment(struct request_queue *q,
				    struct request *req,
				    struct bio *bio)
{
	int nr_phys_segs = bio_phys_segments(q, bio);

	if (req->nr_phys_segments + nr_phys_segs > q->max_hw_segments
	    || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
		req->cmd_flags |= REQ_NOMERGE;
		if (req == q->last_merge)
			q->last_merge = NULL;
		return 0;
	}

	/*
	 * This will form the start of a new hw segment.  Bump both
	 * counters.
	 */
	req->nr_phys_segments += nr_phys_segs;
	return 1;
}

int ll_back_merge_fn(struct request_queue *q, struct request *req,
		     struct bio *bio)
{
	unsigned short max_sectors;

	if (unlikely(blk_pc_request(req)))
		max_sectors = q->max_hw_sectors;
	else
		max_sectors = q->max_sectors;

	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
		req->cmd_flags |= REQ_NOMERGE;
		if (req == q->last_merge)
			q->last_merge = NULL;
		return 0;
	}
	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
		blk_recount_segments(q, req->biotail);
	if (!bio_flagged(bio, BIO_SEG_VALID))
		blk_recount_segments(q, bio);

	return ll_new_hw_segment(q, req, bio);
}

int ll_front_merge_fn(struct request_queue *q, struct request *req,
		      struct bio *bio)
{
	unsigned short max_sectors;

	if (unlikely(blk_pc_request(req)))
		max_sectors = q->max_hw_sectors;
	else
		max_sectors = q->max_sectors;


	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
		req->cmd_flags |= REQ_NOMERGE;
		if (req == q->last_merge)
			q->last_merge = NULL;
		return 0;
	}
	if (!bio_flagged(bio, BIO_SEG_VALID))
		blk_recount_segments(q, bio);
	if (!bio_flagged(req->bio, BIO_SEG_VALID))
		blk_recount_segments(q, req->bio);

	return ll_new_hw_segment(q, req, bio);
}

static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
				struct request *next)
{
	int total_phys_segments;
	unsigned int seg_size =
		req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;

	/*
	 * First check if the either of the requests are re-queued
	 * requests.  Can't merge them if they are.
	 */
	if (req->special || next->special)
		return 0;

	/*
	 * Will it become too large?
	 */
	if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
		return 0;

	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
	if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
		if (req->nr_phys_segments == 1)
			req->bio->bi_seg_front_size = seg_size;
		if (next->nr_phys_segments == 1)
			next->biotail->bi_seg_back_size = seg_size;
		total_phys_segments--;
	}

	if (total_phys_segments > q->max_phys_segments)
		return 0;

	if (total_phys_segments > q->max_hw_segments)
		return 0;

	/* Merge is OK... */
	req->nr_phys_segments = total_phys_segments;
	return 1;
}

/*
 * Has to be called with the request spinlock acquired
 */
static int attempt_merge(struct request_queue *q, struct request *req,
			  struct request *next)
{
	if (!rq_mergeable(req) || !rq_mergeable(next))
		return 0;

	/*
	 * not contiguous
	 */
	if (req->sector + req->nr_sectors != next->sector)
		return 0;

	if (rq_data_dir(req) != rq_data_dir(next)
	    || req->rq_disk != next->rq_disk
	    || next->special)
		return 0;

	if (blk_integrity_rq(req) != blk_integrity_rq(next))
		return 0;

	/*
	 * If we are allowed to merge, then append bio list
	 * from next to rq and release next. merge_requests_fn
	 * will have updated segment counts, update sector
	 * counts here.
	 */
	if (!ll_merge_requests_fn(q, req, next))
		return 0;

	/*
	 * At this point we have either done a back merge
	 * or front merge. We need the smaller start_time of
	 * the merged requests to be the current request
	 * for accounting purposes.
	 */
	if (time_after(req->start_time, next->start_time))
		req->start_time = next->start_time;

	req->biotail->bi_next = next->bio;
	req->biotail = next->biotail;

	req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;

	elv_merge_requests(q, req, next);

	if (req->rq_disk) {
		struct hd_struct *part;
		int cpu;

		cpu = part_stat_lock();
		part = disk_map_sector_rcu(req->rq_disk, req->sector);

		part_round_stats(cpu, part);
		part_dec_in_flight(part);

		part_stat_unlock();
	}

	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
	if (blk_rq_cpu_valid(next))
		req->cpu = next->cpu;

	__blk_put_request(q, next);
	return 1;
}

int attempt_back_merge(struct request_queue *q, struct request *rq)
{
	struct request *next = elv_latter_request(q, rq);

	if (next)
		return attempt_merge(q, rq, next);

	return 0;
}

int attempt_front_merge(struct request_queue *q, struct request *rq)
{
	struct request *prev = elv_former_request(q, rq);

	if (prev)
		return attempt_merge(q, prev, rq);

	return 0;
}
Commit	Line	Data
d6d48196 JA	1	/*
	2	* Functions related to segment and merge handling
	3	*/
	4	#include <linux/kernel.h>
	5	#include <linux/module.h>
	6	#include <linux/bio.h>
	7	#include <linux/blkdev.h>
	8	#include <linux/scatterlist.h>
	9
	10	#include "blk.h"
	11
	12	void blk_recalc_rq_sectors(struct request *rq, int nsect)
	13	{
e17fc0a1	14	if (blk_fs_request(rq) \|\| blk_discard_rq(rq)) {
d6d48196 JA	15	rq->hard_sector += nsect;
	16	rq->hard_nr_sectors -= nsect;
	17
	18	/*
	19	* Move the I/O submission pointers ahead if required.
	20	*/
	21	if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
	22	(rq->sector <= rq->hard_sector)) {
	23	rq->sector = rq->hard_sector;
	24	rq->nr_sectors = rq->hard_nr_sectors;
	25	rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
	26	rq->current_nr_sectors = rq->hard_cur_sectors;
	27	rq->buffer = bio_data(rq->bio);
	28	}
	29
	30	/*
	31	* if total number of sectors is less than the first segment
	32	* size, something has gone terribly wrong
	33	*/
	34	if (rq->nr_sectors < rq->current_nr_sectors) {
6728cb0e	35	printk(KERN_ERR "blk: request botched\n");
d6d48196 JA	36	rq->nr_sectors = rq->current_nr_sectors;
	37	}
	38	}
	39	}
	40
	41	void blk_recalc_rq_segments(struct request *rq)
	42	{
	43	int nr_phys_segs;
d6d48196	44	unsigned int phys_size;
d6d48196 JA	45	struct bio_vec bv, bvprv = NULL;
d6d48196 JA	46	int seg_size;
d6d48196 JA	47	int cluster;
	48	struct req_iterator iter;
	49	int high, highprv = 1;
	50	struct request_queue *q = rq->q;
	51
	52	if (!rq->bio)
	53	return;
	54
75ad23bc	55	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
5df97b91 MP	56	seg_size = 0;
5df97b91 MP	57	phys_size = nr_phys_segs = 0;
d6d48196 JA	58	rq_for_each_segment(bv, rq, iter) {
	59	/*
	60	* the trick here is making sure that a high page is never
	61	* considered part of another segment, since that might
	62	* change with the bounce page.
	63	*/
	64	high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
	65	if (high \|\| highprv)
b8b3e16c	66	goto new_segment;
d6d48196 JA	67	if (cluster) {
	68	if (seg_size + bv->bv_len > q->max_segment_size)
	69	goto new_segment;
	70	if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
	71	goto new_segment;
	72	if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
	73	goto new_segment;
d6d48196 JA	74
d6d48196 JA	75	seg_size += bv->bv_len;
d6d48196 JA	76	bvprv = bv;
	77	continue;
	78	}
	79	new_segment:
86771427 FT	80	if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
	81	rq->bio->bi_seg_front_size = seg_size;
	82
d6d48196 JA	83	nr_phys_segs++;
	84	bvprv = bv;
	85	seg_size = bv->bv_len;
	86	highprv = high;
	87	}
	88
86771427 FT	89	if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
	90	rq->bio->bi_seg_front_size = seg_size;
	91	if (seg_size > rq->biotail->bi_seg_back_size)
	92	rq->biotail->bi_seg_back_size = seg_size;
	93
d6d48196	94	rq->nr_phys_segments = nr_phys_segs;
d6d48196 JA	95	}
	96
	97	void blk_recount_segments(struct request_queue q, struct bio bio)
	98	{
	99	struct request rq;
	100	struct bio *nxt = bio->bi_next;
	101	rq.q = q;
	102	rq.bio = rq.biotail = bio;
	103	bio->bi_next = NULL;
	104	blk_recalc_rq_segments(&rq);
	105	bio->bi_next = nxt;
	106	bio->bi_phys_segments = rq.nr_phys_segments;
d6d48196 JA	107	bio->bi_flags \|= (1 << BIO_SEG_VALID);
	108	}
	109	EXPORT_SYMBOL(blk_recount_segments);
	110
	111	static int blk_phys_contig_segment(struct request_queue q, struct bio bio,
	112	struct bio *nxt)
	113	{
75ad23bc	114	if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
d6d48196 JA	115	return 0;
d6d48196 JA	116
86771427 FT	117	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
86771427 FT	118	q->max_segment_size)
d6d48196 JA	119	return 0;
d6d48196 JA	120
e17fc0a1 DW	121	if (!bio_has_data(bio))
	122	return 1;
	123
	124	if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
	125	return 0;
	126
d6d48196	127	/*
e17fc0a1	128	* bio and nxt are contiguous in memory; check if the queue allows
d6d48196 JA	129	* these two to be merged into one
	130	*/
	131	if (BIO_SEG_BOUNDARY(q, bio, nxt))
	132	return 1;
	133
	134	return 0;
	135	}
	136
d6d48196 JA	137	/*
	138	* map a request to scatterlist, return number of sg entries setup. Caller
	139	* must make sure sg can hold rq->nr_phys_segments entries
	140	*/
	141	int blk_rq_map_sg(struct request_queue q, struct request rq,
	142	struct scatterlist *sglist)
	143	{
	144	struct bio_vec bvec, bvprv;
	145	struct req_iterator iter;
	146	struct scatterlist *sg;
	147	int nsegs, cluster;
	148
	149	nsegs = 0;
75ad23bc	150	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
d6d48196 JA	151
	152	/*
	153	* for each bio in rq
	154	*/
	155	bvprv = NULL;
	156	sg = NULL;
	157	rq_for_each_segment(bvec, rq, iter) {
	158	int nbytes = bvec->bv_len;
	159
	160	if (bvprv && cluster) {
	161	if (sg->length + nbytes > q->max_segment_size)
	162	goto new_segment;
	163
	164	if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
	165	goto new_segment;
	166	if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
	167	goto new_segment;
	168
	169	sg->length += nbytes;
	170	} else {
	171	new_segment:
	172	if (!sg)
	173	sg = sglist;
	174	else {
	175	/*
	176	* If the driver previously mapped a shorter
	177	* list, we could see a termination bit
	178	* prematurely unless it fully inits the sg
	179	* table on each mapping. We KNOW that there
	180	* must be more entries here or the driver
	181	* would be buggy, so force clear the
	182	* termination bit to avoid doing a full
	183	* sg_init_table() in drivers for each command.
	184	*/
	185	sg->page_link &= ~0x02;
	186	sg = sg_next(sg);
	187	}
	188
	189	sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
	190	nsegs++;
	191	}
	192	bvprv = bvec;
	193	} /* segments in rq */
	194
f18573ab FT	195
	196	if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
	197	(rq->data_len & q->dma_pad_mask)) {
	198	unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
	199
	200	sg->length += pad_len;
	201	rq->extra_len += pad_len;
	202	}
	203
2fb98e84	204	if (q->dma_drain_size && q->dma_drain_needed(rq)) {
db0a2e00 TH	205	if (rq->cmd_flags & REQ_RW)
	206	memset(q->dma_drain_buffer, 0, q->dma_drain_size);
	207
d6d48196 JA	208	sg->page_link &= ~0x02;
	209	sg = sg_next(sg);
	210	sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
	211	q->dma_drain_size,
	212	((unsigned long)q->dma_drain_buffer) &
	213	(PAGE_SIZE - 1));
	214	nsegs++;
7a85f889	215	rq->extra_len += q->dma_drain_size;
d6d48196 JA	216	}
	217
	218	if (sg)
	219	sg_mark_end(sg);
	220
	221	return nsegs;
	222	}
d6d48196 JA	223	EXPORT_SYMBOL(blk_rq_map_sg);
d6d48196 JA	224
d6d48196 JA	225	static inline int ll_new_hw_segment(struct request_queue *q,
	226	struct request *req,
	227	struct bio *bio)
	228	{
d6d48196 JA	229	int nr_phys_segs = bio_phys_segments(q, bio);
d6d48196 JA	230
5df97b91	231	if (req->nr_phys_segments + nr_phys_segs > q->max_hw_segments
d6d48196 JA	232	\|\| req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
	233	req->cmd_flags \|= REQ_NOMERGE;
	234	if (req == q->last_merge)
	235	q->last_merge = NULL;
	236	return 0;
	237	}
	238
	239	/*
	240	* This will form the start of a new hw segment. Bump both
	241	* counters.
	242	*/
d6d48196 JA	243	req->nr_phys_segments += nr_phys_segs;
	244	return 1;
	245	}
	246
	247	int ll_back_merge_fn(struct request_queue q, struct request req,
	248	struct bio *bio)
	249	{
	250	unsigned short max_sectors;
d6d48196 JA	251
	252	if (unlikely(blk_pc_request(req)))
	253	max_sectors = q->max_hw_sectors;
	254	else
	255	max_sectors = q->max_sectors;
	256
	257	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
	258	req->cmd_flags \|= REQ_NOMERGE;
	259	if (req == q->last_merge)
	260	q->last_merge = NULL;
	261	return 0;
	262	}
2cdf79ca	263	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
d6d48196	264	blk_recount_segments(q, req->biotail);
2cdf79ca	265	if (!bio_flagged(bio, BIO_SEG_VALID))
d6d48196	266	blk_recount_segments(q, bio);
d6d48196 JA	267
	268	return ll_new_hw_segment(q, req, bio);
	269	}
	270
6728cb0e	271	int ll_front_merge_fn(struct request_queue q, struct request req,
d6d48196 JA	272	struct bio *bio)
	273	{
	274	unsigned short max_sectors;
d6d48196 JA	275
	276	if (unlikely(blk_pc_request(req)))
	277	max_sectors = q->max_hw_sectors;
	278	else
	279	max_sectors = q->max_sectors;
	280
	281
	282	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
	283	req->cmd_flags \|= REQ_NOMERGE;
	284	if (req == q->last_merge)
	285	q->last_merge = NULL;
	286	return 0;
	287	}
2cdf79ca	288	if (!bio_flagged(bio, BIO_SEG_VALID))
d6d48196	289	blk_recount_segments(q, bio);
2cdf79ca	290	if (!bio_flagged(req->bio, BIO_SEG_VALID))
d6d48196	291	blk_recount_segments(q, req->bio);
d6d48196 JA	292
	293	return ll_new_hw_segment(q, req, bio);
	294	}
	295
	296	static int ll_merge_requests_fn(struct request_queue q, struct request req,
	297	struct request *next)
	298	{
	299	int total_phys_segments;
86771427 FT	300	unsigned int seg_size =
86771427 FT	301	req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
d6d48196 JA	302
	303	/*
	304	* First check if the either of the requests are re-queued
	305	* requests. Can't merge them if they are.
	306	*/
	307	if (req->special \|\| next->special)
	308	return 0;
	309
	310	/*
	311	* Will it become too large?
	312	*/
	313	if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
	314	return 0;
	315
	316	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
86771427 FT	317	if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
	318	if (req->nr_phys_segments == 1)
	319	req->bio->bi_seg_front_size = seg_size;
	320	if (next->nr_phys_segments == 1)
	321	next->biotail->bi_seg_back_size = seg_size;
d6d48196	322	total_phys_segments--;
86771427	323	}
d6d48196 JA	324
	325	if (total_phys_segments > q->max_phys_segments)
	326	return 0;
	327
5df97b91	328	if (total_phys_segments > q->max_hw_segments)
d6d48196 JA	329	return 0;
	330
	331	/* Merge is OK... */
	332	req->nr_phys_segments = total_phys_segments;
d6d48196 JA	333	return 1;
	334	}
	335
	336	/*
	337	* Has to be called with the request spinlock acquired
	338	*/
	339	static int attempt_merge(struct request_queue q, struct request req,
	340	struct request *next)
	341	{
	342	if (!rq_mergeable(req) \|\| !rq_mergeable(next))
	343	return 0;
	344
	345	/*
	346	* not contiguous
	347	*/
	348	if (req->sector + req->nr_sectors != next->sector)
	349	return 0;
	350
	351	if (rq_data_dir(req) != rq_data_dir(next)
	352	\|\| req->rq_disk != next->rq_disk
	353	\|\| next->special)
	354	return 0;
	355
7ba1ba12 MP	356	if (blk_integrity_rq(req) != blk_integrity_rq(next))
	357	return 0;
	358
d6d48196 JA	359	/*
	360	* If we are allowed to merge, then append bio list
	361	* from next to rq and release next. merge_requests_fn
	362	* will have updated segment counts, update sector
	363	* counts here.
	364	*/
	365	if (!ll_merge_requests_fn(q, req, next))
	366	return 0;
	367
	368	/*
	369	* At this point we have either done a back merge
	370	* or front merge. We need the smaller start_time of
	371	* the merged requests to be the current request
	372	* for accounting purposes.
	373	*/
	374	if (time_after(req->start_time, next->start_time))
	375	req->start_time = next->start_time;
	376
	377	req->biotail->bi_next = next->bio;
	378	req->biotail = next->biotail;
	379
	380	req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
	381
	382	elv_merge_requests(q, req, next);
	383
	384	if (req->rq_disk) {
e71bf0d0	385	struct hd_struct *part;
c9959059	386	int cpu;
e71bf0d0	387
074a7aca	388	cpu = part_stat_lock();
e71bf0d0	389	part = disk_map_sector_rcu(req->rq_disk, req->sector);
c9959059	390
074a7aca TH	391	part_round_stats(cpu, part);
074a7aca TH	392	part_dec_in_flight(part);
e71bf0d0	393
074a7aca	394	part_stat_unlock();
d6d48196 JA	395	}
	396
	397	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
ab780f1e JA	398	if (blk_rq_cpu_valid(next))
ab780f1e JA	399	req->cpu = next->cpu;
d6d48196 JA	400
	401	__blk_put_request(q, next);
	402	return 1;
	403	}
	404
	405	int attempt_back_merge(struct request_queue q, struct request rq)
	406	{
	407	struct request *next = elv_latter_request(q, rq);
	408
	409	if (next)
	410	return attempt_merge(q, rq, next);
	411
	412	return 0;
	413	}
	414
	415	int attempt_front_merge(struct request_queue q, struct request rq)
	416	{
	417	struct request *prev = elv_former_request(q, rq);
	418
	419	if (prev)
	420	return attempt_merge(q, prev, rq);
	421
	422	return 0;
	423	}