path: root/block/blk-merge.c (plain)
blob: 2642e5fc8b69a03494b62638d4eca98ee07b7edc

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 <trace/events/block.h>
11
12	#include "blk.h"
13
14	static struct bio *blk_bio_discard_split(struct request_queue *q,
15	struct bio *bio,
16	struct bio_set *bs,
17	unsigned *nsegs)
18	{
19	unsigned int max_discard_sectors, granularity;
20	int alignment;
21	sector_t tmp;
22	unsigned split_sectors;
23
24	*nsegs = 1;
25
26	/* Zero-sector (unknown) and one-sector granularities are the same. */
27	granularity = max(q->limits.discard_granularity >> 9, 1U);
28
29	max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
30	max_discard_sectors -= max_discard_sectors % granularity;
31
32	if (unlikely(!max_discard_sectors)) {
33	/* XXX: warn */
34	return NULL;
35	}
36
37	if (bio_sectors(bio) <= max_discard_sectors)
38	return NULL;
39
40	split_sectors = max_discard_sectors;
41
42	/*
43	* If the next starting sector would be misaligned, stop the discard at
44	* the previous aligned sector.
45	*/
46	alignment = (q->limits.discard_alignment >> 9) % granularity;
47
48	tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
49	tmp = sector_div(tmp, granularity);
50
51	if (split_sectors > tmp)
52	split_sectors -= tmp;
53
54	return bio_split(bio, split_sectors, GFP_NOIO, bs);
55	}
56
57	static struct bio *blk_bio_write_same_split(struct request_queue *q,
58	struct bio *bio,
59	struct bio_set *bs,
60	unsigned *nsegs)
61	{
62	*nsegs = 1;
63
64	if (!q->limits.max_write_same_sectors)
65	return NULL;
66
67	if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
68	return NULL;
69
70	return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
71	}
72
73	static inline unsigned get_max_io_size(struct request_queue *q,
74	struct bio *bio)
75	{
76	unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
77	unsigned mask = queue_logical_block_size(q) - 1;
78
79	/* aligned to logical block size */
80	sectors &= ~(mask >> 9);
81
82	return sectors;
83	}
84
85	static struct bio *blk_bio_segment_split(struct request_queue *q,
86	struct bio *bio,
87	struct bio_set *bs,
88	unsigned *segs)
89	{
90	struct bio_vec bv, bvprv, *bvprvp = NULL;
91	struct bvec_iter iter;
92	unsigned seg_size = 0, nsegs = 0, sectors = 0;
93	unsigned front_seg_size = bio->bi_seg_front_size;
94	bool do_split = true;
95	struct bio *new = NULL;
96	const unsigned max_sectors = get_max_io_size(q, bio);
97	unsigned bvecs = 0;
98
99	bio_for_each_segment(bv, bio, iter) {
100	/*
101	* With arbitrary bio size, the incoming bio may be very
102	* big. We have to split the bio into small bios so that
103	* each holds at most BIO_MAX_PAGES bvecs because
104	* bio_clone() can fail to allocate big bvecs.
105	*
106	* It should have been better to apply the limit per
107	* request queue in which bio_clone() is involved,
108	* instead of globally. The biggest blocker is the
109	* bio_clone() in bio bounce.
110	*
111	* If bio is splitted by this reason, we should have
112	* allowed to continue bios merging, but don't do
113	* that now for making the change simple.
114	*
115	* TODO: deal with bio bounce's bio_clone() gracefully
116	* and convert the global limit into per-queue limit.
117	*/
118	if (bvecs++ >= BIO_MAX_PAGES)
119	goto split;
120
121	/*
122	* If the queue doesn't support SG gaps and adding this
123	* offset would create a gap, disallow it.
124	*/
125	if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
126	goto split;
127
128	if (sectors + (bv.bv_len >> 9) > max_sectors) {
129	/*
130	* Consider this a new segment if we're splitting in
131	* the middle of this vector.
132	*/
133	if (nsegs < queue_max_segments(q) &&
134	sectors < max_sectors) {
135	nsegs++;
136	sectors = max_sectors;
137	}
138	if (sectors)
139	goto split;
140	/* Make this single bvec as the 1st segment */
141	}
142
143	if (bvprvp && blk_queue_cluster(q)) {
144	if (seg_size + bv.bv_len > queue_max_segment_size(q))
145	goto new_segment;
146	if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
147	goto new_segment;
148	if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
149	goto new_segment;
150
151	seg_size += bv.bv_len;
152	bvprv = bv;
153	bvprvp = &bvprv;
154	sectors += bv.bv_len >> 9;
155
156	if (nsegs == 1 && seg_size > front_seg_size)
157	front_seg_size = seg_size;
158	continue;
159	}
160	new_segment:
161	if (nsegs == queue_max_segments(q))
162	goto split;
163
164	nsegs++;
165	bvprv = bv;
166	bvprvp = &bvprv;
167	seg_size = bv.bv_len;
168	sectors += bv.bv_len >> 9;
169
170	if (nsegs == 1 && seg_size > front_seg_size)
171	front_seg_size = seg_size;
172	}
173
174	do_split = false;
175	split:
176	*segs = nsegs;
177
178	if (do_split) {
179	new = bio_split(bio, sectors, GFP_NOIO, bs);
180	if (new)
181	bio = new;
182	}
183
184	bio->bi_seg_front_size = front_seg_size;
185	if (seg_size > bio->bi_seg_back_size)
186	bio->bi_seg_back_size = seg_size;
187
188	return do_split ? new : NULL;
189	}
190
191	void blk_queue_split(struct request_queue *q, struct bio **bio,
192	struct bio_set *bs)
193	{
194	struct bio *split, *res;
195	unsigned nsegs;
196
197	switch (bio_op(*bio)) {
198	case REQ_OP_DISCARD:
199	case REQ_OP_SECURE_ERASE:
200	split = blk_bio_discard_split(q, *bio, bs, &nsegs);
201	break;
202	case REQ_OP_WRITE_SAME:
203	split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
204	break;
205	default:
206	split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
207	break;
208	}
209
210	/* physical segments can be figured out during splitting */
211	res = split ? split : *bio;
212	res->bi_phys_segments = nsegs;
213	bio_set_flag(res, BIO_SEG_VALID);
214
215	if (split) {
216	/* there isn't chance to merge the splitted bio */
217	split->bi_opf |= REQ_NOMERGE;
218
219	bio_chain(split, *bio);
220	trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
221	generic_make_request(*bio);
222	*bio = split;
223	}
224	}
225	EXPORT_SYMBOL(blk_queue_split);
226
227	static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
228	struct bio *bio,
229	bool no_sg_merge)
230	{
231	struct bio_vec bv, bvprv = { NULL };
232	int cluster, prev = 0;
233	unsigned int seg_size, nr_phys_segs;
234	struct bio *fbio, *bbio;
235	struct bvec_iter iter;
236
237	if (!bio)
238	return 0;
239
240	/*
241	* This should probably be returning 0, but blk_add_request_payload()
242	* (Christoph!!!!)
243	*/
244	if (bio_op(bio) == REQ_OP_DISCARD || bio_op(bio) == REQ_OP_SECURE_ERASE)
245	return 1;
246
247	if (bio_op(bio) == REQ_OP_WRITE_SAME)
248	return 1;
249
250	fbio = bio;
251	cluster = blk_queue_cluster(q);
252	seg_size = 0;
253	nr_phys_segs = 0;
254	for_each_bio(bio) {
255	bio_for_each_segment(bv, bio, iter) {
256	/*
257	* If SG merging is disabled, each bio vector is
258	* a segment
259	*/
260	if (no_sg_merge)
261	goto new_segment;
262
263	if (prev && cluster) {
264	if (seg_size + bv.bv_len
265	> queue_max_segment_size(q))
266	goto new_segment;
267	if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
268	goto new_segment;
269	if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
270	goto new_segment;
271
272	seg_size += bv.bv_len;
273	bvprv = bv;
274	continue;
275	}
276	new_segment:
277	if (nr_phys_segs == 1 && seg_size >
278	fbio->bi_seg_front_size)
279	fbio->bi_seg_front_size = seg_size;
280
281	nr_phys_segs++;
282	bvprv = bv;
283	prev = 1;
284	seg_size = bv.bv_len;
285	}
286	bbio = bio;
287	}
288
289	if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
290	fbio->bi_seg_front_size = seg_size;
291	if (seg_size > bbio->bi_seg_back_size)
292	bbio->bi_seg_back_size = seg_size;
293
294	return nr_phys_segs;
295	}
296
297	void blk_recalc_rq_segments(struct request *rq)
298	{
299	bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
300	&rq->q->queue_flags);
301
302	rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
303	no_sg_merge);
304	}
305
306	void blk_recount_segments(struct request_queue *q, struct bio *bio)
307	{
308	unsigned short seg_cnt;
309
310	/* estimate segment number by bi_vcnt for non-cloned bio */
311	if (bio_flagged(bio, BIO_CLONED))
312	seg_cnt = bio_segments(bio);
313	else
314	seg_cnt = bio->bi_vcnt;
315
316	if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
317	(seg_cnt < queue_max_segments(q)))
318	bio->bi_phys_segments = seg_cnt;
319	else {
320	struct bio *nxt = bio->bi_next;
321
322	bio->bi_next = NULL;
323	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
324	bio->bi_next = nxt;
325	}
326
327	bio_set_flag(bio, BIO_SEG_VALID);
328	}
329	EXPORT_SYMBOL(blk_recount_segments);
330
331	static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
332	struct bio *nxt)
333	{
334	struct bio_vec end_bv = { NULL }, nxt_bv;
335
336	if (!blk_queue_cluster(q))
337	return 0;
338
339	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
340	queue_max_segment_size(q))
341	return 0;
342
343	if (!bio_has_data(bio))
344	return 1;
345
346	bio_get_last_bvec(bio, &end_bv);
347	bio_get_first_bvec(nxt, &nxt_bv);
348
349	if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
350	return 0;
351
352	/*
353	* bio and nxt are contiguous in memory; check if the queue allows
354	* these two to be merged into one
355	*/
356	if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
357	return 1;
358
359	return 0;
360	}
361
362	static inline void
363	__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
364	struct scatterlist *sglist, struct bio_vec *bvprv,
365	struct scatterlist **sg, int *nsegs, int *cluster)
366	{
367
368	int nbytes = bvec->bv_len;
369
370	if (*sg && *cluster) {
371	if ((*sg)->length + nbytes > queue_max_segment_size(q))
372	goto new_segment;
373
374	if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
375	goto new_segment;
376	if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
377	goto new_segment;
378
379	(*sg)->length += nbytes;
380	} else {
381	new_segment:
382	if (!*sg)
383	*sg = sglist;
384	else {
385	/*
386	* If the driver previously mapped a shorter
387	* list, we could see a termination bit
388	* prematurely unless it fully inits the sg
389	* table on each mapping. We KNOW that there
390	* must be more entries here or the driver
391	* would be buggy, so force clear the
392	* termination bit to avoid doing a full
393	* sg_init_table() in drivers for each command.
394	*/
395	sg_unmark_end(*sg);
396	*sg = sg_next(*sg);
397	}
398
399	sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
400	(*nsegs)++;
401	}
402	*bvprv = *bvec;
403	}
404
405	static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
406	struct scatterlist *sglist,
407	struct scatterlist **sg)
408	{
409	struct bio_vec bvec, bvprv = { NULL };
410	struct bvec_iter iter;
411	int nsegs, cluster;
412
413	nsegs = 0;
414	cluster = blk_queue_cluster(q);
415
416	switch (bio_op(bio)) {
417	case REQ_OP_DISCARD:
418	case REQ_OP_SECURE_ERASE:
419	/*
420	* This is a hack - drivers should be neither modifying the
421	* biovec, nor relying on bi_vcnt - but because of
422	* blk_add_request_payload(), a discard bio may or may not have
423	* a payload we need to set up here (thank you Christoph) and
424	* bi_vcnt is really the only way of telling if we need to.
425	*/
426	if (!bio->bi_vcnt)
427	return 0;
428	/* Fall through */
429	case REQ_OP_WRITE_SAME:
430	*sg = sglist;
431	bvec = bio_iovec(bio);
432	sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
433	return 1;
434	default:
435	break;
436	}
437
438	for_each_bio(bio)
439	bio_for_each_segment(bvec, bio, iter)
440	__blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
441	&nsegs, &cluster);
442
443	return nsegs;
444	}
445
446	/*
447	* map a request to scatterlist, return number of sg entries setup. Caller
448	* must make sure sg can hold rq->nr_phys_segments entries
449	*/
450	int blk_rq_map_sg(struct request_queue *q, struct request *rq,
451	struct scatterlist *sglist)
452	{
453	struct scatterlist *sg = NULL;
454	int nsegs = 0;
455
456	if (rq->bio)
457	nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
458
459	if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
460	(blk_rq_bytes(rq) & q->dma_pad_mask)) {
461	unsigned int pad_len =
462	(q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
463
464	sg->length += pad_len;
465	rq->extra_len += pad_len;
466	}
467
468	if (q->dma_drain_size && q->dma_drain_needed(rq)) {
469	if (op_is_write(req_op(rq)))
470	memset(q->dma_drain_buffer, 0, q->dma_drain_size);
471
472	sg_unmark_end(sg);
473	sg = sg_next(sg);
474	sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
475	q->dma_drain_size,
476	((unsigned long)q->dma_drain_buffer) &
477	(PAGE_SIZE - 1));
478	nsegs++;
479	rq->extra_len += q->dma_drain_size;
480	}
481
482	if (sg)
483	sg_mark_end(sg);
484
485	/*
486	* Something must have been wrong if the figured number of
487	* segment is bigger than number of req's physical segments
488	*/
489	WARN_ON(nsegs > rq->nr_phys_segments);
490
491	return nsegs;
492	}
493	EXPORT_SYMBOL(blk_rq_map_sg);
494
495	static inline int ll_new_hw_segment(struct request_queue *q,
496	struct request *req,
497	struct bio *bio)
498	{
499	int nr_phys_segs = bio_phys_segments(q, bio);
500
501	if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
502	goto no_merge;
503
504	if (blk_integrity_merge_bio(q, req, bio) == false)
505	goto no_merge;
506
507	/*
508	* This will form the start of a new hw segment. Bump both
509	* counters.
510	*/
511	req->nr_phys_segments += nr_phys_segs;
512	return 1;
513
514	no_merge:
515	req->cmd_flags |= REQ_NOMERGE;
516	if (req == q->last_merge)
517	q->last_merge = NULL;
518	return 0;
519	}
520
521	int ll_back_merge_fn(struct request_queue *q, struct request *req,
522	struct bio *bio)
523	{
524	if (req_gap_back_merge(req, bio))
525	return 0;
526	if (blk_integrity_rq(req) &&
527	integrity_req_gap_back_merge(req, bio))
528	return 0;
529	if (blk_rq_sectors(req) + bio_sectors(bio) >
530	blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
531	req->cmd_flags |= REQ_NOMERGE;
532	if (req == q->last_merge)
533	q->last_merge = NULL;
534	return 0;
535	}
536	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
537	blk_recount_segments(q, req->biotail);
538	if (!bio_flagged(bio, BIO_SEG_VALID))
539	blk_recount_segments(q, bio);
540
541	return ll_new_hw_segment(q, req, bio);
542	}
543
544	int ll_front_merge_fn(struct request_queue *q, struct request *req,
545	struct bio *bio)
546	{
547
548	if (req_gap_front_merge(req, bio))
549	return 0;
550	if (blk_integrity_rq(req) &&
551	integrity_req_gap_front_merge(req, bio))
552	return 0;
553	if (blk_rq_sectors(req) + bio_sectors(bio) >
554	blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
555	req->cmd_flags |= REQ_NOMERGE;
556	if (req == q->last_merge)
557	q->last_merge = NULL;
558	return 0;
559	}
560	if (!bio_flagged(bio, BIO_SEG_VALID))
561	blk_recount_segments(q, bio);
562	if (!bio_flagged(req->bio, BIO_SEG_VALID))
563	blk_recount_segments(q, req->bio);
564
565	return ll_new_hw_segment(q, req, bio);
566	}
567
568	/*
569	* blk-mq uses req->special to carry normal driver per-request payload, it
570	* does not indicate a prepared command that we cannot merge with.
571	*/
572	static bool req_no_special_merge(struct request *req)
573	{
574	struct request_queue *q = req->q;
575
576	return !q->mq_ops && req->special;
577	}
578
579	static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
580	struct request *next)
581	{
582	int total_phys_segments;
583	unsigned int seg_size =
584	req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
585
586	/*
587	* First check if the either of the requests are re-queued
588	* requests. Can't merge them if they are.
589	*/
590	if (req_no_special_merge(req) || req_no_special_merge(next))
591	return 0;
592
593	if (req_gap_back_merge(req, next->bio))
594	return 0;
595
596	/*
597	* Will it become too large?
598	*/
599	if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
600	blk_rq_get_max_sectors(req, blk_rq_pos(req)))
601	return 0;
602
603	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
604	if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
605	if (req->nr_phys_segments == 1)
606	req->bio->bi_seg_front_size = seg_size;
607	if (next->nr_phys_segments == 1)
608	next->biotail->bi_seg_back_size = seg_size;
609	total_phys_segments--;
610	}
611
612	if (total_phys_segments > queue_max_segments(q))
613	return 0;
614
615	if (blk_integrity_merge_rq(q, req, next) == false)
616	return 0;
617
618	/* Merge is OK... */
619	req->nr_phys_segments = total_phys_segments;
620	return 1;
621	}
622
623	/**
624	* blk_rq_set_mixed_merge - mark a request as mixed merge
625	* @rq: request to mark as mixed merge
626	*
627	* Description:
628	* @rq is about to be mixed merged. Make sure the attributes
629	* which can be mixed are set in each bio and mark @rq as mixed
630	* merged.
631	*/
632	void blk_rq_set_mixed_merge(struct request *rq)
633	{
634	unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
635	struct bio *bio;
636
637	if (rq->cmd_flags & REQ_MIXED_MERGE)
638	return;
639
640	/*
641	* @rq will no longer represent mixable attributes for all the
642	* contained bios. It will just track those of the first one.
643	* Distributes the attributs to each bio.
644	*/
645	for (bio = rq->bio; bio; bio = bio->bi_next) {
646	WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
647	(bio->bi_opf & REQ_FAILFAST_MASK) != ff);
648	bio->bi_opf |= ff;
649	}
650	rq->cmd_flags |= REQ_MIXED_MERGE;
651	}
652
653	static void blk_account_io_merge(struct request *req)
654	{
655	if (blk_do_io_stat(req)) {
656	struct hd_struct *part;
657	int cpu;
658
659	cpu = part_stat_lock();
660	part = req->part;
661
662	part_round_stats(cpu, part);
663	part_dec_in_flight(part, rq_data_dir(req));
664
665	hd_struct_put(part);
666	part_stat_unlock();
667	}
668	}
669
670	/*
671	* Has to be called with the request spinlock acquired
672	*/
673	static int attempt_merge(struct request_queue *q, struct request *req,
674	struct request *next)
675	{
676	if (!rq_mergeable(req) || !rq_mergeable(next))
677	return 0;
678
679	if (req_op(req) != req_op(next))
680	return 0;
681
682	/*
683	* not contiguous
684	*/
685	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
686	return 0;
687
688	if (rq_data_dir(req) != rq_data_dir(next)
689	|| req->rq_disk != next->rq_disk
690	|| req_no_special_merge(next))
691	return 0;
692
693	if (req_op(req) == REQ_OP_WRITE_SAME &&
694	!blk_write_same_mergeable(req->bio, next->bio))
695	return 0;
696
697	/*
698	* If we are allowed to merge, then append bio list
699	* from next to rq and release next. merge_requests_fn
700	* will have updated segment counts, update sector
701	* counts here.
702	*/
703	if (!ll_merge_requests_fn(q, req, next))
704	return 0;
705
706	/*
707	* If failfast settings disagree or any of the two is already
708	* a mixed merge, mark both as mixed before proceeding. This
709	* makes sure that all involved bios have mixable attributes
710	* set properly.
711	*/
712	if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
713	(req->cmd_flags & REQ_FAILFAST_MASK) !=
714	(next->cmd_flags & REQ_FAILFAST_MASK)) {
715	blk_rq_set_mixed_merge(req);
716	blk_rq_set_mixed_merge(next);
717	}
718
719	/*
720	* At this point we have either done a back merge
721	* or front merge. We need the smaller start_time of
722	* the merged requests to be the current request
723	* for accounting purposes.
724	*/
725	if (time_after(req->start_time, next->start_time))
726	req->start_time = next->start_time;
727
728	req->biotail->bi_next = next->bio;
729	req->biotail = next->biotail;
730
731	req->__data_len += blk_rq_bytes(next);
732
733	elv_merge_requests(q, req, next);
734
735	/*
736	* 'next' is going away, so update stats accordingly
737	*/
738	blk_account_io_merge(next);
739
740	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
741	if (blk_rq_cpu_valid(next))
742	req->cpu = next->cpu;
743
744	/* owner-ship of bio passed from next to req */
745	next->bio = NULL;
746	__blk_put_request(q, next);
747	return 1;
748	}
749
750	int attempt_back_merge(struct request_queue *q, struct request *rq)
751	{
752	struct request *next = elv_latter_request(q, rq);
753
754	if (next)
755	return attempt_merge(q, rq, next);
756
757	return 0;
758	}
759
760	int attempt_front_merge(struct request_queue *q, struct request *rq)
761	{
762	struct request *prev = elv_former_request(q, rq);
763
764	if (prev)
765	return attempt_merge(q, prev, rq);
766
767	return 0;
768	}
769
770	int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
771	struct request *next)
772	{
773	struct elevator_queue *e = q->elevator;
774
775	if (e->type->ops.elevator_allow_rq_merge_fn)
776	if (!e->type->ops.elevator_allow_rq_merge_fn(q, rq, next))
777	return 0;
778
779	return attempt_merge(q, rq, next);
780	}
781
782	bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
783	{
784	if (!rq_mergeable(rq) || !bio_mergeable(bio))
785	return false;
786
787	if (req_op(rq) != bio_op(bio))
788	return false;
789
790	/* different data direction or already started, don't merge */
791	if (bio_data_dir(bio) != rq_data_dir(rq))
792	return false;
793
794	/* must be same device and not a special request */
795	if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
796	return false;
797
798	/* only merge integrity protected bio into ditto rq */
799	if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
800	return false;
801
802	/* must be using the same buffer */
803	if (req_op(rq) == REQ_OP_WRITE_SAME &&
804	!blk_write_same_mergeable(rq->bio, bio))
805	return false;
806
807	return true;
808	}
809
810	int blk_try_merge(struct request *rq, struct bio *bio)
811	{
812	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
813	return ELEVATOR_BACK_MERGE;
814	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
815	return ELEVATOR_FRONT_MERGE;
816	return ELEVATOR_NO_MERGE;
817	}
818