1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Functions related to segment and merge handling
4 */
5#include <linux/kernel.h>
6#include <linux/module.h>
7#include <linux/bio.h>
8#include <linux/blkdev.h>
9#include <linux/blk-integrity.h>
10#include <linux/scatterlist.h>
11#include <linux/part_stat.h>
12#include <linux/blk-cgroup.h>
13
14#include <trace/events/block.h>
15
16#include "blk.h"
17#include "blk-mq-sched.h"
18#include "blk-rq-qos.h"
19#include "blk-throttle.h"
20
21static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
22{
23 *bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
24}
25
26static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
27{
28 struct bvec_iter iter = bio->bi_iter;
29 int idx;
30
31 bio_get_first_bvec(bio, bv);
32 if (bv->bv_len == bio->bi_iter.bi_size)
33 return; /* this bio only has a single bvec */
34
35 bio_advance_iter(bio, iter: &iter, bytes: iter.bi_size);
36
37 if (!iter.bi_bvec_done)
38 idx = iter.bi_idx - 1;
39 else /* in the middle of bvec */
40 idx = iter.bi_idx;
41
42 *bv = bio->bi_io_vec[idx];
43
44 /*
45 * iter.bi_bvec_done records actual length of the last bvec
46 * if this bio ends in the middle of one io vector
47 */
48 if (iter.bi_bvec_done)
49 bv->bv_len = iter.bi_bvec_done;
50}
51
52static inline bool bio_will_gap(struct request_queue *q,
53 struct request *prev_rq, struct bio *prev, struct bio *next)
54{
55 struct bio_vec pb, nb;
56
57 if (!bio_has_data(bio: prev) || !queue_virt_boundary(q))
58 return false;
59
60 /*
61 * Don't merge if the 1st bio starts with non-zero offset, otherwise it
62 * is quite difficult to respect the sg gap limit. We work hard to
63 * merge a huge number of small single bios in case of mkfs.
64 */
65 if (prev_rq)
66 bio_get_first_bvec(bio: prev_rq->bio, bv: &pb);
67 else
68 bio_get_first_bvec(bio: prev, bv: &pb);
69 if (pb.bv_offset & queue_virt_boundary(q))
70 return true;
71
72 /*
73 * We don't need to worry about the situation that the merged segment
74 * ends in unaligned virt boundary:
75 *
76 * - if 'pb' ends aligned, the merged segment ends aligned
77 * - if 'pb' ends unaligned, the next bio must include
78 * one single bvec of 'nb', otherwise the 'nb' can't
79 * merge with 'pb'
80 */
81 bio_get_last_bvec(bio: prev, bv: &pb);
82 bio_get_first_bvec(bio: next, bv: &nb);
83 if (biovec_phys_mergeable(q, vec1: &pb, vec2: &nb))
84 return false;
85 return __bvec_gap_to_prev(lim: &q->limits, bprv: &pb, offset: nb.bv_offset);
86}
87
88static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
89{
90 return bio_will_gap(q: req->q, prev_rq: req, prev: req->biotail, next: bio);
91}
92
93static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
94{
95 return bio_will_gap(q: req->q, NULL, prev: bio, next: req->bio);
96}
97
98/*
99 * The max size one bio can handle is UINT_MAX becasue bvec_iter.bi_size
100 * is defined as 'unsigned int', meantime it has to be aligned to with the
101 * logical block size, which is the minimum accepted unit by hardware.
102 */
103static unsigned int bio_allowed_max_sectors(const struct queue_limits *lim)
104{
105 return round_down(UINT_MAX, lim->logical_block_size) >> SECTOR_SHIFT;
106}
107
108static struct bio *bio_split_discard(struct bio *bio,
109 const struct queue_limits *lim,
110 unsigned *nsegs, struct bio_set *bs)
111{
112 unsigned int max_discard_sectors, granularity;
113 sector_t tmp;
114 unsigned split_sectors;
115
116 *nsegs = 1;
117
118 /* Zero-sector (unknown) and one-sector granularities are the same. */
119 granularity = max(lim->discard_granularity >> 9, 1U);
120
121 max_discard_sectors =
122 min(lim->max_discard_sectors, bio_allowed_max_sectors(lim));
123 max_discard_sectors -= max_discard_sectors % granularity;
124
125 if (unlikely(!max_discard_sectors)) {
126 /* XXX: warn */
127 return NULL;
128 }
129
130 if (bio_sectors(bio) <= max_discard_sectors)
131 return NULL;
132
133 split_sectors = max_discard_sectors;
134
135 /*
136 * If the next starting sector would be misaligned, stop the discard at
137 * the previous aligned sector.
138 */
139 tmp = bio->bi_iter.bi_sector + split_sectors -
140 ((lim->discard_alignment >> 9) % granularity);
141 tmp = sector_div(tmp, granularity);
142
143 if (split_sectors > tmp)
144 split_sectors -= tmp;
145
146 return bio_split(bio, sectors: split_sectors, GFP_NOIO, bs);
147}
148
149static struct bio *bio_split_write_zeroes(struct bio *bio,
150 const struct queue_limits *lim,
151 unsigned *nsegs, struct bio_set *bs)
152{
153 *nsegs = 0;
154 if (!lim->max_write_zeroes_sectors)
155 return NULL;
156 if (bio_sectors(bio) <= lim->max_write_zeroes_sectors)
157 return NULL;
158 return bio_split(bio, sectors: lim->max_write_zeroes_sectors, GFP_NOIO, bs);
159}
160
161/*
162 * Return the maximum number of sectors from the start of a bio that may be
163 * submitted as a single request to a block device. If enough sectors remain,
164 * align the end to the physical block size. Otherwise align the end to the
165 * logical block size. This approach minimizes the number of non-aligned
166 * requests that are submitted to a block device if the start of a bio is not
167 * aligned to a physical block boundary.
168 */
169static inline unsigned get_max_io_size(struct bio *bio,
170 const struct queue_limits *lim)
171{
172 unsigned pbs = lim->physical_block_size >> SECTOR_SHIFT;
173 unsigned lbs = lim->logical_block_size >> SECTOR_SHIFT;
174 unsigned max_sectors = lim->max_sectors, start, end;
175
176 if (lim->chunk_sectors) {
177 max_sectors = min(max_sectors,
178 blk_chunk_sectors_left(bio->bi_iter.bi_sector,
179 lim->chunk_sectors));
180 }
181
182 start = bio->bi_iter.bi_sector & (pbs - 1);
183 end = (start + max_sectors) & ~(pbs - 1);
184 if (end > start)
185 return end - start;
186 return max_sectors & ~(lbs - 1);
187}
188
189/**
190 * get_max_segment_size() - maximum number of bytes to add as a single segment
191 * @lim: Request queue limits.
192 * @start_page: See below.
193 * @offset: Offset from @start_page where to add a segment.
194 *
195 * Returns the maximum number of bytes that can be added as a single segment.
196 */
197static inline unsigned get_max_segment_size(const struct queue_limits *lim,
198 struct page *start_page, unsigned long offset)
199{
200 unsigned long mask = lim->seg_boundary_mask;
201
202 offset = mask & (page_to_phys(start_page) + offset);
203
204 /*
205 * Prevent an overflow if mask = ULONG_MAX and offset = 0 by adding 1
206 * after having calculated the minimum.
207 */
208 return min(mask - offset, (unsigned long)lim->max_segment_size - 1) + 1;
209}
210
211/**
212 * bvec_split_segs - verify whether or not a bvec should be split in the middle
213 * @lim: [in] queue limits to split based on
214 * @bv: [in] bvec to examine
215 * @nsegs: [in,out] Number of segments in the bio being built. Incremented
216 * by the number of segments from @bv that may be appended to that
217 * bio without exceeding @max_segs
218 * @bytes: [in,out] Number of bytes in the bio being built. Incremented
219 * by the number of bytes from @bv that may be appended to that
220 * bio without exceeding @max_bytes
221 * @max_segs: [in] upper bound for *@nsegs
222 * @max_bytes: [in] upper bound for *@bytes
223 *
224 * When splitting a bio, it can happen that a bvec is encountered that is too
225 * big to fit in a single segment and hence that it has to be split in the
226 * middle. This function verifies whether or not that should happen. The value
227 * %true is returned if and only if appending the entire @bv to a bio with
228 * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
229 * the block driver.
230 */
231static bool bvec_split_segs(const struct queue_limits *lim,
232 const struct bio_vec *bv, unsigned *nsegs, unsigned *bytes,
233 unsigned max_segs, unsigned max_bytes)
234{
235 unsigned max_len = min(max_bytes, UINT_MAX) - *bytes;
236 unsigned len = min(bv->bv_len, max_len);
237 unsigned total_len = 0;
238 unsigned seg_size = 0;
239
240 while (len && *nsegs < max_segs) {
241 seg_size = get_max_segment_size(lim, start_page: bv->bv_page,
242 offset: bv->bv_offset + total_len);
243 seg_size = min(seg_size, len);
244
245 (*nsegs)++;
246 total_len += seg_size;
247 len -= seg_size;
248
249 if ((bv->bv_offset + total_len) & lim->virt_boundary_mask)
250 break;
251 }
252
253 *bytes += total_len;
254
255 /* tell the caller to split the bvec if it is too big to fit */
256 return len > 0 || bv->bv_len > max_len;
257}
258
259/**
260 * bio_split_rw - split a bio in two bios
261 * @bio: [in] bio to be split
262 * @lim: [in] queue limits to split based on
263 * @segs: [out] number of segments in the bio with the first half of the sectors
264 * @bs: [in] bio set to allocate the clone from
265 * @max_bytes: [in] maximum number of bytes per bio
266 *
267 * Clone @bio, update the bi_iter of the clone to represent the first sectors
268 * of @bio and update @bio->bi_iter to represent the remaining sectors. The
269 * following is guaranteed for the cloned bio:
270 * - That it has at most @max_bytes worth of data
271 * - That it has at most queue_max_segments(@q) segments.
272 *
273 * Except for discard requests the cloned bio will point at the bi_io_vec of
274 * the original bio. It is the responsibility of the caller to ensure that the
275 * original bio is not freed before the cloned bio. The caller is also
276 * responsible for ensuring that @bs is only destroyed after processing of the
277 * split bio has finished.
278 */
279struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
280 unsigned *segs, struct bio_set *bs, unsigned max_bytes)
281{
282 struct bio_vec bv, bvprv, *bvprvp = NULL;
283 struct bvec_iter iter;
284 unsigned nsegs = 0, bytes = 0;
285
286 bio_for_each_bvec(bv, bio, iter) {
287 /*
288 * If the queue doesn't support SG gaps and adding this
289 * offset would create a gap, disallow it.
290 */
291 if (bvprvp && bvec_gap_to_prev(lim, bprv: bvprvp, offset: bv.bv_offset))
292 goto split;
293
294 if (nsegs < lim->max_segments &&
295 bytes + bv.bv_len <= max_bytes &&
296 bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
297 nsegs++;
298 bytes += bv.bv_len;
299 } else {
300 if (bvec_split_segs(lim, bv: &bv, nsegs: &nsegs, bytes: &bytes,
301 max_segs: lim->max_segments, max_bytes))
302 goto split;
303 }
304
305 bvprv = bv;
306 bvprvp = &bvprv;
307 }
308
309 *segs = nsegs;
310 return NULL;
311split:
312 /*
313 * We can't sanely support splitting for a REQ_NOWAIT bio. End it
314 * with EAGAIN if splitting is required and return an error pointer.
315 */
316 if (bio->bi_opf & REQ_NOWAIT) {
317 bio->bi_status = BLK_STS_AGAIN;
318 bio_endio(bio);
319 return ERR_PTR(error: -EAGAIN);
320 }
321
322 *segs = nsegs;
323
324 /*
325 * Individual bvecs might not be logical block aligned. Round down the
326 * split size so that each bio is properly block size aligned, even if
327 * we do not use the full hardware limits.
328 */
329 bytes = ALIGN_DOWN(bytes, lim->logical_block_size);
330
331 /*
332 * Bio splitting may cause subtle trouble such as hang when doing sync
333 * iopoll in direct IO routine. Given performance gain of iopoll for
334 * big IO can be trival, disable iopoll when split needed.
335 */
336 bio_clear_polled(bio);
337 return bio_split(bio, sectors: bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
338}
339EXPORT_SYMBOL_GPL(bio_split_rw);
340
341/**
342 * __bio_split_to_limits - split a bio to fit the queue limits
343 * @bio: bio to be split
344 * @lim: queue limits to split based on
345 * @nr_segs: returns the number of segments in the returned bio
346 *
347 * Check if @bio needs splitting based on the queue limits, and if so split off
348 * a bio fitting the limits from the beginning of @bio and return it. @bio is
349 * shortened to the remainder and re-submitted.
350 *
351 * The split bio is allocated from @q->bio_split, which is provided by the
352 * block layer.
353 */
354struct bio *__bio_split_to_limits(struct bio *bio,
355 const struct queue_limits *lim,
356 unsigned int *nr_segs)
357{
358 struct bio_set *bs = &bio->bi_bdev->bd_disk->bio_split;
359 struct bio *split;
360
361 switch (bio_op(bio)) {
362 case REQ_OP_DISCARD:
363 case REQ_OP_SECURE_ERASE:
364 split = bio_split_discard(bio, lim, nsegs: nr_segs, bs);
365 break;
366 case REQ_OP_WRITE_ZEROES:
367 split = bio_split_write_zeroes(bio, lim, nsegs: nr_segs, bs);
368 break;
369 default:
370 split = bio_split_rw(bio, lim, nr_segs, bs,
371 get_max_io_size(bio, lim) << SECTOR_SHIFT);
372 if (IS_ERR(ptr: split))
373 return NULL;
374 break;
375 }
376
377 if (split) {
378 /* there isn't chance to merge the split bio */
379 split->bi_opf |= REQ_NOMERGE;
380
381 blkcg_bio_issue_init(bio: split);
382 bio_chain(split, bio);
383 trace_block_split(bio: split, new_sector: bio->bi_iter.bi_sector);
384 submit_bio_noacct(bio);
385 return split;
386 }
387 return bio;
388}
389
390/**
391 * bio_split_to_limits - split a bio to fit the queue limits
392 * @bio: bio to be split
393 *
394 * Check if @bio needs splitting based on the queue limits of @bio->bi_bdev, and
395 * if so split off a bio fitting the limits from the beginning of @bio and
396 * return it. @bio is shortened to the remainder and re-submitted.
397 *
398 * The split bio is allocated from @q->bio_split, which is provided by the
399 * block layer.
400 */
401struct bio *bio_split_to_limits(struct bio *bio)
402{
403 const struct queue_limits *lim = &bdev_get_queue(bdev: bio->bi_bdev)->limits;
404 unsigned int nr_segs;
405
406 if (bio_may_exceed_limits(bio, lim))
407 return __bio_split_to_limits(bio, lim, nr_segs: &nr_segs);
408 return bio;
409}
410EXPORT_SYMBOL(bio_split_to_limits);
411
412unsigned int blk_recalc_rq_segments(struct request *rq)
413{
414 unsigned int nr_phys_segs = 0;
415 unsigned int bytes = 0;
416 struct req_iterator iter;
417 struct bio_vec bv;
418
419 if (!rq->bio)
420 return 0;
421
422 switch (bio_op(bio: rq->bio)) {
423 case REQ_OP_DISCARD:
424 case REQ_OP_SECURE_ERASE:
425 if (queue_max_discard_segments(q: rq->q) > 1) {
426 struct bio *bio = rq->bio;
427
428 for_each_bio(bio)
429 nr_phys_segs++;
430 return nr_phys_segs;
431 }
432 return 1;
433 case REQ_OP_WRITE_ZEROES:
434 return 0;
435 default:
436 break;
437 }
438
439 rq_for_each_bvec(bv, rq, iter)
440 bvec_split_segs(lim: &rq->q->limits, bv: &bv, nsegs: &nr_phys_segs, bytes: &bytes,
441 UINT_MAX, UINT_MAX);
442 return nr_phys_segs;
443}
444
445static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
446 struct scatterlist *sglist)
447{
448 if (!*sg)
449 return sglist;
450
451 /*
452 * If the driver previously mapped a shorter list, we could see a
453 * termination bit prematurely unless it fully inits the sg table
454 * on each mapping. We KNOW that there must be more entries here
455 * or the driver would be buggy, so force clear the termination bit
456 * to avoid doing a full sg_init_table() in drivers for each command.
457 */
458 sg_unmark_end(sg: *sg);
459 return sg_next(*sg);
460}
461
462static unsigned blk_bvec_map_sg(struct request_queue *q,
463 struct bio_vec *bvec, struct scatterlist *sglist,
464 struct scatterlist **sg)
465{
466 unsigned nbytes = bvec->bv_len;
467 unsigned nsegs = 0, total = 0;
468
469 while (nbytes > 0) {
470 unsigned offset = bvec->bv_offset + total;
471 unsigned len = min(get_max_segment_size(&q->limits,
472 bvec->bv_page, offset), nbytes);
473 struct page *page = bvec->bv_page;
474
475 /*
476 * Unfortunately a fair number of drivers barf on scatterlists
477 * that have an offset larger than PAGE_SIZE, despite other
478 * subsystems dealing with that invariant just fine. For now
479 * stick to the legacy format where we never present those from
480 * the block layer, but the code below should be removed once
481 * these offenders (mostly MMC/SD drivers) are fixed.
482 */
483 page += (offset >> PAGE_SHIFT);
484 offset &= ~PAGE_MASK;
485
486 *sg = blk_next_sg(sg, sglist);
487 sg_set_page(sg: *sg, page, len, offset);
488
489 total += len;
490 nbytes -= len;
491 nsegs++;
492 }
493
494 return nsegs;
495}
496
497static inline int __blk_bvec_map_sg(struct bio_vec bv,
498 struct scatterlist *sglist, struct scatterlist **sg)
499{
500 *sg = blk_next_sg(sg, sglist);
501 sg_set_page(sg: *sg, page: bv.bv_page, len: bv.bv_len, offset: bv.bv_offset);
502 return 1;
503}
504
505/* only try to merge bvecs into one sg if they are from two bios */
506static inline bool
507__blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
508 struct bio_vec *bvprv, struct scatterlist **sg)
509{
510
511 int nbytes = bvec->bv_len;
512
513 if (!*sg)
514 return false;
515
516 if ((*sg)->length + nbytes > queue_max_segment_size(q))
517 return false;
518
519 if (!biovec_phys_mergeable(q, vec1: bvprv, vec2: bvec))
520 return false;
521
522 (*sg)->length += nbytes;
523
524 return true;
525}
526
527static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
528 struct scatterlist *sglist,
529 struct scatterlist **sg)
530{
531 struct bio_vec bvec, bvprv = { NULL };
532 struct bvec_iter iter;
533 int nsegs = 0;
534 bool new_bio = false;
535
536 for_each_bio(bio) {
537 bio_for_each_bvec(bvec, bio, iter) {
538 /*
539 * Only try to merge bvecs from two bios given we
540 * have done bio internal merge when adding pages
541 * to bio
542 */
543 if (new_bio &&
544 __blk_segment_map_sg_merge(q, bvec: &bvec, bvprv: &bvprv, sg))
545 goto next_bvec;
546
547 if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
548 nsegs += __blk_bvec_map_sg(bv: bvec, sglist, sg);
549 else
550 nsegs += blk_bvec_map_sg(q, bvec: &bvec, sglist, sg);
551 next_bvec:
552 new_bio = false;
553 }
554 if (likely(bio->bi_iter.bi_size)) {
555 bvprv = bvec;
556 new_bio = true;
557 }
558 }
559
560 return nsegs;
561}
562
563/*
564 * map a request to scatterlist, return number of sg entries setup. Caller
565 * must make sure sg can hold rq->nr_phys_segments entries
566 */
567int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
568 struct scatterlist *sglist, struct scatterlist **last_sg)
569{
570 int nsegs = 0;
571
572 if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
573 nsegs = __blk_bvec_map_sg(bv: rq->special_vec, sglist, sg: last_sg);
574 else if (rq->bio)
575 nsegs = __blk_bios_map_sg(q, bio: rq->bio, sglist, sg: last_sg);
576
577 if (*last_sg)
578 sg_mark_end(sg: *last_sg);
579
580 /*
581 * Something must have been wrong if the figured number of
582 * segment is bigger than number of req's physical segments
583 */
584 WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
585
586 return nsegs;
587}
588EXPORT_SYMBOL(__blk_rq_map_sg);
589
590static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
591 sector_t offset)
592{
593 struct request_queue *q = rq->q;
594 unsigned int max_sectors;
595
596 if (blk_rq_is_passthrough(rq))
597 return q->limits.max_hw_sectors;
598
599 max_sectors = blk_queue_get_max_sectors(q, op: req_op(req: rq));
600 if (!q->limits.chunk_sectors ||
601 req_op(req: rq) == REQ_OP_DISCARD ||
602 req_op(req: rq) == REQ_OP_SECURE_ERASE)
603 return max_sectors;
604 return min(max_sectors,
605 blk_chunk_sectors_left(offset, q->limits.chunk_sectors));
606}
607
608static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
609 unsigned int nr_phys_segs)
610{
611 if (!blk_cgroup_mergeable(rq: req, bio))
612 goto no_merge;
613
614 if (blk_integrity_merge_bio(req->q, req, bio) == false)
615 goto no_merge;
616
617 /* discard request merge won't add new segment */
618 if (req_op(req) == REQ_OP_DISCARD)
619 return 1;
620
621 if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(rq: req))
622 goto no_merge;
623
624 /*
625 * This will form the start of a new hw segment. Bump both
626 * counters.
627 */
628 req->nr_phys_segments += nr_phys_segs;
629 return 1;
630
631no_merge:
632 req_set_nomerge(q: req->q, req);
633 return 0;
634}
635
636int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
637{
638 if (req_gap_back_merge(req, bio))
639 return 0;
640 if (blk_integrity_rq(rq: req) &&
641 integrity_req_gap_back_merge(req, next: bio))
642 return 0;
643 if (!bio_crypt_ctx_back_mergeable(req, bio))
644 return 0;
645 if (blk_rq_sectors(rq: req) + bio_sectors(bio) >
646 blk_rq_get_max_sectors(rq: req, offset: blk_rq_pos(rq: req))) {
647 req_set_nomerge(q: req->q, req);
648 return 0;
649 }
650
651 return ll_new_hw_segment(req, bio, nr_phys_segs: nr_segs);
652}
653
654static int ll_front_merge_fn(struct request *req, struct bio *bio,
655 unsigned int nr_segs)
656{
657 if (req_gap_front_merge(req, bio))
658 return 0;
659 if (blk_integrity_rq(rq: req) &&
660 integrity_req_gap_front_merge(req, bio))
661 return 0;
662 if (!bio_crypt_ctx_front_mergeable(req, bio))
663 return 0;
664 if (blk_rq_sectors(rq: req) + bio_sectors(bio) >
665 blk_rq_get_max_sectors(rq: req, offset: bio->bi_iter.bi_sector)) {
666 req_set_nomerge(q: req->q, req);
667 return 0;
668 }
669
670 return ll_new_hw_segment(req, bio, nr_phys_segs: nr_segs);
671}
672
673static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
674 struct request *next)
675{
676 unsigned short segments = blk_rq_nr_discard_segments(rq: req);
677
678 if (segments >= queue_max_discard_segments(q))
679 goto no_merge;
680 if (blk_rq_sectors(rq: req) + bio_sectors(next->bio) >
681 blk_rq_get_max_sectors(rq: req, offset: blk_rq_pos(rq: req)))
682 goto no_merge;
683
684 req->nr_phys_segments = segments + blk_rq_nr_discard_segments(rq: next);
685 return true;
686no_merge:
687 req_set_nomerge(q, req);
688 return false;
689}
690
691static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
692 struct request *next)
693{
694 int total_phys_segments;
695
696 if (req_gap_back_merge(req, bio: next->bio))
697 return 0;
698
699 /*
700 * Will it become too large?
701 */
702 if ((blk_rq_sectors(rq: req) + blk_rq_sectors(rq: next)) >
703 blk_rq_get_max_sectors(rq: req, offset: blk_rq_pos(rq: req)))
704 return 0;
705
706 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
707 if (total_phys_segments > blk_rq_get_max_segments(rq: req))
708 return 0;
709
710 if (!blk_cgroup_mergeable(rq: req, bio: next->bio))
711 return 0;
712
713 if (blk_integrity_merge_rq(q, req, next) == false)
714 return 0;
715
716 if (!bio_crypt_ctx_merge_rq(req, next))
717 return 0;
718
719 /* Merge is OK... */
720 req->nr_phys_segments = total_phys_segments;
721 return 1;
722}
723
724/**
725 * blk_rq_set_mixed_merge - mark a request as mixed merge
726 * @rq: request to mark as mixed merge
727 *
728 * Description:
729 * @rq is about to be mixed merged. Make sure the attributes
730 * which can be mixed are set in each bio and mark @rq as mixed
731 * merged.
732 */
733void blk_rq_set_mixed_merge(struct request *rq)
734{
735 blk_opf_t ff = rq->cmd_flags & REQ_FAILFAST_MASK;
736 struct bio *bio;
737
738 if (rq->rq_flags & RQF_MIXED_MERGE)
739 return;
740
741 /*
742 * @rq will no longer represent mixable attributes for all the
743 * contained bios. It will just track those of the first one.
744 * Distributes the attributs to each bio.
745 */
746 for (bio = rq->bio; bio; bio = bio->bi_next) {
747 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
748 (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
749 bio->bi_opf |= ff;
750 }
751 rq->rq_flags |= RQF_MIXED_MERGE;
752}
753
754static inline blk_opf_t bio_failfast(const struct bio *bio)
755{
756 if (bio->bi_opf & REQ_RAHEAD)
757 return REQ_FAILFAST_MASK;
758
759 return bio->bi_opf & REQ_FAILFAST_MASK;
760}
761
762/*
763 * After we are marked as MIXED_MERGE, any new RA bio has to be updated
764 * as failfast, and request's failfast has to be updated in case of
765 * front merge.
766 */
767static inline void blk_update_mixed_merge(struct request *req,
768 struct bio *bio, bool front_merge)
769{
770 if (req->rq_flags & RQF_MIXED_MERGE) {
771 if (bio->bi_opf & REQ_RAHEAD)
772 bio->bi_opf |= REQ_FAILFAST_MASK;
773
774 if (front_merge) {
775 req->cmd_flags &= ~REQ_FAILFAST_MASK;
776 req->cmd_flags |= bio->bi_opf & REQ_FAILFAST_MASK;
777 }
778 }
779}
780
781static void blk_account_io_merge_request(struct request *req)
782{
783 if (blk_do_io_stat(rq: req)) {
784 part_stat_lock();
785 part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
786 part_stat_unlock();
787 }
788}
789
790static enum elv_merge blk_try_req_merge(struct request *req,
791 struct request *next)
792{
793 if (blk_discard_mergable(req))
794 return ELEVATOR_DISCARD_MERGE;
795 else if (blk_rq_pos(rq: req) + blk_rq_sectors(rq: req) == blk_rq_pos(rq: next))
796 return ELEVATOR_BACK_MERGE;
797
798 return ELEVATOR_NO_MERGE;
799}
800
801/*
802 * For non-mq, this has to be called with the request spinlock acquired.
803 * For mq with scheduling, the appropriate queue wide lock should be held.
804 */
805static struct request *attempt_merge(struct request_queue *q,
806 struct request *req, struct request *next)
807{
808 if (!rq_mergeable(rq: req) || !rq_mergeable(rq: next))
809 return NULL;
810
811 if (req_op(req) != req_op(req: next))
812 return NULL;
813
814 if (rq_data_dir(req) != rq_data_dir(next))
815 return NULL;
816
817 if (req->ioprio != next->ioprio)
818 return NULL;
819
820 /*
821 * If we are allowed to merge, then append bio list
822 * from next to rq and release next. merge_requests_fn
823 * will have updated segment counts, update sector
824 * counts here. Handle DISCARDs separately, as they
825 * have separate settings.
826 */
827
828 switch (blk_try_req_merge(req, next)) {
829 case ELEVATOR_DISCARD_MERGE:
830 if (!req_attempt_discard_merge(q, req, next))
831 return NULL;
832 break;
833 case ELEVATOR_BACK_MERGE:
834 if (!ll_merge_requests_fn(q, req, next))
835 return NULL;
836 break;
837 default:
838 return NULL;
839 }
840
841 /*
842 * If failfast settings disagree or any of the two is already
843 * a mixed merge, mark both as mixed before proceeding. This
844 * makes sure that all involved bios have mixable attributes
845 * set properly.
846 */
847 if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
848 (req->cmd_flags & REQ_FAILFAST_MASK) !=
849 (next->cmd_flags & REQ_FAILFAST_MASK)) {
850 blk_rq_set_mixed_merge(rq: req);
851 blk_rq_set_mixed_merge(rq: next);
852 }
853
854 /*
855 * At this point we have either done a back merge or front merge. We
856 * need the smaller start_time_ns of the merged requests to be the
857 * current request for accounting purposes.
858 */
859 if (next->start_time_ns < req->start_time_ns)
860 req->start_time_ns = next->start_time_ns;
861
862 req->biotail->bi_next = next->bio;
863 req->biotail = next->biotail;
864
865 req->__data_len += blk_rq_bytes(rq: next);
866
867 if (!blk_discard_mergable(req))
868 elv_merge_requests(q, req, next);
869
870 blk_crypto_rq_put_keyslot(rq: next);
871
872 /*
873 * 'next' is going away, so update stats accordingly
874 */
875 blk_account_io_merge_request(req: next);
876
877 trace_block_rq_merge(rq: next);
878
879 /*
880 * ownership of bio passed from next to req, return 'next' for
881 * the caller to free
882 */
883 next->bio = NULL;
884 return next;
885}
886
887static struct request *attempt_back_merge(struct request_queue *q,
888 struct request *rq)
889{
890 struct request *next = elv_latter_request(q, rq);
891
892 if (next)
893 return attempt_merge(q, req: rq, next);
894
895 return NULL;
896}
897
898static struct request *attempt_front_merge(struct request_queue *q,
899 struct request *rq)
900{
901 struct request *prev = elv_former_request(q, rq);
902
903 if (prev)
904 return attempt_merge(q, req: prev, next: rq);
905
906 return NULL;
907}
908
909/*
910 * Try to merge 'next' into 'rq'. Return true if the merge happened, false
911 * otherwise. The caller is responsible for freeing 'next' if the merge
912 * happened.
913 */
914bool blk_attempt_req_merge(struct request_queue *q, struct request *rq,
915 struct request *next)
916{
917 return attempt_merge(q, req: rq, next);
918}
919
920bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
921{
922 if (!rq_mergeable(rq) || !bio_mergeable(bio))
923 return false;
924
925 if (req_op(req: rq) != bio_op(bio))
926 return false;
927
928 /* different data direction or already started, don't merge */
929 if (bio_data_dir(bio) != rq_data_dir(rq))
930 return false;
931
932 /* don't merge across cgroup boundaries */
933 if (!blk_cgroup_mergeable(rq, bio))
934 return false;
935
936 /* only merge integrity protected bio into ditto rq */
937 if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
938 return false;
939
940 /* Only merge if the crypt contexts are compatible */
941 if (!bio_crypt_rq_ctx_compatible(rq, bio))
942 return false;
943
944 if (rq->ioprio != bio_prio(bio))
945 return false;
946
947 return true;
948}
949
950enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
951{
952 if (blk_discard_mergable(req: rq))
953 return ELEVATOR_DISCARD_MERGE;
954 else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
955 return ELEVATOR_BACK_MERGE;
956 else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
957 return ELEVATOR_FRONT_MERGE;
958 return ELEVATOR_NO_MERGE;
959}
960
961static void blk_account_io_merge_bio(struct request *req)
962{
963 if (!blk_do_io_stat(rq: req))
964 return;
965
966 part_stat_lock();
967 part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
968 part_stat_unlock();
969}
970
971enum bio_merge_status {
972 BIO_MERGE_OK,
973 BIO_MERGE_NONE,
974 BIO_MERGE_FAILED,
975};
976
977static enum bio_merge_status bio_attempt_back_merge(struct request *req,
978 struct bio *bio, unsigned int nr_segs)
979{
980 const blk_opf_t ff = bio_failfast(bio);
981
982 if (!ll_back_merge_fn(req, bio, nr_segs))
983 return BIO_MERGE_FAILED;
984
985 trace_block_bio_backmerge(bio);
986 rq_qos_merge(q: req->q, rq: req, bio);
987
988 if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
989 blk_rq_set_mixed_merge(rq: req);
990
991 blk_update_mixed_merge(req, bio, front_merge: false);
992
993 req->biotail->bi_next = bio;
994 req->biotail = bio;
995 req->__data_len += bio->bi_iter.bi_size;
996
997 bio_crypt_free_ctx(bio);
998
999 blk_account_io_merge_bio(req);
1000 return BIO_MERGE_OK;
1001}
1002
1003static enum bio_merge_status bio_attempt_front_merge(struct request *req,
1004 struct bio *bio, unsigned int nr_segs)
1005{
1006 const blk_opf_t ff = bio_failfast(bio);
1007
1008 if (!ll_front_merge_fn(req, bio, nr_segs))
1009 return BIO_MERGE_FAILED;
1010
1011 trace_block_bio_frontmerge(bio);
1012 rq_qos_merge(q: req->q, rq: req, bio);
1013
1014 if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
1015 blk_rq_set_mixed_merge(rq: req);
1016
1017 blk_update_mixed_merge(req, bio, front_merge: true);
1018
1019 bio->bi_next = req->bio;
1020 req->bio = bio;
1021
1022 req->__sector = bio->bi_iter.bi_sector;
1023 req->__data_len += bio->bi_iter.bi_size;
1024
1025 bio_crypt_do_front_merge(rq: req, bio);
1026
1027 blk_account_io_merge_bio(req);
1028 return BIO_MERGE_OK;
1029}
1030
1031static enum bio_merge_status bio_attempt_discard_merge(struct request_queue *q,
1032 struct request *req, struct bio *bio)
1033{
1034 unsigned short segments = blk_rq_nr_discard_segments(rq: req);
1035
1036 if (segments >= queue_max_discard_segments(q))
1037 goto no_merge;
1038 if (blk_rq_sectors(rq: req) + bio_sectors(bio) >
1039 blk_rq_get_max_sectors(rq: req, offset: blk_rq_pos(rq: req)))
1040 goto no_merge;
1041
1042 rq_qos_merge(q, rq: req, bio);
1043
1044 req->biotail->bi_next = bio;
1045 req->biotail = bio;
1046 req->__data_len += bio->bi_iter.bi_size;
1047 req->nr_phys_segments = segments + 1;
1048
1049 blk_account_io_merge_bio(req);
1050 return BIO_MERGE_OK;
1051no_merge:
1052 req_set_nomerge(q, req);
1053 return BIO_MERGE_FAILED;
1054}
1055
1056static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
1057 struct request *rq,
1058 struct bio *bio,
1059 unsigned int nr_segs,
1060 bool sched_allow_merge)
1061{
1062 if (!blk_rq_merge_ok(rq, bio))
1063 return BIO_MERGE_NONE;
1064
1065 switch (blk_try_merge(rq, bio)) {
1066 case ELEVATOR_BACK_MERGE:
1067 if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
1068 return bio_attempt_back_merge(req: rq, bio, nr_segs);
1069 break;
1070 case ELEVATOR_FRONT_MERGE:
1071 if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
1072 return bio_attempt_front_merge(req: rq, bio, nr_segs);
1073 break;
1074 case ELEVATOR_DISCARD_MERGE:
1075 return bio_attempt_discard_merge(q, req: rq, bio);
1076 default:
1077 return BIO_MERGE_NONE;
1078 }
1079
1080 return BIO_MERGE_FAILED;
1081}
1082
1083/**
1084 * blk_attempt_plug_merge - try to merge with %current's plugged list
1085 * @q: request_queue new bio is being queued at
1086 * @bio: new bio being queued
1087 * @nr_segs: number of segments in @bio
1088 * from the passed in @q already in the plug list
1089 *
1090 * Determine whether @bio being queued on @q can be merged with the previous
1091 * request on %current's plugged list. Returns %true if merge was successful,
1092 * otherwise %false.
1093 *
1094 * Plugging coalesces IOs from the same issuer for the same purpose without
1095 * going through @q->queue_lock. As such it's more of an issuing mechanism
1096 * than scheduling, and the request, while may have elvpriv data, is not
1097 * added on the elevator at this point. In addition, we don't have
1098 * reliable access to the elevator outside queue lock. Only check basic
1099 * merging parameters without querying the elevator.
1100 *
1101 * Caller must ensure !blk_queue_nomerges(q) beforehand.
1102 */
1103bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
1104 unsigned int nr_segs)
1105{
1106 struct blk_plug *plug;
1107 struct request *rq;
1108
1109 plug = blk_mq_plug(bio);
1110 if (!plug || rq_list_empty(plug->mq_list))
1111 return false;
1112
1113 rq_list_for_each(&plug->mq_list, rq) {
1114 if (rq->q == q) {
1115 if (blk_attempt_bio_merge(q, rq, bio, nr_segs, sched_allow_merge: false) ==
1116 BIO_MERGE_OK)
1117 return true;
1118 break;
1119 }
1120
1121 /*
1122 * Only keep iterating plug list for merges if we have multiple
1123 * queues
1124 */
1125 if (!plug->multiple_queues)
1126 break;
1127 }
1128 return false;
1129}
1130
1131/*
1132 * Iterate list of requests and see if we can merge this bio with any
1133 * of them.
1134 */
1135bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
1136 struct bio *bio, unsigned int nr_segs)
1137{
1138 struct request *rq;
1139 int checked = 8;
1140
1141 list_for_each_entry_reverse(rq, list, queuelist) {
1142 if (!checked--)
1143 break;
1144
1145 switch (blk_attempt_bio_merge(q, rq, bio, nr_segs, sched_allow_merge: true)) {
1146 case BIO_MERGE_NONE:
1147 continue;
1148 case BIO_MERGE_OK:
1149 return true;
1150 case BIO_MERGE_FAILED:
1151 return false;
1152 }
1153
1154 }
1155
1156 return false;
1157}
1158EXPORT_SYMBOL_GPL(blk_bio_list_merge);
1159
1160bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
1161 unsigned int nr_segs, struct request **merged_request)
1162{
1163 struct request *rq;
1164
1165 switch (elv_merge(q, &rq, bio)) {
1166 case ELEVATOR_BACK_MERGE:
1167 if (!blk_mq_sched_allow_merge(q, rq, bio))
1168 return false;
1169 if (bio_attempt_back_merge(req: rq, bio, nr_segs) != BIO_MERGE_OK)
1170 return false;
1171 *merged_request = attempt_back_merge(q, rq);
1172 if (!*merged_request)
1173 elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
1174 return true;
1175 case ELEVATOR_FRONT_MERGE:
1176 if (!blk_mq_sched_allow_merge(q, rq, bio))
1177 return false;
1178 if (bio_attempt_front_merge(req: rq, bio, nr_segs) != BIO_MERGE_OK)
1179 return false;
1180 *merged_request = attempt_front_merge(q, rq);
1181 if (!*merged_request)
1182 elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
1183 return true;
1184 case ELEVATOR_DISCARD_MERGE:
1185 return bio_attempt_discard_merge(q, req: rq, bio) == BIO_MERGE_OK;
1186 default:
1187 return false;
1188 }
1189}
1190EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
1191

source code of linux/block/blk-merge.c