xref: /linux/block/blk-merge.c (revision ef9226cd56b718c79184a3466d32984a51cb449c)
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 
21 static 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 
26 static 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.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 
52 static 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(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(prev_rq->bio, &pb);
67 	else
68 		bio_get_first_bvec(prev, &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(prev, &pb);
82 	bio_get_first_bvec(next, &nb);
83 	if (biovec_phys_mergeable(q, &pb, &nb))
84 		return false;
85 	return __bvec_gap_to_prev(&q->limits, &pb, nb.bv_offset);
86 }
87 
88 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
89 {
90 	return bio_will_gap(req->q, req, req->biotail, bio);
91 }
92 
93 static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
94 {
95 	return bio_will_gap(req->q, NULL, bio, 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  */
103 static 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 
108 static 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 	granularity = max(lim->discard_granularity >> 9, 1U);
119 
120 	max_discard_sectors =
121 		min(lim->max_discard_sectors, bio_allowed_max_sectors(lim));
122 	max_discard_sectors -= max_discard_sectors % granularity;
123 	if (unlikely(!max_discard_sectors))
124 		return NULL;
125 
126 	if (bio_sectors(bio) <= max_discard_sectors)
127 		return NULL;
128 
129 	split_sectors = max_discard_sectors;
130 
131 	/*
132 	 * If the next starting sector would be misaligned, stop the discard at
133 	 * the previous aligned sector.
134 	 */
135 	tmp = bio->bi_iter.bi_sector + split_sectors -
136 		((lim->discard_alignment >> 9) % granularity);
137 	tmp = sector_div(tmp, granularity);
138 
139 	if (split_sectors > tmp)
140 		split_sectors -= tmp;
141 
142 	return bio_split(bio, split_sectors, GFP_NOIO, bs);
143 }
144 
145 static struct bio *bio_split_write_zeroes(struct bio *bio,
146 					  const struct queue_limits *lim,
147 					  unsigned *nsegs, struct bio_set *bs)
148 {
149 	*nsegs = 0;
150 	if (!lim->max_write_zeroes_sectors)
151 		return NULL;
152 	if (bio_sectors(bio) <= lim->max_write_zeroes_sectors)
153 		return NULL;
154 	return bio_split(bio, lim->max_write_zeroes_sectors, GFP_NOIO, bs);
155 }
156 
157 /*
158  * Return the maximum number of sectors from the start of a bio that may be
159  * submitted as a single request to a block device. If enough sectors remain,
160  * align the end to the physical block size. Otherwise align the end to the
161  * logical block size. This approach minimizes the number of non-aligned
162  * requests that are submitted to a block device if the start of a bio is not
163  * aligned to a physical block boundary.
164  */
165 static inline unsigned get_max_io_size(struct bio *bio,
166 				       const struct queue_limits *lim)
167 {
168 	unsigned pbs = lim->physical_block_size >> SECTOR_SHIFT;
169 	unsigned lbs = lim->logical_block_size >> SECTOR_SHIFT;
170 	unsigned max_sectors = lim->max_sectors, start, end;
171 
172 	if (lim->chunk_sectors) {
173 		max_sectors = min(max_sectors,
174 			blk_chunk_sectors_left(bio->bi_iter.bi_sector,
175 					       lim->chunk_sectors));
176 	}
177 
178 	start = bio->bi_iter.bi_sector & (pbs - 1);
179 	end = (start + max_sectors) & ~(pbs - 1);
180 	if (end > start)
181 		return end - start;
182 	return max_sectors & ~(lbs - 1);
183 }
184 
185 /**
186  * get_max_segment_size() - maximum number of bytes to add as a single segment
187  * @lim: Request queue limits.
188  * @start_page: See below.
189  * @offset: Offset from @start_page where to add a segment.
190  *
191  * Returns the maximum number of bytes that can be added as a single segment.
192  */
193 static inline unsigned get_max_segment_size(const struct queue_limits *lim,
194 		struct page *start_page, unsigned long offset)
195 {
196 	unsigned long mask = lim->seg_boundary_mask;
197 
198 	offset = mask & (page_to_phys(start_page) + offset);
199 
200 	/*
201 	 * Prevent an overflow if mask = ULONG_MAX and offset = 0 by adding 1
202 	 * after having calculated the minimum.
203 	 */
204 	return min(mask - offset, (unsigned long)lim->max_segment_size - 1) + 1;
205 }
206 
207 /**
208  * bvec_split_segs - verify whether or not a bvec should be split in the middle
209  * @lim:      [in] queue limits to split based on
210  * @bv:       [in] bvec to examine
211  * @nsegs:    [in,out] Number of segments in the bio being built. Incremented
212  *            by the number of segments from @bv that may be appended to that
213  *            bio without exceeding @max_segs
214  * @bytes:    [in,out] Number of bytes in the bio being built. Incremented
215  *            by the number of bytes from @bv that may be appended to that
216  *            bio without exceeding @max_bytes
217  * @max_segs: [in] upper bound for *@nsegs
218  * @max_bytes: [in] upper bound for *@bytes
219  *
220  * When splitting a bio, it can happen that a bvec is encountered that is too
221  * big to fit in a single segment and hence that it has to be split in the
222  * middle. This function verifies whether or not that should happen. The value
223  * %true is returned if and only if appending the entire @bv to a bio with
224  * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
225  * the block driver.
226  */
227 static bool bvec_split_segs(const struct queue_limits *lim,
228 		const struct bio_vec *bv, unsigned *nsegs, unsigned *bytes,
229 		unsigned max_segs, unsigned max_bytes)
230 {
231 	unsigned max_len = min(max_bytes, UINT_MAX) - *bytes;
232 	unsigned len = min(bv->bv_len, max_len);
233 	unsigned total_len = 0;
234 	unsigned seg_size = 0;
235 
236 	while (len && *nsegs < max_segs) {
237 		seg_size = get_max_segment_size(lim, bv->bv_page,
238 						bv->bv_offset + total_len);
239 		seg_size = min(seg_size, len);
240 
241 		(*nsegs)++;
242 		total_len += seg_size;
243 		len -= seg_size;
244 
245 		if ((bv->bv_offset + total_len) & lim->virt_boundary_mask)
246 			break;
247 	}
248 
249 	*bytes += total_len;
250 
251 	/* tell the caller to split the bvec if it is too big to fit */
252 	return len > 0 || bv->bv_len > max_len;
253 }
254 
255 /**
256  * bio_split_rw - split a bio in two bios
257  * @bio:  [in] bio to be split
258  * @lim:  [in] queue limits to split based on
259  * @segs: [out] number of segments in the bio with the first half of the sectors
260  * @bs:	  [in] bio set to allocate the clone from
261  * @max_bytes: [in] maximum number of bytes per bio
262  *
263  * Clone @bio, update the bi_iter of the clone to represent the first sectors
264  * of @bio and update @bio->bi_iter to represent the remaining sectors. The
265  * following is guaranteed for the cloned bio:
266  * - That it has at most @max_bytes worth of data
267  * - That it has at most queue_max_segments(@q) segments.
268  *
269  * Except for discard requests the cloned bio will point at the bi_io_vec of
270  * the original bio. It is the responsibility of the caller to ensure that the
271  * original bio is not freed before the cloned bio. The caller is also
272  * responsible for ensuring that @bs is only destroyed after processing of the
273  * split bio has finished.
274  */
275 struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
276 		unsigned *segs, struct bio_set *bs, unsigned max_bytes)
277 {
278 	struct bio_vec bv, bvprv, *bvprvp = NULL;
279 	struct bvec_iter iter;
280 	unsigned nsegs = 0, bytes = 0;
281 
282 	bio_for_each_bvec(bv, bio, iter) {
283 		/*
284 		 * If the queue doesn't support SG gaps and adding this
285 		 * offset would create a gap, disallow it.
286 		 */
287 		if (bvprvp && bvec_gap_to_prev(lim, bvprvp, bv.bv_offset))
288 			goto split;
289 
290 		if (nsegs < lim->max_segments &&
291 		    bytes + bv.bv_len <= max_bytes &&
292 		    bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
293 			nsegs++;
294 			bytes += bv.bv_len;
295 		} else {
296 			if (bvec_split_segs(lim, &bv, &nsegs, &bytes,
297 					lim->max_segments, max_bytes))
298 				goto split;
299 		}
300 
301 		bvprv = bv;
302 		bvprvp = &bvprv;
303 	}
304 
305 	*segs = nsegs;
306 	return NULL;
307 split:
308 	/*
309 	 * We can't sanely support splitting for a REQ_NOWAIT bio. End it
310 	 * with EAGAIN if splitting is required and return an error pointer.
311 	 */
312 	if (bio->bi_opf & REQ_NOWAIT) {
313 		bio->bi_status = BLK_STS_AGAIN;
314 		bio_endio(bio);
315 		return ERR_PTR(-EAGAIN);
316 	}
317 
318 	*segs = nsegs;
319 
320 	/*
321 	 * Individual bvecs might not be logical block aligned. Round down the
322 	 * split size so that each bio is properly block size aligned, even if
323 	 * we do not use the full hardware limits.
324 	 */
325 	bytes = ALIGN_DOWN(bytes, lim->logical_block_size);
326 
327 	/*
328 	 * Bio splitting may cause subtle trouble such as hang when doing sync
329 	 * iopoll in direct IO routine. Given performance gain of iopoll for
330 	 * big IO can be trival, disable iopoll when split needed.
331 	 */
332 	bio_clear_polled(bio);
333 	return bio_split(bio, bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
334 }
335 EXPORT_SYMBOL_GPL(bio_split_rw);
336 
337 /**
338  * __bio_split_to_limits - split a bio to fit the queue limits
339  * @bio:     bio to be split
340  * @lim:     queue limits to split based on
341  * @nr_segs: returns the number of segments in the returned bio
342  *
343  * Check if @bio needs splitting based on the queue limits, and if so split off
344  * a bio fitting the limits from the beginning of @bio and return it.  @bio is
345  * shortened to the remainder and re-submitted.
346  *
347  * The split bio is allocated from @q->bio_split, which is provided by the
348  * block layer.
349  */
350 struct bio *__bio_split_to_limits(struct bio *bio,
351 				  const struct queue_limits *lim,
352 				  unsigned int *nr_segs)
353 {
354 	struct bio_set *bs = &bio->bi_bdev->bd_disk->bio_split;
355 	struct bio *split;
356 
357 	switch (bio_op(bio)) {
358 	case REQ_OP_DISCARD:
359 	case REQ_OP_SECURE_ERASE:
360 		split = bio_split_discard(bio, lim, nr_segs, bs);
361 		break;
362 	case REQ_OP_WRITE_ZEROES:
363 		split = bio_split_write_zeroes(bio, lim, nr_segs, bs);
364 		break;
365 	default:
366 		split = bio_split_rw(bio, lim, nr_segs, bs,
367 				get_max_io_size(bio, lim) << SECTOR_SHIFT);
368 		if (IS_ERR(split))
369 			return NULL;
370 		break;
371 	}
372 
373 	if (split) {
374 		/* there isn't chance to merge the split bio */
375 		split->bi_opf |= REQ_NOMERGE;
376 
377 		blkcg_bio_issue_init(split);
378 		bio_chain(split, bio);
379 		trace_block_split(split, bio->bi_iter.bi_sector);
380 		submit_bio_noacct(bio);
381 		return split;
382 	}
383 	return bio;
384 }
385 
386 /**
387  * bio_split_to_limits - split a bio to fit the queue limits
388  * @bio:     bio to be split
389  *
390  * Check if @bio needs splitting based on the queue limits of @bio->bi_bdev, and
391  * if so split off a bio fitting the limits from the beginning of @bio and
392  * return it.  @bio is shortened to the remainder and re-submitted.
393  *
394  * The split bio is allocated from @q->bio_split, which is provided by the
395  * block layer.
396  */
397 struct bio *bio_split_to_limits(struct bio *bio)
398 {
399 	const struct queue_limits *lim = &bdev_get_queue(bio->bi_bdev)->limits;
400 	unsigned int nr_segs;
401 
402 	if (bio_may_exceed_limits(bio, lim))
403 		return __bio_split_to_limits(bio, lim, &nr_segs);
404 	return bio;
405 }
406 EXPORT_SYMBOL(bio_split_to_limits);
407 
408 unsigned int blk_recalc_rq_segments(struct request *rq)
409 {
410 	unsigned int nr_phys_segs = 0;
411 	unsigned int bytes = 0;
412 	struct req_iterator iter;
413 	struct bio_vec bv;
414 
415 	if (!rq->bio)
416 		return 0;
417 
418 	switch (bio_op(rq->bio)) {
419 	case REQ_OP_DISCARD:
420 	case REQ_OP_SECURE_ERASE:
421 		if (queue_max_discard_segments(rq->q) > 1) {
422 			struct bio *bio = rq->bio;
423 
424 			for_each_bio(bio)
425 				nr_phys_segs++;
426 			return nr_phys_segs;
427 		}
428 		return 1;
429 	case REQ_OP_WRITE_ZEROES:
430 		return 0;
431 	default:
432 		break;
433 	}
434 
435 	rq_for_each_bvec(bv, rq, iter)
436 		bvec_split_segs(&rq->q->limits, &bv, &nr_phys_segs, &bytes,
437 				UINT_MAX, UINT_MAX);
438 	return nr_phys_segs;
439 }
440 
441 static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
442 		struct scatterlist *sglist)
443 {
444 	if (!*sg)
445 		return sglist;
446 
447 	/*
448 	 * If the driver previously mapped a shorter list, we could see a
449 	 * termination bit prematurely unless it fully inits the sg table
450 	 * on each mapping. We KNOW that there must be more entries here
451 	 * or the driver would be buggy, so force clear the termination bit
452 	 * to avoid doing a full sg_init_table() in drivers for each command.
453 	 */
454 	sg_unmark_end(*sg);
455 	return sg_next(*sg);
456 }
457 
458 static unsigned blk_bvec_map_sg(struct request_queue *q,
459 		struct bio_vec *bvec, struct scatterlist *sglist,
460 		struct scatterlist **sg)
461 {
462 	unsigned nbytes = bvec->bv_len;
463 	unsigned nsegs = 0, total = 0;
464 
465 	while (nbytes > 0) {
466 		unsigned offset = bvec->bv_offset + total;
467 		unsigned len = min(get_max_segment_size(&q->limits,
468 				   bvec->bv_page, offset), nbytes);
469 		struct page *page = bvec->bv_page;
470 
471 		/*
472 		 * Unfortunately a fair number of drivers barf on scatterlists
473 		 * that have an offset larger than PAGE_SIZE, despite other
474 		 * subsystems dealing with that invariant just fine.  For now
475 		 * stick to the legacy format where we never present those from
476 		 * the block layer, but the code below should be removed once
477 		 * these offenders (mostly MMC/SD drivers) are fixed.
478 		 */
479 		page += (offset >> PAGE_SHIFT);
480 		offset &= ~PAGE_MASK;
481 
482 		*sg = blk_next_sg(sg, sglist);
483 		sg_set_page(*sg, page, len, offset);
484 
485 		total += len;
486 		nbytes -= len;
487 		nsegs++;
488 	}
489 
490 	return nsegs;
491 }
492 
493 static inline int __blk_bvec_map_sg(struct bio_vec bv,
494 		struct scatterlist *sglist, struct scatterlist **sg)
495 {
496 	*sg = blk_next_sg(sg, sglist);
497 	sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
498 	return 1;
499 }
500 
501 /* only try to merge bvecs into one sg if they are from two bios */
502 static inline bool
503 __blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
504 			   struct bio_vec *bvprv, struct scatterlist **sg)
505 {
506 
507 	int nbytes = bvec->bv_len;
508 
509 	if (!*sg)
510 		return false;
511 
512 	if ((*sg)->length + nbytes > queue_max_segment_size(q))
513 		return false;
514 
515 	if (!biovec_phys_mergeable(q, bvprv, bvec))
516 		return false;
517 
518 	(*sg)->length += nbytes;
519 
520 	return true;
521 }
522 
523 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
524 			     struct scatterlist *sglist,
525 			     struct scatterlist **sg)
526 {
527 	struct bio_vec bvec, bvprv = { NULL };
528 	struct bvec_iter iter;
529 	int nsegs = 0;
530 	bool new_bio = false;
531 
532 	for_each_bio(bio) {
533 		bio_for_each_bvec(bvec, bio, iter) {
534 			/*
535 			 * Only try to merge bvecs from two bios given we
536 			 * have done bio internal merge when adding pages
537 			 * to bio
538 			 */
539 			if (new_bio &&
540 			    __blk_segment_map_sg_merge(q, &bvec, &bvprv, sg))
541 				goto next_bvec;
542 
543 			if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
544 				nsegs += __blk_bvec_map_sg(bvec, sglist, sg);
545 			else
546 				nsegs += blk_bvec_map_sg(q, &bvec, sglist, sg);
547  next_bvec:
548 			new_bio = false;
549 		}
550 		if (likely(bio->bi_iter.bi_size)) {
551 			bvprv = bvec;
552 			new_bio = true;
553 		}
554 	}
555 
556 	return nsegs;
557 }
558 
559 /*
560  * map a request to scatterlist, return number of sg entries setup. Caller
561  * must make sure sg can hold rq->nr_phys_segments entries
562  */
563 int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
564 		struct scatterlist *sglist, struct scatterlist **last_sg)
565 {
566 	int nsegs = 0;
567 
568 	if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
569 		nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, last_sg);
570 	else if (rq->bio)
571 		nsegs = __blk_bios_map_sg(q, rq->bio, sglist, last_sg);
572 
573 	if (*last_sg)
574 		sg_mark_end(*last_sg);
575 
576 	/*
577 	 * Something must have been wrong if the figured number of
578 	 * segment is bigger than number of req's physical segments
579 	 */
580 	WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
581 
582 	return nsegs;
583 }
584 EXPORT_SYMBOL(__blk_rq_map_sg);
585 
586 static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
587 						  sector_t offset)
588 {
589 	struct request_queue *q = rq->q;
590 	unsigned int max_sectors;
591 
592 	if (blk_rq_is_passthrough(rq))
593 		return q->limits.max_hw_sectors;
594 
595 	max_sectors = blk_queue_get_max_sectors(q, req_op(rq));
596 	if (!q->limits.chunk_sectors ||
597 	    req_op(rq) == REQ_OP_DISCARD ||
598 	    req_op(rq) == REQ_OP_SECURE_ERASE)
599 		return max_sectors;
600 	return min(max_sectors,
601 		   blk_chunk_sectors_left(offset, q->limits.chunk_sectors));
602 }
603 
604 static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
605 		unsigned int nr_phys_segs)
606 {
607 	if (!blk_cgroup_mergeable(req, bio))
608 		goto no_merge;
609 
610 	if (blk_integrity_merge_bio(req->q, req, bio) == false)
611 		goto no_merge;
612 
613 	/* discard request merge won't add new segment */
614 	if (req_op(req) == REQ_OP_DISCARD)
615 		return 1;
616 
617 	if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
618 		goto no_merge;
619 
620 	/*
621 	 * This will form the start of a new hw segment.  Bump both
622 	 * counters.
623 	 */
624 	req->nr_phys_segments += nr_phys_segs;
625 	return 1;
626 
627 no_merge:
628 	req_set_nomerge(req->q, req);
629 	return 0;
630 }
631 
632 int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
633 {
634 	if (req_gap_back_merge(req, bio))
635 		return 0;
636 	if (blk_integrity_rq(req) &&
637 	    integrity_req_gap_back_merge(req, bio))
638 		return 0;
639 	if (!bio_crypt_ctx_back_mergeable(req, bio))
640 		return 0;
641 	if (blk_rq_sectors(req) + bio_sectors(bio) >
642 	    blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
643 		req_set_nomerge(req->q, req);
644 		return 0;
645 	}
646 
647 	return ll_new_hw_segment(req, bio, nr_segs);
648 }
649 
650 static int ll_front_merge_fn(struct request *req, struct bio *bio,
651 		unsigned int nr_segs)
652 {
653 	if (req_gap_front_merge(req, bio))
654 		return 0;
655 	if (blk_integrity_rq(req) &&
656 	    integrity_req_gap_front_merge(req, bio))
657 		return 0;
658 	if (!bio_crypt_ctx_front_mergeable(req, bio))
659 		return 0;
660 	if (blk_rq_sectors(req) + bio_sectors(bio) >
661 	    blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
662 		req_set_nomerge(req->q, req);
663 		return 0;
664 	}
665 
666 	return ll_new_hw_segment(req, bio, nr_segs);
667 }
668 
669 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
670 		struct request *next)
671 {
672 	unsigned short segments = blk_rq_nr_discard_segments(req);
673 
674 	if (segments >= queue_max_discard_segments(q))
675 		goto no_merge;
676 	if (blk_rq_sectors(req) + bio_sectors(next->bio) >
677 	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
678 		goto no_merge;
679 
680 	req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
681 	return true;
682 no_merge:
683 	req_set_nomerge(q, req);
684 	return false;
685 }
686 
687 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
688 				struct request *next)
689 {
690 	int total_phys_segments;
691 
692 	if (req_gap_back_merge(req, next->bio))
693 		return 0;
694 
695 	/*
696 	 * Will it become too large?
697 	 */
698 	if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
699 	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
700 		return 0;
701 
702 	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
703 	if (total_phys_segments > blk_rq_get_max_segments(req))
704 		return 0;
705 
706 	if (!blk_cgroup_mergeable(req, next->bio))
707 		return 0;
708 
709 	if (blk_integrity_merge_rq(q, req, next) == false)
710 		return 0;
711 
712 	if (!bio_crypt_ctx_merge_rq(req, next))
713 		return 0;
714 
715 	/* Merge is OK... */
716 	req->nr_phys_segments = total_phys_segments;
717 	return 1;
718 }
719 
720 /**
721  * blk_rq_set_mixed_merge - mark a request as mixed merge
722  * @rq: request to mark as mixed merge
723  *
724  * Description:
725  *     @rq is about to be mixed merged.  Make sure the attributes
726  *     which can be mixed are set in each bio and mark @rq as mixed
727  *     merged.
728  */
729 static void blk_rq_set_mixed_merge(struct request *rq)
730 {
731 	blk_opf_t ff = rq->cmd_flags & REQ_FAILFAST_MASK;
732 	struct bio *bio;
733 
734 	if (rq->rq_flags & RQF_MIXED_MERGE)
735 		return;
736 
737 	/*
738 	 * @rq will no longer represent mixable attributes for all the
739 	 * contained bios.  It will just track those of the first one.
740 	 * Distributes the attributs to each bio.
741 	 */
742 	for (bio = rq->bio; bio; bio = bio->bi_next) {
743 		WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
744 			     (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
745 		bio->bi_opf |= ff;
746 	}
747 	rq->rq_flags |= RQF_MIXED_MERGE;
748 }
749 
750 static inline blk_opf_t bio_failfast(const struct bio *bio)
751 {
752 	if (bio->bi_opf & REQ_RAHEAD)
753 		return REQ_FAILFAST_MASK;
754 
755 	return bio->bi_opf & REQ_FAILFAST_MASK;
756 }
757 
758 /*
759  * After we are marked as MIXED_MERGE, any new RA bio has to be updated
760  * as failfast, and request's failfast has to be updated in case of
761  * front merge.
762  */
763 static inline void blk_update_mixed_merge(struct request *req,
764 		struct bio *bio, bool front_merge)
765 {
766 	if (req->rq_flags & RQF_MIXED_MERGE) {
767 		if (bio->bi_opf & REQ_RAHEAD)
768 			bio->bi_opf |= REQ_FAILFAST_MASK;
769 
770 		if (front_merge) {
771 			req->cmd_flags &= ~REQ_FAILFAST_MASK;
772 			req->cmd_flags |= bio->bi_opf & REQ_FAILFAST_MASK;
773 		}
774 	}
775 }
776 
777 static void blk_account_io_merge_request(struct request *req)
778 {
779 	if (blk_do_io_stat(req)) {
780 		part_stat_lock();
781 		part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
782 		part_stat_unlock();
783 	}
784 }
785 
786 static enum elv_merge blk_try_req_merge(struct request *req,
787 					struct request *next)
788 {
789 	if (blk_discard_mergable(req))
790 		return ELEVATOR_DISCARD_MERGE;
791 	else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
792 		return ELEVATOR_BACK_MERGE;
793 
794 	return ELEVATOR_NO_MERGE;
795 }
796 
797 /*
798  * For non-mq, this has to be called with the request spinlock acquired.
799  * For mq with scheduling, the appropriate queue wide lock should be held.
800  */
801 static struct request *attempt_merge(struct request_queue *q,
802 				     struct request *req, struct request *next)
803 {
804 	if (!rq_mergeable(req) || !rq_mergeable(next))
805 		return NULL;
806 
807 	if (req_op(req) != req_op(next))
808 		return NULL;
809 
810 	if (rq_data_dir(req) != rq_data_dir(next))
811 		return NULL;
812 
813 	/* Don't merge requests with different write hints. */
814 	if (req->write_hint != next->write_hint)
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(req);
851 		blk_rq_set_mixed_merge(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(next);
866 
867 	if (!blk_discard_mergable(req))
868 		elv_merge_requests(q, req, next);
869 
870 	blk_crypto_rq_put_keyslot(next);
871 
872 	/*
873 	 * 'next' is going away, so update stats accordingly
874 	 */
875 	blk_account_io_merge_request(next);
876 
877 	trace_block_rq_merge(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 
887 static 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, rq, next);
894 
895 	return NULL;
896 }
897 
898 static 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, prev, 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  */
914 bool blk_attempt_req_merge(struct request_queue *q, struct request *rq,
915 			   struct request *next)
916 {
917 	return attempt_merge(q, rq, next);
918 }
919 
920 bool 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(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 	/* Don't merge requests with different write hints. */
945 	if (rq->write_hint != bio->bi_write_hint)
946 		return false;
947 
948 	if (rq->ioprio != bio_prio(bio))
949 		return false;
950 
951 	return true;
952 }
953 
954 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
955 {
956 	if (blk_discard_mergable(rq))
957 		return ELEVATOR_DISCARD_MERGE;
958 	else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
959 		return ELEVATOR_BACK_MERGE;
960 	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
961 		return ELEVATOR_FRONT_MERGE;
962 	return ELEVATOR_NO_MERGE;
963 }
964 
965 static void blk_account_io_merge_bio(struct request *req)
966 {
967 	if (!blk_do_io_stat(req))
968 		return;
969 
970 	part_stat_lock();
971 	part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
972 	part_stat_unlock();
973 }
974 
975 enum bio_merge_status {
976 	BIO_MERGE_OK,
977 	BIO_MERGE_NONE,
978 	BIO_MERGE_FAILED,
979 };
980 
981 static enum bio_merge_status bio_attempt_back_merge(struct request *req,
982 		struct bio *bio, unsigned int nr_segs)
983 {
984 	const blk_opf_t ff = bio_failfast(bio);
985 
986 	if (!ll_back_merge_fn(req, bio, nr_segs))
987 		return BIO_MERGE_FAILED;
988 
989 	trace_block_bio_backmerge(bio);
990 	rq_qos_merge(req->q, req, bio);
991 
992 	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
993 		blk_rq_set_mixed_merge(req);
994 
995 	blk_update_mixed_merge(req, bio, false);
996 
997 	req->biotail->bi_next = bio;
998 	req->biotail = bio;
999 	req->__data_len += bio->bi_iter.bi_size;
1000 
1001 	bio_crypt_free_ctx(bio);
1002 
1003 	blk_account_io_merge_bio(req);
1004 	return BIO_MERGE_OK;
1005 }
1006 
1007 static enum bio_merge_status bio_attempt_front_merge(struct request *req,
1008 		struct bio *bio, unsigned int nr_segs)
1009 {
1010 	const blk_opf_t ff = bio_failfast(bio);
1011 
1012 	if (!ll_front_merge_fn(req, bio, nr_segs))
1013 		return BIO_MERGE_FAILED;
1014 
1015 	trace_block_bio_frontmerge(bio);
1016 	rq_qos_merge(req->q, req, bio);
1017 
1018 	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
1019 		blk_rq_set_mixed_merge(req);
1020 
1021 	blk_update_mixed_merge(req, bio, true);
1022 
1023 	bio->bi_next = req->bio;
1024 	req->bio = bio;
1025 
1026 	req->__sector = bio->bi_iter.bi_sector;
1027 	req->__data_len += bio->bi_iter.bi_size;
1028 
1029 	bio_crypt_do_front_merge(req, bio);
1030 
1031 	blk_account_io_merge_bio(req);
1032 	return BIO_MERGE_OK;
1033 }
1034 
1035 static enum bio_merge_status bio_attempt_discard_merge(struct request_queue *q,
1036 		struct request *req, struct bio *bio)
1037 {
1038 	unsigned short segments = blk_rq_nr_discard_segments(req);
1039 
1040 	if (segments >= queue_max_discard_segments(q))
1041 		goto no_merge;
1042 	if (blk_rq_sectors(req) + bio_sectors(bio) >
1043 	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
1044 		goto no_merge;
1045 
1046 	rq_qos_merge(q, req, bio);
1047 
1048 	req->biotail->bi_next = bio;
1049 	req->biotail = bio;
1050 	req->__data_len += bio->bi_iter.bi_size;
1051 	req->nr_phys_segments = segments + 1;
1052 
1053 	blk_account_io_merge_bio(req);
1054 	return BIO_MERGE_OK;
1055 no_merge:
1056 	req_set_nomerge(q, req);
1057 	return BIO_MERGE_FAILED;
1058 }
1059 
1060 static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
1061 						   struct request *rq,
1062 						   struct bio *bio,
1063 						   unsigned int nr_segs,
1064 						   bool sched_allow_merge)
1065 {
1066 	if (!blk_rq_merge_ok(rq, bio))
1067 		return BIO_MERGE_NONE;
1068 
1069 	switch (blk_try_merge(rq, bio)) {
1070 	case ELEVATOR_BACK_MERGE:
1071 		if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
1072 			return bio_attempt_back_merge(rq, bio, nr_segs);
1073 		break;
1074 	case ELEVATOR_FRONT_MERGE:
1075 		if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
1076 			return bio_attempt_front_merge(rq, bio, nr_segs);
1077 		break;
1078 	case ELEVATOR_DISCARD_MERGE:
1079 		return bio_attempt_discard_merge(q, rq, bio);
1080 	default:
1081 		return BIO_MERGE_NONE;
1082 	}
1083 
1084 	return BIO_MERGE_FAILED;
1085 }
1086 
1087 /**
1088  * blk_attempt_plug_merge - try to merge with %current's plugged list
1089  * @q: request_queue new bio is being queued at
1090  * @bio: new bio being queued
1091  * @nr_segs: number of segments in @bio
1092  * from the passed in @q already in the plug list
1093  *
1094  * Determine whether @bio being queued on @q can be merged with the previous
1095  * request on %current's plugged list.  Returns %true if merge was successful,
1096  * otherwise %false.
1097  *
1098  * Plugging coalesces IOs from the same issuer for the same purpose without
1099  * going through @q->queue_lock.  As such it's more of an issuing mechanism
1100  * than scheduling, and the request, while may have elvpriv data, is not
1101  * added on the elevator at this point.  In addition, we don't have
1102  * reliable access to the elevator outside queue lock.  Only check basic
1103  * merging parameters without querying the elevator.
1104  *
1105  * Caller must ensure !blk_queue_nomerges(q) beforehand.
1106  */
1107 bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
1108 		unsigned int nr_segs)
1109 {
1110 	struct blk_plug *plug;
1111 	struct request *rq;
1112 
1113 	plug = blk_mq_plug(bio);
1114 	if (!plug || rq_list_empty(plug->mq_list))
1115 		return false;
1116 
1117 	rq_list_for_each(&plug->mq_list, rq) {
1118 		if (rq->q == q) {
1119 			if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
1120 			    BIO_MERGE_OK)
1121 				return true;
1122 			break;
1123 		}
1124 
1125 		/*
1126 		 * Only keep iterating plug list for merges if we have multiple
1127 		 * queues
1128 		 */
1129 		if (!plug->multiple_queues)
1130 			break;
1131 	}
1132 	return false;
1133 }
1134 
1135 /*
1136  * Iterate list of requests and see if we can merge this bio with any
1137  * of them.
1138  */
1139 bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
1140 			struct bio *bio, unsigned int nr_segs)
1141 {
1142 	struct request *rq;
1143 	int checked = 8;
1144 
1145 	list_for_each_entry_reverse(rq, list, queuelist) {
1146 		if (!checked--)
1147 			break;
1148 
1149 		switch (blk_attempt_bio_merge(q, rq, bio, nr_segs, true)) {
1150 		case BIO_MERGE_NONE:
1151 			continue;
1152 		case BIO_MERGE_OK:
1153 			return true;
1154 		case BIO_MERGE_FAILED:
1155 			return false;
1156 		}
1157 
1158 	}
1159 
1160 	return false;
1161 }
1162 EXPORT_SYMBOL_GPL(blk_bio_list_merge);
1163 
1164 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
1165 		unsigned int nr_segs, struct request **merged_request)
1166 {
1167 	struct request *rq;
1168 
1169 	switch (elv_merge(q, &rq, bio)) {
1170 	case ELEVATOR_BACK_MERGE:
1171 		if (!blk_mq_sched_allow_merge(q, rq, bio))
1172 			return false;
1173 		if (bio_attempt_back_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
1174 			return false;
1175 		*merged_request = attempt_back_merge(q, rq);
1176 		if (!*merged_request)
1177 			elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
1178 		return true;
1179 	case ELEVATOR_FRONT_MERGE:
1180 		if (!blk_mq_sched_allow_merge(q, rq, bio))
1181 			return false;
1182 		if (bio_attempt_front_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
1183 			return false;
1184 		*merged_request = attempt_front_merge(q, rq);
1185 		if (!*merged_request)
1186 			elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
1187 		return true;
1188 	case ELEVATOR_DISCARD_MERGE:
1189 		return bio_attempt_discard_merge(q, rq, bio) == BIO_MERGE_OK;
1190 	default:
1191 		return false;
1192 	}
1193 }
1194 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
1195