Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/block/blk-merge.c

  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_ZEROES:
203                 split = NULL;
204                 nsegs = (*bio)->bi_phys_segments;
205                 break;
206         case REQ_OP_WRITE_SAME:
207                 split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
208                 break;
209         default:
210                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
211                 break;
212         }
213 
214         /* physical segments can be figured out during splitting */
215         res = split ? split : *bio;
216         res->bi_phys_segments = nsegs;
217         bio_set_flag(res, BIO_SEG_VALID);
218 
219         if (split) {
220                 /* there isn't chance to merge the splitted bio */
221                 split->bi_opf |= REQ_NOMERGE;
222 
223                 bio_chain(split, *bio);
224                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
225                 generic_make_request(*bio);
226                 *bio = split;
227         }
228 }
229 EXPORT_SYMBOL(blk_queue_split);
230 
231 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
232                                              struct bio *bio,
233                                              bool no_sg_merge)
234 {
235         struct bio_vec bv, bvprv = { NULL };
236         int cluster, prev = 0;
237         unsigned int seg_size, nr_phys_segs;
238         struct bio *fbio, *bbio;
239         struct bvec_iter iter;
240 
241         if (!bio)
242                 return 0;
243 
244         switch (bio_op(bio)) {
245         case REQ_OP_DISCARD:
246         case REQ_OP_SECURE_ERASE:
247         case REQ_OP_WRITE_ZEROES:
248                 return 0;
249         case REQ_OP_WRITE_SAME:
250                 return 1;
251         }
252 
253         fbio = bio;
254         cluster = blk_queue_cluster(q);
255         seg_size = 0;
256         nr_phys_segs = 0;
257         for_each_bio(bio) {
258                 bio_for_each_segment(bv, bio, iter) {
259                         /*
260                          * If SG merging is disabled, each bio vector is
261                          * a segment
262                          */
263                         if (no_sg_merge)
264                                 goto new_segment;
265 
266                         if (prev && cluster) {
267                                 if (seg_size + bv.bv_len
268                                     > queue_max_segment_size(q))
269                                         goto new_segment;
270                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
271                                         goto new_segment;
272                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
273                                         goto new_segment;
274 
275                                 seg_size += bv.bv_len;
276                                 bvprv = bv;
277                                 continue;
278                         }
279 new_segment:
280                         if (nr_phys_segs == 1 && seg_size >
281                             fbio->bi_seg_front_size)
282                                 fbio->bi_seg_front_size = seg_size;
283 
284                         nr_phys_segs++;
285                         bvprv = bv;
286                         prev = 1;
287                         seg_size = bv.bv_len;
288                 }
289                 bbio = bio;
290         }
291 
292         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
293                 fbio->bi_seg_front_size = seg_size;
294         if (seg_size > bbio->bi_seg_back_size)
295                 bbio->bi_seg_back_size = seg_size;
296 
297         return nr_phys_segs;
298 }
299 
300 void blk_recalc_rq_segments(struct request *rq)
301 {
302         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
303                         &rq->q->queue_flags);
304 
305         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
306                         no_sg_merge);
307 }
308 
309 void blk_recount_segments(struct request_queue *q, struct bio *bio)
310 {
311         unsigned short seg_cnt;
312 
313         /* estimate segment number by bi_vcnt for non-cloned bio */
314         if (bio_flagged(bio, BIO_CLONED))
315                 seg_cnt = bio_segments(bio);
316         else
317                 seg_cnt = bio->bi_vcnt;
318 
319         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
320                         (seg_cnt < queue_max_segments(q)))
321                 bio->bi_phys_segments = seg_cnt;
322         else {
323                 struct bio *nxt = bio->bi_next;
324 
325                 bio->bi_next = NULL;
326                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
327                 bio->bi_next = nxt;
328         }
329 
330         bio_set_flag(bio, BIO_SEG_VALID);
331 }
332 EXPORT_SYMBOL(blk_recount_segments);
333 
334 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
335                                    struct bio *nxt)
336 {
337         struct bio_vec end_bv = { NULL }, nxt_bv;
338 
339         if (!blk_queue_cluster(q))
340                 return 0;
341 
342         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
343             queue_max_segment_size(q))
344                 return 0;
345 
346         if (!bio_has_data(bio))
347                 return 1;
348 
349         bio_get_last_bvec(bio, &end_bv);
350         bio_get_first_bvec(nxt, &nxt_bv);
351 
352         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
353                 return 0;
354 
355         /*
356          * bio and nxt are contiguous in memory; check if the queue allows
357          * these two to be merged into one
358          */
359         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
360                 return 1;
361 
362         return 0;
363 }
364 
365 static inline void
366 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
367                      struct scatterlist *sglist, struct bio_vec *bvprv,
368                      struct scatterlist **sg, int *nsegs, int *cluster)
369 {
370 
371         int nbytes = bvec->bv_len;
372 
373         if (*sg && *cluster) {
374                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
375                         goto new_segment;
376 
377                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
378                         goto new_segment;
379                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
380                         goto new_segment;
381 
382                 (*sg)->length += nbytes;
383         } else {
384 new_segment:
385                 if (!*sg)
386                         *sg = sglist;
387                 else {
388                         /*
389                          * If the driver previously mapped a shorter
390                          * list, we could see a termination bit
391                          * prematurely unless it fully inits the sg
392                          * table on each mapping. We KNOW that there
393                          * must be more entries here or the driver
394                          * would be buggy, so force clear the
395                          * termination bit to avoid doing a full
396                          * sg_init_table() in drivers for each command.
397                          */
398                         sg_unmark_end(*sg);
399                         *sg = sg_next(*sg);
400                 }
401 
402                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
403                 (*nsegs)++;
404         }
405         *bvprv = *bvec;
406 }
407 
408 static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
409                 struct scatterlist *sglist, struct scatterlist **sg)
410 {
411         *sg = sglist;
412         sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
413         return 1;
414 }
415 
416 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
417                              struct scatterlist *sglist,
418                              struct scatterlist **sg)
419 {
420         struct bio_vec bvec, bvprv = { NULL };
421         struct bvec_iter iter;
422         int cluster = blk_queue_cluster(q), nsegs = 0;
423 
424         for_each_bio(bio)
425                 bio_for_each_segment(bvec, bio, iter)
426                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
427                                              &nsegs, &cluster);
428 
429         return nsegs;
430 }
431 
432 /*
433  * map a request to scatterlist, return number of sg entries setup. Caller
434  * must make sure sg can hold rq->nr_phys_segments entries
435  */
436 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
437                   struct scatterlist *sglist)
438 {
439         struct scatterlist *sg = NULL;
440         int nsegs = 0;
441 
442         if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
443                 nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
444         else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
445                 nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
446         else if (rq->bio)
447                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
448 
449         if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
450             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
451                 unsigned int pad_len =
452                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
453 
454                 sg->length += pad_len;
455                 rq->extra_len += pad_len;
456         }
457 
458         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
459                 if (op_is_write(req_op(rq)))
460                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
461 
462                 sg_unmark_end(sg);
463                 sg = sg_next(sg);
464                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
465                             q->dma_drain_size,
466                             ((unsigned long)q->dma_drain_buffer) &
467                             (PAGE_SIZE - 1));
468                 nsegs++;
469                 rq->extra_len += q->dma_drain_size;
470         }
471 
472         if (sg)
473                 sg_mark_end(sg);
474 
475         /*
476          * Something must have been wrong if the figured number of
477          * segment is bigger than number of req's physical segments
478          */
479         WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
480 
481         return nsegs;
482 }
483 EXPORT_SYMBOL(blk_rq_map_sg);
484 
485 static void req_set_nomerge(struct request_queue *q, struct request *req)
486 {
487         req->cmd_flags |= REQ_NOMERGE;
488         if (req == q->last_merge)
489                 q->last_merge = NULL;
490 }
491 
492 static inline int ll_new_hw_segment(struct request_queue *q,
493                                     struct request *req,
494                                     struct bio *bio)
495 {
496         int nr_phys_segs = bio_phys_segments(q, bio);
497 
498         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
499                 goto no_merge;
500 
501         if (blk_integrity_merge_bio(q, req, bio) == false)
502                 goto no_merge;
503 
504         /*
505          * This will form the start of a new hw segment.  Bump both
506          * counters.
507          */
508         req->nr_phys_segments += nr_phys_segs;
509         return 1;
510 
511 no_merge:
512         req_set_nomerge(q, req);
513         return 0;
514 }
515 
516 int ll_back_merge_fn(struct request_queue *q, struct request *req,
517                      struct bio *bio)
518 {
519         if (req_gap_back_merge(req, bio))
520                 return 0;
521         if (blk_integrity_rq(req) &&
522             integrity_req_gap_back_merge(req, bio))
523                 return 0;
524         if (blk_rq_sectors(req) + bio_sectors(bio) >
525             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
526                 req_set_nomerge(q, req);
527                 return 0;
528         }
529         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
530                 blk_recount_segments(q, req->biotail);
531         if (!bio_flagged(bio, BIO_SEG_VALID))
532                 blk_recount_segments(q, bio);
533 
534         return ll_new_hw_segment(q, req, bio);
535 }
536 
537 int ll_front_merge_fn(struct request_queue *q, struct request *req,
538                       struct bio *bio)
539 {
540 
541         if (req_gap_front_merge(req, bio))
542                 return 0;
543         if (blk_integrity_rq(req) &&
544             integrity_req_gap_front_merge(req, bio))
545                 return 0;
546         if (blk_rq_sectors(req) + bio_sectors(bio) >
547             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
548                 req_set_nomerge(q, req);
549                 return 0;
550         }
551         if (!bio_flagged(bio, BIO_SEG_VALID))
552                 blk_recount_segments(q, bio);
553         if (!bio_flagged(req->bio, BIO_SEG_VALID))
554                 blk_recount_segments(q, req->bio);
555 
556         return ll_new_hw_segment(q, req, bio);
557 }
558 
559 /*
560  * blk-mq uses req->special to carry normal driver per-request payload, it
561  * does not indicate a prepared command that we cannot merge with.
562  */
563 static bool req_no_special_merge(struct request *req)
564 {
565         struct request_queue *q = req->q;
566 
567         return !q->mq_ops && req->special;
568 }
569 
570 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
571                                 struct request *next)
572 {
573         int total_phys_segments;
574         unsigned int seg_size =
575                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
576 
577         /*
578          * First check if the either of the requests are re-queued
579          * requests.  Can't merge them if they are.
580          */
581         if (req_no_special_merge(req) || req_no_special_merge(next))
582                 return 0;
583 
584         if (req_gap_back_merge(req, next->bio))
585                 return 0;
586 
587         /*
588          * Will it become too large?
589          */
590         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
591             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
592                 return 0;
593 
594         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
595         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
596                 if (req->nr_phys_segments == 1)
597                         req->bio->bi_seg_front_size = seg_size;
598                 if (next->nr_phys_segments == 1)
599                         next->biotail->bi_seg_back_size = seg_size;
600                 total_phys_segments--;
601         }
602 
603         if (total_phys_segments > queue_max_segments(q))
604                 return 0;
605 
606         if (blk_integrity_merge_rq(q, req, next) == false)
607                 return 0;
608 
609         /* Merge is OK... */
610         req->nr_phys_segments = total_phys_segments;
611         return 1;
612 }
613 
614 /**
615  * blk_rq_set_mixed_merge - mark a request as mixed merge
616  * @rq: request to mark as mixed merge
617  *
618  * Description:
619  *     @rq is about to be mixed merged.  Make sure the attributes
620  *     which can be mixed are set in each bio and mark @rq as mixed
621  *     merged.
622  */
623 void blk_rq_set_mixed_merge(struct request *rq)
624 {
625         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
626         struct bio *bio;
627 
628         if (rq->rq_flags & RQF_MIXED_MERGE)
629                 return;
630 
631         /*
632          * @rq will no longer represent mixable attributes for all the
633          * contained bios.  It will just track those of the first one.
634          * Distributes the attributs to each bio.
635          */
636         for (bio = rq->bio; bio; bio = bio->bi_next) {
637                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
638                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
639                 bio->bi_opf |= ff;
640         }
641         rq->rq_flags |= RQF_MIXED_MERGE;
642 }
643 
644 static void blk_account_io_merge(struct request *req)
645 {
646         if (blk_do_io_stat(req)) {
647                 struct hd_struct *part;
648                 int cpu;
649 
650                 cpu = part_stat_lock();
651                 part = req->part;
652 
653                 part_round_stats(cpu, part);
654                 part_dec_in_flight(part, rq_data_dir(req));
655 
656                 hd_struct_put(part);
657                 part_stat_unlock();
658         }
659 }
660 
661 /*
662  * Has to be called with the request spinlock acquired
663  */
664 static int attempt_merge(struct request_queue *q, struct request *req,
665                           struct request *next)
666 {
667         if (!rq_mergeable(req) || !rq_mergeable(next))
668                 return 0;
669 
670         if (req_op(req) != req_op(next))
671                 return 0;
672 
673         /*
674          * not contiguous
675          */
676         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
677                 return 0;
678 
679         if (rq_data_dir(req) != rq_data_dir(next)
680             || req->rq_disk != next->rq_disk
681             || req_no_special_merge(next))
682                 return 0;
683 
684         if (req_op(req) == REQ_OP_WRITE_SAME &&
685             !blk_write_same_mergeable(req->bio, next->bio))
686                 return 0;
687 
688         /*
689          * If we are allowed to merge, then append bio list
690          * from next to rq and release next. merge_requests_fn
691          * will have updated segment counts, update sector
692          * counts here.
693          */
694         if (!ll_merge_requests_fn(q, req, next))
695                 return 0;
696 
697         /*
698          * If failfast settings disagree or any of the two is already
699          * a mixed merge, mark both as mixed before proceeding.  This
700          * makes sure that all involved bios have mixable attributes
701          * set properly.
702          */
703         if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
704             (req->cmd_flags & REQ_FAILFAST_MASK) !=
705             (next->cmd_flags & REQ_FAILFAST_MASK)) {
706                 blk_rq_set_mixed_merge(req);
707                 blk_rq_set_mixed_merge(next);
708         }
709 
710         /*
711          * At this point we have either done a back merge
712          * or front merge. We need the smaller start_time of
713          * the merged requests to be the current request
714          * for accounting purposes.
715          */
716         if (time_after(req->start_time, next->start_time))
717                 req->start_time = next->start_time;
718 
719         req->biotail->bi_next = next->bio;
720         req->biotail = next->biotail;
721 
722         req->__data_len += blk_rq_bytes(next);
723 
724         elv_merge_requests(q, req, next);
725 
726         /*
727          * 'next' is going away, so update stats accordingly
728          */
729         blk_account_io_merge(next);
730 
731         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
732         if (blk_rq_cpu_valid(next))
733                 req->cpu = next->cpu;
734 
735         /* owner-ship of bio passed from next to req */
736         next->bio = NULL;
737         __blk_put_request(q, next);
738         return 1;
739 }
740 
741 int attempt_back_merge(struct request_queue *q, struct request *rq)
742 {
743         struct request *next = elv_latter_request(q, rq);
744 
745         if (next)
746                 return attempt_merge(q, rq, next);
747 
748         return 0;
749 }
750 
751 int attempt_front_merge(struct request_queue *q, struct request *rq)
752 {
753         struct request *prev = elv_former_request(q, rq);
754 
755         if (prev)
756                 return attempt_merge(q, prev, rq);
757 
758         return 0;
759 }
760 
761 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
762                           struct request *next)
763 {
764         struct elevator_queue *e = q->elevator;
765 
766         if (e->type->ops.elevator_allow_rq_merge_fn)
767                 if (!e->type->ops.elevator_allow_rq_merge_fn(q, rq, next))
768                         return 0;
769 
770         return attempt_merge(q, rq, next);
771 }
772 
773 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
774 {
775         if (!rq_mergeable(rq) || !bio_mergeable(bio))
776                 return false;
777 
778         if (req_op(rq) != bio_op(bio))
779                 return false;
780 
781         /* different data direction or already started, don't merge */
782         if (bio_data_dir(bio) != rq_data_dir(rq))
783                 return false;
784 
785         /* must be same device and not a special request */
786         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
787                 return false;
788 
789         /* only merge integrity protected bio into ditto rq */
790         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
791                 return false;
792 
793         /* must be using the same buffer */
794         if (req_op(rq) == REQ_OP_WRITE_SAME &&
795             !blk_write_same_mergeable(rq->bio, bio))
796                 return false;
797 
798         return true;
799 }
800 
801 int blk_try_merge(struct request *rq, struct bio *bio)
802 {
803         if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
804                 return ELEVATOR_BACK_MERGE;
805         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
806                 return ELEVATOR_FRONT_MERGE;
807         return ELEVATOR_NO_MERGE;
808 }
809 

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