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