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