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