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