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