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                                          unsigned *nsegs)
  16 {
  17         unsigned int max_discard_sectors, granularity;
  18         int alignment;
  19         sector_t tmp;
  20         unsigned split_sectors;
  21
  22         *nsegs = 1;
  23
  24         /* Zero-sector (unknown) and one-sector granularities are the same.  */
  25         granularity = max(q->limits.discard_granularity >> 9, 1U);
  26
  27         max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
  28         max_discard_sectors -= max_discard_sectors % granularity;
  29
  30         if (unlikely(!max_discard_sectors)) {
  31                 /* XXX: warn */
  32                 return NULL;
  33         }
  34
  35         if (bio_sectors(bio) <= max_discard_sectors)
  36                 return NULL;
  37
  38         split_sectors = max_discard_sectors;
  39
  40         /*
  41          * If the next starting sector would be misaligned, stop the discard at
  42          * the previous aligned sector.
  43          */
  44         alignment = (q->limits.discard_alignment >> 9) % granularity;
  45
  46         tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
  47         tmp = sector_div(tmp, granularity);
  48
  49         if (split_sectors > tmp)
  50                 split_sectors -= tmp;
  51
  52         return bio_split(bio, split_sectors, GFP_NOIO, bs);
  53 }
  54
  55 static struct bio *blk_bio_write_same_split(struct request_queue *q,
  56                                             struct bio *bio,
  57                                             struct bio_set *bs,
  58                                             unsigned *nsegs)
  59 {
  60         *nsegs = 1;
  61
  62         if (!q->limits.max_write_same_sectors)
  63                 return NULL;
  64
  65         if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
  66                 return NULL;
  67
  68         return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
  69 }
  70
  71 static struct bio *blk_bio_segment_split(struct request_queue *q,
  72                                          struct bio *bio,
  73                                          struct bio_set *bs,
  74                                          unsigned *segs)
  75 {
  76         struct bio_vec bv, bvprv, *bvprvp = NULL;
  77         struct bvec_iter iter;
  78         unsigned seg_size = 0, nsegs = 0, sectors = 0;
  79         unsigned front_seg_size = bio->bi_seg_front_size;
  80         bool do_split = true;
  81         struct bio *new = NULL;
  82
  83         bio_for_each_segment(bv, bio, iter) {
  84                 if (sectors + (bv.bv_len >> 9) > blk_max_size_offset(q, bio->bi_iter.bi_sector))
  85                         goto split;
  86
  87                 /*
  88                  * If the queue doesn't support SG gaps and adding this
  89                  * offset would create a gap, disallow it.
  90                  */
  91                 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
  92                         goto split;
  93
  94                 if (bvprvp && blk_queue_cluster(q)) {
  95                         if (seg_size + bv.bv_len > queue_max_segment_size(q))
  96                                 goto new_segment;
  97                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
  98                                 goto new_segment;
  99                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
 100                                 goto new_segment;
 101
 102                         seg_size += bv.bv_len;
 103                         bvprv = bv;
 104                         bvprvp = &bvprv;
 105                         sectors += bv.bv_len >> 9;
 106
 107                         if (nsegs == 1 && seg_size > front_seg_size)
 108                                 front_seg_size = seg_size;
 109                         continue;
 110                 }
 111 new_segment:
 112                 if (nsegs == queue_max_segments(q))
 113                         goto split;
 114
 115                 nsegs++;
 116                 bvprv = bv;
 117                 bvprvp = &bvprv;
 118                 seg_size = bv.bv_len;
 119                 sectors += bv.bv_len >> 9;
 120
 121                 if (nsegs == 1 && seg_size > front_seg_size)
 122                         front_seg_size = seg_size;
 123         }
 124
 125         do_split = false;
 126 split:
 127         *segs = nsegs;
 128
 129         if (do_split) {
 130                 new = bio_split(bio, sectors, GFP_NOIO, bs);
 131                 if (new)
 132                         bio = new;
 133         }
 134
 135         bio->bi_seg_front_size = front_seg_size;
 136         if (seg_size > bio->bi_seg_back_size)
 137                 bio->bi_seg_back_size = seg_size;
 138
 139         return do_split ? new : NULL;
 140 }
 141
 142 void blk_queue_split(struct request_queue *q, struct bio **bio,
 143                      struct bio_set *bs)
 144 {
 145         struct bio *split, *res;
 146         unsigned nsegs;
 147
 148         if ((*bio)->bi_rw & REQ_DISCARD)
 149                 split = blk_bio_discard_split(q, *bio, bs, &nsegs);
 150         else if ((*bio)->bi_rw & REQ_WRITE_SAME)
 151                 split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
 152         else
 153                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
 154
 155         /* physical segments can be figured out during splitting */
 156         res = split ? split : *bio;
 157         res->bi_phys_segments = nsegs;
 158         bio_set_flag(res, BIO_SEG_VALID);
 159
 160         if (split) {
 161                 /* there isn't chance to merge the splitted bio */
 162                 split->bi_rw |= REQ_NOMERGE;
 163
 164                 bio_chain(split, *bio);
 165                 generic_make_request(*bio);
 166                 *bio = split;
 167         }
 168 }
 169 EXPORT_SYMBOL(blk_queue_split);
 170
 171 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 172                                              struct bio *bio,
 173                                              bool no_sg_merge)
 174 {
 175         struct bio_vec bv, bvprv = { NULL };
 176         int cluster, prev = 0;
 177         unsigned int seg_size, nr_phys_segs;
 178         struct bio *fbio, *bbio;
 179         struct bvec_iter iter;
 180
 181         if (!bio)
 182                 return 0;
 183
 184         /*
 185          * This should probably be returning 0, but blk_add_request_payload()
 186          * (Christoph!!!!)
 187          */
 188         if (bio->bi_rw & REQ_DISCARD)
 189                 return 1;
 190
 191         if (bio->bi_rw & REQ_WRITE_SAME)
 192                 return 1;
 193
 194         fbio = bio;
 195         cluster = blk_queue_cluster(q);
 196         seg_size = 0;
 197         nr_phys_segs = 0;
 198         for_each_bio(bio) {
 199                 bio_for_each_segment(bv, bio, iter) {
 200                         /*
 201                          * If SG merging is disabled, each bio vector is
 202                          * a segment
 203                          */
 204                         if (no_sg_merge)
 205                                 goto new_segment;
 206
 207                         if (prev && cluster) {
 208                                 if (seg_size + bv.bv_len
 209                                     > queue_max_segment_size(q))
 210                                         goto new_segment;
 211                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
 212                                         goto new_segment;
 213                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
 214                                         goto new_segment;
 215
 216                                 seg_size += bv.bv_len;
 217                                 bvprv = bv;
 218                                 continue;
 219                         }
 220 new_segment:
 221                         if (nr_phys_segs == 1 && seg_size >
 222                             fbio->bi_seg_front_size)
 223                                 fbio->bi_seg_front_size = seg_size;
 224
 225                         nr_phys_segs++;
 226                         bvprv = bv;
 227                         prev = 1;
 228                         seg_size = bv.bv_len;
 229                 }
 230                 bbio = bio;
 231         }
 232
 233         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
 234                 fbio->bi_seg_front_size = seg_size;
 235         if (seg_size > bbio->bi_seg_back_size)
 236                 bbio->bi_seg_back_size = seg_size;
 237
 238         return nr_phys_segs;
 239 }
 240
 241 void blk_recalc_rq_segments(struct request *rq)
 242 {
 243         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
 244                         &rq->q->queue_flags);
 245
 246         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
 247                         no_sg_merge);
 248 }
 249
 250 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 251 {
 252         unsigned short seg_cnt;
 253
 254         /* estimate segment number by bi_vcnt for non-cloned bio */
 255         if (bio_flagged(bio, BIO_CLONED))
 256                 seg_cnt = bio_segments(bio);
 257         else
 258                 seg_cnt = bio->bi_vcnt;
 259
 260         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 261                         (seg_cnt < queue_max_segments(q)))
 262                 bio->bi_phys_segments = seg_cnt;
 263         else {
 264                 struct bio *nxt = bio->bi_next;
 265
 266                 bio->bi_next = NULL;
 267                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 268                 bio->bi_next = nxt;
 269         }
 270
 271         bio_set_flag(bio, BIO_SEG_VALID);
 272 }
 273 EXPORT_SYMBOL(blk_recount_segments);
 274
 275 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 276                                    struct bio *nxt)
 277 {
 278         struct bio_vec end_bv = { NULL }, nxt_bv;
 279         struct bvec_iter iter;
 280
 281         if (!blk_queue_cluster(q))
 282                 return 0;
 283
 284         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 285             queue_max_segment_size(q))
 286                 return 0;
 287
 288         if (!bio_has_data(bio))
 289                 return 1;
 290
 291         bio_for_each_segment(end_bv, bio, iter)
 292                 if (end_bv.bv_len == iter.bi_size)
 293                         break;
 294
 295         nxt_bv = bio_iovec(nxt);
 296
 297         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 298                 return 0;
 299
 300         /*
 301          * bio and nxt are contiguous in memory; check if the queue allows
 302          * these two to be merged into one
 303          */
 304         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 305                 return 1;
 306
 307         return 0;
 308 }
 309
 310 static inline void
 311 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 312                      struct scatterlist *sglist, struct bio_vec *bvprv,
 313                      struct scatterlist **sg, int *nsegs, int *cluster)
 314 {
 315
 316         int nbytes = bvec->bv_len;
 317
 318         if (*sg && *cluster) {
 319                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 320                         goto new_segment;
 321
 322                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 323                         goto new_segment;
 324                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 325                         goto new_segment;
 326
 327                 (*sg)->length += nbytes;
 328         } else {
 329 new_segment:
 330                 if (!*sg)
 331                         *sg = sglist;
 332                 else {
 333                         /*
 334                          * If the driver previously mapped a shorter
 335                          * list, we could see a termination bit
 336                          * prematurely unless it fully inits the sg
 337                          * table on each mapping. We KNOW that there
 338                          * must be more entries here or the driver
 339                          * would be buggy, so force clear the
 340                          * termination bit to avoid doing a full
 341                          * sg_init_table() in drivers for each command.
 342                          */
 343                         sg_unmark_end(*sg);
 344                         *sg = sg_next(*sg);
 345                 }
 346
 347                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 348                 (*nsegs)++;
 349         }
 350         *bvprv = *bvec;
 351 }
 352
 353 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 354                              struct scatterlist *sglist,
 355                              struct scatterlist **sg)
 356 {
 357         struct bio_vec bvec, bvprv = { NULL };
 358         struct bvec_iter iter;
 359         int nsegs, cluster;
 360
 361         nsegs = 0;
 362         cluster = blk_queue_cluster(q);
 363
 364         if (bio->bi_rw & REQ_DISCARD) {
 365                 /*
 366                  * This is a hack - drivers should be neither modifying the
 367                  * biovec, nor relying on bi_vcnt - but because of
 368                  * blk_add_request_payload(), a discard bio may or may not have
 369                  * a payload we need to set up here (thank you Christoph) and
 370                  * bi_vcnt is really the only way of telling if we need to.
 371                  */
 372
 373                 if (bio->bi_vcnt)
 374                         goto single_segment;
 375
 376                 return 0;
 377         }
 378
 379         if (bio->bi_rw & REQ_WRITE_SAME) {
 380 single_segment:
 381                 *sg = sglist;
 382                 bvec = bio_iovec(bio);
 383                 sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
 384                 return 1;
 385         }
 386
 387         for_each_bio(bio)
 388                 bio_for_each_segment(bvec, bio, iter)
 389                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 390                                              &nsegs, &cluster);
 391
 392         return nsegs;
 393 }
 394
 395 /*
 396  * map a request to scatterlist, return number of sg entries setup. Caller
 397  * must make sure sg can hold rq->nr_phys_segments entries
 398  */
 399 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 400                   struct scatterlist *sglist)
 401 {
 402         struct scatterlist *sg = NULL;
 403         int nsegs = 0;
 404
 405         if (rq->bio)
 406                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 407
 408         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 409             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 410                 unsigned int pad_len =
 411                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 412
 413                 sg->length += pad_len;
 414                 rq->extra_len += pad_len;
 415         }
 416
 417         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 418                 if (rq->cmd_flags & REQ_WRITE)
 419                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 420
 421                 sg_unmark_end(sg);
 422                 sg = sg_next(sg);
 423                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 424                             q->dma_drain_size,
 425                             ((unsigned long)q->dma_drain_buffer) &
 426                             (PAGE_SIZE - 1));
 427                 nsegs++;
 428                 rq->extra_len += q->dma_drain_size;
 429         }
 430
 431         if (sg)
 432                 sg_mark_end(sg);
 433
 434         /*
 435          * Something must have been wrong if the figured number of
 436          * segment is bigger than number of req's physical segments
 437          */
 438         WARN_ON(nsegs > rq->nr_phys_segments);
 439
 440         return nsegs;
 441 }
 442 EXPORT_SYMBOL(blk_rq_map_sg);
 443
 444 static inline int ll_new_hw_segment(struct request_queue *q,
 445                                     struct request *req,
 446                                     struct bio *bio)
 447 {
 448         int nr_phys_segs = bio_phys_segments(q, bio);
 449
 450         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 451                 goto no_merge;
 452
 453         if (blk_integrity_merge_bio(q, req, bio) == false)
 454                 goto no_merge;
 455
 456         /*
 457          * This will form the start of a new hw segment.  Bump both
 458          * counters.
 459          */
 460         req->nr_phys_segments += nr_phys_segs;
 461         return 1;
 462
 463 no_merge:
 464         req->cmd_flags |= REQ_NOMERGE;
 465         if (req == q->last_merge)
 466                 q->last_merge = NULL;
 467         return 0;
 468 }
 469
 470 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 471                      struct bio *bio)
 472 {
 473         if (req_gap_back_merge(req, bio))
 474                 return 0;
 475         if (blk_integrity_rq(req) &&
 476             integrity_req_gap_back_merge(req, bio))
 477                 return 0;
 478         if (blk_rq_sectors(req) + bio_sectors(bio) >
 479             blk_rq_get_max_sectors(req)) {
 480                 req->cmd_flags |= REQ_NOMERGE;
 481                 if (req == q->last_merge)
 482                         q->last_merge = NULL;
 483                 return 0;
 484         }
 485         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 486                 blk_recount_segments(q, req->biotail);
 487         if (!bio_flagged(bio, BIO_SEG_VALID))
 488                 blk_recount_segments(q, bio);
 489
 490         return ll_new_hw_segment(q, req, bio);
 491 }
 492
 493 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 494                       struct bio *bio)
 495 {
 496
 497         if (req_gap_front_merge(req, bio))
 498                 return 0;
 499         if (blk_integrity_rq(req) &&
 500             integrity_req_gap_front_merge(req, bio))
 501                 return 0;
 502         if (blk_rq_sectors(req) + bio_sectors(bio) >
 503             blk_rq_get_max_sectors(req)) {
 504                 req->cmd_flags |= REQ_NOMERGE;
 505                 if (req == q->last_merge)
 506                         q->last_merge = NULL;
 507                 return 0;
 508         }
 509         if (!bio_flagged(bio, BIO_SEG_VALID))
 510                 blk_recount_segments(q, bio);
 511         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 512                 blk_recount_segments(q, req->bio);
 513
 514         return ll_new_hw_segment(q, req, bio);
 515 }
 516
 517 /*
 518  * blk-mq uses req->special to carry normal driver per-request payload, it
 519  * does not indicate a prepared command that we cannot merge with.
 520  */
 521 static bool req_no_special_merge(struct request *req)
 522 {
 523         struct request_queue *q = req->q;
 524
 525         return !q->mq_ops && req->special;
 526 }
 527
 528 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 529                                 struct request *next)
 530 {
 531         int total_phys_segments;
 532         unsigned int seg_size =
 533                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 534
 535         /*
 536          * First check if the either of the requests are re-queued
 537          * requests.  Can't merge them if they are.
 538          */
 539         if (req_no_special_merge(req) || req_no_special_merge(next))
 540                 return 0;
 541
 542         if (req_gap_back_merge(req, next->bio))
 543                 return 0;
 544
 545         /*
 546          * Will it become too large?
 547          */
 548         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 549             blk_rq_get_max_sectors(req))
 550                 return 0;
 551
 552         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 553         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 554                 if (req->nr_phys_segments == 1)
 555                         req->bio->bi_seg_front_size = seg_size;
 556                 if (next->nr_phys_segments == 1)
 557                         next->biotail->bi_seg_back_size = seg_size;
 558                 total_phys_segments--;
 559         }
 560
 561         if (total_phys_segments > queue_max_segments(q))
 562                 return 0;
 563
 564         if (blk_integrity_merge_rq(q, req, next) == false)
 565                 return 0;
 566
 567         /* Merge is OK... */
 568         req->nr_phys_segments = total_phys_segments;
 569         return 1;
 570 }
 571
 572 /**
 573  * blk_rq_set_mixed_merge - mark a request as mixed merge
 574  * @rq: request to mark as mixed merge
 575  *
 576  * Description:
 577  *     @rq is about to be mixed merged.  Make sure the attributes
 578  *     which can be mixed are set in each bio and mark @rq as mixed
 579  *     merged.
 580  */
 581 void blk_rq_set_mixed_merge(struct request *rq)
 582 {
 583         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 584         struct bio *bio;
 585
 586         if (rq->cmd_flags & REQ_MIXED_MERGE)
 587                 return;
 588
 589         /*
 590          * @rq will no longer represent mixable attributes for all the
 591          * contained bios.  It will just track those of the first one.
 592          * Distributes the attributs to each bio.
 593          */
 594         for (bio = rq->bio; bio; bio = bio->bi_next) {
 595                 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
 596                              (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
 597                 bio->bi_rw |= ff;
 598         }
 599         rq->cmd_flags |= REQ_MIXED_MERGE;
 600 }
 601
 602 static void blk_account_io_merge(struct request *req)
 603 {
 604         if (blk_do_io_stat(req)) {
 605                 struct hd_struct *part;
 606                 int cpu;
 607
 608                 cpu = part_stat_lock();
 609                 part = req->part;
 610
 611                 part_round_stats(cpu, part);
 612                 part_dec_in_flight(part, rq_data_dir(req));
 613
 614                 hd_struct_put(part);
 615                 part_stat_unlock();
 616         }
 617 }
 618
 619 /*
 620  * Has to be called with the request spinlock acquired
 621  */
 622 static int attempt_merge(struct request_queue *q, struct request *req,
 623                           struct request *next)
 624 {
 625         if (!rq_mergeable(req) || !rq_mergeable(next))
 626                 return 0;
 627
 628         if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
 629                 return 0;
 630
 631         /*
 632          * not contiguous
 633          */
 634         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 635                 return 0;
 636
 637         if (rq_data_dir(req) != rq_data_dir(next)
 638             || req->rq_disk != next->rq_disk
 639             || req_no_special_merge(next))
 640                 return 0;
 641
 642         if (req->cmd_flags & REQ_WRITE_SAME &&
 643             !blk_write_same_mergeable(req->bio, next->bio))
 644                 return 0;
 645
 646         /*
 647          * If we are allowed to merge, then append bio list
 648          * from next to rq and release next. merge_requests_fn
 649          * will have updated segment counts, update sector
 650          * counts here.
 651          */
 652         if (!ll_merge_requests_fn(q, req, next))
 653                 return 0;
 654
 655         /*
 656          * If failfast settings disagree or any of the two is already
 657          * a mixed merge, mark both as mixed before proceeding.  This
 658          * makes sure that all involved bios have mixable attributes
 659          * set properly.
 660          */
 661         if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
 662             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 663             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 664                 blk_rq_set_mixed_merge(req);
 665                 blk_rq_set_mixed_merge(next);
 666         }
 667
 668         /*
 669          * At this point we have either done a back merge
 670          * or front merge. We need the smaller start_time of
 671          * the merged requests to be the current request
 672          * for accounting purposes.
 673          */
 674         if (time_after(req->start_time, next->start_time))
 675                 req->start_time = next->start_time;
 676
 677         req->biotail->bi_next = next->bio;
 678         req->biotail = next->biotail;
 679
 680         req->__data_len += blk_rq_bytes(next);
 681
 682         elv_merge_requests(q, req, next);
 683
 684         /*
 685          * 'next' is going away, so update stats accordingly
 686          */
 687         blk_account_io_merge(next);
 688
 689         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 690         if (blk_rq_cpu_valid(next))
 691                 req->cpu = next->cpu;
 692
 693         /* owner-ship of bio passed from next to req */
 694         next->bio = NULL;
 695         __blk_put_request(q, next);
 696         return 1;
 697 }
 698
 699 int attempt_back_merge(struct request_queue *q, struct request *rq)
 700 {
 701         struct request *next = elv_latter_request(q, rq);
 702
 703         if (next)
 704                 return attempt_merge(q, rq, next);
 705
 706         return 0;
 707 }
 708
 709 int attempt_front_merge(struct request_queue *q, struct request *rq)
 710 {
 711         struct request *prev = elv_former_request(q, rq);
 712
 713         if (prev)
 714                 return attempt_merge(q, prev, rq);
 715
 716         return 0;
 717 }
 718
 719 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 720                           struct request *next)
 721 {
 722         return attempt_merge(q, rq, next);
 723 }
 724
 725 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 726 {
 727         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 728                 return false;
 729
 730         if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
 731                 return false;
 732
 733         /* different data direction or already started, don't merge */
 734         if (bio_data_dir(bio) != rq_data_dir(rq))
 735                 return false;
 736
 737         /* must be same device and not a special request */
 738         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 739                 return false;
 740
 741         /* only merge integrity protected bio into ditto rq */
 742         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 743                 return false;
 744
 745         /* must be using the same buffer */
 746         if (rq->cmd_flags & REQ_WRITE_SAME &&
 747             !blk_write_same_mergeable(rq->bio, bio))
 748                 return false;
 749
 750         return true;
 751 }
 752
 753 int blk_try_merge(struct request *rq, struct bio *bio)
 754 {
 755         if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 756                 return ELEVATOR_BACK_MERGE;
 757         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 758                 return ELEVATOR_FRONT_MERGE;
 759         return ELEVATOR_NO_MERGE;
 760 }