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 <trace/events/block.h>
  11
  12 #include "blk.h"
  13
  14 static struct bio *blk_bio_discard_split(struct request_queue *q,
  15                                          struct bio *bio,
  16                                          struct bio_set *bs,
  17                                          unsigned *nsegs)
  18 {
  19         unsigned int max_discard_sectors, granularity;
  20         int alignment;
  21         sector_t tmp;
  22         unsigned split_sectors;
  23
  24         *nsegs = 1;
  25
  26         /* Zero-sector (unknown) and one-sector granularities are the same.  */
  27         granularity = max(q->limits.discard_granularity >> 9, 1U);
  28
  29         max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
  30         max_discard_sectors -= max_discard_sectors % granularity;
  31
  32         if (unlikely(!max_discard_sectors)) {
  33                 /* XXX: warn */
  34                 return NULL;
  35         }
  36
  37         if (bio_sectors(bio) <= max_discard_sectors)
  38                 return NULL;
  39
  40         split_sectors = max_discard_sectors;
  41
  42         /*
  43          * If the next starting sector would be misaligned, stop the discard at
  44          * the previous aligned sector.
  45          */
  46         alignment = (q->limits.discard_alignment >> 9) % granularity;
  47
  48         tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
  49         tmp = sector_div(tmp, granularity);
  50
  51         if (split_sectors > tmp)
  52                 split_sectors -= tmp;
  53
  54         return bio_split(bio, split_sectors, GFP_NOIO, bs);
  55 }
  56
  57 static struct bio *blk_bio_write_same_split(struct request_queue *q,
  58                                             struct bio *bio,
  59                                             struct bio_set *bs,
  60                                             unsigned *nsegs)
  61 {
  62         *nsegs = 1;
  63
  64         if (!q->limits.max_write_same_sectors)
  65                 return NULL;
  66
  67         if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
  68                 return NULL;
  69
  70         return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
  71 }
  72
  73 static inline unsigned get_max_io_size(struct request_queue *q,
  74                                        struct bio *bio)
  75 {
  76         unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
  77         unsigned mask = queue_logical_block_size(q) - 1;
  78
  79         /* aligned to logical block size */
  80         sectors &= ~(mask >> 9);
  81
  82         return sectors;
  83 }
  84
  85 static struct bio *blk_bio_segment_split(struct request_queue *q,
  86                                          struct bio *bio,
  87                                          struct bio_set *bs,
  88                                          unsigned *segs)
  89 {
  90         struct bio_vec bv, bvprv, *bvprvp = NULL;
  91         struct bvec_iter iter;
  92         unsigned seg_size = 0, nsegs = 0, sectors = 0;
  93         unsigned front_seg_size = bio->bi_seg_front_size;
  94         bool do_split = true;
  95         struct bio *new = NULL;
  96         const unsigned max_sectors = get_max_io_size(q, bio);
  97         unsigned bvecs = 0;
  98
  99         bio_for_each_segment(bv, bio, iter) {
 100                 /*
 101                  * With arbitrary bio size, the incoming bio may be very
 102                  * big. We have to split the bio into small bios so that
 103                  * each holds at most BIO_MAX_PAGES bvecs because
 104                  * bio_clone() can fail to allocate big bvecs.
 105                  *
 106                  * It should have been better to apply the limit per
 107                  * request queue in which bio_clone() is involved,
 108                  * instead of globally. The biggest blocker is the
 109                  * bio_clone() in bio bounce.
 110                  *
 111                  * If bio is splitted by this reason, we should have
 112                  * allowed to continue bios merging, but don't do
 113                  * that now for making the change simple.
 114                  *
 115                  * TODO: deal with bio bounce's bio_clone() gracefully
 116                  * and convert the global limit into per-queue limit.
 117                  */
 118                 if (bvecs++ >= BIO_MAX_PAGES)
 119                         goto split;
 120
 121                 /*
 122                  * If the queue doesn't support SG gaps and adding this
 123                  * offset would create a gap, disallow it.
 124                  */
 125                 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 126                         goto split;
 127
 128                 if (sectors + (bv.bv_len >> 9) > max_sectors) {
 129                         /*
 130                          * Consider this a new segment if we're splitting in
 131                          * the middle of this vector.
 132                          */
 133                         if (nsegs < queue_max_segments(q) &&
 134                             sectors < max_sectors) {
 135                                 nsegs++;
 136                                 sectors = max_sectors;
 137                         }
 138                         if (sectors)
 139                                 goto split;
 140                         /* Make this single bvec as the 1st segment */
 141                 }
 142
 143                 if (bvprvp && blk_queue_cluster(q)) {
 144                         if (seg_size + bv.bv_len > queue_max_segment_size(q))
 145                                 goto new_segment;
 146                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
 147                                 goto new_segment;
 148                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
 149                                 goto new_segment;
 150
 151                         seg_size += bv.bv_len;
 152                         bvprv = bv;
 153                         bvprvp = &bvprv;
 154                         sectors += bv.bv_len >> 9;
 155
 156                         if (nsegs == 1 && seg_size > front_seg_size)
 157                                 front_seg_size = seg_size;
 158                         continue;
 159                 }
 160 new_segment:
 161                 if (nsegs == queue_max_segments(q))
 162                         goto split;
 163
 164                 nsegs++;
 165                 bvprv = bv;
 166                 bvprvp = &bvprv;
 167                 seg_size = bv.bv_len;
 168                 sectors += bv.bv_len >> 9;
 169
 170                 if (nsegs == 1 && seg_size > front_seg_size)
 171                         front_seg_size = seg_size;
 172         }
 173
 174         do_split = false;
 175 split:
 176         *segs = nsegs;
 177
 178         if (do_split) {
 179                 new = bio_split(bio, sectors, GFP_NOIO, bs);
 180                 if (new)
 181                         bio = new;
 182         }
 183
 184         bio->bi_seg_front_size = front_seg_size;
 185         if (seg_size > bio->bi_seg_back_size)
 186                 bio->bi_seg_back_size = seg_size;
 187
 188         return do_split ? new : NULL;
 189 }
 190
 191 void blk_queue_split(struct request_queue *q, struct bio **bio,
 192                      struct bio_set *bs)
 193 {
 194         struct bio *split, *res;
 195         unsigned nsegs;
 196
 197         switch (bio_op(*bio)) {
 198         case REQ_OP_DISCARD:
 199         case REQ_OP_SECURE_ERASE:
 200                 split = blk_bio_discard_split(q, *bio, bs, &nsegs);
 201                 break;
 202         case REQ_OP_WRITE_SAME:
 203                 split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
 204                 break;
 205         default:
 206                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
 207                 break;
 208         }
 209
 210         /* physical segments can be figured out during splitting */
 211         res = split ? split : *bio;
 212         res->bi_phys_segments = nsegs;
 213         bio_set_flag(res, BIO_SEG_VALID);
 214
 215         if (split) {
 216                 /* there isn't chance to merge the splitted bio */
 217                 split->bi_opf |= REQ_NOMERGE;
 218
 219                 bio_chain(split, *bio);
 220                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
 221                 generic_make_request(*bio);
 222                 *bio = split;
 223         }
 224 }
 225 EXPORT_SYMBOL(blk_queue_split);
 226
 227 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 228                                              struct bio *bio,
 229                                              bool no_sg_merge)
 230 {
 231         struct bio_vec bv, bvprv = { NULL };
 232         int cluster, prev = 0;
 233         unsigned int seg_size, nr_phys_segs;
 234         struct bio *fbio, *bbio;
 235         struct bvec_iter iter;
 236
 237         if (!bio)
 238                 return 0;
 239
 240         /*
 241          * This should probably be returning 0, but blk_add_request_payload()
 242          * (Christoph!!!!)
 243          */
 244         if (bio_op(bio) == REQ_OP_DISCARD || bio_op(bio) == REQ_OP_SECURE_ERASE)
 245                 return 1;
 246
 247         if (bio_op(bio) == REQ_OP_WRITE_SAME)
 248                 return 1;
 249
 250         fbio = bio;
 251         cluster = blk_queue_cluster(q);
 252         seg_size = 0;
 253         nr_phys_segs = 0;
 254         for_each_bio(bio) {
 255                 bio_for_each_segment(bv, bio, iter) {
 256                         /*
 257                          * If SG merging is disabled, each bio vector is
 258                          * a segment
 259                          */
 260                         if (no_sg_merge)
 261                                 goto new_segment;
 262
 263                         if (prev && cluster) {
 264                                 if (seg_size + bv.bv_len
 265                                     > queue_max_segment_size(q))
 266                                         goto new_segment;
 267                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
 268                                         goto new_segment;
 269                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
 270                                         goto new_segment;
 271
 272                                 seg_size += bv.bv_len;
 273                                 bvprv = bv;
 274                                 continue;
 275                         }
 276 new_segment:
 277                         if (nr_phys_segs == 1 && seg_size >
 278                             fbio->bi_seg_front_size)
 279                                 fbio->bi_seg_front_size = seg_size;
 280
 281                         nr_phys_segs++;
 282                         bvprv = bv;
 283                         prev = 1;
 284                         seg_size = bv.bv_len;
 285                 }
 286                 bbio = bio;
 287         }
 288
 289         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
 290                 fbio->bi_seg_front_size = seg_size;
 291         if (seg_size > bbio->bi_seg_back_size)
 292                 bbio->bi_seg_back_size = seg_size;
 293
 294         return nr_phys_segs;
 295 }
 296
 297 void blk_recalc_rq_segments(struct request *rq)
 298 {
 299         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
 300                         &rq->q->queue_flags);
 301
 302         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
 303                         no_sg_merge);
 304 }
 305
 306 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 307 {
 308         unsigned short seg_cnt = bio_segments(bio);
 309
 310         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 311                         (seg_cnt < queue_max_segments(q)))
 312                 bio->bi_phys_segments = seg_cnt;
 313         else {
 314                 struct bio *nxt = bio->bi_next;
 315
 316                 bio->bi_next = NULL;
 317                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 318                 bio->bi_next = nxt;
 319         }
 320
 321         bio_set_flag(bio, BIO_SEG_VALID);
 322 }
 323 EXPORT_SYMBOL(blk_recount_segments);
 324
 325 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 326                                    struct bio *nxt)
 327 {
 328         struct bio_vec end_bv = { NULL }, nxt_bv;
 329
 330         if (!blk_queue_cluster(q))
 331                 return 0;
 332
 333         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 334             queue_max_segment_size(q))
 335                 return 0;
 336
 337         if (!bio_has_data(bio))
 338                 return 1;
 339
 340         bio_get_last_bvec(bio, &end_bv);
 341         bio_get_first_bvec(nxt, &nxt_bv);
 342
 343         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 344                 return 0;
 345
 346         /*
 347          * bio and nxt are contiguous in memory; check if the queue allows
 348          * these two to be merged into one
 349          */
 350         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 351                 return 1;
 352
 353         return 0;
 354 }
 355
 356 static inline void
 357 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 358                      struct scatterlist *sglist, struct bio_vec *bvprv,
 359                      struct scatterlist **sg, int *nsegs, int *cluster)
 360 {
 361
 362         int nbytes = bvec->bv_len;
 363
 364         if (*sg && *cluster) {
 365                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 366                         goto new_segment;
 367
 368                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 369                         goto new_segment;
 370                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 371                         goto new_segment;
 372
 373                 (*sg)->length += nbytes;
 374         } else {
 375 new_segment:
 376                 if (!*sg)
 377                         *sg = sglist;
 378                 else {
 379                         /*
 380                          * If the driver previously mapped a shorter
 381                          * list, we could see a termination bit
 382                          * prematurely unless it fully inits the sg
 383                          * table on each mapping. We KNOW that there
 384                          * must be more entries here or the driver
 385                          * would be buggy, so force clear the
 386                          * termination bit to avoid doing a full
 387                          * sg_init_table() in drivers for each command.
 388                          */
 389                         sg_unmark_end(*sg);
 390                         *sg = sg_next(*sg);
 391                 }
 392
 393                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 394                 (*nsegs)++;
 395         }
 396         *bvprv = *bvec;
 397 }
 398
 399 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 400                              struct scatterlist *sglist,
 401                              struct scatterlist **sg)
 402 {
 403         struct bio_vec bvec, bvprv = { NULL };
 404         struct bvec_iter iter;
 405         int nsegs, cluster;
 406
 407         nsegs = 0;
 408         cluster = blk_queue_cluster(q);
 409
 410         switch (bio_op(bio)) {
 411         case REQ_OP_DISCARD:
 412         case REQ_OP_SECURE_ERASE:
 413                 /*
 414                  * This is a hack - drivers should be neither modifying the
 415                  * biovec, nor relying on bi_vcnt - but because of
 416                  * blk_add_request_payload(), a discard bio may or may not have
 417                  * a payload we need to set up here (thank you Christoph) and
 418                  * bi_vcnt is really the only way of telling if we need to.
 419                  */
 420                 if (!bio->bi_vcnt)
 421                         return 0;
 422                 /* Fall through */
 423         case REQ_OP_WRITE_SAME:
 424                 *sg = sglist;
 425                 bvec = bio_iovec(bio);
 426                 sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
 427                 return 1;
 428         default:
 429                 break;
 430         }
 431
 432         for_each_bio(bio)
 433                 bio_for_each_segment(bvec, bio, iter)
 434                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 435                                              &nsegs, &cluster);
 436
 437         return nsegs;
 438 }
 439
 440 /*
 441  * map a request to scatterlist, return number of sg entries setup. Caller
 442  * must make sure sg can hold rq->nr_phys_segments entries
 443  */
 444 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 445                   struct scatterlist *sglist)
 446 {
 447         struct scatterlist *sg = NULL;
 448         int nsegs = 0;
 449
 450         if (rq->bio)
 451                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 452
 453         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 454             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 455                 unsigned int pad_len =
 456                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 457
 458                 sg->length += pad_len;
 459                 rq->extra_len += pad_len;
 460         }
 461
 462         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 463                 if (op_is_write(req_op(rq)))
 464                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 465
 466                 sg_unmark_end(sg);
 467                 sg = sg_next(sg);
 468                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 469                             q->dma_drain_size,
 470                             ((unsigned long)q->dma_drain_buffer) &
 471                             (PAGE_SIZE - 1));
 472                 nsegs++;
 473                 rq->extra_len += q->dma_drain_size;
 474         }
 475
 476         if (sg)
 477                 sg_mark_end(sg);
 478
 479         /*
 480          * Something must have been wrong if the figured number of
 481          * segment is bigger than number of req's physical segments
 482          */
 483         WARN_ON(nsegs > rq->nr_phys_segments);
 484
 485         return nsegs;
 486 }
 487 EXPORT_SYMBOL(blk_rq_map_sg);
 488
 489 static inline int ll_new_hw_segment(struct request_queue *q,
 490                                     struct request *req,
 491                                     struct bio *bio)
 492 {
 493         int nr_phys_segs = bio_phys_segments(q, bio);
 494
 495         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 496                 goto no_merge;
 497
 498         if (blk_integrity_merge_bio(q, req, bio) == false)
 499                 goto no_merge;
 500
 501         /*
 502          * This will form the start of a new hw segment.  Bump both
 503          * counters.
 504          */
 505         req->nr_phys_segments += nr_phys_segs;
 506         return 1;
 507
 508 no_merge:
 509         req->cmd_flags |= REQ_NOMERGE;
 510         if (req == q->last_merge)
 511                 q->last_merge = NULL;
 512         return 0;
 513 }
 514
 515 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 516                      struct bio *bio)
 517 {
 518         if (req_gap_back_merge(req, bio))
 519                 return 0;
 520         if (blk_integrity_rq(req) &&
 521             integrity_req_gap_back_merge(req, bio))
 522                 return 0;
 523         if (blk_rq_sectors(req) + bio_sectors(bio) >
 524             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
 525                 req->cmd_flags |= REQ_NOMERGE;
 526                 if (req == q->last_merge)
 527                         q->last_merge = NULL;
 528                 return 0;
 529         }
 530         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 531                 blk_recount_segments(q, req->biotail);
 532         if (!bio_flagged(bio, BIO_SEG_VALID))
 533                 blk_recount_segments(q, bio);
 534
 535         return ll_new_hw_segment(q, req, bio);
 536 }
 537
 538 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 539                       struct bio *bio)
 540 {
 541
 542         if (req_gap_front_merge(req, bio))
 543                 return 0;
 544         if (blk_integrity_rq(req) &&
 545             integrity_req_gap_front_merge(req, bio))
 546                 return 0;
 547         if (blk_rq_sectors(req) + bio_sectors(bio) >
 548             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 549                 req->cmd_flags |= REQ_NOMERGE;
 550                 if (req == q->last_merge)
 551                         q->last_merge = NULL;
 552                 return 0;
 553         }
 554         if (!bio_flagged(bio, BIO_SEG_VALID))
 555                 blk_recount_segments(q, bio);
 556         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 557                 blk_recount_segments(q, req->bio);
 558
 559         return ll_new_hw_segment(q, req, bio);
 560 }
 561
 562 /*
 563  * blk-mq uses req->special to carry normal driver per-request payload, it
 564  * does not indicate a prepared command that we cannot merge with.
 565  */
 566 static bool req_no_special_merge(struct request *req)
 567 {
 568         struct request_queue *q = req->q;
 569
 570         return !q->mq_ops && req->special;
 571 }
 572
 573 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 574                                 struct request *next)
 575 {
 576         int total_phys_segments;
 577         unsigned int seg_size =
 578                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 579
 580         /*
 581          * First check if the either of the requests are re-queued
 582          * requests.  Can't merge them if they are.
 583          */
 584         if (req_no_special_merge(req) || req_no_special_merge(next))
 585                 return 0;
 586
 587         if (req_gap_back_merge(req, next->bio))
 588                 return 0;
 589
 590         /*
 591          * Will it become too large?
 592          */
 593         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 594             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 595                 return 0;
 596
 597         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 598         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 599                 if (req->nr_phys_segments == 1)
 600                         req->bio->bi_seg_front_size = seg_size;
 601                 if (next->nr_phys_segments == 1)
 602                         next->biotail->bi_seg_back_size = seg_size;
 603                 total_phys_segments--;
 604         }
 605
 606         if (total_phys_segments > queue_max_segments(q))
 607                 return 0;
 608
 609         if (blk_integrity_merge_rq(q, req, next) == false)
 610                 return 0;
 611
 612         /* Merge is OK... */
 613         req->nr_phys_segments = total_phys_segments;
 614         return 1;
 615 }
 616
 617 /**
 618  * blk_rq_set_mixed_merge - mark a request as mixed merge
 619  * @rq: request to mark as mixed merge
 620  *
 621  * Description:
 622  *     @rq is about to be mixed merged.  Make sure the attributes
 623  *     which can be mixed are set in each bio and mark @rq as mixed
 624  *     merged.
 625  */
 626 void blk_rq_set_mixed_merge(struct request *rq)
 627 {
 628         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 629         struct bio *bio;
 630
 631         if (rq->cmd_flags & REQ_MIXED_MERGE)
 632                 return;
 633
 634         /*
 635          * @rq will no longer represent mixable attributes for all the
 636          * contained bios.  It will just track those of the first one.
 637          * Distributes the attributs to each bio.
 638          */
 639         for (bio = rq->bio; bio; bio = bio->bi_next) {
 640                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
 641                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 642                 bio->bi_opf |= ff;
 643         }
 644         rq->cmd_flags |= REQ_MIXED_MERGE;
 645 }
 646
 647 static void blk_account_io_merge(struct request *req)
 648 {
 649         if (blk_do_io_stat(req)) {
 650                 struct hd_struct *part;
 651                 int cpu;
 652
 653                 cpu = part_stat_lock();
 654                 part = req->part;
 655
 656                 part_round_stats(cpu, part);
 657                 part_dec_in_flight(part, rq_data_dir(req));
 658
 659                 hd_struct_put(part);
 660                 part_stat_unlock();
 661         }
 662 }
 663
 664 /*
 665  * Has to be called with the request spinlock acquired
 666  */
 667 static int attempt_merge(struct request_queue *q, struct request *req,
 668                           struct request *next)
 669 {
 670         if (!rq_mergeable(req) || !rq_mergeable(next))
 671                 return 0;
 672
 673         if (req_op(req) != req_op(next))
 674                 return 0;
 675
 676         /*
 677          * not contiguous
 678          */
 679         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 680                 return 0;
 681
 682         if (rq_data_dir(req) != rq_data_dir(next)
 683             || req->rq_disk != next->rq_disk
 684             || req_no_special_merge(next))
 685                 return 0;
 686
 687         if (req_op(req) == REQ_OP_WRITE_SAME &&
 688             !blk_write_same_mergeable(req->bio, next->bio))
 689                 return 0;
 690
 691         /*
 692          * If we are allowed to merge, then append bio list
 693          * from next to rq and release next. merge_requests_fn
 694          * will have updated segment counts, update sector
 695          * counts here.
 696          */
 697         if (!ll_merge_requests_fn(q, req, next))
 698                 return 0;
 699
 700         /*
 701          * If failfast settings disagree or any of the two is already
 702          * a mixed merge, mark both as mixed before proceeding.  This
 703          * makes sure that all involved bios have mixable attributes
 704          * set properly.
 705          */
 706         if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
 707             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 708             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 709                 blk_rq_set_mixed_merge(req);
 710                 blk_rq_set_mixed_merge(next);
 711         }
 712
 713         /*
 714          * At this point we have either done a back merge
 715          * or front merge. We need the smaller start_time of
 716          * the merged requests to be the current request
 717          * for accounting purposes.
 718          */
 719         if (time_after(req->start_time, next->start_time))
 720                 req->start_time = next->start_time;
 721
 722         req->biotail->bi_next = next->bio;
 723         req->biotail = next->biotail;
 724
 725         req->__data_len += blk_rq_bytes(next);
 726
 727         elv_merge_requests(q, req, next);
 728
 729         /*
 730          * 'next' is going away, so update stats accordingly
 731          */
 732         blk_account_io_merge(next);
 733
 734         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 735         if (blk_rq_cpu_valid(next))
 736                 req->cpu = next->cpu;
 737
 738         /* owner-ship of bio passed from next to req */
 739         next->bio = NULL;
 740         __blk_put_request(q, next);
 741         return 1;
 742 }
 743
 744 int attempt_back_merge(struct request_queue *q, struct request *rq)
 745 {
 746         struct request *next = elv_latter_request(q, rq);
 747
 748         if (next)
 749                 return attempt_merge(q, rq, next);
 750
 751         return 0;
 752 }
 753
 754 int attempt_front_merge(struct request_queue *q, struct request *rq)
 755 {
 756         struct request *prev = elv_former_request(q, rq);
 757
 758         if (prev)
 759                 return attempt_merge(q, prev, rq);
 760
 761         return 0;
 762 }
 763
 764 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 765                           struct request *next)
 766 {
 767         struct elevator_queue *e = q->elevator;
 768
 769         if (e->type->ops.elevator_allow_rq_merge_fn)
 770                 if (!e->type->ops.elevator_allow_rq_merge_fn(q, rq, next))
 771                         return 0;
 772
 773         return attempt_merge(q, rq, next);
 774 }
 775
 776 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 777 {
 778         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 779                 return false;
 780
 781         if (req_op(rq) != bio_op(bio))
 782                 return false;
 783
 784         /* different data direction or already started, don't merge */
 785         if (bio_data_dir(bio) != rq_data_dir(rq))
 786                 return false;
 787
 788         /* must be same device and not a special request */
 789         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 790                 return false;
 791
 792         /* only merge integrity protected bio into ditto rq */
 793         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 794                 return false;
 795
 796         /* must be using the same buffer */
 797         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 798             !blk_write_same_mergeable(rq->bio, bio))
 799                 return false;
 800
 801         return true;
 802 }
 803
 804 int blk_try_merge(struct request *rq, struct bio *bio)
 805 {
 806         if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 807                 return ELEVATOR_BACK_MERGE;
 808         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 809                 return ELEVATOR_FRONT_MERGE;
 810         return ELEVATOR_NO_MERGE;
 811 }