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