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