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