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