block/blk-merge.c

   1 /*
   2  * Functions related to segment and merge handling
   3  */
   4 #include <linux/kernel.h>
   5 #include <linux/module.h>
   6 #include <linux/bio.h>
   7 #include <linux/blkdev.h>
   8 #include <linux/scatterlist.h>
   9
  10 #include <trace/events/block.h>
  11
  12 #include "blk.h"
  13
  14 static struct bio *blk_bio_discard_split(struct request_queue *q,
  15                                          struct bio *bio,
  16                                          struct bio_set *bs,
  17                                          unsigned *nsegs)
  18 {
  19         unsigned int max_discard_sectors, granularity;
  20         int alignment;
  21         sector_t tmp;
  22         unsigned split_sectors;
  23
  24         *nsegs = 1;
  25
  26         /* Zero-sector (unknown) and one-sector granularities are the same.  */
  27         granularity = max(q->limits.discard_granularity >> 9, 1U);
  28
  29         max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
  30         max_discard_sectors -= max_discard_sectors % granularity;
  31
  32         if (unlikely(!max_discard_sectors)) {
  33                 /* XXX: warn */
  34                 return NULL;
  35         }
  36
  37         if (bio_sectors(bio) <= max_discard_sectors)
  38                 return NULL;
  39
  40         split_sectors = max_discard_sectors;
  41
  42         /*
  43          * If the next starting sector would be misaligned, stop the discard at
  44          * the previous aligned sector.
  45          */
  46         alignment = (q->limits.discard_alignment >> 9) % granularity;
  47
  48         tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
  49         tmp = sector_div(tmp, granularity);
  50
  51         if (split_sectors > tmp)
  52                 split_sectors -= tmp;
  53
  54         return bio_split(bio, split_sectors, GFP_NOIO, bs);
  55 }
  56
  57 static struct bio *blk_bio_write_same_split(struct request_queue *q,
  58                                             struct bio *bio,
  59                                             struct bio_set *bs,
  60                                             unsigned *nsegs)
  61 {
  62         *nsegs = 1;
  63
  64         if (!q->limits.max_write_same_sectors)
  65                 return NULL;
  66
  67         if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
  68                 return NULL;
  69
  70         return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
  71 }
  72
  73 static inline unsigned get_max_io_size(struct request_queue *q,
  74                                        struct bio *bio)
  75 {
  76         unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
  77         unsigned mask = queue_logical_block_size(q) - 1;
  78
  79         /* aligned to logical block size */
  80         sectors &= ~(mask >> 9);
  81
  82         return sectors;
  83 }
  84
  85 static struct bio *blk_bio_segment_split(struct request_queue *q,
  86                                          struct bio *bio,
  87                                          struct bio_set *bs,
  88                                          unsigned *segs)
  89 {
  90         struct bio_vec bv, bvprv, *bvprvp = NULL;
  91         struct bvec_iter iter;
  92         unsigned seg_size = 0, nsegs = 0, sectors = 0;
  93         unsigned front_seg_size = bio->bi_seg_front_size;
  94         bool do_split = true;
  95         struct bio *new = NULL;
  96         const unsigned max_sectors = get_max_io_size(q, bio);
  97         unsigned bvecs = 0;
  98
  99         bio_for_each_segment(bv, bio, iter) {
 100                 /*
 101                  * With arbitrary bio size, the incoming bio may be very
 102                  * big. We have to split the bio into small bios so that
 103                  * each holds at most BIO_MAX_PAGES bvecs because
 104                  * bio_clone() can fail to allocate big bvecs.
 105                  *
 106                  * It should have been better to apply the limit per
 107                  * request queue in which bio_clone() is involved,
 108                  * instead of globally. The biggest blocker is the
 109                  * bio_clone() in bio bounce.
 110                  *
 111                  * If bio is splitted by this reason, we should have
 112                  * allowed to continue bios merging, but don't do
 113                  * that now for making the change simple.
 114                  *
 115                  * TODO: deal with bio bounce's bio_clone() gracefully
 116                  * and convert the global limit into per-queue limit.
 117                  */
 118                 if (bvecs++ >= BIO_MAX_PAGES)
 119                         goto split;
 120
 121                 /*
 122                  * If the queue doesn't support SG gaps and adding this
 123                  * offset would create a gap, disallow it.
 124                  */
 125                 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 126                         goto split;
 127
 128                 if (sectors + (bv.bv_len >> 9) > max_sectors) {
 129                         /*
 130                          * Consider this a new segment if we're splitting in
 131                          * the middle of this vector.
 132                          */
 133                         if (nsegs < queue_max_segments(q) &&
 134                             sectors < max_sectors) {
 135                                 nsegs++;
 136                                 sectors = max_sectors;
 137                         }
 138                         if (sectors)
 139                                 goto split;
 140                         /* Make this single bvec as the 1st segment */
 141                 }
 142
 143                 if (bvprvp && blk_queue_cluster(q)) {
 144                         if (seg_size + bv.bv_len > queue_max_segment_size(q))
 145                                 goto new_segment;
 146                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
 147                                 goto new_segment;
 148                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
 149                                 goto new_segment;
 150
 151                         seg_size += bv.bv_len;
 152                         bvprv = bv;
 153                         bvprvp = &bvprv;
 154                         sectors += bv.bv_len >> 9;
 155
 156                         if (nsegs == 1 && seg_size > front_seg_size)
 157                                 front_seg_size = seg_size;
 158                         continue;
 159                 }
 160 new_segment:
 161                 if (nsegs == queue_max_segments(q))
 162                         goto split;
 163
 164                 nsegs++;
 165                 bvprv = bv;
 166                 bvprvp = &bvprv;
 167                 seg_size = bv.bv_len;
 168                 sectors += bv.bv_len >> 9;
 169
 170                 if (nsegs == 1 && seg_size > front_seg_size)
 171                         front_seg_size = seg_size;
 172         }
 173
 174         do_split = false;
 175 split:
 176         *segs = nsegs;
 177
 178         if (do_split) {
 179                 new = bio_split(bio, sectors, GFP_NOIO, bs);
 180                 if (new)
 181                         bio = new;
 182         }
 183
 184         bio->bi_seg_front_size = front_seg_size;
 185         if (seg_size > bio->bi_seg_back_size)
 186                 bio->bi_seg_back_size = seg_size;
 187
 188         return do_split ? new : NULL;
 189 }
 190
 191 void blk_queue_split(struct request_queue *q, struct bio **bio,
 192                      struct bio_set *bs)
 193 {
 194         struct bio *split, *res;
 195         unsigned nsegs;
 196
 197         switch (bio_op(*bio)) {
 198         case REQ_OP_DISCARD:
 199         case REQ_OP_SECURE_ERASE:
 200                 split = blk_bio_discard_split(q, *bio, bs, &nsegs);
 201                 break;
 202         case REQ_OP_WRITE_SAME:
 203                 split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
 204                 break;
 205         default:
 206                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
 207                 break;
 208         }
 209
 210         /* physical segments can be figured out during splitting */
 211         res = split ? split : *bio;
 212         res->bi_phys_segments = nsegs;
 213         bio_set_flag(res, BIO_SEG_VALID);
 214
 215         if (split) {
 216                 /* there isn't chance to merge the splitted bio */
 217                 split->bi_opf |= REQ_NOMERGE;
 218
 219                 bio_chain(split, *bio);
 220                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
 221                 generic_make_request(*bio);
 222                 *bio = split;
 223         }
 224 }
 225 EXPORT_SYMBOL(blk_queue_split);
 226
 227 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 228                                              struct bio *bio,
 229                                              bool no_sg_merge)
 230 {
 231         struct bio_vec bv, bvprv = { NULL };
 232         int cluster, prev = 0;
 233         unsigned int seg_size, nr_phys_segs;
 234         struct bio *fbio, *bbio;
 235         struct bvec_iter iter;
 236
 237         if (!bio)
 238                 return 0;
 239
 240         /*
 241          * This should probably be returning 0, but blk_add_request_payload()
 242          * (Christoph!!!!)
 243          */
 244         if (bio_op(bio) == REQ_OP_DISCARD || bio_op(bio) == REQ_OP_SECURE_ERASE)
 245                 return 1;
 246
 247         if (bio_op(bio) == REQ_OP_WRITE_SAME)
 248                 return 1;
 249
 250         fbio = bio;
 251         cluster = blk_queue_cluster(q);
 252         seg_size = 0;
 253         nr_phys_segs = 0;
 254         for_each_bio(bio) {
 255                 bio_for_each_segment(bv, bio, iter) {
 256                         /*
 257                          * If SG merging is disabled, each bio vector is
 258                          * a segment
 259                          */
 260                         if (no_sg_merge)
 261                                 goto new_segment;
 262
 263                         if (prev && cluster) {
 264                                 if (seg_size + bv.bv_len
 265                                     > queue_max_segment_size(q))
 266                                         goto new_segment;
 267                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
 268                                         goto new_segment;
 269                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
 270                                         goto new_segment;
 271
 272                                 seg_size += bv.bv_len;
 273                                 bvprv = bv;
 274                                 continue;
 275                         }
 276 new_segment:
 277                         if (nr_phys_segs == 1 && seg_size >
 278                             fbio->bi_seg_front_size)
 279                                 fbio->bi_seg_front_size = seg_size;
 280
 281                         nr_phys_segs++;
 282                         bvprv = bv;
 283                         prev = 1;
 284                         seg_size = bv.bv_len;
 285                 }
 286                 bbio = bio;
 287         }
 288
 289         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
 290                 fbio->bi_seg_front_size = seg_size;
 291         if (seg_size > bbio->bi_seg_back_size)
 292                 bbio->bi_seg_back_size = seg_size;
 293
 294         return nr_phys_segs;
 295 }
 296
 297 void blk_recalc_rq_segments(struct request *rq)
 298 {
 299         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
 300                         &rq->q->queue_flags);
 301
 302         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
 303                         no_sg_merge);
 304 }
 305
 306 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 307 {
 308         unsigned short seg_cnt;
 309
 310         /* estimate segment number by bi_vcnt for non-cloned bio */
 311         if (bio_flagged(bio, BIO_CLONED))
 312                 seg_cnt = bio_segments(bio);
 313         else
 314                 seg_cnt = bio->bi_vcnt;
 315
 316         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 317                         (seg_cnt < queue_max_segments(q)))
 318                 bio->bi_phys_segments = seg_cnt;
 319         else {
 320                 struct bio *nxt = bio->bi_next;
 321
 322                 bio->bi_next = NULL;
 323                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 324                 bio->bi_next = nxt;
 325         }
 326
 327         bio_set_flag(bio, BIO_SEG_VALID);
 328 }
 329 EXPORT_SYMBOL(blk_recount_segments);
 330
 331 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 332                                    struct bio *nxt)
 333 {
 334         struct bio_vec end_bv = { NULL }, nxt_bv;
 335
 336         if (!blk_queue_cluster(q))
 337                 return 0;
 338
 339         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 340             queue_max_segment_size(q))
 341                 return 0;
 342
 343         if (!bio_has_data(bio))
 344                 return 1;
 345
 346         bio_get_last_bvec(bio, &end_bv);
 347         bio_get_first_bvec(nxt, &nxt_bv);
 348
 349         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 350                 return 0;
 351
 352         /*
 353          * bio and nxt are contiguous in memory; check if the queue allows
 354          * these two to be merged into one
 355          */
 356         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 357                 return 1;
 358
 359         return 0;
 360 }
 361
 362 static inline void
 363 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 364                      struct scatterlist *sglist, struct bio_vec *bvprv,
 365                      struct scatterlist **sg, int *nsegs, int *cluster)
 366 {
 367
 368         int nbytes = bvec->bv_len;
 369
 370         if (*sg && *cluster) {
 371                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 372                         goto new_segment;
 373
 374                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 375                         goto new_segment;
 376                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 377                         goto new_segment;
 378
 379                 (*sg)->length += nbytes;
 380         } else {
 381 new_segment:
 382                 if (!*sg)
 383                         *sg = sglist;
 384                 else {
 385                         /*
 386                          * If the driver previously mapped a shorter
 387                          * list, we could see a termination bit
 388                          * prematurely unless it fully inits the sg
 389                          * table on each mapping. We KNOW that there
 390                          * must be more entries here or the driver
 391                          * would be buggy, so force clear the
 392                          * termination bit to avoid doing a full
 393                          * sg_init_table() in drivers for each command.
 394                          */
 395                         sg_unmark_end(*sg);
 396                         *sg = sg_next(*sg);
 397                 }
 398
 399                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 400                 (*nsegs)++;
 401         }
 402         *bvprv = *bvec;
 403 }
 404
 405 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 406                              struct scatterlist *sglist,
 407                              struct scatterlist **sg)
 408 {
 409         struct bio_vec bvec, bvprv = { NULL };
 410         struct bvec_iter iter;
 411         int nsegs, cluster;
 412
 413         nsegs = 0;
 414         cluster = blk_queue_cluster(q);
 415
 416         switch (bio_op(bio)) {
 417         case REQ_OP_DISCARD:
 418         case REQ_OP_SECURE_ERASE:
 419                 /*
 420                  * This is a hack - drivers should be neither modifying the
 421                  * biovec, nor relying on bi_vcnt - but because of
 422                  * blk_add_request_payload(), a discard bio may or may not have
 423                  * a payload we need to set up here (thank you Christoph) and
 424                  * bi_vcnt is really the only way of telling if we need to.
 425                  */
 426                 if (!bio->bi_vcnt)
 427                         return 0;
 428                 /* Fall through */
 429         case REQ_OP_WRITE_SAME:
 430                 *sg = sglist;
 431                 bvec = bio_iovec(bio);
 432                 sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
 433                 return 1;
 434         default:
 435                 break;
 436         }
 437
 438         for_each_bio(bio)
 439                 bio_for_each_segment(bvec, bio, iter)
 440                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 441                                              &nsegs, &cluster);
 442
 443         return nsegs;
 444 }
 445
 446 /*
 447  * map a request to scatterlist, return number of sg entries setup. Caller
 448  * must make sure sg can hold rq->nr_phys_segments entries
 449  */
 450 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 451                   struct scatterlist *sglist)
 452 {
 453         struct scatterlist *sg = NULL;
 454         int nsegs = 0;
 455
 456         if (rq->bio)
 457                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 458
 459         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 460             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 461                 unsigned int pad_len =
 462                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 463
 464                 sg->length += pad_len;
 465                 rq->extra_len += pad_len;
 466         }
 467
 468         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 469                 if (op_is_write(req_op(rq)))
 470                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 471
 472                 sg_unmark_end(sg);
 473                 sg = sg_next(sg);
 474                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 475                             q->dma_drain_size,
 476                             ((unsigned long)q->dma_drain_buffer) &
 477                             (PAGE_SIZE - 1));
 478                 nsegs++;
 479                 rq->extra_len += q->dma_drain_size;
 480         }
 481
 482         if (sg)
 483                 sg_mark_end(sg);
 484
 485         /*
 486          * Something must have been wrong if the figured number of
 487          * segment is bigger than number of req's physical segments
 488          */
 489         WARN_ON(nsegs > rq->nr_phys_segments);
 490
 491         return nsegs;
 492 }
 493 EXPORT_SYMBOL(blk_rq_map_sg);
 494
 495 static inline int ll_new_hw_segment(struct request_queue *q,
 496                                     struct request *req,
 497                                     struct bio *bio)
 498 {
 499         int nr_phys_segs = bio_phys_segments(q, bio);
 500
 501         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 502                 goto no_merge;
 503
 504         if (blk_integrity_merge_bio(q, req, bio) == false)
 505                 goto no_merge;
 506
 507         /*
 508          * This will form the start of a new hw segment.  Bump both
 509          * counters.
 510          */
 511         req->nr_phys_segments += nr_phys_segs;
 512         return 1;
 513
 514 no_merge:
 515         req->cmd_flags |= REQ_NOMERGE;
 516         if (req == q->last_merge)
 517                 q->last_merge = NULL;
 518         return 0;
 519 }
 520
 521 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 522                      struct bio *bio)
 523 {
 524         if (req_gap_back_merge(req, bio))
 525                 return 0;
 526         if (blk_integrity_rq(req) &&
 527             integrity_req_gap_back_merge(req, bio))
 528                 return 0;
 529         if (blk_rq_sectors(req) + bio_sectors(bio) >
 530             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
 531                 req->cmd_flags |= REQ_NOMERGE;
 532                 if (req == q->last_merge)
 533                         q->last_merge = NULL;
 534                 return 0;
 535         }
 536         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 537                 blk_recount_segments(q, req->biotail);
 538         if (!bio_flagged(bio, BIO_SEG_VALID))
 539                 blk_recount_segments(q, bio);
 540
 541         return ll_new_hw_segment(q, req, bio);
 542 }
 543
 544 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 545                       struct bio *bio)
 546 {
 547
 548         if (req_gap_front_merge(req, bio))
 549                 return 0;
 550         if (blk_integrity_rq(req) &&
 551             integrity_req_gap_front_merge(req, bio))
 552                 return 0;
 553         if (blk_rq_sectors(req) + bio_sectors(bio) >
 554             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 555                 req->cmd_flags |= REQ_NOMERGE;
 556                 if (req == q->last_merge)
 557                         q->last_merge = NULL;
 558                 return 0;
 559         }
 560         if (!bio_flagged(bio, BIO_SEG_VALID))
 561                 blk_recount_segments(q, bio);
 562         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 563                 blk_recount_segments(q, req->bio);
 564
 565         return ll_new_hw_segment(q, req, bio);
 566 }
 567
 568 /*
 569  * blk-mq uses req->special to carry normal driver per-request payload, it
 570  * does not indicate a prepared command that we cannot merge with.
 571  */
 572 static bool req_no_special_merge(struct request *req)
 573 {
 574         struct request_queue *q = req->q;
 575
 576         return !q->mq_ops && req->special;
 577 }
 578
 579 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 580                                 struct request *next)
 581 {
 582         int total_phys_segments;
 583         unsigned int seg_size =
 584                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 585
 586         /*
 587          * First check if the either of the requests are re-queued
 588          * requests.  Can't merge them if they are.
 589          */
 590         if (req_no_special_merge(req) || req_no_special_merge(next))
 591                 return 0;
 592
 593         if (req_gap_back_merge(req, next->bio))
 594                 return 0;
 595
 596         /*
 597          * Will it become too large?
 598          */
 599         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 600             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 601                 return 0;
 602
 603         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 604         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 605                 if (req->nr_phys_segments == 1)
 606                         req->bio->bi_seg_front_size = seg_size;
 607                 if (next->nr_phys_segments == 1)
 608                         next->biotail->bi_seg_back_size = seg_size;
 609                 total_phys_segments--;
 610         }
 611
 612         if (total_phys_segments > queue_max_segments(q))
 613                 return 0;
 614
 615         if (blk_integrity_merge_rq(q, req, next) == false)
 616                 return 0;
 617
 618         /* Merge is OK... */
 619         req->nr_phys_segments = total_phys_segments;
 620         return 1;
 621 }
 622
 623 /**
 624  * blk_rq_set_mixed_merge - mark a request as mixed merge
 625  * @rq: request to mark as mixed merge
 626  *
 627  * Description:
 628  *     @rq is about to be mixed merged.  Make sure the attributes
 629  *     which can be mixed are set in each bio and mark @rq as mixed
 630  *     merged.
 631  */
 632 void blk_rq_set_mixed_merge(struct request *rq)
 633 {
 634         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 635         struct bio *bio;
 636
 637         if (rq->cmd_flags & REQ_MIXED_MERGE)
 638                 return;
 639
 640         /*
 641          * @rq will no longer represent mixable attributes for all the
 642          * contained bios.  It will just track those of the first one.
 643          * Distributes the attributs to each bio.
 644          */
 645         for (bio = rq->bio; bio; bio = bio->bi_next) {
 646                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
 647                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 648                 bio->bi_opf |= ff;
 649         }
 650         rq->cmd_flags |= REQ_MIXED_MERGE;
 651 }
 652
 653 static void blk_account_io_merge(struct request *req)
 654 {
 655         if (blk_do_io_stat(req)) {
 656                 struct hd_struct *part;
 657                 int cpu;
 658
 659                 cpu = part_stat_lock();
 660                 part = req->part;
 661
 662                 part_round_stats(cpu, part);
 663                 part_dec_in_flight(part, rq_data_dir(req));
 664
 665                 hd_struct_put(part);
 666                 part_stat_unlock();
 667         }
 668 }
 669
 670 /*
 671  * Has to be called with the request spinlock acquired
 672  */
 673 static int attempt_merge(struct request_queue *q, struct request *req,
 674                           struct request *next)
 675 {
 676         if (!rq_mergeable(req) || !rq_mergeable(next))
 677                 return 0;
 678
 679         if (req_op(req) != req_op(next))
 680                 return 0;
 681
 682         /*
 683          * not contiguous
 684          */
 685         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 686                 return 0;
 687
 688         if (rq_data_dir(req) != rq_data_dir(next)
 689             || req->rq_disk != next->rq_disk
 690             || req_no_special_merge(next))
 691                 return 0;
 692
 693         if (req_op(req) == REQ_OP_WRITE_SAME &&
 694             !blk_write_same_mergeable(req->bio, next->bio))
 695                 return 0;
 696
 697         /*
 698          * If we are allowed to merge, then append bio list
 699          * from next to rq and release next. merge_requests_fn
 700          * will have updated segment counts, update sector
 701          * counts here.
 702          */
 703         if (!ll_merge_requests_fn(q, req, next))
 704                 return 0;
 705
 706         /*
 707          * If failfast settings disagree or any of the two is already
 708          * a mixed merge, mark both as mixed before proceeding.  This
 709          * makes sure that all involved bios have mixable attributes
 710          * set properly.
 711          */
 712         if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
 713             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 714             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 715                 blk_rq_set_mixed_merge(req);
 716                 blk_rq_set_mixed_merge(next);
 717         }
 718
 719         /*
 720          * At this point we have either done a back merge
 721          * or front merge. We need the smaller start_time of
 722          * the merged requests to be the current request
 723          * for accounting purposes.
 724          */
 725         if (time_after(req->start_time, next->start_time))
 726                 req->start_time = next->start_time;
 727
 728         req->biotail->bi_next = next->bio;
 729         req->biotail = next->biotail;
 730
 731         req->__data_len += blk_rq_bytes(next);
 732
 733         elv_merge_requests(q, req, next);
 734
 735         /*
 736          * 'next' is going away, so update stats accordingly
 737          */
 738         blk_account_io_merge(next);
 739
 740         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 741         if (blk_rq_cpu_valid(next))
 742                 req->cpu = next->cpu;
 743
 744         /* owner-ship of bio passed from next to req */
 745         next->bio = NULL;
 746         __blk_put_request(q, next);
 747         return 1;
 748 }
 749
 750 int attempt_back_merge(struct request_queue *q, struct request *rq)
 751 {
 752         struct request *next = elv_latter_request(q, rq);
 753
 754         if (next)
 755                 return attempt_merge(q, rq, next);
 756
 757         return 0;
 758 }
 759
 760 int attempt_front_merge(struct request_queue *q, struct request *rq)
 761 {
 762         struct request *prev = elv_former_request(q, rq);
 763
 764         if (prev)
 765                 return attempt_merge(q, prev, rq);
 766
 767         return 0;
 768 }
 769
 770 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 771                           struct request *next)
 772 {
 773         struct elevator_queue *e = q->elevator;
 774
 775         if (e->type->ops.elevator_allow_rq_merge_fn)
 776                 if (!e->type->ops.elevator_allow_rq_merge_fn(q, rq, next))
 777                         return 0;
 778
 779         return attempt_merge(q, rq, next);
 780 }
 781
 782 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 783 {
 784         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 785                 return false;
 786
 787         if (req_op(rq) != bio_op(bio))
 788                 return false;
 789
 790         /* different data direction or already started, don't merge */
 791         if (bio_data_dir(bio) != rq_data_dir(rq))
 792                 return false;
 793
 794         /* must be same device and not a special request */
 795         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 796                 return false;
 797
 798         /* only merge integrity protected bio into ditto rq */
 799         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 800                 return false;
 801
 802         /* must be using the same buffer */
 803         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 804             !blk_write_same_mergeable(rq->bio, bio))
 805                 return false;
 806
 807         return true;
 808 }
 809
 810 int blk_try_merge(struct request *rq, struct bio *bio)
 811 {
 812         if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 813                 return ELEVATOR_BACK_MERGE;
 814         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 815                 return ELEVATOR_FRONT_MERGE;
 816         return ELEVATOR_NO_MERGE;
 817 }