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;
 300
 301         /* estimate segment number by bi_vcnt for non-cloned bio */
 302         if (bio_flagged(bio, BIO_CLONED))
 303                 seg_cnt = bio_segments(bio);
 304         else
 305                 seg_cnt = bio->bi_vcnt;
 306
 307         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 308                         (seg_cnt < queue_max_segments(q)))
 309                 bio->bi_phys_segments = seg_cnt;
 310         else {
 311                 struct bio *nxt = bio->bi_next;
 312
 313                 bio->bi_next = NULL;
 314                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 315                 bio->bi_next = nxt;
 316         }
 317
 318         bio_set_flag(bio, BIO_SEG_VALID);
 319 }
 320 EXPORT_SYMBOL(blk_recount_segments);
 321
 322 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 323                                    struct bio *nxt)
 324 {
 325         struct bio_vec end_bv = { NULL }, nxt_bv;
 326         struct bvec_iter iter;
 327
 328         if (!blk_queue_cluster(q))
 329                 return 0;
 330
 331         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 332             queue_max_segment_size(q))
 333                 return 0;
 334
 335         if (!bio_has_data(bio))
 336                 return 1;
 337
 338         bio_for_each_segment(end_bv, bio, iter)
 339                 if (end_bv.bv_len == iter.bi_size)
 340                         break;
 341
 342         nxt_bv = bio_iovec(nxt);
 343
 344         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 345                 return 0;
 346
 347         /*
 348          * bio and nxt are contiguous in memory; check if the queue allows
 349          * these two to be merged into one
 350          */
 351         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 352                 return 1;
 353
 354         return 0;
 355 }
 356
 357 static inline void
 358 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 359                      struct scatterlist *sglist, struct bio_vec *bvprv,
 360                      struct scatterlist **sg, int *nsegs, int *cluster)
 361 {
 362
 363         int nbytes = bvec->bv_len;
 364
 365         if (*sg && *cluster) {
 366                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 367                         goto new_segment;
 368
 369                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 370                         goto new_segment;
 371                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 372                         goto new_segment;
 373
 374                 (*sg)->length += nbytes;
 375         } else {
 376 new_segment:
 377                 if (!*sg)
 378                         *sg = sglist;
 379                 else {
 380                         /*
 381                          * If the driver previously mapped a shorter
 382                          * list, we could see a termination bit
 383                          * prematurely unless it fully inits the sg
 384                          * table on each mapping. We KNOW that there
 385                          * must be more entries here or the driver
 386                          * would be buggy, so force clear the
 387                          * termination bit to avoid doing a full
 388                          * sg_init_table() in drivers for each command.
 389                          */
 390                         sg_unmark_end(*sg);
 391                         *sg = sg_next(*sg);
 392                 }
 393
 394                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 395                 (*nsegs)++;
 396         }
 397         *bvprv = *bvec;
 398 }
 399
 400 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 401                              struct scatterlist *sglist,
 402                              struct scatterlist **sg)
 403 {
 404         struct bio_vec bvec, bvprv = { NULL };
 405         struct bvec_iter iter;
 406         int nsegs, cluster;
 407
 408         nsegs = 0;
 409         cluster = blk_queue_cluster(q);
 410
 411         if (bio->bi_rw & REQ_DISCARD) {
 412                 /*
 413                  * This is a hack - drivers should be neither modifying the
 414                  * biovec, nor relying on bi_vcnt - but because of
 415                  * blk_add_request_payload(), a discard bio may or may not have
 416                  * a payload we need to set up here (thank you Christoph) and
 417                  * bi_vcnt is really the only way of telling if we need to.
 418                  */
 419
 420                 if (bio->bi_vcnt)
 421                         goto single_segment;
 422
 423                 return 0;
 424         }
 425
 426         if (bio->bi_rw & REQ_WRITE_SAME) {
 427 single_segment:
 428                 *sg = sglist;
 429                 bvec = bio_iovec(bio);
 430                 sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
 431                 return 1;
 432         }
 433
 434         for_each_bio(bio)
 435                 bio_for_each_segment(bvec, bio, iter)
 436                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 437                                              &nsegs, &cluster);
 438
 439         return nsegs;
 440 }
 441
 442 /*
 443  * map a request to scatterlist, return number of sg entries setup. Caller
 444  * must make sure sg can hold rq->nr_phys_segments entries
 445  */
 446 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 447                   struct scatterlist *sglist)
 448 {
 449         struct scatterlist *sg = NULL;
 450         int nsegs = 0;
 451
 452         if (rq->bio)
 453                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 454
 455         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 456             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 457                 unsigned int pad_len =
 458                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 459
 460                 sg->length += pad_len;
 461                 rq->extra_len += pad_len;
 462         }
 463
 464         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 465                 if (rq->cmd_flags & REQ_WRITE)
 466                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 467
 468                 sg_unmark_end(sg);
 469                 sg = sg_next(sg);
 470                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 471                             q->dma_drain_size,
 472                             ((unsigned long)q->dma_drain_buffer) &
 473                             (PAGE_SIZE - 1));
 474                 nsegs++;
 475                 rq->extra_len += q->dma_drain_size;
 476         }
 477
 478         if (sg)
 479                 sg_mark_end(sg);
 480
 481         /*
 482          * Something must have been wrong if the figured number of
 483          * segment is bigger than number of req's physical segments
 484          */
 485         WARN_ON(nsegs > rq->nr_phys_segments);
 486
 487         return nsegs;
 488 }
 489 EXPORT_SYMBOL(blk_rq_map_sg);
 490
 491 static inline int ll_new_hw_segment(struct request_queue *q,
 492                                     struct request *req,
 493                                     struct bio *bio)
 494 {
 495         int nr_phys_segs = bio_phys_segments(q, bio);
 496
 497         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 498                 goto no_merge;
 499
 500         if (blk_integrity_merge_bio(q, req, bio) == false)
 501                 goto no_merge;
 502
 503         /*
 504          * This will form the start of a new hw segment.  Bump both
 505          * counters.
 506          */
 507         req->nr_phys_segments += nr_phys_segs;
 508         return 1;
 509
 510 no_merge:
 511         req->cmd_flags |= REQ_NOMERGE;
 512         if (req == q->last_merge)
 513                 q->last_merge = NULL;
 514         return 0;
 515 }
 516
 517 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 518                      struct bio *bio)
 519 {
 520         if (req_gap_back_merge(req, bio))
 521                 return 0;
 522         if (blk_integrity_rq(req) &&
 523             integrity_req_gap_back_merge(req, bio))
 524                 return 0;
 525         if (blk_rq_sectors(req) + bio_sectors(bio) >
 526             blk_rq_get_max_sectors(req)) {
 527                 req->cmd_flags |= REQ_NOMERGE;
 528                 if (req == q->last_merge)
 529                         q->last_merge = NULL;
 530                 return 0;
 531         }
 532         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 533                 blk_recount_segments(q, req->biotail);
 534         if (!bio_flagged(bio, BIO_SEG_VALID))
 535                 blk_recount_segments(q, bio);
 536
 537         return ll_new_hw_segment(q, req, bio);
 538 }
 539
 540 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 541                       struct bio *bio)
 542 {
 543
 544         if (req_gap_front_merge(req, bio))
 545                 return 0;
 546         if (blk_integrity_rq(req) &&
 547             integrity_req_gap_front_merge(req, bio))
 548                 return 0;
 549         if (blk_rq_sectors(req) + bio_sectors(bio) >
 550             blk_rq_get_max_sectors(req)) {
 551                 req->cmd_flags |= REQ_NOMERGE;
 552                 if (req == q->last_merge)
 553                         q->last_merge = NULL;
 554                 return 0;
 555         }
 556         if (!bio_flagged(bio, BIO_SEG_VALID))
 557                 blk_recount_segments(q, bio);
 558         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 559                 blk_recount_segments(q, req->bio);
 560
 561         return ll_new_hw_segment(q, req, bio);
 562 }
 563
 564 /*
 565  * blk-mq uses req->special to carry normal driver per-request payload, it
 566  * does not indicate a prepared command that we cannot merge with.
 567  */
 568 static bool req_no_special_merge(struct request *req)
 569 {
 570         struct request_queue *q = req->q;
 571
 572         return !q->mq_ops && req->special;
 573 }
 574
 575 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 576                                 struct request *next)
 577 {
 578         int total_phys_segments;
 579         unsigned int seg_size =
 580                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 581
 582         /*
 583          * First check if the either of the requests are re-queued
 584          * requests.  Can't merge them if they are.
 585          */
 586         if (req_no_special_merge(req) || req_no_special_merge(next))
 587                 return 0;
 588
 589         if (req_gap_back_merge(req, next->bio))
 590                 return 0;
 591
 592         /*
 593          * Will it become too large?
 594          */
 595         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 596             blk_rq_get_max_sectors(req))
 597                 return 0;
 598
 599         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 600         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 601                 if (req->nr_phys_segments == 1)
 602                         req->bio->bi_seg_front_size = seg_size;
 603                 if (next->nr_phys_segments == 1)
 604                         next->biotail->bi_seg_back_size = seg_size;
 605                 total_phys_segments--;
 606         }
 607
 608         if (total_phys_segments > queue_max_segments(q))
 609                 return 0;
 610
 611         if (blk_integrity_merge_rq(q, req, next) == false)
 612                 return 0;
 613
 614         /* Merge is OK... */
 615         req->nr_phys_segments = total_phys_segments;
 616         return 1;
 617 }
 618
 619 /**
 620  * blk_rq_set_mixed_merge - mark a request as mixed merge
 621  * @rq: request to mark as mixed merge
 622  *
 623  * Description:
 624  *     @rq is about to be mixed merged.  Make sure the attributes
 625  *     which can be mixed are set in each bio and mark @rq as mixed
 626  *     merged.
 627  */
 628 void blk_rq_set_mixed_merge(struct request *rq)
 629 {
 630         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 631         struct bio *bio;
 632
 633         if (rq->cmd_flags & REQ_MIXED_MERGE)
 634                 return;
 635
 636         /*
 637          * @rq will no longer represent mixable attributes for all the
 638          * contained bios.  It will just track those of the first one.
 639          * Distributes the attributs to each bio.
 640          */
 641         for (bio = rq->bio; bio; bio = bio->bi_next) {
 642                 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
 643                              (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
 644                 bio->bi_rw |= ff;
 645         }
 646         rq->cmd_flags |= REQ_MIXED_MERGE;
 647 }
 648
 649 static void blk_account_io_merge(struct request *req)
 650 {
 651         if (blk_do_io_stat(req)) {
 652                 struct hd_struct *part;
 653                 int cpu;
 654
 655                 cpu = part_stat_lock();
 656                 part = req->part;
 657
 658                 part_round_stats(cpu, part);
 659                 part_dec_in_flight(part, rq_data_dir(req));
 660
 661                 hd_struct_put(part);
 662                 part_stat_unlock();
 663         }
 664 }
 665
 666 /*
 667  * Has to be called with the request spinlock acquired
 668  */
 669 static int attempt_merge(struct request_queue *q, struct request *req,
 670                           struct request *next)
 671 {
 672         if (!rq_mergeable(req) || !rq_mergeable(next))
 673                 return 0;
 674
 675         if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
 676                 return 0;
 677
 678         /*
 679          * not contiguous
 680          */
 681         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 682                 return 0;
 683
 684         if (rq_data_dir(req) != rq_data_dir(next)
 685             || req->rq_disk != next->rq_disk
 686             || req_no_special_merge(next))
 687                 return 0;
 688
 689         if (req->cmd_flags & REQ_WRITE_SAME &&
 690             !blk_write_same_mergeable(req->bio, next->bio))
 691                 return 0;
 692
 693         /*
 694          * If we are allowed to merge, then append bio list
 695          * from next to rq and release next. merge_requests_fn
 696          * will have updated segment counts, update sector
 697          * counts here.
 698          */
 699         if (!ll_merge_requests_fn(q, req, next))
 700                 return 0;
 701
 702         /*
 703          * If failfast settings disagree or any of the two is already
 704          * a mixed merge, mark both as mixed before proceeding.  This
 705          * makes sure that all involved bios have mixable attributes
 706          * set properly.
 707          */
 708         if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
 709             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 710             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 711                 blk_rq_set_mixed_merge(req);
 712                 blk_rq_set_mixed_merge(next);
 713         }
 714
 715         /*
 716          * At this point we have either done a back merge
 717          * or front merge. We need the smaller start_time of
 718          * the merged requests to be the current request
 719          * for accounting purposes.
 720          */
 721         if (time_after(req->start_time, next->start_time))
 722                 req->start_time = next->start_time;
 723
 724         req->biotail->bi_next = next->bio;
 725         req->biotail = next->biotail;
 726
 727         req->__data_len += blk_rq_bytes(next);
 728
 729         elv_merge_requests(q, req, next);
 730
 731         /*
 732          * 'next' is going away, so update stats accordingly
 733          */
 734         blk_account_io_merge(next);
 735
 736         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 737         if (blk_rq_cpu_valid(next))
 738                 req->cpu = next->cpu;
 739
 740         /* owner-ship of bio passed from next to req */
 741         next->bio = NULL;
 742         __blk_put_request(q, next);
 743         return 1;
 744 }
 745
 746 int attempt_back_merge(struct request_queue *q, struct request *rq)
 747 {
 748         struct request *next = elv_latter_request(q, rq);
 749
 750         if (next)
 751                 return attempt_merge(q, rq, next);
 752
 753         return 0;
 754 }
 755
 756 int attempt_front_merge(struct request_queue *q, struct request *rq)
 757 {
 758         struct request *prev = elv_former_request(q, rq);
 759
 760         if (prev)
 761                 return attempt_merge(q, prev, rq);
 762
 763         return 0;
 764 }
 765
 766 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 767                           struct request *next)
 768 {
 769         return attempt_merge(q, rq, next);
 770 }
 771
 772 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 773 {
 774         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 775                 return false;
 776
 777         if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
 778                 return false;
 779
 780         /* different data direction or already started, don't merge */
 781         if (bio_data_dir(bio) != rq_data_dir(rq))
 782                 return false;
 783
 784         /* must be same device and not a special request */
 785         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 786                 return false;
 787
 788         /* only merge integrity protected bio into ditto rq */
 789         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 790                 return false;
 791
 792         /* must be using the same buffer */
 793         if (rq->cmd_flags & REQ_WRITE_SAME &&
 794             !blk_write_same_mergeable(rq->bio, bio))
 795                 return false;
 796
 797         return true;
 798 }
 799
 800 int blk_try_merge(struct request *rq, struct bio *bio)
 801 {
 802         if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 803                 return ELEVATOR_BACK_MERGE;
 804         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 805                 return ELEVATOR_FRONT_MERGE;
 806         return ELEVATOR_NO_MERGE;
 807 }