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