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