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