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_zeroes_split(struct request_queue *q,
  58                 struct bio *bio, struct bio_set *bs, unsigned *nsegs)
  59 {
  60         *nsegs = 1;
  61
  62         if (!q->limits.max_write_zeroes_sectors)
  63                 return NULL;
  64
  65         if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
  66                 return NULL;
  67
  68         return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
  69 }
  70
  71 static struct bio *blk_bio_write_same_split(struct request_queue *q,
  72                                             struct bio *bio,
  73                                             struct bio_set *bs,
  74                                             unsigned *nsegs)
  75 {
  76         *nsegs = 1;
  77
  78         if (!q->limits.max_write_same_sectors)
  79                 return NULL;
  80
  81         if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
  82                 return NULL;
  83
  84         return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
  85 }
  86
  87 static inline unsigned get_max_io_size(struct request_queue *q,
  88                                        struct bio *bio)
  89 {
  90         unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
  91         unsigned mask = queue_logical_block_size(q) - 1;
  92
  93         /* aligned to logical block size */
  94         sectors &= ~(mask >> 9);
  95
  96         return sectors;
  97 }
  98
  99 static struct bio *blk_bio_segment_split(struct request_queue *q,
 100                                          struct bio *bio,
 101                                          struct bio_set *bs,
 102                                          unsigned *segs)
 103 {
 104         struct bio_vec bv, bvprv, *bvprvp = NULL;
 105         struct bvec_iter iter;
 106         unsigned seg_size = 0, nsegs = 0, sectors = 0;
 107         unsigned front_seg_size = bio->bi_seg_front_size;
 108         bool do_split = true;
 109         struct bio *new = NULL;
 110         const unsigned max_sectors = get_max_io_size(q, bio);
 111         unsigned bvecs = 0;
 112
 113         bio_for_each_segment(bv, bio, iter) {
 114                 /*
 115                  * With arbitrary bio size, the incoming bio may be very
 116                  * big. We have to split the bio into small bios so that
 117                  * each holds at most BIO_MAX_PAGES bvecs because
 118                  * bio_clone() can fail to allocate big bvecs.
 119                  *
 120                  * It should have been better to apply the limit per
 121                  * request queue in which bio_clone() is involved,
 122                  * instead of globally. The biggest blocker is the
 123                  * bio_clone() in bio bounce.
 124                  *
 125                  * If bio is splitted by this reason, we should have
 126                  * allowed to continue bios merging, but don't do
 127                  * that now for making the change simple.
 128                  *
 129                  * TODO: deal with bio bounce's bio_clone() gracefully
 130                  * and convert the global limit into per-queue limit.
 131                  */
 132                 if (bvecs++ >= BIO_MAX_PAGES)
 133                         goto split;
 134
 135                 /*
 136                  * If the queue doesn't support SG gaps and adding this
 137                  * offset would create a gap, disallow it.
 138                  */
 139                 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 140                         goto split;
 141
 142                 if (sectors + (bv.bv_len >> 9) > max_sectors) {
 143                         /*
 144                          * Consider this a new segment if we're splitting in
 145                          * the middle of this vector.
 146                          */
 147                         if (nsegs < queue_max_segments(q) &&
 148                             sectors < max_sectors) {
 149                                 nsegs++;
 150                                 sectors = max_sectors;
 151                         }
 152                         if (sectors)
 153                                 goto split;
 154                         /* Make this single bvec as the 1st segment */
 155                 }
 156
 157                 if (bvprvp && blk_queue_cluster(q)) {
 158                         if (seg_size + bv.bv_len > queue_max_segment_size(q))
 159                                 goto new_segment;
 160                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
 161                                 goto new_segment;
 162                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
 163                                 goto new_segment;
 164
 165                         seg_size += bv.bv_len;
 166                         bvprv = bv;
 167                         bvprvp = &bvprv;
 168                         sectors += bv.bv_len >> 9;
 169
 170                         if (nsegs == 1 && seg_size > front_seg_size)
 171                                 front_seg_size = seg_size;
 172                         continue;
 173                 }
 174 new_segment:
 175                 if (nsegs == queue_max_segments(q))
 176                         goto split;
 177
 178                 nsegs++;
 179                 bvprv = bv;
 180                 bvprvp = &bvprv;
 181                 seg_size = bv.bv_len;
 182                 sectors += bv.bv_len >> 9;
 183
 184                 if (nsegs == 1 && seg_size > front_seg_size)
 185                         front_seg_size = seg_size;
 186         }
 187
 188         do_split = false;
 189 split:
 190         *segs = nsegs;
 191
 192         if (do_split) {
 193                 new = bio_split(bio, sectors, GFP_NOIO, bs);
 194                 if (new)
 195                         bio = new;
 196         }
 197
 198         bio->bi_seg_front_size = front_seg_size;
 199         if (seg_size > bio->bi_seg_back_size)
 200                 bio->bi_seg_back_size = seg_size;
 201
 202         return do_split ? new : NULL;
 203 }
 204
 205 void blk_queue_split(struct request_queue *q, struct bio **bio)
 206 {
 207         struct bio *split, *res;
 208         unsigned nsegs;
 209
 210         switch (bio_op(*bio)) {
 211         case REQ_OP_DISCARD:
 212         case REQ_OP_SECURE_ERASE:
 213                 split = blk_bio_discard_split(q, *bio, q->bio_split, &nsegs);
 214                 break;
 215         case REQ_OP_WRITE_ZEROES:
 216                 split = blk_bio_write_zeroes_split(q, *bio, q->bio_split, &nsegs);
 217                 break;
 218         case REQ_OP_WRITE_SAME:
 219                 split = blk_bio_write_same_split(q, *bio, q->bio_split, &nsegs);
 220                 break;
 221         default:
 222                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
 223                 break;
 224         }
 225
 226         /* physical segments can be figured out during splitting */
 227         res = split ? split : *bio;
 228         res->bi_phys_segments = nsegs;
 229         bio_set_flag(res, BIO_SEG_VALID);
 230
 231         if (split) {
 232                 /* there isn't chance to merge the splitted bio */
 233                 split->bi_opf |= REQ_NOMERGE;
 234
 235                 bio_chain(split, *bio);
 236                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
 237                 generic_make_request(*bio);
 238                 *bio = split;
 239         }
 240 }
 241 EXPORT_SYMBOL(blk_queue_split);
 242
 243 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 244                                              struct bio *bio,
 245                                              bool no_sg_merge)
 246 {
 247         struct bio_vec bv, bvprv = { NULL };
 248         int cluster, prev = 0;
 249         unsigned int seg_size, nr_phys_segs;
 250         struct bio *fbio, *bbio;
 251         struct bvec_iter iter;
 252
 253         if (!bio)
 254                 return 0;
 255
 256         switch (bio_op(bio)) {
 257         case REQ_OP_DISCARD:
 258         case REQ_OP_SECURE_ERASE:
 259         case REQ_OP_WRITE_ZEROES:
 260                 return 0;
 261         case REQ_OP_WRITE_SAME:
 262                 return 1;
 263         }
 264
 265         fbio = bio;
 266         cluster = blk_queue_cluster(q);
 267         seg_size = 0;
 268         nr_phys_segs = 0;
 269         for_each_bio(bio) {
 270                 bio_for_each_segment(bv, bio, iter) {
 271                         /*
 272                          * If SG merging is disabled, each bio vector is
 273                          * a segment
 274                          */
 275                         if (no_sg_merge)
 276                                 goto new_segment;
 277
 278                         if (prev && cluster) {
 279                                 if (seg_size + bv.bv_len
 280                                     > queue_max_segment_size(q))
 281                                         goto new_segment;
 282                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
 283                                         goto new_segment;
 284                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
 285                                         goto new_segment;
 286
 287                                 seg_size += bv.bv_len;
 288                                 bvprv = bv;
 289                                 continue;
 290                         }
 291 new_segment:
 292                         if (nr_phys_segs == 1 && seg_size >
 293                             fbio->bi_seg_front_size)
 294                                 fbio->bi_seg_front_size = seg_size;
 295
 296                         nr_phys_segs++;
 297                         bvprv = bv;
 298                         prev = 1;
 299                         seg_size = bv.bv_len;
 300                 }
 301                 bbio = bio;
 302         }
 303
 304         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
 305                 fbio->bi_seg_front_size = seg_size;
 306         if (seg_size > bbio->bi_seg_back_size)
 307                 bbio->bi_seg_back_size = seg_size;
 308
 309         return nr_phys_segs;
 310 }
 311
 312 void blk_recalc_rq_segments(struct request *rq)
 313 {
 314         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
 315                         &rq->q->queue_flags);
 316
 317         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
 318                         no_sg_merge);
 319 }
 320
 321 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 322 {
 323         unsigned short seg_cnt;
 324
 325         /* estimate segment number by bi_vcnt for non-cloned bio */
 326         if (bio_flagged(bio, BIO_CLONED))
 327                 seg_cnt = bio_segments(bio);
 328         else
 329                 seg_cnt = bio->bi_vcnt;
 330
 331         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 332                         (seg_cnt < queue_max_segments(q)))
 333                 bio->bi_phys_segments = seg_cnt;
 334         else {
 335                 struct bio *nxt = bio->bi_next;
 336
 337                 bio->bi_next = NULL;
 338                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 339                 bio->bi_next = nxt;
 340         }
 341
 342         bio_set_flag(bio, BIO_SEG_VALID);
 343 }
 344 EXPORT_SYMBOL(blk_recount_segments);
 345
 346 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 347                                    struct bio *nxt)
 348 {
 349         struct bio_vec end_bv = { NULL }, nxt_bv;
 350
 351         if (!blk_queue_cluster(q))
 352                 return 0;
 353
 354         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 355             queue_max_segment_size(q))
 356                 return 0;
 357
 358         if (!bio_has_data(bio))
 359                 return 1;
 360
 361         bio_get_last_bvec(bio, &end_bv);
 362         bio_get_first_bvec(nxt, &nxt_bv);
 363
 364         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 365                 return 0;
 366
 367         /*
 368          * bio and nxt are contiguous in memory; check if the queue allows
 369          * these two to be merged into one
 370          */
 371         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 372                 return 1;
 373
 374         return 0;
 375 }
 376
 377 static inline void
 378 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 379                      struct scatterlist *sglist, struct bio_vec *bvprv,
 380                      struct scatterlist **sg, int *nsegs, int *cluster)
 381 {
 382
 383         int nbytes = bvec->bv_len;
 384
 385         if (*sg && *cluster) {
 386                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 387                         goto new_segment;
 388
 389                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 390                         goto new_segment;
 391                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 392                         goto new_segment;
 393
 394                 (*sg)->length += nbytes;
 395         } else {
 396 new_segment:
 397                 if (!*sg)
 398                         *sg = sglist;
 399                 else {
 400                         /*
 401                          * If the driver previously mapped a shorter
 402                          * list, we could see a termination bit
 403                          * prematurely unless it fully inits the sg
 404                          * table on each mapping. We KNOW that there
 405                          * must be more entries here or the driver
 406                          * would be buggy, so force clear the
 407                          * termination bit to avoid doing a full
 408                          * sg_init_table() in drivers for each command.
 409                          */
 410                         sg_unmark_end(*sg);
 411                         *sg = sg_next(*sg);
 412                 }
 413
 414                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 415                 (*nsegs)++;
 416         }
 417         *bvprv = *bvec;
 418 }
 419
 420 static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
 421                 struct scatterlist *sglist, struct scatterlist **sg)
 422 {
 423         *sg = sglist;
 424         sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
 425         return 1;
 426 }
 427
 428 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 429                              struct scatterlist *sglist,
 430                              struct scatterlist **sg)
 431 {
 432         struct bio_vec bvec, bvprv = { NULL };
 433         struct bvec_iter iter;
 434         int cluster = blk_queue_cluster(q), nsegs = 0;
 435
 436         for_each_bio(bio)
 437                 bio_for_each_segment(bvec, bio, iter)
 438                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 439                                              &nsegs, &cluster);
 440
 441         return nsegs;
 442 }
 443
 444 /*
 445  * map a request to scatterlist, return number of sg entries setup. Caller
 446  * must make sure sg can hold rq->nr_phys_segments entries
 447  */
 448 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 449                   struct scatterlist *sglist)
 450 {
 451         struct scatterlist *sg = NULL;
 452         int nsegs = 0;
 453
 454         if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
 455                 nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
 456         else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
 457                 nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
 458         else if (rq->bio)
 459                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 460
 461         if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
 462             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 463                 unsigned int pad_len =
 464                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 465
 466                 sg->length += pad_len;
 467                 rq->extra_len += pad_len;
 468         }
 469
 470         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 471                 if (op_is_write(req_op(rq)))
 472                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 473
 474                 sg_unmark_end(sg);
 475                 sg = sg_next(sg);
 476                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 477                             q->dma_drain_size,
 478                             ((unsigned long)q->dma_drain_buffer) &
 479                             (PAGE_SIZE - 1));
 480                 nsegs++;
 481                 rq->extra_len += q->dma_drain_size;
 482         }
 483
 484         if (sg)
 485                 sg_mark_end(sg);
 486
 487         /*
 488          * Something must have been wrong if the figured number of
 489          * segment is bigger than number of req's physical segments
 490          */
 491         WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
 492
 493         return nsegs;
 494 }
 495 EXPORT_SYMBOL(blk_rq_map_sg);
 496
 497 static inline int ll_new_hw_segment(struct request_queue *q,
 498                                     struct request *req,
 499                                     struct bio *bio)
 500 {
 501         int nr_phys_segs = bio_phys_segments(q, bio);
 502
 503         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 504                 goto no_merge;
 505
 506         if (blk_integrity_merge_bio(q, req, bio) == false)
 507                 goto no_merge;
 508
 509         /*
 510          * This will form the start of a new hw segment.  Bump both
 511          * counters.
 512          */
 513         req->nr_phys_segments += nr_phys_segs;
 514         return 1;
 515
 516 no_merge:
 517         req_set_nomerge(q, req);
 518         return 0;
 519 }
 520
 521 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 522                      struct bio *bio)
 523 {
 524         if (req_gap_back_merge(req, bio))
 525                 return 0;
 526         if (blk_integrity_rq(req) &&
 527             integrity_req_gap_back_merge(req, bio))
 528                 return 0;
 529         if (blk_rq_sectors(req) + bio_sectors(bio) >
 530             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
 531                 req_set_nomerge(q, req);
 532                 return 0;
 533         }
 534         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 535                 blk_recount_segments(q, req->biotail);
 536         if (!bio_flagged(bio, BIO_SEG_VALID))
 537                 blk_recount_segments(q, bio);
 538
 539         return ll_new_hw_segment(q, req, bio);
 540 }
 541
 542 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 543                       struct bio *bio)
 544 {
 545
 546         if (req_gap_front_merge(req, bio))
 547                 return 0;
 548         if (blk_integrity_rq(req) &&
 549             integrity_req_gap_front_merge(req, bio))
 550                 return 0;
 551         if (blk_rq_sectors(req) + bio_sectors(bio) >
 552             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 553                 req_set_nomerge(q, req);
 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, blk_rq_pos(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->rq_flags & RQF_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_opf & REQ_FAILFAST_MASK) &&
 643                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 644                 bio->bi_opf |= ff;
 645         }
 646         rq->rq_flags |= RQF_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  * For non-mq, this has to be called with the request spinlock acquired.
 668  * For mq with scheduling, the appropriate queue wide lock should be held.
 669  */
 670 static struct request *attempt_merge(struct request_queue *q,
 671                                      struct request *req, struct request *next)
 672 {
 673         if (!rq_mergeable(req) || !rq_mergeable(next))
 674                 return NULL;
 675
 676         if (req_op(req) != req_op(next))
 677                 return NULL;
 678
 679         /*
 680          * not contiguous
 681          */
 682         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 683                 return NULL;
 684
 685         if (rq_data_dir(req) != rq_data_dir(next)
 686             || req->rq_disk != next->rq_disk
 687             || req_no_special_merge(next))
 688                 return NULL;
 689
 690         if (req_op(req) == REQ_OP_WRITE_SAME &&
 691             !blk_write_same_mergeable(req->bio, next->bio))
 692                 return NULL;
 693
 694         /*
 695          * If we are allowed to merge, then append bio list
 696          * from next to rq and release next. merge_requests_fn
 697          * will have updated segment counts, update sector
 698          * counts here.
 699          */
 700         if (!ll_merge_requests_fn(q, req, next))
 701                 return NULL;
 702
 703         /*
 704          * If failfast settings disagree or any of the two is already
 705          * a mixed merge, mark both as mixed before proceeding.  This
 706          * makes sure that all involved bios have mixable attributes
 707          * set properly.
 708          */
 709         if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
 710             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 711             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 712                 blk_rq_set_mixed_merge(req);
 713                 blk_rq_set_mixed_merge(next);
 714         }
 715
 716         /*
 717          * At this point we have either done a back merge
 718          * or front merge. We need the smaller start_time of
 719          * the merged requests to be the current request
 720          * for accounting purposes.
 721          */
 722         if (time_after(req->start_time, next->start_time))
 723                 req->start_time = next->start_time;
 724
 725         req->biotail->bi_next = next->bio;
 726         req->biotail = next->biotail;
 727
 728         req->__data_len += blk_rq_bytes(next);
 729
 730         elv_merge_requests(q, req, next);
 731
 732         /*
 733          * 'next' is going away, so update stats accordingly
 734          */
 735         blk_account_io_merge(next);
 736
 737         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 738         if (blk_rq_cpu_valid(next))
 739                 req->cpu = next->cpu;
 740
 741         /*
 742          * ownership of bio passed from next to req, return 'next' for
 743          * the caller to free
 744          */
 745         next->bio = NULL;
 746         return next;
 747 }
 748
 749 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
 750 {
 751         struct request *next = elv_latter_request(q, rq);
 752
 753         if (next)
 754                 return attempt_merge(q, rq, next);
 755
 756         return NULL;
 757 }
 758
 759 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
 760 {
 761         struct request *prev = elv_former_request(q, rq);
 762
 763         if (prev)
 764                 return attempt_merge(q, prev, rq);
 765
 766         return NULL;
 767 }
 768
 769 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 770                           struct request *next)
 771 {
 772         struct elevator_queue *e = q->elevator;
 773         struct request *free;
 774
 775         if (!e->uses_mq && e->type->ops.sq.elevator_allow_rq_merge_fn)
 776                 if (!e->type->ops.sq.elevator_allow_rq_merge_fn(q, rq, next))
 777                         return 0;
 778
 779         free = attempt_merge(q, rq, next);
 780         if (free) {
 781                 __blk_put_request(q, free);
 782                 return 1;
 783         }
 784
 785         return 0;
 786 }
 787
 788 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 789 {
 790         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 791                 return false;
 792
 793         if (req_op(rq) != bio_op(bio))
 794                 return false;
 795
 796         /* different data direction or already started, don't merge */
 797         if (bio_data_dir(bio) != rq_data_dir(rq))
 798                 return false;
 799
 800         /* must be same device and not a special request */
 801         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 802                 return false;
 803
 804         /* only merge integrity protected bio into ditto rq */
 805         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 806                 return false;
 807
 808         /* must be using the same buffer */
 809         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 810             !blk_write_same_mergeable(rq->bio, bio))
 811                 return false;
 812
 813         return true;
 814 }
 815
 816 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 817 {
 818         if (req_op(rq) == REQ_OP_DISCARD &&
 819             queue_max_discard_segments(rq->q) > 1)
 820                 return ELEVATOR_DISCARD_MERGE;
 821         else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 822                 return ELEVATOR_BACK_MERGE;
 823         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 824                 return ELEVATOR_FRONT_MERGE;
 825         return ELEVATOR_NO_MERGE;
 826 }