block/blk-merge.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Functions related to segment and merge handling
   4  */
   5 #include <linux/kernel.h>
   6 #include <linux/module.h>
   7 #include <linux/bio.h>
   8 #include <linux/blkdev.h>
   9 #include <linux/scatterlist.h>
  10
  11 #include <trace/events/block.h>
  12
  13 #include "blk.h"
  14
  15 static struct bio *blk_bio_discard_split(struct request_queue *q,
  16                                          struct bio *bio,
  17                                          struct bio_set *bs,
  18                                          unsigned *nsegs)
  19 {
  20         unsigned int max_discard_sectors, granularity;
  21         int alignment;
  22         sector_t tmp;
  23         unsigned split_sectors;
  24
  25         *nsegs = 1;
  26
  27         /* Zero-sector (unknown) and one-sector granularities are the same.  */
  28         granularity = max(q->limits.discard_granularity >> 9, 1U);
  29
  30         max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
  31         max_discard_sectors -= max_discard_sectors % granularity;
  32
  33         if (unlikely(!max_discard_sectors)) {
  34                 /* XXX: warn */
  35                 return NULL;
  36         }
  37
  38         if (bio_sectors(bio) <= max_discard_sectors)
  39                 return NULL;
  40
  41         split_sectors = max_discard_sectors;
  42
  43         /*
  44          * If the next starting sector would be misaligned, stop the discard at
  45          * the previous aligned sector.
  46          */
  47         alignment = (q->limits.discard_alignment >> 9) % granularity;
  48
  49         tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
  50         tmp = sector_div(tmp, granularity);
  51
  52         if (split_sectors > tmp)
  53                 split_sectors -= tmp;
  54
  55         return bio_split(bio, split_sectors, GFP_NOIO, bs);
  56 }
  57
  58 static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
  59                 struct bio *bio, struct bio_set *bs, unsigned *nsegs)
  60 {
  61         *nsegs = 1;
  62
  63         if (!q->limits.max_write_zeroes_sectors)
  64                 return NULL;
  65
  66         if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
  67                 return NULL;
  68
  69         return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
  70 }
  71
  72 static struct bio *blk_bio_write_same_split(struct request_queue *q,
  73                                             struct bio *bio,
  74                                             struct bio_set *bs,
  75                                             unsigned *nsegs)
  76 {
  77         *nsegs = 1;
  78
  79         if (!q->limits.max_write_same_sectors)
  80                 return NULL;
  81
  82         if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
  83                 return NULL;
  84
  85         return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
  86 }
  87
  88 static inline unsigned get_max_io_size(struct request_queue *q,
  89                                        struct bio *bio)
  90 {
  91         unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
  92         unsigned mask = queue_logical_block_size(q) - 1;
  93
  94         /* aligned to logical block size */
  95         sectors &= ~(mask >> 9);
  96
  97         return sectors;
  98 }
  99
 100 static struct bio *blk_bio_segment_split(struct request_queue *q,
 101                                          struct bio *bio,
 102                                          struct bio_set *bs,
 103                                          unsigned *segs)
 104 {
 105         struct bio_vec bv, bvprv, *bvprvp = NULL;
 106         struct bvec_iter iter;
 107         unsigned seg_size = 0, nsegs = 0, sectors = 0;
 108         unsigned front_seg_size = bio->bi_seg_front_size;
 109         bool do_split = true;
 110         struct bio *new = NULL;
 111         const unsigned max_sectors = get_max_io_size(q, bio);
 112
 113         bio_for_each_segment(bv, bio, iter) {
 114                 /*
 115                  * If the queue doesn't support SG gaps and adding this
 116                  * offset would create a gap, disallow it.
 117                  */
 118                 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 119                         goto split;
 120
 121                 if (sectors + (bv.bv_len >> 9) > max_sectors) {
 122                         /*
 123                          * Consider this a new segment if we're splitting in
 124                          * the middle of this vector.
 125                          */
 126                         if (nsegs < queue_max_segments(q) &&
 127                             sectors < max_sectors) {
 128                                 nsegs++;
 129                                 sectors = max_sectors;
 130                         }
 131                         if (sectors)
 132                                 goto split;
 133                         /* Make this single bvec as the 1st segment */
 134                 }
 135
 136                 if (bvprvp && blk_queue_cluster(q)) {
 137                         if (seg_size + bv.bv_len > queue_max_segment_size(q))
 138                                 goto new_segment;
 139                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
 140                                 goto new_segment;
 141                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
 142                                 goto new_segment;
 143
 144                         seg_size += bv.bv_len;
 145                         bvprv = bv;
 146                         bvprvp = &bvprv;
 147                         sectors += bv.bv_len >> 9;
 148
 149                         if (nsegs == 1 && seg_size > front_seg_size)
 150                                 front_seg_size = seg_size;
 151                         continue;
 152                 }
 153 new_segment:
 154                 if (nsegs == queue_max_segments(q))
 155                         goto split;
 156
 157                 nsegs++;
 158                 bvprv = bv;
 159                 bvprvp = &bvprv;
 160                 seg_size = bv.bv_len;
 161                 sectors += bv.bv_len >> 9;
 162
 163                 if (nsegs == 1 && seg_size > front_seg_size)
 164                         front_seg_size = seg_size;
 165         }
 166
 167         do_split = false;
 168 split:
 169         *segs = nsegs;
 170
 171         if (do_split) {
 172                 new = bio_split(bio, sectors, GFP_NOIO, bs);
 173                 if (new)
 174                         bio = new;
 175         }
 176
 177         bio->bi_seg_front_size = front_seg_size;
 178         if (seg_size > bio->bi_seg_back_size)
 179                 bio->bi_seg_back_size = seg_size;
 180
 181         return do_split ? new : NULL;
 182 }
 183
 184 void blk_queue_split(struct request_queue *q, struct bio **bio)
 185 {
 186         struct bio *split, *res;
 187         unsigned nsegs;
 188
 189         switch (bio_op(*bio)) {
 190         case REQ_OP_DISCARD:
 191         case REQ_OP_SECURE_ERASE:
 192                 split = blk_bio_discard_split(q, *bio, q->bio_split, &nsegs);
 193                 break;
 194         case REQ_OP_WRITE_ZEROES:
 195                 split = blk_bio_write_zeroes_split(q, *bio, q->bio_split, &nsegs);
 196                 break;
 197         case REQ_OP_WRITE_SAME:
 198                 split = blk_bio_write_same_split(q, *bio, q->bio_split, &nsegs);
 199                 break;
 200         default:
 201                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
 202                 break;
 203         }
 204
 205         /* physical segments can be figured out during splitting */
 206         res = split ? split : *bio;
 207         res->bi_phys_segments = nsegs;
 208         bio_set_flag(res, BIO_SEG_VALID);
 209
 210         if (split) {
 211                 /* there isn't chance to merge the splitted bio */
 212                 split->bi_opf |= REQ_NOMERGE;
 213
 214                 bio_chain(split, *bio);
 215                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
 216                 generic_make_request(*bio);
 217                 *bio = split;
 218         }
 219 }
 220 EXPORT_SYMBOL(blk_queue_split);
 221
 222 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 223                                              struct bio *bio,
 224                                              bool no_sg_merge)
 225 {
 226         struct bio_vec bv, bvprv = { NULL };
 227         int cluster, prev = 0;
 228         unsigned int seg_size, nr_phys_segs;
 229         struct bio *fbio, *bbio;
 230         struct bvec_iter iter;
 231
 232         if (!bio)
 233                 return 0;
 234
 235         switch (bio_op(bio)) {
 236         case REQ_OP_DISCARD:
 237         case REQ_OP_SECURE_ERASE:
 238         case REQ_OP_WRITE_ZEROES:
 239                 return 0;
 240         case REQ_OP_WRITE_SAME:
 241                 return 1;
 242         }
 243
 244         fbio = bio;
 245         cluster = blk_queue_cluster(q);
 246         seg_size = 0;
 247         nr_phys_segs = 0;
 248         for_each_bio(bio) {
 249                 bio_for_each_segment(bv, bio, iter) {
 250                         /*
 251                          * If SG merging is disabled, each bio vector is
 252                          * a segment
 253                          */
 254                         if (no_sg_merge)
 255                                 goto new_segment;
 256
 257                         if (prev && cluster) {
 258                                 if (seg_size + bv.bv_len
 259                                     > queue_max_segment_size(q))
 260                                         goto new_segment;
 261                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
 262                                         goto new_segment;
 263                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
 264                                         goto new_segment;
 265
 266                                 seg_size += bv.bv_len;
 267                                 bvprv = bv;
 268                                 continue;
 269                         }
 270 new_segment:
 271                         if (nr_phys_segs == 1 && seg_size >
 272                             fbio->bi_seg_front_size)
 273                                 fbio->bi_seg_front_size = seg_size;
 274
 275                         nr_phys_segs++;
 276                         bvprv = bv;
 277                         prev = 1;
 278                         seg_size = bv.bv_len;
 279                 }
 280                 bbio = bio;
 281         }
 282
 283         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
 284                 fbio->bi_seg_front_size = seg_size;
 285         if (seg_size > bbio->bi_seg_back_size)
 286                 bbio->bi_seg_back_size = seg_size;
 287
 288         return nr_phys_segs;
 289 }
 290
 291 void blk_recalc_rq_segments(struct request *rq)
 292 {
 293         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
 294                         &rq->q->queue_flags);
 295
 296         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
 297                         no_sg_merge);
 298 }
 299
 300 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 301 {
 302         unsigned short seg_cnt;
 303
 304         /* estimate segment number by bi_vcnt for non-cloned bio */
 305         if (bio_flagged(bio, BIO_CLONED))
 306                 seg_cnt = bio_segments(bio);
 307         else
 308                 seg_cnt = bio->bi_vcnt;
 309
 310         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 311                         (seg_cnt < queue_max_segments(q)))
 312                 bio->bi_phys_segments = seg_cnt;
 313         else {
 314                 struct bio *nxt = bio->bi_next;
 315
 316                 bio->bi_next = NULL;
 317                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 318                 bio->bi_next = nxt;
 319         }
 320
 321         bio_set_flag(bio, BIO_SEG_VALID);
 322 }
 323 EXPORT_SYMBOL(blk_recount_segments);
 324
 325 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 326                                    struct bio *nxt)
 327 {
 328         struct bio_vec end_bv = { NULL }, nxt_bv;
 329
 330         if (!blk_queue_cluster(q))
 331                 return 0;
 332
 333         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 334             queue_max_segment_size(q))
 335                 return 0;
 336
 337         if (!bio_has_data(bio))
 338                 return 1;
 339
 340         bio_get_last_bvec(bio, &end_bv);
 341         bio_get_first_bvec(nxt, &nxt_bv);
 342
 343         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 344                 return 0;
 345
 346         /*
 347          * bio and nxt are contiguous in memory; check if the queue allows
 348          * these two to be merged into one
 349          */
 350         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 351                 return 1;
 352
 353         return 0;
 354 }
 355
 356 static inline void
 357 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 358                      struct scatterlist *sglist, struct bio_vec *bvprv,
 359                      struct scatterlist **sg, int *nsegs, int *cluster)
 360 {
 361
 362         int nbytes = bvec->bv_len;
 363
 364         if (*sg && *cluster) {
 365                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 366                         goto new_segment;
 367
 368                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 369                         goto new_segment;
 370                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 371                         goto new_segment;
 372
 373                 (*sg)->length += nbytes;
 374         } else {
 375 new_segment:
 376                 if (!*sg)
 377                         *sg = sglist;
 378                 else {
 379                         /*
 380                          * If the driver previously mapped a shorter
 381                          * list, we could see a termination bit
 382                          * prematurely unless it fully inits the sg
 383                          * table on each mapping. We KNOW that there
 384                          * must be more entries here or the driver
 385                          * would be buggy, so force clear the
 386                          * termination bit to avoid doing a full
 387                          * sg_init_table() in drivers for each command.
 388                          */
 389                         sg_unmark_end(*sg);
 390                         *sg = sg_next(*sg);
 391                 }
 392
 393                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 394                 (*nsegs)++;
 395         }
 396         *bvprv = *bvec;
 397 }
 398
 399 static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
 400                 struct scatterlist *sglist, struct scatterlist **sg)
 401 {
 402         *sg = sglist;
 403         sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
 404         return 1;
 405 }
 406
 407 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 408                              struct scatterlist *sglist,
 409                              struct scatterlist **sg)
 410 {
 411         struct bio_vec bvec, bvprv = { NULL };
 412         struct bvec_iter iter;
 413         int cluster = blk_queue_cluster(q), nsegs = 0;
 414
 415         for_each_bio(bio)
 416                 bio_for_each_segment(bvec, bio, iter)
 417                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 418                                              &nsegs, &cluster);
 419
 420         return nsegs;
 421 }
 422
 423 /*
 424  * map a request to scatterlist, return number of sg entries setup. Caller
 425  * must make sure sg can hold rq->nr_phys_segments entries
 426  */
 427 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 428                   struct scatterlist *sglist)
 429 {
 430         struct scatterlist *sg = NULL;
 431         int nsegs = 0;
 432
 433         if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
 434                 nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
 435         else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
 436                 nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
 437         else if (rq->bio)
 438                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 439
 440         if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
 441             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 442                 unsigned int pad_len =
 443                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 444
 445                 sg->length += pad_len;
 446                 rq->extra_len += pad_len;
 447         }
 448
 449         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 450                 if (op_is_write(req_op(rq)))
 451                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 452
 453                 sg_unmark_end(sg);
 454                 sg = sg_next(sg);
 455                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 456                             q->dma_drain_size,
 457                             ((unsigned long)q->dma_drain_buffer) &
 458                             (PAGE_SIZE - 1));
 459                 nsegs++;
 460                 rq->extra_len += q->dma_drain_size;
 461         }
 462
 463         if (sg)
 464                 sg_mark_end(sg);
 465
 466         /*
 467          * Something must have been wrong if the figured number of
 468          * segment is bigger than number of req's physical segments
 469          */
 470         WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
 471
 472         return nsegs;
 473 }
 474 EXPORT_SYMBOL(blk_rq_map_sg);
 475
 476 static inline int ll_new_hw_segment(struct request_queue *q,
 477                                     struct request *req,
 478                                     struct bio *bio)
 479 {
 480         int nr_phys_segs = bio_phys_segments(q, bio);
 481
 482         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 483                 goto no_merge;
 484
 485         if (blk_integrity_merge_bio(q, req, bio) == false)
 486                 goto no_merge;
 487
 488         /*
 489          * This will form the start of a new hw segment.  Bump both
 490          * counters.
 491          */
 492         req->nr_phys_segments += nr_phys_segs;
 493         return 1;
 494
 495 no_merge:
 496         req_set_nomerge(q, req);
 497         return 0;
 498 }
 499
 500 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 501                      struct bio *bio)
 502 {
 503         if (req_gap_back_merge(req, bio))
 504                 return 0;
 505         if (blk_integrity_rq(req) &&
 506             integrity_req_gap_back_merge(req, bio))
 507                 return 0;
 508         if (blk_rq_sectors(req) + bio_sectors(bio) >
 509             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
 510                 req_set_nomerge(q, req);
 511                 return 0;
 512         }
 513         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 514                 blk_recount_segments(q, req->biotail);
 515         if (!bio_flagged(bio, BIO_SEG_VALID))
 516                 blk_recount_segments(q, bio);
 517
 518         return ll_new_hw_segment(q, req, bio);
 519 }
 520
 521 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 522                       struct bio *bio)
 523 {
 524
 525         if (req_gap_front_merge(req, bio))
 526                 return 0;
 527         if (blk_integrity_rq(req) &&
 528             integrity_req_gap_front_merge(req, bio))
 529                 return 0;
 530         if (blk_rq_sectors(req) + bio_sectors(bio) >
 531             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 532                 req_set_nomerge(q, req);
 533                 return 0;
 534         }
 535         if (!bio_flagged(bio, BIO_SEG_VALID))
 536                 blk_recount_segments(q, bio);
 537         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 538                 blk_recount_segments(q, req->bio);
 539
 540         return ll_new_hw_segment(q, req, bio);
 541 }
 542
 543 /*
 544  * blk-mq uses req->special to carry normal driver per-request payload, it
 545  * does not indicate a prepared command that we cannot merge with.
 546  */
 547 static bool req_no_special_merge(struct request *req)
 548 {
 549         struct request_queue *q = req->q;
 550
 551         return !q->mq_ops && req->special;
 552 }
 553
 554 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
 555                 struct request *next)
 556 {
 557         unsigned short segments = blk_rq_nr_discard_segments(req);
 558
 559         if (segments >= queue_max_discard_segments(q))
 560                 goto no_merge;
 561         if (blk_rq_sectors(req) + bio_sectors(next->bio) >
 562             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 563                 goto no_merge;
 564
 565         req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
 566         return true;
 567 no_merge:
 568         req_set_nomerge(q, req);
 569         return false;
 570 }
 571
 572 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 573                                 struct request *next)
 574 {
 575         int total_phys_segments;
 576         unsigned int seg_size =
 577                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 578
 579         /*
 580          * First check if the either of the requests are re-queued
 581          * requests.  Can't merge them if they are.
 582          */
 583         if (req_no_special_merge(req) || req_no_special_merge(next))
 584                 return 0;
 585
 586         if (req_gap_back_merge(req, next->bio))
 587                 return 0;
 588
 589         /*
 590          * Will it become too large?
 591          */
 592         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 593             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 594                 return 0;
 595
 596         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 597         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 598                 if (req->nr_phys_segments == 1)
 599                         req->bio->bi_seg_front_size = seg_size;
 600                 if (next->nr_phys_segments == 1)
 601                         next->biotail->bi_seg_back_size = seg_size;
 602                 total_phys_segments--;
 603         }
 604
 605         if (total_phys_segments > queue_max_segments(q))
 606                 return 0;
 607
 608         if (blk_integrity_merge_rq(q, req, next) == false)
 609                 return 0;
 610
 611         /* Merge is OK... */
 612         req->nr_phys_segments = total_phys_segments;
 613         return 1;
 614 }
 615
 616 /**
 617  * blk_rq_set_mixed_merge - mark a request as mixed merge
 618  * @rq: request to mark as mixed merge
 619  *
 620  * Description:
 621  *     @rq is about to be mixed merged.  Make sure the attributes
 622  *     which can be mixed are set in each bio and mark @rq as mixed
 623  *     merged.
 624  */
 625 void blk_rq_set_mixed_merge(struct request *rq)
 626 {
 627         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 628         struct bio *bio;
 629
 630         if (rq->rq_flags & RQF_MIXED_MERGE)
 631                 return;
 632
 633         /*
 634          * @rq will no longer represent mixable attributes for all the
 635          * contained bios.  It will just track those of the first one.
 636          * Distributes the attributs to each bio.
 637          */
 638         for (bio = rq->bio; bio; bio = bio->bi_next) {
 639                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
 640                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 641                 bio->bi_opf |= ff;
 642         }
 643         rq->rq_flags |= RQF_MIXED_MERGE;
 644 }
 645
 646 static void blk_account_io_merge(struct request *req)
 647 {
 648         if (blk_do_io_stat(req)) {
 649                 struct hd_struct *part;
 650                 int cpu;
 651
 652                 cpu = part_stat_lock();
 653                 part = req->part;
 654
 655                 part_round_stats(req->q, cpu, part);
 656                 part_dec_in_flight(req->q, part, rq_data_dir(req));
 657
 658                 hd_struct_put(part);
 659                 part_stat_unlock();
 660         }
 661 }
 662
 663 /*
 664  * For non-mq, this has to be called with the request spinlock acquired.
 665  * For mq with scheduling, the appropriate queue wide lock should be held.
 666  */
 667 static struct request *attempt_merge(struct request_queue *q,
 668                                      struct request *req, struct request *next)
 669 {
 670         if (!q->mq_ops)
 671                 lockdep_assert_held(q->queue_lock);
 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          * Don't allow merge of different write hints, or for a hint with
 696          * non-hint IO.
 697          */
 698         if (req->write_hint != next->write_hint)
 699                 return NULL;
 700
 701         /*
 702          * If we are allowed to merge, then append bio list
 703          * from next to rq and release next. merge_requests_fn
 704          * will have updated segment counts, update sector
 705          * counts here. Handle DISCARDs separately, as they
 706          * have separate settings.
 707          */
 708         if (req_op(req) == REQ_OP_DISCARD) {
 709                 if (!req_attempt_discard_merge(q, req, next))
 710                         return NULL;
 711         } else if (!ll_merge_requests_fn(q, req, next))
 712                 return NULL;
 713
 714         /*
 715          * If failfast settings disagree or any of the two is already
 716          * a mixed merge, mark both as mixed before proceeding.  This
 717          * makes sure that all involved bios have mixable attributes
 718          * set properly.
 719          */
 720         if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
 721             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 722             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 723                 blk_rq_set_mixed_merge(req);
 724                 blk_rq_set_mixed_merge(next);
 725         }
 726
 727         /*
 728          * At this point we have either done a back merge
 729          * or front merge. We need the smaller start_time of
 730          * the merged requests to be the current request
 731          * for accounting purposes.
 732          */
 733         if (time_after(req->start_time, next->start_time))
 734                 req->start_time = next->start_time;
 735
 736         req->biotail->bi_next = next->bio;
 737         req->biotail = next->biotail;
 738
 739         req->__data_len += blk_rq_bytes(next);
 740
 741         if (req_op(req) != REQ_OP_DISCARD)
 742                 elv_merge_requests(q, req, next);
 743
 744         /*
 745          * 'next' is going away, so update stats accordingly
 746          */
 747         blk_account_io_merge(next);
 748
 749         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 750         if (blk_rq_cpu_valid(next))
 751                 req->cpu = next->cpu;
 752
 753         /*
 754          * ownership of bio passed from next to req, return 'next' for
 755          * the caller to free
 756          */
 757         next->bio = NULL;
 758         return next;
 759 }
 760
 761 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
 762 {
 763         struct request *next = elv_latter_request(q, rq);
 764
 765         if (next)
 766                 return attempt_merge(q, rq, next);
 767
 768         return NULL;
 769 }
 770
 771 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
 772 {
 773         struct request *prev = elv_former_request(q, rq);
 774
 775         if (prev)
 776                 return attempt_merge(q, prev, rq);
 777
 778         return NULL;
 779 }
 780
 781 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 782                           struct request *next)
 783 {
 784         struct elevator_queue *e = q->elevator;
 785         struct request *free;
 786
 787         if (!e->uses_mq && e->type->ops.sq.elevator_allow_rq_merge_fn)
 788                 if (!e->type->ops.sq.elevator_allow_rq_merge_fn(q, rq, next))
 789                         return 0;
 790
 791         free = attempt_merge(q, rq, next);
 792         if (free) {
 793                 __blk_put_request(q, free);
 794                 return 1;
 795         }
 796
 797         return 0;
 798 }
 799
 800 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 801 {
 802         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 803                 return false;
 804
 805         if (req_op(rq) != bio_op(bio))
 806                 return false;
 807
 808         /* different data direction or already started, don't merge */
 809         if (bio_data_dir(bio) != rq_data_dir(rq))
 810                 return false;
 811
 812         /* must be same device and not a special request */
 813         if (rq->rq_disk != bio->bi_disk || req_no_special_merge(rq))
 814                 return false;
 815
 816         /* only merge integrity protected bio into ditto rq */
 817         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 818                 return false;
 819
 820         /* must be using the same buffer */
 821         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 822             !blk_write_same_mergeable(rq->bio, bio))
 823                 return false;
 824
 825         /*
 826          * Don't allow merge of different write hints, or for a hint with
 827          * non-hint IO.
 828          */
 829         if (rq->write_hint != bio->bi_write_hint)
 830                 return false;
 831
 832         return true;
 833 }
 834
 835 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 836 {
 837         if (req_op(rq) == REQ_OP_DISCARD &&
 838             queue_max_discard_segments(rq->q) > 1)
 839                 return ELEVATOR_DISCARD_MERGE;
 840         else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 841                 return ELEVATOR_BACK_MERGE;
 842         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 843                 return ELEVATOR_FRONT_MERGE;
 844         return ELEVATOR_NO_MERGE;
 845 }