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                         goto split;
 132                 }
 133
 134                 if (bvprvp && blk_queue_cluster(q)) {
 135                         if (seg_size + bv.bv_len > queue_max_segment_size(q))
 136                                 goto new_segment;
 137                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
 138                                 goto new_segment;
 139                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
 140                                 goto new_segment;
 141
 142                         seg_size += bv.bv_len;
 143                         bvprv = bv;
 144                         bvprvp = &bvprv;
 145                         sectors += bv.bv_len >> 9;
 146
 147                         continue;
 148                 }
 149 new_segment:
 150                 if (nsegs == queue_max_segments(q))
 151                         goto split;
 152
 153                 if (nsegs == 1 && seg_size > front_seg_size)
 154                         front_seg_size = seg_size;
 155
 156                 nsegs++;
 157                 bvprv = bv;
 158                 bvprvp = &bvprv;
 159                 seg_size = bv.bv_len;
 160                 sectors += bv.bv_len >> 9;
 161
 162         }
 163
 164         do_split = false;
 165 split:
 166         *segs = nsegs;
 167
 168         if (do_split) {
 169                 new = bio_split(bio, sectors, GFP_NOIO, bs);
 170                 if (new)
 171                         bio = new;
 172         }
 173
 174         if (nsegs == 1 && seg_size > front_seg_size)
 175                 front_seg_size = seg_size;
 176         bio->bi_seg_front_size = front_seg_size;
 177         if (seg_size > bio->bi_seg_back_size)
 178                 bio->bi_seg_back_size = seg_size;
 179
 180         return do_split ? new : NULL;
 181 }
 182
 183 void blk_queue_split(struct request_queue *q, struct bio **bio)
 184 {
 185         struct bio *split, *res;
 186         unsigned nsegs;
 187
 188         switch (bio_op(*bio)) {
 189         case REQ_OP_DISCARD:
 190         case REQ_OP_SECURE_ERASE:
 191                 split = blk_bio_discard_split(q, *bio, q->bio_split, &nsegs);
 192                 break;
 193         case REQ_OP_WRITE_ZEROES:
 194                 split = blk_bio_write_zeroes_split(q, *bio, q->bio_split, &nsegs);
 195                 break;
 196         case REQ_OP_WRITE_SAME:
 197                 split = blk_bio_write_same_split(q, *bio, q->bio_split, &nsegs);
 198                 break;
 199         default:
 200                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
 201                 break;
 202         }
 203
 204         /* physical segments can be figured out during splitting */
 205         res = split ? split : *bio;
 206         res->bi_phys_segments = nsegs;
 207         bio_set_flag(res, BIO_SEG_VALID);
 208
 209         if (split) {
 210                 /* there isn't chance to merge the splitted bio */
 211                 split->bi_opf |= REQ_NOMERGE;
 212
 213                 bio_chain(split, *bio);
 214                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
 215                 generic_make_request(*bio);
 216                 *bio = split;
 217         }
 218 }
 219 EXPORT_SYMBOL(blk_queue_split);
 220
 221 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 222                                              struct bio *bio,
 223                                              bool no_sg_merge)
 224 {
 225         struct bio_vec bv, bvprv = { NULL };
 226         int cluster, prev = 0;
 227         unsigned int seg_size, nr_phys_segs;
 228         struct bio *fbio, *bbio;
 229         struct bvec_iter iter;
 230
 231         if (!bio)
 232                 return 0;
 233
 234         switch (bio_op(bio)) {
 235         case REQ_OP_DISCARD:
 236         case REQ_OP_SECURE_ERASE:
 237         case REQ_OP_WRITE_ZEROES:
 238                 return 0;
 239         case REQ_OP_WRITE_SAME:
 240                 return 1;
 241         }
 242
 243         fbio = bio;
 244         cluster = blk_queue_cluster(q);
 245         seg_size = 0;
 246         nr_phys_segs = 0;
 247         for_each_bio(bio) {
 248                 bio_for_each_segment(bv, bio, iter) {
 249                         /*
 250                          * If SG merging is disabled, each bio vector is
 251                          * a segment
 252                          */
 253                         if (no_sg_merge)
 254                                 goto new_segment;
 255
 256                         if (prev && cluster) {
 257                                 if (seg_size + bv.bv_len
 258                                     > queue_max_segment_size(q))
 259                                         goto new_segment;
 260                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
 261                                         goto new_segment;
 262                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
 263                                         goto new_segment;
 264
 265                                 seg_size += bv.bv_len;
 266                                 bvprv = bv;
 267                                 continue;
 268                         }
 269 new_segment:
 270                         if (nr_phys_segs == 1 && seg_size >
 271                             fbio->bi_seg_front_size)
 272                                 fbio->bi_seg_front_size = seg_size;
 273
 274                         nr_phys_segs++;
 275                         bvprv = bv;
 276                         prev = 1;
 277                         seg_size = bv.bv_len;
 278                 }
 279                 bbio = bio;
 280         }
 281
 282         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
 283                 fbio->bi_seg_front_size = seg_size;
 284         if (seg_size > bbio->bi_seg_back_size)
 285                 bbio->bi_seg_back_size = seg_size;
 286
 287         return nr_phys_segs;
 288 }
 289
 290 void blk_recalc_rq_segments(struct request *rq)
 291 {
 292         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
 293                         &rq->q->queue_flags);
 294
 295         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
 296                         no_sg_merge);
 297 }
 298
 299 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 300 {
 301         unsigned short seg_cnt;
 302
 303         /* estimate segment number by bi_vcnt for non-cloned bio */
 304         if (bio_flagged(bio, BIO_CLONED))
 305                 seg_cnt = bio_segments(bio);
 306         else
 307                 seg_cnt = bio->bi_vcnt;
 308
 309         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 310                         (seg_cnt < queue_max_segments(q)))
 311                 bio->bi_phys_segments = seg_cnt;
 312         else {
 313                 struct bio *nxt = bio->bi_next;
 314
 315                 bio->bi_next = NULL;
 316                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 317                 bio->bi_next = nxt;
 318         }
 319
 320         bio_set_flag(bio, BIO_SEG_VALID);
 321 }
 322 EXPORT_SYMBOL(blk_recount_segments);
 323
 324 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 325                                    struct bio *nxt)
 326 {
 327         struct bio_vec end_bv = { NULL }, nxt_bv;
 328
 329         if (!blk_queue_cluster(q))
 330                 return 0;
 331
 332         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 333             queue_max_segment_size(q))
 334                 return 0;
 335
 336         if (!bio_has_data(bio))
 337                 return 1;
 338
 339         bio_get_last_bvec(bio, &end_bv);
 340         bio_get_first_bvec(nxt, &nxt_bv);
 341
 342         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 343                 return 0;
 344
 345         /*
 346          * bio and nxt are contiguous in memory; check if the queue allows
 347          * these two to be merged into one
 348          */
 349         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 350                 return 1;
 351
 352         return 0;
 353 }
 354
 355 static inline void
 356 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 357                      struct scatterlist *sglist, struct bio_vec *bvprv,
 358                      struct scatterlist **sg, int *nsegs, int *cluster)
 359 {
 360
 361         int nbytes = bvec->bv_len;
 362
 363         if (*sg && *cluster) {
 364                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 365                         goto new_segment;
 366
 367                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 368                         goto new_segment;
 369                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 370                         goto new_segment;
 371
 372                 (*sg)->length += nbytes;
 373         } else {
 374 new_segment:
 375                 if (!*sg)
 376                         *sg = sglist;
 377                 else {
 378                         /*
 379                          * If the driver previously mapped a shorter
 380                          * list, we could see a termination bit
 381                          * prematurely unless it fully inits the sg
 382                          * table on each mapping. We KNOW that there
 383                          * must be more entries here or the driver
 384                          * would be buggy, so force clear the
 385                          * termination bit to avoid doing a full
 386                          * sg_init_table() in drivers for each command.
 387                          */
 388                         sg_unmark_end(*sg);
 389                         *sg = sg_next(*sg);
 390                 }
 391
 392                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 393                 (*nsegs)++;
 394         }
 395         *bvprv = *bvec;
 396 }
 397
 398 static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
 399                 struct scatterlist *sglist, struct scatterlist **sg)
 400 {
 401         *sg = sglist;
 402         sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
 403         return 1;
 404 }
 405
 406 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 407                              struct scatterlist *sglist,
 408                              struct scatterlist **sg)
 409 {
 410         struct bio_vec bvec, bvprv = { NULL };
 411         struct bvec_iter iter;
 412         int cluster = blk_queue_cluster(q), nsegs = 0;
 413
 414         for_each_bio(bio)
 415                 bio_for_each_segment(bvec, bio, iter)
 416                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 417                                              &nsegs, &cluster);
 418
 419         return nsegs;
 420 }
 421
 422 /*
 423  * map a request to scatterlist, return number of sg entries setup. Caller
 424  * must make sure sg can hold rq->nr_phys_segments entries
 425  */
 426 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 427                   struct scatterlist *sglist)
 428 {
 429         struct scatterlist *sg = NULL;
 430         int nsegs = 0;
 431
 432         if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
 433                 nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
 434         else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
 435                 nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
 436         else if (rq->bio)
 437                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 438
 439         if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
 440             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 441                 unsigned int pad_len =
 442                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 443
 444                 sg->length += pad_len;
 445                 rq->extra_len += pad_len;
 446         }
 447
 448         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 449                 if (op_is_write(req_op(rq)))
 450                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 451
 452                 sg_unmark_end(sg);
 453                 sg = sg_next(sg);
 454                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 455                             q->dma_drain_size,
 456                             ((unsigned long)q->dma_drain_buffer) &
 457                             (PAGE_SIZE - 1));
 458                 nsegs++;
 459                 rq->extra_len += q->dma_drain_size;
 460         }
 461
 462         if (sg)
 463                 sg_mark_end(sg);
 464
 465         /*
 466          * Something must have been wrong if the figured number of
 467          * segment is bigger than number of req's physical segments
 468          */
 469         WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
 470
 471         return nsegs;
 472 }
 473 EXPORT_SYMBOL(blk_rq_map_sg);
 474
 475 static inline int ll_new_hw_segment(struct request_queue *q,
 476                                     struct request *req,
 477                                     struct bio *bio)
 478 {
 479         int nr_phys_segs = bio_phys_segments(q, bio);
 480
 481         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 482                 goto no_merge;
 483
 484         if (blk_integrity_merge_bio(q, req, bio) == false)
 485                 goto no_merge;
 486
 487         /*
 488          * This will form the start of a new hw segment.  Bump both
 489          * counters.
 490          */
 491         req->nr_phys_segments += nr_phys_segs;
 492         return 1;
 493
 494 no_merge:
 495         req_set_nomerge(q, req);
 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_set_nomerge(q, req);
 510                 return 0;
 511         }
 512         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 513                 blk_recount_segments(q, req->biotail);
 514         if (!bio_flagged(bio, BIO_SEG_VALID))
 515                 blk_recount_segments(q, bio);
 516
 517         return ll_new_hw_segment(q, req, bio);
 518 }
 519
 520 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 521                       struct bio *bio)
 522 {
 523
 524         if (req_gap_front_merge(req, bio))
 525                 return 0;
 526         if (blk_integrity_rq(req) &&
 527             integrity_req_gap_front_merge(req, bio))
 528                 return 0;
 529         if (blk_rq_sectors(req) + bio_sectors(bio) >
 530             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 531                 req_set_nomerge(q, req);
 532                 return 0;
 533         }
 534         if (!bio_flagged(bio, BIO_SEG_VALID))
 535                 blk_recount_segments(q, bio);
 536         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 537                 blk_recount_segments(q, req->bio);
 538
 539         return ll_new_hw_segment(q, req, bio);
 540 }
 541
 542 /*
 543  * blk-mq uses req->special to carry normal driver per-request payload, it
 544  * does not indicate a prepared command that we cannot merge with.
 545  */
 546 static bool req_no_special_merge(struct request *req)
 547 {
 548         struct request_queue *q = req->q;
 549
 550         return !q->mq_ops && req->special;
 551 }
 552
 553 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
 554                 struct request *next)
 555 {
 556         unsigned short segments = blk_rq_nr_discard_segments(req);
 557
 558         if (segments >= queue_max_discard_segments(q))
 559                 goto no_merge;
 560         if (blk_rq_sectors(req) + bio_sectors(next->bio) >
 561             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 562                 goto no_merge;
 563
 564         req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
 565         return true;
 566 no_merge:
 567         req_set_nomerge(q, req);
 568         return false;
 569 }
 570
 571 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 572                                 struct request *next)
 573 {
 574         int total_phys_segments;
 575         unsigned int seg_size =
 576                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 577
 578         /*
 579          * First check if the either of the requests are re-queued
 580          * requests.  Can't merge them if they are.
 581          */
 582         if (req_no_special_merge(req) || req_no_special_merge(next))
 583                 return 0;
 584
 585         if (req_gap_back_merge(req, next->bio))
 586                 return 0;
 587
 588         /*
 589          * Will it become too large?
 590          */
 591         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 592             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 593                 return 0;
 594
 595         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 596         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 597                 if (req->nr_phys_segments == 1)
 598                         req->bio->bi_seg_front_size = seg_size;
 599                 if (next->nr_phys_segments == 1)
 600                         next->biotail->bi_seg_back_size = seg_size;
 601                 total_phys_segments--;
 602         }
 603
 604         if (total_phys_segments > queue_max_segments(q))
 605                 return 0;
 606
 607         if (blk_integrity_merge_rq(q, req, next) == false)
 608                 return 0;
 609
 610         /* Merge is OK... */
 611         req->nr_phys_segments = total_phys_segments;
 612         return 1;
 613 }
 614
 615 /**
 616  * blk_rq_set_mixed_merge - mark a request as mixed merge
 617  * @rq: request to mark as mixed merge
 618  *
 619  * Description:
 620  *     @rq is about to be mixed merged.  Make sure the attributes
 621  *     which can be mixed are set in each bio and mark @rq as mixed
 622  *     merged.
 623  */
 624 void blk_rq_set_mixed_merge(struct request *rq)
 625 {
 626         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 627         struct bio *bio;
 628
 629         if (rq->rq_flags & RQF_MIXED_MERGE)
 630                 return;
 631
 632         /*
 633          * @rq will no longer represent mixable attributes for all the
 634          * contained bios.  It will just track those of the first one.
 635          * Distributes the attributs to each bio.
 636          */
 637         for (bio = rq->bio; bio; bio = bio->bi_next) {
 638                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
 639                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 640                 bio->bi_opf |= ff;
 641         }
 642         rq->rq_flags |= RQF_MIXED_MERGE;
 643 }
 644
 645 static void blk_account_io_merge(struct request *req)
 646 {
 647         if (blk_do_io_stat(req)) {
 648                 struct hd_struct *part;
 649                 int cpu;
 650
 651                 cpu = part_stat_lock();
 652                 part = req->part;
 653
 654                 part_round_stats(req->q, cpu, part);
 655                 part_dec_in_flight(req->q, part, rq_data_dir(req));
 656
 657                 hd_struct_put(part);
 658                 part_stat_unlock();
 659         }
 660 }
 661
 662 /*
 663  * For non-mq, this has to be called with the request spinlock acquired.
 664  * For mq with scheduling, the appropriate queue wide lock should be held.
 665  */
 666 static struct request *attempt_merge(struct request_queue *q,
 667                                      struct request *req, struct request *next)
 668 {
 669         if (!q->mq_ops)
 670                 lockdep_assert_held(q->queue_lock);
 671
 672         if (!rq_mergeable(req) || !rq_mergeable(next))
 673                 return NULL;
 674
 675         if (req_op(req) != req_op(next))
 676                 return NULL;
 677
 678         /*
 679          * not contiguous
 680          */
 681         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 682                 return NULL;
 683
 684         if (rq_data_dir(req) != rq_data_dir(next)
 685             || req->rq_disk != next->rq_disk
 686             || req_no_special_merge(next))
 687                 return NULL;
 688
 689         if (req_op(req) == REQ_OP_WRITE_SAME &&
 690             !blk_write_same_mergeable(req->bio, next->bio))
 691                 return NULL;
 692
 693         /*
 694          * Don't allow merge of different write hints, or for a hint with
 695          * non-hint IO.
 696          */
 697         if (req->write_hint != next->write_hint)
 698                 return NULL;
 699
 700         /*
 701          * If we are allowed to merge, then append bio list
 702          * from next to rq and release next. merge_requests_fn
 703          * will have updated segment counts, update sector
 704          * counts here. Handle DISCARDs separately, as they
 705          * have separate settings.
 706          */
 707         if (req_op(req) == REQ_OP_DISCARD) {
 708                 if (!req_attempt_discard_merge(q, req, next))
 709                         return NULL;
 710         } else if (!ll_merge_requests_fn(q, req, next))
 711                 return NULL;
 712
 713         /*
 714          * If failfast settings disagree or any of the two is already
 715          * a mixed merge, mark both as mixed before proceeding.  This
 716          * makes sure that all involved bios have mixable attributes
 717          * set properly.
 718          */
 719         if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
 720             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 721             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 722                 blk_rq_set_mixed_merge(req);
 723                 blk_rq_set_mixed_merge(next);
 724         }
 725
 726         /*
 727          * At this point we have either done a back merge
 728          * or front merge. We need the smaller start_time of
 729          * the merged requests to be the current request
 730          * for accounting purposes.
 731          */
 732         if (time_after(req->start_time, next->start_time))
 733                 req->start_time = next->start_time;
 734
 735         req->biotail->bi_next = next->bio;
 736         req->biotail = next->biotail;
 737
 738         req->__data_len += blk_rq_bytes(next);
 739
 740         if (req_op(req) != REQ_OP_DISCARD)
 741                 elv_merge_requests(q, req, next);
 742
 743         /*
 744          * 'next' is going away, so update stats accordingly
 745          */
 746         blk_account_io_merge(next);
 747
 748         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 749         if (blk_rq_cpu_valid(next))
 750                 req->cpu = next->cpu;
 751
 752         /*
 753          * ownership of bio passed from next to req, return 'next' for
 754          * the caller to free
 755          */
 756         next->bio = NULL;
 757         return next;
 758 }
 759
 760 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
 761 {
 762         struct request *next = elv_latter_request(q, rq);
 763
 764         if (next)
 765                 return attempt_merge(q, rq, next);
 766
 767         return NULL;
 768 }
 769
 770 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
 771 {
 772         struct request *prev = elv_former_request(q, rq);
 773
 774         if (prev)
 775                 return attempt_merge(q, prev, rq);
 776
 777         return NULL;
 778 }
 779
 780 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 781                           struct request *next)
 782 {
 783         struct elevator_queue *e = q->elevator;
 784         struct request *free;
 785
 786         if (!e->uses_mq && e->type->ops.sq.elevator_allow_rq_merge_fn)
 787                 if (!e->type->ops.sq.elevator_allow_rq_merge_fn(q, rq, next))
 788                         return 0;
 789
 790         free = attempt_merge(q, rq, next);
 791         if (free) {
 792                 __blk_put_request(q, free);
 793                 return 1;
 794         }
 795
 796         return 0;
 797 }
 798
 799 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 800 {
 801         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 802                 return false;
 803
 804         if (req_op(rq) != bio_op(bio))
 805                 return false;
 806
 807         /* different data direction or already started, don't merge */
 808         if (bio_data_dir(bio) != rq_data_dir(rq))
 809                 return false;
 810
 811         /* must be same device and not a special request */
 812         if (rq->rq_disk != bio->bi_disk || req_no_special_merge(rq))
 813                 return false;
 814
 815         /* only merge integrity protected bio into ditto rq */
 816         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 817                 return false;
 818
 819         /* must be using the same buffer */
 820         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 821             !blk_write_same_mergeable(rq->bio, bio))
 822                 return false;
 823
 824         /*
 825          * Don't allow merge of different write hints, or for a hint with
 826          * non-hint IO.
 827          */
 828         if (rq->write_hint != bio->bi_write_hint)
 829                 return false;
 830
 831         return true;
 832 }
 833
 834 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 835 {
 836         if (req_op(rq) == REQ_OP_DISCARD &&
 837             queue_max_discard_segments(rq->q) > 1)
 838                 return ELEVATOR_DISCARD_MERGE;
 839         else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 840                 return ELEVATOR_BACK_MERGE;
 841         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 842                 return ELEVATOR_FRONT_MERGE;
 843         return ELEVATOR_NO_MERGE;
 844 }