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 = bio_segments(bio);
 303
 304         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 305                         (seg_cnt < queue_max_segments(q)))
 306                 bio->bi_phys_segments = seg_cnt;
 307         else {
 308                 struct bio *nxt = bio->bi_next;
 309
 310                 bio->bi_next = NULL;
 311                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 312                 bio->bi_next = nxt;
 313         }
 314
 315         bio_set_flag(bio, BIO_SEG_VALID);
 316 }
 317 EXPORT_SYMBOL(blk_recount_segments);
 318
 319 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 320                                    struct bio *nxt)
 321 {
 322         struct bio_vec end_bv = { NULL }, nxt_bv;
 323
 324         if (!blk_queue_cluster(q))
 325                 return 0;
 326
 327         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 328             queue_max_segment_size(q))
 329                 return 0;
 330
 331         if (!bio_has_data(bio))
 332                 return 1;
 333
 334         bio_get_last_bvec(bio, &end_bv);
 335         bio_get_first_bvec(nxt, &nxt_bv);
 336
 337         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 338                 return 0;
 339
 340         /*
 341          * bio and nxt are contiguous in memory; check if the queue allows
 342          * these two to be merged into one
 343          */
 344         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 345                 return 1;
 346
 347         return 0;
 348 }
 349
 350 static inline void
 351 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 352                      struct scatterlist *sglist, struct bio_vec *bvprv,
 353                      struct scatterlist **sg, int *nsegs, int *cluster)
 354 {
 355
 356         int nbytes = bvec->bv_len;
 357
 358         if (*sg && *cluster) {
 359                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 360                         goto new_segment;
 361
 362                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 363                         goto new_segment;
 364                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 365                         goto new_segment;
 366
 367                 (*sg)->length += nbytes;
 368         } else {
 369 new_segment:
 370                 if (!*sg)
 371                         *sg = sglist;
 372                 else {
 373                         /*
 374                          * If the driver previously mapped a shorter
 375                          * list, we could see a termination bit
 376                          * prematurely unless it fully inits the sg
 377                          * table on each mapping. We KNOW that there
 378                          * must be more entries here or the driver
 379                          * would be buggy, so force clear the
 380                          * termination bit to avoid doing a full
 381                          * sg_init_table() in drivers for each command.
 382                          */
 383                         sg_unmark_end(*sg);
 384                         *sg = sg_next(*sg);
 385                 }
 386
 387                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 388                 (*nsegs)++;
 389         }
 390         *bvprv = *bvec;
 391 }
 392
 393 static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
 394                 struct scatterlist *sglist, struct scatterlist **sg)
 395 {
 396         *sg = sglist;
 397         sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
 398         return 1;
 399 }
 400
 401 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 402                              struct scatterlist *sglist,
 403                              struct scatterlist **sg)
 404 {
 405         struct bio_vec bvec, bvprv = { NULL };
 406         struct bvec_iter iter;
 407         int cluster = blk_queue_cluster(q), nsegs = 0;
 408
 409         for_each_bio(bio)
 410                 bio_for_each_segment(bvec, bio, iter)
 411                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 412                                              &nsegs, &cluster);
 413
 414         return nsegs;
 415 }
 416
 417 /*
 418  * map a request to scatterlist, return number of sg entries setup. Caller
 419  * must make sure sg can hold rq->nr_phys_segments entries
 420  */
 421 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 422                   struct scatterlist *sglist)
 423 {
 424         struct scatterlist *sg = NULL;
 425         int nsegs = 0;
 426
 427         if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
 428                 nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
 429         else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
 430                 nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
 431         else if (rq->bio)
 432                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 433
 434         if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
 435             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 436                 unsigned int pad_len =
 437                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 438
 439                 sg->length += pad_len;
 440                 rq->extra_len += pad_len;
 441         }
 442
 443         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 444                 if (op_is_write(req_op(rq)))
 445                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 446
 447                 sg_unmark_end(sg);
 448                 sg = sg_next(sg);
 449                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 450                             q->dma_drain_size,
 451                             ((unsigned long)q->dma_drain_buffer) &
 452                             (PAGE_SIZE - 1));
 453                 nsegs++;
 454                 rq->extra_len += q->dma_drain_size;
 455         }
 456
 457         if (sg)
 458                 sg_mark_end(sg);
 459
 460         /*
 461          * Something must have been wrong if the figured number of
 462          * segment is bigger than number of req's physical segments
 463          */
 464         WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
 465
 466         return nsegs;
 467 }
 468 EXPORT_SYMBOL(blk_rq_map_sg);
 469
 470 static inline int ll_new_hw_segment(struct request_queue *q,
 471                                     struct request *req,
 472                                     struct bio *bio)
 473 {
 474         int nr_phys_segs = bio_phys_segments(q, bio);
 475
 476         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 477                 goto no_merge;
 478
 479         if (blk_integrity_merge_bio(q, req, bio) == false)
 480                 goto no_merge;
 481
 482         /*
 483          * This will form the start of a new hw segment.  Bump both
 484          * counters.
 485          */
 486         req->nr_phys_segments += nr_phys_segs;
 487         return 1;
 488
 489 no_merge:
 490         req_set_nomerge(q, req);
 491         return 0;
 492 }
 493
 494 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 495                      struct bio *bio)
 496 {
 497         if (req_gap_back_merge(req, bio))
 498                 return 0;
 499         if (blk_integrity_rq(req) &&
 500             integrity_req_gap_back_merge(req, bio))
 501                 return 0;
 502         if (blk_rq_sectors(req) + bio_sectors(bio) >
 503             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
 504                 req_set_nomerge(q, req);
 505                 return 0;
 506         }
 507         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 508                 blk_recount_segments(q, req->biotail);
 509         if (!bio_flagged(bio, BIO_SEG_VALID))
 510                 blk_recount_segments(q, bio);
 511
 512         return ll_new_hw_segment(q, req, bio);
 513 }
 514
 515 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 516                       struct bio *bio)
 517 {
 518
 519         if (req_gap_front_merge(req, bio))
 520                 return 0;
 521         if (blk_integrity_rq(req) &&
 522             integrity_req_gap_front_merge(req, bio))
 523                 return 0;
 524         if (blk_rq_sectors(req) + bio_sectors(bio) >
 525             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 526                 req_set_nomerge(q, req);
 527                 return 0;
 528         }
 529         if (!bio_flagged(bio, BIO_SEG_VALID))
 530                 blk_recount_segments(q, bio);
 531         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 532                 blk_recount_segments(q, req->bio);
 533
 534         return ll_new_hw_segment(q, req, bio);
 535 }
 536
 537 /*
 538  * blk-mq uses req->special to carry normal driver per-request payload, it
 539  * does not indicate a prepared command that we cannot merge with.
 540  */
 541 static bool req_no_special_merge(struct request *req)
 542 {
 543         struct request_queue *q = req->q;
 544
 545         return !q->mq_ops && req->special;
 546 }
 547
 548 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
 549                 struct request *next)
 550 {
 551         unsigned short segments = blk_rq_nr_discard_segments(req);
 552
 553         if (segments >= queue_max_discard_segments(q))
 554                 goto no_merge;
 555         if (blk_rq_sectors(req) + bio_sectors(next->bio) >
 556             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 557                 goto no_merge;
 558
 559         req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
 560         return true;
 561 no_merge:
 562         req_set_nomerge(q, req);
 563         return false;
 564 }
 565
 566 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 567                                 struct request *next)
 568 {
 569         int total_phys_segments;
 570         unsigned int seg_size =
 571                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 572
 573         /*
 574          * First check if the either of the requests are re-queued
 575          * requests.  Can't merge them if they are.
 576          */
 577         if (req_no_special_merge(req) || req_no_special_merge(next))
 578                 return 0;
 579
 580         if (req_gap_back_merge(req, next->bio))
 581                 return 0;
 582
 583         /*
 584          * Will it become too large?
 585          */
 586         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 587             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 588                 return 0;
 589
 590         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 591         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 592                 if (req->nr_phys_segments == 1)
 593                         req->bio->bi_seg_front_size = seg_size;
 594                 if (next->nr_phys_segments == 1)
 595                         next->biotail->bi_seg_back_size = seg_size;
 596                 total_phys_segments--;
 597         }
 598
 599         if (total_phys_segments > queue_max_segments(q))
 600                 return 0;
 601
 602         if (blk_integrity_merge_rq(q, req, next) == false)
 603                 return 0;
 604
 605         /* Merge is OK... */
 606         req->nr_phys_segments = total_phys_segments;
 607         return 1;
 608 }
 609
 610 /**
 611  * blk_rq_set_mixed_merge - mark a request as mixed merge
 612  * @rq: request to mark as mixed merge
 613  *
 614  * Description:
 615  *     @rq is about to be mixed merged.  Make sure the attributes
 616  *     which can be mixed are set in each bio and mark @rq as mixed
 617  *     merged.
 618  */
 619 void blk_rq_set_mixed_merge(struct request *rq)
 620 {
 621         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 622         struct bio *bio;
 623
 624         if (rq->rq_flags & RQF_MIXED_MERGE)
 625                 return;
 626
 627         /*
 628          * @rq will no longer represent mixable attributes for all the
 629          * contained bios.  It will just track those of the first one.
 630          * Distributes the attributs to each bio.
 631          */
 632         for (bio = rq->bio; bio; bio = bio->bi_next) {
 633                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
 634                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 635                 bio->bi_opf |= ff;
 636         }
 637         rq->rq_flags |= RQF_MIXED_MERGE;
 638 }
 639
 640 static void blk_account_io_merge(struct request *req)
 641 {
 642         if (blk_do_io_stat(req)) {
 643                 struct hd_struct *part;
 644                 int cpu;
 645
 646                 cpu = part_stat_lock();
 647                 part = req->part;
 648
 649                 part_round_stats(req->q, cpu, part);
 650                 part_dec_in_flight(req->q, part, rq_data_dir(req));
 651
 652                 hd_struct_put(part);
 653                 part_stat_unlock();
 654         }
 655 }
 656 /*
 657  * Two cases of handling DISCARD merge:
 658  * If max_discard_segments > 1, the driver takes every bio
 659  * as a range and send them to controller together. The ranges
 660  * needn't to be contiguous.
 661  * Otherwise, the bios/requests will be handled as same as
 662  * others which should be contiguous.
 663  */
 664 static inline bool blk_discard_mergable(struct request *req)
 665 {
 666         if (req_op(req) == REQ_OP_DISCARD &&
 667             queue_max_discard_segments(req->q) > 1)
 668                 return true;
 669         return false;
 670 }
 671
 672 enum elv_merge blk_try_req_merge(struct request *req, struct request *next)
 673 {
 674         if (blk_discard_mergable(req))
 675                 return ELEVATOR_DISCARD_MERGE;
 676         else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
 677                 return ELEVATOR_BACK_MERGE;
 678
 679         return ELEVATOR_NO_MERGE;
 680 }
 681
 682 /*
 683  * For non-mq, this has to be called with the request spinlock acquired.
 684  * For mq with scheduling, the appropriate queue wide lock should be held.
 685  */
 686 static struct request *attempt_merge(struct request_queue *q,
 687                                      struct request *req, struct request *next)
 688 {
 689         if (!q->mq_ops)
 690                 lockdep_assert_held(q->queue_lock);
 691
 692         if (!rq_mergeable(req) || !rq_mergeable(next))
 693                 return NULL;
 694
 695         if (req_op(req) != req_op(next))
 696                 return NULL;
 697
 698         if (rq_data_dir(req) != rq_data_dir(next)
 699             || req->rq_disk != next->rq_disk
 700             || req_no_special_merge(next))
 701                 return NULL;
 702
 703         if (req_op(req) == REQ_OP_WRITE_SAME &&
 704             !blk_write_same_mergeable(req->bio, next->bio))
 705                 return NULL;
 706
 707         /*
 708          * Don't allow merge of different write hints, or for a hint with
 709          * non-hint IO.
 710          */
 711         if (req->write_hint != next->write_hint)
 712                 return NULL;
 713
 714         /*
 715          * If we are allowed to merge, then append bio list
 716          * from next to rq and release next. merge_requests_fn
 717          * will have updated segment counts, update sector
 718          * counts here. Handle DISCARDs separately, as they
 719          * have separate settings.
 720          */
 721
 722         switch (blk_try_req_merge(req, next)) {
 723         case ELEVATOR_DISCARD_MERGE:
 724                 if (!req_attempt_discard_merge(q, req, next))
 725                         return NULL;
 726                 break;
 727         case ELEVATOR_BACK_MERGE:
 728                 if (!ll_merge_requests_fn(q, req, next))
 729                         return NULL;
 730                 break;
 731         default:
 732                 return NULL;
 733         }
 734
 735         /*
 736          * If failfast settings disagree or any of the two is already
 737          * a mixed merge, mark both as mixed before proceeding.  This
 738          * makes sure that all involved bios have mixable attributes
 739          * set properly.
 740          */
 741         if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
 742             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 743             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 744                 blk_rq_set_mixed_merge(req);
 745                 blk_rq_set_mixed_merge(next);
 746         }
 747
 748         /*
 749          * At this point we have either done a back merge
 750          * or front merge. We need the smaller start_time of
 751          * the merged requests to be the current request
 752          * for accounting purposes.
 753          */
 754         if (time_after(req->start_time, next->start_time))
 755                 req->start_time = next->start_time;
 756
 757         req->biotail->bi_next = next->bio;
 758         req->biotail = next->biotail;
 759
 760         req->__data_len += blk_rq_bytes(next);
 761
 762         if (!blk_discard_mergable(req))
 763                 elv_merge_requests(q, req, next);
 764
 765         /*
 766          * 'next' is going away, so update stats accordingly
 767          */
 768         blk_account_io_merge(next);
 769
 770         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 771         if (blk_rq_cpu_valid(next))
 772                 req->cpu = next->cpu;
 773
 774         /*
 775          * ownership of bio passed from next to req, return 'next' for
 776          * the caller to free
 777          */
 778         next->bio = NULL;
 779         return next;
 780 }
 781
 782 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
 783 {
 784         struct request *next = elv_latter_request(q, rq);
 785
 786         if (next)
 787                 return attempt_merge(q, rq, next);
 788
 789         return NULL;
 790 }
 791
 792 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
 793 {
 794         struct request *prev = elv_former_request(q, rq);
 795
 796         if (prev)
 797                 return attempt_merge(q, prev, rq);
 798
 799         return NULL;
 800 }
 801
 802 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 803                           struct request *next)
 804 {
 805         struct elevator_queue *e = q->elevator;
 806         struct request *free;
 807
 808         if (!e->uses_mq && e->type->ops.sq.elevator_allow_rq_merge_fn)
 809                 if (!e->type->ops.sq.elevator_allow_rq_merge_fn(q, rq, next))
 810                         return 0;
 811
 812         free = attempt_merge(q, rq, next);
 813         if (free) {
 814                 __blk_put_request(q, free);
 815                 return 1;
 816         }
 817
 818         return 0;
 819 }
 820
 821 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 822 {
 823         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 824                 return false;
 825
 826         if (req_op(rq) != bio_op(bio))
 827                 return false;
 828
 829         /* different data direction or already started, don't merge */
 830         if (bio_data_dir(bio) != rq_data_dir(rq))
 831                 return false;
 832
 833         /* must be same device and not a special request */
 834         if (rq->rq_disk != bio->bi_disk || req_no_special_merge(rq))
 835                 return false;
 836
 837         /* only merge integrity protected bio into ditto rq */
 838         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 839                 return false;
 840
 841         /* must be using the same buffer */
 842         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 843             !blk_write_same_mergeable(rq->bio, bio))
 844                 return false;
 845
 846         /*
 847          * Don't allow merge of different write hints, or for a hint with
 848          * non-hint IO.
 849          */
 850         if (rq->write_hint != bio->bi_write_hint)
 851                 return false;
 852
 853         return true;
 854 }
 855
 856 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 857 {
 858         if (blk_discard_mergable(rq))
 859                 return ELEVATOR_DISCARD_MERGE;
 860         else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 861                 return ELEVATOR_BACK_MERGE;
 862         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 863                 return ELEVATOR_FRONT_MERGE;
 864         return ELEVATOR_NO_MERGE;
 865 }