block/blk-merge.c

   1 /*
   2  * Functions related to segment and merge handling
   3  */
   4 #include <linux/kernel.h>
   5 #include <linux/module.h>
   6 #include <linux/bio.h>
   7 #include <linux/blkdev.h>
   8 #include <linux/scatterlist.h>
   9
  10 #include <trace/events/block.h>
  11
  12 #include "blk.h"
  13
  14 static struct bio *blk_bio_discard_split(struct request_queue *q,
  15                                          struct bio *bio,
  16                                          struct bio_set *bs,
  17                                          unsigned *nsegs)
  18 {
  19         unsigned int max_discard_sectors, granularity;
  20         int alignment;
  21         sector_t tmp;
  22         unsigned split_sectors;
  23
  24         *nsegs = 1;
  25
  26         /* Zero-sector (unknown) and one-sector granularities are the same.  */
  27         granularity = max(q->limits.discard_granularity >> 9, 1U);
  28
  29         max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
  30         max_discard_sectors -= max_discard_sectors % granularity;
  31
  32         if (unlikely(!max_discard_sectors)) {
  33                 /* XXX: warn */
  34                 return NULL;
  35         }
  36
  37         if (bio_sectors(bio) <= max_discard_sectors)
  38                 return NULL;
  39
  40         split_sectors = max_discard_sectors;
  41
  42         /*
  43          * If the next starting sector would be misaligned, stop the discard at
  44          * the previous aligned sector.
  45          */
  46         alignment = (q->limits.discard_alignment >> 9) % granularity;
  47
  48         tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
  49         tmp = sector_div(tmp, granularity);
  50
  51         if (split_sectors > tmp)
  52                 split_sectors -= tmp;
  53
  54         return bio_split(bio, split_sectors, GFP_NOIO, bs);
  55 }
  56
  57 static struct bio *blk_bio_write_same_split(struct request_queue *q,
  58                                             struct bio *bio,
  59                                             struct bio_set *bs,
  60                                             unsigned *nsegs)
  61 {
  62         *nsegs = 1;
  63
  64         if (!q->limits.max_write_same_sectors)
  65                 return NULL;
  66
  67         if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
  68                 return NULL;
  69
  70         return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
  71 }
  72
  73 static inline unsigned get_max_io_size(struct request_queue *q,
  74                                        struct bio *bio)
  75 {
  76         unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
  77         unsigned mask = queue_logical_block_size(q) - 1;
  78
  79         /* aligned to logical block size */
  80         sectors &= ~(mask >> 9);
  81
  82         return sectors;
  83 }
  84
  85 static struct bio *blk_bio_segment_split(struct request_queue *q,
  86                                          struct bio *bio,
  87                                          struct bio_set *bs,
  88                                          unsigned *segs)
  89 {
  90         struct bio_vec bv, bvprv, *bvprvp = NULL;
  91         struct bvec_iter iter;
  92         unsigned seg_size = 0, nsegs = 0, sectors = 0;
  93         unsigned front_seg_size = bio->bi_seg_front_size;
  94         bool do_split = true;
  95         struct bio *new = NULL;
  96         const unsigned max_sectors = get_max_io_size(q, bio);
  97         unsigned bvecs = 0;
  98
  99         bio_for_each_segment(bv, bio, iter) {
 100                 /*
 101                  * With arbitrary bio size, the incoming bio may be very
 102                  * big. We have to split the bio into small bios so that
 103                  * each holds at most BIO_MAX_PAGES bvecs because
 104                  * bio_clone() can fail to allocate big bvecs.
 105                  *
 106                  * It should have been better to apply the limit per
 107                  * request queue in which bio_clone() is involved,
 108                  * instead of globally. The biggest blocker is the
 109                  * bio_clone() in bio bounce.
 110                  *
 111                  * If bio is splitted by this reason, we should have
 112                  * allowed to continue bios merging, but don't do
 113                  * that now for making the change simple.
 114                  *
 115                  * TODO: deal with bio bounce's bio_clone() gracefully
 116                  * and convert the global limit into per-queue limit.
 117                  */
 118                 if (bvecs++ >= BIO_MAX_PAGES)
 119                         goto split;
 120
 121                 /*
 122                  * If the queue doesn't support SG gaps and adding this
 123                  * offset would create a gap, disallow it.
 124                  */
 125                 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 126                         goto split;
 127
 128                 if (sectors + (bv.bv_len >> 9) > max_sectors) {
 129                         /*
 130                          * Consider this a new segment if we're splitting in
 131                          * the middle of this vector.
 132                          */
 133                         if (nsegs < queue_max_segments(q) &&
 134                             sectors < max_sectors) {
 135                                 nsegs++;
 136                                 sectors = max_sectors;
 137                         }
 138                         if (sectors)
 139                                 goto split;
 140                         /* Make this single bvec as the 1st segment */
 141                 }
 142
 143                 if (bvprvp && blk_queue_cluster(q)) {
 144                         if (seg_size + bv.bv_len > queue_max_segment_size(q))
 145                                 goto new_segment;
 146                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
 147                                 goto new_segment;
 148                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
 149                                 goto new_segment;
 150
 151                         seg_size += bv.bv_len;
 152                         bvprv = bv;
 153                         bvprvp = &bvprv;
 154                         sectors += bv.bv_len >> 9;
 155
 156                         if (nsegs == 1 && seg_size > front_seg_size)
 157                                 front_seg_size = seg_size;
 158                         continue;
 159                 }
 160 new_segment:
 161                 if (nsegs == queue_max_segments(q))
 162                         goto split;
 163
 164                 nsegs++;
 165                 bvprv = bv;
 166                 bvprvp = &bvprv;
 167                 seg_size = bv.bv_len;
 168                 sectors += bv.bv_len >> 9;
 169
 170                 if (nsegs == 1 && seg_size > front_seg_size)
 171                         front_seg_size = seg_size;
 172         }
 173
 174         do_split = false;
 175 split:
 176         *segs = nsegs;
 177
 178         if (do_split) {
 179                 new = bio_split(bio, sectors, GFP_NOIO, bs);
 180                 if (new)
 181                         bio = new;
 182         }
 183
 184         bio->bi_seg_front_size = front_seg_size;
 185         if (seg_size > bio->bi_seg_back_size)
 186                 bio->bi_seg_back_size = seg_size;
 187
 188         return do_split ? new : NULL;
 189 }
 190
 191 void blk_queue_split(struct request_queue *q, struct bio **bio,
 192                      struct bio_set *bs)
 193 {
 194         struct bio *split, *res;
 195         unsigned nsegs;
 196
 197         switch (bio_op(*bio)) {
 198         case REQ_OP_DISCARD:
 199         case REQ_OP_SECURE_ERASE:
 200                 split = blk_bio_discard_split(q, *bio, bs, &nsegs);
 201                 break;
 202         case REQ_OP_WRITE_ZEROES:
 203                 split = NULL;
 204                 nsegs = (*bio)->bi_phys_segments;
 205                 break;
 206         case REQ_OP_WRITE_SAME:
 207                 split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
 208                 break;
 209         default:
 210                 split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
 211                 break;
 212         }
 213
 214         /* physical segments can be figured out during splitting */
 215         res = split ? split : *bio;
 216         res->bi_phys_segments = nsegs;
 217         bio_set_flag(res, BIO_SEG_VALID);
 218
 219         if (split) {
 220                 /* there isn't chance to merge the splitted bio */
 221                 split->bi_opf |= REQ_NOMERGE;
 222
 223                 bio_chain(split, *bio);
 224                 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
 225                 generic_make_request(*bio);
 226                 *bio = split;
 227         }
 228 }
 229 EXPORT_SYMBOL(blk_queue_split);
 230
 231 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 232                                              struct bio *bio,
 233                                              bool no_sg_merge)
 234 {
 235         struct bio_vec bv, bvprv = { NULL };
 236         int cluster, prev = 0;
 237         unsigned int seg_size, nr_phys_segs;
 238         struct bio *fbio, *bbio;
 239         struct bvec_iter iter;
 240
 241         if (!bio)
 242                 return 0;
 243
 244         switch (bio_op(bio)) {
 245         case REQ_OP_DISCARD:
 246         case REQ_OP_SECURE_ERASE:
 247         case REQ_OP_WRITE_ZEROES:
 248                 return 0;
 249         case REQ_OP_WRITE_SAME:
 250                 return 1;
 251         }
 252
 253         fbio = bio;
 254         cluster = blk_queue_cluster(q);
 255         seg_size = 0;
 256         nr_phys_segs = 0;
 257         for_each_bio(bio) {
 258                 bio_for_each_segment(bv, bio, iter) {
 259                         /*
 260                          * If SG merging is disabled, each bio vector is
 261                          * a segment
 262                          */
 263                         if (no_sg_merge)
 264                                 goto new_segment;
 265
 266                         if (prev && cluster) {
 267                                 if (seg_size + bv.bv_len
 268                                     > queue_max_segment_size(q))
 269                                         goto new_segment;
 270                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
 271                                         goto new_segment;
 272                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
 273                                         goto new_segment;
 274
 275                                 seg_size += bv.bv_len;
 276                                 bvprv = bv;
 277                                 continue;
 278                         }
 279 new_segment:
 280                         if (nr_phys_segs == 1 && seg_size >
 281                             fbio->bi_seg_front_size)
 282                                 fbio->bi_seg_front_size = seg_size;
 283
 284                         nr_phys_segs++;
 285                         bvprv = bv;
 286                         prev = 1;
 287                         seg_size = bv.bv_len;
 288                 }
 289                 bbio = bio;
 290         }
 291
 292         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
 293                 fbio->bi_seg_front_size = seg_size;
 294         if (seg_size > bbio->bi_seg_back_size)
 295                 bbio->bi_seg_back_size = seg_size;
 296
 297         return nr_phys_segs;
 298 }
 299
 300 void blk_recalc_rq_segments(struct request *rq)
 301 {
 302         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
 303                         &rq->q->queue_flags);
 304
 305         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
 306                         no_sg_merge);
 307 }
 308
 309 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 310 {
 311         unsigned short seg_cnt;
 312
 313         /* estimate segment number by bi_vcnt for non-cloned bio */
 314         if (bio_flagged(bio, BIO_CLONED))
 315                 seg_cnt = bio_segments(bio);
 316         else
 317                 seg_cnt = bio->bi_vcnt;
 318
 319         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 320                         (seg_cnt < queue_max_segments(q)))
 321                 bio->bi_phys_segments = seg_cnt;
 322         else {
 323                 struct bio *nxt = bio->bi_next;
 324
 325                 bio->bi_next = NULL;
 326                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 327                 bio->bi_next = nxt;
 328         }
 329
 330         bio_set_flag(bio, BIO_SEG_VALID);
 331 }
 332 EXPORT_SYMBOL(blk_recount_segments);
 333
 334 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 335                                    struct bio *nxt)
 336 {
 337         struct bio_vec end_bv = { NULL }, nxt_bv;
 338
 339         if (!blk_queue_cluster(q))
 340                 return 0;
 341
 342         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 343             queue_max_segment_size(q))
 344                 return 0;
 345
 346         if (!bio_has_data(bio))
 347                 return 1;
 348
 349         bio_get_last_bvec(bio, &end_bv);
 350         bio_get_first_bvec(nxt, &nxt_bv);
 351
 352         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 353                 return 0;
 354
 355         /*
 356          * bio and nxt are contiguous in memory; check if the queue allows
 357          * these two to be merged into one
 358          */
 359         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 360                 return 1;
 361
 362         return 0;
 363 }
 364
 365 static inline void
 366 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 367                      struct scatterlist *sglist, struct bio_vec *bvprv,
 368                      struct scatterlist **sg, int *nsegs, int *cluster)
 369 {
 370
 371         int nbytes = bvec->bv_len;
 372
 373         if (*sg && *cluster) {
 374                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 375                         goto new_segment;
 376
 377                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 378                         goto new_segment;
 379                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 380                         goto new_segment;
 381
 382                 (*sg)->length += nbytes;
 383         } else {
 384 new_segment:
 385                 if (!*sg)
 386                         *sg = sglist;
 387                 else {
 388                         /*
 389                          * If the driver previously mapped a shorter
 390                          * list, we could see a termination bit
 391                          * prematurely unless it fully inits the sg
 392                          * table on each mapping. We KNOW that there
 393                          * must be more entries here or the driver
 394                          * would be buggy, so force clear the
 395                          * termination bit to avoid doing a full
 396                          * sg_init_table() in drivers for each command.
 397                          */
 398                         sg_unmark_end(*sg);
 399                         *sg = sg_next(*sg);
 400                 }
 401
 402                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 403                 (*nsegs)++;
 404         }
 405         *bvprv = *bvec;
 406 }
 407
 408 static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
 409                 struct scatterlist *sglist, struct scatterlist **sg)
 410 {
 411         *sg = sglist;
 412         sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
 413         return 1;
 414 }
 415
 416 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 417                              struct scatterlist *sglist,
 418                              struct scatterlist **sg)
 419 {
 420         struct bio_vec bvec, bvprv = { NULL };
 421         struct bvec_iter iter;
 422         int cluster = blk_queue_cluster(q), nsegs = 0;
 423
 424         for_each_bio(bio)
 425                 bio_for_each_segment(bvec, bio, iter)
 426                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 427                                              &nsegs, &cluster);
 428
 429         return nsegs;
 430 }
 431
 432 /*
 433  * map a request to scatterlist, return number of sg entries setup. Caller
 434  * must make sure sg can hold rq->nr_phys_segments entries
 435  */
 436 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 437                   struct scatterlist *sglist)
 438 {
 439         struct scatterlist *sg = NULL;
 440         int nsegs = 0;
 441
 442         if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
 443                 nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
 444         else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
 445                 nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
 446         else if (rq->bio)
 447                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 448
 449         if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
 450             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 451                 unsigned int pad_len =
 452                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 453
 454                 sg->length += pad_len;
 455                 rq->extra_len += pad_len;
 456         }
 457
 458         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 459                 if (op_is_write(req_op(rq)))
 460                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 461
 462                 sg_unmark_end(sg);
 463                 sg = sg_next(sg);
 464                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 465                             q->dma_drain_size,
 466                             ((unsigned long)q->dma_drain_buffer) &
 467                             (PAGE_SIZE - 1));
 468                 nsegs++;
 469                 rq->extra_len += q->dma_drain_size;
 470         }
 471
 472         if (sg)
 473                 sg_mark_end(sg);
 474
 475         /*
 476          * Something must have been wrong if the figured number of
 477          * segment is bigger than number of req's physical segments
 478          */
 479         WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
 480
 481         return nsegs;
 482 }
 483 EXPORT_SYMBOL(blk_rq_map_sg);
 484
 485 static inline int ll_new_hw_segment(struct request_queue *q,
 486                                     struct request *req,
 487                                     struct bio *bio)
 488 {
 489         int nr_phys_segs = bio_phys_segments(q, bio);
 490
 491         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 492                 goto no_merge;
 493
 494         if (blk_integrity_merge_bio(q, req, bio) == false)
 495                 goto no_merge;
 496
 497         /*
 498          * This will form the start of a new hw segment.  Bump both
 499          * counters.
 500          */
 501         req->nr_phys_segments += nr_phys_segs;
 502         return 1;
 503
 504 no_merge:
 505         req_set_nomerge(q, req);
 506         return 0;
 507 }
 508
 509 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 510                      struct bio *bio)
 511 {
 512         if (req_gap_back_merge(req, bio))
 513                 return 0;
 514         if (blk_integrity_rq(req) &&
 515             integrity_req_gap_back_merge(req, bio))
 516                 return 0;
 517         if (blk_rq_sectors(req) + bio_sectors(bio) >
 518             blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
 519                 req_set_nomerge(q, req);
 520                 return 0;
 521         }
 522         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 523                 blk_recount_segments(q, req->biotail);
 524         if (!bio_flagged(bio, BIO_SEG_VALID))
 525                 blk_recount_segments(q, bio);
 526
 527         return ll_new_hw_segment(q, req, bio);
 528 }
 529
 530 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 531                       struct bio *bio)
 532 {
 533
 534         if (req_gap_front_merge(req, bio))
 535                 return 0;
 536         if (blk_integrity_rq(req) &&
 537             integrity_req_gap_front_merge(req, bio))
 538                 return 0;
 539         if (blk_rq_sectors(req) + bio_sectors(bio) >
 540             blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
 541                 req_set_nomerge(q, req);
 542                 return 0;
 543         }
 544         if (!bio_flagged(bio, BIO_SEG_VALID))
 545                 blk_recount_segments(q, bio);
 546         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 547                 blk_recount_segments(q, req->bio);
 548
 549         return ll_new_hw_segment(q, req, bio);
 550 }
 551
 552 /*
 553  * blk-mq uses req->special to carry normal driver per-request payload, it
 554  * does not indicate a prepared command that we cannot merge with.
 555  */
 556 static bool req_no_special_merge(struct request *req)
 557 {
 558         struct request_queue *q = req->q;
 559
 560         return !q->mq_ops && req->special;
 561 }
 562
 563 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 564                                 struct request *next)
 565 {
 566         int total_phys_segments;
 567         unsigned int seg_size =
 568                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 569
 570         /*
 571          * First check if the either of the requests are re-queued
 572          * requests.  Can't merge them if they are.
 573          */
 574         if (req_no_special_merge(req) || req_no_special_merge(next))
 575                 return 0;
 576
 577         if (req_gap_back_merge(req, next->bio))
 578                 return 0;
 579
 580         /*
 581          * Will it become too large?
 582          */
 583         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 584             blk_rq_get_max_sectors(req, blk_rq_pos(req)))
 585                 return 0;
 586
 587         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 588         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 589                 if (req->nr_phys_segments == 1)
 590                         req->bio->bi_seg_front_size = seg_size;
 591                 if (next->nr_phys_segments == 1)
 592                         next->biotail->bi_seg_back_size = seg_size;
 593                 total_phys_segments--;
 594         }
 595
 596         if (total_phys_segments > queue_max_segments(q))
 597                 return 0;
 598
 599         if (blk_integrity_merge_rq(q, req, next) == false)
 600                 return 0;
 601
 602         /* Merge is OK... */
 603         req->nr_phys_segments = total_phys_segments;
 604         return 1;
 605 }
 606
 607 /**
 608  * blk_rq_set_mixed_merge - mark a request as mixed merge
 609  * @rq: request to mark as mixed merge
 610  *
 611  * Description:
 612  *     @rq is about to be mixed merged.  Make sure the attributes
 613  *     which can be mixed are set in each bio and mark @rq as mixed
 614  *     merged.
 615  */
 616 void blk_rq_set_mixed_merge(struct request *rq)
 617 {
 618         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 619         struct bio *bio;
 620
 621         if (rq->rq_flags & RQF_MIXED_MERGE)
 622                 return;
 623
 624         /*
 625          * @rq will no longer represent mixable attributes for all the
 626          * contained bios.  It will just track those of the first one.
 627          * Distributes the attributs to each bio.
 628          */
 629         for (bio = rq->bio; bio; bio = bio->bi_next) {
 630                 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
 631                              (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
 632                 bio->bi_opf |= ff;
 633         }
 634         rq->rq_flags |= RQF_MIXED_MERGE;
 635 }
 636
 637 static void blk_account_io_merge(struct request *req)
 638 {
 639         if (blk_do_io_stat(req)) {
 640                 struct hd_struct *part;
 641                 int cpu;
 642
 643                 cpu = part_stat_lock();
 644                 part = req->part;
 645
 646                 part_round_stats(cpu, part);
 647                 part_dec_in_flight(part, rq_data_dir(req));
 648
 649                 hd_struct_put(part);
 650                 part_stat_unlock();
 651         }
 652 }
 653
 654 /*
 655  * For non-mq, this has to be called with the request spinlock acquired.
 656  * For mq with scheduling, the appropriate queue wide lock should be held.
 657  */
 658 static struct request *attempt_merge(struct request_queue *q,
 659                                      struct request *req, struct request *next)
 660 {
 661         if (!rq_mergeable(req) || !rq_mergeable(next))
 662                 return NULL;
 663
 664         if (req_op(req) != req_op(next))
 665                 return NULL;
 666
 667         /*
 668          * not contiguous
 669          */
 670         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 671                 return NULL;
 672
 673         if (rq_data_dir(req) != rq_data_dir(next)
 674             || req->rq_disk != next->rq_disk
 675             || req_no_special_merge(next))
 676                 return NULL;
 677
 678         if (req_op(req) == REQ_OP_WRITE_SAME &&
 679             !blk_write_same_mergeable(req->bio, next->bio))
 680                 return NULL;
 681
 682         /*
 683          * If we are allowed to merge, then append bio list
 684          * from next to rq and release next. merge_requests_fn
 685          * will have updated segment counts, update sector
 686          * counts here.
 687          */
 688         if (!ll_merge_requests_fn(q, req, next))
 689                 return NULL;
 690
 691         /*
 692          * If failfast settings disagree or any of the two is already
 693          * a mixed merge, mark both as mixed before proceeding.  This
 694          * makes sure that all involved bios have mixable attributes
 695          * set properly.
 696          */
 697         if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
 698             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 699             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 700                 blk_rq_set_mixed_merge(req);
 701                 blk_rq_set_mixed_merge(next);
 702         }
 703
 704         /*
 705          * At this point we have either done a back merge
 706          * or front merge. We need the smaller start_time of
 707          * the merged requests to be the current request
 708          * for accounting purposes.
 709          */
 710         if (time_after(req->start_time, next->start_time))
 711                 req->start_time = next->start_time;
 712
 713         req->biotail->bi_next = next->bio;
 714         req->biotail = next->biotail;
 715
 716         req->__data_len += blk_rq_bytes(next);
 717
 718         elv_merge_requests(q, req, next);
 719
 720         /*
 721          * 'next' is going away, so update stats accordingly
 722          */
 723         blk_account_io_merge(next);
 724
 725         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 726         if (blk_rq_cpu_valid(next))
 727                 req->cpu = next->cpu;
 728
 729         /*
 730          * ownership of bio passed from next to req, return 'next' for
 731          * the caller to free
 732          */
 733         next->bio = NULL;
 734         return next;
 735 }
 736
 737 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
 738 {
 739         struct request *next = elv_latter_request(q, rq);
 740
 741         if (next)
 742                 return attempt_merge(q, rq, next);
 743
 744         return NULL;
 745 }
 746
 747 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
 748 {
 749         struct request *prev = elv_former_request(q, rq);
 750
 751         if (prev)
 752                 return attempt_merge(q, prev, rq);
 753
 754         return NULL;
 755 }
 756
 757 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 758                           struct request *next)
 759 {
 760         struct elevator_queue *e = q->elevator;
 761         struct request *free;
 762
 763         if (!e->uses_mq && e->type->ops.sq.elevator_allow_rq_merge_fn)
 764                 if (!e->type->ops.sq.elevator_allow_rq_merge_fn(q, rq, next))
 765                         return 0;
 766
 767         free = attempt_merge(q, rq, next);
 768         if (free) {
 769                 __blk_put_request(q, free);
 770                 return 1;
 771         }
 772
 773         return 0;
 774 }
 775
 776 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 777 {
 778         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 779                 return false;
 780
 781         if (req_op(rq) != bio_op(bio))
 782                 return false;
 783
 784         /* different data direction or already started, don't merge */
 785         if (bio_data_dir(bio) != rq_data_dir(rq))
 786                 return false;
 787
 788         /* must be same device and not a special request */
 789         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 790                 return false;
 791
 792         /* only merge integrity protected bio into ditto rq */
 793         if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
 794                 return false;
 795
 796         /* must be using the same buffer */
 797         if (req_op(rq) == REQ_OP_WRITE_SAME &&
 798             !blk_write_same_mergeable(rq->bio, bio))
 799                 return false;
 800
 801         return true;
 802 }
 803
 804 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 805 {
 806         if (req_op(rq) == REQ_OP_DISCARD &&
 807             queue_max_discard_segments(rq->q) > 1)
 808                 return ELEVATOR_DISCARD_MERGE;
 809         else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 810                 return ELEVATOR_BACK_MERGE;
 811         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 812                 return ELEVATOR_FRONT_MERGE;
 813         return ELEVATOR_NO_MERGE;
 814 }