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