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; 307 308 if (!blk_queue_cluster(q)) 309 return 0; 310 311 if (bio->bi_seg_back_size + nxt->bi_seg_front_size > 312 queue_max_segment_size(q)) 313 return 0; 314 315 if (!bio_has_data(bio)) 316 return 1; 317 318 bio_get_last_bvec(bio, &end_bv); 319 bio_get_first_bvec(nxt, &nxt_bv); 320 321 if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv)) 322 return 0; 323 324 /* 325 * bio and nxt are contiguous in memory; check if the queue allows 326 * these two to be merged into one 327 */ 328 if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv)) 329 return 1; 330 331 return 0; 332 } 333 334 static inline void 335 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec, 336 struct scatterlist *sglist, struct bio_vec *bvprv, 337 struct scatterlist **sg, int *nsegs, int *cluster) 338 { 339 340 int nbytes = bvec->bv_len; 341 342 if (*sg && *cluster) { 343 if ((*sg)->length + nbytes > queue_max_segment_size(q)) 344 goto new_segment; 345 346 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) 347 goto new_segment; 348 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) 349 goto new_segment; 350 351 (*sg)->length += nbytes; 352 } else { 353 new_segment: 354 if (!*sg) 355 *sg = sglist; 356 else { 357 /* 358 * If the driver previously mapped a shorter 359 * list, we could see a termination bit 360 * prematurely unless it fully inits the sg 361 * table on each mapping. We KNOW that there 362 * must be more entries here or the driver 363 * would be buggy, so force clear the 364 * termination bit to avoid doing a full 365 * sg_init_table() in drivers for each command. 366 */ 367 sg_unmark_end(*sg); 368 *sg = sg_next(*sg); 369 } 370 371 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset); 372 (*nsegs)++; 373 } 374 *bvprv = *bvec; 375 } 376 377 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio, 378 struct scatterlist *sglist, 379 struct scatterlist **sg) 380 { 381 struct bio_vec bvec, bvprv = { NULL }; 382 struct bvec_iter iter; 383 int nsegs, cluster; 384 385 nsegs = 0; 386 cluster = blk_queue_cluster(q); 387 388 if (bio->bi_rw & REQ_DISCARD) { 389 /* 390 * This is a hack - drivers should be neither modifying the 391 * biovec, nor relying on bi_vcnt - but because of 392 * blk_add_request_payload(), a discard bio may or may not have 393 * a payload we need to set up here (thank you Christoph) and 394 * bi_vcnt is really the only way of telling if we need to. 395 */ 396 397 if (bio->bi_vcnt) 398 goto single_segment; 399 400 return 0; 401 } 402 403 if (bio->bi_rw & REQ_WRITE_SAME) { 404 single_segment: 405 *sg = sglist; 406 bvec = bio_iovec(bio); 407 sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset); 408 return 1; 409 } 410 411 for_each_bio(bio) 412 bio_for_each_segment(bvec, bio, iter) 413 __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg, 414 &nsegs, &cluster); 415 416 return nsegs; 417 } 418 419 /* 420 * map a request to scatterlist, return number of sg entries setup. Caller 421 * must make sure sg can hold rq->nr_phys_segments entries 422 */ 423 int blk_rq_map_sg(struct request_queue *q, struct request *rq, 424 struct scatterlist *sglist) 425 { 426 struct scatterlist *sg = NULL; 427 int nsegs = 0; 428 429 if (rq->bio) 430 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg); 431 432 if (unlikely(rq->cmd_flags & REQ_COPY_USER) && 433 (blk_rq_bytes(rq) & q->dma_pad_mask)) { 434 unsigned int pad_len = 435 (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1; 436 437 sg->length += pad_len; 438 rq->extra_len += pad_len; 439 } 440 441 if (q->dma_drain_size && q->dma_drain_needed(rq)) { 442 if (rq->cmd_flags & REQ_WRITE) 443 memset(q->dma_drain_buffer, 0, q->dma_drain_size); 444 445 sg_unmark_end(sg); 446 sg = sg_next(sg); 447 sg_set_page(sg, virt_to_page(q->dma_drain_buffer), 448 q->dma_drain_size, 449 ((unsigned long)q->dma_drain_buffer) & 450 (PAGE_SIZE - 1)); 451 nsegs++; 452 rq->extra_len += q->dma_drain_size; 453 } 454 455 if (sg) 456 sg_mark_end(sg); 457 458 /* 459 * Something must have been wrong if the figured number of 460 * segment is bigger than number of req's physical segments 461 */ 462 WARN_ON(nsegs > rq->nr_phys_segments); 463 464 return nsegs; 465 } 466 EXPORT_SYMBOL(blk_rq_map_sg); 467 468 static inline int ll_new_hw_segment(struct request_queue *q, 469 struct request *req, 470 struct bio *bio) 471 { 472 int nr_phys_segs = bio_phys_segments(q, bio); 473 474 if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q)) 475 goto no_merge; 476 477 if (blk_integrity_merge_bio(q, req, bio) == false) 478 goto no_merge; 479 480 /* 481 * This will form the start of a new hw segment. Bump both 482 * counters. 483 */ 484 req->nr_phys_segments += nr_phys_segs; 485 return 1; 486 487 no_merge: 488 req->cmd_flags |= REQ_NOMERGE; 489 if (req == q->last_merge) 490 q->last_merge = NULL; 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)) { 504 req->cmd_flags |= REQ_NOMERGE; 505 if (req == q->last_merge) 506 q->last_merge = NULL; 507 return 0; 508 } 509 if (!bio_flagged(req->biotail, BIO_SEG_VALID)) 510 blk_recount_segments(q, req->biotail); 511 if (!bio_flagged(bio, BIO_SEG_VALID)) 512 blk_recount_segments(q, bio); 513 514 return ll_new_hw_segment(q, req, bio); 515 } 516 517 int ll_front_merge_fn(struct request_queue *q, struct request *req, 518 struct bio *bio) 519 { 520 521 if (req_gap_front_merge(req, bio)) 522 return 0; 523 if (blk_integrity_rq(req) && 524 integrity_req_gap_front_merge(req, bio)) 525 return 0; 526 if (blk_rq_sectors(req) + bio_sectors(bio) > 527 blk_rq_get_max_sectors(req)) { 528 req->cmd_flags |= REQ_NOMERGE; 529 if (req == q->last_merge) 530 q->last_merge = NULL; 531 return 0; 532 } 533 if (!bio_flagged(bio, BIO_SEG_VALID)) 534 blk_recount_segments(q, bio); 535 if (!bio_flagged(req->bio, BIO_SEG_VALID)) 536 blk_recount_segments(q, req->bio); 537 538 return ll_new_hw_segment(q, req, bio); 539 } 540 541 /* 542 * blk-mq uses req->special to carry normal driver per-request payload, it 543 * does not indicate a prepared command that we cannot merge with. 544 */ 545 static bool req_no_special_merge(struct request *req) 546 { 547 struct request_queue *q = req->q; 548 549 return !q->mq_ops && req->special; 550 } 551 552 static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 553 struct request *next) 554 { 555 int total_phys_segments; 556 unsigned int seg_size = 557 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size; 558 559 /* 560 * First check if the either of the requests are re-queued 561 * requests. Can't merge them if they are. 562 */ 563 if (req_no_special_merge(req) || req_no_special_merge(next)) 564 return 0; 565 566 if (req_gap_back_merge(req, next->bio)) 567 return 0; 568 569 /* 570 * Will it become too large? 571 */ 572 if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > 573 blk_rq_get_max_sectors(req)) 574 return 0; 575 576 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; 577 if (blk_phys_contig_segment(q, req->biotail, next->bio)) { 578 if (req->nr_phys_segments == 1) 579 req->bio->bi_seg_front_size = seg_size; 580 if (next->nr_phys_segments == 1) 581 next->biotail->bi_seg_back_size = seg_size; 582 total_phys_segments--; 583 } 584 585 if (total_phys_segments > queue_max_segments(q)) 586 return 0; 587 588 if (blk_integrity_merge_rq(q, req, next) == false) 589 return 0; 590 591 /* Merge is OK... */ 592 req->nr_phys_segments = total_phys_segments; 593 return 1; 594 } 595 596 /** 597 * blk_rq_set_mixed_merge - mark a request as mixed merge 598 * @rq: request to mark as mixed merge 599 * 600 * Description: 601 * @rq is about to be mixed merged. Make sure the attributes 602 * which can be mixed are set in each bio and mark @rq as mixed 603 * merged. 604 */ 605 void blk_rq_set_mixed_merge(struct request *rq) 606 { 607 unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK; 608 struct bio *bio; 609 610 if (rq->cmd_flags & REQ_MIXED_MERGE) 611 return; 612 613 /* 614 * @rq will no longer represent mixable attributes for all the 615 * contained bios. It will just track those of the first one. 616 * Distributes the attributs to each bio. 617 */ 618 for (bio = rq->bio; bio; bio = bio->bi_next) { 619 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) && 620 (bio->bi_rw & REQ_FAILFAST_MASK) != ff); 621 bio->bi_rw |= ff; 622 } 623 rq->cmd_flags |= REQ_MIXED_MERGE; 624 } 625 626 static void blk_account_io_merge(struct request *req) 627 { 628 if (blk_do_io_stat(req)) { 629 struct hd_struct *part; 630 int cpu; 631 632 cpu = part_stat_lock(); 633 part = req->part; 634 635 part_round_stats(cpu, part); 636 part_dec_in_flight(part, rq_data_dir(req)); 637 638 hd_struct_put(part); 639 part_stat_unlock(); 640 } 641 } 642 643 /* 644 * Has to be called with the request spinlock acquired 645 */ 646 static int attempt_merge(struct request_queue *q, struct request *req, 647 struct request *next) 648 { 649 if (!rq_mergeable(req) || !rq_mergeable(next)) 650 return 0; 651 652 if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags)) 653 return 0; 654 655 /* 656 * not contiguous 657 */ 658 if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) 659 return 0; 660 661 if (rq_data_dir(req) != rq_data_dir(next) 662 || req->rq_disk != next->rq_disk 663 || req_no_special_merge(next)) 664 return 0; 665 666 if (req->cmd_flags & REQ_WRITE_SAME && 667 !blk_write_same_mergeable(req->bio, next->bio)) 668 return 0; 669 670 /* 671 * If we are allowed to merge, then append bio list 672 * from next to rq and release next. merge_requests_fn 673 * will have updated segment counts, update sector 674 * counts here. 675 */ 676 if (!ll_merge_requests_fn(q, req, next)) 677 return 0; 678 679 /* 680 * If failfast settings disagree or any of the two is already 681 * a mixed merge, mark both as mixed before proceeding. This 682 * makes sure that all involved bios have mixable attributes 683 * set properly. 684 */ 685 if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE || 686 (req->cmd_flags & REQ_FAILFAST_MASK) != 687 (next->cmd_flags & REQ_FAILFAST_MASK)) { 688 blk_rq_set_mixed_merge(req); 689 blk_rq_set_mixed_merge(next); 690 } 691 692 /* 693 * At this point we have either done a back merge 694 * or front merge. We need the smaller start_time of 695 * the merged requests to be the current request 696 * for accounting purposes. 697 */ 698 if (time_after(req->start_time, next->start_time)) 699 req->start_time = next->start_time; 700 701 req->biotail->bi_next = next->bio; 702 req->biotail = next->biotail; 703 704 req->__data_len += blk_rq_bytes(next); 705 706 elv_merge_requests(q, req, next); 707 708 /* 709 * 'next' is going away, so update stats accordingly 710 */ 711 blk_account_io_merge(next); 712 713 req->ioprio = ioprio_best(req->ioprio, next->ioprio); 714 if (blk_rq_cpu_valid(next)) 715 req->cpu = next->cpu; 716 717 /* owner-ship of bio passed from next to req */ 718 next->bio = NULL; 719 __blk_put_request(q, next); 720 return 1; 721 } 722 723 int attempt_back_merge(struct request_queue *q, struct request *rq) 724 { 725 struct request *next = elv_latter_request(q, rq); 726 727 if (next) 728 return attempt_merge(q, rq, next); 729 730 return 0; 731 } 732 733 int attempt_front_merge(struct request_queue *q, struct request *rq) 734 { 735 struct request *prev = elv_former_request(q, rq); 736 737 if (prev) 738 return attempt_merge(q, prev, rq); 739 740 return 0; 741 } 742 743 int blk_attempt_req_merge(struct request_queue *q, struct request *rq, 744 struct request *next) 745 { 746 return attempt_merge(q, rq, next); 747 } 748 749 bool blk_rq_merge_ok(struct request *rq, struct bio *bio) 750 { 751 if (!rq_mergeable(rq) || !bio_mergeable(bio)) 752 return false; 753 754 if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw)) 755 return false; 756 757 /* different data direction or already started, don't merge */ 758 if (bio_data_dir(bio) != rq_data_dir(rq)) 759 return false; 760 761 /* must be same device and not a special request */ 762 if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq)) 763 return false; 764 765 /* only merge integrity protected bio into ditto rq */ 766 if (blk_integrity_merge_bio(rq->q, rq, bio) == false) 767 return false; 768 769 /* must be using the same buffer */ 770 if (rq->cmd_flags & REQ_WRITE_SAME && 771 !blk_write_same_mergeable(rq->bio, bio)) 772 return false; 773 774 return true; 775 } 776 777 int blk_try_merge(struct request *rq, struct bio *bio) 778 { 779 if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector) 780 return ELEVATOR_BACK_MERGE; 781 else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector) 782 return ELEVATOR_FRONT_MERGE; 783 return ELEVATOR_NO_MERGE; 784 } 785