block/elevator.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  Block device elevator/IO-scheduler.
   4  *
   5  *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
   6  *
   7  * 30042000 Jens Axboe <axboe@kernel.dk> :
   8  *
   9  * Split the elevator a bit so that it is possible to choose a different
  10  * one or even write a new "plug in". There are three pieces:
  11  * - elevator_fn, inserts a new request in the queue list
  12  * - elevator_merge_fn, decides whether a new buffer can be merged with
  13  *   an existing request
  14  * - elevator_dequeue_fn, called when a request is taken off the active list
  15  *
  16  * 20082000 Dave Jones <davej@suse.de> :
  17  * Removed tests for max-bomb-segments, which was breaking elvtune
  18  *  when run without -bN
  19  *
  20  * Jens:
  21  * - Rework again to work with bio instead of buffer_heads
  22  * - loose bi_dev comparisons, partition handling is right now
  23  * - completely modularize elevator setup and teardown
  24  *
  25  */
  26 #include <linux/kernel.h>
  27 #include <linux/fs.h>
  28 #include <linux/blkdev.h>
  29 #include <linux/bio.h>
  30 #include <linux/module.h>
  31 #include <linux/slab.h>
  32 #include <linux/init.h>
  33 #include <linux/compiler.h>
  34 #include <linux/blktrace_api.h>
  35 #include <linux/hash.h>
  36 #include <linux/uaccess.h>
  37 #include <linux/pm_runtime.h>
  38
  39 #include <trace/events/block.h>
  40
  41 #include "elevator.h"
  42 #include "blk.h"
  43 #include "blk-mq-sched.h"
  44 #include "blk-pm.h"
  45 #include "blk-wbt.h"
  46 #include "blk-cgroup.h"
  47
  48 static DEFINE_SPINLOCK(elv_list_lock);
  49 static LIST_HEAD(elv_list);
  50
  51 /*
  52  * Merge hash stuff.
  53  */
  54 #define rq_hash_key(rq)         (blk_rq_pos(rq) + blk_rq_sectors(rq))
  55
  56 /*
  57  * Query io scheduler to see if the current process issuing bio may be
  58  * merged with rq.
  59  */
  60 static bool elv_iosched_allow_bio_merge(struct request *rq, struct bio *bio)
  61 {
  62         struct request_queue *q = rq->q;
  63         struct elevator_queue *e = q->elevator;
  64
  65         if (e->type->ops.allow_merge)
  66                 return e->type->ops.allow_merge(q, rq, bio);
  67
  68         return true;
  69 }
  70
  71 /*
  72  * can we safely merge with this request?
  73  */
  74 bool elv_bio_merge_ok(struct request *rq, struct bio *bio)
  75 {
  76         if (!blk_rq_merge_ok(rq, bio))
  77                 return false;
  78
  79         if (!elv_iosched_allow_bio_merge(rq, bio))
  80                 return false;
  81
  82         return true;
  83 }
  84 EXPORT_SYMBOL(elv_bio_merge_ok);
  85
  86 /**
  87  * elevator_match - Check whether @e's name or alias matches @name
  88  * @e: Scheduler to test
  89  * @name: Elevator name to test
  90  *
  91  * Return true if the elevator @e's name or alias matches @name.
  92  */
  93 static bool elevator_match(const struct elevator_type *e, const char *name)
  94 {
  95         return !strcmp(e->elevator_name, name) ||
  96                 (e->elevator_alias && !strcmp(e->elevator_alias, name));
  97 }
  98
  99 static struct elevator_type *__elevator_find(const char *name)
 100 {
 101         struct elevator_type *e;
 102
 103         list_for_each_entry(e, &elv_list, list)
 104                 if (elevator_match(e, name))
 105                         return e;
 106         return NULL;
 107 }
 108
 109 static struct elevator_type *elevator_find_get(const char *name)
 110 {
 111         struct elevator_type *e;
 112
 113         spin_lock(&elv_list_lock);
 114         e = __elevator_find(name);
 115         if (e && (!elevator_tryget(e)))
 116                 e = NULL;
 117         spin_unlock(&elv_list_lock);
 118         return e;
 119 }
 120
 121 static const struct kobj_type elv_ktype;
 122
 123 struct elevator_queue *elevator_alloc(struct request_queue *q,
 124                                   struct elevator_type *e)
 125 {
 126         struct elevator_queue *eq;
 127
 128         eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node);
 129         if (unlikely(!eq))
 130                 return NULL;
 131
 132         __elevator_get(e);
 133         eq->type = e;
 134         kobject_init(&eq->kobj, &elv_ktype);
 135         mutex_init(&eq->sysfs_lock);
 136         hash_init(eq->hash);
 137
 138         return eq;
 139 }
 140 EXPORT_SYMBOL(elevator_alloc);
 141
 142 static void elevator_release(struct kobject *kobj)
 143 {
 144         struct elevator_queue *e;
 145
 146         e = container_of(kobj, struct elevator_queue, kobj);
 147         elevator_put(e->type);
 148         kfree(e);
 149 }
 150
 151 void elevator_exit(struct request_queue *q)
 152 {
 153         struct elevator_queue *e = q->elevator;
 154
 155         ioc_clear_queue(q);
 156         blk_mq_sched_free_rqs(q);
 157
 158         mutex_lock(&e->sysfs_lock);
 159         blk_mq_exit_sched(q, e);
 160         mutex_unlock(&e->sysfs_lock);
 161
 162         kobject_put(&e->kobj);
 163 }
 164
 165 static inline void __elv_rqhash_del(struct request *rq)
 166 {
 167         hash_del(&rq->hash);
 168         rq->rq_flags &= ~RQF_HASHED;
 169 }
 170
 171 void elv_rqhash_del(struct request_queue *q, struct request *rq)
 172 {
 173         if (ELV_ON_HASH(rq))
 174                 __elv_rqhash_del(rq);
 175 }
 176 EXPORT_SYMBOL_GPL(elv_rqhash_del);
 177
 178 void elv_rqhash_add(struct request_queue *q, struct request *rq)
 179 {
 180         struct elevator_queue *e = q->elevator;
 181
 182         BUG_ON(ELV_ON_HASH(rq));
 183         hash_add(e->hash, &rq->hash, rq_hash_key(rq));
 184         rq->rq_flags |= RQF_HASHED;
 185 }
 186 EXPORT_SYMBOL_GPL(elv_rqhash_add);
 187
 188 void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 189 {
 190         __elv_rqhash_del(rq);
 191         elv_rqhash_add(q, rq);
 192 }
 193
 194 struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 195 {
 196         struct elevator_queue *e = q->elevator;
 197         struct hlist_node *next;
 198         struct request *rq;
 199
 200         hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
 201                 BUG_ON(!ELV_ON_HASH(rq));
 202
 203                 if (unlikely(!rq_mergeable(rq))) {
 204                         __elv_rqhash_del(rq);
 205                         continue;
 206                 }
 207
 208                 if (rq_hash_key(rq) == offset)
 209                         return rq;
 210         }
 211
 212         return NULL;
 213 }
 214
 215 /*
 216  * RB-tree support functions for inserting/lookup/removal of requests
 217  * in a sorted RB tree.
 218  */
 219 void elv_rb_add(struct rb_root *root, struct request *rq)
 220 {
 221         struct rb_node **p = &root->rb_node;
 222         struct rb_node *parent = NULL;
 223         struct request *__rq;
 224
 225         while (*p) {
 226                 parent = *p;
 227                 __rq = rb_entry(parent, struct request, rb_node);
 228
 229                 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
 230                         p = &(*p)->rb_left;
 231                 else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
 232                         p = &(*p)->rb_right;
 233         }
 234
 235         rb_link_node(&rq->rb_node, parent, p);
 236         rb_insert_color(&rq->rb_node, root);
 237 }
 238 EXPORT_SYMBOL(elv_rb_add);
 239
 240 void elv_rb_del(struct rb_root *root, struct request *rq)
 241 {
 242         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 243         rb_erase(&rq->rb_node, root);
 244         RB_CLEAR_NODE(&rq->rb_node);
 245 }
 246 EXPORT_SYMBOL(elv_rb_del);
 247
 248 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 249 {
 250         struct rb_node *n = root->rb_node;
 251         struct request *rq;
 252
 253         while (n) {
 254                 rq = rb_entry(n, struct request, rb_node);
 255
 256                 if (sector < blk_rq_pos(rq))
 257                         n = n->rb_left;
 258                 else if (sector > blk_rq_pos(rq))
 259                         n = n->rb_right;
 260                 else
 261                         return rq;
 262         }
 263
 264         return NULL;
 265 }
 266 EXPORT_SYMBOL(elv_rb_find);
 267
 268 enum elv_merge elv_merge(struct request_queue *q, struct request **req,
 269                 struct bio *bio)
 270 {
 271         struct elevator_queue *e = q->elevator;
 272         struct request *__rq;
 273
 274         /*
 275          * Levels of merges:
 276          *      nomerges:  No merges at all attempted
 277          *      noxmerges: Only simple one-hit cache try
 278          *      merges:    All merge tries attempted
 279          */
 280         if (blk_queue_nomerges(q) || !bio_mergeable(bio))
 281                 return ELEVATOR_NO_MERGE;
 282
 283         /*
 284          * First try one-hit cache.
 285          */
 286         if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
 287                 enum elv_merge ret = blk_try_merge(q->last_merge, bio);
 288
 289                 if (ret != ELEVATOR_NO_MERGE) {
 290                         *req = q->last_merge;
 291                         return ret;
 292                 }
 293         }
 294
 295         if (blk_queue_noxmerges(q))
 296                 return ELEVATOR_NO_MERGE;
 297
 298         /*
 299          * See if our hash lookup can find a potential backmerge.
 300          */
 301         __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
 302         if (__rq && elv_bio_merge_ok(__rq, bio)) {
 303                 *req = __rq;
 304
 305                 if (blk_discard_mergable(__rq))
 306                         return ELEVATOR_DISCARD_MERGE;
 307                 return ELEVATOR_BACK_MERGE;
 308         }
 309
 310         if (e->type->ops.request_merge)
 311                 return e->type->ops.request_merge(q, req, bio);
 312
 313         return ELEVATOR_NO_MERGE;
 314 }
 315
 316 /*
 317  * Attempt to do an insertion back merge. Only check for the case where
 318  * we can append 'rq' to an existing request, so we can throw 'rq' away
 319  * afterwards.
 320  *
 321  * Returns true if we merged, false otherwise. 'free' will contain all
 322  * requests that need to be freed.
 323  */
 324 bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq,
 325                               struct list_head *free)
 326 {
 327         struct request *__rq;
 328         bool ret;
 329
 330         if (blk_queue_nomerges(q))
 331                 return false;
 332
 333         /*
 334          * First try one-hit cache.
 335          */
 336         if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq)) {
 337                 list_add(&rq->queuelist, free);
 338                 return true;
 339         }
 340
 341         if (blk_queue_noxmerges(q))
 342                 return false;
 343
 344         ret = false;
 345         /*
 346          * See if our hash lookup can find a potential backmerge.
 347          */
 348         while (1) {
 349                 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
 350                 if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
 351                         break;
 352
 353                 list_add(&rq->queuelist, free);
 354                 /* The merged request could be merged with others, try again */
 355                 ret = true;
 356                 rq = __rq;
 357         }
 358
 359         return ret;
 360 }
 361
 362 void elv_merged_request(struct request_queue *q, struct request *rq,
 363                 enum elv_merge type)
 364 {
 365         struct elevator_queue *e = q->elevator;
 366
 367         if (e->type->ops.request_merged)
 368                 e->type->ops.request_merged(q, rq, type);
 369
 370         if (type == ELEVATOR_BACK_MERGE)
 371                 elv_rqhash_reposition(q, rq);
 372
 373         q->last_merge = rq;
 374 }
 375
 376 void elv_merge_requests(struct request_queue *q, struct request *rq,
 377                              struct request *next)
 378 {
 379         struct elevator_queue *e = q->elevator;
 380
 381         if (e->type->ops.requests_merged)
 382                 e->type->ops.requests_merged(q, rq, next);
 383
 384         elv_rqhash_reposition(q, rq);
 385         q->last_merge = rq;
 386 }
 387
 388 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 389 {
 390         struct elevator_queue *e = q->elevator;
 391
 392         if (e->type->ops.next_request)
 393                 return e->type->ops.next_request(q, rq);
 394
 395         return NULL;
 396 }
 397
 398 struct request *elv_former_request(struct request_queue *q, struct request *rq)
 399 {
 400         struct elevator_queue *e = q->elevator;
 401
 402         if (e->type->ops.former_request)
 403                 return e->type->ops.former_request(q, rq);
 404
 405         return NULL;
 406 }
 407
 408 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 409
 410 static ssize_t
 411 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 412 {
 413         struct elv_fs_entry *entry = to_elv(attr);
 414         struct elevator_queue *e;
 415         ssize_t error;
 416
 417         if (!entry->show)
 418                 return -EIO;
 419
 420         e = container_of(kobj, struct elevator_queue, kobj);
 421         mutex_lock(&e->sysfs_lock);
 422         error = e->type ? entry->show(e, page) : -ENOENT;
 423         mutex_unlock(&e->sysfs_lock);
 424         return error;
 425 }
 426
 427 static ssize_t
 428 elv_attr_store(struct kobject *kobj, struct attribute *attr,
 429                const char *page, size_t length)
 430 {
 431         struct elv_fs_entry *entry = to_elv(attr);
 432         struct elevator_queue *e;
 433         ssize_t error;
 434
 435         if (!entry->store)
 436                 return -EIO;
 437
 438         e = container_of(kobj, struct elevator_queue, kobj);
 439         mutex_lock(&e->sysfs_lock);
 440         error = e->type ? entry->store(e, page, length) : -ENOENT;
 441         mutex_unlock(&e->sysfs_lock);
 442         return error;
 443 }
 444
 445 static const struct sysfs_ops elv_sysfs_ops = {
 446         .show   = elv_attr_show,
 447         .store  = elv_attr_store,
 448 };
 449
 450 static const struct kobj_type elv_ktype = {
 451         .sysfs_ops      = &elv_sysfs_ops,
 452         .release        = elevator_release,
 453 };
 454
 455 int elv_register_queue(struct request_queue *q, bool uevent)
 456 {
 457         struct elevator_queue *e = q->elevator;
 458         int error;
 459
 460         lockdep_assert_held(&q->sysfs_lock);
 461
 462         error = kobject_add(&e->kobj, &q->disk->queue_kobj, "iosched");
 463         if (!error) {
 464                 struct elv_fs_entry *attr = e->type->elevator_attrs;
 465                 if (attr) {
 466                         while (attr->attr.name) {
 467                                 if (sysfs_create_file(&e->kobj, &attr->attr))
 468                                         break;
 469                                 attr++;
 470                         }
 471                 }
 472                 if (uevent)
 473                         kobject_uevent(&e->kobj, KOBJ_ADD);
 474
 475                 set_bit(ELEVATOR_FLAG_REGISTERED, &e->flags);
 476         }
 477         return error;
 478 }
 479
 480 void elv_unregister_queue(struct request_queue *q)
 481 {
 482         struct elevator_queue *e = q->elevator;
 483
 484         lockdep_assert_held(&q->sysfs_lock);
 485
 486         if (e && test_and_clear_bit(ELEVATOR_FLAG_REGISTERED, &e->flags)) {
 487                 kobject_uevent(&e->kobj, KOBJ_REMOVE);
 488                 kobject_del(&e->kobj);
 489         }
 490 }
 491
 492 int elv_register(struct elevator_type *e)
 493 {
 494         /* finish request is mandatory */
 495         if (WARN_ON_ONCE(!e->ops.finish_request))
 496                 return -EINVAL;
 497         /* insert_requests and dispatch_request are mandatory */
 498         if (WARN_ON_ONCE(!e->ops.insert_requests || !e->ops.dispatch_request))
 499                 return -EINVAL;
 500
 501         /* create icq_cache if requested */
 502         if (e->icq_size) {
 503                 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
 504                     WARN_ON(e->icq_align < __alignof__(struct io_cq)))
 505                         return -EINVAL;
 506
 507                 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
 508                          "%s_io_cq", e->elevator_name);
 509                 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
 510                                                  e->icq_align, 0, NULL);
 511                 if (!e->icq_cache)
 512                         return -ENOMEM;
 513         }
 514
 515         /* register, don't allow duplicate names */
 516         spin_lock(&elv_list_lock);
 517         if (__elevator_find(e->elevator_name)) {
 518                 spin_unlock(&elv_list_lock);
 519                 kmem_cache_destroy(e->icq_cache);
 520                 return -EBUSY;
 521         }
 522         list_add_tail(&e->list, &elv_list);
 523         spin_unlock(&elv_list_lock);
 524
 525         printk(KERN_INFO "io scheduler %s registered\n", e->elevator_name);
 526
 527         return 0;
 528 }
 529 EXPORT_SYMBOL_GPL(elv_register);
 530
 531 void elv_unregister(struct elevator_type *e)
 532 {
 533         /* unregister */
 534         spin_lock(&elv_list_lock);
 535         list_del_init(&e->list);
 536         spin_unlock(&elv_list_lock);
 537
 538         /*
 539          * Destroy icq_cache if it exists.  icq's are RCU managed.  Make
 540          * sure all RCU operations are complete before proceeding.
 541          */
 542         if (e->icq_cache) {
 543                 rcu_barrier();
 544                 kmem_cache_destroy(e->icq_cache);
 545                 e->icq_cache = NULL;
 546         }
 547 }
 548 EXPORT_SYMBOL_GPL(elv_unregister);
 549
 550 static inline bool elv_support_iosched(struct request_queue *q)
 551 {
 552         if (!queue_is_mq(q) ||
 553             (q->tag_set->flags & BLK_MQ_F_NO_SCHED))
 554                 return false;
 555         return true;
 556 }
 557
 558 /*
 559  * For single queue devices, default to using mq-deadline. If we have multiple
 560  * queues or mq-deadline is not available, default to "none".
 561  */
 562 static struct elevator_type *elevator_get_default(struct request_queue *q)
 563 {
 564         if (q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
 565                 return NULL;
 566
 567         if (q->nr_hw_queues != 1 &&
 568             !blk_mq_is_shared_tags(q->tag_set->flags))
 569                 return NULL;
 570
 571         return elevator_find_get("mq-deadline");
 572 }
 573
 574 /*
 575  * Use the default elevator settings. If the chosen elevator initialization
 576  * fails, fall back to the "none" elevator (no elevator).
 577  */
 578 void elevator_init_mq(struct request_queue *q)
 579 {
 580         struct elevator_type *e;
 581         int err;
 582
 583         if (!elv_support_iosched(q))
 584                 return;
 585
 586         WARN_ON_ONCE(blk_queue_registered(q));
 587
 588         if (unlikely(q->elevator))
 589                 return;
 590
 591         e = elevator_get_default(q);
 592         if (!e)
 593                 return;
 594
 595         /*
 596          * We are called before adding disk, when there isn't any FS I/O,
 597          * so freezing queue plus canceling dispatch work is enough to
 598          * drain any dispatch activities originated from passthrough
 599          * requests, then no need to quiesce queue which may add long boot
 600          * latency, especially when lots of disks are involved.
 601          *
 602          * Disk isn't added yet, so verifying queue lock only manually.
 603          */
 604         blk_freeze_queue_start_non_owner(q);
 605         blk_freeze_acquire_lock(q, true, false);
 606         blk_mq_freeze_queue_wait(q);
 607
 608         blk_mq_cancel_work_sync(q);
 609
 610         err = blk_mq_init_sched(q, e);
 611
 612         blk_unfreeze_release_lock(q, true, false);
 613         blk_mq_unfreeze_queue_non_owner(q);
 614
 615         if (err) {
 616                 pr_warn("\"%s\" elevator initialization failed, "
 617                         "falling back to \"none\"\n", e->elevator_name);
 618         }
 619
 620         elevator_put(e);
 621 }
 622
 623 /*
 624  * Switch to new_e io scheduler.
 625  *
 626  * If switching fails, we are most likely running out of memory and not able
 627  * to restore the old io scheduler, so leaving the io scheduler being none.
 628  */
 629 int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 630 {
 631         int ret;
 632
 633         lockdep_assert_held(&q->sysfs_lock);
 634
 635         blk_mq_freeze_queue(q);
 636         blk_mq_quiesce_queue(q);
 637
 638         if (q->elevator) {
 639                 elv_unregister_queue(q);
 640                 elevator_exit(q);
 641         }
 642
 643         ret = blk_mq_init_sched(q, new_e);
 644         if (ret)
 645                 goto out_unfreeze;
 646
 647         ret = elv_register_queue(q, true);
 648         if (ret) {
 649                 elevator_exit(q);
 650                 goto out_unfreeze;
 651         }
 652         blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
 653
 654 out_unfreeze:
 655         blk_mq_unquiesce_queue(q);
 656         blk_mq_unfreeze_queue(q);
 657
 658         if (ret) {
 659                 pr_warn("elv: switch to \"%s\" failed, falling back to \"none\"\n",
 660                         new_e->elevator_name);
 661         }
 662
 663         return ret;
 664 }
 665
 666 void elevator_disable(struct request_queue *q)
 667 {
 668         lockdep_assert_held(&q->sysfs_lock);
 669
 670         blk_mq_freeze_queue(q);
 671         blk_mq_quiesce_queue(q);
 672
 673         elv_unregister_queue(q);
 674         elevator_exit(q);
 675         blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
 676         q->elevator = NULL;
 677         q->nr_requests = q->tag_set->queue_depth;
 678         blk_add_trace_msg(q, "elv switch: none");
 679
 680         blk_mq_unquiesce_queue(q);
 681         blk_mq_unfreeze_queue(q);
 682 }
 683
 684 /*
 685  * Switch this queue to the given IO scheduler.
 686  */
 687 static int elevator_change(struct request_queue *q, const char *elevator_name)
 688 {
 689         struct elevator_type *e;
 690         int ret;
 691
 692         /* Make sure queue is not in the middle of being removed */
 693         if (!blk_queue_registered(q))
 694                 return -ENOENT;
 695
 696         if (!strncmp(elevator_name, "none", 4)) {
 697                 if (q->elevator)
 698                         elevator_disable(q);
 699                 return 0;
 700         }
 701
 702         if (q->elevator && elevator_match(q->elevator->type, elevator_name))
 703                 return 0;
 704
 705         e = elevator_find_get(elevator_name);
 706         if (!e)
 707                 return -EINVAL;
 708         ret = elevator_switch(q, e);
 709         elevator_put(e);
 710         return ret;
 711 }
 712
 713 void elv_iosched_load_module(struct gendisk *disk, const char *buf,
 714                              size_t count)
 715 {
 716         char elevator_name[ELV_NAME_MAX];
 717         struct elevator_type *found;
 718         const char *name;
 719
 720         if (!elv_support_iosched(disk->queue))
 721                 return;
 722
 723         strscpy(elevator_name, buf, sizeof(elevator_name));
 724         name = strstrip(elevator_name);
 725
 726         spin_lock(&elv_list_lock);
 727         found = __elevator_find(name);
 728         spin_unlock(&elv_list_lock);
 729
 730         if (!found)
 731                 request_module("%s-iosched", name);
 732 }
 733
 734 ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 735                           size_t count)
 736 {
 737         char elevator_name[ELV_NAME_MAX];
 738         int ret;
 739
 740         if (!elv_support_iosched(disk->queue))
 741                 return count;
 742
 743         strscpy(elevator_name, buf, sizeof(elevator_name));
 744         ret = elevator_change(disk->queue, strstrip(elevator_name));
 745         if (!ret)
 746                 return count;
 747         return ret;
 748 }
 749
 750 ssize_t elv_iosched_show(struct gendisk *disk, char *name)
 751 {
 752         struct request_queue *q = disk->queue;
 753         struct elevator_queue *eq = q->elevator;
 754         struct elevator_type *cur = NULL, *e;
 755         int len = 0;
 756
 757         if (!elv_support_iosched(q))
 758                 return sprintf(name, "none\n");
 759
 760         if (!q->elevator) {
 761                 len += sprintf(name+len, "[none] ");
 762         } else {
 763                 len += sprintf(name+len, "none ");
 764                 cur = eq->type;
 765         }
 766
 767         spin_lock(&elv_list_lock);
 768         list_for_each_entry(e, &elv_list, list) {
 769                 if (e == cur)
 770                         len += sprintf(name+len, "[%s] ", e->elevator_name);
 771                 else
 772                         len += sprintf(name+len, "%s ", e->elevator_name);
 773         }
 774         spin_unlock(&elv_list_lock);
 775
 776         len += sprintf(name+len, "\n");
 777         return len;
 778 }
 779
 780 struct request *elv_rb_former_request(struct request_queue *q,
 781                                       struct request *rq)
 782 {
 783         struct rb_node *rbprev = rb_prev(&rq->rb_node);
 784
 785         if (rbprev)
 786                 return rb_entry_rq(rbprev);
 787
 788         return NULL;
 789 }
 790 EXPORT_SYMBOL(elv_rb_former_request);
 791
 792 struct request *elv_rb_latter_request(struct request_queue *q,
 793                                       struct request *rq)
 794 {
 795         struct rb_node *rbnext = rb_next(&rq->rb_node);
 796
 797         if (rbnext)
 798                 return rb_entry_rq(rbnext);
 799
 800         return NULL;
 801 }
 802 EXPORT_SYMBOL(elv_rb_latter_request);
 803
 804 static int __init elevator_setup(char *str)
 805 {
 806         pr_warn("Kernel parameter elevator= does not have any effect anymore.\n"
 807                 "Please use sysfs to set IO scheduler for individual devices.\n");
 808         return 1;
 809 }
 810
 811 __setup("elevator=", elevator_setup);