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