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/elevator.h>
  30 #include <linux/bio.h>
  31 #include <linux/module.h>
  32 #include <linux/slab.h>
  33 #include <linux/init.h>
  34 #include <linux/compiler.h>
  35 #include <linux/blktrace_api.h>
  36 #include <linux/hash.h>
  37 #include <linux/uaccess.h>
  38 #include <linux/pm_runtime.h>
  39 #include <linux/blk-cgroup.h>
  40
  41 #include <trace/events/block.h>
  42
  43 #include "blk.h"
  44 #include "blk-mq-sched.h"
  45 #include "blk-pm.h"
  46 #include "blk-wbt.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 int 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 1;
  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 static inline bool elv_support_features(unsigned int elv_features,
  87                                         unsigned int required_features)
  88 {
  89         return (required_features & elv_features) == required_features;
  90 }
  91
  92 /**
  93  * elevator_match - Test an elevator name and features
  94  * @e: Scheduler to test
  95  * @name: Elevator name to test
  96  * @required_features: Features that the elevator must provide
  97  *
  98  * Return true if the elevator @e name matches @name and if @e provides all
  99  * the features specified by @required_features.
 100  */
 101 static bool elevator_match(const struct elevator_type *e, const char *name,
 102                            unsigned int required_features)
 103 {
 104         if (!elv_support_features(e->elevator_features, required_features))
 105                 return false;
 106         if (!strcmp(e->elevator_name, name))
 107                 return true;
 108         if (e->elevator_alias && !strcmp(e->elevator_alias, name))
 109                 return true;
 110
 111         return false;
 112 }
 113
 114 /**
 115  * elevator_find - Find an elevator
 116  * @name: Name of the elevator to find
 117  * @required_features: Features that the elevator must provide
 118  *
 119  * Return the first registered scheduler with name @name and supporting the
 120  * features @required_features and NULL otherwise.
 121  */
 122 static struct elevator_type *elevator_find(const char *name,
 123                                            unsigned int required_features)
 124 {
 125         struct elevator_type *e;
 126
 127         list_for_each_entry(e, &elv_list, list) {
 128                 if (elevator_match(e, name, required_features))
 129                         return e;
 130         }
 131
 132         return NULL;
 133 }
 134
 135 static void elevator_put(struct elevator_type *e)
 136 {
 137         module_put(e->elevator_owner);
 138 }
 139
 140 static struct elevator_type *elevator_get(struct request_queue *q,
 141                                           const char *name, bool try_loading)
 142 {
 143         struct elevator_type *e;
 144
 145         spin_lock(&elv_list_lock);
 146
 147         e = elevator_find(name, q->required_elevator_features);
 148         if (!e && try_loading) {
 149                 spin_unlock(&elv_list_lock);
 150                 request_module("%s-iosched", name);
 151                 spin_lock(&elv_list_lock);
 152                 e = elevator_find(name, q->required_elevator_features);
 153         }
 154
 155         if (e && !try_module_get(e->elevator_owner))
 156                 e = NULL;
 157
 158         spin_unlock(&elv_list_lock);
 159         return e;
 160 }
 161
 162 static struct kobj_type elv_ktype;
 163
 164 struct elevator_queue *elevator_alloc(struct request_queue *q,
 165                                   struct elevator_type *e)
 166 {
 167         struct elevator_queue *eq;
 168
 169         eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node);
 170         if (unlikely(!eq))
 171                 return NULL;
 172
 173         eq->type = e;
 174         kobject_init(&eq->kobj, &elv_ktype);
 175         mutex_init(&eq->sysfs_lock);
 176         hash_init(eq->hash);
 177
 178         return eq;
 179 }
 180 EXPORT_SYMBOL(elevator_alloc);
 181
 182 static void elevator_release(struct kobject *kobj)
 183 {
 184         struct elevator_queue *e;
 185
 186         e = container_of(kobj, struct elevator_queue, kobj);
 187         elevator_put(e->type);
 188         kfree(e);
 189 }
 190
 191 void __elevator_exit(struct request_queue *q, struct elevator_queue *e)
 192 {
 193         mutex_lock(&e->sysfs_lock);
 194         blk_mq_exit_sched(q, e);
 195         mutex_unlock(&e->sysfs_lock);
 196
 197         kobject_put(&e->kobj);
 198 }
 199
 200 static inline void __elv_rqhash_del(struct request *rq)
 201 {
 202         hash_del(&rq->hash);
 203         rq->rq_flags &= ~RQF_HASHED;
 204 }
 205
 206 void elv_rqhash_del(struct request_queue *q, struct request *rq)
 207 {
 208         if (ELV_ON_HASH(rq))
 209                 __elv_rqhash_del(rq);
 210 }
 211 EXPORT_SYMBOL_GPL(elv_rqhash_del);
 212
 213 void elv_rqhash_add(struct request_queue *q, struct request *rq)
 214 {
 215         struct elevator_queue *e = q->elevator;
 216
 217         BUG_ON(ELV_ON_HASH(rq));
 218         hash_add(e->hash, &rq->hash, rq_hash_key(rq));
 219         rq->rq_flags |= RQF_HASHED;
 220 }
 221 EXPORT_SYMBOL_GPL(elv_rqhash_add);
 222
 223 void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 224 {
 225         __elv_rqhash_del(rq);
 226         elv_rqhash_add(q, rq);
 227 }
 228
 229 struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 230 {
 231         struct elevator_queue *e = q->elevator;
 232         struct hlist_node *next;
 233         struct request *rq;
 234
 235         hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
 236                 BUG_ON(!ELV_ON_HASH(rq));
 237
 238                 if (unlikely(!rq_mergeable(rq))) {
 239                         __elv_rqhash_del(rq);
 240                         continue;
 241                 }
 242
 243                 if (rq_hash_key(rq) == offset)
 244                         return rq;
 245         }
 246
 247         return NULL;
 248 }
 249
 250 /*
 251  * RB-tree support functions for inserting/lookup/removal of requests
 252  * in a sorted RB tree.
 253  */
 254 void elv_rb_add(struct rb_root *root, struct request *rq)
 255 {
 256         struct rb_node **p = &root->rb_node;
 257         struct rb_node *parent = NULL;
 258         struct request *__rq;
 259
 260         while (*p) {
 261                 parent = *p;
 262                 __rq = rb_entry(parent, struct request, rb_node);
 263
 264                 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
 265                         p = &(*p)->rb_left;
 266                 else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
 267                         p = &(*p)->rb_right;
 268         }
 269
 270         rb_link_node(&rq->rb_node, parent, p);
 271         rb_insert_color(&rq->rb_node, root);
 272 }
 273 EXPORT_SYMBOL(elv_rb_add);
 274
 275 void elv_rb_del(struct rb_root *root, struct request *rq)
 276 {
 277         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 278         rb_erase(&rq->rb_node, root);
 279         RB_CLEAR_NODE(&rq->rb_node);
 280 }
 281 EXPORT_SYMBOL(elv_rb_del);
 282
 283 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 284 {
 285         struct rb_node *n = root->rb_node;
 286         struct request *rq;
 287
 288         while (n) {
 289                 rq = rb_entry(n, struct request, rb_node);
 290
 291                 if (sector < blk_rq_pos(rq))
 292                         n = n->rb_left;
 293                 else if (sector > blk_rq_pos(rq))
 294                         n = n->rb_right;
 295                 else
 296                         return rq;
 297         }
 298
 299         return NULL;
 300 }
 301 EXPORT_SYMBOL(elv_rb_find);
 302
 303 enum elv_merge elv_merge(struct request_queue *q, struct request **req,
 304                 struct bio *bio)
 305 {
 306         struct elevator_queue *e = q->elevator;
 307         struct request *__rq;
 308
 309         /*
 310          * Levels of merges:
 311          *      nomerges:  No merges at all attempted
 312          *      noxmerges: Only simple one-hit cache try
 313          *      merges:    All merge tries attempted
 314          */
 315         if (blk_queue_nomerges(q) || !bio_mergeable(bio))
 316                 return ELEVATOR_NO_MERGE;
 317
 318         /*
 319          * First try one-hit cache.
 320          */
 321         if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
 322                 enum elv_merge ret = blk_try_merge(q->last_merge, bio);
 323
 324                 if (ret != ELEVATOR_NO_MERGE) {
 325                         *req = q->last_merge;
 326                         return ret;
 327                 }
 328         }
 329
 330         if (blk_queue_noxmerges(q))
 331                 return ELEVATOR_NO_MERGE;
 332
 333         /*
 334          * See if our hash lookup can find a potential backmerge.
 335          */
 336         __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
 337         if (__rq && elv_bio_merge_ok(__rq, bio)) {
 338                 *req = __rq;
 339                 return ELEVATOR_BACK_MERGE;
 340         }
 341
 342         if (e->type->ops.request_merge)
 343                 return e->type->ops.request_merge(q, req, bio);
 344
 345         return ELEVATOR_NO_MERGE;
 346 }
 347
 348 /*
 349  * Attempt to do an insertion back merge. Only check for the case where
 350  * we can append 'rq' to an existing request, so we can throw 'rq' away
 351  * afterwards.
 352  *
 353  * Returns true if we merged, false otherwise
 354  */
 355 bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq)
 356 {
 357         struct request *__rq;
 358         bool ret;
 359
 360         if (blk_queue_nomerges(q))
 361                 return false;
 362
 363         /*
 364          * First try one-hit cache.
 365          */
 366         if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
 367                 return true;
 368
 369         if (blk_queue_noxmerges(q))
 370                 return false;
 371
 372         ret = false;
 373         /*
 374          * See if our hash lookup can find a potential backmerge.
 375          */
 376         while (1) {
 377                 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
 378                 if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
 379                         break;
 380
 381                 /* The merged request could be merged with others, try again */
 382                 ret = true;
 383                 rq = __rq;
 384         }
 385
 386         return ret;
 387 }
 388
 389 void elv_merged_request(struct request_queue *q, struct request *rq,
 390                 enum elv_merge type)
 391 {
 392         struct elevator_queue *e = q->elevator;
 393
 394         if (e->type->ops.request_merged)
 395                 e->type->ops.request_merged(q, rq, type);
 396
 397         if (type == ELEVATOR_BACK_MERGE)
 398                 elv_rqhash_reposition(q, rq);
 399
 400         q->last_merge = rq;
 401 }
 402
 403 void elv_merge_requests(struct request_queue *q, struct request *rq,
 404                              struct request *next)
 405 {
 406         struct elevator_queue *e = q->elevator;
 407
 408         if (e->type->ops.requests_merged)
 409                 e->type->ops.requests_merged(q, rq, next);
 410
 411         elv_rqhash_reposition(q, rq);
 412         q->last_merge = rq;
 413 }
 414
 415 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 416 {
 417         struct elevator_queue *e = q->elevator;
 418
 419         if (e->type->ops.next_request)
 420                 return e->type->ops.next_request(q, rq);
 421
 422         return NULL;
 423 }
 424
 425 struct request *elv_former_request(struct request_queue *q, struct request *rq)
 426 {
 427         struct elevator_queue *e = q->elevator;
 428
 429         if (e->type->ops.former_request)
 430                 return e->type->ops.former_request(q, rq);
 431
 432         return NULL;
 433 }
 434
 435 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 436
 437 static ssize_t
 438 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 439 {
 440         struct elv_fs_entry *entry = to_elv(attr);
 441         struct elevator_queue *e;
 442         ssize_t error;
 443
 444         if (!entry->show)
 445                 return -EIO;
 446
 447         e = container_of(kobj, struct elevator_queue, kobj);
 448         mutex_lock(&e->sysfs_lock);
 449         error = e->type ? entry->show(e, page) : -ENOENT;
 450         mutex_unlock(&e->sysfs_lock);
 451         return error;
 452 }
 453
 454 static ssize_t
 455 elv_attr_store(struct kobject *kobj, struct attribute *attr,
 456                const char *page, size_t length)
 457 {
 458         struct elv_fs_entry *entry = to_elv(attr);
 459         struct elevator_queue *e;
 460         ssize_t error;
 461
 462         if (!entry->store)
 463                 return -EIO;
 464
 465         e = container_of(kobj, struct elevator_queue, kobj);
 466         mutex_lock(&e->sysfs_lock);
 467         error = e->type ? entry->store(e, page, length) : -ENOENT;
 468         mutex_unlock(&e->sysfs_lock);
 469         return error;
 470 }
 471
 472 static const struct sysfs_ops elv_sysfs_ops = {
 473         .show   = elv_attr_show,
 474         .store  = elv_attr_store,
 475 };
 476
 477 static struct kobj_type elv_ktype = {
 478         .sysfs_ops      = &elv_sysfs_ops,
 479         .release        = elevator_release,
 480 };
 481
 482 int elv_register_queue(struct request_queue *q, bool uevent)
 483 {
 484         struct elevator_queue *e = q->elevator;
 485         int error;
 486
 487         lockdep_assert_held(&q->sysfs_lock);
 488
 489         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
 490         if (!error) {
 491                 struct elv_fs_entry *attr = e->type->elevator_attrs;
 492                 if (attr) {
 493                         while (attr->attr.name) {
 494                                 if (sysfs_create_file(&e->kobj, &attr->attr))
 495                                         break;
 496                                 attr++;
 497                         }
 498                 }
 499                 if (uevent)
 500                         kobject_uevent(&e->kobj, KOBJ_ADD);
 501
 502                 e->registered = 1;
 503         }
 504         return error;
 505 }
 506
 507 void elv_unregister_queue(struct request_queue *q)
 508 {
 509         lockdep_assert_held(&q->sysfs_lock);
 510
 511         if (q) {
 512                 struct elevator_queue *e = q->elevator;
 513
 514                 kobject_uevent(&e->kobj, KOBJ_REMOVE);
 515                 kobject_del(&e->kobj);
 516
 517                 e->registered = 0;
 518                 /* Re-enable throttling in case elevator disabled it */
 519                 wbt_enable_default(q);
 520         }
 521 }
 522
 523 int elv_register(struct elevator_type *e)
 524 {
 525         /* create icq_cache if requested */
 526         if (e->icq_size) {
 527                 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
 528                     WARN_ON(e->icq_align < __alignof__(struct io_cq)))
 529                         return -EINVAL;
 530
 531                 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
 532                          "%s_io_cq", e->elevator_name);
 533                 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
 534                                                  e->icq_align, 0, NULL);
 535                 if (!e->icq_cache)
 536                         return -ENOMEM;
 537         }
 538
 539         /* register, don't allow duplicate names */
 540         spin_lock(&elv_list_lock);
 541         if (elevator_find(e->elevator_name, 0)) {
 542                 spin_unlock(&elv_list_lock);
 543                 kmem_cache_destroy(e->icq_cache);
 544                 return -EBUSY;
 545         }
 546         list_add_tail(&e->list, &elv_list);
 547         spin_unlock(&elv_list_lock);
 548
 549         printk(KERN_INFO "io scheduler %s registered\n", e->elevator_name);
 550
 551         return 0;
 552 }
 553 EXPORT_SYMBOL_GPL(elv_register);
 554
 555 void elv_unregister(struct elevator_type *e)
 556 {
 557         /* unregister */
 558         spin_lock(&elv_list_lock);
 559         list_del_init(&e->list);
 560         spin_unlock(&elv_list_lock);
 561
 562         /*
 563          * Destroy icq_cache if it exists.  icq's are RCU managed.  Make
 564          * sure all RCU operations are complete before proceeding.
 565          */
 566         if (e->icq_cache) {
 567                 rcu_barrier();
 568                 kmem_cache_destroy(e->icq_cache);
 569                 e->icq_cache = NULL;
 570         }
 571 }
 572 EXPORT_SYMBOL_GPL(elv_unregister);
 573
 574 int elevator_switch_mq(struct request_queue *q,
 575                               struct elevator_type *new_e)
 576 {
 577         int ret;
 578
 579         lockdep_assert_held(&q->sysfs_lock);
 580
 581         if (q->elevator) {
 582                 if (q->elevator->registered)
 583                         elv_unregister_queue(q);
 584
 585                 ioc_clear_queue(q);
 586                 elevator_exit(q, q->elevator);
 587         }
 588
 589         ret = blk_mq_init_sched(q, new_e);
 590         if (ret)
 591                 goto out;
 592
 593         if (new_e) {
 594                 ret = elv_register_queue(q, true);
 595                 if (ret) {
 596                         elevator_exit(q, q->elevator);
 597                         goto out;
 598                 }
 599         }
 600
 601         if (new_e)
 602                 blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
 603         else
 604                 blk_add_trace_msg(q, "elv switch: none");
 605
 606 out:
 607         return ret;
 608 }
 609
 610 static inline bool elv_support_iosched(struct request_queue *q)
 611 {
 612         if (!queue_is_mq(q) ||
 613             (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED)))
 614                 return false;
 615         return true;
 616 }
 617
 618 /*
 619  * For single queue devices, default to using mq-deadline. If we have multiple
 620  * queues or mq-deadline is not available, default to "none".
 621  */
 622 static struct elevator_type *elevator_get_default(struct request_queue *q)
 623 {
 624         if (q->nr_hw_queues != 1)
 625                 return NULL;
 626
 627         return elevator_get(q, "mq-deadline", false);
 628 }
 629
 630 /*
 631  * Get the first elevator providing the features required by the request queue.
 632  * Default to "none" if no matching elevator is found.
 633  */
 634 static struct elevator_type *elevator_get_by_features(struct request_queue *q)
 635 {
 636         struct elevator_type *e, *found = NULL;
 637
 638         spin_lock(&elv_list_lock);
 639
 640         list_for_each_entry(e, &elv_list, list) {
 641                 if (elv_support_features(e->elevator_features,
 642                                          q->required_elevator_features)) {
 643                         found = e;
 644                         break;
 645                 }
 646         }
 647
 648         if (found && !try_module_get(found->elevator_owner))
 649                 found = NULL;
 650
 651         spin_unlock(&elv_list_lock);
 652         return found;
 653 }
 654
 655 /*
 656  * For a device queue that has no required features, use the default elevator
 657  * settings. Otherwise, use the first elevator available matching the required
 658  * features. If no suitable elevator is find or if the chosen elevator
 659  * initialization fails, fall back to the "none" elevator (no elevator).
 660  */
 661 void elevator_init_mq(struct request_queue *q)
 662 {
 663         struct elevator_type *e;
 664         int err;
 665
 666         if (!elv_support_iosched(q))
 667                 return;
 668
 669         WARN_ON_ONCE(blk_queue_registered(q));
 670
 671         if (unlikely(q->elevator))
 672                 return;
 673
 674         if (!q->required_elevator_features)
 675                 e = elevator_get_default(q);
 676         else
 677                 e = elevator_get_by_features(q);
 678         if (!e)
 679                 return;
 680
 681         blk_mq_freeze_queue(q);
 682         blk_mq_quiesce_queue(q);
 683
 684         err = blk_mq_init_sched(q, e);
 685
 686         blk_mq_unquiesce_queue(q);
 687         blk_mq_unfreeze_queue(q);
 688
 689         if (err) {
 690                 pr_warn("\"%s\" elevator initialization failed, "
 691                         "falling back to \"none\"\n", e->elevator_name);
 692                 elevator_put(e);
 693         }
 694 }
 695
 696
 697 /*
 698  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 699  * we don't free the old io scheduler, before we have allocated what we
 700  * need for the new one. this way we have a chance of going back to the old
 701  * one, if the new one fails init for some reason.
 702  */
 703 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 704 {
 705         int err;
 706
 707         lockdep_assert_held(&q->sysfs_lock);
 708
 709         blk_mq_freeze_queue(q);
 710         blk_mq_quiesce_queue(q);
 711
 712         err = elevator_switch_mq(q, new_e);
 713
 714         blk_mq_unquiesce_queue(q);
 715         blk_mq_unfreeze_queue(q);
 716
 717         return err;
 718 }
 719
 720 /*
 721  * Switch this queue to the given IO scheduler.
 722  */
 723 static int __elevator_change(struct request_queue *q, const char *name)
 724 {
 725         char elevator_name[ELV_NAME_MAX];
 726         struct elevator_type *e;
 727
 728         /* Make sure queue is not in the middle of being removed */
 729         if (!blk_queue_registered(q))
 730                 return -ENOENT;
 731
 732         /*
 733          * Special case for mq, turn off scheduling
 734          */
 735         if (!strncmp(name, "none", 4)) {
 736                 if (!q->elevator)
 737                         return 0;
 738                 return elevator_switch(q, NULL);
 739         }
 740
 741         strlcpy(elevator_name, name, sizeof(elevator_name));
 742         e = elevator_get(q, strstrip(elevator_name), true);
 743         if (!e)
 744                 return -EINVAL;
 745
 746         if (q->elevator &&
 747             elevator_match(q->elevator->type, elevator_name, 0)) {
 748                 elevator_put(e);
 749                 return 0;
 750         }
 751
 752         return elevator_switch(q, e);
 753 }
 754
 755 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
 756                           size_t count)
 757 {
 758         int ret;
 759
 760         if (!elv_support_iosched(q))
 761                 return count;
 762
 763         ret = __elevator_change(q, name);
 764         if (!ret)
 765                 return count;
 766
 767         return ret;
 768 }
 769
 770 ssize_t elv_iosched_show(struct request_queue *q, char *name)
 771 {
 772         struct elevator_queue *e = q->elevator;
 773         struct elevator_type *elv = NULL;
 774         struct elevator_type *__e;
 775         int len = 0;
 776
 777         if (!queue_is_mq(q))
 778                 return sprintf(name, "none\n");
 779
 780         if (!q->elevator)
 781                 len += sprintf(name+len, "[none] ");
 782         else
 783                 elv = e->type;
 784
 785         spin_lock(&elv_list_lock);
 786         list_for_each_entry(__e, &elv_list, list) {
 787                 if (elv && elevator_match(elv, __e->elevator_name, 0)) {
 788                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 789                         continue;
 790                 }
 791                 if (elv_support_iosched(q) &&
 792                     elevator_match(__e, __e->elevator_name,
 793                                    q->required_elevator_features))
 794                         len += sprintf(name+len, "%s ", __e->elevator_name);
 795         }
 796         spin_unlock(&elv_list_lock);
 797
 798         if (q->elevator)
 799                 len += sprintf(name+len, "none");
 800
 801         len += sprintf(len+name, "\n");
 802         return len;
 803 }
 804
 805 struct request *elv_rb_former_request(struct request_queue *q,
 806                                       struct request *rq)
 807 {
 808         struct rb_node *rbprev = rb_prev(&rq->rb_node);
 809
 810         if (rbprev)
 811                 return rb_entry_rq(rbprev);
 812
 813         return NULL;
 814 }
 815 EXPORT_SYMBOL(elv_rb_former_request);
 816
 817 struct request *elv_rb_latter_request(struct request_queue *q,
 818                                       struct request *rq)
 819 {
 820         struct rb_node *rbnext = rb_next(&rq->rb_node);
 821
 822         if (rbnext)
 823                 return rb_entry_rq(rbnext);
 824
 825         return NULL;
 826 }
 827 EXPORT_SYMBOL(elv_rb_latter_request);
 828
 829 static int __init elevator_setup(char *str)
 830 {
 831         pr_warn("Kernel parameter elevator= does not have any effect anymore.\n"
 832                 "Please use sysfs to set IO scheduler for individual devices.\n");
 833         return 1;
 834 }
 835
 836 __setup("elevator=", elevator_setup);