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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
48static DEFINE_SPINLOCK(elv_list_lock);
49static 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 */
60static 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 */
74bool 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}
84EXPORT_SYMBOL(elv_bio_merge_ok);
85
86static inline bool elv_support_features(struct request_queue *q,
87 const struct elevator_type *e)
88{
89 return (q->required_elevator_features & e->elevator_features) ==
90 q->required_elevator_features;
91}
92
93/**
94 * elevator_match - Check whether @e's name or alias matches @name
95 * @e: Scheduler to test
96 * @name: Elevator name to test
97 *
98 * Return true if the elevator @e's name or alias matches @name.
99 */
100static bool elevator_match(const struct elevator_type *e, const char *name)
101{
102 return !strcmp(e->elevator_name, name) ||
103 (e->elevator_alias && !strcmp(e->elevator_alias, name));
104}
105
106static struct elevator_type *__elevator_find(const char *name)
107{
108 struct elevator_type *e;
109
110 list_for_each_entry(e, &elv_list, list)
111 if (elevator_match(e, name))
112 return e;
113 return NULL;
114}
115
116static struct elevator_type *elevator_find_get(struct request_queue *q,
117 const char *name)
118{
119 struct elevator_type *e;
120
121 spin_lock(&elv_list_lock);
122 e = __elevator_find(name);
123 if (e && (!elv_support_features(q, e) || !elevator_tryget(e)))
124 e = NULL;
125 spin_unlock(&elv_list_lock);
126 return e;
127}
128
129static struct kobj_type elv_ktype;
130
131struct elevator_queue *elevator_alloc(struct request_queue *q,
132 struct elevator_type *e)
133{
134 struct elevator_queue *eq;
135
136 eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node);
137 if (unlikely(!eq))
138 return NULL;
139
140 __elevator_get(e);
141 eq->type = e;
142 kobject_init(&eq->kobj, &elv_ktype);
143 mutex_init(&eq->sysfs_lock);
144 hash_init(eq->hash);
145
146 return eq;
147}
148EXPORT_SYMBOL(elevator_alloc);
149
150static void elevator_release(struct kobject *kobj)
151{
152 struct elevator_queue *e;
153
154 e = container_of(kobj, struct elevator_queue, kobj);
155 elevator_put(e->type);
156 kfree(e);
157}
158
159void elevator_exit(struct request_queue *q)
160{
161 struct elevator_queue *e = q->elevator;
162
163 ioc_clear_queue(q);
164 blk_mq_sched_free_rqs(q);
165
166 mutex_lock(&e->sysfs_lock);
167 blk_mq_exit_sched(q, e);
168 mutex_unlock(&e->sysfs_lock);
169
170 kobject_put(&e->kobj);
171}
172
173static inline void __elv_rqhash_del(struct request *rq)
174{
175 hash_del(&rq->hash);
176 rq->rq_flags &= ~RQF_HASHED;
177}
178
179void elv_rqhash_del(struct request_queue *q, struct request *rq)
180{
181 if (ELV_ON_HASH(rq))
182 __elv_rqhash_del(rq);
183}
184EXPORT_SYMBOL_GPL(elv_rqhash_del);
185
186void elv_rqhash_add(struct request_queue *q, struct request *rq)
187{
188 struct elevator_queue *e = q->elevator;
189
190 BUG_ON(ELV_ON_HASH(rq));
191 hash_add(e->hash, &rq->hash, rq_hash_key(rq));
192 rq->rq_flags |= RQF_HASHED;
193}
194EXPORT_SYMBOL_GPL(elv_rqhash_add);
195
196void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
197{
198 __elv_rqhash_del(rq);
199 elv_rqhash_add(q, rq);
200}
201
202struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
203{
204 struct elevator_queue *e = q->elevator;
205 struct hlist_node *next;
206 struct request *rq;
207
208 hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
209 BUG_ON(!ELV_ON_HASH(rq));
210
211 if (unlikely(!rq_mergeable(rq))) {
212 __elv_rqhash_del(rq);
213 continue;
214 }
215
216 if (rq_hash_key(rq) == offset)
217 return rq;
218 }
219
220 return NULL;
221}
222
223/*
224 * RB-tree support functions for inserting/lookup/removal of requests
225 * in a sorted RB tree.
226 */
227void elv_rb_add(struct rb_root *root, struct request *rq)
228{
229 struct rb_node **p = &root->rb_node;
230 struct rb_node *parent = NULL;
231 struct request *__rq;
232
233 while (*p) {
234 parent = *p;
235 __rq = rb_entry(parent, struct request, rb_node);
236
237 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
238 p = &(*p)->rb_left;
239 else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
240 p = &(*p)->rb_right;
241 }
242
243 rb_link_node(&rq->rb_node, parent, p);
244 rb_insert_color(&rq->rb_node, root);
245}
246EXPORT_SYMBOL(elv_rb_add);
247
248void elv_rb_del(struct rb_root *root, struct request *rq)
249{
250 BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
251 rb_erase(&rq->rb_node, root);
252 RB_CLEAR_NODE(&rq->rb_node);
253}
254EXPORT_SYMBOL(elv_rb_del);
255
256struct request *elv_rb_find(struct rb_root *root, sector_t sector)
257{
258 struct rb_node *n = root->rb_node;
259 struct request *rq;
260
261 while (n) {
262 rq = rb_entry(n, struct request, rb_node);
263
264 if (sector < blk_rq_pos(rq))
265 n = n->rb_left;
266 else if (sector > blk_rq_pos(rq))
267 n = n->rb_right;
268 else
269 return rq;
270 }
271
272 return NULL;
273}
274EXPORT_SYMBOL(elv_rb_find);
275
276enum elv_merge elv_merge(struct request_queue *q, struct request **req,
277 struct bio *bio)
278{
279 struct elevator_queue *e = q->elevator;
280 struct request *__rq;
281
282 /*
283 * Levels of merges:
284 * nomerges: No merges at all attempted
285 * noxmerges: Only simple one-hit cache try
286 * merges: All merge tries attempted
287 */
288 if (blk_queue_nomerges(q) || !bio_mergeable(bio))
289 return ELEVATOR_NO_MERGE;
290
291 /*
292 * First try one-hit cache.
293 */
294 if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
295 enum elv_merge ret = blk_try_merge(q->last_merge, bio);
296
297 if (ret != ELEVATOR_NO_MERGE) {
298 *req = q->last_merge;
299 return ret;
300 }
301 }
302
303 if (blk_queue_noxmerges(q))
304 return ELEVATOR_NO_MERGE;
305
306 /*
307 * See if our hash lookup can find a potential backmerge.
308 */
309 __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
310 if (__rq && elv_bio_merge_ok(__rq, bio)) {
311 *req = __rq;
312
313 if (blk_discard_mergable(__rq))
314 return ELEVATOR_DISCARD_MERGE;
315 return ELEVATOR_BACK_MERGE;
316 }
317
318 if (e->type->ops.request_merge)
319 return e->type->ops.request_merge(q, req, bio);
320
321 return ELEVATOR_NO_MERGE;
322}
323
324/*
325 * Attempt to do an insertion back merge. Only check for the case where
326 * we can append 'rq' to an existing request, so we can throw 'rq' away
327 * afterwards.
328 *
329 * Returns true if we merged, false otherwise. 'free' will contain all
330 * requests that need to be freed.
331 */
332bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq,
333 struct list_head *free)
334{
335 struct request *__rq;
336 bool ret;
337
338 if (blk_queue_nomerges(q))
339 return false;
340
341 /*
342 * First try one-hit cache.
343 */
344 if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq)) {
345 list_add(&rq->queuelist, free);
346 return true;
347 }
348
349 if (blk_queue_noxmerges(q))
350 return false;
351
352 ret = false;
353 /*
354 * See if our hash lookup can find a potential backmerge.
355 */
356 while (1) {
357 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
358 if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
359 break;
360
361 list_add(&rq->queuelist, free);
362 /* The merged request could be merged with others, try again */
363 ret = true;
364 rq = __rq;
365 }
366
367 return ret;
368}
369
370void elv_merged_request(struct request_queue *q, struct request *rq,
371 enum elv_merge type)
372{
373 struct elevator_queue *e = q->elevator;
374
375 if (e->type->ops.request_merged)
376 e->type->ops.request_merged(q, rq, type);
377
378 if (type == ELEVATOR_BACK_MERGE)
379 elv_rqhash_reposition(q, rq);
380
381 q->last_merge = rq;
382}
383
384void elv_merge_requests(struct request_queue *q, struct request *rq,
385 struct request *next)
386{
387 struct elevator_queue *e = q->elevator;
388
389 if (e->type->ops.requests_merged)
390 e->type->ops.requests_merged(q, rq, next);
391
392 elv_rqhash_reposition(q, rq);
393 q->last_merge = rq;
394}
395
396struct request *elv_latter_request(struct request_queue *q, struct request *rq)
397{
398 struct elevator_queue *e = q->elevator;
399
400 if (e->type->ops.next_request)
401 return e->type->ops.next_request(q, rq);
402
403 return NULL;
404}
405
406struct request *elv_former_request(struct request_queue *q, struct request *rq)
407{
408 struct elevator_queue *e = q->elevator;
409
410 if (e->type->ops.former_request)
411 return e->type->ops.former_request(q, rq);
412
413 return NULL;
414}
415
416#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
417
418static ssize_t
419elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
420{
421 struct elv_fs_entry *entry = to_elv(attr);
422 struct elevator_queue *e;
423 ssize_t error;
424
425 if (!entry->show)
426 return -EIO;
427
428 e = container_of(kobj, struct elevator_queue, kobj);
429 mutex_lock(&e->sysfs_lock);
430 error = e->type ? entry->show(e, page) : -ENOENT;
431 mutex_unlock(&e->sysfs_lock);
432 return error;
433}
434
435static ssize_t
436elv_attr_store(struct kobject *kobj, struct attribute *attr,
437 const char *page, size_t length)
438{
439 struct elv_fs_entry *entry = to_elv(attr);
440 struct elevator_queue *e;
441 ssize_t error;
442
443 if (!entry->store)
444 return -EIO;
445
446 e = container_of(kobj, struct elevator_queue, kobj);
447 mutex_lock(&e->sysfs_lock);
448 error = e->type ? entry->store(e, page, length) : -ENOENT;
449 mutex_unlock(&e->sysfs_lock);
450 return error;
451}
452
453static const struct sysfs_ops elv_sysfs_ops = {
454 .show = elv_attr_show,
455 .store = elv_attr_store,
456};
457
458static struct kobj_type elv_ktype = {
459 .sysfs_ops = &elv_sysfs_ops,
460 .release = elevator_release,
461};
462
463int elv_register_queue(struct request_queue *q, bool uevent)
464{
465 struct elevator_queue *e = q->elevator;
466 int error;
467
468 lockdep_assert_held(&q->sysfs_lock);
469
470 error = kobject_add(&e->kobj, &q->disk->queue_kobj, "iosched");
471 if (!error) {
472 struct elv_fs_entry *attr = e->type->elevator_attrs;
473 if (attr) {
474 while (attr->attr.name) {
475 if (sysfs_create_file(&e->kobj, &attr->attr))
476 break;
477 attr++;
478 }
479 }
480 if (uevent)
481 kobject_uevent(&e->kobj, KOBJ_ADD);
482
483 set_bit(ELEVATOR_FLAG_REGISTERED, &e->flags);
484 }
485 return error;
486}
487
488void elv_unregister_queue(struct request_queue *q)
489{
490 struct elevator_queue *e = q->elevator;
491
492 lockdep_assert_held(&q->sysfs_lock);
493
494 if (e && test_and_clear_bit(ELEVATOR_FLAG_REGISTERED, &e->flags)) {
495 kobject_uevent(&e->kobj, KOBJ_REMOVE);
496 kobject_del(&e->kobj);
497 }
498}
499
500int elv_register(struct elevator_type *e)
501{
502 /* insert_requests and dispatch_request are mandatory */
503 if (WARN_ON_ONCE(!e->ops.insert_requests || !e->ops.dispatch_request))
504 return -EINVAL;
505
506 /* create icq_cache if requested */
507 if (e->icq_size) {
508 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
509 WARN_ON(e->icq_align < __alignof__(struct io_cq)))
510 return -EINVAL;
511
512 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
513 "%s_io_cq", e->elevator_name);
514 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
515 e->icq_align, 0, NULL);
516 if (!e->icq_cache)
517 return -ENOMEM;
518 }
519
520 /* register, don't allow duplicate names */
521 spin_lock(&elv_list_lock);
522 if (__elevator_find(e->elevator_name)) {
523 spin_unlock(&elv_list_lock);
524 kmem_cache_destroy(e->icq_cache);
525 return -EBUSY;
526 }
527 list_add_tail(&e->list, &elv_list);
528 spin_unlock(&elv_list_lock);
529
530 printk(KERN_INFO "io scheduler %s registered\n", e->elevator_name);
531
532 return 0;
533}
534EXPORT_SYMBOL_GPL(elv_register);
535
536void elv_unregister(struct elevator_type *e)
537{
538 /* unregister */
539 spin_lock(&elv_list_lock);
540 list_del_init(&e->list);
541 spin_unlock(&elv_list_lock);
542
543 /*
544 * Destroy icq_cache if it exists. icq's are RCU managed. Make
545 * sure all RCU operations are complete before proceeding.
546 */
547 if (e->icq_cache) {
548 rcu_barrier();
549 kmem_cache_destroy(e->icq_cache);
550 e->icq_cache = NULL;
551 }
552}
553EXPORT_SYMBOL_GPL(elv_unregister);
554
555static inline bool elv_support_iosched(struct request_queue *q)
556{
557 if (!queue_is_mq(q) ||
558 (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED)))
559 return false;
560 return true;
561}
562
563/*
564 * For single queue devices, default to using mq-deadline. If we have multiple
565 * queues or mq-deadline is not available, default to "none".
566 */
567static struct elevator_type *elevator_get_default(struct request_queue *q)
568{
569 if (q->tag_set && q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
570 return NULL;
571
572 if (q->nr_hw_queues != 1 &&
573 !blk_mq_is_shared_tags(q->tag_set->flags))
574 return NULL;
575
576 return elevator_find_get(q, "mq-deadline");
577}
578
579/*
580 * Get the first elevator providing the features required by the request queue.
581 * Default to "none" if no matching elevator is found.
582 */
583static struct elevator_type *elevator_get_by_features(struct request_queue *q)
584{
585 struct elevator_type *e, *found = NULL;
586
587 spin_lock(&elv_list_lock);
588
589 list_for_each_entry(e, &elv_list, list) {
590 if (elv_support_features(q, e)) {
591 found = e;
592 break;
593 }
594 }
595
596 if (found && !elevator_tryget(found))
597 found = NULL;
598
599 spin_unlock(&elv_list_lock);
600 return found;
601}
602
603/*
604 * For a device queue that has no required features, use the default elevator
605 * settings. Otherwise, use the first elevator available matching the required
606 * features. If no suitable elevator is find or if the chosen elevator
607 * initialization fails, fall back to the "none" elevator (no elevator).
608 */
609void elevator_init_mq(struct request_queue *q)
610{
611 struct elevator_type *e;
612 int err;
613
614 if (!elv_support_iosched(q))
615 return;
616
617 WARN_ON_ONCE(blk_queue_registered(q));
618
619 if (unlikely(q->elevator))
620 return;
621
622 if (!q->required_elevator_features)
623 e = elevator_get_default(q);
624 else
625 e = elevator_get_by_features(q);
626 if (!e)
627 return;
628
629 /*
630 * We are called before adding disk, when there isn't any FS I/O,
631 * so freezing queue plus canceling dispatch work is enough to
632 * drain any dispatch activities originated from passthrough
633 * requests, then no need to quiesce queue which may add long boot
634 * latency, especially when lots of disks are involved.
635 */
636 blk_mq_freeze_queue(q);
637 blk_mq_cancel_work_sync(q);
638
639 err = blk_mq_init_sched(q, e);
640
641 blk_mq_unfreeze_queue(q);
642
643 if (err) {
644 pr_warn("\"%s\" elevator initialization failed, "
645 "falling back to \"none\"\n", e->elevator_name);
646 }
647
648 elevator_put(e);
649}
650
651/*
652 * Switch to new_e io scheduler.
653 *
654 * If switching fails, we are most likely running out of memory and not able
655 * to restore the old io scheduler, so leaving the io scheduler being none.
656 */
657int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
658{
659 int ret;
660
661 lockdep_assert_held(&q->sysfs_lock);
662
663 blk_mq_freeze_queue(q);
664 blk_mq_quiesce_queue(q);
665
666 if (q->elevator) {
667 elv_unregister_queue(q);
668 elevator_exit(q);
669 }
670
671 ret = blk_mq_init_sched(q, new_e);
672 if (ret)
673 goto out_unfreeze;
674
675 ret = elv_register_queue(q, true);
676 if (ret) {
677 elevator_exit(q);
678 goto out_unfreeze;
679 }
680 blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
681
682out_unfreeze:
683 blk_mq_unquiesce_queue(q);
684 blk_mq_unfreeze_queue(q);
685
686 if (ret) {
687 pr_warn("elv: switch to \"%s\" failed, falling back to \"none\"\n",
688 new_e->elevator_name);
689 }
690
691 return ret;
692}
693
694void elevator_disable(struct request_queue *q)
695{
696 lockdep_assert_held(&q->sysfs_lock);
697
698 blk_mq_freeze_queue(q);
699 blk_mq_quiesce_queue(q);
700
701 elv_unregister_queue(q);
702 elevator_exit(q);
703 blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
704 q->elevator = NULL;
705 q->nr_requests = q->tag_set->queue_depth;
706 blk_add_trace_msg(q, "elv switch: none");
707
708 blk_mq_unquiesce_queue(q);
709 blk_mq_unfreeze_queue(q);
710}
711
712/*
713 * Switch this queue to the given IO scheduler.
714 */
715static int elevator_change(struct request_queue *q, const char *elevator_name)
716{
717 struct elevator_type *e;
718 int ret;
719
720 /* Make sure queue is not in the middle of being removed */
721 if (!blk_queue_registered(q))
722 return -ENOENT;
723
724 if (!strncmp(elevator_name, "none", 4)) {
725 if (q->elevator)
726 elevator_disable(q);
727 return 0;
728 }
729
730 if (q->elevator && elevator_match(q->elevator->type, elevator_name))
731 return 0;
732
733 e = elevator_find_get(q, elevator_name);
734 if (!e) {
735 request_module("%s-iosched", elevator_name);
736 e = elevator_find_get(q, elevator_name);
737 if (!e)
738 return -EINVAL;
739 }
740 ret = elevator_switch(q, e);
741 elevator_put(e);
742 return ret;
743}
744
745ssize_t elv_iosched_store(struct request_queue *q, const char *buf,
746 size_t count)
747{
748 char elevator_name[ELV_NAME_MAX];
749 int ret;
750
751 if (!elv_support_iosched(q))
752 return count;
753
754 strlcpy(elevator_name, buf, sizeof(elevator_name));
755 ret = elevator_change(q, strstrip(elevator_name));
756 if (!ret)
757 return count;
758 return ret;
759}
760
761ssize_t elv_iosched_show(struct request_queue *q, char *name)
762{
763 struct elevator_queue *eq = q->elevator;
764 struct elevator_type *cur = NULL, *e;
765 int len = 0;
766
767 if (!elv_support_iosched(q))
768 return sprintf(name, "none\n");
769
770 if (!q->elevator) {
771 len += sprintf(name+len, "[none] ");
772 } else {
773 len += sprintf(name+len, "none ");
774 cur = eq->type;
775 }
776
777 spin_lock(&elv_list_lock);
778 list_for_each_entry(e, &elv_list, list) {
779 if (e == cur)
780 len += sprintf(name+len, "[%s] ", e->elevator_name);
781 else if (elv_support_features(q, e))
782 len += sprintf(name+len, "%s ", e->elevator_name);
783 }
784 spin_unlock(&elv_list_lock);
785
786 len += sprintf(name+len, "\n");
787 return len;
788}
789
790struct request *elv_rb_former_request(struct request_queue *q,
791 struct request *rq)
792{
793 struct rb_node *rbprev = rb_prev(&rq->rb_node);
794
795 if (rbprev)
796 return rb_entry_rq(rbprev);
797
798 return NULL;
799}
800EXPORT_SYMBOL(elv_rb_former_request);
801
802struct request *elv_rb_latter_request(struct request_queue *q,
803 struct request *rq)
804{
805 struct rb_node *rbnext = rb_next(&rq->rb_node);
806
807 if (rbnext)
808 return rb_entry_rq(rbnext);
809
810 return NULL;
811}
812EXPORT_SYMBOL(elv_rb_latter_request);
813
814static int __init elevator_setup(char *str)
815{
816 pr_warn("Kernel parameter elevator= does not have any effect anymore.\n"
817 "Please use sysfs to set IO scheduler for individual devices.\n");
818 return 1;
819}
820
821__setup("elevator=", elevator_setup);
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
48static DEFINE_SPINLOCK(elv_list_lock);
49static 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 */
60static 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 */
74bool 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}
84EXPORT_SYMBOL(elv_bio_merge_ok);
85
86static 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 */
101static 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 */
122static 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
135static void elevator_put(struct elevator_type *e)
136{
137 module_put(e->elevator_owner);
138}
139
140static 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
162static struct kobj_type elv_ktype;
163
164struct 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}
180EXPORT_SYMBOL(elevator_alloc);
181
182static 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
191void __elevator_exit(struct request_queue *q, struct elevator_queue *e)
192{
193 mutex_lock(&e->sysfs_lock);
194 if (e->type->ops.exit_sched)
195 blk_mq_exit_sched(q, e);
196 mutex_unlock(&e->sysfs_lock);
197
198 kobject_put(&e->kobj);
199}
200
201static inline void __elv_rqhash_del(struct request *rq)
202{
203 hash_del(&rq->hash);
204 rq->rq_flags &= ~RQF_HASHED;
205}
206
207void elv_rqhash_del(struct request_queue *q, struct request *rq)
208{
209 if (ELV_ON_HASH(rq))
210 __elv_rqhash_del(rq);
211}
212EXPORT_SYMBOL_GPL(elv_rqhash_del);
213
214void elv_rqhash_add(struct request_queue *q, struct request *rq)
215{
216 struct elevator_queue *e = q->elevator;
217
218 BUG_ON(ELV_ON_HASH(rq));
219 hash_add(e->hash, &rq->hash, rq_hash_key(rq));
220 rq->rq_flags |= RQF_HASHED;
221}
222EXPORT_SYMBOL_GPL(elv_rqhash_add);
223
224void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
225{
226 __elv_rqhash_del(rq);
227 elv_rqhash_add(q, rq);
228}
229
230struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
231{
232 struct elevator_queue *e = q->elevator;
233 struct hlist_node *next;
234 struct request *rq;
235
236 hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
237 BUG_ON(!ELV_ON_HASH(rq));
238
239 if (unlikely(!rq_mergeable(rq))) {
240 __elv_rqhash_del(rq);
241 continue;
242 }
243
244 if (rq_hash_key(rq) == offset)
245 return rq;
246 }
247
248 return NULL;
249}
250
251/*
252 * RB-tree support functions for inserting/lookup/removal of requests
253 * in a sorted RB tree.
254 */
255void elv_rb_add(struct rb_root *root, struct request *rq)
256{
257 struct rb_node **p = &root->rb_node;
258 struct rb_node *parent = NULL;
259 struct request *__rq;
260
261 while (*p) {
262 parent = *p;
263 __rq = rb_entry(parent, struct request, rb_node);
264
265 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
266 p = &(*p)->rb_left;
267 else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
268 p = &(*p)->rb_right;
269 }
270
271 rb_link_node(&rq->rb_node, parent, p);
272 rb_insert_color(&rq->rb_node, root);
273}
274EXPORT_SYMBOL(elv_rb_add);
275
276void elv_rb_del(struct rb_root *root, struct request *rq)
277{
278 BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
279 rb_erase(&rq->rb_node, root);
280 RB_CLEAR_NODE(&rq->rb_node);
281}
282EXPORT_SYMBOL(elv_rb_del);
283
284struct request *elv_rb_find(struct rb_root *root, sector_t sector)
285{
286 struct rb_node *n = root->rb_node;
287 struct request *rq;
288
289 while (n) {
290 rq = rb_entry(n, struct request, rb_node);
291
292 if (sector < blk_rq_pos(rq))
293 n = n->rb_left;
294 else if (sector > blk_rq_pos(rq))
295 n = n->rb_right;
296 else
297 return rq;
298 }
299
300 return NULL;
301}
302EXPORT_SYMBOL(elv_rb_find);
303
304enum elv_merge elv_merge(struct request_queue *q, struct request **req,
305 struct bio *bio)
306{
307 struct elevator_queue *e = q->elevator;
308 struct request *__rq;
309
310 /*
311 * Levels of merges:
312 * nomerges: No merges at all attempted
313 * noxmerges: Only simple one-hit cache try
314 * merges: All merge tries attempted
315 */
316 if (blk_queue_nomerges(q) || !bio_mergeable(bio))
317 return ELEVATOR_NO_MERGE;
318
319 /*
320 * First try one-hit cache.
321 */
322 if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
323 enum elv_merge ret = blk_try_merge(q->last_merge, bio);
324
325 if (ret != ELEVATOR_NO_MERGE) {
326 *req = q->last_merge;
327 return ret;
328 }
329 }
330
331 if (blk_queue_noxmerges(q))
332 return ELEVATOR_NO_MERGE;
333
334 /*
335 * See if our hash lookup can find a potential backmerge.
336 */
337 __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
338 if (__rq && elv_bio_merge_ok(__rq, bio)) {
339 *req = __rq;
340 return ELEVATOR_BACK_MERGE;
341 }
342
343 if (e->type->ops.request_merge)
344 return e->type->ops.request_merge(q, req, bio);
345
346 return ELEVATOR_NO_MERGE;
347}
348
349/*
350 * Attempt to do an insertion back merge. Only check for the case where
351 * we can append 'rq' to an existing request, so we can throw 'rq' away
352 * afterwards.
353 *
354 * Returns true if we merged, false otherwise
355 */
356bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq)
357{
358 struct request *__rq;
359 bool ret;
360
361 if (blk_queue_nomerges(q))
362 return false;
363
364 /*
365 * First try one-hit cache.
366 */
367 if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
368 return true;
369
370 if (blk_queue_noxmerges(q))
371 return false;
372
373 ret = false;
374 /*
375 * See if our hash lookup can find a potential backmerge.
376 */
377 while (1) {
378 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
379 if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
380 break;
381
382 /* The merged request could be merged with others, try again */
383 ret = true;
384 rq = __rq;
385 }
386
387 return ret;
388}
389
390void elv_merged_request(struct request_queue *q, struct request *rq,
391 enum elv_merge type)
392{
393 struct elevator_queue *e = q->elevator;
394
395 if (e->type->ops.request_merged)
396 e->type->ops.request_merged(q, rq, type);
397
398 if (type == ELEVATOR_BACK_MERGE)
399 elv_rqhash_reposition(q, rq);
400
401 q->last_merge = rq;
402}
403
404void elv_merge_requests(struct request_queue *q, struct request *rq,
405 struct request *next)
406{
407 struct elevator_queue *e = q->elevator;
408
409 if (e->type->ops.requests_merged)
410 e->type->ops.requests_merged(q, rq, next);
411
412 elv_rqhash_reposition(q, rq);
413 q->last_merge = rq;
414}
415
416struct request *elv_latter_request(struct request_queue *q, struct request *rq)
417{
418 struct elevator_queue *e = q->elevator;
419
420 if (e->type->ops.next_request)
421 return e->type->ops.next_request(q, rq);
422
423 return NULL;
424}
425
426struct request *elv_former_request(struct request_queue *q, struct request *rq)
427{
428 struct elevator_queue *e = q->elevator;
429
430 if (e->type->ops.former_request)
431 return e->type->ops.former_request(q, rq);
432
433 return NULL;
434}
435
436#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
437
438static ssize_t
439elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
440{
441 struct elv_fs_entry *entry = to_elv(attr);
442 struct elevator_queue *e;
443 ssize_t error;
444
445 if (!entry->show)
446 return -EIO;
447
448 e = container_of(kobj, struct elevator_queue, kobj);
449 mutex_lock(&e->sysfs_lock);
450 error = e->type ? entry->show(e, page) : -ENOENT;
451 mutex_unlock(&e->sysfs_lock);
452 return error;
453}
454
455static ssize_t
456elv_attr_store(struct kobject *kobj, struct attribute *attr,
457 const char *page, size_t length)
458{
459 struct elv_fs_entry *entry = to_elv(attr);
460 struct elevator_queue *e;
461 ssize_t error;
462
463 if (!entry->store)
464 return -EIO;
465
466 e = container_of(kobj, struct elevator_queue, kobj);
467 mutex_lock(&e->sysfs_lock);
468 error = e->type ? entry->store(e, page, length) : -ENOENT;
469 mutex_unlock(&e->sysfs_lock);
470 return error;
471}
472
473static const struct sysfs_ops elv_sysfs_ops = {
474 .show = elv_attr_show,
475 .store = elv_attr_store,
476};
477
478static struct kobj_type elv_ktype = {
479 .sysfs_ops = &elv_sysfs_ops,
480 .release = elevator_release,
481};
482
483/*
484 * elv_register_queue is called from either blk_register_queue or
485 * elevator_switch, elevator switch is prevented from being happen
486 * in the two paths, so it is safe to not hold q->sysfs_lock.
487 */
488int elv_register_queue(struct request_queue *q, bool uevent)
489{
490 struct elevator_queue *e = q->elevator;
491 int error;
492
493 error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
494 if (!error) {
495 struct elv_fs_entry *attr = e->type->elevator_attrs;
496 if (attr) {
497 while (attr->attr.name) {
498 if (sysfs_create_file(&e->kobj, &attr->attr))
499 break;
500 attr++;
501 }
502 }
503 if (uevent)
504 kobject_uevent(&e->kobj, KOBJ_ADD);
505
506 e->registered = 1;
507 }
508 return error;
509}
510
511/*
512 * elv_unregister_queue is called from either blk_unregister_queue or
513 * elevator_switch, elevator switch is prevented from being happen
514 * in the two paths, so it is safe to not hold q->sysfs_lock.
515 */
516void elv_unregister_queue(struct request_queue *q)
517{
518 if (q) {
519 struct elevator_queue *e = q->elevator;
520
521 kobject_uevent(&e->kobj, KOBJ_REMOVE);
522 kobject_del(&e->kobj);
523
524 e->registered = 0;
525 /* Re-enable throttling in case elevator disabled it */
526 wbt_enable_default(q);
527 }
528}
529
530int elv_register(struct elevator_type *e)
531{
532 /* create icq_cache if requested */
533 if (e->icq_size) {
534 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
535 WARN_ON(e->icq_align < __alignof__(struct io_cq)))
536 return -EINVAL;
537
538 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
539 "%s_io_cq", e->elevator_name);
540 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
541 e->icq_align, 0, NULL);
542 if (!e->icq_cache)
543 return -ENOMEM;
544 }
545
546 /* register, don't allow duplicate names */
547 spin_lock(&elv_list_lock);
548 if (elevator_find(e->elevator_name, 0)) {
549 spin_unlock(&elv_list_lock);
550 kmem_cache_destroy(e->icq_cache);
551 return -EBUSY;
552 }
553 list_add_tail(&e->list, &elv_list);
554 spin_unlock(&elv_list_lock);
555
556 printk(KERN_INFO "io scheduler %s registered\n", e->elevator_name);
557
558 return 0;
559}
560EXPORT_SYMBOL_GPL(elv_register);
561
562void elv_unregister(struct elevator_type *e)
563{
564 /* unregister */
565 spin_lock(&elv_list_lock);
566 list_del_init(&e->list);
567 spin_unlock(&elv_list_lock);
568
569 /*
570 * Destroy icq_cache if it exists. icq's are RCU managed. Make
571 * sure all RCU operations are complete before proceeding.
572 */
573 if (e->icq_cache) {
574 rcu_barrier();
575 kmem_cache_destroy(e->icq_cache);
576 e->icq_cache = NULL;
577 }
578}
579EXPORT_SYMBOL_GPL(elv_unregister);
580
581int elevator_switch_mq(struct request_queue *q,
582 struct elevator_type *new_e)
583{
584 int ret;
585
586 lockdep_assert_held(&q->sysfs_lock);
587
588 if (q->elevator) {
589 if (q->elevator->registered)
590 elv_unregister_queue(q);
591
592 ioc_clear_queue(q);
593 elevator_exit(q, q->elevator);
594 }
595
596 ret = blk_mq_init_sched(q, new_e);
597 if (ret)
598 goto out;
599
600 if (new_e) {
601 ret = elv_register_queue(q, true);
602 if (ret) {
603 elevator_exit(q, q->elevator);
604 goto out;
605 }
606 }
607
608 if (new_e)
609 blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
610 else
611 blk_add_trace_msg(q, "elv switch: none");
612
613out:
614 return ret;
615}
616
617static inline bool elv_support_iosched(struct request_queue *q)
618{
619 if (!q->mq_ops ||
620 (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED)))
621 return false;
622 return true;
623}
624
625/*
626 * For single queue devices, default to using mq-deadline. If we have multiple
627 * queues or mq-deadline is not available, default to "none".
628 */
629static struct elevator_type *elevator_get_default(struct request_queue *q)
630{
631 if (q->nr_hw_queues != 1)
632 return NULL;
633
634 return elevator_get(q, "mq-deadline", false);
635}
636
637/*
638 * Get the first elevator providing the features required by the request queue.
639 * Default to "none" if no matching elevator is found.
640 */
641static struct elevator_type *elevator_get_by_features(struct request_queue *q)
642{
643 struct elevator_type *e, *found = NULL;
644
645 spin_lock(&elv_list_lock);
646
647 list_for_each_entry(e, &elv_list, list) {
648 if (elv_support_features(e->elevator_features,
649 q->required_elevator_features)) {
650 found = e;
651 break;
652 }
653 }
654
655 if (found && !try_module_get(found->elevator_owner))
656 found = NULL;
657
658 spin_unlock(&elv_list_lock);
659 return found;
660}
661
662/*
663 * For a device queue that has no required features, use the default elevator
664 * settings. Otherwise, use the first elevator available matching the required
665 * features. If no suitable elevator is find or if the chosen elevator
666 * initialization fails, fall back to the "none" elevator (no elevator).
667 */
668void elevator_init_mq(struct request_queue *q)
669{
670 struct elevator_type *e;
671 int err;
672
673 if (!elv_support_iosched(q))
674 return;
675
676 WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags));
677
678 if (unlikely(q->elevator))
679 return;
680
681 if (!q->required_elevator_features)
682 e = elevator_get_default(q);
683 else
684 e = elevator_get_by_features(q);
685 if (!e)
686 return;
687
688 blk_mq_freeze_queue(q);
689 blk_mq_quiesce_queue(q);
690
691 err = blk_mq_init_sched(q, e);
692
693 blk_mq_unquiesce_queue(q);
694 blk_mq_unfreeze_queue(q);
695
696 if (err) {
697 pr_warn("\"%s\" elevator initialization failed, "
698 "falling back to \"none\"\n", e->elevator_name);
699 elevator_put(e);
700 }
701}
702
703
704/*
705 * switch to new_e io scheduler. be careful not to introduce deadlocks -
706 * we don't free the old io scheduler, before we have allocated what we
707 * need for the new one. this way we have a chance of going back to the old
708 * one, if the new one fails init for some reason.
709 */
710static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
711{
712 int err;
713
714 lockdep_assert_held(&q->sysfs_lock);
715
716 blk_mq_freeze_queue(q);
717 blk_mq_quiesce_queue(q);
718
719 err = elevator_switch_mq(q, new_e);
720
721 blk_mq_unquiesce_queue(q);
722 blk_mq_unfreeze_queue(q);
723
724 return err;
725}
726
727/*
728 * Switch this queue to the given IO scheduler.
729 */
730static int __elevator_change(struct request_queue *q, const char *name)
731{
732 char elevator_name[ELV_NAME_MAX];
733 struct elevator_type *e;
734
735 /* Make sure queue is not in the middle of being removed */
736 if (!blk_queue_registered(q))
737 return -ENOENT;
738
739 /*
740 * Special case for mq, turn off scheduling
741 */
742 if (!strncmp(name, "none", 4)) {
743 if (!q->elevator)
744 return 0;
745 return elevator_switch(q, NULL);
746 }
747
748 strlcpy(elevator_name, name, sizeof(elevator_name));
749 e = elevator_get(q, strstrip(elevator_name), true);
750 if (!e)
751 return -EINVAL;
752
753 if (q->elevator &&
754 elevator_match(q->elevator->type, elevator_name, 0)) {
755 elevator_put(e);
756 return 0;
757 }
758
759 return elevator_switch(q, e);
760}
761
762ssize_t elv_iosched_store(struct request_queue *q, const char *name,
763 size_t count)
764{
765 int ret;
766
767 if (!queue_is_mq(q) || !elv_support_iosched(q))
768 return count;
769
770 ret = __elevator_change(q, name);
771 if (!ret)
772 return count;
773
774 return ret;
775}
776
777ssize_t elv_iosched_show(struct request_queue *q, char *name)
778{
779 struct elevator_queue *e = q->elevator;
780 struct elevator_type *elv = NULL;
781 struct elevator_type *__e;
782 int len = 0;
783
784 if (!queue_is_mq(q))
785 return sprintf(name, "none\n");
786
787 if (!q->elevator)
788 len += sprintf(name+len, "[none] ");
789 else
790 elv = e->type;
791
792 spin_lock(&elv_list_lock);
793 list_for_each_entry(__e, &elv_list, list) {
794 if (elv && elevator_match(elv, __e->elevator_name, 0)) {
795 len += sprintf(name+len, "[%s] ", elv->elevator_name);
796 continue;
797 }
798 if (elv_support_iosched(q) &&
799 elevator_match(__e, __e->elevator_name,
800 q->required_elevator_features))
801 len += sprintf(name+len, "%s ", __e->elevator_name);
802 }
803 spin_unlock(&elv_list_lock);
804
805 if (q->elevator)
806 len += sprintf(name+len, "none");
807
808 len += sprintf(len+name, "\n");
809 return len;
810}
811
812struct request *elv_rb_former_request(struct request_queue *q,
813 struct request *rq)
814{
815 struct rb_node *rbprev = rb_prev(&rq->rb_node);
816
817 if (rbprev)
818 return rb_entry_rq(rbprev);
819
820 return NULL;
821}
822EXPORT_SYMBOL(elv_rb_former_request);
823
824struct request *elv_rb_latter_request(struct request_queue *q,
825 struct request *rq)
826{
827 struct rb_node *rbnext = rb_next(&rq->rb_node);
828
829 if (rbnext)
830 return rb_entry_rq(rbnext);
831
832 return NULL;
833}
834EXPORT_SYMBOL(elv_rb_latter_request);
835
836static int __init elevator_setup(char *str)
837{
838 pr_warn("Kernel parameter elevator= does not have any effect anymore.\n"
839 "Please use sysfs to set IO scheduler for individual devices.\n");
840 return 1;
841}
842
843__setup("elevator=", elevator_setup);