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(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(lock: &elv_list_lock);
126 return e;
127}
128
129static const 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(size: sizeof(*eq), GFP_KERNEL, node: q->node);
137 if (unlikely(!eq))
138 return NULL;
139
140 __elevator_get(e);
141 eq->type = e;
142 kobject_init(kobj: &eq->kobj, ktype: &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: e->type);
156 kfree(objp: 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(lock: &e->sysfs_lock);
169
170 kobject_put(kobj: &e->kobj);
171}
172
173static inline void __elv_rqhash_del(struct request *rq)
174{
175 hash_del(node: &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: __rq))
238 p = &(*p)->rb_left;
239 else if (blk_rq_pos(rq) >= blk_rq_pos(rq: __rq))
240 p = &(*p)->rb_right;
241 }
242
243 rb_link_node(node: &rq->rb_node, parent, rb_link: 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(rq: 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, offset: bio->bi_iter.bi_sector);
310 if (__rq && elv_bio_merge_ok(__rq, bio)) {
311 *req = __rq;
312
313 if (blk_discard_mergable(req: __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, rq: q->last_merge, next: rq)) {
345 list_add(new: &rq->queuelist, head: 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, offset: blk_rq_pos(rq));
358 if (!__rq || !blk_attempt_req_merge(q, rq: __rq, next: rq))
359 break;
360
361 list_add(new: &rq->queuelist, head: 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(lock: &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(lock: &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 const 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(kobj: &e->kobj, parent: &q->disk->queue_kobj, fmt: "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(kobj: &e->kobj, attr: &attr->attr))
476 break;
477 attr++;
478 }
479 }
480 if (uevent)
481 kobject_uevent(kobj: &e->kobj, action: KOBJ_ADD);
482
483 set_bit(ELEVATOR_FLAG_REGISTERED, addr: &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, addr: &e->flags)) {
495 kobject_uevent(kobj: &e->kobj, action: KOBJ_REMOVE);
496 kobject_del(kobj: &e->kobj);
497 }
498}
499
500int elv_register(struct elevator_type *e)
501{
502 /* finish request is mandatory */
503 if (WARN_ON_ONCE(!e->ops.finish_request))
504 return -EINVAL;
505 /* insert_requests and dispatch_request are mandatory */
506 if (WARN_ON_ONCE(!e->ops.insert_requests || !e->ops.dispatch_request))
507 return -EINVAL;
508
509 /* create icq_cache if requested */
510 if (e->icq_size) {
511 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
512 WARN_ON(e->icq_align < __alignof__(struct io_cq)))
513 return -EINVAL;
514
515 snprintf(buf: e->icq_cache_name, size: sizeof(e->icq_cache_name),
516 fmt: "%s_io_cq", e->elevator_name);
517 e->icq_cache = kmem_cache_create(name: e->icq_cache_name, size: e->icq_size,
518 align: e->icq_align, flags: 0, NULL);
519 if (!e->icq_cache)
520 return -ENOMEM;
521 }
522
523 /* register, don't allow duplicate names */
524 spin_lock(lock: &elv_list_lock);
525 if (__elevator_find(name: e->elevator_name)) {
526 spin_unlock(lock: &elv_list_lock);
527 kmem_cache_destroy(s: e->icq_cache);
528 return -EBUSY;
529 }
530 list_add_tail(new: &e->list, head: &elv_list);
531 spin_unlock(lock: &elv_list_lock);
532
533 printk(KERN_INFO "io scheduler %s registered\n", e->elevator_name);
534
535 return 0;
536}
537EXPORT_SYMBOL_GPL(elv_register);
538
539void elv_unregister(struct elevator_type *e)
540{
541 /* unregister */
542 spin_lock(lock: &elv_list_lock);
543 list_del_init(entry: &e->list);
544 spin_unlock(lock: &elv_list_lock);
545
546 /*
547 * Destroy icq_cache if it exists. icq's are RCU managed. Make
548 * sure all RCU operations are complete before proceeding.
549 */
550 if (e->icq_cache) {
551 rcu_barrier();
552 kmem_cache_destroy(s: e->icq_cache);
553 e->icq_cache = NULL;
554 }
555}
556EXPORT_SYMBOL_GPL(elv_unregister);
557
558static inline bool elv_support_iosched(struct request_queue *q)
559{
560 if (!queue_is_mq(q) ||
561 (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED)))
562 return false;
563 return true;
564}
565
566/*
567 * For single queue devices, default to using mq-deadline. If we have multiple
568 * queues or mq-deadline is not available, default to "none".
569 */
570static struct elevator_type *elevator_get_default(struct request_queue *q)
571{
572 if (q->tag_set && q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
573 return NULL;
574
575 if (q->nr_hw_queues != 1 &&
576 !blk_mq_is_shared_tags(flags: q->tag_set->flags))
577 return NULL;
578
579 return elevator_find_get(q, name: "mq-deadline");
580}
581
582/*
583 * Get the first elevator providing the features required by the request queue.
584 * Default to "none" if no matching elevator is found.
585 */
586static struct elevator_type *elevator_get_by_features(struct request_queue *q)
587{
588 struct elevator_type *e, *found = NULL;
589
590 spin_lock(lock: &elv_list_lock);
591
592 list_for_each_entry(e, &elv_list, list) {
593 if (elv_support_features(q, e)) {
594 found = e;
595 break;
596 }
597 }
598
599 if (found && !elevator_tryget(e: found))
600 found = NULL;
601
602 spin_unlock(lock: &elv_list_lock);
603 return found;
604}
605
606/*
607 * For a device queue that has no required features, use the default elevator
608 * settings. Otherwise, use the first elevator available matching the required
609 * features. If no suitable elevator is find or if the chosen elevator
610 * initialization fails, fall back to the "none" elevator (no elevator).
611 */
612void elevator_init_mq(struct request_queue *q)
613{
614 struct elevator_type *e;
615 int err;
616
617 if (!elv_support_iosched(q))
618 return;
619
620 WARN_ON_ONCE(blk_queue_registered(q));
621
622 if (unlikely(q->elevator))
623 return;
624
625 if (!q->required_elevator_features)
626 e = elevator_get_default(q);
627 else
628 e = elevator_get_by_features(q);
629 if (!e)
630 return;
631
632 /*
633 * We are called before adding disk, when there isn't any FS I/O,
634 * so freezing queue plus canceling dispatch work is enough to
635 * drain any dispatch activities originated from passthrough
636 * requests, then no need to quiesce queue which may add long boot
637 * latency, especially when lots of disks are involved.
638 */
639 blk_mq_freeze_queue(q);
640 blk_mq_cancel_work_sync(q);
641
642 err = blk_mq_init_sched(q, e);
643
644 blk_mq_unfreeze_queue(q);
645
646 if (err) {
647 pr_warn("\"%s\" elevator initialization failed, "
648 "falling back to \"none\"\n", e->elevator_name);
649 }
650
651 elevator_put(e);
652}
653
654/*
655 * Switch to new_e io scheduler.
656 *
657 * If switching fails, we are most likely running out of memory and not able
658 * to restore the old io scheduler, so leaving the io scheduler being none.
659 */
660int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
661{
662 int ret;
663
664 lockdep_assert_held(&q->sysfs_lock);
665
666 blk_mq_freeze_queue(q);
667 blk_mq_quiesce_queue(q);
668
669 if (q->elevator) {
670 elv_unregister_queue(q);
671 elevator_exit(q);
672 }
673
674 ret = blk_mq_init_sched(q, e: new_e);
675 if (ret)
676 goto out_unfreeze;
677
678 ret = elv_register_queue(q, uevent: true);
679 if (ret) {
680 elevator_exit(q);
681 goto out_unfreeze;
682 }
683 blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
684
685out_unfreeze:
686 blk_mq_unquiesce_queue(q);
687 blk_mq_unfreeze_queue(q);
688
689 if (ret) {
690 pr_warn("elv: switch to \"%s\" failed, falling back to \"none\"\n",
691 new_e->elevator_name);
692 }
693
694 return ret;
695}
696
697void elevator_disable(struct request_queue *q)
698{
699 lockdep_assert_held(&q->sysfs_lock);
700
701 blk_mq_freeze_queue(q);
702 blk_mq_quiesce_queue(q);
703
704 elv_unregister_queue(q);
705 elevator_exit(q);
706 blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
707 q->elevator = NULL;
708 q->nr_requests = q->tag_set->queue_depth;
709 blk_add_trace_msg(q, "elv switch: none");
710
711 blk_mq_unquiesce_queue(q);
712 blk_mq_unfreeze_queue(q);
713}
714
715/*
716 * Switch this queue to the given IO scheduler.
717 */
718static int elevator_change(struct request_queue *q, const char *elevator_name)
719{
720 struct elevator_type *e;
721 int ret;
722
723 /* Make sure queue is not in the middle of being removed */
724 if (!blk_queue_registered(q))
725 return -ENOENT;
726
727 if (!strncmp(elevator_name, "none", 4)) {
728 if (q->elevator)
729 elevator_disable(q);
730 return 0;
731 }
732
733 if (q->elevator && elevator_match(e: q->elevator->type, name: elevator_name))
734 return 0;
735
736 e = elevator_find_get(q, name: elevator_name);
737 if (!e) {
738 request_module("%s-iosched", elevator_name);
739 e = elevator_find_get(q, name: elevator_name);
740 if (!e)
741 return -EINVAL;
742 }
743 ret = elevator_switch(q, new_e: e);
744 elevator_put(e);
745 return ret;
746}
747
748ssize_t elv_iosched_store(struct request_queue *q, const char *buf,
749 size_t count)
750{
751 char elevator_name[ELV_NAME_MAX];
752 int ret;
753
754 if (!elv_support_iosched(q))
755 return count;
756
757 strscpy(p: elevator_name, q: buf, size: sizeof(elevator_name));
758 ret = elevator_change(q, elevator_name: strstrip(str: elevator_name));
759 if (!ret)
760 return count;
761 return ret;
762}
763
764ssize_t elv_iosched_show(struct request_queue *q, char *name)
765{
766 struct elevator_queue *eq = q->elevator;
767 struct elevator_type *cur = NULL, *e;
768 int len = 0;
769
770 if (!elv_support_iosched(q))
771 return sprintf(buf: name, fmt: "none\n");
772
773 if (!q->elevator) {
774 len += sprintf(buf: name+len, fmt: "[none] ");
775 } else {
776 len += sprintf(buf: name+len, fmt: "none ");
777 cur = eq->type;
778 }
779
780 spin_lock(lock: &elv_list_lock);
781 list_for_each_entry(e, &elv_list, list) {
782 if (e == cur)
783 len += sprintf(buf: name+len, fmt: "[%s] ", e->elevator_name);
784 else if (elv_support_features(q, e))
785 len += sprintf(buf: name+len, fmt: "%s ", e->elevator_name);
786 }
787 spin_unlock(lock: &elv_list_lock);
788
789 len += sprintf(buf: name+len, fmt: "\n");
790 return len;
791}
792
793struct request *elv_rb_former_request(struct request_queue *q,
794 struct request *rq)
795{
796 struct rb_node *rbprev = rb_prev(&rq->rb_node);
797
798 if (rbprev)
799 return rb_entry_rq(rbprev);
800
801 return NULL;
802}
803EXPORT_SYMBOL(elv_rb_former_request);
804
805struct request *elv_rb_latter_request(struct request_queue *q,
806 struct request *rq)
807{
808 struct rb_node *rbnext = rb_next(&rq->rb_node);
809
810 if (rbnext)
811 return rb_entry_rq(rbnext);
812
813 return NULL;
814}
815EXPORT_SYMBOL(elv_rb_latter_request);
816
817static int __init elevator_setup(char *str)
818{
819 pr_warn("Kernel parameter elevator= does not have any effect anymore.\n"
820 "Please use sysfs to set IO scheduler for individual devices.\n");
821 return 1;
822}
823
824__setup("elevator=", elevator_setup);
825

source code of linux/block/elevator.c