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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/*
2 * Block device elevator/IO-scheduler.
3 *
4 * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
5 *
6 * 30042000 Jens Axboe <axboe@kernel.dk> :
7 *
8 * Split the elevator a bit so that it is possible to choose a different
9 * one or even write a new "plug in". There are three pieces:
10 * - elevator_fn, inserts a new request in the queue list
11 * - elevator_merge_fn, decides whether a new buffer can be merged with
12 * an existing request
13 * - elevator_dequeue_fn, called when a request is taken off the active list
14 *
15 * 20082000 Dave Jones <davej@suse.de> :
16 * Removed tests for max-bomb-segments, which was breaking elvtune
17 * when run without -bN
18 *
19 * Jens:
20 * - Rework again to work with bio instead of buffer_heads
21 * - loose bi_dev comparisons, partition handling is right now
22 * - completely modularize elevator setup and teardown
23 *
24 */
25#include <linux/kernel.h>
26#include <linux/fs.h>
27#include <linux/blkdev.h>
28#include <linux/elevator.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
38#include <trace/events/block.h>
39
40#include "blk.h"
41#include "blk-cgroup.h"
42
43static DEFINE_SPINLOCK(elv_list_lock);
44static LIST_HEAD(elv_list);
45
46/*
47 * Merge hash stuff.
48 */
49static const int elv_hash_shift = 6;
50#define ELV_HASH_BLOCK(sec) ((sec) >> 3)
51#define ELV_HASH_FN(sec) \
52 (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
53#define ELV_HASH_ENTRIES (1 << elv_hash_shift)
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_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.elevator_allow_merge_fn)
66 return e->type->ops.elevator_allow_merge_fn(q, rq, bio);
67
68 return 1;
69}
70
71/*
72 * can we safely merge with this request?
73 */
74bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
75{
76 if (!blk_rq_merge_ok(rq, bio))
77 return 0;
78
79 if (!elv_iosched_allow_merge(rq, bio))
80 return 0;
81
82 return 1;
83}
84EXPORT_SYMBOL(elv_rq_merge_ok);
85
86static struct elevator_type *elevator_find(const char *name)
87{
88 struct elevator_type *e;
89
90 list_for_each_entry(e, &elv_list, list) {
91 if (!strcmp(e->elevator_name, name))
92 return e;
93 }
94
95 return NULL;
96}
97
98static void elevator_put(struct elevator_type *e)
99{
100 module_put(e->elevator_owner);
101}
102
103static struct elevator_type *elevator_get(const char *name)
104{
105 struct elevator_type *e;
106
107 spin_lock(&elv_list_lock);
108
109 e = elevator_find(name);
110 if (!e) {
111 spin_unlock(&elv_list_lock);
112 request_module("%s-iosched", name);
113 spin_lock(&elv_list_lock);
114 e = elevator_find(name);
115 }
116
117 if (e && !try_module_get(e->elevator_owner))
118 e = NULL;
119
120 spin_unlock(&elv_list_lock);
121
122 return e;
123}
124
125static char chosen_elevator[ELV_NAME_MAX];
126
127static int __init elevator_setup(char *str)
128{
129 /*
130 * Be backwards-compatible with previous kernels, so users
131 * won't get the wrong elevator.
132 */
133 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
134 return 1;
135}
136
137__setup("elevator=", elevator_setup);
138
139static struct kobj_type elv_ktype;
140
141static struct elevator_queue *elevator_alloc(struct request_queue *q,
142 struct elevator_type *e)
143{
144 struct elevator_queue *eq;
145 int i;
146
147 eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
148 if (unlikely(!eq))
149 goto err;
150
151 eq->type = e;
152 kobject_init(&eq->kobj, &elv_ktype);
153 mutex_init(&eq->sysfs_lock);
154
155 eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
156 GFP_KERNEL, q->node);
157 if (!eq->hash)
158 goto err;
159
160 for (i = 0; i < ELV_HASH_ENTRIES; i++)
161 INIT_HLIST_HEAD(&eq->hash[i]);
162
163 return eq;
164err:
165 kfree(eq);
166 elevator_put(e);
167 return NULL;
168}
169
170static void elevator_release(struct kobject *kobj)
171{
172 struct elevator_queue *e;
173
174 e = container_of(kobj, struct elevator_queue, kobj);
175 elevator_put(e->type);
176 kfree(e->hash);
177 kfree(e);
178}
179
180int elevator_init(struct request_queue *q, char *name)
181{
182 struct elevator_type *e = NULL;
183 int err;
184
185 if (unlikely(q->elevator))
186 return 0;
187
188 INIT_LIST_HEAD(&q->queue_head);
189 q->last_merge = NULL;
190 q->end_sector = 0;
191 q->boundary_rq = NULL;
192
193 if (name) {
194 e = elevator_get(name);
195 if (!e)
196 return -EINVAL;
197 }
198
199 if (!e && *chosen_elevator) {
200 e = elevator_get(chosen_elevator);
201 if (!e)
202 printk(KERN_ERR "I/O scheduler %s not found\n",
203 chosen_elevator);
204 }
205
206 if (!e) {
207 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
208 if (!e) {
209 printk(KERN_ERR
210 "Default I/O scheduler not found. " \
211 "Using noop.\n");
212 e = elevator_get("noop");
213 }
214 }
215
216 q->elevator = elevator_alloc(q, e);
217 if (!q->elevator)
218 return -ENOMEM;
219
220 err = e->ops.elevator_init_fn(q);
221 if (err) {
222 kobject_put(&q->elevator->kobj);
223 return err;
224 }
225
226 return 0;
227}
228EXPORT_SYMBOL(elevator_init);
229
230void elevator_exit(struct elevator_queue *e)
231{
232 mutex_lock(&e->sysfs_lock);
233 if (e->type->ops.elevator_exit_fn)
234 e->type->ops.elevator_exit_fn(e);
235 mutex_unlock(&e->sysfs_lock);
236
237 kobject_put(&e->kobj);
238}
239EXPORT_SYMBOL(elevator_exit);
240
241static inline void __elv_rqhash_del(struct request *rq)
242{
243 hlist_del_init(&rq->hash);
244}
245
246static void elv_rqhash_del(struct request_queue *q, struct request *rq)
247{
248 if (ELV_ON_HASH(rq))
249 __elv_rqhash_del(rq);
250}
251
252static void elv_rqhash_add(struct request_queue *q, struct request *rq)
253{
254 struct elevator_queue *e = q->elevator;
255
256 BUG_ON(ELV_ON_HASH(rq));
257 hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
258}
259
260static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
261{
262 __elv_rqhash_del(rq);
263 elv_rqhash_add(q, rq);
264}
265
266static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
267{
268 struct elevator_queue *e = q->elevator;
269 struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
270 struct hlist_node *entry, *next;
271 struct request *rq;
272
273 hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
274 BUG_ON(!ELV_ON_HASH(rq));
275
276 if (unlikely(!rq_mergeable(rq))) {
277 __elv_rqhash_del(rq);
278 continue;
279 }
280
281 if (rq_hash_key(rq) == offset)
282 return rq;
283 }
284
285 return NULL;
286}
287
288/*
289 * RB-tree support functions for inserting/lookup/removal of requests
290 * in a sorted RB tree.
291 */
292void elv_rb_add(struct rb_root *root, struct request *rq)
293{
294 struct rb_node **p = &root->rb_node;
295 struct rb_node *parent = NULL;
296 struct request *__rq;
297
298 while (*p) {
299 parent = *p;
300 __rq = rb_entry(parent, struct request, rb_node);
301
302 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
303 p = &(*p)->rb_left;
304 else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
305 p = &(*p)->rb_right;
306 }
307
308 rb_link_node(&rq->rb_node, parent, p);
309 rb_insert_color(&rq->rb_node, root);
310}
311EXPORT_SYMBOL(elv_rb_add);
312
313void elv_rb_del(struct rb_root *root, struct request *rq)
314{
315 BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
316 rb_erase(&rq->rb_node, root);
317 RB_CLEAR_NODE(&rq->rb_node);
318}
319EXPORT_SYMBOL(elv_rb_del);
320
321struct request *elv_rb_find(struct rb_root *root, sector_t sector)
322{
323 struct rb_node *n = root->rb_node;
324 struct request *rq;
325
326 while (n) {
327 rq = rb_entry(n, struct request, rb_node);
328
329 if (sector < blk_rq_pos(rq))
330 n = n->rb_left;
331 else if (sector > blk_rq_pos(rq))
332 n = n->rb_right;
333 else
334 return rq;
335 }
336
337 return NULL;
338}
339EXPORT_SYMBOL(elv_rb_find);
340
341/*
342 * Insert rq into dispatch queue of q. Queue lock must be held on
343 * entry. rq is sort instead into the dispatch queue. To be used by
344 * specific elevators.
345 */
346void elv_dispatch_sort(struct request_queue *q, struct request *rq)
347{
348 sector_t boundary;
349 struct list_head *entry;
350 int stop_flags;
351
352 if (q->last_merge == rq)
353 q->last_merge = NULL;
354
355 elv_rqhash_del(q, rq);
356
357 q->nr_sorted--;
358
359 boundary = q->end_sector;
360 stop_flags = REQ_SOFTBARRIER | REQ_STARTED;
361 list_for_each_prev(entry, &q->queue_head) {
362 struct request *pos = list_entry_rq(entry);
363
364 if ((rq->cmd_flags & REQ_DISCARD) !=
365 (pos->cmd_flags & REQ_DISCARD))
366 break;
367 if (rq_data_dir(rq) != rq_data_dir(pos))
368 break;
369 if (pos->cmd_flags & stop_flags)
370 break;
371 if (blk_rq_pos(rq) >= boundary) {
372 if (blk_rq_pos(pos) < boundary)
373 continue;
374 } else {
375 if (blk_rq_pos(pos) >= boundary)
376 break;
377 }
378 if (blk_rq_pos(rq) >= blk_rq_pos(pos))
379 break;
380 }
381
382 list_add(&rq->queuelist, entry);
383}
384EXPORT_SYMBOL(elv_dispatch_sort);
385
386/*
387 * Insert rq into dispatch queue of q. Queue lock must be held on
388 * entry. rq is added to the back of the dispatch queue. To be used by
389 * specific elevators.
390 */
391void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
392{
393 if (q->last_merge == rq)
394 q->last_merge = NULL;
395
396 elv_rqhash_del(q, rq);
397
398 q->nr_sorted--;
399
400 q->end_sector = rq_end_sector(rq);
401 q->boundary_rq = rq;
402 list_add_tail(&rq->queuelist, &q->queue_head);
403}
404EXPORT_SYMBOL(elv_dispatch_add_tail);
405
406int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
407{
408 struct elevator_queue *e = q->elevator;
409 struct request *__rq;
410 int ret;
411
412 /*
413 * Levels of merges:
414 * nomerges: No merges at all attempted
415 * noxmerges: Only simple one-hit cache try
416 * merges: All merge tries attempted
417 */
418 if (blk_queue_nomerges(q))
419 return ELEVATOR_NO_MERGE;
420
421 /*
422 * First try one-hit cache.
423 */
424 if (q->last_merge && elv_rq_merge_ok(q->last_merge, bio)) {
425 ret = blk_try_merge(q->last_merge, bio);
426 if (ret != ELEVATOR_NO_MERGE) {
427 *req = q->last_merge;
428 return ret;
429 }
430 }
431
432 if (blk_queue_noxmerges(q))
433 return ELEVATOR_NO_MERGE;
434
435 /*
436 * See if our hash lookup can find a potential backmerge.
437 */
438 __rq = elv_rqhash_find(q, bio->bi_sector);
439 if (__rq && elv_rq_merge_ok(__rq, bio)) {
440 *req = __rq;
441 return ELEVATOR_BACK_MERGE;
442 }
443
444 if (e->type->ops.elevator_merge_fn)
445 return e->type->ops.elevator_merge_fn(q, req, bio);
446
447 return ELEVATOR_NO_MERGE;
448}
449
450/*
451 * Attempt to do an insertion back merge. Only check for the case where
452 * we can append 'rq' to an existing request, so we can throw 'rq' away
453 * afterwards.
454 *
455 * Returns true if we merged, false otherwise
456 */
457static bool elv_attempt_insert_merge(struct request_queue *q,
458 struct request *rq)
459{
460 struct request *__rq;
461
462 if (blk_queue_nomerges(q))
463 return false;
464
465 /*
466 * First try one-hit cache.
467 */
468 if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
469 return true;
470
471 if (blk_queue_noxmerges(q))
472 return false;
473
474 /*
475 * See if our hash lookup can find a potential backmerge.
476 */
477 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
478 if (__rq && blk_attempt_req_merge(q, __rq, rq))
479 return true;
480
481 return false;
482}
483
484void elv_merged_request(struct request_queue *q, struct request *rq, int type)
485{
486 struct elevator_queue *e = q->elevator;
487
488 if (e->type->ops.elevator_merged_fn)
489 e->type->ops.elevator_merged_fn(q, rq, type);
490
491 if (type == ELEVATOR_BACK_MERGE)
492 elv_rqhash_reposition(q, rq);
493
494 q->last_merge = rq;
495}
496
497void elv_merge_requests(struct request_queue *q, struct request *rq,
498 struct request *next)
499{
500 struct elevator_queue *e = q->elevator;
501 const int next_sorted = next->cmd_flags & REQ_SORTED;
502
503 if (next_sorted && e->type->ops.elevator_merge_req_fn)
504 e->type->ops.elevator_merge_req_fn(q, rq, next);
505
506 elv_rqhash_reposition(q, rq);
507
508 if (next_sorted) {
509 elv_rqhash_del(q, next);
510 q->nr_sorted--;
511 }
512
513 q->last_merge = rq;
514}
515
516void elv_bio_merged(struct request_queue *q, struct request *rq,
517 struct bio *bio)
518{
519 struct elevator_queue *e = q->elevator;
520
521 if (e->type->ops.elevator_bio_merged_fn)
522 e->type->ops.elevator_bio_merged_fn(q, rq, bio);
523}
524
525void elv_requeue_request(struct request_queue *q, struct request *rq)
526{
527 /*
528 * it already went through dequeue, we need to decrement the
529 * in_flight count again
530 */
531 if (blk_account_rq(rq)) {
532 q->in_flight[rq_is_sync(rq)]--;
533 if (rq->cmd_flags & REQ_SORTED)
534 elv_deactivate_rq(q, rq);
535 }
536
537 rq->cmd_flags &= ~REQ_STARTED;
538
539 __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
540}
541
542void elv_drain_elevator(struct request_queue *q)
543{
544 static int printed;
545
546 lockdep_assert_held(q->queue_lock);
547
548 while (q->elevator->type->ops.elevator_dispatch_fn(q, 1))
549 ;
550 if (q->nr_sorted && printed++ < 10) {
551 printk(KERN_ERR "%s: forced dispatching is broken "
552 "(nr_sorted=%u), please report this\n",
553 q->elevator->type->elevator_name, q->nr_sorted);
554 }
555}
556
557void __elv_add_request(struct request_queue *q, struct request *rq, int where)
558{
559 trace_block_rq_insert(q, rq);
560
561 rq->q = q;
562
563 if (rq->cmd_flags & REQ_SOFTBARRIER) {
564 /* barriers are scheduling boundary, update end_sector */
565 if (rq->cmd_type == REQ_TYPE_FS ||
566 (rq->cmd_flags & REQ_DISCARD)) {
567 q->end_sector = rq_end_sector(rq);
568 q->boundary_rq = rq;
569 }
570 } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
571 (where == ELEVATOR_INSERT_SORT ||
572 where == ELEVATOR_INSERT_SORT_MERGE))
573 where = ELEVATOR_INSERT_BACK;
574
575 switch (where) {
576 case ELEVATOR_INSERT_REQUEUE:
577 case ELEVATOR_INSERT_FRONT:
578 rq->cmd_flags |= REQ_SOFTBARRIER;
579 list_add(&rq->queuelist, &q->queue_head);
580 break;
581
582 case ELEVATOR_INSERT_BACK:
583 rq->cmd_flags |= REQ_SOFTBARRIER;
584 elv_drain_elevator(q);
585 list_add_tail(&rq->queuelist, &q->queue_head);
586 /*
587 * We kick the queue here for the following reasons.
588 * - The elevator might have returned NULL previously
589 * to delay requests and returned them now. As the
590 * queue wasn't empty before this request, ll_rw_blk
591 * won't run the queue on return, resulting in hang.
592 * - Usually, back inserted requests won't be merged
593 * with anything. There's no point in delaying queue
594 * processing.
595 */
596 __blk_run_queue(q);
597 break;
598
599 case ELEVATOR_INSERT_SORT_MERGE:
600 /*
601 * If we succeed in merging this request with one in the
602 * queue already, we are done - rq has now been freed,
603 * so no need to do anything further.
604 */
605 if (elv_attempt_insert_merge(q, rq))
606 break;
607 case ELEVATOR_INSERT_SORT:
608 BUG_ON(rq->cmd_type != REQ_TYPE_FS &&
609 !(rq->cmd_flags & REQ_DISCARD));
610 rq->cmd_flags |= REQ_SORTED;
611 q->nr_sorted++;
612 if (rq_mergeable(rq)) {
613 elv_rqhash_add(q, rq);
614 if (!q->last_merge)
615 q->last_merge = rq;
616 }
617
618 /*
619 * Some ioscheds (cfq) run q->request_fn directly, so
620 * rq cannot be accessed after calling
621 * elevator_add_req_fn.
622 */
623 q->elevator->type->ops.elevator_add_req_fn(q, rq);
624 break;
625
626 case ELEVATOR_INSERT_FLUSH:
627 rq->cmd_flags |= REQ_SOFTBARRIER;
628 blk_insert_flush(rq);
629 break;
630 default:
631 printk(KERN_ERR "%s: bad insertion point %d\n",
632 __func__, where);
633 BUG();
634 }
635}
636EXPORT_SYMBOL(__elv_add_request);
637
638void elv_add_request(struct request_queue *q, struct request *rq, int where)
639{
640 unsigned long flags;
641
642 spin_lock_irqsave(q->queue_lock, flags);
643 __elv_add_request(q, rq, where);
644 spin_unlock_irqrestore(q->queue_lock, flags);
645}
646EXPORT_SYMBOL(elv_add_request);
647
648struct request *elv_latter_request(struct request_queue *q, struct request *rq)
649{
650 struct elevator_queue *e = q->elevator;
651
652 if (e->type->ops.elevator_latter_req_fn)
653 return e->type->ops.elevator_latter_req_fn(q, rq);
654 return NULL;
655}
656
657struct request *elv_former_request(struct request_queue *q, struct request *rq)
658{
659 struct elevator_queue *e = q->elevator;
660
661 if (e->type->ops.elevator_former_req_fn)
662 return e->type->ops.elevator_former_req_fn(q, rq);
663 return NULL;
664}
665
666int elv_set_request(struct request_queue *q, struct request *rq,
667 struct bio *bio, gfp_t gfp_mask)
668{
669 struct elevator_queue *e = q->elevator;
670
671 if (e->type->ops.elevator_set_req_fn)
672 return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
673 return 0;
674}
675
676void elv_put_request(struct request_queue *q, struct request *rq)
677{
678 struct elevator_queue *e = q->elevator;
679
680 if (e->type->ops.elevator_put_req_fn)
681 e->type->ops.elevator_put_req_fn(rq);
682}
683
684int elv_may_queue(struct request_queue *q, int rw)
685{
686 struct elevator_queue *e = q->elevator;
687
688 if (e->type->ops.elevator_may_queue_fn)
689 return e->type->ops.elevator_may_queue_fn(q, rw);
690
691 return ELV_MQUEUE_MAY;
692}
693
694void elv_abort_queue(struct request_queue *q)
695{
696 struct request *rq;
697
698 blk_abort_flushes(q);
699
700 while (!list_empty(&q->queue_head)) {
701 rq = list_entry_rq(q->queue_head.next);
702 rq->cmd_flags |= REQ_QUIET;
703 trace_block_rq_abort(q, rq);
704 /*
705 * Mark this request as started so we don't trigger
706 * any debug logic in the end I/O path.
707 */
708 blk_start_request(rq);
709 __blk_end_request_all(rq, -EIO);
710 }
711}
712EXPORT_SYMBOL(elv_abort_queue);
713
714void elv_completed_request(struct request_queue *q, struct request *rq)
715{
716 struct elevator_queue *e = q->elevator;
717
718 /*
719 * request is released from the driver, io must be done
720 */
721 if (blk_account_rq(rq)) {
722 q->in_flight[rq_is_sync(rq)]--;
723 if ((rq->cmd_flags & REQ_SORTED) &&
724 e->type->ops.elevator_completed_req_fn)
725 e->type->ops.elevator_completed_req_fn(q, rq);
726 }
727}
728
729#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
730
731static ssize_t
732elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
733{
734 struct elv_fs_entry *entry = to_elv(attr);
735 struct elevator_queue *e;
736 ssize_t error;
737
738 if (!entry->show)
739 return -EIO;
740
741 e = container_of(kobj, struct elevator_queue, kobj);
742 mutex_lock(&e->sysfs_lock);
743 error = e->type ? entry->show(e, page) : -ENOENT;
744 mutex_unlock(&e->sysfs_lock);
745 return error;
746}
747
748static ssize_t
749elv_attr_store(struct kobject *kobj, struct attribute *attr,
750 const char *page, size_t length)
751{
752 struct elv_fs_entry *entry = to_elv(attr);
753 struct elevator_queue *e;
754 ssize_t error;
755
756 if (!entry->store)
757 return -EIO;
758
759 e = container_of(kobj, struct elevator_queue, kobj);
760 mutex_lock(&e->sysfs_lock);
761 error = e->type ? entry->store(e, page, length) : -ENOENT;
762 mutex_unlock(&e->sysfs_lock);
763 return error;
764}
765
766static const struct sysfs_ops elv_sysfs_ops = {
767 .show = elv_attr_show,
768 .store = elv_attr_store,
769};
770
771static struct kobj_type elv_ktype = {
772 .sysfs_ops = &elv_sysfs_ops,
773 .release = elevator_release,
774};
775
776int elv_register_queue(struct request_queue *q)
777{
778 struct elevator_queue *e = q->elevator;
779 int error;
780
781 error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
782 if (!error) {
783 struct elv_fs_entry *attr = e->type->elevator_attrs;
784 if (attr) {
785 while (attr->attr.name) {
786 if (sysfs_create_file(&e->kobj, &attr->attr))
787 break;
788 attr++;
789 }
790 }
791 kobject_uevent(&e->kobj, KOBJ_ADD);
792 e->registered = 1;
793 }
794 return error;
795}
796EXPORT_SYMBOL(elv_register_queue);
797
798void elv_unregister_queue(struct request_queue *q)
799{
800 if (q) {
801 struct elevator_queue *e = q->elevator;
802
803 kobject_uevent(&e->kobj, KOBJ_REMOVE);
804 kobject_del(&e->kobj);
805 e->registered = 0;
806 }
807}
808EXPORT_SYMBOL(elv_unregister_queue);
809
810int elv_register(struct elevator_type *e)
811{
812 char *def = "";
813
814 /* create icq_cache if requested */
815 if (e->icq_size) {
816 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
817 WARN_ON(e->icq_align < __alignof__(struct io_cq)))
818 return -EINVAL;
819
820 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
821 "%s_io_cq", e->elevator_name);
822 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
823 e->icq_align, 0, NULL);
824 if (!e->icq_cache)
825 return -ENOMEM;
826 }
827
828 /* register, don't allow duplicate names */
829 spin_lock(&elv_list_lock);
830 if (elevator_find(e->elevator_name)) {
831 spin_unlock(&elv_list_lock);
832 if (e->icq_cache)
833 kmem_cache_destroy(e->icq_cache);
834 return -EBUSY;
835 }
836 list_add_tail(&e->list, &elv_list);
837 spin_unlock(&elv_list_lock);
838
839 /* print pretty message */
840 if (!strcmp(e->elevator_name, chosen_elevator) ||
841 (!*chosen_elevator &&
842 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
843 def = " (default)";
844
845 printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
846 def);
847 return 0;
848}
849EXPORT_SYMBOL_GPL(elv_register);
850
851void elv_unregister(struct elevator_type *e)
852{
853 /* unregister */
854 spin_lock(&elv_list_lock);
855 list_del_init(&e->list);
856 spin_unlock(&elv_list_lock);
857
858 /*
859 * Destroy icq_cache if it exists. icq's are RCU managed. Make
860 * sure all RCU operations are complete before proceeding.
861 */
862 if (e->icq_cache) {
863 rcu_barrier();
864 kmem_cache_destroy(e->icq_cache);
865 e->icq_cache = NULL;
866 }
867}
868EXPORT_SYMBOL_GPL(elv_unregister);
869
870/*
871 * switch to new_e io scheduler. be careful not to introduce deadlocks -
872 * we don't free the old io scheduler, before we have allocated what we
873 * need for the new one. this way we have a chance of going back to the old
874 * one, if the new one fails init for some reason.
875 */
876static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
877{
878 struct elevator_queue *old = q->elevator;
879 bool registered = old->registered;
880 int err;
881
882 /*
883 * Turn on BYPASS and drain all requests w/ elevator private data.
884 * Block layer doesn't call into a quiesced elevator - all requests
885 * are directly put on the dispatch list without elevator data
886 * using INSERT_BACK. All requests have SOFTBARRIER set and no
887 * merge happens either.
888 */
889 blk_queue_bypass_start(q);
890
891 /* unregister and clear all auxiliary data of the old elevator */
892 if (registered)
893 elv_unregister_queue(q);
894
895 spin_lock_irq(q->queue_lock);
896 ioc_clear_queue(q);
897 spin_unlock_irq(q->queue_lock);
898
899 /* allocate, init and register new elevator */
900 err = -ENOMEM;
901 q->elevator = elevator_alloc(q, new_e);
902 if (!q->elevator)
903 goto fail_init;
904
905 err = new_e->ops.elevator_init_fn(q);
906 if (err) {
907 kobject_put(&q->elevator->kobj);
908 goto fail_init;
909 }
910
911 if (registered) {
912 err = elv_register_queue(q);
913 if (err)
914 goto fail_register;
915 }
916
917 /* done, kill the old one and finish */
918 elevator_exit(old);
919 blk_queue_bypass_end(q);
920
921 blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
922
923 return 0;
924
925fail_register:
926 elevator_exit(q->elevator);
927fail_init:
928 /* switch failed, restore and re-register old elevator */
929 q->elevator = old;
930 elv_register_queue(q);
931 blk_queue_bypass_end(q);
932
933 return err;
934}
935
936/*
937 * Switch this queue to the given IO scheduler.
938 */
939int elevator_change(struct request_queue *q, const char *name)
940{
941 char elevator_name[ELV_NAME_MAX];
942 struct elevator_type *e;
943
944 if (!q->elevator)
945 return -ENXIO;
946
947 strlcpy(elevator_name, name, sizeof(elevator_name));
948 e = elevator_get(strstrip(elevator_name));
949 if (!e) {
950 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
951 return -EINVAL;
952 }
953
954 if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
955 elevator_put(e);
956 return 0;
957 }
958
959 return elevator_switch(q, e);
960}
961EXPORT_SYMBOL(elevator_change);
962
963ssize_t elv_iosched_store(struct request_queue *q, const char *name,
964 size_t count)
965{
966 int ret;
967
968 if (!q->elevator)
969 return count;
970
971 ret = elevator_change(q, name);
972 if (!ret)
973 return count;
974
975 printk(KERN_ERR "elevator: switch to %s failed\n", name);
976 return ret;
977}
978
979ssize_t elv_iosched_show(struct request_queue *q, char *name)
980{
981 struct elevator_queue *e = q->elevator;
982 struct elevator_type *elv;
983 struct elevator_type *__e;
984 int len = 0;
985
986 if (!q->elevator || !blk_queue_stackable(q))
987 return sprintf(name, "none\n");
988
989 elv = e->type;
990
991 spin_lock(&elv_list_lock);
992 list_for_each_entry(__e, &elv_list, list) {
993 if (!strcmp(elv->elevator_name, __e->elevator_name))
994 len += sprintf(name+len, "[%s] ", elv->elevator_name);
995 else
996 len += sprintf(name+len, "%s ", __e->elevator_name);
997 }
998 spin_unlock(&elv_list_lock);
999
1000 len += sprintf(len+name, "\n");
1001 return len;
1002}
1003
1004struct request *elv_rb_former_request(struct request_queue *q,
1005 struct request *rq)
1006{
1007 struct rb_node *rbprev = rb_prev(&rq->rb_node);
1008
1009 if (rbprev)
1010 return rb_entry_rq(rbprev);
1011
1012 return NULL;
1013}
1014EXPORT_SYMBOL(elv_rb_former_request);
1015
1016struct request *elv_rb_latter_request(struct request_queue *q,
1017 struct request *rq)
1018{
1019 struct rb_node *rbnext = rb_next(&rq->rb_node);
1020
1021 if (rbnext)
1022 return rb_entry_rq(rbnext);
1023
1024 return NULL;
1025}
1026EXPORT_SYMBOL(elv_rb_latter_request);