ARM: pxa: ssp: Check return values from phandle lookups
[linux-2.6.git] / block / elevator.c
blob668394d185885bc3fcc878697878a4cb07be899e
1 /*
2 * Block device elevator/IO-scheduler.
4 * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
6 * 30042000 Jens Axboe <axboe@kernel.dk> :
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
15 * 20082000 Dave Jones <davej@suse.de> :
16 * Removed tests for max-bomb-segments, which was breaking elvtune
17 * when run without -bN
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
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 #include <linux/pm_runtime.h>
39 #include <trace/events/block.h>
41 #include "blk.h"
42 #include "blk-cgroup.h"
44 static DEFINE_SPINLOCK(elv_list_lock);
45 static LIST_HEAD(elv_list);
48 * Merge hash stuff.
50 #define rq_hash_key(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq))
53 * Query io scheduler to see if the current process issuing bio may be
54 * merged with rq.
56 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
58 struct request_queue *q = rq->q;
59 struct elevator_queue *e = q->elevator;
61 if (e->type->ops.elevator_allow_merge_fn)
62 return e->type->ops.elevator_allow_merge_fn(q, rq, bio);
64 return 1;
68 * can we safely merge with this request?
70 bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
72 if (!blk_rq_merge_ok(rq, bio))
73 return 0;
75 if (!elv_iosched_allow_merge(rq, bio))
76 return 0;
78 return 1;
80 EXPORT_SYMBOL(elv_rq_merge_ok);
82 static struct elevator_type *elevator_find(const char *name)
84 struct elevator_type *e;
86 list_for_each_entry(e, &elv_list, list) {
87 if (!strcmp(e->elevator_name, name))
88 return e;
91 return NULL;
94 static void elevator_put(struct elevator_type *e)
96 module_put(e->elevator_owner);
99 static struct elevator_type *elevator_get(const char *name, bool try_loading)
101 struct elevator_type *e;
103 spin_lock(&elv_list_lock);
105 e = elevator_find(name);
106 if (!e && try_loading) {
107 spin_unlock(&elv_list_lock);
108 request_module("%s-iosched", name);
109 spin_lock(&elv_list_lock);
110 e = elevator_find(name);
113 if (e && !try_module_get(e->elevator_owner))
114 e = NULL;
116 spin_unlock(&elv_list_lock);
118 return e;
121 static char chosen_elevator[ELV_NAME_MAX];
123 static int __init elevator_setup(char *str)
126 * Be backwards-compatible with previous kernels, so users
127 * won't get the wrong elevator.
129 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
130 return 1;
133 __setup("elevator=", elevator_setup);
135 /* called during boot to load the elevator chosen by the elevator param */
136 void __init load_default_elevator_module(void)
138 struct elevator_type *e;
140 if (!chosen_elevator[0])
141 return;
143 spin_lock(&elv_list_lock);
144 e = elevator_find(chosen_elevator);
145 spin_unlock(&elv_list_lock);
147 if (!e)
148 request_module("%s-iosched", chosen_elevator);
151 static struct kobj_type elv_ktype;
153 struct elevator_queue *elevator_alloc(struct request_queue *q,
154 struct elevator_type *e)
156 struct elevator_queue *eq;
158 eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
159 if (unlikely(!eq))
160 goto err;
162 eq->type = e;
163 kobject_init(&eq->kobj, &elv_ktype);
164 mutex_init(&eq->sysfs_lock);
165 hash_init(eq->hash);
167 return eq;
168 err:
169 kfree(eq);
170 elevator_put(e);
171 return NULL;
173 EXPORT_SYMBOL(elevator_alloc);
175 static void elevator_release(struct kobject *kobj)
177 struct elevator_queue *e;
179 e = container_of(kobj, struct elevator_queue, kobj);
180 elevator_put(e->type);
181 kfree(e);
184 int elevator_init(struct request_queue *q, char *name)
186 struct elevator_type *e = NULL;
187 int err;
189 if (unlikely(q->elevator))
190 return 0;
192 INIT_LIST_HEAD(&q->queue_head);
193 q->last_merge = NULL;
194 q->end_sector = 0;
195 q->boundary_rq = NULL;
197 if (name) {
198 e = elevator_get(name, true);
199 if (!e)
200 return -EINVAL;
204 * Use the default elevator specified by config boot param or
205 * config option. Don't try to load modules as we could be running
206 * off async and request_module() isn't allowed from async.
208 if (!e && *chosen_elevator) {
209 e = elevator_get(chosen_elevator, false);
210 if (!e)
211 printk(KERN_ERR "I/O scheduler %s not found\n",
212 chosen_elevator);
215 if (!e) {
216 e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
217 if (!e) {
218 printk(KERN_ERR
219 "Default I/O scheduler not found. " \
220 "Using noop.\n");
221 e = elevator_get("noop", false);
225 err = e->ops.elevator_init_fn(q, e);
226 return 0;
228 EXPORT_SYMBOL(elevator_init);
230 void elevator_exit(struct elevator_queue *e)
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);
237 kobject_put(&e->kobj);
239 EXPORT_SYMBOL(elevator_exit);
241 static inline void __elv_rqhash_del(struct request *rq)
243 hash_del(&rq->hash);
246 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
248 if (ELV_ON_HASH(rq))
249 __elv_rqhash_del(rq);
252 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
254 struct elevator_queue *e = q->elevator;
256 BUG_ON(ELV_ON_HASH(rq));
257 hash_add(e->hash, &rq->hash, rq_hash_key(rq));
260 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
262 __elv_rqhash_del(rq);
263 elv_rqhash_add(q, rq);
266 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
268 struct elevator_queue *e = q->elevator;
269 struct hlist_node *next;
270 struct request *rq;
272 hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
273 BUG_ON(!ELV_ON_HASH(rq));
275 if (unlikely(!rq_mergeable(rq))) {
276 __elv_rqhash_del(rq);
277 continue;
280 if (rq_hash_key(rq) == offset)
281 return rq;
284 return NULL;
288 * RB-tree support functions for inserting/lookup/removal of requests
289 * in a sorted RB tree.
291 void elv_rb_add(struct rb_root *root, struct request *rq)
293 struct rb_node **p = &root->rb_node;
294 struct rb_node *parent = NULL;
295 struct request *__rq;
297 while (*p) {
298 parent = *p;
299 __rq = rb_entry(parent, struct request, rb_node);
301 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
302 p = &(*p)->rb_left;
303 else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
304 p = &(*p)->rb_right;
307 rb_link_node(&rq->rb_node, parent, p);
308 rb_insert_color(&rq->rb_node, root);
310 EXPORT_SYMBOL(elv_rb_add);
312 void elv_rb_del(struct rb_root *root, struct request *rq)
314 BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
315 rb_erase(&rq->rb_node, root);
316 RB_CLEAR_NODE(&rq->rb_node);
318 EXPORT_SYMBOL(elv_rb_del);
320 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
322 struct rb_node *n = root->rb_node;
323 struct request *rq;
325 while (n) {
326 rq = rb_entry(n, struct request, rb_node);
328 if (sector < blk_rq_pos(rq))
329 n = n->rb_left;
330 else if (sector > blk_rq_pos(rq))
331 n = n->rb_right;
332 else
333 return rq;
336 return NULL;
338 EXPORT_SYMBOL(elv_rb_find);
341 * Insert rq into dispatch queue of q. Queue lock must be held on
342 * entry. rq is sort instead into the dispatch queue. To be used by
343 * specific elevators.
345 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
347 sector_t boundary;
348 struct list_head *entry;
349 int stop_flags;
351 if (q->last_merge == rq)
352 q->last_merge = NULL;
354 elv_rqhash_del(q, rq);
356 q->nr_sorted--;
358 boundary = q->end_sector;
359 stop_flags = REQ_SOFTBARRIER | REQ_STARTED;
360 list_for_each_prev(entry, &q->queue_head) {
361 struct request *pos = list_entry_rq(entry);
363 if ((rq->cmd_flags & REQ_DISCARD) !=
364 (pos->cmd_flags & REQ_DISCARD))
365 break;
366 if (rq_data_dir(rq) != rq_data_dir(pos))
367 break;
368 if (pos->cmd_flags & stop_flags)
369 break;
370 if (blk_rq_pos(rq) >= boundary) {
371 if (blk_rq_pos(pos) < boundary)
372 continue;
373 } else {
374 if (blk_rq_pos(pos) >= boundary)
375 break;
377 if (blk_rq_pos(rq) >= blk_rq_pos(pos))
378 break;
381 list_add(&rq->queuelist, entry);
383 EXPORT_SYMBOL(elv_dispatch_sort);
386 * Insert rq into dispatch queue of q. Queue lock must be held on
387 * entry. rq is added to the back of the dispatch queue. To be used by
388 * specific elevators.
390 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
392 if (q->last_merge == rq)
393 q->last_merge = NULL;
395 elv_rqhash_del(q, rq);
397 q->nr_sorted--;
399 q->end_sector = rq_end_sector(rq);
400 q->boundary_rq = rq;
401 list_add_tail(&rq->queuelist, &q->queue_head);
403 EXPORT_SYMBOL(elv_dispatch_add_tail);
405 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
407 struct elevator_queue *e = q->elevator;
408 struct request *__rq;
409 int ret;
412 * Levels of merges:
413 * nomerges: No merges at all attempted
414 * noxmerges: Only simple one-hit cache try
415 * merges: All merge tries attempted
417 if (blk_queue_nomerges(q))
418 return ELEVATOR_NO_MERGE;
421 * First try one-hit cache.
423 if (q->last_merge && elv_rq_merge_ok(q->last_merge, bio)) {
424 ret = blk_try_merge(q->last_merge, bio);
425 if (ret != ELEVATOR_NO_MERGE) {
426 *req = q->last_merge;
427 return ret;
431 if (blk_queue_noxmerges(q))
432 return ELEVATOR_NO_MERGE;
435 * See if our hash lookup can find a potential backmerge.
437 __rq = elv_rqhash_find(q, bio->bi_sector);
438 if (__rq && elv_rq_merge_ok(__rq, bio)) {
439 *req = __rq;
440 return ELEVATOR_BACK_MERGE;
443 if (e->type->ops.elevator_merge_fn)
444 return e->type->ops.elevator_merge_fn(q, req, bio);
446 return ELEVATOR_NO_MERGE;
450 * Attempt to do an insertion back merge. Only check for the case where
451 * we can append 'rq' to an existing request, so we can throw 'rq' away
452 * afterwards.
454 * Returns true if we merged, false otherwise
456 static bool elv_attempt_insert_merge(struct request_queue *q,
457 struct request *rq)
459 struct request *__rq;
460 bool ret;
462 if (blk_queue_nomerges(q))
463 return false;
466 * First try one-hit cache.
468 if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
469 return true;
471 if (blk_queue_noxmerges(q))
472 return false;
474 ret = false;
476 * See if our hash lookup can find a potential backmerge.
478 while (1) {
479 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
480 if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
481 break;
483 /* The merged request could be merged with others, try again */
484 ret = true;
485 rq = __rq;
488 return ret;
491 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
493 struct elevator_queue *e = q->elevator;
495 if (e->type->ops.elevator_merged_fn)
496 e->type->ops.elevator_merged_fn(q, rq, type);
498 if (type == ELEVATOR_BACK_MERGE)
499 elv_rqhash_reposition(q, rq);
501 q->last_merge = rq;
504 void elv_merge_requests(struct request_queue *q, struct request *rq,
505 struct request *next)
507 struct elevator_queue *e = q->elevator;
508 const int next_sorted = next->cmd_flags & REQ_SORTED;
510 if (next_sorted && e->type->ops.elevator_merge_req_fn)
511 e->type->ops.elevator_merge_req_fn(q, rq, next);
513 elv_rqhash_reposition(q, rq);
515 if (next_sorted) {
516 elv_rqhash_del(q, next);
517 q->nr_sorted--;
520 q->last_merge = rq;
523 void elv_bio_merged(struct request_queue *q, struct request *rq,
524 struct bio *bio)
526 struct elevator_queue *e = q->elevator;
528 if (e->type->ops.elevator_bio_merged_fn)
529 e->type->ops.elevator_bio_merged_fn(q, rq, bio);
532 #ifdef CONFIG_PM_RUNTIME
533 static void blk_pm_requeue_request(struct request *rq)
535 if (rq->q->dev && !(rq->cmd_flags & REQ_PM))
536 rq->q->nr_pending--;
539 static void blk_pm_add_request(struct request_queue *q, struct request *rq)
541 if (q->dev && !(rq->cmd_flags & REQ_PM) && q->nr_pending++ == 0 &&
542 (q->rpm_status == RPM_SUSPENDED || q->rpm_status == RPM_SUSPENDING))
543 pm_request_resume(q->dev);
545 #else
546 static inline void blk_pm_requeue_request(struct request *rq) {}
547 static inline void blk_pm_add_request(struct request_queue *q,
548 struct request *rq)
551 #endif
553 void elv_requeue_request(struct request_queue *q, struct request *rq)
556 * it already went through dequeue, we need to decrement the
557 * in_flight count again
559 if (blk_account_rq(rq)) {
560 q->in_flight[rq_is_sync(rq)]--;
561 if (rq->cmd_flags & REQ_SORTED)
562 elv_deactivate_rq(q, rq);
565 rq->cmd_flags &= ~REQ_STARTED;
567 blk_pm_requeue_request(rq);
569 __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
572 void elv_drain_elevator(struct request_queue *q)
574 static int printed;
576 lockdep_assert_held(q->queue_lock);
578 while (q->elevator->type->ops.elevator_dispatch_fn(q, 1))
580 if (q->nr_sorted && printed++ < 10) {
581 printk(KERN_ERR "%s: forced dispatching is broken "
582 "(nr_sorted=%u), please report this\n",
583 q->elevator->type->elevator_name, q->nr_sorted);
587 void __elv_add_request(struct request_queue *q, struct request *rq, int where)
589 trace_block_rq_insert(q, rq);
591 blk_pm_add_request(q, rq);
593 rq->q = q;
595 if (rq->cmd_flags & REQ_SOFTBARRIER) {
596 /* barriers are scheduling boundary, update end_sector */
597 if (rq->cmd_type == REQ_TYPE_FS) {
598 q->end_sector = rq_end_sector(rq);
599 q->boundary_rq = rq;
601 } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
602 (where == ELEVATOR_INSERT_SORT ||
603 where == ELEVATOR_INSERT_SORT_MERGE))
604 where = ELEVATOR_INSERT_BACK;
606 switch (where) {
607 case ELEVATOR_INSERT_REQUEUE:
608 case ELEVATOR_INSERT_FRONT:
609 rq->cmd_flags |= REQ_SOFTBARRIER;
610 list_add(&rq->queuelist, &q->queue_head);
611 break;
613 case ELEVATOR_INSERT_BACK:
614 rq->cmd_flags |= REQ_SOFTBARRIER;
615 elv_drain_elevator(q);
616 list_add_tail(&rq->queuelist, &q->queue_head);
618 * We kick the queue here for the following reasons.
619 * - The elevator might have returned NULL previously
620 * to delay requests and returned them now. As the
621 * queue wasn't empty before this request, ll_rw_blk
622 * won't run the queue on return, resulting in hang.
623 * - Usually, back inserted requests won't be merged
624 * with anything. There's no point in delaying queue
625 * processing.
627 __blk_run_queue(q);
628 break;
630 case ELEVATOR_INSERT_SORT_MERGE:
632 * If we succeed in merging this request with one in the
633 * queue already, we are done - rq has now been freed,
634 * so no need to do anything further.
636 if (elv_attempt_insert_merge(q, rq))
637 break;
638 case ELEVATOR_INSERT_SORT:
639 BUG_ON(rq->cmd_type != REQ_TYPE_FS);
640 rq->cmd_flags |= REQ_SORTED;
641 q->nr_sorted++;
642 if (rq_mergeable(rq)) {
643 elv_rqhash_add(q, rq);
644 if (!q->last_merge)
645 q->last_merge = rq;
649 * Some ioscheds (cfq) run q->request_fn directly, so
650 * rq cannot be accessed after calling
651 * elevator_add_req_fn.
653 q->elevator->type->ops.elevator_add_req_fn(q, rq);
654 break;
656 case ELEVATOR_INSERT_FLUSH:
657 rq->cmd_flags |= REQ_SOFTBARRIER;
658 blk_insert_flush(rq);
659 break;
660 default:
661 printk(KERN_ERR "%s: bad insertion point %d\n",
662 __func__, where);
663 BUG();
666 EXPORT_SYMBOL(__elv_add_request);
668 void elv_add_request(struct request_queue *q, struct request *rq, int where)
670 unsigned long flags;
672 spin_lock_irqsave(q->queue_lock, flags);
673 __elv_add_request(q, rq, where);
674 spin_unlock_irqrestore(q->queue_lock, flags);
676 EXPORT_SYMBOL(elv_add_request);
678 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
680 struct elevator_queue *e = q->elevator;
682 if (e->type->ops.elevator_latter_req_fn)
683 return e->type->ops.elevator_latter_req_fn(q, rq);
684 return NULL;
687 struct request *elv_former_request(struct request_queue *q, struct request *rq)
689 struct elevator_queue *e = q->elevator;
691 if (e->type->ops.elevator_former_req_fn)
692 return e->type->ops.elevator_former_req_fn(q, rq);
693 return NULL;
696 int elv_set_request(struct request_queue *q, struct request *rq,
697 struct bio *bio, gfp_t gfp_mask)
699 struct elevator_queue *e = q->elevator;
701 if (e->type->ops.elevator_set_req_fn)
702 return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
703 return 0;
706 void elv_put_request(struct request_queue *q, struct request *rq)
708 struct elevator_queue *e = q->elevator;
710 if (e->type->ops.elevator_put_req_fn)
711 e->type->ops.elevator_put_req_fn(rq);
714 int elv_may_queue(struct request_queue *q, int rw)
716 struct elevator_queue *e = q->elevator;
718 if (e->type->ops.elevator_may_queue_fn)
719 return e->type->ops.elevator_may_queue_fn(q, rw);
721 return ELV_MQUEUE_MAY;
724 void elv_abort_queue(struct request_queue *q)
726 struct request *rq;
728 blk_abort_flushes(q);
730 while (!list_empty(&q->queue_head)) {
731 rq = list_entry_rq(q->queue_head.next);
732 rq->cmd_flags |= REQ_QUIET;
733 trace_block_rq_abort(q, rq);
735 * Mark this request as started so we don't trigger
736 * any debug logic in the end I/O path.
738 blk_start_request(rq);
739 __blk_end_request_all(rq, -EIO);
742 EXPORT_SYMBOL(elv_abort_queue);
744 void elv_completed_request(struct request_queue *q, struct request *rq)
746 struct elevator_queue *e = q->elevator;
749 * request is released from the driver, io must be done
751 if (blk_account_rq(rq)) {
752 q->in_flight[rq_is_sync(rq)]--;
753 if ((rq->cmd_flags & REQ_SORTED) &&
754 e->type->ops.elevator_completed_req_fn)
755 e->type->ops.elevator_completed_req_fn(q, rq);
759 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
761 static ssize_t
762 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
764 struct elv_fs_entry *entry = to_elv(attr);
765 struct elevator_queue *e;
766 ssize_t error;
768 if (!entry->show)
769 return -EIO;
771 e = container_of(kobj, struct elevator_queue, kobj);
772 mutex_lock(&e->sysfs_lock);
773 error = e->type ? entry->show(e, page) : -ENOENT;
774 mutex_unlock(&e->sysfs_lock);
775 return error;
778 static ssize_t
779 elv_attr_store(struct kobject *kobj, struct attribute *attr,
780 const char *page, size_t length)
782 struct elv_fs_entry *entry = to_elv(attr);
783 struct elevator_queue *e;
784 ssize_t error;
786 if (!entry->store)
787 return -EIO;
789 e = container_of(kobj, struct elevator_queue, kobj);
790 mutex_lock(&e->sysfs_lock);
791 error = e->type ? entry->store(e, page, length) : -ENOENT;
792 mutex_unlock(&e->sysfs_lock);
793 return error;
796 static const struct sysfs_ops elv_sysfs_ops = {
797 .show = elv_attr_show,
798 .store = elv_attr_store,
801 static struct kobj_type elv_ktype = {
802 .sysfs_ops = &elv_sysfs_ops,
803 .release = elevator_release,
806 int elv_register_queue(struct request_queue *q)
808 struct elevator_queue *e = q->elevator;
809 int error;
811 error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
812 if (!error) {
813 struct elv_fs_entry *attr = e->type->elevator_attrs;
814 if (attr) {
815 while (attr->attr.name) {
816 if (sysfs_create_file(&e->kobj, &attr->attr))
817 break;
818 attr++;
821 kobject_uevent(&e->kobj, KOBJ_ADD);
822 e->registered = 1;
824 return error;
826 EXPORT_SYMBOL(elv_register_queue);
828 void elv_unregister_queue(struct request_queue *q)
830 if (q) {
831 struct elevator_queue *e = q->elevator;
833 kobject_uevent(&e->kobj, KOBJ_REMOVE);
834 kobject_del(&e->kobj);
835 e->registered = 0;
838 EXPORT_SYMBOL(elv_unregister_queue);
840 int elv_register(struct elevator_type *e)
842 char *def = "";
844 /* create icq_cache if requested */
845 if (e->icq_size) {
846 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
847 WARN_ON(e->icq_align < __alignof__(struct io_cq)))
848 return -EINVAL;
850 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
851 "%s_io_cq", e->elevator_name);
852 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
853 e->icq_align, 0, NULL);
854 if (!e->icq_cache)
855 return -ENOMEM;
858 /* register, don't allow duplicate names */
859 spin_lock(&elv_list_lock);
860 if (elevator_find(e->elevator_name)) {
861 spin_unlock(&elv_list_lock);
862 if (e->icq_cache)
863 kmem_cache_destroy(e->icq_cache);
864 return -EBUSY;
866 list_add_tail(&e->list, &elv_list);
867 spin_unlock(&elv_list_lock);
869 /* print pretty message */
870 if (!strcmp(e->elevator_name, chosen_elevator) ||
871 (!*chosen_elevator &&
872 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
873 def = " (default)";
875 printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
876 def);
877 return 0;
879 EXPORT_SYMBOL_GPL(elv_register);
881 void elv_unregister(struct elevator_type *e)
883 /* unregister */
884 spin_lock(&elv_list_lock);
885 list_del_init(&e->list);
886 spin_unlock(&elv_list_lock);
889 * Destroy icq_cache if it exists. icq's are RCU managed. Make
890 * sure all RCU operations are complete before proceeding.
892 if (e->icq_cache) {
893 rcu_barrier();
894 kmem_cache_destroy(e->icq_cache);
895 e->icq_cache = NULL;
898 EXPORT_SYMBOL_GPL(elv_unregister);
901 * switch to new_e io scheduler. be careful not to introduce deadlocks -
902 * we don't free the old io scheduler, before we have allocated what we
903 * need for the new one. this way we have a chance of going back to the old
904 * one, if the new one fails init for some reason.
906 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
908 struct elevator_queue *old = q->elevator;
909 bool registered = old->registered;
910 int err;
913 * Turn on BYPASS and drain all requests w/ elevator private data.
914 * Block layer doesn't call into a quiesced elevator - all requests
915 * are directly put on the dispatch list without elevator data
916 * using INSERT_BACK. All requests have SOFTBARRIER set and no
917 * merge happens either.
919 blk_queue_bypass_start(q);
921 /* unregister and clear all auxiliary data of the old elevator */
922 if (registered)
923 elv_unregister_queue(q);
925 spin_lock_irq(q->queue_lock);
926 ioc_clear_queue(q);
927 spin_unlock_irq(q->queue_lock);
929 /* allocate, init and register new elevator */
930 err = new_e->ops.elevator_init_fn(q, new_e);
931 if (err)
932 goto fail_init;
934 if (registered) {
935 err = elv_register_queue(q);
936 if (err)
937 goto fail_register;
940 /* done, kill the old one and finish */
941 elevator_exit(old);
942 blk_queue_bypass_end(q);
944 blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
946 return 0;
948 fail_register:
949 elevator_exit(q->elevator);
950 fail_init:
951 /* switch failed, restore and re-register old elevator */
952 q->elevator = old;
953 elv_register_queue(q);
954 blk_queue_bypass_end(q);
956 return err;
960 * Switch this queue to the given IO scheduler.
962 int elevator_change(struct request_queue *q, const char *name)
964 char elevator_name[ELV_NAME_MAX];
965 struct elevator_type *e;
967 if (!q->elevator)
968 return -ENXIO;
970 strlcpy(elevator_name, name, sizeof(elevator_name));
971 e = elevator_get(strstrip(elevator_name), true);
972 if (!e) {
973 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
974 return -EINVAL;
977 if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
978 elevator_put(e);
979 return 0;
982 return elevator_switch(q, e);
984 EXPORT_SYMBOL(elevator_change);
986 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
987 size_t count)
989 int ret;
991 if (!q->elevator)
992 return count;
994 ret = elevator_change(q, name);
995 if (!ret)
996 return count;
998 printk(KERN_ERR "elevator: switch to %s failed\n", name);
999 return ret;
1002 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1004 struct elevator_queue *e = q->elevator;
1005 struct elevator_type *elv;
1006 struct elevator_type *__e;
1007 int len = 0;
1009 if (!q->elevator || !blk_queue_stackable(q))
1010 return sprintf(name, "none\n");
1012 elv = e->type;
1014 spin_lock(&elv_list_lock);
1015 list_for_each_entry(__e, &elv_list, list) {
1016 if (!strcmp(elv->elevator_name, __e->elevator_name))
1017 len += sprintf(name+len, "[%s] ", elv->elevator_name);
1018 else
1019 len += sprintf(name+len, "%s ", __e->elevator_name);
1021 spin_unlock(&elv_list_lock);
1023 len += sprintf(len+name, "\n");
1024 return len;
1027 struct request *elv_rb_former_request(struct request_queue *q,
1028 struct request *rq)
1030 struct rb_node *rbprev = rb_prev(&rq->rb_node);
1032 if (rbprev)
1033 return rb_entry_rq(rbprev);
1035 return NULL;
1037 EXPORT_SYMBOL(elv_rb_former_request);
1039 struct request *elv_rb_latter_request(struct request_queue *q,
1040 struct request *rq)
1042 struct rb_node *rbnext = rb_next(&rq->rb_node);
1044 if (rbnext)
1045 return rb_entry_rq(rbnext);
1047 return NULL;
1049 EXPORT_SYMBOL(elv_rb_latter_request);