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
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
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>
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/delay.h>
35 #include <linux/blktrace_api.h>
36 #include <linux/hash.h>
37 #include <linux/uaccess.h>
39 #include <trace/events/block.h>
43 static DEFINE_SPINLOCK(elv_list_lock);
44 static LIST_HEAD(elv_list);
49 static 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))
57 * Query io scheduler to see if the current process issuing bio may be
60 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
62 struct request_queue *q = rq->q;
63 struct elevator_queue *e = q->elevator;
65 if (e->ops->elevator_allow_merge_fn)
66 return e->ops->elevator_allow_merge_fn(q, rq, bio);
72 * can we safely merge with this request?
74 int elv_rq_merge_ok(struct request *rq, struct bio *bio)
76 if (!rq_mergeable(rq))
80 * Don't merge file system requests and discard requests
82 if (bio_rw_flagged(bio, BIO_RW_DISCARD) !=
83 bio_rw_flagged(rq->bio, BIO_RW_DISCARD))
87 * different data direction or already started, don't merge
89 if (bio_data_dir(bio) != rq_data_dir(rq))
93 * must be same device and not a special request
95 if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
99 * only merge integrity protected bio into ditto rq
101 if (bio_integrity(bio) != blk_integrity_rq(rq))
104 if (!elv_iosched_allow_merge(rq, bio))
109 EXPORT_SYMBOL(elv_rq_merge_ok);
111 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
113 int ret = ELEVATOR_NO_MERGE;
116 * we can merge and sequence is ok, check if it's possible
118 if (elv_rq_merge_ok(__rq, bio)) {
119 if (blk_rq_pos(__rq) + blk_rq_sectors(__rq) == bio->bi_sector)
120 ret = ELEVATOR_BACK_MERGE;
121 else if (blk_rq_pos(__rq) - bio_sectors(bio) == bio->bi_sector)
122 ret = ELEVATOR_FRONT_MERGE;
128 static struct elevator_type *elevator_find(const char *name)
130 struct elevator_type *e;
132 list_for_each_entry(e, &elv_list, list) {
133 if (!strcmp(e->elevator_name, name))
140 static void elevator_put(struct elevator_type *e)
142 module_put(e->elevator_owner);
145 static struct elevator_type *elevator_get(const char *name)
147 struct elevator_type *e;
149 spin_lock(&elv_list_lock);
151 e = elevator_find(name);
153 char elv[ELV_NAME_MAX + strlen("-iosched")];
155 spin_unlock(&elv_list_lock);
157 snprintf(elv, sizeof(elv), "%s-iosched", name);
159 request_module("%s", elv);
160 spin_lock(&elv_list_lock);
161 e = elevator_find(name);
164 if (e && !try_module_get(e->elevator_owner))
167 spin_unlock(&elv_list_lock);
172 static void *elevator_init_queue(struct request_queue *q,
173 struct elevator_queue *eq)
175 return eq->ops->elevator_init_fn(q);
178 static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
182 eq->elevator_data = data;
185 static char chosen_elevator[16];
187 static int __init elevator_setup(char *str)
190 * Be backwards-compatible with previous kernels, so users
191 * won't get the wrong elevator.
193 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
197 __setup("elevator=", elevator_setup);
199 static struct kobj_type elv_ktype;
201 static struct elevator_queue *elevator_alloc(struct request_queue *q,
202 struct elevator_type *e)
204 struct elevator_queue *eq;
207 eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
212 eq->elevator_type = e;
213 kobject_init(&eq->kobj, &elv_ktype);
214 mutex_init(&eq->sysfs_lock);
216 eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
217 GFP_KERNEL, q->node);
221 for (i = 0; i < ELV_HASH_ENTRIES; i++)
222 INIT_HLIST_HEAD(&eq->hash[i]);
231 static void elevator_release(struct kobject *kobj)
233 struct elevator_queue *e;
235 e = container_of(kobj, struct elevator_queue, kobj);
236 elevator_put(e->elevator_type);
241 int elevator_init(struct request_queue *q, char *name)
243 struct elevator_type *e = NULL;
244 struct elevator_queue *eq;
247 if (unlikely(q->elevator))
250 INIT_LIST_HEAD(&q->queue_head);
251 q->last_merge = NULL;
253 q->boundary_rq = NULL;
256 e = elevator_get(name);
261 if (!e && *chosen_elevator) {
262 e = elevator_get(chosen_elevator);
264 printk(KERN_ERR "I/O scheduler %s not found\n",
269 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
272 "Default I/O scheduler not found. " \
274 e = elevator_get("noop");
278 eq = elevator_alloc(q, e);
282 data = elevator_init_queue(q, eq);
284 kobject_put(&eq->kobj);
288 elevator_attach(q, eq, data);
291 EXPORT_SYMBOL(elevator_init);
293 void elevator_exit(struct elevator_queue *e)
295 mutex_lock(&e->sysfs_lock);
296 if (e->ops->elevator_exit_fn)
297 e->ops->elevator_exit_fn(e);
299 mutex_unlock(&e->sysfs_lock);
301 kobject_put(&e->kobj);
303 EXPORT_SYMBOL(elevator_exit);
305 static inline void __elv_rqhash_del(struct request *rq)
307 hlist_del_init(&rq->hash);
310 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
313 __elv_rqhash_del(rq);
316 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
318 struct elevator_queue *e = q->elevator;
320 BUG_ON(ELV_ON_HASH(rq));
321 hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
324 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
326 __elv_rqhash_del(rq);
327 elv_rqhash_add(q, rq);
330 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
332 struct elevator_queue *e = q->elevator;
333 struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
334 struct hlist_node *entry, *next;
337 hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
338 BUG_ON(!ELV_ON_HASH(rq));
340 if (unlikely(!rq_mergeable(rq))) {
341 __elv_rqhash_del(rq);
345 if (rq_hash_key(rq) == offset)
353 * RB-tree support functions for inserting/lookup/removal of requests
354 * in a sorted RB tree.
356 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
358 struct rb_node **p = &root->rb_node;
359 struct rb_node *parent = NULL;
360 struct request *__rq;
364 __rq = rb_entry(parent, struct request, rb_node);
366 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
368 else if (blk_rq_pos(rq) > blk_rq_pos(__rq))
374 rb_link_node(&rq->rb_node, parent, p);
375 rb_insert_color(&rq->rb_node, root);
378 EXPORT_SYMBOL(elv_rb_add);
380 void elv_rb_del(struct rb_root *root, struct request *rq)
382 BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
383 rb_erase(&rq->rb_node, root);
384 RB_CLEAR_NODE(&rq->rb_node);
386 EXPORT_SYMBOL(elv_rb_del);
388 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
390 struct rb_node *n = root->rb_node;
394 rq = rb_entry(n, struct request, rb_node);
396 if (sector < blk_rq_pos(rq))
398 else if (sector > blk_rq_pos(rq))
406 EXPORT_SYMBOL(elv_rb_find);
409 * Insert rq into dispatch queue of q. Queue lock must be held on
410 * entry. rq is sort instead into the dispatch queue. To be used by
411 * specific elevators.
413 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
416 struct list_head *entry;
419 if (q->last_merge == rq)
420 q->last_merge = NULL;
422 elv_rqhash_del(q, rq);
426 boundary = q->end_sector;
427 stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
428 list_for_each_prev(entry, &q->queue_head) {
429 struct request *pos = list_entry_rq(entry);
431 if (blk_discard_rq(rq) != blk_discard_rq(pos))
433 if (rq_data_dir(rq) != rq_data_dir(pos))
435 if (pos->cmd_flags & stop_flags)
437 if (blk_rq_pos(rq) >= boundary) {
438 if (blk_rq_pos(pos) < boundary)
441 if (blk_rq_pos(pos) >= boundary)
444 if (blk_rq_pos(rq) >= blk_rq_pos(pos))
448 list_add(&rq->queuelist, entry);
450 EXPORT_SYMBOL(elv_dispatch_sort);
453 * Insert rq into dispatch queue of q. Queue lock must be held on
454 * entry. rq is added to the back of the dispatch queue. To be used by
455 * specific elevators.
457 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
459 if (q->last_merge == rq)
460 q->last_merge = NULL;
462 elv_rqhash_del(q, rq);
466 q->end_sector = rq_end_sector(rq);
468 list_add_tail(&rq->queuelist, &q->queue_head);
470 EXPORT_SYMBOL(elv_dispatch_add_tail);
472 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
474 struct elevator_queue *e = q->elevator;
475 struct request *__rq;
480 * nomerges: No merges at all attempted
481 * noxmerges: Only simple one-hit cache try
482 * merges: All merge tries attempted
484 if (blk_queue_nomerges(q))
485 return ELEVATOR_NO_MERGE;
488 * First try one-hit cache.
491 ret = elv_try_merge(q->last_merge, bio);
492 if (ret != ELEVATOR_NO_MERGE) {
493 *req = q->last_merge;
498 if (blk_queue_noxmerges(q))
499 return ELEVATOR_NO_MERGE;
502 * See if our hash lookup can find a potential backmerge.
504 __rq = elv_rqhash_find(q, bio->bi_sector);
505 if (__rq && elv_rq_merge_ok(__rq, bio)) {
507 return ELEVATOR_BACK_MERGE;
510 if (e->ops->elevator_merge_fn)
511 return e->ops->elevator_merge_fn(q, req, bio);
513 return ELEVATOR_NO_MERGE;
516 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
518 struct elevator_queue *e = q->elevator;
520 if (e->ops->elevator_merged_fn)
521 e->ops->elevator_merged_fn(q, rq, type);
523 if (type == ELEVATOR_BACK_MERGE)
524 elv_rqhash_reposition(q, rq);
529 void elv_merge_requests(struct request_queue *q, struct request *rq,
530 struct request *next)
532 struct elevator_queue *e = q->elevator;
534 if (e->ops->elevator_merge_req_fn)
535 e->ops->elevator_merge_req_fn(q, rq, next);
537 elv_rqhash_reposition(q, rq);
538 elv_rqhash_del(q, next);
544 void elv_bio_merged(struct request_queue *q, struct request *rq,
547 struct elevator_queue *e = q->elevator;
549 if (e->ops->elevator_bio_merged_fn)
550 e->ops->elevator_bio_merged_fn(q, rq, bio);
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 (blk_sorted_rq(rq))
562 elv_deactivate_rq(q, rq);
565 rq->cmd_flags &= ~REQ_STARTED;
567 elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
570 void elv_drain_elevator(struct request_queue *q)
573 while (q->elevator->ops->elevator_dispatch_fn(q, 1))
575 if (q->nr_sorted == 0)
577 if (printed++ < 10) {
578 printk(KERN_ERR "%s: forced dispatching is broken "
579 "(nr_sorted=%u), please report this\n",
580 q->elevator->elevator_type->elevator_name, q->nr_sorted);
585 * Call with queue lock held, interrupts disabled
587 void elv_quiesce_start(struct request_queue *q)
592 queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
595 * make sure we don't have any requests in flight
597 elv_drain_elevator(q);
598 while (q->rq.elvpriv) {
600 spin_unlock_irq(q->queue_lock);
602 spin_lock_irq(q->queue_lock);
603 elv_drain_elevator(q);
607 void elv_quiesce_end(struct request_queue *q)
609 queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
612 void elv_insert(struct request_queue *q, struct request *rq, int where)
614 struct list_head *pos;
618 trace_block_rq_insert(q, rq);
623 case ELEVATOR_INSERT_FRONT:
624 rq->cmd_flags |= REQ_SOFTBARRIER;
626 list_add(&rq->queuelist, &q->queue_head);
629 case ELEVATOR_INSERT_BACK:
630 rq->cmd_flags |= REQ_SOFTBARRIER;
631 elv_drain_elevator(q);
632 list_add_tail(&rq->queuelist, &q->queue_head);
634 * We kick the queue here for the following reasons.
635 * - The elevator might have returned NULL previously
636 * to delay requests and returned them now. As the
637 * queue wasn't empty before this request, ll_rw_blk
638 * won't run the queue on return, resulting in hang.
639 * - Usually, back inserted requests won't be merged
640 * with anything. There's no point in delaying queue
646 case ELEVATOR_INSERT_SORT:
647 BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
648 rq->cmd_flags |= REQ_SORTED;
650 if (rq_mergeable(rq)) {
651 elv_rqhash_add(q, rq);
657 * Some ioscheds (cfq) run q->request_fn directly, so
658 * rq cannot be accessed after calling
659 * elevator_add_req_fn.
661 q->elevator->ops->elevator_add_req_fn(q, rq);
664 case ELEVATOR_INSERT_REQUEUE:
666 * If ordered flush isn't in progress, we do front
667 * insertion; otherwise, requests should be requeued
670 rq->cmd_flags |= REQ_SOFTBARRIER;
673 * Most requeues happen because of a busy condition,
674 * don't force unplug of the queue for that case.
678 if (q->ordseq == 0) {
679 list_add(&rq->queuelist, &q->queue_head);
683 ordseq = blk_ordered_req_seq(rq);
685 list_for_each(pos, &q->queue_head) {
686 struct request *pos_rq = list_entry_rq(pos);
687 if (ordseq <= blk_ordered_req_seq(pos_rq))
691 list_add_tail(&rq->queuelist, pos);
695 printk(KERN_ERR "%s: bad insertion point %d\n",
700 if (unplug_it && blk_queue_plugged(q)) {
701 int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
702 - queue_in_flight(q);
704 if (nrq >= q->unplug_thresh)
705 __generic_unplug_device(q);
709 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
713 rq->cmd_flags |= REQ_ORDERED_COLOR;
715 if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
717 * toggle ordered color
719 if (blk_barrier_rq(rq))
723 * barriers implicitly indicate back insertion
725 if (where == ELEVATOR_INSERT_SORT)
726 where = ELEVATOR_INSERT_BACK;
729 * this request is scheduling boundary, update
732 if (blk_fs_request(rq) || blk_discard_rq(rq)) {
733 q->end_sector = rq_end_sector(rq);
736 } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
737 where == ELEVATOR_INSERT_SORT)
738 where = ELEVATOR_INSERT_BACK;
743 elv_insert(q, rq, where);
745 EXPORT_SYMBOL(__elv_add_request);
747 void elv_add_request(struct request_queue *q, struct request *rq, int where,
752 spin_lock_irqsave(q->queue_lock, flags);
753 __elv_add_request(q, rq, where, plug);
754 spin_unlock_irqrestore(q->queue_lock, flags);
756 EXPORT_SYMBOL(elv_add_request);
758 int elv_queue_empty(struct request_queue *q)
760 struct elevator_queue *e = q->elevator;
762 if (!list_empty(&q->queue_head))
765 if (e->ops->elevator_queue_empty_fn)
766 return e->ops->elevator_queue_empty_fn(q);
770 EXPORT_SYMBOL(elv_queue_empty);
772 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
774 struct elevator_queue *e = q->elevator;
776 if (e->ops->elevator_latter_req_fn)
777 return e->ops->elevator_latter_req_fn(q, rq);
781 struct request *elv_former_request(struct request_queue *q, struct request *rq)
783 struct elevator_queue *e = q->elevator;
785 if (e->ops->elevator_former_req_fn)
786 return e->ops->elevator_former_req_fn(q, rq);
790 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
792 struct elevator_queue *e = q->elevator;
794 if (e->ops->elevator_set_req_fn)
795 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
797 rq->elevator_private = NULL;
801 void elv_put_request(struct request_queue *q, struct request *rq)
803 struct elevator_queue *e = q->elevator;
805 if (e->ops->elevator_put_req_fn)
806 e->ops->elevator_put_req_fn(rq);
809 int elv_may_queue(struct request_queue *q, int rw)
811 struct elevator_queue *e = q->elevator;
813 if (e->ops->elevator_may_queue_fn)
814 return e->ops->elevator_may_queue_fn(q, rw);
816 return ELV_MQUEUE_MAY;
819 void elv_abort_queue(struct request_queue *q)
823 while (!list_empty(&q->queue_head)) {
824 rq = list_entry_rq(q->queue_head.next);
825 rq->cmd_flags |= REQ_QUIET;
826 trace_block_rq_abort(q, rq);
828 * Mark this request as started so we don't trigger
829 * any debug logic in the end I/O path.
831 blk_start_request(rq);
832 __blk_end_request_all(rq, -EIO);
835 EXPORT_SYMBOL(elv_abort_queue);
837 void elv_completed_request(struct request_queue *q, struct request *rq)
839 struct elevator_queue *e = q->elevator;
842 * request is released from the driver, io must be done
844 if (blk_account_rq(rq)) {
845 q->in_flight[rq_is_sync(rq)]--;
846 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
847 e->ops->elevator_completed_req_fn(q, rq);
851 * Check if the queue is waiting for fs requests to be
852 * drained for flush sequence.
854 if (unlikely(q->ordseq)) {
855 struct request *next = NULL;
857 if (!list_empty(&q->queue_head))
858 next = list_entry_rq(q->queue_head.next);
860 if (!queue_in_flight(q) &&
861 blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
862 (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
863 blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
869 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
872 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
874 struct elv_fs_entry *entry = to_elv(attr);
875 struct elevator_queue *e;
881 e = container_of(kobj, struct elevator_queue, kobj);
882 mutex_lock(&e->sysfs_lock);
883 error = e->ops ? entry->show(e, page) : -ENOENT;
884 mutex_unlock(&e->sysfs_lock);
889 elv_attr_store(struct kobject *kobj, struct attribute *attr,
890 const char *page, size_t length)
892 struct elv_fs_entry *entry = to_elv(attr);
893 struct elevator_queue *e;
899 e = container_of(kobj, struct elevator_queue, kobj);
900 mutex_lock(&e->sysfs_lock);
901 error = e->ops ? entry->store(e, page, length) : -ENOENT;
902 mutex_unlock(&e->sysfs_lock);
906 static const struct sysfs_ops elv_sysfs_ops = {
907 .show = elv_attr_show,
908 .store = elv_attr_store,
911 static struct kobj_type elv_ktype = {
912 .sysfs_ops = &elv_sysfs_ops,
913 .release = elevator_release,
916 int elv_register_queue(struct request_queue *q)
918 struct elevator_queue *e = q->elevator;
921 error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
923 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
925 while (attr->attr.name) {
926 if (sysfs_create_file(&e->kobj, &attr->attr))
931 kobject_uevent(&e->kobj, KOBJ_ADD);
935 EXPORT_SYMBOL(elv_register_queue);
937 static void __elv_unregister_queue(struct elevator_queue *e)
939 kobject_uevent(&e->kobj, KOBJ_REMOVE);
940 kobject_del(&e->kobj);
943 void elv_unregister_queue(struct request_queue *q)
946 __elv_unregister_queue(q->elevator);
948 EXPORT_SYMBOL(elv_unregister_queue);
950 void elv_register(struct elevator_type *e)
954 spin_lock(&elv_list_lock);
955 BUG_ON(elevator_find(e->elevator_name));
956 list_add_tail(&e->list, &elv_list);
957 spin_unlock(&elv_list_lock);
959 if (!strcmp(e->elevator_name, chosen_elevator) ||
960 (!*chosen_elevator &&
961 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
964 printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
967 EXPORT_SYMBOL_GPL(elv_register);
969 void elv_unregister(struct elevator_type *e)
971 struct task_struct *g, *p;
974 * Iterate every thread in the process to remove the io contexts.
977 read_lock(&tasklist_lock);
978 do_each_thread(g, p) {
981 e->ops.trim(p->io_context);
983 } while_each_thread(g, p);
984 read_unlock(&tasklist_lock);
987 spin_lock(&elv_list_lock);
988 list_del_init(&e->list);
989 spin_unlock(&elv_list_lock);
991 EXPORT_SYMBOL_GPL(elv_unregister);
994 * switch to new_e io scheduler. be careful not to introduce deadlocks -
995 * we don't free the old io scheduler, before we have allocated what we
996 * need for the new one. this way we have a chance of going back to the old
997 * one, if the new one fails init for some reason.
999 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1001 struct elevator_queue *old_elevator, *e;
1005 * Allocate new elevator
1007 e = elevator_alloc(q, new_e);
1011 data = elevator_init_queue(q, e);
1013 kobject_put(&e->kobj);
1018 * Turn on BYPASS and drain all requests w/ elevator private data
1020 spin_lock_irq(q->queue_lock);
1021 elv_quiesce_start(q);
1024 * Remember old elevator.
1026 old_elevator = q->elevator;
1029 * attach and start new elevator
1031 elevator_attach(q, e, data);
1033 spin_unlock_irq(q->queue_lock);
1035 __elv_unregister_queue(old_elevator);
1037 if (elv_register_queue(q))
1041 * finally exit old elevator and turn off BYPASS.
1043 elevator_exit(old_elevator);
1044 spin_lock_irq(q->queue_lock);
1046 spin_unlock_irq(q->queue_lock);
1048 blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1054 * switch failed, exit the new io scheduler and reattach the old
1055 * one again (along with re-adding the sysfs dir)
1058 q->elevator = old_elevator;
1059 elv_register_queue(q);
1061 spin_lock_irq(q->queue_lock);
1062 queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1063 spin_unlock_irq(q->queue_lock);
1068 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1071 char elevator_name[ELV_NAME_MAX];
1072 struct elevator_type *e;
1077 strlcpy(elevator_name, name, sizeof(elevator_name));
1078 e = elevator_get(strstrip(elevator_name));
1080 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1084 if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1089 if (!elevator_switch(q, e))
1090 printk(KERN_ERR "elevator: switch to %s failed\n",
1095 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1097 struct elevator_queue *e = q->elevator;
1098 struct elevator_type *elv;
1099 struct elevator_type *__e;
1102 if (!q->elevator || !blk_queue_stackable(q))
1103 return sprintf(name, "none\n");
1105 elv = e->elevator_type;
1107 spin_lock(&elv_list_lock);
1108 list_for_each_entry(__e, &elv_list, list) {
1109 if (!strcmp(elv->elevator_name, __e->elevator_name))
1110 len += sprintf(name+len, "[%s] ", elv->elevator_name);
1112 len += sprintf(name+len, "%s ", __e->elevator_name);
1114 spin_unlock(&elv_list_lock);
1116 len += sprintf(len+name, "\n");
1120 struct request *elv_rb_former_request(struct request_queue *q,
1123 struct rb_node *rbprev = rb_prev(&rq->rb_node);
1126 return rb_entry_rq(rbprev);
1130 EXPORT_SYMBOL(elv_rb_former_request);
1132 struct request *elv_rb_latter_request(struct request_queue *q,
1135 struct rb_node *rbnext = rb_next(&rq->rb_node);
1138 return rb_entry_rq(rbnext);
1142 EXPORT_SYMBOL(elv_rb_latter_request);