Root/block/elevator.c

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 */
49#define rq_hash_key(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq))
50
51/*
52 * Query io scheduler to see if the current process issuing bio may be
53 * merged with rq.
54 */
55static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
56{
57    struct request_queue *q = rq->q;
58    struct elevator_queue *e = q->elevator;
59
60    if (e->type->ops.elevator_allow_merge_fn)
61        return e->type->ops.elevator_allow_merge_fn(q, rq, bio);
62
63    return 1;
64}
65
66/*
67 * can we safely merge with this request?
68 */
69bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
70{
71    if (!blk_rq_merge_ok(rq, bio))
72        return 0;
73
74    if (!elv_iosched_allow_merge(rq, bio))
75        return 0;
76
77    return 1;
78}
79EXPORT_SYMBOL(elv_rq_merge_ok);
80
81static struct elevator_type *elevator_find(const char *name)
82{
83    struct elevator_type *e;
84
85    list_for_each_entry(e, &elv_list, list) {
86        if (!strcmp(e->elevator_name, name))
87            return e;
88    }
89
90    return NULL;
91}
92
93static void elevator_put(struct elevator_type *e)
94{
95    module_put(e->elevator_owner);
96}
97
98static struct elevator_type *elevator_get(const char *name, bool try_loading)
99{
100    struct elevator_type *e;
101
102    spin_lock(&elv_list_lock);
103
104    e = elevator_find(name);
105    if (!e && try_loading) {
106        spin_unlock(&elv_list_lock);
107        request_module("%s-iosched", name);
108        spin_lock(&elv_list_lock);
109        e = elevator_find(name);
110    }
111
112    if (e && !try_module_get(e->elevator_owner))
113        e = NULL;
114
115    spin_unlock(&elv_list_lock);
116
117    return e;
118}
119
120static char chosen_elevator[ELV_NAME_MAX];
121
122static int __init elevator_setup(char *str)
123{
124    /*
125     * Be backwards-compatible with previous kernels, so users
126     * won't get the wrong elevator.
127     */
128    strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
129    return 1;
130}
131
132__setup("elevator=", elevator_setup);
133
134/* called during boot to load the elevator chosen by the elevator param */
135void __init load_default_elevator_module(void)
136{
137    struct elevator_type *e;
138
139    if (!chosen_elevator[0])
140        return;
141
142    spin_lock(&elv_list_lock);
143    e = elevator_find(chosen_elevator);
144    spin_unlock(&elv_list_lock);
145
146    if (!e)
147        request_module("%s-iosched", chosen_elevator);
148}
149
150static struct kobj_type elv_ktype;
151
152static struct elevator_queue *elevator_alloc(struct request_queue *q,
153                  struct elevator_type *e)
154{
155    struct elevator_queue *eq;
156
157    eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
158    if (unlikely(!eq))
159        goto err;
160
161    eq->type = e;
162    kobject_init(&eq->kobj, &elv_ktype);
163    mutex_init(&eq->sysfs_lock);
164    hash_init(eq->hash);
165
166    return eq;
167err:
168    kfree(eq);
169    elevator_put(e);
170    return NULL;
171}
172
173static void elevator_release(struct kobject *kobj)
174{
175    struct elevator_queue *e;
176
177    e = container_of(kobj, struct elevator_queue, kobj);
178    elevator_put(e->type);
179    kfree(e);
180}
181
182int elevator_init(struct request_queue *q, char *name)
183{
184    struct elevator_type *e = NULL;
185    int err;
186
187    if (unlikely(q->elevator))
188        return 0;
189
190    INIT_LIST_HEAD(&q->queue_head);
191    q->last_merge = NULL;
192    q->end_sector = 0;
193    q->boundary_rq = NULL;
194
195    if (name) {
196        e = elevator_get(name, true);
197        if (!e)
198            return -EINVAL;
199    }
200
201    /*
202     * Use the default elevator specified by config boot param or
203     * config option. Don't try to load modules as we could be running
204     * off async and request_module() isn't allowed from async.
205     */
206    if (!e && *chosen_elevator) {
207        e = elevator_get(chosen_elevator, false);
208        if (!e)
209            printk(KERN_ERR "I/O scheduler %s not found\n",
210                            chosen_elevator);
211    }
212
213    if (!e) {
214        e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
215        if (!e) {
216            printk(KERN_ERR
217                "Default I/O scheduler not found. " \
218                "Using noop.\n");
219            e = elevator_get("noop", false);
220        }
221    }
222
223    q->elevator = elevator_alloc(q, e);
224    if (!q->elevator)
225        return -ENOMEM;
226
227    err = e->ops.elevator_init_fn(q);
228    if (err) {
229        kobject_put(&q->elevator->kobj);
230        return err;
231    }
232
233    return 0;
234}
235EXPORT_SYMBOL(elevator_init);
236
237void elevator_exit(struct elevator_queue *e)
238{
239    mutex_lock(&e->sysfs_lock);
240    if (e->type->ops.elevator_exit_fn)
241        e->type->ops.elevator_exit_fn(e);
242    mutex_unlock(&e->sysfs_lock);
243
244    kobject_put(&e->kobj);
245}
246EXPORT_SYMBOL(elevator_exit);
247
248static inline void __elv_rqhash_del(struct request *rq)
249{
250    hash_del(&rq->hash);
251}
252
253static void elv_rqhash_del(struct request_queue *q, struct request *rq)
254{
255    if (ELV_ON_HASH(rq))
256        __elv_rqhash_del(rq);
257}
258
259static void elv_rqhash_add(struct request_queue *q, struct request *rq)
260{
261    struct elevator_queue *e = q->elevator;
262
263    BUG_ON(ELV_ON_HASH(rq));
264    hash_add(e->hash, &rq->hash, rq_hash_key(rq));
265}
266
267static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
268{
269    __elv_rqhash_del(rq);
270    elv_rqhash_add(q, rq);
271}
272
273static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
274{
275    struct elevator_queue *e = q->elevator;
276    struct hlist_node *next;
277    struct request *rq;
278
279    hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
280        BUG_ON(!ELV_ON_HASH(rq));
281
282        if (unlikely(!rq_mergeable(rq))) {
283            __elv_rqhash_del(rq);
284            continue;
285        }
286
287        if (rq_hash_key(rq) == offset)
288            return rq;
289    }
290
291    return NULL;
292}
293
294/*
295 * RB-tree support functions for inserting/lookup/removal of requests
296 * in a sorted RB tree.
297 */
298void elv_rb_add(struct rb_root *root, struct request *rq)
299{
300    struct rb_node **p = &root->rb_node;
301    struct rb_node *parent = NULL;
302    struct request *__rq;
303
304    while (*p) {
305        parent = *p;
306        __rq = rb_entry(parent, struct request, rb_node);
307
308        if (blk_rq_pos(rq) < blk_rq_pos(__rq))
309            p = &(*p)->rb_left;
310        else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
311            p = &(*p)->rb_right;
312    }
313
314    rb_link_node(&rq->rb_node, parent, p);
315    rb_insert_color(&rq->rb_node, root);
316}
317EXPORT_SYMBOL(elv_rb_add);
318
319void elv_rb_del(struct rb_root *root, struct request *rq)
320{
321    BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
322    rb_erase(&rq->rb_node, root);
323    RB_CLEAR_NODE(&rq->rb_node);
324}
325EXPORT_SYMBOL(elv_rb_del);
326
327struct request *elv_rb_find(struct rb_root *root, sector_t sector)
328{
329    struct rb_node *n = root->rb_node;
330    struct request *rq;
331
332    while (n) {
333        rq = rb_entry(n, struct request, rb_node);
334
335        if (sector < blk_rq_pos(rq))
336            n = n->rb_left;
337        else if (sector > blk_rq_pos(rq))
338            n = n->rb_right;
339        else
340            return rq;
341    }
342
343    return NULL;
344}
345EXPORT_SYMBOL(elv_rb_find);
346
347/*
348 * Insert rq into dispatch queue of q. Queue lock must be held on
349 * entry. rq is sort instead into the dispatch queue. To be used by
350 * specific elevators.
351 */
352void elv_dispatch_sort(struct request_queue *q, struct request *rq)
353{
354    sector_t boundary;
355    struct list_head *entry;
356    int stop_flags;
357
358    if (q->last_merge == rq)
359        q->last_merge = NULL;
360
361    elv_rqhash_del(q, rq);
362
363    q->nr_sorted--;
364
365    boundary = q->end_sector;
366    stop_flags = REQ_SOFTBARRIER | REQ_STARTED;
367    list_for_each_prev(entry, &q->queue_head) {
368        struct request *pos = list_entry_rq(entry);
369
370        if ((rq->cmd_flags & REQ_DISCARD) !=
371            (pos->cmd_flags & REQ_DISCARD))
372            break;
373        if (rq_data_dir(rq) != rq_data_dir(pos))
374            break;
375        if (pos->cmd_flags & stop_flags)
376            break;
377        if (blk_rq_pos(rq) >= boundary) {
378            if (blk_rq_pos(pos) < boundary)
379                continue;
380        } else {
381            if (blk_rq_pos(pos) >= boundary)
382                break;
383        }
384        if (blk_rq_pos(rq) >= blk_rq_pos(pos))
385            break;
386    }
387
388    list_add(&rq->queuelist, entry);
389}
390EXPORT_SYMBOL(elv_dispatch_sort);
391
392/*
393 * Insert rq into dispatch queue of q. Queue lock must be held on
394 * entry. rq is added to the back of the dispatch queue. To be used by
395 * specific elevators.
396 */
397void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
398{
399    if (q->last_merge == rq)
400        q->last_merge = NULL;
401
402    elv_rqhash_del(q, rq);
403
404    q->nr_sorted--;
405
406    q->end_sector = rq_end_sector(rq);
407    q->boundary_rq = rq;
408    list_add_tail(&rq->queuelist, &q->queue_head);
409}
410EXPORT_SYMBOL(elv_dispatch_add_tail);
411
412int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
413{
414    struct elevator_queue *e = q->elevator;
415    struct request *__rq;
416    int ret;
417
418    /*
419     * Levels of merges:
420     * nomerges: No merges at all attempted
421     * noxmerges: Only simple one-hit cache try
422     * merges: All merge tries attempted
423     */
424    if (blk_queue_nomerges(q))
425        return ELEVATOR_NO_MERGE;
426
427    /*
428     * First try one-hit cache.
429     */
430    if (q->last_merge && elv_rq_merge_ok(q->last_merge, bio)) {
431        ret = blk_try_merge(q->last_merge, bio);
432        if (ret != ELEVATOR_NO_MERGE) {
433            *req = q->last_merge;
434            return ret;
435        }
436    }
437
438    if (blk_queue_noxmerges(q))
439        return ELEVATOR_NO_MERGE;
440
441    /*
442     * See if our hash lookup can find a potential backmerge.
443     */
444    __rq = elv_rqhash_find(q, bio->bi_sector);
445    if (__rq && elv_rq_merge_ok(__rq, bio)) {
446        *req = __rq;
447        return ELEVATOR_BACK_MERGE;
448    }
449
450    if (e->type->ops.elevator_merge_fn)
451        return e->type->ops.elevator_merge_fn(q, req, bio);
452
453    return ELEVATOR_NO_MERGE;
454}
455
456/*
457 * Attempt to do an insertion back merge. Only check for the case where
458 * we can append 'rq' to an existing request, so we can throw 'rq' away
459 * afterwards.
460 *
461 * Returns true if we merged, false otherwise
462 */
463static bool elv_attempt_insert_merge(struct request_queue *q,
464                     struct request *rq)
465{
466    struct request *__rq;
467    bool ret;
468
469    if (blk_queue_nomerges(q))
470        return false;
471
472    /*
473     * First try one-hit cache.
474     */
475    if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
476        return true;
477
478    if (blk_queue_noxmerges(q))
479        return false;
480
481    ret = false;
482    /*
483     * See if our hash lookup can find a potential backmerge.
484     */
485    while (1) {
486        __rq = elv_rqhash_find(q, blk_rq_pos(rq));
487        if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
488            break;
489
490        /* The merged request could be merged with others, try again */
491        ret = true;
492        rq = __rq;
493    }
494
495    return ret;
496}
497
498void elv_merged_request(struct request_queue *q, struct request *rq, int type)
499{
500    struct elevator_queue *e = q->elevator;
501
502    if (e->type->ops.elevator_merged_fn)
503        e->type->ops.elevator_merged_fn(q, rq, type);
504
505    if (type == ELEVATOR_BACK_MERGE)
506        elv_rqhash_reposition(q, rq);
507
508    q->last_merge = rq;
509}
510
511void elv_merge_requests(struct request_queue *q, struct request *rq,
512                 struct request *next)
513{
514    struct elevator_queue *e = q->elevator;
515    const int next_sorted = next->cmd_flags & REQ_SORTED;
516
517    if (next_sorted && e->type->ops.elevator_merge_req_fn)
518        e->type->ops.elevator_merge_req_fn(q, rq, next);
519
520    elv_rqhash_reposition(q, rq);
521
522    if (next_sorted) {
523        elv_rqhash_del(q, next);
524        q->nr_sorted--;
525    }
526
527    q->last_merge = rq;
528}
529
530void elv_bio_merged(struct request_queue *q, struct request *rq,
531            struct bio *bio)
532{
533    struct elevator_queue *e = q->elevator;
534
535    if (e->type->ops.elevator_bio_merged_fn)
536        e->type->ops.elevator_bio_merged_fn(q, rq, bio);
537}
538
539void elv_requeue_request(struct request_queue *q, struct request *rq)
540{
541    /*
542     * it already went through dequeue, we need to decrement the
543     * in_flight count again
544     */
545    if (blk_account_rq(rq)) {
546        q->in_flight[rq_is_sync(rq)]--;
547        if (rq->cmd_flags & REQ_SORTED)
548            elv_deactivate_rq(q, rq);
549    }
550
551    rq->cmd_flags &= ~REQ_STARTED;
552
553    __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
554}
555
556void elv_drain_elevator(struct request_queue *q)
557{
558    static int printed;
559
560    lockdep_assert_held(q->queue_lock);
561
562    while (q->elevator->type->ops.elevator_dispatch_fn(q, 1))
563        ;
564    if (q->nr_sorted && printed++ < 10) {
565        printk(KERN_ERR "%s: forced dispatching is broken "
566               "(nr_sorted=%u), please report this\n",
567               q->elevator->type->elevator_name, q->nr_sorted);
568    }
569}
570
571void __elv_add_request(struct request_queue *q, struct request *rq, int where)
572{
573    trace_block_rq_insert(q, rq);
574
575    rq->q = q;
576
577    if (rq->cmd_flags & REQ_SOFTBARRIER) {
578        /* barriers are scheduling boundary, update end_sector */
579        if (rq->cmd_type == REQ_TYPE_FS) {
580            q->end_sector = rq_end_sector(rq);
581            q->boundary_rq = rq;
582        }
583    } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
584            (where == ELEVATOR_INSERT_SORT ||
585             where == ELEVATOR_INSERT_SORT_MERGE))
586        where = ELEVATOR_INSERT_BACK;
587
588    switch (where) {
589    case ELEVATOR_INSERT_REQUEUE:
590    case ELEVATOR_INSERT_FRONT:
591        rq->cmd_flags |= REQ_SOFTBARRIER;
592        list_add(&rq->queuelist, &q->queue_head);
593        break;
594
595    case ELEVATOR_INSERT_BACK:
596        rq->cmd_flags |= REQ_SOFTBARRIER;
597        elv_drain_elevator(q);
598        list_add_tail(&rq->queuelist, &q->queue_head);
599        /*
600         * We kick the queue here for the following reasons.
601         * - The elevator might have returned NULL previously
602         * to delay requests and returned them now. As the
603         * queue wasn't empty before this request, ll_rw_blk
604         * won't run the queue on return, resulting in hang.
605         * - Usually, back inserted requests won't be merged
606         * with anything. There's no point in delaying queue
607         * processing.
608         */
609        __blk_run_queue(q);
610        break;
611
612    case ELEVATOR_INSERT_SORT_MERGE:
613        /*
614         * If we succeed in merging this request with one in the
615         * queue already, we are done - rq has now been freed,
616         * so no need to do anything further.
617         */
618        if (elv_attempt_insert_merge(q, rq))
619            break;
620    case ELEVATOR_INSERT_SORT:
621        BUG_ON(rq->cmd_type != REQ_TYPE_FS);
622        rq->cmd_flags |= REQ_SORTED;
623        q->nr_sorted++;
624        if (rq_mergeable(rq)) {
625            elv_rqhash_add(q, rq);
626            if (!q->last_merge)
627                q->last_merge = rq;
628        }
629
630        /*
631         * Some ioscheds (cfq) run q->request_fn directly, so
632         * rq cannot be accessed after calling
633         * elevator_add_req_fn.
634         */
635        q->elevator->type->ops.elevator_add_req_fn(q, rq);
636        break;
637
638    case ELEVATOR_INSERT_FLUSH:
639        rq->cmd_flags |= REQ_SOFTBARRIER;
640        blk_insert_flush(rq);
641        break;
642    default:
643        printk(KERN_ERR "%s: bad insertion point %d\n",
644               __func__, where);
645        BUG();
646    }
647}
648EXPORT_SYMBOL(__elv_add_request);
649
650void elv_add_request(struct request_queue *q, struct request *rq, int where)
651{
652    unsigned long flags;
653
654    spin_lock_irqsave(q->queue_lock, flags);
655    __elv_add_request(q, rq, where);
656    spin_unlock_irqrestore(q->queue_lock, flags);
657}
658EXPORT_SYMBOL(elv_add_request);
659
660struct request *elv_latter_request(struct request_queue *q, struct request *rq)
661{
662    struct elevator_queue *e = q->elevator;
663
664    if (e->type->ops.elevator_latter_req_fn)
665        return e->type->ops.elevator_latter_req_fn(q, rq);
666    return NULL;
667}
668
669struct request *elv_former_request(struct request_queue *q, struct request *rq)
670{
671    struct elevator_queue *e = q->elevator;
672
673    if (e->type->ops.elevator_former_req_fn)
674        return e->type->ops.elevator_former_req_fn(q, rq);
675    return NULL;
676}
677
678int elv_set_request(struct request_queue *q, struct request *rq,
679            struct bio *bio, gfp_t gfp_mask)
680{
681    struct elevator_queue *e = q->elevator;
682
683    if (e->type->ops.elevator_set_req_fn)
684        return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
685    return 0;
686}
687
688void elv_put_request(struct request_queue *q, struct request *rq)
689{
690    struct elevator_queue *e = q->elevator;
691
692    if (e->type->ops.elevator_put_req_fn)
693        e->type->ops.elevator_put_req_fn(rq);
694}
695
696int elv_may_queue(struct request_queue *q, int rw)
697{
698    struct elevator_queue *e = q->elevator;
699
700    if (e->type->ops.elevator_may_queue_fn)
701        return e->type->ops.elevator_may_queue_fn(q, rw);
702
703    return ELV_MQUEUE_MAY;
704}
705
706void elv_abort_queue(struct request_queue *q)
707{
708    struct request *rq;
709
710    blk_abort_flushes(q);
711
712    while (!list_empty(&q->queue_head)) {
713        rq = list_entry_rq(q->queue_head.next);
714        rq->cmd_flags |= REQ_QUIET;
715        trace_block_rq_abort(q, rq);
716        /*
717         * Mark this request as started so we don't trigger
718         * any debug logic in the end I/O path.
719         */
720        blk_start_request(rq);
721        __blk_end_request_all(rq, -EIO);
722    }
723}
724EXPORT_SYMBOL(elv_abort_queue);
725
726void elv_completed_request(struct request_queue *q, struct request *rq)
727{
728    struct elevator_queue *e = q->elevator;
729
730    /*
731     * request is released from the driver, io must be done
732     */
733    if (blk_account_rq(rq)) {
734        q->in_flight[rq_is_sync(rq)]--;
735        if ((rq->cmd_flags & REQ_SORTED) &&
736            e->type->ops.elevator_completed_req_fn)
737            e->type->ops.elevator_completed_req_fn(q, rq);
738    }
739}
740
741#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
742
743static ssize_t
744elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
745{
746    struct elv_fs_entry *entry = to_elv(attr);
747    struct elevator_queue *e;
748    ssize_t error;
749
750    if (!entry->show)
751        return -EIO;
752
753    e = container_of(kobj, struct elevator_queue, kobj);
754    mutex_lock(&e->sysfs_lock);
755    error = e->type ? entry->show(e, page) : -ENOENT;
756    mutex_unlock(&e->sysfs_lock);
757    return error;
758}
759
760static ssize_t
761elv_attr_store(struct kobject *kobj, struct attribute *attr,
762           const char *page, size_t length)
763{
764    struct elv_fs_entry *entry = to_elv(attr);
765    struct elevator_queue *e;
766    ssize_t error;
767
768    if (!entry->store)
769        return -EIO;
770
771    e = container_of(kobj, struct elevator_queue, kobj);
772    mutex_lock(&e->sysfs_lock);
773    error = e->type ? entry->store(e, page, length) : -ENOENT;
774    mutex_unlock(&e->sysfs_lock);
775    return error;
776}
777
778static const struct sysfs_ops elv_sysfs_ops = {
779    .show = elv_attr_show,
780    .store = elv_attr_store,
781};
782
783static struct kobj_type elv_ktype = {
784    .sysfs_ops = &elv_sysfs_ops,
785    .release = elevator_release,
786};
787
788int elv_register_queue(struct request_queue *q)
789{
790    struct elevator_queue *e = q->elevator;
791    int error;
792
793    error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
794    if (!error) {
795        struct elv_fs_entry *attr = e->type->elevator_attrs;
796        if (attr) {
797            while (attr->attr.name) {
798                if (sysfs_create_file(&e->kobj, &attr->attr))
799                    break;
800                attr++;
801            }
802        }
803        kobject_uevent(&e->kobj, KOBJ_ADD);
804        e->registered = 1;
805    }
806    return error;
807}
808EXPORT_SYMBOL(elv_register_queue);
809
810void elv_unregister_queue(struct request_queue *q)
811{
812    if (q) {
813        struct elevator_queue *e = q->elevator;
814
815        kobject_uevent(&e->kobj, KOBJ_REMOVE);
816        kobject_del(&e->kobj);
817        e->registered = 0;
818    }
819}
820EXPORT_SYMBOL(elv_unregister_queue);
821
822int elv_register(struct elevator_type *e)
823{
824    char *def = "";
825
826    /* create icq_cache if requested */
827    if (e->icq_size) {
828        if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
829            WARN_ON(e->icq_align < __alignof__(struct io_cq)))
830            return -EINVAL;
831
832        snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
833             "%s_io_cq", e->elevator_name);
834        e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
835                         e->icq_align, 0, NULL);
836        if (!e->icq_cache)
837            return -ENOMEM;
838    }
839
840    /* register, don't allow duplicate names */
841    spin_lock(&elv_list_lock);
842    if (elevator_find(e->elevator_name)) {
843        spin_unlock(&elv_list_lock);
844        if (e->icq_cache)
845            kmem_cache_destroy(e->icq_cache);
846        return -EBUSY;
847    }
848    list_add_tail(&e->list, &elv_list);
849    spin_unlock(&elv_list_lock);
850
851    /* print pretty message */
852    if (!strcmp(e->elevator_name, chosen_elevator) ||
853            (!*chosen_elevator &&
854             !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
855                def = " (default)";
856
857    printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
858                                def);
859    return 0;
860}
861EXPORT_SYMBOL_GPL(elv_register);
862
863void elv_unregister(struct elevator_type *e)
864{
865    /* unregister */
866    spin_lock(&elv_list_lock);
867    list_del_init(&e->list);
868    spin_unlock(&elv_list_lock);
869
870    /*
871     * Destroy icq_cache if it exists. icq's are RCU managed. Make
872     * sure all RCU operations are complete before proceeding.
873     */
874    if (e->icq_cache) {
875        rcu_barrier();
876        kmem_cache_destroy(e->icq_cache);
877        e->icq_cache = NULL;
878    }
879}
880EXPORT_SYMBOL_GPL(elv_unregister);
881
882/*
883 * switch to new_e io scheduler. be careful not to introduce deadlocks -
884 * we don't free the old io scheduler, before we have allocated what we
885 * need for the new one. this way we have a chance of going back to the old
886 * one, if the new one fails init for some reason.
887 */
888static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
889{
890    struct elevator_queue *old = q->elevator;
891    bool registered = old->registered;
892    int err;
893
894    /*
895     * Turn on BYPASS and drain all requests w/ elevator private data.
896     * Block layer doesn't call into a quiesced elevator - all requests
897     * are directly put on the dispatch list without elevator data
898     * using INSERT_BACK. All requests have SOFTBARRIER set and no
899     * merge happens either.
900     */
901    blk_queue_bypass_start(q);
902
903    /* unregister and clear all auxiliary data of the old elevator */
904    if (registered)
905        elv_unregister_queue(q);
906
907    spin_lock_irq(q->queue_lock);
908    ioc_clear_queue(q);
909    spin_unlock_irq(q->queue_lock);
910
911    /* allocate, init and register new elevator */
912    err = -ENOMEM;
913    q->elevator = elevator_alloc(q, new_e);
914    if (!q->elevator)
915        goto fail_init;
916
917    err = new_e->ops.elevator_init_fn(q);
918    if (err) {
919        kobject_put(&q->elevator->kobj);
920        goto fail_init;
921    }
922
923    if (registered) {
924        err = elv_register_queue(q);
925        if (err)
926            goto fail_register;
927    }
928
929    /* done, kill the old one and finish */
930    elevator_exit(old);
931    blk_queue_bypass_end(q);
932
933    blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
934
935    return 0;
936
937fail_register:
938    elevator_exit(q->elevator);
939fail_init:
940    /* switch failed, restore and re-register old elevator */
941    q->elevator = old;
942    elv_register_queue(q);
943    blk_queue_bypass_end(q);
944
945    return err;
946}
947
948/*
949 * Switch this queue to the given IO scheduler.
950 */
951int elevator_change(struct request_queue *q, const char *name)
952{
953    char elevator_name[ELV_NAME_MAX];
954    struct elevator_type *e;
955
956    if (!q->elevator)
957        return -ENXIO;
958
959    strlcpy(elevator_name, name, sizeof(elevator_name));
960    e = elevator_get(strstrip(elevator_name), true);
961    if (!e) {
962        printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
963        return -EINVAL;
964    }
965
966    if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
967        elevator_put(e);
968        return 0;
969    }
970
971    return elevator_switch(q, e);
972}
973EXPORT_SYMBOL(elevator_change);
974
975ssize_t elv_iosched_store(struct request_queue *q, const char *name,
976              size_t count)
977{
978    int ret;
979
980    if (!q->elevator)
981        return count;
982
983    ret = elevator_change(q, name);
984    if (!ret)
985        return count;
986
987    printk(KERN_ERR "elevator: switch to %s failed\n", name);
988    return ret;
989}
990
991ssize_t elv_iosched_show(struct request_queue *q, char *name)
992{
993    struct elevator_queue *e = q->elevator;
994    struct elevator_type *elv;
995    struct elevator_type *__e;
996    int len = 0;
997
998    if (!q->elevator || !blk_queue_stackable(q))
999        return sprintf(name, "none\n");
1000
1001    elv = e->type;
1002
1003    spin_lock(&elv_list_lock);
1004    list_for_each_entry(__e, &elv_list, list) {
1005        if (!strcmp(elv->elevator_name, __e->elevator_name))
1006            len += sprintf(name+len, "[%s] ", elv->elevator_name);
1007        else
1008            len += sprintf(name+len, "%s ", __e->elevator_name);
1009    }
1010    spin_unlock(&elv_list_lock);
1011
1012    len += sprintf(len+name, "\n");
1013    return len;
1014}
1015
1016struct request *elv_rb_former_request(struct request_queue *q,
1017                      struct request *rq)
1018{
1019    struct rb_node *rbprev = rb_prev(&rq->rb_node);
1020
1021    if (rbprev)
1022        return rb_entry_rq(rbprev);
1023
1024    return NULL;
1025}
1026EXPORT_SYMBOL(elv_rb_former_request);
1027
1028struct request *elv_rb_latter_request(struct request_queue *q,
1029                      struct request *rq)
1030{
1031    struct rb_node *rbnext = rb_next(&rq->rb_node);
1032
1033    if (rbnext)
1034        return rb_entry_rq(rbnext);
1035
1036    return NULL;
1037}
1038EXPORT_SYMBOL(elv_rb_latter_request);
1039

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