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/delay.h>
35#include <linux/blktrace_api.h>
36#include <linux/hash.h>
37#include <linux/uaccess.h>
38
39#include <trace/events/block.h>
40
41#include "blk.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->ops->elevator_allow_merge_fn)
66        return e->ops->elevator_allow_merge_fn(q, rq, bio);
67
68    return 1;
69}
70
71/*
72 * can we safely merge with this request?
73 */
74int elv_rq_merge_ok(struct request *rq, struct bio *bio)
75{
76    if (!rq_mergeable(rq))
77        return 0;
78
79    /*
80     * Don't merge file system requests and discard requests
81     */
82    if (bio_rw_flagged(bio, BIO_RW_DISCARD) !=
83        bio_rw_flagged(rq->bio, BIO_RW_DISCARD))
84        return 0;
85
86    /*
87     * different data direction or already started, don't merge
88     */
89    if (bio_data_dir(bio) != rq_data_dir(rq))
90        return 0;
91
92    /*
93     * must be same device and not a special request
94     */
95    if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
96        return 0;
97
98    /*
99     * only merge integrity protected bio into ditto rq
100     */
101    if (bio_integrity(bio) != blk_integrity_rq(rq))
102        return 0;
103
104    if (!elv_iosched_allow_merge(rq, bio))
105        return 0;
106
107    return 1;
108}
109EXPORT_SYMBOL(elv_rq_merge_ok);
110
111static inline int elv_try_merge(struct request *__rq, struct bio *bio)
112{
113    int ret = ELEVATOR_NO_MERGE;
114
115    /*
116     * we can merge and sequence is ok, check if it's possible
117     */
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;
123    }
124
125    return ret;
126}
127
128static struct elevator_type *elevator_find(const char *name)
129{
130    struct elevator_type *e;
131
132    list_for_each_entry(e, &elv_list, list) {
133        if (!strcmp(e->elevator_name, name))
134            return e;
135    }
136
137    return NULL;
138}
139
140static void elevator_put(struct elevator_type *e)
141{
142    module_put(e->elevator_owner);
143}
144
145static struct elevator_type *elevator_get(const char *name)
146{
147    struct elevator_type *e;
148
149    spin_lock(&elv_list_lock);
150
151    e = elevator_find(name);
152    if (!e) {
153        char elv[ELV_NAME_MAX + strlen("-iosched")];
154
155        spin_unlock(&elv_list_lock);
156
157        snprintf(elv, sizeof(elv), "%s-iosched", name);
158
159        request_module("%s", elv);
160        spin_lock(&elv_list_lock);
161        e = elevator_find(name);
162    }
163
164    if (e && !try_module_get(e->elevator_owner))
165        e = NULL;
166
167    spin_unlock(&elv_list_lock);
168
169    return e;
170}
171
172static void *elevator_init_queue(struct request_queue *q,
173                 struct elevator_queue *eq)
174{
175    return eq->ops->elevator_init_fn(q);
176}
177
178static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
179               void *data)
180{
181    q->elevator = eq;
182    eq->elevator_data = data;
183}
184
185static char chosen_elevator[16];
186
187static int __init elevator_setup(char *str)
188{
189    /*
190     * Be backwards-compatible with previous kernels, so users
191     * won't get the wrong elevator.
192     */
193    strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
194    return 1;
195}
196
197__setup("elevator=", elevator_setup);
198
199static struct kobj_type elv_ktype;
200
201static struct elevator_queue *elevator_alloc(struct request_queue *q,
202                  struct elevator_type *e)
203{
204    struct elevator_queue *eq;
205    int i;
206
207    eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
208    if (unlikely(!eq))
209        goto err;
210
211    eq->ops = &e->ops;
212    eq->elevator_type = e;
213    kobject_init(&eq->kobj, &elv_ktype);
214    mutex_init(&eq->sysfs_lock);
215
216    eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
217                    GFP_KERNEL, q->node);
218    if (!eq->hash)
219        goto err;
220
221    for (i = 0; i < ELV_HASH_ENTRIES; i++)
222        INIT_HLIST_HEAD(&eq->hash[i]);
223
224    return eq;
225err:
226    kfree(eq);
227    elevator_put(e);
228    return NULL;
229}
230
231static void elevator_release(struct kobject *kobj)
232{
233    struct elevator_queue *e;
234
235    e = container_of(kobj, struct elevator_queue, kobj);
236    elevator_put(e->elevator_type);
237    kfree(e->hash);
238    kfree(e);
239}
240
241int elevator_init(struct request_queue *q, char *name)
242{
243    struct elevator_type *e = NULL;
244    struct elevator_queue *eq;
245    void *data;
246
247    if (unlikely(q->elevator))
248        return 0;
249
250    INIT_LIST_HEAD(&q->queue_head);
251    q->last_merge = NULL;
252    q->end_sector = 0;
253    q->boundary_rq = NULL;
254
255    if (name) {
256        e = elevator_get(name);
257        if (!e)
258            return -EINVAL;
259    }
260
261    if (!e && *chosen_elevator) {
262        e = elevator_get(chosen_elevator);
263        if (!e)
264            printk(KERN_ERR "I/O scheduler %s not found\n",
265                            chosen_elevator);
266    }
267
268    if (!e) {
269        e = elevator_get(CONFIG_DEFAULT_IOSCHED);
270        if (!e) {
271            printk(KERN_ERR
272                "Default I/O scheduler not found. " \
273                "Using noop.\n");
274            e = elevator_get("noop");
275        }
276    }
277
278    eq = elevator_alloc(q, e);
279    if (!eq)
280        return -ENOMEM;
281
282    data = elevator_init_queue(q, eq);
283    if (!data) {
284        kobject_put(&eq->kobj);
285        return -ENOMEM;
286    }
287
288    elevator_attach(q, eq, data);
289    return 0;
290}
291EXPORT_SYMBOL(elevator_init);
292
293void elevator_exit(struct elevator_queue *e)
294{
295    mutex_lock(&e->sysfs_lock);
296    if (e->ops->elevator_exit_fn)
297        e->ops->elevator_exit_fn(e);
298    e->ops = NULL;
299    mutex_unlock(&e->sysfs_lock);
300
301    kobject_put(&e->kobj);
302}
303EXPORT_SYMBOL(elevator_exit);
304
305static inline void __elv_rqhash_del(struct request *rq)
306{
307    hlist_del_init(&rq->hash);
308}
309
310static void elv_rqhash_del(struct request_queue *q, struct request *rq)
311{
312    if (ELV_ON_HASH(rq))
313        __elv_rqhash_del(rq);
314}
315
316static void elv_rqhash_add(struct request_queue *q, struct request *rq)
317{
318    struct elevator_queue *e = q->elevator;
319
320    BUG_ON(ELV_ON_HASH(rq));
321    hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
322}
323
324static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
325{
326    __elv_rqhash_del(rq);
327    elv_rqhash_add(q, rq);
328}
329
330static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
331{
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;
335    struct request *rq;
336
337    hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
338        BUG_ON(!ELV_ON_HASH(rq));
339
340        if (unlikely(!rq_mergeable(rq))) {
341            __elv_rqhash_del(rq);
342            continue;
343        }
344
345        if (rq_hash_key(rq) == offset)
346            return rq;
347    }
348
349    return NULL;
350}
351
352/*
353 * RB-tree support functions for inserting/lookup/removal of requests
354 * in a sorted RB tree.
355 */
356struct request *elv_rb_add(struct rb_root *root, struct request *rq)
357{
358    struct rb_node **p = &root->rb_node;
359    struct rb_node *parent = NULL;
360    struct request *__rq;
361
362    while (*p) {
363        parent = *p;
364        __rq = rb_entry(parent, struct request, rb_node);
365
366        if (blk_rq_pos(rq) < blk_rq_pos(__rq))
367            p = &(*p)->rb_left;
368        else if (blk_rq_pos(rq) > blk_rq_pos(__rq))
369            p = &(*p)->rb_right;
370        else
371            return __rq;
372    }
373
374    rb_link_node(&rq->rb_node, parent, p);
375    rb_insert_color(&rq->rb_node, root);
376    return NULL;
377}
378EXPORT_SYMBOL(elv_rb_add);
379
380void elv_rb_del(struct rb_root *root, struct request *rq)
381{
382    BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
383    rb_erase(&rq->rb_node, root);
384    RB_CLEAR_NODE(&rq->rb_node);
385}
386EXPORT_SYMBOL(elv_rb_del);
387
388struct request *elv_rb_find(struct rb_root *root, sector_t sector)
389{
390    struct rb_node *n = root->rb_node;
391    struct request *rq;
392
393    while (n) {
394        rq = rb_entry(n, struct request, rb_node);
395
396        if (sector < blk_rq_pos(rq))
397            n = n->rb_left;
398        else if (sector > blk_rq_pos(rq))
399            n = n->rb_right;
400        else
401            return rq;
402    }
403
404    return NULL;
405}
406EXPORT_SYMBOL(elv_rb_find);
407
408/*
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.
412 */
413void elv_dispatch_sort(struct request_queue *q, struct request *rq)
414{
415    sector_t boundary;
416    struct list_head *entry;
417    int stop_flags;
418
419    if (q->last_merge == rq)
420        q->last_merge = NULL;
421
422    elv_rqhash_del(q, rq);
423
424    q->nr_sorted--;
425
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);
430
431        if (blk_discard_rq(rq) != blk_discard_rq(pos))
432            break;
433        if (rq_data_dir(rq) != rq_data_dir(pos))
434            break;
435        if (pos->cmd_flags & stop_flags)
436            break;
437        if (blk_rq_pos(rq) >= boundary) {
438            if (blk_rq_pos(pos) < boundary)
439                continue;
440        } else {
441            if (blk_rq_pos(pos) >= boundary)
442                break;
443        }
444        if (blk_rq_pos(rq) >= blk_rq_pos(pos))
445            break;
446    }
447
448    list_add(&rq->queuelist, entry);
449}
450EXPORT_SYMBOL(elv_dispatch_sort);
451
452/*
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.
456 */
457void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
458{
459    if (q->last_merge == rq)
460        q->last_merge = NULL;
461
462    elv_rqhash_del(q, rq);
463
464    q->nr_sorted--;
465
466    q->end_sector = rq_end_sector(rq);
467    q->boundary_rq = rq;
468    list_add_tail(&rq->queuelist, &q->queue_head);
469}
470EXPORT_SYMBOL(elv_dispatch_add_tail);
471
472int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
473{
474    struct elevator_queue *e = q->elevator;
475    struct request *__rq;
476    int ret;
477
478    /*
479     * Levels of merges:
480     * nomerges: No merges at all attempted
481     * noxmerges: Only simple one-hit cache try
482     * merges: All merge tries attempted
483     */
484    if (blk_queue_nomerges(q))
485        return ELEVATOR_NO_MERGE;
486
487    /*
488     * First try one-hit cache.
489     */
490    if (q->last_merge) {
491        ret = elv_try_merge(q->last_merge, bio);
492        if (ret != ELEVATOR_NO_MERGE) {
493            *req = q->last_merge;
494            return ret;
495        }
496    }
497
498    if (blk_queue_noxmerges(q))
499        return ELEVATOR_NO_MERGE;
500
501    /*
502     * See if our hash lookup can find a potential backmerge.
503     */
504    __rq = elv_rqhash_find(q, bio->bi_sector);
505    if (__rq && elv_rq_merge_ok(__rq, bio)) {
506        *req = __rq;
507        return ELEVATOR_BACK_MERGE;
508    }
509
510    if (e->ops->elevator_merge_fn)
511        return e->ops->elevator_merge_fn(q, req, bio);
512
513    return ELEVATOR_NO_MERGE;
514}
515
516void elv_merged_request(struct request_queue *q, struct request *rq, int type)
517{
518    struct elevator_queue *e = q->elevator;
519
520    if (e->ops->elevator_merged_fn)
521        e->ops->elevator_merged_fn(q, rq, type);
522
523    if (type == ELEVATOR_BACK_MERGE)
524        elv_rqhash_reposition(q, rq);
525
526    q->last_merge = rq;
527}
528
529void elv_merge_requests(struct request_queue *q, struct request *rq,
530                 struct request *next)
531{
532    struct elevator_queue *e = q->elevator;
533
534    if (e->ops->elevator_merge_req_fn)
535        e->ops->elevator_merge_req_fn(q, rq, next);
536
537    elv_rqhash_reposition(q, rq);
538    elv_rqhash_del(q, next);
539
540    q->nr_sorted--;
541    q->last_merge = rq;
542}
543
544void elv_bio_merged(struct request_queue *q, struct request *rq,
545            struct bio *bio)
546{
547    struct elevator_queue *e = q->elevator;
548
549    if (e->ops->elevator_bio_merged_fn)
550        e->ops->elevator_bio_merged_fn(q, rq, bio);
551}
552
553void elv_requeue_request(struct request_queue *q, struct request *rq)
554{
555    /*
556     * it already went through dequeue, we need to decrement the
557     * in_flight count again
558     */
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);
563    }
564
565    rq->cmd_flags &= ~REQ_STARTED;
566
567    elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
568}
569
570void elv_drain_elevator(struct request_queue *q)
571{
572    static int printed;
573    while (q->elevator->ops->elevator_dispatch_fn(q, 1))
574        ;
575    if (q->nr_sorted == 0)
576        return;
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);
581    }
582}
583
584/*
585 * Call with queue lock held, interrupts disabled
586 */
587void elv_quiesce_start(struct request_queue *q)
588{
589    if (!q->elevator)
590        return;
591
592    queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
593
594    /*
595     * make sure we don't have any requests in flight
596     */
597    elv_drain_elevator(q);
598    while (q->rq.elvpriv) {
599        __blk_run_queue(q);
600        spin_unlock_irq(q->queue_lock);
601        msleep(10);
602        spin_lock_irq(q->queue_lock);
603        elv_drain_elevator(q);
604    }
605}
606
607void elv_quiesce_end(struct request_queue *q)
608{
609    queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
610}
611
612void elv_insert(struct request_queue *q, struct request *rq, int where)
613{
614    struct list_head *pos;
615    unsigned ordseq;
616    int unplug_it = 1;
617
618    trace_block_rq_insert(q, rq);
619
620    rq->q = q;
621
622    switch (where) {
623    case ELEVATOR_INSERT_FRONT:
624        rq->cmd_flags |= REQ_SOFTBARRIER;
625
626        list_add(&rq->queuelist, &q->queue_head);
627        break;
628
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);
633        /*
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
641         * processing.
642         */
643        __blk_run_queue(q);
644        break;
645
646    case ELEVATOR_INSERT_SORT:
647        BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
648        rq->cmd_flags |= REQ_SORTED;
649        q->nr_sorted++;
650        if (rq_mergeable(rq)) {
651            elv_rqhash_add(q, rq);
652            if (!q->last_merge)
653                q->last_merge = rq;
654        }
655
656        /*
657         * Some ioscheds (cfq) run q->request_fn directly, so
658         * rq cannot be accessed after calling
659         * elevator_add_req_fn.
660         */
661        q->elevator->ops->elevator_add_req_fn(q, rq);
662        break;
663
664    case ELEVATOR_INSERT_REQUEUE:
665        /*
666         * If ordered flush isn't in progress, we do front
667         * insertion; otherwise, requests should be requeued
668         * in ordseq order.
669         */
670        rq->cmd_flags |= REQ_SOFTBARRIER;
671
672        /*
673         * Most requeues happen because of a busy condition,
674         * don't force unplug of the queue for that case.
675         */
676        unplug_it = 0;
677
678        if (q->ordseq == 0) {
679            list_add(&rq->queuelist, &q->queue_head);
680            break;
681        }
682
683        ordseq = blk_ordered_req_seq(rq);
684
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))
688                break;
689        }
690
691        list_add_tail(&rq->queuelist, pos);
692        break;
693
694    default:
695        printk(KERN_ERR "%s: bad insertion point %d\n",
696               __func__, where);
697        BUG();
698    }
699
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);
703
704        if (nrq >= q->unplug_thresh)
705            __generic_unplug_device(q);
706    }
707}
708
709void __elv_add_request(struct request_queue *q, struct request *rq, int where,
710               int plug)
711{
712    if (q->ordcolor)
713        rq->cmd_flags |= REQ_ORDERED_COLOR;
714
715    if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
716        /*
717         * toggle ordered color
718         */
719        if (blk_barrier_rq(rq))
720            q->ordcolor ^= 1;
721
722        /*
723         * barriers implicitly indicate back insertion
724         */
725        if (where == ELEVATOR_INSERT_SORT)
726            where = ELEVATOR_INSERT_BACK;
727
728        /*
729         * this request is scheduling boundary, update
730         * end_sector
731         */
732        if (blk_fs_request(rq) || blk_discard_rq(rq)) {
733            q->end_sector = rq_end_sector(rq);
734            q->boundary_rq = rq;
735        }
736    } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
737            where == ELEVATOR_INSERT_SORT)
738        where = ELEVATOR_INSERT_BACK;
739
740    if (plug)
741        blk_plug_device(q);
742
743    elv_insert(q, rq, where);
744}
745EXPORT_SYMBOL(__elv_add_request);
746
747void elv_add_request(struct request_queue *q, struct request *rq, int where,
748             int plug)
749{
750    unsigned long flags;
751
752    spin_lock_irqsave(q->queue_lock, flags);
753    __elv_add_request(q, rq, where, plug);
754    spin_unlock_irqrestore(q->queue_lock, flags);
755}
756EXPORT_SYMBOL(elv_add_request);
757
758int elv_queue_empty(struct request_queue *q)
759{
760    struct elevator_queue *e = q->elevator;
761
762    if (!list_empty(&q->queue_head))
763        return 0;
764
765    if (e->ops->elevator_queue_empty_fn)
766        return e->ops->elevator_queue_empty_fn(q);
767
768    return 1;
769}
770EXPORT_SYMBOL(elv_queue_empty);
771
772struct request *elv_latter_request(struct request_queue *q, struct request *rq)
773{
774    struct elevator_queue *e = q->elevator;
775
776    if (e->ops->elevator_latter_req_fn)
777        return e->ops->elevator_latter_req_fn(q, rq);
778    return NULL;
779}
780
781struct request *elv_former_request(struct request_queue *q, struct request *rq)
782{
783    struct elevator_queue *e = q->elevator;
784
785    if (e->ops->elevator_former_req_fn)
786        return e->ops->elevator_former_req_fn(q, rq);
787    return NULL;
788}
789
790int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
791{
792    struct elevator_queue *e = q->elevator;
793
794    if (e->ops->elevator_set_req_fn)
795        return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
796
797    rq->elevator_private = NULL;
798    return 0;
799}
800
801void elv_put_request(struct request_queue *q, struct request *rq)
802{
803    struct elevator_queue *e = q->elevator;
804
805    if (e->ops->elevator_put_req_fn)
806        e->ops->elevator_put_req_fn(rq);
807}
808
809int elv_may_queue(struct request_queue *q, int rw)
810{
811    struct elevator_queue *e = q->elevator;
812
813    if (e->ops->elevator_may_queue_fn)
814        return e->ops->elevator_may_queue_fn(q, rw);
815
816    return ELV_MQUEUE_MAY;
817}
818
819void elv_abort_queue(struct request_queue *q)
820{
821    struct request *rq;
822
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);
827        /*
828         * Mark this request as started so we don't trigger
829         * any debug logic in the end I/O path.
830         */
831        blk_start_request(rq);
832        __blk_end_request_all(rq, -EIO);
833    }
834}
835EXPORT_SYMBOL(elv_abort_queue);
836
837void elv_completed_request(struct request_queue *q, struct request *rq)
838{
839    struct elevator_queue *e = q->elevator;
840
841    /*
842     * request is released from the driver, io must be done
843     */
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);
848    }
849
850    /*
851     * Check if the queue is waiting for fs requests to be
852     * drained for flush sequence.
853     */
854    if (unlikely(q->ordseq)) {
855        struct request *next = NULL;
856
857        if (!list_empty(&q->queue_head))
858            next = list_entry_rq(q->queue_head.next);
859
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);
864            __blk_run_queue(q);
865        }
866    }
867}
868
869#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
870
871static ssize_t
872elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
873{
874    struct elv_fs_entry *entry = to_elv(attr);
875    struct elevator_queue *e;
876    ssize_t error;
877
878    if (!entry->show)
879        return -EIO;
880
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);
885    return error;
886}
887
888static ssize_t
889elv_attr_store(struct kobject *kobj, struct attribute *attr,
890           const char *page, size_t length)
891{
892    struct elv_fs_entry *entry = to_elv(attr);
893    struct elevator_queue *e;
894    ssize_t error;
895
896    if (!entry->store)
897        return -EIO;
898
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);
903    return error;
904}
905
906static const struct sysfs_ops elv_sysfs_ops = {
907    .show = elv_attr_show,
908    .store = elv_attr_store,
909};
910
911static struct kobj_type elv_ktype = {
912    .sysfs_ops = &elv_sysfs_ops,
913    .release = elevator_release,
914};
915
916int elv_register_queue(struct request_queue *q)
917{
918    struct elevator_queue *e = q->elevator;
919    int error;
920
921    error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
922    if (!error) {
923        struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
924        if (attr) {
925            while (attr->attr.name) {
926                if (sysfs_create_file(&e->kobj, &attr->attr))
927                    break;
928                attr++;
929            }
930        }
931        kobject_uevent(&e->kobj, KOBJ_ADD);
932    }
933    return error;
934}
935EXPORT_SYMBOL(elv_register_queue);
936
937static void __elv_unregister_queue(struct elevator_queue *e)
938{
939    kobject_uevent(&e->kobj, KOBJ_REMOVE);
940    kobject_del(&e->kobj);
941}
942
943void elv_unregister_queue(struct request_queue *q)
944{
945    if (q)
946        __elv_unregister_queue(q->elevator);
947}
948EXPORT_SYMBOL(elv_unregister_queue);
949
950void elv_register(struct elevator_type *e)
951{
952    char *def = "";
953
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);
958
959    if (!strcmp(e->elevator_name, chosen_elevator) ||
960            (!*chosen_elevator &&
961             !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
962                def = " (default)";
963
964    printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
965                                def);
966}
967EXPORT_SYMBOL_GPL(elv_register);
968
969void elv_unregister(struct elevator_type *e)
970{
971    struct task_struct *g, *p;
972
973    /*
974     * Iterate every thread in the process to remove the io contexts.
975     */
976    if (e->ops.trim) {
977        read_lock(&tasklist_lock);
978        do_each_thread(g, p) {
979            task_lock(p);
980            if (p->io_context)
981                e->ops.trim(p->io_context);
982            task_unlock(p);
983        } while_each_thread(g, p);
984        read_unlock(&tasklist_lock);
985    }
986
987    spin_lock(&elv_list_lock);
988    list_del_init(&e->list);
989    spin_unlock(&elv_list_lock);
990}
991EXPORT_SYMBOL_GPL(elv_unregister);
992
993/*
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.
998 */
999static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1000{
1001    struct elevator_queue *old_elevator, *e;
1002    void *data;
1003
1004    /*
1005     * Allocate new elevator
1006     */
1007    e = elevator_alloc(q, new_e);
1008    if (!e)
1009        return 0;
1010
1011    data = elevator_init_queue(q, e);
1012    if (!data) {
1013        kobject_put(&e->kobj);
1014        return 0;
1015    }
1016
1017    /*
1018     * Turn on BYPASS and drain all requests w/ elevator private data
1019     */
1020    spin_lock_irq(q->queue_lock);
1021    elv_quiesce_start(q);
1022
1023    /*
1024     * Remember old elevator.
1025     */
1026    old_elevator = q->elevator;
1027
1028    /*
1029     * attach and start new elevator
1030     */
1031    elevator_attach(q, e, data);
1032
1033    spin_unlock_irq(q->queue_lock);
1034
1035    __elv_unregister_queue(old_elevator);
1036
1037    if (elv_register_queue(q))
1038        goto fail_register;
1039
1040    /*
1041     * finally exit old elevator and turn off BYPASS.
1042     */
1043    elevator_exit(old_elevator);
1044    spin_lock_irq(q->queue_lock);
1045    elv_quiesce_end(q);
1046    spin_unlock_irq(q->queue_lock);
1047
1048    blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1049
1050    return 1;
1051
1052fail_register:
1053    /*
1054     * switch failed, exit the new io scheduler and reattach the old
1055     * one again (along with re-adding the sysfs dir)
1056     */
1057    elevator_exit(e);
1058    q->elevator = old_elevator;
1059    elv_register_queue(q);
1060
1061    spin_lock_irq(q->queue_lock);
1062    queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1063    spin_unlock_irq(q->queue_lock);
1064
1065    return 0;
1066}
1067
1068ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1069              size_t count)
1070{
1071    char elevator_name[ELV_NAME_MAX];
1072    struct elevator_type *e;
1073
1074    if (!q->elevator)
1075        return count;
1076
1077    strlcpy(elevator_name, name, sizeof(elevator_name));
1078    e = elevator_get(strstrip(elevator_name));
1079    if (!e) {
1080        printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1081        return -EINVAL;
1082    }
1083
1084    if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1085        elevator_put(e);
1086        return count;
1087    }
1088
1089    if (!elevator_switch(q, e))
1090        printk(KERN_ERR "elevator: switch to %s failed\n",
1091                            elevator_name);
1092    return count;
1093}
1094
1095ssize_t elv_iosched_show(struct request_queue *q, char *name)
1096{
1097    struct elevator_queue *e = q->elevator;
1098    struct elevator_type *elv;
1099    struct elevator_type *__e;
1100    int len = 0;
1101
1102    if (!q->elevator || !blk_queue_stackable(q))
1103        return sprintf(name, "none\n");
1104
1105    elv = e->elevator_type;
1106
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);
1111        else
1112            len += sprintf(name+len, "%s ", __e->elevator_name);
1113    }
1114    spin_unlock(&elv_list_lock);
1115
1116    len += sprintf(len+name, "\n");
1117    return len;
1118}
1119
1120struct request *elv_rb_former_request(struct request_queue *q,
1121                      struct request *rq)
1122{
1123    struct rb_node *rbprev = rb_prev(&rq->rb_node);
1124
1125    if (rbprev)
1126        return rb_entry_rq(rbprev);
1127
1128    return NULL;
1129}
1130EXPORT_SYMBOL(elv_rb_former_request);
1131
1132struct request *elv_rb_latter_request(struct request_queue *q,
1133                      struct request *rq)
1134{
1135    struct rb_node *rbnext = rb_next(&rq->rb_node);
1136
1137    if (rbnext)
1138        return rb_entry_rq(rbnext);
1139
1140    return NULL;
1141}
1142EXPORT_SYMBOL(elv_rb_latter_request);
1143

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