block: add function call to switch the IO scheduler from a driver
[linux-3.10.git] / 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
43 static DEFINE_SPINLOCK(elv_list_lock);
44 static LIST_HEAD(elv_list);
45
46 /*
47  * Merge hash stuff.
48  */
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))
55
56 /*
57  * Query io scheduler to see if the current process issuing bio may be
58  * merged with rq.
59  */
60 static 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  */
74 int 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->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD))
83                 return 0;
84
85         /*
86          * Don't merge discard requests and secure discard requests
87          */
88         if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE))
89                 return 0;
90
91         /*
92          * different data direction or already started, don't merge
93          */
94         if (bio_data_dir(bio) != rq_data_dir(rq))
95                 return 0;
96
97         /*
98          * must be same device and not a special request
99          */
100         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
101                 return 0;
102
103         /*
104          * only merge integrity protected bio into ditto rq
105          */
106         if (bio_integrity(bio) != blk_integrity_rq(rq))
107                 return 0;
108
109         if (!elv_iosched_allow_merge(rq, bio))
110                 return 0;
111
112         return 1;
113 }
114 EXPORT_SYMBOL(elv_rq_merge_ok);
115
116 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
117 {
118         int ret = ELEVATOR_NO_MERGE;
119
120         /*
121          * we can merge and sequence is ok, check if it's possible
122          */
123         if (elv_rq_merge_ok(__rq, bio)) {
124                 if (blk_rq_pos(__rq) + blk_rq_sectors(__rq) == bio->bi_sector)
125                         ret = ELEVATOR_BACK_MERGE;
126                 else if (blk_rq_pos(__rq) - bio_sectors(bio) == bio->bi_sector)
127                         ret = ELEVATOR_FRONT_MERGE;
128         }
129
130         return ret;
131 }
132
133 static struct elevator_type *elevator_find(const char *name)
134 {
135         struct elevator_type *e;
136
137         list_for_each_entry(e, &elv_list, list) {
138                 if (!strcmp(e->elevator_name, name))
139                         return e;
140         }
141
142         return NULL;
143 }
144
145 static void elevator_put(struct elevator_type *e)
146 {
147         module_put(e->elevator_owner);
148 }
149
150 static struct elevator_type *elevator_get(const char *name)
151 {
152         struct elevator_type *e;
153
154         spin_lock(&elv_list_lock);
155
156         e = elevator_find(name);
157         if (!e) {
158                 char elv[ELV_NAME_MAX + strlen("-iosched")];
159
160                 spin_unlock(&elv_list_lock);
161
162                 snprintf(elv, sizeof(elv), "%s-iosched", name);
163
164                 request_module("%s", elv);
165                 spin_lock(&elv_list_lock);
166                 e = elevator_find(name);
167         }
168
169         if (e && !try_module_get(e->elevator_owner))
170                 e = NULL;
171
172         spin_unlock(&elv_list_lock);
173
174         return e;
175 }
176
177 static void *elevator_init_queue(struct request_queue *q,
178                                  struct elevator_queue *eq)
179 {
180         return eq->ops->elevator_init_fn(q);
181 }
182
183 static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
184                            void *data)
185 {
186         q->elevator = eq;
187         eq->elevator_data = data;
188 }
189
190 static char chosen_elevator[16];
191
192 static int __init elevator_setup(char *str)
193 {
194         /*
195          * Be backwards-compatible with previous kernels, so users
196          * won't get the wrong elevator.
197          */
198         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
199         return 1;
200 }
201
202 __setup("elevator=", elevator_setup);
203
204 static struct kobj_type elv_ktype;
205
206 static struct elevator_queue *elevator_alloc(struct request_queue *q,
207                                   struct elevator_type *e)
208 {
209         struct elevator_queue *eq;
210         int i;
211
212         eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
213         if (unlikely(!eq))
214                 goto err;
215
216         eq->ops = &e->ops;
217         eq->elevator_type = e;
218         kobject_init(&eq->kobj, &elv_ktype);
219         mutex_init(&eq->sysfs_lock);
220
221         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
222                                         GFP_KERNEL, q->node);
223         if (!eq->hash)
224                 goto err;
225
226         for (i = 0; i < ELV_HASH_ENTRIES; i++)
227                 INIT_HLIST_HEAD(&eq->hash[i]);
228
229         return eq;
230 err:
231         kfree(eq);
232         elevator_put(e);
233         return NULL;
234 }
235
236 static void elevator_release(struct kobject *kobj)
237 {
238         struct elevator_queue *e;
239
240         e = container_of(kobj, struct elevator_queue, kobj);
241         elevator_put(e->elevator_type);
242         kfree(e->hash);
243         kfree(e);
244 }
245
246 int elevator_init(struct request_queue *q, char *name)
247 {
248         struct elevator_type *e = NULL;
249         struct elevator_queue *eq;
250         void *data;
251
252         if (unlikely(q->elevator))
253                 return 0;
254
255         INIT_LIST_HEAD(&q->queue_head);
256         q->last_merge = NULL;
257         q->end_sector = 0;
258         q->boundary_rq = NULL;
259
260         if (name) {
261                 e = elevator_get(name);
262                 if (!e)
263                         return -EINVAL;
264         }
265
266         if (!e && *chosen_elevator) {
267                 e = elevator_get(chosen_elevator);
268                 if (!e)
269                         printk(KERN_ERR "I/O scheduler %s not found\n",
270                                                         chosen_elevator);
271         }
272
273         if (!e) {
274                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
275                 if (!e) {
276                         printk(KERN_ERR
277                                 "Default I/O scheduler not found. " \
278                                 "Using noop.\n");
279                         e = elevator_get("noop");
280                 }
281         }
282
283         eq = elevator_alloc(q, e);
284         if (!eq)
285                 return -ENOMEM;
286
287         data = elevator_init_queue(q, eq);
288         if (!data) {
289                 kobject_put(&eq->kobj);
290                 return -ENOMEM;
291         }
292
293         elevator_attach(q, eq, data);
294         return 0;
295 }
296 EXPORT_SYMBOL(elevator_init);
297
298 void elevator_exit(struct elevator_queue *e)
299 {
300         mutex_lock(&e->sysfs_lock);
301         if (e->ops->elevator_exit_fn)
302                 e->ops->elevator_exit_fn(e);
303         e->ops = NULL;
304         mutex_unlock(&e->sysfs_lock);
305
306         kobject_put(&e->kobj);
307 }
308 EXPORT_SYMBOL(elevator_exit);
309
310 static inline void __elv_rqhash_del(struct request *rq)
311 {
312         hlist_del_init(&rq->hash);
313 }
314
315 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
316 {
317         if (ELV_ON_HASH(rq))
318                 __elv_rqhash_del(rq);
319 }
320
321 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
322 {
323         struct elevator_queue *e = q->elevator;
324
325         BUG_ON(ELV_ON_HASH(rq));
326         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
327 }
328
329 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
330 {
331         __elv_rqhash_del(rq);
332         elv_rqhash_add(q, rq);
333 }
334
335 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
336 {
337         struct elevator_queue *e = q->elevator;
338         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
339         struct hlist_node *entry, *next;
340         struct request *rq;
341
342         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
343                 BUG_ON(!ELV_ON_HASH(rq));
344
345                 if (unlikely(!rq_mergeable(rq))) {
346                         __elv_rqhash_del(rq);
347                         continue;
348                 }
349
350                 if (rq_hash_key(rq) == offset)
351                         return rq;
352         }
353
354         return NULL;
355 }
356
357 /*
358  * RB-tree support functions for inserting/lookup/removal of requests
359  * in a sorted RB tree.
360  */
361 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
362 {
363         struct rb_node **p = &root->rb_node;
364         struct rb_node *parent = NULL;
365         struct request *__rq;
366
367         while (*p) {
368                 parent = *p;
369                 __rq = rb_entry(parent, struct request, rb_node);
370
371                 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
372                         p = &(*p)->rb_left;
373                 else if (blk_rq_pos(rq) > blk_rq_pos(__rq))
374                         p = &(*p)->rb_right;
375                 else
376                         return __rq;
377         }
378
379         rb_link_node(&rq->rb_node, parent, p);
380         rb_insert_color(&rq->rb_node, root);
381         return NULL;
382 }
383 EXPORT_SYMBOL(elv_rb_add);
384
385 void elv_rb_del(struct rb_root *root, struct request *rq)
386 {
387         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
388         rb_erase(&rq->rb_node, root);
389         RB_CLEAR_NODE(&rq->rb_node);
390 }
391 EXPORT_SYMBOL(elv_rb_del);
392
393 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
394 {
395         struct rb_node *n = root->rb_node;
396         struct request *rq;
397
398         while (n) {
399                 rq = rb_entry(n, struct request, rb_node);
400
401                 if (sector < blk_rq_pos(rq))
402                         n = n->rb_left;
403                 else if (sector > blk_rq_pos(rq))
404                         n = n->rb_right;
405                 else
406                         return rq;
407         }
408
409         return NULL;
410 }
411 EXPORT_SYMBOL(elv_rb_find);
412
413 /*
414  * Insert rq into dispatch queue of q.  Queue lock must be held on
415  * entry.  rq is sort instead into the dispatch queue. To be used by
416  * specific elevators.
417  */
418 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
419 {
420         sector_t boundary;
421         struct list_head *entry;
422         int stop_flags;
423
424         if (q->last_merge == rq)
425                 q->last_merge = NULL;
426
427         elv_rqhash_del(q, rq);
428
429         q->nr_sorted--;
430
431         boundary = q->end_sector;
432         stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
433         list_for_each_prev(entry, &q->queue_head) {
434                 struct request *pos = list_entry_rq(entry);
435
436                 if ((rq->cmd_flags & REQ_DISCARD) !=
437                     (pos->cmd_flags & REQ_DISCARD))
438                         break;
439                 if (rq_data_dir(rq) != rq_data_dir(pos))
440                         break;
441                 if (pos->cmd_flags & stop_flags)
442                         break;
443                 if (blk_rq_pos(rq) >= boundary) {
444                         if (blk_rq_pos(pos) < boundary)
445                                 continue;
446                 } else {
447                         if (blk_rq_pos(pos) >= boundary)
448                                 break;
449                 }
450                 if (blk_rq_pos(rq) >= blk_rq_pos(pos))
451                         break;
452         }
453
454         list_add(&rq->queuelist, entry);
455 }
456 EXPORT_SYMBOL(elv_dispatch_sort);
457
458 /*
459  * Insert rq into dispatch queue of q.  Queue lock must be held on
460  * entry.  rq is added to the back of the dispatch queue. To be used by
461  * specific elevators.
462  */
463 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
464 {
465         if (q->last_merge == rq)
466                 q->last_merge = NULL;
467
468         elv_rqhash_del(q, rq);
469
470         q->nr_sorted--;
471
472         q->end_sector = rq_end_sector(rq);
473         q->boundary_rq = rq;
474         list_add_tail(&rq->queuelist, &q->queue_head);
475 }
476 EXPORT_SYMBOL(elv_dispatch_add_tail);
477
478 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
479 {
480         struct elevator_queue *e = q->elevator;
481         struct request *__rq;
482         int ret;
483
484         /*
485          * Levels of merges:
486          *      nomerges:  No merges at all attempted
487          *      noxmerges: Only simple one-hit cache try
488          *      merges:    All merge tries attempted
489          */
490         if (blk_queue_nomerges(q))
491                 return ELEVATOR_NO_MERGE;
492
493         /*
494          * First try one-hit cache.
495          */
496         if (q->last_merge) {
497                 ret = elv_try_merge(q->last_merge, bio);
498                 if (ret != ELEVATOR_NO_MERGE) {
499                         *req = q->last_merge;
500                         return ret;
501                 }
502         }
503
504         if (blk_queue_noxmerges(q))
505                 return ELEVATOR_NO_MERGE;
506
507         /*
508          * See if our hash lookup can find a potential backmerge.
509          */
510         __rq = elv_rqhash_find(q, bio->bi_sector);
511         if (__rq && elv_rq_merge_ok(__rq, bio)) {
512                 *req = __rq;
513                 return ELEVATOR_BACK_MERGE;
514         }
515
516         if (e->ops->elevator_merge_fn)
517                 return e->ops->elevator_merge_fn(q, req, bio);
518
519         return ELEVATOR_NO_MERGE;
520 }
521
522 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
523 {
524         struct elevator_queue *e = q->elevator;
525
526         if (e->ops->elevator_merged_fn)
527                 e->ops->elevator_merged_fn(q, rq, type);
528
529         if (type == ELEVATOR_BACK_MERGE)
530                 elv_rqhash_reposition(q, rq);
531
532         q->last_merge = rq;
533 }
534
535 void elv_merge_requests(struct request_queue *q, struct request *rq,
536                              struct request *next)
537 {
538         struct elevator_queue *e = q->elevator;
539
540         if (e->ops->elevator_merge_req_fn)
541                 e->ops->elevator_merge_req_fn(q, rq, next);
542
543         elv_rqhash_reposition(q, rq);
544         elv_rqhash_del(q, next);
545
546         q->nr_sorted--;
547         q->last_merge = rq;
548 }
549
550 void elv_bio_merged(struct request_queue *q, struct request *rq,
551                         struct bio *bio)
552 {
553         struct elevator_queue *e = q->elevator;
554
555         if (e->ops->elevator_bio_merged_fn)
556                 e->ops->elevator_bio_merged_fn(q, rq, bio);
557 }
558
559 void elv_requeue_request(struct request_queue *q, struct request *rq)
560 {
561         /*
562          * it already went through dequeue, we need to decrement the
563          * in_flight count again
564          */
565         if (blk_account_rq(rq)) {
566                 q->in_flight[rq_is_sync(rq)]--;
567                 if (rq->cmd_flags & REQ_SORTED)
568                         elv_deactivate_rq(q, rq);
569         }
570
571         rq->cmd_flags &= ~REQ_STARTED;
572
573         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
574 }
575
576 void elv_drain_elevator(struct request_queue *q)
577 {
578         static int printed;
579         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
580                 ;
581         if (q->nr_sorted == 0)
582                 return;
583         if (printed++ < 10) {
584                 printk(KERN_ERR "%s: forced dispatching is broken "
585                        "(nr_sorted=%u), please report this\n",
586                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
587         }
588 }
589
590 /*
591  * Call with queue lock held, interrupts disabled
592  */
593 void elv_quiesce_start(struct request_queue *q)
594 {
595         if (!q->elevator)
596                 return;
597
598         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
599
600         /*
601          * make sure we don't have any requests in flight
602          */
603         elv_drain_elevator(q);
604         while (q->rq.elvpriv) {
605                 __blk_run_queue(q);
606                 spin_unlock_irq(q->queue_lock);
607                 msleep(10);
608                 spin_lock_irq(q->queue_lock);
609                 elv_drain_elevator(q);
610         }
611 }
612
613 void elv_quiesce_end(struct request_queue *q)
614 {
615         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
616 }
617
618 void elv_insert(struct request_queue *q, struct request *rq, int where)
619 {
620         struct list_head *pos;
621         unsigned ordseq;
622         int unplug_it = 1;
623
624         trace_block_rq_insert(q, rq);
625
626         rq->q = q;
627
628         switch (where) {
629         case ELEVATOR_INSERT_FRONT:
630                 rq->cmd_flags |= REQ_SOFTBARRIER;
631
632                 list_add(&rq->queuelist, &q->queue_head);
633                 break;
634
635         case ELEVATOR_INSERT_BACK:
636                 rq->cmd_flags |= REQ_SOFTBARRIER;
637                 elv_drain_elevator(q);
638                 list_add_tail(&rq->queuelist, &q->queue_head);
639                 /*
640                  * We kick the queue here for the following reasons.
641                  * - The elevator might have returned NULL previously
642                  *   to delay requests and returned them now.  As the
643                  *   queue wasn't empty before this request, ll_rw_blk
644                  *   won't run the queue on return, resulting in hang.
645                  * - Usually, back inserted requests won't be merged
646                  *   with anything.  There's no point in delaying queue
647                  *   processing.
648                  */
649                 __blk_run_queue(q);
650                 break;
651
652         case ELEVATOR_INSERT_SORT:
653                 BUG_ON(rq->cmd_type != REQ_TYPE_FS &&
654                        !(rq->cmd_flags & REQ_DISCARD));
655                 rq->cmd_flags |= REQ_SORTED;
656                 q->nr_sorted++;
657                 if (rq_mergeable(rq)) {
658                         elv_rqhash_add(q, rq);
659                         if (!q->last_merge)
660                                 q->last_merge = rq;
661                 }
662
663                 /*
664                  * Some ioscheds (cfq) run q->request_fn directly, so
665                  * rq cannot be accessed after calling
666                  * elevator_add_req_fn.
667                  */
668                 q->elevator->ops->elevator_add_req_fn(q, rq);
669                 break;
670
671         case ELEVATOR_INSERT_REQUEUE:
672                 /*
673                  * If ordered flush isn't in progress, we do front
674                  * insertion; otherwise, requests should be requeued
675                  * in ordseq order.
676                  */
677                 rq->cmd_flags |= REQ_SOFTBARRIER;
678
679                 /*
680                  * Most requeues happen because of a busy condition,
681                  * don't force unplug of the queue for that case.
682                  */
683                 unplug_it = 0;
684
685                 if (q->ordseq == 0) {
686                         list_add(&rq->queuelist, &q->queue_head);
687                         break;
688                 }
689
690                 ordseq = blk_ordered_req_seq(rq);
691
692                 list_for_each(pos, &q->queue_head) {
693                         struct request *pos_rq = list_entry_rq(pos);
694                         if (ordseq <= blk_ordered_req_seq(pos_rq))
695                                 break;
696                 }
697
698                 list_add_tail(&rq->queuelist, pos);
699                 break;
700
701         default:
702                 printk(KERN_ERR "%s: bad insertion point %d\n",
703                        __func__, where);
704                 BUG();
705         }
706
707         if (unplug_it && blk_queue_plugged(q)) {
708                 int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
709                                 - queue_in_flight(q);
710
711                 if (nrq >= q->unplug_thresh)
712                         __generic_unplug_device(q);
713         }
714 }
715
716 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
717                        int plug)
718 {
719         if (q->ordcolor)
720                 rq->cmd_flags |= REQ_ORDERED_COLOR;
721
722         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
723                 /*
724                  * toggle ordered color
725                  */
726                 if (rq->cmd_flags & REQ_HARDBARRIER)
727                         q->ordcolor ^= 1;
728
729                 /*
730                  * barriers implicitly indicate back insertion
731                  */
732                 if (where == ELEVATOR_INSERT_SORT)
733                         where = ELEVATOR_INSERT_BACK;
734
735                 /*
736                  * this request is scheduling boundary, update
737                  * end_sector
738                  */
739                 if (rq->cmd_type == REQ_TYPE_FS ||
740                     (rq->cmd_flags & REQ_DISCARD)) {
741                         q->end_sector = rq_end_sector(rq);
742                         q->boundary_rq = rq;
743                 }
744         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
745                     where == ELEVATOR_INSERT_SORT)
746                 where = ELEVATOR_INSERT_BACK;
747
748         if (plug)
749                 blk_plug_device(q);
750
751         elv_insert(q, rq, where);
752 }
753 EXPORT_SYMBOL(__elv_add_request);
754
755 void elv_add_request(struct request_queue *q, struct request *rq, int where,
756                      int plug)
757 {
758         unsigned long flags;
759
760         spin_lock_irqsave(q->queue_lock, flags);
761         __elv_add_request(q, rq, where, plug);
762         spin_unlock_irqrestore(q->queue_lock, flags);
763 }
764 EXPORT_SYMBOL(elv_add_request);
765
766 int elv_queue_empty(struct request_queue *q)
767 {
768         struct elevator_queue *e = q->elevator;
769
770         if (!list_empty(&q->queue_head))
771                 return 0;
772
773         if (e->ops->elevator_queue_empty_fn)
774                 return e->ops->elevator_queue_empty_fn(q);
775
776         return 1;
777 }
778 EXPORT_SYMBOL(elv_queue_empty);
779
780 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
781 {
782         struct elevator_queue *e = q->elevator;
783
784         if (e->ops->elevator_latter_req_fn)
785                 return e->ops->elevator_latter_req_fn(q, rq);
786         return NULL;
787 }
788
789 struct request *elv_former_request(struct request_queue *q, struct request *rq)
790 {
791         struct elevator_queue *e = q->elevator;
792
793         if (e->ops->elevator_former_req_fn)
794                 return e->ops->elevator_former_req_fn(q, rq);
795         return NULL;
796 }
797
798 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
799 {
800         struct elevator_queue *e = q->elevator;
801
802         if (e->ops->elevator_set_req_fn)
803                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
804
805         rq->elevator_private = NULL;
806         return 0;
807 }
808
809 void elv_put_request(struct request_queue *q, struct request *rq)
810 {
811         struct elevator_queue *e = q->elevator;
812
813         if (e->ops->elevator_put_req_fn)
814                 e->ops->elevator_put_req_fn(rq);
815 }
816
817 int elv_may_queue(struct request_queue *q, int rw)
818 {
819         struct elevator_queue *e = q->elevator;
820
821         if (e->ops->elevator_may_queue_fn)
822                 return e->ops->elevator_may_queue_fn(q, rw);
823
824         return ELV_MQUEUE_MAY;
825 }
826
827 void elv_abort_queue(struct request_queue *q)
828 {
829         struct request *rq;
830
831         while (!list_empty(&q->queue_head)) {
832                 rq = list_entry_rq(q->queue_head.next);
833                 rq->cmd_flags |= REQ_QUIET;
834                 trace_block_rq_abort(q, rq);
835                 /*
836                  * Mark this request as started so we don't trigger
837                  * any debug logic in the end I/O path.
838                  */
839                 blk_start_request(rq);
840                 __blk_end_request_all(rq, -EIO);
841         }
842 }
843 EXPORT_SYMBOL(elv_abort_queue);
844
845 void elv_completed_request(struct request_queue *q, struct request *rq)
846 {
847         struct elevator_queue *e = q->elevator;
848
849         /*
850          * request is released from the driver, io must be done
851          */
852         if (blk_account_rq(rq)) {
853                 q->in_flight[rq_is_sync(rq)]--;
854                 if ((rq->cmd_flags & REQ_SORTED) &&
855                     e->ops->elevator_completed_req_fn)
856                         e->ops->elevator_completed_req_fn(q, rq);
857         }
858
859         /*
860          * Check if the queue is waiting for fs requests to be
861          * drained for flush sequence.
862          */
863         if (unlikely(q->ordseq)) {
864                 struct request *next = NULL;
865
866                 if (!list_empty(&q->queue_head))
867                         next = list_entry_rq(q->queue_head.next);
868
869                 if (!queue_in_flight(q) &&
870                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
871                     (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
872                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
873                         __blk_run_queue(q);
874                 }
875         }
876 }
877
878 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
879
880 static ssize_t
881 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
882 {
883         struct elv_fs_entry *entry = to_elv(attr);
884         struct elevator_queue *e;
885         ssize_t error;
886
887         if (!entry->show)
888                 return -EIO;
889
890         e = container_of(kobj, struct elevator_queue, kobj);
891         mutex_lock(&e->sysfs_lock);
892         error = e->ops ? entry->show(e, page) : -ENOENT;
893         mutex_unlock(&e->sysfs_lock);
894         return error;
895 }
896
897 static ssize_t
898 elv_attr_store(struct kobject *kobj, struct attribute *attr,
899                const char *page, size_t length)
900 {
901         struct elv_fs_entry *entry = to_elv(attr);
902         struct elevator_queue *e;
903         ssize_t error;
904
905         if (!entry->store)
906                 return -EIO;
907
908         e = container_of(kobj, struct elevator_queue, kobj);
909         mutex_lock(&e->sysfs_lock);
910         error = e->ops ? entry->store(e, page, length) : -ENOENT;
911         mutex_unlock(&e->sysfs_lock);
912         return error;
913 }
914
915 static const struct sysfs_ops elv_sysfs_ops = {
916         .show   = elv_attr_show,
917         .store  = elv_attr_store,
918 };
919
920 static struct kobj_type elv_ktype = {
921         .sysfs_ops      = &elv_sysfs_ops,
922         .release        = elevator_release,
923 };
924
925 int elv_register_queue(struct request_queue *q)
926 {
927         struct elevator_queue *e = q->elevator;
928         int error;
929
930         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
931         if (!error) {
932                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
933                 if (attr) {
934                         while (attr->attr.name) {
935                                 if (sysfs_create_file(&e->kobj, &attr->attr))
936                                         break;
937                                 attr++;
938                         }
939                 }
940                 kobject_uevent(&e->kobj, KOBJ_ADD);
941         }
942         return error;
943 }
944 EXPORT_SYMBOL(elv_register_queue);
945
946 static void __elv_unregister_queue(struct elevator_queue *e)
947 {
948         kobject_uevent(&e->kobj, KOBJ_REMOVE);
949         kobject_del(&e->kobj);
950 }
951
952 void elv_unregister_queue(struct request_queue *q)
953 {
954         if (q)
955                 __elv_unregister_queue(q->elevator);
956 }
957 EXPORT_SYMBOL(elv_unregister_queue);
958
959 void elv_register(struct elevator_type *e)
960 {
961         char *def = "";
962
963         spin_lock(&elv_list_lock);
964         BUG_ON(elevator_find(e->elevator_name));
965         list_add_tail(&e->list, &elv_list);
966         spin_unlock(&elv_list_lock);
967
968         if (!strcmp(e->elevator_name, chosen_elevator) ||
969                         (!*chosen_elevator &&
970                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
971                                 def = " (default)";
972
973         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
974                                                                 def);
975 }
976 EXPORT_SYMBOL_GPL(elv_register);
977
978 void elv_unregister(struct elevator_type *e)
979 {
980         struct task_struct *g, *p;
981
982         /*
983          * Iterate every thread in the process to remove the io contexts.
984          */
985         if (e->ops.trim) {
986                 read_lock(&tasklist_lock);
987                 do_each_thread(g, p) {
988                         task_lock(p);
989                         if (p->io_context)
990                                 e->ops.trim(p->io_context);
991                         task_unlock(p);
992                 } while_each_thread(g, p);
993                 read_unlock(&tasklist_lock);
994         }
995
996         spin_lock(&elv_list_lock);
997         list_del_init(&e->list);
998         spin_unlock(&elv_list_lock);
999 }
1000 EXPORT_SYMBOL_GPL(elv_unregister);
1001
1002 /*
1003  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1004  * we don't free the old io scheduler, before we have allocated what we
1005  * need for the new one. this way we have a chance of going back to the old
1006  * one, if the new one fails init for some reason.
1007  */
1008 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1009 {
1010         struct elevator_queue *old_elevator, *e;
1011         void *data;
1012         int err;
1013
1014         /*
1015          * Allocate new elevator
1016          */
1017         e = elevator_alloc(q, new_e);
1018         if (!e)
1019                 return -ENOMEM;
1020
1021         data = elevator_init_queue(q, e);
1022         if (!data) {
1023                 kobject_put(&e->kobj);
1024                 return -ENOMEM;
1025         }
1026
1027         /*
1028          * Turn on BYPASS and drain all requests w/ elevator private data
1029          */
1030         spin_lock_irq(q->queue_lock);
1031         elv_quiesce_start(q);
1032
1033         /*
1034          * Remember old elevator.
1035          */
1036         old_elevator = q->elevator;
1037
1038         /*
1039          * attach and start new elevator
1040          */
1041         elevator_attach(q, e, data);
1042
1043         spin_unlock_irq(q->queue_lock);
1044
1045         __elv_unregister_queue(old_elevator);
1046
1047         err = elv_register_queue(q);
1048         if (err)
1049                 goto fail_register;
1050
1051         /*
1052          * finally exit old elevator and turn off BYPASS.
1053          */
1054         elevator_exit(old_elevator);
1055         spin_lock_irq(q->queue_lock);
1056         elv_quiesce_end(q);
1057         spin_unlock_irq(q->queue_lock);
1058
1059         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1060
1061         return 0;
1062
1063 fail_register:
1064         /*
1065          * switch failed, exit the new io scheduler and reattach the old
1066          * one again (along with re-adding the sysfs dir)
1067          */
1068         elevator_exit(e);
1069         q->elevator = old_elevator;
1070         elv_register_queue(q);
1071
1072         spin_lock_irq(q->queue_lock);
1073         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1074         spin_unlock_irq(q->queue_lock);
1075
1076         return err;
1077 }
1078
1079 /*
1080  * Switch this queue to the given IO scheduler.
1081  */
1082 int elevator_change(struct request_queue *q, const char *name)
1083 {
1084         char elevator_name[ELV_NAME_MAX];
1085         struct elevator_type *e;
1086
1087         if (!q->elevator)
1088                 return -ENXIO;
1089
1090         strlcpy(elevator_name, name, sizeof(elevator_name));
1091         e = elevator_get(strstrip(elevator_name));
1092         if (!e) {
1093                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1094                 return -EINVAL;
1095         }
1096
1097         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1098                 elevator_put(e);
1099                 return 0;
1100         }
1101
1102         return elevator_switch(q, e);
1103 }
1104 EXPORT_SYMBOL(elevator_change);
1105
1106 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1107                           size_t count)
1108 {
1109         int ret;
1110
1111         if (!q->elevator)
1112                 return count;
1113
1114         ret = elevator_change(q, name);
1115         if (!ret)
1116                 return count;
1117
1118         printk(KERN_ERR "elevator: switch to %s failed\n", name);
1119         return ret;
1120 }
1121
1122 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1123 {
1124         struct elevator_queue *e = q->elevator;
1125         struct elevator_type *elv;
1126         struct elevator_type *__e;
1127         int len = 0;
1128
1129         if (!q->elevator || !blk_queue_stackable(q))
1130                 return sprintf(name, "none\n");
1131
1132         elv = e->elevator_type;
1133
1134         spin_lock(&elv_list_lock);
1135         list_for_each_entry(__e, &elv_list, list) {
1136                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1137                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1138                 else
1139                         len += sprintf(name+len, "%s ", __e->elevator_name);
1140         }
1141         spin_unlock(&elv_list_lock);
1142
1143         len += sprintf(len+name, "\n");
1144         return len;
1145 }
1146
1147 struct request *elv_rb_former_request(struct request_queue *q,
1148                                       struct request *rq)
1149 {
1150         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1151
1152         if (rbprev)
1153                 return rb_entry_rq(rbprev);
1154
1155         return NULL;
1156 }
1157 EXPORT_SYMBOL(elv_rb_former_request);
1158
1159 struct request *elv_rb_latter_request(struct request_queue *q,
1160                                       struct request *rq)
1161 {
1162         struct rb_node *rbnext = rb_next(&rq->rb_node);
1163
1164         if (rbnext)
1165                 return rb_entry_rq(rbnext);
1166
1167         return NULL;
1168 }
1169 EXPORT_SYMBOL(elv_rb_latter_request);