d265963d1ed333fc6babce13d5fb4112f74bde12
[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
38 #include <asm/uaccess.h>
39
40 static DEFINE_SPINLOCK(elv_list_lock);
41 static LIST_HEAD(elv_list);
42
43 /*
44  * Merge hash stuff.
45  */
46 static const int elv_hash_shift = 6;
47 #define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
48 #define ELV_HASH_FN(sec)        (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
49 #define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
50 #define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
51 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
52
53 /*
54  * Query io scheduler to see if the current process issuing bio may be
55  * merged with rq.
56  */
57 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
58 {
59         request_queue_t *q = rq->q;
60         elevator_t *e = q->elevator;
61
62         if (e->ops->elevator_allow_merge_fn)
63                 return e->ops->elevator_allow_merge_fn(q, rq, bio);
64
65         return 1;
66 }
67
68 /*
69  * can we safely merge with this request?
70  */
71 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
72 {
73         if (!rq_mergeable(rq))
74                 return 0;
75
76         /*
77          * different data direction or already started, don't merge
78          */
79         if (bio_data_dir(bio) != rq_data_dir(rq))
80                 return 0;
81
82         /*
83          * must be same device and not a special request
84          */
85         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
86                 return 0;
87
88         if (!elv_iosched_allow_merge(rq, bio))
89                 return 0;
90
91         return 1;
92 }
93 EXPORT_SYMBOL(elv_rq_merge_ok);
94
95 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
96 {
97         int ret = ELEVATOR_NO_MERGE;
98
99         /*
100          * we can merge and sequence is ok, check if it's possible
101          */
102         if (elv_rq_merge_ok(__rq, bio)) {
103                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
104                         ret = ELEVATOR_BACK_MERGE;
105                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
106                         ret = ELEVATOR_FRONT_MERGE;
107         }
108
109         return ret;
110 }
111
112 static struct elevator_type *elevator_find(const char *name)
113 {
114         struct elevator_type *e;
115
116         list_for_each_entry(e, &elv_list, list) {
117                 if (!strcmp(e->elevator_name, name))
118                         return e;
119         }
120
121         return NULL;
122 }
123
124 static void elevator_put(struct elevator_type *e)
125 {
126         module_put(e->elevator_owner);
127 }
128
129 static struct elevator_type *elevator_get(const char *name)
130 {
131         struct elevator_type *e;
132
133         spin_lock(&elv_list_lock);
134
135         e = elevator_find(name);
136         if (e && !try_module_get(e->elevator_owner))
137                 e = NULL;
138
139         spin_unlock(&elv_list_lock);
140
141         return e;
142 }
143
144 static void *elevator_init_queue(request_queue_t *q, struct elevator_queue *eq)
145 {
146         return eq->ops->elevator_init_fn(q);
147 }
148
149 static void elevator_attach(request_queue_t *q, struct elevator_queue *eq,
150                            void *data)
151 {
152         q->elevator = eq;
153         eq->elevator_data = data;
154 }
155
156 static char chosen_elevator[16];
157
158 static int __init elevator_setup(char *str)
159 {
160         /*
161          * Be backwards-compatible with previous kernels, so users
162          * won't get the wrong elevator.
163          */
164         if (!strcmp(str, "as"))
165                 strcpy(chosen_elevator, "anticipatory");
166         else
167                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
168         return 1;
169 }
170
171 __setup("elevator=", elevator_setup);
172
173 static struct kobj_type elv_ktype;
174
175 static elevator_t *elevator_alloc(request_queue_t *q, struct elevator_type *e)
176 {
177         elevator_t *eq;
178         int i;
179
180         eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL | __GFP_ZERO, q->node);
181         if (unlikely(!eq))
182                 goto err;
183
184         eq->ops = &e->ops;
185         eq->elevator_type = e;
186         kobject_init(&eq->kobj);
187         snprintf(eq->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
188         eq->kobj.ktype = &elv_ktype;
189         mutex_init(&eq->sysfs_lock);
190
191         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
192                                         GFP_KERNEL, q->node);
193         if (!eq->hash)
194                 goto err;
195
196         for (i = 0; i < ELV_HASH_ENTRIES; i++)
197                 INIT_HLIST_HEAD(&eq->hash[i]);
198
199         return eq;
200 err:
201         kfree(eq);
202         elevator_put(e);
203         return NULL;
204 }
205
206 static void elevator_release(struct kobject *kobj)
207 {
208         elevator_t *e = container_of(kobj, elevator_t, kobj);
209
210         elevator_put(e->elevator_type);
211         kfree(e->hash);
212         kfree(e);
213 }
214
215 int elevator_init(request_queue_t *q, char *name)
216 {
217         struct elevator_type *e = NULL;
218         struct elevator_queue *eq;
219         int ret = 0;
220         void *data;
221
222         INIT_LIST_HEAD(&q->queue_head);
223         q->last_merge = NULL;
224         q->end_sector = 0;
225         q->boundary_rq = NULL;
226
227         if (name && !(e = elevator_get(name)))
228                 return -EINVAL;
229
230         if (!e && *chosen_elevator && !(e = elevator_get(chosen_elevator)))
231                 printk("I/O scheduler %s not found\n", chosen_elevator);
232
233         if (!e && !(e = elevator_get(CONFIG_DEFAULT_IOSCHED))) {
234                 printk("Default I/O scheduler not found, using no-op\n");
235                 e = elevator_get("noop");
236         }
237
238         eq = elevator_alloc(q, e);
239         if (!eq)
240                 return -ENOMEM;
241
242         data = elevator_init_queue(q, eq);
243         if (!data) {
244                 kobject_put(&eq->kobj);
245                 return -ENOMEM;
246         }
247
248         elevator_attach(q, eq, data);
249         return ret;
250 }
251
252 EXPORT_SYMBOL(elevator_init);
253
254 void elevator_exit(elevator_t *e)
255 {
256         mutex_lock(&e->sysfs_lock);
257         if (e->ops->elevator_exit_fn)
258                 e->ops->elevator_exit_fn(e);
259         e->ops = NULL;
260         mutex_unlock(&e->sysfs_lock);
261
262         kobject_put(&e->kobj);
263 }
264
265 EXPORT_SYMBOL(elevator_exit);
266
267 static void elv_activate_rq(request_queue_t *q, struct request *rq)
268 {
269         elevator_t *e = q->elevator;
270
271         if (e->ops->elevator_activate_req_fn)
272                 e->ops->elevator_activate_req_fn(q, rq);
273 }
274
275 static void elv_deactivate_rq(request_queue_t *q, struct request *rq)
276 {
277         elevator_t *e = q->elevator;
278
279         if (e->ops->elevator_deactivate_req_fn)
280                 e->ops->elevator_deactivate_req_fn(q, rq);
281 }
282
283 static inline void __elv_rqhash_del(struct request *rq)
284 {
285         hlist_del_init(&rq->hash);
286 }
287
288 static void elv_rqhash_del(request_queue_t *q, struct request *rq)
289 {
290         if (ELV_ON_HASH(rq))
291                 __elv_rqhash_del(rq);
292 }
293
294 static void elv_rqhash_add(request_queue_t *q, struct request *rq)
295 {
296         elevator_t *e = q->elevator;
297
298         BUG_ON(ELV_ON_HASH(rq));
299         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
300 }
301
302 static void elv_rqhash_reposition(request_queue_t *q, struct request *rq)
303 {
304         __elv_rqhash_del(rq);
305         elv_rqhash_add(q, rq);
306 }
307
308 static struct request *elv_rqhash_find(request_queue_t *q, sector_t offset)
309 {
310         elevator_t *e = q->elevator;
311         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
312         struct hlist_node *entry, *next;
313         struct request *rq;
314
315         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
316                 BUG_ON(!ELV_ON_HASH(rq));
317
318                 if (unlikely(!rq_mergeable(rq))) {
319                         __elv_rqhash_del(rq);
320                         continue;
321                 }
322
323                 if (rq_hash_key(rq) == offset)
324                         return rq;
325         }
326
327         return NULL;
328 }
329
330 /*
331  * RB-tree support functions for inserting/lookup/removal of requests
332  * in a sorted RB tree.
333  */
334 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
335 {
336         struct rb_node **p = &root->rb_node;
337         struct rb_node *parent = NULL;
338         struct request *__rq;
339
340         while (*p) {
341                 parent = *p;
342                 __rq = rb_entry(parent, struct request, rb_node);
343
344                 if (rq->sector < __rq->sector)
345                         p = &(*p)->rb_left;
346                 else if (rq->sector > __rq->sector)
347                         p = &(*p)->rb_right;
348                 else
349                         return __rq;
350         }
351
352         rb_link_node(&rq->rb_node, parent, p);
353         rb_insert_color(&rq->rb_node, root);
354         return NULL;
355 }
356
357 EXPORT_SYMBOL(elv_rb_add);
358
359 void elv_rb_del(struct rb_root *root, struct request *rq)
360 {
361         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
362         rb_erase(&rq->rb_node, root);
363         RB_CLEAR_NODE(&rq->rb_node);
364 }
365
366 EXPORT_SYMBOL(elv_rb_del);
367
368 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
369 {
370         struct rb_node *n = root->rb_node;
371         struct request *rq;
372
373         while (n) {
374                 rq = rb_entry(n, struct request, rb_node);
375
376                 if (sector < rq->sector)
377                         n = n->rb_left;
378                 else if (sector > rq->sector)
379                         n = n->rb_right;
380                 else
381                         return rq;
382         }
383
384         return NULL;
385 }
386
387 EXPORT_SYMBOL(elv_rb_find);
388
389 /*
390  * Insert rq into dispatch queue of q.  Queue lock must be held on
391  * entry.  rq is sort insted into the dispatch queue. To be used by
392  * specific elevators.
393  */
394 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
395 {
396         sector_t boundary;
397         struct list_head *entry;
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         boundary = q->end_sector;
407
408         list_for_each_prev(entry, &q->queue_head) {
409                 struct request *pos = list_entry_rq(entry);
410
411                 if (rq_data_dir(rq) != rq_data_dir(pos))
412                         break;
413                 if (pos->cmd_flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
414                         break;
415                 if (rq->sector >= boundary) {
416                         if (pos->sector < boundary)
417                                 continue;
418                 } else {
419                         if (pos->sector >= boundary)
420                                 break;
421                 }
422                 if (rq->sector >= pos->sector)
423                         break;
424         }
425
426         list_add(&rq->queuelist, entry);
427 }
428
429 EXPORT_SYMBOL(elv_dispatch_sort);
430
431 /*
432  * Insert rq into dispatch queue of q.  Queue lock must be held on
433  * entry.  rq is added to the back of the dispatch queue. To be used by
434  * specific elevators.
435  */
436 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
437 {
438         if (q->last_merge == rq)
439                 q->last_merge = NULL;
440
441         elv_rqhash_del(q, rq);
442
443         q->nr_sorted--;
444
445         q->end_sector = rq_end_sector(rq);
446         q->boundary_rq = rq;
447         list_add_tail(&rq->queuelist, &q->queue_head);
448 }
449
450 EXPORT_SYMBOL(elv_dispatch_add_tail);
451
452 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
453 {
454         elevator_t *e = q->elevator;
455         struct request *__rq;
456         int ret;
457
458         /*
459          * First try one-hit cache.
460          */
461         if (q->last_merge) {
462                 ret = elv_try_merge(q->last_merge, bio);
463                 if (ret != ELEVATOR_NO_MERGE) {
464                         *req = q->last_merge;
465                         return ret;
466                 }
467         }
468
469         /*
470          * See if our hash lookup can find a potential backmerge.
471          */
472         __rq = elv_rqhash_find(q, bio->bi_sector);
473         if (__rq && elv_rq_merge_ok(__rq, bio)) {
474                 *req = __rq;
475                 return ELEVATOR_BACK_MERGE;
476         }
477
478         if (e->ops->elevator_merge_fn)
479                 return e->ops->elevator_merge_fn(q, req, bio);
480
481         return ELEVATOR_NO_MERGE;
482 }
483
484 void elv_merged_request(request_queue_t *q, struct request *rq, int type)
485 {
486         elevator_t *e = q->elevator;
487
488         if (e->ops->elevator_merged_fn)
489                 e->ops->elevator_merged_fn(q, rq, type);
490
491         if (type == ELEVATOR_BACK_MERGE)
492                 elv_rqhash_reposition(q, rq);
493
494         q->last_merge = rq;
495 }
496
497 void elv_merge_requests(request_queue_t *q, struct request *rq,
498                              struct request *next)
499 {
500         elevator_t *e = q->elevator;
501
502         if (e->ops->elevator_merge_req_fn)
503                 e->ops->elevator_merge_req_fn(q, rq, next);
504
505         elv_rqhash_reposition(q, rq);
506         elv_rqhash_del(q, next);
507
508         q->nr_sorted--;
509         q->last_merge = rq;
510 }
511
512 void elv_requeue_request(request_queue_t *q, struct request *rq)
513 {
514         /*
515          * it already went through dequeue, we need to decrement the
516          * in_flight count again
517          */
518         if (blk_account_rq(rq)) {
519                 q->in_flight--;
520                 if (blk_sorted_rq(rq))
521                         elv_deactivate_rq(q, rq);
522         }
523
524         rq->cmd_flags &= ~REQ_STARTED;
525
526         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
527 }
528
529 static void elv_drain_elevator(request_queue_t *q)
530 {
531         static int printed;
532         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
533                 ;
534         if (q->nr_sorted == 0)
535                 return;
536         if (printed++ < 10) {
537                 printk(KERN_ERR "%s: forced dispatching is broken "
538                        "(nr_sorted=%u), please report this\n",
539                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
540         }
541 }
542
543 void elv_insert(request_queue_t *q, struct request *rq, int where)
544 {
545         struct list_head *pos;
546         unsigned ordseq;
547         int unplug_it = 1;
548
549         blk_add_trace_rq(q, rq, BLK_TA_INSERT);
550
551         rq->q = q;
552
553         switch (where) {
554         case ELEVATOR_INSERT_FRONT:
555                 rq->cmd_flags |= REQ_SOFTBARRIER;
556
557                 list_add(&rq->queuelist, &q->queue_head);
558                 break;
559
560         case ELEVATOR_INSERT_BACK:
561                 rq->cmd_flags |= REQ_SOFTBARRIER;
562                 elv_drain_elevator(q);
563                 list_add_tail(&rq->queuelist, &q->queue_head);
564                 /*
565                  * We kick the queue here for the following reasons.
566                  * - The elevator might have returned NULL previously
567                  *   to delay requests and returned them now.  As the
568                  *   queue wasn't empty before this request, ll_rw_blk
569                  *   won't run the queue on return, resulting in hang.
570                  * - Usually, back inserted requests won't be merged
571                  *   with anything.  There's no point in delaying queue
572                  *   processing.
573                  */
574                 blk_remove_plug(q);
575                 q->request_fn(q);
576                 break;
577
578         case ELEVATOR_INSERT_SORT:
579                 BUG_ON(!blk_fs_request(rq));
580                 rq->cmd_flags |= REQ_SORTED;
581                 q->nr_sorted++;
582                 if (rq_mergeable(rq)) {
583                         elv_rqhash_add(q, rq);
584                         if (!q->last_merge)
585                                 q->last_merge = rq;
586                 }
587
588                 /*
589                  * Some ioscheds (cfq) run q->request_fn directly, so
590                  * rq cannot be accessed after calling
591                  * elevator_add_req_fn.
592                  */
593                 q->elevator->ops->elevator_add_req_fn(q, rq);
594                 break;
595
596         case ELEVATOR_INSERT_REQUEUE:
597                 /*
598                  * If ordered flush isn't in progress, we do front
599                  * insertion; otherwise, requests should be requeued
600                  * in ordseq order.
601                  */
602                 rq->cmd_flags |= REQ_SOFTBARRIER;
603
604                 /*
605                  * Most requeues happen because of a busy condition,
606                  * don't force unplug of the queue for that case.
607                  */
608                 unplug_it = 0;
609
610                 if (q->ordseq == 0) {
611                         list_add(&rq->queuelist, &q->queue_head);
612                         break;
613                 }
614
615                 ordseq = blk_ordered_req_seq(rq);
616
617                 list_for_each(pos, &q->queue_head) {
618                         struct request *pos_rq = list_entry_rq(pos);
619                         if (ordseq <= blk_ordered_req_seq(pos_rq))
620                                 break;
621                 }
622
623                 list_add_tail(&rq->queuelist, pos);
624                 break;
625
626         default:
627                 printk(KERN_ERR "%s: bad insertion point %d\n",
628                        __FUNCTION__, where);
629                 BUG();
630         }
631
632         if (unplug_it && blk_queue_plugged(q)) {
633                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
634                         - q->in_flight;
635
636                 if (nrq >= q->unplug_thresh)
637                         __generic_unplug_device(q);
638         }
639 }
640
641 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
642                        int plug)
643 {
644         if (q->ordcolor)
645                 rq->cmd_flags |= REQ_ORDERED_COLOR;
646
647         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
648                 /*
649                  * toggle ordered color
650                  */
651                 if (blk_barrier_rq(rq))
652                         q->ordcolor ^= 1;
653
654                 /*
655                  * barriers implicitly indicate back insertion
656                  */
657                 if (where == ELEVATOR_INSERT_SORT)
658                         where = ELEVATOR_INSERT_BACK;
659
660                 /*
661                  * this request is scheduling boundary, update
662                  * end_sector
663                  */
664                 if (blk_fs_request(rq)) {
665                         q->end_sector = rq_end_sector(rq);
666                         q->boundary_rq = rq;
667                 }
668         } else if (!(rq->cmd_flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
669                 where = ELEVATOR_INSERT_BACK;
670
671         if (plug)
672                 blk_plug_device(q);
673
674         elv_insert(q, rq, where);
675 }
676
677 EXPORT_SYMBOL(__elv_add_request);
678
679 void elv_add_request(request_queue_t *q, struct request *rq, int where,
680                      int plug)
681 {
682         unsigned long flags;
683
684         spin_lock_irqsave(q->queue_lock, flags);
685         __elv_add_request(q, rq, where, plug);
686         spin_unlock_irqrestore(q->queue_lock, flags);
687 }
688
689 EXPORT_SYMBOL(elv_add_request);
690
691 static inline struct request *__elv_next_request(request_queue_t *q)
692 {
693         struct request *rq;
694
695         while (1) {
696                 while (!list_empty(&q->queue_head)) {
697                         rq = list_entry_rq(q->queue_head.next);
698                         if (blk_do_ordered(q, &rq))
699                                 return rq;
700                 }
701
702                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
703                         return NULL;
704         }
705 }
706
707 struct request *elv_next_request(request_queue_t *q)
708 {
709         struct request *rq;
710         int ret;
711
712         while ((rq = __elv_next_request(q)) != NULL) {
713                 if (!(rq->cmd_flags & REQ_STARTED)) {
714                         /*
715                          * This is the first time the device driver
716                          * sees this request (possibly after
717                          * requeueing).  Notify IO scheduler.
718                          */
719                         if (blk_sorted_rq(rq))
720                                 elv_activate_rq(q, rq);
721
722                         /*
723                          * just mark as started even if we don't start
724                          * it, a request that has been delayed should
725                          * not be passed by new incoming requests
726                          */
727                         rq->cmd_flags |= REQ_STARTED;
728                         blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
729                 }
730
731                 if (!q->boundary_rq || q->boundary_rq == rq) {
732                         q->end_sector = rq_end_sector(rq);
733                         q->boundary_rq = NULL;
734                 }
735
736                 if ((rq->cmd_flags & REQ_DONTPREP) || !q->prep_rq_fn)
737                         break;
738
739                 ret = q->prep_rq_fn(q, rq);
740                 if (ret == BLKPREP_OK) {
741                         break;
742                 } else if (ret == BLKPREP_DEFER) {
743                         /*
744                          * the request may have been (partially) prepped.
745                          * we need to keep this request in the front to
746                          * avoid resource deadlock.  REQ_STARTED will
747                          * prevent other fs requests from passing this one.
748                          */
749                         rq = NULL;
750                         break;
751                 } else if (ret == BLKPREP_KILL) {
752                         int nr_bytes = rq->hard_nr_sectors << 9;
753
754                         if (!nr_bytes)
755                                 nr_bytes = rq->data_len;
756
757                         blkdev_dequeue_request(rq);
758                         rq->cmd_flags |= REQ_QUIET;
759                         end_that_request_chunk(rq, 0, nr_bytes);
760                         end_that_request_last(rq, 0);
761                 } else {
762                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
763                                                                 ret);
764                         break;
765                 }
766         }
767
768         return rq;
769 }
770
771 EXPORT_SYMBOL(elv_next_request);
772
773 void elv_dequeue_request(request_queue_t *q, struct request *rq)
774 {
775         BUG_ON(list_empty(&rq->queuelist));
776         BUG_ON(ELV_ON_HASH(rq));
777
778         list_del_init(&rq->queuelist);
779
780         /*
781          * the time frame between a request being removed from the lists
782          * and to it is freed is accounted as io that is in progress at
783          * the driver side.
784          */
785         if (blk_account_rq(rq))
786                 q->in_flight++;
787 }
788
789 EXPORT_SYMBOL(elv_dequeue_request);
790
791 int elv_queue_empty(request_queue_t *q)
792 {
793         elevator_t *e = q->elevator;
794
795         if (!list_empty(&q->queue_head))
796                 return 0;
797
798         if (e->ops->elevator_queue_empty_fn)
799                 return e->ops->elevator_queue_empty_fn(q);
800
801         return 1;
802 }
803
804 EXPORT_SYMBOL(elv_queue_empty);
805
806 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
807 {
808         elevator_t *e = q->elevator;
809
810         if (e->ops->elevator_latter_req_fn)
811                 return e->ops->elevator_latter_req_fn(q, rq);
812         return NULL;
813 }
814
815 struct request *elv_former_request(request_queue_t *q, struct request *rq)
816 {
817         elevator_t *e = q->elevator;
818
819         if (e->ops->elevator_former_req_fn)
820                 return e->ops->elevator_former_req_fn(q, rq);
821         return NULL;
822 }
823
824 int elv_set_request(request_queue_t *q, struct request *rq, gfp_t gfp_mask)
825 {
826         elevator_t *e = q->elevator;
827
828         if (e->ops->elevator_set_req_fn)
829                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
830
831         rq->elevator_private = NULL;
832         return 0;
833 }
834
835 void elv_put_request(request_queue_t *q, struct request *rq)
836 {
837         elevator_t *e = q->elevator;
838
839         if (e->ops->elevator_put_req_fn)
840                 e->ops->elevator_put_req_fn(rq);
841 }
842
843 int elv_may_queue(request_queue_t *q, int rw)
844 {
845         elevator_t *e = q->elevator;
846
847         if (e->ops->elevator_may_queue_fn)
848                 return e->ops->elevator_may_queue_fn(q, rw);
849
850         return ELV_MQUEUE_MAY;
851 }
852
853 void elv_completed_request(request_queue_t *q, struct request *rq)
854 {
855         elevator_t *e = q->elevator;
856
857         /*
858          * request is released from the driver, io must be done
859          */
860         if (blk_account_rq(rq)) {
861                 q->in_flight--;
862                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
863                         e->ops->elevator_completed_req_fn(q, rq);
864         }
865
866         /*
867          * Check if the queue is waiting for fs requests to be
868          * drained for flush sequence.
869          */
870         if (unlikely(q->ordseq)) {
871                 struct request *first_rq = list_entry_rq(q->queue_head.next);
872                 if (q->in_flight == 0 &&
873                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
874                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
875                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
876                         q->request_fn(q);
877                 }
878         }
879 }
880
881 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
882
883 static ssize_t
884 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
885 {
886         elevator_t *e = container_of(kobj, elevator_t, kobj);
887         struct elv_fs_entry *entry = to_elv(attr);
888         ssize_t error;
889
890         if (!entry->show)
891                 return -EIO;
892
893         mutex_lock(&e->sysfs_lock);
894         error = e->ops ? entry->show(e, page) : -ENOENT;
895         mutex_unlock(&e->sysfs_lock);
896         return error;
897 }
898
899 static ssize_t
900 elv_attr_store(struct kobject *kobj, struct attribute *attr,
901                const char *page, size_t length)
902 {
903         elevator_t *e = container_of(kobj, elevator_t, kobj);
904         struct elv_fs_entry *entry = to_elv(attr);
905         ssize_t error;
906
907         if (!entry->store)
908                 return -EIO;
909
910         mutex_lock(&e->sysfs_lock);
911         error = e->ops ? entry->store(e, page, length) : -ENOENT;
912         mutex_unlock(&e->sysfs_lock);
913         return error;
914 }
915
916 static struct sysfs_ops elv_sysfs_ops = {
917         .show   = elv_attr_show,
918         .store  = elv_attr_store,
919 };
920
921 static struct kobj_type elv_ktype = {
922         .sysfs_ops      = &elv_sysfs_ops,
923         .release        = elevator_release,
924 };
925
926 int elv_register_queue(struct request_queue *q)
927 {
928         elevator_t *e = q->elevator;
929         int error;
930
931         e->kobj.parent = &q->kobj;
932
933         error = kobject_add(&e->kobj);
934         if (!error) {
935                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
936                 if (attr) {
937                         while (attr->attr.name) {
938                                 if (sysfs_create_file(&e->kobj, &attr->attr))
939                                         break;
940                                 attr++;
941                         }
942                 }
943                 kobject_uevent(&e->kobj, KOBJ_ADD);
944         }
945         return error;
946 }
947
948 static void __elv_unregister_queue(elevator_t *e)
949 {
950         kobject_uevent(&e->kobj, KOBJ_REMOVE);
951         kobject_del(&e->kobj);
952 }
953
954 void elv_unregister_queue(struct request_queue *q)
955 {
956         if (q)
957                 __elv_unregister_queue(q->elevator);
958 }
959
960 int elv_register(struct elevator_type *e)
961 {
962         char *def = "";
963
964         spin_lock(&elv_list_lock);
965         BUG_ON(elevator_find(e->elevator_name));
966         list_add_tail(&e->list, &elv_list);
967         spin_unlock(&elv_list_lock);
968
969         if (!strcmp(e->elevator_name, chosen_elevator) ||
970                         (!*chosen_elevator &&
971                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
972                                 def = " (default)";
973
974         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name, def);
975         return 0;
976 }
977 EXPORT_SYMBOL_GPL(elv_register);
978
979 void elv_unregister(struct elevator_type *e)
980 {
981         struct task_struct *g, *p;
982
983         /*
984          * Iterate every thread in the process to remove the io contexts.
985          */
986         if (e->ops.trim) {
987                 read_lock(&tasklist_lock);
988                 do_each_thread(g, p) {
989                         task_lock(p);
990                         if (p->io_context)
991                                 e->ops.trim(p->io_context);
992                         task_unlock(p);
993                 } while_each_thread(g, p);
994                 read_unlock(&tasklist_lock);
995         }
996
997         spin_lock(&elv_list_lock);
998         list_del_init(&e->list);
999         spin_unlock(&elv_list_lock);
1000 }
1001 EXPORT_SYMBOL_GPL(elv_unregister);
1002
1003 /*
1004  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1005  * we don't free the old io scheduler, before we have allocated what we
1006  * need for the new one. this way we have a chance of going back to the old
1007  * one, if the new one fails init for some reason.
1008  */
1009 static int elevator_switch(request_queue_t *q, struct elevator_type *new_e)
1010 {
1011         elevator_t *old_elevator, *e;
1012         void *data;
1013
1014         /*
1015          * Allocate new elevator
1016          */
1017         e = elevator_alloc(q, new_e);
1018         if (!e)
1019                 return 0;
1020
1021         data = elevator_init_queue(q, e);
1022         if (!data) {
1023                 kobject_put(&e->kobj);
1024                 return 0;
1025         }
1026
1027         /*
1028          * Turn on BYPASS and drain all requests w/ elevator private data
1029          */
1030         spin_lock_irq(q->queue_lock);
1031
1032         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1033
1034         elv_drain_elevator(q);
1035
1036         while (q->rq.elvpriv) {
1037                 blk_remove_plug(q);
1038                 q->request_fn(q);
1039                 spin_unlock_irq(q->queue_lock);
1040                 msleep(10);
1041                 spin_lock_irq(q->queue_lock);
1042                 elv_drain_elevator(q);
1043         }
1044
1045         /*
1046          * Remember old elevator.
1047          */
1048         old_elevator = q->elevator;
1049
1050         /*
1051          * attach and start new elevator
1052          */
1053         elevator_attach(q, e, data);
1054
1055         spin_unlock_irq(q->queue_lock);
1056
1057         __elv_unregister_queue(old_elevator);
1058
1059         if (elv_register_queue(q))
1060                 goto fail_register;
1061
1062         /*
1063          * finally exit old elevator and turn off BYPASS.
1064          */
1065         elevator_exit(old_elevator);
1066         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1067         return 1;
1068
1069 fail_register:
1070         /*
1071          * switch failed, exit the new io scheduler and reattach the old
1072          * one again (along with re-adding the sysfs dir)
1073          */
1074         elevator_exit(e);
1075         q->elevator = old_elevator;
1076         elv_register_queue(q);
1077         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1078         return 0;
1079 }
1080
1081 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
1082 {
1083         char elevator_name[ELV_NAME_MAX];
1084         size_t len;
1085         struct elevator_type *e;
1086
1087         elevator_name[sizeof(elevator_name) - 1] = '\0';
1088         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
1089         len = strlen(elevator_name);
1090
1091         if (len && elevator_name[len - 1] == '\n')
1092                 elevator_name[len - 1] = '\0';
1093
1094         e = elevator_get(elevator_name);
1095         if (!e) {
1096                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1097                 return -EINVAL;
1098         }
1099
1100         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1101                 elevator_put(e);
1102                 return count;
1103         }
1104
1105         if (!elevator_switch(q, e))
1106                 printk(KERN_ERR "elevator: switch to %s failed\n",elevator_name);
1107         return count;
1108 }
1109
1110 ssize_t elv_iosched_show(request_queue_t *q, char *name)
1111 {
1112         elevator_t *e = q->elevator;
1113         struct elevator_type *elv = e->elevator_type;
1114         struct elevator_type *__e;
1115         int len = 0;
1116
1117         spin_lock(&elv_list_lock);
1118         list_for_each_entry(__e, &elv_list, list) {
1119                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1120                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1121                 else
1122                         len += sprintf(name+len, "%s ", __e->elevator_name);
1123         }
1124         spin_unlock(&elv_list_lock);
1125
1126         len += sprintf(len+name, "\n");
1127         return len;
1128 }
1129
1130 struct request *elv_rb_former_request(request_queue_t *q, struct request *rq)
1131 {
1132         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1133
1134         if (rbprev)
1135                 return rb_entry_rq(rbprev);
1136
1137         return NULL;
1138 }
1139
1140 EXPORT_SYMBOL(elv_rb_former_request);
1141
1142 struct request *elv_rb_latter_request(request_queue_t *q, struct request *rq)
1143 {
1144         struct rb_node *rbnext = rb_next(&rq->rb_node);
1145
1146         if (rbnext)
1147                 return rb_entry_rq(rbnext);
1148
1149         return NULL;
1150 }
1151
1152 EXPORT_SYMBOL(elv_rb_latter_request);