415144372c75e6ca8ad1f632da9b2c18213f92c0
[linux-2.6.git] / drivers / block / elevator.c
1 /*
2  *  linux/drivers/block/elevator.c
3  *
4  *  Block device elevator/IO-scheduler.
5  *
6  *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
7  *
8  * 30042000 Jens Axboe <axboe@suse.de> :
9  *
10  * Split the elevator a bit so that it is possible to choose a different
11  * one or even write a new "plug in". There are three pieces:
12  * - elevator_fn, inserts a new request in the queue list
13  * - elevator_merge_fn, decides whether a new buffer can be merged with
14  *   an existing request
15  * - elevator_dequeue_fn, called when a request is taken off the active list
16  *
17  * 20082000 Dave Jones <davej@suse.de> :
18  * Removed tests for max-bomb-segments, which was breaking elvtune
19  *  when run without -bN
20  *
21  * Jens:
22  * - Rework again to work with bio instead of buffer_heads
23  * - loose bi_dev comparisons, partition handling is right now
24  * - completely modularize elevator setup and teardown
25  *
26  */
27 #include <linux/kernel.h>
28 #include <linux/fs.h>
29 #include <linux/blkdev.h>
30 #include <linux/elevator.h>
31 #include <linux/bio.h>
32 #include <linux/config.h>
33 #include <linux/module.h>
34 #include <linux/slab.h>
35 #include <linux/init.h>
36 #include <linux/compiler.h>
37
38 #include <asm/uaccess.h>
39
40 static DEFINE_SPINLOCK(elv_list_lock);
41 static LIST_HEAD(elv_list);
42
43 /*
44  * can we safely merge with this request?
45  */
46 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
47 {
48         if (!rq_mergeable(rq))
49                 return 0;
50
51         /*
52          * different data direction or already started, don't merge
53          */
54         if (bio_data_dir(bio) != rq_data_dir(rq))
55                 return 0;
56
57         /*
58          * same device and no special stuff set, merge is ok
59          */
60         if (rq->rq_disk == bio->bi_bdev->bd_disk &&
61             !rq->waiting && !rq->special)
62                 return 1;
63
64         return 0;
65 }
66 EXPORT_SYMBOL(elv_rq_merge_ok);
67
68 inline int elv_try_merge(struct request *__rq, struct bio *bio)
69 {
70         int ret = ELEVATOR_NO_MERGE;
71
72         /*
73          * we can merge and sequence is ok, check if it's possible
74          */
75         if (elv_rq_merge_ok(__rq, bio)) {
76                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
77                         ret = ELEVATOR_BACK_MERGE;
78                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
79                         ret = ELEVATOR_FRONT_MERGE;
80         }
81
82         return ret;
83 }
84 EXPORT_SYMBOL(elv_try_merge);
85
86 static struct elevator_type *elevator_find(const char *name)
87 {
88         struct elevator_type *e = NULL;
89         struct list_head *entry;
90
91         list_for_each(entry, &elv_list) {
92                 struct elevator_type *__e;
93
94                 __e = list_entry(entry, struct elevator_type, list);
95
96                 if (!strcmp(__e->elevator_name, name)) {
97                         e = __e;
98                         break;
99                 }
100         }
101
102         return e;
103 }
104
105 static void elevator_put(struct elevator_type *e)
106 {
107         module_put(e->elevator_owner);
108 }
109
110 static struct elevator_type *elevator_get(const char *name)
111 {
112         struct elevator_type *e;
113
114         spin_lock_irq(&elv_list_lock);
115
116         e = elevator_find(name);
117         if (e && !try_module_get(e->elevator_owner))
118                 e = NULL;
119
120         spin_unlock_irq(&elv_list_lock);
121
122         return e;
123 }
124
125 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
126                            struct elevator_queue *eq)
127 {
128         int ret = 0;
129
130         memset(eq, 0, sizeof(*eq));
131         eq->ops = &e->ops;
132         eq->elevator_type = e;
133
134         INIT_LIST_HEAD(&q->queue_head);
135         q->last_merge = NULL;
136         q->elevator = eq;
137         q->end_sector = 0;
138         q->boundary_rq = NULL;
139         q->max_back_kb = 0;
140
141         if (eq->ops->elevator_init_fn)
142                 ret = eq->ops->elevator_init_fn(q, eq);
143
144         return ret;
145 }
146
147 static char chosen_elevator[16];
148
149 static void elevator_setup_default(void)
150 {
151         struct elevator_type *e;
152
153         /*
154          * check if default is set and exists
155          */
156         if (chosen_elevator[0] && (e = elevator_get(chosen_elevator))) {
157                 elevator_put(e);
158                 return;
159         }
160
161 #if defined(CONFIG_IOSCHED_AS)
162         strcpy(chosen_elevator, "anticipatory");
163 #elif defined(CONFIG_IOSCHED_DEADLINE)
164         strcpy(chosen_elevator, "deadline");
165 #elif defined(CONFIG_IOSCHED_CFQ)
166         strcpy(chosen_elevator, "cfq");
167 #elif defined(CONFIG_IOSCHED_NOOP)
168         strcpy(chosen_elevator, "noop");
169 #else
170 #error "You must build at least 1 IO scheduler into the kernel"
171 #endif
172 }
173
174 static int __init elevator_setup(char *str)
175 {
176         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
177         return 0;
178 }
179
180 __setup("elevator=", elevator_setup);
181
182 int elevator_init(request_queue_t *q, char *name)
183 {
184         struct elevator_type *e = NULL;
185         struct elevator_queue *eq;
186         int ret = 0;
187
188         elevator_setup_default();
189
190         if (!name)
191                 name = chosen_elevator;
192
193         e = elevator_get(name);
194         if (!e)
195                 return -EINVAL;
196
197         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
198         if (!eq) {
199                 elevator_put(e->elevator_type);
200                 return -ENOMEM;
201         }
202
203         ret = elevator_attach(q, e, eq);
204         if (ret) {
205                 kfree(eq);
206                 elevator_put(e->elevator_type);
207         }
208
209         return ret;
210 }
211
212 void elevator_exit(elevator_t *e)
213 {
214         if (e->ops->elevator_exit_fn)
215                 e->ops->elevator_exit_fn(e);
216
217         elevator_put(e->elevator_type);
218         e->elevator_type = NULL;
219         kfree(e);
220 }
221
222 /*
223  * Insert rq into dispatch queue of q.  Queue lock must be held on
224  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
225  * appended to the dispatch queue.  To be used by specific elevators.
226  */
227 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
228 {
229         sector_t boundary;
230         unsigned max_back;
231         struct list_head *entry;
232
233         if (q->last_merge == rq)
234                 q->last_merge = NULL;
235
236         boundary = q->end_sector;
237         max_back = q->max_back_kb * 2;
238         boundary = boundary > max_back ? boundary - max_back : 0;
239         
240         list_for_each_prev(entry, &q->queue_head) {
241                 struct request *pos = list_entry_rq(entry);
242
243                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
244                         break;
245                 if (rq->sector >= boundary) {
246                         if (pos->sector < boundary)
247                                 continue;
248                 } else {
249                         if (pos->sector >= boundary)
250                                 break;
251                 }
252                 if (rq->sector >= pos->sector)
253                         break;
254         }
255
256         list_add(&rq->queuelist, entry);
257 }
258
259 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
260 {
261         elevator_t *e = q->elevator;
262         int ret;
263
264         if (q->last_merge) {
265                 ret = elv_try_merge(q->last_merge, bio);
266                 if (ret != ELEVATOR_NO_MERGE) {
267                         *req = q->last_merge;
268                         return ret;
269                 }
270         }
271
272         if (e->ops->elevator_merge_fn)
273                 return e->ops->elevator_merge_fn(q, req, bio);
274
275         return ELEVATOR_NO_MERGE;
276 }
277
278 void elv_merged_request(request_queue_t *q, struct request *rq)
279 {
280         elevator_t *e = q->elevator;
281
282         if (e->ops->elevator_merged_fn)
283                 e->ops->elevator_merged_fn(q, rq);
284
285         q->last_merge = rq;
286 }
287
288 void elv_merge_requests(request_queue_t *q, struct request *rq,
289                              struct request *next)
290 {
291         elevator_t *e = q->elevator;
292
293         if (e->ops->elevator_merge_req_fn)
294                 e->ops->elevator_merge_req_fn(q, rq, next);
295
296         q->last_merge = rq;
297 }
298
299 void elv_requeue_request(request_queue_t *q, struct request *rq)
300 {
301         elevator_t *e = q->elevator;
302
303         /*
304          * it already went through dequeue, we need to decrement the
305          * in_flight count again
306          */
307         if (blk_account_rq(rq)) {
308                 q->in_flight--;
309                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
310                         e->ops->elevator_deactivate_req_fn(q, rq);
311         }
312
313         rq->flags &= ~REQ_STARTED;
314
315         /*
316          * if this is the flush, requeue the original instead and drop the flush
317          */
318         if (rq->flags & REQ_BAR_FLUSH) {
319                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
320                 rq = rq->end_io_data;
321         }
322
323         __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
324 }
325
326 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
327                        int plug)
328 {
329         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
330                 /*
331                  * barriers implicitly indicate back insertion
332                  */
333                 if (where == ELEVATOR_INSERT_SORT)
334                         where = ELEVATOR_INSERT_BACK;
335
336                 /*
337                  * this request is scheduling boundary, update end_sector
338                  */
339                 if (blk_fs_request(rq)) {
340                         q->end_sector = rq_end_sector(rq);
341                         q->boundary_rq = rq;
342                 }
343         }
344
345         if (plug)
346                 blk_plug_device(q);
347
348         rq->q = q;
349
350         if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
351                 /*
352                  * if drain is set, store the request "locally". when the drain
353                  * is finished, the requests will be handed ordered to the io
354                  * scheduler
355                  */
356                 list_add_tail(&rq->queuelist, &q->drain_list);
357                 return;
358         }
359
360         switch (where) {
361         case ELEVATOR_INSERT_FRONT:
362                 rq->flags |= REQ_SOFTBARRIER;
363
364                 list_add(&rq->queuelist, &q->queue_head);
365                 break;
366
367         case ELEVATOR_INSERT_BACK:
368                 rq->flags |= REQ_SOFTBARRIER;
369
370                 while (q->elevator->ops->elevator_dispatch_fn(q, 1))
371                         ;
372                 list_add_tail(&rq->queuelist, &q->queue_head);
373                 /*
374                  * We kick the queue here for the following reasons.
375                  * - The elevator might have returned NULL previously
376                  *   to delay requests and returned them now.  As the
377                  *   queue wasn't empty before this request, ll_rw_blk
378                  *   won't run the queue on return, resulting in hang.
379                  * - Usually, back inserted requests won't be merged
380                  *   with anything.  There's no point in delaying queue
381                  *   processing.
382                  */
383                 blk_remove_plug(q);
384                 q->request_fn(q);
385                 break;
386
387         case ELEVATOR_INSERT_SORT:
388                 BUG_ON(!blk_fs_request(rq));
389                 rq->flags |= REQ_SORTED;
390                 q->elevator->ops->elevator_add_req_fn(q, rq);
391                 if (q->last_merge == NULL && rq_mergeable(rq))
392                         q->last_merge = rq;
393                 break;
394
395         default:
396                 printk(KERN_ERR "%s: bad insertion point %d\n",
397                        __FUNCTION__, where);
398                 BUG();
399         }
400
401         if (blk_queue_plugged(q)) {
402                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
403                         - q->in_flight;
404
405                 if (nrq >= q->unplug_thresh)
406                         __generic_unplug_device(q);
407         }
408 }
409
410 void elv_add_request(request_queue_t *q, struct request *rq, int where,
411                      int plug)
412 {
413         unsigned long flags;
414
415         spin_lock_irqsave(q->queue_lock, flags);
416         __elv_add_request(q, rq, where, plug);
417         spin_unlock_irqrestore(q->queue_lock, flags);
418 }
419
420 static inline struct request *__elv_next_request(request_queue_t *q)
421 {
422         struct request *rq;
423
424         if (unlikely(list_empty(&q->queue_head) &&
425                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
426                 return NULL;
427
428         rq = list_entry_rq(q->queue_head.next);
429
430         /*
431          * if this is a barrier write and the device has to issue a
432          * flush sequence to support it, check how far we are
433          */
434         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
435                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
436
437                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
438                     !blk_barrier_preflush(rq))
439                         rq = blk_start_pre_flush(q, rq);
440         }
441
442         return rq;
443 }
444
445 struct request *elv_next_request(request_queue_t *q)
446 {
447         struct request *rq;
448         int ret;
449
450         while ((rq = __elv_next_request(q)) != NULL) {
451                 if (!(rq->flags & REQ_STARTED)) {
452                         elevator_t *e = q->elevator;
453
454                         /*
455                          * This is the first time the device driver
456                          * sees this request (possibly after
457                          * requeueing).  Notify IO scheduler.
458                          */
459                         if (blk_sorted_rq(rq) &&
460                             e->ops->elevator_activate_req_fn)
461                                 e->ops->elevator_activate_req_fn(q, rq);
462
463                         /*
464                          * just mark as started even if we don't start
465                          * it, a request that has been delayed should
466                          * not be passed by new incoming requests
467                          */
468                         rq->flags |= REQ_STARTED;
469                 }
470
471                 if (!q->boundary_rq || q->boundary_rq == rq) {
472                         q->end_sector = rq_end_sector(rq);
473                         q->boundary_rq = NULL;
474                 }
475
476                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
477                         break;
478
479                 ret = q->prep_rq_fn(q, rq);
480                 if (ret == BLKPREP_OK) {
481                         break;
482                 } else if (ret == BLKPREP_DEFER) {
483                         /*
484                          * the request may have been (partially) prepped.
485                          * we need to keep this request in the front to
486                          * avoid resource deadlock.  REQ_STARTED will
487                          * prevent other fs requests from passing this one.
488                          */
489                         rq = NULL;
490                         break;
491                 } else if (ret == BLKPREP_KILL) {
492                         int nr_bytes = rq->hard_nr_sectors << 9;
493
494                         if (!nr_bytes)
495                                 nr_bytes = rq->data_len;
496
497                         blkdev_dequeue_request(rq);
498                         rq->flags |= REQ_QUIET;
499                         end_that_request_chunk(rq, 0, nr_bytes);
500                         end_that_request_last(rq);
501                 } else {
502                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
503                                                                 ret);
504                         break;
505                 }
506         }
507
508         return rq;
509 }
510
511 void elv_dequeue_request(request_queue_t *q, struct request *rq)
512 {
513         BUG_ON(list_empty(&rq->queuelist));
514
515         list_del_init(&rq->queuelist);
516
517         /*
518          * the time frame between a request being removed from the lists
519          * and to it is freed is accounted as io that is in progress at
520          * the driver side.
521          */
522         if (blk_account_rq(rq))
523                 q->in_flight++;
524 }
525
526 int elv_queue_empty(request_queue_t *q)
527 {
528         elevator_t *e = q->elevator;
529
530         if (!list_empty(&q->queue_head))
531                 return 0;
532
533         if (e->ops->elevator_queue_empty_fn)
534                 return e->ops->elevator_queue_empty_fn(q);
535
536         return 1;
537 }
538
539 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
540 {
541         struct list_head *next;
542
543         elevator_t *e = q->elevator;
544
545         if (e->ops->elevator_latter_req_fn)
546                 return e->ops->elevator_latter_req_fn(q, rq);
547
548         next = rq->queuelist.next;
549         if (next != &q->queue_head && next != &rq->queuelist)
550                 return list_entry_rq(next);
551
552         return NULL;
553 }
554
555 struct request *elv_former_request(request_queue_t *q, struct request *rq)
556 {
557         struct list_head *prev;
558
559         elevator_t *e = q->elevator;
560
561         if (e->ops->elevator_former_req_fn)
562                 return e->ops->elevator_former_req_fn(q, rq);
563
564         prev = rq->queuelist.prev;
565         if (prev != &q->queue_head && prev != &rq->queuelist)
566                 return list_entry_rq(prev);
567
568         return NULL;
569 }
570
571 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
572                     int gfp_mask)
573 {
574         elevator_t *e = q->elevator;
575
576         if (e->ops->elevator_set_req_fn)
577                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
578
579         rq->elevator_private = NULL;
580         return 0;
581 }
582
583 void elv_put_request(request_queue_t *q, struct request *rq)
584 {
585         elevator_t *e = q->elevator;
586
587         if (e->ops->elevator_put_req_fn)
588                 e->ops->elevator_put_req_fn(q, rq);
589 }
590
591 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
592 {
593         elevator_t *e = q->elevator;
594
595         if (e->ops->elevator_may_queue_fn)
596                 return e->ops->elevator_may_queue_fn(q, rw, bio);
597
598         return ELV_MQUEUE_MAY;
599 }
600
601 void elv_completed_request(request_queue_t *q, struct request *rq)
602 {
603         elevator_t *e = q->elevator;
604
605         /*
606          * request is released from the driver, io must be done
607          */
608         if (blk_account_rq(rq)) {
609                 q->in_flight--;
610                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
611                         e->ops->elevator_completed_req_fn(q, rq);
612         }
613 }
614
615 int elv_register_queue(struct request_queue *q)
616 {
617         elevator_t *e = q->elevator;
618
619         e->kobj.parent = kobject_get(&q->kobj);
620         if (!e->kobj.parent)
621                 return -EBUSY;
622
623         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
624         e->kobj.ktype = e->elevator_type->elevator_ktype;
625
626         return kobject_register(&e->kobj);
627 }
628
629 void elv_unregister_queue(struct request_queue *q)
630 {
631         if (q) {
632                 elevator_t *e = q->elevator;
633                 kobject_unregister(&e->kobj);
634                 kobject_put(&q->kobj);
635         }
636 }
637
638 int elv_register(struct elevator_type *e)
639 {
640         spin_lock_irq(&elv_list_lock);
641         if (elevator_find(e->elevator_name))
642                 BUG();
643         list_add_tail(&e->list, &elv_list);
644         spin_unlock_irq(&elv_list_lock);
645
646         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
647         if (!strcmp(e->elevator_name, chosen_elevator))
648                 printk(" (default)");
649         printk("\n");
650         return 0;
651 }
652 EXPORT_SYMBOL_GPL(elv_register);
653
654 void elv_unregister(struct elevator_type *e)
655 {
656         spin_lock_irq(&elv_list_lock);
657         list_del_init(&e->list);
658         spin_unlock_irq(&elv_list_lock);
659 }
660 EXPORT_SYMBOL_GPL(elv_unregister);
661
662 /*
663  * switch to new_e io scheduler. be careful not to introduce deadlocks -
664  * we don't free the old io scheduler, before we have allocated what we
665  * need for the new one. this way we have a chance of going back to the old
666  * one, if the new one fails init for some reason. we also do an intermediate
667  * switch to noop to ensure safety with stack-allocated requests, since they
668  * don't originate from the block layer allocator. noop is safe here, because
669  * it never needs to touch the elevator itself for completion events. DRAIN
670  * flags will make sure we don't touch it for additions either.
671  */
672 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
673 {
674         elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
675         struct elevator_type *noop_elevator = NULL;
676         elevator_t *old_elevator;
677
678         if (!e)
679                 goto error;
680
681         /*
682          * first step, drain requests from the block freelist
683          */
684         blk_wait_queue_drained(q, 0);
685
686         /*
687          * unregister old elevator data
688          */
689         elv_unregister_queue(q);
690         old_elevator = q->elevator;
691
692         /*
693          * next step, switch to noop since it uses no private rq structures
694          * and doesn't allocate any memory for anything. then wait for any
695          * non-fs requests in-flight
696          */
697         noop_elevator = elevator_get("noop");
698         spin_lock_irq(q->queue_lock);
699         elevator_attach(q, noop_elevator, e);
700         spin_unlock_irq(q->queue_lock);
701
702         blk_wait_queue_drained(q, 1);
703
704         /*
705          * attach and start new elevator
706          */
707         if (elevator_attach(q, new_e, e))
708                 goto fail;
709
710         if (elv_register_queue(q))
711                 goto fail_register;
712
713         /*
714          * finally exit old elevator and start queue again
715          */
716         elevator_exit(old_elevator);
717         blk_finish_queue_drain(q);
718         elevator_put(noop_elevator);
719         return;
720
721 fail_register:
722         /*
723          * switch failed, exit the new io scheduler and reattach the old
724          * one again (along with re-adding the sysfs dir)
725          */
726         elevator_exit(e);
727 fail:
728         q->elevator = old_elevator;
729         elv_register_queue(q);
730         blk_finish_queue_drain(q);
731 error:
732         if (noop_elevator)
733                 elevator_put(noop_elevator);
734         elevator_put(new_e);
735         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
736 }
737
738 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
739 {
740         char elevator_name[ELV_NAME_MAX];
741         struct elevator_type *e;
742
743         memset(elevator_name, 0, sizeof(elevator_name));
744         strncpy(elevator_name, name, sizeof(elevator_name));
745
746         if (elevator_name[strlen(elevator_name) - 1] == '\n')
747                 elevator_name[strlen(elevator_name) - 1] = '\0';
748
749         e = elevator_get(elevator_name);
750         if (!e) {
751                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
752                 return -EINVAL;
753         }
754
755         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
756                 return count;
757
758         elevator_switch(q, e);
759         return count;
760 }
761
762 ssize_t elv_iosched_show(request_queue_t *q, char *name)
763 {
764         elevator_t *e = q->elevator;
765         struct elevator_type *elv = e->elevator_type;
766         struct list_head *entry;
767         int len = 0;
768
769         spin_lock_irq(q->queue_lock);
770         list_for_each(entry, &elv_list) {
771                 struct elevator_type *__e;
772
773                 __e = list_entry(entry, struct elevator_type, list);
774                 if (!strcmp(elv->elevator_name, __e->elevator_name))
775                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
776                 else
777                         len += sprintf(name+len, "%s ", __e->elevator_name);
778         }
779         spin_unlock_irq(q->queue_lock);
780
781         len += sprintf(len+name, "\n");
782         return len;
783 }
784
785 EXPORT_SYMBOL(elv_dispatch_sort);
786 EXPORT_SYMBOL(elv_add_request);
787 EXPORT_SYMBOL(__elv_add_request);
788 EXPORT_SYMBOL(elv_requeue_request);
789 EXPORT_SYMBOL(elv_next_request);
790 EXPORT_SYMBOL(elv_dequeue_request);
791 EXPORT_SYMBOL(elv_queue_empty);
792 EXPORT_SYMBOL(elv_completed_request);
793 EXPORT_SYMBOL(elevator_exit);
794 EXPORT_SYMBOL(elevator_init);