[BLOCK] elevator init fixes
[linux-3.10.git] / 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 #include <linux/delay.h>
38
39 #include <asm/uaccess.h>
40
41 static DEFINE_SPINLOCK(elv_list_lock);
42 static LIST_HEAD(elv_list);
43
44 /*
45  * can we safely merge with this request?
46  */
47 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
48 {
49         if (!rq_mergeable(rq))
50                 return 0;
51
52         /*
53          * different data direction or already started, don't merge
54          */
55         if (bio_data_dir(bio) != rq_data_dir(rq))
56                 return 0;
57
58         /*
59          * same device and no special stuff set, merge is ok
60          */
61         if (rq->rq_disk == bio->bi_bdev->bd_disk &&
62             !rq->waiting && !rq->special)
63                 return 1;
64
65         return 0;
66 }
67 EXPORT_SYMBOL(elv_rq_merge_ok);
68
69 inline int elv_try_merge(struct request *__rq, struct bio *bio)
70 {
71         int ret = ELEVATOR_NO_MERGE;
72
73         /*
74          * we can merge and sequence is ok, check if it's possible
75          */
76         if (elv_rq_merge_ok(__rq, bio)) {
77                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
78                         ret = ELEVATOR_BACK_MERGE;
79                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
80                         ret = ELEVATOR_FRONT_MERGE;
81         }
82
83         return ret;
84 }
85 EXPORT_SYMBOL(elv_try_merge);
86
87 static struct elevator_type *elevator_find(const char *name)
88 {
89         struct elevator_type *e = NULL;
90         struct list_head *entry;
91
92         list_for_each(entry, &elv_list) {
93                 struct elevator_type *__e;
94
95                 __e = list_entry(entry, struct elevator_type, list);
96
97                 if (!strcmp(__e->elevator_name, name)) {
98                         e = __e;
99                         break;
100                 }
101         }
102
103         return e;
104 }
105
106 static void elevator_put(struct elevator_type *e)
107 {
108         module_put(e->elevator_owner);
109 }
110
111 static struct elevator_type *elevator_get(const char *name)
112 {
113         struct elevator_type *e;
114
115         spin_lock_irq(&elv_list_lock);
116
117         e = elevator_find(name);
118         if (e && !try_module_get(e->elevator_owner))
119                 e = NULL;
120
121         spin_unlock_irq(&elv_list_lock);
122
123         return e;
124 }
125
126 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
127                            struct elevator_queue *eq)
128 {
129         int ret = 0;
130
131         memset(eq, 0, sizeof(*eq));
132         eq->ops = &e->ops;
133         eq->elevator_type = e;
134
135         q->elevator = eq;
136
137         if (eq->ops->elevator_init_fn)
138                 ret = eq->ops->elevator_init_fn(q, eq);
139
140         return ret;
141 }
142
143 static char chosen_elevator[16];
144
145 static void elevator_setup_default(void)
146 {
147         struct elevator_type *e;
148
149         /*
150          * If default has not been set, use the compiled-in selection.
151          */
152         if (!chosen_elevator[0])
153                 strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
154
155         /*
156          * If the given scheduler is not available, fall back to no-op.
157          */
158         if (!(e = elevator_find(chosen_elevator)))
159                 strcpy(chosen_elevator, "noop");
160         elevator_put(e);
161 }
162
163 static int __init elevator_setup(char *str)
164 {
165         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
166         return 0;
167 }
168
169 __setup("elevator=", elevator_setup);
170
171 int elevator_init(request_queue_t *q, char *name)
172 {
173         struct elevator_type *e = NULL;
174         struct elevator_queue *eq;
175         int ret = 0;
176
177         INIT_LIST_HEAD(&q->queue_head);
178         q->last_merge = NULL;
179         q->end_sector = 0;
180         q->boundary_rq = NULL;
181
182         elevator_setup_default();
183
184         if (!name)
185                 name = chosen_elevator;
186
187         e = elevator_get(name);
188         if (!e)
189                 return -EINVAL;
190
191         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
192         if (!eq) {
193                 elevator_put(e);
194                 return -ENOMEM;
195         }
196
197         ret = elevator_attach(q, e, eq);
198         if (ret) {
199                 kfree(eq);
200                 elevator_put(e);
201         }
202
203         return ret;
204 }
205
206 void elevator_exit(elevator_t *e)
207 {
208         if (e->ops->elevator_exit_fn)
209                 e->ops->elevator_exit_fn(e);
210
211         elevator_put(e->elevator_type);
212         e->elevator_type = NULL;
213         kfree(e);
214 }
215
216 /*
217  * Insert rq into dispatch queue of q.  Queue lock must be held on
218  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
219  * appended to the dispatch queue.  To be used by specific elevators.
220  */
221 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
222 {
223         sector_t boundary;
224         struct list_head *entry;
225
226         if (q->last_merge == rq)
227                 q->last_merge = NULL;
228
229         boundary = q->end_sector;
230
231         list_for_each_prev(entry, &q->queue_head) {
232                 struct request *pos = list_entry_rq(entry);
233
234                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
235                         break;
236                 if (rq->sector >= boundary) {
237                         if (pos->sector < boundary)
238                                 continue;
239                 } else {
240                         if (pos->sector >= boundary)
241                                 break;
242                 }
243                 if (rq->sector >= pos->sector)
244                         break;
245         }
246
247         list_add(&rq->queuelist, entry);
248 }
249
250 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
251 {
252         elevator_t *e = q->elevator;
253         int ret;
254
255         if (q->last_merge) {
256                 ret = elv_try_merge(q->last_merge, bio);
257                 if (ret != ELEVATOR_NO_MERGE) {
258                         *req = q->last_merge;
259                         return ret;
260                 }
261         }
262
263         if (e->ops->elevator_merge_fn)
264                 return e->ops->elevator_merge_fn(q, req, bio);
265
266         return ELEVATOR_NO_MERGE;
267 }
268
269 void elv_merged_request(request_queue_t *q, struct request *rq)
270 {
271         elevator_t *e = q->elevator;
272
273         if (e->ops->elevator_merged_fn)
274                 e->ops->elevator_merged_fn(q, rq);
275
276         q->last_merge = rq;
277 }
278
279 void elv_merge_requests(request_queue_t *q, struct request *rq,
280                              struct request *next)
281 {
282         elevator_t *e = q->elevator;
283
284         if (e->ops->elevator_merge_req_fn)
285                 e->ops->elevator_merge_req_fn(q, rq, next);
286
287         q->last_merge = rq;
288 }
289
290 void elv_requeue_request(request_queue_t *q, struct request *rq)
291 {
292         elevator_t *e = q->elevator;
293
294         /*
295          * it already went through dequeue, we need to decrement the
296          * in_flight count again
297          */
298         if (blk_account_rq(rq)) {
299                 q->in_flight--;
300                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
301                         e->ops->elevator_deactivate_req_fn(q, rq);
302         }
303
304         rq->flags &= ~REQ_STARTED;
305
306         /*
307          * if this is the flush, requeue the original instead and drop the flush
308          */
309         if (rq->flags & REQ_BAR_FLUSH) {
310                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
311                 rq = rq->end_io_data;
312         }
313
314         __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
315 }
316
317 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
318                        int plug)
319 {
320         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
321                 /*
322                  * barriers implicitly indicate back insertion
323                  */
324                 if (where == ELEVATOR_INSERT_SORT)
325                         where = ELEVATOR_INSERT_BACK;
326
327                 /*
328                  * this request is scheduling boundary, update end_sector
329                  */
330                 if (blk_fs_request(rq)) {
331                         q->end_sector = rq_end_sector(rq);
332                         q->boundary_rq = rq;
333                 }
334         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
335                 where = ELEVATOR_INSERT_BACK;
336
337         if (plug)
338                 blk_plug_device(q);
339
340         rq->q = q;
341
342         switch (where) {
343         case ELEVATOR_INSERT_FRONT:
344                 rq->flags |= REQ_SOFTBARRIER;
345
346                 list_add(&rq->queuelist, &q->queue_head);
347                 break;
348
349         case ELEVATOR_INSERT_BACK:
350                 rq->flags |= REQ_SOFTBARRIER;
351
352                 while (q->elevator->ops->elevator_dispatch_fn(q, 1))
353                         ;
354                 list_add_tail(&rq->queuelist, &q->queue_head);
355                 /*
356                  * We kick the queue here for the following reasons.
357                  * - The elevator might have returned NULL previously
358                  *   to delay requests and returned them now.  As the
359                  *   queue wasn't empty before this request, ll_rw_blk
360                  *   won't run the queue on return, resulting in hang.
361                  * - Usually, back inserted requests won't be merged
362                  *   with anything.  There's no point in delaying queue
363                  *   processing.
364                  */
365                 blk_remove_plug(q);
366                 q->request_fn(q);
367                 break;
368
369         case ELEVATOR_INSERT_SORT:
370                 BUG_ON(!blk_fs_request(rq));
371                 rq->flags |= REQ_SORTED;
372                 if (q->last_merge == NULL && rq_mergeable(rq))
373                         q->last_merge = rq;
374                 /*
375                  * Some ioscheds (cfq) run q->request_fn directly, so
376                  * rq cannot be accessed after calling
377                  * elevator_add_req_fn.
378                  */
379                 q->elevator->ops->elevator_add_req_fn(q, rq);
380                 break;
381
382         default:
383                 printk(KERN_ERR "%s: bad insertion point %d\n",
384                        __FUNCTION__, where);
385                 BUG();
386         }
387
388         if (blk_queue_plugged(q)) {
389                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
390                         - q->in_flight;
391
392                 if (nrq >= q->unplug_thresh)
393                         __generic_unplug_device(q);
394         }
395 }
396
397 void elv_add_request(request_queue_t *q, struct request *rq, int where,
398                      int plug)
399 {
400         unsigned long flags;
401
402         spin_lock_irqsave(q->queue_lock, flags);
403         __elv_add_request(q, rq, where, plug);
404         spin_unlock_irqrestore(q->queue_lock, flags);
405 }
406
407 static inline struct request *__elv_next_request(request_queue_t *q)
408 {
409         struct request *rq;
410
411         if (unlikely(list_empty(&q->queue_head) &&
412                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
413                 return NULL;
414
415         rq = list_entry_rq(q->queue_head.next);
416
417         /*
418          * if this is a barrier write and the device has to issue a
419          * flush sequence to support it, check how far we are
420          */
421         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
422                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
423
424                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
425                     !blk_barrier_preflush(rq))
426                         rq = blk_start_pre_flush(q, rq);
427         }
428
429         return rq;
430 }
431
432 struct request *elv_next_request(request_queue_t *q)
433 {
434         struct request *rq;
435         int ret;
436
437         while ((rq = __elv_next_request(q)) != NULL) {
438                 if (!(rq->flags & REQ_STARTED)) {
439                         elevator_t *e = q->elevator;
440
441                         /*
442                          * This is the first time the device driver
443                          * sees this request (possibly after
444                          * requeueing).  Notify IO scheduler.
445                          */
446                         if (blk_sorted_rq(rq) &&
447                             e->ops->elevator_activate_req_fn)
448                                 e->ops->elevator_activate_req_fn(q, rq);
449
450                         /*
451                          * just mark as started even if we don't start
452                          * it, a request that has been delayed should
453                          * not be passed by new incoming requests
454                          */
455                         rq->flags |= REQ_STARTED;
456                 }
457
458                 if (!q->boundary_rq || q->boundary_rq == rq) {
459                         q->end_sector = rq_end_sector(rq);
460                         q->boundary_rq = NULL;
461                 }
462
463                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
464                         break;
465
466                 ret = q->prep_rq_fn(q, rq);
467                 if (ret == BLKPREP_OK) {
468                         break;
469                 } else if (ret == BLKPREP_DEFER) {
470                         /*
471                          * the request may have been (partially) prepped.
472                          * we need to keep this request in the front to
473                          * avoid resource deadlock.  REQ_STARTED will
474                          * prevent other fs requests from passing this one.
475                          */
476                         rq = NULL;
477                         break;
478                 } else if (ret == BLKPREP_KILL) {
479                         int nr_bytes = rq->hard_nr_sectors << 9;
480
481                         if (!nr_bytes)
482                                 nr_bytes = rq->data_len;
483
484                         blkdev_dequeue_request(rq);
485                         rq->flags |= REQ_QUIET;
486                         end_that_request_chunk(rq, 0, nr_bytes);
487                         end_that_request_last(rq);
488                 } else {
489                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
490                                                                 ret);
491                         break;
492                 }
493         }
494
495         return rq;
496 }
497
498 void elv_dequeue_request(request_queue_t *q, struct request *rq)
499 {
500         BUG_ON(list_empty(&rq->queuelist));
501
502         list_del_init(&rq->queuelist);
503
504         /*
505          * the time frame between a request being removed from the lists
506          * and to it is freed is accounted as io that is in progress at
507          * the driver side.
508          */
509         if (blk_account_rq(rq))
510                 q->in_flight++;
511 }
512
513 int elv_queue_empty(request_queue_t *q)
514 {
515         elevator_t *e = q->elevator;
516
517         if (!list_empty(&q->queue_head))
518                 return 0;
519
520         if (e->ops->elevator_queue_empty_fn)
521                 return e->ops->elevator_queue_empty_fn(q);
522
523         return 1;
524 }
525
526 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
527 {
528         struct list_head *next;
529
530         elevator_t *e = q->elevator;
531
532         if (e->ops->elevator_latter_req_fn)
533                 return e->ops->elevator_latter_req_fn(q, rq);
534
535         next = rq->queuelist.next;
536         if (next != &q->queue_head && next != &rq->queuelist)
537                 return list_entry_rq(next);
538
539         return NULL;
540 }
541
542 struct request *elv_former_request(request_queue_t *q, struct request *rq)
543 {
544         struct list_head *prev;
545
546         elevator_t *e = q->elevator;
547
548         if (e->ops->elevator_former_req_fn)
549                 return e->ops->elevator_former_req_fn(q, rq);
550
551         prev = rq->queuelist.prev;
552         if (prev != &q->queue_head && prev != &rq->queuelist)
553                 return list_entry_rq(prev);
554
555         return NULL;
556 }
557
558 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
559                     gfp_t gfp_mask)
560 {
561         elevator_t *e = q->elevator;
562
563         if (e->ops->elevator_set_req_fn)
564                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
565
566         rq->elevator_private = NULL;
567         return 0;
568 }
569
570 void elv_put_request(request_queue_t *q, struct request *rq)
571 {
572         elevator_t *e = q->elevator;
573
574         if (e->ops->elevator_put_req_fn)
575                 e->ops->elevator_put_req_fn(q, rq);
576 }
577
578 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
579 {
580         elevator_t *e = q->elevator;
581
582         if (e->ops->elevator_may_queue_fn)
583                 return e->ops->elevator_may_queue_fn(q, rw, bio);
584
585         return ELV_MQUEUE_MAY;
586 }
587
588 void elv_completed_request(request_queue_t *q, struct request *rq)
589 {
590         elevator_t *e = q->elevator;
591
592         /*
593          * request is released from the driver, io must be done
594          */
595         if (blk_account_rq(rq)) {
596                 q->in_flight--;
597                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
598                         e->ops->elevator_completed_req_fn(q, rq);
599         }
600 }
601
602 int elv_register_queue(struct request_queue *q)
603 {
604         elevator_t *e = q->elevator;
605
606         e->kobj.parent = kobject_get(&q->kobj);
607         if (!e->kobj.parent)
608                 return -EBUSY;
609
610         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
611         e->kobj.ktype = e->elevator_type->elevator_ktype;
612
613         return kobject_register(&e->kobj);
614 }
615
616 void elv_unregister_queue(struct request_queue *q)
617 {
618         if (q) {
619                 elevator_t *e = q->elevator;
620                 kobject_unregister(&e->kobj);
621                 kobject_put(&q->kobj);
622         }
623 }
624
625 int elv_register(struct elevator_type *e)
626 {
627         spin_lock_irq(&elv_list_lock);
628         if (elevator_find(e->elevator_name))
629                 BUG();
630         list_add_tail(&e->list, &elv_list);
631         spin_unlock_irq(&elv_list_lock);
632
633         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
634         if (!strcmp(e->elevator_name, chosen_elevator))
635                 printk(" (default)");
636         printk("\n");
637         return 0;
638 }
639 EXPORT_SYMBOL_GPL(elv_register);
640
641 void elv_unregister(struct elevator_type *e)
642 {
643         struct task_struct *g, *p;
644
645         /*
646          * Iterate every thread in the process to remove the io contexts.
647          */
648         read_lock(&tasklist_lock);
649         do_each_thread(g, p) {
650                 struct io_context *ioc = p->io_context;
651                 if (ioc && ioc->cic) {
652                         ioc->cic->exit(ioc->cic);
653                         ioc->cic->dtor(ioc->cic);
654                         ioc->cic = NULL;
655                 }
656                 if (ioc && ioc->aic) {
657                         ioc->aic->exit(ioc->aic);
658                         ioc->aic->dtor(ioc->aic);
659                         ioc->aic = NULL;
660                 }
661         } while_each_thread(g, p);
662         read_unlock(&tasklist_lock);
663
664         spin_lock_irq(&elv_list_lock);
665         list_del_init(&e->list);
666         spin_unlock_irq(&elv_list_lock);
667 }
668 EXPORT_SYMBOL_GPL(elv_unregister);
669
670 /*
671  * switch to new_e io scheduler. be careful not to introduce deadlocks -
672  * we don't free the old io scheduler, before we have allocated what we
673  * need for the new one. this way we have a chance of going back to the old
674  * one, if the new one fails init for some reason.
675  */
676 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
677 {
678         elevator_t *old_elevator, *e;
679
680         /*
681          * Allocate new elevator
682          */
683         e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
684         if (!e)
685                 goto error;
686
687         /*
688          * Turn on BYPASS and drain all requests w/ elevator private data
689          */
690         spin_lock_irq(q->queue_lock);
691
692         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
693
694         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
695                 ;
696
697         while (q->rq.elvpriv) {
698                 spin_unlock_irq(q->queue_lock);
699                 msleep(10);
700                 spin_lock_irq(q->queue_lock);
701         }
702
703         spin_unlock_irq(q->queue_lock);
704
705         /*
706          * unregister old elevator data
707          */
708         elv_unregister_queue(q);
709         old_elevator = q->elevator;
710
711         /*
712          * attach and start new elevator
713          */
714         if (elevator_attach(q, new_e, e))
715                 goto fail;
716
717         if (elv_register_queue(q))
718                 goto fail_register;
719
720         /*
721          * finally exit old elevator and turn off BYPASS.
722          */
723         elevator_exit(old_elevator);
724         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
725         return;
726
727 fail_register:
728         /*
729          * switch failed, exit the new io scheduler and reattach the old
730          * one again (along with re-adding the sysfs dir)
731          */
732         elevator_exit(e);
733         e = NULL;
734 fail:
735         q->elevator = old_elevator;
736         elv_register_queue(q);
737         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
738         kfree(e);
739 error:
740         elevator_put(new_e);
741         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
742 }
743
744 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
745 {
746         char elevator_name[ELV_NAME_MAX];
747         struct elevator_type *e;
748
749         memset(elevator_name, 0, sizeof(elevator_name));
750         strncpy(elevator_name, name, sizeof(elevator_name));
751
752         if (elevator_name[strlen(elevator_name) - 1] == '\n')
753                 elevator_name[strlen(elevator_name) - 1] = '\0';
754
755         e = elevator_get(elevator_name);
756         if (!e) {
757                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
758                 return -EINVAL;
759         }
760
761         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
762                 elevator_put(e);
763                 return count;
764         }
765
766         elevator_switch(q, e);
767         return count;
768 }
769
770 ssize_t elv_iosched_show(request_queue_t *q, char *name)
771 {
772         elevator_t *e = q->elevator;
773         struct elevator_type *elv = e->elevator_type;
774         struct list_head *entry;
775         int len = 0;
776
777         spin_lock_irq(q->queue_lock);
778         list_for_each(entry, &elv_list) {
779                 struct elevator_type *__e;
780
781                 __e = list_entry(entry, struct elevator_type, list);
782                 if (!strcmp(elv->elevator_name, __e->elevator_name))
783                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
784                 else
785                         len += sprintf(name+len, "%s ", __e->elevator_name);
786         }
787         spin_unlock_irq(q->queue_lock);
788
789         len += sprintf(len+name, "\n");
790         return len;
791 }
792
793 EXPORT_SYMBOL(elv_dispatch_sort);
794 EXPORT_SYMBOL(elv_add_request);
795 EXPORT_SYMBOL(__elv_add_request);
796 EXPORT_SYMBOL(elv_requeue_request);
797 EXPORT_SYMBOL(elv_next_request);
798 EXPORT_SYMBOL(elv_dequeue_request);
799 EXPORT_SYMBOL(elv_queue_empty);
800 EXPORT_SYMBOL(elv_completed_request);
801 EXPORT_SYMBOL(elevator_exit);
802 EXPORT_SYMBOL(elevator_init);