dbbea73a8b10b513bd335f42129d38838d551794
[linux-2.6.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@suse.de> :
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/config.h>
31 #include <linux/module.h>
32 #include <linux/slab.h>
33 #include <linux/init.h>
34 #include <linux/compiler.h>
35 #include <linux/delay.h>
36
37 #include <asm/uaccess.h>
38
39 static DEFINE_SPINLOCK(elv_list_lock);
40 static LIST_HEAD(elv_list);
41
42 /*
43  * can we safely merge with this request?
44  */
45 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
46 {
47         if (!rq_mergeable(rq))
48                 return 0;
49
50         /*
51          * different data direction or already started, don't merge
52          */
53         if (bio_data_dir(bio) != rq_data_dir(rq))
54                 return 0;
55
56         /*
57          * same device and no special stuff set, merge is ok
58          */
59         if (rq->rq_disk == bio->bi_bdev->bd_disk &&
60             !rq->waiting && !rq->special)
61                 return 1;
62
63         return 0;
64 }
65 EXPORT_SYMBOL(elv_rq_merge_ok);
66
67 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
68 {
69         int ret = ELEVATOR_NO_MERGE;
70
71         /*
72          * we can merge and sequence is ok, check if it's possible
73          */
74         if (elv_rq_merge_ok(__rq, bio)) {
75                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
76                         ret = ELEVATOR_BACK_MERGE;
77                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
78                         ret = ELEVATOR_FRONT_MERGE;
79         }
80
81         return ret;
82 }
83
84 static struct elevator_type *elevator_find(const char *name)
85 {
86         struct elevator_type *e = NULL;
87         struct list_head *entry;
88
89         list_for_each(entry, &elv_list) {
90                 struct elevator_type *__e;
91
92                 __e = list_entry(entry, struct elevator_type, list);
93
94                 if (!strcmp(__e->elevator_name, name)) {
95                         e = __e;
96                         break;
97                 }
98         }
99
100         return e;
101 }
102
103 static void elevator_put(struct elevator_type *e)
104 {
105         module_put(e->elevator_owner);
106 }
107
108 static struct elevator_type *elevator_get(const char *name)
109 {
110         struct elevator_type *e;
111
112         spin_lock_irq(&elv_list_lock);
113
114         e = elevator_find(name);
115         if (e && !try_module_get(e->elevator_owner))
116                 e = NULL;
117
118         spin_unlock_irq(&elv_list_lock);
119
120         return e;
121 }
122
123 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
124                            struct elevator_queue *eq)
125 {
126         int ret = 0;
127
128         memset(eq, 0, sizeof(*eq));
129         eq->ops = &e->ops;
130         eq->elevator_type = e;
131
132         q->elevator = eq;
133
134         if (eq->ops->elevator_init_fn)
135                 ret = eq->ops->elevator_init_fn(q, eq);
136
137         return ret;
138 }
139
140 static char chosen_elevator[16];
141
142 static int __init elevator_setup(char *str)
143 {
144         /*
145          * Be backwards-compatible with previous kernels, so users
146          * won't get the wrong elevator.
147          */
148         if (!strcmp(str, "as"))
149                 strcpy(chosen_elevator, "anticipatory");
150         else
151                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
152         return 0;
153 }
154
155 __setup("elevator=", elevator_setup);
156
157 int elevator_init(request_queue_t *q, char *name)
158 {
159         struct elevator_type *e = NULL;
160         struct elevator_queue *eq;
161         int ret = 0;
162
163         INIT_LIST_HEAD(&q->queue_head);
164         q->last_merge = NULL;
165         q->end_sector = 0;
166         q->boundary_rq = NULL;
167
168         if (name && !(e = elevator_get(name)))
169                 return -EINVAL;
170
171         if (!e && !(e = elevator_get(chosen_elevator))) {
172                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
173                 if (*chosen_elevator)
174                         printk("I/O scheduler %s not found\n", chosen_elevator);
175         }
176
177         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
178         if (!eq) {
179                 elevator_put(e);
180                 return -ENOMEM;
181         }
182
183         ret = elevator_attach(q, e, eq);
184         if (ret) {
185                 kfree(eq);
186                 elevator_put(e);
187         }
188
189         return ret;
190 }
191
192 void elevator_exit(elevator_t *e)
193 {
194         if (e->ops->elevator_exit_fn)
195                 e->ops->elevator_exit_fn(e);
196
197         elevator_put(e->elevator_type);
198         e->elevator_type = NULL;
199         kfree(e);
200 }
201
202 /*
203  * Insert rq into dispatch queue of q.  Queue lock must be held on
204  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
205  * appended to the dispatch queue.  To be used by specific elevators.
206  */
207 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
208 {
209         sector_t boundary;
210         struct list_head *entry;
211
212         if (q->last_merge == rq)
213                 q->last_merge = NULL;
214         q->nr_sorted--;
215
216         boundary = q->end_sector;
217
218         list_for_each_prev(entry, &q->queue_head) {
219                 struct request *pos = list_entry_rq(entry);
220
221                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
222                         break;
223                 if (rq->sector >= boundary) {
224                         if (pos->sector < boundary)
225                                 continue;
226                 } else {
227                         if (pos->sector >= boundary)
228                                 break;
229                 }
230                 if (rq->sector >= pos->sector)
231                         break;
232         }
233
234         list_add(&rq->queuelist, entry);
235 }
236
237 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
238 {
239         elevator_t *e = q->elevator;
240         int ret;
241
242         if (q->last_merge) {
243                 ret = elv_try_merge(q->last_merge, bio);
244                 if (ret != ELEVATOR_NO_MERGE) {
245                         *req = q->last_merge;
246                         return ret;
247                 }
248         }
249
250         if (e->ops->elevator_merge_fn)
251                 return e->ops->elevator_merge_fn(q, req, bio);
252
253         return ELEVATOR_NO_MERGE;
254 }
255
256 void elv_merged_request(request_queue_t *q, struct request *rq)
257 {
258         elevator_t *e = q->elevator;
259
260         if (e->ops->elevator_merged_fn)
261                 e->ops->elevator_merged_fn(q, rq);
262
263         q->last_merge = rq;
264 }
265
266 void elv_merge_requests(request_queue_t *q, struct request *rq,
267                              struct request *next)
268 {
269         elevator_t *e = q->elevator;
270
271         if (e->ops->elevator_merge_req_fn)
272                 e->ops->elevator_merge_req_fn(q, rq, next);
273         q->nr_sorted--;
274
275         q->last_merge = rq;
276 }
277
278 void elv_requeue_request(request_queue_t *q, struct request *rq)
279 {
280         elevator_t *e = q->elevator;
281
282         /*
283          * it already went through dequeue, we need to decrement the
284          * in_flight count again
285          */
286         if (blk_account_rq(rq)) {
287                 q->in_flight--;
288                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
289                         e->ops->elevator_deactivate_req_fn(q, rq);
290         }
291
292         rq->flags &= ~REQ_STARTED;
293
294         __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE, 0);
295 }
296
297 static void elv_drain_elevator(request_queue_t *q)
298 {
299         static int printed;
300         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
301                 ;
302         if (q->nr_sorted == 0)
303                 return;
304         if (printed++ < 10) {
305                 printk(KERN_ERR "%s: forced dispatching is broken "
306                        "(nr_sorted=%u), please report this\n",
307                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
308         }
309 }
310
311 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
312                        int plug)
313 {
314         struct list_head *pos;
315         unsigned ordseq;
316
317         if (q->ordcolor)
318                 rq->flags |= REQ_ORDERED_COLOR;
319
320         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
321                 /*
322                  * toggle ordered color
323                  */
324                 q->ordcolor ^= 1;
325
326                 /*
327                  * barriers implicitly indicate back insertion
328                  */
329                 if (where == ELEVATOR_INSERT_SORT)
330                         where = ELEVATOR_INSERT_BACK;
331
332                 /*
333                  * this request is scheduling boundary, update end_sector
334                  */
335                 if (blk_fs_request(rq)) {
336                         q->end_sector = rq_end_sector(rq);
337                         q->boundary_rq = rq;
338                 }
339         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
340                 where = ELEVATOR_INSERT_BACK;
341
342         if (plug)
343                 blk_plug_device(q);
344
345         rq->q = q;
346
347         switch (where) {
348         case ELEVATOR_INSERT_FRONT:
349                 rq->flags |= REQ_SOFTBARRIER;
350
351                 list_add(&rq->queuelist, &q->queue_head);
352                 break;
353
354         case ELEVATOR_INSERT_BACK:
355                 rq->flags |= REQ_SOFTBARRIER;
356                 elv_drain_elevator(q);
357                 list_add_tail(&rq->queuelist, &q->queue_head);
358                 /*
359                  * We kick the queue here for the following reasons.
360                  * - The elevator might have returned NULL previously
361                  *   to delay requests and returned them now.  As the
362                  *   queue wasn't empty before this request, ll_rw_blk
363                  *   won't run the queue on return, resulting in hang.
364                  * - Usually, back inserted requests won't be merged
365                  *   with anything.  There's no point in delaying queue
366                  *   processing.
367                  */
368                 blk_remove_plug(q);
369                 q->request_fn(q);
370                 break;
371
372         case ELEVATOR_INSERT_SORT:
373                 BUG_ON(!blk_fs_request(rq));
374                 rq->flags |= REQ_SORTED;
375                 q->nr_sorted++;
376                 if (q->last_merge == NULL && rq_mergeable(rq))
377                         q->last_merge = rq;
378                 /*
379                  * Some ioscheds (cfq) run q->request_fn directly, so
380                  * rq cannot be accessed after calling
381                  * elevator_add_req_fn.
382                  */
383                 q->elevator->ops->elevator_add_req_fn(q, rq);
384                 break;
385
386         case ELEVATOR_INSERT_REQUEUE:
387                 /*
388                  * If ordered flush isn't in progress, we do front
389                  * insertion; otherwise, requests should be requeued
390                  * in ordseq order.
391                  */
392                 rq->flags |= REQ_SOFTBARRIER;
393
394                 if (q->ordseq == 0) {
395                         list_add(&rq->queuelist, &q->queue_head);
396                         break;
397                 }
398
399                 ordseq = blk_ordered_req_seq(rq);
400
401                 list_for_each(pos, &q->queue_head) {
402                         struct request *pos_rq = list_entry_rq(pos);
403                         if (ordseq <= blk_ordered_req_seq(pos_rq))
404                                 break;
405                 }
406
407                 list_add_tail(&rq->queuelist, pos);
408                 break;
409
410         default:
411                 printk(KERN_ERR "%s: bad insertion point %d\n",
412                        __FUNCTION__, where);
413                 BUG();
414         }
415
416         if (blk_queue_plugged(q)) {
417                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
418                         - q->in_flight;
419
420                 if (nrq >= q->unplug_thresh)
421                         __generic_unplug_device(q);
422         }
423 }
424
425 void elv_add_request(request_queue_t *q, struct request *rq, int where,
426                      int plug)
427 {
428         unsigned long flags;
429
430         spin_lock_irqsave(q->queue_lock, flags);
431         __elv_add_request(q, rq, where, plug);
432         spin_unlock_irqrestore(q->queue_lock, flags);
433 }
434
435 static inline struct request *__elv_next_request(request_queue_t *q)
436 {
437         struct request *rq;
438
439         while (1) {
440                 while (!list_empty(&q->queue_head)) {
441                         rq = list_entry_rq(q->queue_head.next);
442                         if (blk_do_ordered(q, &rq))
443                                 return rq;
444                 }
445
446                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
447                         return NULL;
448         }
449 }
450
451 struct request *elv_next_request(request_queue_t *q)
452 {
453         struct request *rq;
454         int ret;
455
456         while ((rq = __elv_next_request(q)) != NULL) {
457                 if (!(rq->flags & REQ_STARTED)) {
458                         elevator_t *e = q->elevator;
459
460                         /*
461                          * This is the first time the device driver
462                          * sees this request (possibly after
463                          * requeueing).  Notify IO scheduler.
464                          */
465                         if (blk_sorted_rq(rq) &&
466                             e->ops->elevator_activate_req_fn)
467                                 e->ops->elevator_activate_req_fn(q, rq);
468
469                         /*
470                          * just mark as started even if we don't start
471                          * it, a request that has been delayed should
472                          * not be passed by new incoming requests
473                          */
474                         rq->flags |= REQ_STARTED;
475                 }
476
477                 if (!q->boundary_rq || q->boundary_rq == rq) {
478                         q->end_sector = rq_end_sector(rq);
479                         q->boundary_rq = NULL;
480                 }
481
482                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
483                         break;
484
485                 ret = q->prep_rq_fn(q, rq);
486                 if (ret == BLKPREP_OK) {
487                         break;
488                 } else if (ret == BLKPREP_DEFER) {
489                         /*
490                          * the request may have been (partially) prepped.
491                          * we need to keep this request in the front to
492                          * avoid resource deadlock.  REQ_STARTED will
493                          * prevent other fs requests from passing this one.
494                          */
495                         rq = NULL;
496                         break;
497                 } else if (ret == BLKPREP_KILL) {
498                         int nr_bytes = rq->hard_nr_sectors << 9;
499
500                         if (!nr_bytes)
501                                 nr_bytes = rq->data_len;
502
503                         blkdev_dequeue_request(rq);
504                         rq->flags |= REQ_QUIET;
505                         end_that_request_chunk(rq, 0, nr_bytes);
506                         end_that_request_last(rq, 0);
507                 } else {
508                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
509                                                                 ret);
510                         break;
511                 }
512         }
513
514         return rq;
515 }
516
517 void elv_dequeue_request(request_queue_t *q, struct request *rq)
518 {
519         BUG_ON(list_empty(&rq->queuelist));
520
521         list_del_init(&rq->queuelist);
522
523         /*
524          * the time frame between a request being removed from the lists
525          * and to it is freed is accounted as io that is in progress at
526          * the driver side.
527          */
528         if (blk_account_rq(rq))
529                 q->in_flight++;
530 }
531
532 int elv_queue_empty(request_queue_t *q)
533 {
534         elevator_t *e = q->elevator;
535
536         if (!list_empty(&q->queue_head))
537                 return 0;
538
539         if (e->ops->elevator_queue_empty_fn)
540                 return e->ops->elevator_queue_empty_fn(q);
541
542         return 1;
543 }
544
545 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
546 {
547         elevator_t *e = q->elevator;
548
549         if (e->ops->elevator_latter_req_fn)
550                 return e->ops->elevator_latter_req_fn(q, rq);
551         return NULL;
552 }
553
554 struct request *elv_former_request(request_queue_t *q, struct request *rq)
555 {
556         elevator_t *e = q->elevator;
557
558         if (e->ops->elevator_former_req_fn)
559                 return e->ops->elevator_former_req_fn(q, rq);
560         return NULL;
561 }
562
563 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
564                     gfp_t gfp_mask)
565 {
566         elevator_t *e = q->elevator;
567
568         if (e->ops->elevator_set_req_fn)
569                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
570
571         rq->elevator_private = NULL;
572         return 0;
573 }
574
575 void elv_put_request(request_queue_t *q, struct request *rq)
576 {
577         elevator_t *e = q->elevator;
578
579         if (e->ops->elevator_put_req_fn)
580                 e->ops->elevator_put_req_fn(q, rq);
581 }
582
583 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
584 {
585         elevator_t *e = q->elevator;
586
587         if (e->ops->elevator_may_queue_fn)
588                 return e->ops->elevator_may_queue_fn(q, rw, bio);
589
590         return ELV_MQUEUE_MAY;
591 }
592
593 void elv_completed_request(request_queue_t *q, struct request *rq)
594 {
595         elevator_t *e = q->elevator;
596
597         /*
598          * request is released from the driver, io must be done
599          */
600         if (blk_account_rq(rq)) {
601                 q->in_flight--;
602                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
603                         e->ops->elevator_completed_req_fn(q, rq);
604         }
605
606         /*
607          * Check if the queue is waiting for fs requests to be
608          * drained for flush sequence.
609          */
610         if (unlikely(q->ordseq)) {
611                 struct request *first_rq = list_entry_rq(q->queue_head.next);
612                 if (q->in_flight == 0 &&
613                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
614                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
615                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
616                         q->request_fn(q);
617                 }
618         }
619 }
620
621 int elv_register_queue(struct request_queue *q)
622 {
623         elevator_t *e = q->elevator;
624
625         e->kobj.parent = kobject_get(&q->kobj);
626         if (!e->kobj.parent)
627                 return -EBUSY;
628
629         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
630         e->kobj.ktype = e->elevator_type->elevator_ktype;
631
632         return kobject_register(&e->kobj);
633 }
634
635 void elv_unregister_queue(struct request_queue *q)
636 {
637         if (q) {
638                 elevator_t *e = q->elevator;
639                 kobject_unregister(&e->kobj);
640                 kobject_put(&q->kobj);
641         }
642 }
643
644 int elv_register(struct elevator_type *e)
645 {
646         spin_lock_irq(&elv_list_lock);
647         if (elevator_find(e->elevator_name))
648                 BUG();
649         list_add_tail(&e->list, &elv_list);
650         spin_unlock_irq(&elv_list_lock);
651
652         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
653         if (!strcmp(e->elevator_name, chosen_elevator) ||
654                         (!*chosen_elevator &&
655                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
656                                 printk(" (default)");
657         printk("\n");
658         return 0;
659 }
660 EXPORT_SYMBOL_GPL(elv_register);
661
662 void elv_unregister(struct elevator_type *e)
663 {
664         struct task_struct *g, *p;
665
666         /*
667          * Iterate every thread in the process to remove the io contexts.
668          */
669         read_lock(&tasklist_lock);
670         do_each_thread(g, p) {
671                 struct io_context *ioc = p->io_context;
672                 if (ioc && ioc->cic) {
673                         ioc->cic->exit(ioc->cic);
674                         ioc->cic->dtor(ioc->cic);
675                         ioc->cic = NULL;
676                 }
677                 if (ioc && ioc->aic) {
678                         ioc->aic->exit(ioc->aic);
679                         ioc->aic->dtor(ioc->aic);
680                         ioc->aic = NULL;
681                 }
682         } while_each_thread(g, p);
683         read_unlock(&tasklist_lock);
684
685         spin_lock_irq(&elv_list_lock);
686         list_del_init(&e->list);
687         spin_unlock_irq(&elv_list_lock);
688 }
689 EXPORT_SYMBOL_GPL(elv_unregister);
690
691 /*
692  * switch to new_e io scheduler. be careful not to introduce deadlocks -
693  * we don't free the old io scheduler, before we have allocated what we
694  * need for the new one. this way we have a chance of going back to the old
695  * one, if the new one fails init for some reason.
696  */
697 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
698 {
699         elevator_t *old_elevator, *e;
700
701         /*
702          * Allocate new elevator
703          */
704         e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
705         if (!e)
706                 goto error;
707
708         /*
709          * Turn on BYPASS and drain all requests w/ elevator private data
710          */
711         spin_lock_irq(q->queue_lock);
712
713         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
714
715         elv_drain_elevator(q);
716
717         while (q->rq.elvpriv) {
718                 blk_remove_plug(q);
719                 q->request_fn(q);
720                 spin_unlock_irq(q->queue_lock);
721                 msleep(10);
722                 spin_lock_irq(q->queue_lock);
723                 elv_drain_elevator(q);
724         }
725
726         spin_unlock_irq(q->queue_lock);
727
728         /*
729          * unregister old elevator data
730          */
731         elv_unregister_queue(q);
732         old_elevator = q->elevator;
733
734         /*
735          * attach and start new elevator
736          */
737         if (elevator_attach(q, new_e, e))
738                 goto fail;
739
740         if (elv_register_queue(q))
741                 goto fail_register;
742
743         /*
744          * finally exit old elevator and turn off BYPASS.
745          */
746         elevator_exit(old_elevator);
747         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
748         return;
749
750 fail_register:
751         /*
752          * switch failed, exit the new io scheduler and reattach the old
753          * one again (along with re-adding the sysfs dir)
754          */
755         elevator_exit(e);
756         e = NULL;
757 fail:
758         q->elevator = old_elevator;
759         elv_register_queue(q);
760         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
761         kfree(e);
762 error:
763         elevator_put(new_e);
764         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
765 }
766
767 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
768 {
769         char elevator_name[ELV_NAME_MAX];
770         size_t len;
771         struct elevator_type *e;
772
773         elevator_name[sizeof(elevator_name) - 1] = '\0';
774         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
775         len = strlen(elevator_name);
776
777         if (len && elevator_name[len - 1] == '\n')
778                 elevator_name[len - 1] = '\0';
779
780         e = elevator_get(elevator_name);
781         if (!e) {
782                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
783                 return -EINVAL;
784         }
785
786         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
787                 elevator_put(e);
788                 return count;
789         }
790
791         elevator_switch(q, e);
792         return count;
793 }
794
795 ssize_t elv_iosched_show(request_queue_t *q, char *name)
796 {
797         elevator_t *e = q->elevator;
798         struct elevator_type *elv = e->elevator_type;
799         struct list_head *entry;
800         int len = 0;
801
802         spin_lock_irq(q->queue_lock);
803         list_for_each(entry, &elv_list) {
804                 struct elevator_type *__e;
805
806                 __e = list_entry(entry, struct elevator_type, list);
807                 if (!strcmp(elv->elevator_name, __e->elevator_name))
808                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
809                 else
810                         len += sprintf(name+len, "%s ", __e->elevator_name);
811         }
812         spin_unlock_irq(q->queue_lock);
813
814         len += sprintf(len+name, "\n");
815         return len;
816 }
817
818 EXPORT_SYMBOL(elv_dispatch_sort);
819 EXPORT_SYMBOL(elv_add_request);
820 EXPORT_SYMBOL(__elv_add_request);
821 EXPORT_SYMBOL(elv_requeue_request);
822 EXPORT_SYMBOL(elv_next_request);
823 EXPORT_SYMBOL(elv_dequeue_request);
824 EXPORT_SYMBOL(elv_queue_empty);
825 EXPORT_SYMBOL(elv_completed_request);
826 EXPORT_SYMBOL(elevator_exit);
827 EXPORT_SYMBOL(elevator_init);