[PATCH] b44: update version to 1.01
[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 #include <linux/blktrace_api.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 static 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
85 static struct elevator_type *elevator_find(const char *name)
86 {
87         struct elevator_type *e = NULL;
88         struct list_head *entry;
89
90         list_for_each(entry, &elv_list) {
91                 struct elevator_type *__e;
92
93                 __e = list_entry(entry, struct elevator_type, list);
94
95                 if (!strcmp(__e->elevator_name, name)) {
96                         e = __e;
97                         break;
98                 }
99         }
100
101         return e;
102 }
103
104 static void elevator_put(struct elevator_type *e)
105 {
106         module_put(e->elevator_owner);
107 }
108
109 static struct elevator_type *elevator_get(const char *name)
110 {
111         struct elevator_type *e;
112
113         spin_lock_irq(&elv_list_lock);
114
115         e = elevator_find(name);
116         if (e && !try_module_get(e->elevator_owner))
117                 e = NULL;
118
119         spin_unlock_irq(&elv_list_lock);
120
121         return e;
122 }
123
124 static void *elevator_init_queue(request_queue_t *q, struct elevator_queue *eq)
125 {
126         return eq->ops->elevator_init_fn(q, eq);
127 }
128
129 static void elevator_attach(request_queue_t *q, struct elevator_queue *eq,
130                            void *data)
131 {
132         q->elevator = eq;
133         eq->elevator_data = data;
134 }
135
136 static char chosen_elevator[16];
137
138 static int __init elevator_setup(char *str)
139 {
140         /*
141          * Be backwards-compatible with previous kernels, so users
142          * won't get the wrong elevator.
143          */
144         if (!strcmp(str, "as"))
145                 strcpy(chosen_elevator, "anticipatory");
146         else
147                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
148         return 1;
149 }
150
151 __setup("elevator=", elevator_setup);
152
153 static struct kobj_type elv_ktype;
154
155 static elevator_t *elevator_alloc(struct elevator_type *e)
156 {
157         elevator_t *eq = kmalloc(sizeof(elevator_t), GFP_KERNEL);
158         if (eq) {
159                 memset(eq, 0, sizeof(*eq));
160                 eq->ops = &e->ops;
161                 eq->elevator_type = e;
162                 kobject_init(&eq->kobj);
163                 snprintf(eq->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
164                 eq->kobj.ktype = &elv_ktype;
165                 mutex_init(&eq->sysfs_lock);
166         } else {
167                 elevator_put(e);
168         }
169         return eq;
170 }
171
172 static void elevator_release(struct kobject *kobj)
173 {
174         elevator_t *e = container_of(kobj, elevator_t, kobj);
175         elevator_put(e->elevator_type);
176         kfree(e);
177 }
178
179 int elevator_init(request_queue_t *q, char *name)
180 {
181         struct elevator_type *e = NULL;
182         struct elevator_queue *eq;
183         int ret = 0;
184         void *data;
185
186         INIT_LIST_HEAD(&q->queue_head);
187         q->last_merge = NULL;
188         q->end_sector = 0;
189         q->boundary_rq = NULL;
190
191         if (name && !(e = elevator_get(name)))
192                 return -EINVAL;
193
194         if (!e && *chosen_elevator && !(e = elevator_get(chosen_elevator)))
195                 printk("I/O scheduler %s not found\n", chosen_elevator);
196
197         if (!e && !(e = elevator_get(CONFIG_DEFAULT_IOSCHED))) {
198                 printk("Default I/O scheduler not found, using no-op\n");
199                 e = elevator_get("noop");
200         }
201
202         eq = elevator_alloc(e);
203         if (!eq)
204                 return -ENOMEM;
205
206         data = elevator_init_queue(q, eq);
207         if (!data) {
208                 kobject_put(&eq->kobj);
209                 return -ENOMEM;
210         }
211
212         elevator_attach(q, eq, data);
213         return ret;
214 }
215
216 void elevator_exit(elevator_t *e)
217 {
218         mutex_lock(&e->sysfs_lock);
219         if (e->ops->elevator_exit_fn)
220                 e->ops->elevator_exit_fn(e);
221         e->ops = NULL;
222         mutex_unlock(&e->sysfs_lock);
223
224         kobject_put(&e->kobj);
225 }
226
227 /*
228  * Insert rq into dispatch queue of q.  Queue lock must be held on
229  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
230  * appended to the dispatch queue.  To be used by specific elevators.
231  */
232 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
233 {
234         sector_t boundary;
235         struct list_head *entry;
236
237         if (q->last_merge == rq)
238                 q->last_merge = NULL;
239         q->nr_sorted--;
240
241         boundary = q->end_sector;
242
243         list_for_each_prev(entry, &q->queue_head) {
244                 struct request *pos = list_entry_rq(entry);
245
246                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
247                         break;
248                 if (rq->sector >= boundary) {
249                         if (pos->sector < boundary)
250                                 continue;
251                 } else {
252                         if (pos->sector >= boundary)
253                                 break;
254                 }
255                 if (rq->sector >= pos->sector)
256                         break;
257         }
258
259         list_add(&rq->queuelist, entry);
260 }
261
262 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
263 {
264         elevator_t *e = q->elevator;
265         int ret;
266
267         if (q->last_merge) {
268                 ret = elv_try_merge(q->last_merge, bio);
269                 if (ret != ELEVATOR_NO_MERGE) {
270                         *req = q->last_merge;
271                         return ret;
272                 }
273         }
274
275         if (e->ops->elevator_merge_fn)
276                 return e->ops->elevator_merge_fn(q, req, bio);
277
278         return ELEVATOR_NO_MERGE;
279 }
280
281 void elv_merged_request(request_queue_t *q, struct request *rq)
282 {
283         elevator_t *e = q->elevator;
284
285         if (e->ops->elevator_merged_fn)
286                 e->ops->elevator_merged_fn(q, rq);
287
288         q->last_merge = rq;
289 }
290
291 void elv_merge_requests(request_queue_t *q, struct request *rq,
292                              struct request *next)
293 {
294         elevator_t *e = q->elevator;
295
296         if (e->ops->elevator_merge_req_fn)
297                 e->ops->elevator_merge_req_fn(q, rq, next);
298         q->nr_sorted--;
299
300         q->last_merge = rq;
301 }
302
303 void elv_requeue_request(request_queue_t *q, struct request *rq)
304 {
305         elevator_t *e = q->elevator;
306
307         /*
308          * it already went through dequeue, we need to decrement the
309          * in_flight count again
310          */
311         if (blk_account_rq(rq)) {
312                 q->in_flight--;
313                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
314                         e->ops->elevator_deactivate_req_fn(q, rq);
315         }
316
317         rq->flags &= ~REQ_STARTED;
318
319         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
320 }
321
322 static void elv_drain_elevator(request_queue_t *q)
323 {
324         static int printed;
325         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
326                 ;
327         if (q->nr_sorted == 0)
328                 return;
329         if (printed++ < 10) {
330                 printk(KERN_ERR "%s: forced dispatching is broken "
331                        "(nr_sorted=%u), please report this\n",
332                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
333         }
334 }
335
336 void elv_insert(request_queue_t *q, struct request *rq, int where)
337 {
338         struct list_head *pos;
339         unsigned ordseq;
340         int unplug_it = 1;
341
342         blk_add_trace_rq(q, rq, BLK_TA_INSERT);
343
344         rq->q = q;
345
346         switch (where) {
347         case ELEVATOR_INSERT_FRONT:
348                 rq->flags |= REQ_SOFTBARRIER;
349
350                 list_add(&rq->queuelist, &q->queue_head);
351                 break;
352
353         case ELEVATOR_INSERT_BACK:
354                 rq->flags |= REQ_SOFTBARRIER;
355                 elv_drain_elevator(q);
356                 list_add_tail(&rq->queuelist, &q->queue_head);
357                 /*
358                  * We kick the queue here for the following reasons.
359                  * - The elevator might have returned NULL previously
360                  *   to delay requests and returned them now.  As the
361                  *   queue wasn't empty before this request, ll_rw_blk
362                  *   won't run the queue on return, resulting in hang.
363                  * - Usually, back inserted requests won't be merged
364                  *   with anything.  There's no point in delaying queue
365                  *   processing.
366                  */
367                 blk_remove_plug(q);
368                 q->request_fn(q);
369                 break;
370
371         case ELEVATOR_INSERT_SORT:
372                 BUG_ON(!blk_fs_request(rq));
373                 rq->flags |= REQ_SORTED;
374                 q->nr_sorted++;
375                 if (q->last_merge == NULL && rq_mergeable(rq))
376                         q->last_merge = rq;
377                 /*
378                  * Some ioscheds (cfq) run q->request_fn directly, so
379                  * rq cannot be accessed after calling
380                  * elevator_add_req_fn.
381                  */
382                 q->elevator->ops->elevator_add_req_fn(q, rq);
383                 break;
384
385         case ELEVATOR_INSERT_REQUEUE:
386                 /*
387                  * If ordered flush isn't in progress, we do front
388                  * insertion; otherwise, requests should be requeued
389                  * in ordseq order.
390                  */
391                 rq->flags |= REQ_SOFTBARRIER;
392
393                 if (q->ordseq == 0) {
394                         list_add(&rq->queuelist, &q->queue_head);
395                         break;
396                 }
397
398                 ordseq = blk_ordered_req_seq(rq);
399
400                 list_for_each(pos, &q->queue_head) {
401                         struct request *pos_rq = list_entry_rq(pos);
402                         if (ordseq <= blk_ordered_req_seq(pos_rq))
403                                 break;
404                 }
405
406                 list_add_tail(&rq->queuelist, pos);
407                 /*
408                  * most requeues happen because of a busy condition, don't
409                  * force unplug of the queue for that case.
410                  */
411                 unplug_it = 0;
412                 break;
413
414         default:
415                 printk(KERN_ERR "%s: bad insertion point %d\n",
416                        __FUNCTION__, where);
417                 BUG();
418         }
419
420         if (unplug_it && blk_queue_plugged(q)) {
421                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
422                         - q->in_flight;
423
424                 if (nrq >= q->unplug_thresh)
425                         __generic_unplug_device(q);
426         }
427 }
428
429 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
430                        int plug)
431 {
432         if (q->ordcolor)
433                 rq->flags |= REQ_ORDERED_COLOR;
434
435         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
436                 /*
437                  * toggle ordered color
438                  */
439                 if (blk_barrier_rq(rq))
440                         q->ordcolor ^= 1;
441
442                 /*
443                  * barriers implicitly indicate back insertion
444                  */
445                 if (where == ELEVATOR_INSERT_SORT)
446                         where = ELEVATOR_INSERT_BACK;
447
448                 /*
449                  * this request is scheduling boundary, update
450                  * end_sector
451                  */
452                 if (blk_fs_request(rq)) {
453                         q->end_sector = rq_end_sector(rq);
454                         q->boundary_rq = rq;
455                 }
456         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
457                 where = ELEVATOR_INSERT_BACK;
458
459         if (plug)
460                 blk_plug_device(q);
461
462         elv_insert(q, rq, where);
463 }
464
465 void elv_add_request(request_queue_t *q, struct request *rq, int where,
466                      int plug)
467 {
468         unsigned long flags;
469
470         spin_lock_irqsave(q->queue_lock, flags);
471         __elv_add_request(q, rq, where, plug);
472         spin_unlock_irqrestore(q->queue_lock, flags);
473 }
474
475 static inline struct request *__elv_next_request(request_queue_t *q)
476 {
477         struct request *rq;
478
479         while (1) {
480                 while (!list_empty(&q->queue_head)) {
481                         rq = list_entry_rq(q->queue_head.next);
482                         if (blk_do_ordered(q, &rq))
483                                 return rq;
484                 }
485
486                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
487                         return NULL;
488         }
489 }
490
491 struct request *elv_next_request(request_queue_t *q)
492 {
493         struct request *rq;
494         int ret;
495
496         while ((rq = __elv_next_request(q)) != NULL) {
497                 if (!(rq->flags & REQ_STARTED)) {
498                         elevator_t *e = q->elevator;
499
500                         /*
501                          * This is the first time the device driver
502                          * sees this request (possibly after
503                          * requeueing).  Notify IO scheduler.
504                          */
505                         if (blk_sorted_rq(rq) &&
506                             e->ops->elevator_activate_req_fn)
507                                 e->ops->elevator_activate_req_fn(q, rq);
508
509                         /*
510                          * just mark as started even if we don't start
511                          * it, a request that has been delayed should
512                          * not be passed by new incoming requests
513                          */
514                         rq->flags |= REQ_STARTED;
515                         blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
516                 }
517
518                 if (!q->boundary_rq || q->boundary_rq == rq) {
519                         q->end_sector = rq_end_sector(rq);
520                         q->boundary_rq = NULL;
521                 }
522
523                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
524                         break;
525
526                 ret = q->prep_rq_fn(q, rq);
527                 if (ret == BLKPREP_OK) {
528                         break;
529                 } else if (ret == BLKPREP_DEFER) {
530                         /*
531                          * the request may have been (partially) prepped.
532                          * we need to keep this request in the front to
533                          * avoid resource deadlock.  REQ_STARTED will
534                          * prevent other fs requests from passing this one.
535                          */
536                         rq = NULL;
537                         break;
538                 } else if (ret == BLKPREP_KILL) {
539                         int nr_bytes = rq->hard_nr_sectors << 9;
540
541                         if (!nr_bytes)
542                                 nr_bytes = rq->data_len;
543
544                         blkdev_dequeue_request(rq);
545                         rq->flags |= REQ_QUIET;
546                         end_that_request_chunk(rq, 0, nr_bytes);
547                         end_that_request_last(rq, 0);
548                 } else {
549                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
550                                                                 ret);
551                         break;
552                 }
553         }
554
555         return rq;
556 }
557
558 void elv_dequeue_request(request_queue_t *q, struct request *rq)
559 {
560         BUG_ON(list_empty(&rq->queuelist));
561
562         list_del_init(&rq->queuelist);
563
564         /*
565          * the time frame between a request being removed from the lists
566          * and to it is freed is accounted as io that is in progress at
567          * the driver side.
568          */
569         if (blk_account_rq(rq))
570                 q->in_flight++;
571 }
572
573 int elv_queue_empty(request_queue_t *q)
574 {
575         elevator_t *e = q->elevator;
576
577         if (!list_empty(&q->queue_head))
578                 return 0;
579
580         if (e->ops->elevator_queue_empty_fn)
581                 return e->ops->elevator_queue_empty_fn(q);
582
583         return 1;
584 }
585
586 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
587 {
588         elevator_t *e = q->elevator;
589
590         if (e->ops->elevator_latter_req_fn)
591                 return e->ops->elevator_latter_req_fn(q, rq);
592         return NULL;
593 }
594
595 struct request *elv_former_request(request_queue_t *q, struct request *rq)
596 {
597         elevator_t *e = q->elevator;
598
599         if (e->ops->elevator_former_req_fn)
600                 return e->ops->elevator_former_req_fn(q, rq);
601         return NULL;
602 }
603
604 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
605                     gfp_t gfp_mask)
606 {
607         elevator_t *e = q->elevator;
608
609         if (e->ops->elevator_set_req_fn)
610                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
611
612         rq->elevator_private = NULL;
613         return 0;
614 }
615
616 void elv_put_request(request_queue_t *q, struct request *rq)
617 {
618         elevator_t *e = q->elevator;
619
620         if (e->ops->elevator_put_req_fn)
621                 e->ops->elevator_put_req_fn(q, rq);
622 }
623
624 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
625 {
626         elevator_t *e = q->elevator;
627
628         if (e->ops->elevator_may_queue_fn)
629                 return e->ops->elevator_may_queue_fn(q, rw, bio);
630
631         return ELV_MQUEUE_MAY;
632 }
633
634 void elv_completed_request(request_queue_t *q, struct request *rq)
635 {
636         elevator_t *e = q->elevator;
637
638         /*
639          * request is released from the driver, io must be done
640          */
641         if (blk_account_rq(rq)) {
642                 q->in_flight--;
643                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
644                         e->ops->elevator_completed_req_fn(q, rq);
645         }
646
647         /*
648          * Check if the queue is waiting for fs requests to be
649          * drained for flush sequence.
650          */
651         if (unlikely(q->ordseq)) {
652                 struct request *first_rq = list_entry_rq(q->queue_head.next);
653                 if (q->in_flight == 0 &&
654                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
655                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
656                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
657                         q->request_fn(q);
658                 }
659         }
660 }
661
662 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
663
664 static ssize_t
665 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
666 {
667         elevator_t *e = container_of(kobj, elevator_t, kobj);
668         struct elv_fs_entry *entry = to_elv(attr);
669         ssize_t error;
670
671         if (!entry->show)
672                 return -EIO;
673
674         mutex_lock(&e->sysfs_lock);
675         error = e->ops ? entry->show(e, page) : -ENOENT;
676         mutex_unlock(&e->sysfs_lock);
677         return error;
678 }
679
680 static ssize_t
681 elv_attr_store(struct kobject *kobj, struct attribute *attr,
682                const char *page, size_t length)
683 {
684         elevator_t *e = container_of(kobj, elevator_t, kobj);
685         struct elv_fs_entry *entry = to_elv(attr);
686         ssize_t error;
687
688         if (!entry->store)
689                 return -EIO;
690
691         mutex_lock(&e->sysfs_lock);
692         error = e->ops ? entry->store(e, page, length) : -ENOENT;
693         mutex_unlock(&e->sysfs_lock);
694         return error;
695 }
696
697 static struct sysfs_ops elv_sysfs_ops = {
698         .show   = elv_attr_show,
699         .store  = elv_attr_store,
700 };
701
702 static struct kobj_type elv_ktype = {
703         .sysfs_ops      = &elv_sysfs_ops,
704         .release        = elevator_release,
705 };
706
707 int elv_register_queue(struct request_queue *q)
708 {
709         elevator_t *e = q->elevator;
710         int error;
711
712         e->kobj.parent = &q->kobj;
713
714         error = kobject_add(&e->kobj);
715         if (!error) {
716                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
717                 if (attr) {
718                         while (attr->attr.name) {
719                                 if (sysfs_create_file(&e->kobj, &attr->attr))
720                                         break;
721                                 attr++;
722                         }
723                 }
724                 kobject_uevent(&e->kobj, KOBJ_ADD);
725         }
726         return error;
727 }
728
729 static void __elv_unregister_queue(elevator_t *e)
730 {
731         kobject_uevent(&e->kobj, KOBJ_REMOVE);
732         kobject_del(&e->kobj);
733 }
734
735 void elv_unregister_queue(struct request_queue *q)
736 {
737         if (q)
738                 __elv_unregister_queue(q->elevator);
739 }
740
741 int elv_register(struct elevator_type *e)
742 {
743         spin_lock_irq(&elv_list_lock);
744         BUG_ON(elevator_find(e->elevator_name));
745         list_add_tail(&e->list, &elv_list);
746         spin_unlock_irq(&elv_list_lock);
747
748         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
749         if (!strcmp(e->elevator_name, chosen_elevator) ||
750                         (!*chosen_elevator &&
751                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
752                                 printk(" (default)");
753         printk("\n");
754         return 0;
755 }
756 EXPORT_SYMBOL_GPL(elv_register);
757
758 void elv_unregister(struct elevator_type *e)
759 {
760         struct task_struct *g, *p;
761
762         /*
763          * Iterate every thread in the process to remove the io contexts.
764          */
765         if (e->ops.trim) {
766                 read_lock(&tasklist_lock);
767                 do_each_thread(g, p) {
768                         task_lock(p);
769                         e->ops.trim(p->io_context);
770                         task_unlock(p);
771                 } while_each_thread(g, p);
772                 read_unlock(&tasklist_lock);
773         }
774
775         spin_lock_irq(&elv_list_lock);
776         list_del_init(&e->list);
777         spin_unlock_irq(&elv_list_lock);
778 }
779 EXPORT_SYMBOL_GPL(elv_unregister);
780
781 /*
782  * switch to new_e io scheduler. be careful not to introduce deadlocks -
783  * we don't free the old io scheduler, before we have allocated what we
784  * need for the new one. this way we have a chance of going back to the old
785  * one, if the new one fails init for some reason.
786  */
787 static int elevator_switch(request_queue_t *q, struct elevator_type *new_e)
788 {
789         elevator_t *old_elevator, *e;
790         void *data;
791
792         /*
793          * Allocate new elevator
794          */
795         e = elevator_alloc(new_e);
796         if (!e)
797                 return 0;
798
799         data = elevator_init_queue(q, e);
800         if (!data) {
801                 kobject_put(&e->kobj);
802                 return 0;
803         }
804
805         /*
806          * Turn on BYPASS and drain all requests w/ elevator private data
807          */
808         spin_lock_irq(q->queue_lock);
809
810         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
811
812         elv_drain_elevator(q);
813
814         while (q->rq.elvpriv) {
815                 blk_remove_plug(q);
816                 q->request_fn(q);
817                 spin_unlock_irq(q->queue_lock);
818                 msleep(10);
819                 spin_lock_irq(q->queue_lock);
820                 elv_drain_elevator(q);
821         }
822
823         /*
824          * Remember old elevator.
825          */
826         old_elevator = q->elevator;
827
828         /*
829          * attach and start new elevator
830          */
831         elevator_attach(q, e, data);
832
833         spin_unlock_irq(q->queue_lock);
834
835         __elv_unregister_queue(old_elevator);
836
837         if (elv_register_queue(q))
838                 goto fail_register;
839
840         /*
841          * finally exit old elevator and turn off BYPASS.
842          */
843         elevator_exit(old_elevator);
844         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
845         return 1;
846
847 fail_register:
848         /*
849          * switch failed, exit the new io scheduler and reattach the old
850          * one again (along with re-adding the sysfs dir)
851          */
852         elevator_exit(e);
853         e = NULL;
854         q->elevator = old_elevator;
855         elv_register_queue(q);
856         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
857         if (e)
858                 kobject_put(&e->kobj);
859         return 0;
860 }
861
862 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
863 {
864         char elevator_name[ELV_NAME_MAX];
865         size_t len;
866         struct elevator_type *e;
867
868         elevator_name[sizeof(elevator_name) - 1] = '\0';
869         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
870         len = strlen(elevator_name);
871
872         if (len && elevator_name[len - 1] == '\n')
873                 elevator_name[len - 1] = '\0';
874
875         e = elevator_get(elevator_name);
876         if (!e) {
877                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
878                 return -EINVAL;
879         }
880
881         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
882                 elevator_put(e);
883                 return count;
884         }
885
886         if (!elevator_switch(q, e))
887                 printk(KERN_ERR "elevator: switch to %s failed\n",elevator_name);
888         return count;
889 }
890
891 ssize_t elv_iosched_show(request_queue_t *q, char *name)
892 {
893         elevator_t *e = q->elevator;
894         struct elevator_type *elv = e->elevator_type;
895         struct list_head *entry;
896         int len = 0;
897
898         spin_lock_irq(q->queue_lock);
899         list_for_each(entry, &elv_list) {
900                 struct elevator_type *__e;
901
902                 __e = list_entry(entry, struct elevator_type, list);
903                 if (!strcmp(elv->elevator_name, __e->elevator_name))
904                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
905                 else
906                         len += sprintf(name+len, "%s ", __e->elevator_name);
907         }
908         spin_unlock_irq(q->queue_lock);
909
910         len += sprintf(len+name, "\n");
911         return len;
912 }
913
914 EXPORT_SYMBOL(elv_dispatch_sort);
915 EXPORT_SYMBOL(elv_add_request);
916 EXPORT_SYMBOL(__elv_add_request);
917 EXPORT_SYMBOL(elv_next_request);
918 EXPORT_SYMBOL(elv_dequeue_request);
919 EXPORT_SYMBOL(elv_queue_empty);
920 EXPORT_SYMBOL(elevator_exit);
921 EXPORT_SYMBOL(elevator_init);