ed6f8f32d27ee8d09f5c3673852d416bad228862
[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@kernel.dk> :
7  *
8  * Split the elevator a bit so that it is possible to choose a different
9  * one or even write a new "plug in". There are three pieces:
10  * - elevator_fn, inserts a new request in the queue list
11  * - elevator_merge_fn, decides whether a new buffer can be merged with
12  *   an existing request
13  * - elevator_dequeue_fn, called when a request is taken off the active list
14  *
15  * 20082000 Dave Jones <davej@suse.de> :
16  * Removed tests for max-bomb-segments, which was breaking elvtune
17  *  when run without -bN
18  *
19  * Jens:
20  * - Rework again to work with bio instead of buffer_heads
21  * - loose bi_dev comparisons, partition handling is right now
22  * - completely modularize elevator setup and teardown
23  *
24  */
25 #include <linux/kernel.h>
26 #include <linux/fs.h>
27 #include <linux/blkdev.h>
28 #include <linux/elevator.h>
29 #include <linux/bio.h>
30 #include <linux/module.h>
31 #include <linux/slab.h>
32 #include <linux/init.h>
33 #include <linux/compiler.h>
34 #include <linux/delay.h>
35 #include <linux/blktrace_api.h>
36 #include <linux/hash.h>
37
38 #include <asm/uaccess.h>
39
40 static DEFINE_SPINLOCK(elv_list_lock);
41 static LIST_HEAD(elv_list);
42
43 /*
44  * Merge hash stuff.
45  */
46 static const int elv_hash_shift = 6;
47 #define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
48 #define ELV_HASH_FN(sec)        \
49                 (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
50 #define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
51 #define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
52 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
53
54 /*
55  * Query io scheduler to see if the current process issuing bio may be
56  * merged with rq.
57  */
58 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
59 {
60         struct request_queue *q = rq->q;
61         elevator_t *e = q->elevator;
62
63         if (e->ops->elevator_allow_merge_fn)
64                 return e->ops->elevator_allow_merge_fn(q, rq, bio);
65
66         return 1;
67 }
68
69 /*
70  * can we safely merge with this request?
71  */
72 int elv_rq_merge_ok(struct request *rq, struct bio *bio)
73 {
74         if (!rq_mergeable(rq))
75                 return 0;
76
77         /*
78          * different data direction or already started, don't merge
79          */
80         if (bio_data_dir(bio) != rq_data_dir(rq))
81                 return 0;
82
83         /*
84          * must be same device and not a special request
85          */
86         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
87                 return 0;
88
89         /*
90          * only merge integrity protected bio into ditto rq
91          */
92         if (bio_integrity(bio) != blk_integrity_rq(rq))
93                 return 0;
94
95         if (!elv_iosched_allow_merge(rq, bio))
96                 return 0;
97
98         return 1;
99 }
100 EXPORT_SYMBOL(elv_rq_merge_ok);
101
102 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
103 {
104         int ret = ELEVATOR_NO_MERGE;
105
106         /*
107          * we can merge and sequence is ok, check if it's possible
108          */
109         if (elv_rq_merge_ok(__rq, bio)) {
110                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
111                         ret = ELEVATOR_BACK_MERGE;
112                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
113                         ret = ELEVATOR_FRONT_MERGE;
114         }
115
116         return ret;
117 }
118
119 static struct elevator_type *elevator_find(const char *name)
120 {
121         struct elevator_type *e;
122
123         list_for_each_entry(e, &elv_list, list) {
124                 if (!strcmp(e->elevator_name, name))
125                         return e;
126         }
127
128         return NULL;
129 }
130
131 static void elevator_put(struct elevator_type *e)
132 {
133         module_put(e->elevator_owner);
134 }
135
136 static struct elevator_type *elevator_get(const char *name)
137 {
138         struct elevator_type *e;
139
140         spin_lock(&elv_list_lock);
141
142         e = elevator_find(name);
143         if (!e) {
144                 char elv[ELV_NAME_MAX + strlen("-iosched")];
145
146                 spin_unlock(&elv_list_lock);
147
148                 if (!strcmp(name, "anticipatory"))
149                         sprintf(elv, "as-iosched");
150                 else
151                         sprintf(elv, "%s-iosched", name);
152
153                 request_module("%s", elv);
154                 spin_lock(&elv_list_lock);
155                 e = elevator_find(name);
156         }
157
158         if (e && !try_module_get(e->elevator_owner))
159                 e = NULL;
160
161         spin_unlock(&elv_list_lock);
162
163         return e;
164 }
165
166 static void *elevator_init_queue(struct request_queue *q,
167                                  struct elevator_queue *eq)
168 {
169         return eq->ops->elevator_init_fn(q);
170 }
171
172 static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
173                            void *data)
174 {
175         q->elevator = eq;
176         eq->elevator_data = data;
177 }
178
179 static char chosen_elevator[16];
180
181 static int __init elevator_setup(char *str)
182 {
183         /*
184          * Be backwards-compatible with previous kernels, so users
185          * won't get the wrong elevator.
186          */
187         if (!strcmp(str, "as"))
188                 strcpy(chosen_elevator, "anticipatory");
189         else
190                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
191         return 1;
192 }
193
194 __setup("elevator=", elevator_setup);
195
196 static struct kobj_type elv_ktype;
197
198 static elevator_t *elevator_alloc(struct request_queue *q,
199                                   struct elevator_type *e)
200 {
201         elevator_t *eq;
202         int i;
203
204         eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL | __GFP_ZERO, q->node);
205         if (unlikely(!eq))
206                 goto err;
207
208         eq->ops = &e->ops;
209         eq->elevator_type = e;
210         kobject_init(&eq->kobj, &elv_ktype);
211         mutex_init(&eq->sysfs_lock);
212
213         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
214                                         GFP_KERNEL, q->node);
215         if (!eq->hash)
216                 goto err;
217
218         for (i = 0; i < ELV_HASH_ENTRIES; i++)
219                 INIT_HLIST_HEAD(&eq->hash[i]);
220
221         return eq;
222 err:
223         kfree(eq);
224         elevator_put(e);
225         return NULL;
226 }
227
228 static void elevator_release(struct kobject *kobj)
229 {
230         elevator_t *e = container_of(kobj, elevator_t, kobj);
231
232         elevator_put(e->elevator_type);
233         kfree(e->hash);
234         kfree(e);
235 }
236
237 int elevator_init(struct request_queue *q, char *name)
238 {
239         struct elevator_type *e = NULL;
240         struct elevator_queue *eq;
241         int ret = 0;
242         void *data;
243
244         INIT_LIST_HEAD(&q->queue_head);
245         q->last_merge = NULL;
246         q->end_sector = 0;
247         q->boundary_rq = NULL;
248
249         if (name) {
250                 e = elevator_get(name);
251                 if (!e)
252                         return -EINVAL;
253         }
254
255         if (!e && *chosen_elevator) {
256                 e = elevator_get(chosen_elevator);
257                 if (!e)
258                         printk(KERN_ERR "I/O scheduler %s not found\n",
259                                                         chosen_elevator);
260         }
261
262         if (!e) {
263                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
264                 if (!e) {
265                         printk(KERN_ERR
266                                 "Default I/O scheduler not found. " \
267                                 "Using noop.\n");
268                         e = elevator_get("noop");
269                 }
270         }
271
272         eq = elevator_alloc(q, e);
273         if (!eq)
274                 return -ENOMEM;
275
276         data = elevator_init_queue(q, eq);
277         if (!data) {
278                 kobject_put(&eq->kobj);
279                 return -ENOMEM;
280         }
281
282         elevator_attach(q, eq, data);
283         return ret;
284 }
285 EXPORT_SYMBOL(elevator_init);
286
287 void elevator_exit(elevator_t *e)
288 {
289         mutex_lock(&e->sysfs_lock);
290         if (e->ops->elevator_exit_fn)
291                 e->ops->elevator_exit_fn(e);
292         e->ops = NULL;
293         mutex_unlock(&e->sysfs_lock);
294
295         kobject_put(&e->kobj);
296 }
297 EXPORT_SYMBOL(elevator_exit);
298
299 static void elv_activate_rq(struct request_queue *q, struct request *rq)
300 {
301         elevator_t *e = q->elevator;
302
303         if (e->ops->elevator_activate_req_fn)
304                 e->ops->elevator_activate_req_fn(q, rq);
305 }
306
307 static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
308 {
309         elevator_t *e = q->elevator;
310
311         if (e->ops->elevator_deactivate_req_fn)
312                 e->ops->elevator_deactivate_req_fn(q, rq);
313 }
314
315 static inline void __elv_rqhash_del(struct request *rq)
316 {
317         hlist_del_init(&rq->hash);
318 }
319
320 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
321 {
322         if (ELV_ON_HASH(rq))
323                 __elv_rqhash_del(rq);
324 }
325
326 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
327 {
328         elevator_t *e = q->elevator;
329
330         BUG_ON(ELV_ON_HASH(rq));
331         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
332 }
333
334 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
335 {
336         __elv_rqhash_del(rq);
337         elv_rqhash_add(q, rq);
338 }
339
340 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
341 {
342         elevator_t *e = q->elevator;
343         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
344         struct hlist_node *entry, *next;
345         struct request *rq;
346
347         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
348                 BUG_ON(!ELV_ON_HASH(rq));
349
350                 if (unlikely(!rq_mergeable(rq))) {
351                         __elv_rqhash_del(rq);
352                         continue;
353                 }
354
355                 if (rq_hash_key(rq) == offset)
356                         return rq;
357         }
358
359         return NULL;
360 }
361
362 /*
363  * RB-tree support functions for inserting/lookup/removal of requests
364  * in a sorted RB tree.
365  */
366 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
367 {
368         struct rb_node **p = &root->rb_node;
369         struct rb_node *parent = NULL;
370         struct request *__rq;
371
372         while (*p) {
373                 parent = *p;
374                 __rq = rb_entry(parent, struct request, rb_node);
375
376                 if (rq->sector < __rq->sector)
377                         p = &(*p)->rb_left;
378                 else if (rq->sector > __rq->sector)
379                         p = &(*p)->rb_right;
380                 else
381                         return __rq;
382         }
383
384         rb_link_node(&rq->rb_node, parent, p);
385         rb_insert_color(&rq->rb_node, root);
386         return NULL;
387 }
388 EXPORT_SYMBOL(elv_rb_add);
389
390 void elv_rb_del(struct rb_root *root, struct request *rq)
391 {
392         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
393         rb_erase(&rq->rb_node, root);
394         RB_CLEAR_NODE(&rq->rb_node);
395 }
396 EXPORT_SYMBOL(elv_rb_del);
397
398 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
399 {
400         struct rb_node *n = root->rb_node;
401         struct request *rq;
402
403         while (n) {
404                 rq = rb_entry(n, struct request, rb_node);
405
406                 if (sector < rq->sector)
407                         n = n->rb_left;
408                 else if (sector > rq->sector)
409                         n = n->rb_right;
410                 else
411                         return rq;
412         }
413
414         return NULL;
415 }
416 EXPORT_SYMBOL(elv_rb_find);
417
418 /*
419  * Insert rq into dispatch queue of q.  Queue lock must be held on
420  * entry.  rq is sort instead into the dispatch queue. To be used by
421  * specific elevators.
422  */
423 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
424 {
425         sector_t boundary;
426         struct list_head *entry;
427         int stop_flags;
428
429         if (q->last_merge == rq)
430                 q->last_merge = NULL;
431
432         elv_rqhash_del(q, rq);
433
434         q->nr_sorted--;
435
436         boundary = q->end_sector;
437         stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
438         list_for_each_prev(entry, &q->queue_head) {
439                 struct request *pos = list_entry_rq(entry);
440
441                 if (rq_data_dir(rq) != rq_data_dir(pos))
442                         break;
443                 if (pos->cmd_flags & stop_flags)
444                         break;
445                 if (rq->sector >= boundary) {
446                         if (pos->sector < boundary)
447                                 continue;
448                 } else {
449                         if (pos->sector >= boundary)
450                                 break;
451                 }
452                 if (rq->sector >= pos->sector)
453                         break;
454         }
455
456         list_add(&rq->queuelist, entry);
457 }
458 EXPORT_SYMBOL(elv_dispatch_sort);
459
460 /*
461  * Insert rq into dispatch queue of q.  Queue lock must be held on
462  * entry.  rq is added to the back of the dispatch queue. To be used by
463  * specific elevators.
464  */
465 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
466 {
467         if (q->last_merge == rq)
468                 q->last_merge = NULL;
469
470         elv_rqhash_del(q, rq);
471
472         q->nr_sorted--;
473
474         q->end_sector = rq_end_sector(rq);
475         q->boundary_rq = rq;
476         list_add_tail(&rq->queuelist, &q->queue_head);
477 }
478 EXPORT_SYMBOL(elv_dispatch_add_tail);
479
480 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
481 {
482         elevator_t *e = q->elevator;
483         struct request *__rq;
484         int ret;
485
486         /*
487          * First try one-hit cache.
488          */
489         if (q->last_merge) {
490                 ret = elv_try_merge(q->last_merge, bio);
491                 if (ret != ELEVATOR_NO_MERGE) {
492                         *req = q->last_merge;
493                         return ret;
494                 }
495         }
496
497         if (blk_queue_nomerges(q))
498                 return ELEVATOR_NO_MERGE;
499
500         /*
501          * See if our hash lookup can find a potential backmerge.
502          */
503         __rq = elv_rqhash_find(q, bio->bi_sector);
504         if (__rq && elv_rq_merge_ok(__rq, bio)) {
505                 *req = __rq;
506                 return ELEVATOR_BACK_MERGE;
507         }
508
509         if (e->ops->elevator_merge_fn)
510                 return e->ops->elevator_merge_fn(q, req, bio);
511
512         return ELEVATOR_NO_MERGE;
513 }
514
515 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
516 {
517         elevator_t *e = q->elevator;
518
519         if (e->ops->elevator_merged_fn)
520                 e->ops->elevator_merged_fn(q, rq, type);
521
522         if (type == ELEVATOR_BACK_MERGE)
523                 elv_rqhash_reposition(q, rq);
524
525         q->last_merge = rq;
526 }
527
528 void elv_merge_requests(struct request_queue *q, struct request *rq,
529                              struct request *next)
530 {
531         elevator_t *e = q->elevator;
532
533         if (e->ops->elevator_merge_req_fn)
534                 e->ops->elevator_merge_req_fn(q, rq, next);
535
536         elv_rqhash_reposition(q, rq);
537         elv_rqhash_del(q, next);
538
539         q->nr_sorted--;
540         q->last_merge = rq;
541 }
542
543 void elv_requeue_request(struct request_queue *q, struct request *rq)
544 {
545         /*
546          * it already went through dequeue, we need to decrement the
547          * in_flight count again
548          */
549         if (blk_account_rq(rq)) {
550                 q->in_flight--;
551                 if (blk_sorted_rq(rq))
552                         elv_deactivate_rq(q, rq);
553         }
554
555         rq->cmd_flags &= ~REQ_STARTED;
556
557         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
558 }
559
560 static void elv_drain_elevator(struct request_queue *q)
561 {
562         static int printed;
563         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
564                 ;
565         if (q->nr_sorted == 0)
566                 return;
567         if (printed++ < 10) {
568                 printk(KERN_ERR "%s: forced dispatching is broken "
569                        "(nr_sorted=%u), please report this\n",
570                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
571         }
572 }
573
574 void elv_insert(struct request_queue *q, struct request *rq, int where)
575 {
576         struct list_head *pos;
577         unsigned ordseq;
578         int unplug_it = 1;
579
580         blk_add_trace_rq(q, rq, BLK_TA_INSERT);
581
582         rq->q = q;
583
584         switch (where) {
585         case ELEVATOR_INSERT_FRONT:
586                 rq->cmd_flags |= REQ_SOFTBARRIER;
587
588                 list_add(&rq->queuelist, &q->queue_head);
589                 break;
590
591         case ELEVATOR_INSERT_BACK:
592                 rq->cmd_flags |= REQ_SOFTBARRIER;
593                 elv_drain_elevator(q);
594                 list_add_tail(&rq->queuelist, &q->queue_head);
595                 /*
596                  * We kick the queue here for the following reasons.
597                  * - The elevator might have returned NULL previously
598                  *   to delay requests and returned them now.  As the
599                  *   queue wasn't empty before this request, ll_rw_blk
600                  *   won't run the queue on return, resulting in hang.
601                  * - Usually, back inserted requests won't be merged
602                  *   with anything.  There's no point in delaying queue
603                  *   processing.
604                  */
605                 blk_remove_plug(q);
606                 q->request_fn(q);
607                 break;
608
609         case ELEVATOR_INSERT_SORT:
610                 BUG_ON(!blk_fs_request(rq));
611                 rq->cmd_flags |= REQ_SORTED;
612                 q->nr_sorted++;
613                 if (rq_mergeable(rq)) {
614                         elv_rqhash_add(q, rq);
615                         if (!q->last_merge)
616                                 q->last_merge = rq;
617                 }
618
619                 /*
620                  * Some ioscheds (cfq) run q->request_fn directly, so
621                  * rq cannot be accessed after calling
622                  * elevator_add_req_fn.
623                  */
624                 q->elevator->ops->elevator_add_req_fn(q, rq);
625                 break;
626
627         case ELEVATOR_INSERT_REQUEUE:
628                 /*
629                  * If ordered flush isn't in progress, we do front
630                  * insertion; otherwise, requests should be requeued
631                  * in ordseq order.
632                  */
633                 rq->cmd_flags |= REQ_SOFTBARRIER;
634
635                 /*
636                  * Most requeues happen because of a busy condition,
637                  * don't force unplug of the queue for that case.
638                  */
639                 unplug_it = 0;
640
641                 if (q->ordseq == 0) {
642                         list_add(&rq->queuelist, &q->queue_head);
643                         break;
644                 }
645
646                 ordseq = blk_ordered_req_seq(rq);
647
648                 list_for_each(pos, &q->queue_head) {
649                         struct request *pos_rq = list_entry_rq(pos);
650                         if (ordseq <= blk_ordered_req_seq(pos_rq))
651                                 break;
652                 }
653
654                 list_add_tail(&rq->queuelist, pos);
655                 break;
656
657         default:
658                 printk(KERN_ERR "%s: bad insertion point %d\n",
659                        __func__, where);
660                 BUG();
661         }
662
663         if (unplug_it && blk_queue_plugged(q)) {
664                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
665                         - q->in_flight;
666
667                 if (nrq >= q->unplug_thresh)
668                         __generic_unplug_device(q);
669         }
670 }
671
672 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
673                        int plug)
674 {
675         if (q->ordcolor)
676                 rq->cmd_flags |= REQ_ORDERED_COLOR;
677
678         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
679                 /*
680                  * toggle ordered color
681                  */
682                 if (blk_barrier_rq(rq))
683                         q->ordcolor ^= 1;
684
685                 /*
686                  * barriers implicitly indicate back insertion
687                  */
688                 if (where == ELEVATOR_INSERT_SORT)
689                         where = ELEVATOR_INSERT_BACK;
690
691                 /*
692                  * this request is scheduling boundary, update
693                  * end_sector
694                  */
695                 if (blk_fs_request(rq)) {
696                         q->end_sector = rq_end_sector(rq);
697                         q->boundary_rq = rq;
698                 }
699         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
700                     where == ELEVATOR_INSERT_SORT)
701                 where = ELEVATOR_INSERT_BACK;
702
703         if (plug)
704                 blk_plug_device(q);
705
706         elv_insert(q, rq, where);
707 }
708 EXPORT_SYMBOL(__elv_add_request);
709
710 void elv_add_request(struct request_queue *q, struct request *rq, int where,
711                      int plug)
712 {
713         unsigned long flags;
714
715         spin_lock_irqsave(q->queue_lock, flags);
716         __elv_add_request(q, rq, where, plug);
717         spin_unlock_irqrestore(q->queue_lock, flags);
718 }
719 EXPORT_SYMBOL(elv_add_request);
720
721 static inline struct request *__elv_next_request(struct request_queue *q)
722 {
723         struct request *rq;
724
725         while (1) {
726                 while (!list_empty(&q->queue_head)) {
727                         rq = list_entry_rq(q->queue_head.next);
728                         if (blk_do_ordered(q, &rq))
729                                 return rq;
730                 }
731
732                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
733                         return NULL;
734         }
735 }
736
737 struct request *elv_next_request(struct request_queue *q)
738 {
739         struct request *rq;
740         int ret;
741
742         while ((rq = __elv_next_request(q)) != NULL) {
743                 /*
744                  * Kill the empty barrier place holder, the driver must
745                  * not ever see it.
746                  */
747                 if (blk_empty_barrier(rq)) {
748                         end_queued_request(rq, 1);
749                         continue;
750                 }
751                 if (!(rq->cmd_flags & REQ_STARTED)) {
752                         /*
753                          * This is the first time the device driver
754                          * sees this request (possibly after
755                          * requeueing).  Notify IO scheduler.
756                          */
757                         if (blk_sorted_rq(rq))
758                                 elv_activate_rq(q, rq);
759
760                         /*
761                          * just mark as started even if we don't start
762                          * it, a request that has been delayed should
763                          * not be passed by new incoming requests
764                          */
765                         rq->cmd_flags |= REQ_STARTED;
766                         blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
767                 }
768
769                 if (!q->boundary_rq || q->boundary_rq == rq) {
770                         q->end_sector = rq_end_sector(rq);
771                         q->boundary_rq = NULL;
772                 }
773
774                 if (rq->cmd_flags & REQ_DONTPREP)
775                         break;
776
777                 if (q->dma_drain_size && rq->data_len) {
778                         /*
779                          * make sure space for the drain appears we
780                          * know we can do this because max_hw_segments
781                          * has been adjusted to be one fewer than the
782                          * device can handle
783                          */
784                         rq->nr_phys_segments++;
785                         rq->nr_hw_segments++;
786                 }
787
788                 if (!q->prep_rq_fn)
789                         break;
790
791                 ret = q->prep_rq_fn(q, rq);
792                 if (ret == BLKPREP_OK) {
793                         break;
794                 } else if (ret == BLKPREP_DEFER) {
795                         /*
796                          * the request may have been (partially) prepped.
797                          * we need to keep this request in the front to
798                          * avoid resource deadlock.  REQ_STARTED will
799                          * prevent other fs requests from passing this one.
800                          */
801                         if (q->dma_drain_size && rq->data_len &&
802                             !(rq->cmd_flags & REQ_DONTPREP)) {
803                                 /*
804                                  * remove the space for the drain we added
805                                  * so that we don't add it again
806                                  */
807                                 --rq->nr_phys_segments;
808                                 --rq->nr_hw_segments;
809                         }
810
811                         rq = NULL;
812                         break;
813                 } else if (ret == BLKPREP_KILL) {
814                         rq->cmd_flags |= REQ_QUIET;
815                         end_queued_request(rq, 0);
816                 } else {
817                         printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
818                         break;
819                 }
820         }
821
822         return rq;
823 }
824 EXPORT_SYMBOL(elv_next_request);
825
826 void elv_dequeue_request(struct request_queue *q, struct request *rq)
827 {
828         BUG_ON(list_empty(&rq->queuelist));
829         BUG_ON(ELV_ON_HASH(rq));
830
831         list_del_init(&rq->queuelist);
832
833         /*
834          * the time frame between a request being removed from the lists
835          * and to it is freed is accounted as io that is in progress at
836          * the driver side.
837          */
838         if (blk_account_rq(rq))
839                 q->in_flight++;
840 }
841 EXPORT_SYMBOL(elv_dequeue_request);
842
843 int elv_queue_empty(struct request_queue *q)
844 {
845         elevator_t *e = q->elevator;
846
847         if (!list_empty(&q->queue_head))
848                 return 0;
849
850         if (e->ops->elevator_queue_empty_fn)
851                 return e->ops->elevator_queue_empty_fn(q);
852
853         return 1;
854 }
855 EXPORT_SYMBOL(elv_queue_empty);
856
857 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
858 {
859         elevator_t *e = q->elevator;
860
861         if (e->ops->elevator_latter_req_fn)
862                 return e->ops->elevator_latter_req_fn(q, rq);
863         return NULL;
864 }
865
866 struct request *elv_former_request(struct request_queue *q, struct request *rq)
867 {
868         elevator_t *e = q->elevator;
869
870         if (e->ops->elevator_former_req_fn)
871                 return e->ops->elevator_former_req_fn(q, rq);
872         return NULL;
873 }
874
875 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
876 {
877         elevator_t *e = q->elevator;
878
879         if (e->ops->elevator_set_req_fn)
880                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
881
882         rq->elevator_private = NULL;
883         return 0;
884 }
885
886 void elv_put_request(struct request_queue *q, struct request *rq)
887 {
888         elevator_t *e = q->elevator;
889
890         if (e->ops->elevator_put_req_fn)
891                 e->ops->elevator_put_req_fn(rq);
892 }
893
894 int elv_may_queue(struct request_queue *q, int rw)
895 {
896         elevator_t *e = q->elevator;
897
898         if (e->ops->elevator_may_queue_fn)
899                 return e->ops->elevator_may_queue_fn(q, rw);
900
901         return ELV_MQUEUE_MAY;
902 }
903
904 void elv_completed_request(struct request_queue *q, struct request *rq)
905 {
906         elevator_t *e = q->elevator;
907
908         /*
909          * request is released from the driver, io must be done
910          */
911         if (blk_account_rq(rq)) {
912                 q->in_flight--;
913                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
914                         e->ops->elevator_completed_req_fn(q, rq);
915         }
916
917         /*
918          * Check if the queue is waiting for fs requests to be
919          * drained for flush sequence.
920          */
921         if (unlikely(q->ordseq)) {
922                 struct request *first_rq = list_entry_rq(q->queue_head.next);
923                 if (q->in_flight == 0 &&
924                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
925                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
926                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
927                         q->request_fn(q);
928                 }
929         }
930 }
931
932 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
933
934 static ssize_t
935 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
936 {
937         elevator_t *e = container_of(kobj, elevator_t, kobj);
938         struct elv_fs_entry *entry = to_elv(attr);
939         ssize_t error;
940
941         if (!entry->show)
942                 return -EIO;
943
944         mutex_lock(&e->sysfs_lock);
945         error = e->ops ? entry->show(e, page) : -ENOENT;
946         mutex_unlock(&e->sysfs_lock);
947         return error;
948 }
949
950 static ssize_t
951 elv_attr_store(struct kobject *kobj, struct attribute *attr,
952                const char *page, size_t length)
953 {
954         elevator_t *e = container_of(kobj, elevator_t, kobj);
955         struct elv_fs_entry *entry = to_elv(attr);
956         ssize_t error;
957
958         if (!entry->store)
959                 return -EIO;
960
961         mutex_lock(&e->sysfs_lock);
962         error = e->ops ? entry->store(e, page, length) : -ENOENT;
963         mutex_unlock(&e->sysfs_lock);
964         return error;
965 }
966
967 static struct sysfs_ops elv_sysfs_ops = {
968         .show   = elv_attr_show,
969         .store  = elv_attr_store,
970 };
971
972 static struct kobj_type elv_ktype = {
973         .sysfs_ops      = &elv_sysfs_ops,
974         .release        = elevator_release,
975 };
976
977 int elv_register_queue(struct request_queue *q)
978 {
979         elevator_t *e = q->elevator;
980         int error;
981
982         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
983         if (!error) {
984                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
985                 if (attr) {
986                         while (attr->attr.name) {
987                                 if (sysfs_create_file(&e->kobj, &attr->attr))
988                                         break;
989                                 attr++;
990                         }
991                 }
992                 kobject_uevent(&e->kobj, KOBJ_ADD);
993         }
994         return error;
995 }
996
997 static void __elv_unregister_queue(elevator_t *e)
998 {
999         kobject_uevent(&e->kobj, KOBJ_REMOVE);
1000         kobject_del(&e->kobj);
1001 }
1002
1003 void elv_unregister_queue(struct request_queue *q)
1004 {
1005         if (q)
1006                 __elv_unregister_queue(q->elevator);
1007 }
1008
1009 void elv_register(struct elevator_type *e)
1010 {
1011         char *def = "";
1012
1013         spin_lock(&elv_list_lock);
1014         BUG_ON(elevator_find(e->elevator_name));
1015         list_add_tail(&e->list, &elv_list);
1016         spin_unlock(&elv_list_lock);
1017
1018         if (!strcmp(e->elevator_name, chosen_elevator) ||
1019                         (!*chosen_elevator &&
1020                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1021                                 def = " (default)";
1022
1023         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1024                                                                 def);
1025 }
1026 EXPORT_SYMBOL_GPL(elv_register);
1027
1028 void elv_unregister(struct elevator_type *e)
1029 {
1030         struct task_struct *g, *p;
1031
1032         /*
1033          * Iterate every thread in the process to remove the io contexts.
1034          */
1035         if (e->ops.trim) {
1036                 read_lock(&tasklist_lock);
1037                 do_each_thread(g, p) {
1038                         task_lock(p);
1039                         if (p->io_context)
1040                                 e->ops.trim(p->io_context);
1041                         task_unlock(p);
1042                 } while_each_thread(g, p);
1043                 read_unlock(&tasklist_lock);
1044         }
1045
1046         spin_lock(&elv_list_lock);
1047         list_del_init(&e->list);
1048         spin_unlock(&elv_list_lock);
1049 }
1050 EXPORT_SYMBOL_GPL(elv_unregister);
1051
1052 /*
1053  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1054  * we don't free the old io scheduler, before we have allocated what we
1055  * need for the new one. this way we have a chance of going back to the old
1056  * one, if the new one fails init for some reason.
1057  */
1058 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1059 {
1060         elevator_t *old_elevator, *e;
1061         void *data;
1062
1063         /*
1064          * Allocate new elevator
1065          */
1066         e = elevator_alloc(q, new_e);
1067         if (!e)
1068                 return 0;
1069
1070         data = elevator_init_queue(q, e);
1071         if (!data) {
1072                 kobject_put(&e->kobj);
1073                 return 0;
1074         }
1075
1076         /*
1077          * Turn on BYPASS and drain all requests w/ elevator private data
1078          */
1079         spin_lock_irq(q->queue_lock);
1080
1081         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
1082
1083         elv_drain_elevator(q);
1084
1085         while (q->rq.elvpriv) {
1086                 blk_remove_plug(q);
1087                 q->request_fn(q);
1088                 spin_unlock_irq(q->queue_lock);
1089                 msleep(10);
1090                 spin_lock_irq(q->queue_lock);
1091                 elv_drain_elevator(q);
1092         }
1093
1094         /*
1095          * Remember old elevator.
1096          */
1097         old_elevator = q->elevator;
1098
1099         /*
1100          * attach and start new elevator
1101          */
1102         elevator_attach(q, e, data);
1103
1104         spin_unlock_irq(q->queue_lock);
1105
1106         __elv_unregister_queue(old_elevator);
1107
1108         if (elv_register_queue(q))
1109                 goto fail_register;
1110
1111         /*
1112          * finally exit old elevator and turn off BYPASS.
1113          */
1114         elevator_exit(old_elevator);
1115         spin_lock_irq(q->queue_lock);
1116         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1117         spin_unlock_irq(q->queue_lock);
1118
1119         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1120
1121         return 1;
1122
1123 fail_register:
1124         /*
1125          * switch failed, exit the new io scheduler and reattach the old
1126          * one again (along with re-adding the sysfs dir)
1127          */
1128         elevator_exit(e);
1129         q->elevator = old_elevator;
1130         elv_register_queue(q);
1131
1132         spin_lock_irq(q->queue_lock);
1133         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1134         spin_unlock_irq(q->queue_lock);
1135
1136         return 0;
1137 }
1138
1139 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1140                           size_t count)
1141 {
1142         char elevator_name[ELV_NAME_MAX];
1143         size_t len;
1144         struct elevator_type *e;
1145
1146         elevator_name[sizeof(elevator_name) - 1] = '\0';
1147         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
1148         len = strlen(elevator_name);
1149
1150         if (len && elevator_name[len - 1] == '\n')
1151                 elevator_name[len - 1] = '\0';
1152
1153         e = elevator_get(elevator_name);
1154         if (!e) {
1155                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1156                 return -EINVAL;
1157         }
1158
1159         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1160                 elevator_put(e);
1161                 return count;
1162         }
1163
1164         if (!elevator_switch(q, e))
1165                 printk(KERN_ERR "elevator: switch to %s failed\n",
1166                                                         elevator_name);
1167         return count;
1168 }
1169
1170 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1171 {
1172         elevator_t *e = q->elevator;
1173         struct elevator_type *elv = e->elevator_type;
1174         struct elevator_type *__e;
1175         int len = 0;
1176
1177         spin_lock(&elv_list_lock);
1178         list_for_each_entry(__e, &elv_list, list) {
1179                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1180                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1181                 else
1182                         len += sprintf(name+len, "%s ", __e->elevator_name);
1183         }
1184         spin_unlock(&elv_list_lock);
1185
1186         len += sprintf(len+name, "\n");
1187         return len;
1188 }
1189
1190 struct request *elv_rb_former_request(struct request_queue *q,
1191                                       struct request *rq)
1192 {
1193         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1194
1195         if (rbprev)
1196                 return rb_entry_rq(rbprev);
1197
1198         return NULL;
1199 }
1200 EXPORT_SYMBOL(elv_rb_former_request);
1201
1202 struct request *elv_rb_latter_request(struct request_queue *q,
1203                                       struct request *rq)
1204 {
1205         struct rb_node *rbnext = rb_next(&rq->rb_node);
1206
1207         if (rbnext)
1208                 return rb_entry_rq(rbnext);
1209
1210         return NULL;
1211 }
1212 EXPORT_SYMBOL(elv_rb_latter_request);