blktrace: port to tracepoints
[linux-3.10.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 <trace/block.h>
37 #include <linux/hash.h>
38 #include <linux/uaccess.h>
39
40 #include "blk.h"
41
42 static DEFINE_SPINLOCK(elv_list_lock);
43 static LIST_HEAD(elv_list);
44
45 /*
46  * Merge hash stuff.
47  */
48 static const int elv_hash_shift = 6;
49 #define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
50 #define ELV_HASH_FN(sec)        \
51                 (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
52 #define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
53 #define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
54 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
55
56 /*
57  * Query io scheduler to see if the current process issuing bio may be
58  * merged with rq.
59  */
60 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
61 {
62         struct request_queue *q = rq->q;
63         elevator_t *e = q->elevator;
64
65         if (e->ops->elevator_allow_merge_fn)
66                 return e->ops->elevator_allow_merge_fn(q, rq, bio);
67
68         return 1;
69 }
70
71 /*
72  * can we safely merge with this request?
73  */
74 int elv_rq_merge_ok(struct request *rq, struct bio *bio)
75 {
76         if (!rq_mergeable(rq))
77                 return 0;
78
79         /*
80          * Don't merge file system requests and discard requests
81          */
82         if (bio_discard(bio) != bio_discard(rq->bio))
83                 return 0;
84
85         /*
86          * different data direction or already started, don't merge
87          */
88         if (bio_data_dir(bio) != rq_data_dir(rq))
89                 return 0;
90
91         /*
92          * must be same device and not a special request
93          */
94         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
95                 return 0;
96
97         /*
98          * only merge integrity protected bio into ditto rq
99          */
100         if (bio_integrity(bio) != blk_integrity_rq(rq))
101                 return 0;
102
103         if (!elv_iosched_allow_merge(rq, bio))
104                 return 0;
105
106         return 1;
107 }
108 EXPORT_SYMBOL(elv_rq_merge_ok);
109
110 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
111 {
112         int ret = ELEVATOR_NO_MERGE;
113
114         /*
115          * we can merge and sequence is ok, check if it's possible
116          */
117         if (elv_rq_merge_ok(__rq, bio)) {
118                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
119                         ret = ELEVATOR_BACK_MERGE;
120                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
121                         ret = ELEVATOR_FRONT_MERGE;
122         }
123
124         return ret;
125 }
126
127 static struct elevator_type *elevator_find(const char *name)
128 {
129         struct elevator_type *e;
130
131         list_for_each_entry(e, &elv_list, list) {
132                 if (!strcmp(e->elevator_name, name))
133                         return e;
134         }
135
136         return NULL;
137 }
138
139 static void elevator_put(struct elevator_type *e)
140 {
141         module_put(e->elevator_owner);
142 }
143
144 static struct elevator_type *elevator_get(const char *name)
145 {
146         struct elevator_type *e;
147
148         spin_lock(&elv_list_lock);
149
150         e = elevator_find(name);
151         if (!e) {
152                 char elv[ELV_NAME_MAX + strlen("-iosched")];
153
154                 spin_unlock(&elv_list_lock);
155
156                 if (!strcmp(name, "anticipatory"))
157                         sprintf(elv, "as-iosched");
158                 else
159                         sprintf(elv, "%s-iosched", name);
160
161                 request_module("%s", elv);
162                 spin_lock(&elv_list_lock);
163                 e = elevator_find(name);
164         }
165
166         if (e && !try_module_get(e->elevator_owner))
167                 e = NULL;
168
169         spin_unlock(&elv_list_lock);
170
171         return e;
172 }
173
174 static void *elevator_init_queue(struct request_queue *q,
175                                  struct elevator_queue *eq)
176 {
177         return eq->ops->elevator_init_fn(q);
178 }
179
180 static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
181                            void *data)
182 {
183         q->elevator = eq;
184         eq->elevator_data = data;
185 }
186
187 static char chosen_elevator[16];
188
189 static int __init elevator_setup(char *str)
190 {
191         /*
192          * Be backwards-compatible with previous kernels, so users
193          * won't get the wrong elevator.
194          */
195         if (!strcmp(str, "as"))
196                 strcpy(chosen_elevator, "anticipatory");
197         else
198                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
199         return 1;
200 }
201
202 __setup("elevator=", elevator_setup);
203
204 static struct kobj_type elv_ktype;
205
206 static elevator_t *elevator_alloc(struct request_queue *q,
207                                   struct elevator_type *e)
208 {
209         elevator_t *eq;
210         int i;
211
212         eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL | __GFP_ZERO, q->node);
213         if (unlikely(!eq))
214                 goto err;
215
216         eq->ops = &e->ops;
217         eq->elevator_type = e;
218         kobject_init(&eq->kobj, &elv_ktype);
219         mutex_init(&eq->sysfs_lock);
220
221         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
222                                         GFP_KERNEL, q->node);
223         if (!eq->hash)
224                 goto err;
225
226         for (i = 0; i < ELV_HASH_ENTRIES; i++)
227                 INIT_HLIST_HEAD(&eq->hash[i]);
228
229         return eq;
230 err:
231         kfree(eq);
232         elevator_put(e);
233         return NULL;
234 }
235
236 static void elevator_release(struct kobject *kobj)
237 {
238         elevator_t *e = container_of(kobj, elevator_t, kobj);
239
240         elevator_put(e->elevator_type);
241         kfree(e->hash);
242         kfree(e);
243 }
244
245 int elevator_init(struct request_queue *q, char *name)
246 {
247         struct elevator_type *e = NULL;
248         struct elevator_queue *eq;
249         int ret = 0;
250         void *data;
251
252         INIT_LIST_HEAD(&q->queue_head);
253         q->last_merge = NULL;
254         q->end_sector = 0;
255         q->boundary_rq = NULL;
256
257         if (name) {
258                 e = elevator_get(name);
259                 if (!e)
260                         return -EINVAL;
261         }
262
263         if (!e && *chosen_elevator) {
264                 e = elevator_get(chosen_elevator);
265                 if (!e)
266                         printk(KERN_ERR "I/O scheduler %s not found\n",
267                                                         chosen_elevator);
268         }
269
270         if (!e) {
271                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
272                 if (!e) {
273                         printk(KERN_ERR
274                                 "Default I/O scheduler not found. " \
275                                 "Using noop.\n");
276                         e = elevator_get("noop");
277                 }
278         }
279
280         eq = elevator_alloc(q, e);
281         if (!eq)
282                 return -ENOMEM;
283
284         data = elevator_init_queue(q, eq);
285         if (!data) {
286                 kobject_put(&eq->kobj);
287                 return -ENOMEM;
288         }
289
290         elevator_attach(q, eq, data);
291         return ret;
292 }
293 EXPORT_SYMBOL(elevator_init);
294
295 void elevator_exit(elevator_t *e)
296 {
297         mutex_lock(&e->sysfs_lock);
298         if (e->ops->elevator_exit_fn)
299                 e->ops->elevator_exit_fn(e);
300         e->ops = NULL;
301         mutex_unlock(&e->sysfs_lock);
302
303         kobject_put(&e->kobj);
304 }
305 EXPORT_SYMBOL(elevator_exit);
306
307 static void elv_activate_rq(struct request_queue *q, struct request *rq)
308 {
309         elevator_t *e = q->elevator;
310
311         if (e->ops->elevator_activate_req_fn)
312                 e->ops->elevator_activate_req_fn(q, rq);
313 }
314
315 static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
316 {
317         elevator_t *e = q->elevator;
318
319         if (e->ops->elevator_deactivate_req_fn)
320                 e->ops->elevator_deactivate_req_fn(q, rq);
321 }
322
323 static inline void __elv_rqhash_del(struct request *rq)
324 {
325         hlist_del_init(&rq->hash);
326 }
327
328 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
329 {
330         if (ELV_ON_HASH(rq))
331                 __elv_rqhash_del(rq);
332 }
333
334 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
335 {
336         elevator_t *e = q->elevator;
337
338         BUG_ON(ELV_ON_HASH(rq));
339         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
340 }
341
342 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
343 {
344         __elv_rqhash_del(rq);
345         elv_rqhash_add(q, rq);
346 }
347
348 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
349 {
350         elevator_t *e = q->elevator;
351         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
352         struct hlist_node *entry, *next;
353         struct request *rq;
354
355         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
356                 BUG_ON(!ELV_ON_HASH(rq));
357
358                 if (unlikely(!rq_mergeable(rq))) {
359                         __elv_rqhash_del(rq);
360                         continue;
361                 }
362
363                 if (rq_hash_key(rq) == offset)
364                         return rq;
365         }
366
367         return NULL;
368 }
369
370 /*
371  * RB-tree support functions for inserting/lookup/removal of requests
372  * in a sorted RB tree.
373  */
374 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
375 {
376         struct rb_node **p = &root->rb_node;
377         struct rb_node *parent = NULL;
378         struct request *__rq;
379
380         while (*p) {
381                 parent = *p;
382                 __rq = rb_entry(parent, struct request, rb_node);
383
384                 if (rq->sector < __rq->sector)
385                         p = &(*p)->rb_left;
386                 else if (rq->sector > __rq->sector)
387                         p = &(*p)->rb_right;
388                 else
389                         return __rq;
390         }
391
392         rb_link_node(&rq->rb_node, parent, p);
393         rb_insert_color(&rq->rb_node, root);
394         return NULL;
395 }
396 EXPORT_SYMBOL(elv_rb_add);
397
398 void elv_rb_del(struct rb_root *root, struct request *rq)
399 {
400         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
401         rb_erase(&rq->rb_node, root);
402         RB_CLEAR_NODE(&rq->rb_node);
403 }
404 EXPORT_SYMBOL(elv_rb_del);
405
406 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
407 {
408         struct rb_node *n = root->rb_node;
409         struct request *rq;
410
411         while (n) {
412                 rq = rb_entry(n, struct request, rb_node);
413
414                 if (sector < rq->sector)
415                         n = n->rb_left;
416                 else if (sector > rq->sector)
417                         n = n->rb_right;
418                 else
419                         return rq;
420         }
421
422         return NULL;
423 }
424 EXPORT_SYMBOL(elv_rb_find);
425
426 /*
427  * Insert rq into dispatch queue of q.  Queue lock must be held on
428  * entry.  rq is sort instead into the dispatch queue. To be used by
429  * specific elevators.
430  */
431 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
432 {
433         sector_t boundary;
434         struct list_head *entry;
435         int stop_flags;
436
437         if (q->last_merge == rq)
438                 q->last_merge = NULL;
439
440         elv_rqhash_del(q, rq);
441
442         q->nr_sorted--;
443
444         boundary = q->end_sector;
445         stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
446         list_for_each_prev(entry, &q->queue_head) {
447                 struct request *pos = list_entry_rq(entry);
448
449                 if (blk_discard_rq(rq) != blk_discard_rq(pos))
450                         break;
451                 if (rq_data_dir(rq) != rq_data_dir(pos))
452                         break;
453                 if (pos->cmd_flags & stop_flags)
454                         break;
455                 if (rq->sector >= boundary) {
456                         if (pos->sector < boundary)
457                                 continue;
458                 } else {
459                         if (pos->sector >= boundary)
460                                 break;
461                 }
462                 if (rq->sector >= pos->sector)
463                         break;
464         }
465
466         list_add(&rq->queuelist, entry);
467 }
468 EXPORT_SYMBOL(elv_dispatch_sort);
469
470 /*
471  * Insert rq into dispatch queue of q.  Queue lock must be held on
472  * entry.  rq is added to the back of the dispatch queue. To be used by
473  * specific elevators.
474  */
475 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
476 {
477         if (q->last_merge == rq)
478                 q->last_merge = NULL;
479
480         elv_rqhash_del(q, rq);
481
482         q->nr_sorted--;
483
484         q->end_sector = rq_end_sector(rq);
485         q->boundary_rq = rq;
486         list_add_tail(&rq->queuelist, &q->queue_head);
487 }
488 EXPORT_SYMBOL(elv_dispatch_add_tail);
489
490 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
491 {
492         elevator_t *e = q->elevator;
493         struct request *__rq;
494         int ret;
495
496         /*
497          * First try one-hit cache.
498          */
499         if (q->last_merge) {
500                 ret = elv_try_merge(q->last_merge, bio);
501                 if (ret != ELEVATOR_NO_MERGE) {
502                         *req = q->last_merge;
503                         return ret;
504                 }
505         }
506
507         if (blk_queue_nomerges(q))
508                 return ELEVATOR_NO_MERGE;
509
510         /*
511          * See if our hash lookup can find a potential backmerge.
512          */
513         __rq = elv_rqhash_find(q, bio->bi_sector);
514         if (__rq && elv_rq_merge_ok(__rq, bio)) {
515                 *req = __rq;
516                 return ELEVATOR_BACK_MERGE;
517         }
518
519         if (e->ops->elevator_merge_fn)
520                 return e->ops->elevator_merge_fn(q, req, bio);
521
522         return ELEVATOR_NO_MERGE;
523 }
524
525 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
526 {
527         elevator_t *e = q->elevator;
528
529         if (e->ops->elevator_merged_fn)
530                 e->ops->elevator_merged_fn(q, rq, type);
531
532         if (type == ELEVATOR_BACK_MERGE)
533                 elv_rqhash_reposition(q, rq);
534
535         q->last_merge = rq;
536 }
537
538 void elv_merge_requests(struct request_queue *q, struct request *rq,
539                              struct request *next)
540 {
541         elevator_t *e = q->elevator;
542
543         if (e->ops->elevator_merge_req_fn)
544                 e->ops->elevator_merge_req_fn(q, rq, next);
545
546         elv_rqhash_reposition(q, rq);
547         elv_rqhash_del(q, next);
548
549         q->nr_sorted--;
550         q->last_merge = rq;
551 }
552
553 void elv_requeue_request(struct request_queue *q, struct request *rq)
554 {
555         /*
556          * it already went through dequeue, we need to decrement the
557          * in_flight count again
558          */
559         if (blk_account_rq(rq)) {
560                 q->in_flight--;
561                 if (blk_sorted_rq(rq))
562                         elv_deactivate_rq(q, rq);
563         }
564
565         rq->cmd_flags &= ~REQ_STARTED;
566
567         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
568 }
569
570 static void elv_drain_elevator(struct request_queue *q)
571 {
572         static int printed;
573         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
574                 ;
575         if (q->nr_sorted == 0)
576                 return;
577         if (printed++ < 10) {
578                 printk(KERN_ERR "%s: forced dispatching is broken "
579                        "(nr_sorted=%u), please report this\n",
580                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
581         }
582 }
583
584 void elv_insert(struct request_queue *q, struct request *rq, int where)
585 {
586         struct list_head *pos;
587         unsigned ordseq;
588         int unplug_it = 1;
589
590         trace_block_rq_insert(q, rq);
591
592         rq->q = q;
593
594         switch (where) {
595         case ELEVATOR_INSERT_FRONT:
596                 rq->cmd_flags |= REQ_SOFTBARRIER;
597
598                 list_add(&rq->queuelist, &q->queue_head);
599                 break;
600
601         case ELEVATOR_INSERT_BACK:
602                 rq->cmd_flags |= REQ_SOFTBARRIER;
603                 elv_drain_elevator(q);
604                 list_add_tail(&rq->queuelist, &q->queue_head);
605                 /*
606                  * We kick the queue here for the following reasons.
607                  * - The elevator might have returned NULL previously
608                  *   to delay requests and returned them now.  As the
609                  *   queue wasn't empty before this request, ll_rw_blk
610                  *   won't run the queue on return, resulting in hang.
611                  * - Usually, back inserted requests won't be merged
612                  *   with anything.  There's no point in delaying queue
613                  *   processing.
614                  */
615                 blk_remove_plug(q);
616                 blk_start_queueing(q);
617                 break;
618
619         case ELEVATOR_INSERT_SORT:
620                 BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
621                 rq->cmd_flags |= REQ_SORTED;
622                 q->nr_sorted++;
623                 if (rq_mergeable(rq)) {
624                         elv_rqhash_add(q, rq);
625                         if (!q->last_merge)
626                                 q->last_merge = rq;
627                 }
628
629                 /*
630                  * Some ioscheds (cfq) run q->request_fn directly, so
631                  * rq cannot be accessed after calling
632                  * elevator_add_req_fn.
633                  */
634                 q->elevator->ops->elevator_add_req_fn(q, rq);
635                 break;
636
637         case ELEVATOR_INSERT_REQUEUE:
638                 /*
639                  * If ordered flush isn't in progress, we do front
640                  * insertion; otherwise, requests should be requeued
641                  * in ordseq order.
642                  */
643                 rq->cmd_flags |= REQ_SOFTBARRIER;
644
645                 /*
646                  * Most requeues happen because of a busy condition,
647                  * don't force unplug of the queue for that case.
648                  */
649                 unplug_it = 0;
650
651                 if (q->ordseq == 0) {
652                         list_add(&rq->queuelist, &q->queue_head);
653                         break;
654                 }
655
656                 ordseq = blk_ordered_req_seq(rq);
657
658                 list_for_each(pos, &q->queue_head) {
659                         struct request *pos_rq = list_entry_rq(pos);
660                         if (ordseq <= blk_ordered_req_seq(pos_rq))
661                                 break;
662                 }
663
664                 list_add_tail(&rq->queuelist, pos);
665                 break;
666
667         default:
668                 printk(KERN_ERR "%s: bad insertion point %d\n",
669                        __func__, where);
670                 BUG();
671         }
672
673         if (unplug_it && blk_queue_plugged(q)) {
674                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
675                         - q->in_flight;
676
677                 if (nrq >= q->unplug_thresh)
678                         __generic_unplug_device(q);
679         }
680 }
681
682 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
683                        int plug)
684 {
685         if (q->ordcolor)
686                 rq->cmd_flags |= REQ_ORDERED_COLOR;
687
688         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
689                 /*
690                  * toggle ordered color
691                  */
692                 if (blk_barrier_rq(rq))
693                         q->ordcolor ^= 1;
694
695                 /*
696                  * barriers implicitly indicate back insertion
697                  */
698                 if (where == ELEVATOR_INSERT_SORT)
699                         where = ELEVATOR_INSERT_BACK;
700
701                 /*
702                  * this request is scheduling boundary, update
703                  * end_sector
704                  */
705                 if (blk_fs_request(rq) || blk_discard_rq(rq)) {
706                         q->end_sector = rq_end_sector(rq);
707                         q->boundary_rq = rq;
708                 }
709         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
710                     where == ELEVATOR_INSERT_SORT)
711                 where = ELEVATOR_INSERT_BACK;
712
713         if (plug)
714                 blk_plug_device(q);
715
716         elv_insert(q, rq, where);
717 }
718 EXPORT_SYMBOL(__elv_add_request);
719
720 void elv_add_request(struct request_queue *q, struct request *rq, int where,
721                      int plug)
722 {
723         unsigned long flags;
724
725         spin_lock_irqsave(q->queue_lock, flags);
726         __elv_add_request(q, rq, where, plug);
727         spin_unlock_irqrestore(q->queue_lock, flags);
728 }
729 EXPORT_SYMBOL(elv_add_request);
730
731 static inline struct request *__elv_next_request(struct request_queue *q)
732 {
733         struct request *rq;
734
735         while (1) {
736                 while (!list_empty(&q->queue_head)) {
737                         rq = list_entry_rq(q->queue_head.next);
738                         if (blk_do_ordered(q, &rq))
739                                 return rq;
740                 }
741
742                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
743                         return NULL;
744         }
745 }
746
747 struct request *elv_next_request(struct request_queue *q)
748 {
749         struct request *rq;
750         int ret;
751
752         while ((rq = __elv_next_request(q)) != NULL) {
753                 /*
754                  * Kill the empty barrier place holder, the driver must
755                  * not ever see it.
756                  */
757                 if (blk_empty_barrier(rq)) {
758                         __blk_end_request(rq, 0, blk_rq_bytes(rq));
759                         continue;
760                 }
761                 if (!(rq->cmd_flags & REQ_STARTED)) {
762                         /*
763                          * This is the first time the device driver
764                          * sees this request (possibly after
765                          * requeueing).  Notify IO scheduler.
766                          */
767                         if (blk_sorted_rq(rq))
768                                 elv_activate_rq(q, rq);
769
770                         /*
771                          * just mark as started even if we don't start
772                          * it, a request that has been delayed should
773                          * not be passed by new incoming requests
774                          */
775                         rq->cmd_flags |= REQ_STARTED;
776                         trace_block_rq_issue(q, rq);
777                 }
778
779                 if (!q->boundary_rq || q->boundary_rq == rq) {
780                         q->end_sector = rq_end_sector(rq);
781                         q->boundary_rq = NULL;
782                 }
783
784                 if (rq->cmd_flags & REQ_DONTPREP)
785                         break;
786
787                 if (q->dma_drain_size && rq->data_len) {
788                         /*
789                          * make sure space for the drain appears we
790                          * know we can do this because max_hw_segments
791                          * has been adjusted to be one fewer than the
792                          * device can handle
793                          */
794                         rq->nr_phys_segments++;
795                 }
796
797                 if (!q->prep_rq_fn)
798                         break;
799
800                 ret = q->prep_rq_fn(q, rq);
801                 if (ret == BLKPREP_OK) {
802                         break;
803                 } else if (ret == BLKPREP_DEFER) {
804                         /*
805                          * the request may have been (partially) prepped.
806                          * we need to keep this request in the front to
807                          * avoid resource deadlock.  REQ_STARTED will
808                          * prevent other fs requests from passing this one.
809                          */
810                         if (q->dma_drain_size && rq->data_len &&
811                             !(rq->cmd_flags & REQ_DONTPREP)) {
812                                 /*
813                                  * remove the space for the drain we added
814                                  * so that we don't add it again
815                                  */
816                                 --rq->nr_phys_segments;
817                         }
818
819                         rq = NULL;
820                         break;
821                 } else if (ret == BLKPREP_KILL) {
822                         rq->cmd_flags |= REQ_QUIET;
823                         __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
824                 } else {
825                         printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
826                         break;
827                 }
828         }
829
830         return rq;
831 }
832 EXPORT_SYMBOL(elv_next_request);
833
834 void elv_dequeue_request(struct request_queue *q, struct request *rq)
835 {
836         BUG_ON(list_empty(&rq->queuelist));
837         BUG_ON(ELV_ON_HASH(rq));
838
839         list_del_init(&rq->queuelist);
840
841         /*
842          * the time frame between a request being removed from the lists
843          * and to it is freed is accounted as io that is in progress at
844          * the driver side.
845          */
846         if (blk_account_rq(rq))
847                 q->in_flight++;
848
849         /*
850          * We are now handing the request to the hardware, add the
851          * timeout handler.
852          */
853         blk_add_timer(rq);
854 }
855 EXPORT_SYMBOL(elv_dequeue_request);
856
857 int elv_queue_empty(struct request_queue *q)
858 {
859         elevator_t *e = q->elevator;
860
861         if (!list_empty(&q->queue_head))
862                 return 0;
863
864         if (e->ops->elevator_queue_empty_fn)
865                 return e->ops->elevator_queue_empty_fn(q);
866
867         return 1;
868 }
869 EXPORT_SYMBOL(elv_queue_empty);
870
871 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
872 {
873         elevator_t *e = q->elevator;
874
875         if (e->ops->elevator_latter_req_fn)
876                 return e->ops->elevator_latter_req_fn(q, rq);
877         return NULL;
878 }
879
880 struct request *elv_former_request(struct request_queue *q, struct request *rq)
881 {
882         elevator_t *e = q->elevator;
883
884         if (e->ops->elevator_former_req_fn)
885                 return e->ops->elevator_former_req_fn(q, rq);
886         return NULL;
887 }
888
889 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
890 {
891         elevator_t *e = q->elevator;
892
893         if (e->ops->elevator_set_req_fn)
894                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
895
896         rq->elevator_private = NULL;
897         return 0;
898 }
899
900 void elv_put_request(struct request_queue *q, struct request *rq)
901 {
902         elevator_t *e = q->elevator;
903
904         if (e->ops->elevator_put_req_fn)
905                 e->ops->elevator_put_req_fn(rq);
906 }
907
908 int elv_may_queue(struct request_queue *q, int rw)
909 {
910         elevator_t *e = q->elevator;
911
912         if (e->ops->elevator_may_queue_fn)
913                 return e->ops->elevator_may_queue_fn(q, rw);
914
915         return ELV_MQUEUE_MAY;
916 }
917
918 void elv_abort_queue(struct request_queue *q)
919 {
920         struct request *rq;
921
922         while (!list_empty(&q->queue_head)) {
923                 rq = list_entry_rq(q->queue_head.next);
924                 rq->cmd_flags |= REQ_QUIET;
925                 trace_block_rq_abort(q, rq);
926                 __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
927         }
928 }
929 EXPORT_SYMBOL(elv_abort_queue);
930
931 void elv_completed_request(struct request_queue *q, struct request *rq)
932 {
933         elevator_t *e = q->elevator;
934
935         /*
936          * request is released from the driver, io must be done
937          */
938         if (blk_account_rq(rq)) {
939                 q->in_flight--;
940                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
941                         e->ops->elevator_completed_req_fn(q, rq);
942         }
943
944         /*
945          * Check if the queue is waiting for fs requests to be
946          * drained for flush sequence.
947          */
948         if (unlikely(q->ordseq)) {
949                 struct request *first_rq = list_entry_rq(q->queue_head.next);
950                 if (q->in_flight == 0 &&
951                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
952                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
953                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
954                         blk_start_queueing(q);
955                 }
956         }
957 }
958
959 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
960
961 static ssize_t
962 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
963 {
964         elevator_t *e = container_of(kobj, elevator_t, kobj);
965         struct elv_fs_entry *entry = to_elv(attr);
966         ssize_t error;
967
968         if (!entry->show)
969                 return -EIO;
970
971         mutex_lock(&e->sysfs_lock);
972         error = e->ops ? entry->show(e, page) : -ENOENT;
973         mutex_unlock(&e->sysfs_lock);
974         return error;
975 }
976
977 static ssize_t
978 elv_attr_store(struct kobject *kobj, struct attribute *attr,
979                const char *page, size_t length)
980 {
981         elevator_t *e = container_of(kobj, elevator_t, kobj);
982         struct elv_fs_entry *entry = to_elv(attr);
983         ssize_t error;
984
985         if (!entry->store)
986                 return -EIO;
987
988         mutex_lock(&e->sysfs_lock);
989         error = e->ops ? entry->store(e, page, length) : -ENOENT;
990         mutex_unlock(&e->sysfs_lock);
991         return error;
992 }
993
994 static struct sysfs_ops elv_sysfs_ops = {
995         .show   = elv_attr_show,
996         .store  = elv_attr_store,
997 };
998
999 static struct kobj_type elv_ktype = {
1000         .sysfs_ops      = &elv_sysfs_ops,
1001         .release        = elevator_release,
1002 };
1003
1004 int elv_register_queue(struct request_queue *q)
1005 {
1006         elevator_t *e = q->elevator;
1007         int error;
1008
1009         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1010         if (!error) {
1011                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1012                 if (attr) {
1013                         while (attr->attr.name) {
1014                                 if (sysfs_create_file(&e->kobj, &attr->attr))
1015                                         break;
1016                                 attr++;
1017                         }
1018                 }
1019                 kobject_uevent(&e->kobj, KOBJ_ADD);
1020         }
1021         return error;
1022 }
1023
1024 static void __elv_unregister_queue(elevator_t *e)
1025 {
1026         kobject_uevent(&e->kobj, KOBJ_REMOVE);
1027         kobject_del(&e->kobj);
1028 }
1029
1030 void elv_unregister_queue(struct request_queue *q)
1031 {
1032         if (q)
1033                 __elv_unregister_queue(q->elevator);
1034 }
1035
1036 void elv_register(struct elevator_type *e)
1037 {
1038         char *def = "";
1039
1040         spin_lock(&elv_list_lock);
1041         BUG_ON(elevator_find(e->elevator_name));
1042         list_add_tail(&e->list, &elv_list);
1043         spin_unlock(&elv_list_lock);
1044
1045         if (!strcmp(e->elevator_name, chosen_elevator) ||
1046                         (!*chosen_elevator &&
1047                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1048                                 def = " (default)";
1049
1050         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1051                                                                 def);
1052 }
1053 EXPORT_SYMBOL_GPL(elv_register);
1054
1055 void elv_unregister(struct elevator_type *e)
1056 {
1057         struct task_struct *g, *p;
1058
1059         /*
1060          * Iterate every thread in the process to remove the io contexts.
1061          */
1062         if (e->ops.trim) {
1063                 read_lock(&tasklist_lock);
1064                 do_each_thread(g, p) {
1065                         task_lock(p);
1066                         if (p->io_context)
1067                                 e->ops.trim(p->io_context);
1068                         task_unlock(p);
1069                 } while_each_thread(g, p);
1070                 read_unlock(&tasklist_lock);
1071         }
1072
1073         spin_lock(&elv_list_lock);
1074         list_del_init(&e->list);
1075         spin_unlock(&elv_list_lock);
1076 }
1077 EXPORT_SYMBOL_GPL(elv_unregister);
1078
1079 /*
1080  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1081  * we don't free the old io scheduler, before we have allocated what we
1082  * need for the new one. this way we have a chance of going back to the old
1083  * one, if the new one fails init for some reason.
1084  */
1085 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1086 {
1087         elevator_t *old_elevator, *e;
1088         void *data;
1089
1090         /*
1091          * Allocate new elevator
1092          */
1093         e = elevator_alloc(q, new_e);
1094         if (!e)
1095                 return 0;
1096
1097         data = elevator_init_queue(q, e);
1098         if (!data) {
1099                 kobject_put(&e->kobj);
1100                 return 0;
1101         }
1102
1103         /*
1104          * Turn on BYPASS and drain all requests w/ elevator private data
1105          */
1106         spin_lock_irq(q->queue_lock);
1107
1108         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
1109
1110         elv_drain_elevator(q);
1111
1112         while (q->rq.elvpriv) {
1113                 blk_start_queueing(q);
1114                 spin_unlock_irq(q->queue_lock);
1115                 msleep(10);
1116                 spin_lock_irq(q->queue_lock);
1117                 elv_drain_elevator(q);
1118         }
1119
1120         /*
1121          * Remember old elevator.
1122          */
1123         old_elevator = q->elevator;
1124
1125         /*
1126          * attach and start new elevator
1127          */
1128         elevator_attach(q, e, data);
1129
1130         spin_unlock_irq(q->queue_lock);
1131
1132         __elv_unregister_queue(old_elevator);
1133
1134         if (elv_register_queue(q))
1135                 goto fail_register;
1136
1137         /*
1138          * finally exit old elevator and turn off BYPASS.
1139          */
1140         elevator_exit(old_elevator);
1141         spin_lock_irq(q->queue_lock);
1142         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1143         spin_unlock_irq(q->queue_lock);
1144
1145         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1146
1147         return 1;
1148
1149 fail_register:
1150         /*
1151          * switch failed, exit the new io scheduler and reattach the old
1152          * one again (along with re-adding the sysfs dir)
1153          */
1154         elevator_exit(e);
1155         q->elevator = old_elevator;
1156         elv_register_queue(q);
1157
1158         spin_lock_irq(q->queue_lock);
1159         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1160         spin_unlock_irq(q->queue_lock);
1161
1162         return 0;
1163 }
1164
1165 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1166                           size_t count)
1167 {
1168         char elevator_name[ELV_NAME_MAX];
1169         struct elevator_type *e;
1170
1171         strlcpy(elevator_name, name, sizeof(elevator_name));
1172         strstrip(elevator_name);
1173
1174         e = elevator_get(elevator_name);
1175         if (!e) {
1176                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1177                 return -EINVAL;
1178         }
1179
1180         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1181                 elevator_put(e);
1182                 return count;
1183         }
1184
1185         if (!elevator_switch(q, e))
1186                 printk(KERN_ERR "elevator: switch to %s failed\n",
1187                                                         elevator_name);
1188         return count;
1189 }
1190
1191 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1192 {
1193         elevator_t *e = q->elevator;
1194         struct elevator_type *elv = e->elevator_type;
1195         struct elevator_type *__e;
1196         int len = 0;
1197
1198         spin_lock(&elv_list_lock);
1199         list_for_each_entry(__e, &elv_list, list) {
1200                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1201                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1202                 else
1203                         len += sprintf(name+len, "%s ", __e->elevator_name);
1204         }
1205         spin_unlock(&elv_list_lock);
1206
1207         len += sprintf(len+name, "\n");
1208         return len;
1209 }
1210
1211 struct request *elv_rb_former_request(struct request_queue *q,
1212                                       struct request *rq)
1213 {
1214         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1215
1216         if (rbprev)
1217                 return rb_entry_rq(rbprev);
1218
1219         return NULL;
1220 }
1221 EXPORT_SYMBOL(elv_rb_former_request);
1222
1223 struct request *elv_rb_latter_request(struct request_queue *q,
1224                                       struct request *rq)
1225 {
1226         struct rb_node *rbnext = rb_next(&rq->rb_node);
1227
1228         if (rbnext)
1229                 return rb_entry_rq(rbnext);
1230
1231         return NULL;
1232 }
1233 EXPORT_SYMBOL(elv_rb_latter_request);