block: kill blk_start_queueing()
[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 DEFINE_TRACE(block_rq_abort);
46
47 /*
48  * Merge hash stuff.
49  */
50 static const int elv_hash_shift = 6;
51 #define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
52 #define ELV_HASH_FN(sec)        \
53                 (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
54 #define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
55 #define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
56 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
57
58 DEFINE_TRACE(block_rq_insert);
59 DEFINE_TRACE(block_rq_issue);
60
61 /*
62  * Query io scheduler to see if the current process issuing bio may be
63  * merged with rq.
64  */
65 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
66 {
67         struct request_queue *q = rq->q;
68         struct elevator_queue *e = q->elevator;
69
70         if (e->ops->elevator_allow_merge_fn)
71                 return e->ops->elevator_allow_merge_fn(q, rq, bio);
72
73         return 1;
74 }
75
76 /*
77  * can we safely merge with this request?
78  */
79 int elv_rq_merge_ok(struct request *rq, struct bio *bio)
80 {
81         if (!rq_mergeable(rq))
82                 return 0;
83
84         /*
85          * Don't merge file system requests and discard requests
86          */
87         if (bio_discard(bio) != bio_discard(rq->bio))
88                 return 0;
89
90         /*
91          * different data direction or already started, don't merge
92          */
93         if (bio_data_dir(bio) != rq_data_dir(rq))
94                 return 0;
95
96         /*
97          * must be same device and not a special request
98          */
99         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
100                 return 0;
101
102         /*
103          * only merge integrity protected bio into ditto rq
104          */
105         if (bio_integrity(bio) != blk_integrity_rq(rq))
106                 return 0;
107
108         if (!elv_iosched_allow_merge(rq, bio))
109                 return 0;
110
111         return 1;
112 }
113 EXPORT_SYMBOL(elv_rq_merge_ok);
114
115 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
116 {
117         int ret = ELEVATOR_NO_MERGE;
118
119         /*
120          * we can merge and sequence is ok, check if it's possible
121          */
122         if (elv_rq_merge_ok(__rq, bio)) {
123                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
124                         ret = ELEVATOR_BACK_MERGE;
125                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
126                         ret = ELEVATOR_FRONT_MERGE;
127         }
128
129         return ret;
130 }
131
132 static struct elevator_type *elevator_find(const char *name)
133 {
134         struct elevator_type *e;
135
136         list_for_each_entry(e, &elv_list, list) {
137                 if (!strcmp(e->elevator_name, name))
138                         return e;
139         }
140
141         return NULL;
142 }
143
144 static void elevator_put(struct elevator_type *e)
145 {
146         module_put(e->elevator_owner);
147 }
148
149 static struct elevator_type *elevator_get(const char *name)
150 {
151         struct elevator_type *e;
152
153         spin_lock(&elv_list_lock);
154
155         e = elevator_find(name);
156         if (!e) {
157                 char elv[ELV_NAME_MAX + strlen("-iosched")];
158
159                 spin_unlock(&elv_list_lock);
160
161                 if (!strcmp(name, "anticipatory"))
162                         sprintf(elv, "as-iosched");
163                 else
164                         sprintf(elv, "%s-iosched", name);
165
166                 request_module("%s", elv);
167                 spin_lock(&elv_list_lock);
168                 e = elevator_find(name);
169         }
170
171         if (e && !try_module_get(e->elevator_owner))
172                 e = NULL;
173
174         spin_unlock(&elv_list_lock);
175
176         return e;
177 }
178
179 static void *elevator_init_queue(struct request_queue *q,
180                                  struct elevator_queue *eq)
181 {
182         return eq->ops->elevator_init_fn(q);
183 }
184
185 static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
186                            void *data)
187 {
188         q->elevator = eq;
189         eq->elevator_data = data;
190 }
191
192 static char chosen_elevator[16];
193
194 static int __init elevator_setup(char *str)
195 {
196         /*
197          * Be backwards-compatible with previous kernels, so users
198          * won't get the wrong elevator.
199          */
200         if (!strcmp(str, "as"))
201                 strcpy(chosen_elevator, "anticipatory");
202         else
203                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
204         return 1;
205 }
206
207 __setup("elevator=", elevator_setup);
208
209 static struct kobj_type elv_ktype;
210
211 static struct elevator_queue *elevator_alloc(struct request_queue *q,
212                                   struct elevator_type *e)
213 {
214         struct elevator_queue *eq;
215         int i;
216
217         eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
218         if (unlikely(!eq))
219                 goto err;
220
221         eq->ops = &e->ops;
222         eq->elevator_type = e;
223         kobject_init(&eq->kobj, &elv_ktype);
224         mutex_init(&eq->sysfs_lock);
225
226         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
227                                         GFP_KERNEL, q->node);
228         if (!eq->hash)
229                 goto err;
230
231         for (i = 0; i < ELV_HASH_ENTRIES; i++)
232                 INIT_HLIST_HEAD(&eq->hash[i]);
233
234         return eq;
235 err:
236         kfree(eq);
237         elevator_put(e);
238         return NULL;
239 }
240
241 static void elevator_release(struct kobject *kobj)
242 {
243         struct elevator_queue *e;
244
245         e = container_of(kobj, struct elevator_queue, kobj);
246         elevator_put(e->elevator_type);
247         kfree(e->hash);
248         kfree(e);
249 }
250
251 int elevator_init(struct request_queue *q, char *name)
252 {
253         struct elevator_type *e = NULL;
254         struct elevator_queue *eq;
255         int ret = 0;
256         void *data;
257
258         INIT_LIST_HEAD(&q->queue_head);
259         q->last_merge = NULL;
260         q->end_sector = 0;
261         q->boundary_rq = NULL;
262
263         if (name) {
264                 e = elevator_get(name);
265                 if (!e)
266                         return -EINVAL;
267         }
268
269         if (!e && *chosen_elevator) {
270                 e = elevator_get(chosen_elevator);
271                 if (!e)
272                         printk(KERN_ERR "I/O scheduler %s not found\n",
273                                                         chosen_elevator);
274         }
275
276         if (!e) {
277                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
278                 if (!e) {
279                         printk(KERN_ERR
280                                 "Default I/O scheduler not found. " \
281                                 "Using noop.\n");
282                         e = elevator_get("noop");
283                 }
284         }
285
286         eq = elevator_alloc(q, e);
287         if (!eq)
288                 return -ENOMEM;
289
290         data = elevator_init_queue(q, eq);
291         if (!data) {
292                 kobject_put(&eq->kobj);
293                 return -ENOMEM;
294         }
295
296         elevator_attach(q, eq, data);
297         return ret;
298 }
299 EXPORT_SYMBOL(elevator_init);
300
301 void elevator_exit(struct elevator_queue *e)
302 {
303         mutex_lock(&e->sysfs_lock);
304         if (e->ops->elevator_exit_fn)
305                 e->ops->elevator_exit_fn(e);
306         e->ops = NULL;
307         mutex_unlock(&e->sysfs_lock);
308
309         kobject_put(&e->kobj);
310 }
311 EXPORT_SYMBOL(elevator_exit);
312
313 static void elv_activate_rq(struct request_queue *q, struct request *rq)
314 {
315         struct elevator_queue *e = q->elevator;
316
317         if (e->ops->elevator_activate_req_fn)
318                 e->ops->elevator_activate_req_fn(q, rq);
319 }
320
321 static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
322 {
323         struct elevator_queue *e = q->elevator;
324
325         if (e->ops->elevator_deactivate_req_fn)
326                 e->ops->elevator_deactivate_req_fn(q, rq);
327 }
328
329 static inline void __elv_rqhash_del(struct request *rq)
330 {
331         hlist_del_init(&rq->hash);
332 }
333
334 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
335 {
336         if (ELV_ON_HASH(rq))
337                 __elv_rqhash_del(rq);
338 }
339
340 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
341 {
342         struct elevator_queue *e = q->elevator;
343
344         BUG_ON(ELV_ON_HASH(rq));
345         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
346 }
347
348 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
349 {
350         __elv_rqhash_del(rq);
351         elv_rqhash_add(q, rq);
352 }
353
354 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
355 {
356         struct elevator_queue *e = q->elevator;
357         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
358         struct hlist_node *entry, *next;
359         struct request *rq;
360
361         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
362                 BUG_ON(!ELV_ON_HASH(rq));
363
364                 if (unlikely(!rq_mergeable(rq))) {
365                         __elv_rqhash_del(rq);
366                         continue;
367                 }
368
369                 if (rq_hash_key(rq) == offset)
370                         return rq;
371         }
372
373         return NULL;
374 }
375
376 /*
377  * RB-tree support functions for inserting/lookup/removal of requests
378  * in a sorted RB tree.
379  */
380 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
381 {
382         struct rb_node **p = &root->rb_node;
383         struct rb_node *parent = NULL;
384         struct request *__rq;
385
386         while (*p) {
387                 parent = *p;
388                 __rq = rb_entry(parent, struct request, rb_node);
389
390                 if (rq->sector < __rq->sector)
391                         p = &(*p)->rb_left;
392                 else if (rq->sector > __rq->sector)
393                         p = &(*p)->rb_right;
394                 else
395                         return __rq;
396         }
397
398         rb_link_node(&rq->rb_node, parent, p);
399         rb_insert_color(&rq->rb_node, root);
400         return NULL;
401 }
402 EXPORT_SYMBOL(elv_rb_add);
403
404 void elv_rb_del(struct rb_root *root, struct request *rq)
405 {
406         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
407         rb_erase(&rq->rb_node, root);
408         RB_CLEAR_NODE(&rq->rb_node);
409 }
410 EXPORT_SYMBOL(elv_rb_del);
411
412 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
413 {
414         struct rb_node *n = root->rb_node;
415         struct request *rq;
416
417         while (n) {
418                 rq = rb_entry(n, struct request, rb_node);
419
420                 if (sector < rq->sector)
421                         n = n->rb_left;
422                 else if (sector > rq->sector)
423                         n = n->rb_right;
424                 else
425                         return rq;
426         }
427
428         return NULL;
429 }
430 EXPORT_SYMBOL(elv_rb_find);
431
432 /*
433  * Insert rq into dispatch queue of q.  Queue lock must be held on
434  * entry.  rq is sort instead into the dispatch queue. To be used by
435  * specific elevators.
436  */
437 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
438 {
439         sector_t boundary;
440         struct list_head *entry;
441         int stop_flags;
442
443         if (q->last_merge == rq)
444                 q->last_merge = NULL;
445
446         elv_rqhash_del(q, rq);
447
448         q->nr_sorted--;
449
450         boundary = q->end_sector;
451         stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
452         list_for_each_prev(entry, &q->queue_head) {
453                 struct request *pos = list_entry_rq(entry);
454
455                 if (blk_discard_rq(rq) != blk_discard_rq(pos))
456                         break;
457                 if (rq_data_dir(rq) != rq_data_dir(pos))
458                         break;
459                 if (pos->cmd_flags & stop_flags)
460                         break;
461                 if (rq->sector >= boundary) {
462                         if (pos->sector < boundary)
463                                 continue;
464                 } else {
465                         if (pos->sector >= boundary)
466                                 break;
467                 }
468                 if (rq->sector >= pos->sector)
469                         break;
470         }
471
472         list_add(&rq->queuelist, entry);
473 }
474 EXPORT_SYMBOL(elv_dispatch_sort);
475
476 /*
477  * Insert rq into dispatch queue of q.  Queue lock must be held on
478  * entry.  rq is added to the back of the dispatch queue. To be used by
479  * specific elevators.
480  */
481 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
482 {
483         if (q->last_merge == rq)
484                 q->last_merge = NULL;
485
486         elv_rqhash_del(q, rq);
487
488         q->nr_sorted--;
489
490         q->end_sector = rq_end_sector(rq);
491         q->boundary_rq = rq;
492         list_add_tail(&rq->queuelist, &q->queue_head);
493 }
494 EXPORT_SYMBOL(elv_dispatch_add_tail);
495
496 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
497 {
498         struct elevator_queue *e = q->elevator;
499         struct request *__rq;
500         int ret;
501
502         /*
503          * First try one-hit cache.
504          */
505         if (q->last_merge) {
506                 ret = elv_try_merge(q->last_merge, bio);
507                 if (ret != ELEVATOR_NO_MERGE) {
508                         *req = q->last_merge;
509                         return ret;
510                 }
511         }
512
513         if (blk_queue_nomerges(q))
514                 return ELEVATOR_NO_MERGE;
515
516         /*
517          * See if our hash lookup can find a potential backmerge.
518          */
519         __rq = elv_rqhash_find(q, bio->bi_sector);
520         if (__rq && elv_rq_merge_ok(__rq, bio)) {
521                 *req = __rq;
522                 return ELEVATOR_BACK_MERGE;
523         }
524
525         if (e->ops->elevator_merge_fn)
526                 return e->ops->elevator_merge_fn(q, req, bio);
527
528         return ELEVATOR_NO_MERGE;
529 }
530
531 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
532 {
533         struct elevator_queue *e = q->elevator;
534
535         if (e->ops->elevator_merged_fn)
536                 e->ops->elevator_merged_fn(q, rq, type);
537
538         if (type == ELEVATOR_BACK_MERGE)
539                 elv_rqhash_reposition(q, rq);
540
541         q->last_merge = rq;
542 }
543
544 void elv_merge_requests(struct request_queue *q, struct request *rq,
545                              struct request *next)
546 {
547         struct elevator_queue *e = q->elevator;
548
549         if (e->ops->elevator_merge_req_fn)
550                 e->ops->elevator_merge_req_fn(q, rq, next);
551
552         elv_rqhash_reposition(q, rq);
553         elv_rqhash_del(q, next);
554
555         q->nr_sorted--;
556         q->last_merge = rq;
557 }
558
559 void elv_requeue_request(struct request_queue *q, struct request *rq)
560 {
561         /*
562          * it already went through dequeue, we need to decrement the
563          * in_flight count again
564          */
565         if (blk_account_rq(rq)) {
566                 q->in_flight--;
567                 if (blk_sorted_rq(rq))
568                         elv_deactivate_rq(q, rq);
569         }
570
571         rq->cmd_flags &= ~REQ_STARTED;
572
573         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
574 }
575
576 void elv_drain_elevator(struct request_queue *q)
577 {
578         static int printed;
579         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
580                 ;
581         if (q->nr_sorted == 0)
582                 return;
583         if (printed++ < 10) {
584                 printk(KERN_ERR "%s: forced dispatching is broken "
585                        "(nr_sorted=%u), please report this\n",
586                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
587         }
588 }
589
590 /*
591  * Call with queue lock held, interrupts disabled
592  */
593 void elv_quiesce_start(struct request_queue *q)
594 {
595         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
596
597         /*
598          * make sure we don't have any requests in flight
599          */
600         elv_drain_elevator(q);
601         while (q->rq.elvpriv) {
602                 __blk_run_queue(q);
603                 spin_unlock_irq(q->queue_lock);
604                 msleep(10);
605                 spin_lock_irq(q->queue_lock);
606                 elv_drain_elevator(q);
607         }
608 }
609
610 void elv_quiesce_end(struct request_queue *q)
611 {
612         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
613 }
614
615 void elv_insert(struct request_queue *q, struct request *rq, int where)
616 {
617         struct list_head *pos;
618         unsigned ordseq;
619         int unplug_it = 1;
620
621         trace_block_rq_insert(q, rq);
622
623         rq->q = q;
624
625         switch (where) {
626         case ELEVATOR_INSERT_FRONT:
627                 rq->cmd_flags |= REQ_SOFTBARRIER;
628
629                 list_add(&rq->queuelist, &q->queue_head);
630                 break;
631
632         case ELEVATOR_INSERT_BACK:
633                 rq->cmd_flags |= REQ_SOFTBARRIER;
634                 elv_drain_elevator(q);
635                 list_add_tail(&rq->queuelist, &q->queue_head);
636                 /*
637                  * We kick the queue here for the following reasons.
638                  * - The elevator might have returned NULL previously
639                  *   to delay requests and returned them now.  As the
640                  *   queue wasn't empty before this request, ll_rw_blk
641                  *   won't run the queue on return, resulting in hang.
642                  * - Usually, back inserted requests won't be merged
643                  *   with anything.  There's no point in delaying queue
644                  *   processing.
645                  */
646                 __blk_run_queue(q);
647                 break;
648
649         case ELEVATOR_INSERT_SORT:
650                 BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
651                 rq->cmd_flags |= REQ_SORTED;
652                 q->nr_sorted++;
653                 if (rq_mergeable(rq)) {
654                         elv_rqhash_add(q, rq);
655                         if (!q->last_merge)
656                                 q->last_merge = rq;
657                 }
658
659                 /*
660                  * Some ioscheds (cfq) run q->request_fn directly, so
661                  * rq cannot be accessed after calling
662                  * elevator_add_req_fn.
663                  */
664                 q->elevator->ops->elevator_add_req_fn(q, rq);
665                 break;
666
667         case ELEVATOR_INSERT_REQUEUE:
668                 /*
669                  * If ordered flush isn't in progress, we do front
670                  * insertion; otherwise, requests should be requeued
671                  * in ordseq order.
672                  */
673                 rq->cmd_flags |= REQ_SOFTBARRIER;
674
675                 /*
676                  * Most requeues happen because of a busy condition,
677                  * don't force unplug of the queue for that case.
678                  */
679                 unplug_it = 0;
680
681                 if (q->ordseq == 0) {
682                         list_add(&rq->queuelist, &q->queue_head);
683                         break;
684                 }
685
686                 ordseq = blk_ordered_req_seq(rq);
687
688                 list_for_each(pos, &q->queue_head) {
689                         struct request *pos_rq = list_entry_rq(pos);
690                         if (ordseq <= blk_ordered_req_seq(pos_rq))
691                                 break;
692                 }
693
694                 list_add_tail(&rq->queuelist, pos);
695                 break;
696
697         default:
698                 printk(KERN_ERR "%s: bad insertion point %d\n",
699                        __func__, where);
700                 BUG();
701         }
702
703         if (unplug_it && blk_queue_plugged(q)) {
704                 int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
705                         - q->in_flight;
706
707                 if (nrq >= q->unplug_thresh)
708                         __generic_unplug_device(q);
709         }
710 }
711
712 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
713                        int plug)
714 {
715         if (q->ordcolor)
716                 rq->cmd_flags |= REQ_ORDERED_COLOR;
717
718         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
719                 /*
720                  * toggle ordered color
721                  */
722                 if (blk_barrier_rq(rq))
723                         q->ordcolor ^= 1;
724
725                 /*
726                  * barriers implicitly indicate back insertion
727                  */
728                 if (where == ELEVATOR_INSERT_SORT)
729                         where = ELEVATOR_INSERT_BACK;
730
731                 /*
732                  * this request is scheduling boundary, update
733                  * end_sector
734                  */
735                 if (blk_fs_request(rq) || blk_discard_rq(rq)) {
736                         q->end_sector = rq_end_sector(rq);
737                         q->boundary_rq = rq;
738                 }
739         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
740                     where == ELEVATOR_INSERT_SORT)
741                 where = ELEVATOR_INSERT_BACK;
742
743         if (plug)
744                 blk_plug_device(q);
745
746         elv_insert(q, rq, where);
747 }
748 EXPORT_SYMBOL(__elv_add_request);
749
750 void elv_add_request(struct request_queue *q, struct request *rq, int where,
751                      int plug)
752 {
753         unsigned long flags;
754
755         spin_lock_irqsave(q->queue_lock, flags);
756         __elv_add_request(q, rq, where, plug);
757         spin_unlock_irqrestore(q->queue_lock, flags);
758 }
759 EXPORT_SYMBOL(elv_add_request);
760
761 static inline struct request *__elv_next_request(struct request_queue *q)
762 {
763         struct request *rq;
764
765         while (1) {
766                 while (!list_empty(&q->queue_head)) {
767                         rq = list_entry_rq(q->queue_head.next);
768                         if (blk_do_ordered(q, &rq))
769                                 return rq;
770                 }
771
772                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
773                         return NULL;
774         }
775 }
776
777 struct request *elv_next_request(struct request_queue *q)
778 {
779         struct request *rq;
780         int ret;
781
782         while ((rq = __elv_next_request(q)) != NULL) {
783                 if (!(rq->cmd_flags & REQ_STARTED)) {
784                         /*
785                          * This is the first time the device driver
786                          * sees this request (possibly after
787                          * requeueing).  Notify IO scheduler.
788                          */
789                         if (blk_sorted_rq(rq))
790                                 elv_activate_rq(q, rq);
791
792                         /*
793                          * just mark as started even if we don't start
794                          * it, a request that has been delayed should
795                          * not be passed by new incoming requests
796                          */
797                         rq->cmd_flags |= REQ_STARTED;
798                         trace_block_rq_issue(q, rq);
799                 }
800
801                 if (!q->boundary_rq || q->boundary_rq == rq) {
802                         q->end_sector = rq_end_sector(rq);
803                         q->boundary_rq = NULL;
804                 }
805
806                 if (rq->cmd_flags & REQ_DONTPREP)
807                         break;
808
809                 if (q->dma_drain_size && rq->data_len) {
810                         /*
811                          * make sure space for the drain appears we
812                          * know we can do this because max_hw_segments
813                          * has been adjusted to be one fewer than the
814                          * device can handle
815                          */
816                         rq->nr_phys_segments++;
817                 }
818
819                 if (!q->prep_rq_fn)
820                         break;
821
822                 ret = q->prep_rq_fn(q, rq);
823                 if (ret == BLKPREP_OK) {
824                         break;
825                 } else if (ret == BLKPREP_DEFER) {
826                         /*
827                          * the request may have been (partially) prepped.
828                          * we need to keep this request in the front to
829                          * avoid resource deadlock.  REQ_STARTED will
830                          * prevent other fs requests from passing this one.
831                          */
832                         if (q->dma_drain_size && rq->data_len &&
833                             !(rq->cmd_flags & REQ_DONTPREP)) {
834                                 /*
835                                  * remove the space for the drain we added
836                                  * so that we don't add it again
837                                  */
838                                 --rq->nr_phys_segments;
839                         }
840
841                         rq = NULL;
842                         break;
843                 } else if (ret == BLKPREP_KILL) {
844                         rq->cmd_flags |= REQ_QUIET;
845                         __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
846                 } else {
847                         printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
848                         break;
849                 }
850         }
851
852         return rq;
853 }
854 EXPORT_SYMBOL(elv_next_request);
855
856 void elv_dequeue_request(struct request_queue *q, struct request *rq)
857 {
858         BUG_ON(list_empty(&rq->queuelist));
859         BUG_ON(ELV_ON_HASH(rq));
860
861         list_del_init(&rq->queuelist);
862
863         /*
864          * the time frame between a request being removed from the lists
865          * and to it is freed is accounted as io that is in progress at
866          * the driver side.
867          */
868         if (blk_account_rq(rq))
869                 q->in_flight++;
870 }
871
872 int elv_queue_empty(struct request_queue *q)
873 {
874         struct elevator_queue *e = q->elevator;
875
876         if (!list_empty(&q->queue_head))
877                 return 0;
878
879         if (e->ops->elevator_queue_empty_fn)
880                 return e->ops->elevator_queue_empty_fn(q);
881
882         return 1;
883 }
884 EXPORT_SYMBOL(elv_queue_empty);
885
886 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
887 {
888         struct elevator_queue *e = q->elevator;
889
890         if (e->ops->elevator_latter_req_fn)
891                 return e->ops->elevator_latter_req_fn(q, rq);
892         return NULL;
893 }
894
895 struct request *elv_former_request(struct request_queue *q, struct request *rq)
896 {
897         struct elevator_queue *e = q->elevator;
898
899         if (e->ops->elevator_former_req_fn)
900                 return e->ops->elevator_former_req_fn(q, rq);
901         return NULL;
902 }
903
904 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
905 {
906         struct elevator_queue *e = q->elevator;
907
908         if (e->ops->elevator_set_req_fn)
909                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
910
911         rq->elevator_private = NULL;
912         return 0;
913 }
914
915 void elv_put_request(struct request_queue *q, struct request *rq)
916 {
917         struct elevator_queue *e = q->elevator;
918
919         if (e->ops->elevator_put_req_fn)
920                 e->ops->elevator_put_req_fn(rq);
921 }
922
923 int elv_may_queue(struct request_queue *q, int rw)
924 {
925         struct elevator_queue *e = q->elevator;
926
927         if (e->ops->elevator_may_queue_fn)
928                 return e->ops->elevator_may_queue_fn(q, rw);
929
930         return ELV_MQUEUE_MAY;
931 }
932
933 void elv_abort_queue(struct request_queue *q)
934 {
935         struct request *rq;
936
937         while (!list_empty(&q->queue_head)) {
938                 rq = list_entry_rq(q->queue_head.next);
939                 rq->cmd_flags |= REQ_QUIET;
940                 trace_block_rq_abort(q, rq);
941                 __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
942         }
943 }
944 EXPORT_SYMBOL(elv_abort_queue);
945
946 void elv_completed_request(struct request_queue *q, struct request *rq)
947 {
948         struct elevator_queue *e = q->elevator;
949
950         /*
951          * request is released from the driver, io must be done
952          */
953         if (blk_account_rq(rq)) {
954                 q->in_flight--;
955                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
956                         e->ops->elevator_completed_req_fn(q, rq);
957         }
958
959         /*
960          * Check if the queue is waiting for fs requests to be
961          * drained for flush sequence.
962          */
963         if (unlikely(q->ordseq)) {
964                 struct request *next = NULL;
965
966                 if (!list_empty(&q->queue_head))
967                         next = list_entry_rq(q->queue_head.next);
968
969                 if (!q->in_flight &&
970                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
971                     (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
972                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
973                         __blk_run_queue(q);
974                 }
975         }
976 }
977
978 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
979
980 static ssize_t
981 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
982 {
983         struct elv_fs_entry *entry = to_elv(attr);
984         struct elevator_queue *e;
985         ssize_t error;
986
987         if (!entry->show)
988                 return -EIO;
989
990         e = container_of(kobj, struct elevator_queue, kobj);
991         mutex_lock(&e->sysfs_lock);
992         error = e->ops ? entry->show(e, page) : -ENOENT;
993         mutex_unlock(&e->sysfs_lock);
994         return error;
995 }
996
997 static ssize_t
998 elv_attr_store(struct kobject *kobj, struct attribute *attr,
999                const char *page, size_t length)
1000 {
1001         struct elv_fs_entry *entry = to_elv(attr);
1002         struct elevator_queue *e;
1003         ssize_t error;
1004
1005         if (!entry->store)
1006                 return -EIO;
1007
1008         e = container_of(kobj, struct elevator_queue, kobj);
1009         mutex_lock(&e->sysfs_lock);
1010         error = e->ops ? entry->store(e, page, length) : -ENOENT;
1011         mutex_unlock(&e->sysfs_lock);
1012         return error;
1013 }
1014
1015 static struct sysfs_ops elv_sysfs_ops = {
1016         .show   = elv_attr_show,
1017         .store  = elv_attr_store,
1018 };
1019
1020 static struct kobj_type elv_ktype = {
1021         .sysfs_ops      = &elv_sysfs_ops,
1022         .release        = elevator_release,
1023 };
1024
1025 int elv_register_queue(struct request_queue *q)
1026 {
1027         struct elevator_queue *e = q->elevator;
1028         int error;
1029
1030         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1031         if (!error) {
1032                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1033                 if (attr) {
1034                         while (attr->attr.name) {
1035                                 if (sysfs_create_file(&e->kobj, &attr->attr))
1036                                         break;
1037                                 attr++;
1038                         }
1039                 }
1040                 kobject_uevent(&e->kobj, KOBJ_ADD);
1041         }
1042         return error;
1043 }
1044
1045 static void __elv_unregister_queue(struct elevator_queue *e)
1046 {
1047         kobject_uevent(&e->kobj, KOBJ_REMOVE);
1048         kobject_del(&e->kobj);
1049 }
1050
1051 void elv_unregister_queue(struct request_queue *q)
1052 {
1053         if (q)
1054                 __elv_unregister_queue(q->elevator);
1055 }
1056
1057 void elv_register(struct elevator_type *e)
1058 {
1059         char *def = "";
1060
1061         spin_lock(&elv_list_lock);
1062         BUG_ON(elevator_find(e->elevator_name));
1063         list_add_tail(&e->list, &elv_list);
1064         spin_unlock(&elv_list_lock);
1065
1066         if (!strcmp(e->elevator_name, chosen_elevator) ||
1067                         (!*chosen_elevator &&
1068                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1069                                 def = " (default)";
1070
1071         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1072                                                                 def);
1073 }
1074 EXPORT_SYMBOL_GPL(elv_register);
1075
1076 void elv_unregister(struct elevator_type *e)
1077 {
1078         struct task_struct *g, *p;
1079
1080         /*
1081          * Iterate every thread in the process to remove the io contexts.
1082          */
1083         if (e->ops.trim) {
1084                 read_lock(&tasklist_lock);
1085                 do_each_thread(g, p) {
1086                         task_lock(p);
1087                         if (p->io_context)
1088                                 e->ops.trim(p->io_context);
1089                         task_unlock(p);
1090                 } while_each_thread(g, p);
1091                 read_unlock(&tasklist_lock);
1092         }
1093
1094         spin_lock(&elv_list_lock);
1095         list_del_init(&e->list);
1096         spin_unlock(&elv_list_lock);
1097 }
1098 EXPORT_SYMBOL_GPL(elv_unregister);
1099
1100 /*
1101  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1102  * we don't free the old io scheduler, before we have allocated what we
1103  * need for the new one. this way we have a chance of going back to the old
1104  * one, if the new one fails init for some reason.
1105  */
1106 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1107 {
1108         struct elevator_queue *old_elevator, *e;
1109         void *data;
1110
1111         /*
1112          * Allocate new elevator
1113          */
1114         e = elevator_alloc(q, new_e);
1115         if (!e)
1116                 return 0;
1117
1118         data = elevator_init_queue(q, e);
1119         if (!data) {
1120                 kobject_put(&e->kobj);
1121                 return 0;
1122         }
1123
1124         /*
1125          * Turn on BYPASS and drain all requests w/ elevator private data
1126          */
1127         spin_lock_irq(q->queue_lock);
1128         elv_quiesce_start(q);
1129
1130         /*
1131          * Remember old elevator.
1132          */
1133         old_elevator = q->elevator;
1134
1135         /*
1136          * attach and start new elevator
1137          */
1138         elevator_attach(q, e, data);
1139
1140         spin_unlock_irq(q->queue_lock);
1141
1142         __elv_unregister_queue(old_elevator);
1143
1144         if (elv_register_queue(q))
1145                 goto fail_register;
1146
1147         /*
1148          * finally exit old elevator and turn off BYPASS.
1149          */
1150         elevator_exit(old_elevator);
1151         spin_lock_irq(q->queue_lock);
1152         elv_quiesce_end(q);
1153         spin_unlock_irq(q->queue_lock);
1154
1155         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1156
1157         return 1;
1158
1159 fail_register:
1160         /*
1161          * switch failed, exit the new io scheduler and reattach the old
1162          * one again (along with re-adding the sysfs dir)
1163          */
1164         elevator_exit(e);
1165         q->elevator = old_elevator;
1166         elv_register_queue(q);
1167
1168         spin_lock_irq(q->queue_lock);
1169         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1170         spin_unlock_irq(q->queue_lock);
1171
1172         return 0;
1173 }
1174
1175 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1176                           size_t count)
1177 {
1178         char elevator_name[ELV_NAME_MAX];
1179         struct elevator_type *e;
1180
1181         strlcpy(elevator_name, name, sizeof(elevator_name));
1182         strstrip(elevator_name);
1183
1184         e = elevator_get(elevator_name);
1185         if (!e) {
1186                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1187                 return -EINVAL;
1188         }
1189
1190         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1191                 elevator_put(e);
1192                 return count;
1193         }
1194
1195         if (!elevator_switch(q, e))
1196                 printk(KERN_ERR "elevator: switch to %s failed\n",
1197                                                         elevator_name);
1198         return count;
1199 }
1200
1201 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1202 {
1203         struct elevator_queue *e = q->elevator;
1204         struct elevator_type *elv = e->elevator_type;
1205         struct elevator_type *__e;
1206         int len = 0;
1207
1208         spin_lock(&elv_list_lock);
1209         list_for_each_entry(__e, &elv_list, list) {
1210                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1211                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1212                 else
1213                         len += sprintf(name+len, "%s ", __e->elevator_name);
1214         }
1215         spin_unlock(&elv_list_lock);
1216
1217         len += sprintf(len+name, "\n");
1218         return len;
1219 }
1220
1221 struct request *elv_rb_former_request(struct request_queue *q,
1222                                       struct request *rq)
1223 {
1224         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1225
1226         if (rbprev)
1227                 return rb_entry_rq(rbprev);
1228
1229         return NULL;
1230 }
1231 EXPORT_SYMBOL(elv_rb_former_request);
1232
1233 struct request *elv_rb_latter_request(struct request_queue *q,
1234                                       struct request *rq)
1235 {
1236         struct rb_node *rbnext = rb_next(&rq->rb_node);
1237
1238         if (rbnext)
1239                 return rb_entry_rq(rbnext);
1240
1241         return NULL;
1242 }
1243 EXPORT_SYMBOL(elv_rb_latter_request);