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