x86: add uniq_ioapic_id to mpparse_32.c
[sfrench/cifs-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 inline 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         /*
492          * See if our hash lookup can find a potential backmerge.
493          */
494         __rq = elv_rqhash_find(q, bio->bi_sector);
495         if (__rq && elv_rq_merge_ok(__rq, bio)) {
496                 *req = __rq;
497                 return ELEVATOR_BACK_MERGE;
498         }
499
500         if (e->ops->elevator_merge_fn)
501                 return e->ops->elevator_merge_fn(q, req, bio);
502
503         return ELEVATOR_NO_MERGE;
504 }
505
506 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
507 {
508         elevator_t *e = q->elevator;
509
510         if (e->ops->elevator_merged_fn)
511                 e->ops->elevator_merged_fn(q, rq, type);
512
513         if (type == ELEVATOR_BACK_MERGE)
514                 elv_rqhash_reposition(q, rq);
515
516         q->last_merge = rq;
517 }
518
519 void elv_merge_requests(struct request_queue *q, struct request *rq,
520                              struct request *next)
521 {
522         elevator_t *e = q->elevator;
523
524         if (e->ops->elevator_merge_req_fn)
525                 e->ops->elevator_merge_req_fn(q, rq, next);
526
527         elv_rqhash_reposition(q, rq);
528         elv_rqhash_del(q, next);
529
530         q->nr_sorted--;
531         q->last_merge = rq;
532 }
533
534 void elv_requeue_request(struct request_queue *q, struct request *rq)
535 {
536         /*
537          * it already went through dequeue, we need to decrement the
538          * in_flight count again
539          */
540         if (blk_account_rq(rq)) {
541                 q->in_flight--;
542                 if (blk_sorted_rq(rq))
543                         elv_deactivate_rq(q, rq);
544         }
545
546         rq->cmd_flags &= ~REQ_STARTED;
547
548         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
549 }
550
551 static void elv_drain_elevator(struct request_queue *q)
552 {
553         static int printed;
554         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
555                 ;
556         if (q->nr_sorted == 0)
557                 return;
558         if (printed++ < 10) {
559                 printk(KERN_ERR "%s: forced dispatching is broken "
560                        "(nr_sorted=%u), please report this\n",
561                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
562         }
563 }
564
565 void elv_insert(struct request_queue *q, struct request *rq, int where)
566 {
567         struct list_head *pos;
568         unsigned ordseq;
569         int unplug_it = 1;
570
571         blk_add_trace_rq(q, rq, BLK_TA_INSERT);
572
573         rq->q = q;
574
575         switch (where) {
576         case ELEVATOR_INSERT_FRONT:
577                 rq->cmd_flags |= REQ_SOFTBARRIER;
578
579                 list_add(&rq->queuelist, &q->queue_head);
580                 break;
581
582         case ELEVATOR_INSERT_BACK:
583                 rq->cmd_flags |= REQ_SOFTBARRIER;
584                 elv_drain_elevator(q);
585                 list_add_tail(&rq->queuelist, &q->queue_head);
586                 /*
587                  * We kick the queue here for the following reasons.
588                  * - The elevator might have returned NULL previously
589                  *   to delay requests and returned them now.  As the
590                  *   queue wasn't empty before this request, ll_rw_blk
591                  *   won't run the queue on return, resulting in hang.
592                  * - Usually, back inserted requests won't be merged
593                  *   with anything.  There's no point in delaying queue
594                  *   processing.
595                  */
596                 blk_remove_plug(q);
597                 q->request_fn(q);
598                 break;
599
600         case ELEVATOR_INSERT_SORT:
601                 BUG_ON(!blk_fs_request(rq));
602                 rq->cmd_flags |= REQ_SORTED;
603                 q->nr_sorted++;
604                 if (rq_mergeable(rq)) {
605                         elv_rqhash_add(q, rq);
606                         if (!q->last_merge)
607                                 q->last_merge = rq;
608                 }
609
610                 /*
611                  * Some ioscheds (cfq) run q->request_fn directly, so
612                  * rq cannot be accessed after calling
613                  * elevator_add_req_fn.
614                  */
615                 q->elevator->ops->elevator_add_req_fn(q, rq);
616                 break;
617
618         case ELEVATOR_INSERT_REQUEUE:
619                 /*
620                  * If ordered flush isn't in progress, we do front
621                  * insertion; otherwise, requests should be requeued
622                  * in ordseq order.
623                  */
624                 rq->cmd_flags |= REQ_SOFTBARRIER;
625
626                 /*
627                  * Most requeues happen because of a busy condition,
628                  * don't force unplug of the queue for that case.
629                  */
630                 unplug_it = 0;
631
632                 if (q->ordseq == 0) {
633                         list_add(&rq->queuelist, &q->queue_head);
634                         break;
635                 }
636
637                 ordseq = blk_ordered_req_seq(rq);
638
639                 list_for_each(pos, &q->queue_head) {
640                         struct request *pos_rq = list_entry_rq(pos);
641                         if (ordseq <= blk_ordered_req_seq(pos_rq))
642                                 break;
643                 }
644
645                 list_add_tail(&rq->queuelist, pos);
646                 break;
647
648         default:
649                 printk(KERN_ERR "%s: bad insertion point %d\n",
650                        __FUNCTION__, where);
651                 BUG();
652         }
653
654         if (unplug_it && blk_queue_plugged(q)) {
655                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
656                         - q->in_flight;
657
658                 if (nrq >= q->unplug_thresh)
659                         __generic_unplug_device(q);
660         }
661 }
662
663 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
664                        int plug)
665 {
666         if (q->ordcolor)
667                 rq->cmd_flags |= REQ_ORDERED_COLOR;
668
669         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
670                 /*
671                  * toggle ordered color
672                  */
673                 if (blk_barrier_rq(rq))
674                         q->ordcolor ^= 1;
675
676                 /*
677                  * barriers implicitly indicate back insertion
678                  */
679                 if (where == ELEVATOR_INSERT_SORT)
680                         where = ELEVATOR_INSERT_BACK;
681
682                 /*
683                  * this request is scheduling boundary, update
684                  * end_sector
685                  */
686                 if (blk_fs_request(rq)) {
687                         q->end_sector = rq_end_sector(rq);
688                         q->boundary_rq = rq;
689                 }
690         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
691                     where == ELEVATOR_INSERT_SORT)
692                 where = ELEVATOR_INSERT_BACK;
693
694         if (plug)
695                 blk_plug_device(q);
696
697         elv_insert(q, rq, where);
698 }
699 EXPORT_SYMBOL(__elv_add_request);
700
701 void elv_add_request(struct request_queue *q, struct request *rq, int where,
702                      int plug)
703 {
704         unsigned long flags;
705
706         spin_lock_irqsave(q->queue_lock, flags);
707         __elv_add_request(q, rq, where, plug);
708         spin_unlock_irqrestore(q->queue_lock, flags);
709 }
710 EXPORT_SYMBOL(elv_add_request);
711
712 static inline struct request *__elv_next_request(struct request_queue *q)
713 {
714         struct request *rq;
715
716         while (1) {
717                 while (!list_empty(&q->queue_head)) {
718                         rq = list_entry_rq(q->queue_head.next);
719                         if (blk_do_ordered(q, &rq))
720                                 return rq;
721                 }
722
723                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
724                         return NULL;
725         }
726 }
727
728 struct request *elv_next_request(struct request_queue *q)
729 {
730         struct request *rq;
731         int ret;
732
733         while ((rq = __elv_next_request(q)) != NULL) {
734                 /*
735                  * Kill the empty barrier place holder, the driver must
736                  * not ever see it.
737                  */
738                 if (blk_empty_barrier(rq)) {
739                         end_queued_request(rq, 1);
740                         continue;
741                 }
742                 if (!(rq->cmd_flags & REQ_STARTED)) {
743                         /*
744                          * This is the first time the device driver
745                          * sees this request (possibly after
746                          * requeueing).  Notify IO scheduler.
747                          */
748                         if (blk_sorted_rq(rq))
749                                 elv_activate_rq(q, rq);
750
751                         /*
752                          * just mark as started even if we don't start
753                          * it, a request that has been delayed should
754                          * not be passed by new incoming requests
755                          */
756                         rq->cmd_flags |= REQ_STARTED;
757                         blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
758                 }
759
760                 if (!q->boundary_rq || q->boundary_rq == rq) {
761                         q->end_sector = rq_end_sector(rq);
762                         q->boundary_rq = NULL;
763                 }
764
765                 if (rq->cmd_flags & REQ_DONTPREP)
766                         break;
767
768                 if (q->dma_drain_size && rq->data_len) {
769                         /*
770                          * make sure space for the drain appears we
771                          * know we can do this because max_hw_segments
772                          * has been adjusted to be one fewer than the
773                          * device can handle
774                          */
775                         rq->nr_phys_segments++;
776                         rq->nr_hw_segments++;
777                 }
778
779                 if (!q->prep_rq_fn)
780                         break;
781
782                 ret = q->prep_rq_fn(q, rq);
783                 if (ret == BLKPREP_OK) {
784                         break;
785                 } else if (ret == BLKPREP_DEFER) {
786                         /*
787                          * the request may have been (partially) prepped.
788                          * we need to keep this request in the front to
789                          * avoid resource deadlock.  REQ_STARTED will
790                          * prevent other fs requests from passing this one.
791                          */
792                         if (q->dma_drain_size && rq->data_len &&
793                             !(rq->cmd_flags & REQ_DONTPREP)) {
794                                 /*
795                                  * remove the space for the drain we added
796                                  * so that we don't add it again
797                                  */
798                                 --rq->nr_phys_segments;
799                                 --rq->nr_hw_segments;
800                         }
801
802                         rq = NULL;
803                         break;
804                 } else if (ret == BLKPREP_KILL) {
805                         rq->cmd_flags |= REQ_QUIET;
806                         end_queued_request(rq, 0);
807                 } else {
808                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
809                                                                 ret);
810                         break;
811                 }
812         }
813
814         return rq;
815 }
816 EXPORT_SYMBOL(elv_next_request);
817
818 void elv_dequeue_request(struct request_queue *q, struct request *rq)
819 {
820         BUG_ON(list_empty(&rq->queuelist));
821         BUG_ON(ELV_ON_HASH(rq));
822
823         list_del_init(&rq->queuelist);
824
825         /*
826          * the time frame between a request being removed from the lists
827          * and to it is freed is accounted as io that is in progress at
828          * the driver side.
829          */
830         if (blk_account_rq(rq))
831                 q->in_flight++;
832 }
833 EXPORT_SYMBOL(elv_dequeue_request);
834
835 int elv_queue_empty(struct request_queue *q)
836 {
837         elevator_t *e = q->elevator;
838
839         if (!list_empty(&q->queue_head))
840                 return 0;
841
842         if (e->ops->elevator_queue_empty_fn)
843                 return e->ops->elevator_queue_empty_fn(q);
844
845         return 1;
846 }
847 EXPORT_SYMBOL(elv_queue_empty);
848
849 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
850 {
851         elevator_t *e = q->elevator;
852
853         if (e->ops->elevator_latter_req_fn)
854                 return e->ops->elevator_latter_req_fn(q, rq);
855         return NULL;
856 }
857
858 struct request *elv_former_request(struct request_queue *q, struct request *rq)
859 {
860         elevator_t *e = q->elevator;
861
862         if (e->ops->elevator_former_req_fn)
863                 return e->ops->elevator_former_req_fn(q, rq);
864         return NULL;
865 }
866
867 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
868 {
869         elevator_t *e = q->elevator;
870
871         if (e->ops->elevator_set_req_fn)
872                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
873
874         rq->elevator_private = NULL;
875         return 0;
876 }
877
878 void elv_put_request(struct request_queue *q, struct request *rq)
879 {
880         elevator_t *e = q->elevator;
881
882         if (e->ops->elevator_put_req_fn)
883                 e->ops->elevator_put_req_fn(rq);
884 }
885
886 int elv_may_queue(struct request_queue *q, int rw)
887 {
888         elevator_t *e = q->elevator;
889
890         if (e->ops->elevator_may_queue_fn)
891                 return e->ops->elevator_may_queue_fn(q, rw);
892
893         return ELV_MQUEUE_MAY;
894 }
895
896 void elv_completed_request(struct request_queue *q, struct request *rq)
897 {
898         elevator_t *e = q->elevator;
899
900         /*
901          * request is released from the driver, io must be done
902          */
903         if (blk_account_rq(rq)) {
904                 q->in_flight--;
905                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
906                         e->ops->elevator_completed_req_fn(q, rq);
907         }
908
909         /*
910          * Check if the queue is waiting for fs requests to be
911          * drained for flush sequence.
912          */
913         if (unlikely(q->ordseq)) {
914                 struct request *first_rq = list_entry_rq(q->queue_head.next);
915                 if (q->in_flight == 0 &&
916                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
917                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
918                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
919                         q->request_fn(q);
920                 }
921         }
922 }
923
924 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
925
926 static ssize_t
927 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
928 {
929         elevator_t *e = container_of(kobj, elevator_t, kobj);
930         struct elv_fs_entry *entry = to_elv(attr);
931         ssize_t error;
932
933         if (!entry->show)
934                 return -EIO;
935
936         mutex_lock(&e->sysfs_lock);
937         error = e->ops ? entry->show(e, page) : -ENOENT;
938         mutex_unlock(&e->sysfs_lock);
939         return error;
940 }
941
942 static ssize_t
943 elv_attr_store(struct kobject *kobj, struct attribute *attr,
944                const char *page, size_t length)
945 {
946         elevator_t *e = container_of(kobj, elevator_t, kobj);
947         struct elv_fs_entry *entry = to_elv(attr);
948         ssize_t error;
949
950         if (!entry->store)
951                 return -EIO;
952
953         mutex_lock(&e->sysfs_lock);
954         error = e->ops ? entry->store(e, page, length) : -ENOENT;
955         mutex_unlock(&e->sysfs_lock);
956         return error;
957 }
958
959 static struct sysfs_ops elv_sysfs_ops = {
960         .show   = elv_attr_show,
961         .store  = elv_attr_store,
962 };
963
964 static struct kobj_type elv_ktype = {
965         .sysfs_ops      = &elv_sysfs_ops,
966         .release        = elevator_release,
967 };
968
969 int elv_register_queue(struct request_queue *q)
970 {
971         elevator_t *e = q->elevator;
972         int error;
973
974         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
975         if (!error) {
976                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
977                 if (attr) {
978                         while (attr->attr.name) {
979                                 if (sysfs_create_file(&e->kobj, &attr->attr))
980                                         break;
981                                 attr++;
982                         }
983                 }
984                 kobject_uevent(&e->kobj, KOBJ_ADD);
985         }
986         return error;
987 }
988
989 static void __elv_unregister_queue(elevator_t *e)
990 {
991         kobject_uevent(&e->kobj, KOBJ_REMOVE);
992         kobject_del(&e->kobj);
993 }
994
995 void elv_unregister_queue(struct request_queue *q)
996 {
997         if (q)
998                 __elv_unregister_queue(q->elevator);
999 }
1000
1001 void elv_register(struct elevator_type *e)
1002 {
1003         char *def = "";
1004
1005         spin_lock(&elv_list_lock);
1006         BUG_ON(elevator_find(e->elevator_name));
1007         list_add_tail(&e->list, &elv_list);
1008         spin_unlock(&elv_list_lock);
1009
1010         if (!strcmp(e->elevator_name, chosen_elevator) ||
1011                         (!*chosen_elevator &&
1012                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1013                                 def = " (default)";
1014
1015         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1016                                                                 def);
1017 }
1018 EXPORT_SYMBOL_GPL(elv_register);
1019
1020 void elv_unregister(struct elevator_type *e)
1021 {
1022         struct task_struct *g, *p;
1023
1024         /*
1025          * Iterate every thread in the process to remove the io contexts.
1026          */
1027         if (e->ops.trim) {
1028                 read_lock(&tasklist_lock);
1029                 do_each_thread(g, p) {
1030                         task_lock(p);
1031                         if (p->io_context)
1032                                 e->ops.trim(p->io_context);
1033                         task_unlock(p);
1034                 } while_each_thread(g, p);
1035                 read_unlock(&tasklist_lock);
1036         }
1037
1038         spin_lock(&elv_list_lock);
1039         list_del_init(&e->list);
1040         spin_unlock(&elv_list_lock);
1041 }
1042 EXPORT_SYMBOL_GPL(elv_unregister);
1043
1044 /*
1045  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1046  * we don't free the old io scheduler, before we have allocated what we
1047  * need for the new one. this way we have a chance of going back to the old
1048  * one, if the new one fails init for some reason.
1049  */
1050 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1051 {
1052         elevator_t *old_elevator, *e;
1053         void *data;
1054
1055         /*
1056          * Allocate new elevator
1057          */
1058         e = elevator_alloc(q, new_e);
1059         if (!e)
1060                 return 0;
1061
1062         data = elevator_init_queue(q, e);
1063         if (!data) {
1064                 kobject_put(&e->kobj);
1065                 return 0;
1066         }
1067
1068         /*
1069          * Turn on BYPASS and drain all requests w/ elevator private data
1070          */
1071         spin_lock_irq(q->queue_lock);
1072
1073         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1074
1075         elv_drain_elevator(q);
1076
1077         while (q->rq.elvpriv) {
1078                 blk_remove_plug(q);
1079                 q->request_fn(q);
1080                 spin_unlock_irq(q->queue_lock);
1081                 msleep(10);
1082                 spin_lock_irq(q->queue_lock);
1083                 elv_drain_elevator(q);
1084         }
1085
1086         /*
1087          * Remember old elevator.
1088          */
1089         old_elevator = q->elevator;
1090
1091         /*
1092          * attach and start new elevator
1093          */
1094         elevator_attach(q, e, data);
1095
1096         spin_unlock_irq(q->queue_lock);
1097
1098         __elv_unregister_queue(old_elevator);
1099
1100         if (elv_register_queue(q))
1101                 goto fail_register;
1102
1103         /*
1104          * finally exit old elevator and turn off BYPASS.
1105          */
1106         elevator_exit(old_elevator);
1107         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1108         return 1;
1109
1110 fail_register:
1111         /*
1112          * switch failed, exit the new io scheduler and reattach the old
1113          * one again (along with re-adding the sysfs dir)
1114          */
1115         elevator_exit(e);
1116         q->elevator = old_elevator;
1117         elv_register_queue(q);
1118         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1119         return 0;
1120 }
1121
1122 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1123                           size_t count)
1124 {
1125         char elevator_name[ELV_NAME_MAX];
1126         size_t len;
1127         struct elevator_type *e;
1128
1129         elevator_name[sizeof(elevator_name) - 1] = '\0';
1130         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
1131         len = strlen(elevator_name);
1132
1133         if (len && elevator_name[len - 1] == '\n')
1134                 elevator_name[len - 1] = '\0';
1135
1136         e = elevator_get(elevator_name);
1137         if (!e) {
1138                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1139                 return -EINVAL;
1140         }
1141
1142         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1143                 elevator_put(e);
1144                 return count;
1145         }
1146
1147         if (!elevator_switch(q, e))
1148                 printk(KERN_ERR "elevator: switch to %s failed\n",
1149                                                         elevator_name);
1150         return count;
1151 }
1152
1153 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1154 {
1155         elevator_t *e = q->elevator;
1156         struct elevator_type *elv = e->elevator_type;
1157         struct elevator_type *__e;
1158         int len = 0;
1159
1160         spin_lock(&elv_list_lock);
1161         list_for_each_entry(__e, &elv_list, list) {
1162                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1163                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1164                 else
1165                         len += sprintf(name+len, "%s ", __e->elevator_name);
1166         }
1167         spin_unlock(&elv_list_lock);
1168
1169         len += sprintf(len+name, "\n");
1170         return len;
1171 }
1172
1173 struct request *elv_rb_former_request(struct request_queue *q,
1174                                       struct request *rq)
1175 {
1176         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1177
1178         if (rbprev)
1179                 return rb_entry_rq(rbprev);
1180
1181         return NULL;
1182 }
1183 EXPORT_SYMBOL(elv_rb_former_request);
1184
1185 struct request *elv_rb_latter_request(struct request_queue *q,
1186                                       struct request *rq)
1187 {
1188         struct rb_node *rbnext = rb_next(&rq->rb_node);
1189
1190         if (rbnext)
1191                 return rb_entry_rq(rbnext);
1192
1193         return NULL;
1194 }
1195 EXPORT_SYMBOL(elv_rb_latter_request);