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TOMOYO Linux Cross Reference
Linux/block/elevator.c

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  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/blktrace_api.h>
 35 #include <linux/hash.h>
 36 #include <linux/uaccess.h>
 37 #include <linux/pm_runtime.h>
 38 #include <linux/blk-cgroup.h>
 39 
 40 #include <trace/events/block.h>
 41 
 42 #include "blk.h"
 43 
 44 static DEFINE_SPINLOCK(elv_list_lock);
 45 static LIST_HEAD(elv_list);
 46 
 47 /*
 48  * Merge hash stuff.
 49  */
 50 #define rq_hash_key(rq)         (blk_rq_pos(rq) + blk_rq_sectors(rq))
 51 
 52 /*
 53  * Query io scheduler to see if the current process issuing bio may be
 54  * merged with rq.
 55  */
 56 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
 57 {
 58         struct request_queue *q = rq->q;
 59         struct elevator_queue *e = q->elevator;
 60 
 61         if (e->type->ops.elevator_allow_merge_fn)
 62                 return e->type->ops.elevator_allow_merge_fn(q, rq, bio);
 63 
 64         return 1;
 65 }
 66 
 67 /*
 68  * can we safely merge with this request?
 69  */
 70 bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
 71 {
 72         if (!blk_rq_merge_ok(rq, bio))
 73                 return 0;
 74 
 75         if (!elv_iosched_allow_merge(rq, bio))
 76                 return 0;
 77 
 78         return 1;
 79 }
 80 EXPORT_SYMBOL(elv_rq_merge_ok);
 81 
 82 static struct elevator_type *elevator_find(const char *name)
 83 {
 84         struct elevator_type *e;
 85 
 86         list_for_each_entry(e, &elv_list, list) {
 87                 if (!strcmp(e->elevator_name, name))
 88                         return e;
 89         }
 90 
 91         return NULL;
 92 }
 93 
 94 static void elevator_put(struct elevator_type *e)
 95 {
 96         module_put(e->elevator_owner);
 97 }
 98 
 99 static struct elevator_type *elevator_get(const char *name, bool try_loading)
100 {
101         struct elevator_type *e;
102 
103         spin_lock(&elv_list_lock);
104 
105         e = elevator_find(name);
106         if (!e && try_loading) {
107                 spin_unlock(&elv_list_lock);
108                 request_module("%s-iosched", name);
109                 spin_lock(&elv_list_lock);
110                 e = elevator_find(name);
111         }
112 
113         if (e && !try_module_get(e->elevator_owner))
114                 e = NULL;
115 
116         spin_unlock(&elv_list_lock);
117 
118         return e;
119 }
120 
121 static char chosen_elevator[ELV_NAME_MAX];
122 
123 static int __init elevator_setup(char *str)
124 {
125         /*
126          * Be backwards-compatible with previous kernels, so users
127          * won't get the wrong elevator.
128          */
129         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
130         return 1;
131 }
132 
133 __setup("elevator=", elevator_setup);
134 
135 /* called during boot to load the elevator chosen by the elevator param */
136 void __init load_default_elevator_module(void)
137 {
138         struct elevator_type *e;
139 
140         if (!chosen_elevator[0])
141                 return;
142 
143         spin_lock(&elv_list_lock);
144         e = elevator_find(chosen_elevator);
145         spin_unlock(&elv_list_lock);
146 
147         if (!e)
148                 request_module("%s-iosched", chosen_elevator);
149 }
150 
151 static struct kobj_type elv_ktype;
152 
153 struct elevator_queue *elevator_alloc(struct request_queue *q,
154                                   struct elevator_type *e)
155 {
156         struct elevator_queue *eq;
157 
158         eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node);
159         if (unlikely(!eq))
160                 return NULL;
161 
162         eq->type = e;
163         kobject_init(&eq->kobj, &elv_ktype);
164         mutex_init(&eq->sysfs_lock);
165         hash_init(eq->hash);
166 
167         return eq;
168 }
169 EXPORT_SYMBOL(elevator_alloc);
170 
171 static void elevator_release(struct kobject *kobj)
172 {
173         struct elevator_queue *e;
174 
175         e = container_of(kobj, struct elevator_queue, kobj);
176         elevator_put(e->type);
177         kfree(e);
178 }
179 
180 int elevator_init(struct request_queue *q, char *name)
181 {
182         struct elevator_type *e = NULL;
183         int err;
184 
185         /*
186          * q->sysfs_lock must be held to provide mutual exclusion between
187          * elevator_switch() and here.
188          */
189         lockdep_assert_held(&q->sysfs_lock);
190 
191         if (unlikely(q->elevator))
192                 return 0;
193 
194         INIT_LIST_HEAD(&q->queue_head);
195         q->last_merge = NULL;
196         q->end_sector = 0;
197         q->boundary_rq = NULL;
198 
199         if (name) {
200                 e = elevator_get(name, true);
201                 if (!e)
202                         return -EINVAL;
203         }
204 
205         /*
206          * Use the default elevator specified by config boot param or
207          * config option.  Don't try to load modules as we could be running
208          * off async and request_module() isn't allowed from async.
209          */
210         if (!e && *chosen_elevator) {
211                 e = elevator_get(chosen_elevator, false);
212                 if (!e)
213                         printk(KERN_ERR "I/O scheduler %s not found\n",
214                                                         chosen_elevator);
215         }
216 
217         if (!e) {
218                 e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
219                 if (!e) {
220                         printk(KERN_ERR
221                                 "Default I/O scheduler not found. " \
222                                 "Using noop.\n");
223                         e = elevator_get("noop", false);
224                 }
225         }
226 
227         err = e->ops.elevator_init_fn(q, e);
228         if (err)
229                 elevator_put(e);
230         return err;
231 }
232 EXPORT_SYMBOL(elevator_init);
233 
234 void elevator_exit(struct elevator_queue *e)
235 {
236         mutex_lock(&e->sysfs_lock);
237         if (e->type->ops.elevator_exit_fn)
238                 e->type->ops.elevator_exit_fn(e);
239         mutex_unlock(&e->sysfs_lock);
240 
241         kobject_put(&e->kobj);
242 }
243 EXPORT_SYMBOL(elevator_exit);
244 
245 static inline void __elv_rqhash_del(struct request *rq)
246 {
247         hash_del(&rq->hash);
248         rq->cmd_flags &= ~REQ_HASHED;
249 }
250 
251 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
252 {
253         if (ELV_ON_HASH(rq))
254                 __elv_rqhash_del(rq);
255 }
256 
257 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
258 {
259         struct elevator_queue *e = q->elevator;
260 
261         BUG_ON(ELV_ON_HASH(rq));
262         hash_add(e->hash, &rq->hash, rq_hash_key(rq));
263         rq->cmd_flags |= REQ_HASHED;
264 }
265 
266 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
267 {
268         __elv_rqhash_del(rq);
269         elv_rqhash_add(q, rq);
270 }
271 
272 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
273 {
274         struct elevator_queue *e = q->elevator;
275         struct hlist_node *next;
276         struct request *rq;
277 
278         hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
279                 BUG_ON(!ELV_ON_HASH(rq));
280 
281                 if (unlikely(!rq_mergeable(rq))) {
282                         __elv_rqhash_del(rq);
283                         continue;
284                 }
285 
286                 if (rq_hash_key(rq) == offset)
287                         return rq;
288         }
289 
290         return NULL;
291 }
292 
293 /*
294  * RB-tree support functions for inserting/lookup/removal of requests
295  * in a sorted RB tree.
296  */
297 void elv_rb_add(struct rb_root *root, struct request *rq)
298 {
299         struct rb_node **p = &root->rb_node;
300         struct rb_node *parent = NULL;
301         struct request *__rq;
302 
303         while (*p) {
304                 parent = *p;
305                 __rq = rb_entry(parent, struct request, rb_node);
306 
307                 if (blk_rq_pos(rq) < blk_rq_pos(__rq))
308                         p = &(*p)->rb_left;
309                 else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
310                         p = &(*p)->rb_right;
311         }
312 
313         rb_link_node(&rq->rb_node, parent, p);
314         rb_insert_color(&rq->rb_node, root);
315 }
316 EXPORT_SYMBOL(elv_rb_add);
317 
318 void elv_rb_del(struct rb_root *root, struct request *rq)
319 {
320         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
321         rb_erase(&rq->rb_node, root);
322         RB_CLEAR_NODE(&rq->rb_node);
323 }
324 EXPORT_SYMBOL(elv_rb_del);
325 
326 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
327 {
328         struct rb_node *n = root->rb_node;
329         struct request *rq;
330 
331         while (n) {
332                 rq = rb_entry(n, struct request, rb_node);
333 
334                 if (sector < blk_rq_pos(rq))
335                         n = n->rb_left;
336                 else if (sector > blk_rq_pos(rq))
337                         n = n->rb_right;
338                 else
339                         return rq;
340         }
341 
342         return NULL;
343 }
344 EXPORT_SYMBOL(elv_rb_find);
345 
346 /*
347  * Insert rq into dispatch queue of q.  Queue lock must be held on
348  * entry.  rq is sort instead into the dispatch queue. To be used by
349  * specific elevators.
350  */
351 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
352 {
353         sector_t boundary;
354         struct list_head *entry;
355         int stop_flags;
356 
357         if (q->last_merge == rq)
358                 q->last_merge = NULL;
359 
360         elv_rqhash_del(q, rq);
361 
362         q->nr_sorted--;
363 
364         boundary = q->end_sector;
365         stop_flags = REQ_SOFTBARRIER | REQ_STARTED;
366         list_for_each_prev(entry, &q->queue_head) {
367                 struct request *pos = list_entry_rq(entry);
368 
369                 if ((rq->cmd_flags & REQ_DISCARD) !=
370                     (pos->cmd_flags & REQ_DISCARD))
371                         break;
372                 if (rq_data_dir(rq) != rq_data_dir(pos))
373                         break;
374                 if (pos->cmd_flags & stop_flags)
375                         break;
376                 if (blk_rq_pos(rq) >= boundary) {
377                         if (blk_rq_pos(pos) < boundary)
378                                 continue;
379                 } else {
380                         if (blk_rq_pos(pos) >= boundary)
381                                 break;
382                 }
383                 if (blk_rq_pos(rq) >= blk_rq_pos(pos))
384                         break;
385         }
386 
387         list_add(&rq->queuelist, entry);
388 }
389 EXPORT_SYMBOL(elv_dispatch_sort);
390 
391 /*
392  * Insert rq into dispatch queue of q.  Queue lock must be held on
393  * entry.  rq is added to the back of the dispatch queue. To be used by
394  * specific elevators.
395  */
396 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
397 {
398         if (q->last_merge == rq)
399                 q->last_merge = NULL;
400 
401         elv_rqhash_del(q, rq);
402 
403         q->nr_sorted--;
404 
405         q->end_sector = rq_end_sector(rq);
406         q->boundary_rq = rq;
407         list_add_tail(&rq->queuelist, &q->queue_head);
408 }
409 EXPORT_SYMBOL(elv_dispatch_add_tail);
410 
411 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
412 {
413         struct elevator_queue *e = q->elevator;
414         struct request *__rq;
415         int ret;
416 
417         /*
418          * Levels of merges:
419          *      nomerges:  No merges at all attempted
420          *      noxmerges: Only simple one-hit cache try
421          *      merges:    All merge tries attempted
422          */
423         if (blk_queue_nomerges(q))
424                 return ELEVATOR_NO_MERGE;
425 
426         /*
427          * First try one-hit cache.
428          */
429         if (q->last_merge && elv_rq_merge_ok(q->last_merge, bio)) {
430                 ret = blk_try_merge(q->last_merge, bio);
431                 if (ret != ELEVATOR_NO_MERGE) {
432                         *req = q->last_merge;
433                         return ret;
434                 }
435         }
436 
437         if (blk_queue_noxmerges(q))
438                 return ELEVATOR_NO_MERGE;
439 
440         /*
441          * See if our hash lookup can find a potential backmerge.
442          */
443         __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
444         if (__rq && elv_rq_merge_ok(__rq, bio)) {
445                 *req = __rq;
446                 return ELEVATOR_BACK_MERGE;
447         }
448 
449         if (e->type->ops.elevator_merge_fn)
450                 return e->type->ops.elevator_merge_fn(q, req, bio);
451 
452         return ELEVATOR_NO_MERGE;
453 }
454 
455 /*
456  * Attempt to do an insertion back merge. Only check for the case where
457  * we can append 'rq' to an existing request, so we can throw 'rq' away
458  * afterwards.
459  *
460  * Returns true if we merged, false otherwise
461  */
462 static bool elv_attempt_insert_merge(struct request_queue *q,
463                                      struct request *rq)
464 {
465         struct request *__rq;
466         bool ret;
467 
468         if (blk_queue_nomerges(q))
469                 return false;
470 
471         /*
472          * First try one-hit cache.
473          */
474         if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
475                 return true;
476 
477         if (blk_queue_noxmerges(q))
478                 return false;
479 
480         ret = false;
481         /*
482          * See if our hash lookup can find a potential backmerge.
483          */
484         while (1) {
485                 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
486                 if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
487                         break;
488 
489                 /* The merged request could be merged with others, try again */
490                 ret = true;
491                 rq = __rq;
492         }
493 
494         return ret;
495 }
496 
497 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
498 {
499         struct elevator_queue *e = q->elevator;
500 
501         if (e->type->ops.elevator_merged_fn)
502                 e->type->ops.elevator_merged_fn(q, rq, type);
503 
504         if (type == ELEVATOR_BACK_MERGE)
505                 elv_rqhash_reposition(q, rq);
506 
507         q->last_merge = rq;
508 }
509 
510 void elv_merge_requests(struct request_queue *q, struct request *rq,
511                              struct request *next)
512 {
513         struct elevator_queue *e = q->elevator;
514         const int next_sorted = next->cmd_flags & REQ_SORTED;
515 
516         if (next_sorted && e->type->ops.elevator_merge_req_fn)
517                 e->type->ops.elevator_merge_req_fn(q, rq, next);
518 
519         elv_rqhash_reposition(q, rq);
520 
521         if (next_sorted) {
522                 elv_rqhash_del(q, next);
523                 q->nr_sorted--;
524         }
525 
526         q->last_merge = rq;
527 }
528 
529 void elv_bio_merged(struct request_queue *q, struct request *rq,
530                         struct bio *bio)
531 {
532         struct elevator_queue *e = q->elevator;
533 
534         if (e->type->ops.elevator_bio_merged_fn)
535                 e->type->ops.elevator_bio_merged_fn(q, rq, bio);
536 }
537 
538 #ifdef CONFIG_PM
539 static void blk_pm_requeue_request(struct request *rq)
540 {
541         if (rq->q->dev && !(rq->cmd_flags & REQ_PM))
542                 rq->q->nr_pending--;
543 }
544 
545 static void blk_pm_add_request(struct request_queue *q, struct request *rq)
546 {
547         if (q->dev && !(rq->cmd_flags & REQ_PM) && q->nr_pending++ == 0 &&
548             (q->rpm_status == RPM_SUSPENDED || q->rpm_status == RPM_SUSPENDING))
549                 pm_request_resume(q->dev);
550 }
551 #else
552 static inline void blk_pm_requeue_request(struct request *rq) {}
553 static inline void blk_pm_add_request(struct request_queue *q,
554                                       struct request *rq)
555 {
556 }
557 #endif
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[rq_is_sync(rq)]--;
567                 if (rq->cmd_flags & REQ_SORTED)
568                         elv_deactivate_rq(q, rq);
569         }
570 
571         rq->cmd_flags &= ~REQ_STARTED;
572 
573         blk_pm_requeue_request(rq);
574 
575         __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
576 }
577 
578 void elv_drain_elevator(struct request_queue *q)
579 {
580         static int printed;
581 
582         lockdep_assert_held(q->queue_lock);
583 
584         while (q->elevator->type->ops.elevator_dispatch_fn(q, 1))
585                 ;
586         if (q->nr_sorted && printed++ < 10) {
587                 printk(KERN_ERR "%s: forced dispatching is broken "
588                        "(nr_sorted=%u), please report this\n",
589                        q->elevator->type->elevator_name, q->nr_sorted);
590         }
591 }
592 
593 void __elv_add_request(struct request_queue *q, struct request *rq, int where)
594 {
595         trace_block_rq_insert(q, rq);
596 
597         blk_pm_add_request(q, rq);
598 
599         rq->q = q;
600 
601         if (rq->cmd_flags & REQ_SOFTBARRIER) {
602                 /* barriers are scheduling boundary, update end_sector */
603                 if (rq->cmd_type == REQ_TYPE_FS) {
604                         q->end_sector = rq_end_sector(rq);
605                         q->boundary_rq = rq;
606                 }
607         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
608                     (where == ELEVATOR_INSERT_SORT ||
609                      where == ELEVATOR_INSERT_SORT_MERGE))
610                 where = ELEVATOR_INSERT_BACK;
611 
612         switch (where) {
613         case ELEVATOR_INSERT_REQUEUE:
614         case ELEVATOR_INSERT_FRONT:
615                 rq->cmd_flags |= REQ_SOFTBARRIER;
616                 list_add(&rq->queuelist, &q->queue_head);
617                 break;
618 
619         case ELEVATOR_INSERT_BACK:
620                 rq->cmd_flags |= REQ_SOFTBARRIER;
621                 elv_drain_elevator(q);
622                 list_add_tail(&rq->queuelist, &q->queue_head);
623                 /*
624                  * We kick the queue here for the following reasons.
625                  * - The elevator might have returned NULL previously
626                  *   to delay requests and returned them now.  As the
627                  *   queue wasn't empty before this request, ll_rw_blk
628                  *   won't run the queue on return, resulting in hang.
629                  * - Usually, back inserted requests won't be merged
630                  *   with anything.  There's no point in delaying queue
631                  *   processing.
632                  */
633                 __blk_run_queue(q);
634                 break;
635 
636         case ELEVATOR_INSERT_SORT_MERGE:
637                 /*
638                  * If we succeed in merging this request with one in the
639                  * queue already, we are done - rq has now been freed,
640                  * so no need to do anything further.
641                  */
642                 if (elv_attempt_insert_merge(q, rq))
643                         break;
644         case ELEVATOR_INSERT_SORT:
645                 BUG_ON(rq->cmd_type != REQ_TYPE_FS);
646                 rq->cmd_flags |= REQ_SORTED;
647                 q->nr_sorted++;
648                 if (rq_mergeable(rq)) {
649                         elv_rqhash_add(q, rq);
650                         if (!q->last_merge)
651                                 q->last_merge = rq;
652                 }
653 
654                 /*
655                  * Some ioscheds (cfq) run q->request_fn directly, so
656                  * rq cannot be accessed after calling
657                  * elevator_add_req_fn.
658                  */
659                 q->elevator->type->ops.elevator_add_req_fn(q, rq);
660                 break;
661 
662         case ELEVATOR_INSERT_FLUSH:
663                 rq->cmd_flags |= REQ_SOFTBARRIER;
664                 blk_insert_flush(rq);
665                 break;
666         default:
667                 printk(KERN_ERR "%s: bad insertion point %d\n",
668                        __func__, where);
669                 BUG();
670         }
671 }
672 EXPORT_SYMBOL(__elv_add_request);
673 
674 void elv_add_request(struct request_queue *q, struct request *rq, int where)
675 {
676         unsigned long flags;
677 
678         spin_lock_irqsave(q->queue_lock, flags);
679         __elv_add_request(q, rq, where);
680         spin_unlock_irqrestore(q->queue_lock, flags);
681 }
682 EXPORT_SYMBOL(elv_add_request);
683 
684 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
685 {
686         struct elevator_queue *e = q->elevator;
687 
688         if (e->type->ops.elevator_latter_req_fn)
689                 return e->type->ops.elevator_latter_req_fn(q, rq);
690         return NULL;
691 }
692 
693 struct request *elv_former_request(struct request_queue *q, struct request *rq)
694 {
695         struct elevator_queue *e = q->elevator;
696 
697         if (e->type->ops.elevator_former_req_fn)
698                 return e->type->ops.elevator_former_req_fn(q, rq);
699         return NULL;
700 }
701 
702 int elv_set_request(struct request_queue *q, struct request *rq,
703                     struct bio *bio, gfp_t gfp_mask)
704 {
705         struct elevator_queue *e = q->elevator;
706 
707         if (e->type->ops.elevator_set_req_fn)
708                 return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
709         return 0;
710 }
711 
712 void elv_put_request(struct request_queue *q, struct request *rq)
713 {
714         struct elevator_queue *e = q->elevator;
715 
716         if (e->type->ops.elevator_put_req_fn)
717                 e->type->ops.elevator_put_req_fn(rq);
718 }
719 
720 int elv_may_queue(struct request_queue *q, int rw)
721 {
722         struct elevator_queue *e = q->elevator;
723 
724         if (e->type->ops.elevator_may_queue_fn)
725                 return e->type->ops.elevator_may_queue_fn(q, rw);
726 
727         return ELV_MQUEUE_MAY;
728 }
729 
730 void elv_completed_request(struct request_queue *q, struct request *rq)
731 {
732         struct elevator_queue *e = q->elevator;
733 
734         /*
735          * request is released from the driver, io must be done
736          */
737         if (blk_account_rq(rq)) {
738                 q->in_flight[rq_is_sync(rq)]--;
739                 if ((rq->cmd_flags & REQ_SORTED) &&
740                     e->type->ops.elevator_completed_req_fn)
741                         e->type->ops.elevator_completed_req_fn(q, rq);
742         }
743 }
744 
745 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
746 
747 static ssize_t
748 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
749 {
750         struct elv_fs_entry *entry = to_elv(attr);
751         struct elevator_queue *e;
752         ssize_t error;
753 
754         if (!entry->show)
755                 return -EIO;
756 
757         e = container_of(kobj, struct elevator_queue, kobj);
758         mutex_lock(&e->sysfs_lock);
759         error = e->type ? entry->show(e, page) : -ENOENT;
760         mutex_unlock(&e->sysfs_lock);
761         return error;
762 }
763 
764 static ssize_t
765 elv_attr_store(struct kobject *kobj, struct attribute *attr,
766                const char *page, size_t length)
767 {
768         struct elv_fs_entry *entry = to_elv(attr);
769         struct elevator_queue *e;
770         ssize_t error;
771 
772         if (!entry->store)
773                 return -EIO;
774 
775         e = container_of(kobj, struct elevator_queue, kobj);
776         mutex_lock(&e->sysfs_lock);
777         error = e->type ? entry->store(e, page, length) : -ENOENT;
778         mutex_unlock(&e->sysfs_lock);
779         return error;
780 }
781 
782 static const struct sysfs_ops elv_sysfs_ops = {
783         .show   = elv_attr_show,
784         .store  = elv_attr_store,
785 };
786 
787 static struct kobj_type elv_ktype = {
788         .sysfs_ops      = &elv_sysfs_ops,
789         .release        = elevator_release,
790 };
791 
792 int elv_register_queue(struct request_queue *q)
793 {
794         struct elevator_queue *e = q->elevator;
795         int error;
796 
797         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
798         if (!error) {
799                 struct elv_fs_entry *attr = e->type->elevator_attrs;
800                 if (attr) {
801                         while (attr->attr.name) {
802                                 if (sysfs_create_file(&e->kobj, &attr->attr))
803                                         break;
804                                 attr++;
805                         }
806                 }
807                 kobject_uevent(&e->kobj, KOBJ_ADD);
808                 e->registered = 1;
809                 if (e->type->ops.elevator_registered_fn)
810                         e->type->ops.elevator_registered_fn(q);
811         }
812         return error;
813 }
814 EXPORT_SYMBOL(elv_register_queue);
815 
816 void elv_unregister_queue(struct request_queue *q)
817 {
818         if (q) {
819                 struct elevator_queue *e = q->elevator;
820 
821                 kobject_uevent(&e->kobj, KOBJ_REMOVE);
822                 kobject_del(&e->kobj);
823                 e->registered = 0;
824         }
825 }
826 EXPORT_SYMBOL(elv_unregister_queue);
827 
828 int elv_register(struct elevator_type *e)
829 {
830         char *def = "";
831 
832         /* create icq_cache if requested */
833         if (e->icq_size) {
834                 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
835                     WARN_ON(e->icq_align < __alignof__(struct io_cq)))
836                         return -EINVAL;
837 
838                 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
839                          "%s_io_cq", e->elevator_name);
840                 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
841                                                  e->icq_align, 0, NULL);
842                 if (!e->icq_cache)
843                         return -ENOMEM;
844         }
845 
846         /* register, don't allow duplicate names */
847         spin_lock(&elv_list_lock);
848         if (elevator_find(e->elevator_name)) {
849                 spin_unlock(&elv_list_lock);
850                 if (e->icq_cache)
851                         kmem_cache_destroy(e->icq_cache);
852                 return -EBUSY;
853         }
854         list_add_tail(&e->list, &elv_list);
855         spin_unlock(&elv_list_lock);
856 
857         /* print pretty message */
858         if (!strcmp(e->elevator_name, chosen_elevator) ||
859                         (!*chosen_elevator &&
860                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
861                                 def = " (default)";
862 
863         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
864                                                                 def);
865         return 0;
866 }
867 EXPORT_SYMBOL_GPL(elv_register);
868 
869 void elv_unregister(struct elevator_type *e)
870 {
871         /* unregister */
872         spin_lock(&elv_list_lock);
873         list_del_init(&e->list);
874         spin_unlock(&elv_list_lock);
875 
876         /*
877          * Destroy icq_cache if it exists.  icq's are RCU managed.  Make
878          * sure all RCU operations are complete before proceeding.
879          */
880         if (e->icq_cache) {
881                 rcu_barrier();
882                 kmem_cache_destroy(e->icq_cache);
883                 e->icq_cache = NULL;
884         }
885 }
886 EXPORT_SYMBOL_GPL(elv_unregister);
887 
888 /*
889  * switch to new_e io scheduler. be careful not to introduce deadlocks -
890  * we don't free the old io scheduler, before we have allocated what we
891  * need for the new one. this way we have a chance of going back to the old
892  * one, if the new one fails init for some reason.
893  */
894 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
895 {
896         struct elevator_queue *old = q->elevator;
897         bool registered = old->registered;
898         int err;
899 
900         /*
901          * Turn on BYPASS and drain all requests w/ elevator private data.
902          * Block layer doesn't call into a quiesced elevator - all requests
903          * are directly put on the dispatch list without elevator data
904          * using INSERT_BACK.  All requests have SOFTBARRIER set and no
905          * merge happens either.
906          */
907         blk_queue_bypass_start(q);
908 
909         /* unregister and clear all auxiliary data of the old elevator */
910         if (registered)
911                 elv_unregister_queue(q);
912 
913         spin_lock_irq(q->queue_lock);
914         ioc_clear_queue(q);
915         spin_unlock_irq(q->queue_lock);
916 
917         /* allocate, init and register new elevator */
918         err = new_e->ops.elevator_init_fn(q, new_e);
919         if (err)
920                 goto fail_init;
921 
922         if (registered) {
923                 err = elv_register_queue(q);
924                 if (err)
925                         goto fail_register;
926         }
927 
928         /* done, kill the old one and finish */
929         elevator_exit(old);
930         blk_queue_bypass_end(q);
931 
932         blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
933 
934         return 0;
935 
936 fail_register:
937         elevator_exit(q->elevator);
938 fail_init:
939         /* switch failed, restore and re-register old elevator */
940         q->elevator = old;
941         elv_register_queue(q);
942         blk_queue_bypass_end(q);
943 
944         return err;
945 }
946 
947 /*
948  * Switch this queue to the given IO scheduler.
949  */
950 static int __elevator_change(struct request_queue *q, const char *name)
951 {
952         char elevator_name[ELV_NAME_MAX];
953         struct elevator_type *e;
954 
955         if (!q->elevator)
956                 return -ENXIO;
957 
958         strlcpy(elevator_name, name, sizeof(elevator_name));
959         e = elevator_get(strstrip(elevator_name), true);
960         if (!e) {
961                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
962                 return -EINVAL;
963         }
964 
965         if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
966                 elevator_put(e);
967                 return 0;
968         }
969 
970         return elevator_switch(q, e);
971 }
972 
973 int elevator_change(struct request_queue *q, const char *name)
974 {
975         int ret;
976 
977         /* Protect q->elevator from elevator_init() */
978         mutex_lock(&q->sysfs_lock);
979         ret = __elevator_change(q, name);
980         mutex_unlock(&q->sysfs_lock);
981 
982         return ret;
983 }
984 EXPORT_SYMBOL(elevator_change);
985 
986 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
987                           size_t count)
988 {
989         int ret;
990 
991         if (!q->elevator)
992                 return count;
993 
994         ret = __elevator_change(q, name);
995         if (!ret)
996                 return count;
997 
998         printk(KERN_ERR "elevator: switch to %s failed\n", name);
999         return ret;
1000 }
1001 
1002 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1003 {
1004         struct elevator_queue *e = q->elevator;
1005         struct elevator_type *elv;
1006         struct elevator_type *__e;
1007         int len = 0;
1008 
1009         if (!q->elevator || !blk_queue_stackable(q))
1010                 return sprintf(name, "none\n");
1011 
1012         elv = e->type;
1013 
1014         spin_lock(&elv_list_lock);
1015         list_for_each_entry(__e, &elv_list, list) {
1016                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1017                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1018                 else
1019                         len += sprintf(name+len, "%s ", __e->elevator_name);
1020         }
1021         spin_unlock(&elv_list_lock);
1022 
1023         len += sprintf(len+name, "\n");
1024         return len;
1025 }
1026 
1027 struct request *elv_rb_former_request(struct request_queue *q,
1028                                       struct request *rq)
1029 {
1030         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1031 
1032         if (rbprev)
1033                 return rb_entry_rq(rbprev);
1034 
1035         return NULL;
1036 }
1037 EXPORT_SYMBOL(elv_rb_former_request);
1038 
1039 struct request *elv_rb_latter_request(struct request_queue *q,
1040                                       struct request *rq)
1041 {
1042         struct rb_node *rbnext = rb_next(&rq->rb_node);
1043 
1044         if (rbnext)
1045                 return rb_entry_rq(rbnext);
1046 
1047         return NULL;
1048 }
1049 EXPORT_SYMBOL(elv_rb_latter_request);
1050 

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