Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/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/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_bio_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_bio_merge_fn)
 62                 return e->type->ops.elevator_allow_bio_merge_fn(q, rq, bio);
 63 
 64         return 1;
 65 }
 66 
 67 /*
 68  * can we safely merge with this request?
 69  */
 70 bool elv_bio_merge_ok(struct request *rq, struct bio *bio)
 71 {
 72         if (!blk_rq_merge_ok(rq, bio))
 73                 return false;
 74 
 75         if (!elv_iosched_allow_bio_merge(rq, bio))
 76                 return false;
 77 
 78         return true;
 79 }
 80 EXPORT_SYMBOL(elv_bio_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->rq_flags &= ~RQF_HASHED;
249 }
250 
251 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 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->rq_flags |= RQF_HASHED;
264 }
265 
266 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 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 
356         if (q->last_merge == rq)
357                 q->last_merge = NULL;
358 
359         elv_rqhash_del(q, rq);
360 
361         q->nr_sorted--;
362 
363         boundary = q->end_sector;
364         list_for_each_prev(entry, &q->queue_head) {
365                 struct request *pos = list_entry_rq(entry);
366 
367                 if (req_op(rq) != req_op(pos))
368                         break;
369                 if (rq_data_dir(rq) != rq_data_dir(pos))
370                         break;
371                 if (pos->rq_flags & (RQF_STARTED | RQF_SOFTBARRIER))
372                         break;
373                 if (blk_rq_pos(rq) >= boundary) {
374                         if (blk_rq_pos(pos) < boundary)
375                                 continue;
376                 } else {
377                         if (blk_rq_pos(pos) >= boundary)
378                                 break;
379                 }
380                 if (blk_rq_pos(rq) >= blk_rq_pos(pos))
381                         break;
382         }
383 
384         list_add(&rq->queuelist, entry);
385 }
386 EXPORT_SYMBOL(elv_dispatch_sort);
387 
388 /*
389  * Insert rq into dispatch queue of q.  Queue lock must be held on
390  * entry.  rq is added to the back of the dispatch queue. To be used by
391  * specific elevators.
392  */
393 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
394 {
395         if (q->last_merge == rq)
396                 q->last_merge = NULL;
397 
398         elv_rqhash_del(q, rq);
399 
400         q->nr_sorted--;
401 
402         q->end_sector = rq_end_sector(rq);
403         q->boundary_rq = rq;
404         list_add_tail(&rq->queuelist, &q->queue_head);
405 }
406 EXPORT_SYMBOL(elv_dispatch_add_tail);
407 
408 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
409 {
410         struct elevator_queue *e = q->elevator;
411         struct request *__rq;
412         int ret;
413 
414         /*
415          * Levels of merges:
416          *      nomerges:  No merges at all attempted
417          *      noxmerges: Only simple one-hit cache try
418          *      merges:    All merge tries attempted
419          */
420         if (blk_queue_nomerges(q) || !bio_mergeable(bio))
421                 return ELEVATOR_NO_MERGE;
422 
423         /*
424          * First try one-hit cache.
425          */
426         if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
427                 ret = blk_try_merge(q->last_merge, bio);
428                 if (ret != ELEVATOR_NO_MERGE) {
429                         *req = q->last_merge;
430                         return ret;
431                 }
432         }
433 
434         if (blk_queue_noxmerges(q))
435                 return ELEVATOR_NO_MERGE;
436 
437         /*
438          * See if our hash lookup can find a potential backmerge.
439          */
440         __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
441         if (__rq && elv_bio_merge_ok(__rq, bio)) {
442                 *req = __rq;
443                 return ELEVATOR_BACK_MERGE;
444         }
445 
446         if (e->type->ops.elevator_merge_fn)
447                 return e->type->ops.elevator_merge_fn(q, req, bio);
448 
449         return ELEVATOR_NO_MERGE;
450 }
451 
452 /*
453  * Attempt to do an insertion back merge. Only check for the case where
454  * we can append 'rq' to an existing request, so we can throw 'rq' away
455  * afterwards.
456  *
457  * Returns true if we merged, false otherwise
458  */
459 static bool elv_attempt_insert_merge(struct request_queue *q,
460                                      struct request *rq)
461 {
462         struct request *__rq;
463         bool ret;
464 
465         if (blk_queue_nomerges(q))
466                 return false;
467 
468         /*
469          * First try one-hit cache.
470          */
471         if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
472                 return true;
473 
474         if (blk_queue_noxmerges(q))
475                 return false;
476 
477         ret = false;
478         /*
479          * See if our hash lookup can find a potential backmerge.
480          */
481         while (1) {
482                 __rq = elv_rqhash_find(q, blk_rq_pos(rq));
483                 if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
484                         break;
485 
486                 /* The merged request could be merged with others, try again */
487                 ret = true;
488                 rq = __rq;
489         }
490 
491         return ret;
492 }
493 
494 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
495 {
496         struct elevator_queue *e = q->elevator;
497 
498         if (e->type->ops.elevator_merged_fn)
499                 e->type->ops.elevator_merged_fn(q, rq, type);
500 
501         if (type == ELEVATOR_BACK_MERGE)
502                 elv_rqhash_reposition(q, rq);
503 
504         q->last_merge = rq;
505 }
506 
507 void elv_merge_requests(struct request_queue *q, struct request *rq,
508                              struct request *next)
509 {
510         struct elevator_queue *e = q->elevator;
511         const int next_sorted = next->rq_flags & RQF_SORTED;
512 
513         if (next_sorted && e->type->ops.elevator_merge_req_fn)
514                 e->type->ops.elevator_merge_req_fn(q, rq, next);
515 
516         elv_rqhash_reposition(q, rq);
517 
518         if (next_sorted) {
519                 elv_rqhash_del(q, next);
520                 q->nr_sorted--;
521         }
522 
523         q->last_merge = rq;
524 }
525 
526 void elv_bio_merged(struct request_queue *q, struct request *rq,
527                         struct bio *bio)
528 {
529         struct elevator_queue *e = q->elevator;
530 
531         if (e->type->ops.elevator_bio_merged_fn)
532                 e->type->ops.elevator_bio_merged_fn(q, rq, bio);
533 }
534 
535 #ifdef CONFIG_PM
536 static void blk_pm_requeue_request(struct request *rq)
537 {
538         if (rq->q->dev && !(rq->rq_flags & RQF_PM))
539                 rq->q->nr_pending--;
540 }
541 
542 static void blk_pm_add_request(struct request_queue *q, struct request *rq)
543 {
544         if (q->dev && !(rq->rq_flags & RQF_PM) && q->nr_pending++ == 0 &&
545             (q->rpm_status == RPM_SUSPENDED || q->rpm_status == RPM_SUSPENDING))
546                 pm_request_resume(q->dev);
547 }
548 #else
549 static inline void blk_pm_requeue_request(struct request *rq) {}
550 static inline void blk_pm_add_request(struct request_queue *q,
551                                       struct request *rq)
552 {
553 }
554 #endif
555 
556 void elv_requeue_request(struct request_queue *q, struct request *rq)
557 {
558         /*
559          * it already went through dequeue, we need to decrement the
560          * in_flight count again
561          */
562         if (blk_account_rq(rq)) {
563                 q->in_flight[rq_is_sync(rq)]--;
564                 if (rq->rq_flags & RQF_SORTED)
565                         elv_deactivate_rq(q, rq);
566         }
567 
568         rq->rq_flags &= ~RQF_STARTED;
569 
570         blk_pm_requeue_request(rq);
571 
572         __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
573 }
574 
575 void elv_drain_elevator(struct request_queue *q)
576 {
577         static int printed;
578 
579         lockdep_assert_held(q->queue_lock);
580 
581         while (q->elevator->type->ops.elevator_dispatch_fn(q, 1))
582                 ;
583         if (q->nr_sorted && printed++ < 10) {
584                 printk(KERN_ERR "%s: forced dispatching is broken "
585                        "(nr_sorted=%u), please report this\n",
586                        q->elevator->type->elevator_name, q->nr_sorted);
587         }
588 }
589 
590 void __elv_add_request(struct request_queue *q, struct request *rq, int where)
591 {
592         trace_block_rq_insert(q, rq);
593 
594         blk_pm_add_request(q, rq);
595 
596         rq->q = q;
597 
598         if (rq->rq_flags & RQF_SOFTBARRIER) {
599                 /* barriers are scheduling boundary, update end_sector */
600                 if (rq->cmd_type == REQ_TYPE_FS) {
601                         q->end_sector = rq_end_sector(rq);
602                         q->boundary_rq = rq;
603                 }
604         } else if (!(rq->rq_flags & RQF_ELVPRIV) &&
605                     (where == ELEVATOR_INSERT_SORT ||
606                      where == ELEVATOR_INSERT_SORT_MERGE))
607                 where = ELEVATOR_INSERT_BACK;
608 
609         switch (where) {
610         case ELEVATOR_INSERT_REQUEUE:
611         case ELEVATOR_INSERT_FRONT:
612                 rq->rq_flags |= RQF_SOFTBARRIER;
613                 list_add(&rq->queuelist, &q->queue_head);
614                 break;
615 
616         case ELEVATOR_INSERT_BACK:
617                 rq->rq_flags |= RQF_SOFTBARRIER;
618                 elv_drain_elevator(q);
619                 list_add_tail(&rq->queuelist, &q->queue_head);
620                 /*
621                  * We kick the queue here for the following reasons.
622                  * - The elevator might have returned NULL previously
623                  *   to delay requests and returned them now.  As the
624                  *   queue wasn't empty before this request, ll_rw_blk
625                  *   won't run the queue on return, resulting in hang.
626                  * - Usually, back inserted requests won't be merged
627                  *   with anything.  There's no point in delaying queue
628                  *   processing.
629                  */
630                 __blk_run_queue(q);
631                 break;
632 
633         case ELEVATOR_INSERT_SORT_MERGE:
634                 /*
635                  * If we succeed in merging this request with one in the
636                  * queue already, we are done - rq has now been freed,
637                  * so no need to do anything further.
638                  */
639                 if (elv_attempt_insert_merge(q, rq))
640                         break;
641         case ELEVATOR_INSERT_SORT:
642                 BUG_ON(rq->cmd_type != REQ_TYPE_FS);
643                 rq->rq_flags |= RQF_SORTED;
644                 q->nr_sorted++;
645                 if (rq_mergeable(rq)) {
646                         elv_rqhash_add(q, rq);
647                         if (!q->last_merge)
648                                 q->last_merge = rq;
649                 }
650 
651                 /*
652                  * Some ioscheds (cfq) run q->request_fn directly, so
653                  * rq cannot be accessed after calling
654                  * elevator_add_req_fn.
655                  */
656                 q->elevator->type->ops.elevator_add_req_fn(q, rq);
657                 break;
658 
659         case ELEVATOR_INSERT_FLUSH:
660                 rq->rq_flags |= RQF_SOFTBARRIER;
661                 blk_insert_flush(rq);
662                 break;
663         default:
664                 printk(KERN_ERR "%s: bad insertion point %d\n",
665                        __func__, where);
666                 BUG();
667         }
668 }
669 EXPORT_SYMBOL(__elv_add_request);
670 
671 void elv_add_request(struct request_queue *q, struct request *rq, int where)
672 {
673         unsigned long flags;
674 
675         spin_lock_irqsave(q->queue_lock, flags);
676         __elv_add_request(q, rq, where);
677         spin_unlock_irqrestore(q->queue_lock, flags);
678 }
679 EXPORT_SYMBOL(elv_add_request);
680 
681 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
682 {
683         struct elevator_queue *e = q->elevator;
684 
685         if (e->type->ops.elevator_latter_req_fn)
686                 return e->type->ops.elevator_latter_req_fn(q, rq);
687         return NULL;
688 }
689 
690 struct request *elv_former_request(struct request_queue *q, struct request *rq)
691 {
692         struct elevator_queue *e = q->elevator;
693 
694         if (e->type->ops.elevator_former_req_fn)
695                 return e->type->ops.elevator_former_req_fn(q, rq);
696         return NULL;
697 }
698 
699 int elv_set_request(struct request_queue *q, struct request *rq,
700                     struct bio *bio, gfp_t gfp_mask)
701 {
702         struct elevator_queue *e = q->elevator;
703 
704         if (e->type->ops.elevator_set_req_fn)
705                 return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
706         return 0;
707 }
708 
709 void elv_put_request(struct request_queue *q, struct request *rq)
710 {
711         struct elevator_queue *e = q->elevator;
712 
713         if (e->type->ops.elevator_put_req_fn)
714                 e->type->ops.elevator_put_req_fn(rq);
715 }
716 
717 int elv_may_queue(struct request_queue *q, unsigned int op)
718 {
719         struct elevator_queue *e = q->elevator;
720 
721         if (e->type->ops.elevator_may_queue_fn)
722                 return e->type->ops.elevator_may_queue_fn(q, op);
723 
724         return ELV_MQUEUE_MAY;
725 }
726 
727 void elv_completed_request(struct request_queue *q, struct request *rq)
728 {
729         struct elevator_queue *e = q->elevator;
730 
731         /*
732          * request is released from the driver, io must be done
733          */
734         if (blk_account_rq(rq)) {
735                 q->in_flight[rq_is_sync(rq)]--;
736                 if ((rq->rq_flags & RQF_SORTED) &&
737                     e->type->ops.elevator_completed_req_fn)
738                         e->type->ops.elevator_completed_req_fn(q, rq);
739         }
740 }
741 
742 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
743 
744 static ssize_t
745 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
746 {
747         struct elv_fs_entry *entry = to_elv(attr);
748         struct elevator_queue *e;
749         ssize_t error;
750 
751         if (!entry->show)
752                 return -EIO;
753 
754         e = container_of(kobj, struct elevator_queue, kobj);
755         mutex_lock(&e->sysfs_lock);
756         error = e->type ? entry->show(e, page) : -ENOENT;
757         mutex_unlock(&e->sysfs_lock);
758         return error;
759 }
760 
761 static ssize_t
762 elv_attr_store(struct kobject *kobj, struct attribute *attr,
763                const char *page, size_t length)
764 {
765         struct elv_fs_entry *entry = to_elv(attr);
766         struct elevator_queue *e;
767         ssize_t error;
768 
769         if (!entry->store)
770                 return -EIO;
771 
772         e = container_of(kobj, struct elevator_queue, kobj);
773         mutex_lock(&e->sysfs_lock);
774         error = e->type ? entry->store(e, page, length) : -ENOENT;
775         mutex_unlock(&e->sysfs_lock);
776         return error;
777 }
778 
779 static const struct sysfs_ops elv_sysfs_ops = {
780         .show   = elv_attr_show,
781         .store  = elv_attr_store,
782 };
783 
784 static struct kobj_type elv_ktype = {
785         .sysfs_ops      = &elv_sysfs_ops,
786         .release        = elevator_release,
787 };
788 
789 int elv_register_queue(struct request_queue *q)
790 {
791         struct elevator_queue *e = q->elevator;
792         int error;
793 
794         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
795         if (!error) {
796                 struct elv_fs_entry *attr = e->type->elevator_attrs;
797                 if (attr) {
798                         while (attr->attr.name) {
799                                 if (sysfs_create_file(&e->kobj, &attr->attr))
800                                         break;
801                                 attr++;
802                         }
803                 }
804                 kobject_uevent(&e->kobj, KOBJ_ADD);
805                 e->registered = 1;
806                 if (e->type->ops.elevator_registered_fn)
807                         e->type->ops.elevator_registered_fn(q);
808         }
809         return error;
810 }
811 EXPORT_SYMBOL(elv_register_queue);
812 
813 void elv_unregister_queue(struct request_queue *q)
814 {
815         if (q) {
816                 struct elevator_queue *e = q->elevator;
817 
818                 kobject_uevent(&e->kobj, KOBJ_REMOVE);
819                 kobject_del(&e->kobj);
820                 e->registered = 0;
821         }
822 }
823 EXPORT_SYMBOL(elv_unregister_queue);
824 
825 int elv_register(struct elevator_type *e)
826 {
827         char *def = "";
828 
829         /* create icq_cache if requested */
830         if (e->icq_size) {
831                 if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
832                     WARN_ON(e->icq_align < __alignof__(struct io_cq)))
833                         return -EINVAL;
834 
835                 snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
836                          "%s_io_cq", e->elevator_name);
837                 e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
838                                                  e->icq_align, 0, NULL);
839                 if (!e->icq_cache)
840                         return -ENOMEM;
841         }
842 
843         /* register, don't allow duplicate names */
844         spin_lock(&elv_list_lock);
845         if (elevator_find(e->elevator_name)) {
846                 spin_unlock(&elv_list_lock);
847                 if (e->icq_cache)
848                         kmem_cache_destroy(e->icq_cache);
849                 return -EBUSY;
850         }
851         list_add_tail(&e->list, &elv_list);
852         spin_unlock(&elv_list_lock);
853 
854         /* print pretty message */
855         if (!strcmp(e->elevator_name, chosen_elevator) ||
856                         (!*chosen_elevator &&
857                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
858                                 def = " (default)";
859 
860         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
861                                                                 def);
862         return 0;
863 }
864 EXPORT_SYMBOL_GPL(elv_register);
865 
866 void elv_unregister(struct elevator_type *e)
867 {
868         /* unregister */
869         spin_lock(&elv_list_lock);
870         list_del_init(&e->list);
871         spin_unlock(&elv_list_lock);
872 
873         /*
874          * Destroy icq_cache if it exists.  icq's are RCU managed.  Make
875          * sure all RCU operations are complete before proceeding.
876          */
877         if (e->icq_cache) {
878                 rcu_barrier();
879                 kmem_cache_destroy(e->icq_cache);
880                 e->icq_cache = NULL;
881         }
882 }
883 EXPORT_SYMBOL_GPL(elv_unregister);
884 
885 /*
886  * switch to new_e io scheduler. be careful not to introduce deadlocks -
887  * we don't free the old io scheduler, before we have allocated what we
888  * need for the new one. this way we have a chance of going back to the old
889  * one, if the new one fails init for some reason.
890  */
891 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
892 {
893         struct elevator_queue *old = q->elevator;
894         bool registered = old->registered;
895         int err;
896 
897         /*
898          * Turn on BYPASS and drain all requests w/ elevator private data.
899          * Block layer doesn't call into a quiesced elevator - all requests
900          * are directly put on the dispatch list without elevator data
901          * using INSERT_BACK.  All requests have SOFTBARRIER set and no
902          * merge happens either.
903          */
904         blk_queue_bypass_start(q);
905 
906         /* unregister and clear all auxiliary data of the old elevator */
907         if (registered)
908                 elv_unregister_queue(q);
909 
910         spin_lock_irq(q->queue_lock);
911         ioc_clear_queue(q);
912         spin_unlock_irq(q->queue_lock);
913 
914         /* allocate, init and register new elevator */
915         err = new_e->ops.elevator_init_fn(q, new_e);
916         if (err)
917                 goto fail_init;
918 
919         if (registered) {
920                 err = elv_register_queue(q);
921                 if (err)
922                         goto fail_register;
923         }
924 
925         /* done, kill the old one and finish */
926         elevator_exit(old);
927         blk_queue_bypass_end(q);
928 
929         blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
930 
931         return 0;
932 
933 fail_register:
934         elevator_exit(q->elevator);
935 fail_init:
936         /* switch failed, restore and re-register old elevator */
937         q->elevator = old;
938         elv_register_queue(q);
939         blk_queue_bypass_end(q);
940 
941         return err;
942 }
943 
944 /*
945  * Switch this queue to the given IO scheduler.
946  */
947 static int __elevator_change(struct request_queue *q, const char *name)
948 {
949         char elevator_name[ELV_NAME_MAX];
950         struct elevator_type *e;
951 
952         if (!q->elevator)
953                 return -ENXIO;
954 
955         strlcpy(elevator_name, name, sizeof(elevator_name));
956         e = elevator_get(strstrip(elevator_name), true);
957         if (!e) {
958                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
959                 return -EINVAL;
960         }
961 
962         if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
963                 elevator_put(e);
964                 return 0;
965         }
966 
967         return elevator_switch(q, e);
968 }
969 
970 int elevator_change(struct request_queue *q, const char *name)
971 {
972         int ret;
973 
974         /* Protect q->elevator from elevator_init() */
975         mutex_lock(&q->sysfs_lock);
976         ret = __elevator_change(q, name);
977         mutex_unlock(&q->sysfs_lock);
978 
979         return ret;
980 }
981 EXPORT_SYMBOL(elevator_change);
982 
983 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
984                           size_t count)
985 {
986         int ret;
987 
988         if (!q->elevator)
989                 return count;
990 
991         ret = __elevator_change(q, name);
992         if (!ret)
993                 return count;
994 
995         printk(KERN_ERR "elevator: switch to %s failed\n", name);
996         return ret;
997 }
998 
999 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1000 {
1001         struct elevator_queue *e = q->elevator;
1002         struct elevator_type *elv;
1003         struct elevator_type *__e;
1004         int len = 0;
1005 
1006         if (!q->elevator || !blk_queue_stackable(q))
1007                 return sprintf(name, "none\n");
1008 
1009         elv = e->type;
1010 
1011         spin_lock(&elv_list_lock);
1012         list_for_each_entry(__e, &elv_list, list) {
1013                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1014                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1015                 else
1016                         len += sprintf(name+len, "%s ", __e->elevator_name);
1017         }
1018         spin_unlock(&elv_list_lock);
1019 
1020         len += sprintf(len+name, "\n");
1021         return len;
1022 }
1023 
1024 struct request *elv_rb_former_request(struct request_queue *q,
1025                                       struct request *rq)
1026 {
1027         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1028 
1029         if (rbprev)
1030                 return rb_entry_rq(rbprev);
1031 
1032         return NULL;
1033 }
1034 EXPORT_SYMBOL(elv_rb_former_request);
1035 
1036 struct request *elv_rb_latter_request(struct request_queue *q,
1037                                       struct request *rq)
1038 {
1039         struct rb_node *rbnext = rb_next(&rq->rb_node);
1040 
1041         if (rbnext)
1042                 return rb_entry_rq(rbnext);
1043 
1044         return NULL;
1045 }
1046 EXPORT_SYMBOL(elv_rb_latter_request);
1047 

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