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
  38#include <trace/events/block.h>
  39
  40#include "blk.h"
  41#include "blk-cgroup.h"
  42
  43static DEFINE_SPINLOCK(elv_list_lock);
  44static LIST_HEAD(elv_list);
  45
  46/*
  47 * Merge hash stuff.
  48 */
  49static const int elv_hash_shift = 6;
  50#define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
  51#define ELV_HASH_FN(sec)        \
  52                (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
  53#define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
  54#define rq_hash_key(rq)         (blk_rq_pos(rq) + blk_rq_sectors(rq))
  55
  56/*
  57 * Query io scheduler to see if the current process issuing bio may be
  58 * merged with rq.
  59 */
  60static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
  61{
  62        struct request_queue *q = rq->q;
  63        struct elevator_queue *e = q->elevator;
  64
  65        if (e->type->ops.elevator_allow_merge_fn)
  66                return e->type->ops.elevator_allow_merge_fn(q, rq, bio);
  67
  68        return 1;
  69}
  70
  71/*
  72 * can we safely merge with this request?
  73 */
  74bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
  75{
  76        if (!blk_rq_merge_ok(rq, bio))
  77                return 0;
  78
  79        if (!elv_iosched_allow_merge(rq, bio))
  80                return 0;
  81
  82        return 1;
  83}
  84EXPORT_SYMBOL(elv_rq_merge_ok);
  85
  86static struct elevator_type *elevator_find(const char *name)
  87{
  88        struct elevator_type *e;
  89
  90        list_for_each_entry(e, &elv_list, list) {
  91                if (!strcmp(e->elevator_name, name))
  92                        return e;
  93        }
  94
  95        return NULL;
  96}
  97
  98static void elevator_put(struct elevator_type *e)
  99{
 100        module_put(e->elevator_owner);
 101}
 102
 103static struct elevator_type *elevator_get(const char *name)
 104{
 105        struct elevator_type *e;
 106
 107        spin_lock(&elv_list_lock);
 108
 109        e = elevator_find(name);
 110        if (!e) {
 111                spin_unlock(&elv_list_lock);
 112                request_module("%s-iosched", name);
 113                spin_lock(&elv_list_lock);
 114                e = elevator_find(name);
 115        }
 116
 117        if (e && !try_module_get(e->elevator_owner))
 118                e = NULL;
 119
 120        spin_unlock(&elv_list_lock);
 121
 122        return e;
 123}
 124
 125static char chosen_elevator[ELV_NAME_MAX];
 126
 127static int __init elevator_setup(char *str)
 128{
 129        /*
 130         * Be backwards-compatible with previous kernels, so users
 131         * won't get the wrong elevator.
 132         */
 133        strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 134        return 1;
 135}
 136
 137__setup("elevator=", elevator_setup);
 138
 139static struct kobj_type elv_ktype;
 140
 141static struct elevator_queue *elevator_alloc(struct request_queue *q,
 142                                  struct elevator_type *e)
 143{
 144        struct elevator_queue *eq;
 145        int i;
 146
 147        eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
 148        if (unlikely(!eq))
 149                goto err;
 150
 151        eq->type = e;
 152        kobject_init(&eq->kobj, &elv_ktype);
 153        mutex_init(&eq->sysfs_lock);
 154
 155        eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
 156                                        GFP_KERNEL, q->node);
 157        if (!eq->hash)
 158                goto err;
 159
 160        for (i = 0; i < ELV_HASH_ENTRIES; i++)
 161                INIT_HLIST_HEAD(&eq->hash[i]);
 162
 163        return eq;
 164err:
 165        kfree(eq);
 166        elevator_put(e);
 167        return NULL;
 168}
 169
 170static void elevator_release(struct kobject *kobj)
 171{
 172        struct elevator_queue *e;
 173
 174        e = container_of(kobj, struct elevator_queue, kobj);
 175        elevator_put(e->type);
 176        kfree(e->hash);
 177        kfree(e);
 178}
 179
 180int elevator_init(struct request_queue *q, char *name)
 181{
 182        struct elevator_type *e = NULL;
 183        int err;
 184
 185        if (unlikely(q->elevator))
 186                return 0;
 187
 188        INIT_LIST_HEAD(&q->queue_head);
 189        q->last_merge = NULL;
 190        q->end_sector = 0;
 191        q->boundary_rq = NULL;
 192
 193        if (name) {
 194                e = elevator_get(name);
 195                if (!e)
 196                        return -EINVAL;
 197        }
 198
 199        if (!e && *chosen_elevator) {
 200                e = elevator_get(chosen_elevator);
 201                if (!e)
 202                        printk(KERN_ERR "I/O scheduler %s not found\n",
 203                                                        chosen_elevator);
 204        }
 205
 206        if (!e) {
 207                e = elevator_get(CONFIG_DEFAULT_IOSCHED);
 208                if (!e) {
 209                        printk(KERN_ERR
 210                                "Default I/O scheduler not found. " \
 211                                "Using noop.\n");
 212                        e = elevator_get("noop");
 213                }
 214        }
 215
 216        q->elevator = elevator_alloc(q, e);
 217        if (!q->elevator)
 218                return -ENOMEM;
 219
 220        err = e->ops.elevator_init_fn(q);
 221        if (err) {
 222                kobject_put(&q->elevator->kobj);
 223                return err;
 224        }
 225
 226        return 0;
 227}
 228EXPORT_SYMBOL(elevator_init);
 229
 230void elevator_exit(struct elevator_queue *e)
 231{
 232        mutex_lock(&e->sysfs_lock);
 233        if (e->type->ops.elevator_exit_fn)
 234                e->type->ops.elevator_exit_fn(e);
 235        mutex_unlock(&e->sysfs_lock);
 236
 237        kobject_put(&e->kobj);
 238}
 239EXPORT_SYMBOL(elevator_exit);
 240
 241static inline void __elv_rqhash_del(struct request *rq)
 242{
 243        hlist_del_init(&rq->hash);
 244}
 245
 246static void elv_rqhash_del(struct request_queue *q, struct request *rq)
 247{
 248        if (ELV_ON_HASH(rq))
 249                __elv_rqhash_del(rq);
 250}
 251
 252static void elv_rqhash_add(struct request_queue *q, struct request *rq)
 253{
 254        struct elevator_queue *e = q->elevator;
 255
 256        BUG_ON(ELV_ON_HASH(rq));
 257        hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
 258}
 259
 260static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 261{
 262        __elv_rqhash_del(rq);
 263        elv_rqhash_add(q, rq);
 264}
 265
 266static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 267{
 268        struct elevator_queue *e = q->elevator;
 269        struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
 270        struct hlist_node *entry, *next;
 271        struct request *rq;
 272
 273        hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
 274                BUG_ON(!ELV_ON_HASH(rq));
 275
 276                if (unlikely(!rq_mergeable(rq))) {
 277                        __elv_rqhash_del(rq);
 278                        continue;
 279                }
 280
 281                if (rq_hash_key(rq) == offset)
 282                        return rq;
 283        }
 284
 285        return NULL;
 286}
 287
 288/*
 289 * RB-tree support functions for inserting/lookup/removal of requests
 290 * in a sorted RB tree.
 291 */
 292void elv_rb_add(struct rb_root *root, struct request *rq)
 293{
 294        struct rb_node **p = &root->rb_node;
 295        struct rb_node *parent = NULL;
 296        struct request *__rq;
 297
 298        while (*p) {
 299                parent = *p;
 300                __rq = rb_entry(parent, struct request, rb_node);
 301
 302                if (blk_rq_pos(rq) < blk_rq_pos(__rq))
 303                        p = &(*p)->rb_left;
 304                else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
 305                        p = &(*p)->rb_right;
 306        }
 307
 308        rb_link_node(&rq->rb_node, parent, p);
 309        rb_insert_color(&rq->rb_node, root);
 310}
 311EXPORT_SYMBOL(elv_rb_add);
 312
 313void elv_rb_del(struct rb_root *root, struct request *rq)
 314{
 315        BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 316        rb_erase(&rq->rb_node, root);
 317        RB_CLEAR_NODE(&rq->rb_node);
 318}
 319EXPORT_SYMBOL(elv_rb_del);
 320
 321struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 322{
 323        struct rb_node *n = root->rb_node;
 324        struct request *rq;
 325
 326        while (n) {
 327                rq = rb_entry(n, struct request, rb_node);
 328
 329                if (sector < blk_rq_pos(rq))
 330                        n = n->rb_left;
 331                else if (sector > blk_rq_pos(rq))
 332                        n = n->rb_right;
 333                else
 334                        return rq;
 335        }
 336
 337        return NULL;
 338}
 339EXPORT_SYMBOL(elv_rb_find);
 340
 341/*
 342 * Insert rq into dispatch queue of q.  Queue lock must be held on
 343 * entry.  rq is sort instead into the dispatch queue. To be used by
 344 * specific elevators.
 345 */
 346void elv_dispatch_sort(struct request_queue *q, struct request *rq)
 347{
 348        sector_t boundary;
 349        struct list_head *entry;
 350        int stop_flags;
 351
 352        if (q->last_merge == rq)
 353                q->last_merge = NULL;
 354
 355        elv_rqhash_del(q, rq);
 356
 357        q->nr_sorted--;
 358
 359        boundary = q->end_sector;
 360        stop_flags = REQ_SOFTBARRIER | REQ_STARTED;
 361        list_for_each_prev(entry, &q->queue_head) {
 362                struct request *pos = list_entry_rq(entry);
 363
 364                if ((rq->cmd_flags & REQ_DISCARD) !=
 365                    (pos->cmd_flags & REQ_DISCARD))
 366                        break;
 367                if (rq_data_dir(rq) != rq_data_dir(pos))
 368                        break;
 369                if (pos->cmd_flags & stop_flags)
 370                        break;
 371                if (blk_rq_pos(rq) >= boundary) {
 372                        if (blk_rq_pos(pos) < boundary)
 373                                continue;
 374                } else {
 375                        if (blk_rq_pos(pos) >= boundary)
 376                                break;
 377                }
 378                if (blk_rq_pos(rq) >= blk_rq_pos(pos))
 379                        break;
 380        }
 381
 382        list_add(&rq->queuelist, entry);
 383}
 384EXPORT_SYMBOL(elv_dispatch_sort);
 385
 386/*
 387 * Insert rq into dispatch queue of q.  Queue lock must be held on
 388 * entry.  rq is added to the back of the dispatch queue. To be used by
 389 * specific elevators.
 390 */
 391void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 392{
 393        if (q->last_merge == rq)
 394                q->last_merge = NULL;
 395
 396        elv_rqhash_del(q, rq);
 397
 398        q->nr_sorted--;
 399
 400        q->end_sector = rq_end_sector(rq);
 401        q->boundary_rq = rq;
 402        list_add_tail(&rq->queuelist, &q->queue_head);
 403}
 404EXPORT_SYMBOL(elv_dispatch_add_tail);
 405
 406int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 407{
 408        struct elevator_queue *e = q->elevator;
 409        struct request *__rq;
 410        int ret;
 411
 412        /*
 413         * Levels of merges:
 414         *      nomerges:  No merges at all attempted
 415         *      noxmerges: Only simple one-hit cache try
 416         *      merges:    All merge tries attempted
 417         */
 418        if (blk_queue_nomerges(q))
 419                return ELEVATOR_NO_MERGE;
 420
 421        /*
 422         * First try one-hit cache.
 423         */
 424        if (q->last_merge && elv_rq_merge_ok(q->last_merge, bio)) {
 425                ret = blk_try_merge(q->last_merge, bio);
 426                if (ret != ELEVATOR_NO_MERGE) {
 427                        *req = q->last_merge;
 428                        return ret;
 429                }
 430        }
 431
 432        if (blk_queue_noxmerges(q))
 433                return ELEVATOR_NO_MERGE;
 434
 435        /*
 436         * See if our hash lookup can find a potential backmerge.
 437         */
 438        __rq = elv_rqhash_find(q, bio->bi_sector);
 439        if (__rq && elv_rq_merge_ok(__rq, bio)) {
 440                *req = __rq;
 441                return ELEVATOR_BACK_MERGE;
 442        }
 443
 444        if (e->type->ops.elevator_merge_fn)
 445                return e->type->ops.elevator_merge_fn(q, req, bio);
 446
 447        return ELEVATOR_NO_MERGE;
 448}
 449
 450/*
 451 * Attempt to do an insertion back merge. Only check for the case where
 452 * we can append 'rq' to an existing request, so we can throw 'rq' away
 453 * afterwards.
 454 *
 455 * Returns true if we merged, false otherwise
 456 */
 457static bool elv_attempt_insert_merge(struct request_queue *q,
 458                                     struct request *rq)
 459{
 460        struct request *__rq;
 461
 462        if (blk_queue_nomerges(q))
 463                return false;
 464
 465        /*
 466         * First try one-hit cache.
 467         */
 468        if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
 469                return true;
 470
 471        if (blk_queue_noxmerges(q))
 472                return false;
 473
 474        /*
 475         * See if our hash lookup can find a potential backmerge.
 476         */
 477        __rq = elv_rqhash_find(q, blk_rq_pos(rq));
 478        if (__rq && blk_attempt_req_merge(q, __rq, rq))
 479                return true;
 480
 481        return false;
 482}
 483
 484void elv_merged_request(struct request_queue *q, struct request *rq, int type)
 485{
 486        struct elevator_queue *e = q->elevator;
 487
 488        if (e->type->ops.elevator_merged_fn)
 489                e->type->ops.elevator_merged_fn(q, rq, type);
 490
 491        if (type == ELEVATOR_BACK_MERGE)
 492                elv_rqhash_reposition(q, rq);
 493
 494        q->last_merge = rq;
 495}
 496
 497void elv_merge_requests(struct request_queue *q, struct request *rq,
 498                             struct request *next)
 499{
 500        struct elevator_queue *e = q->elevator;
 501        const int next_sorted = next->cmd_flags & REQ_SORTED;
 502
 503        if (next_sorted && e->type->ops.elevator_merge_req_fn)
 504                e->type->ops.elevator_merge_req_fn(q, rq, next);
 505
 506        elv_rqhash_reposition(q, rq);
 507
 508        if (next_sorted) {
 509                elv_rqhash_del(q, next);
 510                q->nr_sorted--;
 511        }
 512
 513        q->last_merge = rq;
 514}
 515
 516void elv_bio_merged(struct request_queue *q, struct request *rq,
 517                        struct bio *bio)
 518{
 519        struct elevator_queue *e = q->elevator;
 520
 521        if (e->type->ops.elevator_bio_merged_fn)
 522                e->type->ops.elevator_bio_merged_fn(q, rq, bio);
 523}
 524
 525void elv_requeue_request(struct request_queue *q, struct request *rq)
 526{
 527        /*
 528         * it already went through dequeue, we need to decrement the
 529         * in_flight count again
 530         */
 531        if (blk_account_rq(rq)) {
 532                q->in_flight[rq_is_sync(rq)]--;
 533                if (rq->cmd_flags & REQ_SORTED)
 534                        elv_deactivate_rq(q, rq);
 535        }
 536
 537        rq->cmd_flags &= ~REQ_STARTED;
 538
 539        __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
 540}
 541
 542void elv_drain_elevator(struct request_queue *q)
 543{
 544        static int printed;
 545
 546        lockdep_assert_held(q->queue_lock);
 547
 548        while (q->elevator->type->ops.elevator_dispatch_fn(q, 1))
 549                ;
 550        if (q->nr_sorted && printed++ < 10) {
 551                printk(KERN_ERR "%s: forced dispatching is broken "
 552                       "(nr_sorted=%u), please report this\n",
 553                       q->elevator->type->elevator_name, q->nr_sorted);
 554        }
 555}
 556
 557void __elv_add_request(struct request_queue *q, struct request *rq, int where)
 558{
 559        trace_block_rq_insert(q, rq);
 560
 561        rq->q = q;
 562
 563        if (rq->cmd_flags & REQ_SOFTBARRIER) {
 564                /* barriers are scheduling boundary, update end_sector */
 565                if (rq->cmd_type == REQ_TYPE_FS) {
 566                        q->end_sector = rq_end_sector(rq);
 567                        q->boundary_rq = rq;
 568                }
 569        } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
 570                    (where == ELEVATOR_INSERT_SORT ||
 571                     where == ELEVATOR_INSERT_SORT_MERGE))
 572                where = ELEVATOR_INSERT_BACK;
 573
 574        switch (where) {
 575        case ELEVATOR_INSERT_REQUEUE:
 576        case ELEVATOR_INSERT_FRONT:
 577                rq->cmd_flags |= REQ_SOFTBARRIER;
 578                list_add(&rq->queuelist, &q->queue_head);
 579                break;
 580
 581        case ELEVATOR_INSERT_BACK:
 582                rq->cmd_flags |= REQ_SOFTBARRIER;
 583                elv_drain_elevator(q);
 584                list_add_tail(&rq->queuelist, &q->queue_head);
 585                /*
 586                 * We kick the queue here for the following reasons.
 587                 * - The elevator might have returned NULL previously
 588                 *   to delay requests and returned them now.  As the
 589                 *   queue wasn't empty before this request, ll_rw_blk
 590                 *   won't run the queue on return, resulting in hang.
 591                 * - Usually, back inserted requests won't be merged
 592                 *   with anything.  There's no point in delaying queue
 593                 *   processing.
 594                 */
 595                __blk_run_queue(q);
 596                break;
 597
 598        case ELEVATOR_INSERT_SORT_MERGE:
 599                /*
 600                 * If we succeed in merging this request with one in the
 601                 * queue already, we are done - rq has now been freed,
 602                 * so no need to do anything further.
 603                 */
 604                if (elv_attempt_insert_merge(q, rq))
 605                        break;
 606        case ELEVATOR_INSERT_SORT:
 607                BUG_ON(rq->cmd_type != REQ_TYPE_FS);
 608                rq->cmd_flags |= REQ_SORTED;
 609                q->nr_sorted++;
 610                if (rq_mergeable(rq)) {
 611                        elv_rqhash_add(q, rq);
 612                        if (!q->last_merge)
 613                                q->last_merge = rq;
 614                }
 615
 616                /*
 617                 * Some ioscheds (cfq) run q->request_fn directly, so
 618                 * rq cannot be accessed after calling
 619                 * elevator_add_req_fn.
 620                 */
 621                q->elevator->type->ops.elevator_add_req_fn(q, rq);
 622                break;
 623
 624        case ELEVATOR_INSERT_FLUSH:
 625                rq->cmd_flags |= REQ_SOFTBARRIER;
 626                blk_insert_flush(rq);
 627                break;
 628        default:
 629                printk(KERN_ERR "%s: bad insertion point %d\n",
 630                       __func__, where);
 631                BUG();
 632        }
 633}
 634EXPORT_SYMBOL(__elv_add_request);
 635
 636void elv_add_request(struct request_queue *q, struct request *rq, int where)
 637{
 638        unsigned long flags;
 639
 640        spin_lock_irqsave(q->queue_lock, flags);
 641        __elv_add_request(q, rq, where);
 642        spin_unlock_irqrestore(q->queue_lock, flags);
 643}
 644EXPORT_SYMBOL(elv_add_request);
 645
 646struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 647{
 648        struct elevator_queue *e = q->elevator;
 649
 650        if (e->type->ops.elevator_latter_req_fn)
 651                return e->type->ops.elevator_latter_req_fn(q, rq);
 652        return NULL;
 653}
 654
 655struct request *elv_former_request(struct request_queue *q, struct request *rq)
 656{
 657        struct elevator_queue *e = q->elevator;
 658
 659        if (e->type->ops.elevator_former_req_fn)
 660                return e->type->ops.elevator_former_req_fn(q, rq);
 661        return NULL;
 662}
 663
 664int elv_set_request(struct request_queue *q, struct request *rq,
 665                    struct bio *bio, gfp_t gfp_mask)
 666{
 667        struct elevator_queue *e = q->elevator;
 668
 669        if (e->type->ops.elevator_set_req_fn)
 670                return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
 671        return 0;
 672}
 673
 674void elv_put_request(struct request_queue *q, struct request *rq)
 675{
 676        struct elevator_queue *e = q->elevator;
 677
 678        if (e->type->ops.elevator_put_req_fn)
 679                e->type->ops.elevator_put_req_fn(rq);
 680}
 681
 682int elv_may_queue(struct request_queue *q, int rw)
 683{
 684        struct elevator_queue *e = q->elevator;
 685
 686        if (e->type->ops.elevator_may_queue_fn)
 687                return e->type->ops.elevator_may_queue_fn(q, rw);
 688
 689        return ELV_MQUEUE_MAY;
 690}
 691
 692void elv_abort_queue(struct request_queue *q)
 693{
 694        struct request *rq;
 695
 696        blk_abort_flushes(q);
 697
 698        while (!list_empty(&q->queue_head)) {
 699                rq = list_entry_rq(q->queue_head.next);
 700                rq->cmd_flags |= REQ_QUIET;
 701                trace_block_rq_abort(q, rq);
 702                /*
 703                 * Mark this request as started so we don't trigger
 704                 * any debug logic in the end I/O path.
 705                 */
 706                blk_start_request(rq);
 707                __blk_end_request_all(rq, -EIO);
 708        }
 709}
 710EXPORT_SYMBOL(elv_abort_queue);
 711
 712void elv_completed_request(struct request_queue *q, struct request *rq)
 713{
 714        struct elevator_queue *e = q->elevator;
 715
 716        /*
 717         * request is released from the driver, io must be done
 718         */
 719        if (blk_account_rq(rq)) {
 720                q->in_flight[rq_is_sync(rq)]--;
 721                if ((rq->cmd_flags & REQ_SORTED) &&
 722                    e->type->ops.elevator_completed_req_fn)
 723                        e->type->ops.elevator_completed_req_fn(q, rq);
 724        }
 725}
 726
 727#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 728
 729static ssize_t
 730elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 731{
 732        struct elv_fs_entry *entry = to_elv(attr);
 733        struct elevator_queue *e;
 734        ssize_t error;
 735
 736        if (!entry->show)
 737                return -EIO;
 738
 739        e = container_of(kobj, struct elevator_queue, kobj);
 740        mutex_lock(&e->sysfs_lock);
 741        error = e->type ? entry->show(e, page) : -ENOENT;
 742        mutex_unlock(&e->sysfs_lock);
 743        return error;
 744}
 745
 746static ssize_t
 747elv_attr_store(struct kobject *kobj, struct attribute *attr,
 748               const char *page, size_t length)
 749{
 750        struct elv_fs_entry *entry = to_elv(attr);
 751        struct elevator_queue *e;
 752        ssize_t error;
 753
 754        if (!entry->store)
 755                return -EIO;
 756
 757        e = container_of(kobj, struct elevator_queue, kobj);
 758        mutex_lock(&e->sysfs_lock);
 759        error = e->type ? entry->store(e, page, length) : -ENOENT;
 760        mutex_unlock(&e->sysfs_lock);
 761        return error;
 762}
 763
 764static const struct sysfs_ops elv_sysfs_ops = {
 765        .show   = elv_attr_show,
 766        .store  = elv_attr_store,
 767};
 768
 769static struct kobj_type elv_ktype = {
 770        .sysfs_ops      = &elv_sysfs_ops,
 771        .release        = elevator_release,
 772};
 773
 774int elv_register_queue(struct request_queue *q)
 775{
 776        struct elevator_queue *e = q->elevator;
 777        int error;
 778
 779        error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
 780        if (!error) {
 781                struct elv_fs_entry *attr = e->type->elevator_attrs;
 782                if (attr) {
 783                        while (attr->attr.name) {
 784                                if (sysfs_create_file(&e->kobj, &attr->attr))
 785                                        break;
 786                                attr++;
 787                        }
 788                }
 789                kobject_uevent(&e->kobj, KOBJ_ADD);
 790                e->registered = 1;
 791        }
 792        return error;
 793}
 794EXPORT_SYMBOL(elv_register_queue);
 795
 796void elv_unregister_queue(struct request_queue *q)
 797{
 798        if (q) {
 799                struct elevator_queue *e = q->elevator;
 800
 801                kobject_uevent(&e->kobj, KOBJ_REMOVE);
 802                kobject_del(&e->kobj);
 803                e->registered = 0;
 804        }
 805}
 806EXPORT_SYMBOL(elv_unregister_queue);
 807
 808int elv_register(struct elevator_type *e)
 809{
 810        char *def = "";
 811
 812        /* create icq_cache if requested */
 813        if (e->icq_size) {
 814                if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
 815                    WARN_ON(e->icq_align < __alignof__(struct io_cq)))
 816                        return -EINVAL;
 817
 818                snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
 819                         "%s_io_cq", e->elevator_name);
 820                e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
 821                                                 e->icq_align, 0, NULL);
 822                if (!e->icq_cache)
 823                        return -ENOMEM;
 824        }
 825
 826        /* register, don't allow duplicate names */
 827        spin_lock(&elv_list_lock);
 828        if (elevator_find(e->elevator_name)) {
 829                spin_unlock(&elv_list_lock);
 830                if (e->icq_cache)
 831                        kmem_cache_destroy(e->icq_cache);
 832                return -EBUSY;
 833        }
 834        list_add_tail(&e->list, &elv_list);
 835        spin_unlock(&elv_list_lock);
 836
 837        /* print pretty message */
 838        if (!strcmp(e->elevator_name, chosen_elevator) ||
 839                        (!*chosen_elevator &&
 840                         !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
 841                                def = " (default)";
 842
 843        printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
 844                                                                def);
 845        return 0;
 846}
 847EXPORT_SYMBOL_GPL(elv_register);
 848
 849void elv_unregister(struct elevator_type *e)
 850{
 851        /* unregister */
 852        spin_lock(&elv_list_lock);
 853        list_del_init(&e->list);
 854        spin_unlock(&elv_list_lock);
 855
 856        /*
 857         * Destroy icq_cache if it exists.  icq's are RCU managed.  Make
 858         * sure all RCU operations are complete before proceeding.
 859         */
 860        if (e->icq_cache) {
 861                rcu_barrier();
 862                kmem_cache_destroy(e->icq_cache);
 863                e->icq_cache = NULL;
 864        }
 865}
 866EXPORT_SYMBOL_GPL(elv_unregister);
 867
 868/*
 869 * switch to new_e io scheduler. be careful not to introduce deadlocks -
 870 * we don't free the old io scheduler, before we have allocated what we
 871 * need for the new one. this way we have a chance of going back to the old
 872 * one, if the new one fails init for some reason.
 873 */
 874static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 875{
 876        struct elevator_queue *old = q->elevator;
 877        bool registered = old->registered;
 878        int err;
 879
 880        /*
 881         * Turn on BYPASS and drain all requests w/ elevator private data.
 882         * Block layer doesn't call into a quiesced elevator - all requests
 883         * are directly put on the dispatch list without elevator data
 884         * using INSERT_BACK.  All requests have SOFTBARRIER set and no
 885         * merge happens either.
 886         */
 887        blk_queue_bypass_start(q);
 888
 889        /* unregister and clear all auxiliary data of the old elevator */
 890        if (registered)
 891                elv_unregister_queue(q);
 892
 893        spin_lock_irq(q->queue_lock);
 894        ioc_clear_queue(q);
 895        spin_unlock_irq(q->queue_lock);
 896
 897        /* allocate, init and register new elevator */
 898        err = -ENOMEM;
 899        q->elevator = elevator_alloc(q, new_e);
 900        if (!q->elevator)
 901                goto fail_init;
 902
 903        err = new_e->ops.elevator_init_fn(q);
 904        if (err) {
 905                kobject_put(&q->elevator->kobj);
 906                goto fail_init;
 907        }
 908
 909        if (registered) {
 910                err = elv_register_queue(q);
 911                if (err)
 912                        goto fail_register;
 913        }
 914
 915        /* done, kill the old one and finish */
 916        elevator_exit(old);
 917        blk_queue_bypass_end(q);
 918
 919        blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
 920
 921        return 0;
 922
 923fail_register:
 924        elevator_exit(q->elevator);
 925fail_init:
 926        /* switch failed, restore and re-register old elevator */
 927        q->elevator = old;
 928        elv_register_queue(q);
 929        blk_queue_bypass_end(q);
 930
 931        return err;
 932}
 933
 934/*
 935 * Switch this queue to the given IO scheduler.
 936 */
 937int elevator_change(struct request_queue *q, const char *name)
 938{
 939        char elevator_name[ELV_NAME_MAX];
 940        struct elevator_type *e;
 941
 942        if (!q->elevator)
 943                return -ENXIO;
 944
 945        strlcpy(elevator_name, name, sizeof(elevator_name));
 946        e = elevator_get(strstrip(elevator_name));
 947        if (!e) {
 948                printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 949                return -EINVAL;
 950        }
 951
 952        if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
 953                elevator_put(e);
 954                return 0;
 955        }
 956
 957        return elevator_switch(q, e);
 958}
 959EXPORT_SYMBOL(elevator_change);
 960
 961ssize_t elv_iosched_store(struct request_queue *q, const char *name,
 962                          size_t count)
 963{
 964        int ret;
 965
 966        if (!q->elevator)
 967                return count;
 968
 969        ret = elevator_change(q, name);
 970        if (!ret)
 971                return count;
 972
 973        printk(KERN_ERR "elevator: switch to %s failed\n", name);
 974        return ret;
 975}
 976
 977ssize_t elv_iosched_show(struct request_queue *q, char *name)
 978{
 979        struct elevator_queue *e = q->elevator;
 980        struct elevator_type *elv;
 981        struct elevator_type *__e;
 982        int len = 0;
 983
 984        if (!q->elevator || !blk_queue_stackable(q))
 985                return sprintf(name, "none\n");
 986
 987        elv = e->type;
 988
 989        spin_lock(&elv_list_lock);
 990        list_for_each_entry(__e, &elv_list, list) {
 991                if (!strcmp(elv->elevator_name, __e->elevator_name))
 992                        len += sprintf(name+len, "[%s] ", elv->elevator_name);
 993                else
 994                        len += sprintf(name+len, "%s ", __e->elevator_name);
 995        }
 996        spin_unlock(&elv_list_lock);
 997
 998        len += sprintf(len+name, "\n");
 999        return len;
1000}
1001
1002struct request *elv_rb_former_request(struct request_queue *q,
1003                                      struct request *rq)
1004{
1005        struct rb_node *rbprev = rb_prev(&rq->rb_node);
1006
1007        if (rbprev)
1008                return rb_entry_rq(rbprev);
1009
1010        return NULL;
1011}
1012EXPORT_SYMBOL(elv_rb_former_request);
1013
1014struct request *elv_rb_latter_request(struct request_queue *q,
1015                                      struct request *rq)
1016{
1017        struct rb_node *rbnext = rb_next(&rq->rb_node);
1018
1019        if (rbnext)
1020                return rb_entry_rq(rbnext);
1021
1022        return NULL;
1023}
1024EXPORT_SYMBOL(elv_rb_latter_request);
1025
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