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
  39#include <trace/events/block.h>
  40
  41#include "blk.h"
  42#include "blk-cgroup.h"
  43
  44static DEFINE_SPINLOCK(elv_list_lock);
  45static 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 */
  56static 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 */
  70bool 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}
  80EXPORT_SYMBOL(elv_rq_merge_ok);
  81
  82static 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
  94static void elevator_put(struct elevator_type *e)
  95{
  96        module_put(e->elevator_owner);
  97}
  98
  99static 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
 121static char chosen_elevator[ELV_NAME_MAX];
 122
 123static 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 */
 136void __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
 151static struct kobj_type elv_ktype;
 152
 153struct elevator_queue *elevator_alloc(struct request_queue *q,
 154                                  struct elevator_type *e)
 155{
 156        struct elevator_queue *eq;
 157
 158        eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
 159        if (unlikely(!eq))
 160                goto err;
 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;
 168err:
 169        kfree(eq);
 170        elevator_put(e);
 171        return NULL;
 172}
 173EXPORT_SYMBOL(elevator_alloc);
 174
 175static void elevator_release(struct kobject *kobj)
 176{
 177        struct elevator_queue *e;
 178
 179        e = container_of(kobj, struct elevator_queue, kobj);
 180        elevator_put(e->type);
 181        kfree(e);
 182}
 183
 184int elevator_init(struct request_queue *q, char *name)
 185{
 186        struct elevator_type *e = NULL;
 187        int err;
 188
 189        /*
 190         * q->sysfs_lock must be held to provide mutual exclusion between
 191         * elevator_switch() and here.
 192         */
 193        lockdep_assert_held(&q->sysfs_lock);
 194
 195        if (unlikely(q->elevator))
 196                return 0;
 197
 198        INIT_LIST_HEAD(&q->queue_head);
 199        q->last_merge = NULL;
 200        q->end_sector = 0;
 201        q->boundary_rq = NULL;
 202
 203        if (name) {
 204                e = elevator_get(name, true);
 205                if (!e)
 206                        return -EINVAL;
 207        }
 208
 209        /*
 210         * Use the default elevator specified by config boot param or
 211         * config option.  Don't try to load modules as we could be running
 212         * off async and request_module() isn't allowed from async.
 213         */
 214        if (!e && *chosen_elevator) {
 215                e = elevator_get(chosen_elevator, false);
 216                if (!e)
 217                        printk(KERN_ERR "I/O scheduler %s not found\n",
 218                                                        chosen_elevator);
 219        }
 220
 221        if (!e) {
 222                e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
 223                if (!e) {
 224                        printk(KERN_ERR
 225                                "Default I/O scheduler not found. " \
 226                                "Using noop.\n");
 227                        e = elevator_get("noop", false);
 228                }
 229        }
 230
 231        err = e->ops.elevator_init_fn(q, e);
 232        return 0;
 233}
 234EXPORT_SYMBOL(elevator_init);
 235
 236void elevator_exit(struct elevator_queue *e)
 237{
 238        mutex_lock(&e->sysfs_lock);
 239        if (e->type->ops.elevator_exit_fn)
 240                e->type->ops.elevator_exit_fn(e);
 241        mutex_unlock(&e->sysfs_lock);
 242
 243        kobject_put(&e->kobj);
 244}
 245EXPORT_SYMBOL(elevator_exit);
 246
 247static inline void __elv_rqhash_del(struct request *rq)
 248{
 249        hash_del(&rq->hash);
 250}
 251
 252static void elv_rqhash_del(struct request_queue *q, struct request *rq)
 253{
 254        if (ELV_ON_HASH(rq))
 255                __elv_rqhash_del(rq);
 256}
 257
 258static void elv_rqhash_add(struct request_queue *q, struct request *rq)
 259{
 260        struct elevator_queue *e = q->elevator;
 261
 262        BUG_ON(ELV_ON_HASH(rq));
 263        hash_add(e->hash, &rq->hash, rq_hash_key(rq));
 264}
 265
 266static 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
 272static 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 */
 297void 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}
 316EXPORT_SYMBOL(elv_rb_add);
 317
 318void 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}
 324EXPORT_SYMBOL(elv_rb_del);
 325
 326struct 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}
 344EXPORT_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 */
 351void 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}
 389EXPORT_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 */
 396void 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}
 409EXPORT_SYMBOL(elv_dispatch_add_tail);
 410
 411int 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_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 */
 462static 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
 497void 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
 510void 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
 529void 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_RUNTIME
 539static 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
 545static 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
 552static inline void blk_pm_requeue_request(struct request *rq) {}
 553static inline void blk_pm_add_request(struct request_queue *q,
 554                                      struct request *rq)
 555{
 556}
 557#endif
 558
 559void 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
 578void 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
 593void __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}
 672EXPORT_SYMBOL(__elv_add_request);
 673
 674void 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}
 682EXPORT_SYMBOL(elv_add_request);
 683
 684struct 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
 693struct 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
 702int 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
 712void 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
 720int 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
 730void elv_abort_queue(struct request_queue *q)
 731{
 732        struct request *rq;
 733
 734        blk_abort_flushes(q);
 735
 736        while (!list_empty(&q->queue_head)) {
 737                rq = list_entry_rq(q->queue_head.next);
 738                rq->cmd_flags |= REQ_QUIET;
 739                trace_block_rq_abort(q, rq);
 740                /*
 741                 * Mark this request as started so we don't trigger
 742                 * any debug logic in the end I/O path.
 743                 */
 744                blk_start_request(rq);
 745                __blk_end_request_all(rq, -EIO);
 746        }
 747}
 748EXPORT_SYMBOL(elv_abort_queue);
 749
 750void elv_completed_request(struct request_queue *q, struct request *rq)
 751{
 752        struct elevator_queue *e = q->elevator;
 753
 754        /*
 755         * request is released from the driver, io must be done
 756         */
 757        if (blk_account_rq(rq)) {
 758                q->in_flight[rq_is_sync(rq)]--;
 759                if ((rq->cmd_flags & REQ_SORTED) &&
 760                    e->type->ops.elevator_completed_req_fn)
 761                        e->type->ops.elevator_completed_req_fn(q, rq);
 762        }
 763}
 764
 765#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 766
 767static ssize_t
 768elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 769{
 770        struct elv_fs_entry *entry = to_elv(attr);
 771        struct elevator_queue *e;
 772        ssize_t error;
 773
 774        if (!entry->show)
 775                return -EIO;
 776
 777        e = container_of(kobj, struct elevator_queue, kobj);
 778        mutex_lock(&e->sysfs_lock);
 779        error = e->type ? entry->show(e, page) : -ENOENT;
 780        mutex_unlock(&e->sysfs_lock);
 781        return error;
 782}
 783
 784static ssize_t
 785elv_attr_store(struct kobject *kobj, struct attribute *attr,
 786               const char *page, size_t length)
 787{
 788        struct elv_fs_entry *entry = to_elv(attr);
 789        struct elevator_queue *e;
 790        ssize_t error;
 791
 792        if (!entry->store)
 793                return -EIO;
 794
 795        e = container_of(kobj, struct elevator_queue, kobj);
 796        mutex_lock(&e->sysfs_lock);
 797        error = e->type ? entry->store(e, page, length) : -ENOENT;
 798        mutex_unlock(&e->sysfs_lock);
 799        return error;
 800}
 801
 802static const struct sysfs_ops elv_sysfs_ops = {
 803        .show   = elv_attr_show,
 804        .store  = elv_attr_store,
 805};
 806
 807static struct kobj_type elv_ktype = {
 808        .sysfs_ops      = &elv_sysfs_ops,
 809        .release        = elevator_release,
 810};
 811
 812int elv_register_queue(struct request_queue *q)
 813{
 814        struct elevator_queue *e = q->elevator;
 815        int error;
 816
 817        error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
 818        if (!error) {
 819                struct elv_fs_entry *attr = e->type->elevator_attrs;
 820                if (attr) {
 821                        while (attr->attr.name) {
 822                                if (sysfs_create_file(&e->kobj, &attr->attr))
 823                                        break;
 824                                attr++;
 825                        }
 826                }
 827                kobject_uevent(&e->kobj, KOBJ_ADD);
 828                e->registered = 1;
 829        }
 830        return error;
 831}
 832EXPORT_SYMBOL(elv_register_queue);
 833
 834void elv_unregister_queue(struct request_queue *q)
 835{
 836        if (q) {
 837                struct elevator_queue *e = q->elevator;
 838
 839                kobject_uevent(&e->kobj, KOBJ_REMOVE);
 840                kobject_del(&e->kobj);
 841                e->registered = 0;
 842        }
 843}
 844EXPORT_SYMBOL(elv_unregister_queue);
 845
 846int elv_register(struct elevator_type *e)
 847{
 848        char *def = "";
 849
 850        /* create icq_cache if requested */
 851        if (e->icq_size) {
 852                if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
 853                    WARN_ON(e->icq_align < __alignof__(struct io_cq)))
 854                        return -EINVAL;
 855
 856                snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
 857                         "%s_io_cq", e->elevator_name);
 858                e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
 859                                                 e->icq_align, 0, NULL);
 860                if (!e->icq_cache)
 861                        return -ENOMEM;
 862        }
 863
 864        /* register, don't allow duplicate names */
 865        spin_lock(&elv_list_lock);
 866        if (elevator_find(e->elevator_name)) {
 867                spin_unlock(&elv_list_lock);
 868                if (e->icq_cache)
 869                        kmem_cache_destroy(e->icq_cache);
 870                return -EBUSY;
 871        }
 872        list_add_tail(&e->list, &elv_list);
 873        spin_unlock(&elv_list_lock);
 874
 875        /* print pretty message */
 876        if (!strcmp(e->elevator_name, chosen_elevator) ||
 877                        (!*chosen_elevator &&
 878                         !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
 879                                def = " (default)";
 880
 881        printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
 882                                                                def);
 883        return 0;
 884}
 885EXPORT_SYMBOL_GPL(elv_register);
 886
 887void elv_unregister(struct elevator_type *e)
 888{
 889        /* unregister */
 890        spin_lock(&elv_list_lock);
 891        list_del_init(&e->list);
 892        spin_unlock(&elv_list_lock);
 893
 894        /*
 895         * Destroy icq_cache if it exists.  icq's are RCU managed.  Make
 896         * sure all RCU operations are complete before proceeding.
 897         */
 898        if (e->icq_cache) {
 899                rcu_barrier();
 900                kmem_cache_destroy(e->icq_cache);
 901                e->icq_cache = NULL;
 902        }
 903}
 904EXPORT_SYMBOL_GPL(elv_unregister);
 905
 906/*
 907 * switch to new_e io scheduler. be careful not to introduce deadlocks -
 908 * we don't free the old io scheduler, before we have allocated what we
 909 * need for the new one. this way we have a chance of going back to the old
 910 * one, if the new one fails init for some reason.
 911 */
 912static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 913{
 914        struct elevator_queue *old = q->elevator;
 915        bool registered = old->registered;
 916        int err;
 917
 918        /*
 919         * Turn on BYPASS and drain all requests w/ elevator private data.
 920         * Block layer doesn't call into a quiesced elevator - all requests
 921         * are directly put on the dispatch list without elevator data
 922         * using INSERT_BACK.  All requests have SOFTBARRIER set and no
 923         * merge happens either.
 924         */
 925        blk_queue_bypass_start(q);
 926
 927        /* unregister and clear all auxiliary data of the old elevator */
 928        if (registered)
 929                elv_unregister_queue(q);
 930
 931        spin_lock_irq(q->queue_lock);
 932        ioc_clear_queue(q);
 933        spin_unlock_irq(q->queue_lock);
 934
 935        /* allocate, init and register new elevator */
 936        err = new_e->ops.elevator_init_fn(q, new_e);
 937        if (err)
 938                goto fail_init;
 939
 940        if (registered) {
 941                err = elv_register_queue(q);
 942                if (err)
 943                        goto fail_register;
 944        }
 945
 946        /* done, kill the old one and finish */
 947        elevator_exit(old);
 948        blk_queue_bypass_end(q);
 949
 950        blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
 951
 952        return 0;
 953
 954fail_register:
 955        elevator_exit(q->elevator);
 956fail_init:
 957        /* switch failed, restore and re-register old elevator */
 958        q->elevator = old;
 959        elv_register_queue(q);
 960        blk_queue_bypass_end(q);
 961
 962        return err;
 963}
 964
 965/*
 966 * Switch this queue to the given IO scheduler.
 967 */
 968static int __elevator_change(struct request_queue *q, const char *name)
 969{
 970        char elevator_name[ELV_NAME_MAX];
 971        struct elevator_type *e;
 972
 973        if (!q->elevator)
 974                return -ENXIO;
 975
 976        strlcpy(elevator_name, name, sizeof(elevator_name));
 977        e = elevator_get(strstrip(elevator_name), true);
 978        if (!e) {
 979                printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 980                return -EINVAL;
 981        }
 982
 983        if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
 984                elevator_put(e);
 985                return 0;
 986        }
 987
 988        return elevator_switch(q, e);
 989}
 990
 991int elevator_change(struct request_queue *q, const char *name)
 992{
 993        int ret;
 994
 995        /* Protect q->elevator from elevator_init() */
 996        mutex_lock(&q->sysfs_lock);
 997        ret = __elevator_change(q, name);
 998        mutex_unlock(&q->sysfs_lock);
 999
1000        return ret;
1001}
1002EXPORT_SYMBOL(elevator_change);
1003
1004ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1005                          size_t count)
1006{
1007        int ret;
1008
1009        if (!q->elevator)
1010                return count;
1011
1012        ret = __elevator_change(q, name);
1013        if (!ret)
1014                return count;
1015
1016        printk(KERN_ERR "elevator: switch to %s failed\n", name);
1017        return ret;
1018}
1019
1020ssize_t elv_iosched_show(struct request_queue *q, char *name)
1021{
1022        struct elevator_queue *e = q->elevator;
1023        struct elevator_type *elv;
1024        struct elevator_type *__e;
1025        int len = 0;
1026
1027        if (!q->elevator || !blk_queue_stackable(q))
1028                return sprintf(name, "none\n");
1029
1030        elv = e->type;
1031
1032        spin_lock(&elv_list_lock);
1033        list_for_each_entry(__e, &elv_list, list) {
1034                if (!strcmp(elv->elevator_name, __e->elevator_name))
1035                        len += sprintf(name+len, "[%s] ", elv->elevator_name);
1036                else
1037                        len += sprintf(name+len, "%s ", __e->elevator_name);
1038        }
1039        spin_unlock(&elv_list_lock);
1040
1041        len += sprintf(len+name, "\n");
1042        return len;
1043}
1044
1045struct request *elv_rb_former_request(struct request_queue *q,
1046                                      struct request *rq)
1047{
1048        struct rb_node *rbprev = rb_prev(&rq->rb_node);
1049
1050        if (rbprev)
1051                return rb_entry_rq(rbprev);
1052
1053        return NULL;
1054}
1055EXPORT_SYMBOL(elv_rb_former_request);
1056
1057struct request *elv_rb_latter_request(struct request_queue *q,
1058                                      struct request *rq)
1059{
1060        struct rb_node *rbnext = rb_next(&rq->rb_node);
1061
1062        if (rbnext)
1063                return rb_entry_rq(rbnext);
1064
1065        return NULL;
1066}
1067EXPORT_SYMBOL(elv_rb_latter_request);
1068