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/delay.h>
  35#include <linux/blktrace_api.h>
  36#include <trace/block.h>
  37#include <linux/hash.h>
  38#include <linux/uaccess.h>
  39
  40#include "blk.h"
  41
  42static DEFINE_SPINLOCK(elv_list_lock);
  43static LIST_HEAD(elv_list);
  44
  45DEFINE_TRACE(block_rq_abort);
  46
  47/*
  48 * Merge hash stuff.
  49 */
  50static const int elv_hash_shift = 6;
  51#define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
  52#define ELV_HASH_FN(sec)        \
  53                (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
  54#define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
  55#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
  56#define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
  57
  58DEFINE_TRACE(block_rq_insert);
  59DEFINE_TRACE(block_rq_issue);
  60
  61/*
  62 * Query io scheduler to see if the current process issuing bio may be
  63 * merged with rq.
  64 */
  65static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
  66{
  67        struct request_queue *q = rq->q;
  68        struct elevator_queue *e = q->elevator;
  69
  70        if (e->ops->elevator_allow_merge_fn)
  71                return e->ops->elevator_allow_merge_fn(q, rq, bio);
  72
  73        return 1;
  74}
  75
  76/*
  77 * can we safely merge with this request?
  78 */
  79int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  80{
  81        if (!rq_mergeable(rq))
  82                return 0;
  83
  84        /*
  85         * Don't merge file system requests and discard requests
  86         */
  87        if (bio_discard(bio) != bio_discard(rq->bio))
  88                return 0;
  89
  90        /*
  91         * different data direction or already started, don't merge
  92         */
  93        if (bio_data_dir(bio) != rq_data_dir(rq))
  94                return 0;
  95
  96        /*
  97         * must be same device and not a special request
  98         */
  99        if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
 100                return 0;
 101
 102        /*
 103         * only merge integrity protected bio into ditto rq
 104         */
 105        if (bio_integrity(bio) != blk_integrity_rq(rq))
 106                return 0;
 107
 108        if (!elv_iosched_allow_merge(rq, bio))
 109                return 0;
 110
 111        return 1;
 112}
 113EXPORT_SYMBOL(elv_rq_merge_ok);
 114
 115static inline int elv_try_merge(struct request *__rq, struct bio *bio)
 116{
 117        int ret = ELEVATOR_NO_MERGE;
 118
 119        /*
 120         * we can merge and sequence is ok, check if it's possible
 121         */
 122        if (elv_rq_merge_ok(__rq, bio)) {
 123                if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
 124                        ret = ELEVATOR_BACK_MERGE;
 125                else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
 126                        ret = ELEVATOR_FRONT_MERGE;
 127        }
 128
 129        return ret;
 130}
 131
 132static struct elevator_type *elevator_find(const char *name)
 133{
 134        struct elevator_type *e;
 135
 136        list_for_each_entry(e, &elv_list, list) {
 137                if (!strcmp(e->elevator_name, name))
 138                        return e;
 139        }
 140
 141        return NULL;
 142}
 143
 144static void elevator_put(struct elevator_type *e)
 145{
 146        module_put(e->elevator_owner);
 147}
 148
 149static struct elevator_type *elevator_get(const char *name)
 150{
 151        struct elevator_type *e;
 152
 153        spin_lock(&elv_list_lock);
 154
 155        e = elevator_find(name);
 156        if (!e) {
 157                char elv[ELV_NAME_MAX + strlen("-iosched")];
 158
 159                spin_unlock(&elv_list_lock);
 160
 161                if (!strcmp(name, "anticipatory"))
 162                        sprintf(elv, "as-iosched");
 163                else
 164                        sprintf(elv, "%s-iosched", name);
 165
 166                request_module("%s", elv);
 167                spin_lock(&elv_list_lock);
 168                e = elevator_find(name);
 169        }
 170
 171        if (e && !try_module_get(e->elevator_owner))
 172                e = NULL;
 173
 174        spin_unlock(&elv_list_lock);
 175
 176        return e;
 177}
 178
 179static void *elevator_init_queue(struct request_queue *q,
 180                                 struct elevator_queue *eq)
 181{
 182        return eq->ops->elevator_init_fn(q);
 183}
 184
 185static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
 186                           void *data)
 187{
 188        q->elevator = eq;
 189        eq->elevator_data = data;
 190}
 191
 192static char chosen_elevator[16];
 193
 194static int __init elevator_setup(char *str)
 195{
 196        /*
 197         * Be backwards-compatible with previous kernels, so users
 198         * won't get the wrong elevator.
 199         */
 200        if (!strcmp(str, "as"))
 201                strcpy(chosen_elevator, "anticipatory");
 202        else
 203                strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 204        return 1;
 205}
 206
 207__setup("elevator=", elevator_setup);
 208
 209static struct kobj_type elv_ktype;
 210
 211static struct elevator_queue *elevator_alloc(struct request_queue *q,
 212                                  struct elevator_type *e)
 213{
 214        struct elevator_queue *eq;
 215        int i;
 216
 217        eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
 218        if (unlikely(!eq))
 219                goto err;
 220
 221        eq->ops = &e->ops;
 222        eq->elevator_type = e;
 223        kobject_init(&eq->kobj, &elv_ktype);
 224        mutex_init(&eq->sysfs_lock);
 225
 226        eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
 227                                        GFP_KERNEL, q->node);
 228        if (!eq->hash)
 229                goto err;
 230
 231        for (i = 0; i < ELV_HASH_ENTRIES; i++)
 232                INIT_HLIST_HEAD(&eq->hash[i]);
 233
 234        return eq;
 235err:
 236        kfree(eq);
 237        elevator_put(e);
 238        return NULL;
 239}
 240
 241static void elevator_release(struct kobject *kobj)
 242{
 243        struct elevator_queue *e;
 244
 245        e = container_of(kobj, struct elevator_queue, kobj);
 246        elevator_put(e->elevator_type);
 247        kfree(e->hash);
 248        kfree(e);
 249}
 250
 251int elevator_init(struct request_queue *q, char *name)
 252{
 253        struct elevator_type *e = NULL;
 254        struct elevator_queue *eq;
 255        int ret = 0;
 256        void *data;
 257
 258        INIT_LIST_HEAD(&q->queue_head);
 259        q->last_merge = NULL;
 260        q->end_sector = 0;
 261        q->boundary_rq = NULL;
 262
 263        if (name) {
 264                e = elevator_get(name);
 265                if (!e)
 266                        return -EINVAL;
 267        }
 268
 269        if (!e && *chosen_elevator) {
 270                e = elevator_get(chosen_elevator);
 271                if (!e)
 272                        printk(KERN_ERR "I/O scheduler %s not found\n",
 273                                                        chosen_elevator);
 274        }
 275
 276        if (!e) {
 277                e = elevator_get(CONFIG_DEFAULT_IOSCHED);
 278                if (!e) {
 279                        printk(KERN_ERR
 280                                "Default I/O scheduler not found. " \
 281                                "Using noop.\n");
 282                        e = elevator_get("noop");
 283                }
 284        }
 285
 286        eq = elevator_alloc(q, e);
 287        if (!eq)
 288                return -ENOMEM;
 289
 290        data = elevator_init_queue(q, eq);
 291        if (!data) {
 292                kobject_put(&eq->kobj);
 293                return -ENOMEM;
 294        }
 295
 296        elevator_attach(q, eq, data);
 297        return ret;
 298}
 299EXPORT_SYMBOL(elevator_init);
 300
 301void elevator_exit(struct elevator_queue *e)
 302{
 303        mutex_lock(&e->sysfs_lock);
 304        if (e->ops->elevator_exit_fn)
 305                e->ops->elevator_exit_fn(e);
 306        e->ops = NULL;
 307        mutex_unlock(&e->sysfs_lock);
 308
 309        kobject_put(&e->kobj);
 310}
 311EXPORT_SYMBOL(elevator_exit);
 312
 313static void elv_activate_rq(struct request_queue *q, struct request *rq)
 314{
 315        struct elevator_queue *e = q->elevator;
 316
 317        if (e->ops->elevator_activate_req_fn)
 318                e->ops->elevator_activate_req_fn(q, rq);
 319}
 320
 321static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
 322{
 323        struct elevator_queue *e = q->elevator;
 324
 325        if (e->ops->elevator_deactivate_req_fn)
 326                e->ops->elevator_deactivate_req_fn(q, rq);
 327}
 328
 329static inline void __elv_rqhash_del(struct request *rq)
 330{
 331        hlist_del_init(&rq->hash);
 332}
 333
 334static void elv_rqhash_del(struct request_queue *q, struct request *rq)
 335{
 336        if (ELV_ON_HASH(rq))
 337                __elv_rqhash_del(rq);
 338}
 339
 340static void elv_rqhash_add(struct request_queue *q, struct request *rq)
 341{
 342        struct elevator_queue *e = q->elevator;
 343
 344        BUG_ON(ELV_ON_HASH(rq));
 345        hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
 346}
 347
 348static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 349{
 350        __elv_rqhash_del(rq);
 351        elv_rqhash_add(q, rq);
 352}
 353
 354static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 355{
 356        struct elevator_queue *e = q->elevator;
 357        struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
 358        struct hlist_node *entry, *next;
 359        struct request *rq;
 360
 361        hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
 362                BUG_ON(!ELV_ON_HASH(rq));
 363
 364                if (unlikely(!rq_mergeable(rq))) {
 365                        __elv_rqhash_del(rq);
 366                        continue;
 367                }
 368
 369                if (rq_hash_key(rq) == offset)
 370                        return rq;
 371        }
 372
 373        return NULL;
 374}
 375
 376/*
 377 * RB-tree support functions for inserting/lookup/removal of requests
 378 * in a sorted RB tree.
 379 */
 380struct request *elv_rb_add(struct rb_root *root, struct request *rq)
 381{
 382        struct rb_node **p = &root->rb_node;
 383        struct rb_node *parent = NULL;
 384        struct request *__rq;
 385
 386        while (*p) {
 387                parent = *p;
 388                __rq = rb_entry(parent, struct request, rb_node);
 389
 390                if (rq->sector < __rq->sector)
 391                        p = &(*p)->rb_left;
 392                else if (rq->sector > __rq->sector)
 393                        p = &(*p)->rb_right;
 394                else
 395                        return __rq;
 396        }
 397
 398        rb_link_node(&rq->rb_node, parent, p);
 399        rb_insert_color(&rq->rb_node, root);
 400        return NULL;
 401}
 402EXPORT_SYMBOL(elv_rb_add);
 403
 404void elv_rb_del(struct rb_root *root, struct request *rq)
 405{
 406        BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 407        rb_erase(&rq->rb_node, root);
 408        RB_CLEAR_NODE(&rq->rb_node);
 409}
 410EXPORT_SYMBOL(elv_rb_del);
 411
 412struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 413{
 414        struct rb_node *n = root->rb_node;
 415        struct request *rq;
 416
 417        while (n) {
 418                rq = rb_entry(n, struct request, rb_node);
 419
 420                if (sector < rq->sector)
 421                        n = n->rb_left;
 422                else if (sector > rq->sector)
 423                        n = n->rb_right;
 424                else
 425                        return rq;
 426        }
 427
 428        return NULL;
 429}
 430EXPORT_SYMBOL(elv_rb_find);
 431
 432/*
 433 * Insert rq into dispatch queue of q.  Queue lock must be held on
 434 * entry.  rq is sort instead into the dispatch queue. To be used by
 435 * specific elevators.
 436 */
 437void elv_dispatch_sort(struct request_queue *q, struct request *rq)
 438{
 439        sector_t boundary;
 440        struct list_head *entry;
 441        int stop_flags;
 442
 443        if (q->last_merge == rq)
 444                q->last_merge = NULL;
 445
 446        elv_rqhash_del(q, rq);
 447
 448        q->nr_sorted--;
 449
 450        boundary = q->end_sector;
 451        stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
 452        list_for_each_prev(entry, &q->queue_head) {
 453                struct request *pos = list_entry_rq(entry);
 454
 455                if (blk_discard_rq(rq) != blk_discard_rq(pos))
 456                        break;
 457                if (rq_data_dir(rq) != rq_data_dir(pos))
 458                        break;
 459                if (pos->cmd_flags & stop_flags)
 460                        break;
 461                if (rq->sector >= boundary) {
 462                        if (pos->sector < boundary)
 463                                continue;
 464                } else {
 465                        if (pos->sector >= boundary)
 466                                break;
 467                }
 468                if (rq->sector >= pos->sector)
 469                        break;
 470        }
 471
 472        list_add(&rq->queuelist, entry);
 473}
 474EXPORT_SYMBOL(elv_dispatch_sort);
 475
 476/*
 477 * Insert rq into dispatch queue of q.  Queue lock must be held on
 478 * entry.  rq is added to the back of the dispatch queue. To be used by
 479 * specific elevators.
 480 */
 481void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 482{
 483        if (q->last_merge == rq)
 484                q->last_merge = NULL;
 485
 486        elv_rqhash_del(q, rq);
 487
 488        q->nr_sorted--;
 489
 490        q->end_sector = rq_end_sector(rq);
 491        q->boundary_rq = rq;
 492        list_add_tail(&rq->queuelist, &q->queue_head);
 493}
 494EXPORT_SYMBOL(elv_dispatch_add_tail);
 495
 496int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 497{
 498        struct elevator_queue *e = q->elevator;
 499        struct request *__rq;
 500        int ret;
 501
 502        /*
 503         * First try one-hit cache.
 504         */
 505        if (q->last_merge) {
 506                ret = elv_try_merge(q->last_merge, bio);
 507                if (ret != ELEVATOR_NO_MERGE) {
 508                        *req = q->last_merge;
 509                        return ret;
 510                }
 511        }
 512
 513        if (blk_queue_nomerges(q))
 514                return ELEVATOR_NO_MERGE;
 515
 516        /*
 517         * See if our hash lookup can find a potential backmerge.
 518         */
 519        __rq = elv_rqhash_find(q, bio->bi_sector);
 520        if (__rq && elv_rq_merge_ok(__rq, bio)) {
 521                *req = __rq;
 522                return ELEVATOR_BACK_MERGE;
 523        }
 524
 525        if (e->ops->elevator_merge_fn)
 526                return e->ops->elevator_merge_fn(q, req, bio);
 527
 528        return ELEVATOR_NO_MERGE;
 529}
 530
 531void elv_merged_request(struct request_queue *q, struct request *rq, int type)
 532{
 533        struct elevator_queue *e = q->elevator;
 534
 535        if (e->ops->elevator_merged_fn)
 536                e->ops->elevator_merged_fn(q, rq, type);
 537
 538        if (type == ELEVATOR_BACK_MERGE)
 539                elv_rqhash_reposition(q, rq);
 540
 541        q->last_merge = rq;
 542}
 543
 544void elv_merge_requests(struct request_queue *q, struct request *rq,
 545                             struct request *next)
 546{
 547        struct elevator_queue *e = q->elevator;
 548
 549        if (e->ops->elevator_merge_req_fn)
 550                e->ops->elevator_merge_req_fn(q, rq, next);
 551
 552        elv_rqhash_reposition(q, rq);
 553        elv_rqhash_del(q, next);
 554
 555        q->nr_sorted--;
 556        q->last_merge = rq;
 557}
 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--;
 567                if (blk_sorted_rq(rq))
 568                        elv_deactivate_rq(q, rq);
 569        }
 570
 571        rq->cmd_flags &= ~REQ_STARTED;
 572
 573        elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 574}
 575
 576void elv_drain_elevator(struct request_queue *q)
 577{
 578        static int printed;
 579        while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 580                ;
 581        if (q->nr_sorted == 0)
 582                return;
 583        if (printed++ < 10) {
 584                printk(KERN_ERR "%s: forced dispatching is broken "
 585                       "(nr_sorted=%u), please report this\n",
 586                       q->elevator->elevator_type->elevator_name, q->nr_sorted);
 587        }
 588}
 589
 590/*
 591 * Call with queue lock held, interrupts disabled
 592 */
 593void elv_quiesce_start(struct request_queue *q)
 594{
 595        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
 596
 597        /*
 598         * make sure we don't have any requests in flight
 599         */
 600        elv_drain_elevator(q);
 601        while (q->rq.elvpriv) {
 602                blk_start_queueing(q);
 603                spin_unlock_irq(q->queue_lock);
 604                msleep(10);
 605                spin_lock_irq(q->queue_lock);
 606                elv_drain_elevator(q);
 607        }
 608}
 609
 610void elv_quiesce_end(struct request_queue *q)
 611{
 612        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
 613}
 614
 615void elv_insert(struct request_queue *q, struct request *rq, int where)
 616{
 617        struct list_head *pos;
 618        unsigned ordseq;
 619        int unplug_it = 1;
 620
 621        trace_block_rq_insert(q, rq);
 622
 623        rq->q = q;
 624
 625        switch (where) {
 626        case ELEVATOR_INSERT_FRONT:
 627                rq->cmd_flags |= REQ_SOFTBARRIER;
 628
 629                list_add(&rq->queuelist, &q->queue_head);
 630                break;
 631
 632        case ELEVATOR_INSERT_BACK:
 633                rq->cmd_flags |= REQ_SOFTBARRIER;
 634                elv_drain_elevator(q);
 635                list_add_tail(&rq->queuelist, &q->queue_head);
 636                /*
 637                 * We kick the queue here for the following reasons.
 638                 * - The elevator might have returned NULL previously
 639                 *   to delay requests and returned them now.  As the
 640                 *   queue wasn't empty before this request, ll_rw_blk
 641                 *   won't run the queue on return, resulting in hang.
 642                 * - Usually, back inserted requests won't be merged
 643                 *   with anything.  There's no point in delaying queue
 644                 *   processing.
 645                 */
 646                blk_remove_plug(q);
 647                blk_start_queueing(q);
 648                break;
 649
 650        case ELEVATOR_INSERT_SORT:
 651                BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
 652                rq->cmd_flags |= REQ_SORTED;
 653                q->nr_sorted++;
 654                if (rq_mergeable(rq)) {
 655                        elv_rqhash_add(q, rq);
 656                        if (!q->last_merge)
 657                                q->last_merge = rq;
 658                }
 659
 660                /*
 661                 * Some ioscheds (cfq) run q->request_fn directly, so
 662                 * rq cannot be accessed after calling
 663                 * elevator_add_req_fn.
 664                 */
 665                q->elevator->ops->elevator_add_req_fn(q, rq);
 666                break;
 667
 668        case ELEVATOR_INSERT_REQUEUE:
 669                /*
 670                 * If ordered flush isn't in progress, we do front
 671                 * insertion; otherwise, requests should be requeued
 672                 * in ordseq order.
 673                 */
 674                rq->cmd_flags |= REQ_SOFTBARRIER;
 675
 676                /*
 677                 * Most requeues happen because of a busy condition,
 678                 * don't force unplug of the queue for that case.
 679                 */
 680                unplug_it = 0;
 681
 682                if (q->ordseq == 0) {
 683                        list_add(&rq->queuelist, &q->queue_head);
 684                        break;
 685                }
 686
 687                ordseq = blk_ordered_req_seq(rq);
 688
 689                list_for_each(pos, &q->queue_head) {
 690                        struct request *pos_rq = list_entry_rq(pos);
 691                        if (ordseq <= blk_ordered_req_seq(pos_rq))
 692                                break;
 693                }
 694
 695                list_add_tail(&rq->queuelist, pos);
 696                break;
 697
 698        default:
 699                printk(KERN_ERR "%s: bad insertion point %d\n",
 700                       __func__, where);
 701                BUG();
 702        }
 703
 704        if (unplug_it && blk_queue_plugged(q)) {
 705                int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
 706                        - q->in_flight;
 707
 708                if (nrq >= q->unplug_thresh)
 709                        __generic_unplug_device(q);
 710        }
 711}
 712
 713void __elv_add_request(struct request_queue *q, struct request *rq, int where,
 714                       int plug)
 715{
 716        if (q->ordcolor)
 717                rq->cmd_flags |= REQ_ORDERED_COLOR;
 718
 719        if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 720                /*
 721                 * toggle ordered color
 722                 */
 723                if (blk_barrier_rq(rq))
 724                        q->ordcolor ^= 1;
 725
 726                /*
 727                 * barriers implicitly indicate back insertion
 728                 */
 729                if (where == ELEVATOR_INSERT_SORT)
 730                        where = ELEVATOR_INSERT_BACK;
 731
 732                /*
 733                 * this request is scheduling boundary, update
 734                 * end_sector
 735                 */
 736                if (blk_fs_request(rq) || blk_discard_rq(rq)) {
 737                        q->end_sector = rq_end_sector(rq);
 738                        q->boundary_rq = rq;
 739                }
 740        } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
 741                    where == ELEVATOR_INSERT_SORT)
 742                where = ELEVATOR_INSERT_BACK;
 743
 744        if (plug)
 745                blk_plug_device(q);
 746
 747        elv_insert(q, rq, where);
 748}
 749EXPORT_SYMBOL(__elv_add_request);
 750
 751void elv_add_request(struct request_queue *q, struct request *rq, int where,
 752                     int plug)
 753{
 754        unsigned long flags;
 755
 756        spin_lock_irqsave(q->queue_lock, flags);
 757        __elv_add_request(q, rq, where, plug);
 758        spin_unlock_irqrestore(q->queue_lock, flags);
 759}
 760EXPORT_SYMBOL(elv_add_request);
 761
 762static inline struct request *__elv_next_request(struct request_queue *q)
 763{
 764        struct request *rq;
 765
 766        while (1) {
 767                while (!list_empty(&q->queue_head)) {
 768                        rq = list_entry_rq(q->queue_head.next);
 769                        if (blk_do_ordered(q, &rq))
 770                                return rq;
 771                }
 772
 773                if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 774                        return NULL;
 775        }
 776}
 777
 778struct request *elv_next_request(struct request_queue *q)
 779{
 780        struct request *rq;
 781        int ret;
 782
 783        while ((rq = __elv_next_request(q)) != NULL) {
 784                if (!(rq->cmd_flags & REQ_STARTED)) {
 785                        /*
 786                         * This is the first time the device driver
 787                         * sees this request (possibly after
 788                         * requeueing).  Notify IO scheduler.
 789                         */
 790                        if (blk_sorted_rq(rq))
 791                                elv_activate_rq(q, rq);
 792
 793                        /*
 794                         * just mark as started even if we don't start
 795                         * it, a request that has been delayed should
 796                         * not be passed by new incoming requests
 797                         */
 798                        rq->cmd_flags |= REQ_STARTED;
 799                        trace_block_rq_issue(q, rq);
 800                }
 801
 802                if (!q->boundary_rq || q->boundary_rq == rq) {
 803                        q->end_sector = rq_end_sector(rq);
 804                        q->boundary_rq = NULL;
 805                }
 806
 807                if (rq->cmd_flags & REQ_DONTPREP)
 808                        break;
 809
 810                if (q->dma_drain_size && rq->data_len) {
 811                        /*
 812                         * make sure space for the drain appears we
 813                         * know we can do this because max_hw_segments
 814                         * has been adjusted to be one fewer than the
 815                         * device can handle
 816                         */
 817                        rq->nr_phys_segments++;
 818                }
 819
 820                if (!q->prep_rq_fn)
 821                        break;
 822
 823                ret = q->prep_rq_fn(q, rq);
 824                if (ret == BLKPREP_OK) {
 825                        break;
 826                } else if (ret == BLKPREP_DEFER) {
 827                        /*
 828                         * the request may have been (partially) prepped.
 829                         * we need to keep this request in the front to
 830                         * avoid resource deadlock.  REQ_STARTED will
 831                         * prevent other fs requests from passing this one.
 832                         */
 833                        if (q->dma_drain_size && rq->data_len &&
 834                            !(rq->cmd_flags & REQ_DONTPREP)) {
 835                                /*
 836                                 * remove the space for the drain we added
 837                                 * so that we don't add it again
 838                                 */
 839                                --rq->nr_phys_segments;
 840                        }
 841
 842                        rq = NULL;
 843                        break;
 844                } else if (ret == BLKPREP_KILL) {
 845                        rq->cmd_flags |= REQ_QUIET;
 846                        __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 847                } else {
 848                        printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
 849                        break;
 850                }
 851        }
 852
 853        return rq;
 854}
 855EXPORT_SYMBOL(elv_next_request);
 856
 857void elv_dequeue_request(struct request_queue *q, struct request *rq)
 858{
 859        BUG_ON(list_empty(&rq->queuelist));
 860        BUG_ON(ELV_ON_HASH(rq));
 861
 862        list_del_init(&rq->queuelist);
 863
 864        /*
 865         * the time frame between a request being removed from the lists
 866         * and to it is freed is accounted as io that is in progress at
 867         * the driver side.
 868         */
 869        if (blk_account_rq(rq))
 870                q->in_flight++;
 871}
 872
 873int elv_queue_empty(struct request_queue *q)
 874{
 875        struct elevator_queue *e = q->elevator;
 876
 877        if (!list_empty(&q->queue_head))
 878                return 0;
 879
 880        if (e->ops->elevator_queue_empty_fn)
 881                return e->ops->elevator_queue_empty_fn(q);
 882
 883        return 1;
 884}
 885EXPORT_SYMBOL(elv_queue_empty);
 886
 887struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 888{
 889        struct elevator_queue *e = q->elevator;
 890
 891        if (e->ops->elevator_latter_req_fn)
 892                return e->ops->elevator_latter_req_fn(q, rq);
 893        return NULL;
 894}
 895
 896struct request *elv_former_request(struct request_queue *q, struct request *rq)
 897{
 898        struct elevator_queue *e = q->elevator;
 899
 900        if (e->ops->elevator_former_req_fn)
 901                return e->ops->elevator_former_req_fn(q, rq);
 902        return NULL;
 903}
 904
 905int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
 906{
 907        struct elevator_queue *e = q->elevator;
 908
 909        if (e->ops->elevator_set_req_fn)
 910                return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
 911
 912        rq->elevator_private = NULL;
 913        return 0;
 914}
 915
 916void elv_put_request(struct request_queue *q, struct request *rq)
 917{
 918        struct elevator_queue *e = q->elevator;
 919
 920        if (e->ops->elevator_put_req_fn)
 921                e->ops->elevator_put_req_fn(rq);
 922}
 923
 924int elv_may_queue(struct request_queue *q, int rw)
 925{
 926        struct elevator_queue *e = q->elevator;
 927
 928        if (e->ops->elevator_may_queue_fn)
 929                return e->ops->elevator_may_queue_fn(q, rw);
 930
 931        return ELV_MQUEUE_MAY;
 932}
 933
 934void elv_abort_queue(struct request_queue *q)
 935{
 936        struct request *rq;
 937
 938        while (!list_empty(&q->queue_head)) {
 939                rq = list_entry_rq(q->queue_head.next);
 940                rq->cmd_flags |= REQ_QUIET;
 941                trace_block_rq_abort(q, rq);
 942                __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 943        }
 944}
 945EXPORT_SYMBOL(elv_abort_queue);
 946
 947void elv_completed_request(struct request_queue *q, struct request *rq)
 948{
 949        struct elevator_queue *e = q->elevator;
 950
 951        /*
 952         * request is released from the driver, io must be done
 953         */
 954        if (blk_account_rq(rq)) {
 955                q->in_flight--;
 956                if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 957                        e->ops->elevator_completed_req_fn(q, rq);
 958        }
 959
 960        /*
 961         * Check if the queue is waiting for fs requests to be
 962         * drained for flush sequence.
 963         */
 964        if (unlikely(q->ordseq)) {
 965                struct request *next = NULL;
 966
 967                if (!list_empty(&q->queue_head))
 968                        next = list_entry_rq(q->queue_head.next);
 969
 970                if (!q->in_flight &&
 971                    blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 972                    (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
 973                        blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 974                        blk_start_queueing(q);
 975                }
 976        }
 977}
 978
 979#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 980
 981static ssize_t
 982elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 983{
 984        struct elv_fs_entry *entry = to_elv(attr);
 985        struct elevator_queue *e;
 986        ssize_t error;
 987
 988        if (!entry->show)
 989                return -EIO;
 990
 991        e = container_of(kobj, struct elevator_queue, kobj);
 992        mutex_lock(&e->sysfs_lock);
 993        error = e->ops ? entry->show(e, page) : -ENOENT;
 994        mutex_unlock(&e->sysfs_lock);
 995        return error;
 996}
 997
 998static ssize_t
 999elv_attr_store(struct kobject *kobj, struct attribute *attr,
1000               const char *page, size_t length)
1001{
1002        struct elv_fs_entry *entry = to_elv(attr);
1003        struct elevator_queue *e;
1004        ssize_t error;
1005
1006        if (!entry->store)
1007                return -EIO;
1008
1009        e = container_of(kobj, struct elevator_queue, kobj);
1010        mutex_lock(&e->sysfs_lock);
1011        error = e->ops ? entry->store(e, page, length) : -ENOENT;
1012        mutex_unlock(&e->sysfs_lock);
1013        return error;
1014}
1015
1016static struct sysfs_ops elv_sysfs_ops = {
1017        .show   = elv_attr_show,
1018        .store  = elv_attr_store,
1019};
1020
1021static struct kobj_type elv_ktype = {
1022        .sysfs_ops      = &elv_sysfs_ops,
1023        .release        = elevator_release,
1024};
1025
1026int elv_register_queue(struct request_queue *q)
1027{
1028        struct elevator_queue *e = q->elevator;
1029        int error;
1030
1031        error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1032        if (!error) {
1033                struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1034                if (attr) {
1035                        while (attr->attr.name) {
1036                                if (sysfs_create_file(&e->kobj, &attr->attr))
1037                                        break;
1038                                attr++;
1039                        }
1040                }
1041                kobject_uevent(&e->kobj, KOBJ_ADD);
1042        }
1043        return error;
1044}
1045
1046static void __elv_unregister_queue(struct elevator_queue *e)
1047{
1048        kobject_uevent(&e->kobj, KOBJ_REMOVE);
1049        kobject_del(&e->kobj);
1050}
1051
1052void elv_unregister_queue(struct request_queue *q)
1053{
1054        if (q)
1055                __elv_unregister_queue(q->elevator);
1056}
1057
1058void elv_register(struct elevator_type *e)
1059{
1060        char *def = "";
1061
1062        spin_lock(&elv_list_lock);
1063        BUG_ON(elevator_find(e->elevator_name));
1064        list_add_tail(&e->list, &elv_list);
1065        spin_unlock(&elv_list_lock);
1066
1067        if (!strcmp(e->elevator_name, chosen_elevator) ||
1068                        (!*chosen_elevator &&
1069                         !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1070                                def = " (default)";
1071
1072        printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1073                                                                def);
1074}
1075EXPORT_SYMBOL_GPL(elv_register);
1076
1077void elv_unregister(struct elevator_type *e)
1078{
1079        struct task_struct *g, *p;
1080
1081        /*
1082         * Iterate every thread in the process to remove the io contexts.
1083         */
1084        if (e->ops.trim) {
1085                read_lock(&tasklist_lock);
1086                do_each_thread(g, p) {
1087                        task_lock(p);
1088                        if (p->io_context)
1089                                e->ops.trim(p->io_context);
1090                        task_unlock(p);
1091                } while_each_thread(g, p);
1092                read_unlock(&tasklist_lock);
1093        }
1094
1095        spin_lock(&elv_list_lock);
1096        list_del_init(&e->list);
1097        spin_unlock(&elv_list_lock);
1098}
1099EXPORT_SYMBOL_GPL(elv_unregister);
1100
1101/*
1102 * switch to new_e io scheduler. be careful not to introduce deadlocks -
1103 * we don't free the old io scheduler, before we have allocated what we
1104 * need for the new one. this way we have a chance of going back to the old
1105 * one, if the new one fails init for some reason.
1106 */
1107static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1108{
1109        struct elevator_queue *old_elevator, *e;
1110        void *data;
1111
1112        /*
1113         * Allocate new elevator
1114         */
1115        e = elevator_alloc(q, new_e);
1116        if (!e)
1117                return 0;
1118
1119        data = elevator_init_queue(q, e);
1120        if (!data) {
1121                kobject_put(&e->kobj);
1122                return 0;
1123        }
1124
1125        /*
1126         * Turn on BYPASS and drain all requests w/ elevator private data
1127         */
1128        spin_lock_irq(q->queue_lock);
1129        elv_quiesce_start(q);
1130
1131        /*
1132         * Remember old elevator.
1133         */
1134        old_elevator = q->elevator;
1135
1136        /*
1137         * attach and start new elevator
1138         */
1139        elevator_attach(q, e, data);
1140
1141        spin_unlock_irq(q->queue_lock);
1142
1143        __elv_unregister_queue(old_elevator);
1144
1145        if (elv_register_queue(q))
1146                goto fail_register;
1147
1148        /*
1149         * finally exit old elevator and turn off BYPASS.
1150         */
1151        elevator_exit(old_elevator);
1152        spin_lock_irq(q->queue_lock);
1153        elv_quiesce_end(q);
1154        spin_unlock_irq(q->queue_lock);
1155
1156        blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1157
1158        return 1;
1159
1160fail_register:
1161        /*
1162         * switch failed, exit the new io scheduler and reattach the old
1163         * one again (along with re-adding the sysfs dir)
1164         */
1165        elevator_exit(e);
1166        q->elevator = old_elevator;
1167        elv_register_queue(q);
1168
1169        spin_lock_irq(q->queue_lock);
1170        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1171        spin_unlock_irq(q->queue_lock);
1172
1173        return 0;
1174}
1175
1176ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1177                          size_t count)
1178{
1179        char elevator_name[ELV_NAME_MAX];
1180        struct elevator_type *e;
1181
1182        strlcpy(elevator_name, name, sizeof(elevator_name));
1183        strstrip(elevator_name);
1184
1185        e = elevator_get(elevator_name);
1186        if (!e) {
1187                printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1188                return -EINVAL;
1189        }
1190
1191        if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1192                elevator_put(e);
1193                return count;
1194        }
1195
1196        if (!elevator_switch(q, e))
1197                printk(KERN_ERR "elevator: switch to %s failed\n",
1198                                                        elevator_name);
1199        return count;
1200}
1201
1202ssize_t elv_iosched_show(struct request_queue *q, char *name)
1203{
1204        struct elevator_queue *e = q->elevator;
1205        struct elevator_type *elv = e->elevator_type;
1206        struct elevator_type *__e;
1207        int len = 0;
1208
1209        spin_lock(&elv_list_lock);
1210        list_for_each_entry(__e, &elv_list, list) {
1211                if (!strcmp(elv->elevator_name, __e->elevator_name))
1212                        len += sprintf(name+len, "[%s] ", elv->elevator_name);
1213                else
1214                        len += sprintf(name+len, "%s ", __e->elevator_name);
1215        }
1216        spin_unlock(&elv_list_lock);
1217
1218        len += sprintf(len+name, "\n");
1219        return len;
1220}
1221
1222struct request *elv_rb_former_request(struct request_queue *q,
1223                                      struct request *rq)
1224{
1225        struct rb_node *rbprev = rb_prev(&rq->rb_node);
1226
1227        if (rbprev)
1228                return rb_entry_rq(rbprev);
1229
1230        return NULL;
1231}
1232EXPORT_SYMBOL(elv_rb_former_request);
1233
1234struct request *elv_rb_latter_request(struct request_queue *q,
1235                                      struct request *rq)
1236{
1237        struct rb_node *rbnext = rb_next(&rq->rb_node);
1238
1239        if (rbnext)
1240                return rb_entry_rq(rbnext);
1241
1242        return NULL;
1243}
1244EXPORT_SYMBOL(elv_rb_latter_request);
1245