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
 576static void 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
 590void elv_insert(struct request_queue *q, struct request *rq, int where)
 591{
 592        struct list_head *pos;
 593        unsigned ordseq;
 594        int unplug_it = 1;
 595
 596        trace_block_rq_insert(q, rq);
 597
 598        rq->q = q;
 599
 600        switch (where) {
 601        case ELEVATOR_INSERT_FRONT:
 602                rq->cmd_flags |= REQ_SOFTBARRIER;
 603
 604                list_add(&rq->queuelist, &q->queue_head);
 605                break;
 606
 607        case ELEVATOR_INSERT_BACK:
 608                rq->cmd_flags |= REQ_SOFTBARRIER;
 609                elv_drain_elevator(q);
 610                list_add_tail(&rq->queuelist, &q->queue_head);
 611                /*
 612                 * We kick the queue here for the following reasons.
 613                 * - The elevator might have returned NULL previously
 614                 *   to delay requests and returned them now.  As the
 615                 *   queue wasn't empty before this request, ll_rw_blk
 616                 *   won't run the queue on return, resulting in hang.
 617                 * - Usually, back inserted requests won't be merged
 618                 *   with anything.  There's no point in delaying queue
 619                 *   processing.
 620                 */
 621                blk_remove_plug(q);
 622                blk_start_queueing(q);
 623                break;
 624
 625        case ELEVATOR_INSERT_SORT:
 626                BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
 627                rq->cmd_flags |= REQ_SORTED;
 628                q->nr_sorted++;
 629                if (rq_mergeable(rq)) {
 630                        elv_rqhash_add(q, rq);
 631                        if (!q->last_merge)
 632                                q->last_merge = rq;
 633                }
 634
 635                /*
 636                 * Some ioscheds (cfq) run q->request_fn directly, so
 637                 * rq cannot be accessed after calling
 638                 * elevator_add_req_fn.
 639                 */
 640                q->elevator->ops->elevator_add_req_fn(q, rq);
 641                break;
 642
 643        case ELEVATOR_INSERT_REQUEUE:
 644                /*
 645                 * If ordered flush isn't in progress, we do front
 646                 * insertion; otherwise, requests should be requeued
 647                 * in ordseq order.
 648                 */
 649                rq->cmd_flags |= REQ_SOFTBARRIER;
 650
 651                /*
 652                 * Most requeues happen because of a busy condition,
 653                 * don't force unplug of the queue for that case.
 654                 */
 655                unplug_it = 0;
 656
 657                if (q->ordseq == 0) {
 658                        list_add(&rq->queuelist, &q->queue_head);
 659                        break;
 660                }
 661
 662                ordseq = blk_ordered_req_seq(rq);
 663
 664                list_for_each(pos, &q->queue_head) {
 665                        struct request *pos_rq = list_entry_rq(pos);
 666                        if (ordseq <= blk_ordered_req_seq(pos_rq))
 667                                break;
 668                }
 669
 670                list_add_tail(&rq->queuelist, pos);
 671                break;
 672
 673        default:
 674                printk(KERN_ERR "%s: bad insertion point %d\n",
 675                       __func__, where);
 676                BUG();
 677        }
 678
 679        if (unplug_it && blk_queue_plugged(q)) {
 680                int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 681                        - q->in_flight;
 682
 683                if (nrq >= q->unplug_thresh)
 684                        __generic_unplug_device(q);
 685        }
 686}
 687
 688void __elv_add_request(struct request_queue *q, struct request *rq, int where,
 689                       int plug)
 690{
 691        if (q->ordcolor)
 692                rq->cmd_flags |= REQ_ORDERED_COLOR;
 693
 694        if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 695                /*
 696                 * toggle ordered color
 697                 */
 698                if (blk_barrier_rq(rq))
 699                        q->ordcolor ^= 1;
 700
 701                /*
 702                 * barriers implicitly indicate back insertion
 703                 */
 704                if (where == ELEVATOR_INSERT_SORT)
 705                        where = ELEVATOR_INSERT_BACK;
 706
 707                /*
 708                 * this request is scheduling boundary, update
 709                 * end_sector
 710                 */
 711                if (blk_fs_request(rq) || blk_discard_rq(rq)) {
 712                        q->end_sector = rq_end_sector(rq);
 713                        q->boundary_rq = rq;
 714                }
 715        } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
 716                    where == ELEVATOR_INSERT_SORT)
 717                where = ELEVATOR_INSERT_BACK;
 718
 719        if (plug)
 720                blk_plug_device(q);
 721
 722        elv_insert(q, rq, where);
 723}
 724EXPORT_SYMBOL(__elv_add_request);
 725
 726void elv_add_request(struct request_queue *q, struct request *rq, int where,
 727                     int plug)
 728{
 729        unsigned long flags;
 730
 731        spin_lock_irqsave(q->queue_lock, flags);
 732        __elv_add_request(q, rq, where, plug);
 733        spin_unlock_irqrestore(q->queue_lock, flags);
 734}
 735EXPORT_SYMBOL(elv_add_request);
 736
 737static inline struct request *__elv_next_request(struct request_queue *q)
 738{
 739        struct request *rq;
 740
 741        while (1) {
 742                while (!list_empty(&q->queue_head)) {
 743                        rq = list_entry_rq(q->queue_head.next);
 744                        if (blk_do_ordered(q, &rq))
 745                                return rq;
 746                }
 747
 748                if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 749                        return NULL;
 750        }
 751}
 752
 753struct request *elv_next_request(struct request_queue *q)
 754{
 755        struct request *rq;
 756        int ret;
 757
 758        while ((rq = __elv_next_request(q)) != NULL) {
 759                if (!(rq->cmd_flags & REQ_STARTED)) {
 760                        /*
 761                         * This is the first time the device driver
 762                         * sees this request (possibly after
 763                         * requeueing).  Notify IO scheduler.
 764                         */
 765                        if (blk_sorted_rq(rq))
 766                                elv_activate_rq(q, rq);
 767
 768                        /*
 769                         * just mark as started even if we don't start
 770                         * it, a request that has been delayed should
 771                         * not be passed by new incoming requests
 772                         */
 773                        rq->cmd_flags |= REQ_STARTED;
 774                        trace_block_rq_issue(q, rq);
 775                }
 776
 777                if (!q->boundary_rq || q->boundary_rq == rq) {
 778                        q->end_sector = rq_end_sector(rq);
 779                        q->boundary_rq = NULL;
 780                }
 781
 782                if (rq->cmd_flags & REQ_DONTPREP)
 783                        break;
 784
 785                if (q->dma_drain_size && rq->data_len) {
 786                        /*
 787                         * make sure space for the drain appears we
 788                         * know we can do this because max_hw_segments
 789                         * has been adjusted to be one fewer than the
 790                         * device can handle
 791                         */
 792                        rq->nr_phys_segments++;
 793                }
 794
 795                if (!q->prep_rq_fn)
 796                        break;
 797
 798                ret = q->prep_rq_fn(q, rq);
 799                if (ret == BLKPREP_OK) {
 800                        break;
 801                } else if (ret == BLKPREP_DEFER) {
 802                        /*
 803                         * the request may have been (partially) prepped.
 804                         * we need to keep this request in the front to
 805                         * avoid resource deadlock.  REQ_STARTED will
 806                         * prevent other fs requests from passing this one.
 807                         */
 808                        if (q->dma_drain_size && rq->data_len &&
 809                            !(rq->cmd_flags & REQ_DONTPREP)) {
 810                                /*
 811                                 * remove the space for the drain we added
 812                                 * so that we don't add it again
 813                                 */
 814                                --rq->nr_phys_segments;
 815                        }
 816
 817                        rq = NULL;
 818                        break;
 819                } else if (ret == BLKPREP_KILL) {
 820                        rq->cmd_flags |= REQ_QUIET;
 821                        __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 822                } else {
 823                        printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
 824                        break;
 825                }
 826        }
 827
 828        return rq;
 829}
 830EXPORT_SYMBOL(elv_next_request);
 831
 832void elv_dequeue_request(struct request_queue *q, struct request *rq)
 833{
 834        BUG_ON(list_empty(&rq->queuelist));
 835        BUG_ON(ELV_ON_HASH(rq));
 836
 837        list_del_init(&rq->queuelist);
 838
 839        /*
 840         * the time frame between a request being removed from the lists
 841         * and to it is freed is accounted as io that is in progress at
 842         * the driver side.
 843         */
 844        if (blk_account_rq(rq))
 845                q->in_flight++;
 846}
 847
 848int elv_queue_empty(struct request_queue *q)
 849{
 850        struct elevator_queue *e = q->elevator;
 851
 852        if (!list_empty(&q->queue_head))
 853                return 0;
 854
 855        if (e->ops->elevator_queue_empty_fn)
 856                return e->ops->elevator_queue_empty_fn(q);
 857
 858        return 1;
 859}
 860EXPORT_SYMBOL(elv_queue_empty);
 861
 862struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 863{
 864        struct elevator_queue *e = q->elevator;
 865
 866        if (e->ops->elevator_latter_req_fn)
 867                return e->ops->elevator_latter_req_fn(q, rq);
 868        return NULL;
 869}
 870
 871struct request *elv_former_request(struct request_queue *q, struct request *rq)
 872{
 873        struct elevator_queue *e = q->elevator;
 874
 875        if (e->ops->elevator_former_req_fn)
 876                return e->ops->elevator_former_req_fn(q, rq);
 877        return NULL;
 878}
 879
 880int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
 881{
 882        struct elevator_queue *e = q->elevator;
 883
 884        if (e->ops->elevator_set_req_fn)
 885                return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
 886
 887        rq->elevator_private = NULL;
 888        return 0;
 889}
 890
 891void elv_put_request(struct request_queue *q, struct request *rq)
 892{
 893        struct elevator_queue *e = q->elevator;
 894
 895        if (e->ops->elevator_put_req_fn)
 896                e->ops->elevator_put_req_fn(rq);
 897}
 898
 899int elv_may_queue(struct request_queue *q, int rw)
 900{
 901        struct elevator_queue *e = q->elevator;
 902
 903        if (e->ops->elevator_may_queue_fn)
 904                return e->ops->elevator_may_queue_fn(q, rw);
 905
 906        return ELV_MQUEUE_MAY;
 907}
 908
 909void elv_abort_queue(struct request_queue *q)
 910{
 911        struct request *rq;
 912
 913        while (!list_empty(&q->queue_head)) {
 914                rq = list_entry_rq(q->queue_head.next);
 915                rq->cmd_flags |= REQ_QUIET;
 916                trace_block_rq_abort(q, rq);
 917                __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 918        }
 919}
 920EXPORT_SYMBOL(elv_abort_queue);
 921
 922void elv_completed_request(struct request_queue *q, struct request *rq)
 923{
 924        struct elevator_queue *e = q->elevator;
 925
 926        /*
 927         * request is released from the driver, io must be done
 928         */
 929        if (blk_account_rq(rq)) {
 930                q->in_flight--;
 931                if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 932                        e->ops->elevator_completed_req_fn(q, rq);
 933        }
 934
 935        /*
 936         * Check if the queue is waiting for fs requests to be
 937         * drained for flush sequence.
 938         */
 939        if (unlikely(q->ordseq)) {
 940                struct request *next = NULL;
 941
 942                if (!list_empty(&q->queue_head))
 943                        next = list_entry_rq(q->queue_head.next);
 944
 945                if (!q->in_flight &&
 946                    blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 947                    (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
 948                        blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 949                        blk_start_queueing(q);
 950                }
 951        }
 952}
 953
 954#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 955
 956static ssize_t
 957elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 958{
 959        struct elv_fs_entry *entry = to_elv(attr);
 960        struct elevator_queue *e;
 961        ssize_t error;
 962
 963        if (!entry->show)
 964                return -EIO;
 965
 966        e = container_of(kobj, struct elevator_queue, kobj);
 967        mutex_lock(&e->sysfs_lock);
 968        error = e->ops ? entry->show(e, page) : -ENOENT;
 969        mutex_unlock(&e->sysfs_lock);
 970        return error;
 971}
 972
 973static ssize_t
 974elv_attr_store(struct kobject *kobj, struct attribute *attr,
 975               const char *page, size_t length)
 976{
 977        struct elv_fs_entry *entry = to_elv(attr);
 978        struct elevator_queue *e;
 979        ssize_t error;
 980
 981        if (!entry->store)
 982                return -EIO;
 983
 984        e = container_of(kobj, struct elevator_queue, kobj);
 985        mutex_lock(&e->sysfs_lock);
 986        error = e->ops ? entry->store(e, page, length) : -ENOENT;
 987        mutex_unlock(&e->sysfs_lock);
 988        return error;
 989}
 990
 991static struct sysfs_ops elv_sysfs_ops = {
 992        .show   = elv_attr_show,
 993        .store  = elv_attr_store,
 994};
 995
 996static struct kobj_type elv_ktype = {
 997        .sysfs_ops      = &elv_sysfs_ops,
 998        .release        = elevator_release,
 999};
1000
1001int elv_register_queue(struct request_queue *q)
1002{
1003        struct elevator_queue *e = q->elevator;
1004        int error;
1005
1006        error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1007        if (!error) {
1008                struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1009                if (attr) {
1010                        while (attr->attr.name) {
1011                                if (sysfs_create_file(&e->kobj, &attr->attr))
1012                                        break;
1013                                attr++;
1014                        }
1015                }
1016                kobject_uevent(&e->kobj, KOBJ_ADD);
1017        }
1018        return error;
1019}
1020
1021static void __elv_unregister_queue(struct elevator_queue *e)
1022{
1023        kobject_uevent(&e->kobj, KOBJ_REMOVE);
1024        kobject_del(&e->kobj);
1025}
1026
1027void elv_unregister_queue(struct request_queue *q)
1028{
1029        if (q)
1030                __elv_unregister_queue(q->elevator);
1031}
1032
1033void elv_register(struct elevator_type *e)
1034{
1035        char *def = "";
1036
1037        spin_lock(&elv_list_lock);
1038        BUG_ON(elevator_find(e->elevator_name));
1039        list_add_tail(&e->list, &elv_list);
1040        spin_unlock(&elv_list_lock);
1041
1042        if (!strcmp(e->elevator_name, chosen_elevator) ||
1043                        (!*chosen_elevator &&
1044                         !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1045                                def = " (default)";
1046
1047        printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1048                                                                def);
1049}
1050EXPORT_SYMBOL_GPL(elv_register);
1051
1052void elv_unregister(struct elevator_type *e)
1053{
1054        struct task_struct *g, *p;
1055
1056        /*
1057         * Iterate every thread in the process to remove the io contexts.
1058         */
1059        if (e->ops.trim) {
1060                read_lock(&tasklist_lock);
1061                do_each_thread(g, p) {
1062                        task_lock(p);
1063                        if (p->io_context)
1064                                e->ops.trim(p->io_context);
1065                        task_unlock(p);
1066                } while_each_thread(g, p);
1067                read_unlock(&tasklist_lock);
1068        }
1069
1070        spin_lock(&elv_list_lock);
1071        list_del_init(&e->list);
1072        spin_unlock(&elv_list_lock);
1073}
1074EXPORT_SYMBOL_GPL(elv_unregister);
1075
1076/*
1077 * switch to new_e io scheduler. be careful not to introduce deadlocks -
1078 * we don't free the old io scheduler, before we have allocated what we
1079 * need for the new one. this way we have a chance of going back to the old
1080 * one, if the new one fails init for some reason.
1081 */
1082static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1083{
1084        struct elevator_queue *old_elevator, *e;
1085        void *data;
1086
1087        /*
1088         * Allocate new elevator
1089         */
1090        e = elevator_alloc(q, new_e);
1091        if (!e)
1092                return 0;
1093
1094        data = elevator_init_queue(q, e);
1095        if (!data) {
1096                kobject_put(&e->kobj);
1097                return 0;
1098        }
1099
1100        /*
1101         * Turn on BYPASS and drain all requests w/ elevator private data
1102         */
1103        spin_lock_irq(q->queue_lock);
1104
1105        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
1106
1107        elv_drain_elevator(q);
1108
1109        while (q->rq.elvpriv) {
1110                blk_start_queueing(q);
1111                spin_unlock_irq(q->queue_lock);
1112                msleep(10);
1113                spin_lock_irq(q->queue_lock);
1114                elv_drain_elevator(q);
1115        }
1116
1117        /*
1118         * Remember old elevator.
1119         */
1120        old_elevator = q->elevator;
1121
1122        /*
1123         * attach and start new elevator
1124         */
1125        elevator_attach(q, e, data);
1126
1127        spin_unlock_irq(q->queue_lock);
1128
1129        __elv_unregister_queue(old_elevator);
1130
1131        if (elv_register_queue(q))
1132                goto fail_register;
1133
1134        /*
1135         * finally exit old elevator and turn off BYPASS.
1136         */
1137        elevator_exit(old_elevator);
1138        spin_lock_irq(q->queue_lock);
1139        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1140        spin_unlock_irq(q->queue_lock);
1141
1142        blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1143
1144        return 1;
1145
1146fail_register:
1147        /*
1148         * switch failed, exit the new io scheduler and reattach the old
1149         * one again (along with re-adding the sysfs dir)
1150         */
1151        elevator_exit(e);
1152        q->elevator = old_elevator;
1153        elv_register_queue(q);
1154
1155        spin_lock_irq(q->queue_lock);
1156        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1157        spin_unlock_irq(q->queue_lock);
1158
1159        return 0;
1160}
1161
1162ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1163                          size_t count)
1164{
1165        char elevator_name[ELV_NAME_MAX];
1166        struct elevator_type *e;
1167
1168        strlcpy(elevator_name, name, sizeof(elevator_name));
1169        strstrip(elevator_name);
1170
1171        e = elevator_get(elevator_name);
1172        if (!e) {
1173                printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1174                return -EINVAL;
1175        }
1176
1177        if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1178                elevator_put(e);
1179                return count;
1180        }
1181
1182        if (!elevator_switch(q, e))
1183                printk(KERN_ERR "elevator: switch to %s failed\n",
1184                                                        elevator_name);
1185        return count;
1186}
1187
1188ssize_t elv_iosched_show(struct request_queue *q, char *name)
1189{
1190        struct elevator_queue *e = q->elevator;
1191        struct elevator_type *elv = e->elevator_type;
1192        struct elevator_type *__e;
1193        int len = 0;
1194
1195        spin_lock(&elv_list_lock);
1196        list_for_each_entry(__e, &elv_list, list) {
1197                if (!strcmp(elv->elevator_name, __e->elevator_name))
1198                        len += sprintf(name+len, "[%s] ", elv->elevator_name);
1199                else
1200                        len += sprintf(name+len, "%s ", __e->elevator_name);
1201        }
1202        spin_unlock(&elv_list_lock);
1203
1204        len += sprintf(len+name, "\n");
1205        return len;
1206}
1207
1208struct request *elv_rb_former_request(struct request_queue *q,
1209                                      struct request *rq)
1210{
1211        struct rb_node *rbprev = rb_prev(&rq->rb_node);
1212
1213        if (rbprev)
1214                return rb_entry_rq(rbprev);
1215
1216        return NULL;
1217}
1218EXPORT_SYMBOL(elv_rb_former_request);
1219
1220struct request *elv_rb_latter_request(struct request_queue *q,
1221                                      struct request *rq)
1222{
1223        struct rb_node *rbnext = rb_next(&rq->rb_node);
1224
1225        if (rbnext)
1226                return rb_entry_rq(rbnext);
1227
1228        return NULL;
1229}
1230EXPORT_SYMBOL(elv_rb_latter_request);
1231