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 <linux/hash.h>
  37#include <linux/uaccess.h>
  38
  39#include "blk.h"
  40
  41static DEFINE_SPINLOCK(elv_list_lock);
  42static LIST_HEAD(elv_list);
  43
  44/*
  45 * Merge hash stuff.
  46 */
  47static const int elv_hash_shift = 6;
  48#define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
  49#define ELV_HASH_FN(sec)        \
  50                (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
  51#define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
  52#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
  53#define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
  54
  55/*
  56 * Query io scheduler to see if the current process issuing bio may be
  57 * merged with rq.
  58 */
  59static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
  60{
  61        struct request_queue *q = rq->q;
  62        elevator_t *e = q->elevator;
  63
  64        if (e->ops->elevator_allow_merge_fn)
  65                return e->ops->elevator_allow_merge_fn(q, rq, bio);
  66
  67        return 1;
  68}
  69
  70/*
  71 * can we safely merge with this request?
  72 */
  73int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  74{
  75        if (!rq_mergeable(rq))
  76                return 0;
  77
  78        /*
  79         * Don't merge file system requests and discard requests
  80         */
  81        if (bio_discard(bio) != bio_discard(rq->bio))
  82                return 0;
  83
  84        /*
  85         * different data direction or already started, don't merge
  86         */
  87        if (bio_data_dir(bio) != rq_data_dir(rq))
  88                return 0;
  89
  90        /*
  91         * must be same device and not a special request
  92         */
  93        if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
  94                return 0;
  95
  96        /*
  97         * only merge integrity protected bio into ditto rq
  98         */
  99        if (bio_integrity(bio) != blk_integrity_rq(rq))
 100                return 0;
 101
 102        if (!elv_iosched_allow_merge(rq, bio))
 103                return 0;
 104
 105        return 1;
 106}
 107EXPORT_SYMBOL(elv_rq_merge_ok);
 108
 109static inline int elv_try_merge(struct request *__rq, struct bio *bio)
 110{
 111        int ret = ELEVATOR_NO_MERGE;
 112
 113        /*
 114         * we can merge and sequence is ok, check if it's possible
 115         */
 116        if (elv_rq_merge_ok(__rq, bio)) {
 117                if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
 118                        ret = ELEVATOR_BACK_MERGE;
 119                else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
 120                        ret = ELEVATOR_FRONT_MERGE;
 121        }
 122
 123        return ret;
 124}
 125
 126static struct elevator_type *elevator_find(const char *name)
 127{
 128        struct elevator_type *e;
 129
 130        list_for_each_entry(e, &elv_list, list) {
 131                if (!strcmp(e->elevator_name, name))
 132                        return e;
 133        }
 134
 135        return NULL;
 136}
 137
 138static void elevator_put(struct elevator_type *e)
 139{
 140        module_put(e->elevator_owner);
 141}
 142
 143static struct elevator_type *elevator_get(const char *name)
 144{
 145        struct elevator_type *e;
 146
 147        spin_lock(&elv_list_lock);
 148
 149        e = elevator_find(name);
 150        if (!e) {
 151                char elv[ELV_NAME_MAX + strlen("-iosched")];
 152
 153                spin_unlock(&elv_list_lock);
 154
 155                if (!strcmp(name, "anticipatory"))
 156                        sprintf(elv, "as-iosched");
 157                else
 158                        sprintf(elv, "%s-iosched", name);
 159
 160                request_module("%s", elv);
 161                spin_lock(&elv_list_lock);
 162                e = elevator_find(name);
 163        }
 164
 165        if (e && !try_module_get(e->elevator_owner))
 166                e = NULL;
 167
 168        spin_unlock(&elv_list_lock);
 169
 170        return e;
 171}
 172
 173static void *elevator_init_queue(struct request_queue *q,
 174                                 struct elevator_queue *eq)
 175{
 176        return eq->ops->elevator_init_fn(q);
 177}
 178
 179static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
 180                           void *data)
 181{
 182        q->elevator = eq;
 183        eq->elevator_data = data;
 184}
 185
 186static char chosen_elevator[16];
 187
 188static int __init elevator_setup(char *str)
 189{
 190        /*
 191         * Be backwards-compatible with previous kernels, so users
 192         * won't get the wrong elevator.
 193         */
 194        if (!strcmp(str, "as"))
 195                strcpy(chosen_elevator, "anticipatory");
 196        else
 197                strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 198        return 1;
 199}
 200
 201__setup("elevator=", elevator_setup);
 202
 203static struct kobj_type elv_ktype;
 204
 205static elevator_t *elevator_alloc(struct request_queue *q,
 206                                  struct elevator_type *e)
 207{
 208        elevator_t *eq;
 209        int i;
 210
 211        eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL | __GFP_ZERO, q->node);
 212        if (unlikely(!eq))
 213                goto err;
 214
 215        eq->ops = &e->ops;
 216        eq->elevator_type = e;
 217        kobject_init(&eq->kobj, &elv_ktype);
 218        mutex_init(&eq->sysfs_lock);
 219
 220        eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
 221                                        GFP_KERNEL, q->node);
 222        if (!eq->hash)
 223                goto err;
 224
 225        for (i = 0; i < ELV_HASH_ENTRIES; i++)
 226                INIT_HLIST_HEAD(&eq->hash[i]);
 227
 228        return eq;
 229err:
 230        kfree(eq);
 231        elevator_put(e);
 232        return NULL;
 233}
 234
 235static void elevator_release(struct kobject *kobj)
 236{
 237        elevator_t *e = container_of(kobj, elevator_t, kobj);
 238
 239        elevator_put(e->elevator_type);
 240        kfree(e->hash);
 241        kfree(e);
 242}
 243
 244int elevator_init(struct request_queue *q, char *name)
 245{
 246        struct elevator_type *e = NULL;
 247        struct elevator_queue *eq;
 248        int ret = 0;
 249        void *data;
 250
 251        INIT_LIST_HEAD(&q->queue_head);
 252        q->last_merge = NULL;
 253        q->end_sector = 0;
 254        q->boundary_rq = NULL;
 255
 256        if (name) {
 257                e = elevator_get(name);
 258                if (!e)
 259                        return -EINVAL;
 260        }
 261
 262        if (!e && *chosen_elevator) {
 263                e = elevator_get(chosen_elevator);
 264                if (!e)
 265                        printk(KERN_ERR "I/O scheduler %s not found\n",
 266                                                        chosen_elevator);
 267        }
 268
 269        if (!e) {
 270                e = elevator_get(CONFIG_DEFAULT_IOSCHED);
 271                if (!e) {
 272                        printk(KERN_ERR
 273                                "Default I/O scheduler not found. " \
 274                                "Using noop.\n");
 275                        e = elevator_get("noop");
 276                }
 277        }
 278
 279        eq = elevator_alloc(q, e);
 280        if (!eq)
 281                return -ENOMEM;
 282
 283        data = elevator_init_queue(q, eq);
 284        if (!data) {
 285                kobject_put(&eq->kobj);
 286                return -ENOMEM;
 287        }
 288
 289        elevator_attach(q, eq, data);
 290        return ret;
 291}
 292EXPORT_SYMBOL(elevator_init);
 293
 294void elevator_exit(elevator_t *e)
 295{
 296        mutex_lock(&e->sysfs_lock);
 297        if (e->ops->elevator_exit_fn)
 298                e->ops->elevator_exit_fn(e);
 299        e->ops = NULL;
 300        mutex_unlock(&e->sysfs_lock);
 301
 302        kobject_put(&e->kobj);
 303}
 304EXPORT_SYMBOL(elevator_exit);
 305
 306static void elv_activate_rq(struct request_queue *q, struct request *rq)
 307{
 308        elevator_t *e = q->elevator;
 309
 310        if (e->ops->elevator_activate_req_fn)
 311                e->ops->elevator_activate_req_fn(q, rq);
 312}
 313
 314static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
 315{
 316        elevator_t *e = q->elevator;
 317
 318        if (e->ops->elevator_deactivate_req_fn)
 319                e->ops->elevator_deactivate_req_fn(q, rq);
 320}
 321
 322static inline void __elv_rqhash_del(struct request *rq)
 323{
 324        hlist_del_init(&rq->hash);
 325}
 326
 327static void elv_rqhash_del(struct request_queue *q, struct request *rq)
 328{
 329        if (ELV_ON_HASH(rq))
 330                __elv_rqhash_del(rq);
 331}
 332
 333static void elv_rqhash_add(struct request_queue *q, struct request *rq)
 334{
 335        elevator_t *e = q->elevator;
 336
 337        BUG_ON(ELV_ON_HASH(rq));
 338        hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
 339}
 340
 341static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 342{
 343        __elv_rqhash_del(rq);
 344        elv_rqhash_add(q, rq);
 345}
 346
 347static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 348{
 349        elevator_t *e = q->elevator;
 350        struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
 351        struct hlist_node *entry, *next;
 352        struct request *rq;
 353
 354        hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
 355                BUG_ON(!ELV_ON_HASH(rq));
 356
 357                if (unlikely(!rq_mergeable(rq))) {
 358                        __elv_rqhash_del(rq);
 359                        continue;
 360                }
 361
 362                if (rq_hash_key(rq) == offset)
 363                        return rq;
 364        }
 365
 366        return NULL;
 367}
 368
 369/*
 370 * RB-tree support functions for inserting/lookup/removal of requests
 371 * in a sorted RB tree.
 372 */
 373struct request *elv_rb_add(struct rb_root *root, struct request *rq)
 374{
 375        struct rb_node **p = &root->rb_node;
 376        struct rb_node *parent = NULL;
 377        struct request *__rq;
 378
 379        while (*p) {
 380                parent = *p;
 381                __rq = rb_entry(parent, struct request, rb_node);
 382
 383                if (rq->sector < __rq->sector)
 384                        p = &(*p)->rb_left;
 385                else if (rq->sector > __rq->sector)
 386                        p = &(*p)->rb_right;
 387                else
 388                        return __rq;
 389        }
 390
 391        rb_link_node(&rq->rb_node, parent, p);
 392        rb_insert_color(&rq->rb_node, root);
 393        return NULL;
 394}
 395EXPORT_SYMBOL(elv_rb_add);
 396
 397void elv_rb_del(struct rb_root *root, struct request *rq)
 398{
 399        BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 400        rb_erase(&rq->rb_node, root);
 401        RB_CLEAR_NODE(&rq->rb_node);
 402}
 403EXPORT_SYMBOL(elv_rb_del);
 404
 405struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 406{
 407        struct rb_node *n = root->rb_node;
 408        struct request *rq;
 409
 410        while (n) {
 411                rq = rb_entry(n, struct request, rb_node);
 412
 413                if (sector < rq->sector)
 414                        n = n->rb_left;
 415                else if (sector > rq->sector)
 416                        n = n->rb_right;
 417                else
 418                        return rq;
 419        }
 420
 421        return NULL;
 422}
 423EXPORT_SYMBOL(elv_rb_find);
 424
 425/*
 426 * Insert rq into dispatch queue of q.  Queue lock must be held on
 427 * entry.  rq is sort instead into the dispatch queue. To be used by
 428 * specific elevators.
 429 */
 430void elv_dispatch_sort(struct request_queue *q, struct request *rq)
 431{
 432        sector_t boundary;
 433        struct list_head *entry;
 434        int stop_flags;
 435
 436        if (q->last_merge == rq)
 437                q->last_merge = NULL;
 438
 439        elv_rqhash_del(q, rq);
 440
 441        q->nr_sorted--;
 442
 443        boundary = q->end_sector;
 444        stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
 445        list_for_each_prev(entry, &q->queue_head) {
 446                struct request *pos = list_entry_rq(entry);
 447
 448                if (blk_discard_rq(rq) != blk_discard_rq(pos))
 449                        break;
 450                if (rq_data_dir(rq) != rq_data_dir(pos))
 451                        break;
 452                if (pos->cmd_flags & stop_flags)
 453                        break;
 454                if (rq->sector >= boundary) {
 455                        if (pos->sector < boundary)
 456                                continue;
 457                } else {
 458                        if (pos->sector >= boundary)
 459                                break;
 460                }
 461                if (rq->sector >= pos->sector)
 462                        break;
 463        }
 464
 465        list_add(&rq->queuelist, entry);
 466}
 467EXPORT_SYMBOL(elv_dispatch_sort);
 468
 469/*
 470 * Insert rq into dispatch queue of q.  Queue lock must be held on
 471 * entry.  rq is added to the back of the dispatch queue. To be used by
 472 * specific elevators.
 473 */
 474void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 475{
 476        if (q->last_merge == rq)
 477                q->last_merge = NULL;
 478
 479        elv_rqhash_del(q, rq);
 480
 481        q->nr_sorted--;
 482
 483        q->end_sector = rq_end_sector(rq);
 484        q->boundary_rq = rq;
 485        list_add_tail(&rq->queuelist, &q->queue_head);
 486}
 487EXPORT_SYMBOL(elv_dispatch_add_tail);
 488
 489int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 490{
 491        elevator_t *e = q->elevator;
 492        struct request *__rq;
 493        int ret;
 494
 495        /*
 496         * First try one-hit cache.
 497         */
 498        if (q->last_merge) {
 499                ret = elv_try_merge(q->last_merge, bio);
 500                if (ret != ELEVATOR_NO_MERGE) {
 501                        *req = q->last_merge;
 502                        return ret;
 503                }
 504        }
 505
 506        if (blk_queue_nomerges(q))
 507                return ELEVATOR_NO_MERGE;
 508
 509        /*
 510         * See if our hash lookup can find a potential backmerge.
 511         */
 512        __rq = elv_rqhash_find(q, bio->bi_sector);
 513        if (__rq && elv_rq_merge_ok(__rq, bio)) {
 514                *req = __rq;
 515                return ELEVATOR_BACK_MERGE;
 516        }
 517
 518        if (e->ops->elevator_merge_fn)
 519                return e->ops->elevator_merge_fn(q, req, bio);
 520
 521        return ELEVATOR_NO_MERGE;
 522}
 523
 524void elv_merged_request(struct request_queue *q, struct request *rq, int type)
 525{
 526        elevator_t *e = q->elevator;
 527
 528        if (e->ops->elevator_merged_fn)
 529                e->ops->elevator_merged_fn(q, rq, type);
 530
 531        if (type == ELEVATOR_BACK_MERGE)
 532                elv_rqhash_reposition(q, rq);
 533
 534        q->last_merge = rq;
 535}
 536
 537void elv_merge_requests(struct request_queue *q, struct request *rq,
 538                             struct request *next)
 539{
 540        elevator_t *e = q->elevator;
 541
 542        if (e->ops->elevator_merge_req_fn)
 543                e->ops->elevator_merge_req_fn(q, rq, next);
 544
 545        elv_rqhash_reposition(q, rq);
 546        elv_rqhash_del(q, next);
 547
 548        q->nr_sorted--;
 549        q->last_merge = rq;
 550}
 551
 552void elv_requeue_request(struct request_queue *q, struct request *rq)
 553{
 554        /*
 555         * it already went through dequeue, we need to decrement the
 556         * in_flight count again
 557         */
 558        if (blk_account_rq(rq)) {
 559                q->in_flight--;
 560                if (blk_sorted_rq(rq))
 561                        elv_deactivate_rq(q, rq);
 562        }
 563
 564        rq->cmd_flags &= ~REQ_STARTED;
 565
 566        elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 567}
 568
 569static void elv_drain_elevator(struct request_queue *q)
 570{
 571        static int printed;
 572        while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 573                ;
 574        if (q->nr_sorted == 0)
 575                return;
 576        if (printed++ < 10) {
 577                printk(KERN_ERR "%s: forced dispatching is broken "
 578                       "(nr_sorted=%u), please report this\n",
 579                       q->elevator->elevator_type->elevator_name, q->nr_sorted);
 580        }
 581}
 582
 583void elv_insert(struct request_queue *q, struct request *rq, int where)
 584{
 585        struct list_head *pos;
 586        unsigned ordseq;
 587        int unplug_it = 1;
 588
 589        blk_add_trace_rq(q, rq, BLK_TA_INSERT);
 590
 591        rq->q = q;
 592
 593        switch (where) {
 594        case ELEVATOR_INSERT_FRONT:
 595                rq->cmd_flags |= REQ_SOFTBARRIER;
 596
 597                list_add(&rq->queuelist, &q->queue_head);
 598                break;
 599
 600        case ELEVATOR_INSERT_BACK:
 601                rq->cmd_flags |= REQ_SOFTBARRIER;
 602                elv_drain_elevator(q);
 603                list_add_tail(&rq->queuelist, &q->queue_head);
 604                /*
 605                 * We kick the queue here for the following reasons.
 606                 * - The elevator might have returned NULL previously
 607                 *   to delay requests and returned them now.  As the
 608                 *   queue wasn't empty before this request, ll_rw_blk
 609                 *   won't run the queue on return, resulting in hang.
 610                 * - Usually, back inserted requests won't be merged
 611                 *   with anything.  There's no point in delaying queue
 612                 *   processing.
 613                 */
 614                blk_remove_plug(q);
 615                blk_start_queueing(q);
 616                break;
 617
 618        case ELEVATOR_INSERT_SORT:
 619                BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
 620                rq->cmd_flags |= REQ_SORTED;
 621                q->nr_sorted++;
 622                if (rq_mergeable(rq)) {
 623                        elv_rqhash_add(q, rq);
 624                        if (!q->last_merge)
 625                                q->last_merge = rq;
 626                }
 627
 628                /*
 629                 * Some ioscheds (cfq) run q->request_fn directly, so
 630                 * rq cannot be accessed after calling
 631                 * elevator_add_req_fn.
 632                 */
 633                q->elevator->ops->elevator_add_req_fn(q, rq);
 634                break;
 635
 636        case ELEVATOR_INSERT_REQUEUE:
 637                /*
 638                 * If ordered flush isn't in progress, we do front
 639                 * insertion; otherwise, requests should be requeued
 640                 * in ordseq order.
 641                 */
 642                rq->cmd_flags |= REQ_SOFTBARRIER;
 643
 644                /*
 645                 * Most requeues happen because of a busy condition,
 646                 * don't force unplug of the queue for that case.
 647                 */
 648                unplug_it = 0;
 649
 650                if (q->ordseq == 0) {
 651                        list_add(&rq->queuelist, &q->queue_head);
 652                        break;
 653                }
 654
 655                ordseq = blk_ordered_req_seq(rq);
 656
 657                list_for_each(pos, &q->queue_head) {
 658                        struct request *pos_rq = list_entry_rq(pos);
 659                        if (ordseq <= blk_ordered_req_seq(pos_rq))
 660                                break;
 661                }
 662
 663                list_add_tail(&rq->queuelist, pos);
 664                break;
 665
 666        default:
 667                printk(KERN_ERR "%s: bad insertion point %d\n",
 668                       __func__, where);
 669                BUG();
 670        }
 671
 672        if (unplug_it && blk_queue_plugged(q)) {
 673                int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 674                        - q->in_flight;
 675
 676                if (nrq >= q->unplug_thresh)
 677                        __generic_unplug_device(q);
 678        }
 679}
 680
 681void __elv_add_request(struct request_queue *q, struct request *rq, int where,
 682                       int plug)
 683{
 684        if (q->ordcolor)
 685                rq->cmd_flags |= REQ_ORDERED_COLOR;
 686
 687        if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 688                /*
 689                 * toggle ordered color
 690                 */
 691                if (blk_barrier_rq(rq))
 692                        q->ordcolor ^= 1;
 693
 694                /*
 695                 * barriers implicitly indicate back insertion
 696                 */
 697                if (where == ELEVATOR_INSERT_SORT)
 698                        where = ELEVATOR_INSERT_BACK;
 699
 700                /*
 701                 * this request is scheduling boundary, update
 702                 * end_sector
 703                 */
 704                if (blk_fs_request(rq) || blk_discard_rq(rq)) {
 705                        q->end_sector = rq_end_sector(rq);
 706                        q->boundary_rq = rq;
 707                }
 708        } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
 709                    where == ELEVATOR_INSERT_SORT)
 710                where = ELEVATOR_INSERT_BACK;
 711
 712        if (plug)
 713                blk_plug_device(q);
 714
 715        elv_insert(q, rq, where);
 716}
 717EXPORT_SYMBOL(__elv_add_request);
 718
 719void elv_add_request(struct request_queue *q, struct request *rq, int where,
 720                     int plug)
 721{
 722        unsigned long flags;
 723
 724        spin_lock_irqsave(q->queue_lock, flags);
 725        __elv_add_request(q, rq, where, plug);
 726        spin_unlock_irqrestore(q->queue_lock, flags);
 727}
 728EXPORT_SYMBOL(elv_add_request);
 729
 730static inline struct request *__elv_next_request(struct request_queue *q)
 731{
 732        struct request *rq;
 733
 734        while (1) {
 735                while (!list_empty(&q->queue_head)) {
 736                        rq = list_entry_rq(q->queue_head.next);
 737                        if (blk_do_ordered(q, &rq))
 738                                return rq;
 739                }
 740
 741                if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 742                        return NULL;
 743        }
 744}
 745
 746struct request *elv_next_request(struct request_queue *q)
 747{
 748        struct request *rq;
 749        int ret;
 750
 751        while ((rq = __elv_next_request(q)) != NULL) {
 752                /*
 753                 * Kill the empty barrier place holder, the driver must
 754                 * not ever see it.
 755                 */
 756                if (blk_empty_barrier(rq)) {
 757                        __blk_end_request(rq, 0, blk_rq_bytes(rq));
 758                        continue;
 759                }
 760                if (!(rq->cmd_flags & REQ_STARTED)) {
 761                        /*
 762                         * This is the first time the device driver
 763                         * sees this request (possibly after
 764                         * requeueing).  Notify IO scheduler.
 765                         */
 766                        if (blk_sorted_rq(rq))
 767                                elv_activate_rq(q, rq);
 768
 769                        /*
 770                         * just mark as started even if we don't start
 771                         * it, a request that has been delayed should
 772                         * not be passed by new incoming requests
 773                         */
 774                        rq->cmd_flags |= REQ_STARTED;
 775                        blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
 776                }
 777
 778                if (!q->boundary_rq || q->boundary_rq == rq) {
 779                        q->end_sector = rq_end_sector(rq);
 780                        q->boundary_rq = NULL;
 781                }
 782
 783                if (rq->cmd_flags & REQ_DONTPREP)
 784                        break;
 785
 786                if (q->dma_drain_size && rq->data_len) {
 787                        /*
 788                         * make sure space for the drain appears we
 789                         * know we can do this because max_hw_segments
 790                         * has been adjusted to be one fewer than the
 791                         * device can handle
 792                         */
 793                        rq->nr_phys_segments++;
 794                }
 795
 796                if (!q->prep_rq_fn)
 797                        break;
 798
 799                ret = q->prep_rq_fn(q, rq);
 800                if (ret == BLKPREP_OK) {
 801                        break;
 802                } else if (ret == BLKPREP_DEFER) {
 803                        /*
 804                         * the request may have been (partially) prepped.
 805                         * we need to keep this request in the front to
 806                         * avoid resource deadlock.  REQ_STARTED will
 807                         * prevent other fs requests from passing this one.
 808                         */
 809                        if (q->dma_drain_size && rq->data_len &&
 810                            !(rq->cmd_flags & REQ_DONTPREP)) {
 811                                /*
 812                                 * remove the space for the drain we added
 813                                 * so that we don't add it again
 814                                 */
 815                                --rq->nr_phys_segments;
 816                        }
 817
 818                        rq = NULL;
 819                        break;
 820                } else if (ret == BLKPREP_KILL) {
 821                        rq->cmd_flags |= REQ_QUIET;
 822                        __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 823                } else {
 824                        printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
 825                        break;
 826                }
 827        }
 828
 829        return rq;
 830}
 831EXPORT_SYMBOL(elv_next_request);
 832
 833void elv_dequeue_request(struct request_queue *q, struct request *rq)
 834{
 835        BUG_ON(list_empty(&rq->queuelist));
 836        BUG_ON(ELV_ON_HASH(rq));
 837
 838        list_del_init(&rq->queuelist);
 839
 840        /*
 841         * the time frame between a request being removed from the lists
 842         * and to it is freed is accounted as io that is in progress at
 843         * the driver side.
 844         */
 845        if (blk_account_rq(rq))
 846                q->in_flight++;
 847}
 848
 849int elv_queue_empty(struct request_queue *q)
 850{
 851        elevator_t *e = q->elevator;
 852
 853        if (!list_empty(&q->queue_head))
 854                return 0;
 855
 856        if (e->ops->elevator_queue_empty_fn)
 857                return e->ops->elevator_queue_empty_fn(q);
 858
 859        return 1;
 860}
 861EXPORT_SYMBOL(elv_queue_empty);
 862
 863struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 864{
 865        elevator_t *e = q->elevator;
 866
 867        if (e->ops->elevator_latter_req_fn)
 868                return e->ops->elevator_latter_req_fn(q, rq);
 869        return NULL;
 870}
 871
 872struct request *elv_former_request(struct request_queue *q, struct request *rq)
 873{
 874        elevator_t *e = q->elevator;
 875
 876        if (e->ops->elevator_former_req_fn)
 877                return e->ops->elevator_former_req_fn(q, rq);
 878        return NULL;
 879}
 880
 881int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
 882{
 883        elevator_t *e = q->elevator;
 884
 885        if (e->ops->elevator_set_req_fn)
 886                return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
 887
 888        rq->elevator_private = NULL;
 889        return 0;
 890}
 891
 892void elv_put_request(struct request_queue *q, struct request *rq)
 893{
 894        elevator_t *e = q->elevator;
 895
 896        if (e->ops->elevator_put_req_fn)
 897                e->ops->elevator_put_req_fn(rq);
 898}
 899
 900int elv_may_queue(struct request_queue *q, int rw)
 901{
 902        elevator_t *e = q->elevator;
 903
 904        if (e->ops->elevator_may_queue_fn)
 905                return e->ops->elevator_may_queue_fn(q, rw);
 906
 907        return ELV_MQUEUE_MAY;
 908}
 909
 910void elv_abort_queue(struct request_queue *q)
 911{
 912        struct request *rq;
 913
 914        while (!list_empty(&q->queue_head)) {
 915                rq = list_entry_rq(q->queue_head.next);
 916                rq->cmd_flags |= REQ_QUIET;
 917                blk_add_trace_rq(q, rq, BLK_TA_ABORT);
 918                __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 919        }
 920}
 921EXPORT_SYMBOL(elv_abort_queue);
 922
 923void elv_completed_request(struct request_queue *q, struct request *rq)
 924{
 925        elevator_t *e = q->elevator;
 926
 927        /*
 928         * request is released from the driver, io must be done
 929         */
 930        if (blk_account_rq(rq)) {
 931                q->in_flight--;
 932                if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 933                        e->ops->elevator_completed_req_fn(q, rq);
 934        }
 935
 936        /*
 937         * Check if the queue is waiting for fs requests to be
 938         * drained for flush sequence.
 939         */
 940        if (unlikely(q->ordseq)) {
 941                struct request *first_rq = list_entry_rq(q->queue_head.next);
 942                if (q->in_flight == 0 &&
 943                    blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 944                    blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
 945                        blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 946                        blk_start_queueing(q);
 947                }
 948        }
 949}
 950
 951#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 952
 953static ssize_t
 954elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 955{
 956        elevator_t *e = container_of(kobj, elevator_t, kobj);
 957        struct elv_fs_entry *entry = to_elv(attr);
 958        ssize_t error;
 959
 960        if (!entry->show)
 961                return -EIO;
 962
 963        mutex_lock(&e->sysfs_lock);
 964        error = e->ops ? entry->show(e, page) : -ENOENT;
 965        mutex_unlock(&e->sysfs_lock);
 966        return error;
 967}
 968
 969static ssize_t
 970elv_attr_store(struct kobject *kobj, struct attribute *attr,
 971               const char *page, size_t length)
 972{
 973        elevator_t *e = container_of(kobj, elevator_t, kobj);
 974        struct elv_fs_entry *entry = to_elv(attr);
 975        ssize_t error;
 976
 977        if (!entry->store)
 978                return -EIO;
 979
 980        mutex_lock(&e->sysfs_lock);
 981        error = e->ops ? entry->store(e, page, length) : -ENOENT;
 982        mutex_unlock(&e->sysfs_lock);
 983        return error;
 984}
 985
 986static struct sysfs_ops elv_sysfs_ops = {
 987        .show   = elv_attr_show,
 988        .store  = elv_attr_store,
 989};
 990
 991static struct kobj_type elv_ktype = {
 992        .sysfs_ops      = &elv_sysfs_ops,
 993        .release        = elevator_release,
 994};
 995
 996int elv_register_queue(struct request_queue *q)
 997{
 998        elevator_t *e = q->elevator;
 999        int error;
1000
1001        error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1002        if (!error) {
1003                struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1004                if (attr) {
1005                        while (attr->attr.name) {
1006                                if (sysfs_create_file(&e->kobj, &attr->attr))
1007                                        break;
1008                                attr++;
1009                        }
1010                }
1011                kobject_uevent(&e->kobj, KOBJ_ADD);
1012        }
1013        return error;
1014}
1015
1016static void __elv_unregister_queue(elevator_t *e)
1017{
1018        kobject_uevent(&e->kobj, KOBJ_REMOVE);
1019        kobject_del(&e->kobj);
1020}
1021
1022void elv_unregister_queue(struct request_queue *q)
1023{
1024        if (q)
1025                __elv_unregister_queue(q->elevator);
1026}
1027
1028void elv_register(struct elevator_type *e)
1029{
1030        char *def = "";
1031
1032        spin_lock(&elv_list_lock);
1033        BUG_ON(elevator_find(e->elevator_name));
1034        list_add_tail(&e->list, &elv_list);
1035        spin_unlock(&elv_list_lock);
1036
1037        if (!strcmp(e->elevator_name, chosen_elevator) ||
1038                        (!*chosen_elevator &&
1039                         !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1040                                def = " (default)";
1041
1042        printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1043                                                                def);
1044}
1045EXPORT_SYMBOL_GPL(elv_register);
1046
1047void elv_unregister(struct elevator_type *e)
1048{
1049        struct task_struct *g, *p;
1050
1051        /*
1052         * Iterate every thread in the process to remove the io contexts.
1053         */
1054        if (e->ops.trim) {
1055                read_lock(&tasklist_lock);
1056                do_each_thread(g, p) {
1057                        task_lock(p);
1058                        if (p->io_context)
1059                                e->ops.trim(p->io_context);
1060                        task_unlock(p);
1061                } while_each_thread(g, p);
1062                read_unlock(&tasklist_lock);
1063        }
1064
1065        spin_lock(&elv_list_lock);
1066        list_del_init(&e->list);
1067        spin_unlock(&elv_list_lock);
1068}
1069EXPORT_SYMBOL_GPL(elv_unregister);
1070
1071/*
1072 * switch to new_e io scheduler. be careful not to introduce deadlocks -
1073 * we don't free the old io scheduler, before we have allocated what we
1074 * need for the new one. this way we have a chance of going back to the old
1075 * one, if the new one fails init for some reason.
1076 */
1077static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1078{
1079        elevator_t *old_elevator, *e;
1080        void *data;
1081
1082        /*
1083         * Allocate new elevator
1084         */
1085        e = elevator_alloc(q, new_e);
1086        if (!e)
1087                return 0;
1088
1089        data = elevator_init_queue(q, e);
1090        if (!data) {
1091                kobject_put(&e->kobj);
1092                return 0;
1093        }
1094
1095        /*
1096         * Turn on BYPASS and drain all requests w/ elevator private data
1097         */
1098        spin_lock_irq(q->queue_lock);
1099
1100        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
1101
1102        elv_drain_elevator(q);
1103
1104        while (q->rq.elvpriv) {
1105                blk_start_queueing(q);
1106                spin_unlock_irq(q->queue_lock);
1107                msleep(10);
1108                spin_lock_irq(q->queue_lock);
1109                elv_drain_elevator(q);
1110        }
1111
1112        /*
1113         * Remember old elevator.
1114         */
1115        old_elevator = q->elevator;
1116
1117        /*
1118         * attach and start new elevator
1119         */
1120        elevator_attach(q, e, data);
1121
1122        spin_unlock_irq(q->queue_lock);
1123
1124        __elv_unregister_queue(old_elevator);
1125
1126        if (elv_register_queue(q))
1127                goto fail_register;
1128
1129        /*
1130         * finally exit old elevator and turn off BYPASS.
1131         */
1132        elevator_exit(old_elevator);
1133        spin_lock_irq(q->queue_lock);
1134        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1135        spin_unlock_irq(q->queue_lock);
1136
1137        blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1138
1139        return 1;
1140
1141fail_register:
1142        /*
1143         * switch failed, exit the new io scheduler and reattach the old
1144         * one again (along with re-adding the sysfs dir)
1145         */
1146        elevator_exit(e);
1147        q->elevator = old_elevator;
1148        elv_register_queue(q);
1149
1150        spin_lock_irq(q->queue_lock);
1151        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1152        spin_unlock_irq(q->queue_lock);
1153
1154        return 0;
1155}
1156
1157ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1158                          size_t count)
1159{
1160        char elevator_name[ELV_NAME_MAX];
1161        struct elevator_type *e;
1162
1163        strlcpy(elevator_name, name, sizeof(elevator_name));
1164        strstrip(elevator_name);
1165
1166        e = elevator_get(elevator_name);
1167        if (!e) {
1168                printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1169                return -EINVAL;
1170        }
1171
1172        if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1173                elevator_put(e);
1174                return count;
1175        }
1176
1177        if (!elevator_switch(q, e))
1178                printk(KERN_ERR "elevator: switch to %s failed\n",
1179                                                        elevator_name);
1180        return count;
1181}
1182
1183ssize_t elv_iosched_show(struct request_queue *q, char *name)
1184{
1185        elevator_t *e = q->elevator;
1186        struct elevator_type *elv = e->elevator_type;
1187        struct elevator_type *__e;
1188        int len = 0;
1189
1190        spin_lock(&elv_list_lock);
1191        list_for_each_entry(__e, &elv_list, list) {
1192                if (!strcmp(elv->elevator_name, __e->elevator_name))
1193                        len += sprintf(name+len, "[%s] ", elv->elevator_name);
1194                else
1195                        len += sprintf(name+len, "%s ", __e->elevator_name);
1196        }
1197        spin_unlock(&elv_list_lock);
1198
1199        len += sprintf(len+name, "\n");
1200        return len;
1201}
1202
1203struct request *elv_rb_former_request(struct request_queue *q,
1204                                      struct request *rq)
1205{
1206        struct rb_node *rbprev = rb_prev(&rq->rb_node);
1207
1208        if (rbprev)
1209                return rb_entry_rq(rbprev);
1210
1211        return NULL;
1212}
1213EXPORT_SYMBOL(elv_rb_former_request);
1214
1215struct request *elv_rb_latter_request(struct request_queue *q,
1216                                      struct request *rq)
1217{
1218        struct rb_node *rbnext = rb_next(&rq->rb_node);
1219
1220        if (rbnext)
1221                return rb_entry_rq(rbnext);
1222
1223        return NULL;
1224}
1225EXPORT_SYMBOL(elv_rb_latter_request);
1226
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