drivers/block/elevator.c

   1 /*
   2  *  linux/drivers/block/elevator.c
   3  *
   4  *  Block device elevator/IO-scheduler.
   5  *
   6  *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
   7  *
   8  * 30042000 Jens Axboe <axboe@suse.de> :
   9  *
  10  * Split the elevator a bit so that it is possible to choose a different
  11  * one or even write a new "plug in". There are three pieces:
  12  * - elevator_fn, inserts a new request in the queue list
  13  * - elevator_merge_fn, decides whether a new buffer can be merged with
  14  *   an existing request
  15  * - elevator_dequeue_fn, called when a request is taken off the active list
  16  *
  17  * 20082000 Dave Jones <davej@suse.de> :
  18  * Removed tests for max-bomb-segments, which was breaking elvtune
  19  *  when run without -bN
  20  *
  21  * Jens:
  22  * - Rework again to work with bio instead of buffer_heads
  23  * - loose bi_dev comparisons, partition handling is right now
  24  * - completely modularize elevator setup and teardown
  25  *
  26  */
  27 #include <linux/kernel.h>
  28 #include <linux/fs.h>
  29 #include <linux/blkdev.h>
  30 #include <linux/elevator.h>
  31 #include <linux/bio.h>
  32 #include <linux/config.h>
  33 #include <linux/module.h>
  34 #include <linux/slab.h>
  35 #include <linux/init.h>
  36 #include <linux/compiler.h>
  37
  38 #include <asm/uaccess.h>
  39
  40 static DEFINE_SPINLOCK(elv_list_lock);
  41 static LIST_HEAD(elv_list);
  42
  43 /*
  44  * can we safely merge with this request?
  45  */
  46 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  47 {
  48         if (!rq_mergeable(rq))
  49                 return 0;
  50
  51         /*
  52          * different data direction or already started, don't merge
  53          */
  54         if (bio_data_dir(bio) != rq_data_dir(rq))
  55                 return 0;
  56
  57         /*
  58          * same device and no special stuff set, merge is ok
  59          */
  60         if (rq->rq_disk == bio->bi_bdev->bd_disk &&
  61             !rq->waiting && !rq->special)
  62                 return 1;
  63
  64         return 0;
  65 }
  66 EXPORT_SYMBOL(elv_rq_merge_ok);
  67
  68 inline int elv_try_merge(struct request *__rq, struct bio *bio)
  69 {
  70         int ret = ELEVATOR_NO_MERGE;
  71
  72         /*
  73          * we can merge and sequence is ok, check if it's possible
  74          */
  75         if (elv_rq_merge_ok(__rq, bio)) {
  76                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
  77                         ret = ELEVATOR_BACK_MERGE;
  78                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
  79                         ret = ELEVATOR_FRONT_MERGE;
  80         }
  81
  82         return ret;
  83 }
  84 EXPORT_SYMBOL(elv_try_merge);
  85
  86 static struct elevator_type *elevator_find(const char *name)
  87 {
  88         struct elevator_type *e = NULL;
  89         struct list_head *entry;
  90
  91         list_for_each(entry, &elv_list) {
  92                 struct elevator_type *__e;
  93
  94                 __e = list_entry(entry, struct elevator_type, list);
  95
  96                 if (!strcmp(__e->elevator_name, name)) {
  97                         e = __e;
  98                         break;
  99                 }
 100         }
 101
 102         return e;
 103 }
 104
 105 static void elevator_put(struct elevator_type *e)
 106 {
 107         module_put(e->elevator_owner);
 108 }
 109
 110 static struct elevator_type *elevator_get(const char *name)
 111 {
 112         struct elevator_type *e;
 113
 114         spin_lock_irq(&elv_list_lock);
 115
 116         e = elevator_find(name);
 117         if (e && !try_module_get(e->elevator_owner))
 118                 e = NULL;
 119
 120         spin_unlock_irq(&elv_list_lock);
 121
 122         return e;
 123 }
 124
 125 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
 126                            struct elevator_queue *eq)
 127 {
 128         int ret = 0;
 129
 130         memset(eq, 0, sizeof(*eq));
 131         eq->ops = &e->ops;
 132         eq->elevator_type = e;
 133
 134         INIT_LIST_HEAD(&q->queue_head);
 135         q->last_merge = NULL;
 136         q->elevator = eq;
 137         q->end_sector = 0;
 138         q->boundary_rq = NULL;
 139         q->max_back_kb = 0;
 140
 141         if (eq->ops->elevator_init_fn)
 142                 ret = eq->ops->elevator_init_fn(q, eq);
 143
 144         return ret;
 145 }
 146
 147 static char chosen_elevator[16];
 148
 149 static void elevator_setup_default(void)
 150 {
 151         struct elevator_type *e;
 152
 153         /*
 154          * check if default is set and exists
 155          */
 156         if (chosen_elevator[0] && (e = elevator_get(chosen_elevator))) {
 157                 elevator_put(e);
 158                 return;
 159         }
 160
 161 #if defined(CONFIG_IOSCHED_AS)
 162         strcpy(chosen_elevator, "anticipatory");
 163 #elif defined(CONFIG_IOSCHED_DEADLINE)
 164         strcpy(chosen_elevator, "deadline");
 165 #elif defined(CONFIG_IOSCHED_CFQ)
 166         strcpy(chosen_elevator, "cfq");
 167 #elif defined(CONFIG_IOSCHED_NOOP)
 168         strcpy(chosen_elevator, "noop");
 169 #else
 170 #error "You must build at least 1 IO scheduler into the kernel"
 171 #endif
 172 }
 173
 174 static int __init elevator_setup(char *str)
 175 {
 176         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 177         return 0;
 178 }
 179
 180 __setup("elevator=", elevator_setup);
 181
 182 int elevator_init(request_queue_t *q, char *name)
 183 {
 184         struct elevator_type *e = NULL;
 185         struct elevator_queue *eq;
 186         int ret = 0;
 187
 188         elevator_setup_default();
 189
 190         if (!name)
 191                 name = chosen_elevator;
 192
 193         e = elevator_get(name);
 194         if (!e)
 195                 return -EINVAL;
 196
 197         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
 198         if (!eq) {
 199                 elevator_put(e->elevator_type);
 200                 return -ENOMEM;
 201         }
 202
 203         ret = elevator_attach(q, e, eq);
 204         if (ret) {
 205                 kfree(eq);
 206                 elevator_put(e->elevator_type);
 207         }
 208
 209         return ret;
 210 }
 211
 212 void elevator_exit(elevator_t *e)
 213 {
 214         if (e->ops->elevator_exit_fn)
 215                 e->ops->elevator_exit_fn(e);
 216
 217         elevator_put(e->elevator_type);
 218         e->elevator_type = NULL;
 219         kfree(e);
 220 }
 221
 222 /*
 223  * Insert rq into dispatch queue of q.  Queue lock must be held on
 224  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 225  * appended to the dispatch queue.  To be used by specific elevators.
 226  */
 227 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 228 {
 229         sector_t boundary;
 230         unsigned max_back;
 231         struct list_head *entry;
 232
 233         if (q->last_merge == rq)
 234                 q->last_merge = NULL;
 235
 236         boundary = q->end_sector;
 237         max_back = q->max_back_kb * 2;
 238         boundary = boundary > max_back ? boundary - max_back : 0;
 239
 240         list_for_each_prev(entry, &q->queue_head) {
 241                 struct request *pos = list_entry_rq(entry);
 242
 243                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
 244                         break;
 245                 if (rq->sector >= boundary) {
 246                         if (pos->sector < boundary)
 247                                 continue;
 248                 } else {
 249                         if (pos->sector >= boundary)
 250                                 break;
 251                 }
 252                 if (rq->sector >= pos->sector)
 253                         break;
 254         }
 255
 256         list_add(&rq->queuelist, entry);
 257 }
 258
 259 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 260 {
 261         elevator_t *e = q->elevator;
 262         int ret;
 263
 264         if (q->last_merge) {
 265                 ret = elv_try_merge(q->last_merge, bio);
 266                 if (ret != ELEVATOR_NO_MERGE) {
 267                         *req = q->last_merge;
 268                         return ret;
 269                 }
 270         }
 271
 272         if (e->ops->elevator_merge_fn)
 273                 return e->ops->elevator_merge_fn(q, req, bio);
 274
 275         return ELEVATOR_NO_MERGE;
 276 }
 277
 278 void elv_merged_request(request_queue_t *q, struct request *rq)
 279 {
 280         elevator_t *e = q->elevator;
 281
 282         if (e->ops->elevator_merged_fn)
 283                 e->ops->elevator_merged_fn(q, rq);
 284
 285         q->last_merge = rq;
 286 }
 287
 288 void elv_merge_requests(request_queue_t *q, struct request *rq,
 289                              struct request *next)
 290 {
 291         elevator_t *e = q->elevator;
 292
 293         if (e->ops->elevator_merge_req_fn)
 294                 e->ops->elevator_merge_req_fn(q, rq, next);
 295
 296         q->last_merge = rq;
 297 }
 298
 299 void elv_requeue_request(request_queue_t *q, struct request *rq)
 300 {
 301         elevator_t *e = q->elevator;
 302
 303         /*
 304          * it already went through dequeue, we need to decrement the
 305          * in_flight count again
 306          */
 307         if (blk_account_rq(rq)) {
 308                 q->in_flight--;
 309                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
 310                         e->ops->elevator_deactivate_req_fn(q, rq);
 311         }
 312
 313         rq->flags &= ~REQ_STARTED;
 314
 315         /*
 316          * if this is the flush, requeue the original instead and drop the flush
 317          */
 318         if (rq->flags & REQ_BAR_FLUSH) {
 319                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
 320                 rq = rq->end_io_data;
 321         }
 322
 323         __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
 324 }
 325
 326 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 327                        int plug)
 328 {
 329         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 330                 /*
 331                  * barriers implicitly indicate back insertion
 332                  */
 333                 if (where == ELEVATOR_INSERT_SORT)
 334                         where = ELEVATOR_INSERT_BACK;
 335
 336                 /*
 337                  * this request is scheduling boundary, update end_sector
 338                  */
 339                 if (blk_fs_request(rq)) {
 340                         q->end_sector = rq_end_sector(rq);
 341                         q->boundary_rq = rq;
 342                 }
 343         }
 344
 345         if (plug)
 346                 blk_plug_device(q);
 347
 348         rq->q = q;
 349
 350         if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
 351                 /*
 352                  * if drain is set, store the request "locally". when the drain
 353                  * is finished, the requests will be handed ordered to the io
 354                  * scheduler
 355                  */
 356                 list_add_tail(&rq->queuelist, &q->drain_list);
 357                 return;
 358         }
 359
 360         switch (where) {
 361         case ELEVATOR_INSERT_FRONT:
 362                 rq->flags |= REQ_SOFTBARRIER;
 363
 364                 list_add(&rq->queuelist, &q->queue_head);
 365                 break;
 366
 367         case ELEVATOR_INSERT_BACK:
 368                 rq->flags |= REQ_SOFTBARRIER;
 369
 370                 while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 371                         ;
 372                 list_add_tail(&rq->queuelist, &q->queue_head);
 373                 /*
 374                  * We kick the queue here for the following reasons.
 375                  * - The elevator might have returned NULL previously
 376                  *   to delay requests and returned them now.  As the
 377                  *   queue wasn't empty before this request, ll_rw_blk
 378                  *   won't run the queue on return, resulting in hang.
 379                  * - Usually, back inserted requests won't be merged
 380                  *   with anything.  There's no point in delaying queue
 381                  *   processing.
 382                  */
 383                 blk_remove_plug(q);
 384                 q->request_fn(q);
 385                 break;
 386
 387         case ELEVATOR_INSERT_SORT:
 388                 BUG_ON(!blk_fs_request(rq));
 389                 rq->flags |= REQ_SORTED;
 390                 q->elevator->ops->elevator_add_req_fn(q, rq);
 391                 if (q->last_merge == NULL && rq_mergeable(rq))
 392                         q->last_merge = rq;
 393                 break;
 394
 395         default:
 396                 printk(KERN_ERR "%s: bad insertion point %d\n",
 397                        __FUNCTION__, where);
 398                 BUG();
 399         }
 400
 401         if (blk_queue_plugged(q)) {
 402                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 403                         - q->in_flight;
 404
 405                 if (nrq >= q->unplug_thresh)
 406                         __generic_unplug_device(q);
 407         }
 408 }
 409
 410 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 411                      int plug)
 412 {
 413         unsigned long flags;
 414
 415         spin_lock_irqsave(q->queue_lock, flags);
 416         __elv_add_request(q, rq, where, plug);
 417         spin_unlock_irqrestore(q->queue_lock, flags);
 418 }
 419
 420 static inline struct request *__elv_next_request(request_queue_t *q)
 421 {
 422         struct request *rq;
 423
 424         if (unlikely(list_empty(&q->queue_head) &&
 425                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
 426                 return NULL;
 427
 428         rq = list_entry_rq(q->queue_head.next);
 429
 430         /*
 431          * if this is a barrier write and the device has to issue a
 432          * flush sequence to support it, check how far we are
 433          */
 434         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
 435                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
 436
 437                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
 438                     !blk_barrier_preflush(rq))
 439                         rq = blk_start_pre_flush(q, rq);
 440         }
 441
 442         return rq;
 443 }
 444
 445 struct request *elv_next_request(request_queue_t *q)
 446 {
 447         struct request *rq;
 448         int ret;
 449
 450         while ((rq = __elv_next_request(q)) != NULL) {
 451                 if (!(rq->flags & REQ_STARTED)) {
 452                         elevator_t *e = q->elevator;
 453
 454                         /*
 455                          * This is the first time the device driver
 456                          * sees this request (possibly after
 457                          * requeueing).  Notify IO scheduler.
 458                          */
 459                         if (blk_sorted_rq(rq) &&
 460                             e->ops->elevator_activate_req_fn)
 461                                 e->ops->elevator_activate_req_fn(q, rq);
 462
 463                         /*
 464                          * just mark as started even if we don't start
 465                          * it, a request that has been delayed should
 466                          * not be passed by new incoming requests
 467                          */
 468                         rq->flags |= REQ_STARTED;
 469                 }
 470
 471                 if (!q->boundary_rq || q->boundary_rq == rq) {
 472                         q->end_sector = rq_end_sector(rq);
 473                         q->boundary_rq = NULL;
 474                 }
 475
 476                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 477                         break;
 478
 479                 ret = q->prep_rq_fn(q, rq);
 480                 if (ret == BLKPREP_OK) {
 481                         break;
 482                 } else if (ret == BLKPREP_DEFER) {
 483                         /*
 484                          * the request may have been (partially) prepped.
 485                          * we need to keep this request in the front to
 486                          * avoid resource deadlock.  REQ_STARTED will
 487                          * prevent other fs requests from passing this one.
 488                          */
 489                         rq = NULL;
 490                         break;
 491                 } else if (ret == BLKPREP_KILL) {
 492                         int nr_bytes = rq->hard_nr_sectors << 9;
 493
 494                         if (!nr_bytes)
 495                                 nr_bytes = rq->data_len;
 496
 497                         blkdev_dequeue_request(rq);
 498                         rq->flags |= REQ_QUIET;
 499                         end_that_request_chunk(rq, 0, nr_bytes);
 500                         end_that_request_last(rq);
 501                 } else {
 502                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 503                                                                 ret);
 504                         break;
 505                 }
 506         }
 507
 508         return rq;
 509 }
 510
 511 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 512 {
 513         BUG_ON(list_empty(&rq->queuelist));
 514
 515         list_del_init(&rq->queuelist);
 516
 517         /*
 518          * the time frame between a request being removed from the lists
 519          * and to it is freed is accounted as io that is in progress at
 520          * the driver side.
 521          */
 522         if (blk_account_rq(rq))
 523                 q->in_flight++;
 524 }
 525
 526 int elv_queue_empty(request_queue_t *q)
 527 {
 528         elevator_t *e = q->elevator;
 529
 530         if (!list_empty(&q->queue_head))
 531                 return 0;
 532
 533         if (e->ops->elevator_queue_empty_fn)
 534                 return e->ops->elevator_queue_empty_fn(q);
 535
 536         return 1;
 537 }
 538
 539 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 540 {
 541         struct list_head *next;
 542
 543         elevator_t *e = q->elevator;
 544
 545         if (e->ops->elevator_latter_req_fn)
 546                 return e->ops->elevator_latter_req_fn(q, rq);
 547
 548         next = rq->queuelist.next;
 549         if (next != &q->queue_head && next != &rq->queuelist)
 550                 return list_entry_rq(next);
 551
 552         return NULL;
 553 }
 554
 555 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 556 {
 557         struct list_head *prev;
 558
 559         elevator_t *e = q->elevator;
 560
 561         if (e->ops->elevator_former_req_fn)
 562                 return e->ops->elevator_former_req_fn(q, rq);
 563
 564         prev = rq->queuelist.prev;
 565         if (prev != &q->queue_head && prev != &rq->queuelist)
 566                 return list_entry_rq(prev);
 567
 568         return NULL;
 569 }
 570
 571 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 572                     int gfp_mask)
 573 {
 574         elevator_t *e = q->elevator;
 575
 576         if (e->ops->elevator_set_req_fn)
 577                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
 578
 579         rq->elevator_private = NULL;
 580         return 0;
 581 }
 582
 583 void elv_put_request(request_queue_t *q, struct request *rq)
 584 {
 585         elevator_t *e = q->elevator;
 586
 587         if (e->ops->elevator_put_req_fn)
 588                 e->ops->elevator_put_req_fn(q, rq);
 589 }
 590
 591 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
 592 {
 593         elevator_t *e = q->elevator;
 594
 595         if (e->ops->elevator_may_queue_fn)
 596                 return e->ops->elevator_may_queue_fn(q, rw, bio);
 597
 598         return ELV_MQUEUE_MAY;
 599 }
 600
 601 void elv_completed_request(request_queue_t *q, struct request *rq)
 602 {
 603         elevator_t *e = q->elevator;
 604
 605         /*
 606          * request is released from the driver, io must be done
 607          */
 608         if (blk_account_rq(rq)) {
 609                 q->in_flight--;
 610                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 611                         e->ops->elevator_completed_req_fn(q, rq);
 612         }
 613 }
 614
 615 int elv_register_queue(struct request_queue *q)
 616 {
 617         elevator_t *e = q->elevator;
 618
 619         e->kobj.parent = kobject_get(&q->kobj);
 620         if (!e->kobj.parent)
 621                 return -EBUSY;
 622
 623         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 624         e->kobj.ktype = e->elevator_type->elevator_ktype;
 625
 626         return kobject_register(&e->kobj);
 627 }
 628
 629 void elv_unregister_queue(struct request_queue *q)
 630 {
 631         if (q) {
 632                 elevator_t *e = q->elevator;
 633                 kobject_unregister(&e->kobj);
 634                 kobject_put(&q->kobj);
 635         }
 636 }
 637
 638 int elv_register(struct elevator_type *e)
 639 {
 640         spin_lock_irq(&elv_list_lock);
 641         if (elevator_find(e->elevator_name))
 642                 BUG();
 643         list_add_tail(&e->list, &elv_list);
 644         spin_unlock_irq(&elv_list_lock);
 645
 646         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 647         if (!strcmp(e->elevator_name, chosen_elevator))
 648                 printk(" (default)");
 649         printk("\n");
 650         return 0;
 651 }
 652 EXPORT_SYMBOL_GPL(elv_register);
 653
 654 void elv_unregister(struct elevator_type *e)
 655 {
 656         spin_lock_irq(&elv_list_lock);
 657         list_del_init(&e->list);
 658         spin_unlock_irq(&elv_list_lock);
 659 }
 660 EXPORT_SYMBOL_GPL(elv_unregister);
 661
 662 /*
 663  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 664  * we don't free the old io scheduler, before we have allocated what we
 665  * need for the new one. this way we have a chance of going back to the old
 666  * one, if the new one fails init for some reason. we also do an intermediate
 667  * switch to noop to ensure safety with stack-allocated requests, since they
 668  * don't originate from the block layer allocator. noop is safe here, because
 669  * it never needs to touch the elevator itself for completion events. DRAIN
 670  * flags will make sure we don't touch it for additions either.
 671  */
 672 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
 673 {
 674         elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
 675         struct elevator_type *noop_elevator = NULL;
 676         elevator_t *old_elevator;
 677
 678         if (!e)
 679                 goto error;
 680
 681         /*
 682          * first step, drain requests from the block freelist
 683          */
 684         blk_wait_queue_drained(q, 0);
 685
 686         /*
 687          * unregister old elevator data
 688          */
 689         elv_unregister_queue(q);
 690         old_elevator = q->elevator;
 691
 692         /*
 693          * next step, switch to noop since it uses no private rq structures
 694          * and doesn't allocate any memory for anything. then wait for any
 695          * non-fs requests in-flight
 696          */
 697         noop_elevator = elevator_get("noop");
 698         spin_lock_irq(q->queue_lock);
 699         elevator_attach(q, noop_elevator, e);
 700         spin_unlock_irq(q->queue_lock);
 701
 702         blk_wait_queue_drained(q, 1);
 703
 704         /*
 705          * attach and start new elevator
 706          */
 707         if (elevator_attach(q, new_e, e))
 708                 goto fail;
 709
 710         if (elv_register_queue(q))
 711                 goto fail_register;
 712
 713         /*
 714          * finally exit old elevator and start queue again
 715          */
 716         elevator_exit(old_elevator);
 717         blk_finish_queue_drain(q);
 718         elevator_put(noop_elevator);
 719         return;
 720
 721 fail_register:
 722         /*
 723          * switch failed, exit the new io scheduler and reattach the old
 724          * one again (along with re-adding the sysfs dir)
 725          */
 726         elevator_exit(e);
 727 fail:
 728         q->elevator = old_elevator;
 729         elv_register_queue(q);
 730         blk_finish_queue_drain(q);
 731 error:
 732         if (noop_elevator)
 733                 elevator_put(noop_elevator);
 734         elevator_put(new_e);
 735         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
 736 }
 737
 738 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
 739 {
 740         char elevator_name[ELV_NAME_MAX];
 741         struct elevator_type *e;
 742
 743         memset(elevator_name, 0, sizeof(elevator_name));
 744         strncpy(elevator_name, name, sizeof(elevator_name));
 745
 746         if (elevator_name[strlen(elevator_name) - 1] == '\n')
 747                 elevator_name[strlen(elevator_name) - 1] = '\0';
 748
 749         e = elevator_get(elevator_name);
 750         if (!e) {
 751                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 752                 return -EINVAL;
 753         }
 754
 755         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
 756                 return count;
 757
 758         elevator_switch(q, e);
 759         return count;
 760 }
 761
 762 ssize_t elv_iosched_show(request_queue_t *q, char *name)
 763 {
 764         elevator_t *e = q->elevator;
 765         struct elevator_type *elv = e->elevator_type;
 766         struct list_head *entry;
 767         int len = 0;
 768
 769         spin_lock_irq(q->queue_lock);
 770         list_for_each(entry, &elv_list) {
 771                 struct elevator_type *__e;
 772
 773                 __e = list_entry(entry, struct elevator_type, list);
 774                 if (!strcmp(elv->elevator_name, __e->elevator_name))
 775                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 776                 else
 777                         len += sprintf(name+len, "%s ", __e->elevator_name);
 778         }
 779         spin_unlock_irq(q->queue_lock);
 780
 781         len += sprintf(len+name, "\n");
 782         return len;
 783 }
 784
 785 EXPORT_SYMBOL(elv_dispatch_sort);
 786 EXPORT_SYMBOL(elv_add_request);
 787 EXPORT_SYMBOL(__elv_add_request);
 788 EXPORT_SYMBOL(elv_requeue_request);
 789 EXPORT_SYMBOL(elv_next_request);
 790 EXPORT_SYMBOL(elv_dequeue_request);
 791 EXPORT_SYMBOL(elv_queue_empty);
 792 EXPORT_SYMBOL(elv_completed_request);
 793 EXPORT_SYMBOL(elevator_exit);
 794 EXPORT_SYMBOL(elevator_init);