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