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 #include <linux/delay.h>
  38
  39 #include <asm/uaccess.h>
  40
  41 static DEFINE_SPINLOCK(elv_list_lock);
  42 static LIST_HEAD(elv_list);
  43
  44 /*
  45  * can we safely merge with this request?
  46  */
  47 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  48 {
  49         if (!rq_mergeable(rq))
  50                 return 0;
  51
  52         /*
  53          * different data direction or already started, don't merge
  54          */
  55         if (bio_data_dir(bio) != rq_data_dir(rq))
  56                 return 0;
  57
  58         /*
  59          * same device and no special stuff set, merge is ok
  60          */
  61         if (rq->rq_disk == bio->bi_bdev->bd_disk &&
  62             !rq->waiting && !rq->special)
  63                 return 1;
  64
  65         return 0;
  66 }
  67 EXPORT_SYMBOL(elv_rq_merge_ok);
  68
  69 inline int elv_try_merge(struct request *__rq, struct bio *bio)
  70 {
  71         int ret = ELEVATOR_NO_MERGE;
  72
  73         /*
  74          * we can merge and sequence is ok, check if it's possible
  75          */
  76         if (elv_rq_merge_ok(__rq, bio)) {
  77                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
  78                         ret = ELEVATOR_BACK_MERGE;
  79                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
  80                         ret = ELEVATOR_FRONT_MERGE;
  81         }
  82
  83         return ret;
  84 }
  85 EXPORT_SYMBOL(elv_try_merge);
  86
  87 static struct elevator_type *elevator_find(const char *name)
  88 {
  89         struct elevator_type *e = NULL;
  90         struct list_head *entry;
  91
  92         list_for_each(entry, &elv_list) {
  93                 struct elevator_type *__e;
  94
  95                 __e = list_entry(entry, struct elevator_type, list);
  96
  97                 if (!strcmp(__e->elevator_name, name)) {
  98                         e = __e;
  99                         break;
 100                 }
 101         }
 102
 103         return e;
 104 }
 105
 106 static void elevator_put(struct elevator_type *e)
 107 {
 108         module_put(e->elevator_owner);
 109 }
 110
 111 static struct elevator_type *elevator_get(const char *name)
 112 {
 113         struct elevator_type *e;
 114
 115         spin_lock_irq(&elv_list_lock);
 116
 117         e = elevator_find(name);
 118         if (e && !try_module_get(e->elevator_owner))
 119                 e = NULL;
 120
 121         spin_unlock_irq(&elv_list_lock);
 122
 123         return e;
 124 }
 125
 126 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
 127                            struct elevator_queue *eq)
 128 {
 129         int ret = 0;
 130
 131         memset(eq, 0, sizeof(*eq));
 132         eq->ops = &e->ops;
 133         eq->elevator_type = e;
 134
 135         q->elevator = eq;
 136
 137         if (eq->ops->elevator_init_fn)
 138                 ret = eq->ops->elevator_init_fn(q, eq);
 139
 140         return ret;
 141 }
 142
 143 static char chosen_elevator[16];
 144
 145 static void elevator_setup_default(void)
 146 {
 147         struct elevator_type *e;
 148
 149         /*
 150          * If default has not been set, use the compiled-in selection.
 151          */
 152         if (!chosen_elevator[0])
 153                 strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
 154
 155         /*
 156          * If the given scheduler is not available, fall back to no-op.
 157          */
 158         if ((e = elevator_find(chosen_elevator)))
 159                 elevator_put(e);
 160         else
 161                 strcpy(chosen_elevator, "noop");
 162 }
 163
 164 static int __init elevator_setup(char *str)
 165 {
 166         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 167         return 0;
 168 }
 169
 170 __setup("elevator=", elevator_setup);
 171
 172 int elevator_init(request_queue_t *q, char *name)
 173 {
 174         struct elevator_type *e = NULL;
 175         struct elevator_queue *eq;
 176         int ret = 0;
 177
 178         INIT_LIST_HEAD(&q->queue_head);
 179         q->last_merge = NULL;
 180         q->end_sector = 0;
 181         q->boundary_rq = NULL;
 182
 183         elevator_setup_default();
 184
 185         if (!name)
 186                 name = chosen_elevator;
 187
 188         e = elevator_get(name);
 189         if (!e)
 190                 return -EINVAL;
 191
 192         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
 193         if (!eq) {
 194                 elevator_put(e);
 195                 return -ENOMEM;
 196         }
 197
 198         ret = elevator_attach(q, e, eq);
 199         if (ret) {
 200                 kfree(eq);
 201                 elevator_put(e);
 202         }
 203
 204         return ret;
 205 }
 206
 207 void elevator_exit(elevator_t *e)
 208 {
 209         if (e->ops->elevator_exit_fn)
 210                 e->ops->elevator_exit_fn(e);
 211
 212         elevator_put(e->elevator_type);
 213         e->elevator_type = NULL;
 214         kfree(e);
 215 }
 216
 217 /*
 218  * Insert rq into dispatch queue of q.  Queue lock must be held on
 219  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 220  * appended to the dispatch queue.  To be used by specific elevators.
 221  */
 222 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 223 {
 224         sector_t boundary;
 225         struct list_head *entry;
 226
 227         if (q->last_merge == rq)
 228                 q->last_merge = NULL;
 229         q->nr_sorted--;
 230
 231         boundary = q->end_sector;
 232
 233         list_for_each_prev(entry, &q->queue_head) {
 234                 struct request *pos = list_entry_rq(entry);
 235
 236                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
 237                         break;
 238                 if (rq->sector >= boundary) {
 239                         if (pos->sector < boundary)
 240                                 continue;
 241                 } else {
 242                         if (pos->sector >= boundary)
 243                                 break;
 244                 }
 245                 if (rq->sector >= pos->sector)
 246                         break;
 247         }
 248
 249         list_add(&rq->queuelist, entry);
 250 }
 251
 252 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 253 {
 254         elevator_t *e = q->elevator;
 255         int ret;
 256
 257         if (q->last_merge) {
 258                 ret = elv_try_merge(q->last_merge, bio);
 259                 if (ret != ELEVATOR_NO_MERGE) {
 260                         *req = q->last_merge;
 261                         return ret;
 262                 }
 263         }
 264
 265         if (e->ops->elevator_merge_fn)
 266                 return e->ops->elevator_merge_fn(q, req, bio);
 267
 268         return ELEVATOR_NO_MERGE;
 269 }
 270
 271 void elv_merged_request(request_queue_t *q, struct request *rq)
 272 {
 273         elevator_t *e = q->elevator;
 274
 275         if (e->ops->elevator_merged_fn)
 276                 e->ops->elevator_merged_fn(q, rq);
 277
 278         q->last_merge = rq;
 279 }
 280
 281 void elv_merge_requests(request_queue_t *q, struct request *rq,
 282                              struct request *next)
 283 {
 284         elevator_t *e = q->elevator;
 285
 286         if (e->ops->elevator_merge_req_fn)
 287                 e->ops->elevator_merge_req_fn(q, rq, next);
 288         q->nr_sorted--;
 289
 290         q->last_merge = rq;
 291 }
 292
 293 void elv_requeue_request(request_queue_t *q, struct request *rq)
 294 {
 295         elevator_t *e = q->elevator;
 296
 297         /*
 298          * it already went through dequeue, we need to decrement the
 299          * in_flight count again
 300          */
 301         if (blk_account_rq(rq)) {
 302                 q->in_flight--;
 303                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
 304                         e->ops->elevator_deactivate_req_fn(q, rq);
 305         }
 306
 307         rq->flags &= ~REQ_STARTED;
 308
 309         /*
 310          * if this is the flush, requeue the original instead and drop the flush
 311          */
 312         if (rq->flags & REQ_BAR_FLUSH) {
 313                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
 314                 rq = rq->end_io_data;
 315         }
 316
 317         __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
 318 }
 319
 320 static void elv_drain_elevator(request_queue_t *q)
 321 {
 322         static int printed;
 323         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 324                 ;
 325         if (q->nr_sorted == 0)
 326                 return;
 327         if (printed++ < 10) {
 328                 printk(KERN_ERR "%s: forced dispatching is broken "
 329                        "(nr_sorted=%u), please report this\n",
 330                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 331         }
 332 }
 333
 334 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 335                        int plug)
 336 {
 337         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 338                 /*
 339                  * barriers implicitly indicate back insertion
 340                  */
 341                 if (where == ELEVATOR_INSERT_SORT)
 342                         where = ELEVATOR_INSERT_BACK;
 343
 344                 /*
 345                  * this request is scheduling boundary, update end_sector
 346                  */
 347                 if (blk_fs_request(rq)) {
 348                         q->end_sector = rq_end_sector(rq);
 349                         q->boundary_rq = rq;
 350                 }
 351         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
 352                 where = ELEVATOR_INSERT_BACK;
 353
 354         if (plug)
 355                 blk_plug_device(q);
 356
 357         rq->q = q;
 358
 359         switch (where) {
 360         case ELEVATOR_INSERT_FRONT:
 361                 rq->flags |= REQ_SOFTBARRIER;
 362
 363                 list_add(&rq->queuelist, &q->queue_head);
 364                 break;
 365
 366         case ELEVATOR_INSERT_BACK:
 367                 rq->flags |= REQ_SOFTBARRIER;
 368                 elv_drain_elevator(q);
 369                 list_add_tail(&rq->queuelist, &q->queue_head);
 370                 /*
 371                  * We kick the queue here for the following reasons.
 372                  * - The elevator might have returned NULL previously
 373                  *   to delay requests and returned them now.  As the
 374                  *   queue wasn't empty before this request, ll_rw_blk
 375                  *   won't run the queue on return, resulting in hang.
 376                  * - Usually, back inserted requests won't be merged
 377                  *   with anything.  There's no point in delaying queue
 378                  *   processing.
 379                  */
 380                 blk_remove_plug(q);
 381                 q->request_fn(q);
 382                 break;
 383
 384         case ELEVATOR_INSERT_SORT:
 385                 BUG_ON(!blk_fs_request(rq));
 386                 rq->flags |= REQ_SORTED;
 387                 q->nr_sorted++;
 388                 if (q->last_merge == NULL && rq_mergeable(rq))
 389                         q->last_merge = rq;
 390                 /*
 391                  * Some ioscheds (cfq) run q->request_fn directly, so
 392                  * rq cannot be accessed after calling
 393                  * elevator_add_req_fn.
 394                  */
 395                 q->elevator->ops->elevator_add_req_fn(q, rq);
 396                 break;
 397
 398         default:
 399                 printk(KERN_ERR "%s: bad insertion point %d\n",
 400                        __FUNCTION__, where);
 401                 BUG();
 402         }
 403
 404         if (blk_queue_plugged(q)) {
 405                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 406                         - q->in_flight;
 407
 408                 if (nrq >= q->unplug_thresh)
 409                         __generic_unplug_device(q);
 410         }
 411 }
 412
 413 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 414                      int plug)
 415 {
 416         unsigned long flags;
 417
 418         spin_lock_irqsave(q->queue_lock, flags);
 419         __elv_add_request(q, rq, where, plug);
 420         spin_unlock_irqrestore(q->queue_lock, flags);
 421 }
 422
 423 static inline struct request *__elv_next_request(request_queue_t *q)
 424 {
 425         struct request *rq;
 426
 427         if (unlikely(list_empty(&q->queue_head) &&
 428                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
 429                 return NULL;
 430
 431         rq = list_entry_rq(q->queue_head.next);
 432
 433         /*
 434          * if this is a barrier write and the device has to issue a
 435          * flush sequence to support it, check how far we are
 436          */
 437         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
 438                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
 439
 440                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
 441                     !blk_barrier_preflush(rq))
 442                         rq = blk_start_pre_flush(q, rq);
 443         }
 444
 445         return rq;
 446 }
 447
 448 struct request *elv_next_request(request_queue_t *q)
 449 {
 450         struct request *rq;
 451         int ret;
 452
 453         while ((rq = __elv_next_request(q)) != NULL) {
 454                 if (!(rq->flags & REQ_STARTED)) {
 455                         elevator_t *e = q->elevator;
 456
 457                         /*
 458                          * This is the first time the device driver
 459                          * sees this request (possibly after
 460                          * requeueing).  Notify IO scheduler.
 461                          */
 462                         if (blk_sorted_rq(rq) &&
 463                             e->ops->elevator_activate_req_fn)
 464                                 e->ops->elevator_activate_req_fn(q, rq);
 465
 466                         /*
 467                          * just mark as started even if we don't start
 468                          * it, a request that has been delayed should
 469                          * not be passed by new incoming requests
 470                          */
 471                         rq->flags |= REQ_STARTED;
 472                 }
 473
 474                 if (!q->boundary_rq || q->boundary_rq == rq) {
 475                         q->end_sector = rq_end_sector(rq);
 476                         q->boundary_rq = NULL;
 477                 }
 478
 479                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 480                         break;
 481
 482                 ret = q->prep_rq_fn(q, rq);
 483                 if (ret == BLKPREP_OK) {
 484                         break;
 485                 } else if (ret == BLKPREP_DEFER) {
 486                         /*
 487                          * the request may have been (partially) prepped.
 488                          * we need to keep this request in the front to
 489                          * avoid resource deadlock.  REQ_STARTED will
 490                          * prevent other fs requests from passing this one.
 491                          */
 492                         rq = NULL;
 493                         break;
 494                 } else if (ret == BLKPREP_KILL) {
 495                         int nr_bytes = rq->hard_nr_sectors << 9;
 496
 497                         if (!nr_bytes)
 498                                 nr_bytes = rq->data_len;
 499
 500                         blkdev_dequeue_request(rq);
 501                         rq->flags |= REQ_QUIET;
 502                         end_that_request_chunk(rq, 0, nr_bytes);
 503                         end_that_request_last(rq);
 504                 } else {
 505                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 506                                                                 ret);
 507                         break;
 508                 }
 509         }
 510
 511         return rq;
 512 }
 513
 514 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 515 {
 516         BUG_ON(list_empty(&rq->queuelist));
 517
 518         list_del_init(&rq->queuelist);
 519
 520         /*
 521          * the time frame between a request being removed from the lists
 522          * and to it is freed is accounted as io that is in progress at
 523          * the driver side.
 524          */
 525         if (blk_account_rq(rq))
 526                 q->in_flight++;
 527 }
 528
 529 int elv_queue_empty(request_queue_t *q)
 530 {
 531         elevator_t *e = q->elevator;
 532
 533         if (!list_empty(&q->queue_head))
 534                 return 0;
 535
 536         if (e->ops->elevator_queue_empty_fn)
 537                 return e->ops->elevator_queue_empty_fn(q);
 538
 539         return 1;
 540 }
 541
 542 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 543 {
 544         elevator_t *e = q->elevator;
 545
 546         if (e->ops->elevator_latter_req_fn)
 547                 return e->ops->elevator_latter_req_fn(q, rq);
 548         return NULL;
 549 }
 550
 551 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 552 {
 553         elevator_t *e = q->elevator;
 554
 555         if (e->ops->elevator_former_req_fn)
 556                 return e->ops->elevator_former_req_fn(q, rq);
 557         return NULL;
 558 }
 559
 560 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 561                     gfp_t gfp_mask)
 562 {
 563         elevator_t *e = q->elevator;
 564
 565         if (e->ops->elevator_set_req_fn)
 566                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
 567
 568         rq->elevator_private = NULL;
 569         return 0;
 570 }
 571
 572 void elv_put_request(request_queue_t *q, struct request *rq)
 573 {
 574         elevator_t *e = q->elevator;
 575
 576         if (e->ops->elevator_put_req_fn)
 577                 e->ops->elevator_put_req_fn(q, rq);
 578 }
 579
 580 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
 581 {
 582         elevator_t *e = q->elevator;
 583
 584         if (e->ops->elevator_may_queue_fn)
 585                 return e->ops->elevator_may_queue_fn(q, rw, bio);
 586
 587         return ELV_MQUEUE_MAY;
 588 }
 589
 590 void elv_completed_request(request_queue_t *q, struct request *rq)
 591 {
 592         elevator_t *e = q->elevator;
 593
 594         /*
 595          * request is released from the driver, io must be done
 596          */
 597         if (blk_account_rq(rq)) {
 598                 q->in_flight--;
 599                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 600                         e->ops->elevator_completed_req_fn(q, rq);
 601         }
 602 }
 603
 604 int elv_register_queue(struct request_queue *q)
 605 {
 606         elevator_t *e = q->elevator;
 607
 608         e->kobj.parent = kobject_get(&q->kobj);
 609         if (!e->kobj.parent)
 610                 return -EBUSY;
 611
 612         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 613         e->kobj.ktype = e->elevator_type->elevator_ktype;
 614
 615         return kobject_register(&e->kobj);
 616 }
 617
 618 void elv_unregister_queue(struct request_queue *q)
 619 {
 620         if (q) {
 621                 elevator_t *e = q->elevator;
 622                 kobject_unregister(&e->kobj);
 623                 kobject_put(&q->kobj);
 624         }
 625 }
 626
 627 int elv_register(struct elevator_type *e)
 628 {
 629         spin_lock_irq(&elv_list_lock);
 630         if (elevator_find(e->elevator_name))
 631                 BUG();
 632         list_add_tail(&e->list, &elv_list);
 633         spin_unlock_irq(&elv_list_lock);
 634
 635         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 636         if (!strcmp(e->elevator_name, chosen_elevator))
 637                 printk(" (default)");
 638         printk("\n");
 639         return 0;
 640 }
 641 EXPORT_SYMBOL_GPL(elv_register);
 642
 643 void elv_unregister(struct elevator_type *e)
 644 {
 645         struct task_struct *g, *p;
 646
 647         /*
 648          * Iterate every thread in the process to remove the io contexts.
 649          */
 650         read_lock(&tasklist_lock);
 651         do_each_thread(g, p) {
 652                 struct io_context *ioc = p->io_context;
 653                 if (ioc && ioc->cic) {
 654                         ioc->cic->exit(ioc->cic);
 655                         ioc->cic->dtor(ioc->cic);
 656                         ioc->cic = NULL;
 657                 }
 658                 if (ioc && ioc->aic) {
 659                         ioc->aic->exit(ioc->aic);
 660                         ioc->aic->dtor(ioc->aic);
 661                         ioc->aic = NULL;
 662                 }
 663         } while_each_thread(g, p);
 664         read_unlock(&tasklist_lock);
 665
 666         spin_lock_irq(&elv_list_lock);
 667         list_del_init(&e->list);
 668         spin_unlock_irq(&elv_list_lock);
 669 }
 670 EXPORT_SYMBOL_GPL(elv_unregister);
 671
 672 /*
 673  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 674  * we don't free the old io scheduler, before we have allocated what we
 675  * need for the new one. this way we have a chance of going back to the old
 676  * one, if the new one fails init for some reason.
 677  */
 678 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
 679 {
 680         elevator_t *old_elevator, *e;
 681
 682         /*
 683          * Allocate new elevator
 684          */
 685         e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
 686         if (!e)
 687                 goto error;
 688
 689         /*
 690          * Turn on BYPASS and drain all requests w/ elevator private data
 691          */
 692         spin_lock_irq(q->queue_lock);
 693
 694         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 695
 696         elv_drain_elevator(q);
 697
 698         while (q->rq.elvpriv) {
 699                 blk_remove_plug(q);
 700                 q->request_fn(q);
 701                 spin_unlock_irq(q->queue_lock);
 702                 msleep(10);
 703                 spin_lock_irq(q->queue_lock);
 704                 elv_drain_elevator(q);
 705         }
 706
 707         spin_unlock_irq(q->queue_lock);
 708
 709         /*
 710          * unregister old elevator data
 711          */
 712         elv_unregister_queue(q);
 713         old_elevator = q->elevator;
 714
 715         /*
 716          * attach and start new elevator
 717          */
 718         if (elevator_attach(q, new_e, e))
 719                 goto fail;
 720
 721         if (elv_register_queue(q))
 722                 goto fail_register;
 723
 724         /*
 725          * finally exit old elevator and turn off BYPASS.
 726          */
 727         elevator_exit(old_elevator);
 728         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 729         return;
 730
 731 fail_register:
 732         /*
 733          * switch failed, exit the new io scheduler and reattach the old
 734          * one again (along with re-adding the sysfs dir)
 735          */
 736         elevator_exit(e);
 737         e = NULL;
 738 fail:
 739         q->elevator = old_elevator;
 740         elv_register_queue(q);
 741         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 742         kfree(e);
 743 error:
 744         elevator_put(new_e);
 745         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
 746 }
 747
 748 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
 749 {
 750         char elevator_name[ELV_NAME_MAX];
 751         size_t len;
 752         struct elevator_type *e;
 753
 754         elevator_name[sizeof(elevator_name) - 1] = '\0';
 755         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
 756         len = strlen(elevator_name);
 757
 758         if (len && elevator_name[len - 1] == '\n')
 759                 elevator_name[len - 1] = '\0';
 760
 761         e = elevator_get(elevator_name);
 762         if (!e) {
 763                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 764                 return -EINVAL;
 765         }
 766
 767         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
 768                 elevator_put(e);
 769                 return count;
 770         }
 771
 772         elevator_switch(q, e);
 773         return count;
 774 }
 775
 776 ssize_t elv_iosched_show(request_queue_t *q, char *name)
 777 {
 778         elevator_t *e = q->elevator;
 779         struct elevator_type *elv = e->elevator_type;
 780         struct list_head *entry;
 781         int len = 0;
 782
 783         spin_lock_irq(q->queue_lock);
 784         list_for_each(entry, &elv_list) {
 785                 struct elevator_type *__e;
 786
 787                 __e = list_entry(entry, struct elevator_type, list);
 788                 if (!strcmp(elv->elevator_name, __e->elevator_name))
 789                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 790                 else
 791                         len += sprintf(name+len, "%s ", __e->elevator_name);
 792         }
 793         spin_unlock_irq(q->queue_lock);
 794
 795         len += sprintf(len+name, "\n");
 796         return len;
 797 }
 798
 799 EXPORT_SYMBOL(elv_dispatch_sort);
 800 EXPORT_SYMBOL(elv_add_request);
 801 EXPORT_SYMBOL(__elv_add_request);
 802 EXPORT_SYMBOL(elv_requeue_request);
 803 EXPORT_SYMBOL(elv_next_request);
 804 EXPORT_SYMBOL(elv_dequeue_request);
 805 EXPORT_SYMBOL(elv_queue_empty);
 806 EXPORT_SYMBOL(elv_completed_request);
 807 EXPORT_SYMBOL(elevator_exit);
 808 EXPORT_SYMBOL(elevator_init);