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 inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
  87 {
  88         if (q->last_merge)
  89                 return elv_try_merge(q->last_merge, bio);
  90
  91         return ELEVATOR_NO_MERGE;
  92 }
  93 EXPORT_SYMBOL(elv_try_last_merge);
  94
  95 static struct elevator_type *elevator_find(const char *name)
  96 {
  97         struct elevator_type *e = NULL;
  98         struct list_head *entry;
  99
 100         list_for_each(entry, &elv_list) {
 101                 struct elevator_type *__e;
 102
 103                 __e = list_entry(entry, struct elevator_type, list);
 104
 105                 if (!strcmp(__e->elevator_name, name)) {
 106                         e = __e;
 107                         break;
 108                 }
 109         }
 110
 111         return e;
 112 }
 113
 114 static void elevator_put(struct elevator_type *e)
 115 {
 116         module_put(e->elevator_owner);
 117 }
 118
 119 static struct elevator_type *elevator_get(const char *name)
 120 {
 121         struct elevator_type *e;
 122
 123         spin_lock_irq(&elv_list_lock);
 124
 125         e = elevator_find(name);
 126         if (e && !try_module_get(e->elevator_owner))
 127                 e = NULL;
 128
 129         spin_unlock_irq(&elv_list_lock);
 130
 131         return e;
 132 }
 133
 134 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
 135                            struct elevator_queue *eq)
 136 {
 137         int ret = 0;
 138
 139         memset(eq, 0, sizeof(*eq));
 140         eq->ops = &e->ops;
 141         eq->elevator_type = e;
 142
 143         INIT_LIST_HEAD(&q->queue_head);
 144         q->last_merge = NULL;
 145         q->elevator = eq;
 146         q->end_sector = 0;
 147         q->boundary_rq = NULL;
 148         q->max_back_kb = 0;
 149
 150         if (eq->ops->elevator_init_fn)
 151                 ret = eq->ops->elevator_init_fn(q, eq);
 152
 153         return ret;
 154 }
 155
 156 static char chosen_elevator[16];
 157
 158 static void elevator_setup_default(void)
 159 {
 160         struct elevator_type *e;
 161
 162         /*
 163          * check if default is set and exists
 164          */
 165         if (chosen_elevator[0] && (e = elevator_get(chosen_elevator))) {
 166                 elevator_put(e);
 167                 return;
 168         }
 169
 170 #if defined(CONFIG_IOSCHED_AS)
 171         strcpy(chosen_elevator, "anticipatory");
 172 #elif defined(CONFIG_IOSCHED_DEADLINE)
 173         strcpy(chosen_elevator, "deadline");
 174 #elif defined(CONFIG_IOSCHED_CFQ)
 175         strcpy(chosen_elevator, "cfq");
 176 #elif defined(CONFIG_IOSCHED_NOOP)
 177         strcpy(chosen_elevator, "noop");
 178 #else
 179 #error "You must build at least 1 IO scheduler into the kernel"
 180 #endif
 181 }
 182
 183 static int __init elevator_setup(char *str)
 184 {
 185         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 186         return 0;
 187 }
 188
 189 __setup("elevator=", elevator_setup);
 190
 191 int elevator_init(request_queue_t *q, char *name)
 192 {
 193         struct elevator_type *e = NULL;
 194         struct elevator_queue *eq;
 195         int ret = 0;
 196
 197         elevator_setup_default();
 198
 199         if (!name)
 200                 name = chosen_elevator;
 201
 202         e = elevator_get(name);
 203         if (!e)
 204                 return -EINVAL;
 205
 206         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
 207         if (!eq) {
 208                 elevator_put(e->elevator_type);
 209                 return -ENOMEM;
 210         }
 211
 212         ret = elevator_attach(q, e, eq);
 213         if (ret) {
 214                 kfree(eq);
 215                 elevator_put(e->elevator_type);
 216         }
 217
 218         return ret;
 219 }
 220
 221 void elevator_exit(elevator_t *e)
 222 {
 223         if (e->ops->elevator_exit_fn)
 224                 e->ops->elevator_exit_fn(e);
 225
 226         elevator_put(e->elevator_type);
 227         e->elevator_type = NULL;
 228         kfree(e);
 229 }
 230
 231 /*
 232  * Insert rq into dispatch queue of q.  Queue lock must be held on
 233  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 234  * appended to the dispatch queue.  To be used by specific elevators.
 235  */
 236 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 237 {
 238         sector_t boundary;
 239         unsigned max_back;
 240         struct list_head *entry;
 241
 242         boundary = q->end_sector;
 243         max_back = q->max_back_kb * 2;
 244         boundary = boundary > max_back ? boundary - max_back : 0;
 245
 246         list_for_each_prev(entry, &q->queue_head) {
 247                 struct request *pos = list_entry_rq(entry);
 248
 249                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
 250                         break;
 251                 if (rq->sector >= boundary) {
 252                         if (pos->sector < boundary)
 253                                 continue;
 254                 } else {
 255                         if (pos->sector >= boundary)
 256                                 break;
 257                 }
 258                 if (rq->sector >= pos->sector)
 259                         break;
 260         }
 261
 262         list_add(&rq->queuelist, entry);
 263 }
 264
 265 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 266 {
 267         elevator_t *e = q->elevator;
 268
 269         if (e->ops->elevator_merge_fn)
 270                 return e->ops->elevator_merge_fn(q, req, bio);
 271
 272         return ELEVATOR_NO_MERGE;
 273 }
 274
 275 void elv_merged_request(request_queue_t *q, struct request *rq)
 276 {
 277         elevator_t *e = q->elevator;
 278
 279         if (e->ops->elevator_merged_fn)
 280                 e->ops->elevator_merged_fn(q, rq);
 281 }
 282
 283 void elv_merge_requests(request_queue_t *q, struct request *rq,
 284                              struct request *next)
 285 {
 286         elevator_t *e = q->elevator;
 287
 288         if (q->last_merge == next)
 289                 q->last_merge = NULL;
 290
 291         if (e->ops->elevator_merge_req_fn)
 292                 e->ops->elevator_merge_req_fn(q, rq, next);
 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                 break;
 388
 389         default:
 390                 printk(KERN_ERR "%s: bad insertion point %d\n",
 391                        __FUNCTION__, where);
 392                 BUG();
 393         }
 394
 395         if (blk_queue_plugged(q)) {
 396                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 397                         - q->in_flight;
 398
 399                 if (nrq >= q->unplug_thresh)
 400                         __generic_unplug_device(q);
 401         }
 402 }
 403
 404 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 405                      int plug)
 406 {
 407         unsigned long flags;
 408
 409         spin_lock_irqsave(q->queue_lock, flags);
 410         __elv_add_request(q, rq, where, plug);
 411         spin_unlock_irqrestore(q->queue_lock, flags);
 412 }
 413
 414 static inline struct request *__elv_next_request(request_queue_t *q)
 415 {
 416         struct request *rq;
 417
 418         if (unlikely(list_empty(&q->queue_head) &&
 419                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
 420                 return NULL;
 421
 422         rq = list_entry_rq(q->queue_head.next);
 423
 424         /*
 425          * if this is a barrier write and the device has to issue a
 426          * flush sequence to support it, check how far we are
 427          */
 428         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
 429                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
 430
 431                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
 432                     !blk_barrier_preflush(rq))
 433                         rq = blk_start_pre_flush(q, rq);
 434         }
 435
 436         return rq;
 437 }
 438
 439 struct request *elv_next_request(request_queue_t *q)
 440 {
 441         struct request *rq;
 442         int ret;
 443
 444         while ((rq = __elv_next_request(q)) != NULL) {
 445                 if (!(rq->flags & REQ_STARTED)) {
 446                         elevator_t *e = q->elevator;
 447
 448                         /*
 449                          * This is the first time the device driver
 450                          * sees this request (possibly after
 451                          * requeueing).  Notify IO scheduler.
 452                          */
 453                         if (blk_sorted_rq(rq) &&
 454                             e->ops->elevator_activate_req_fn)
 455                                 e->ops->elevator_activate_req_fn(q, rq);
 456
 457                         /*
 458                          * just mark as started even if we don't start
 459                          * it, a request that has been delayed should
 460                          * not be passed by new incoming requests
 461                          */
 462                         rq->flags |= REQ_STARTED;
 463                 }
 464
 465                 if (rq == q->last_merge)
 466                         q->last_merge = NULL;
 467
 468                 if (!q->boundary_rq || q->boundary_rq == rq) {
 469                         q->end_sector = rq_end_sector(rq);
 470                         q->boundary_rq = NULL;
 471                 }
 472
 473                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 474                         break;
 475
 476                 ret = q->prep_rq_fn(q, rq);
 477                 if (ret == BLKPREP_OK) {
 478                         break;
 479                 } else if (ret == BLKPREP_DEFER) {
 480                         /*
 481                          * the request may have been (partially) prepped.
 482                          * we need to keep this request in the front to
 483                          * avoid resource deadlock.  REQ_STARTED will
 484                          * prevent other fs requests from passing this one.
 485                          */
 486                         rq = NULL;
 487                         break;
 488                 } else if (ret == BLKPREP_KILL) {
 489                         int nr_bytes = rq->hard_nr_sectors << 9;
 490
 491                         if (!nr_bytes)
 492                                 nr_bytes = rq->data_len;
 493
 494                         blkdev_dequeue_request(rq);
 495                         rq->flags |= REQ_QUIET;
 496                         end_that_request_chunk(rq, 0, nr_bytes);
 497                         end_that_request_last(rq);
 498                 } else {
 499                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 500                                                                 ret);
 501                         break;
 502                 }
 503         }
 504
 505         return rq;
 506 }
 507
 508 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 509 {
 510         BUG_ON(list_empty(&rq->queuelist));
 511
 512         list_del_init(&rq->queuelist);
 513
 514         /*
 515          * the time frame between a request being removed from the lists
 516          * and to it is freed is accounted as io that is in progress at
 517          * the driver side.
 518          */
 519         if (blk_account_rq(rq))
 520                 q->in_flight++;
 521
 522         /*
 523          * the main clearing point for q->last_merge is on retrieval of
 524          * request by driver (it calls elv_next_request()), but it _can_
 525          * also happen here if a request is added to the queue but later
 526          * deleted without ever being given to driver (merged with another
 527          * request).
 528          */
 529         if (rq == q->last_merge)
 530                 q->last_merge = NULL;
 531 }
 532
 533 int elv_queue_empty(request_queue_t *q)
 534 {
 535         elevator_t *e = q->elevator;
 536
 537         if (!list_empty(&q->queue_head))
 538                 return 0;
 539
 540         if (e->ops->elevator_queue_empty_fn)
 541                 return e->ops->elevator_queue_empty_fn(q);
 542
 543         return 1;
 544 }
 545
 546 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 547 {
 548         struct list_head *next;
 549
 550         elevator_t *e = q->elevator;
 551
 552         if (e->ops->elevator_latter_req_fn)
 553                 return e->ops->elevator_latter_req_fn(q, rq);
 554
 555         next = rq->queuelist.next;
 556         if (next != &q->queue_head && next != &rq->queuelist)
 557                 return list_entry_rq(next);
 558
 559         return NULL;
 560 }
 561
 562 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 563 {
 564         struct list_head *prev;
 565
 566         elevator_t *e = q->elevator;
 567
 568         if (e->ops->elevator_former_req_fn)
 569                 return e->ops->elevator_former_req_fn(q, rq);
 570
 571         prev = rq->queuelist.prev;
 572         if (prev != &q->queue_head && prev != &rq->queuelist)
 573                 return list_entry_rq(prev);
 574
 575         return NULL;
 576 }
 577
 578 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 579                     int gfp_mask)
 580 {
 581         elevator_t *e = q->elevator;
 582
 583         if (e->ops->elevator_set_req_fn)
 584                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
 585
 586         rq->elevator_private = NULL;
 587         return 0;
 588 }
 589
 590 void elv_put_request(request_queue_t *q, struct request *rq)
 591 {
 592         elevator_t *e = q->elevator;
 593
 594         if (e->ops->elevator_put_req_fn)
 595                 e->ops->elevator_put_req_fn(q, rq);
 596 }
 597
 598 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
 599 {
 600         elevator_t *e = q->elevator;
 601
 602         if (e->ops->elevator_may_queue_fn)
 603                 return e->ops->elevator_may_queue_fn(q, rw, bio);
 604
 605         return ELV_MQUEUE_MAY;
 606 }
 607
 608 void elv_completed_request(request_queue_t *q, struct request *rq)
 609 {
 610         elevator_t *e = q->elevator;
 611
 612         /*
 613          * request is released from the driver, io must be done
 614          */
 615         if (blk_account_rq(rq)) {
 616                 q->in_flight--;
 617                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 618                         e->ops->elevator_completed_req_fn(q, rq);
 619         }
 620 }
 621
 622 int elv_register_queue(struct request_queue *q)
 623 {
 624         elevator_t *e = q->elevator;
 625
 626         e->kobj.parent = kobject_get(&q->kobj);
 627         if (!e->kobj.parent)
 628                 return -EBUSY;
 629
 630         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 631         e->kobj.ktype = e->elevator_type->elevator_ktype;
 632
 633         return kobject_register(&e->kobj);
 634 }
 635
 636 void elv_unregister_queue(struct request_queue *q)
 637 {
 638         if (q) {
 639                 elevator_t *e = q->elevator;
 640                 kobject_unregister(&e->kobj);
 641                 kobject_put(&q->kobj);
 642         }
 643 }
 644
 645 int elv_register(struct elevator_type *e)
 646 {
 647         spin_lock_irq(&elv_list_lock);
 648         if (elevator_find(e->elevator_name))
 649                 BUG();
 650         list_add_tail(&e->list, &elv_list);
 651         spin_unlock_irq(&elv_list_lock);
 652
 653         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 654         if (!strcmp(e->elevator_name, chosen_elevator))
 655                 printk(" (default)");
 656         printk("\n");
 657         return 0;
 658 }
 659 EXPORT_SYMBOL_GPL(elv_register);
 660
 661 void elv_unregister(struct elevator_type *e)
 662 {
 663         spin_lock_irq(&elv_list_lock);
 664         list_del_init(&e->list);
 665         spin_unlock_irq(&elv_list_lock);
 666 }
 667 EXPORT_SYMBOL_GPL(elv_unregister);
 668
 669 /*
 670  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 671  * we don't free the old io scheduler, before we have allocated what we
 672  * need for the new one. this way we have a chance of going back to the old
 673  * one, if the new one fails init for some reason. we also do an intermediate
 674  * switch to noop to ensure safety with stack-allocated requests, since they
 675  * don't originate from the block layer allocator. noop is safe here, because
 676  * it never needs to touch the elevator itself for completion events. DRAIN
 677  * flags will make sure we don't touch it for additions either.
 678  */
 679 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
 680 {
 681         elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
 682         struct elevator_type *noop_elevator = NULL;
 683         elevator_t *old_elevator;
 684
 685         if (!e)
 686                 goto error;
 687
 688         /*
 689          * first step, drain requests from the block freelist
 690          */
 691         blk_wait_queue_drained(q, 0);
 692
 693         /*
 694          * unregister old elevator data
 695          */
 696         elv_unregister_queue(q);
 697         old_elevator = q->elevator;
 698
 699         /*
 700          * next step, switch to noop since it uses no private rq structures
 701          * and doesn't allocate any memory for anything. then wait for any
 702          * non-fs requests in-flight
 703          */
 704         noop_elevator = elevator_get("noop");
 705         spin_lock_irq(q->queue_lock);
 706         elevator_attach(q, noop_elevator, e);
 707         spin_unlock_irq(q->queue_lock);
 708
 709         blk_wait_queue_drained(q, 1);
 710
 711         /*
 712          * attach and start new elevator
 713          */
 714         if (elevator_attach(q, new_e, e))
 715                 goto fail;
 716
 717         if (elv_register_queue(q))
 718                 goto fail_register;
 719
 720         /*
 721          * finally exit old elevator and start queue again
 722          */
 723         elevator_exit(old_elevator);
 724         blk_finish_queue_drain(q);
 725         elevator_put(noop_elevator);
 726         return;
 727
 728 fail_register:
 729         /*
 730          * switch failed, exit the new io scheduler and reattach the old
 731          * one again (along with re-adding the sysfs dir)
 732          */
 733         elevator_exit(e);
 734 fail:
 735         q->elevator = old_elevator;
 736         elv_register_queue(q);
 737         blk_finish_queue_drain(q);
 738 error:
 739         if (noop_elevator)
 740                 elevator_put(noop_elevator);
 741         elevator_put(new_e);
 742         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
 743 }
 744
 745 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
 746 {
 747         char elevator_name[ELV_NAME_MAX];
 748         struct elevator_type *e;
 749
 750         memset(elevator_name, 0, sizeof(elevator_name));
 751         strncpy(elevator_name, name, sizeof(elevator_name));
 752
 753         if (elevator_name[strlen(elevator_name) - 1] == '\n')
 754                 elevator_name[strlen(elevator_name) - 1] = '\0';
 755
 756         e = elevator_get(elevator_name);
 757         if (!e) {
 758                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 759                 return -EINVAL;
 760         }
 761
 762         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
 763                 return count;
 764
 765         elevator_switch(q, e);
 766         return count;
 767 }
 768
 769 ssize_t elv_iosched_show(request_queue_t *q, char *name)
 770 {
 771         elevator_t *e = q->elevator;
 772         struct elevator_type *elv = e->elevator_type;
 773         struct list_head *entry;
 774         int len = 0;
 775
 776         spin_lock_irq(q->queue_lock);
 777         list_for_each(entry, &elv_list) {
 778                 struct elevator_type *__e;
 779
 780                 __e = list_entry(entry, struct elevator_type, list);
 781                 if (!strcmp(elv->elevator_name, __e->elevator_name))
 782                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 783                 else
 784                         len += sprintf(name+len, "%s ", __e->elevator_name);
 785         }
 786         spin_unlock_irq(q->queue_lock);
 787
 788         len += sprintf(len+name, "\n");
 789         return len;
 790 }
 791
 792 EXPORT_SYMBOL(elv_dispatch_sort);
 793 EXPORT_SYMBOL(elv_add_request);
 794 EXPORT_SYMBOL(__elv_add_request);
 795 EXPORT_SYMBOL(elv_requeue_request);
 796 EXPORT_SYMBOL(elv_next_request);
 797 EXPORT_SYMBOL(elv_dequeue_request);
 798 EXPORT_SYMBOL(elv_queue_empty);
 799 EXPORT_SYMBOL(elv_completed_request);
 800 EXPORT_SYMBOL(elevator_exit);
 801 EXPORT_SYMBOL(elevator_init);