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