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   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
 230         boundary = q->end_sector;
 231
 232         list_for_each_prev(entry, &q->queue_head) {
 233                 struct request *pos = list_entry_rq(entry);
 234
 235                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
 236                         break;
 237                 if (rq->sector >= boundary) {
 238                         if (pos->sector < boundary)
 239                                 continue;
 240                 } else {
 241                         if (pos->sector >= boundary)
 242                                 break;
 243                 }
 244                 if (rq->sector >= pos->sector)
 245                         break;
 246         }
 247
 248         list_add(&rq->queuelist, entry);
 249 }
 250
 251 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 252 {
 253         elevator_t *e = q->elevator;
 254         int ret;
 255
 256         if (q->last_merge) {
 257                 ret = elv_try_merge(q->last_merge, bio);
 258                 if (ret != ELEVATOR_NO_MERGE) {
 259                         *req = q->last_merge;
 260                         return ret;
 261                 }
 262         }
 263
 264         if (e->ops->elevator_merge_fn)
 265                 return e->ops->elevator_merge_fn(q, req, bio);
 266
 267         return ELEVATOR_NO_MERGE;
 268 }
 269
 270 void elv_merged_request(request_queue_t *q, struct request *rq)
 271 {
 272         elevator_t *e = q->elevator;
 273
 274         if (e->ops->elevator_merged_fn)
 275                 e->ops->elevator_merged_fn(q, rq);
 276
 277         q->last_merge = rq;
 278 }
 279
 280 void elv_merge_requests(request_queue_t *q, struct request *rq,
 281                              struct request *next)
 282 {
 283         elevator_t *e = q->elevator;
 284
 285         if (e->ops->elevator_merge_req_fn)
 286                 e->ops->elevator_merge_req_fn(q, rq, next);
 287
 288         q->last_merge = rq;
 289 }
 290
 291 void elv_requeue_request(request_queue_t *q, struct request *rq)
 292 {
 293         elevator_t *e = q->elevator;
 294
 295         /*
 296          * it already went through dequeue, we need to decrement the
 297          * in_flight count again
 298          */
 299         if (blk_account_rq(rq)) {
 300                 q->in_flight--;
 301                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
 302                         e->ops->elevator_deactivate_req_fn(q, rq);
 303         }
 304
 305         rq->flags &= ~REQ_STARTED;
 306
 307         /*
 308          * if this is the flush, requeue the original instead and drop the flush
 309          */
 310         if (rq->flags & REQ_BAR_FLUSH) {
 311                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
 312                 rq = rq->end_io_data;
 313         }
 314
 315         __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
 316 }
 317
 318 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 319                        int plug)
 320 {
 321         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 322                 /*
 323                  * barriers implicitly indicate back insertion
 324                  */
 325                 if (where == ELEVATOR_INSERT_SORT)
 326                         where = ELEVATOR_INSERT_BACK;
 327
 328                 /*
 329                  * this request is scheduling boundary, update end_sector
 330                  */
 331                 if (blk_fs_request(rq)) {
 332                         q->end_sector = rq_end_sector(rq);
 333                         q->boundary_rq = rq;
 334                 }
 335         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
 336                 where = ELEVATOR_INSERT_BACK;
 337
 338         if (plug)
 339                 blk_plug_device(q);
 340
 341         rq->q = q;
 342
 343         switch (where) {
 344         case ELEVATOR_INSERT_FRONT:
 345                 rq->flags |= REQ_SOFTBARRIER;
 346
 347                 list_add(&rq->queuelist, &q->queue_head);
 348                 break;
 349
 350         case ELEVATOR_INSERT_BACK:
 351                 rq->flags |= REQ_SOFTBARRIER;
 352
 353                 while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 354                         ;
 355                 list_add_tail(&rq->queuelist, &q->queue_head);
 356                 /*
 357                  * We kick the queue here for the following reasons.
 358                  * - The elevator might have returned NULL previously
 359                  *   to delay requests and returned them now.  As the
 360                  *   queue wasn't empty before this request, ll_rw_blk
 361                  *   won't run the queue on return, resulting in hang.
 362                  * - Usually, back inserted requests won't be merged
 363                  *   with anything.  There's no point in delaying queue
 364                  *   processing.
 365                  */
 366                 blk_remove_plug(q);
 367                 q->request_fn(q);
 368                 break;
 369
 370         case ELEVATOR_INSERT_SORT:
 371                 BUG_ON(!blk_fs_request(rq));
 372                 rq->flags |= REQ_SORTED;
 373                 if (q->last_merge == NULL && rq_mergeable(rq))
 374                         q->last_merge = rq;
 375                 /*
 376                  * Some ioscheds (cfq) run q->request_fn directly, so
 377                  * rq cannot be accessed after calling
 378                  * elevator_add_req_fn.
 379                  */
 380                 q->elevator->ops->elevator_add_req_fn(q, rq);
 381                 break;
 382
 383         default:
 384                 printk(KERN_ERR "%s: bad insertion point %d\n",
 385                        __FUNCTION__, where);
 386                 BUG();
 387         }
 388
 389         if (blk_queue_plugged(q)) {
 390                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 391                         - q->in_flight;
 392
 393                 if (nrq >= q->unplug_thresh)
 394                         __generic_unplug_device(q);
 395         }
 396 }
 397
 398 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 399                      int plug)
 400 {
 401         unsigned long flags;
 402
 403         spin_lock_irqsave(q->queue_lock, flags);
 404         __elv_add_request(q, rq, where, plug);
 405         spin_unlock_irqrestore(q->queue_lock, flags);
 406 }
 407
 408 static inline struct request *__elv_next_request(request_queue_t *q)
 409 {
 410         struct request *rq;
 411
 412         if (unlikely(list_empty(&q->queue_head) &&
 413                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
 414                 return NULL;
 415
 416         rq = list_entry_rq(q->queue_head.next);
 417
 418         /*
 419          * if this is a barrier write and the device has to issue a
 420          * flush sequence to support it, check how far we are
 421          */
 422         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
 423                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
 424
 425                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
 426                     !blk_barrier_preflush(rq))
 427                         rq = blk_start_pre_flush(q, rq);
 428         }
 429
 430         return rq;
 431 }
 432
 433 struct request *elv_next_request(request_queue_t *q)
 434 {
 435         struct request *rq;
 436         int ret;
 437
 438         while ((rq = __elv_next_request(q)) != NULL) {
 439                 if (!(rq->flags & REQ_STARTED)) {
 440                         elevator_t *e = q->elevator;
 441
 442                         /*
 443                          * This is the first time the device driver
 444                          * sees this request (possibly after
 445                          * requeueing).  Notify IO scheduler.
 446                          */
 447                         if (blk_sorted_rq(rq) &&
 448                             e->ops->elevator_activate_req_fn)
 449                                 e->ops->elevator_activate_req_fn(q, rq);
 450
 451                         /*
 452                          * just mark as started even if we don't start
 453                          * it, a request that has been delayed should
 454                          * not be passed by new incoming requests
 455                          */
 456                         rq->flags |= REQ_STARTED;
 457                 }
 458
 459                 if (!q->boundary_rq || q->boundary_rq == rq) {
 460                         q->end_sector = rq_end_sector(rq);
 461                         q->boundary_rq = NULL;
 462                 }
 463
 464                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 465                         break;
 466
 467                 ret = q->prep_rq_fn(q, rq);
 468                 if (ret == BLKPREP_OK) {
 469                         break;
 470                 } else if (ret == BLKPREP_DEFER) {
 471                         /*
 472                          * the request may have been (partially) prepped.
 473                          * we need to keep this request in the front to
 474                          * avoid resource deadlock.  REQ_STARTED will
 475                          * prevent other fs requests from passing this one.
 476                          */
 477                         rq = NULL;
 478                         break;
 479                 } else if (ret == BLKPREP_KILL) {
 480                         int nr_bytes = rq->hard_nr_sectors << 9;
 481
 482                         if (!nr_bytes)
 483                                 nr_bytes = rq->data_len;
 484
 485                         blkdev_dequeue_request(rq);
 486                         rq->flags |= REQ_QUIET;
 487                         end_that_request_chunk(rq, 0, nr_bytes);
 488                         end_that_request_last(rq);
 489                 } else {
 490                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 491                                                                 ret);
 492                         break;
 493                 }
 494         }
 495
 496         return rq;
 497 }
 498
 499 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 500 {
 501         BUG_ON(list_empty(&rq->queuelist));
 502
 503         list_del_init(&rq->queuelist);
 504
 505         /*
 506          * the time frame between a request being removed from the lists
 507          * and to it is freed is accounted as io that is in progress at
 508          * the driver side.
 509          */
 510         if (blk_account_rq(rq))
 511                 q->in_flight++;
 512 }
 513
 514 int elv_queue_empty(request_queue_t *q)
 515 {
 516         elevator_t *e = q->elevator;
 517
 518         if (!list_empty(&q->queue_head))
 519                 return 0;
 520
 521         if (e->ops->elevator_queue_empty_fn)
 522                 return e->ops->elevator_queue_empty_fn(q);
 523
 524         return 1;
 525 }
 526
 527 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 528 {
 529         struct list_head *next;
 530
 531         elevator_t *e = q->elevator;
 532
 533         if (e->ops->elevator_latter_req_fn)
 534                 return e->ops->elevator_latter_req_fn(q, rq);
 535
 536         next = rq->queuelist.next;
 537         if (next != &q->queue_head && next != &rq->queuelist)
 538                 return list_entry_rq(next);
 539
 540         return NULL;
 541 }
 542
 543 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 544 {
 545         struct list_head *prev;
 546
 547         elevator_t *e = q->elevator;
 548
 549         if (e->ops->elevator_former_req_fn)
 550                 return e->ops->elevator_former_req_fn(q, rq);
 551
 552         prev = rq->queuelist.prev;
 553         if (prev != &q->queue_head && prev != &rq->queuelist)
 554                 return list_entry_rq(prev);
 555
 556         return NULL;
 557 }
 558
 559 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 560                     gfp_t gfp_mask)
 561 {
 562         elevator_t *e = q->elevator;
 563
 564         if (e->ops->elevator_set_req_fn)
 565                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
 566
 567         rq->elevator_private = NULL;
 568         return 0;
 569 }
 570
 571 void elv_put_request(request_queue_t *q, struct request *rq)
 572 {
 573         elevator_t *e = q->elevator;
 574
 575         if (e->ops->elevator_put_req_fn)
 576                 e->ops->elevator_put_req_fn(q, rq);
 577 }
 578
 579 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
 580 {
 581         elevator_t *e = q->elevator;
 582
 583         if (e->ops->elevator_may_queue_fn)
 584                 return e->ops->elevator_may_queue_fn(q, rw, bio);
 585
 586         return ELV_MQUEUE_MAY;
 587 }
 588
 589 void elv_completed_request(request_queue_t *q, struct request *rq)
 590 {
 591         elevator_t *e = q->elevator;
 592
 593         /*
 594          * request is released from the driver, io must be done
 595          */
 596         if (blk_account_rq(rq)) {
 597                 q->in_flight--;
 598                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 599                         e->ops->elevator_completed_req_fn(q, rq);
 600         }
 601 }
 602
 603 int elv_register_queue(struct request_queue *q)
 604 {
 605         elevator_t *e = q->elevator;
 606
 607         e->kobj.parent = kobject_get(&q->kobj);
 608         if (!e->kobj.parent)
 609                 return -EBUSY;
 610
 611         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 612         e->kobj.ktype = e->elevator_type->elevator_ktype;
 613
 614         return kobject_register(&e->kobj);
 615 }
 616
 617 void elv_unregister_queue(struct request_queue *q)
 618 {
 619         if (q) {
 620                 elevator_t *e = q->elevator;
 621                 kobject_unregister(&e->kobj);
 622                 kobject_put(&q->kobj);
 623         }
 624 }
 625
 626 int elv_register(struct elevator_type *e)
 627 {
 628         spin_lock_irq(&elv_list_lock);
 629         if (elevator_find(e->elevator_name))
 630                 BUG();
 631         list_add_tail(&e->list, &elv_list);
 632         spin_unlock_irq(&elv_list_lock);
 633
 634         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 635         if (!strcmp(e->elevator_name, chosen_elevator))
 636                 printk(" (default)");
 637         printk("\n");
 638         return 0;
 639 }
 640 EXPORT_SYMBOL_GPL(elv_register);
 641
 642 void elv_unregister(struct elevator_type *e)
 643 {
 644         struct task_struct *g, *p;
 645
 646         /*
 647          * Iterate every thread in the process to remove the io contexts.
 648          */
 649         read_lock(&tasklist_lock);
 650         do_each_thread(g, p) {
 651                 struct io_context *ioc = p->io_context;
 652                 if (ioc && ioc->cic) {
 653                         ioc->cic->exit(ioc->cic);
 654                         ioc->cic->dtor(ioc->cic);
 655                         ioc->cic = NULL;
 656                 }
 657                 if (ioc && ioc->aic) {
 658                         ioc->aic->exit(ioc->aic);
 659                         ioc->aic->dtor(ioc->aic);
 660                         ioc->aic = NULL;
 661                 }
 662         } while_each_thread(g, p);
 663         read_unlock(&tasklist_lock);
 664
 665         spin_lock_irq(&elv_list_lock);
 666         list_del_init(&e->list);
 667         spin_unlock_irq(&elv_list_lock);
 668 }
 669 EXPORT_SYMBOL_GPL(elv_unregister);
 670
 671 /*
 672  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 673  * we don't free the old io scheduler, before we have allocated what we
 674  * need for the new one. this way we have a chance of going back to the old
 675  * one, if the new one fails init for some reason.
 676  */
 677 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
 678 {
 679         elevator_t *old_elevator, *e;
 680
 681         /*
 682          * Allocate new elevator
 683          */
 684         e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
 685         if (!e)
 686                 goto error;
 687
 688         /*
 689          * Turn on BYPASS and drain all requests w/ elevator private data
 690          */
 691         spin_lock_irq(q->queue_lock);
 692
 693         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 694
 695         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 696                 ;
 697
 698         while (q->rq.elvpriv) {
 699                 spin_unlock_irq(q->queue_lock);
 700                 msleep(10);
 701                 spin_lock_irq(q->queue_lock);
 702         }
 703
 704         spin_unlock_irq(q->queue_lock);
 705
 706         /*
 707          * unregister old elevator data
 708          */
 709         elv_unregister_queue(q);
 710         old_elevator = q->elevator;
 711
 712         /*
 713          * attach and start new elevator
 714          */
 715         if (elevator_attach(q, new_e, e))
 716                 goto fail;
 717
 718         if (elv_register_queue(q))
 719                 goto fail_register;
 720
 721         /*
 722          * finally exit old elevator and turn off BYPASS.
 723          */
 724         elevator_exit(old_elevator);
 725         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 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         e = NULL;
 735 fail:
 736         q->elevator = old_elevator;
 737         elv_register_queue(q);
 738         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 739         kfree(e);
 740 error:
 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                 elevator_put(e);
 764                 return count;
 765         }
 766
 767         elevator_switch(q, e);
 768         return count;
 769 }
 770
 771 ssize_t elv_iosched_show(request_queue_t *q, char *name)
 772 {
 773         elevator_t *e = q->elevator;
 774         struct elevator_type *elv = e->elevator_type;
 775         struct list_head *entry;
 776         int len = 0;
 777
 778         spin_lock_irq(q->queue_lock);
 779         list_for_each(entry, &elv_list) {
 780                 struct elevator_type *__e;
 781
 782                 __e = list_entry(entry, struct elevator_type, list);
 783                 if (!strcmp(elv->elevator_name, __e->elevator_name))
 784                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 785                 else
 786                         len += sprintf(name+len, "%s ", __e->elevator_name);
 787         }
 788         spin_unlock_irq(q->queue_lock);
 789
 790         len += sprintf(len+name, "\n");
 791         return len;
 792 }
 793
 794 EXPORT_SYMBOL(elv_dispatch_sort);
 795 EXPORT_SYMBOL(elv_add_request);
 796 EXPORT_SYMBOL(__elv_add_request);
 797 EXPORT_SYMBOL(elv_requeue_request);
 798 EXPORT_SYMBOL(elv_next_request);
 799 EXPORT_SYMBOL(elv_dequeue_request);
 800 EXPORT_SYMBOL(elv_queue_empty);
 801 EXPORT_SYMBOL(elv_completed_request);
 802 EXPORT_SYMBOL(elevator_exit);
 803 EXPORT_SYMBOL(elevator_init);