block/elevator.c

   1 /*
   2  *  Block device elevator/IO-scheduler.
   3  *
   4  *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
   5  *
   6  * 30042000 Jens Axboe <axboe@suse.de> :
   7  *
   8  * Split the elevator a bit so that it is possible to choose a different
   9  * one or even write a new "plug in". There are three pieces:
  10  * - elevator_fn, inserts a new request in the queue list
  11  * - elevator_merge_fn, decides whether a new buffer can be merged with
  12  *   an existing request
  13  * - elevator_dequeue_fn, called when a request is taken off the active list
  14  *
  15  * 20082000 Dave Jones <davej@suse.de> :
  16  * Removed tests for max-bomb-segments, which was breaking elvtune
  17  *  when run without -bN
  18  *
  19  * Jens:
  20  * - Rework again to work with bio instead of buffer_heads
  21  * - loose bi_dev comparisons, partition handling is right now
  22  * - completely modularize elevator setup and teardown
  23  *
  24  */
  25 #include <linux/kernel.h>
  26 #include <linux/fs.h>
  27 #include <linux/blkdev.h>
  28 #include <linux/elevator.h>
  29 #include <linux/bio.h>
  30 #include <linux/config.h>
  31 #include <linux/module.h>
  32 #include <linux/slab.h>
  33 #include <linux/init.h>
  34 #include <linux/compiler.h>
  35 #include <linux/delay.h>
  36
  37 #include <asm/uaccess.h>
  38
  39 static DEFINE_SPINLOCK(elv_list_lock);
  40 static LIST_HEAD(elv_list);
  41
  42 /*
  43  * can we safely merge with this request?
  44  */
  45 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  46 {
  47         if (!rq_mergeable(rq))
  48                 return 0;
  49
  50         /*
  51          * different data direction or already started, don't merge
  52          */
  53         if (bio_data_dir(bio) != rq_data_dir(rq))
  54                 return 0;
  55
  56         /*
  57          * same device and no special stuff set, merge is ok
  58          */
  59         if (rq->rq_disk == bio->bi_bdev->bd_disk &&
  60             !rq->waiting && !rq->special)
  61                 return 1;
  62
  63         return 0;
  64 }
  65 EXPORT_SYMBOL(elv_rq_merge_ok);
  66
  67 inline int elv_try_merge(struct request *__rq, struct bio *bio)
  68 {
  69         int ret = ELEVATOR_NO_MERGE;
  70
  71         /*
  72          * we can merge and sequence is ok, check if it's possible
  73          */
  74         if (elv_rq_merge_ok(__rq, bio)) {
  75                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
  76                         ret = ELEVATOR_BACK_MERGE;
  77                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
  78                         ret = ELEVATOR_FRONT_MERGE;
  79         }
  80
  81         return ret;
  82 }
  83 EXPORT_SYMBOL(elv_try_merge);
  84
  85 static struct elevator_type *elevator_find(const char *name)
  86 {
  87         struct elevator_type *e = NULL;
  88         struct list_head *entry;
  89
  90         list_for_each(entry, &elv_list) {
  91                 struct elevator_type *__e;
  92
  93                 __e = list_entry(entry, struct elevator_type, list);
  94
  95                 if (!strcmp(__e->elevator_name, name)) {
  96                         e = __e;
  97                         break;
  98                 }
  99         }
 100
 101         return e;
 102 }
 103
 104 static void elevator_put(struct elevator_type *e)
 105 {
 106         module_put(e->elevator_owner);
 107 }
 108
 109 static struct elevator_type *elevator_get(const char *name)
 110 {
 111         struct elevator_type *e;
 112
 113         spin_lock_irq(&elv_list_lock);
 114
 115         e = elevator_find(name);
 116         if (e && !try_module_get(e->elevator_owner))
 117                 e = NULL;
 118
 119         spin_unlock_irq(&elv_list_lock);
 120
 121         return e;
 122 }
 123
 124 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
 125                            struct elevator_queue *eq)
 126 {
 127         int ret = 0;
 128
 129         memset(eq, 0, sizeof(*eq));
 130         eq->ops = &e->ops;
 131         eq->elevator_type = e;
 132
 133         q->elevator = eq;
 134
 135         if (eq->ops->elevator_init_fn)
 136                 ret = eq->ops->elevator_init_fn(q, eq);
 137
 138         return ret;
 139 }
 140
 141 static char chosen_elevator[16];
 142
 143 static void elevator_setup_default(void)
 144 {
 145         struct elevator_type *e;
 146
 147         /*
 148          * If default has not been set, use the compiled-in selection.
 149          */
 150         if (!chosen_elevator[0])
 151                 strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
 152
 153         /*
 154          * If the given scheduler is not available, fall back to no-op.
 155          */
 156         if ((e = elevator_find(chosen_elevator)))
 157                 elevator_put(e);
 158         else
 159                 strcpy(chosen_elevator, "noop");
 160 }
 161
 162 static int __init elevator_setup(char *str)
 163 {
 164         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 165         return 0;
 166 }
 167
 168 __setup("elevator=", elevator_setup);
 169
 170 int elevator_init(request_queue_t *q, char *name)
 171 {
 172         struct elevator_type *e = NULL;
 173         struct elevator_queue *eq;
 174         int ret = 0;
 175
 176         INIT_LIST_HEAD(&q->queue_head);
 177         q->last_merge = NULL;
 178         q->end_sector = 0;
 179         q->boundary_rq = NULL;
 180
 181         elevator_setup_default();
 182
 183         if (!name)
 184                 name = chosen_elevator;
 185
 186         e = elevator_get(name);
 187         if (!e)
 188                 return -EINVAL;
 189
 190         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
 191         if (!eq) {
 192                 elevator_put(e);
 193                 return -ENOMEM;
 194         }
 195
 196         ret = elevator_attach(q, e, eq);
 197         if (ret) {
 198                 kfree(eq);
 199                 elevator_put(e);
 200         }
 201
 202         return ret;
 203 }
 204
 205 void elevator_exit(elevator_t *e)
 206 {
 207         if (e->ops->elevator_exit_fn)
 208                 e->ops->elevator_exit_fn(e);
 209
 210         elevator_put(e->elevator_type);
 211         e->elevator_type = NULL;
 212         kfree(e);
 213 }
 214
 215 /*
 216  * Insert rq into dispatch queue of q.  Queue lock must be held on
 217  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 218  * appended to the dispatch queue.  To be used by specific elevators.
 219  */
 220 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 221 {
 222         sector_t boundary;
 223         struct list_head *entry;
 224
 225         if (q->last_merge == rq)
 226                 q->last_merge = NULL;
 227         q->nr_sorted--;
 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         q->nr_sorted--;
 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 static void elv_drain_elevator(request_queue_t *q)
 319 {
 320         static int printed;
 321         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 322                 ;
 323         if (q->nr_sorted == 0)
 324                 return;
 325         if (printed++ < 10) {
 326                 printk(KERN_ERR "%s: forced dispatching is broken "
 327                        "(nr_sorted=%u), please report this\n",
 328                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 329         }
 330 }
 331
 332 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 333                        int plug)
 334 {
 335         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 336                 /*
 337                  * barriers implicitly indicate back insertion
 338                  */
 339                 if (where == ELEVATOR_INSERT_SORT)
 340                         where = ELEVATOR_INSERT_BACK;
 341
 342                 /*
 343                  * this request is scheduling boundary, update end_sector
 344                  */
 345                 if (blk_fs_request(rq)) {
 346                         q->end_sector = rq_end_sector(rq);
 347                         q->boundary_rq = rq;
 348                 }
 349         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
 350                 where = ELEVATOR_INSERT_BACK;
 351
 352         if (plug)
 353                 blk_plug_device(q);
 354
 355         rq->q = q;
 356
 357         switch (where) {
 358         case ELEVATOR_INSERT_FRONT:
 359                 rq->flags |= REQ_SOFTBARRIER;
 360
 361                 list_add(&rq->queuelist, &q->queue_head);
 362                 break;
 363
 364         case ELEVATOR_INSERT_BACK:
 365                 rq->flags |= REQ_SOFTBARRIER;
 366                 elv_drain_elevator(q);
 367                 list_add_tail(&rq->queuelist, &q->queue_head);
 368                 /*
 369                  * We kick the queue here for the following reasons.
 370                  * - The elevator might have returned NULL previously
 371                  *   to delay requests and returned them now.  As the
 372                  *   queue wasn't empty before this request, ll_rw_blk
 373                  *   won't run the queue on return, resulting in hang.
 374                  * - Usually, back inserted requests won't be merged
 375                  *   with anything.  There's no point in delaying queue
 376                  *   processing.
 377                  */
 378                 blk_remove_plug(q);
 379                 q->request_fn(q);
 380                 break;
 381
 382         case ELEVATOR_INSERT_SORT:
 383                 BUG_ON(!blk_fs_request(rq));
 384                 rq->flags |= REQ_SORTED;
 385                 q->nr_sorted++;
 386                 if (q->last_merge == NULL && rq_mergeable(rq))
 387                         q->last_merge = rq;
 388                 /*
 389                  * Some ioscheds (cfq) run q->request_fn directly, so
 390                  * rq cannot be accessed after calling
 391                  * elevator_add_req_fn.
 392                  */
 393                 q->elevator->ops->elevator_add_req_fn(q, rq);
 394                 break;
 395
 396         default:
 397                 printk(KERN_ERR "%s: bad insertion point %d\n",
 398                        __FUNCTION__, where);
 399                 BUG();
 400         }
 401
 402         if (blk_queue_plugged(q)) {
 403                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 404                         - q->in_flight;
 405
 406                 if (nrq >= q->unplug_thresh)
 407                         __generic_unplug_device(q);
 408         }
 409 }
 410
 411 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 412                      int plug)
 413 {
 414         unsigned long flags;
 415
 416         spin_lock_irqsave(q->queue_lock, flags);
 417         __elv_add_request(q, rq, where, plug);
 418         spin_unlock_irqrestore(q->queue_lock, flags);
 419 }
 420
 421 static inline struct request *__elv_next_request(request_queue_t *q)
 422 {
 423         struct request *rq;
 424
 425         if (unlikely(list_empty(&q->queue_head) &&
 426                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
 427                 return NULL;
 428
 429         rq = list_entry_rq(q->queue_head.next);
 430
 431         /*
 432          * if this is a barrier write and the device has to issue a
 433          * flush sequence to support it, check how far we are
 434          */
 435         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
 436                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
 437
 438                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
 439                     !blk_barrier_preflush(rq))
 440                         rq = blk_start_pre_flush(q, rq);
 441         }
 442
 443         return rq;
 444 }
 445
 446 struct request *elv_next_request(request_queue_t *q)
 447 {
 448         struct request *rq;
 449         int ret;
 450
 451         while ((rq = __elv_next_request(q)) != NULL) {
 452                 if (!(rq->flags & REQ_STARTED)) {
 453                         elevator_t *e = q->elevator;
 454
 455                         /*
 456                          * This is the first time the device driver
 457                          * sees this request (possibly after
 458                          * requeueing).  Notify IO scheduler.
 459                          */
 460                         if (blk_sorted_rq(rq) &&
 461                             e->ops->elevator_activate_req_fn)
 462                                 e->ops->elevator_activate_req_fn(q, rq);
 463
 464                         /*
 465                          * just mark as started even if we don't start
 466                          * it, a request that has been delayed should
 467                          * not be passed by new incoming requests
 468                          */
 469                         rq->flags |= REQ_STARTED;
 470                 }
 471
 472                 if (!q->boundary_rq || q->boundary_rq == rq) {
 473                         q->end_sector = rq_end_sector(rq);
 474                         q->boundary_rq = NULL;
 475                 }
 476
 477                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 478                         break;
 479
 480                 ret = q->prep_rq_fn(q, rq);
 481                 if (ret == BLKPREP_OK) {
 482                         break;
 483                 } else if (ret == BLKPREP_DEFER) {
 484                         /*
 485                          * the request may have been (partially) prepped.
 486                          * we need to keep this request in the front to
 487                          * avoid resource deadlock.  REQ_STARTED will
 488                          * prevent other fs requests from passing this one.
 489                          */
 490                         rq = NULL;
 491                         break;
 492                 } else if (ret == BLKPREP_KILL) {
 493                         int nr_bytes = rq->hard_nr_sectors << 9;
 494
 495                         if (!nr_bytes)
 496                                 nr_bytes = rq->data_len;
 497
 498                         blkdev_dequeue_request(rq);
 499                         rq->flags |= REQ_QUIET;
 500                         end_that_request_chunk(rq, 0, nr_bytes);
 501                         end_that_request_last(rq);
 502                 } else {
 503                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 504                                                                 ret);
 505                         break;
 506                 }
 507         }
 508
 509         return rq;
 510 }
 511
 512 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 513 {
 514         BUG_ON(list_empty(&rq->queuelist));
 515
 516         list_del_init(&rq->queuelist);
 517
 518         /*
 519          * the time frame between a request being removed from the lists
 520          * and to it is freed is accounted as io that is in progress at
 521          * the driver side.
 522          */
 523         if (blk_account_rq(rq))
 524                 q->in_flight++;
 525 }
 526
 527 int elv_queue_empty(request_queue_t *q)
 528 {
 529         elevator_t *e = q->elevator;
 530
 531         if (!list_empty(&q->queue_head))
 532                 return 0;
 533
 534         if (e->ops->elevator_queue_empty_fn)
 535                 return e->ops->elevator_queue_empty_fn(q);
 536
 537         return 1;
 538 }
 539
 540 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 541 {
 542         elevator_t *e = q->elevator;
 543
 544         if (e->ops->elevator_latter_req_fn)
 545                 return e->ops->elevator_latter_req_fn(q, rq);
 546         return NULL;
 547 }
 548
 549 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 550 {
 551         elevator_t *e = q->elevator;
 552
 553         if (e->ops->elevator_former_req_fn)
 554                 return e->ops->elevator_former_req_fn(q, rq);
 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         elv_drain_elevator(q);
 695
 696         while (q->rq.elvpriv) {
 697                 blk_remove_plug(q);
 698                 q->request_fn(q);
 699                 spin_unlock_irq(q->queue_lock);
 700                 msleep(10);
 701                 spin_lock_irq(q->queue_lock);
 702                 elv_drain_elevator(q);
 703         }
 704
 705         spin_unlock_irq(q->queue_lock);
 706
 707         /*
 708          * unregister old elevator data
 709          */
 710         elv_unregister_queue(q);
 711         old_elevator = q->elevator;
 712
 713         /*
 714          * attach and start new elevator
 715          */
 716         if (elevator_attach(q, new_e, e))
 717                 goto fail;
 718
 719         if (elv_register_queue(q))
 720                 goto fail_register;
 721
 722         /*
 723          * finally exit old elevator and turn off BYPASS.
 724          */
 725         elevator_exit(old_elevator);
 726         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 727         return;
 728
 729 fail_register:
 730         /*
 731          * switch failed, exit the new io scheduler and reattach the old
 732          * one again (along with re-adding the sysfs dir)
 733          */
 734         elevator_exit(e);
 735         e = NULL;
 736 fail:
 737         q->elevator = old_elevator;
 738         elv_register_queue(q);
 739         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 740         kfree(e);
 741 error:
 742         elevator_put(new_e);
 743         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
 744 }
 745
 746 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
 747 {
 748         char elevator_name[ELV_NAME_MAX];
 749         size_t len;
 750         struct elevator_type *e;
 751
 752         elevator_name[sizeof(elevator_name) - 1] = '\0';
 753         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
 754         len = strlen(elevator_name);
 755
 756         if (len && elevator_name[len - 1] == '\n')
 757                 elevator_name[len - 1] = '\0';
 758
 759         e = elevator_get(elevator_name);
 760         if (!e) {
 761                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 762                 return -EINVAL;
 763         }
 764
 765         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
 766                 elevator_put(e);
 767                 return count;
 768         }
 769
 770         elevator_switch(q, e);
 771         return count;
 772 }
 773
 774 ssize_t elv_iosched_show(request_queue_t *q, char *name)
 775 {
 776         elevator_t *e = q->elevator;
 777         struct elevator_type *elv = e->elevator_type;
 778         struct list_head *entry;
 779         int len = 0;
 780
 781         spin_lock_irq(q->queue_lock);
 782         list_for_each(entry, &elv_list) {
 783                 struct elevator_type *__e;
 784
 785                 __e = list_entry(entry, struct elevator_type, list);
 786                 if (!strcmp(elv->elevator_name, __e->elevator_name))
 787                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 788                 else
 789                         len += sprintf(name+len, "%s ", __e->elevator_name);
 790         }
 791         spin_unlock_irq(q->queue_lock);
 792
 793         len += sprintf(len+name, "\n");
 794         return len;
 795 }
 796
 797 EXPORT_SYMBOL(elv_dispatch_sort);
 798 EXPORT_SYMBOL(elv_add_request);
 799 EXPORT_SYMBOL(__elv_add_request);
 800 EXPORT_SYMBOL(elv_requeue_request);
 801 EXPORT_SYMBOL(elv_next_request);
 802 EXPORT_SYMBOL(elv_dequeue_request);
 803 EXPORT_SYMBOL(elv_queue_empty);
 804 EXPORT_SYMBOL(elv_completed_request);
 805 EXPORT_SYMBOL(elevator_exit);
 806 EXPORT_SYMBOL(elevator_init);