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 #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          * check if default is set and exists
 151          */
 152         if (chosen_elevator[0] && (e = elevator_get(chosen_elevator))) {
 153                 elevator_put(e);
 154                 return;
 155         }
 156
 157 #if defined(CONFIG_IOSCHED_AS)
 158         strcpy(chosen_elevator, "anticipatory");
 159 #elif defined(CONFIG_IOSCHED_DEADLINE)
 160         strcpy(chosen_elevator, "deadline");
 161 #elif defined(CONFIG_IOSCHED_CFQ)
 162         strcpy(chosen_elevator, "cfq");
 163 #elif defined(CONFIG_IOSCHED_NOOP)
 164         strcpy(chosen_elevator, "noop");
 165 #else
 166 #error "You must build at least 1 IO scheduler into the kernel"
 167 #endif
 168 }
 169
 170 static int __init elevator_setup(char *str)
 171 {
 172         strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 173         return 0;
 174 }
 175
 176 __setup("elevator=", elevator_setup);
 177
 178 int elevator_init(request_queue_t *q, char *name)
 179 {
 180         struct elevator_type *e = NULL;
 181         struct elevator_queue *eq;
 182         int ret = 0;
 183
 184         INIT_LIST_HEAD(&q->queue_head);
 185         q->last_merge = NULL;
 186         q->end_sector = 0;
 187         q->boundary_rq = NULL;
 188
 189         elevator_setup_default();
 190
 191         if (!name)
 192                 name = chosen_elevator;
 193
 194         e = elevator_get(name);
 195         if (!e)
 196                 return -EINVAL;
 197
 198         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
 199         if (!eq) {
 200                 elevator_put(e->elevator_type);
 201                 return -ENOMEM;
 202         }
 203
 204         ret = elevator_attach(q, e, eq);
 205         if (ret) {
 206                 kfree(eq);
 207                 elevator_put(e->elevator_type);
 208         }
 209
 210         return ret;
 211 }
 212
 213 void elevator_exit(elevator_t *e)
 214 {
 215         if (e->ops->elevator_exit_fn)
 216                 e->ops->elevator_exit_fn(e);
 217
 218         elevator_put(e->elevator_type);
 219         e->elevator_type = NULL;
 220         kfree(e);
 221 }
 222
 223 /*
 224  * Insert rq into dispatch queue of q.  Queue lock must be held on
 225  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 226  * appended to the dispatch queue.  To be used by specific elevators.
 227  */
 228 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 229 {
 230         sector_t boundary;
 231         struct list_head *entry;
 232
 233         if (q->last_merge == rq)
 234                 q->last_merge = NULL;
 235
 236         boundary = q->end_sector;
 237
 238         list_for_each_prev(entry, &q->queue_head) {
 239                 struct request *pos = list_entry_rq(entry);
 240
 241                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
 242                         break;
 243                 if (rq->sector >= boundary) {
 244                         if (pos->sector < boundary)
 245                                 continue;
 246                 } else {
 247                         if (pos->sector >= boundary)
 248                                 break;
 249                 }
 250                 if (rq->sector >= pos->sector)
 251                         break;
 252         }
 253
 254         list_add(&rq->queuelist, entry);
 255 }
 256
 257 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 258 {
 259         elevator_t *e = q->elevator;
 260         int ret;
 261
 262         if (q->last_merge) {
 263                 ret = elv_try_merge(q->last_merge, bio);
 264                 if (ret != ELEVATOR_NO_MERGE) {
 265                         *req = q->last_merge;
 266                         return ret;
 267                 }
 268         }
 269
 270         if (e->ops->elevator_merge_fn)
 271                 return e->ops->elevator_merge_fn(q, req, bio);
 272
 273         return ELEVATOR_NO_MERGE;
 274 }
 275
 276 void elv_merged_request(request_queue_t *q, struct request *rq)
 277 {
 278         elevator_t *e = q->elevator;
 279
 280         if (e->ops->elevator_merged_fn)
 281                 e->ops->elevator_merged_fn(q, rq);
 282
 283         q->last_merge = rq;
 284 }
 285
 286 void elv_merge_requests(request_queue_t *q, struct request *rq,
 287                              struct request *next)
 288 {
 289         elevator_t *e = q->elevator;
 290
 291         if (e->ops->elevator_merge_req_fn)
 292                 e->ops->elevator_merge_req_fn(q, rq, next);
 293
 294         q->last_merge = rq;
 295 }
 296
 297 void elv_requeue_request(request_queue_t *q, struct request *rq)
 298 {
 299         elevator_t *e = q->elevator;
 300
 301         /*
 302          * it already went through dequeue, we need to decrement the
 303          * in_flight count again
 304          */
 305         if (blk_account_rq(rq)) {
 306                 q->in_flight--;
 307                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
 308                         e->ops->elevator_deactivate_req_fn(q, rq);
 309         }
 310
 311         rq->flags &= ~REQ_STARTED;
 312
 313         /*
 314          * if this is the flush, requeue the original instead and drop the flush
 315          */
 316         if (rq->flags & REQ_BAR_FLUSH) {
 317                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
 318                 rq = rq->end_io_data;
 319         }
 320
 321         __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
 322 }
 323
 324 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 325                        int plug)
 326 {
 327         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 328                 /*
 329                  * barriers implicitly indicate back insertion
 330                  */
 331                 if (where == ELEVATOR_INSERT_SORT)
 332                         where = ELEVATOR_INSERT_BACK;
 333
 334                 /*
 335                  * this request is scheduling boundary, update end_sector
 336                  */
 337                 if (blk_fs_request(rq)) {
 338                         q->end_sector = rq_end_sector(rq);
 339                         q->boundary_rq = rq;
 340                 }
 341         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
 342                 where = ELEVATOR_INSERT_BACK;
 343
 344         if (plug)
 345                 blk_plug_device(q);
 346
 347         rq->q = q;
 348
 349         switch (where) {
 350         case ELEVATOR_INSERT_FRONT:
 351                 rq->flags |= REQ_SOFTBARRIER;
 352
 353                 list_add(&rq->queuelist, &q->queue_head);
 354                 break;
 355
 356         case ELEVATOR_INSERT_BACK:
 357                 rq->flags |= REQ_SOFTBARRIER;
 358
 359                 while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 360                         ;
 361                 list_add_tail(&rq->queuelist, &q->queue_head);
 362                 /*
 363                  * We kick the queue here for the following reasons.
 364                  * - The elevator might have returned NULL previously
 365                  *   to delay requests and returned them now.  As the
 366                  *   queue wasn't empty before this request, ll_rw_blk
 367                  *   won't run the queue on return, resulting in hang.
 368                  * - Usually, back inserted requests won't be merged
 369                  *   with anything.  There's no point in delaying queue
 370                  *   processing.
 371                  */
 372                 blk_remove_plug(q);
 373                 q->request_fn(q);
 374                 break;
 375
 376         case ELEVATOR_INSERT_SORT:
 377                 BUG_ON(!blk_fs_request(rq));
 378                 rq->flags |= REQ_SORTED;
 379                 q->elevator->ops->elevator_add_req_fn(q, rq);
 380                 if (q->last_merge == NULL && rq_mergeable(rq))
 381                         q->last_merge = rq;
 382                 break;
 383
 384         default:
 385                 printk(KERN_ERR "%s: bad insertion point %d\n",
 386                        __FUNCTION__, where);
 387                 BUG();
 388         }
 389
 390         if (blk_queue_plugged(q)) {
 391                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 392                         - q->in_flight;
 393
 394                 if (nrq >= q->unplug_thresh)
 395                         __generic_unplug_device(q);
 396         }
 397 }
 398
 399 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 400                      int plug)
 401 {
 402         unsigned long flags;
 403
 404         spin_lock_irqsave(q->queue_lock, flags);
 405         __elv_add_request(q, rq, where, plug);
 406         spin_unlock_irqrestore(q->queue_lock, flags);
 407 }
 408
 409 static inline struct request *__elv_next_request(request_queue_t *q)
 410 {
 411         struct request *rq;
 412
 413         if (unlikely(list_empty(&q->queue_head) &&
 414                      !q->elevator->ops->elevator_dispatch_fn(q, 0)))
 415                 return NULL;
 416
 417         rq = list_entry_rq(q->queue_head.next);
 418
 419         /*
 420          * if this is a barrier write and the device has to issue a
 421          * flush sequence to support it, check how far we are
 422          */
 423         if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
 424                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
 425
 426                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
 427                     !blk_barrier_preflush(rq))
 428                         rq = blk_start_pre_flush(q, rq);
 429         }
 430
 431         return rq;
 432 }
 433
 434 struct request *elv_next_request(request_queue_t *q)
 435 {
 436         struct request *rq;
 437         int ret;
 438
 439         while ((rq = __elv_next_request(q)) != NULL) {
 440                 if (!(rq->flags & REQ_STARTED)) {
 441                         elevator_t *e = q->elevator;
 442
 443                         /*
 444                          * This is the first time the device driver
 445                          * sees this request (possibly after
 446                          * requeueing).  Notify IO scheduler.
 447                          */
 448                         if (blk_sorted_rq(rq) &&
 449                             e->ops->elevator_activate_req_fn)
 450                                 e->ops->elevator_activate_req_fn(q, rq);
 451
 452                         /*
 453                          * just mark as started even if we don't start
 454                          * it, a request that has been delayed should
 455                          * not be passed by new incoming requests
 456                          */
 457                         rq->flags |= REQ_STARTED;
 458                 }
 459
 460                 if (!q->boundary_rq || q->boundary_rq == rq) {
 461                         q->end_sector = rq_end_sector(rq);
 462                         q->boundary_rq = NULL;
 463                 }
 464
 465                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 466                         break;
 467
 468                 ret = q->prep_rq_fn(q, rq);
 469                 if (ret == BLKPREP_OK) {
 470                         break;
 471                 } else if (ret == BLKPREP_DEFER) {
 472                         /*
 473                          * the request may have been (partially) prepped.
 474                          * we need to keep this request in the front to
 475                          * avoid resource deadlock.  REQ_STARTED will
 476                          * prevent other fs requests from passing this one.
 477                          */
 478                         rq = NULL;
 479                         break;
 480                 } else if (ret == BLKPREP_KILL) {
 481                         int nr_bytes = rq->hard_nr_sectors << 9;
 482
 483                         if (!nr_bytes)
 484                                 nr_bytes = rq->data_len;
 485
 486                         blkdev_dequeue_request(rq);
 487                         rq->flags |= REQ_QUIET;
 488                         end_that_request_chunk(rq, 0, nr_bytes);
 489                         end_that_request_last(rq);
 490                 } else {
 491                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 492                                                                 ret);
 493                         break;
 494                 }
 495         }
 496
 497         return rq;
 498 }
 499
 500 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 501 {
 502         BUG_ON(list_empty(&rq->queuelist));
 503
 504         list_del_init(&rq->queuelist);
 505
 506         /*
 507          * the time frame between a request being removed from the lists
 508          * and to it is freed is accounted as io that is in progress at
 509          * the driver side.
 510          */
 511         if (blk_account_rq(rq))
 512                 q->in_flight++;
 513 }
 514
 515 int elv_queue_empty(request_queue_t *q)
 516 {
 517         elevator_t *e = q->elevator;
 518
 519         if (!list_empty(&q->queue_head))
 520                 return 0;
 521
 522         if (e->ops->elevator_queue_empty_fn)
 523                 return e->ops->elevator_queue_empty_fn(q);
 524
 525         return 1;
 526 }
 527
 528 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 529 {
 530         struct list_head *next;
 531
 532         elevator_t *e = q->elevator;
 533
 534         if (e->ops->elevator_latter_req_fn)
 535                 return e->ops->elevator_latter_req_fn(q, rq);
 536
 537         next = rq->queuelist.next;
 538         if (next != &q->queue_head && next != &rq->queuelist)
 539                 return list_entry_rq(next);
 540
 541         return NULL;
 542 }
 543
 544 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 545 {
 546         struct list_head *prev;
 547
 548         elevator_t *e = q->elevator;
 549
 550         if (e->ops->elevator_former_req_fn)
 551                 return e->ops->elevator_former_req_fn(q, rq);
 552
 553         prev = rq->queuelist.prev;
 554         if (prev != &q->queue_head && prev != &rq->queuelist)
 555                 return list_entry_rq(prev);
 556
 557         return NULL;
 558 }
 559
 560 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 561                     gfp_t gfp_mask)
 562 {
 563         elevator_t *e = q->elevator;
 564
 565         if (e->ops->elevator_set_req_fn)
 566                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
 567
 568         rq->elevator_private = NULL;
 569         return 0;
 570 }
 571
 572 void elv_put_request(request_queue_t *q, struct request *rq)
 573 {
 574         elevator_t *e = q->elevator;
 575
 576         if (e->ops->elevator_put_req_fn)
 577                 e->ops->elevator_put_req_fn(q, rq);
 578 }
 579
 580 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
 581 {
 582         elevator_t *e = q->elevator;
 583
 584         if (e->ops->elevator_may_queue_fn)
 585                 return e->ops->elevator_may_queue_fn(q, rw, bio);
 586
 587         return ELV_MQUEUE_MAY;
 588 }
 589
 590 void elv_completed_request(request_queue_t *q, struct request *rq)
 591 {
 592         elevator_t *e = q->elevator;
 593
 594         /*
 595          * request is released from the driver, io must be done
 596          */
 597         if (blk_account_rq(rq)) {
 598                 q->in_flight--;
 599                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 600                         e->ops->elevator_completed_req_fn(q, rq);
 601         }
 602 }
 603
 604 int elv_register_queue(struct request_queue *q)
 605 {
 606         elevator_t *e = q->elevator;
 607
 608         e->kobj.parent = kobject_get(&q->kobj);
 609         if (!e->kobj.parent)
 610                 return -EBUSY;
 611
 612         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 613         e->kobj.ktype = e->elevator_type->elevator_ktype;
 614
 615         return kobject_register(&e->kobj);
 616 }
 617
 618 void elv_unregister_queue(struct request_queue *q)
 619 {
 620         if (q) {
 621                 elevator_t *e = q->elevator;
 622                 kobject_unregister(&e->kobj);
 623                 kobject_put(&q->kobj);
 624         }
 625 }
 626
 627 int elv_register(struct elevator_type *e)
 628 {
 629         spin_lock_irq(&elv_list_lock);
 630         if (elevator_find(e->elevator_name))
 631                 BUG();
 632         list_add_tail(&e->list, &elv_list);
 633         spin_unlock_irq(&elv_list_lock);
 634
 635         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 636         if (!strcmp(e->elevator_name, chosen_elevator))
 637                 printk(" (default)");
 638         printk("\n");
 639         return 0;
 640 }
 641 EXPORT_SYMBOL_GPL(elv_register);
 642
 643 void elv_unregister(struct elevator_type *e)
 644 {
 645         struct task_struct *g, *p;
 646
 647         /*
 648          * Iterate every thread in the process to remove the io contexts.
 649          */
 650         read_lock(&tasklist_lock);
 651         do_each_thread(g, p) {
 652                 struct io_context *ioc = p->io_context;
 653                 if (ioc && ioc->cic) {
 654                         ioc->cic->exit(ioc->cic);
 655                         ioc->cic->dtor(ioc->cic);
 656                         ioc->cic = NULL;
 657                 }
 658                 if (ioc && ioc->aic) {
 659                         ioc->aic->exit(ioc->aic);
 660                         ioc->aic->dtor(ioc->aic);
 661                         ioc->aic = NULL;
 662                 }
 663         } while_each_thread(g, p);
 664         read_unlock(&tasklist_lock);
 665
 666         spin_lock_irq(&elv_list_lock);
 667         list_del_init(&e->list);
 668         spin_unlock_irq(&elv_list_lock);
 669 }
 670 EXPORT_SYMBOL_GPL(elv_unregister);
 671
 672 /*
 673  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 674  * we don't free the old io scheduler, before we have allocated what we
 675  * need for the new one. this way we have a chance of going back to the old
 676  * one, if the new one fails init for some reason.
 677  */
 678 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
 679 {
 680         elevator_t *old_elevator, *e;
 681
 682         /*
 683          * Allocate new elevator
 684          */
 685         e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
 686         if (!e)
 687                 goto error;
 688
 689         /*
 690          * Turn on BYPASS and drain all requests w/ elevator private data
 691          */
 692         spin_lock_irq(q->queue_lock);
 693
 694         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 695
 696         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 697                 ;
 698
 699         while (q->rq.elvpriv) {
 700                 spin_unlock_irq(q->queue_lock);
 701                 msleep(10);
 702                 spin_lock_irq(q->queue_lock);
 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         struct elevator_type *e;
 750
 751         memset(elevator_name, 0, sizeof(elevator_name));
 752         strncpy(elevator_name, name, sizeof(elevator_name));
 753
 754         if (elevator_name[strlen(elevator_name) - 1] == '\n')
 755                 elevator_name[strlen(elevator_name) - 1] = '\0';
 756
 757         e = elevator_get(elevator_name);
 758         if (!e) {
 759                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 760                 return -EINVAL;
 761         }
 762
 763         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
 764                 return count;
 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);