SAFE public projects git trees. - safe/jmp/linux-2.6/blob - 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 static 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
  84 static struct elevator_type *elevator_find(const char *name)
  85 {
  86         struct elevator_type *e = NULL;
  87         struct list_head *entry;
  88
  89         list_for_each(entry, &elv_list) {
  90                 struct elevator_type *__e;
  91
  92                 __e = list_entry(entry, struct elevator_type, list);
  93
  94                 if (!strcmp(__e->elevator_name, name)) {
  95                         e = __e;
  96                         break;
  97                 }
  98         }
  99
 100         return e;
 101 }
 102
 103 static void elevator_put(struct elevator_type *e)
 104 {
 105         module_put(e->elevator_owner);
 106 }
 107
 108 static struct elevator_type *elevator_get(const char *name)
 109 {
 110         struct elevator_type *e;
 111
 112         spin_lock_irq(&elv_list_lock);
 113
 114         e = elevator_find(name);
 115         if (e && !try_module_get(e->elevator_owner))
 116                 e = NULL;
 117
 118         spin_unlock_irq(&elv_list_lock);
 119
 120         return e;
 121 }
 122
 123 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
 124                            struct elevator_queue *eq)
 125 {
 126         int ret = 0;
 127
 128         memset(eq, 0, sizeof(*eq));
 129         eq->ops = &e->ops;
 130         eq->elevator_type = e;
 131
 132         q->elevator = eq;
 133
 134         if (eq->ops->elevator_init_fn)
 135                 ret = eq->ops->elevator_init_fn(q, eq);
 136
 137         return ret;
 138 }
 139
 140 static char chosen_elevator[16];
 141
 142 static int __init elevator_setup(char *str)
 143 {
 144         /*
 145          * Be backwards-compatible with previous kernels, so users
 146          * won't get the wrong elevator.
 147          */
 148         if (!strcmp(str, "as"))
 149                 strcpy(chosen_elevator, "anticipatory");
 150         else
 151                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 152         return 0;
 153 }
 154
 155 __setup("elevator=", elevator_setup);
 156
 157 int elevator_init(request_queue_t *q, char *name)
 158 {
 159         struct elevator_type *e = NULL;
 160         struct elevator_queue *eq;
 161         int ret = 0;
 162
 163         INIT_LIST_HEAD(&q->queue_head);
 164         q->last_merge = NULL;
 165         q->end_sector = 0;
 166         q->boundary_rq = NULL;
 167
 168         if (name && !(e = elevator_get(name)))
 169                 return -EINVAL;
 170
 171         if (!e && !(e = elevator_get(chosen_elevator))) {
 172                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
 173                 if (*chosen_elevator)
 174                         printk("I/O scheduler %s not found\n", chosen_elevator);
 175         }
 176
 177         eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
 178         if (!eq) {
 179                 elevator_put(e);
 180                 return -ENOMEM;
 181         }
 182
 183         ret = elevator_attach(q, e, eq);
 184         if (ret) {
 185                 kfree(eq);
 186                 elevator_put(e);
 187         }
 188
 189         return ret;
 190 }
 191
 192 void elevator_exit(elevator_t *e)
 193 {
 194         if (e->ops->elevator_exit_fn)
 195                 e->ops->elevator_exit_fn(e);
 196
 197         elevator_put(e->elevator_type);
 198         e->elevator_type = NULL;
 199         kfree(e);
 200 }
 201
 202 /*
 203  * Insert rq into dispatch queue of q.  Queue lock must be held on
 204  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 205  * appended to the dispatch queue.  To be used by specific elevators.
 206  */
 207 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 208 {
 209         sector_t boundary;
 210         struct list_head *entry;
 211
 212         if (q->last_merge == rq)
 213                 q->last_merge = NULL;
 214         q->nr_sorted--;
 215
 216         boundary = q->end_sector;
 217
 218         list_for_each_prev(entry, &q->queue_head) {
 219                 struct request *pos = list_entry_rq(entry);
 220
 221                 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
 222                         break;
 223                 if (rq->sector >= boundary) {
 224                         if (pos->sector < boundary)
 225                                 continue;
 226                 } else {
 227                         if (pos->sector >= boundary)
 228                                 break;
 229                 }
 230                 if (rq->sector >= pos->sector)
 231                         break;
 232         }
 233
 234         list_add(&rq->queuelist, entry);
 235 }
 236
 237 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 238 {
 239         elevator_t *e = q->elevator;
 240         int ret;
 241
 242         if (q->last_merge) {
 243                 ret = elv_try_merge(q->last_merge, bio);
 244                 if (ret != ELEVATOR_NO_MERGE) {
 245                         *req = q->last_merge;
 246                         return ret;
 247                 }
 248         }
 249
 250         if (e->ops->elevator_merge_fn)
 251                 return e->ops->elevator_merge_fn(q, req, bio);
 252
 253         return ELEVATOR_NO_MERGE;
 254 }
 255
 256 void elv_merged_request(request_queue_t *q, struct request *rq)
 257 {
 258         elevator_t *e = q->elevator;
 259
 260         if (e->ops->elevator_merged_fn)
 261                 e->ops->elevator_merged_fn(q, rq);
 262
 263         q->last_merge = rq;
 264 }
 265
 266 void elv_merge_requests(request_queue_t *q, struct request *rq,
 267                              struct request *next)
 268 {
 269         elevator_t *e = q->elevator;
 270
 271         if (e->ops->elevator_merge_req_fn)
 272                 e->ops->elevator_merge_req_fn(q, rq, next);
 273         q->nr_sorted--;
 274
 275         q->last_merge = rq;
 276 }
 277
 278 void elv_requeue_request(request_queue_t *q, struct request *rq)
 279 {
 280         elevator_t *e = q->elevator;
 281
 282         /*
 283          * it already went through dequeue, we need to decrement the
 284          * in_flight count again
 285          */
 286         if (blk_account_rq(rq)) {
 287                 q->in_flight--;
 288                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
 289                         e->ops->elevator_deactivate_req_fn(q, rq);
 290         }
 291
 292         rq->flags &= ~REQ_STARTED;
 293
 294         __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE, 0);
 295 }
 296
 297 static void elv_drain_elevator(request_queue_t *q)
 298 {
 299         static int printed;
 300         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 301                 ;
 302         if (q->nr_sorted == 0)
 303                 return;
 304         if (printed++ < 10) {
 305                 printk(KERN_ERR "%s: forced dispatching is broken "
 306                        "(nr_sorted=%u), please report this\n",
 307                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 308         }
 309 }
 310
 311 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 312                        int plug)
 313 {
 314         struct list_head *pos;
 315         unsigned ordseq;
 316
 317         if (q->ordcolor)
 318                 rq->flags |= REQ_ORDERED_COLOR;
 319
 320         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 321                 /*
 322                  * toggle ordered color
 323                  */
 324                 q->ordcolor ^= 1;
 325
 326                 /*
 327                  * barriers implicitly indicate back insertion
 328                  */
 329                 if (where == ELEVATOR_INSERT_SORT)
 330                         where = ELEVATOR_INSERT_BACK;
 331
 332                 /*
 333                  * this request is scheduling boundary, update end_sector
 334                  */
 335                 if (blk_fs_request(rq)) {
 336                         q->end_sector = rq_end_sector(rq);
 337                         q->boundary_rq = rq;
 338                 }
 339         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
 340                 where = ELEVATOR_INSERT_BACK;
 341
 342         if (plug)
 343                 blk_plug_device(q);
 344
 345         rq->q = q;
 346
 347         switch (where) {
 348         case ELEVATOR_INSERT_FRONT:
 349                 rq->flags |= REQ_SOFTBARRIER;
 350
 351                 list_add(&rq->queuelist, &q->queue_head);
 352                 break;
 353
 354         case ELEVATOR_INSERT_BACK:
 355                 rq->flags |= REQ_SOFTBARRIER;
 356                 elv_drain_elevator(q);
 357                 list_add_tail(&rq->queuelist, &q->queue_head);
 358                 /*
 359                  * We kick the queue here for the following reasons.
 360                  * - The elevator might have returned NULL previously
 361                  *   to delay requests and returned them now.  As the
 362                  *   queue wasn't empty before this request, ll_rw_blk
 363                  *   won't run the queue on return, resulting in hang.
 364                  * - Usually, back inserted requests won't be merged
 365                  *   with anything.  There's no point in delaying queue
 366                  *   processing.
 367                  */
 368                 blk_remove_plug(q);
 369                 q->request_fn(q);
 370                 break;
 371
 372         case ELEVATOR_INSERT_SORT:
 373                 BUG_ON(!blk_fs_request(rq));
 374                 rq->flags |= REQ_SORTED;
 375                 q->nr_sorted++;
 376                 if (q->last_merge == NULL && rq_mergeable(rq))
 377                         q->last_merge = rq;
 378                 /*
 379                  * Some ioscheds (cfq) run q->request_fn directly, so
 380                  * rq cannot be accessed after calling
 381                  * elevator_add_req_fn.
 382                  */
 383                 q->elevator->ops->elevator_add_req_fn(q, rq);
 384                 break;
 385
 386         case ELEVATOR_INSERT_REQUEUE:
 387                 /*
 388                  * If ordered flush isn't in progress, we do front
 389                  * insertion; otherwise, requests should be requeued
 390                  * in ordseq order.
 391                  */
 392                 rq->flags |= REQ_SOFTBARRIER;
 393
 394                 if (q->ordseq == 0) {
 395                         list_add(&rq->queuelist, &q->queue_head);
 396                         break;
 397                 }
 398
 399                 ordseq = blk_ordered_req_seq(rq);
 400
 401                 list_for_each(pos, &q->queue_head) {
 402                         struct request *pos_rq = list_entry_rq(pos);
 403                         if (ordseq <= blk_ordered_req_seq(pos_rq))
 404                                 break;
 405                 }
 406
 407                 list_add_tail(&rq->queuelist, pos);
 408                 break;
 409
 410         default:
 411                 printk(KERN_ERR "%s: bad insertion point %d\n",
 412                        __FUNCTION__, where);
 413                 BUG();
 414         }
 415
 416         if (blk_queue_plugged(q)) {
 417                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 418                         - q->in_flight;
 419
 420                 if (nrq >= q->unplug_thresh)
 421                         __generic_unplug_device(q);
 422         }
 423 }
 424
 425 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 426                      int plug)
 427 {
 428         unsigned long flags;
 429
 430         spin_lock_irqsave(q->queue_lock, flags);
 431         __elv_add_request(q, rq, where, plug);
 432         spin_unlock_irqrestore(q->queue_lock, flags);
 433 }
 434
 435 static inline struct request *__elv_next_request(request_queue_t *q)
 436 {
 437         struct request *rq;
 438
 439         while (1) {
 440                 while (!list_empty(&q->queue_head)) {
 441                         rq = list_entry_rq(q->queue_head.next);
 442                         if (blk_do_ordered(q, &rq))
 443                                 return rq;
 444                 }
 445
 446                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 447                         return NULL;
 448         }
 449 }
 450
 451 struct request *elv_next_request(request_queue_t *q)
 452 {
 453         struct request *rq;
 454         int ret;
 455
 456         while ((rq = __elv_next_request(q)) != NULL) {
 457                 if (!(rq->flags & REQ_STARTED)) {
 458                         elevator_t *e = q->elevator;
 459
 460                         /*
 461                          * This is the first time the device driver
 462                          * sees this request (possibly after
 463                          * requeueing).  Notify IO scheduler.
 464                          */
 465                         if (blk_sorted_rq(rq) &&
 466                             e->ops->elevator_activate_req_fn)
 467                                 e->ops->elevator_activate_req_fn(q, rq);
 468
 469                         /*
 470                          * just mark as started even if we don't start
 471                          * it, a request that has been delayed should
 472                          * not be passed by new incoming requests
 473                          */
 474                         rq->flags |= REQ_STARTED;
 475                 }
 476
 477                 if (!q->boundary_rq || q->boundary_rq == rq) {
 478                         q->end_sector = rq_end_sector(rq);
 479                         q->boundary_rq = NULL;
 480                 }
 481
 482                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 483                         break;
 484
 485                 ret = q->prep_rq_fn(q, rq);
 486                 if (ret == BLKPREP_OK) {
 487                         break;
 488                 } else if (ret == BLKPREP_DEFER) {
 489                         /*
 490                          * the request may have been (partially) prepped.
 491                          * we need to keep this request in the front to
 492                          * avoid resource deadlock.  REQ_STARTED will
 493                          * prevent other fs requests from passing this one.
 494                          */
 495                         rq = NULL;
 496                         break;
 497                 } else if (ret == BLKPREP_KILL) {
 498                         int nr_bytes = rq->hard_nr_sectors << 9;
 499
 500                         if (!nr_bytes)
 501                                 nr_bytes = rq->data_len;
 502
 503                         blkdev_dequeue_request(rq);
 504                         rq->flags |= REQ_QUIET;
 505                         end_that_request_chunk(rq, 0, nr_bytes);
 506                         end_that_request_last(rq, 0);
 507                 } else {
 508                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 509                                                                 ret);
 510                         break;
 511                 }
 512         }
 513
 514         return rq;
 515 }
 516
 517 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 518 {
 519         BUG_ON(list_empty(&rq->queuelist));
 520
 521         list_del_init(&rq->queuelist);
 522
 523         /*
 524          * the time frame between a request being removed from the lists
 525          * and to it is freed is accounted as io that is in progress at
 526          * the driver side.
 527          */
 528         if (blk_account_rq(rq))
 529                 q->in_flight++;
 530 }
 531
 532 int elv_queue_empty(request_queue_t *q)
 533 {
 534         elevator_t *e = q->elevator;
 535
 536         if (!list_empty(&q->queue_head))
 537                 return 0;
 538
 539         if (e->ops->elevator_queue_empty_fn)
 540                 return e->ops->elevator_queue_empty_fn(q);
 541
 542         return 1;
 543 }
 544
 545 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 546 {
 547         elevator_t *e = q->elevator;
 548
 549         if (e->ops->elevator_latter_req_fn)
 550                 return e->ops->elevator_latter_req_fn(q, rq);
 551         return NULL;
 552 }
 553
 554 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 555 {
 556         elevator_t *e = q->elevator;
 557
 558         if (e->ops->elevator_former_req_fn)
 559                 return e->ops->elevator_former_req_fn(q, rq);
 560         return NULL;
 561 }
 562
 563 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 564                     gfp_t gfp_mask)
 565 {
 566         elevator_t *e = q->elevator;
 567
 568         if (e->ops->elevator_set_req_fn)
 569                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
 570
 571         rq->elevator_private = NULL;
 572         return 0;
 573 }
 574
 575 void elv_put_request(request_queue_t *q, struct request *rq)
 576 {
 577         elevator_t *e = q->elevator;
 578
 579         if (e->ops->elevator_put_req_fn)
 580                 e->ops->elevator_put_req_fn(q, rq);
 581 }
 582
 583 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
 584 {
 585         elevator_t *e = q->elevator;
 586
 587         if (e->ops->elevator_may_queue_fn)
 588                 return e->ops->elevator_may_queue_fn(q, rw, bio);
 589
 590         return ELV_MQUEUE_MAY;
 591 }
 592
 593 void elv_completed_request(request_queue_t *q, struct request *rq)
 594 {
 595         elevator_t *e = q->elevator;
 596
 597         /*
 598          * request is released from the driver, io must be done
 599          */
 600         if (blk_account_rq(rq)) {
 601                 q->in_flight--;
 602                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 603                         e->ops->elevator_completed_req_fn(q, rq);
 604         }
 605
 606         /*
 607          * Check if the queue is waiting for fs requests to be
 608          * drained for flush sequence.
 609          */
 610         if (unlikely(q->ordseq)) {
 611                 struct request *first_rq = list_entry_rq(q->queue_head.next);
 612                 if (q->in_flight == 0 &&
 613                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 614                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
 615                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 616                         q->request_fn(q);
 617                 }
 618         }
 619 }
 620
 621 int elv_register_queue(struct request_queue *q)
 622 {
 623         elevator_t *e = q->elevator;
 624
 625         e->kobj.parent = kobject_get(&q->kobj);
 626         if (!e->kobj.parent)
 627                 return -EBUSY;
 628
 629         snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 630         e->kobj.ktype = e->elevator_type->elevator_ktype;
 631
 632         return kobject_register(&e->kobj);
 633 }
 634
 635 void elv_unregister_queue(struct request_queue *q)
 636 {
 637         if (q) {
 638                 elevator_t *e = q->elevator;
 639                 kobject_unregister(&e->kobj);
 640                 kobject_put(&q->kobj);
 641         }
 642 }
 643
 644 int elv_register(struct elevator_type *e)
 645 {
 646         spin_lock_irq(&elv_list_lock);
 647         if (elevator_find(e->elevator_name))
 648                 BUG();
 649         list_add_tail(&e->list, &elv_list);
 650         spin_unlock_irq(&elv_list_lock);
 651
 652         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 653         if (!strcmp(e->elevator_name, chosen_elevator) ||
 654                         (!*chosen_elevator &&
 655                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
 656                                 printk(" (default)");
 657         printk("\n");
 658         return 0;
 659 }
 660 EXPORT_SYMBOL_GPL(elv_register);
 661
 662 void elv_unregister(struct elevator_type *e)
 663 {
 664         struct task_struct *g, *p;
 665
 666         /*
 667          * Iterate every thread in the process to remove the io contexts.
 668          */
 669         read_lock(&tasklist_lock);
 670         do_each_thread(g, p) {
 671                 struct io_context *ioc = p->io_context;
 672                 if (ioc && ioc->cic) {
 673                         ioc->cic->exit(ioc->cic);
 674                         ioc->cic->dtor(ioc->cic);
 675                         ioc->cic = NULL;
 676                 }
 677                 if (ioc && ioc->aic) {
 678                         ioc->aic->exit(ioc->aic);
 679                         ioc->aic->dtor(ioc->aic);
 680                         ioc->aic = NULL;
 681                 }
 682         } while_each_thread(g, p);
 683         read_unlock(&tasklist_lock);
 684
 685         spin_lock_irq(&elv_list_lock);
 686         list_del_init(&e->list);
 687         spin_unlock_irq(&elv_list_lock);
 688 }
 689 EXPORT_SYMBOL_GPL(elv_unregister);
 690
 691 /*
 692  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 693  * we don't free the old io scheduler, before we have allocated what we
 694  * need for the new one. this way we have a chance of going back to the old
 695  * one, if the new one fails init for some reason.
 696  */
 697 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
 698 {
 699         elevator_t *old_elevator, *e;
 700
 701         /*
 702          * Allocate new elevator
 703          */
 704         e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
 705         if (!e)
 706                 goto error;
 707
 708         /*
 709          * Turn on BYPASS and drain all requests w/ elevator private data
 710          */
 711         spin_lock_irq(q->queue_lock);
 712
 713         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 714
 715         elv_drain_elevator(q);
 716
 717         while (q->rq.elvpriv) {
 718                 blk_remove_plug(q);
 719                 q->request_fn(q);
 720                 spin_unlock_irq(q->queue_lock);
 721                 msleep(10);
 722                 spin_lock_irq(q->queue_lock);
 723                 elv_drain_elevator(q);
 724         }
 725
 726         spin_unlock_irq(q->queue_lock);
 727
 728         /*
 729          * unregister old elevator data
 730          */
 731         elv_unregister_queue(q);
 732         old_elevator = q->elevator;
 733
 734         /*
 735          * attach and start new elevator
 736          */
 737         if (elevator_attach(q, new_e, e))
 738                 goto fail;
 739
 740         if (elv_register_queue(q))
 741                 goto fail_register;
 742
 743         /*
 744          * finally exit old elevator and turn off BYPASS.
 745          */
 746         elevator_exit(old_elevator);
 747         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 748         return;
 749
 750 fail_register:
 751         /*
 752          * switch failed, exit the new io scheduler and reattach the old
 753          * one again (along with re-adding the sysfs dir)
 754          */
 755         elevator_exit(e);
 756         e = NULL;
 757 fail:
 758         q->elevator = old_elevator;
 759         elv_register_queue(q);
 760         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 761         kfree(e);
 762 error:
 763         elevator_put(new_e);
 764         printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
 765 }
 766
 767 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
 768 {
 769         char elevator_name[ELV_NAME_MAX];
 770         size_t len;
 771         struct elevator_type *e;
 772
 773         elevator_name[sizeof(elevator_name) - 1] = '\0';
 774         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
 775         len = strlen(elevator_name);
 776
 777         if (len && elevator_name[len - 1] == '\n')
 778                 elevator_name[len - 1] = '\0';
 779
 780         e = elevator_get(elevator_name);
 781         if (!e) {
 782                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 783                 return -EINVAL;
 784         }
 785
 786         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
 787                 elevator_put(e);
 788                 return count;
 789         }
 790
 791         elevator_switch(q, e);
 792         return count;
 793 }
 794
 795 ssize_t elv_iosched_show(request_queue_t *q, char *name)
 796 {
 797         elevator_t *e = q->elevator;
 798         struct elevator_type *elv = e->elevator_type;
 799         struct list_head *entry;
 800         int len = 0;
 801
 802         spin_lock_irq(q->queue_lock);
 803         list_for_each(entry, &elv_list) {
 804                 struct elevator_type *__e;
 805
 806                 __e = list_entry(entry, struct elevator_type, list);
 807                 if (!strcmp(elv->elevator_name, __e->elevator_name))
 808                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 809                 else
 810                         len += sprintf(name+len, "%s ", __e->elevator_name);
 811         }
 812         spin_unlock_irq(q->queue_lock);
 813
 814         len += sprintf(len+name, "\n");
 815         return len;
 816 }
 817
 818 EXPORT_SYMBOL(elv_dispatch_sort);
 819 EXPORT_SYMBOL(elv_add_request);
 820 EXPORT_SYMBOL(__elv_add_request);
 821 EXPORT_SYMBOL(elv_requeue_request);
 822 EXPORT_SYMBOL(elv_next_request);
 823 EXPORT_SYMBOL(elv_dequeue_request);
 824 EXPORT_SYMBOL(elv_queue_empty);
 825 EXPORT_SYMBOL(elv_completed_request);
 826 EXPORT_SYMBOL(elevator_exit);
 827 EXPORT_SYMBOL(elevator_init);