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   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_queue *eq)
 124 {
 125         int ret = 0;
 126
 127         q->elevator = eq;
 128
 129         if (eq->ops->elevator_init_fn)
 130                 ret = eq->ops->elevator_init_fn(q, eq);
 131
 132         return ret;
 133 }
 134
 135 static char chosen_elevator[16];
 136
 137 static int __init elevator_setup(char *str)
 138 {
 139         /*
 140          * Be backwards-compatible with previous kernels, so users
 141          * won't get the wrong elevator.
 142          */
 143         if (!strcmp(str, "as"))
 144                 strcpy(chosen_elevator, "anticipatory");
 145         else
 146                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 147         return 0;
 148 }
 149
 150 __setup("elevator=", elevator_setup);
 151
 152 static struct kobj_type elv_ktype;
 153
 154 static elevator_t *elevator_alloc(struct elevator_type *e)
 155 {
 156         elevator_t *eq = kmalloc(sizeof(elevator_t), GFP_KERNEL);
 157         if (eq) {
 158                 memset(eq, 0, sizeof(*eq));
 159                 eq->ops = &e->ops;
 160                 eq->elevator_type = e;
 161                 kobject_init(&eq->kobj);
 162                 snprintf(eq->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 163                 eq->kobj.ktype = &elv_ktype;
 164                 mutex_init(&eq->sysfs_lock);
 165         } else {
 166                 elevator_put(e);
 167         }
 168         return eq;
 169 }
 170
 171 static void elevator_release(struct kobject *kobj)
 172 {
 173         elevator_t *e = container_of(kobj, elevator_t, kobj);
 174         elevator_put(e->elevator_type);
 175         kfree(e);
 176 }
 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         if (name && !(e = elevator_get(name)))
 190                 return -EINVAL;
 191
 192         if (!e && *chosen_elevator && !(e = elevator_get(chosen_elevator)))
 193                 printk("I/O scheduler %s not found\n", chosen_elevator);
 194
 195         if (!e && !(e = elevator_get(CONFIG_DEFAULT_IOSCHED))) {
 196                 printk("Default I/O scheduler not found, using no-op\n");
 197                 e = elevator_get("noop");
 198         }
 199
 200         eq = elevator_alloc(e);
 201         if (!eq)
 202                 return -ENOMEM;
 203
 204         ret = elevator_attach(q, eq);
 205         if (ret)
 206                 kobject_put(&eq->kobj);
 207
 208         return ret;
 209 }
 210
 211 void elevator_exit(elevator_t *e)
 212 {
 213         mutex_lock(&e->sysfs_lock);
 214         if (e->ops->elevator_exit_fn)
 215                 e->ops->elevator_exit_fn(e);
 216         e->ops = NULL;
 217         mutex_unlock(&e->sysfs_lock);
 218
 219         kobject_put(&e->kobj);
 220 }
 221
 222 /*
 223  * Insert rq into dispatch queue of q.  Queue lock must be held on
 224  * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 225  * appended to the dispatch queue.  To be used by specific elevators.
 226  */
 227 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 228 {
 229         sector_t boundary;
 230         struct list_head *entry;
 231
 232         if (q->last_merge == rq)
 233                 q->last_merge = NULL;
 234         q->nr_sorted--;
 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         q->nr_sorted--;
 294
 295         q->last_merge = rq;
 296 }
 297
 298 void elv_requeue_request(request_queue_t *q, struct request *rq)
 299 {
 300         elevator_t *e = q->elevator;
 301
 302         /*
 303          * it already went through dequeue, we need to decrement the
 304          * in_flight count again
 305          */
 306         if (blk_account_rq(rq)) {
 307                 q->in_flight--;
 308                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
 309                         e->ops->elevator_deactivate_req_fn(q, rq);
 310         }
 311
 312         rq->flags &= ~REQ_STARTED;
 313
 314         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 315 }
 316
 317 static void elv_drain_elevator(request_queue_t *q)
 318 {
 319         static int printed;
 320         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 321                 ;
 322         if (q->nr_sorted == 0)
 323                 return;
 324         if (printed++ < 10) {
 325                 printk(KERN_ERR "%s: forced dispatching is broken "
 326                        "(nr_sorted=%u), please report this\n",
 327                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 328         }
 329 }
 330
 331 void elv_insert(request_queue_t *q, struct request *rq, int where)
 332 {
 333         struct list_head *pos;
 334         unsigned ordseq;
 335
 336         rq->q = q;
 337
 338         switch (where) {
 339         case ELEVATOR_INSERT_FRONT:
 340                 rq->flags |= REQ_SOFTBARRIER;
 341
 342                 list_add(&rq->queuelist, &q->queue_head);
 343                 break;
 344
 345         case ELEVATOR_INSERT_BACK:
 346                 rq->flags |= REQ_SOFTBARRIER;
 347                 elv_drain_elevator(q);
 348                 list_add_tail(&rq->queuelist, &q->queue_head);
 349                 /*
 350                  * We kick the queue here for the following reasons.
 351                  * - The elevator might have returned NULL previously
 352                  *   to delay requests and returned them now.  As the
 353                  *   queue wasn't empty before this request, ll_rw_blk
 354                  *   won't run the queue on return, resulting in hang.
 355                  * - Usually, back inserted requests won't be merged
 356                  *   with anything.  There's no point in delaying queue
 357                  *   processing.
 358                  */
 359                 blk_remove_plug(q);
 360                 q->request_fn(q);
 361                 break;
 362
 363         case ELEVATOR_INSERT_SORT:
 364                 BUG_ON(!blk_fs_request(rq));
 365                 rq->flags |= REQ_SORTED;
 366                 q->nr_sorted++;
 367                 if (q->last_merge == NULL && rq_mergeable(rq))
 368                         q->last_merge = rq;
 369                 /*
 370                  * Some ioscheds (cfq) run q->request_fn directly, so
 371                  * rq cannot be accessed after calling
 372                  * elevator_add_req_fn.
 373                  */
 374                 q->elevator->ops->elevator_add_req_fn(q, rq);
 375                 break;
 376
 377         case ELEVATOR_INSERT_REQUEUE:
 378                 /*
 379                  * If ordered flush isn't in progress, we do front
 380                  * insertion; otherwise, requests should be requeued
 381                  * in ordseq order.
 382                  */
 383                 rq->flags |= REQ_SOFTBARRIER;
 384
 385                 if (q->ordseq == 0) {
 386                         list_add(&rq->queuelist, &q->queue_head);
 387                         break;
 388                 }
 389
 390                 ordseq = blk_ordered_req_seq(rq);
 391
 392                 list_for_each(pos, &q->queue_head) {
 393                         struct request *pos_rq = list_entry_rq(pos);
 394                         if (ordseq <= blk_ordered_req_seq(pos_rq))
 395                                 break;
 396                 }
 397
 398                 list_add_tail(&rq->queuelist, pos);
 399                 break;
 400
 401         default:
 402                 printk(KERN_ERR "%s: bad insertion point %d\n",
 403                        __FUNCTION__, where);
 404                 BUG();
 405         }
 406
 407         if (blk_queue_plugged(q)) {
 408                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 409                         - q->in_flight;
 410
 411                 if (nrq >= q->unplug_thresh)
 412                         __generic_unplug_device(q);
 413         }
 414 }
 415
 416 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 417                        int plug)
 418 {
 419         if (q->ordcolor)
 420                 rq->flags |= REQ_ORDERED_COLOR;
 421
 422         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 423                 /*
 424                  * toggle ordered color
 425                  */
 426                 if (blk_barrier_rq(rq))
 427                         q->ordcolor ^= 1;
 428
 429                 /*
 430                  * barriers implicitly indicate back insertion
 431                  */
 432                 if (where == ELEVATOR_INSERT_SORT)
 433                         where = ELEVATOR_INSERT_BACK;
 434
 435                 /*
 436                  * this request is scheduling boundary, update
 437                  * end_sector
 438                  */
 439                 if (blk_fs_request(rq)) {
 440                         q->end_sector = rq_end_sector(rq);
 441                         q->boundary_rq = rq;
 442                 }
 443         } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
 444                 where = ELEVATOR_INSERT_BACK;
 445
 446         if (plug)
 447                 blk_plug_device(q);
 448
 449         elv_insert(q, rq, where);
 450 }
 451
 452 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 453                      int plug)
 454 {
 455         unsigned long flags;
 456
 457         spin_lock_irqsave(q->queue_lock, flags);
 458         __elv_add_request(q, rq, where, plug);
 459         spin_unlock_irqrestore(q->queue_lock, flags);
 460 }
 461
 462 static inline struct request *__elv_next_request(request_queue_t *q)
 463 {
 464         struct request *rq;
 465
 466         while (1) {
 467                 while (!list_empty(&q->queue_head)) {
 468                         rq = list_entry_rq(q->queue_head.next);
 469                         if (blk_do_ordered(q, &rq))
 470                                 return rq;
 471                 }
 472
 473                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 474                         return NULL;
 475         }
 476 }
 477
 478 struct request *elv_next_request(request_queue_t *q)
 479 {
 480         struct request *rq;
 481         int ret;
 482
 483         while ((rq = __elv_next_request(q)) != NULL) {
 484                 if (!(rq->flags & REQ_STARTED)) {
 485                         elevator_t *e = q->elevator;
 486
 487                         /*
 488                          * This is the first time the device driver
 489                          * sees this request (possibly after
 490                          * requeueing).  Notify IO scheduler.
 491                          */
 492                         if (blk_sorted_rq(rq) &&
 493                             e->ops->elevator_activate_req_fn)
 494                                 e->ops->elevator_activate_req_fn(q, rq);
 495
 496                         /*
 497                          * just mark as started even if we don't start
 498                          * it, a request that has been delayed should
 499                          * not be passed by new incoming requests
 500                          */
 501                         rq->flags |= REQ_STARTED;
 502                 }
 503
 504                 if (!q->boundary_rq || q->boundary_rq == rq) {
 505                         q->end_sector = rq_end_sector(rq);
 506                         q->boundary_rq = NULL;
 507                 }
 508
 509                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
 510                         break;
 511
 512                 ret = q->prep_rq_fn(q, rq);
 513                 if (ret == BLKPREP_OK) {
 514                         break;
 515                 } else if (ret == BLKPREP_DEFER) {
 516                         /*
 517                          * the request may have been (partially) prepped.
 518                          * we need to keep this request in the front to
 519                          * avoid resource deadlock.  REQ_STARTED will
 520                          * prevent other fs requests from passing this one.
 521                          */
 522                         rq = NULL;
 523                         break;
 524                 } else if (ret == BLKPREP_KILL) {
 525                         int nr_bytes = rq->hard_nr_sectors << 9;
 526
 527                         if (!nr_bytes)
 528                                 nr_bytes = rq->data_len;
 529
 530                         blkdev_dequeue_request(rq);
 531                         rq->flags |= REQ_QUIET;
 532                         end_that_request_chunk(rq, 0, nr_bytes);
 533                         end_that_request_last(rq, 0);
 534                 } else {
 535                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 536                                                                 ret);
 537                         break;
 538                 }
 539         }
 540
 541         return rq;
 542 }
 543
 544 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 545 {
 546         BUG_ON(list_empty(&rq->queuelist));
 547
 548         list_del_init(&rq->queuelist);
 549
 550         /*
 551          * the time frame between a request being removed from the lists
 552          * and to it is freed is accounted as io that is in progress at
 553          * the driver side.
 554          */
 555         if (blk_account_rq(rq))
 556                 q->in_flight++;
 557 }
 558
 559 int elv_queue_empty(request_queue_t *q)
 560 {
 561         elevator_t *e = q->elevator;
 562
 563         if (!list_empty(&q->queue_head))
 564                 return 0;
 565
 566         if (e->ops->elevator_queue_empty_fn)
 567                 return e->ops->elevator_queue_empty_fn(q);
 568
 569         return 1;
 570 }
 571
 572 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 573 {
 574         elevator_t *e = q->elevator;
 575
 576         if (e->ops->elevator_latter_req_fn)
 577                 return e->ops->elevator_latter_req_fn(q, rq);
 578         return NULL;
 579 }
 580
 581 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 582 {
 583         elevator_t *e = q->elevator;
 584
 585         if (e->ops->elevator_former_req_fn)
 586                 return e->ops->elevator_former_req_fn(q, rq);
 587         return NULL;
 588 }
 589
 590 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 591                     gfp_t gfp_mask)
 592 {
 593         elevator_t *e = q->elevator;
 594
 595         if (e->ops->elevator_set_req_fn)
 596                 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
 597
 598         rq->elevator_private = NULL;
 599         return 0;
 600 }
 601
 602 void elv_put_request(request_queue_t *q, struct request *rq)
 603 {
 604         elevator_t *e = q->elevator;
 605
 606         if (e->ops->elevator_put_req_fn)
 607                 e->ops->elevator_put_req_fn(q, rq);
 608 }
 609
 610 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
 611 {
 612         elevator_t *e = q->elevator;
 613
 614         if (e->ops->elevator_may_queue_fn)
 615                 return e->ops->elevator_may_queue_fn(q, rw, bio);
 616
 617         return ELV_MQUEUE_MAY;
 618 }
 619
 620 void elv_completed_request(request_queue_t *q, struct request *rq)
 621 {
 622         elevator_t *e = q->elevator;
 623
 624         /*
 625          * request is released from the driver, io must be done
 626          */
 627         if (blk_account_rq(rq)) {
 628                 q->in_flight--;
 629                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 630                         e->ops->elevator_completed_req_fn(q, rq);
 631         }
 632
 633         /*
 634          * Check if the queue is waiting for fs requests to be
 635          * drained for flush sequence.
 636          */
 637         if (unlikely(q->ordseq)) {
 638                 struct request *first_rq = list_entry_rq(q->queue_head.next);
 639                 if (q->in_flight == 0 &&
 640                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 641                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
 642                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 643                         q->request_fn(q);
 644                 }
 645         }
 646 }
 647
 648 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 649
 650 static ssize_t
 651 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 652 {
 653         elevator_t *e = container_of(kobj, elevator_t, kobj);
 654         struct elv_fs_entry *entry = to_elv(attr);
 655         ssize_t error;
 656
 657         if (!entry->show)
 658                 return -EIO;
 659
 660         mutex_lock(&e->sysfs_lock);
 661         error = e->ops ? entry->show(e, page) : -ENOENT;
 662         mutex_unlock(&e->sysfs_lock);
 663         return error;
 664 }
 665
 666 static ssize_t
 667 elv_attr_store(struct kobject *kobj, struct attribute *attr,
 668                const char *page, size_t length)
 669 {
 670         elevator_t *e = container_of(kobj, elevator_t, kobj);
 671         struct elv_fs_entry *entry = to_elv(attr);
 672         ssize_t error;
 673
 674         if (!entry->store)
 675                 return -EIO;
 676
 677         mutex_lock(&e->sysfs_lock);
 678         error = e->ops ? entry->store(e, page, length) : -ENOENT;
 679         mutex_unlock(&e->sysfs_lock);
 680         return error;
 681 }
 682
 683 static struct sysfs_ops elv_sysfs_ops = {
 684         .show   = elv_attr_show,
 685         .store  = elv_attr_store,
 686 };
 687
 688 static struct kobj_type elv_ktype = {
 689         .sysfs_ops      = &elv_sysfs_ops,
 690         .release        = elevator_release,
 691 };
 692
 693 int elv_register_queue(struct request_queue *q)
 694 {
 695         elevator_t *e = q->elevator;
 696         int error;
 697
 698         e->kobj.parent = &q->kobj;
 699
 700         error = kobject_add(&e->kobj);
 701         if (!error) {
 702                 struct attribute **attr = e->elevator_type->elevator_attrs;
 703                 if (attr) {
 704                         while (*attr) {
 705                                 if (sysfs_create_file(&e->kobj,*attr++))
 706                                         break;
 707                         }
 708                 }
 709                 kobject_uevent(&e->kobj, KOBJ_ADD);
 710         }
 711         return error;
 712 }
 713
 714 void elv_unregister_queue(struct request_queue *q)
 715 {
 716         if (q) {
 717                 elevator_t *e = q->elevator;
 718                 kobject_uevent(&e->kobj, KOBJ_REMOVE);
 719                 kobject_del(&e->kobj);
 720         }
 721 }
 722
 723 int elv_register(struct elevator_type *e)
 724 {
 725         spin_lock_irq(&elv_list_lock);
 726         if (elevator_find(e->elevator_name))
 727                 BUG();
 728         list_add_tail(&e->list, &elv_list);
 729         spin_unlock_irq(&elv_list_lock);
 730
 731         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 732         if (!strcmp(e->elevator_name, chosen_elevator) ||
 733                         (!*chosen_elevator &&
 734                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
 735                                 printk(" (default)");
 736         printk("\n");
 737         return 0;
 738 }
 739 EXPORT_SYMBOL_GPL(elv_register);
 740
 741 void elv_unregister(struct elevator_type *e)
 742 {
 743         struct task_struct *g, *p;
 744
 745         /*
 746          * Iterate every thread in the process to remove the io contexts.
 747          */
 748         if (e->ops.trim) {
 749                 read_lock(&tasklist_lock);
 750                 do_each_thread(g, p) {
 751                         task_lock(p);
 752                         e->ops.trim(p->io_context);
 753                         task_unlock(p);
 754                 } while_each_thread(g, p);
 755                 read_unlock(&tasklist_lock);
 756         }
 757
 758         spin_lock_irq(&elv_list_lock);
 759         list_del_init(&e->list);
 760         spin_unlock_irq(&elv_list_lock);
 761 }
 762 EXPORT_SYMBOL_GPL(elv_unregister);
 763
 764 /*
 765  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 766  * we don't free the old io scheduler, before we have allocated what we
 767  * need for the new one. this way we have a chance of going back to the old
 768  * one, if the new one fails init for some reason.
 769  */
 770 static int elevator_switch(request_queue_t *q, struct elevator_type *new_e)
 771 {
 772         elevator_t *old_elevator, *e;
 773
 774         /*
 775          * Allocate new elevator
 776          */
 777         e = elevator_alloc(new_e);
 778         if (!e)
 779                 return 0;
 780
 781         /*
 782          * Turn on BYPASS and drain all requests w/ elevator private data
 783          */
 784         spin_lock_irq(q->queue_lock);
 785
 786         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 787
 788         elv_drain_elevator(q);
 789
 790         while (q->rq.elvpriv) {
 791                 blk_remove_plug(q);
 792                 q->request_fn(q);
 793                 spin_unlock_irq(q->queue_lock);
 794                 msleep(10);
 795                 spin_lock_irq(q->queue_lock);
 796                 elv_drain_elevator(q);
 797         }
 798
 799         spin_unlock_irq(q->queue_lock);
 800
 801         /*
 802          * unregister old elevator data
 803          */
 804         elv_unregister_queue(q);
 805         old_elevator = q->elevator;
 806
 807         /*
 808          * attach and start new elevator
 809          */
 810         if (elevator_attach(q, e))
 811                 goto fail;
 812
 813         if (elv_register_queue(q))
 814                 goto fail_register;
 815
 816         /*
 817          * finally exit old elevator and turn off BYPASS.
 818          */
 819         elevator_exit(old_elevator);
 820         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 821         return 1;
 822
 823 fail_register:
 824         /*
 825          * switch failed, exit the new io scheduler and reattach the old
 826          * one again (along with re-adding the sysfs dir)
 827          */
 828         elevator_exit(e);
 829         e = NULL;
 830 fail:
 831         q->elevator = old_elevator;
 832         elv_register_queue(q);
 833         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
 834         if (e)
 835                 kobject_put(&e->kobj);
 836         return 0;
 837 }
 838
 839 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
 840 {
 841         char elevator_name[ELV_NAME_MAX];
 842         size_t len;
 843         struct elevator_type *e;
 844
 845         elevator_name[sizeof(elevator_name) - 1] = '\0';
 846         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
 847         len = strlen(elevator_name);
 848
 849         if (len && elevator_name[len - 1] == '\n')
 850                 elevator_name[len - 1] = '\0';
 851
 852         e = elevator_get(elevator_name);
 853         if (!e) {
 854                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
 855                 return -EINVAL;
 856         }
 857
 858         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
 859                 elevator_put(e);
 860                 return count;
 861         }
 862
 863         if (!elevator_switch(q, e))
 864                 printk(KERN_ERR "elevator: switch to %s failed\n",elevator_name);
 865         return count;
 866 }
 867
 868 ssize_t elv_iosched_show(request_queue_t *q, char *name)
 869 {
 870         elevator_t *e = q->elevator;
 871         struct elevator_type *elv = e->elevator_type;
 872         struct list_head *entry;
 873         int len = 0;
 874
 875         spin_lock_irq(q->queue_lock);
 876         list_for_each(entry, &elv_list) {
 877                 struct elevator_type *__e;
 878
 879                 __e = list_entry(entry, struct elevator_type, list);
 880                 if (!strcmp(elv->elevator_name, __e->elevator_name))
 881                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
 882                 else
 883                         len += sprintf(name+len, "%s ", __e->elevator_name);
 884         }
 885         spin_unlock_irq(q->queue_lock);
 886
 887         len += sprintf(len+name, "\n");
 888         return len;
 889 }
 890
 891 EXPORT_SYMBOL(elv_dispatch_sort);
 892 EXPORT_SYMBOL(elv_add_request);
 893 EXPORT_SYMBOL(__elv_add_request);
 894 EXPORT_SYMBOL(elv_requeue_request);
 895 EXPORT_SYMBOL(elv_next_request);
 896 EXPORT_SYMBOL(elv_dequeue_request);
 897 EXPORT_SYMBOL(elv_queue_empty);
 898 EXPORT_SYMBOL(elv_completed_request);
 899 EXPORT_SYMBOL(elevator_exit);
 900 EXPORT_SYMBOL(elevator_init);