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@kernel.dk> :
   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/module.h>
  31 #include <linux/slab.h>
  32 #include <linux/init.h>
  33 #include <linux/compiler.h>
  34 #include <linux/delay.h>
  35 #include <linux/blktrace_api.h>
  36 #include <linux/hash.h>
  37
  38 #include <asm/uaccess.h>
  39
  40 static DEFINE_SPINLOCK(elv_list_lock);
  41 static LIST_HEAD(elv_list);
  42
  43 /*
  44  * Merge hash stuff.
  45  */
  46 static const int elv_hash_shift = 6;
  47 #define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
  48 #define ELV_HASH_FN(sec)        (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
  49 #define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
  50 #define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
  51 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
  52
  53 /*
  54  * Query io scheduler to see if the current process issuing bio may be
  55  * merged with rq.
  56  */
  57 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
  58 {
  59         request_queue_t *q = rq->q;
  60         elevator_t *e = q->elevator;
  61
  62         if (e->ops->elevator_allow_merge_fn)
  63                 return e->ops->elevator_allow_merge_fn(q, rq, bio);
  64
  65         return 1;
  66 }
  67
  68 /*
  69  * can we safely merge with this request?
  70  */
  71 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  72 {
  73         if (!rq_mergeable(rq))
  74                 return 0;
  75
  76         /*
  77          * different data direction or already started, don't merge
  78          */
  79         if (bio_data_dir(bio) != rq_data_dir(rq))
  80                 return 0;
  81
  82         /*
  83          * must be same device and not a special request
  84          */
  85         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
  86                 return 0;
  87
  88         if (!elv_iosched_allow_merge(rq, bio))
  89                 return 0;
  90
  91         return 1;
  92 }
  93 EXPORT_SYMBOL(elv_rq_merge_ok);
  94
  95 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
  96 {
  97         int ret = ELEVATOR_NO_MERGE;
  98
  99         /*
 100          * we can merge and sequence is ok, check if it's possible
 101          */
 102         if (elv_rq_merge_ok(__rq, bio)) {
 103                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
 104                         ret = ELEVATOR_BACK_MERGE;
 105                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
 106                         ret = ELEVATOR_FRONT_MERGE;
 107         }
 108
 109         return ret;
 110 }
 111
 112 static struct elevator_type *elevator_find(const char *name)
 113 {
 114         struct elevator_type *e;
 115         struct list_head *entry;
 116
 117         list_for_each(entry, &elv_list) {
 118
 119                 e = list_entry(entry, struct elevator_type, list);
 120
 121                 if (!strcmp(e->elevator_name, name))
 122                         return e;
 123         }
 124
 125         return NULL;
 126 }
 127
 128 static void elevator_put(struct elevator_type *e)
 129 {
 130         module_put(e->elevator_owner);
 131 }
 132
 133 static struct elevator_type *elevator_get(const char *name)
 134 {
 135         struct elevator_type *e;
 136
 137         spin_lock_irq(&elv_list_lock);
 138
 139         e = elevator_find(name);
 140         if (e && !try_module_get(e->elevator_owner))
 141                 e = NULL;
 142
 143         spin_unlock_irq(&elv_list_lock);
 144
 145         return e;
 146 }
 147
 148 static void *elevator_init_queue(request_queue_t *q, struct elevator_queue *eq)
 149 {
 150         return eq->ops->elevator_init_fn(q);
 151 }
 152
 153 static void elevator_attach(request_queue_t *q, struct elevator_queue *eq,
 154                            void *data)
 155 {
 156         q->elevator = eq;
 157         eq->elevator_data = data;
 158 }
 159
 160 static char chosen_elevator[16];
 161
 162 static int __init elevator_setup(char *str)
 163 {
 164         /*
 165          * Be backwards-compatible with previous kernels, so users
 166          * won't get the wrong elevator.
 167          */
 168         if (!strcmp(str, "as"))
 169                 strcpy(chosen_elevator, "anticipatory");
 170         else
 171                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 172         return 1;
 173 }
 174
 175 __setup("elevator=", elevator_setup);
 176
 177 static struct kobj_type elv_ktype;
 178
 179 static elevator_t *elevator_alloc(request_queue_t *q, struct elevator_type *e)
 180 {
 181         elevator_t *eq;
 182         int i;
 183
 184         eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL, q->node);
 185         if (unlikely(!eq))
 186                 goto err;
 187
 188         memset(eq, 0, sizeof(*eq));
 189         eq->ops = &e->ops;
 190         eq->elevator_type = e;
 191         kobject_init(&eq->kobj);
 192         snprintf(eq->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
 193         eq->kobj.ktype = &elv_ktype;
 194         mutex_init(&eq->sysfs_lock);
 195
 196         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
 197                                         GFP_KERNEL, q->node);
 198         if (!eq->hash)
 199                 goto err;
 200
 201         for (i = 0; i < ELV_HASH_ENTRIES; i++)
 202                 INIT_HLIST_HEAD(&eq->hash[i]);
 203
 204         return eq;
 205 err:
 206         kfree(eq);
 207         elevator_put(e);
 208         return NULL;
 209 }
 210
 211 static void elevator_release(struct kobject *kobj)
 212 {
 213         elevator_t *e = container_of(kobj, elevator_t, kobj);
 214
 215         elevator_put(e->elevator_type);
 216         kfree(e->hash);
 217         kfree(e);
 218 }
 219
 220 int elevator_init(request_queue_t *q, char *name)
 221 {
 222         struct elevator_type *e = NULL;
 223         struct elevator_queue *eq;
 224         int ret = 0;
 225         void *data;
 226
 227         INIT_LIST_HEAD(&q->queue_head);
 228         q->last_merge = NULL;
 229         q->end_sector = 0;
 230         q->boundary_rq = NULL;
 231
 232         if (name && !(e = elevator_get(name)))
 233                 return -EINVAL;
 234
 235         if (!e && *chosen_elevator && !(e = elevator_get(chosen_elevator)))
 236                 printk("I/O scheduler %s not found\n", chosen_elevator);
 237
 238         if (!e && !(e = elevator_get(CONFIG_DEFAULT_IOSCHED))) {
 239                 printk("Default I/O scheduler not found, using no-op\n");
 240                 e = elevator_get("noop");
 241         }
 242
 243         eq = elevator_alloc(q, e);
 244         if (!eq)
 245                 return -ENOMEM;
 246
 247         data = elevator_init_queue(q, eq);
 248         if (!data) {
 249                 kobject_put(&eq->kobj);
 250                 return -ENOMEM;
 251         }
 252
 253         elevator_attach(q, eq, data);
 254         return ret;
 255 }
 256
 257 EXPORT_SYMBOL(elevator_init);
 258
 259 void elevator_exit(elevator_t *e)
 260 {
 261         mutex_lock(&e->sysfs_lock);
 262         if (e->ops->elevator_exit_fn)
 263                 e->ops->elevator_exit_fn(e);
 264         e->ops = NULL;
 265         mutex_unlock(&e->sysfs_lock);
 266
 267         kobject_put(&e->kobj);
 268 }
 269
 270 EXPORT_SYMBOL(elevator_exit);
 271
 272 static inline void __elv_rqhash_del(struct request *rq)
 273 {
 274         hlist_del_init(&rq->hash);
 275 }
 276
 277 static void elv_rqhash_del(request_queue_t *q, struct request *rq)
 278 {
 279         if (ELV_ON_HASH(rq))
 280                 __elv_rqhash_del(rq);
 281 }
 282
 283 static void elv_rqhash_add(request_queue_t *q, struct request *rq)
 284 {
 285         elevator_t *e = q->elevator;
 286
 287         BUG_ON(ELV_ON_HASH(rq));
 288         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
 289 }
 290
 291 static void elv_rqhash_reposition(request_queue_t *q, struct request *rq)
 292 {
 293         __elv_rqhash_del(rq);
 294         elv_rqhash_add(q, rq);
 295 }
 296
 297 static struct request *elv_rqhash_find(request_queue_t *q, sector_t offset)
 298 {
 299         elevator_t *e = q->elevator;
 300         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
 301         struct hlist_node *entry, *next;
 302         struct request *rq;
 303
 304         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
 305                 BUG_ON(!ELV_ON_HASH(rq));
 306
 307                 if (unlikely(!rq_mergeable(rq))) {
 308                         __elv_rqhash_del(rq);
 309                         continue;
 310                 }
 311
 312                 if (rq_hash_key(rq) == offset)
 313                         return rq;
 314         }
 315
 316         return NULL;
 317 }
 318
 319 /*
 320  * RB-tree support functions for inserting/lookup/removal of requests
 321  * in a sorted RB tree.
 322  */
 323 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
 324 {
 325         struct rb_node **p = &root->rb_node;
 326         struct rb_node *parent = NULL;
 327         struct request *__rq;
 328
 329         while (*p) {
 330                 parent = *p;
 331                 __rq = rb_entry(parent, struct request, rb_node);
 332
 333                 if (rq->sector < __rq->sector)
 334                         p = &(*p)->rb_left;
 335                 else if (rq->sector > __rq->sector)
 336                         p = &(*p)->rb_right;
 337                 else
 338                         return __rq;
 339         }
 340
 341         rb_link_node(&rq->rb_node, parent, p);
 342         rb_insert_color(&rq->rb_node, root);
 343         return NULL;
 344 }
 345
 346 EXPORT_SYMBOL(elv_rb_add);
 347
 348 void elv_rb_del(struct rb_root *root, struct request *rq)
 349 {
 350         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 351         rb_erase(&rq->rb_node, root);
 352         RB_CLEAR_NODE(&rq->rb_node);
 353 }
 354
 355 EXPORT_SYMBOL(elv_rb_del);
 356
 357 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 358 {
 359         struct rb_node *n = root->rb_node;
 360         struct request *rq;
 361
 362         while (n) {
 363                 rq = rb_entry(n, struct request, rb_node);
 364
 365                 if (sector < rq->sector)
 366                         n = n->rb_left;
 367                 else if (sector > rq->sector)
 368                         n = n->rb_right;
 369                 else
 370                         return rq;
 371         }
 372
 373         return NULL;
 374 }
 375
 376 EXPORT_SYMBOL(elv_rb_find);
 377
 378 /*
 379  * Insert rq into dispatch queue of q.  Queue lock must be held on
 380  * entry.  rq is sort insted into the dispatch queue. To be used by
 381  * specific elevators.
 382  */
 383 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
 384 {
 385         sector_t boundary;
 386         struct list_head *entry;
 387
 388         if (q->last_merge == rq)
 389                 q->last_merge = NULL;
 390
 391         elv_rqhash_del(q, rq);
 392
 393         q->nr_sorted--;
 394
 395         boundary = q->end_sector;
 396
 397         list_for_each_prev(entry, &q->queue_head) {
 398                 struct request *pos = list_entry_rq(entry);
 399
 400                 if (pos->cmd_flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
 401                         break;
 402                 if (rq->sector >= boundary) {
 403                         if (pos->sector < boundary)
 404                                 continue;
 405                 } else {
 406                         if (pos->sector >= boundary)
 407                                 break;
 408                 }
 409                 if (rq->sector >= pos->sector)
 410                         break;
 411         }
 412
 413         list_add(&rq->queuelist, entry);
 414 }
 415
 416 EXPORT_SYMBOL(elv_dispatch_sort);
 417
 418 /*
 419  * Insert rq into dispatch queue of q.  Queue lock must be held on
 420  * entry.  rq is added to the back of the dispatch queue. To be used by
 421  * specific elevators.
 422  */
 423 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 424 {
 425         if (q->last_merge == rq)
 426                 q->last_merge = NULL;
 427
 428         elv_rqhash_del(q, rq);
 429
 430         q->nr_sorted--;
 431
 432         q->end_sector = rq_end_sector(rq);
 433         q->boundary_rq = rq;
 434         list_add_tail(&rq->queuelist, &q->queue_head);
 435 }
 436
 437 EXPORT_SYMBOL(elv_dispatch_add_tail);
 438
 439 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 440 {
 441         elevator_t *e = q->elevator;
 442         struct request *__rq;
 443         int ret;
 444
 445         /*
 446          * First try one-hit cache.
 447          */
 448         if (q->last_merge) {
 449                 ret = elv_try_merge(q->last_merge, bio);
 450                 if (ret != ELEVATOR_NO_MERGE) {
 451                         *req = q->last_merge;
 452                         return ret;
 453                 }
 454         }
 455
 456         /*
 457          * See if our hash lookup can find a potential backmerge.
 458          */
 459         __rq = elv_rqhash_find(q, bio->bi_sector);
 460         if (__rq && elv_rq_merge_ok(__rq, bio)) {
 461                 *req = __rq;
 462                 return ELEVATOR_BACK_MERGE;
 463         }
 464
 465         if (e->ops->elevator_merge_fn)
 466                 return e->ops->elevator_merge_fn(q, req, bio);
 467
 468         return ELEVATOR_NO_MERGE;
 469 }
 470
 471 void elv_merged_request(request_queue_t *q, struct request *rq, int type)
 472 {
 473         elevator_t *e = q->elevator;
 474
 475         if (e->ops->elevator_merged_fn)
 476                 e->ops->elevator_merged_fn(q, rq, type);
 477
 478         if (type == ELEVATOR_BACK_MERGE)
 479                 elv_rqhash_reposition(q, rq);
 480
 481         q->last_merge = rq;
 482 }
 483
 484 void elv_merge_requests(request_queue_t *q, struct request *rq,
 485                              struct request *next)
 486 {
 487         elevator_t *e = q->elevator;
 488
 489         if (e->ops->elevator_merge_req_fn)
 490                 e->ops->elevator_merge_req_fn(q, rq, next);
 491
 492         elv_rqhash_reposition(q, rq);
 493         elv_rqhash_del(q, next);
 494
 495         q->nr_sorted--;
 496         q->last_merge = rq;
 497 }
 498
 499 void elv_requeue_request(request_queue_t *q, struct request *rq)
 500 {
 501         elevator_t *e = q->elevator;
 502
 503         /*
 504          * it already went through dequeue, we need to decrement the
 505          * in_flight count again
 506          */
 507         if (blk_account_rq(rq)) {
 508                 q->in_flight--;
 509                 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
 510                         e->ops->elevator_deactivate_req_fn(q, rq);
 511         }
 512
 513         rq->cmd_flags &= ~REQ_STARTED;
 514
 515         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 516 }
 517
 518 static void elv_drain_elevator(request_queue_t *q)
 519 {
 520         static int printed;
 521         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 522                 ;
 523         if (q->nr_sorted == 0)
 524                 return;
 525         if (printed++ < 10) {
 526                 printk(KERN_ERR "%s: forced dispatching is broken "
 527                        "(nr_sorted=%u), please report this\n",
 528                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 529         }
 530 }
 531
 532 void elv_insert(request_queue_t *q, struct request *rq, int where)
 533 {
 534         struct list_head *pos;
 535         unsigned ordseq;
 536         int unplug_it = 1;
 537
 538         blk_add_trace_rq(q, rq, BLK_TA_INSERT);
 539
 540         rq->q = q;
 541
 542         switch (where) {
 543         case ELEVATOR_INSERT_FRONT:
 544                 rq->cmd_flags |= REQ_SOFTBARRIER;
 545
 546                 list_add(&rq->queuelist, &q->queue_head);
 547                 break;
 548
 549         case ELEVATOR_INSERT_BACK:
 550                 rq->cmd_flags |= REQ_SOFTBARRIER;
 551                 elv_drain_elevator(q);
 552                 list_add_tail(&rq->queuelist, &q->queue_head);
 553                 /*
 554                  * We kick the queue here for the following reasons.
 555                  * - The elevator might have returned NULL previously
 556                  *   to delay requests and returned them now.  As the
 557                  *   queue wasn't empty before this request, ll_rw_blk
 558                  *   won't run the queue on return, resulting in hang.
 559                  * - Usually, back inserted requests won't be merged
 560                  *   with anything.  There's no point in delaying queue
 561                  *   processing.
 562                  */
 563                 blk_remove_plug(q);
 564                 q->request_fn(q);
 565                 break;
 566
 567         case ELEVATOR_INSERT_SORT:
 568                 BUG_ON(!blk_fs_request(rq));
 569                 rq->cmd_flags |= REQ_SORTED;
 570                 q->nr_sorted++;
 571                 if (rq_mergeable(rq)) {
 572                         elv_rqhash_add(q, rq);
 573                         if (!q->last_merge)
 574                                 q->last_merge = rq;
 575                 }
 576
 577                 /*
 578                  * Some ioscheds (cfq) run q->request_fn directly, so
 579                  * rq cannot be accessed after calling
 580                  * elevator_add_req_fn.
 581                  */
 582                 q->elevator->ops->elevator_add_req_fn(q, rq);
 583                 break;
 584
 585         case ELEVATOR_INSERT_REQUEUE:
 586                 /*
 587                  * If ordered flush isn't in progress, we do front
 588                  * insertion; otherwise, requests should be requeued
 589                  * in ordseq order.
 590                  */
 591                 rq->cmd_flags |= REQ_SOFTBARRIER;
 592
 593                 /*
 594                  * Most requeues happen because of a busy condition,
 595                  * don't force unplug of the queue for that case.
 596                  */
 597                 unplug_it = 0;
 598
 599                 if (q->ordseq == 0) {
 600                         list_add(&rq->queuelist, &q->queue_head);
 601                         break;
 602                 }
 603
 604                 ordseq = blk_ordered_req_seq(rq);
 605
 606                 list_for_each(pos, &q->queue_head) {
 607                         struct request *pos_rq = list_entry_rq(pos);
 608                         if (ordseq <= blk_ordered_req_seq(pos_rq))
 609                                 break;
 610                 }
 611
 612                 list_add_tail(&rq->queuelist, pos);
 613                 break;
 614
 615         default:
 616                 printk(KERN_ERR "%s: bad insertion point %d\n",
 617                        __FUNCTION__, where);
 618                 BUG();
 619         }
 620
 621         if (unplug_it && blk_queue_plugged(q)) {
 622                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 623                         - q->in_flight;
 624
 625                 if (nrq >= q->unplug_thresh)
 626                         __generic_unplug_device(q);
 627         }
 628 }
 629
 630 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 631                        int plug)
 632 {
 633         if (q->ordcolor)
 634                 rq->cmd_flags |= REQ_ORDERED_COLOR;
 635
 636         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 637                 /*
 638                  * toggle ordered color
 639                  */
 640                 if (blk_barrier_rq(rq))
 641                         q->ordcolor ^= 1;
 642
 643                 /*
 644                  * barriers implicitly indicate back insertion
 645                  */
 646                 if (where == ELEVATOR_INSERT_SORT)
 647                         where = ELEVATOR_INSERT_BACK;
 648
 649                 /*
 650                  * this request is scheduling boundary, update
 651                  * end_sector
 652                  */
 653                 if (blk_fs_request(rq)) {
 654                         q->end_sector = rq_end_sector(rq);
 655                         q->boundary_rq = rq;
 656                 }
 657         } else if (!(rq->cmd_flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
 658                 where = ELEVATOR_INSERT_BACK;
 659
 660         if (plug)
 661                 blk_plug_device(q);
 662
 663         elv_insert(q, rq, where);
 664 }
 665
 666 EXPORT_SYMBOL(__elv_add_request);
 667
 668 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 669                      int plug)
 670 {
 671         unsigned long flags;
 672
 673         spin_lock_irqsave(q->queue_lock, flags);
 674         __elv_add_request(q, rq, where, plug);
 675         spin_unlock_irqrestore(q->queue_lock, flags);
 676 }
 677
 678 EXPORT_SYMBOL(elv_add_request);
 679
 680 static inline struct request *__elv_next_request(request_queue_t *q)
 681 {
 682         struct request *rq;
 683
 684         while (1) {
 685                 while (!list_empty(&q->queue_head)) {
 686                         rq = list_entry_rq(q->queue_head.next);
 687                         if (blk_do_ordered(q, &rq))
 688                                 return rq;
 689                 }
 690
 691                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 692                         return NULL;
 693         }
 694 }
 695
 696 struct request *elv_next_request(request_queue_t *q)
 697 {
 698         struct request *rq;
 699         int ret;
 700
 701         while ((rq = __elv_next_request(q)) != NULL) {
 702                 if (!(rq->cmd_flags & REQ_STARTED)) {
 703                         elevator_t *e = q->elevator;
 704
 705                         /*
 706                          * This is the first time the device driver
 707                          * sees this request (possibly after
 708                          * requeueing).  Notify IO scheduler.
 709                          */
 710                         if (blk_sorted_rq(rq) &&
 711                             e->ops->elevator_activate_req_fn)
 712                                 e->ops->elevator_activate_req_fn(q, rq);
 713
 714                         /*
 715                          * just mark as started even if we don't start
 716                          * it, a request that has been delayed should
 717                          * not be passed by new incoming requests
 718                          */
 719                         rq->cmd_flags |= REQ_STARTED;
 720                         blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
 721                 }
 722
 723                 if (!q->boundary_rq || q->boundary_rq == rq) {
 724                         q->end_sector = rq_end_sector(rq);
 725                         q->boundary_rq = NULL;
 726                 }
 727
 728                 if ((rq->cmd_flags & REQ_DONTPREP) || !q->prep_rq_fn)
 729                         break;
 730
 731                 ret = q->prep_rq_fn(q, rq);
 732                 if (ret == BLKPREP_OK) {
 733                         break;
 734                 } else if (ret == BLKPREP_DEFER) {
 735                         /*
 736                          * the request may have been (partially) prepped.
 737                          * we need to keep this request in the front to
 738                          * avoid resource deadlock.  REQ_STARTED will
 739                          * prevent other fs requests from passing this one.
 740                          */
 741                         rq = NULL;
 742                         break;
 743                 } else if (ret == BLKPREP_KILL) {
 744                         int nr_bytes = rq->hard_nr_sectors << 9;
 745
 746                         if (!nr_bytes)
 747                                 nr_bytes = rq->data_len;
 748
 749                         blkdev_dequeue_request(rq);
 750                         rq->cmd_flags |= REQ_QUIET;
 751                         end_that_request_chunk(rq, 0, nr_bytes);
 752                         end_that_request_last(rq, 0);
 753                 } else {
 754                         printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
 755                                                                 ret);
 756                         break;
 757                 }
 758         }
 759
 760         return rq;
 761 }
 762
 763 EXPORT_SYMBOL(elv_next_request);
 764
 765 void elv_dequeue_request(request_queue_t *q, struct request *rq)
 766 {
 767         BUG_ON(list_empty(&rq->queuelist));
 768         BUG_ON(ELV_ON_HASH(rq));
 769
 770         list_del_init(&rq->queuelist);
 771
 772         /*
 773          * the time frame between a request being removed from the lists
 774          * and to it is freed is accounted as io that is in progress at
 775          * the driver side.
 776          */
 777         if (blk_account_rq(rq))
 778                 q->in_flight++;
 779 }
 780
 781 EXPORT_SYMBOL(elv_dequeue_request);
 782
 783 int elv_queue_empty(request_queue_t *q)
 784 {
 785         elevator_t *e = q->elevator;
 786
 787         if (!list_empty(&q->queue_head))
 788                 return 0;
 789
 790         if (e->ops->elevator_queue_empty_fn)
 791                 return e->ops->elevator_queue_empty_fn(q);
 792
 793         return 1;
 794 }
 795
 796 EXPORT_SYMBOL(elv_queue_empty);
 797
 798 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
 799 {
 800         elevator_t *e = q->elevator;
 801
 802         if (e->ops->elevator_latter_req_fn)
 803                 return e->ops->elevator_latter_req_fn(q, rq);
 804         return NULL;
 805 }
 806
 807 struct request *elv_former_request(request_queue_t *q, struct request *rq)
 808 {
 809         elevator_t *e = q->elevator;
 810
 811         if (e->ops->elevator_former_req_fn)
 812                 return e->ops->elevator_former_req_fn(q, rq);
 813         return NULL;
 814 }
 815
 816 int elv_set_request(request_queue_t *q, struct request *rq, gfp_t gfp_mask)
 817 {
 818         elevator_t *e = q->elevator;
 819
 820         if (e->ops->elevator_set_req_fn)
 821                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
 822
 823         rq->elevator_private = NULL;
 824         return 0;
 825 }
 826
 827 void elv_put_request(request_queue_t *q, struct request *rq)
 828 {
 829         elevator_t *e = q->elevator;
 830
 831         if (e->ops->elevator_put_req_fn)
 832                 e->ops->elevator_put_req_fn(rq);
 833 }
 834
 835 int elv_may_queue(request_queue_t *q, int rw)
 836 {
 837         elevator_t *e = q->elevator;
 838
 839         if (e->ops->elevator_may_queue_fn)
 840                 return e->ops->elevator_may_queue_fn(q, rw);
 841
 842         return ELV_MQUEUE_MAY;
 843 }
 844
 845 void elv_completed_request(request_queue_t *q, struct request *rq)
 846 {
 847         elevator_t *e = q->elevator;
 848
 849         /*
 850          * request is released from the driver, io must be done
 851          */
 852         if (blk_account_rq(rq)) {
 853                 q->in_flight--;
 854                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 855                         e->ops->elevator_completed_req_fn(q, rq);
 856         }
 857
 858         /*
 859          * Check if the queue is waiting for fs requests to be
 860          * drained for flush sequence.
 861          */
 862         if (unlikely(q->ordseq)) {
 863                 struct request *first_rq = list_entry_rq(q->queue_head.next);
 864                 if (q->in_flight == 0 &&
 865                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 866                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
 867                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 868                         q->request_fn(q);
 869                 }
 870         }
 871 }
 872
 873 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 874
 875 static ssize_t
 876 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 877 {
 878         elevator_t *e = container_of(kobj, elevator_t, kobj);
 879         struct elv_fs_entry *entry = to_elv(attr);
 880         ssize_t error;
 881
 882         if (!entry->show)
 883                 return -EIO;
 884
 885         mutex_lock(&e->sysfs_lock);
 886         error = e->ops ? entry->show(e, page) : -ENOENT;
 887         mutex_unlock(&e->sysfs_lock);
 888         return error;
 889 }
 890
 891 static ssize_t
 892 elv_attr_store(struct kobject *kobj, struct attribute *attr,
 893                const char *page, size_t length)
 894 {
 895         elevator_t *e = container_of(kobj, elevator_t, kobj);
 896         struct elv_fs_entry *entry = to_elv(attr);
 897         ssize_t error;
 898
 899         if (!entry->store)
 900                 return -EIO;
 901
 902         mutex_lock(&e->sysfs_lock);
 903         error = e->ops ? entry->store(e, page, length) : -ENOENT;
 904         mutex_unlock(&e->sysfs_lock);
 905         return error;
 906 }
 907
 908 static struct sysfs_ops elv_sysfs_ops = {
 909         .show   = elv_attr_show,
 910         .store  = elv_attr_store,
 911 };
 912
 913 static struct kobj_type elv_ktype = {
 914         .sysfs_ops      = &elv_sysfs_ops,
 915         .release        = elevator_release,
 916 };
 917
 918 int elv_register_queue(struct request_queue *q)
 919 {
 920         elevator_t *e = q->elevator;
 921         int error;
 922
 923         e->kobj.parent = &q->kobj;
 924
 925         error = kobject_add(&e->kobj);
 926         if (!error) {
 927                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
 928                 if (attr) {
 929                         while (attr->attr.name) {
 930                                 if (sysfs_create_file(&e->kobj, &attr->attr))
 931                                         break;
 932                                 attr++;
 933                         }
 934                 }
 935                 kobject_uevent(&e->kobj, KOBJ_ADD);
 936         }
 937         return error;
 938 }
 939
 940 static void __elv_unregister_queue(elevator_t *e)
 941 {
 942         kobject_uevent(&e->kobj, KOBJ_REMOVE);
 943         kobject_del(&e->kobj);
 944 }
 945
 946 void elv_unregister_queue(struct request_queue *q)
 947 {
 948         if (q)
 949                 __elv_unregister_queue(q->elevator);
 950 }
 951
 952 int elv_register(struct elevator_type *e)
 953 {
 954         spin_lock_irq(&elv_list_lock);
 955         BUG_ON(elevator_find(e->elevator_name));
 956         list_add_tail(&e->list, &elv_list);
 957         spin_unlock_irq(&elv_list_lock);
 958
 959         printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 960         if (!strcmp(e->elevator_name, chosen_elevator) ||
 961                         (!*chosen_elevator &&
 962                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
 963                                 printk(" (default)");
 964         printk("\n");
 965         return 0;
 966 }
 967 EXPORT_SYMBOL_GPL(elv_register);
 968
 969 void elv_unregister(struct elevator_type *e)
 970 {
 971         struct task_struct *g, *p;
 972
 973         /*
 974          * Iterate every thread in the process to remove the io contexts.
 975          */
 976         if (e->ops.trim) {
 977                 read_lock(&tasklist_lock);
 978                 do_each_thread(g, p) {
 979                         task_lock(p);
 980                         if (p->io_context)
 981                                 e->ops.trim(p->io_context);
 982                         task_unlock(p);
 983                 } while_each_thread(g, p);
 984                 read_unlock(&tasklist_lock);
 985         }
 986
 987         spin_lock_irq(&elv_list_lock);
 988         list_del_init(&e->list);
 989         spin_unlock_irq(&elv_list_lock);
 990 }
 991 EXPORT_SYMBOL_GPL(elv_unregister);
 992
 993 /*
 994  * switch to new_e io scheduler. be careful not to introduce deadlocks -
 995  * we don't free the old io scheduler, before we have allocated what we
 996  * need for the new one. this way we have a chance of going back to the old
 997  * one, if the new one fails init for some reason.
 998  */
 999 static int elevator_switch(request_queue_t *q, struct elevator_type *new_e)
1000 {
1001         elevator_t *old_elevator, *e;
1002         void *data;
1003
1004         /*
1005          * Allocate new elevator
1006          */
1007         e = elevator_alloc(q, new_e);
1008         if (!e)
1009                 return 0;
1010
1011         data = elevator_init_queue(q, e);
1012         if (!data) {
1013                 kobject_put(&e->kobj);
1014                 return 0;
1015         }
1016
1017         /*
1018          * Turn on BYPASS and drain all requests w/ elevator private data
1019          */
1020         spin_lock_irq(q->queue_lock);
1021
1022         set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1023
1024         elv_drain_elevator(q);
1025
1026         while (q->rq.elvpriv) {
1027                 blk_remove_plug(q);
1028                 q->request_fn(q);
1029                 spin_unlock_irq(q->queue_lock);
1030                 msleep(10);
1031                 spin_lock_irq(q->queue_lock);
1032                 elv_drain_elevator(q);
1033         }
1034
1035         /*
1036          * Remember old elevator.
1037          */
1038         old_elevator = q->elevator;
1039
1040         /*
1041          * attach and start new elevator
1042          */
1043         elevator_attach(q, e, data);
1044
1045         spin_unlock_irq(q->queue_lock);
1046
1047         __elv_unregister_queue(old_elevator);
1048
1049         if (elv_register_queue(q))
1050                 goto fail_register;
1051
1052         /*
1053          * finally exit old elevator and turn off BYPASS.
1054          */
1055         elevator_exit(old_elevator);
1056         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1057         return 1;
1058
1059 fail_register:
1060         /*
1061          * switch failed, exit the new io scheduler and reattach the old
1062          * one again (along with re-adding the sysfs dir)
1063          */
1064         elevator_exit(e);
1065         q->elevator = old_elevator;
1066         elv_register_queue(q);
1067         clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
1068         return 0;
1069 }
1070
1071 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
1072 {
1073         char elevator_name[ELV_NAME_MAX];
1074         size_t len;
1075         struct elevator_type *e;
1076
1077         elevator_name[sizeof(elevator_name) - 1] = '\0';
1078         strncpy(elevator_name, name, sizeof(elevator_name) - 1);
1079         len = strlen(elevator_name);
1080
1081         if (len && elevator_name[len - 1] == '\n')
1082                 elevator_name[len - 1] = '\0';
1083
1084         e = elevator_get(elevator_name);
1085         if (!e) {
1086                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1087                 return -EINVAL;
1088         }
1089
1090         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1091                 elevator_put(e);
1092                 return count;
1093         }
1094
1095         if (!elevator_switch(q, e))
1096                 printk(KERN_ERR "elevator: switch to %s failed\n",elevator_name);
1097         return count;
1098 }
1099
1100 ssize_t elv_iosched_show(request_queue_t *q, char *name)
1101 {
1102         elevator_t *e = q->elevator;
1103         struct elevator_type *elv = e->elevator_type;
1104         struct list_head *entry;
1105         int len = 0;
1106
1107         spin_lock_irq(&elv_list_lock);
1108         list_for_each(entry, &elv_list) {
1109                 struct elevator_type *__e;
1110
1111                 __e = list_entry(entry, struct elevator_type, list);
1112                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1113                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1114                 else
1115                         len += sprintf(name+len, "%s ", __e->elevator_name);
1116         }
1117         spin_unlock_irq(&elv_list_lock);
1118
1119         len += sprintf(len+name, "\n");
1120         return len;
1121 }
1122
1123 struct request *elv_rb_former_request(request_queue_t *q, struct request *rq)
1124 {
1125         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1126
1127         if (rbprev)
1128                 return rb_entry_rq(rbprev);
1129
1130         return NULL;
1131 }
1132
1133 EXPORT_SYMBOL(elv_rb_former_request);
1134
1135 struct request *elv_rb_latter_request(request_queue_t *q, struct request *rq)
1136 {
1137         struct rb_node *rbnext = rb_next(&rq->rb_node);
1138
1139         if (rbnext)
1140                 return rb_entry_rq(rbnext);
1141
1142         return NULL;
1143 }
1144
1145 EXPORT_SYMBOL(elv_rb_latter_request);