git.oblomov.eu Git - 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@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 #include <linux/uaccess.h>
  38
  39 #include "blk.h"
  40
  41 static DEFINE_SPINLOCK(elv_list_lock);
  42 static LIST_HEAD(elv_list);
  43
  44 /*
  45  * Merge hash stuff.
  46  */
  47 static const int elv_hash_shift = 6;
  48 #define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
  49 #define ELV_HASH_FN(sec)        \
  50                 (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
  51 #define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
  52 #define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
  53 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
  54
  55 /*
  56  * Query io scheduler to see if the current process issuing bio may be
  57  * merged with rq.
  58  */
  59 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
  60 {
  61         struct request_queue *q = rq->q;
  62         elevator_t *e = q->elevator;
  63
  64         if (e->ops->elevator_allow_merge_fn)
  65                 return e->ops->elevator_allow_merge_fn(q, rq, bio);
  66
  67         return 1;
  68 }
  69
  70 /*
  71  * can we safely merge with this request?
  72  */
  73 int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  74 {
  75         if (!rq_mergeable(rq))
  76                 return 0;
  77
  78         /*
  79          * Don't merge file system requests and discard requests
  80          */
  81         if (bio_discard(bio) != bio_discard(rq->bio))
  82                 return 0;
  83
  84         /*
  85          * different data direction or already started, don't merge
  86          */
  87         if (bio_data_dir(bio) != rq_data_dir(rq))
  88                 return 0;
  89
  90         /*
  91          * must be same device and not a special request
  92          */
  93         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
  94                 return 0;
  95
  96         /*
  97          * only merge integrity protected bio into ditto rq
  98          */
  99         if (bio_integrity(bio) != blk_integrity_rq(rq))
 100                 return 0;
 101
 102         if (!elv_iosched_allow_merge(rq, bio))
 103                 return 0;
 104
 105         return 1;
 106 }
 107 EXPORT_SYMBOL(elv_rq_merge_ok);
 108
 109 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
 110 {
 111         int ret = ELEVATOR_NO_MERGE;
 112
 113         /*
 114          * we can merge and sequence is ok, check if it's possible
 115          */
 116         if (elv_rq_merge_ok(__rq, bio)) {
 117                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
 118                         ret = ELEVATOR_BACK_MERGE;
 119                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
 120                         ret = ELEVATOR_FRONT_MERGE;
 121         }
 122
 123         return ret;
 124 }
 125
 126 static struct elevator_type *elevator_find(const char *name)
 127 {
 128         struct elevator_type *e;
 129
 130         list_for_each_entry(e, &elv_list, list) {
 131                 if (!strcmp(e->elevator_name, name))
 132                         return e;
 133         }
 134
 135         return NULL;
 136 }
 137
 138 static void elevator_put(struct elevator_type *e)
 139 {
 140         module_put(e->elevator_owner);
 141 }
 142
 143 static struct elevator_type *elevator_get(const char *name)
 144 {
 145         struct elevator_type *e;
 146
 147         spin_lock(&elv_list_lock);
 148
 149         e = elevator_find(name);
 150         if (!e) {
 151                 char elv[ELV_NAME_MAX + strlen("-iosched")];
 152
 153                 spin_unlock(&elv_list_lock);
 154
 155                 if (!strcmp(name, "anticipatory"))
 156                         sprintf(elv, "as-iosched");
 157                 else
 158                         sprintf(elv, "%s-iosched", name);
 159
 160                 request_module("%s", elv);
 161                 spin_lock(&elv_list_lock);
 162                 e = elevator_find(name);
 163         }
 164
 165         if (e && !try_module_get(e->elevator_owner))
 166                 e = NULL;
 167
 168         spin_unlock(&elv_list_lock);
 169
 170         return e;
 171 }
 172
 173 static void *elevator_init_queue(struct request_queue *q,
 174                                  struct elevator_queue *eq)
 175 {
 176         return eq->ops->elevator_init_fn(q);
 177 }
 178
 179 static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
 180                            void *data)
 181 {
 182         q->elevator = eq;
 183         eq->elevator_data = data;
 184 }
 185
 186 static char chosen_elevator[16];
 187
 188 static int __init elevator_setup(char *str)
 189 {
 190         /*
 191          * Be backwards-compatible with previous kernels, so users
 192          * won't get the wrong elevator.
 193          */
 194         if (!strcmp(str, "as"))
 195                 strcpy(chosen_elevator, "anticipatory");
 196         else
 197                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 198         return 1;
 199 }
 200
 201 __setup("elevator=", elevator_setup);
 202
 203 static struct kobj_type elv_ktype;
 204
 205 static elevator_t *elevator_alloc(struct request_queue *q,
 206                                   struct elevator_type *e)
 207 {
 208         elevator_t *eq;
 209         int i;
 210
 211         eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL | __GFP_ZERO, q->node);
 212         if (unlikely(!eq))
 213                 goto err;
 214
 215         eq->ops = &e->ops;
 216         eq->elevator_type = e;
 217         kobject_init(&eq->kobj, &elv_ktype);
 218         mutex_init(&eq->sysfs_lock);
 219
 220         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
 221                                         GFP_KERNEL, q->node);
 222         if (!eq->hash)
 223                 goto err;
 224
 225         for (i = 0; i < ELV_HASH_ENTRIES; i++)
 226                 INIT_HLIST_HEAD(&eq->hash[i]);
 227
 228         return eq;
 229 err:
 230         kfree(eq);
 231         elevator_put(e);
 232         return NULL;
 233 }
 234
 235 static void elevator_release(struct kobject *kobj)
 236 {
 237         elevator_t *e = container_of(kobj, elevator_t, kobj);
 238
 239         elevator_put(e->elevator_type);
 240         kfree(e->hash);
 241         kfree(e);
 242 }
 243
 244 int elevator_init(struct request_queue *q, char *name)
 245 {
 246         struct elevator_type *e = NULL;
 247         struct elevator_queue *eq;
 248         int ret = 0;
 249         void *data;
 250
 251         INIT_LIST_HEAD(&q->queue_head);
 252         q->last_merge = NULL;
 253         q->end_sector = 0;
 254         q->boundary_rq = NULL;
 255
 256         if (name) {
 257                 e = elevator_get(name);
 258                 if (!e)
 259                         return -EINVAL;
 260         }
 261
 262         if (!e && *chosen_elevator) {
 263                 e = elevator_get(chosen_elevator);
 264                 if (!e)
 265                         printk(KERN_ERR "I/O scheduler %s not found\n",
 266                                                         chosen_elevator);
 267         }
 268
 269         if (!e) {
 270                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
 271                 if (!e) {
 272                         printk(KERN_ERR
 273                                 "Default I/O scheduler not found. " \
 274                                 "Using noop.\n");
 275                         e = elevator_get("noop");
 276                 }
 277         }
 278
 279         eq = elevator_alloc(q, e);
 280         if (!eq)
 281                 return -ENOMEM;
 282
 283         data = elevator_init_queue(q, eq);
 284         if (!data) {
 285                 kobject_put(&eq->kobj);
 286                 return -ENOMEM;
 287         }
 288
 289         elevator_attach(q, eq, data);
 290         return ret;
 291 }
 292 EXPORT_SYMBOL(elevator_init);
 293
 294 void elevator_exit(elevator_t *e)
 295 {
 296         mutex_lock(&e->sysfs_lock);
 297         if (e->ops->elevator_exit_fn)
 298                 e->ops->elevator_exit_fn(e);
 299         e->ops = NULL;
 300         mutex_unlock(&e->sysfs_lock);
 301
 302         kobject_put(&e->kobj);
 303 }
 304 EXPORT_SYMBOL(elevator_exit);
 305
 306 static void elv_activate_rq(struct request_queue *q, struct request *rq)
 307 {
 308         elevator_t *e = q->elevator;
 309
 310         if (e->ops->elevator_activate_req_fn)
 311                 e->ops->elevator_activate_req_fn(q, rq);
 312 }
 313
 314 static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
 315 {
 316         elevator_t *e = q->elevator;
 317
 318         if (e->ops->elevator_deactivate_req_fn)
 319                 e->ops->elevator_deactivate_req_fn(q, rq);
 320 }
 321
 322 static inline void __elv_rqhash_del(struct request *rq)
 323 {
 324         hlist_del_init(&rq->hash);
 325 }
 326
 327 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
 328 {
 329         if (ELV_ON_HASH(rq))
 330                 __elv_rqhash_del(rq);
 331 }
 332
 333 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
 334 {
 335         elevator_t *e = q->elevator;
 336
 337         BUG_ON(ELV_ON_HASH(rq));
 338         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
 339 }
 340
 341 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 342 {
 343         __elv_rqhash_del(rq);
 344         elv_rqhash_add(q, rq);
 345 }
 346
 347 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 348 {
 349         elevator_t *e = q->elevator;
 350         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
 351         struct hlist_node *entry, *next;
 352         struct request *rq;
 353
 354         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
 355                 BUG_ON(!ELV_ON_HASH(rq));
 356
 357                 if (unlikely(!rq_mergeable(rq))) {
 358                         __elv_rqhash_del(rq);
 359                         continue;
 360                 }
 361
 362                 if (rq_hash_key(rq) == offset)
 363                         return rq;
 364         }
 365
 366         return NULL;
 367 }
 368
 369 /*
 370  * RB-tree support functions for inserting/lookup/removal of requests
 371  * in a sorted RB tree.
 372  */
 373 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
 374 {
 375         struct rb_node **p = &root->rb_node;
 376         struct rb_node *parent = NULL;
 377         struct request *__rq;
 378
 379         while (*p) {
 380                 parent = *p;
 381                 __rq = rb_entry(parent, struct request, rb_node);
 382
 383                 if (rq->sector < __rq->sector)
 384                         p = &(*p)->rb_left;
 385                 else if (rq->sector > __rq->sector)
 386                         p = &(*p)->rb_right;
 387                 else
 388                         return __rq;
 389         }
 390
 391         rb_link_node(&rq->rb_node, parent, p);
 392         rb_insert_color(&rq->rb_node, root);
 393         return NULL;
 394 }
 395 EXPORT_SYMBOL(elv_rb_add);
 396
 397 void elv_rb_del(struct rb_root *root, struct request *rq)
 398 {
 399         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 400         rb_erase(&rq->rb_node, root);
 401         RB_CLEAR_NODE(&rq->rb_node);
 402 }
 403 EXPORT_SYMBOL(elv_rb_del);
 404
 405 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 406 {
 407         struct rb_node *n = root->rb_node;
 408         struct request *rq;
 409
 410         while (n) {
 411                 rq = rb_entry(n, struct request, rb_node);
 412
 413                 if (sector < rq->sector)
 414                         n = n->rb_left;
 415                 else if (sector > rq->sector)
 416                         n = n->rb_right;
 417                 else
 418                         return rq;
 419         }
 420
 421         return NULL;
 422 }
 423 EXPORT_SYMBOL(elv_rb_find);
 424
 425 /*
 426  * Insert rq into dispatch queue of q.  Queue lock must be held on
 427  * entry.  rq is sort instead into the dispatch queue. To be used by
 428  * specific elevators.
 429  */
 430 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
 431 {
 432         sector_t boundary;
 433         struct list_head *entry;
 434         int stop_flags;
 435
 436         if (q->last_merge == rq)
 437                 q->last_merge = NULL;
 438
 439         elv_rqhash_del(q, rq);
 440
 441         q->nr_sorted--;
 442
 443         boundary = q->end_sector;
 444         stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
 445         list_for_each_prev(entry, &q->queue_head) {
 446                 struct request *pos = list_entry_rq(entry);
 447
 448                 if (blk_discard_rq(rq) != blk_discard_rq(pos))
 449                         break;
 450                 if (rq_data_dir(rq) != rq_data_dir(pos))
 451                         break;
 452                 if (pos->cmd_flags & stop_flags)
 453                         break;
 454                 if (rq->sector >= boundary) {
 455                         if (pos->sector < boundary)
 456                                 continue;
 457                 } else {
 458                         if (pos->sector >= boundary)
 459                                 break;
 460                 }
 461                 if (rq->sector >= pos->sector)
 462                         break;
 463         }
 464
 465         list_add(&rq->queuelist, entry);
 466 }
 467 EXPORT_SYMBOL(elv_dispatch_sort);
 468
 469 /*
 470  * Insert rq into dispatch queue of q.  Queue lock must be held on
 471  * entry.  rq is added to the back of the dispatch queue. To be used by
 472  * specific elevators.
 473  */
 474 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 475 {
 476         if (q->last_merge == rq)
 477                 q->last_merge = NULL;
 478
 479         elv_rqhash_del(q, rq);
 480
 481         q->nr_sorted--;
 482
 483         q->end_sector = rq_end_sector(rq);
 484         q->boundary_rq = rq;
 485         list_add_tail(&rq->queuelist, &q->queue_head);
 486 }
 487 EXPORT_SYMBOL(elv_dispatch_add_tail);
 488
 489 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 490 {
 491         elevator_t *e = q->elevator;
 492         struct request *__rq;
 493         int ret;
 494
 495         /*
 496          * First try one-hit cache.
 497          */
 498         if (q->last_merge) {
 499                 ret = elv_try_merge(q->last_merge, bio);
 500                 if (ret != ELEVATOR_NO_MERGE) {
 501                         *req = q->last_merge;
 502                         return ret;
 503                 }
 504         }
 505
 506         if (blk_queue_nomerges(q))
 507                 return ELEVATOR_NO_MERGE;
 508
 509         /*
 510          * See if our hash lookup can find a potential backmerge.
 511          */
 512         __rq = elv_rqhash_find(q, bio->bi_sector);
 513         if (__rq && elv_rq_merge_ok(__rq, bio)) {
 514                 *req = __rq;
 515                 return ELEVATOR_BACK_MERGE;
 516         }
 517
 518         if (e->ops->elevator_merge_fn)
 519                 return e->ops->elevator_merge_fn(q, req, bio);
 520
 521         return ELEVATOR_NO_MERGE;
 522 }
 523
 524 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
 525 {
 526         elevator_t *e = q->elevator;
 527
 528         if (e->ops->elevator_merged_fn)
 529                 e->ops->elevator_merged_fn(q, rq, type);
 530
 531         if (type == ELEVATOR_BACK_MERGE)
 532                 elv_rqhash_reposition(q, rq);
 533
 534         q->last_merge = rq;
 535 }
 536
 537 void elv_merge_requests(struct request_queue *q, struct request *rq,
 538                              struct request *next)
 539 {
 540         elevator_t *e = q->elevator;
 541
 542         if (e->ops->elevator_merge_req_fn)
 543                 e->ops->elevator_merge_req_fn(q, rq, next);
 544
 545         elv_rqhash_reposition(q, rq);
 546         elv_rqhash_del(q, next);
 547
 548         q->nr_sorted--;
 549         q->last_merge = rq;
 550 }
 551
 552 void elv_requeue_request(struct request_queue *q, struct request *rq)
 553 {
 554         /*
 555          * it already went through dequeue, we need to decrement the
 556          * in_flight count again
 557          */
 558         if (blk_account_rq(rq)) {
 559                 q->in_flight--;
 560                 if (blk_sorted_rq(rq))
 561                         elv_deactivate_rq(q, rq);
 562         }
 563
 564         rq->cmd_flags &= ~REQ_STARTED;
 565
 566         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 567 }
 568
 569 static void elv_drain_elevator(struct request_queue *q)
 570 {
 571         static int printed;
 572         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 573                 ;
 574         if (q->nr_sorted == 0)
 575                 return;
 576         if (printed++ < 10) {
 577                 printk(KERN_ERR "%s: forced dispatching is broken "
 578                        "(nr_sorted=%u), please report this\n",
 579                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 580         }
 581 }
 582
 583 void elv_insert(struct request_queue *q, struct request *rq, int where)
 584 {
 585         struct list_head *pos;
 586         unsigned ordseq;
 587         int unplug_it = 1;
 588
 589         blk_add_trace_rq(q, rq, BLK_TA_INSERT);
 590
 591         rq->q = q;
 592
 593         switch (where) {
 594         case ELEVATOR_INSERT_FRONT:
 595                 rq->cmd_flags |= REQ_SOFTBARRIER;
 596
 597                 list_add(&rq->queuelist, &q->queue_head);
 598                 break;
 599
 600         case ELEVATOR_INSERT_BACK:
 601                 rq->cmd_flags |= REQ_SOFTBARRIER;
 602                 elv_drain_elevator(q);
 603                 list_add_tail(&rq->queuelist, &q->queue_head);
 604                 /*
 605                  * We kick the queue here for the following reasons.
 606                  * - The elevator might have returned NULL previously
 607                  *   to delay requests and returned them now.  As the
 608                  *   queue wasn't empty before this request, ll_rw_blk
 609                  *   won't run the queue on return, resulting in hang.
 610                  * - Usually, back inserted requests won't be merged
 611                  *   with anything.  There's no point in delaying queue
 612                  *   processing.
 613                  */
 614                 blk_remove_plug(q);
 615                 blk_start_queueing(q);
 616                 break;
 617
 618         case ELEVATOR_INSERT_SORT:
 619                 BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
 620                 rq->cmd_flags |= REQ_SORTED;
 621                 q->nr_sorted++;
 622                 if (rq_mergeable(rq)) {
 623                         elv_rqhash_add(q, rq);
 624                         if (!q->last_merge)
 625                                 q->last_merge = rq;
 626                 }
 627
 628                 /*
 629                  * Some ioscheds (cfq) run q->request_fn directly, so
 630                  * rq cannot be accessed after calling
 631                  * elevator_add_req_fn.
 632                  */
 633                 q->elevator->ops->elevator_add_req_fn(q, rq);
 634                 break;
 635
 636         case ELEVATOR_INSERT_REQUEUE:
 637                 /*
 638                  * If ordered flush isn't in progress, we do front
 639                  * insertion; otherwise, requests should be requeued
 640                  * in ordseq order.
 641                  */
 642                 rq->cmd_flags |= REQ_SOFTBARRIER;
 643
 644                 /*
 645                  * Most requeues happen because of a busy condition,
 646                  * don't force unplug of the queue for that case.
 647                  */
 648                 unplug_it = 0;
 649
 650                 if (q->ordseq == 0) {
 651                         list_add(&rq->queuelist, &q->queue_head);
 652                         break;
 653                 }
 654
 655                 ordseq = blk_ordered_req_seq(rq);
 656
 657                 list_for_each(pos, &q->queue_head) {
 658                         struct request *pos_rq = list_entry_rq(pos);
 659                         if (ordseq <= blk_ordered_req_seq(pos_rq))
 660                                 break;
 661                 }
 662
 663                 list_add_tail(&rq->queuelist, pos);
 664                 break;
 665
 666         default:
 667                 printk(KERN_ERR "%s: bad insertion point %d\n",
 668                        __func__, where);
 669                 BUG();
 670         }
 671
 672         if (unplug_it && blk_queue_plugged(q)) {
 673                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 674                         - q->in_flight;
 675
 676                 if (nrq >= q->unplug_thresh)
 677                         __generic_unplug_device(q);
 678         }
 679 }
 680
 681 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
 682                        int plug)
 683 {
 684         if (q->ordcolor)
 685                 rq->cmd_flags |= REQ_ORDERED_COLOR;
 686
 687         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 688                 /*
 689                  * toggle ordered color
 690                  */
 691                 if (blk_barrier_rq(rq))
 692                         q->ordcolor ^= 1;
 693
 694                 /*
 695                  * barriers implicitly indicate back insertion
 696                  */
 697                 if (where == ELEVATOR_INSERT_SORT)
 698                         where = ELEVATOR_INSERT_BACK;
 699
 700                 /*
 701                  * this request is scheduling boundary, update
 702                  * end_sector
 703                  */
 704                 if (blk_fs_request(rq) || blk_discard_rq(rq)) {
 705                         q->end_sector = rq_end_sector(rq);
 706                         q->boundary_rq = rq;
 707                 }
 708         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
 709                     where == ELEVATOR_INSERT_SORT)
 710                 where = ELEVATOR_INSERT_BACK;
 711
 712         if (plug)
 713                 blk_plug_device(q);
 714
 715         elv_insert(q, rq, where);
 716 }
 717 EXPORT_SYMBOL(__elv_add_request);
 718
 719 void elv_add_request(struct request_queue *q, struct request *rq, int where,
 720                      int plug)
 721 {
 722         unsigned long flags;
 723
 724         spin_lock_irqsave(q->queue_lock, flags);
 725         __elv_add_request(q, rq, where, plug);
 726         spin_unlock_irqrestore(q->queue_lock, flags);
 727 }
 728 EXPORT_SYMBOL(elv_add_request);
 729
 730 static inline struct request *__elv_next_request(struct request_queue *q)
 731 {
 732         struct request *rq;
 733
 734         while (1) {
 735                 while (!list_empty(&q->queue_head)) {
 736                         rq = list_entry_rq(q->queue_head.next);
 737                         if (blk_do_ordered(q, &rq))
 738                                 return rq;
 739                 }
 740
 741                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 742                         return NULL;
 743         }
 744 }
 745
 746 struct request *elv_next_request(struct request_queue *q)
 747 {
 748         struct request *rq;
 749         int ret;
 750
 751         while ((rq = __elv_next_request(q)) != NULL) {
 752                 /*
 753                  * Kill the empty barrier place holder, the driver must
 754                  * not ever see it.
 755                  */
 756                 if (blk_empty_barrier(rq)) {
 757                         __blk_end_request(rq, 0, blk_rq_bytes(rq));
 758                         continue;
 759                 }
 760                 if (!(rq->cmd_flags & REQ_STARTED)) {
 761                         /*
 762                          * This is the first time the device driver
 763                          * sees this request (possibly after
 764                          * requeueing).  Notify IO scheduler.
 765                          */
 766                         if (blk_sorted_rq(rq))
 767                                 elv_activate_rq(q, rq);
 768
 769                         /*
 770                          * just mark as started even if we don't start
 771                          * it, a request that has been delayed should
 772                          * not be passed by new incoming requests
 773                          */
 774                         rq->cmd_flags |= REQ_STARTED;
 775                         blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
 776                 }
 777
 778                 if (!q->boundary_rq || q->boundary_rq == rq) {
 779                         q->end_sector = rq_end_sector(rq);
 780                         q->boundary_rq = NULL;
 781                 }
 782
 783                 if (rq->cmd_flags & REQ_DONTPREP)
 784                         break;
 785
 786                 if (q->dma_drain_size && rq->data_len) {
 787                         /*
 788                          * make sure space for the drain appears we
 789                          * know we can do this because max_hw_segments
 790                          * has been adjusted to be one fewer than the
 791                          * device can handle
 792                          */
 793                         rq->nr_phys_segments++;
 794                 }
 795
 796                 if (!q->prep_rq_fn)
 797                         break;
 798
 799                 ret = q->prep_rq_fn(q, rq);
 800                 if (ret == BLKPREP_OK) {
 801                         break;
 802                 } else if (ret == BLKPREP_DEFER) {
 803                         /*
 804                          * the request may have been (partially) prepped.
 805                          * we need to keep this request in the front to
 806                          * avoid resource deadlock.  REQ_STARTED will
 807                          * prevent other fs requests from passing this one.
 808                          */
 809                         if (q->dma_drain_size && rq->data_len &&
 810                             !(rq->cmd_flags & REQ_DONTPREP)) {
 811                                 /*
 812                                  * remove the space for the drain we added
 813                                  * so that we don't add it again
 814                                  */
 815                                 --rq->nr_phys_segments;
 816                         }
 817
 818                         rq = NULL;
 819                         break;
 820                 } else if (ret == BLKPREP_KILL) {
 821                         rq->cmd_flags |= REQ_QUIET;
 822                         __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 823                 } else {
 824                         printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
 825                         break;
 826                 }
 827         }
 828
 829         return rq;
 830 }
 831 EXPORT_SYMBOL(elv_next_request);
 832
 833 void elv_dequeue_request(struct request_queue *q, struct request *rq)
 834 {
 835         BUG_ON(list_empty(&rq->queuelist));
 836         BUG_ON(ELV_ON_HASH(rq));
 837
 838         list_del_init(&rq->queuelist);
 839
 840         /*
 841          * the time frame between a request being removed from the lists
 842          * and to it is freed is accounted as io that is in progress at
 843          * the driver side.
 844          */
 845         if (blk_account_rq(rq))
 846                 q->in_flight++;
 847 }
 848
 849 int elv_queue_empty(struct request_queue *q)
 850 {
 851         elevator_t *e = q->elevator;
 852
 853         if (!list_empty(&q->queue_head))
 854                 return 0;
 855
 856         if (e->ops->elevator_queue_empty_fn)
 857                 return e->ops->elevator_queue_empty_fn(q);
 858
 859         return 1;
 860 }
 861 EXPORT_SYMBOL(elv_queue_empty);
 862
 863 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 864 {
 865         elevator_t *e = q->elevator;
 866
 867         if (e->ops->elevator_latter_req_fn)
 868                 return e->ops->elevator_latter_req_fn(q, rq);
 869         return NULL;
 870 }
 871
 872 struct request *elv_former_request(struct request_queue *q, struct request *rq)
 873 {
 874         elevator_t *e = q->elevator;
 875
 876         if (e->ops->elevator_former_req_fn)
 877                 return e->ops->elevator_former_req_fn(q, rq);
 878         return NULL;
 879 }
 880
 881 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
 882 {
 883         elevator_t *e = q->elevator;
 884
 885         if (e->ops->elevator_set_req_fn)
 886                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
 887
 888         rq->elevator_private = NULL;
 889         return 0;
 890 }
 891
 892 void elv_put_request(struct request_queue *q, struct request *rq)
 893 {
 894         elevator_t *e = q->elevator;
 895
 896         if (e->ops->elevator_put_req_fn)
 897                 e->ops->elevator_put_req_fn(rq);
 898 }
 899
 900 int elv_may_queue(struct request_queue *q, int rw)
 901 {
 902         elevator_t *e = q->elevator;
 903
 904         if (e->ops->elevator_may_queue_fn)
 905                 return e->ops->elevator_may_queue_fn(q, rw);
 906
 907         return ELV_MQUEUE_MAY;
 908 }
 909
 910 void elv_abort_queue(struct request_queue *q)
 911 {
 912         struct request *rq;
 913
 914         while (!list_empty(&q->queue_head)) {
 915                 rq = list_entry_rq(q->queue_head.next);
 916                 rq->cmd_flags |= REQ_QUIET;
 917                 blk_add_trace_rq(q, rq, BLK_TA_ABORT);
 918                 __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 919         }
 920 }
 921 EXPORT_SYMBOL(elv_abort_queue);
 922
 923 void elv_completed_request(struct request_queue *q, struct request *rq)
 924 {
 925         elevator_t *e = q->elevator;
 926
 927         /*
 928          * request is released from the driver, io must be done
 929          */
 930         if (blk_account_rq(rq)) {
 931                 q->in_flight--;
 932                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 933                         e->ops->elevator_completed_req_fn(q, rq);
 934         }
 935
 936         /*
 937          * Check if the queue is waiting for fs requests to be
 938          * drained for flush sequence.
 939          */
 940         if (unlikely(q->ordseq)) {
 941                 struct request *first_rq = list_entry_rq(q->queue_head.next);
 942                 if (q->in_flight == 0 &&
 943                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 944                     blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
 945                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 946                         blk_start_queueing(q);
 947                 }
 948         }
 949 }
 950
 951 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 952
 953 static ssize_t
 954 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 955 {
 956         elevator_t *e = container_of(kobj, elevator_t, kobj);
 957         struct elv_fs_entry *entry = to_elv(attr);
 958         ssize_t error;
 959
 960         if (!entry->show)
 961                 return -EIO;
 962
 963         mutex_lock(&e->sysfs_lock);
 964         error = e->ops ? entry->show(e, page) : -ENOENT;
 965         mutex_unlock(&e->sysfs_lock);
 966         return error;
 967 }
 968
 969 static ssize_t
 970 elv_attr_store(struct kobject *kobj, struct attribute *attr,
 971                const char *page, size_t length)
 972 {
 973         elevator_t *e = container_of(kobj, elevator_t, kobj);
 974         struct elv_fs_entry *entry = to_elv(attr);
 975         ssize_t error;
 976
 977         if (!entry->store)
 978                 return -EIO;
 979
 980         mutex_lock(&e->sysfs_lock);
 981         error = e->ops ? entry->store(e, page, length) : -ENOENT;
 982         mutex_unlock(&e->sysfs_lock);
 983         return error;
 984 }
 985
 986 static struct sysfs_ops elv_sysfs_ops = {
 987         .show   = elv_attr_show,
 988         .store  = elv_attr_store,
 989 };
 990
 991 static struct kobj_type elv_ktype = {
 992         .sysfs_ops      = &elv_sysfs_ops,
 993         .release        = elevator_release,
 994 };
 995
 996 int elv_register_queue(struct request_queue *q)
 997 {
 998         elevator_t *e = q->elevator;
 999         int error;
1000
1001         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1002         if (!error) {
1003                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1004                 if (attr) {
1005                         while (attr->attr.name) {
1006                                 if (sysfs_create_file(&e->kobj, &attr->attr))
1007                                         break;
1008                                 attr++;
1009                         }
1010                 }
1011                 kobject_uevent(&e->kobj, KOBJ_ADD);
1012         }
1013         return error;
1014 }
1015
1016 static void __elv_unregister_queue(elevator_t *e)
1017 {
1018         kobject_uevent(&e->kobj, KOBJ_REMOVE);
1019         kobject_del(&e->kobj);
1020 }
1021
1022 void elv_unregister_queue(struct request_queue *q)
1023 {
1024         if (q)
1025                 __elv_unregister_queue(q->elevator);
1026 }
1027
1028 void elv_register(struct elevator_type *e)
1029 {
1030         char *def = "";
1031
1032         spin_lock(&elv_list_lock);
1033         BUG_ON(elevator_find(e->elevator_name));
1034         list_add_tail(&e->list, &elv_list);
1035         spin_unlock(&elv_list_lock);
1036
1037         if (!strcmp(e->elevator_name, chosen_elevator) ||
1038                         (!*chosen_elevator &&
1039                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1040                                 def = " (default)";
1041
1042         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1043                                                                 def);
1044 }
1045 EXPORT_SYMBOL_GPL(elv_register);
1046
1047 void elv_unregister(struct elevator_type *e)
1048 {
1049         struct task_struct *g, *p;
1050
1051         /*
1052          * Iterate every thread in the process to remove the io contexts.
1053          */
1054         if (e->ops.trim) {
1055                 read_lock(&tasklist_lock);
1056                 do_each_thread(g, p) {
1057                         task_lock(p);
1058                         if (p->io_context)
1059                                 e->ops.trim(p->io_context);
1060                         task_unlock(p);
1061                 } while_each_thread(g, p);
1062                 read_unlock(&tasklist_lock);
1063         }
1064
1065         spin_lock(&elv_list_lock);
1066         list_del_init(&e->list);
1067         spin_unlock(&elv_list_lock);
1068 }
1069 EXPORT_SYMBOL_GPL(elv_unregister);
1070
1071 /*
1072  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1073  * we don't free the old io scheduler, before we have allocated what we
1074  * need for the new one. this way we have a chance of going back to the old
1075  * one, if the new one fails init for some reason.
1076  */
1077 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1078 {
1079         elevator_t *old_elevator, *e;
1080         void *data;
1081
1082         /*
1083          * Allocate new elevator
1084          */
1085         e = elevator_alloc(q, new_e);
1086         if (!e)
1087                 return 0;
1088
1089         data = elevator_init_queue(q, e);
1090         if (!data) {
1091                 kobject_put(&e->kobj);
1092                 return 0;
1093         }
1094
1095         /*
1096          * Turn on BYPASS and drain all requests w/ elevator private data
1097          */
1098         spin_lock_irq(q->queue_lock);
1099
1100         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
1101
1102         elv_drain_elevator(q);
1103
1104         while (q->rq.elvpriv) {
1105                 blk_start_queueing(q);
1106                 spin_unlock_irq(q->queue_lock);
1107                 msleep(10);
1108                 spin_lock_irq(q->queue_lock);
1109                 elv_drain_elevator(q);
1110         }
1111
1112         /*
1113          * Remember old elevator.
1114          */
1115         old_elevator = q->elevator;
1116
1117         /*
1118          * attach and start new elevator
1119          */
1120         elevator_attach(q, e, data);
1121
1122         spin_unlock_irq(q->queue_lock);
1123
1124         __elv_unregister_queue(old_elevator);
1125
1126         if (elv_register_queue(q))
1127                 goto fail_register;
1128
1129         /*
1130          * finally exit old elevator and turn off BYPASS.
1131          */
1132         elevator_exit(old_elevator);
1133         spin_lock_irq(q->queue_lock);
1134         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1135         spin_unlock_irq(q->queue_lock);
1136
1137         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1138
1139         return 1;
1140
1141 fail_register:
1142         /*
1143          * switch failed, exit the new io scheduler and reattach the old
1144          * one again (along with re-adding the sysfs dir)
1145          */
1146         elevator_exit(e);
1147         q->elevator = old_elevator;
1148         elv_register_queue(q);
1149
1150         spin_lock_irq(q->queue_lock);
1151         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1152         spin_unlock_irq(q->queue_lock);
1153
1154         return 0;
1155 }
1156
1157 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1158                           size_t count)
1159 {
1160         char elevator_name[ELV_NAME_MAX];
1161         struct elevator_type *e;
1162
1163         strlcpy(elevator_name, name, sizeof(elevator_name));
1164         strstrip(elevator_name);
1165
1166         e = elevator_get(elevator_name);
1167         if (!e) {
1168                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1169                 return -EINVAL;
1170         }
1171
1172         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1173                 elevator_put(e);
1174                 return count;
1175         }
1176
1177         if (!elevator_switch(q, e))
1178                 printk(KERN_ERR "elevator: switch to %s failed\n",
1179                                                         elevator_name);
1180         return count;
1181 }
1182
1183 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1184 {
1185         elevator_t *e = q->elevator;
1186         struct elevator_type *elv = e->elevator_type;
1187         struct elevator_type *__e;
1188         int len = 0;
1189
1190         spin_lock(&elv_list_lock);
1191         list_for_each_entry(__e, &elv_list, list) {
1192                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1193                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1194                 else
1195                         len += sprintf(name+len, "%s ", __e->elevator_name);
1196         }
1197         spin_unlock(&elv_list_lock);
1198
1199         len += sprintf(len+name, "\n");
1200         return len;
1201 }
1202
1203 struct request *elv_rb_former_request(struct request_queue *q,
1204                                       struct request *rq)
1205 {
1206         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1207
1208         if (rbprev)
1209                 return rb_entry_rq(rbprev);
1210
1211         return NULL;
1212 }
1213 EXPORT_SYMBOL(elv_rb_former_request);
1214
1215 struct request *elv_rb_latter_request(struct request_queue *q,
1216                                       struct request *rq)
1217 {
1218         struct rb_node *rbnext = rb_next(&rq->rb_node);
1219
1220         if (rbnext)
1221                 return rb_entry_rq(rbnext);
1222
1223         return NULL;
1224 }
1225 EXPORT_SYMBOL(elv_rb_latter_request);