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