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   1 /*
   2  *  Block device elevator/IO-scheduler.
   3  *
   4  *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
   5  *
   6  * 30042000 Jens Axboe <axboe@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 <trace/block.h>
  37 #include <linux/hash.h>
  38 #include <linux/uaccess.h>
  39
  40 #include "blk.h"
  41
  42 static DEFINE_SPINLOCK(elv_list_lock);
  43 static LIST_HEAD(elv_list);
  44
  45 DEFINE_TRACE(block_rq_abort);
  46
  47 /*
  48  * Merge hash stuff.
  49  */
  50 static const int elv_hash_shift = 6;
  51 #define ELV_HASH_BLOCK(sec)     ((sec) >> 3)
  52 #define ELV_HASH_FN(sec)        \
  53                 (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
  54 #define ELV_HASH_ENTRIES        (1 << elv_hash_shift)
  55 #define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
  56 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
  57
  58 DEFINE_TRACE(block_rq_insert);
  59 DEFINE_TRACE(block_rq_issue);
  60
  61 /*
  62  * Query io scheduler to see if the current process issuing bio may be
  63  * merged with rq.
  64  */
  65 static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
  66 {
  67         struct request_queue *q = rq->q;
  68         elevator_t *e = q->elevator;
  69
  70         if (e->ops->elevator_allow_merge_fn)
  71                 return e->ops->elevator_allow_merge_fn(q, rq, bio);
  72
  73         return 1;
  74 }
  75
  76 /*
  77  * can we safely merge with this request?
  78  */
  79 int elv_rq_merge_ok(struct request *rq, struct bio *bio)
  80 {
  81         if (!rq_mergeable(rq))
  82                 return 0;
  83
  84         /*
  85          * Don't merge file system requests and discard requests
  86          */
  87         if (bio_discard(bio) != bio_discard(rq->bio))
  88                 return 0;
  89
  90         /*
  91          * different data direction or already started, don't merge
  92          */
  93         if (bio_data_dir(bio) != rq_data_dir(rq))
  94                 return 0;
  95
  96         /*
  97          * must be same device and not a special request
  98          */
  99         if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
 100                 return 0;
 101
 102         /*
 103          * only merge integrity protected bio into ditto rq
 104          */
 105         if (bio_integrity(bio) != blk_integrity_rq(rq))
 106                 return 0;
 107
 108         if (!elv_iosched_allow_merge(rq, bio))
 109                 return 0;
 110
 111         return 1;
 112 }
 113 EXPORT_SYMBOL(elv_rq_merge_ok);
 114
 115 static inline int elv_try_merge(struct request *__rq, struct bio *bio)
 116 {
 117         int ret = ELEVATOR_NO_MERGE;
 118
 119         /*
 120          * we can merge and sequence is ok, check if it's possible
 121          */
 122         if (elv_rq_merge_ok(__rq, bio)) {
 123                 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
 124                         ret = ELEVATOR_BACK_MERGE;
 125                 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
 126                         ret = ELEVATOR_FRONT_MERGE;
 127         }
 128
 129         return ret;
 130 }
 131
 132 static struct elevator_type *elevator_find(const char *name)
 133 {
 134         struct elevator_type *e;
 135
 136         list_for_each_entry(e, &elv_list, list) {
 137                 if (!strcmp(e->elevator_name, name))
 138                         return e;
 139         }
 140
 141         return NULL;
 142 }
 143
 144 static void elevator_put(struct elevator_type *e)
 145 {
 146         module_put(e->elevator_owner);
 147 }
 148
 149 static struct elevator_type *elevator_get(const char *name)
 150 {
 151         struct elevator_type *e;
 152
 153         spin_lock(&elv_list_lock);
 154
 155         e = elevator_find(name);
 156         if (!e) {
 157                 char elv[ELV_NAME_MAX + strlen("-iosched")];
 158
 159                 spin_unlock(&elv_list_lock);
 160
 161                 if (!strcmp(name, "anticipatory"))
 162                         sprintf(elv, "as-iosched");
 163                 else
 164                         sprintf(elv, "%s-iosched", name);
 165
 166                 request_module("%s", elv);
 167                 spin_lock(&elv_list_lock);
 168                 e = elevator_find(name);
 169         }
 170
 171         if (e && !try_module_get(e->elevator_owner))
 172                 e = NULL;
 173
 174         spin_unlock(&elv_list_lock);
 175
 176         return e;
 177 }
 178
 179 static void *elevator_init_queue(struct request_queue *q,
 180                                  struct elevator_queue *eq)
 181 {
 182         return eq->ops->elevator_init_fn(q);
 183 }
 184
 185 static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
 186                            void *data)
 187 {
 188         q->elevator = eq;
 189         eq->elevator_data = data;
 190 }
 191
 192 static char chosen_elevator[16];
 193
 194 static int __init elevator_setup(char *str)
 195 {
 196         /*
 197          * Be backwards-compatible with previous kernels, so users
 198          * won't get the wrong elevator.
 199          */
 200         if (!strcmp(str, "as"))
 201                 strcpy(chosen_elevator, "anticipatory");
 202         else
 203                 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 204         return 1;
 205 }
 206
 207 __setup("elevator=", elevator_setup);
 208
 209 static struct kobj_type elv_ktype;
 210
 211 static elevator_t *elevator_alloc(struct request_queue *q,
 212                                   struct elevator_type *e)
 213 {
 214         elevator_t *eq;
 215         int i;
 216
 217         eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL | __GFP_ZERO, q->node);
 218         if (unlikely(!eq))
 219                 goto err;
 220
 221         eq->ops = &e->ops;
 222         eq->elevator_type = e;
 223         kobject_init(&eq->kobj, &elv_ktype);
 224         mutex_init(&eq->sysfs_lock);
 225
 226         eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
 227                                         GFP_KERNEL, q->node);
 228         if (!eq->hash)
 229                 goto err;
 230
 231         for (i = 0; i < ELV_HASH_ENTRIES; i++)
 232                 INIT_HLIST_HEAD(&eq->hash[i]);
 233
 234         return eq;
 235 err:
 236         kfree(eq);
 237         elevator_put(e);
 238         return NULL;
 239 }
 240
 241 static void elevator_release(struct kobject *kobj)
 242 {
 243         elevator_t *e = container_of(kobj, elevator_t, kobj);
 244
 245         elevator_put(e->elevator_type);
 246         kfree(e->hash);
 247         kfree(e);
 248 }
 249
 250 int elevator_init(struct request_queue *q, char *name)
 251 {
 252         struct elevator_type *e = NULL;
 253         struct elevator_queue *eq;
 254         int ret = 0;
 255         void *data;
 256
 257         INIT_LIST_HEAD(&q->queue_head);
 258         q->last_merge = NULL;
 259         q->end_sector = 0;
 260         q->boundary_rq = NULL;
 261
 262         if (name) {
 263                 e = elevator_get(name);
 264                 if (!e)
 265                         return -EINVAL;
 266         }
 267
 268         if (!e && *chosen_elevator) {
 269                 e = elevator_get(chosen_elevator);
 270                 if (!e)
 271                         printk(KERN_ERR "I/O scheduler %s not found\n",
 272                                                         chosen_elevator);
 273         }
 274
 275         if (!e) {
 276                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
 277                 if (!e) {
 278                         printk(KERN_ERR
 279                                 "Default I/O scheduler not found. " \
 280                                 "Using noop.\n");
 281                         e = elevator_get("noop");
 282                 }
 283         }
 284
 285         eq = elevator_alloc(q, e);
 286         if (!eq)
 287                 return -ENOMEM;
 288
 289         data = elevator_init_queue(q, eq);
 290         if (!data) {
 291                 kobject_put(&eq->kobj);
 292                 return -ENOMEM;
 293         }
 294
 295         elevator_attach(q, eq, data);
 296         return ret;
 297 }
 298 EXPORT_SYMBOL(elevator_init);
 299
 300 void elevator_exit(elevator_t *e)
 301 {
 302         mutex_lock(&e->sysfs_lock);
 303         if (e->ops->elevator_exit_fn)
 304                 e->ops->elevator_exit_fn(e);
 305         e->ops = NULL;
 306         mutex_unlock(&e->sysfs_lock);
 307
 308         kobject_put(&e->kobj);
 309 }
 310 EXPORT_SYMBOL(elevator_exit);
 311
 312 static void elv_activate_rq(struct request_queue *q, struct request *rq)
 313 {
 314         elevator_t *e = q->elevator;
 315
 316         if (e->ops->elevator_activate_req_fn)
 317                 e->ops->elevator_activate_req_fn(q, rq);
 318 }
 319
 320 static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
 321 {
 322         elevator_t *e = q->elevator;
 323
 324         if (e->ops->elevator_deactivate_req_fn)
 325                 e->ops->elevator_deactivate_req_fn(q, rq);
 326 }
 327
 328 static inline void __elv_rqhash_del(struct request *rq)
 329 {
 330         hlist_del_init(&rq->hash);
 331 }
 332
 333 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
 334 {
 335         if (ELV_ON_HASH(rq))
 336                 __elv_rqhash_del(rq);
 337 }
 338
 339 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
 340 {
 341         elevator_t *e = q->elevator;
 342
 343         BUG_ON(ELV_ON_HASH(rq));
 344         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
 345 }
 346
 347 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 348 {
 349         __elv_rqhash_del(rq);
 350         elv_rqhash_add(q, rq);
 351 }
 352
 353 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 354 {
 355         elevator_t *e = q->elevator;
 356         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
 357         struct hlist_node *entry, *next;
 358         struct request *rq;
 359
 360         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
 361                 BUG_ON(!ELV_ON_HASH(rq));
 362
 363                 if (unlikely(!rq_mergeable(rq))) {
 364                         __elv_rqhash_del(rq);
 365                         continue;
 366                 }
 367
 368                 if (rq_hash_key(rq) == offset)
 369                         return rq;
 370         }
 371
 372         return NULL;
 373 }
 374
 375 /*
 376  * RB-tree support functions for inserting/lookup/removal of requests
 377  * in a sorted RB tree.
 378  */
 379 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
 380 {
 381         struct rb_node **p = &root->rb_node;
 382         struct rb_node *parent = NULL;
 383         struct request *__rq;
 384
 385         while (*p) {
 386                 parent = *p;
 387                 __rq = rb_entry(parent, struct request, rb_node);
 388
 389                 if (rq->sector < __rq->sector)
 390                         p = &(*p)->rb_left;
 391                 else if (rq->sector > __rq->sector)
 392                         p = &(*p)->rb_right;
 393                 else
 394                         return __rq;
 395         }
 396
 397         rb_link_node(&rq->rb_node, parent, p);
 398         rb_insert_color(&rq->rb_node, root);
 399         return NULL;
 400 }
 401 EXPORT_SYMBOL(elv_rb_add);
 402
 403 void elv_rb_del(struct rb_root *root, struct request *rq)
 404 {
 405         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 406         rb_erase(&rq->rb_node, root);
 407         RB_CLEAR_NODE(&rq->rb_node);
 408 }
 409 EXPORT_SYMBOL(elv_rb_del);
 410
 411 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 412 {
 413         struct rb_node *n = root->rb_node;
 414         struct request *rq;
 415
 416         while (n) {
 417                 rq = rb_entry(n, struct request, rb_node);
 418
 419                 if (sector < rq->sector)
 420                         n = n->rb_left;
 421                 else if (sector > rq->sector)
 422                         n = n->rb_right;
 423                 else
 424                         return rq;
 425         }
 426
 427         return NULL;
 428 }
 429 EXPORT_SYMBOL(elv_rb_find);
 430
 431 /*
 432  * Insert rq into dispatch queue of q.  Queue lock must be held on
 433  * entry.  rq is sort instead into the dispatch queue. To be used by
 434  * specific elevators.
 435  */
 436 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
 437 {
 438         sector_t boundary;
 439         struct list_head *entry;
 440         int stop_flags;
 441
 442         if (q->last_merge == rq)
 443                 q->last_merge = NULL;
 444
 445         elv_rqhash_del(q, rq);
 446
 447         q->nr_sorted--;
 448
 449         boundary = q->end_sector;
 450         stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
 451         list_for_each_prev(entry, &q->queue_head) {
 452                 struct request *pos = list_entry_rq(entry);
 453
 454                 if (blk_discard_rq(rq) != blk_discard_rq(pos))
 455                         break;
 456                 if (rq_data_dir(rq) != rq_data_dir(pos))
 457                         break;
 458                 if (pos->cmd_flags & stop_flags)
 459                         break;
 460                 if (rq->sector >= boundary) {
 461                         if (pos->sector < boundary)
 462                                 continue;
 463                 } else {
 464                         if (pos->sector >= boundary)
 465                                 break;
 466                 }
 467                 if (rq->sector >= pos->sector)
 468                         break;
 469         }
 470
 471         list_add(&rq->queuelist, entry);
 472 }
 473 EXPORT_SYMBOL(elv_dispatch_sort);
 474
 475 /*
 476  * Insert rq into dispatch queue of q.  Queue lock must be held on
 477  * entry.  rq is added to the back of the dispatch queue. To be used by
 478  * specific elevators.
 479  */
 480 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 481 {
 482         if (q->last_merge == rq)
 483                 q->last_merge = NULL;
 484
 485         elv_rqhash_del(q, rq);
 486
 487         q->nr_sorted--;
 488
 489         q->end_sector = rq_end_sector(rq);
 490         q->boundary_rq = rq;
 491         list_add_tail(&rq->queuelist, &q->queue_head);
 492 }
 493 EXPORT_SYMBOL(elv_dispatch_add_tail);
 494
 495 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 496 {
 497         elevator_t *e = q->elevator;
 498         struct request *__rq;
 499         int ret;
 500
 501         /*
 502          * First try one-hit cache.
 503          */
 504         if (q->last_merge) {
 505                 ret = elv_try_merge(q->last_merge, bio);
 506                 if (ret != ELEVATOR_NO_MERGE) {
 507                         *req = q->last_merge;
 508                         return ret;
 509                 }
 510         }
 511
 512         if (blk_queue_nomerges(q))
 513                 return ELEVATOR_NO_MERGE;
 514
 515         /*
 516          * See if our hash lookup can find a potential backmerge.
 517          */
 518         __rq = elv_rqhash_find(q, bio->bi_sector);
 519         if (__rq && elv_rq_merge_ok(__rq, bio)) {
 520                 *req = __rq;
 521                 return ELEVATOR_BACK_MERGE;
 522         }
 523
 524         if (e->ops->elevator_merge_fn)
 525                 return e->ops->elevator_merge_fn(q, req, bio);
 526
 527         return ELEVATOR_NO_MERGE;
 528 }
 529
 530 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
 531 {
 532         elevator_t *e = q->elevator;
 533
 534         if (e->ops->elevator_merged_fn)
 535                 e->ops->elevator_merged_fn(q, rq, type);
 536
 537         if (type == ELEVATOR_BACK_MERGE)
 538                 elv_rqhash_reposition(q, rq);
 539
 540         q->last_merge = rq;
 541 }
 542
 543 void elv_merge_requests(struct request_queue *q, struct request *rq,
 544                              struct request *next)
 545 {
 546         elevator_t *e = q->elevator;
 547
 548         if (e->ops->elevator_merge_req_fn)
 549                 e->ops->elevator_merge_req_fn(q, rq, next);
 550
 551         elv_rqhash_reposition(q, rq);
 552         elv_rqhash_del(q, next);
 553
 554         q->nr_sorted--;
 555         q->last_merge = rq;
 556 }
 557
 558 void elv_requeue_request(struct request_queue *q, struct request *rq)
 559 {
 560         /*
 561          * it already went through dequeue, we need to decrement the
 562          * in_flight count again
 563          */
 564         if (blk_account_rq(rq)) {
 565                 q->in_flight--;
 566                 if (blk_sorted_rq(rq))
 567                         elv_deactivate_rq(q, rq);
 568         }
 569
 570         rq->cmd_flags &= ~REQ_STARTED;
 571
 572         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 573 }
 574
 575 static void elv_drain_elevator(struct request_queue *q)
 576 {
 577         static int printed;
 578         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 579                 ;
 580         if (q->nr_sorted == 0)
 581                 return;
 582         if (printed++ < 10) {
 583                 printk(KERN_ERR "%s: forced dispatching is broken "
 584                        "(nr_sorted=%u), please report this\n",
 585                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 586         }
 587 }
 588
 589 void elv_insert(struct request_queue *q, struct request *rq, int where)
 590 {
 591         struct list_head *pos;
 592         unsigned ordseq;
 593         int unplug_it = 1;
 594
 595         trace_block_rq_insert(q, rq);
 596
 597         rq->q = q;
 598
 599         switch (where) {
 600         case ELEVATOR_INSERT_FRONT:
 601                 rq->cmd_flags |= REQ_SOFTBARRIER;
 602
 603                 list_add(&rq->queuelist, &q->queue_head);
 604                 break;
 605
 606         case ELEVATOR_INSERT_BACK:
 607                 rq->cmd_flags |= REQ_SOFTBARRIER;
 608                 elv_drain_elevator(q);
 609                 list_add_tail(&rq->queuelist, &q->queue_head);
 610                 /*
 611                  * We kick the queue here for the following reasons.
 612                  * - The elevator might have returned NULL previously
 613                  *   to delay requests and returned them now.  As the
 614                  *   queue wasn't empty before this request, ll_rw_blk
 615                  *   won't run the queue on return, resulting in hang.
 616                  * - Usually, back inserted requests won't be merged
 617                  *   with anything.  There's no point in delaying queue
 618                  *   processing.
 619                  */
 620                 blk_remove_plug(q);
 621                 blk_start_queueing(q);
 622                 break;
 623
 624         case ELEVATOR_INSERT_SORT:
 625                 BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
 626                 rq->cmd_flags |= REQ_SORTED;
 627                 q->nr_sorted++;
 628                 if (rq_mergeable(rq)) {
 629                         elv_rqhash_add(q, rq);
 630                         if (!q->last_merge)
 631                                 q->last_merge = rq;
 632                 }
 633
 634                 /*
 635                  * Some ioscheds (cfq) run q->request_fn directly, so
 636                  * rq cannot be accessed after calling
 637                  * elevator_add_req_fn.
 638                  */
 639                 q->elevator->ops->elevator_add_req_fn(q, rq);
 640                 break;
 641
 642         case ELEVATOR_INSERT_REQUEUE:
 643                 /*
 644                  * If ordered flush isn't in progress, we do front
 645                  * insertion; otherwise, requests should be requeued
 646                  * in ordseq order.
 647                  */
 648                 rq->cmd_flags |= REQ_SOFTBARRIER;
 649
 650                 /*
 651                  * Most requeues happen because of a busy condition,
 652                  * don't force unplug of the queue for that case.
 653                  */
 654                 unplug_it = 0;
 655
 656                 if (q->ordseq == 0) {
 657                         list_add(&rq->queuelist, &q->queue_head);
 658                         break;
 659                 }
 660
 661                 ordseq = blk_ordered_req_seq(rq);
 662
 663                 list_for_each(pos, &q->queue_head) {
 664                         struct request *pos_rq = list_entry_rq(pos);
 665                         if (ordseq <= blk_ordered_req_seq(pos_rq))
 666                                 break;
 667                 }
 668
 669                 list_add_tail(&rq->queuelist, pos);
 670                 break;
 671
 672         default:
 673                 printk(KERN_ERR "%s: bad insertion point %d\n",
 674                        __func__, where);
 675                 BUG();
 676         }
 677
 678         if (unplug_it && blk_queue_plugged(q)) {
 679                 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 680                         - q->in_flight;
 681
 682                 if (nrq >= q->unplug_thresh)
 683                         __generic_unplug_device(q);
 684         }
 685 }
 686
 687 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
 688                        int plug)
 689 {
 690         if (q->ordcolor)
 691                 rq->cmd_flags |= REQ_ORDERED_COLOR;
 692
 693         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 694                 /*
 695                  * toggle ordered color
 696                  */
 697                 if (blk_barrier_rq(rq))
 698                         q->ordcolor ^= 1;
 699
 700                 /*
 701                  * barriers implicitly indicate back insertion
 702                  */
 703                 if (where == ELEVATOR_INSERT_SORT)
 704                         where = ELEVATOR_INSERT_BACK;
 705
 706                 /*
 707                  * this request is scheduling boundary, update
 708                  * end_sector
 709                  */
 710                 if (blk_fs_request(rq) || blk_discard_rq(rq)) {
 711                         q->end_sector = rq_end_sector(rq);
 712                         q->boundary_rq = rq;
 713                 }
 714         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
 715                     where == ELEVATOR_INSERT_SORT)
 716                 where = ELEVATOR_INSERT_BACK;
 717
 718         if (plug)
 719                 blk_plug_device(q);
 720
 721         elv_insert(q, rq, where);
 722 }
 723 EXPORT_SYMBOL(__elv_add_request);
 724
 725 void elv_add_request(struct request_queue *q, struct request *rq, int where,
 726                      int plug)
 727 {
 728         unsigned long flags;
 729
 730         spin_lock_irqsave(q->queue_lock, flags);
 731         __elv_add_request(q, rq, where, plug);
 732         spin_unlock_irqrestore(q->queue_lock, flags);
 733 }
 734 EXPORT_SYMBOL(elv_add_request);
 735
 736 static inline struct request *__elv_next_request(struct request_queue *q)
 737 {
 738         struct request *rq;
 739
 740         while (1) {
 741                 while (!list_empty(&q->queue_head)) {
 742                         rq = list_entry_rq(q->queue_head.next);
 743                         if (blk_do_ordered(q, &rq))
 744                                 return rq;
 745                 }
 746
 747                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 748                         return NULL;
 749         }
 750 }
 751
 752 struct request *elv_next_request(struct request_queue *q)
 753 {
 754         struct request *rq;
 755         int ret;
 756
 757         while ((rq = __elv_next_request(q)) != NULL) {
 758                 if (!(rq->cmd_flags & REQ_STARTED)) {
 759                         /*
 760                          * This is the first time the device driver
 761                          * sees this request (possibly after
 762                          * requeueing).  Notify IO scheduler.
 763                          */
 764                         if (blk_sorted_rq(rq))
 765                                 elv_activate_rq(q, rq);
 766
 767                         /*
 768                          * just mark as started even if we don't start
 769                          * it, a request that has been delayed should
 770                          * not be passed by new incoming requests
 771                          */
 772                         rq->cmd_flags |= REQ_STARTED;
 773                         trace_block_rq_issue(q, rq);
 774                 }
 775
 776                 if (!q->boundary_rq || q->boundary_rq == rq) {
 777                         q->end_sector = rq_end_sector(rq);
 778                         q->boundary_rq = NULL;
 779                 }
 780
 781                 if (rq->cmd_flags & REQ_DONTPREP)
 782                         break;
 783
 784                 if (q->dma_drain_size && rq->data_len) {
 785                         /*
 786                          * make sure space for the drain appears we
 787                          * know we can do this because max_hw_segments
 788                          * has been adjusted to be one fewer than the
 789                          * device can handle
 790                          */
 791                         rq->nr_phys_segments++;
 792                 }
 793
 794                 if (!q->prep_rq_fn)
 795                         break;
 796
 797                 ret = q->prep_rq_fn(q, rq);
 798                 if (ret == BLKPREP_OK) {
 799                         break;
 800                 } else if (ret == BLKPREP_DEFER) {
 801                         /*
 802                          * the request may have been (partially) prepped.
 803                          * we need to keep this request in the front to
 804                          * avoid resource deadlock.  REQ_STARTED will
 805                          * prevent other fs requests from passing this one.
 806                          */
 807                         if (q->dma_drain_size && rq->data_len &&
 808                             !(rq->cmd_flags & REQ_DONTPREP)) {
 809                                 /*
 810                                  * remove the space for the drain we added
 811                                  * so that we don't add it again
 812                                  */
 813                                 --rq->nr_phys_segments;
 814                         }
 815
 816                         rq = NULL;
 817                         break;
 818                 } else if (ret == BLKPREP_KILL) {
 819                         rq->cmd_flags |= REQ_QUIET;
 820                         __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 821                 } else {
 822                         printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
 823                         break;
 824                 }
 825         }
 826
 827         return rq;
 828 }
 829 EXPORT_SYMBOL(elv_next_request);
 830
 831 void elv_dequeue_request(struct request_queue *q, struct request *rq)
 832 {
 833         BUG_ON(list_empty(&rq->queuelist));
 834         BUG_ON(ELV_ON_HASH(rq));
 835
 836         list_del_init(&rq->queuelist);
 837
 838         /*
 839          * the time frame between a request being removed from the lists
 840          * and to it is freed is accounted as io that is in progress at
 841          * the driver side.
 842          */
 843         if (blk_account_rq(rq))
 844                 q->in_flight++;
 845 }
 846
 847 int elv_queue_empty(struct request_queue *q)
 848 {
 849         elevator_t *e = q->elevator;
 850
 851         if (!list_empty(&q->queue_head))
 852                 return 0;
 853
 854         if (e->ops->elevator_queue_empty_fn)
 855                 return e->ops->elevator_queue_empty_fn(q);
 856
 857         return 1;
 858 }
 859 EXPORT_SYMBOL(elv_queue_empty);
 860
 861 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 862 {
 863         elevator_t *e = q->elevator;
 864
 865         if (e->ops->elevator_latter_req_fn)
 866                 return e->ops->elevator_latter_req_fn(q, rq);
 867         return NULL;
 868 }
 869
 870 struct request *elv_former_request(struct request_queue *q, struct request *rq)
 871 {
 872         elevator_t *e = q->elevator;
 873
 874         if (e->ops->elevator_former_req_fn)
 875                 return e->ops->elevator_former_req_fn(q, rq);
 876         return NULL;
 877 }
 878
 879 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
 880 {
 881         elevator_t *e = q->elevator;
 882
 883         if (e->ops->elevator_set_req_fn)
 884                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
 885
 886         rq->elevator_private = NULL;
 887         return 0;
 888 }
 889
 890 void elv_put_request(struct request_queue *q, struct request *rq)
 891 {
 892         elevator_t *e = q->elevator;
 893
 894         if (e->ops->elevator_put_req_fn)
 895                 e->ops->elevator_put_req_fn(rq);
 896 }
 897
 898 int elv_may_queue(struct request_queue *q, int rw)
 899 {
 900         elevator_t *e = q->elevator;
 901
 902         if (e->ops->elevator_may_queue_fn)
 903                 return e->ops->elevator_may_queue_fn(q, rw);
 904
 905         return ELV_MQUEUE_MAY;
 906 }
 907
 908 void elv_abort_queue(struct request_queue *q)
 909 {
 910         struct request *rq;
 911
 912         while (!list_empty(&q->queue_head)) {
 913                 rq = list_entry_rq(q->queue_head.next);
 914                 rq->cmd_flags |= REQ_QUIET;
 915                 trace_block_rq_abort(q, rq);
 916                 __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 917         }
 918 }
 919 EXPORT_SYMBOL(elv_abort_queue);
 920
 921 void elv_completed_request(struct request_queue *q, struct request *rq)
 922 {
 923         elevator_t *e = q->elevator;
 924
 925         /*
 926          * request is released from the driver, io must be done
 927          */
 928         if (blk_account_rq(rq)) {
 929                 q->in_flight--;
 930                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 931                         e->ops->elevator_completed_req_fn(q, rq);
 932         }
 933
 934         /*
 935          * Check if the queue is waiting for fs requests to be
 936          * drained for flush sequence.
 937          */
 938         if (unlikely(q->ordseq)) {
 939                 struct request *next = NULL;
 940
 941                 if (!list_empty(&q->queue_head))
 942                         next = list_entry_rq(q->queue_head.next);
 943
 944                 if (!q->in_flight &&
 945                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 946                     (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
 947                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 948                         blk_start_queueing(q);
 949                 }
 950         }
 951 }
 952
 953 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 954
 955 static ssize_t
 956 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 957 {
 958         elevator_t *e = container_of(kobj, elevator_t, kobj);
 959         struct elv_fs_entry *entry = to_elv(attr);
 960         ssize_t error;
 961
 962         if (!entry->show)
 963                 return -EIO;
 964
 965         mutex_lock(&e->sysfs_lock);
 966         error = e->ops ? entry->show(e, page) : -ENOENT;
 967         mutex_unlock(&e->sysfs_lock);
 968         return error;
 969 }
 970
 971 static ssize_t
 972 elv_attr_store(struct kobject *kobj, struct attribute *attr,
 973                const char *page, size_t length)
 974 {
 975         elevator_t *e = container_of(kobj, elevator_t, kobj);
 976         struct elv_fs_entry *entry = to_elv(attr);
 977         ssize_t error;
 978
 979         if (!entry->store)
 980                 return -EIO;
 981
 982         mutex_lock(&e->sysfs_lock);
 983         error = e->ops ? entry->store(e, page, length) : -ENOENT;
 984         mutex_unlock(&e->sysfs_lock);
 985         return error;
 986 }
 987
 988 static struct sysfs_ops elv_sysfs_ops = {
 989         .show   = elv_attr_show,
 990         .store  = elv_attr_store,
 991 };
 992
 993 static struct kobj_type elv_ktype = {
 994         .sysfs_ops      = &elv_sysfs_ops,
 995         .release        = elevator_release,
 996 };
 997
 998 int elv_register_queue(struct request_queue *q)
 999 {
1000         elevator_t *e = q->elevator;
1001         int error;
1002
1003         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1004         if (!error) {
1005                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1006                 if (attr) {
1007                         while (attr->attr.name) {
1008                                 if (sysfs_create_file(&e->kobj, &attr->attr))
1009                                         break;
1010                                 attr++;
1011                         }
1012                 }
1013                 kobject_uevent(&e->kobj, KOBJ_ADD);
1014         }
1015         return error;
1016 }
1017
1018 static void __elv_unregister_queue(elevator_t *e)
1019 {
1020         kobject_uevent(&e->kobj, KOBJ_REMOVE);
1021         kobject_del(&e->kobj);
1022 }
1023
1024 void elv_unregister_queue(struct request_queue *q)
1025 {
1026         if (q)
1027                 __elv_unregister_queue(q->elevator);
1028 }
1029
1030 void elv_register(struct elevator_type *e)
1031 {
1032         char *def = "";
1033
1034         spin_lock(&elv_list_lock);
1035         BUG_ON(elevator_find(e->elevator_name));
1036         list_add_tail(&e->list, &elv_list);
1037         spin_unlock(&elv_list_lock);
1038
1039         if (!strcmp(e->elevator_name, chosen_elevator) ||
1040                         (!*chosen_elevator &&
1041                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1042                                 def = " (default)";
1043
1044         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1045                                                                 def);
1046 }
1047 EXPORT_SYMBOL_GPL(elv_register);
1048
1049 void elv_unregister(struct elevator_type *e)
1050 {
1051         struct task_struct *g, *p;
1052
1053         /*
1054          * Iterate every thread in the process to remove the io contexts.
1055          */
1056         if (e->ops.trim) {
1057                 read_lock(&tasklist_lock);
1058                 do_each_thread(g, p) {
1059                         task_lock(p);
1060                         if (p->io_context)
1061                                 e->ops.trim(p->io_context);
1062                         task_unlock(p);
1063                 } while_each_thread(g, p);
1064                 read_unlock(&tasklist_lock);
1065         }
1066
1067         spin_lock(&elv_list_lock);
1068         list_del_init(&e->list);
1069         spin_unlock(&elv_list_lock);
1070 }
1071 EXPORT_SYMBOL_GPL(elv_unregister);
1072
1073 /*
1074  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1075  * we don't free the old io scheduler, before we have allocated what we
1076  * need for the new one. this way we have a chance of going back to the old
1077  * one, if the new one fails init for some reason.
1078  */
1079 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1080 {
1081         elevator_t *old_elevator, *e;
1082         void *data;
1083
1084         /*
1085          * Allocate new elevator
1086          */
1087         e = elevator_alloc(q, new_e);
1088         if (!e)
1089                 return 0;
1090
1091         data = elevator_init_queue(q, e);
1092         if (!data) {
1093                 kobject_put(&e->kobj);
1094                 return 0;
1095         }
1096
1097         /*
1098          * Turn on BYPASS and drain all requests w/ elevator private data
1099          */
1100         spin_lock_irq(q->queue_lock);
1101
1102         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
1103
1104         elv_drain_elevator(q);
1105
1106         while (q->rq.elvpriv) {
1107                 blk_start_queueing(q);
1108                 spin_unlock_irq(q->queue_lock);
1109                 msleep(10);
1110                 spin_lock_irq(q->queue_lock);
1111                 elv_drain_elevator(q);
1112         }
1113
1114         /*
1115          * Remember old elevator.
1116          */
1117         old_elevator = q->elevator;
1118
1119         /*
1120          * attach and start new elevator
1121          */
1122         elevator_attach(q, e, data);
1123
1124         spin_unlock_irq(q->queue_lock);
1125
1126         __elv_unregister_queue(old_elevator);
1127
1128         if (elv_register_queue(q))
1129                 goto fail_register;
1130
1131         /*
1132          * finally exit old elevator and turn off BYPASS.
1133          */
1134         elevator_exit(old_elevator);
1135         spin_lock_irq(q->queue_lock);
1136         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1137         spin_unlock_irq(q->queue_lock);
1138
1139         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1140
1141         return 1;
1142
1143 fail_register:
1144         /*
1145          * switch failed, exit the new io scheduler and reattach the old
1146          * one again (along with re-adding the sysfs dir)
1147          */
1148         elevator_exit(e);
1149         q->elevator = old_elevator;
1150         elv_register_queue(q);
1151
1152         spin_lock_irq(q->queue_lock);
1153         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1154         spin_unlock_irq(q->queue_lock);
1155
1156         return 0;
1157 }
1158
1159 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1160                           size_t count)
1161 {
1162         char elevator_name[ELV_NAME_MAX];
1163         struct elevator_type *e;
1164
1165         strlcpy(elevator_name, name, sizeof(elevator_name));
1166         strstrip(elevator_name);
1167
1168         e = elevator_get(elevator_name);
1169         if (!e) {
1170                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1171                 return -EINVAL;
1172         }
1173
1174         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1175                 elevator_put(e);
1176                 return count;
1177         }
1178
1179         if (!elevator_switch(q, e))
1180                 printk(KERN_ERR "elevator: switch to %s failed\n",
1181                                                         elevator_name);
1182         return count;
1183 }
1184
1185 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1186 {
1187         elevator_t *e = q->elevator;
1188         struct elevator_type *elv = e->elevator_type;
1189         struct elevator_type *__e;
1190         int len = 0;
1191
1192         spin_lock(&elv_list_lock);
1193         list_for_each_entry(__e, &elv_list, list) {
1194                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1195                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1196                 else
1197                         len += sprintf(name+len, "%s ", __e->elevator_name);
1198         }
1199         spin_unlock(&elv_list_lock);
1200
1201         len += sprintf(len+name, "\n");
1202         return len;
1203 }
1204
1205 struct request *elv_rb_former_request(struct request_queue *q,
1206                                       struct request *rq)
1207 {
1208         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1209
1210         if (rbprev)
1211                 return rb_entry_rq(rbprev);
1212
1213         return NULL;
1214 }
1215 EXPORT_SYMBOL(elv_rb_former_request);
1216
1217 struct request *elv_rb_latter_request(struct request_queue *q,
1218                                       struct request *rq)
1219 {
1220         struct rb_node *rbnext = rb_next(&rq->rb_node);
1221
1222         if (rbnext)
1223                 return rb_entry_rq(rbnext);
1224
1225         return NULL;
1226 }
1227 EXPORT_SYMBOL(elv_rb_latter_request);