SAFE public projects git trees. - safe/jmp/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 <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         struct elevator_queue *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 struct elevator_queue *elevator_alloc(struct request_queue *q,
 212                                   struct elevator_type *e)
 213 {
 214         struct elevator_queue *eq;
 215         int i;
 216
 217         eq = kmalloc_node(sizeof(*eq), 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         struct elevator_queue *e;
 244
 245         e = container_of(kobj, struct elevator_queue, kobj);
 246         elevator_put(e->elevator_type);
 247         kfree(e->hash);
 248         kfree(e);
 249 }
 250
 251 int elevator_init(struct request_queue *q, char *name)
 252 {
 253         struct elevator_type *e = NULL;
 254         struct elevator_queue *eq;
 255         int ret = 0;
 256         void *data;
 257
 258         INIT_LIST_HEAD(&q->queue_head);
 259         q->last_merge = NULL;
 260         q->end_sector = 0;
 261         q->boundary_rq = NULL;
 262
 263         if (name) {
 264                 e = elevator_get(name);
 265                 if (!e)
 266                         return -EINVAL;
 267         }
 268
 269         if (!e && *chosen_elevator) {
 270                 e = elevator_get(chosen_elevator);
 271                 if (!e)
 272                         printk(KERN_ERR "I/O scheduler %s not found\n",
 273                                                         chosen_elevator);
 274         }
 275
 276         if (!e) {
 277                 e = elevator_get(CONFIG_DEFAULT_IOSCHED);
 278                 if (!e) {
 279                         printk(KERN_ERR
 280                                 "Default I/O scheduler not found. " \
 281                                 "Using noop.\n");
 282                         e = elevator_get("noop");
 283                 }
 284         }
 285
 286         eq = elevator_alloc(q, e);
 287         if (!eq)
 288                 return -ENOMEM;
 289
 290         data = elevator_init_queue(q, eq);
 291         if (!data) {
 292                 kobject_put(&eq->kobj);
 293                 return -ENOMEM;
 294         }
 295
 296         elevator_attach(q, eq, data);
 297         return ret;
 298 }
 299 EXPORT_SYMBOL(elevator_init);
 300
 301 void elevator_exit(struct elevator_queue *e)
 302 {
 303         mutex_lock(&e->sysfs_lock);
 304         if (e->ops->elevator_exit_fn)
 305                 e->ops->elevator_exit_fn(e);
 306         e->ops = NULL;
 307         mutex_unlock(&e->sysfs_lock);
 308
 309         kobject_put(&e->kobj);
 310 }
 311 EXPORT_SYMBOL(elevator_exit);
 312
 313 static void elv_activate_rq(struct request_queue *q, struct request *rq)
 314 {
 315         struct elevator_queue *e = q->elevator;
 316
 317         if (e->ops->elevator_activate_req_fn)
 318                 e->ops->elevator_activate_req_fn(q, rq);
 319 }
 320
 321 static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
 322 {
 323         struct elevator_queue *e = q->elevator;
 324
 325         if (e->ops->elevator_deactivate_req_fn)
 326                 e->ops->elevator_deactivate_req_fn(q, rq);
 327 }
 328
 329 static inline void __elv_rqhash_del(struct request *rq)
 330 {
 331         hlist_del_init(&rq->hash);
 332 }
 333
 334 static void elv_rqhash_del(struct request_queue *q, struct request *rq)
 335 {
 336         if (ELV_ON_HASH(rq))
 337                 __elv_rqhash_del(rq);
 338 }
 339
 340 static void elv_rqhash_add(struct request_queue *q, struct request *rq)
 341 {
 342         struct elevator_queue *e = q->elevator;
 343
 344         BUG_ON(ELV_ON_HASH(rq));
 345         hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
 346 }
 347
 348 static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
 349 {
 350         __elv_rqhash_del(rq);
 351         elv_rqhash_add(q, rq);
 352 }
 353
 354 static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
 355 {
 356         struct elevator_queue *e = q->elevator;
 357         struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
 358         struct hlist_node *entry, *next;
 359         struct request *rq;
 360
 361         hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
 362                 BUG_ON(!ELV_ON_HASH(rq));
 363
 364                 if (unlikely(!rq_mergeable(rq))) {
 365                         __elv_rqhash_del(rq);
 366                         continue;
 367                 }
 368
 369                 if (rq_hash_key(rq) == offset)
 370                         return rq;
 371         }
 372
 373         return NULL;
 374 }
 375
 376 /*
 377  * RB-tree support functions for inserting/lookup/removal of requests
 378  * in a sorted RB tree.
 379  */
 380 struct request *elv_rb_add(struct rb_root *root, struct request *rq)
 381 {
 382         struct rb_node **p = &root->rb_node;
 383         struct rb_node *parent = NULL;
 384         struct request *__rq;
 385
 386         while (*p) {
 387                 parent = *p;
 388                 __rq = rb_entry(parent, struct request, rb_node);
 389
 390                 if (rq->sector < __rq->sector)
 391                         p = &(*p)->rb_left;
 392                 else if (rq->sector > __rq->sector)
 393                         p = &(*p)->rb_right;
 394                 else
 395                         return __rq;
 396         }
 397
 398         rb_link_node(&rq->rb_node, parent, p);
 399         rb_insert_color(&rq->rb_node, root);
 400         return NULL;
 401 }
 402 EXPORT_SYMBOL(elv_rb_add);
 403
 404 void elv_rb_del(struct rb_root *root, struct request *rq)
 405 {
 406         BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
 407         rb_erase(&rq->rb_node, root);
 408         RB_CLEAR_NODE(&rq->rb_node);
 409 }
 410 EXPORT_SYMBOL(elv_rb_del);
 411
 412 struct request *elv_rb_find(struct rb_root *root, sector_t sector)
 413 {
 414         struct rb_node *n = root->rb_node;
 415         struct request *rq;
 416
 417         while (n) {
 418                 rq = rb_entry(n, struct request, rb_node);
 419
 420                 if (sector < rq->sector)
 421                         n = n->rb_left;
 422                 else if (sector > rq->sector)
 423                         n = n->rb_right;
 424                 else
 425                         return rq;
 426         }
 427
 428         return NULL;
 429 }
 430 EXPORT_SYMBOL(elv_rb_find);
 431
 432 /*
 433  * Insert rq into dispatch queue of q.  Queue lock must be held on
 434  * entry.  rq is sort instead into the dispatch queue. To be used by
 435  * specific elevators.
 436  */
 437 void elv_dispatch_sort(struct request_queue *q, struct request *rq)
 438 {
 439         sector_t boundary;
 440         struct list_head *entry;
 441         int stop_flags;
 442
 443         if (q->last_merge == rq)
 444                 q->last_merge = NULL;
 445
 446         elv_rqhash_del(q, rq);
 447
 448         q->nr_sorted--;
 449
 450         boundary = q->end_sector;
 451         stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;
 452         list_for_each_prev(entry, &q->queue_head) {
 453                 struct request *pos = list_entry_rq(entry);
 454
 455                 if (blk_discard_rq(rq) != blk_discard_rq(pos))
 456                         break;
 457                 if (rq_data_dir(rq) != rq_data_dir(pos))
 458                         break;
 459                 if (pos->cmd_flags & stop_flags)
 460                         break;
 461                 if (rq->sector >= boundary) {
 462                         if (pos->sector < boundary)
 463                                 continue;
 464                 } else {
 465                         if (pos->sector >= boundary)
 466                                 break;
 467                 }
 468                 if (rq->sector >= pos->sector)
 469                         break;
 470         }
 471
 472         list_add(&rq->queuelist, entry);
 473 }
 474 EXPORT_SYMBOL(elv_dispatch_sort);
 475
 476 /*
 477  * Insert rq into dispatch queue of q.  Queue lock must be held on
 478  * entry.  rq is added to the back of the dispatch queue. To be used by
 479  * specific elevators.
 480  */
 481 void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 482 {
 483         if (q->last_merge == rq)
 484                 q->last_merge = NULL;
 485
 486         elv_rqhash_del(q, rq);
 487
 488         q->nr_sorted--;
 489
 490         q->end_sector = rq_end_sector(rq);
 491         q->boundary_rq = rq;
 492         list_add_tail(&rq->queuelist, &q->queue_head);
 493 }
 494 EXPORT_SYMBOL(elv_dispatch_add_tail);
 495
 496 int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 497 {
 498         struct elevator_queue *e = q->elevator;
 499         struct request *__rq;
 500         int ret;
 501
 502         /*
 503          * First try one-hit cache.
 504          */
 505         if (q->last_merge) {
 506                 ret = elv_try_merge(q->last_merge, bio);
 507                 if (ret != ELEVATOR_NO_MERGE) {
 508                         *req = q->last_merge;
 509                         return ret;
 510                 }
 511         }
 512
 513         if (blk_queue_nomerges(q))
 514                 return ELEVATOR_NO_MERGE;
 515
 516         /*
 517          * See if our hash lookup can find a potential backmerge.
 518          */
 519         __rq = elv_rqhash_find(q, bio->bi_sector);
 520         if (__rq && elv_rq_merge_ok(__rq, bio)) {
 521                 *req = __rq;
 522                 return ELEVATOR_BACK_MERGE;
 523         }
 524
 525         if (e->ops->elevator_merge_fn)
 526                 return e->ops->elevator_merge_fn(q, req, bio);
 527
 528         return ELEVATOR_NO_MERGE;
 529 }
 530
 531 void elv_merged_request(struct request_queue *q, struct request *rq, int type)
 532 {
 533         struct elevator_queue *e = q->elevator;
 534
 535         if (e->ops->elevator_merged_fn)
 536                 e->ops->elevator_merged_fn(q, rq, type);
 537
 538         if (type == ELEVATOR_BACK_MERGE)
 539                 elv_rqhash_reposition(q, rq);
 540
 541         q->last_merge = rq;
 542 }
 543
 544 void elv_merge_requests(struct request_queue *q, struct request *rq,
 545                              struct request *next)
 546 {
 547         struct elevator_queue *e = q->elevator;
 548
 549         if (e->ops->elevator_merge_req_fn)
 550                 e->ops->elevator_merge_req_fn(q, rq, next);
 551
 552         elv_rqhash_reposition(q, rq);
 553         elv_rqhash_del(q, next);
 554
 555         q->nr_sorted--;
 556         q->last_merge = rq;
 557 }
 558
 559 void elv_requeue_request(struct request_queue *q, struct request *rq)
 560 {
 561         /*
 562          * it already went through dequeue, we need to decrement the
 563          * in_flight count again
 564          */
 565         if (blk_account_rq(rq)) {
 566                 q->in_flight--;
 567                 if (blk_sorted_rq(rq))
 568                         elv_deactivate_rq(q, rq);
 569         }
 570
 571         rq->cmd_flags &= ~REQ_STARTED;
 572
 573         elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 574 }
 575
 576 void elv_drain_elevator(struct request_queue *q)
 577 {
 578         static int printed;
 579         while (q->elevator->ops->elevator_dispatch_fn(q, 1))
 580                 ;
 581         if (q->nr_sorted == 0)
 582                 return;
 583         if (printed++ < 10) {
 584                 printk(KERN_ERR "%s: forced dispatching is broken "
 585                        "(nr_sorted=%u), please report this\n",
 586                        q->elevator->elevator_type->elevator_name, q->nr_sorted);
 587         }
 588 }
 589
 590 /*
 591  * Call with queue lock held, interrupts disabled
 592  */
 593 void elv_quiesce_start(struct request_queue *q)
 594 {
 595         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
 596
 597         /*
 598          * make sure we don't have any requests in flight
 599          */
 600         elv_drain_elevator(q);
 601         while (q->rq.elvpriv) {
 602                 __blk_run_queue(q);
 603                 spin_unlock_irq(q->queue_lock);
 604                 msleep(10);
 605                 spin_lock_irq(q->queue_lock);
 606                 elv_drain_elevator(q);
 607         }
 608 }
 609
 610 void elv_quiesce_end(struct request_queue *q)
 611 {
 612         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
 613 }
 614
 615 void elv_insert(struct request_queue *q, struct request *rq, int where)
 616 {
 617         struct list_head *pos;
 618         unsigned ordseq;
 619         int unplug_it = 1;
 620
 621         trace_block_rq_insert(q, rq);
 622
 623         rq->q = q;
 624
 625         switch (where) {
 626         case ELEVATOR_INSERT_FRONT:
 627                 rq->cmd_flags |= REQ_SOFTBARRIER;
 628
 629                 list_add(&rq->queuelist, &q->queue_head);
 630                 break;
 631
 632         case ELEVATOR_INSERT_BACK:
 633                 rq->cmd_flags |= REQ_SOFTBARRIER;
 634                 elv_drain_elevator(q);
 635                 list_add_tail(&rq->queuelist, &q->queue_head);
 636                 /*
 637                  * We kick the queue here for the following reasons.
 638                  * - The elevator might have returned NULL previously
 639                  *   to delay requests and returned them now.  As the
 640                  *   queue wasn't empty before this request, ll_rw_blk
 641                  *   won't run the queue on return, resulting in hang.
 642                  * - Usually, back inserted requests won't be merged
 643                  *   with anything.  There's no point in delaying queue
 644                  *   processing.
 645                  */
 646                 __blk_run_queue(q);
 647                 break;
 648
 649         case ELEVATOR_INSERT_SORT:
 650                 BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
 651                 rq->cmd_flags |= REQ_SORTED;
 652                 q->nr_sorted++;
 653                 if (rq_mergeable(rq)) {
 654                         elv_rqhash_add(q, rq);
 655                         if (!q->last_merge)
 656                                 q->last_merge = rq;
 657                 }
 658
 659                 /*
 660                  * Some ioscheds (cfq) run q->request_fn directly, so
 661                  * rq cannot be accessed after calling
 662                  * elevator_add_req_fn.
 663                  */
 664                 q->elevator->ops->elevator_add_req_fn(q, rq);
 665                 break;
 666
 667         case ELEVATOR_INSERT_REQUEUE:
 668                 /*
 669                  * If ordered flush isn't in progress, we do front
 670                  * insertion; otherwise, requests should be requeued
 671                  * in ordseq order.
 672                  */
 673                 rq->cmd_flags |= REQ_SOFTBARRIER;
 674
 675                 /*
 676                  * Most requeues happen because of a busy condition,
 677                  * don't force unplug of the queue for that case.
 678                  */
 679                 unplug_it = 0;
 680
 681                 if (q->ordseq == 0) {
 682                         list_add(&rq->queuelist, &q->queue_head);
 683                         break;
 684                 }
 685
 686                 ordseq = blk_ordered_req_seq(rq);
 687
 688                 list_for_each(pos, &q->queue_head) {
 689                         struct request *pos_rq = list_entry_rq(pos);
 690                         if (ordseq <= blk_ordered_req_seq(pos_rq))
 691                                 break;
 692                 }
 693
 694                 list_add_tail(&rq->queuelist, pos);
 695                 break;
 696
 697         default:
 698                 printk(KERN_ERR "%s: bad insertion point %d\n",
 699                        __func__, where);
 700                 BUG();
 701         }
 702
 703         if (unplug_it && blk_queue_plugged(q)) {
 704                 int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
 705                         - q->in_flight;
 706
 707                 if (nrq >= q->unplug_thresh)
 708                         __generic_unplug_device(q);
 709         }
 710 }
 711
 712 void __elv_add_request(struct request_queue *q, struct request *rq, int where,
 713                        int plug)
 714 {
 715         if (q->ordcolor)
 716                 rq->cmd_flags |= REQ_ORDERED_COLOR;
 717
 718         if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
 719                 /*
 720                  * toggle ordered color
 721                  */
 722                 if (blk_barrier_rq(rq))
 723                         q->ordcolor ^= 1;
 724
 725                 /*
 726                  * barriers implicitly indicate back insertion
 727                  */
 728                 if (where == ELEVATOR_INSERT_SORT)
 729                         where = ELEVATOR_INSERT_BACK;
 730
 731                 /*
 732                  * this request is scheduling boundary, update
 733                  * end_sector
 734                  */
 735                 if (blk_fs_request(rq) || blk_discard_rq(rq)) {
 736                         q->end_sector = rq_end_sector(rq);
 737                         q->boundary_rq = rq;
 738                 }
 739         } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
 740                     where == ELEVATOR_INSERT_SORT)
 741                 where = ELEVATOR_INSERT_BACK;
 742
 743         if (plug)
 744                 blk_plug_device(q);
 745
 746         elv_insert(q, rq, where);
 747 }
 748 EXPORT_SYMBOL(__elv_add_request);
 749
 750 void elv_add_request(struct request_queue *q, struct request *rq, int where,
 751                      int plug)
 752 {
 753         unsigned long flags;
 754
 755         spin_lock_irqsave(q->queue_lock, flags);
 756         __elv_add_request(q, rq, where, plug);
 757         spin_unlock_irqrestore(q->queue_lock, flags);
 758 }
 759 EXPORT_SYMBOL(elv_add_request);
 760
 761 static inline struct request *__elv_next_request(struct request_queue *q)
 762 {
 763         struct request *rq;
 764
 765         while (1) {
 766                 while (!list_empty(&q->queue_head)) {
 767                         rq = list_entry_rq(q->queue_head.next);
 768                         if (blk_do_ordered(q, &rq))
 769                                 return rq;
 770                 }
 771
 772                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
 773                         return NULL;
 774         }
 775 }
 776
 777 struct request *elv_next_request(struct request_queue *q)
 778 {
 779         struct request *rq;
 780         int ret;
 781
 782         while ((rq = __elv_next_request(q)) != NULL) {
 783                 if (!(rq->cmd_flags & REQ_STARTED)) {
 784                         /*
 785                          * This is the first time the device driver
 786                          * sees this request (possibly after
 787                          * requeueing).  Notify IO scheduler.
 788                          */
 789                         if (blk_sorted_rq(rq))
 790                                 elv_activate_rq(q, rq);
 791
 792                         /*
 793                          * just mark as started even if we don't start
 794                          * it, a request that has been delayed should
 795                          * not be passed by new incoming requests
 796                          */
 797                         rq->cmd_flags |= REQ_STARTED;
 798                         trace_block_rq_issue(q, rq);
 799                 }
 800
 801                 if (!q->boundary_rq || q->boundary_rq == rq) {
 802                         q->end_sector = rq_end_sector(rq);
 803                         q->boundary_rq = NULL;
 804                 }
 805
 806                 if (rq->cmd_flags & REQ_DONTPREP)
 807                         break;
 808
 809                 if (q->dma_drain_size && rq->data_len) {
 810                         /*
 811                          * make sure space for the drain appears we
 812                          * know we can do this because max_hw_segments
 813                          * has been adjusted to be one fewer than the
 814                          * device can handle
 815                          */
 816                         rq->nr_phys_segments++;
 817                 }
 818
 819                 if (!q->prep_rq_fn)
 820                         break;
 821
 822                 ret = q->prep_rq_fn(q, rq);
 823                 if (ret == BLKPREP_OK) {
 824                         break;
 825                 } else if (ret == BLKPREP_DEFER) {
 826                         /*
 827                          * the request may have been (partially) prepped.
 828                          * we need to keep this request in the front to
 829                          * avoid resource deadlock.  REQ_STARTED will
 830                          * prevent other fs requests from passing this one.
 831                          */
 832                         if (q->dma_drain_size && rq->data_len &&
 833                             !(rq->cmd_flags & REQ_DONTPREP)) {
 834                                 /*
 835                                  * remove the space for the drain we added
 836                                  * so that we don't add it again
 837                                  */
 838                                 --rq->nr_phys_segments;
 839                         }
 840
 841                         rq = NULL;
 842                         break;
 843                 } else if (ret == BLKPREP_KILL) {
 844                         rq->cmd_flags |= REQ_QUIET;
 845                         __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 846                 } else {
 847                         printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
 848                         break;
 849                 }
 850         }
 851
 852         return rq;
 853 }
 854 EXPORT_SYMBOL(elv_next_request);
 855
 856 void elv_dequeue_request(struct request_queue *q, struct request *rq)
 857 {
 858         BUG_ON(list_empty(&rq->queuelist));
 859         BUG_ON(ELV_ON_HASH(rq));
 860
 861         list_del_init(&rq->queuelist);
 862
 863         /*
 864          * the time frame between a request being removed from the lists
 865          * and to it is freed is accounted as io that is in progress at
 866          * the driver side.
 867          */
 868         if (blk_account_rq(rq))
 869                 q->in_flight++;
 870 }
 871
 872 int elv_queue_empty(struct request_queue *q)
 873 {
 874         struct elevator_queue *e = q->elevator;
 875
 876         if (!list_empty(&q->queue_head))
 877                 return 0;
 878
 879         if (e->ops->elevator_queue_empty_fn)
 880                 return e->ops->elevator_queue_empty_fn(q);
 881
 882         return 1;
 883 }
 884 EXPORT_SYMBOL(elv_queue_empty);
 885
 886 struct request *elv_latter_request(struct request_queue *q, struct request *rq)
 887 {
 888         struct elevator_queue *e = q->elevator;
 889
 890         if (e->ops->elevator_latter_req_fn)
 891                 return e->ops->elevator_latter_req_fn(q, rq);
 892         return NULL;
 893 }
 894
 895 struct request *elv_former_request(struct request_queue *q, struct request *rq)
 896 {
 897         struct elevator_queue *e = q->elevator;
 898
 899         if (e->ops->elevator_former_req_fn)
 900                 return e->ops->elevator_former_req_fn(q, rq);
 901         return NULL;
 902 }
 903
 904 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
 905 {
 906         struct elevator_queue *e = q->elevator;
 907
 908         if (e->ops->elevator_set_req_fn)
 909                 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
 910
 911         rq->elevator_private = NULL;
 912         return 0;
 913 }
 914
 915 void elv_put_request(struct request_queue *q, struct request *rq)
 916 {
 917         struct elevator_queue *e = q->elevator;
 918
 919         if (e->ops->elevator_put_req_fn)
 920                 e->ops->elevator_put_req_fn(rq);
 921 }
 922
 923 int elv_may_queue(struct request_queue *q, int rw)
 924 {
 925         struct elevator_queue *e = q->elevator;
 926
 927         if (e->ops->elevator_may_queue_fn)
 928                 return e->ops->elevator_may_queue_fn(q, rw);
 929
 930         return ELV_MQUEUE_MAY;
 931 }
 932
 933 void elv_abort_queue(struct request_queue *q)
 934 {
 935         struct request *rq;
 936
 937         while (!list_empty(&q->queue_head)) {
 938                 rq = list_entry_rq(q->queue_head.next);
 939                 rq->cmd_flags |= REQ_QUIET;
 940                 trace_block_rq_abort(q, rq);
 941                 __blk_end_request(rq, -EIO, blk_rq_bytes(rq));
 942         }
 943 }
 944 EXPORT_SYMBOL(elv_abort_queue);
 945
 946 void elv_completed_request(struct request_queue *q, struct request *rq)
 947 {
 948         struct elevator_queue *e = q->elevator;
 949
 950         /*
 951          * request is released from the driver, io must be done
 952          */
 953         if (blk_account_rq(rq)) {
 954                 q->in_flight--;
 955                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
 956                         e->ops->elevator_completed_req_fn(q, rq);
 957         }
 958
 959         /*
 960          * Check if the queue is waiting for fs requests to be
 961          * drained for flush sequence.
 962          */
 963         if (unlikely(q->ordseq)) {
 964                 struct request *next = NULL;
 965
 966                 if (!list_empty(&q->queue_head))
 967                         next = list_entry_rq(q->queue_head.next);
 968
 969                 if (!q->in_flight &&
 970                     blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
 971                     (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
 972                         blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
 973                         __blk_run_queue(q);
 974                 }
 975         }
 976 }
 977
 978 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
 979
 980 static ssize_t
 981 elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
 982 {
 983         struct elv_fs_entry *entry = to_elv(attr);
 984         struct elevator_queue *e;
 985         ssize_t error;
 986
 987         if (!entry->show)
 988                 return -EIO;
 989
 990         e = container_of(kobj, struct elevator_queue, kobj);
 991         mutex_lock(&e->sysfs_lock);
 992         error = e->ops ? entry->show(e, page) : -ENOENT;
 993         mutex_unlock(&e->sysfs_lock);
 994         return error;
 995 }
 996
 997 static ssize_t
 998 elv_attr_store(struct kobject *kobj, struct attribute *attr,
 999                const char *page, size_t length)
1000 {
1001         struct elv_fs_entry *entry = to_elv(attr);
1002         struct elevator_queue *e;
1003         ssize_t error;
1004
1005         if (!entry->store)
1006                 return -EIO;
1007
1008         e = container_of(kobj, struct elevator_queue, kobj);
1009         mutex_lock(&e->sysfs_lock);
1010         error = e->ops ? entry->store(e, page, length) : -ENOENT;
1011         mutex_unlock(&e->sysfs_lock);
1012         return error;
1013 }
1014
1015 static struct sysfs_ops elv_sysfs_ops = {
1016         .show   = elv_attr_show,
1017         .store  = elv_attr_store,
1018 };
1019
1020 static struct kobj_type elv_ktype = {
1021         .sysfs_ops      = &elv_sysfs_ops,
1022         .release        = elevator_release,
1023 };
1024
1025 int elv_register_queue(struct request_queue *q)
1026 {
1027         struct elevator_queue *e = q->elevator;
1028         int error;
1029
1030         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
1031         if (!error) {
1032                 struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
1033                 if (attr) {
1034                         while (attr->attr.name) {
1035                                 if (sysfs_create_file(&e->kobj, &attr->attr))
1036                                         break;
1037                                 attr++;
1038                         }
1039                 }
1040                 kobject_uevent(&e->kobj, KOBJ_ADD);
1041         }
1042         return error;
1043 }
1044
1045 static void __elv_unregister_queue(struct elevator_queue *e)
1046 {
1047         kobject_uevent(&e->kobj, KOBJ_REMOVE);
1048         kobject_del(&e->kobj);
1049 }
1050
1051 void elv_unregister_queue(struct request_queue *q)
1052 {
1053         if (q)
1054                 __elv_unregister_queue(q->elevator);
1055 }
1056
1057 void elv_register(struct elevator_type *e)
1058 {
1059         char *def = "";
1060
1061         spin_lock(&elv_list_lock);
1062         BUG_ON(elevator_find(e->elevator_name));
1063         list_add_tail(&e->list, &elv_list);
1064         spin_unlock(&elv_list_lock);
1065
1066         if (!strcmp(e->elevator_name, chosen_elevator) ||
1067                         (!*chosen_elevator &&
1068                          !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
1069                                 def = " (default)";
1070
1071         printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
1072                                                                 def);
1073 }
1074 EXPORT_SYMBOL_GPL(elv_register);
1075
1076 void elv_unregister(struct elevator_type *e)
1077 {
1078         struct task_struct *g, *p;
1079
1080         /*
1081          * Iterate every thread in the process to remove the io contexts.
1082          */
1083         if (e->ops.trim) {
1084                 read_lock(&tasklist_lock);
1085                 do_each_thread(g, p) {
1086                         task_lock(p);
1087                         if (p->io_context)
1088                                 e->ops.trim(p->io_context);
1089                         task_unlock(p);
1090                 } while_each_thread(g, p);
1091                 read_unlock(&tasklist_lock);
1092         }
1093
1094         spin_lock(&elv_list_lock);
1095         list_del_init(&e->list);
1096         spin_unlock(&elv_list_lock);
1097 }
1098 EXPORT_SYMBOL_GPL(elv_unregister);
1099
1100 /*
1101  * switch to new_e io scheduler. be careful not to introduce deadlocks -
1102  * we don't free the old io scheduler, before we have allocated what we
1103  * need for the new one. this way we have a chance of going back to the old
1104  * one, if the new one fails init for some reason.
1105  */
1106 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
1107 {
1108         struct elevator_queue *old_elevator, *e;
1109         void *data;
1110
1111         /*
1112          * Allocate new elevator
1113          */
1114         e = elevator_alloc(q, new_e);
1115         if (!e)
1116                 return 0;
1117
1118         data = elevator_init_queue(q, e);
1119         if (!data) {
1120                 kobject_put(&e->kobj);
1121                 return 0;
1122         }
1123
1124         /*
1125          * Turn on BYPASS and drain all requests w/ elevator private data
1126          */
1127         spin_lock_irq(q->queue_lock);
1128         elv_quiesce_start(q);
1129
1130         /*
1131          * Remember old elevator.
1132          */
1133         old_elevator = q->elevator;
1134
1135         /*
1136          * attach and start new elevator
1137          */
1138         elevator_attach(q, e, data);
1139
1140         spin_unlock_irq(q->queue_lock);
1141
1142         __elv_unregister_queue(old_elevator);
1143
1144         if (elv_register_queue(q))
1145                 goto fail_register;
1146
1147         /*
1148          * finally exit old elevator and turn off BYPASS.
1149          */
1150         elevator_exit(old_elevator);
1151         spin_lock_irq(q->queue_lock);
1152         elv_quiesce_end(q);
1153         spin_unlock_irq(q->queue_lock);
1154
1155         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1156
1157         return 1;
1158
1159 fail_register:
1160         /*
1161          * switch failed, exit the new io scheduler and reattach the old
1162          * one again (along with re-adding the sysfs dir)
1163          */
1164         elevator_exit(e);
1165         q->elevator = old_elevator;
1166         elv_register_queue(q);
1167
1168         spin_lock_irq(q->queue_lock);
1169         queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1170         spin_unlock_irq(q->queue_lock);
1171
1172         return 0;
1173 }
1174
1175 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1176                           size_t count)
1177 {
1178         char elevator_name[ELV_NAME_MAX];
1179         struct elevator_type *e;
1180
1181         strlcpy(elevator_name, name, sizeof(elevator_name));
1182         strstrip(elevator_name);
1183
1184         e = elevator_get(elevator_name);
1185         if (!e) {
1186                 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1187                 return -EINVAL;
1188         }
1189
1190         if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1191                 elevator_put(e);
1192                 return count;
1193         }
1194
1195         if (!elevator_switch(q, e))
1196                 printk(KERN_ERR "elevator: switch to %s failed\n",
1197                                                         elevator_name);
1198         return count;
1199 }
1200
1201 ssize_t elv_iosched_show(struct request_queue *q, char *name)
1202 {
1203         struct elevator_queue *e = q->elevator;
1204         struct elevator_type *elv = e->elevator_type;
1205         struct elevator_type *__e;
1206         int len = 0;
1207
1208         spin_lock(&elv_list_lock);
1209         list_for_each_entry(__e, &elv_list, list) {
1210                 if (!strcmp(elv->elevator_name, __e->elevator_name))
1211                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
1212                 else
1213                         len += sprintf(name+len, "%s ", __e->elevator_name);
1214         }
1215         spin_unlock(&elv_list_lock);
1216
1217         len += sprintf(len+name, "\n");
1218         return len;
1219 }
1220
1221 struct request *elv_rb_former_request(struct request_queue *q,
1222                                       struct request *rq)
1223 {
1224         struct rb_node *rbprev = rb_prev(&rq->rb_node);
1225
1226         if (rbprev)
1227                 return rb_entry_rq(rbprev);
1228
1229         return NULL;
1230 }
1231 EXPORT_SYMBOL(elv_rb_former_request);
1232
1233 struct request *elv_rb_latter_request(struct request_queue *q,
1234                                       struct request *rq)
1235 {
1236         struct rb_node *rbnext = rb_next(&rq->rb_node);
1237
1238         if (rbnext)
1239                 return rb_entry_rq(rbnext);
1240
1241         return NULL;
1242 }
1243 EXPORT_SYMBOL(elv_rb_latter_request);