/*

   *  Block device elevator/IO-scheduler.
   *
   *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
   *

   * 30042000 Jens Axboe <axboe@kernel.dk> :

   *
   * Split the elevator a bit so that it is possible to choose a different
   * one or even write a new "plug in". There are three pieces:
   * - elevator_fn, inserts a new request in the queue list
   * - elevator_merge_fn, decides whether a new buffer can be merged with
   *   an existing request
   * - elevator_dequeue_fn, called when a request is taken off the active list
   *
   * 20082000 Dave Jones <davej@suse.de> :
   * Removed tests for max-bomb-segments, which was breaking elvtune
   *  when run without -bN
   *
   * Jens:
   * - Rework again to work with bio instead of buffer_heads
   * - loose bi_dev comparisons, partition handling is right now
   * - completely modularize elevator setup and teardown
   *
   */
  #include <linux/kernel.h>
  #include <linux/fs.h>
  #include <linux/blkdev.h>
  #include <linux/elevator.h>
  #include <linux/bio.h>

  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/compiler.h>

  #include <linux/delay.h>

  #include <linux/blktrace_api.h>

  #include <linux/hash.h>

  #include <linux/uaccess.h>

  #include <trace/events/block.h>

  #include "blk.h"

  static DEFINE_SPINLOCK(elv_list_lock);
  static LIST_HEAD(elv_list);
  
  /*

   * Merge hash stuff.
   */
  static const int elv_hash_shift = 6;
  #define ELV_HASH_BLOCK(sec)	((sec) >> 3)

  #define ELV_HASH_FN(sec)	\
  		(hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))

  #define ELV_HASH_ENTRIES	(1 << elv_hash_shift)

  #define rq_hash_key(rq)		(blk_rq_pos(rq) + blk_rq_sectors(rq))

  
  /*

   * Query io scheduler to see if the current process issuing bio may be
   * merged with rq.
   */
  static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
  {

  	struct request_queue *q = rq->q;

  	struct elevator_queue *e = q->elevator;

  
  	if (e->ops->elevator_allow_merge_fn)
  		return e->ops->elevator_allow_merge_fn(q, rq, bio);
  
  	return 1;
  }
  
  /*

   * can we safely merge with this request?
   */

  int elv_rq_merge_ok(struct request *rq, struct bio *bio)

  {
  	if (!rq_mergeable(rq))
  		return 0;
  
  	/*

  	 * Don't merge file system requests and discard requests
  	 */

  	if (bio_rw_flagged(bio, BIO_RW_DISCARD) !=
  	    bio_rw_flagged(rq->bio, BIO_RW_DISCARD))

  		return 0;
  
  	/*

  	 * different data direction or already started, don't merge
  	 */
  	if (bio_data_dir(bio) != rq_data_dir(rq))
  		return 0;
  
  	/*

  	 * must be same device and not a special request

  	 */

  	if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)

  		return 0;

  	/*
  	 * only merge integrity protected bio into ditto rq
  	 */
  	if (bio_integrity(bio) != blk_integrity_rq(rq))
  		return 0;

  	if (!elv_iosched_allow_merge(rq, bio))
  		return 0;

  	return 1;

  }
  EXPORT_SYMBOL(elv_rq_merge_ok);

  static inline int elv_try_merge(struct request *__rq, struct bio *bio)

  {
  	int ret = ELEVATOR_NO_MERGE;
  
  	/*
  	 * we can merge and sequence is ok, check if it's possible
  	 */
  	if (elv_rq_merge_ok(__rq, bio)) {

  		if (blk_rq_pos(__rq) + blk_rq_sectors(__rq) == bio->bi_sector)

  			ret = ELEVATOR_BACK_MERGE;

  		else if (blk_rq_pos(__rq) - bio_sectors(bio) == bio->bi_sector)

  			ret = ELEVATOR_FRONT_MERGE;
  	}
  
  	return ret;
  }

  static struct elevator_type *elevator_find(const char *name)
  {

  	struct elevator_type *e;

  	list_for_each_entry(e, &elv_list, list) {

  		if (!strcmp(e->elevator_name, name))
  			return e;

  	}

  	return NULL;

  }
  
  static void elevator_put(struct elevator_type *e)
  {
  	module_put(e->elevator_owner);
  }
  
  static struct elevator_type *elevator_get(const char *name)
  {

  	struct elevator_type *e;

  	spin_lock(&elv_list_lock);

  
  	e = elevator_find(name);

  	if (!e) {
  		char elv[ELV_NAME_MAX + strlen("-iosched")];
  
  		spin_unlock(&elv_list_lock);

  		sprintf(elv, "%s-iosched", name);

  		request_module("%s", elv);

  		spin_lock(&elv_list_lock);
  		e = elevator_find(name);
  	}

  	if (e && !try_module_get(e->elevator_owner))
  		e = NULL;

  	spin_unlock(&elv_list_lock);

  
  	return e;
  }

  static void *elevator_init_queue(struct request_queue *q,
  				 struct elevator_queue *eq)

  {

  	return eq->ops->elevator_init_fn(q);

  }

  static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,

  			   void *data)
  {

  	q->elevator = eq;

  	eq->elevator_data = data;

  }
  
  static char chosen_elevator[16];

  static int __init elevator_setup(char *str)

  {

  	/*
  	 * Be backwards-compatible with previous kernels, so users
  	 * won't get the wrong elevator.
  	 */

  	strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);

  	return 1;

  }
  
  __setup("elevator=", elevator_setup);

  static struct kobj_type elv_ktype;

  static struct elevator_queue *elevator_alloc(struct request_queue *q,

  				  struct elevator_type *e)

  {

  	struct elevator_queue *eq;

  	int i;

  	eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);

  	if (unlikely(!eq))
  		goto err;

  	eq->ops = &e->ops;
  	eq->elevator_type = e;

  	kobject_init(&eq->kobj, &elv_ktype);

  	mutex_init(&eq->sysfs_lock);

  	eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
  					GFP_KERNEL, q->node);

  	if (!eq->hash)
  		goto err;
  
  	for (i = 0; i < ELV_HASH_ENTRIES; i++)
  		INIT_HLIST_HEAD(&eq->hash[i]);

  	return eq;

  err:
  	kfree(eq);
  	elevator_put(e);
  	return NULL;

  }
  
  static void elevator_release(struct kobject *kobj)
  {

  	struct elevator_queue *e;

  	e = container_of(kobj, struct elevator_queue, kobj);

  	elevator_put(e->elevator_type);

  	kfree(e->hash);

  	kfree(e);
  }

  int elevator_init(struct request_queue *q, char *name)

  {
  	struct elevator_type *e = NULL;
  	struct elevator_queue *eq;
  	int ret = 0;

  	void *data;

  	INIT_LIST_HEAD(&q->queue_head);
  	q->last_merge = NULL;
  	q->end_sector = 0;
  	q->boundary_rq = NULL;

  	if (name) {
  		e = elevator_get(name);
  		if (!e)
  			return -EINVAL;
  	}

  	if (!e && *chosen_elevator) {
  		e = elevator_get(chosen_elevator);
  		if (!e)
  			printk(KERN_ERR "I/O scheduler %s not found
  ",
  							chosen_elevator);
  	}

  	if (!e) {
  		e = elevator_get(CONFIG_DEFAULT_IOSCHED);
  		if (!e) {
  			printk(KERN_ERR
  				"Default I/O scheduler not found. " \
  				"Using noop.
  ");
  			e = elevator_get("noop");
  		}

  	}

  	eq = elevator_alloc(q, e);

  	if (!eq)

  		return -ENOMEM;

  	data = elevator_init_queue(q, eq);
  	if (!data) {

  		kobject_put(&eq->kobj);

  		return -ENOMEM;
  	}

  	elevator_attach(q, eq, data);

  	return ret;
  }

  EXPORT_SYMBOL(elevator_init);

  void elevator_exit(struct elevator_queue *e)

  {

  	mutex_lock(&e->sysfs_lock);

  	if (e->ops->elevator_exit_fn)
  		e->ops->elevator_exit_fn(e);

  	e->ops = NULL;
  	mutex_unlock(&e->sysfs_lock);

  	kobject_put(&e->kobj);

  }

  EXPORT_SYMBOL(elevator_exit);

  static inline void __elv_rqhash_del(struct request *rq)
  {
  	hlist_del_init(&rq->hash);
  }

  static void elv_rqhash_del(struct request_queue *q, struct request *rq)

  {
  	if (ELV_ON_HASH(rq))
  		__elv_rqhash_del(rq);
  }

  static void elv_rqhash_add(struct request_queue *q, struct request *rq)

  {

  	struct elevator_queue *e = q->elevator;

  
  	BUG_ON(ELV_ON_HASH(rq));
  	hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
  }

  static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)

  {
  	__elv_rqhash_del(rq);
  	elv_rqhash_add(q, rq);
  }

  static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)

  {

  	struct elevator_queue *e = q->elevator;

  	struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
  	struct hlist_node *entry, *next;
  	struct request *rq;
  
  	hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
  		BUG_ON(!ELV_ON_HASH(rq));
  
  		if (unlikely(!rq_mergeable(rq))) {
  			__elv_rqhash_del(rq);
  			continue;
  		}
  
  		if (rq_hash_key(rq) == offset)
  			return rq;
  	}
  
  	return NULL;
  }

  /*

   * RB-tree support functions for inserting/lookup/removal of requests
   * in a sorted RB tree.
   */
  struct request *elv_rb_add(struct rb_root *root, struct request *rq)
  {
  	struct rb_node **p = &root->rb_node;
  	struct rb_node *parent = NULL;
  	struct request *__rq;
  
  	while (*p) {
  		parent = *p;
  		__rq = rb_entry(parent, struct request, rb_node);

  		if (blk_rq_pos(rq) < blk_rq_pos(__rq))

  			p = &(*p)->rb_left;

  		else if (blk_rq_pos(rq) > blk_rq_pos(__rq))

  			p = &(*p)->rb_right;
  		else
  			return __rq;
  	}
  
  	rb_link_node(&rq->rb_node, parent, p);
  	rb_insert_color(&rq->rb_node, root);
  	return NULL;
  }

  EXPORT_SYMBOL(elv_rb_add);
  
  void elv_rb_del(struct rb_root *root, struct request *rq)
  {
  	BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
  	rb_erase(&rq->rb_node, root);
  	RB_CLEAR_NODE(&rq->rb_node);
  }

  EXPORT_SYMBOL(elv_rb_del);
  
  struct request *elv_rb_find(struct rb_root *root, sector_t sector)
  {
  	struct rb_node *n = root->rb_node;
  	struct request *rq;
  
  	while (n) {
  		rq = rb_entry(n, struct request, rb_node);

  		if (sector < blk_rq_pos(rq))

  			n = n->rb_left;

  		else if (sector > blk_rq_pos(rq))

  			n = n->rb_right;
  		else
  			return rq;
  	}
  
  	return NULL;
  }

  EXPORT_SYMBOL(elv_rb_find);
  
  /*

   * Insert rq into dispatch queue of q.  Queue lock must be held on

   * entry.  rq is sort instead into the dispatch queue. To be used by

   * specific elevators.

   */

  void elv_dispatch_sort(struct request_queue *q, struct request *rq)

  {
  	sector_t boundary;

  	struct list_head *entry;

  	int stop_flags;

  	if (q->last_merge == rq)
  		q->last_merge = NULL;

  
  	elv_rqhash_del(q, rq);

  	q->nr_sorted--;

  	boundary = q->end_sector;

  	stop_flags = REQ_SOFTBARRIER | REQ_HARDBARRIER | REQ_STARTED;

  	list_for_each_prev(entry, &q->queue_head) {
  		struct request *pos = list_entry_rq(entry);

  		if (blk_discard_rq(rq) != blk_discard_rq(pos))
  			break;

  		if (rq_data_dir(rq) != rq_data_dir(pos))
  			break;

  		if (pos->cmd_flags & stop_flags)

  			break;

  		if (blk_rq_pos(rq) >= boundary) {
  			if (blk_rq_pos(pos) < boundary)

  				continue;
  		} else {

  			if (blk_rq_pos(pos) >= boundary)

  				break;
  		}

  		if (blk_rq_pos(rq) >= blk_rq_pos(pos))

  			break;
  	}
  
  	list_add(&rq->queuelist, entry);
  }

  EXPORT_SYMBOL(elv_dispatch_sort);

  /*

   * Insert rq into dispatch queue of q.  Queue lock must be held on
   * entry.  rq is added to the back of the dispatch queue. To be used by
   * specific elevators.

   */
  void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
  {
  	if (q->last_merge == rq)
  		q->last_merge = NULL;
  
  	elv_rqhash_del(q, rq);
  
  	q->nr_sorted--;
  
  	q->end_sector = rq_end_sector(rq);
  	q->boundary_rq = rq;
  	list_add_tail(&rq->queuelist, &q->queue_head);
  }

  EXPORT_SYMBOL(elv_dispatch_add_tail);

  int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)

  {

  	struct elevator_queue *e = q->elevator;

  	struct request *__rq;

  	int ret;

  	/*
  	 * First try one-hit cache.
  	 */

  	if (q->last_merge) {
  		ret = elv_try_merge(q->last_merge, bio);
  		if (ret != ELEVATOR_NO_MERGE) {
  			*req = q->last_merge;
  			return ret;
  		}
  	}

  	if (blk_queue_nomerges(q))
  		return ELEVATOR_NO_MERGE;

  	/*
  	 * See if our hash lookup can find a potential backmerge.
  	 */
  	__rq = elv_rqhash_find(q, bio->bi_sector);
  	if (__rq && elv_rq_merge_ok(__rq, bio)) {
  		*req = __rq;
  		return ELEVATOR_BACK_MERGE;
  	}

  	if (e->ops->elevator_merge_fn)
  		return e->ops->elevator_merge_fn(q, req, bio);
  
  	return ELEVATOR_NO_MERGE;
  }

  void elv_merged_request(struct request_queue *q, struct request *rq, int type)

  {

  	struct elevator_queue *e = q->elevator;

  
  	if (e->ops->elevator_merged_fn)

  		e->ops->elevator_merged_fn(q, rq, type);

  	if (type == ELEVATOR_BACK_MERGE)
  		elv_rqhash_reposition(q, rq);

  	q->last_merge = rq;

  }

  void elv_merge_requests(struct request_queue *q, struct request *rq,

  			     struct request *next)
  {

  	struct elevator_queue *e = q->elevator;

  	if (e->ops->elevator_merge_req_fn)
  		e->ops->elevator_merge_req_fn(q, rq, next);

  	elv_rqhash_reposition(q, rq);
  	elv_rqhash_del(q, next);
  
  	q->nr_sorted--;

  	q->last_merge = rq;

  }

  void elv_requeue_request(struct request_queue *q, struct request *rq)

  {

  	/*
  	 * it already went through dequeue, we need to decrement the
  	 * in_flight count again
  	 */

  	if (blk_account_rq(rq)) {

  		q->in_flight[rq_is_sync(rq)]--;

  		if (blk_sorted_rq(rq))
  			elv_deactivate_rq(q, rq);

  	}

  	rq->cmd_flags &= ~REQ_STARTED;

  	elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);

  }

  void elv_drain_elevator(struct request_queue *q)

  {
  	static int printed;
  	while (q->elevator->ops->elevator_dispatch_fn(q, 1))
  		;
  	if (q->nr_sorted == 0)
  		return;
  	if (printed++ < 10) {
  		printk(KERN_ERR "%s: forced dispatching is broken "
  		       "(nr_sorted=%u), please report this
  ",
  		       q->elevator->elevator_type->elevator_name, q->nr_sorted);
  	}
  }

  /*
   * Call with queue lock held, interrupts disabled
   */

  void elv_quiesce_start(struct request_queue *q)

  {

  	if (!q->elevator)
  		return;

  	queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
  
  	/*
  	 * make sure we don't have any requests in flight
  	 */
  	elv_drain_elevator(q);
  	while (q->rq.elvpriv) {

  		__blk_run_queue(q);

  		spin_unlock_irq(q->queue_lock);
  		msleep(10);
  		spin_lock_irq(q->queue_lock);
  		elv_drain_elevator(q);
  	}
  }

  void elv_quiesce_end(struct request_queue *q)

  {
  	queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
  }

  void elv_insert(struct request_queue *q, struct request *rq, int where)

  {

  	struct list_head *pos;
  	unsigned ordseq;

  	int unplug_it = 1;

  	trace_block_rq_insert(q, rq);

  	rq->q = q;

  	switch (where) {
  	case ELEVATOR_INSERT_FRONT:

  		rq->cmd_flags |= REQ_SOFTBARRIER;

  
  		list_add(&rq->queuelist, &q->queue_head);
  		break;
  
  	case ELEVATOR_INSERT_BACK:

  		rq->cmd_flags |= REQ_SOFTBARRIER;

  		elv_drain_elevator(q);

  		list_add_tail(&rq->queuelist, &q->queue_head);
  		/*
  		 * We kick the queue here for the following reasons.
  		 * - The elevator might have returned NULL previously
  		 *   to delay requests and returned them now.  As the
  		 *   queue wasn't empty before this request, ll_rw_blk
  		 *   won't run the queue on return, resulting in hang.
  		 * - Usually, back inserted requests won't be merged
  		 *   with anything.  There's no point in delaying queue
  		 *   processing.
  		 */

  		__blk_run_queue(q);

  		break;
  
  	case ELEVATOR_INSERT_SORT:

  		BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));

  		rq->cmd_flags |= REQ_SORTED;

  		q->nr_sorted++;

  		if (rq_mergeable(rq)) {
  			elv_rqhash_add(q, rq);
  			if (!q->last_merge)
  				q->last_merge = rq;
  		}

  		/*
  		 * Some ioscheds (cfq) run q->request_fn directly, so
  		 * rq cannot be accessed after calling
  		 * elevator_add_req_fn.
  		 */
  		q->elevator->ops->elevator_add_req_fn(q, rq);

  		break;

  	case ELEVATOR_INSERT_REQUEUE:
  		/*
  		 * If ordered flush isn't in progress, we do front
  		 * insertion; otherwise, requests should be requeued
  		 * in ordseq order.
  		 */

  		rq->cmd_flags |= REQ_SOFTBARRIER;

  		/*
  		 * Most requeues happen because of a busy condition,
  		 * don't force unplug of the queue for that case.
  		 */
  		unplug_it = 0;

  		if (q->ordseq == 0) {
  			list_add(&rq->queuelist, &q->queue_head);
  			break;
  		}
  
  		ordseq = blk_ordered_req_seq(rq);
  
  		list_for_each(pos, &q->queue_head) {
  			struct request *pos_rq = list_entry_rq(pos);
  			if (ordseq <= blk_ordered_req_seq(pos_rq))
  				break;
  		}
  
  		list_add_tail(&rq->queuelist, pos);
  		break;

  	default:
  		printk(KERN_ERR "%s: bad insertion point %d
  ",

  		       __func__, where);

  		BUG();
  	}

  	if (unplug_it && blk_queue_plugged(q)) {

  		int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]

  				- queue_in_flight(q);

  
  		if (nrq >= q->unplug_thresh)
  			__generic_unplug_device(q);
  	}

  }

  void __elv_add_request(struct request_queue *q, struct request *rq, int where,

  		       int plug)
  {
  	if (q->ordcolor)

  		rq->cmd_flags |= REQ_ORDERED_COLOR;

  	if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {

  		/*
  		 * toggle ordered color
  		 */
  		if (blk_barrier_rq(rq))
  			q->ordcolor ^= 1;
  
  		/*
  		 * barriers implicitly indicate back insertion
  		 */
  		if (where == ELEVATOR_INSERT_SORT)
  			where = ELEVATOR_INSERT_BACK;
  
  		/*
  		 * this request is scheduling boundary, update
  		 * end_sector
  		 */

  		if (blk_fs_request(rq) || blk_discard_rq(rq)) {

  			q->end_sector = rq_end_sector(rq);
  			q->boundary_rq = rq;
  		}

  	} else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
  		    where == ELEVATOR_INSERT_SORT)

  		where = ELEVATOR_INSERT_BACK;
  
  	if (plug)
  		blk_plug_device(q);
  
  	elv_insert(q, rq, where);
  }

  EXPORT_SYMBOL(__elv_add_request);

  void elv_add_request(struct request_queue *q, struct request *rq, int where,

  		     int plug)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(q->queue_lock, flags);
  	__elv_add_request(q, rq, where, plug);
  	spin_unlock_irqrestore(q->queue_lock, flags);
  }

  EXPORT_SYMBOL(elv_add_request);

  int elv_queue_empty(struct request_queue *q)

  {

  	struct elevator_queue *e = q->elevator;

  	if (!list_empty(&q->queue_head))
  		return 0;

  	if (e->ops->elevator_queue_empty_fn)
  		return e->ops->elevator_queue_empty_fn(q);

  	return 1;

  }

  EXPORT_SYMBOL(elv_queue_empty);

  struct request *elv_latter_request(struct request_queue *q, struct request *rq)

  {

  	struct elevator_queue *e = q->elevator;

  
  	if (e->ops->elevator_latter_req_fn)
  		return e->ops->elevator_latter_req_fn(q, rq);

  	return NULL;
  }

  struct request *elv_former_request(struct request_queue *q, struct request *rq)

  {

  	struct elevator_queue *e = q->elevator;

  
  	if (e->ops->elevator_former_req_fn)
  		return e->ops->elevator_former_req_fn(q, rq);

  	return NULL;
  }

  int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)

  {

  	struct elevator_queue *e = q->elevator;

  
  	if (e->ops->elevator_set_req_fn)

  		return e->ops->elevator_set_req_fn(q, rq, gfp_mask);

  
  	rq->elevator_private = NULL;
  	return 0;
  }

  void elv_put_request(struct request_queue *q, struct request *rq)

  {

  	struct elevator_queue *e = q->elevator;

  
  	if (e->ops->elevator_put_req_fn)

  		e->ops->elevator_put_req_fn(rq);

  }

  int elv_may_queue(struct request_queue *q, int rw)

  {

  	struct elevator_queue *e = q->elevator;

  
  	if (e->ops->elevator_may_queue_fn)

  		return e->ops->elevator_may_queue_fn(q, rw);

  
  	return ELV_MQUEUE_MAY;
  }

  void elv_abort_queue(struct request_queue *q)
  {
  	struct request *rq;
  
  	while (!list_empty(&q->queue_head)) {
  		rq = list_entry_rq(q->queue_head.next);
  		rq->cmd_flags |= REQ_QUIET;

  		trace_block_rq_abort(q, rq);

  		/*
  		 * Mark this request as started so we don't trigger
  		 * any debug logic in the end I/O path.
  		 */
  		blk_start_request(rq);

  		__blk_end_request_all(rq, -EIO);

  	}
  }
  EXPORT_SYMBOL(elv_abort_queue);

  void elv_completed_request(struct request_queue *q, struct request *rq)

  {

  	struct elevator_queue *e = q->elevator;

  
  	/*
  	 * request is released from the driver, io must be done
  	 */

  	if (blk_account_rq(rq)) {

  		q->in_flight[rq_is_sync(rq)]--;

  		if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
  			e->ops->elevator_completed_req_fn(q, rq);
  	}

  	/*
  	 * Check if the queue is waiting for fs requests to be
  	 * drained for flush sequence.
  	 */
  	if (unlikely(q->ordseq)) {

  		struct request *next = NULL;
  
  		if (!list_empty(&q->queue_head))
  			next = list_entry_rq(q->queue_head.next);

  		if (!queue_in_flight(q) &&

  		    blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&

  		    (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {

  			blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);

  			__blk_run_queue(q);

  		}

  	}

  }

  #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
  
  static ssize_t
  elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)

  {

  	struct elv_fs_entry *entry = to_elv(attr);

  	struct elevator_queue *e;

  	ssize_t error;
  
  	if (!entry->show)
  		return -EIO;

  	e = container_of(kobj, struct elevator_queue, kobj);

  	mutex_lock(&e->sysfs_lock);
  	error = e->ops ? entry->show(e, page) : -ENOENT;
  	mutex_unlock(&e->sysfs_lock);
  	return error;
  }

  static ssize_t
  elv_attr_store(struct kobject *kobj, struct attribute *attr,
  	       const char *page, size_t length)
  {

  	struct elv_fs_entry *entry = to_elv(attr);

  	struct elevator_queue *e;

  	ssize_t error;

  	if (!entry->store)
  		return -EIO;

  	e = container_of(kobj, struct elevator_queue, kobj);

  	mutex_lock(&e->sysfs_lock);
  	error = e->ops ? entry->store(e, page, length) : -ENOENT;
  	mutex_unlock(&e->sysfs_lock);
  	return error;
  }
  
  static struct sysfs_ops elv_sysfs_ops = {
  	.show	= elv_attr_show,
  	.store	= elv_attr_store,
  };
  
  static struct kobj_type elv_ktype = {
  	.sysfs_ops	= &elv_sysfs_ops,
  	.release	= elevator_release,
  };
  
  int elv_register_queue(struct request_queue *q)
  {

  	struct elevator_queue *e = q->elevator;

  	int error;

  	error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");

  	if (!error) {

  		struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;

  		if (attr) {

  			while (attr->attr.name) {
  				if (sysfs_create_file(&e->kobj, &attr->attr))

  					break;

  				attr++;

  			}
  		}
  		kobject_uevent(&e->kobj, KOBJ_ADD);
  	}
  	return error;

  }

  static void __elv_unregister_queue(struct elevator_queue *e)

  {
  	kobject_uevent(&e->kobj, KOBJ_REMOVE);
  	kobject_del(&e->kobj);
  }

  void elv_unregister_queue(struct request_queue *q)
  {

  	if (q)
  		__elv_unregister_queue(q->elevator);

  }

  void elv_register(struct elevator_type *e)

  {

  	char *def = "";

  
  	spin_lock(&elv_list_lock);

  	BUG_ON(elevator_find(e->elevator_name));

  	list_add_tail(&e->list, &elv_list);

  	spin_unlock(&elv_list_lock);

  	if (!strcmp(e->elevator_name, chosen_elevator) ||
  			(!*chosen_elevator &&
  			 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))

  				def = " (default)";

  	printk(KERN_INFO "io scheduler %s registered%s
  ", e->elevator_name,
  								def);

  }
  EXPORT_SYMBOL_GPL(elv_register);
  
  void elv_unregister(struct elevator_type *e)
  {

  	struct task_struct *g, *p;
  
  	/*
  	 * Iterate every thread in the process to remove the io contexts.
  	 */

  	if (e->ops.trim) {
  		read_lock(&tasklist_lock);
  		do_each_thread(g, p) {
  			task_lock(p);

  			if (p->io_context)
  				e->ops.trim(p->io_context);

  			task_unlock(p);
  		} while_each_thread(g, p);
  		read_unlock(&tasklist_lock);
  	}

  	spin_lock(&elv_list_lock);

  	list_del_init(&e->list);

  	spin_unlock(&elv_list_lock);

  }
  EXPORT_SYMBOL_GPL(elv_unregister);
  
  /*
   * switch to new_e io scheduler. be careful not to introduce deadlocks -
   * we don't free the old io scheduler, before we have allocated what we
   * need for the new one. this way we have a chance of going back to the old

   * one, if the new one fails init for some reason.

   */

  static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)

  {

  	struct elevator_queue *old_elevator, *e;

  	void *data;

  	/*
  	 * Allocate new elevator
  	 */

  	e = elevator_alloc(q, new_e);

  	if (!e)

  		return 0;

  	data = elevator_init_queue(q, e);
  	if (!data) {
  		kobject_put(&e->kobj);
  		return 0;
  	}

  	/*

  	 * Turn on BYPASS and drain all requests w/ elevator private data

  	 */

  	spin_lock_irq(q->queue_lock);

  	elv_quiesce_start(q);

  	/*

  	 * Remember old elevator.

  	 */

  	old_elevator = q->elevator;
  
  	/*

  	 * attach and start new elevator
  	 */

  	elevator_attach(q, e, data);
  
  	spin_unlock_irq(q->queue_lock);
  
  	__elv_unregister_queue(old_elevator);

  
  	if (elv_register_queue(q))
  		goto fail_register;
  
  	/*

  	 * finally exit old elevator and turn off BYPASS.

  	 */
  	elevator_exit(old_elevator);

  	spin_lock_irq(q->queue_lock);

  	elv_quiesce_end(q);

  	spin_unlock_irq(q->queue_lock);

  	blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);

  	return 1;

  
  fail_register:
  	/*
  	 * switch failed, exit the new io scheduler and reattach the old
  	 * one again (along with re-adding the sysfs dir)
  	 */
  	elevator_exit(e);

  	q->elevator = old_elevator;
  	elv_register_queue(q);

  
  	spin_lock_irq(q->queue_lock);
  	queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
  	spin_unlock_irq(q->queue_lock);

  	return 0;

  }

  ssize_t elv_iosched_store(struct request_queue *q, const char *name,
  			  size_t count)

  {
  	char elevator_name[ELV_NAME_MAX];
  	struct elevator_type *e;

  	if (!q->elevator)
  		return count;

  	strlcpy(elevator_name, name, sizeof(elevator_name));

  	e = elevator_get(strstrip(elevator_name));

  	if (!e) {
  		printk(KERN_ERR "elevator: type %s not found
  ", elevator_name);
  		return -EINVAL;
  	}

  	if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
  		elevator_put(e);

  		return count;

  	}

  	if (!elevator_switch(q, e))

  		printk(KERN_ERR "elevator: switch to %s failed
  ",
  							elevator_name);

  	return count;
  }

  ssize_t elv_iosched_show(struct request_queue *q, char *name)

  {

  	struct elevator_queue *e = q->elevator;

  	struct elevator_type *elv;

  	struct elevator_type *__e;

  	int len = 0;

  	if (!q->elevator)
  		return sprintf(name, "none
  ");
  
  	elv = e->elevator_type;

  	spin_lock(&elv_list_lock);

  	list_for_each_entry(__e, &elv_list, list) {

  		if (!strcmp(elv->elevator_name, __e->elevator_name))
  			len += sprintf(name+len, "[%s] ", elv->elevator_name);
  		else
  			len += sprintf(name+len, "%s ", __e->elevator_name);
  	}

  	spin_unlock(&elv_list_lock);

  
  	len += sprintf(len+name, "
  ");
  	return len;
  }

  struct request *elv_rb_former_request(struct request_queue *q,
  				      struct request *rq)

  {
  	struct rb_node *rbprev = rb_prev(&rq->rb_node);
  
  	if (rbprev)
  		return rb_entry_rq(rbprev);
  
  	return NULL;
  }

  EXPORT_SYMBOL(elv_rb_former_request);

  struct request *elv_rb_latter_request(struct request_queue *q,
  				      struct request *rq)

  {
  	struct rb_node *rbnext = rb_next(&rq->rb_node);
  
  	if (rbnext)
  		return rb_entry_rq(rbnext);
  
  	return NULL;
  }

  EXPORT_SYMBOL(elv_rb_latter_request);