/*

   *  CFQ, or complete fairness queueing, disk scheduler.
   *
   *  Based on ideas from a previously unfinished io
   *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
   *
   *  Copyright (C) 2003 Jens Axboe <axboe@suse.de>
   */
  #include <linux/kernel.h>
  #include <linux/fs.h>
  #include <linux/blkdev.h>
  #include <linux/elevator.h>
  #include <linux/bio.h>
  #include <linux/config.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/compiler.h>
  #include <linux/hash.h>
  #include <linux/rbtree.h>
  #include <linux/mempool.h>

  #include <linux/ioprio.h>
  #include <linux/writeback.h>

  
  /*
   * tunables
   */

  static const int cfq_quantum = 4;		/* max queue in one round of service */
  static const int cfq_queued = 8;		/* minimum rq allocate limit per-queue*/
  static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
  static const int cfq_back_max = 16 * 1024;	/* maximum backwards seek, in KiB */
  static const int cfq_back_penalty = 2;		/* penalty of a backwards seek */

  static const int cfq_slice_sync = HZ / 10;

  static int cfq_slice_async = HZ / 25;

  static const int cfq_slice_async_rq = 2;

  static int cfq_slice_idle = HZ / 100;

  
  #define CFQ_IDLE_GRACE		(HZ / 10)
  #define CFQ_SLICE_SCALE		(5)
  
  #define CFQ_KEY_ASYNC		(0)

  #define CFQ_KEY_ANY		(0xffff)

  
  /*
   * disable queueing at the driver/hardware level
   */

  static const int cfq_max_depth = 2;

  /*
   * for the hash of cfqq inside the cfqd
   */
  #define CFQ_QHASH_SHIFT		6
  #define CFQ_QHASH_ENTRIES	(1 << CFQ_QHASH_SHIFT)
  #define list_entry_qhash(entry)	hlist_entry((entry), struct cfq_queue, cfq_hash)
  
  /*
   * for the hash of crq inside the cfqq
   */
  #define CFQ_MHASH_SHIFT		6
  #define CFQ_MHASH_BLOCK(sec)	((sec) >> 3)
  #define CFQ_MHASH_ENTRIES	(1 << CFQ_MHASH_SHIFT)
  #define CFQ_MHASH_FN(sec)	hash_long(CFQ_MHASH_BLOCK(sec), CFQ_MHASH_SHIFT)
  #define rq_hash_key(rq)		((rq)->sector + (rq)->nr_sectors)
  #define list_entry_hash(ptr)	hlist_entry((ptr), struct cfq_rq, hash)
  
  #define list_entry_cfqq(ptr)	list_entry((ptr), struct cfq_queue, cfq_list)

  #define list_entry_fifo(ptr)	list_entry((ptr), struct request, queuelist)

  
  #define RQ_DATA(rq)		(rq)->elevator_private
  
  /*
   * rb-tree defines
   */
  #define RB_NONE			(2)
  #define RB_EMPTY(node)		((node)->rb_node == NULL)
  #define RB_CLEAR_COLOR(node)	(node)->rb_color = RB_NONE
  #define RB_CLEAR(node)		do {	\
  	(node)->rb_parent = NULL;	\
  	RB_CLEAR_COLOR((node));		\
  	(node)->rb_right = NULL;	\
  	(node)->rb_left = NULL;		\
  } while (0)
  #define RB_CLEAR_ROOT(root)	((root)->rb_node = NULL)

  #define rb_entry_crq(node)	rb_entry((node), struct cfq_rq, rb_node)
  #define rq_rb_key(rq)		(rq)->sector

  static kmem_cache_t *crq_pool;
  static kmem_cache_t *cfq_pool;
  static kmem_cache_t *cfq_ioc_pool;

  #define CFQ_PRIO_LISTS		IOPRIO_BE_NR
  #define cfq_class_idle(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
  #define cfq_class_be(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_BE)
  #define cfq_class_rt(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_RT)

  #define ASYNC			(0)
  #define SYNC			(1)
  
  #define cfq_cfqq_dispatched(cfqq)	\
  	((cfqq)->on_dispatch[ASYNC] + (cfqq)->on_dispatch[SYNC])
  
  #define cfq_cfqq_class_sync(cfqq)	((cfqq)->key != CFQ_KEY_ASYNC)
  
  #define cfq_cfqq_sync(cfqq)		\
  	(cfq_cfqq_class_sync(cfqq) || (cfqq)->on_dispatch[SYNC])

  
  /*
   * Per block device queue structure
   */

  struct cfq_data {

  	atomic_t ref;
  	request_queue_t *queue;
  
  	/*
  	 * rr list of queues with requests and the count of them
  	 */
  	struct list_head rr_list[CFQ_PRIO_LISTS];
  	struct list_head busy_rr;
  	struct list_head cur_rr;
  	struct list_head idle_rr;
  	unsigned int busy_queues;
  
  	/*
  	 * non-ordered list of empty cfqq's
  	 */

  	struct list_head empty_list;

  	/*
  	 * cfqq lookup hash
  	 */

  	struct hlist_head *cfq_hash;

  	/*
  	 * global crq hash for all queues
  	 */
  	struct hlist_head *crq_hash;

  
  	unsigned int max_queued;

  	mempool_t *crq_pool;

  	int rq_in_driver;

  	/*
  	 * schedule slice state info
  	 */
  	/*
  	 * idle window management
  	 */
  	struct timer_list idle_slice_timer;
  	struct work_struct unplug_work;

  	struct cfq_queue *active_queue;
  	struct cfq_io_context *active_cic;
  	int cur_prio, cur_end_prio;
  	unsigned int dispatch_slice;
  
  	struct timer_list idle_class_timer;

  
  	sector_t last_sector;

  	unsigned long last_end_request;

  	unsigned int rq_starved;

  
  	/*
  	 * tunables, see top of file
  	 */
  	unsigned int cfq_quantum;
  	unsigned int cfq_queued;

  	unsigned int cfq_fifo_expire[2];

  	unsigned int cfq_back_penalty;
  	unsigned int cfq_back_max;

  	unsigned int cfq_slice[2];
  	unsigned int cfq_slice_async_rq;
  	unsigned int cfq_slice_idle;
  	unsigned int cfq_max_depth;

  };

  /*
   * Per process-grouping structure
   */

  struct cfq_queue {
  	/* reference count */
  	atomic_t ref;
  	/* parent cfq_data */
  	struct cfq_data *cfqd;

  	/* cfqq lookup hash */

  	struct hlist_node cfq_hash;
  	/* hash key */

  	unsigned int key;

  	/* on either rr or empty list of cfqd */
  	struct list_head cfq_list;
  	/* sorted list of pending requests */
  	struct rb_root sort_list;
  	/* if fifo isn't expired, next request to serve */
  	struct cfq_rq *next_crq;
  	/* requests queued in sort_list */
  	int queued[2];
  	/* currently allocated requests */
  	int allocated[2];
  	/* fifo list of requests in sort_list */

  	struct list_head fifo;

  	unsigned long slice_start;
  	unsigned long slice_end;
  	unsigned long slice_left;
  	unsigned long service_last;

  	/* number of requests that are on the dispatch list */
  	int on_dispatch[2];

  
  	/* io prio of this group */
  	unsigned short ioprio, org_ioprio;
  	unsigned short ioprio_class, org_ioprio_class;

  	/* various state flags, see below */
  	unsigned int flags;

  };
  
  struct cfq_rq {
  	struct rb_node rb_node;
  	sector_t rb_key;
  	struct request *request;
  	struct hlist_node hash;
  
  	struct cfq_queue *cfq_queue;
  	struct cfq_io_context *io_context;

  	unsigned int crq_flags;

  };

  enum cfqq_state_flags {
  	CFQ_CFQQ_FLAG_on_rr = 0,
  	CFQ_CFQQ_FLAG_wait_request,
  	CFQ_CFQQ_FLAG_must_alloc,
  	CFQ_CFQQ_FLAG_must_alloc_slice,
  	CFQ_CFQQ_FLAG_must_dispatch,
  	CFQ_CFQQ_FLAG_fifo_expire,
  	CFQ_CFQQ_FLAG_idle_window,
  	CFQ_CFQQ_FLAG_prio_changed,
  	CFQ_CFQQ_FLAG_expired,
  };
  
  #define CFQ_CFQQ_FNS(name)						\
  static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)		\
  {									\
  	cfqq->flags |= (1 << CFQ_CFQQ_FLAG_##name);			\
  }									\
  static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)	\
  {									\
  	cfqq->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);			\
  }									\
  static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)		\
  {									\
  	return (cfqq->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;	\
  }
  
  CFQ_CFQQ_FNS(on_rr);
  CFQ_CFQQ_FNS(wait_request);
  CFQ_CFQQ_FNS(must_alloc);
  CFQ_CFQQ_FNS(must_alloc_slice);
  CFQ_CFQQ_FNS(must_dispatch);
  CFQ_CFQQ_FNS(fifo_expire);
  CFQ_CFQQ_FNS(idle_window);
  CFQ_CFQQ_FNS(prio_changed);
  CFQ_CFQQ_FNS(expired);
  #undef CFQ_CFQQ_FNS
  
  enum cfq_rq_state_flags {

  	CFQ_CRQ_FLAG_is_sync = 0,

  };
  
  #define CFQ_CRQ_FNS(name)						\
  static inline void cfq_mark_crq_##name(struct cfq_rq *crq)		\
  {									\
  	crq->crq_flags |= (1 << CFQ_CRQ_FLAG_##name);			\
  }									\
  static inline void cfq_clear_crq_##name(struct cfq_rq *crq)		\
  {									\
  	crq->crq_flags &= ~(1 << CFQ_CRQ_FLAG_##name);			\
  }									\
  static inline int cfq_crq_##name(const struct cfq_rq *crq)		\
  {									\
  	return (crq->crq_flags & (1 << CFQ_CRQ_FLAG_##name)) != 0;	\
  }

  CFQ_CRQ_FNS(is_sync);

  #undef CFQ_CRQ_FNS
  
  static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsigned short);

  static void cfq_dispatch_insert(request_queue_t *, struct cfq_rq *);

  static void cfq_put_cfqd(struct cfq_data *cfqd);

  #define process_sync(tsk)	((tsk)->flags & PF_SYNCWRITE)

  
  /*
   * lots of deadline iosched dupes, can be abstracted later...
   */
  static inline void cfq_del_crq_hash(struct cfq_rq *crq)
  {
  	hlist_del_init(&crq->hash);
  }

  static inline void cfq_add_crq_hash(struct cfq_data *cfqd, struct cfq_rq *crq)
  {
  	const int hash_idx = CFQ_MHASH_FN(rq_hash_key(crq->request));

  	hlist_add_head(&crq->hash, &cfqd->crq_hash[hash_idx]);
  }
  
  static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
  {
  	struct hlist_head *hash_list = &cfqd->crq_hash[CFQ_MHASH_FN(offset)];
  	struct hlist_node *entry, *next;
  
  	hlist_for_each_safe(entry, next, hash_list) {
  		struct cfq_rq *crq = list_entry_hash(entry);
  		struct request *__rq = crq->request;

  		if (!rq_mergeable(__rq)) {
  			cfq_del_crq_hash(crq);
  			continue;
  		}
  
  		if (rq_hash_key(__rq) == offset)
  			return __rq;
  	}
  
  	return NULL;
  }

  /*
   * scheduler run of queue, if there are requests pending and no one in the
   * driver that will restart queueing
   */
  static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
  {

  	if (!cfqd->rq_in_driver && cfqd->busy_queues)

  		kblockd_schedule_work(&cfqd->unplug_work);
  }
  
  static int cfq_queue_empty(request_queue_t *q)
  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	return !cfqd->busy_queues;

  }

  /*
   * Lifted from AS - choose which of crq1 and crq2 that is best served now.
   * We choose the request that is closest to the head right now. Distance
   * behind the head are penalized and only allowed to a certain extent.
   */
  static struct cfq_rq *
  cfq_choose_req(struct cfq_data *cfqd, struct cfq_rq *crq1, struct cfq_rq *crq2)
  {
  	sector_t last, s1, s2, d1 = 0, d2 = 0;
  	int r1_wrap = 0, r2_wrap = 0;	/* requests are behind the disk head */
  	unsigned long back_max;
  
  	if (crq1 == NULL || crq1 == crq2)
  		return crq2;
  	if (crq2 == NULL)
  		return crq1;

  	if (cfq_crq_is_sync(crq1) && !cfq_crq_is_sync(crq2))
  		return crq1;
  	else if (cfq_crq_is_sync(crq2) && !cfq_crq_is_sync(crq1))

  		return crq2;

  
  	s1 = crq1->request->sector;
  	s2 = crq2->request->sector;
  
  	last = cfqd->last_sector;

  	/*
  	 * by definition, 1KiB is 2 sectors
  	 */
  	back_max = cfqd->cfq_back_max * 2;
  
  	/*
  	 * Strict one way elevator _except_ in the case where we allow
  	 * short backward seeks which are biased as twice the cost of a
  	 * similar forward seek.
  	 */
  	if (s1 >= last)
  		d1 = s1 - last;
  	else if (s1 + back_max >= last)
  		d1 = (last - s1) * cfqd->cfq_back_penalty;
  	else
  		r1_wrap = 1;
  
  	if (s2 >= last)
  		d2 = s2 - last;
  	else if (s2 + back_max >= last)
  		d2 = (last - s2) * cfqd->cfq_back_penalty;
  	else
  		r2_wrap = 1;
  
  	/* Found required data */
  	if (!r1_wrap && r2_wrap)
  		return crq1;
  	else if (!r2_wrap && r1_wrap)
  		return crq2;
  	else if (r1_wrap && r2_wrap) {
  		/* both behind the head */
  		if (s1 <= s2)
  			return crq1;
  		else
  			return crq2;
  	}
  
  	/* Both requests in front of the head */
  	if (d1 < d2)
  		return crq1;
  	else if (d2 < d1)
  		return crq2;
  	else {
  		if (s1 >= s2)
  			return crq1;
  		else
  			return crq2;
  	}
  }
  
  /*
   * would be nice to take fifo expire time into account as well
   */
  static struct cfq_rq *
  cfq_find_next_crq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  		  struct cfq_rq *last)
  {
  	struct cfq_rq *crq_next = NULL, *crq_prev = NULL;
  	struct rb_node *rbnext, *rbprev;

  	if (!(rbnext = rb_next(&last->rb_node))) {

  		rbnext = rb_first(&cfqq->sort_list);

  		if (rbnext == &last->rb_node)
  			rbnext = NULL;
  	}

  
  	rbprev = rb_prev(&last->rb_node);
  
  	if (rbprev)
  		crq_prev = rb_entry_crq(rbprev);
  	if (rbnext)
  		crq_next = rb_entry_crq(rbnext);
  
  	return cfq_choose_req(cfqd, crq_next, crq_prev);
  }
  
  static void cfq_update_next_crq(struct cfq_rq *crq)
  {
  	struct cfq_queue *cfqq = crq->cfq_queue;
  
  	if (cfqq->next_crq == crq)
  		cfqq->next_crq = cfq_find_next_crq(cfqq->cfqd, cfqq, crq);
  }

  static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)

  {

  	struct cfq_data *cfqd = cfqq->cfqd;
  	struct list_head *list, *entry;

  	BUG_ON(!cfq_cfqq_on_rr(cfqq));

  	list_del(&cfqq->cfq_list);

  	if (cfq_class_rt(cfqq))
  		list = &cfqd->cur_rr;
  	else if (cfq_class_idle(cfqq))
  		list = &cfqd->idle_rr;
  	else {
  		/*
  		 * if cfqq has requests in flight, don't allow it to be
  		 * found in cfq_set_active_queue before it has finished them.
  		 * this is done to increase fairness between a process that
  		 * has lots of io pending vs one that only generates one
  		 * sporadically or synchronously
  		 */

  		if (cfq_cfqq_dispatched(cfqq))

  			list = &cfqd->busy_rr;
  		else
  			list = &cfqd->rr_list[cfqq->ioprio];

  	}

  	/*
  	 * if queue was preempted, just add to front to be fair. busy_rr
  	 * isn't sorted.
  	 */
  	if (preempted || list == &cfqd->busy_rr) {
  		list_add(&cfqq->cfq_list, list);

  		return;

  	}

  
  	/*

  	 * sort by when queue was last serviced

  	 */

  	entry = list;
  	while ((entry = entry->prev) != list) {

  		struct cfq_queue *__cfqq = list_entry_cfqq(entry);

  		if (!__cfqq->service_last)
  			break;
  		if (time_before(__cfqq->service_last, cfqq->service_last))

  			break;

  	}
  
  	list_add(&cfqq->cfq_list, entry);
  }
  
  /*
   * add to busy list of queues for service, trying to be fair in ordering

   * the pending list according to last request service

   */
  static inline void

  cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)

  {

  	BUG_ON(cfq_cfqq_on_rr(cfqq));
  	cfq_mark_cfqq_on_rr(cfqq);

  	cfqd->busy_queues++;

  	cfq_resort_rr_list(cfqq, 0);

  }
  
  static inline void
  cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {

  	BUG_ON(!cfq_cfqq_on_rr(cfqq));
  	cfq_clear_cfqq_on_rr(cfqq);

  	list_move(&cfqq->cfq_list, &cfqd->empty_list);

  
  	BUG_ON(!cfqd->busy_queues);
  	cfqd->busy_queues--;
  }
  
  /*
   * rb tree support functions
   */
  static inline void cfq_del_crq_rb(struct cfq_rq *crq)
  {
  	struct cfq_queue *cfqq = crq->cfq_queue;

  	struct cfq_data *cfqd = cfqq->cfqd;
  	const int sync = cfq_crq_is_sync(crq);

  	BUG_ON(!cfqq->queued[sync]);
  	cfqq->queued[sync]--;

  	cfq_update_next_crq(crq);

  	rb_erase(&crq->rb_node, &cfqq->sort_list);
  	RB_CLEAR_COLOR(&crq->rb_node);

  	if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY(&cfqq->sort_list))
  		cfq_del_cfqq_rr(cfqd, cfqq);

  }
  
  static struct cfq_rq *
  __cfq_add_crq_rb(struct cfq_rq *crq)
  {
  	struct rb_node **p = &crq->cfq_queue->sort_list.rb_node;
  	struct rb_node *parent = NULL;
  	struct cfq_rq *__crq;
  
  	while (*p) {
  		parent = *p;
  		__crq = rb_entry_crq(parent);
  
  		if (crq->rb_key < __crq->rb_key)
  			p = &(*p)->rb_left;
  		else if (crq->rb_key > __crq->rb_key)
  			p = &(*p)->rb_right;
  		else
  			return __crq;
  	}
  
  	rb_link_node(&crq->rb_node, parent, p);
  	return NULL;
  }
  
  static void cfq_add_crq_rb(struct cfq_rq *crq)
  {
  	struct cfq_queue *cfqq = crq->cfq_queue;
  	struct cfq_data *cfqd = cfqq->cfqd;
  	struct request *rq = crq->request;
  	struct cfq_rq *__alias;
  
  	crq->rb_key = rq_rb_key(rq);

  	cfqq->queued[cfq_crq_is_sync(crq)]++;

  
  	/*
  	 * looks a little odd, but the first insert might return an alias.
  	 * if that happens, put the alias on the dispatch list
  	 */
  	while ((__alias = __cfq_add_crq_rb(crq)) != NULL)

  		cfq_dispatch_insert(cfqd->queue, __alias);

  
  	rb_insert_color(&crq->rb_node, &cfqq->sort_list);

  	if (!cfq_cfqq_on_rr(cfqq))

  		cfq_add_cfqq_rr(cfqd, cfqq);

  
  	/*
  	 * check if this request is a better next-serve candidate
  	 */
  	cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);
  }
  
  static inline void
  cfq_reposition_crq_rb(struct cfq_queue *cfqq, struct cfq_rq *crq)
  {

  	rb_erase(&crq->rb_node, &cfqq->sort_list);
  	cfqq->queued[cfq_crq_is_sync(crq)]--;

  
  	cfq_add_crq_rb(crq);
  }

  static struct request *cfq_find_rq_rb(struct cfq_data *cfqd, sector_t sector)

  {

  	struct cfq_queue *cfqq = cfq_find_cfq_hash(cfqd, current->pid, CFQ_KEY_ANY);

  	struct rb_node *n;
  
  	if (!cfqq)
  		goto out;
  
  	n = cfqq->sort_list.rb_node;
  	while (n) {
  		struct cfq_rq *crq = rb_entry_crq(n);
  
  		if (sector < crq->rb_key)
  			n = n->rb_left;
  		else if (sector > crq->rb_key)
  			n = n->rb_right;
  		else
  			return crq->request;
  	}
  
  out:
  	return NULL;
  }

  static void cfq_activate_request(request_queue_t *q, struct request *rq)

  {

  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	cfqd->rq_in_driver++;

  }

  static void cfq_deactivate_request(request_queue_t *q, struct request *rq)

  {

  	struct cfq_data *cfqd = q->elevator->elevator_data;
  
  	WARN_ON(!cfqd->rq_in_driver);
  	cfqd->rq_in_driver--;

  }

  static void cfq_remove_request(struct request *rq)

  {
  	struct cfq_rq *crq = RQ_DATA(rq);

  	list_del_init(&rq->queuelist);
  	cfq_del_crq_rb(crq);

  	cfq_del_crq_hash(crq);

  }
  
  static int
  cfq_merge(request_queue_t *q, struct request **req, struct bio *bio)
  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	struct request *__rq;
  	int ret;

  	__rq = cfq_find_rq_hash(cfqd, bio->bi_sector);

  	if (__rq && elv_rq_merge_ok(__rq, bio)) {
  		ret = ELEVATOR_BACK_MERGE;
  		goto out;

  	}
  
  	__rq = cfq_find_rq_rb(cfqd, bio->bi_sector + bio_sectors(bio));

  	if (__rq && elv_rq_merge_ok(__rq, bio)) {
  		ret = ELEVATOR_FRONT_MERGE;
  		goto out;

  	}
  
  	return ELEVATOR_NO_MERGE;
  out:

  	*req = __rq;
  	return ret;
  }
  
  static void cfq_merged_request(request_queue_t *q, struct request *req)
  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	struct cfq_rq *crq = RQ_DATA(req);
  
  	cfq_del_crq_hash(crq);
  	cfq_add_crq_hash(cfqd, crq);

  	if (rq_rb_key(req) != crq->rb_key) {

  		struct cfq_queue *cfqq = crq->cfq_queue;
  
  		cfq_update_next_crq(crq);
  		cfq_reposition_crq_rb(cfqq, crq);
  	}

  }
  
  static void
  cfq_merged_requests(request_queue_t *q, struct request *rq,
  		    struct request *next)
  {

  	cfq_merged_request(q, rq);

  	/*
  	 * reposition in fifo if next is older than rq
  	 */
  	if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
  	    time_before(next->start_time, rq->start_time))
  		list_move(&rq->queuelist, &next->queuelist);

  	cfq_remove_request(next);

  }
  
  static inline void
  __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	if (cfqq) {
  		/*
  		 * stop potential idle class queues waiting service
  		 */
  		del_timer(&cfqd->idle_class_timer);
  
  		cfqq->slice_start = jiffies;
  		cfqq->slice_end = 0;
  		cfqq->slice_left = 0;

  		cfq_clear_cfqq_must_alloc_slice(cfqq);
  		cfq_clear_cfqq_fifo_expire(cfqq);
  		cfq_clear_cfqq_expired(cfqq);

  	}
  
  	cfqd->active_queue = cfqq;
  }
  
  /*
   * 0
   * 0,1
   * 0,1,2
   * 0,1,2,3
   * 0,1,2,3,4
   * 0,1,2,3,4,5
   * 0,1,2,3,4,5,6
   * 0,1,2,3,4,5,6,7
   */
  static int cfq_get_next_prio_level(struct cfq_data *cfqd)
  {
  	int prio, wrap;
  
  	prio = -1;
  	wrap = 0;
  	do {
  		int p;
  
  		for (p = cfqd->cur_prio; p <= cfqd->cur_end_prio; p++) {
  			if (!list_empty(&cfqd->rr_list[p])) {
  				prio = p;
  				break;
  			}
  		}
  
  		if (prio != -1)
  			break;
  		cfqd->cur_prio = 0;
  		if (++cfqd->cur_end_prio == CFQ_PRIO_LISTS) {
  			cfqd->cur_end_prio = 0;
  			if (wrap)
  				break;
  			wrap = 1;

  		}

  	} while (1);
  
  	if (unlikely(prio == -1))
  		return -1;
  
  	BUG_ON(prio >= CFQ_PRIO_LISTS);
  
  	list_splice_init(&cfqd->rr_list[prio], &cfqd->cur_rr);
  
  	cfqd->cur_prio = prio + 1;
  	if (cfqd->cur_prio > cfqd->cur_end_prio) {
  		cfqd->cur_end_prio = cfqd->cur_prio;
  		cfqd->cur_prio = 0;
  	}
  	if (cfqd->cur_end_prio == CFQ_PRIO_LISTS) {
  		cfqd->cur_prio = 0;
  		cfqd->cur_end_prio = 0;

  	}

  	return prio;
  }

  static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)

  {

  	struct cfq_queue *cfqq;
  
  	/*
  	 * if current queue is expired but not done with its requests yet,
  	 * wait for that to happen
  	 */
  	if ((cfqq = cfqd->active_queue) != NULL) {
  		if (cfq_cfqq_expired(cfqq) && cfq_cfqq_dispatched(cfqq))
  			return NULL;
  	}

  
  	/*
  	 * if current list is non-empty, grab first entry. if it is empty,
  	 * get next prio level and grab first entry then if any are spliced
  	 */
  	if (!list_empty(&cfqd->cur_rr) || cfq_get_next_prio_level(cfqd) != -1)
  		cfqq = list_entry_cfqq(cfqd->cur_rr.next);
  
  	/*
  	 * if we have idle queues and no rt or be queues had pending
  	 * requests, either allow immediate service if the grace period
  	 * has passed or arm the idle grace timer
  	 */
  	if (!cfqq && !list_empty(&cfqd->idle_rr)) {
  		unsigned long end = cfqd->last_end_request + CFQ_IDLE_GRACE;
  
  		if (time_after_eq(jiffies, end))
  			cfqq = list_entry_cfqq(cfqd->idle_rr.next);
  		else
  			mod_timer(&cfqd->idle_class_timer, end);
  	}
  
  	__cfq_set_active_queue(cfqd, cfqq);

  	return cfqq;

  }
  
  /*
   * current cfqq expired its slice (or was too idle), select new one
   */

  static void
  __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  		    int preempted)

  {

  	unsigned long now = jiffies;

  	if (cfq_cfqq_wait_request(cfqq))
  		del_timer(&cfqd->idle_slice_timer);

  	if (!preempted && !cfq_cfqq_dispatched(cfqq))
  		cfqq->service_last = now;

  	cfq_clear_cfqq_must_dispatch(cfqq);
  	cfq_clear_cfqq_wait_request(cfqq);

  	/*
  	 * store what was left of this slice, if the queue idled out
  	 * or was preempted
  	 */

  	if (time_after(cfqq->slice_end, now))
  		cfqq->slice_left = cfqq->slice_end - now;

  	else
  		cfqq->slice_left = 0;

  	if (cfq_cfqq_on_rr(cfqq))
  		cfq_resort_rr_list(cfqq, preempted);

  	if (cfqq == cfqd->active_queue)

  		cfqd->active_queue = NULL;

  	if (cfqd->active_cic) {
  		put_io_context(cfqd->active_cic->ioc);
  		cfqd->active_cic = NULL;

  	}
  
  	cfqd->dispatch_slice = 0;
  }

  static inline void cfq_slice_expired(struct cfq_data *cfqd, int preempted)
  {
  	struct cfq_queue *cfqq = cfqd->active_queue;
  
  	if (cfqq) {
  		/*
  		 * use deferred expiry, if there are requests in progress as
  		 * not to disturb the slice of the next queue
  		 */
  		if (cfq_cfqq_dispatched(cfqq))
  			cfq_mark_cfqq_expired(cfqq);
  		else
  			__cfq_slice_expired(cfqd, cfqq, preempted);
  	}
  }

  static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  
  {
  	WARN_ON(!RB_EMPTY(&cfqq->sort_list));
  	WARN_ON(cfqq != cfqd->active_queue);
  
  	/*
  	 * idle is disabled, either manually or by past process history
  	 */
  	if (!cfqd->cfq_slice_idle)
  		return 0;

  	if (!cfq_cfqq_idle_window(cfqq))

  		return 0;
  	/*
  	 * task has exited, don't wait
  	 */
  	if (cfqd->active_cic && !cfqd->active_cic->ioc->task)
  		return 0;

  	cfq_mark_cfqq_must_dispatch(cfqq);
  	cfq_mark_cfqq_wait_request(cfqq);

  
  	if (!timer_pending(&cfqd->idle_slice_timer)) {

  		unsigned long slice_left = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);

  		cfqd->idle_slice_timer.expires = jiffies + slice_left;

  		add_timer(&cfqd->idle_slice_timer);
  	}
  
  	return 1;

  }

  static void cfq_dispatch_insert(request_queue_t *q, struct cfq_rq *crq)

  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	struct cfq_queue *cfqq = crq->cfq_queue;

  
  	cfqq->next_crq = cfq_find_next_crq(cfqd, cfqq, crq);

  	cfq_remove_request(crq->request);

  	cfqq->on_dispatch[cfq_crq_is_sync(crq)]++;

  	elv_dispatch_sort(q, crq->request);

  }
  
  /*
   * return expired entry, or NULL to just start from scratch in rbtree
   */
  static inline struct cfq_rq *cfq_check_fifo(struct cfq_queue *cfqq)
  {
  	struct cfq_data *cfqd = cfqq->cfqd;

  	struct request *rq;

  	struct cfq_rq *crq;

  	if (cfq_cfqq_fifo_expire(cfqq))

  		return NULL;

  	if (!list_empty(&cfqq->fifo)) {

  		int fifo = cfq_cfqq_class_sync(cfqq);

  		crq = RQ_DATA(list_entry_fifo(cfqq->fifo.next));
  		rq = crq->request;
  		if (time_after(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo])) {

  			cfq_mark_cfqq_fifo_expire(cfqq);

  			return crq;
  		}

  	}
  
  	return NULL;
  }
  
  /*

   * Scale schedule slice based on io priority. Use the sync time slice only
   * if a queue is marked sync and has sync io queued. A sync queue with async
   * io only, should not get full sync slice length.

   */

  static inline int
  cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	const int base_slice = cfqd->cfq_slice[cfq_cfqq_sync(cfqq)];
  
  	WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
  
  	return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - cfqq->ioprio));
  }

  static inline void

  cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)

  {

  	cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
  }

  static inline int
  cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	const int base_rq = cfqd->cfq_slice_async_rq;

  	WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

  	return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio));

  }

  /*
   * get next queue for service
   */

  static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)

  {

  	unsigned long now = jiffies;

  	struct cfq_queue *cfqq;

  	cfqq = cfqd->active_queue;
  	if (!cfqq)
  		goto new_queue;

  	if (cfq_cfqq_expired(cfqq))
  		goto new_queue;

  	/*
  	 * slice has expired
  	 */

  	if (!cfq_cfqq_must_dispatch(cfqq) && time_after(now, cfqq->slice_end))
  		goto expire;

  	/*
  	 * if queue has requests, dispatch one. if not, check if
  	 * enough slice is left to wait for one
  	 */
  	if (!RB_EMPTY(&cfqq->sort_list))
  		goto keep_queue;

  	else if (cfq_cfqq_class_sync(cfqq) &&

  		 time_before(now, cfqq->slice_end)) {
  		if (cfq_arm_slice_timer(cfqd, cfqq))
  			return NULL;
  	}

  expire:

  	cfq_slice_expired(cfqd, 0);

  new_queue:
  	cfqq = cfq_set_active_queue(cfqd);

  keep_queue:

  	return cfqq;

  }
  
  static int
  __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  			int max_dispatch)
  {
  	int dispatched = 0;
  
  	BUG_ON(RB_EMPTY(&cfqq->sort_list));
  
  	do {
  		struct cfq_rq *crq;

  
  		/*

  		 * follow expired path, else get first next available

  		 */

  		if ((crq = cfq_check_fifo(cfqq)) == NULL)
  			crq = cfqq->next_crq;
  
  		/*
  		 * finally, insert request into driver dispatch list
  		 */

  		cfq_dispatch_insert(cfqd->queue, crq);

  		cfqd->dispatch_slice++;
  		dispatched++;

  		if (!cfqd->active_cic) {
  			atomic_inc(&crq->io_context->ioc->refcount);
  			cfqd->active_cic = crq->io_context;
  		}

  		if (RB_EMPTY(&cfqq->sort_list))
  			break;
  
  	} while (dispatched < max_dispatch);
  
  	/*
  	 * if slice end isn't set yet, set it. if at least one request was
  	 * sync, use the sync time slice value
  	 */
  	if (!cfqq->slice_end)
  		cfq_set_prio_slice(cfqd, cfqq);
  
  	/*
  	 * expire an async queue immediately if it has used up its slice. idle
  	 * queue always expire after 1 dispatch round.
  	 */
  	if ((!cfq_cfqq_sync(cfqq) &&
  	    cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
  	    cfq_class_idle(cfqq))
  		cfq_slice_expired(cfqd, 0);
  
  	return dispatched;
  }
  
  static int

  cfq_forced_dispatch_cfqqs(struct list_head *list)
  {
  	int dispatched = 0;
  	struct cfq_queue *cfqq, *next;
  	struct cfq_rq *crq;
  
  	list_for_each_entry_safe(cfqq, next, list, cfq_list) {
  		while ((crq = cfqq->next_crq)) {
  			cfq_dispatch_insert(cfqq->cfqd->queue, crq);
  			dispatched++;
  		}
  		BUG_ON(!list_empty(&cfqq->fifo));
  	}
  	return dispatched;
  }
  
  static int
  cfq_forced_dispatch(struct cfq_data *cfqd)
  {
  	int i, dispatched = 0;
  
  	for (i = 0; i < CFQ_PRIO_LISTS; i++)
  		dispatched += cfq_forced_dispatch_cfqqs(&cfqd->rr_list[i]);
  
  	dispatched += cfq_forced_dispatch_cfqqs(&cfqd->busy_rr);
  	dispatched += cfq_forced_dispatch_cfqqs(&cfqd->cur_rr);
  	dispatched += cfq_forced_dispatch_cfqqs(&cfqd->idle_rr);
  
  	cfq_slice_expired(cfqd, 0);
  
  	BUG_ON(cfqd->busy_queues);
  
  	return dispatched;
  }
  
  static int

  cfq_dispatch_requests(request_queue_t *q, int force)

  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	struct cfq_queue *cfqq;
  
  	if (!cfqd->busy_queues)
  		return 0;

  	if (unlikely(force))
  		return cfq_forced_dispatch(cfqd);
  
  	cfqq = cfq_select_queue(cfqd);

  	if (cfqq) {

  		int max_dispatch;
  
  		/*
  		 * if idle window is disabled, allow queue buildup
  		 */
  		if (!cfq_cfqq_idle_window(cfqq) &&
  		    cfqd->rq_in_driver >= cfqd->cfq_max_depth)
  			return 0;

  		cfq_clear_cfqq_must_dispatch(cfqq);
  		cfq_clear_cfqq_wait_request(cfqq);

  		del_timer(&cfqd->idle_slice_timer);

  		max_dispatch = cfqd->cfq_quantum;
  		if (cfq_class_idle(cfqq))
  			max_dispatch = 1;

  		return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);

  	}

  	return 0;

  }

  /*
   * task holds one reference to the queue, dropped when task exits. each crq
   * in-flight on this queue also holds a reference, dropped when crq is freed.
   *
   * queue lock must be held here.
   */
  static void cfq_put_queue(struct cfq_queue *cfqq)
  {

  	struct cfq_data *cfqd = cfqq->cfqd;
  
  	BUG_ON(atomic_read(&cfqq->ref) <= 0);

  
  	if (!atomic_dec_and_test(&cfqq->ref))
  		return;
  
  	BUG_ON(rb_first(&cfqq->sort_list));

  	BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);

  	BUG_ON(cfq_cfqq_on_rr(cfqq));

  	if (unlikely(cfqd->active_queue == cfqq)) {

  		__cfq_slice_expired(cfqd, cfqq, 0);
  		cfq_schedule_dispatch(cfqd);

  	}

  	cfq_put_cfqd(cfqq->cfqd);
  
  	/*
  	 * it's on the empty list and still hashed
  	 */
  	list_del(&cfqq->cfq_list);
  	hlist_del(&cfqq->cfq_hash);
  	kmem_cache_free(cfq_pool, cfqq);
  }
  
  static inline struct cfq_queue *

  __cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned int prio,
  		    const int hashval)

  {
  	struct hlist_head *hash_list = &cfqd->cfq_hash[hashval];
  	struct hlist_node *entry, *next;
  
  	hlist_for_each_safe(entry, next, hash_list) {
  		struct cfq_queue *__cfqq = list_entry_qhash(entry);

  		const unsigned short __p = IOPRIO_PRIO_VALUE(__cfqq->ioprio_class, __cfqq->ioprio);

  		if (__cfqq->key == key && (__p == prio || prio == CFQ_KEY_ANY))

  			return __cfqq;
  	}
  
  	return NULL;
  }
  
  static struct cfq_queue *

  cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned short prio)

  {

  	return __cfq_find_cfq_hash(cfqd, key, prio, hash_long(key, CFQ_QHASH_SHIFT));

  }

  static void cfq_free_io_context(struct cfq_io_context *cic)

  {

  	struct cfq_io_context *__cic;
  	struct list_head *entry, *next;

  	list_for_each_safe(entry, next, &cic->list) {
  		__cic = list_entry(entry, struct cfq_io_context, list);
  		kmem_cache_free(cfq_ioc_pool, __cic);

  	}

  	kmem_cache_free(cfq_ioc_pool, cic);

  }

  /*
   * Called with interrupts disabled
   */
  static void cfq_exit_single_io_context(struct cfq_io_context *cic)

  {

  	struct cfq_data *cfqd = cic->cfqq->cfqd;
  	request_queue_t *q = cfqd->queue;
  
  	WARN_ON(!irqs_disabled());
  
  	spin_lock(q->queue_lock);
  
  	if (unlikely(cic->cfqq == cfqd->active_queue)) {

  		__cfq_slice_expired(cfqd, cic->cfqq, 0);
  		cfq_schedule_dispatch(cfqd);

  	}
  
  	cfq_put_queue(cic->cfqq);
  	cic->cfqq = NULL;
  	spin_unlock(q->queue_lock);

  }
  
  /*

   * Another task may update the task cic list, if it is doing a queue lookup
   * on its behalf. cfq_cic_lock excludes such concurrent updates

   */
  static void cfq_exit_io_context(struct cfq_io_context *cic)
  {

  	struct cfq_io_context *__cic;
  	struct list_head *entry;

  	unsigned long flags;

  	local_irq_save(flags);

  	/*
  	 * put the reference this task is holding to the various queues
  	 */

  	list_for_each(entry, &cic->list) {

  		__cic = list_entry(entry, struct cfq_io_context, list);

  		cfq_exit_single_io_context(__cic);

  	}

  	cfq_exit_single_io_context(cic);
  	local_irq_restore(flags);

  }

  static struct cfq_io_context *

  cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)

  {

  	struct cfq_io_context *cic = kmem_cache_alloc(cfq_ioc_pool, gfp_mask);

  
  	if (cic) {

  		INIT_LIST_HEAD(&cic->list);
  		cic->cfqq = NULL;

  		cic->key = NULL;
  		cic->last_end_request = jiffies;
  		cic->ttime_total = 0;
  		cic->ttime_samples = 0;
  		cic->ttime_mean = 0;
  		cic->dtor = cfq_free_io_context;
  		cic->exit = cfq_exit_io_context;

  	}
  
  	return cic;
  }

  static void cfq_init_prio_data(struct cfq_queue *cfqq)
  {
  	struct task_struct *tsk = current;
  	int ioprio_class;

  	if (!cfq_cfqq_prio_changed(cfqq))

  		return;
  
  	ioprio_class = IOPRIO_PRIO_CLASS(tsk->ioprio);
  	switch (ioprio_class) {
  		default:
  			printk(KERN_ERR "cfq: bad prio %x
  ", ioprio_class);
  		case IOPRIO_CLASS_NONE:
  			/*
  			 * no prio set, place us in the middle of the BE classes
  			 */
  			cfqq->ioprio = task_nice_ioprio(tsk);
  			cfqq->ioprio_class = IOPRIO_CLASS_BE;
  			break;
  		case IOPRIO_CLASS_RT:
  			cfqq->ioprio = task_ioprio(tsk);
  			cfqq->ioprio_class = IOPRIO_CLASS_RT;
  			break;
  		case IOPRIO_CLASS_BE:
  			cfqq->ioprio = task_ioprio(tsk);
  			cfqq->ioprio_class = IOPRIO_CLASS_BE;
  			break;
  		case IOPRIO_CLASS_IDLE:
  			cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
  			cfqq->ioprio = 7;

  			cfq_clear_cfqq_idle_window(cfqq);

  			break;
  	}
  
  	/*
  	 * keep track of original prio settings in case we have to temporarily
  	 * elevate the priority of this queue
  	 */
  	cfqq->org_ioprio = cfqq->ioprio;
  	cfqq->org_ioprio_class = cfqq->ioprio_class;

  	if (cfq_cfqq_on_rr(cfqq))

  		cfq_resort_rr_list(cfqq, 0);

  	cfq_clear_cfqq_prio_changed(cfqq);

  }
  
  static inline void changed_ioprio(struct cfq_queue *cfqq)
  {
  	if (cfqq) {
  		struct cfq_data *cfqd = cfqq->cfqd;
  
  		spin_lock(cfqd->queue->queue_lock);

  		cfq_mark_cfqq_prio_changed(cfqq);

  		cfq_init_prio_data(cfqq);
  		spin_unlock(cfqd->queue->queue_lock);
  	}
  }
  
  /*
   * callback from sys_ioprio_set, irqs are disabled
   */
  static int cfq_ioc_set_ioprio(struct io_context *ioc, unsigned int ioprio)
  {
  	struct cfq_io_context *cic = ioc->cic;
  
  	changed_ioprio(cic->cfqq);
  
  	list_for_each_entry(cic, &cic->list, list)
  		changed_ioprio(cic->cfqq);
  
  	return 0;
  }
  
  static struct cfq_queue *

  cfq_get_queue(struct cfq_data *cfqd, unsigned int key, unsigned short ioprio,

  	      gfp_t gfp_mask)

  {
  	const int hashval = hash_long(key, CFQ_QHASH_SHIFT);
  	struct cfq_queue *cfqq, *new_cfqq = NULL;
  
  retry:

  	cfqq = __cfq_find_cfq_hash(cfqd, key, ioprio, hashval);

  
  	if (!cfqq) {
  		if (new_cfqq) {
  			cfqq = new_cfqq;
  			new_cfqq = NULL;
  		} else if (gfp_mask & __GFP_WAIT) {
  			spin_unlock_irq(cfqd->queue->queue_lock);
  			new_cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
  			spin_lock_irq(cfqd->queue->queue_lock);
  			goto retry;
  		} else {
  			cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
  			if (!cfqq)
  				goto out;
  		}
  
  		memset(cfqq, 0, sizeof(*cfqq));
  
  		INIT_HLIST_NODE(&cfqq->cfq_hash);
  		INIT_LIST_HEAD(&cfqq->cfq_list);
  		RB_CLEAR_ROOT(&cfqq->sort_list);
  		INIT_LIST_HEAD(&cfqq->fifo);
  
  		cfqq->key = key;
  		hlist_add_head(&cfqq->cfq_hash, &cfqd->cfq_hash[hashval]);
  		atomic_set(&cfqq->ref, 0);
  		cfqq->cfqd = cfqd;
  		atomic_inc(&cfqd->ref);
  		cfqq->service_last = 0;
  		/*
  		 * set ->slice_left to allow preemption for a new process
  		 */
  		cfqq->slice_left = 2 * cfqd->cfq_slice_idle;

  		cfq_mark_cfqq_idle_window(cfqq);
  		cfq_mark_cfqq_prio_changed(cfqq);
  		cfq_init_prio_data(cfqq);

  	}
  
  	if (new_cfqq)
  		kmem_cache_free(cfq_pool, new_cfqq);
  
  	atomic_inc(&cfqq->ref);
  out:
  	WARN_ON((gfp_mask & __GFP_WAIT) && !cfqq);
  	return cfqq;
  }

  /*
   * Setup general io context and cfq io context. There can be several cfq
   * io contexts per general io context, if this process is doing io to more
   * than one device managed by cfq. Note that caller is holding a reference to
   * cfqq, so we don't need to worry about it disappearing
   */
  static struct cfq_io_context *

  cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, gfp_t gfp_mask)

  {

  	struct io_context *ioc = NULL;

  	struct cfq_io_context *cic;

  	might_sleep_if(gfp_mask & __GFP_WAIT);

  	ioc = get_io_context(gfp_mask);

  	if (!ioc)
  		return NULL;
  
  	if ((cic = ioc->cic) == NULL) {

  		cic = cfq_alloc_io_context(cfqd, gfp_mask);

  
  		if (cic == NULL)
  			goto err;

  		/*
  		 * manually increment generic io_context usage count, it
  		 * cannot go away since we are already holding one ref to it
  		 */

  		ioc->cic = cic;

  		ioc->set_ioprio = cfq_ioc_set_ioprio;

  		cic->ioc = ioc;

  		cic->key = cfqd;
  		atomic_inc(&cfqd->ref);

  	} else {
  		struct cfq_io_context *__cic;

  
  		/*

  		 * the first cic on the list is actually the head itself

  		 */

  		if (cic->key == cfqd)

  			goto out;
  
  		/*
  		 * cic exists, check if we already are there. linear search
  		 * should be ok here, the list will usually not be more than
  		 * 1 or a few entries long
  		 */

  		list_for_each_entry(__cic, &cic->list, list) {
  			/*
  			 * this process is already holding a reference to
  			 * this queue, so no need to get one more
  			 */

  			if (__cic->key == cfqd) {

  				cic = __cic;

  				goto out;
  			}
  		}

  
  		/*
  		 * nope, process doesn't have a cic assoicated with this
  		 * cfqq yet. get a new one and add to list
  		 */

  		__cic = cfq_alloc_io_context(cfqd, gfp_mask);

  		if (__cic == NULL)
  			goto err;
  
  		__cic->ioc = ioc;

  		__cic->key = cfqd;
  		atomic_inc(&cfqd->ref);

  		list_add(&__cic->list, &cic->list);

  		cic = __cic;

  	}
  
  out:

  	return cic;
  err:
  	put_io_context(ioc);
  	return NULL;
  }

  static void
  cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)

  {

  	unsigned long elapsed, ttime;

  	/*
  	 * if this context already has stuff queued, thinktime is from
  	 * last queue not last end
  	 */
  #if 0
  	if (time_after(cic->last_end_request, cic->last_queue))
  		elapsed = jiffies - cic->last_end_request;
  	else
  		elapsed = jiffies - cic->last_queue;
  #else
  		elapsed = jiffies - cic->last_end_request;
  #endif

  	ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);

  	cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
  	cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
  	cic->ttime_mean = (cic->ttime_total + 128) / cic->ttime_samples;
  }

  #define sample_valid(samples)	((samples) > 80)

  /*
   * Disable idle window if the process thinks too long or seeks so much that
   * it doesn't matter
   */
  static void
  cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  		       struct cfq_io_context *cic)
  {

  	int enable_idle = cfq_cfqq_idle_window(cfqq);

  	if (!cic->ioc->task || !cfqd->cfq_slice_idle)
  		enable_idle = 0;
  	else if (sample_valid(cic->ttime_samples)) {
  		if (cic->ttime_mean > cfqd->cfq_slice_idle)
  			enable_idle = 0;
  		else
  			enable_idle = 1;

  	}

  	if (enable_idle)
  		cfq_mark_cfqq_idle_window(cfqq);
  	else
  		cfq_clear_cfqq_idle_window(cfqq);

  }

  
  /*
   * Check if new_cfqq should preempt the currently active queue. Return 0 for
   * no or if we aren't sure, a 1 will cause a preempt.
   */
  static int
  cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
  		   struct cfq_rq *crq)
  {
  	struct cfq_queue *cfqq = cfqd->active_queue;
  
  	if (cfq_class_idle(new_cfqq))
  		return 0;
  
  	if (!cfqq)
  		return 1;
  
  	if (cfq_class_idle(cfqq))
  		return 1;

  	if (!cfq_cfqq_wait_request(new_cfqq))

  		return 0;
  	/*
  	 * if it doesn't have slice left, forget it
  	 */
  	if (new_cfqq->slice_left < cfqd->cfq_slice_idle)
  		return 0;

  	if (cfq_crq_is_sync(crq) && !cfq_cfqq_sync(cfqq))

  		return 1;
  
  	return 0;
  }
  
  /*
   * cfqq preempts the active queue. if we allowed preempt with no slice left,
   * let it have half of its nominal slice.
   */
  static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	struct cfq_queue *__cfqq, *next;
  
  	list_for_each_entry_safe(__cfqq, next, &cfqd->cur_rr, cfq_list)
  		cfq_resort_rr_list(__cfqq, 1);
  
  	if (!cfqq->slice_left)
  		cfqq->slice_left = cfq_prio_to_slice(cfqd, cfqq) / 2;
  
  	cfqq->slice_end = cfqq->slice_left + jiffies;

  	__cfq_slice_expired(cfqd, cfqq, 1);

  	__cfq_set_active_queue(cfqd, cfqq);
  }
  
  /*
   * should really be a ll_rw_blk.c helper
   */
  static void cfq_start_queueing(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
  	request_queue_t *q = cfqd->queue;
  
  	if (!blk_queue_plugged(q))
  		q->request_fn(q);
  	else
  		__generic_unplug_device(q);
  }
  
  /*
   * Called when a new fs request (crq) is added (to cfqq). Check if there's
   * something we should do about it
   */
  static void
  cfq_crq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  		 struct cfq_rq *crq)
  {

  	struct cfq_io_context *cic;

  
  	cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);

  	/*
  	 * we never wait for an async request and we don't allow preemption
  	 * of an async request. so just return early
  	 */
  	if (!cfq_crq_is_sync(crq))
  		return;

  	cic = crq->io_context;

  	cfq_update_io_thinktime(cfqd, cic);
  	cfq_update_idle_window(cfqd, cfqq, cic);
  
  	cic->last_queue = jiffies;

  
  	if (cfqq == cfqd->active_queue) {
  		/*
  		 * if we are waiting for a request for this queue, let it rip
  		 * immediately and flag that we must not expire this queue
  		 * just now
  		 */

  		if (cfq_cfqq_wait_request(cfqq)) {
  			cfq_mark_cfqq_must_dispatch(cfqq);

  			del_timer(&cfqd->idle_slice_timer);
  			cfq_start_queueing(cfqd, cfqq);
  		}
  	} else if (cfq_should_preempt(cfqd, cfqq, crq)) {
  		/*
  		 * not the active queue - expire current slice if it is
  		 * idle and has expired it's mean thinktime or this new queue
  		 * has some old slice time left and is of higher priority
  		 */
  		cfq_preempt_queue(cfqd, cfqq);

  		cfq_mark_cfqq_must_dispatch(cfqq);

  		cfq_start_queueing(cfqd, cfqq);
  	}

  }

  static void cfq_insert_request(request_queue_t *q, struct request *rq)

  {

  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	struct cfq_rq *crq = RQ_DATA(rq);
  	struct cfq_queue *cfqq = crq->cfq_queue;
  
  	cfq_init_prio_data(cfqq);

  
  	cfq_add_crq_rb(crq);

  	list_add_tail(&rq->queuelist, &cfqq->fifo);

  	if (rq_mergeable(rq))

  		cfq_add_crq_hash(cfqd, crq);

  	cfq_crq_enqueued(cfqd, cfqq, crq);

  }

  static void cfq_completed_request(request_queue_t *q, struct request *rq)
  {
  	struct cfq_rq *crq = RQ_DATA(rq);

  	struct cfq_queue *cfqq = crq->cfq_queue;
  	struct cfq_data *cfqd = cfqq->cfqd;
  	const int sync = cfq_crq_is_sync(crq);
  	unsigned long now;

  	now = jiffies;

  	WARN_ON(!cfqd->rq_in_driver);
  	WARN_ON(!cfqq->on_dispatch[sync]);
  	cfqd->rq_in_driver--;
  	cfqq->on_dispatch[sync]--;

  	if (!cfq_class_idle(cfqq))
  		cfqd->last_end_request = now;

  	if (!cfq_cfqq_dispatched(cfqq)) {
  		if (cfq_cfqq_on_rr(cfqq)) {
  			cfqq->service_last = now;
  			cfq_resort_rr_list(cfqq, 0);
  		}
  		if (cfq_cfqq_expired(cfqq)) {
  			__cfq_slice_expired(cfqd, cfqq, 0);
  			cfq_schedule_dispatch(cfqd);
  		}

  	}

  	if (cfq_crq_is_sync(crq))
  		crq->io_context->last_end_request = now;

  }
  
  static struct request *
  cfq_former_request(request_queue_t *q, struct request *rq)
  {
  	struct cfq_rq *crq = RQ_DATA(rq);
  	struct rb_node *rbprev = rb_prev(&crq->rb_node);
  
  	if (rbprev)
  		return rb_entry_crq(rbprev)->request;
  
  	return NULL;
  }
  
  static struct request *
  cfq_latter_request(request_queue_t *q, struct request *rq)
  {
  	struct cfq_rq *crq = RQ_DATA(rq);
  	struct rb_node *rbnext = rb_next(&crq->rb_node);
  
  	if (rbnext)
  		return rb_entry_crq(rbnext)->request;
  
  	return NULL;
  }

  /*
   * we temporarily boost lower priority queues if they are holding fs exclusive
   * resources. they are boosted to normal prio (CLASS_BE/4)
   */
  static void cfq_prio_boost(struct cfq_queue *cfqq)

  {

  	const int ioprio_class = cfqq->ioprio_class;
  	const int ioprio = cfqq->ioprio;

  	if (has_fs_excl()) {
  		/*
  		 * boost idle prio on transactions that would lock out other
  		 * users of the filesystem
  		 */
  		if (cfq_class_idle(cfqq))
  			cfqq->ioprio_class = IOPRIO_CLASS_BE;
  		if (cfqq->ioprio > IOPRIO_NORM)
  			cfqq->ioprio = IOPRIO_NORM;
  	} else {
  		/*
  		 * check if we need to unboost the queue
  		 */
  		if (cfqq->ioprio_class != cfqq->org_ioprio_class)
  			cfqq->ioprio_class = cfqq->org_ioprio_class;
  		if (cfqq->ioprio != cfqq->org_ioprio)
  			cfqq->ioprio = cfqq->org_ioprio;
  	}

  	/*
  	 * refile between round-robin lists if we moved the priority class
  	 */
  	if ((ioprio_class != cfqq->ioprio_class || ioprio != cfqq->ioprio) &&

  	    cfq_cfqq_on_rr(cfqq))

  		cfq_resort_rr_list(cfqq, 0);
  }

  static inline pid_t cfq_queue_pid(struct task_struct *task, int rw)
  {
  	if (rw == READ || process_sync(task))
  		return task->pid;

  	return CFQ_KEY_ASYNC;
  }

  static inline int
  __cfq_may_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq,
  		struct task_struct *task, int rw)
  {

  #if 1
  	if ((cfq_cfqq_wait_request(cfqq) || cfq_cfqq_must_alloc(cfqq)) &&

  	    !cfq_cfqq_must_alloc_slice(cfqq)) {

  		cfq_mark_cfqq_must_alloc_slice(cfqq);

  		return ELV_MQUEUE_MUST;

  	}

  	return ELV_MQUEUE_MAY;

  #else

  	if (!cfqq || task->flags & PF_MEMALLOC)
  		return ELV_MQUEUE_MAY;

  	if (!cfqq->allocated[rw] || cfq_cfqq_must_alloc(cfqq)) {
  		if (cfq_cfqq_wait_request(cfqq))

  			return ELV_MQUEUE_MUST;

  		/*
  		 * only allow 1 ELV_MQUEUE_MUST per slice, otherwise we
  		 * can quickly flood the queue with writes from a single task
  		 */

  		if (rw == READ || !cfq_cfqq_must_alloc_slice(cfqq)) {

  			cfq_mark_cfqq_must_alloc_slice(cfqq);

  			return ELV_MQUEUE_MUST;

  		}

  
  		return ELV_MQUEUE_MAY;

  	}

  	if (cfq_class_idle(cfqq))
  		return ELV_MQUEUE_NO;
  	if (cfqq->allocated[rw] >= cfqd->max_queued) {
  		struct io_context *ioc = get_io_context(GFP_ATOMIC);
  		int ret = ELV_MQUEUE_NO;

  		if (ioc && ioc->nr_batch_requests)
  			ret = ELV_MQUEUE_MAY;
  
  		put_io_context(ioc);
  		return ret;
  	}
  
  	return ELV_MQUEUE_MAY;
  #endif
  }
  
  static int cfq_may_queue(request_queue_t *q, int rw, struct bio *bio)
  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	struct task_struct *tsk = current;
  	struct cfq_queue *cfqq;
  
  	/*
  	 * don't force setup of a queue from here, as a call to may_queue
  	 * does not necessarily imply that a request actually will be queued.
  	 * so just lookup a possibly existing queue, or return 'may queue'
  	 * if that fails
  	 */

  	cfqq = cfq_find_cfq_hash(cfqd, cfq_queue_pid(tsk, rw), tsk->ioprio);

  	if (cfqq) {
  		cfq_init_prio_data(cfqq);
  		cfq_prio_boost(cfqq);
  
  		return __cfq_may_queue(cfqd, cfqq, tsk, rw);
  	}
  
  	return ELV_MQUEUE_MAY;

  }
  
  static void cfq_check_waiters(request_queue_t *q, struct cfq_queue *cfqq)
  {

  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	struct request_list *rl = &q->rq;

  	if (cfqq->allocated[READ] <= cfqd->max_queued || cfqd->rq_starved) {
  		smp_mb();
  		if (waitqueue_active(&rl->wait[READ]))
  			wake_up(&rl->wait[READ]);
  	}
  
  	if (cfqq->allocated[WRITE] <= cfqd->max_queued || cfqd->rq_starved) {
  		smp_mb();
  		if (waitqueue_active(&rl->wait[WRITE]))
  			wake_up(&rl->wait[WRITE]);
  	}

  }
  
  /*
   * queue lock held here
   */
  static void cfq_put_request(request_queue_t *q, struct request *rq)
  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	struct cfq_rq *crq = RQ_DATA(rq);
  
  	if (crq) {
  		struct cfq_queue *cfqq = crq->cfq_queue;

  		const int rw = rq_data_dir(rq);

  		BUG_ON(!cfqq->allocated[rw]);
  		cfqq->allocated[rw]--;

  		put_io_context(crq->io_context->ioc);

  
  		mempool_free(crq, cfqd->crq_pool);
  		rq->elevator_private = NULL;

  		cfq_check_waiters(q, cfqq);
  		cfq_put_queue(cfqq);
  	}
  }
  
  /*

   * Allocate cfq data structures associated with this request.

   */

  static int
  cfq_set_request(request_queue_t *q, struct request *rq, struct bio *bio,

  		gfp_t gfp_mask)

  {
  	struct cfq_data *cfqd = q->elevator->elevator_data;

  	struct task_struct *tsk = current;

  	struct cfq_io_context *cic;
  	const int rw = rq_data_dir(rq);

  	pid_t key = cfq_queue_pid(tsk, rw);

  	struct cfq_queue *cfqq;

  	struct cfq_rq *crq;
  	unsigned long flags;
  
  	might_sleep_if(gfp_mask & __GFP_WAIT);

  	cic = cfq_get_io_context(cfqd, key, gfp_mask);

  	spin_lock_irqsave(q->queue_lock, flags);

  	if (!cic)
  		goto queue_fail;
  
  	if (!cic->cfqq) {

  		cfqq = cfq_get_queue(cfqd, key, tsk->ioprio, gfp_mask);

  		if (!cfqq)
  			goto queue_fail;

  		cic->cfqq = cfqq;
  	} else
  		cfqq = cic->cfqq;

  
  	cfqq->allocated[rw]++;

  	cfq_clear_cfqq_must_alloc(cfqq);

  	cfqd->rq_starved = 0;
  	atomic_inc(&cfqq->ref);

  	spin_unlock_irqrestore(q->queue_lock, flags);

  	crq = mempool_alloc(cfqd->crq_pool, gfp_mask);
  	if (crq) {
  		RB_CLEAR(&crq->rb_node);
  		crq->rb_key = 0;
  		crq->request = rq;
  		INIT_HLIST_NODE(&crq->hash);
  		crq->cfq_queue = cfqq;
  		crq->io_context = cic;

  
  		if (rw == READ || process_sync(tsk))
  			cfq_mark_crq_is_sync(crq);
  		else
  			cfq_clear_crq_is_sync(crq);

  		rq->elevator_private = crq;

  		return 0;
  	}

  	spin_lock_irqsave(q->queue_lock, flags);
  	cfqq->allocated[rw]--;

  	if (!(cfqq->allocated[0] + cfqq->allocated[1]))

  		cfq_mark_cfqq_must_alloc(cfqq);

  	cfq_put_queue(cfqq);

  queue_fail:
  	if (cic)
  		put_io_context(cic->ioc);
  	/*
  	 * mark us rq allocation starved. we need to kickstart the process
  	 * ourselves if there are no pending requests that can do it for us.
  	 * that would be an extremely rare OOM situation
  	 */
  	cfqd->rq_starved = 1;

  	cfq_schedule_dispatch(cfqd);

  	spin_unlock_irqrestore(q->queue_lock, flags);
  	return 1;
  }

  static void cfq_kick_queue(void *data)
  {
  	request_queue_t *q = data;
  	struct cfq_data *cfqd = q->elevator->elevator_data;
  	unsigned long flags;
  
  	spin_lock_irqsave(q->queue_lock, flags);
  
  	if (cfqd->rq_starved) {
  		struct request_list *rl = &q->rq;
  
  		/*
  		 * we aren't guaranteed to get a request after this, but we
  		 * have to be opportunistic
  		 */
  		smp_mb();
  		if (waitqueue_active(&rl->wait[READ]))
  			wake_up(&rl->wait[READ]);
  		if (waitqueue_active(&rl->wait[WRITE]))
  			wake_up(&rl->wait[WRITE]);
  	}
  
  	blk_remove_plug(q);
  	q->request_fn(q);
  	spin_unlock_irqrestore(q->queue_lock, flags);
  }
  
  /*
   * Timer running if the active_queue is currently idling inside its time slice
   */
  static void cfq_idle_slice_timer(unsigned long data)
  {
  	struct cfq_data *cfqd = (struct cfq_data *) data;
  	struct cfq_queue *cfqq;
  	unsigned long flags;
  
  	spin_lock_irqsave(cfqd->queue->queue_lock, flags);
  
  	if ((cfqq = cfqd->active_queue) != NULL) {
  		unsigned long now = jiffies;
  
  		/*
  		 * expired
  		 */
  		if (time_after(now, cfqq->slice_end))
  			goto expire;
  
  		/*
  		 * only expire and reinvoke request handler, if there are
  		 * other queues with pending requests
  		 */

  		if (!cfqd->busy_queues) {

  			cfqd->idle_slice_timer.expires = min(now + cfqd->cfq_slice_idle, cfqq->slice_end);
  			add_timer(&cfqd->idle_slice_timer);
  			goto out_cont;
  		}
  
  		/*
  		 * not expired and it has a request pending, let it dispatch
  		 */
  		if (!RB_EMPTY(&cfqq->sort_list)) {

  			cfq_mark_cfqq_must_dispatch(cfqq);

  			goto out_kick;
  		}
  	}
  expire:
  	cfq_slice_expired(cfqd, 0);
  out_kick:

  	cfq_schedule_dispatch(cfqd);

  out_cont:
  	spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
  }
  
  /*
   * Timer running if an idle class queue is waiting for service
   */
  static void cfq_idle_class_timer(unsigned long data)
  {
  	struct cfq_data *cfqd = (struct cfq_data *) data;
  	unsigned long flags, end;
  
  	spin_lock_irqsave(cfqd->queue->queue_lock, flags);
  
  	/*
  	 * race with a non-idle queue, reset timer
  	 */
  	end = cfqd->last_end_request + CFQ_IDLE_GRACE;
  	if (!time_after_eq(jiffies, end)) {
  		cfqd->idle_class_timer.expires = end;
  		add_timer(&cfqd->idle_class_timer);
  	} else

  		cfq_schedule_dispatch(cfqd);

  
  	spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
  }

  static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
  {
  	del_timer_sync(&cfqd->idle_slice_timer);
  	del_timer_sync(&cfqd->idle_class_timer);
  	blk_sync_queue(cfqd->queue);
  }

  static void cfq_put_cfqd(struct cfq_data *cfqd)
  {
  	request_queue_t *q = cfqd->queue;
  
  	if (!atomic_dec_and_test(&cfqd->ref))
  		return;

  	cfq_shutdown_timer_wq(cfqd);

  	blk_put_queue(q);

  	mempool_destroy(cfqd->crq_pool);
  	kfree(cfqd->crq_hash);
  	kfree(cfqd->cfq_hash);
  	kfree(cfqd);
  }
  
  static void cfq_exit_queue(elevator_t *e)
  {

  	struct cfq_data *cfqd = e->elevator_data;

  	cfq_shutdown_timer_wq(cfqd);

  	cfq_put_cfqd(cfqd);

  }
  
  static int cfq_init_queue(request_queue_t *q, elevator_t *e)
  {
  	struct cfq_data *cfqd;
  	int i;
  
  	cfqd = kmalloc(sizeof(*cfqd), GFP_KERNEL);
  	if (!cfqd)
  		return -ENOMEM;
  
  	memset(cfqd, 0, sizeof(*cfqd));

  
  	for (i = 0; i < CFQ_PRIO_LISTS; i++)
  		INIT_LIST_HEAD(&cfqd->rr_list[i]);
  
  	INIT_LIST_HEAD(&cfqd->busy_rr);
  	INIT_LIST_HEAD(&cfqd->cur_rr);
  	INIT_LIST_HEAD(&cfqd->idle_rr);

  	INIT_LIST_HEAD(&cfqd->empty_list);
  
  	cfqd->crq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_MHASH_ENTRIES, GFP_KERNEL);
  	if (!cfqd->crq_hash)
  		goto out_crqhash;
  
  	cfqd->cfq_hash = kmalloc(sizeof(struct hlist_head) * CFQ_QHASH_ENTRIES, GFP_KERNEL);
  	if (!cfqd->cfq_hash)
  		goto out_cfqhash;
  
  	cfqd->crq_pool = mempool_create(BLKDEV_MIN_RQ, mempool_alloc_slab, mempool_free_slab, crq_pool);
  	if (!cfqd->crq_pool)
  		goto out_crqpool;
  
  	for (i = 0; i < CFQ_MHASH_ENTRIES; i++)
  		INIT_HLIST_HEAD(&cfqd->crq_hash[i]);
  	for (i = 0; i < CFQ_QHASH_ENTRIES; i++)
  		INIT_HLIST_HEAD(&cfqd->cfq_hash[i]);
  
  	e->elevator_data = cfqd;
  
  	cfqd->queue = q;

  	atomic_inc(&q->refcnt);

  	cfqd->max_queued = q->nr_requests / 4;

  	q->nr_batching = cfq_queued;

  
  	init_timer(&cfqd->idle_slice_timer);
  	cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
  	cfqd->idle_slice_timer.data = (unsigned long) cfqd;
  
  	init_timer(&cfqd->idle_class_timer);
  	cfqd->idle_class_timer.function = cfq_idle_class_timer;
  	cfqd->idle_class_timer.data = (unsigned long) cfqd;
  
  	INIT_WORK(&cfqd->unplug_work, cfq_kick_queue, q);

  	atomic_set(&cfqd->ref, 1);
  
  	cfqd->cfq_queued = cfq_queued;
  	cfqd->cfq_quantum = cfq_quantum;

  	cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
  	cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];

  	cfqd->cfq_back_max = cfq_back_max;
  	cfqd->cfq_back_penalty = cfq_back_penalty;

  	cfqd->cfq_slice[0] = cfq_slice_async;
  	cfqd->cfq_slice[1] = cfq_slice_sync;
  	cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
  	cfqd->cfq_slice_idle = cfq_slice_idle;
  	cfqd->cfq_max_depth = cfq_max_depth;

  	return 0;
  out_crqpool:
  	kfree(cfqd->cfq_hash);
  out_cfqhash:
  	kfree(cfqd->crq_hash);
  out_crqhash:
  	kfree(cfqd);
  	return -ENOMEM;
  }
  
  static void cfq_slab_kill(void)
  {
  	if (crq_pool)
  		kmem_cache_destroy(crq_pool);
  	if (cfq_pool)
  		kmem_cache_destroy(cfq_pool);
  	if (cfq_ioc_pool)
  		kmem_cache_destroy(cfq_ioc_pool);
  }
  
  static int __init cfq_slab_setup(void)
  {
  	crq_pool = kmem_cache_create("crq_pool", sizeof(struct cfq_rq), 0, 0,
  					NULL, NULL);
  	if (!crq_pool)
  		goto fail;
  
  	cfq_pool = kmem_cache_create("cfq_pool", sizeof(struct cfq_queue), 0, 0,
  					NULL, NULL);
  	if (!cfq_pool)
  		goto fail;
  
  	cfq_ioc_pool = kmem_cache_create("cfq_ioc_pool",
  			sizeof(struct cfq_io_context), 0, 0, NULL, NULL);
  	if (!cfq_ioc_pool)
  		goto fail;
  
  	return 0;
  fail:
  	cfq_slab_kill();
  	return -ENOMEM;
  }

  /*
   * sysfs parts below -->
   */
  struct cfq_fs_entry {
  	struct attribute attr;
  	ssize_t (*show)(struct cfq_data *, char *);
  	ssize_t (*store)(struct cfq_data *, const char *, size_t);
  };
  
  static ssize_t
  cfq_var_show(unsigned int var, char *page)
  {
  	return sprintf(page, "%d
  ", var);
  }
  
  static ssize_t
  cfq_var_store(unsigned int *var, const char *page, size_t count)
  {
  	char *p = (char *) page;
  
  	*var = simple_strtoul(p, &p, 10);
  	return count;
  }

  #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)				\
  static ssize_t __FUNC(struct cfq_data *cfqd, char *page)		\
  {									\
  	unsigned int __data = __VAR;					\
  	if (__CONV)							\
  		__data = jiffies_to_msecs(__data);			\
  	return cfq_var_show(__data, (page));				\
  }
  SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
  SHOW_FUNCTION(cfq_queued_show, cfqd->cfq_queued, 0);

  SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
  SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);

  SHOW_FUNCTION(cfq_back_max_show, cfqd->cfq_back_max, 0);
  SHOW_FUNCTION(cfq_back_penalty_show, cfqd->cfq_back_penalty, 0);

  SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
  SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
  SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
  SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
  SHOW_FUNCTION(cfq_max_depth_show, cfqd->cfq_max_depth, 0);

  #undef SHOW_FUNCTION
  
  #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
  static ssize_t __FUNC(struct cfq_data *cfqd, const char *page, size_t count)	\
  {									\
  	unsigned int __data;						\
  	int ret = cfq_var_store(&__data, (page), count);		\
  	if (__data < (MIN))						\
  		__data = (MIN);						\
  	else if (__data > (MAX))					\
  		__data = (MAX);						\
  	if (__CONV)							\
  		*(__PTR) = msecs_to_jiffies(__data);			\
  	else								\
  		*(__PTR) = __data;					\
  	return ret;							\
  }
  STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
  STORE_FUNCTION(cfq_queued_store, &cfqd->cfq_queued, 1, UINT_MAX, 0);

  STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1, UINT_MAX, 1);
  STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1, UINT_MAX, 1);

  STORE_FUNCTION(cfq_back_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
  STORE_FUNCTION(cfq_back_penalty_store, &cfqd->cfq_back_penalty, 1, UINT_MAX, 0);

  STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
  STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
  STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
  STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1, UINT_MAX, 0);
  STORE_FUNCTION(cfq_max_depth_store, &cfqd->cfq_max_depth, 1, UINT_MAX, 0);

  #undef STORE_FUNCTION
  
  static struct cfq_fs_entry cfq_quantum_entry = {
  	.attr = {.name = "quantum", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_quantum_show,
  	.store = cfq_quantum_store,
  };
  static struct cfq_fs_entry cfq_queued_entry = {
  	.attr = {.name = "queued", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_queued_show,
  	.store = cfq_queued_store,
  };

  static struct cfq_fs_entry cfq_fifo_expire_sync_entry = {

  	.attr = {.name = "fifo_expire_sync", .mode = S_IRUGO | S_IWUSR },

  	.show = cfq_fifo_expire_sync_show,
  	.store = cfq_fifo_expire_sync_store,

  };

  static struct cfq_fs_entry cfq_fifo_expire_async_entry = {

  	.attr = {.name = "fifo_expire_async", .mode = S_IRUGO | S_IWUSR },

  	.show = cfq_fifo_expire_async_show,
  	.store = cfq_fifo_expire_async_store,

  };
  static struct cfq_fs_entry cfq_back_max_entry = {
  	.attr = {.name = "back_seek_max", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_back_max_show,
  	.store = cfq_back_max_store,
  };
  static struct cfq_fs_entry cfq_back_penalty_entry = {
  	.attr = {.name = "back_seek_penalty", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_back_penalty_show,
  	.store = cfq_back_penalty_store,
  };

  static struct cfq_fs_entry cfq_slice_sync_entry = {
  	.attr = {.name = "slice_sync", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_slice_sync_show,
  	.store = cfq_slice_sync_store,

  };

  static struct cfq_fs_entry cfq_slice_async_entry = {
  	.attr = {.name = "slice_async", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_slice_async_show,
  	.store = cfq_slice_async_store,
  };
  static struct cfq_fs_entry cfq_slice_async_rq_entry = {
  	.attr = {.name = "slice_async_rq", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_slice_async_rq_show,
  	.store = cfq_slice_async_rq_store,
  };
  static struct cfq_fs_entry cfq_slice_idle_entry = {
  	.attr = {.name = "slice_idle", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_slice_idle_show,
  	.store = cfq_slice_idle_store,
  };
  static struct cfq_fs_entry cfq_max_depth_entry = {
  	.attr = {.name = "max_depth", .mode = S_IRUGO | S_IWUSR },
  	.show = cfq_max_depth_show,
  	.store = cfq_max_depth_store,

  };

  static struct attribute *default_attrs[] = {
  	&cfq_quantum_entry.attr,
  	&cfq_queued_entry.attr,

  	&cfq_fifo_expire_sync_entry.attr,
  	&cfq_fifo_expire_async_entry.attr,

  	&cfq_back_max_entry.attr,
  	&cfq_back_penalty_entry.attr,

  	&cfq_slice_sync_entry.attr,
  	&cfq_slice_async_entry.attr,
  	&cfq_slice_async_rq_entry.attr,
  	&cfq_slice_idle_entry.attr,
  	&cfq_max_depth_entry.attr,

  	NULL,
  };
  
  #define to_cfq(atr) container_of((atr), struct cfq_fs_entry, attr)
  
  static ssize_t
  cfq_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
  {
  	elevator_t *e = container_of(kobj, elevator_t, kobj);
  	struct cfq_fs_entry *entry = to_cfq(attr);
  
  	if (!entry->show)

  		return -EIO;

  
  	return entry->show(e->elevator_data, page);
  }
  
  static ssize_t
  cfq_attr_store(struct kobject *kobj, struct attribute *attr,
  	       const char *page, size_t length)
  {
  	elevator_t *e = container_of(kobj, elevator_t, kobj);
  	struct cfq_fs_entry *entry = to_cfq(attr);
  
  	if (!entry->store)

  		return -EIO;

  
  	return entry->store(e->elevator_data, page, length);
  }
  
  static struct sysfs_ops cfq_sysfs_ops = {
  	.show	= cfq_attr_show,
  	.store	= cfq_attr_store,
  };
  
  static struct kobj_type cfq_ktype = {
  	.sysfs_ops	= &cfq_sysfs_ops,
  	.default_attrs	= default_attrs,
  };
  
  static struct elevator_type iosched_cfq = {
  	.ops = {
  		.elevator_merge_fn = 		cfq_merge,
  		.elevator_merged_fn =		cfq_merged_request,
  		.elevator_merge_req_fn =	cfq_merged_requests,

  		.elevator_dispatch_fn =		cfq_dispatch_requests,

  		.elevator_add_req_fn =		cfq_insert_request,

  		.elevator_activate_req_fn =	cfq_activate_request,

  		.elevator_deactivate_req_fn =	cfq_deactivate_request,
  		.elevator_queue_empty_fn =	cfq_queue_empty,
  		.elevator_completed_req_fn =	cfq_completed_request,
  		.elevator_former_req_fn =	cfq_former_request,
  		.elevator_latter_req_fn =	cfq_latter_request,
  		.elevator_set_req_fn =		cfq_set_request,
  		.elevator_put_req_fn =		cfq_put_request,
  		.elevator_may_queue_fn =	cfq_may_queue,
  		.elevator_init_fn =		cfq_init_queue,
  		.elevator_exit_fn =		cfq_exit_queue,
  	},
  	.elevator_ktype =	&cfq_ktype,
  	.elevator_name =	"cfq",
  	.elevator_owner =	THIS_MODULE,
  };
  
  static int __init cfq_init(void)
  {
  	int ret;

  	/*
  	 * could be 0 on HZ < 1000 setups
  	 */
  	if (!cfq_slice_async)
  		cfq_slice_async = 1;
  	if (!cfq_slice_idle)
  		cfq_slice_idle = 1;

  	if (cfq_slab_setup())
  		return -ENOMEM;
  
  	ret = elv_register(&iosched_cfq);

  	if (ret)
  		cfq_slab_kill();

  	return ret;
  }
  
  static void __exit cfq_exit(void)
  {

  	elv_unregister(&iosched_cfq);

  	cfq_slab_kill();

  }
  
  module_init(cfq_init);
  module_exit(cfq_exit);
  
  MODULE_AUTHOR("Jens Axboe");
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");