/*
 *  linux/drivers/block/cfq-iosched.c
 *
 *  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>

static unsigned long max_elapsed_crq;
static unsigned long max_elapsed_dispatch;

/*
 * tunables
 */
static int cfq_quantum = 4;             /* max queue in one round of service */
static int cfq_queued = 8;              /* minimum rq allocate limit per-queue*/
static int cfq_service = HZ;            /* period over which service is avg */
static int cfq_fifo_expire_r = HZ / 2;  /* fifo timeout for sync requests */
static int cfq_fifo_expire_w = 5 * HZ;  /* fifo timeout for async requests */
static int cfq_fifo_rate = HZ / 8;      /* fifo expiry rate */
static int cfq_back_max = 16 * 1024;    /* maximum backwards seek, in KiB */
static int cfq_back_penalty = 2;        /* penalty of a backwards seek */

/*
 * 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 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 ON_RB(node)             ((node)->rb_color != RB_NONE)
#define rb_entry_crq(node)      rb_entry((node), struct cfq_rq, rb_node)
#define rq_rb_key(rq)           (rq)->sector

/*
 * threshold for switching off non-tag accounting
 */
#define CFQ_MAX_TAG             (4)

/*
 * sort key types and names
 */
enum {
        CFQ_KEY_PGID,
        CFQ_KEY_TGID,
        CFQ_KEY_UID,
        CFQ_KEY_GID,
        CFQ_KEY_LAST,
};

static char *cfq_key_types[] = { "pgid", "tgid", "uid", "gid", NULL };

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

struct cfq_data {
        struct list_head rr_list;
        struct list_head empty_list;

        struct hlist_head *cfq_hash;
        struct hlist_head *crq_hash;

        /* queues on rr_list (ie they have pending requests */
        unsigned int busy_queues;

        unsigned int max_queued;

        atomic_t ref;

        int key_type;

        mempool_t *crq_pool;

        request_queue_t *queue;

        sector_t last_sector;

        int rq_in_driver;

        /*
         * tunables, see top of file
         */
        unsigned int cfq_quantum;
        unsigned int cfq_queued;
        unsigned int cfq_fifo_expire_r;
        unsigned int cfq_fifo_expire_w;
        unsigned int cfq_fifo_batch_expire;
        unsigned int cfq_back_penalty;
        unsigned int cfq_back_max;
        unsigned int find_best_crq;

        unsigned int cfq_tagged;
};

struct cfq_queue {
        /* reference count */
        atomic_t ref;
        /* parent cfq_data */
        struct cfq_data *cfqd;
        /* hash of mergeable requests */
        struct hlist_node cfq_hash;
        /* hash key */
        unsigned long key;
        /* whether queue is on rr (or empty) list */
        int on_rr;
        /* 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[2];
        /* last time fifo expired */
        unsigned long last_fifo_expire;

        int key_type;

        unsigned long service_start;
        unsigned long service_used;

        unsigned int max_rate;

        /* number of requests that have been handed to the driver */
        int in_flight;
        /* number of currently allocated requests */
        int alloc_limit[2];
};

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 long service_start;
        unsigned long queue_start;

        unsigned int in_flight : 1;
        unsigned int accounted : 1;
        unsigned int is_sync   : 1;
        unsigned int is_write  : 1;
};

static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned long);
static void cfq_dispatch_sort(request_queue_t *, struct cfq_rq *);
static void cfq_update_next_crq(struct cfq_rq *);
static void cfq_put_cfqd(struct cfq_data *cfqd);

/*
 * what the fairness is based on (ie how processes are grouped and
 * differentiated)
 */
static inline unsigned long
cfq_hash_key(struct cfq_data *cfqd, struct task_struct *tsk)
{
        /*
         * optimize this so that ->key_type is the offset into the struct
         */
        switch (cfqd->key_type) {
                case CFQ_KEY_PGID:
                        return process_group(tsk);
                default:
                case CFQ_KEY_TGID:
                        return tsk->tgid;
                case CFQ_KEY_UID:
                        return tsk->uid;
                case CFQ_KEY_GID:
                        return tsk->gid;
        }
}

/*
 * 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 void cfq_remove_merge_hints(request_queue_t *q, struct cfq_rq *crq)
{
        cfq_del_crq_hash(crq);

        if (q->last_merge == crq->request)
                q->last_merge = NULL;

        cfq_update_next_crq(crq);
}

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));

        BUG_ON(!hlist_unhashed(&crq->hash));

        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;

                BUG_ON(hlist_unhashed(&crq->hash));

                if (!rq_mergeable(__rq)) {
                        cfq_del_crq_hash(crq);
                        continue;
                }

                if (rq_hash_key(__rq) == offset)
                        return __rq;
        }

        return NULL;
}

/*
 * 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;

        s1 = crq1->request->sector;
        s2 = crq2->request->sector;

        last = cfqd->last_sector;

#if 0
        if (!list_empty(&cfqd->queue->queue_head)) {
                struct list_head *entry = &cfqd->queue->queue_head;
                unsigned long distance = ~0UL;
                struct request *rq;

                while ((entry = entry->prev) != &cfqd->queue->queue_head) {
                        rq = list_entry_rq(entry);

                        if (blk_barrier_rq(rq))
                                break;

                        if (distance < abs(s1 - rq->sector + rq->nr_sectors)) {
                                distance = abs(s1 - rq->sector +rq->nr_sectors);
                                last = rq->sector + rq->nr_sectors;
                        }
                        if (distance < abs(s2 - rq->sector + rq->nr_sectors)) {
                                distance = abs(s2 - rq->sector +rq->nr_sectors);
                                last = rq->sector + rq->nr_sectors;
                        }
                }
        }
#endif

        /*
         * 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 (!ON_RB(&last->rb_node))
                return NULL;

        if ((rbnext = rb_next(&last->rb_node)) == NULL)
                rbnext = rb_first(&cfqq->sort_list);

        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 int cfq_check_sort_rr_list(struct cfq_queue *cfqq)
{
        struct list_head *head = &cfqq->cfqd->rr_list;
        struct list_head *next, *prev;

        /*
         * list might still be ordered
         */
        next = cfqq->cfq_list.next;
        if (next != head) {
                struct cfq_queue *cnext = list_entry_cfqq(next);

                if (cfqq->service_used > cnext->service_used)
                        return 1;
        }

        prev = cfqq->cfq_list.prev;
        if (prev != head) {
                struct cfq_queue *cprev = list_entry_cfqq(prev);

                if (cfqq->service_used < cprev->service_used)
                        return 1;
        }

        return 0;
}

static void cfq_sort_rr_list(struct cfq_queue *cfqq, int new_queue)
{
        struct list_head *entry = &cfqq->cfqd->rr_list;

        if (!cfqq->on_rr)
                return;
        if (!new_queue && !cfq_check_sort_rr_list(cfqq))
                return;

        list_del(&cfqq->cfq_list);

        /*
         * sort by our mean service_used, sub-sort by in-flight requests
         */
        while ((entry = entry->prev) != &cfqq->cfqd->rr_list) {
                struct cfq_queue *__cfqq = list_entry_cfqq(entry);

                if (cfqq->service_used > __cfqq->service_used)
                        break;
                else if (cfqq->service_used == __cfqq->service_used) {
                        struct list_head *prv;

                        while ((prv = entry->prev) != &cfqq->cfqd->rr_list) {
                                __cfqq = list_entry_cfqq(prv);

                                WARN_ON(__cfqq->service_used > cfqq->service_used);
                                if (cfqq->service_used != __cfqq->service_used)
                                        break;
                                if (cfqq->in_flight > __cfqq->in_flight)
                                        break;

                                entry = prv;
                        }
                }
        }

        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 requests serviced
 */
static inline void
cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        /*
         * it's currently on the empty list
         */
        cfqq->on_rr = 1;
        cfqd->busy_queues++;

        if (time_after(jiffies, cfqq->service_start + cfq_service))
                cfqq->service_used >>= 3;

        cfq_sort_rr_list(cfqq, 1);
}

static inline void
cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        list_move(&cfqq->cfq_list, &cfqd->empty_list);
        cfqq->on_rr = 0;

        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;

        if (ON_RB(&crq->rb_node)) {
                struct cfq_data *cfqd = cfqq->cfqd;

                BUG_ON(!cfqq->queued[crq->is_sync]);

                cfq_update_next_crq(crq);

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

                if (RB_EMPTY(&cfqq->sort_list) && cfqq->on_rr)
                        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[crq->is_sync]++;

        /*
         * 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_sort(cfqd->queue, __alias);

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

        if (!cfqq->on_rr)
                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)
{
        if (ON_RB(&crq->rb_node)) {
                rb_erase(&crq->rb_node, &cfqq->sort_list);
                cfqq->queued[crq->is_sync]--;
        }

        cfq_add_crq_rb(crq);
}

static struct request *
cfq_find_rq_rb(struct cfq_data *cfqd, sector_t sector)
{
        const unsigned long key = cfq_hash_key(cfqd, current);
        struct cfq_queue *cfqq = cfq_find_cfq_hash(cfqd, key);
        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;
}

/*
 * make sure the service time gets corrected on reissue of this request
 */
static void cfq_requeue_request(request_queue_t *q, struct request *rq)
{
        struct cfq_rq *crq = RQ_DATA(rq);

        if (crq) {
                struct cfq_queue *cfqq = crq->cfq_queue;

                if (cfqq->cfqd->cfq_tagged) {
                        cfqq->service_used--;
                        cfq_sort_rr_list(cfqq, 0);
                }

                if (crq->accounted) {
                        crq->accounted = 0;
                        cfqq->cfqd->rq_in_driver--;
                }
        }
        list_add(&rq->queuelist, &q->queue_head);
}

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

        if (crq) {
                cfq_remove_merge_hints(q, crq);
                list_del_init(&rq->queuelist);

                if (crq->cfq_queue)
                        cfq_del_crq_rb(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;

        ret = elv_try_last_merge(q, bio);
        if (ret != ELEVATOR_NO_MERGE) {
                __rq = q->last_merge;
                goto out_insert;
        }

        __rq = cfq_find_rq_hash(cfqd, bio->bi_sector);
        if (__rq) {
                BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);

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

        return ELEVATOR_NO_MERGE;
out:
        q->last_merge = __rq;
out_insert:
        *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 (ON_RB(&crq->rb_node) && (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);
        }

        q->last_merge = req;
}

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

        cfq_merged_request(q, rq);

        if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist)) {
                if (time_before(cnext->queue_start, crq->queue_start)) {
                        list_move(&rq->queuelist, &next->queuelist);
                        crq->queue_start = cnext->queue_start;
                }
        }

        cfq_update_next_crq(cnext);
        cfq_remove_request(q, next);
}

/*
 * we dispatch cfqd->cfq_quantum requests in total from the rr_list queues,
 * this function sector sorts the selected request to minimize seeks. we start
 * at cfqd->last_sector, not 0.
 */
static void cfq_dispatch_sort(request_queue_t *q, struct cfq_rq *crq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq = crq->cfq_queue;
        struct list_head *head = &q->queue_head, *entry = head;
        struct request *__rq;
        sector_t last;

        cfq_del_crq_rb(crq);
        cfq_remove_merge_hints(q, crq);
        list_del(&crq->request->queuelist);

        last = cfqd->last_sector;
        while ((entry = entry->prev) != head) {
                __rq = list_entry_rq(entry);

                if (blk_barrier_rq(crq->request))
                        break;
                if (!blk_fs_request(crq->request))
                        break;

                if (crq->request->sector > __rq->sector)
                        break;
                if (__rq->sector > last && crq->request->sector < last) {
                        last = crq->request->sector;
                        break;
                }
        }

        cfqd->last_sector = last;
        crq->in_flight = 1;
        cfqq->in_flight++;
        list_add(&crq->request->queuelist, entry);
}

/*
 * 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;
        const int reads = !list_empty(&cfqq->fifo[0]);
        const int writes = !list_empty(&cfqq->fifo[1]);
        unsigned long now = jiffies;
        struct cfq_rq *crq;

        if (time_before(now, cfqq->last_fifo_expire + cfqd->cfq_fifo_batch_expire))
                return NULL;

        crq = RQ_DATA(list_entry(cfqq->fifo[0].next, struct request, queuelist));
        if (reads && time_after(now, crq->queue_start + cfqd->cfq_fifo_expire_r)) {
                cfqq->last_fifo_expire = now;
                return crq;
        }

        crq = RQ_DATA(list_entry(cfqq->fifo[1].next, struct request, queuelist));
        if (writes && time_after(now, crq->queue_start + cfqd->cfq_fifo_expire_w)) {
                cfqq->last_fifo_expire = now;
                return crq;
        }

        return NULL;
}

/*
 * dispatch a single request from given queue
 */
static inline void
cfq_dispatch_request(request_queue_t *q, struct cfq_data *cfqd,
                     struct cfq_queue *cfqq)
{
        struct cfq_rq *crq;

        /*
         * follow expired path, else get first next available
         */
        if ((crq = cfq_check_fifo(cfqq)) == NULL) {
                if (cfqd->find_best_crq)
                        crq = cfqq->next_crq;
                else
                        crq = rb_entry_crq(rb_first(&cfqq->sort_list));
        }

        cfqd->last_sector = crq->request->sector + crq->request->nr_sectors;

        /*
         * finally, insert request into driver list
         */
        cfq_dispatch_sort(q, crq);
}

static int cfq_dispatch_requests(request_queue_t *q, int max_dispatch)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq;
        struct list_head *entry, *tmp;
        int queued, busy_queues, first_round;

        if (list_empty(&cfqd->rr_list))
                return 0;

        queued = 0;
        first_round = 1;
restart:
        busy_queues = 0;
        list_for_each_safe(entry, tmp, &cfqd->rr_list) {
                cfqq = list_entry_cfqq(entry);

                BUG_ON(RB_EMPTY(&cfqq->sort_list));

                /*
                 * first round of queueing, only select from queues that
                 * don't already have io in-flight
                 */
                if (first_round && cfqq->in_flight)
                        continue;

                cfq_dispatch_request(q, cfqd, cfqq);

                if (!RB_EMPTY(&cfqq->sort_list))
                        busy_queues++;

                queued++;
        }

        if ((queued < max_dispatch) && (busy_queues || first_round)) {
                first_round = 0;
                goto restart;
        }

        return queued;
}

static inline void cfq_account_dispatch(struct cfq_rq *crq)
{
        struct cfq_queue *cfqq = crq->cfq_queue;
        struct cfq_data *cfqd = cfqq->cfqd;
        unsigned long now, elapsed;

        if (!blk_fs_request(crq->request))
                return;

        /*
         * accounted bit is necessary since some drivers will call
         * elv_next_request() many times for the same request (eg ide)
         */
        if (crq->accounted)
                return;

        now = jiffies;
        if (cfqq->service_start == ~0UL)
                cfqq->service_start = now;

        /*
         * on drives with tagged command queueing, command turn-around time
         * doesn't necessarily reflect the time spent processing this very
         * command inside the drive. so do the accounting differently there,
         * by just sorting on the number of requests
         */
        if (cfqd->cfq_tagged) {
                if (time_after(now, cfqq->service_start + cfq_service)) {
                        cfqq->service_start = now;
                        cfqq->service_used /= 10;
                }

                cfqq->service_used++;
                cfq_sort_rr_list(cfqq, 0);
        }

        elapsed = now - crq->queue_start;
        if (elapsed > max_elapsed_dispatch)
                max_elapsed_dispatch = elapsed;

        crq->accounted = 1;
        crq->service_start = now;

        if (++cfqd->rq_in_driver >= CFQ_MAX_TAG && !cfqd->cfq_tagged) {
                cfqq->cfqd->cfq_tagged = 1;
                printk("cfq: depth %d reached, tagging now on\n", CFQ_MAX_TAG);
        }
}

static inline void
cfq_account_completion(struct cfq_queue *cfqq, struct cfq_rq *crq)
{
        struct cfq_data *cfqd = cfqq->cfqd;

        if (!crq->accounted)
                return;

        WARN_ON(!cfqd->rq_in_driver);
        cfqd->rq_in_driver--;

        if (!cfqd->cfq_tagged) {
                unsigned long now = jiffies;
                unsigned long duration = now - crq->service_start;

                if (time_after(now, cfqq->service_start + cfq_service)) {
                        cfqq->service_start = now;
                        cfqq->service_used >>= 3;
                }

                cfqq->service_used += duration;
                cfq_sort_rr_list(cfqq, 0);

                if (duration > max_elapsed_crq)
                        max_elapsed_crq = duration;
        }
}

static struct request *cfq_next_request(request_queue_t *q)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct request *rq;

        if (!list_empty(&q->queue_head)) {
                struct cfq_rq *crq;
dispatch:
                rq = list_entry_rq(q->queue_head.next);

                if ((crq = RQ_DATA(rq)) != NULL) {
                        cfq_remove_merge_hints(q, crq);
                        cfq_account_dispatch(crq);
                }

                return rq;
        }

        if (cfq_dispatch_requests(q, cfqd->cfq_quantum))
                goto dispatch;

        return NULL;
}

/*
 * 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)
{
        BUG_ON(!atomic_read(&cfqq->ref));

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

        BUG_ON(rb_first(&cfqq->sort_list));
        BUG_ON(cfqq->on_rr);

        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 long key, 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);

                if (__cfqq->key == key)
                        return __cfqq;
        }

        return NULL;
}

static struct cfq_queue *
cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned long key)
{
        return __cfq_find_cfq_hash(cfqd, key, hash_long(key, CFQ_QHASH_SHIFT));
}

static inline void
cfq_rehash_cfqq(struct cfq_data *cfqd, struct cfq_queue **cfqq,
                struct cfq_io_context *cic)
{
        unsigned long hashkey = cfq_hash_key(cfqd, current);
        unsigned long hashval = hash_long(hashkey, CFQ_QHASH_SHIFT);
        struct cfq_queue *__cfqq;
        unsigned long flags;

        spin_lock_irqsave(cfqd->queue->queue_lock, flags);

        hlist_del(&(*cfqq)->cfq_hash);

        __cfqq = __cfq_find_cfq_hash(cfqd, hashkey, hashval);
        if (!__cfqq || __cfqq == *cfqq) {
                __cfqq = *cfqq;
                hlist_add_head(&__cfqq->cfq_hash, &cfqd->cfq_hash[hashval]);
                __cfqq->key_type = cfqd->key_type;
        } else {
                atomic_inc(&__cfqq->ref);
                cic->cfqq = __cfqq;
                cfq_put_queue(*cfqq);
                *cfqq = __cfqq;
        }

        cic->cfqq = __cfqq;
        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_free_io_context(struct cfq_io_context *cic)
{
        kmem_cache_free(cfq_ioc_pool, cic);
}

/*
 * locking hierarchy is: io_context lock -> queue locks
 */
static void cfq_exit_io_context(struct cfq_io_context *cic)
{
        struct cfq_queue *cfqq = cic->cfqq;
        struct list_head *entry = &cic->list;
        request_queue_t *q;
        unsigned long flags;

        /*
         * put the reference this task is holding to the various queues
         */
        spin_lock_irqsave(&cic->ioc->lock, flags);
        while ((entry = cic->list.next) != &cic->list) {
                struct cfq_io_context *__cic;

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

                q = __cic->cfqq->cfqd->queue;
                spin_lock(q->queue_lock);
                cfq_put_queue(__cic->cfqq);
                spin_unlock(q->queue_lock);
        }

        q = cfqq->cfqd->queue;
        spin_lock(q->queue_lock);
        cfq_put_queue(cfqq);
        spin_unlock(q->queue_lock);

        cic->cfqq = NULL;
        spin_unlock_irqrestore(&cic->ioc->lock, flags);
}

static struct cfq_io_context *cfq_alloc_io_context(int gfp_flags)
{
        struct cfq_io_context *cic = kmem_cache_alloc(cfq_ioc_pool, gfp_flags);

        if (cic) {
                cic->dtor = cfq_free_io_context;
                cic->exit = cfq_exit_io_context;
                INIT_LIST_HEAD(&cic->list);
                cic->cfqq = NULL;
        }

        return cic;
}

/*
 * 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_queue **cfqq, int gfp_flags)
{
        struct cfq_data *cfqd = (*cfqq)->cfqd;
        struct cfq_queue *__cfqq = *cfqq;
        struct cfq_io_context *cic;
        struct io_context *ioc;

        might_sleep_if(gfp_flags & __GFP_WAIT);

        ioc = get_io_context(gfp_flags);
        if (!ioc)
                return NULL;

        if ((cic = ioc->cic) == NULL) {
                cic = cfq_alloc_io_context(gfp_flags);

                if (cic == NULL)
                        goto err;

                ioc->cic = cic;
                cic->ioc = ioc;
                cic->cfqq = __cfqq;
                atomic_inc(&__cfqq->ref);
        } else {
                struct cfq_io_context *__cic;
                unsigned long flags;

                /*
                 * since the first cic on the list is actually the head
                 * itself, need to check this here or we'll duplicate an
                 * cic per ioc for no reason
                 */
                if (cic->cfqq == __cfqq)
                        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
                 */
                spin_lock_irqsave(&ioc->lock, flags);
                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->cfqq == __cfqq) {
                                cic = __cic;
                                spin_unlock_irqrestore(&ioc->lock, flags);
                                goto out;
                        }
                }
                spin_unlock_irqrestore(&ioc->lock, flags);

                /*
                 * 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(gfp_flags);
                if (__cic == NULL)
                        goto err;

                __cic->ioc = ioc;
                __cic->cfqq = __cfqq;
                atomic_inc(&__cfqq->ref);
                spin_lock_irqsave(&ioc->lock, flags);
                list_add(&__cic->list, &cic->list);
                spin_unlock_irqrestore(&ioc->lock, flags);

                cic = __cic;
                *cfqq = __cfqq;
        }

out:
        /*
         * if key_type has been changed on the fly, we lazily rehash
         * each queue at lookup time
         */
        if ((*cfqq)->key_type != cfqd->key_type)
                cfq_rehash_cfqq(cfqd, cfqq, cic);

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

static struct cfq_queue *
__cfq_get_queue(struct cfq_data *cfqd, unsigned long key, int 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, 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
                        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[0]);
                INIT_LIST_HEAD(&cfqq->fifo[1]);

                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->key_type = cfqd->key_type;
                cfqq->service_start = ~0UL;
        }

        if (new_cfqq)
                kmem_cache_free(cfq_pool, new_cfqq);

        atomic_inc(&cfqq->ref);
out:
        WARN_ON((gfp_mask & __GFP_WAIT) && !cfqq);
        return cfqq;
}

static void cfq_enqueue(struct cfq_data *cfqd, struct cfq_rq *crq)
{
        crq->is_sync = 0;
        if (rq_data_dir(crq->request) == READ || current->flags & PF_SYNCWRITE)
                crq->is_sync = 1;

        cfq_add_crq_rb(crq);
        crq->queue_start = jiffies;

        list_add_tail(&crq->request->queuelist, &crq->cfq_queue->fifo[crq->is_sync]);
}

static void
cfq_insert_request(request_queue_t *q, struct request *rq, int where)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_rq *crq = RQ_DATA(rq);

        switch (where) {
                case ELEVATOR_INSERT_BACK:
                        while (cfq_dispatch_requests(q, cfqd->cfq_quantum))
                                ;
                        list_add_tail(&rq->queuelist, &q->queue_head);
                        break;
                case ELEVATOR_INSERT_FRONT:
                        list_add(&rq->queuelist, &q->queue_head);
                        break;
                case ELEVATOR_INSERT_SORT:
                        BUG_ON(!blk_fs_request(rq));
                        cfq_enqueue(cfqd, crq);
                        break;
                default:
                        printk("%s: bad insert point %d\n", __FUNCTION__,where);
                        return;
        }

        if (rq_mergeable(rq)) {
                cfq_add_crq_hash(cfqd, crq);

                if (!q->last_merge)
                        q->last_merge = rq;
        }
}

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

        return list_empty(&q->queue_head) && list_empty(&cfqd->rr_list);
}

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

        if (unlikely(!blk_fs_request(rq)))
                return;

        cfqq = crq->cfq_queue;

        if (crq->in_flight) {
                WARN_ON(!cfqq->in_flight);
                cfqq->in_flight--;
        }

        cfq_account_completion(cfqq, crq);
}

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;
}

static int cfq_may_queue(request_queue_t *q, int rw)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq;
        int ret = ELV_MQUEUE_MAY;

        if (current->flags & PF_MEMALLOC)
                return ELV_MQUEUE_MAY;

        cfqq = cfq_find_cfq_hash(cfqd, cfq_hash_key(cfqd, current));
        if (cfqq) {
                int limit = cfqd->max_queued;

                if (cfqq->allocated[rw] < cfqd->cfq_queued)
                        return ELV_MQUEUE_MUST;

                if (cfqd->busy_queues)
                        limit = q->nr_requests / cfqd->busy_queues;

                if (limit < cfqd->cfq_queued)
                        limit = cfqd->cfq_queued;
                else if (limit > cfqd->max_queued)
                        limit = cfqd->max_queued;

                if (cfqq->allocated[rw] >= limit) {
                        if (limit > cfqq->alloc_limit[rw])
                                cfqq->alloc_limit[rw] = limit;

                        ret = ELV_MQUEUE_NO;
                }
        }

        return ret;
}

static void cfq_check_waiters(request_queue_t *q, struct cfq_queue *cfqq)
{
        struct request_list *rl = &q->rq;
        const int write = waitqueue_active(&rl->wait[WRITE]);
        const int read = waitqueue_active(&rl->wait[READ]);

        if (read && cfqq->allocated[READ] < cfqq->alloc_limit[READ])
                wake_up(&rl->wait[READ]);
        if (write && cfqq->allocated[WRITE] < cfqq->alloc_limit[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;

                BUG_ON(q->last_merge == rq);
                BUG_ON(!hlist_unhashed(&crq->hash));

                if (crq->io_context)
                        put_io_context(crq->io_context->ioc);

                BUG_ON(!cfqq->allocated[crq->is_write]);
                cfqq->allocated[crq->is_write]--;

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

                smp_mb();
                cfq_check_waiters(q, cfqq);
                cfq_put_queue(cfqq);
        }
}

/*
 * Allocate cfq data structures associated with this request. A queue and
 */
static int cfq_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_io_context *cic;
        const int rw = rq_data_dir(rq);
        struct cfq_queue *cfqq, *saved_cfqq;
        struct cfq_rq *crq;
        unsigned long flags;

        might_sleep_if(gfp_mask & __GFP_WAIT);

        spin_lock_irqsave(q->queue_lock, flags);

        cfqq = __cfq_get_queue(cfqd, cfq_hash_key(cfqd, current), gfp_mask);
        if (!cfqq)
                goto out_lock;

repeat:
        if (cfqq->allocated[rw] >= cfqd->max_queued)
                goto out_lock;

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

        /*
         * if hashing type has changed, the cfq_queue might change here.
         */
        saved_cfqq = cfqq;
        cic = cfq_get_io_context(&cfqq, gfp_mask);
        if (!cic)
                goto err;

        /*
         * repeat allocation checks on queue change
         */
        if (unlikely(saved_cfqq != cfqq)) {
                spin_lock_irqsave(q->queue_lock, flags);
                saved_cfqq->allocated[rw]--;
                goto repeat;
        }

        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;
                crq->service_start = crq->queue_start = 0;
                crq->in_flight = crq->accounted = crq->is_sync = 0;
                crq->is_write = rw;
                rq->elevator_private = crq;
                cfqq->alloc_limit[rw] = 0;
                return 0;
        }

        put_io_context(cic->ioc);
err:
        spin_lock_irqsave(q->queue_lock, flags);
        cfqq->allocated[rw]--;
        cfq_put_queue(cfqq);
out_lock:
        spin_unlock_irqrestore(q->queue_lock, flags);
        return 1;
}

static void cfq_put_cfqd(struct cfq_data *cfqd)
{
        request_queue_t *q = cfqd->queue;

        if (!atomic_dec_and_test(&cfqd->ref))
                return;

        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)
{
        cfq_put_cfqd(e->elevator_data);
}

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));
        INIT_LIST_HEAD(&cfqd->rr_list);
        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);

        /*
         * just set it to some high value, we want anyone to be able to queue
         * some requests. fairness is handled differently
         */
        q->nr_requests = 1024;
        cfqd->max_queued = q->nr_requests / 16;
        q->nr_batching = cfq_queued;
        cfqd->key_type = CFQ_KEY_TGID;
        cfqd->find_best_crq = 1;
        atomic_set(&cfqd->ref, 1);

        cfqd->cfq_queued = cfq_queued;
        cfqd->cfq_quantum = cfq_quantum;
        cfqd->cfq_fifo_expire_r = cfq_fifo_expire_r;
        cfqd->cfq_fifo_expire_w = cfq_fifo_expire_w;
        cfqd->cfq_fifo_batch_expire = cfq_fifo_rate;
        cfqd->cfq_back_max = cfq_back_max;
        cfqd->cfq_back_penalty = cfq_back_penalty;

        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\n", 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;
}

static ssize_t
cfq_clear_elapsed(struct cfq_data *cfqd, const char *page, size_t count)
{
        max_elapsed_dispatch = max_elapsed_crq = 0;
        return count;
}

static ssize_t
cfq_set_key_type(struct cfq_data *cfqd, const char *page, size_t count)
{
        spin_lock_irq(cfqd->queue->queue_lock);
        if (!strncmp(page, "pgid", 4))
                cfqd->key_type = CFQ_KEY_PGID;
        else if (!strncmp(page, "tgid", 4))
                cfqd->key_type = CFQ_KEY_TGID;
        else if (!strncmp(page, "uid", 3))
                cfqd->key_type = CFQ_KEY_UID;
        else if (!strncmp(page, "gid", 3))
                cfqd->key_type = CFQ_KEY_GID;
        spin_unlock_irq(cfqd->queue->queue_lock);
        return count;
}

static ssize_t
cfq_read_key_type(struct cfq_data *cfqd, char *page)
{
        ssize_t len = 0;
        int i;

        for (i = CFQ_KEY_PGID; i < CFQ_KEY_LAST; i++) {
                if (cfqd->key_type == i)
                        len += sprintf(page+len, "[%s] ", cfq_key_types[i]);
                else
                        len += sprintf(page+len, "%s ", cfq_key_types[i]);
        }
        len += sprintf(page+len, "\n");
        return len;
}

#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_r_show, cfqd->cfq_fifo_expire_r, 1);
SHOW_FUNCTION(cfq_fifo_expire_w_show, cfqd->cfq_fifo_expire_w, 1);
SHOW_FUNCTION(cfq_fifo_batch_expire_show, cfqd->cfq_fifo_batch_expire, 1);
SHOW_FUNCTION(cfq_find_best_show, cfqd->find_best_crq, 0);
SHOW_FUNCTION(cfq_back_max_show, cfqd->cfq_back_max, 0);
SHOW_FUNCTION(cfq_back_penalty_show, cfqd->cfq_back_penalty, 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_r_store, &cfqd->cfq_fifo_expire_r, 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_fifo_expire_w_store, &cfqd->cfq_fifo_expire_w, 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_fifo_batch_expire_store, &cfqd->cfq_fifo_batch_expire, 0, UINT_MAX, 1);
STORE_FUNCTION(cfq_find_best_store, &cfqd->find_best_crq, 0, 1, 0);
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);
#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_r_entry = {
        .attr = {.name = "fifo_expire_sync", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_fifo_expire_r_show,
        .store = cfq_fifo_expire_r_store,
};
static struct cfq_fs_entry cfq_fifo_expire_w_entry = {
        .attr = {.name = "fifo_expire_async", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_fifo_expire_w_show,
        .store = cfq_fifo_expire_w_store,
};
static struct cfq_fs_entry cfq_fifo_batch_expire_entry = {
        .attr = {.name = "fifo_batch_expire", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_fifo_batch_expire_show,
        .store = cfq_fifo_batch_expire_store,
};
static struct cfq_fs_entry cfq_find_best_entry = {
        .attr = {.name = "find_best_crq", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_find_best_show,
        .store = cfq_find_best_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_clear_elapsed_entry = {
        .attr = {.name = "clear_elapsed", .mode = S_IWUSR },
        .store = cfq_clear_elapsed,
};
static struct cfq_fs_entry cfq_key_type_entry = {
        .attr = {.name = "key_type", .mode = S_IRUGO | S_IWUSR },
        .show = cfq_read_key_type,
        .store = cfq_set_key_type,
};

static struct attribute *default_attrs[] = {
        &cfq_quantum_entry.attr,
        &cfq_queued_entry.attr,
        &cfq_fifo_expire_r_entry.attr,
        &cfq_fifo_expire_w_entry.attr,
        &cfq_fifo_batch_expire_entry.attr,
        &cfq_key_type_entry.attr,
        &cfq_find_best_entry.attr,
        &cfq_back_max_entry.attr,
        &cfq_back_penalty_entry.attr,
        &cfq_clear_elapsed_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 0;

        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 -EINVAL;

        return entry->store(e->elevator_data, page, length);
}

static struct sysfs_ops cfq_sysfs_ops = {
        .show   = cfq_attr_show,
        .store  = cfq_attr_store,
};

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_next_req_fn =         cfq_next_request,
                .elevator_add_req_fn =          cfq_insert_request,
                .elevator_remove_req_fn =       cfq_remove_request,
                .elevator_requeue_req_fn =      cfq_requeue_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;

        if (cfq_slab_setup())
                return -ENOMEM;

        ret = elv_register(&iosched_cfq);
        if (!ret) {
                __module_get(THIS_MODULE);
                return 0;
        }

        cfq_slab_kill();
        return ret;
}

static void __exit cfq_exit(void)
{
        cfq_slab_kill();
        elv_unregister(&iosched_cfq);
}

module_init(cfq_init);
module_exit(cfq_exit);

MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");