/*
 *  Deadline i/o scheduler.
 *
 *  Copyright (C) 2002 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/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/hash.h>
#include <linux/rbtree.h>

/*
 * See Documentation/block/deadline-iosched.txt
 */
static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
static const int writes_starved = 2;    /* max times reads can starve a write */
static const int fifo_batch = 16;       /* # of sequential requests treated as one
                                     by the above parameters. For throughput. */

static const int deadline_hash_shift = 5;
#define DL_HASH_BLOCK(sec)      ((sec) >> 3)
#define DL_HASH_FN(sec)         (hash_long(DL_HASH_BLOCK((sec)), deadline_hash_shift))
#define DL_HASH_ENTRIES         (1 << deadline_hash_shift)
#define rq_hash_key(rq)         ((rq)->sector + (rq)->nr_sectors)
#define ON_HASH(drq)            (!hlist_unhashed(&(drq)->hash))

struct deadline_data {
        /*
         * run time data
         */

        /*
         * requests (deadline_rq s) are present on both sort_list and fifo_list
         */
        struct rb_root sort_list[2];    
        struct list_head fifo_list[2];
        
        /*
         * next in sort order. read, write or both are NULL
         */
        struct deadline_rq *next_drq[2];
        struct hlist_head *hash;        /* request hash */
        unsigned int batching;          /* number of sequential requests made */
        sector_t last_sector;           /* head position */
        unsigned int starved;           /* times reads have starved writes */

        /*
         * settings that change how the i/o scheduler behaves
         */
        int fifo_expire[2];
        int fifo_batch;
        int writes_starved;
        int front_merges;

        mempool_t *drq_pool;
};

/*
 * pre-request data.
 */
struct deadline_rq {
        /*
         * rbtree index, key is the starting offset
         */
        struct rb_node rb_node;
        sector_t rb_key;

        struct request *request;

        /*
         * request hash, key is the ending offset (for back merge lookup)
         */
        struct hlist_node hash;

        /*
         * expire fifo
         */
        struct list_head fifo;
        unsigned long expires;
};

static void deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq);

static kmem_cache_t *drq_pool;

#define RQ_DATA(rq)     ((struct deadline_rq *) (rq)->elevator_private)

/*
 * the back merge hash support functions
 */
static inline void __deadline_del_drq_hash(struct deadline_rq *drq)
{
        hlist_del_init(&drq->hash);
}

static inline void deadline_del_drq_hash(struct deadline_rq *drq)
{
        if (ON_HASH(drq))
                __deadline_del_drq_hash(drq);
}

static inline void
deadline_add_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
{
        struct request *rq = drq->request;

        BUG_ON(ON_HASH(drq));

        hlist_add_head(&drq->hash, &dd->hash[DL_HASH_FN(rq_hash_key(rq))]);
}

/*
 * move hot entry to front of chain
 */
static inline void
deadline_hot_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
{
        struct request *rq = drq->request;
        struct hlist_head *head = &dd->hash[DL_HASH_FN(rq_hash_key(rq))];

        if (ON_HASH(drq) && &drq->hash != head->first) {
                hlist_del(&drq->hash);
                hlist_add_head(&drq->hash, head);
        }
}

static struct request *
deadline_find_drq_hash(struct deadline_data *dd, sector_t offset)
{
        struct hlist_head *hash_list = &dd->hash[DL_HASH_FN(offset)];
        struct hlist_node *entry, *next;
        struct deadline_rq *drq;

        hlist_for_each_entry_safe(drq, entry, next, hash_list, hash) {
                struct request *__rq = drq->request;

                BUG_ON(!ON_HASH(drq));

                if (!rq_mergeable(__rq)) {
                        __deadline_del_drq_hash(drq);
                        continue;
                }

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

        return NULL;
}

/*
 * rb tree support functions
 */
#define rb_entry_drq(node)      rb_entry((node), struct deadline_rq, rb_node)
#define DRQ_RB_ROOT(dd, drq)    (&(dd)->sort_list[rq_data_dir((drq)->request)])
#define rq_rb_key(rq)           (rq)->sector

static struct deadline_rq *
__deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
        struct rb_node **p = &DRQ_RB_ROOT(dd, drq)->rb_node;
        struct rb_node *parent = NULL;
        struct deadline_rq *__drq;

        while (*p) {
                parent = *p;
                __drq = rb_entry_drq(parent);

                if (drq->rb_key < __drq->rb_key)
                        p = &(*p)->rb_left;
                else if (drq->rb_key > __drq->rb_key)
                        p = &(*p)->rb_right;
                else
                        return __drq;
        }

        rb_link_node(&drq->rb_node, parent, p);
        return NULL;
}

static void
deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
        struct deadline_rq *__alias;

        drq->rb_key = rq_rb_key(drq->request);

retry:
        __alias = __deadline_add_drq_rb(dd, drq);
        if (!__alias) {
                rb_insert_color(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
                return;
        }

        deadline_move_request(dd, __alias);
        goto retry;
}

static inline void
deadline_del_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
        const int data_dir = rq_data_dir(drq->request);

        if (dd->next_drq[data_dir] == drq) {
                struct rb_node *rbnext = rb_next(&drq->rb_node);

                dd->next_drq[data_dir] = NULL;
                if (rbnext)
                        dd->next_drq[data_dir] = rb_entry_drq(rbnext);
        }

        BUG_ON(!RB_EMPTY_NODE(&drq->rb_node));
        rb_erase(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
        RB_CLEAR_NODE(&drq->rb_node);
}

static struct request *
deadline_find_drq_rb(struct deadline_data *dd, sector_t sector, int data_dir)
{
        struct rb_node *n = dd->sort_list[data_dir].rb_node;
        struct deadline_rq *drq;

        while (n) {
                drq = rb_entry_drq(n);

                if (sector < drq->rb_key)
                        n = n->rb_left;
                else if (sector > drq->rb_key)
                        n = n->rb_right;
                else
                        return drq->request;
        }

        return NULL;
}

/*
 * deadline_find_first_drq finds the first (lowest sector numbered) request
 * for the specified data_dir. Used to sweep back to the start of the disk
 * (1-way elevator) after we process the last (highest sector) request.
 */
static struct deadline_rq *
deadline_find_first_drq(struct deadline_data *dd, int data_dir)
{
        struct rb_node *n = dd->sort_list[data_dir].rb_node;

        for (;;) {
                if (n->rb_left == NULL)
                        return rb_entry_drq(n);
                
                n = n->rb_left;
        }
}

/*
 * add drq to rbtree and fifo
 */
static void
deadline_add_request(struct request_queue *q, struct request *rq)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        struct deadline_rq *drq = RQ_DATA(rq);

        const int data_dir = rq_data_dir(drq->request);

        deadline_add_drq_rb(dd, drq);
        /*
         * set expire time (only used for reads) and add to fifo list
         */
        drq->expires = jiffies + dd->fifo_expire[data_dir];
        list_add_tail(&drq->fifo, &dd->fifo_list[data_dir]);

        if (rq_mergeable(rq))
                deadline_add_drq_hash(dd, drq);
}

/*
 * remove rq from rbtree, fifo, and hash
 */
static void deadline_remove_request(request_queue_t *q, struct request *rq)
{
        struct deadline_rq *drq = RQ_DATA(rq);
        struct deadline_data *dd = q->elevator->elevator_data;

        list_del_init(&drq->fifo);
        deadline_del_drq_rb(dd, drq);
        deadline_del_drq_hash(drq);
}

static int
deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        struct request *__rq;
        int ret;

        /*
         * see if the merge hash can satisfy a back merge
         */
        __rq = deadline_find_drq_hash(dd, 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;
                }
        }

        /*
         * check for front merge
         */
        if (dd->front_merges) {
                sector_t rb_key = bio->bi_sector + bio_sectors(bio);

                __rq = deadline_find_drq_rb(dd, rb_key, bio_data_dir(bio));
                if (__rq) {
                        BUG_ON(rb_key != rq_rb_key(__rq));

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

        return ELEVATOR_NO_MERGE;
out:
        if (ret)
                deadline_hot_drq_hash(dd, RQ_DATA(__rq));
        *req = __rq;
        return ret;
}

static void deadline_merged_request(request_queue_t *q, struct request *req)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        struct deadline_rq *drq = RQ_DATA(req);

        /*
         * hash always needs to be repositioned, key is end sector
         */
        deadline_del_drq_hash(drq);
        deadline_add_drq_hash(dd, drq);

        /*
         * if the merge was a front merge, we need to reposition request
         */
        if (rq_rb_key(req) != drq->rb_key) {
                deadline_del_drq_rb(dd, drq);
                deadline_add_drq_rb(dd, drq);
        }
}

static void
deadline_merged_requests(request_queue_t *q, struct request *req,
                         struct request *next)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        struct deadline_rq *drq = RQ_DATA(req);
        struct deadline_rq *dnext = RQ_DATA(next);

        BUG_ON(!drq);
        BUG_ON(!dnext);

        /*
         * reposition drq (this is the merged request) in hash, and in rbtree
         * in case of a front merge
         */
        deadline_del_drq_hash(drq);
        deadline_add_drq_hash(dd, drq);

        if (rq_rb_key(req) != drq->rb_key) {
                deadline_del_drq_rb(dd, drq);
                deadline_add_drq_rb(dd, drq);
        }

        /*
         * if dnext expires before drq, assign its expire time to drq
         * and move into dnext position (dnext will be deleted) in fifo
         */
        if (!list_empty(&drq->fifo) && !list_empty(&dnext->fifo)) {
                if (time_before(dnext->expires, drq->expires)) {
                        list_move(&drq->fifo, &dnext->fifo);
                        drq->expires = dnext->expires;
                }
        }

        /*
         * kill knowledge of next, this one is a goner
         */
        deadline_remove_request(q, next);
}

/*
 * move request from sort list to dispatch queue.
 */
static inline void
deadline_move_to_dispatch(struct deadline_data *dd, struct deadline_rq *drq)
{
        request_queue_t *q = drq->request->q;

        deadline_remove_request(q, drq->request);
        elv_dispatch_add_tail(q, drq->request);
}

/*
 * move an entry to dispatch queue
 */
static void
deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq)
{
        const int data_dir = rq_data_dir(drq->request);
        struct rb_node *rbnext = rb_next(&drq->rb_node);

        dd->next_drq[READ] = NULL;
        dd->next_drq[WRITE] = NULL;

        if (rbnext)
                dd->next_drq[data_dir] = rb_entry_drq(rbnext);
        
        dd->last_sector = drq->request->sector + drq->request->nr_sectors;

        /*
         * take it off the sort and fifo list, move
         * to dispatch queue
         */
        deadline_move_to_dispatch(dd, drq);
}

#define list_entry_fifo(ptr)    list_entry((ptr), struct deadline_rq, fifo)

/*
 * deadline_check_fifo returns 0 if there are no expired reads on the fifo,
 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
 */
static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
{
        struct deadline_rq *drq = list_entry_fifo(dd->fifo_list[ddir].next);

        /*
         * drq is expired!
         */
        if (time_after(jiffies, drq->expires))
                return 1;

        return 0;
}

/*
 * deadline_dispatch_requests selects the best request according to
 * read/write expire, fifo_batch, etc
 */
static int deadline_dispatch_requests(request_queue_t *q, int force)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        const int reads = !list_empty(&dd->fifo_list[READ]);
        const int writes = !list_empty(&dd->fifo_list[WRITE]);
        struct deadline_rq *drq;
        int data_dir;

        /*
         * batches are currently reads XOR writes
         */
        if (dd->next_drq[WRITE])
                drq = dd->next_drq[WRITE];
        else
                drq = dd->next_drq[READ];

        if (drq) {
                /* we have a "next request" */
                
                if (dd->last_sector != drq->request->sector)
                        /* end the batch on a non sequential request */
                        dd->batching += dd->fifo_batch;
                
                if (dd->batching < dd->fifo_batch)
                        /* we are still entitled to batch */
                        goto dispatch_request;
        }

        /*
         * at this point we are not running a batch. select the appropriate
         * data direction (read / write)
         */

        if (reads) {
                BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));

                if (writes && (dd->starved++ >= dd->writes_starved))
                        goto dispatch_writes;

                data_dir = READ;

                goto dispatch_find_request;
        }

        /*
         * there are either no reads or writes have been starved
         */

        if (writes) {
dispatch_writes:
                BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));

                dd->starved = 0;

                data_dir = WRITE;

                goto dispatch_find_request;
        }

        return 0;

dispatch_find_request:
        /*
         * we are not running a batch, find best request for selected data_dir
         */
        if (deadline_check_fifo(dd, data_dir)) {
                /* An expired request exists - satisfy it */
                dd->batching = 0;
                drq = list_entry_fifo(dd->fifo_list[data_dir].next);
                
        } else if (dd->next_drq[data_dir]) {
                /*
                 * The last req was the same dir and we have a next request in
                 * sort order. No expired requests so continue on from here.
                 */
                drq = dd->next_drq[data_dir];
        } else {
                /*
                 * The last req was the other direction or we have run out of
                 * higher-sectored requests. Go back to the lowest sectored
                 * request (1 way elevator) and start a new batch.
                 */
                dd->batching = 0;
                drq = deadline_find_first_drq(dd, data_dir);
        }

dispatch_request:
        /*
         * drq is the selected appropriate request.
         */
        dd->batching++;
        deadline_move_request(dd, drq);

        return 1;
}

static int deadline_queue_empty(request_queue_t *q)
{
        struct deadline_data *dd = q->elevator->elevator_data;

        return list_empty(&dd->fifo_list[WRITE])
                && list_empty(&dd->fifo_list[READ]);
}

static struct request *
deadline_former_request(request_queue_t *q, struct request *rq)
{
        struct deadline_rq *drq = RQ_DATA(rq);
        struct rb_node *rbprev = rb_prev(&drq->rb_node);

        if (rbprev)
                return rb_entry_drq(rbprev)->request;

        return NULL;
}

static struct request *
deadline_latter_request(request_queue_t *q, struct request *rq)
{
        struct deadline_rq *drq = RQ_DATA(rq);
        struct rb_node *rbnext = rb_next(&drq->rb_node);

        if (rbnext)
                return rb_entry_drq(rbnext)->request;

        return NULL;
}

static void deadline_exit_queue(elevator_t *e)
{
        struct deadline_data *dd = e->elevator_data;

        BUG_ON(!list_empty(&dd->fifo_list[READ]));
        BUG_ON(!list_empty(&dd->fifo_list[WRITE]));

        mempool_destroy(dd->drq_pool);
        kfree(dd->hash);
        kfree(dd);
}

/*
 * initialize elevator private data (deadline_data), and alloc a drq for
 * each request on the free lists
 */
static void *deadline_init_queue(request_queue_t *q, elevator_t *e)
{
        struct deadline_data *dd;
        int i;

        if (!drq_pool)
                return NULL;

        dd = kmalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
        if (!dd)
                return NULL;
        memset(dd, 0, sizeof(*dd));

        dd->hash = kmalloc_node(sizeof(struct hlist_head)*DL_HASH_ENTRIES,
                                GFP_KERNEL, q->node);
        if (!dd->hash) {
                kfree(dd);
                return NULL;
        }

        dd->drq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
                                        mempool_free_slab, drq_pool, q->node);
        if (!dd->drq_pool) {
                kfree(dd->hash);
                kfree(dd);
                return NULL;
        }

        for (i = 0; i < DL_HASH_ENTRIES; i++)
                INIT_HLIST_HEAD(&dd->hash[i]);

        INIT_LIST_HEAD(&dd->fifo_list[READ]);
        INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
        dd->sort_list[READ] = RB_ROOT;
        dd->sort_list[WRITE] = RB_ROOT;
        dd->fifo_expire[READ] = read_expire;
        dd->fifo_expire[WRITE] = write_expire;
        dd->writes_starved = writes_starved;
        dd->front_merges = 1;
        dd->fifo_batch = fifo_batch;
        return dd;
}

static void deadline_put_request(request_queue_t *q, struct request *rq)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        struct deadline_rq *drq = RQ_DATA(rq);

        mempool_free(drq, dd->drq_pool);
        rq->elevator_private = NULL;
}

static int
deadline_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
                     gfp_t gfp_mask)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        struct deadline_rq *drq;

        drq = mempool_alloc(dd->drq_pool, gfp_mask);
        if (drq) {
                memset(drq, 0, sizeof(*drq));
                RB_CLEAR_NODE(&drq->rb_node);
                drq->request = rq;

                INIT_HLIST_NODE(&drq->hash);

                INIT_LIST_HEAD(&drq->fifo);

                rq->elevator_private = drq;
                return 0;
        }

        return 1;
}

/*
 * sysfs parts below
 */

static ssize_t
deadline_var_show(int var, char *page)
{
        return sprintf(page, "%d\n", var);
}

static ssize_t
deadline_var_store(int *var, const char *page, size_t count)
{
        char *p = (char *) page;

        *var = simple_strtol(p, &p, 10);
        return count;
}

#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
static ssize_t __FUNC(elevator_t *e, char *page)                        \
{                                                                       \
        struct deadline_data *dd = e->elevator_data;                    \
        int __data = __VAR;                                             \
        if (__CONV)                                                     \
                __data = jiffies_to_msecs(__data);                      \
        return deadline_var_show(__data, (page));                       \
}
SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
static ssize_t __FUNC(elevator_t *e, const char *page, size_t count)    \
{                                                                       \
        struct deadline_data *dd = e->elevator_data;                    \
        int __data;                                                     \
        int ret = deadline_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(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
#undef STORE_FUNCTION

#define DD_ATTR(name) \
        __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
                                      deadline_##name##_store)

static struct elv_fs_entry deadline_attrs[] = {
        DD_ATTR(read_expire),
        DD_ATTR(write_expire),
        DD_ATTR(writes_starved),
        DD_ATTR(front_merges),
        DD_ATTR(fifo_batch),
        __ATTR_NULL
};

static struct elevator_type iosched_deadline = {
        .ops = {
                .elevator_merge_fn =            deadline_merge,
                .elevator_merged_fn =           deadline_merged_request,
                .elevator_merge_req_fn =        deadline_merged_requests,
                .elevator_dispatch_fn =         deadline_dispatch_requests,
                .elevator_add_req_fn =          deadline_add_request,
                .elevator_queue_empty_fn =      deadline_queue_empty,
                .elevator_former_req_fn =       deadline_former_request,
                .elevator_latter_req_fn =       deadline_latter_request,
                .elevator_set_req_fn =          deadline_set_request,
                .elevator_put_req_fn =          deadline_put_request,
                .elevator_init_fn =             deadline_init_queue,
                .elevator_exit_fn =             deadline_exit_queue,
        },

        .elevator_attrs = deadline_attrs,
        .elevator_name = "deadline",
        .elevator_owner = THIS_MODULE,
};

static int __init deadline_init(void)
{
        int ret;

        drq_pool = kmem_cache_create("deadline_drq", sizeof(struct deadline_rq),
                                     0, 0, NULL, NULL);

        if (!drq_pool)
                return -ENOMEM;

        ret = elv_register(&iosched_deadline);
        if (ret)
                kmem_cache_destroy(drq_pool);

        return ret;
}

static void __exit deadline_exit(void)
{
        kmem_cache_destroy(drq_pool);
        elv_unregister(&iosched_deadline);
}

module_init(deadline_init);
module_exit(deadline_exit);

MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("deadline IO scheduler");