/*
 *  Deadline i/o scheduler.
 *
 *  Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
 */
#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/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. */

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 request *next_rq[2];
        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;
};

static void deadline_move_request(struct deadline_data *, struct request *);

#define RQ_RB_ROOT(dd, rq)      (&(dd)->sort_list[rq_data_dir((rq))])

/*
 * get the request after `rq' in sector-sorted order
 */
static inline struct request *
deadline_latter_request(struct request *rq)
{
        struct rb_node *node = rb_next(&rq->rb_node);

        if (node)
                return rb_entry_rq(node);

        return NULL;
}

static void
deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
{
        struct rb_root *root = RQ_RB_ROOT(dd, rq);
        struct request *__alias;

retry:
        __alias = elv_rb_add(root, rq);
        if (unlikely(__alias)) {
                deadline_move_request(dd, __alias);
                goto retry;
        }
}

static inline void
deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
{
        const int data_dir = rq_data_dir(rq);

        if (dd->next_rq[data_dir] == rq)
                dd->next_rq[data_dir] = deadline_latter_request(rq);

        elv_rb_del(RQ_RB_ROOT(dd, rq), rq);
}

/*
 * add rq to rbtree and fifo
 */
static void
deadline_add_request(struct request_queue *q, struct request *rq)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        const int data_dir = rq_data_dir(rq);

        deadline_add_rq_rb(dd, rq);

        /*
         * set expire time (only used for reads) and add to fifo list
         */
        rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
        list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
}

/*
 * remove rq from rbtree and fifo.
 */
static void deadline_remove_request(struct request_queue *q, struct request *rq)
{
        struct deadline_data *dd = q->elevator->elevator_data;

        rq_fifo_clear(rq);
        deadline_del_rq_rb(dd, rq);
}

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

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

                __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
                if (__rq) {
                        BUG_ON(sector != __rq->sector);

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

        return ELEVATOR_NO_MERGE;
out:
        *req = __rq;
        return ret;
}

static void deadline_merged_request(struct request_queue *q,
                                    struct request *req, int type)
{
        struct deadline_data *dd = q->elevator->elevator_data;

        /*
         * if the merge was a front merge, we need to reposition request
         */
        if (type == ELEVATOR_FRONT_MERGE) {
                elv_rb_del(RQ_RB_ROOT(dd, req), req);
                deadline_add_rq_rb(dd, req);
        }
}

static void
deadline_merged_requests(struct request_queue *q, struct request *req,
                         struct request *next)
{
        /*
         * if next expires before rq, assign its expire time to rq
         * and move into next position (next will be deleted) in fifo
         */
        if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
                if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
                        list_move(&req->queuelist, &next->queuelist);
                        rq_set_fifo_time(req, rq_fifo_time(next));
                }
        }

        /*
         * 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 request *rq)
{
        struct request_queue *q = rq->q;

        deadline_remove_request(q, rq);
        elv_dispatch_add_tail(q, rq);
}

/*
 * move an entry to dispatch queue
 */
static void
deadline_move_request(struct deadline_data *dd, struct request *rq)
{
        const int data_dir = rq_data_dir(rq);

        dd->next_rq[READ] = NULL;
        dd->next_rq[WRITE] = NULL;
        dd->next_rq[data_dir] = deadline_latter_request(rq);

        dd->last_sector = rq->sector + rq->nr_sectors;

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

/*
 * 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 request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);

        /*
         * rq is expired!
         */
        if (time_after(jiffies, rq_fifo_time(rq)))
                return 1;

        return 0;
}

/*
 * deadline_dispatch_requests selects the best request according to
 * read/write expire, fifo_batch, etc
 */
static int deadline_dispatch_requests(struct request_queue *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 request *rq;
        int data_dir;

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

        if (rq) {
                /* we have a "next request" */
                
                if (dd->last_sector != rq->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) || !dd->next_rq[data_dir]) {
                /*
                 * A deadline has expired, the last request was in the other
                 * direction, or we have run out of higher-sectored requests.
                 * Start again from the request with the earliest expiry time.
                 */
                rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
        } else {
                /*
                 * The last req was the same dir and we have a next request in
                 * sort order. No expired requests so continue on from here.
                 */
                rq = dd->next_rq[data_dir];
        }

        dd->batching = 0;

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

        return 1;
}

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

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

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]));

        kfree(dd);
}

/*
 * initialize elevator private data (deadline_data).
 */
static void *deadline_init_queue(struct request_queue *q)
{
        struct deadline_data *dd;

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

        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;
}

/*
 * 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 =       elv_rb_former_request,
                .elevator_latter_req_fn =       elv_rb_latter_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)
{
        elv_register(&iosched_deadline);

        return 0;
}

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

module_init(deadline_init);
module_exit(deadline_exit);

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