/*

   *  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 *);

  static inline struct rb_root *
  deadline_rb_root(struct deadline_data *dd, struct request *rq)
  {
  	return &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 = deadline_rb_root(dd, rq);

  	elv_rb_add(root, rq);

  }
  
  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(deadline_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 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 != blk_rq_pos(__rq));

  
  			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(deadline_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_end_sector(rq);

  
  	/*
  	 * 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 requests 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 && dd->batching < dd->fifo_batch)
  		/* we have a next request 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 void deadline_exit_queue(struct elevator_queue *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
  ", 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(struct elevator_queue *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(struct elevator_queue *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_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");