Linux deadline io 调度算法

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, 
};

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; 
}; 

/* 
* 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]); 
}

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_end_sector(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; 
}

if (__rq) 
{ 
BUG_ON(sector != blk_rq_pos(__rq)); 
if (elv_rq_merge_ok(__rq, bio)) 
{ 
ret = ELEVATOR_FRONT_MERGE; 
goto out; 
} 
}

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); 
}

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; 
}

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; 

const int reads = !list_empty(&dd->fifo_list[READ]); 
const int writes = !list_empty(&dd->fifo_list[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; 
} 

if (writes) 
{ 
dispatch_writes: 
BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE])); 
dd->starved = 0; 
data_dir = WRITE; 
goto dispatch_find_request; 
} 

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_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); 
} 

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 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); 
}

/* 
* 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; 

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];	//按照请求的起始地址，将请求在红黑树中排序
	struct list_head fifo_list[2];//按照请求超时的先后顺序，将请求在链表中排序

	/*
	 * next in sort order. read, write or both are NULL
	 */
	struct request *next_rq[2];//指向 sort_list 中的下一个请求
	/* 当前连续提交的请求数目，只要小于fifo_batch就可以进行连续提交 */
	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];//可以设置读写请求的超时时间
	int fifo_batch;//在一次读/写请求处理方向上，最多可连续提交的请求数
	int writes_starved;//读请求最多可饥饿写请求的次数
	int front_merges;//是否开启前向merge，根据文件的一般访问模式，前向merge的效果不是很好
};

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);
	/*
	struct request结构中内嵌一个struct rb_node(这也正是红黑树的使用模式)
	通过获取rb_node的地址+rb_node在request中的偏移地址来获取request的地址
	*/
	return NULL;
}

static void
deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
{
	struct rb_root *root = deadline_rb_root(dd, rq);//根据请求rq的读写方向，获取相应读写请求红黑树的根结点
	struct request *__alias;
	
	/*
	将请求rq插入相应的读写请求红黑树
	注意:插入成功才返回NULL，插入不成功，说明该请求原本就存在
	如果该请求原本就存在，就需要将该请求从io调度队列分发到块设备的dispatch队列
	*/
	while (unlikely(__alias = elv_rb_add(root, rq)))
		deadline_move_request(dd, __alias);
}

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

	/*
	如果待删除的请求是next_rq请求队列中的第一个请求，
	就需要将next_rq请求队列中的第一个请求设置为待删除请求的下一个请求，再执行删除请求操作，
	否则，直接删除该请求
	*/
	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;//获取请求的io调度队列
	const int data_dir = rq_data_dir(rq);//判断请求的读写类型

	deadline_add_rq_rb(dd, rq);
	/*
	1、请求原本存存在于调度队列中
	根据请求类型(读or写)，将请求插入调度队列相应的读写红黑树中
	2、请求原本存在于调度队列中
	将请求从调度队列发往块设备的请求队列
	*/

	/*
	 * set expire time and add to fifo list
	 */
	rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);//设置请求的超时时间
	list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);//将请求加入调度队列的fifo队列中
}

/*
 * 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;//获取请求的调度队列

	rq_fifo_clear(rq);//将请求从调度队列的fifo_list队列中删除
	deadline_del_rq_rb(dd, rq);//将请求从调度队列的红黑树中删除
}

/*
	该deadline_merge函数中试图将bio插入到请求的链表头。????????????????????????????
	在该函数中通过elv_rb_find函数在读写的排序队列sort_list中（通过红黑二叉树来实现）
	查找可以把bio插入到请求的链表头的req，
	（这里只是找到可以插入的req，究竟bio是否可以插入到此req中是在执行插入的时候才做判断）
	如果找到，则返回ELEVATOR_FRONT_MERGE，否则返回ELEVATOR_NO_MERGE。
*/
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) {//判断是否执行前向merge操作
		sector_t sector = bio->bi_sector + bio_sectors(bio);
		//通过bio请求的起始地址 + bio请求的长度 获取bio请求的结束地址
		__rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
		/*
		通过elv_rb_find()函数判断是否存在与该bio请求连续的请求:
		1、返回值为NULL，说明不存在前向连续的请求
		2、返回值不为NULL，说明存在前向连续的请求，有进行合并操作的可能性，并返回指向与bio请求连续的请求的指针
		*/
		if (__rq) {
			BUG_ON(sector != blk_rq_pos(__rq));

			if (elv_rq_merge_ok(__rq, bio)) {//判断是否可以对该request安全的进行merge操作
				ret = ELEVATOR_FRONT_MERGE;//可以进行前向merge操作
				goto out;
			}
		}
	}

	return ELEVATOR_NO_MERGE;
	/*
	返回ELEVATOR_NO_MERGE有三种情况:
	1、front_merges被设置为0
	2、front_merges被设置为1，但是不存在与bio连续的request
	3、front_merges被设置为1，也存在与bio连续的request，但是不能针对该request进行merge操作
	*/
out:
	*req = __rq;//将执行merge操作的request
	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) {
		/*
		如果做了一个前向merge，需要将那个request先删除，然后又插入,
		是为了继续进行有可能的前向merge。
		*/
		elv_rb_del(deadline_rb_root(dd, req), req);
		deadline_add_rq_rb(dd, req);
	}
}

//删除合并之后的另一个请求next
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);//将请求从deadline调度器的sort_list 和 fifo_list中删除
	elv_dispatch_add_tail(q, rq);//将请求加入块设备的请求队列的尾部
}

/*
 * 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])
 */

//判断fifo_list中的第一个请求是否超时
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)//存在请求，并且连续提交的请求数没有超过上限，可以继续分发请求
		/* 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) {//存在读请求，优先处理读请求
		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));

		if (writes && (dd->starved++ >= dd->writes_starved))
			//如果存在写请求，并且饥饿写请求的次数已达上限，就需要分发写请求
			goto dispatch_writes;

		data_dir = READ;

		goto dispatch_find_request;
	}

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

	if (writes) {//没有读请求，或者写请求被饥饿的次数已达上限，就要处理写请求
dispatch_writes:
		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));

		dd->starved = 0;//进行一次写请求处理之后，就需要重新设置写请求被饥饿的次数为0

		data_dir = WRITE;

		goto dispatch_find_request;
	}

	return 0;//如果既没有读请求，又没有写请求，就返回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]) {
		/*
		如果本次处理方向的fifo_list中有超时请求，或者本次处理方向扫描到电梯尾，
		都会返回来处理等待最久的request，并从这个request开始继续进行电梯扫描
		*/
		/*
		 * 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 {
		/*
		如果既没有发生超时，也没有扫描到电梯末尾，
		则沿sector递增方向上的下一个request就是当前要处理的request
		*/
		/*
		 * 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;//进行一次处理之后，需要重新设置batching值

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

	return 1;
}

//判断deadline调度器中是否存在请求
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(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\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(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_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);//注册一个调度器类型

	return 0;
}

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

module_init(deadline_init);
module_exit(deadline_exit);