seq_file应用

　　seq_file接口，在kernel 2.6中将代替老的proc接口

　　seq_file接口的实现，引入了对象、迭代子等概念，这类似于C++中的泛型技术

　　如果对泛型技术有一定的了解，则会对seq_file接口的理解有一定的帮助

　　下面是原文的实例代码，略作注释：

/*

* Simple demonstration of the seq_file interface.

*

* $Id: seq.c,v 1.1 2003/02/10 21:02:02 corbet Exp $

*/

#include

#include

#include

#include

#include

#include

MODULE_AUTHOR("Jonathan Corbet");

MODULE_LICENSE("Dual BSD/GPL");

/* 使用seq_file接口，需要实现4个函数：start()、next()、stop()、show()，这4个函数用于对设备的输出信息的迭代访问（控制）*/

/*

* The sequence iterator functions. We simply use the count of the

* next line as our internal position.

*/

/*start()函数，用于设置访问设备的起始位置；本示例的设备位置的含义与proc文件的偏移量相同；返回值作为迭代子*/

static void *ct_seq_start(struct seq_file *s, loff_t *pos)

{

loff_t *spos = kmalloc(sizeof(loff_t), GFP_KERNEL);

if (! spos)

　return NULL;

*spos = *pos;

return spos;

}

/*next()函数，用于实现迭代子的访问步长，本示例的步长是偏移量递加，每次加1；返回值是新的迭代子*/

static void *ct_seq_next(struct seq_file *s, void *v, loff_t *pos)

{

loff_t *spos = (loff_t *) v;

*pos = ++(*spos);

return spos;

}

/*stop()函数，完成一些清理函数*/

static void ct_seq_stop(struct seq_file *s, void *v)

{

kfree (v);

}

/*

* The show function.

*/

/*show()函数，用于向proc文件输出设备需要输出的信息；本示例中仅输出迭代子的序列号*/

static int ct_seq_show(struct seq_file *s, void *v)

{

loff_t *spos = (loff_t *) v;

seq_printf(s, "%Ldn", *spos);

return 0;

}

/*

* Tie them all together into a set of seq_operations.

*/

/*seq_file接口的函数操作集*/

static struct seq_operations ct_seq_ops = {

.start = ct_seq_start,

.next = ct_seq_next,

.stop = ct_seq_stop,

.show = ct_seq_show

};

/*

* Time to set up the file operations for our /proc file. In this case,

* all we need is an open function which sets up the sequence ops.

*/

/*proc接口的open方法实现，open()函数将proc文件与seq_file接口的函数操作集关联起来*/

static int ct_open(struct inode *inode, struct file *file)

{

return seq_open(file, &ct_seq_ops);

};

/*

* The file operations structure contains our open function along with

* set of the canned seq_ ops.

*/

/*proc接口的函数操作集，除open方法外，其他方法不需要实现，已经由seq_file的内部代码实现完毕*/

static struct file_operations ct_file_ops = {

.owner = THIS_MODULE,

.open = ct_open,

.read = seq_read,

.llseek = seq_lseek,

.release = seq_release

};

/*

* Module setup and teardown.

*/

/*模块初始化，创建proc文件*/

static int ct_init(void)

{

struct proc_dir_entry *entry;

entry = create_proc_entry("sequence", 0, NULL);

if (entry)

　entry->proc_fops = &ct_file_ops;

return 0;

}

/*模块注销，删除所创建的proc文件*/

static void ct_exit(void)

{

remove_proc_entry("sequence", NULL);

}

module_init(ct_init);

module_exit(ct_exit);