2.6驱动移植系列之support_interfaces(2)-seq_fi..

/*
 * Simple demonstration of the seq_file interface.
 *
 * $Id: seq.c,v 1.1 2003/02/10 21:02:02 corbet Exp $
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/slab.h>

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, "%Ld\n", *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);