procfs信息读取实现案例

 

/**********************************************
 * Author: lewiyon@hotmail.com
 * File name: proc_sample.c
 * Description: create a file "proc_example" in the /proc, 
 *              which allows read.
 * Date: 2011-12-11
 * Version: V1.0
 *********************************************/

#include <linux/kernel.h>	/* We're doing kernel work */
#include <linux/module.h>	/* Specifically, a module */
#include <linux/proc_fs.h>	/* Necessary because we use proc fs */
#include <asm/uaccess.h>	/* for get_user and put_user */

#define MESSAGE_LENGTH 80
#define PROC_NAME "proc_sample"

unsigned int flag = 100; 

static struct proc_dir_entry *proc_sample;
static struct proc_dir_entry *sample, *sample_r;

/**
 * proc_read_data()
 * @page - buffer to write the data in
 * @start - where the actual data has been written in page
 * @offset - same meaning as the read system call
 * @count - same meaning as the read system call
 * @eof - set if no more data needs to be returned
 * @data - pointer to our soft state
 */
static int proc_read_data(char *page, char **stat, off_t off,
                          int count, int *eof, void *data)
{
    int len;
    len = sprintf(page, "jiffies = %ld\n", jiffies);
    return len;
}

/* 
 * 模块初始化 
 */
static int __init sample_init(void)
{	
    int ret = 0;
    
    /*
     * proc_mkdir(name, parent)
     * 在parent对应的目录下创建name目录
     * 返回目录对应的proc_dir_dentry
     */
    proc_sample = proc_mkdir(PROC_NAME, NULL);	
    if (NULL == proc_sample) {
        ret = -ENOMEM;	
        goto proc_sample_err;
    }
    /*
     * create_proc_entry(name, mode,parent)
     * 在parent对应的目录下创建name文件
     * 返回目录对应的proc_dir_dentry
     */
    sample = create_proc_entry("sample", 0644, proc_sample);	
    if (NULL == sample) {
        ret = -ENOMEM;	
        goto sample_err;
    }
    
    sample_r = create_proc_read_entry("sample_r", 0444, 
                proc_sample, proc_read_data, NULL);	
    if (NULL == sample_r) {
        ret = -ENOMEM;	
        goto sample_r_err;
    }

    printk(KERN_INFO "Create sample\n"); 
    return ret;

sample_r_err:
    remove_proc_entry("sample", proc_sample);
sample_err:
    remove_proc_entry(PROC_NAME, NULL);
proc_sample_err:
    return ret;
}

/*
 * 模块清理
 */
static void __exit sample_exit(void)
{
    remove_proc_entry("sample", proc_sample);
    remove_proc_entry("sample_r", proc_sample);
    remove_proc_entry(PROC_NAME, NULL);
    printk(KERN_INFO "Remove /proc/proc_sample\n");
}

module_init(sample_init);
module_exit(sample_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("lewiyon <lewiyon@hotmail.com>");

在/proc/创建文件目录proc_sampe，然后在其下创建了两个文件。其中sample_r可读取数据