/*chardev.c*/#include <linux/kernel.h>#include <linux/fs.h>/*for file-f_op*/#include <linux/module.h>#include <asm/uaccess.h>/*for copy_to_user()*/#include <linux/cdev.h>/*for cdev ,cdev_init,cdev_add....*/MODULE_LICENSE("GPL");#define DP_MAJOR 250  /*the major number of the chardev*/#define DP_MINOR 0    /*the minor number of the chardev*/static int char_read(struct file *filp, char __user *buffer, size_t, loff_t *);/*the read operation of the chardev----read the data from kernel*/static int char_open(struct inode *,struct file *);/*open the chardev*/static int char_write(struct file *filp, const char __user *buffer, size_t, loff_t *);/*write data to kernel*/static int char_release(struct inode *, struct file *);/*release the chardev*/static int chropen;/*the chardev open or not*/struct cdev *chardev;/*define a char device*/static int len; static const struct file_operations char_ops = {　　.owner = THIS_MODULE,    .read = char_read,    .write = char_write,    .open = char_open,    .release = char_release,}; static int __init char_init(void){    dev_t dev;    printk(KERN_ALERT"Initing......\n");    dev=MKDEV(DP_MAJOR,DP_MINOR);    chardev = cdev_alloc( );     if(chardev==NULL)    {        return -1;    }    if(register_chrdev_region(dev,10,"chardev"))//注册设备号       {        printk(KERN_ALERT"Register char dev error\n");        return -1;    }    chropen=0;    len=0;    cdev_init(chardev,&char_ops);//初始化cdev    if(cdev_add(chardev,dev,1))//添加cdev到系统    {        printk(KERN_ALERT"Add char dev error\n");    }     return 0;} static int char_open(struct inode *inode, struct file *file){    if(chropen==0)    {        chropen++;    }    else    {        printk(KERN_ALERT"Another process open the char device\n");        return -1;    }    try_module_get(THIS_MODULE);    return 0;} static int char_release(struct inode *inode, struct file *file){    chropen--;    module_put(THIS_MODULE);    return 0;} static int char_read(struct file *filp, char __user *buffer, size_t length, loff_t *offset){    if(length<12)    {        if(!copy_to_user(buffer,"hello world!",length))        {            return 0;        }    }    else    {        if(!copy_to_user(buffer,"hello world!",strlen("hello world!")))        {            return 0;        }    }    return -1;} static int char_write(struct file *filp, const char __user  *buffer, size_t length, loff_t *offset){    return 0;} static void __exit module_close(void){    len=0;    printk(KERN_ALERT"Unloading..........\n");         unregister_chrdev_region(MKDEV(DP_MAJOR,DP_MINOR),10);//注销cdev设备号    cdev_del(chardev);//从系统删除设备cdev} module_init(char_init);module_exit(module_close);

/*main.c*/#include <stdio.h>#include <stdlib.h>#include <sys/types.h>#include <sys/stat.h>#include <unistd.h>#include <fcntl.h>#include <string.h>  int main(void){int testdev;int i,rf=0;char buf[15]; memset(buf, 0, sizeof(buf));testdev = open("/dev/chardev0",O_RDWR);if ( testdev == -1 ){perror("open\n");exit(0);} rf=read(testdev,buf,12);if(rf<0)perror("read error\n");printf("R:%s\n",buf);close(testdev);return 0;}

ifneq ($(KERNELRELEASE),)obj-m := chardev.oelseKERNELDIR ?= /lib/modules/$(shell uname -r)/buildPWD := $(shell pwd)default:    $(MAKE) -C $(KERNELDIR) M=$(PWD) modulesendif