2.6驱动程序-字符驱动

/*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.o

else

KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

default:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

endif