Simplest character device driver

1.A device node needs to be created first

mknod /dev/xxx c 111 0

创建一个名字为xxx的字符设备, c表示字符设备, 主设备号是111, This device number is0.

2. 驱动程序

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/module.h>

static int first_drv_open(struct inode *inodep, struct file *filep)
{
    
    printk("open\n");
    return 0;
}

static ssize_t first_drv_write(struct file *filep, const char __user *buf,size_t len, loff_t *ppos)
{
    
    printk("write\n");
    return 0;
}

static const struct file_operations first_drv_file_operation = {
    
    .owner = THIS_MODULE,
    .open = first_drv_open,
    .write = first_drv_write,
};

static int __init first_drv_init(void)
{
    
    register_chrdev(111,"first_drv", &first_drv_file_operation);
    printk("first_drv_init\n");
    return 0;
}

static void __exit first_drv_exit(void)
{
    
    //注册字符设备 主设备号是111.Since the device number is not specified by our driver,默认是0.
    unregister_chrdev(111,"first_drv_exit"); 
    printk("first_drv_exit\n");
}

module_init(first_drv_init);
module_exit(first_drv_exit);
MODULE_LICENSE("GPL");

3. 应用程序,调用驱动程序

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(void)
{
    
    char buf[10];
    /* 以可读可写方式打开/dev/目录下的xxx设备,open的返回值是一个文件描述符 */
    int fd = open("/dev/xxx", O_RDWR);    
    if(fd < 0)        /* 文件描述符小于0表示打开文件失败 */
    {
       
        printf("open /dev/xxx fail\n");
        return -1; 
    }   
 
    /* written in this file5个字节,写入的内容是bufthe first five bytes in  */
    write(fd, buf, 5); 
    
    return 0;
}

4.测试效果

The test effect needs to be usedsudo dmesg来查看. 如下图所示: