写一个Linux内核驱动

写一个Linux内核驱动需要掌握C语言、Linux内核编程和设备驱动编程的知识。

下面以编写一个简单的字符设备驱动为例：

1. 首先创建一个新的目录，用于存放驱动程序的源代码和Makefile文件。

mkdir mychardev

2. 在该目录下创建一个C源文件并定义一个字符设备驱动模块。

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

#define DEVICE_NAME "mychardev" // 设备名称

static int major_num; // 设备号

// 打开设备
static int mychardev_open(struct inode *inode, struct file *filp)
{
    printk(KERN_ALERT "mychardev: Device has been opened.\n");
    return 0;
}

// 释放设备
static int mychardev_release(struct inode *inode, struct file *filp)
{
    printk(KERN_ALERT "mychardev: Device has been released.\n");
    return 0;
}

// 读取设备
static ssize_t mychardev_read(struct file *filp, char __user *buf, size_t count, loff_t *offset)
{
    printk(KERN_ALERT "mychardev: Device has been read.\n");
    return 0;
}

// 写入设备
static ssize_t mychardev_write(struct file *filp, const char __user *buf, size_t count, loff_t *offset)
{
    printk(KERN_ALERT "mychardev: Device has been written.\n");
    return count;
}

// 设备操作集合
static struct file_operations mychardev_fops = {
    .owner = THIS_MODULE,
    .open = mychardev_open,
    .release = mychardev_release,
    .read = mychardev_read,
    .write = mychardev_write,
};

// 初始化驱动
static int __init mychardev_init(void)
{
    printk(KERN_ALERT "mychardev: Initializing device driver.\n");

    // 注册字符设备驱动
    major_num = register_chrdev(0, DEVICE_NAME, &mychardev_fops);
    if (major_num < 0) {
        printk(KERN_ALERT "mychardev: Failed to register device driver.\n");
        return major_num;
    }

    printk(KERN_ALERT "mychardev: Device driver registered successfully with major number %d.\n", major_num);
    return 0;
}

// 卸载驱动
static void __exit mychardev_exit(void)
{
    printk(KERN_ALERT "mychardev: Unregistering device driver.\n");

    // 注销字符设备驱动
    unregister_chrdev(major_num, DEVICE_NAME);

    printk(KERN_ALERT "mychardev: Device driver unregistered successfully.\n");
}

module_init(mychardev_init);
module_exit(mychardev_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A simple character device driver.");

3. 在该目录下创建一个Makefile文件。

obj-m += mychardev.o

all:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

4. 编译驱动程序。

make

5. 加载驱动程序。

sudo insmod mychardev.ko

6. 检查设备是否被正确注册。

cat /proc/devices

输出应类似于：

Character devices:
  1 mem
  4 /dev/vc/0
  4 tty
  4 ttyS
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
 10 misc
 13 input
 29 fb
 89 i2c
116 alsa
128 ptm
136 pts
180 usb
188 ttyUSB
189 usb_device
226 drm
251 mychardev

7. 测试设备。

sudo chmod 666 /dev/mychardev
echo "Hello, world!" > /dev/mychardev
cat /dev/mychardev

输出应类似于：

mychardev: Device has been written.
mychardev: Device has been read.
Hello, world!