编写字符设备驱动程序

编写字符设备驱动程序需要以下步骤：

1. 创建设备文件：
在/dev目录下创建设备文件，使用mknod命令或者调用系统函数makedev()来创建设备文件。

2. 定义设备结构体：
定义一个结构体来描述设备的属性，包括设备号、设备名称、设备操作函数等。

3. 初始化设备结构体：
在设备结构体中初始化设备的属性，例如设备名称、设备号、设备操作函数等。

4. 实现设备操作函数：
设备操作函数包括打开设备、关闭设备、读取设备和写入设备等。

5. 注册字符设备驱动：
通过调用系统函数register_chrdev()来注册字符设备驱动。

6. 卸载字符设备驱动：
通过调用系统函数unregister_chrdev()来卸载字符设备驱动。

以下是一个简单的字符设备驱动程序示例：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>

#define DEVICE_NAME "my_device"
#define BUFFER_SIZE 1024

static char device_buffer[BUFFER_SIZE];
static dev_t dev_num;
static struct cdev *driver_object;
static struct class *device_class;

static int driver_open(struct inode *gerbe, struct file *filep)
{
    printk(KERN_INFO "Driver: open()\n");
    return 0;
}

static int driver_close(struct inode *gerbe, struct file *filep)
{
    printk(KERN_INFO "Driver: close()\n");
    return 0;
}

static ssize_t driver_read(struct file *filep, char *buffer, size_t len, loff_t *offset)
{
    int bytes_read = 0;
    printk(KERN_INFO "Driver: read()\n");

    if (*offset >= BUFFER_SIZE)
        return 0;

    if (*offset + len > BUFFER_SIZE)
        len = BUFFER_SIZE - *offset;

    bytes_read = copy_to_user(buffer, device_buffer + *offset, len);
    *offset += len - bytes_read;
    return len - bytes_read;
}

static ssize_t driver_write(struct file *filep, const char *buffer, size_t len, loff_t *offset)
{
    int bytes_write = 0;
    printk(KERN_INFO "Driver: write()\n");

    if (*offset >= BUFFER_SIZE)
        return -ENOSPC;

    if (*offset + len > BUFFER_SIZE)
        len = BUFFER_SIZE - *offset;

    bytes_write = copy_from_user(device_buffer + *offset, buffer, len);
    *offset += len - bytes_write;
    return len - bytes_write;
}

static struct file_operations fops = {
    .owner = THIS_MODULE,
    .open = driver_open,
    .release = driver_close,
    .read = driver_read,
    .write = driver_write,
};

static int __init driver_init(void)
{
    int ret;
    printk(KERN_INFO "Driver: initialization started\n");

    ret = alloc_chrdev_region(&dev_num, 0, 1, DEVICE_NAME);
    if (ret < 0) {
        printk(KERN_ALERT "Driver: failed to allocate major number\n");
        return ret;
    }

    driver_object = cdev_alloc();
    if (driver_object == NULL) {
        printk(KERN_ALERT "Driver: failed to allocate cdev object\n");
        unregister_chrdev_region(dev_num, 1);
        return -ENOMEM;
    }

    driver_object->ops = &fops;
    ret = cdev_add(driver_object, dev_num, 1);
    if (ret < 0) {
        printk(KERN_ALERT "Driver: failed to add character device\n");
        cdev_del(driver_object);
        unregister_chrdev_region(dev_num, 1);
        return ret;
    }

    device_class = class_create(THIS_MODULE, DEVICE_NAME);
    if (IS_ERR(device_class)) {
        printk(KERN_ALERT "Driver: failed to create device class\n");
        cdev_del(driver_object);
        unregister_chrdev_region(dev_num, 1);
        return PTR_ERR(device_class);
    }

    device_create(device_class, NULL, dev_num, NULL, DEVICE_NAME);
    printk(KERN_INFO "Driver: initialization completed\n");
    return 0;
}

static void __exit driver_exit(void)
{
    printk(KERN_INFO "Driver: exiting\n");
    device_destroy(device_class, dev_num);
    class_destroy(device_class);
    cdev_del(driver_object);
    unregister_chrdev_region(dev_num, 1);
}

module_init(driver_init);
module_exit(driver_exit);
MODULE_LICENSE("GPL");

这是一个非常简单的字符设备驱动程序示例，它创建一个名为“my_device”的设备，并实现了打开、关闭、读取和写入设备操作。