第三章里面，我们使用mknod创建设备节点，常规操作是在驱动init的时候就创建好，使用class_create和device_create创建。

#include "asm/uaccess.h"
#include "linux/scatterlist.h"
#include "linux/types.h"
#include <linux/mm.h>
#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mman.h>
#include <linux/random.h>
#include <linux/init.h>
#include <linux/raw.h>
#include <linux/tty.h>
#include <linux/capability.h>
#include <linux/ptrace.h>
#include <linux/device.h>
#include <linux/highmem.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/splice.h>
#include <linux/pfn.h>
#include <linux/export.h>
#include <linux/io.h>
#include <linux/uio.h>
#include <linux/module.h>#include <linux/uaccess.h>#define DEVICE_NAME "hello_device"
static struct class *hello_class;
static struct device *hello_device;
static int major;
#define hello_buf_size 100
static unsigned char hello_buf[hello_buf_size];//ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
//参数含义依次为 要读取的文件指针 用户保存数据的buf 读取数据大小 文件内容的偏移量
static ssize_t hello_read (struct file * filp, char __user *buf, size_t size, loff_t *offset)
{unsigned long len = size > hello_buf_size ? hello_buf_size : size;unsigned long ret = copy_to_user(buf, hello_buf, len);printk("%s %s %d ret = %ld\n", __FILE__, __FUNCTION__, __LINE__, ret);return len;
}//ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
//参数含义依次为 要写入的文件指针 用户要写入的数据buf 写入数据大小 文件内容的偏移量
static ssize_t hello_write (struct file *filp, const char __user *buf, size_t size, loff_t *offset)
{unsigned long len = size > hello_buf_size ? hello_buf_size : size;unsigned long ret = copy_from_user(hello_buf, buf, len);printk("%s %s %d ret = %ld\n", __FILE__, __FUNCTION__, __LINE__, ret);return len;
}//int (*open) (struct inode *, struct file *);
//参数含义依次为 文件索引节点 文件指针
static int hello_open (struct inode *node, struct file *filp)
{printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);return 0;
}//int (*release) (struct inode *, struct file *);
//参数含义依次为 文件索引节点 文件指针
static int hello_release (struct inode *node, struct file *filp)
{printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);return 0; 
}/*构建file_operations结构体*/
static const struct file_operations hello_fops = {.owner      = THIS_MODULE,.read		= hello_read,.write		= hello_write,.open		= hello_open,.release    = hello_release,
};/*init函数,实现register_chrdev*/
static int __init hello_init(void)
{//数含义依次为 主设备号，如果为0，内核会自动分配一个可用的。设备名，会在/proc/devices中显示。 file_operations结构体//注册成功就返回主设备号major = register_chrdev(0, DEVICE_NAME, &hello_fops);//为这个模块创建一个名为hello的类  在/sys/class/下会生成hello目录hello_class = class_create(THIS_MODULE, "hello");if (IS_ERR(hello_class)) {pr_err("failed to allocate class\n");return PTR_ERR(hello_class);}//在/sys/class/hello类下创建一个hello设备，同时在/dev/下创建一个hello节点hello_device = device_create(hello_class, NULL, MKDEV(major, 0), NULL, "hello");if (IS_ERR(hello_device)) {pr_err("failed to allocate device\n");return PTR_ERR(hello_device);}printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);return 0;
}/*exit函数unregister_chrdev*/
static void __exit hello_exit(void)
{//先销毁设备，后销毁类device_destroy(hello_class, MKDEV(major, 0));class_destroy(hello_class);unregister_chrdev(major, DEVICE_NAME);printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
}module_init(hello_init);
module_exit(hello_exit);
//遵循GPL协议
MODULE_LICENSE("GPL");

现在insmod驱动后，就会在/dev/下自动生成hello节点(/dev/hello)，/sys/class/下生成hello目录并在hello目录下生成一个hello设备的信息目录(/sys/class/hello/hello)