注册字符类设备

• 注册杂项设备:

misc_register(&misc_dev);

• 注销杂项设备:

misc_deregister(&misc_dev);

• cdev结构体:描述字符设备的一个结构体
• 字符类设备的一些操作是在 #include <linux/cdev.h> 头文件下

struct cdev {struct kobject kobj;struct module *owner;const struct file_operations *ops;struct list_head list;dev_t dev;unsigned int count;
};

1. 步骤一:定义一个cdev结构体
2. 步骤二:使用cdev init 函数初始化cdev结构体成员变量

void cdev init(struct cdev *, const struct file_operations *);

• 参数:
  第一个:要初始化的cdev
• 第二个:文件操作集
  cdev->ops = fops;实际就是把文件操作集写个ops

3. 步骤三:使用cdev_add函数注册到内核

int cdev_add(struct cdev *, dev_t, unsigned);

参数:

• 第一个: cdev的结构体指针
• 第二个:设备号
• 第三个:次设备号的数量

设备的注销

void cdev_del(struct cdev *);

参数

• 第一个 设备号

字符类设备注册后并不会自动生成设备节点

• 我们需要使用 mknod 命令创建一个设备节点

• 格式

  mknod 名称 类型 主设备号 次设备号
  

• 举例 c 代表字符型

  mknod /dev/test c 247 0
  

  代码

  • app.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>int main(int argc, char *argv[]){int fd;char buf[64] = {0};char buf_write[64] = "write aaaaaaaaa";fd = open("/dev/test",O_RDWR);if (fd < 0){printf("open error \n");return fd;}// printf("open success \n");// read(fd,buf,sizeof(buf));// write(fd,buf_write,sizeof(buf_write));// printf("buf is %s\n",buf);// close(fd);return 0;
}

• chrdev.c

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>
//设备的数量
#define DEVICE_NUMBER 1
//静态名称
#define DEVICE_SNAME "schrdev"
//动态名称
#define DEVICE_ANAME "achrdev"
//次设备号的起始地址
#define DEVICE_MINOR_NUMBER 0//主设备号，次设备号
static int major_num, minor_num;struct cdev cdev;module_param(major_num,int,S_IRUSR);
module_param(minor_num,int,S_IRUSR);int chrdev_open(struct inode * inode, struct file * file){printk("chrdev_open 已经打开了");return 0;}struct file_operations chrdev_ops =
{.owner = THIS_MODULE,.open = chrdev_open, };static int hello_init(void){dev_t dev_num;int ret;if (major_num){dev_num = MKDEV(major_num, minor_num);printk("major_num = %d \n",major_num);printk("minor_num = %d \n",minor_num);ret = register_chrdev_region(dev_num,DEVICE_NUMBER,DEVICE_SNAME);if (ret <0 ){printk("register_chrdev_region 注册失败了 \n");}printk("register_chrdev_region 注册成功了 \n");      }else {ret = alloc_chrdev_region(&dev_num, DEVICE_MINOR_NUMBER, DEVICE_NUMBER, DEVICE_ANAME);if (ret < 0 ){printk("alloc_chrdev_region 失败了 \n");}major_num = MAJOR(dev_num);minor_num = MINOR(dev_num);printk("major_num = %d \n",major_num);printk("minor_num = %d \n",minor_num);printk("alloc_chrdev_region 成功了 \n");}cdev.owner = THIS_MODULE;cdev_init(&cdev, &chrdev_ops);cdev_add(&cdev, dev_num, DEVICE_NUMBER);printk(KERN_ALERT "Hello , World\n"); //内核空间里没有printf，用printkreturn 0;}static void hello_exit(void){unregister_chrdev_region(MKDEV(major_num, minor_num), DEVICE_NUMBER);cdev_del(&cdev);printk(KERN_ALERT "Goodbye 注销成功 , World\n");
}//模块的注册
module_init(hello_init);
//模块的卸载
module_exit(hello_exit);
MODULE_LICENSE("Dual BSD/GPL");