#include <linux/init.h>

#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/cdev.h>

#include <linux/fs.h>

int demo_major = ;

int demo_minor = ;

int demo_count = ;

struct cdev cdev;

int  demo_open(struct inode *inodep, struct file * filep) // 打开设备

{

    printk("%s,%d\n", __func__, __LINE__);

    return ;

}

int demo_release(struct inode * inodep, struct file * filep)  // 关闭设备

{

    printk("%s,%d\n", __func__, __LINE__);

    return ;

}

struct file_operations  fops =

{

    .owner = THIS_MODULE,

    .open = demo_open,

    .release = demo_release,

};

static int __init demo_init(void)

{

    int ret = ;

    dev_t  devno;

    printk("%s,%d\n", __func__, __LINE__);

    //使用下列宏则可以通过主设备号和次设备号生成 dev_t

    devno = MKDEV(demo_major, demo_minor);

    printk("devno:%d\n", devno);

    printk("demo_major:%d\n", demo_major);

    /**在调用 cdev_add()函数向系统注册字符设备之前，

      *应首先调用 register_chrdev_region()或alloc_chrdev_region()函数向系统申请设备号

      **/

    if (demo_major)//静态申请

    {

        ret = register_chrdev_region(devno, , "demo");

    }

    else //动态分配

    {

        ret = alloc_chrdev_region(&devno, , , "demo");

    }

    if(ret)

    {

        printk("Failed to register_chrdev_region.\n");

        return ret;

    }

    //cdev_init()函数用于初始化 cdev 的成员，并建立 cdev 和 file_operations 之间的连接

    cdev_init(&cdev, &fops);

    cdev.owner = THIS_MODULE;

    //系统添加一个 cdev，完成字符设备的注册。

    ret = cdev_add(&cdev, devno, demo_count);

    if(ret)

    {

        printk(KERN_NOTICE " Failed to cdev_add [Error] %d adding demo%d", ret, demo_count);

        unregister_chrdev_region(devno, demo_count);

        return ret;

    }

    return ;

}

static void __exit demo_exit(void)

{

    printk("%s,%d\n", __func__, __LINE__);

    //删除一个 cdev，完成字符设备的注销。

    cdev_del(&cdev);

    //在调用cdev_del()函数从系统注销字符设备之后，unregister_chrdev_region()应该被调用以释放原先申请的设备号

    unregister_chrdev_region( MKDEV(demo_major, demo_minor), demo_count );

}

module_init(demo_init);

module_exit(demo_exit);

MODULE_AUTHOR(" libra13179 ");

MODULE_LICENSE("GPL v2");

VERS = $(shell uname -r)

# Kernel modules

obj-m += demo.o

# Specify flags for the module compilation.

#EXTRA_CFLAGS=-g -O0

build: kernel_modules

kernel_modules:

    make -C /lib/modules/$(KVERS)/build M=$(CURDIR) modules

clean:

    make -C /lib/modules/$(KVERS)/build M=$(CURDIR) clean

 struct cdev

 {

     struct kobject kobj; /* 内嵌的 kobject 对象 */

     struct module *owner;    /*所属模块*/

     struct file_operations *ops;  /*文件操作结构体*/

     struct list_head list;

     dev_t dev;           /*设备号*/

     unsigned int count;

 };

cdev结构体

#define MAJOR(dev)    ((unsigned int) ((dev) >> MINORBITS))

#define MINOR(dev)    ((unsigned int) ((dev) & MINORMASK))

#define MKDEV(ma,mi)    (((ma) << MINORBITS) | (mi))

void cdev_init(struct cdev *, const struct file_operations *);//初始化cdev的成员，并建立cdev和file_operations之间关联起来 

struct cdev *cdev_alloc(void);//动态申请（构造）cdev内存（设备对象）

void cdev_put(struct cdev *p);//释放cdev内存

int cdev_add(struct cdev *, dev_t, unsigned);//注册cdev设备对象（添加到系统字符设备列表中）

void cdev_del(struct cdev *);//将cdev对象从系统中移除（注销 ）

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <stdio.h>

int main(int argc, const char *argv[])

{

    int fd;

    int val = ;

    fd = open("/dev/xyz", O_RDWR);

    if (fd < )

    {

        printf("can't open!\n");

        return -;

    }

    else

    {

        printf("open success.\n");

    }

    getchar();

    close(fd);

    return ;

}

root@lin-virtual-machine:/home/lin/demo# gcc -o demodrvtest demodrvtest.c
root@lin-virtual-machine:/home/lin/demo# ls
demo~    demodrvtest    demo.mod.c  Makefile~       Untitled Document~
demo.c   demodrvtest.c  demo.mod.o  modules.order
demo.c~  demo.ko        demo.o      Module.symvers

root@lin-virtual-machine:/home/lin/demo# pwd

/home/lin/demo

root@lin-virtual-machine:/home/lin/demo# ./demodrvtest

can't open!

root@lin-virtual-machine:/home/lin/demo# mknod /dev/xyz c

root@lin-virtual-machine:/home/lin/demo# ./demodrvtest

open success.