Linux驱动学习（3-设备节点-手动创建）

模块代码chr_test.c

/** * To test the chr_dev for AP operation * by wozon * * */#include <linux/module.h>#include <linux/kernel.h>#include <linux/init.h>#include <linux/cdev.h>#include <linux/fs.h>MODULE_LICENSE ("GPL");dev_t dev;struct cdev cdev;int chr_open(struct inode *i, struct file *f){    printk("AP opened!\n");    return 0;}int chr_close(struct inode *i, struct file *filp){    printk("AP closed!\n");    return 0;}struct file_operations chr_fops={    .owner = THIS_MODULE,    .open = chr_open,    .release = chr_close,};//模块加载函数int __init init_module (void){    int rst = 0;    dev = MKDEV(249,1);   //创建设备节点    rst = register_chrdev_region(dev,1,"shuibian");  //向内核注册设备号    if(rst != 0)    {        rst = -1;        goto exit0;    }    cdev_init(&cdev,&chr_fops);//字符设备驱动控制块初始化    rst = cdev_add(&cdev,dev,1);//向内核添加字符设备驱动控制块    if(rst != 0)    {        rst = -2;        goto exit1;    }    printk("Chr,This module was added by the kernel!\n");    goto exit0;exit1:    unregister_chrdev_region(dev,1);//注销设备号exit0:    return rst;}//模块卸载函数void __exit cleanup_module (void){    cdev_del(&cdev);//从内核中删除字符设备控制块。    unregister_chrdev_region(dev,1);    printk("This module was removed by the kernel!\n");}

应用程序代码test.c

/* * test.c */#include <stdio.h>#include <unistd.h>#include <fcntl.h>#include <stdlib.h>#include <string.h>#include <sys/types.h>#include <sys/ioctl.h>int main (void) {    int fd;    fd = open ("/dev/sb13",O_RDWR);    if (fd < 0) {      perror("open");      exit(0);    }    printf ("/dev/chrdev opened, fd=%d\n",fd);    close (fd);    printf ("/dev/chrdev closed!\n");    return 0;}

Makefile

#To display info during Ccompiling$(warning KERNELRELEASE=$(KERNELRELEASE))#To check the KERNELRELEASE enviroment valueifeq ($(KERNELRELEASE),)#It's NULL, so to set the enviroment valueKERNELDIR ?= /lib/modules/$(shell uname -r)/buildPWD :=$(shell pwd)modules:    $(MAKE) -C $(KERNELDIR) M=$(PWD) modulesmodules_install:    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_installclean:    rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions Module* modules*.PHONY: modules modules_install clean#To create obj fileelse        obj-m := chr_test.oendif

先编译模块文件，在终端里面输入make，按下回车

生成chr_test.ko文件。
进入root用户，手动创建设备节点：mknod /dev/ c 249 1

可以看出在/dev/目录下面生成了sb13设备
将chr_test.ko文件加载进内核里面 insmod chr_test.ko
编译test.c文件，生成应用程序

执行应用程序 sudo ./a.out

可以看出，正常访问到了我们刚刚创建的设备节点。

ps：我们这样通过手动方式创建设备节点，然后编辑模块代码，用应用程序来访问，很复杂，尤其是作为别人项目一部分时，就更加不便维护，下一节我们将讲解自动创建设备节点的方法。