简单的字符驱动笔记

#include <linux/module.h>#include <linux/init.h>#include <linux/fs.h>#include <asm/uaccess.h>MODULE_LICENSE("GPL"); /*用于声明模块的许可证*/MODULE_AUTHOR("[e-mail]");/*用于声明模块的作者*/#define MAJOR_NUM 254 /*主设备号*/static ssize_t gobalvar_read (struct file* ,char* ,size_t ,loff_t*);static ssize_t gobalvar_write (struct file* ,const char* ,size_t ,loff_t*);struct file_operations gobalvar_fops={read : gobalvar_read,write : gobalvaar_write,};static int gobal_var=0; /*"gobalvar"设备的全局变量*/static int __init gobalvar_init( void ){int ret;ret=register_chrdev(MORJOR_NUM,"gobalvar",&gobalvar_fops); /*注册设备驱动*/if( ret ){printk("gobalvar register failure !");}else{printk("gobalvar register success !"); /*注册成功返回0*/}return ret;}static void __exit gobalvar_exit( void ){int ret;ret=unregister_chrdev(MORJOR_NUM,"gobalvar"); /*注销设备驱动*/if( ret ){printk("gobalvar unregister failure !");}else{printk("gobalvar unregister success !"); /*注销成功返回0*/}}static ssize_t gobalvar_read(struct file *filp ,char *buf ,size_t len ,loff_t *off){if( copy_to_user(buf,&gobal_var,sizeof(int)) ) /*将gobal_var从内核空间复制到用户空间*/{return -EFAULT;}return sizeof(int);}static ssize_t gobalvar_write(struct file *filp ,const char *buf ,size_t len ,loff_t *off){if( copy_from_user(&gobal_var,buf,sizeof(int)) ) /*将用户空间的数据复制到内核空间的gobal_var*/{return -EFAULT;}return sizeof(int);}module_init(gobal_init);module_exit(gobal_exit);gcc -D_KERNE_-DMODULE-DLINUX -I 源代码的路径 -c -o gobalvar.o gobalvar.cinsmod gobalvar.o /*加载模块*/cat /proc/devices /*查看设备,可以看到设备田添加了*/mknod /dev/gobalvar c 254 0 /*创建设备节点,用户进程可以通过/dev/gobalvar这个路径访问到这个全局变量虚拟设备了*/写一个用户态的程序gobalvartest.c来验证上述设备:#include <sys/types.h>#include <sys/stat.h>#include <stdio.h>#include <fcntl.h>int main( void ){int fd,num;fd=open("/dev/gobalvar",O_RDWR,S_IRUSR|S_IWUSR); /*打开"/dev/gobalvar"*/if(-1!=fd){read(fd,&num,sizeof(int)); /*初次读gobalvar*/printf("The gobalvar is %d !/n",num);printf("Please input the num written to gobalvar !/n"); /*写gobalvar*/scanf("%d",&num);write(fd,&num,sizeof(int));read(fd,&num,sizeof(int)); /*再次读gobalvar*/printf("The gobalvar is %d !/n",num);close(fd); /*关闭"/dev/gobalvar"*/}else{printf("Device open failure !/n");;}return 0;}编译上述文件: gcc -o gobalvartest.o gobalvartest.c运行: ./gobalvartest.o 可以发现"gobalvar"设备可以正确的读写