最简单的字符设备驱动gobalvar

最简单的字符设备驱动gobalvar

drv：

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <asm/uaccess.h> 
MODULE_LICENSE("GPL");

#define MAJOR_NUM 1024 //主设备号

static ssize_t globalvar_read(struct file *, char *, size_t, loff_t*);
static ssize_t globalvar_write(struct file *, const char *, size_t, loff_t*);

static int global_var = 0; //"globalvar"设备的全局变量


static ssize_t globalvar_read(struct file *filp, char *buf, size_t len, loff_t *off)
{  
      if (copy_to_user(buf, &global_var, sizeof(int))){ //将global_var从内核空间复制到用户空间
            return - EFAULT;
      } 
      printk("globalvar_read enter ,the data is %d\n",global_var);
      return sizeof(int);
}

static ssize_t globalvar_write(struct file *filp, const char *buf, size_t len, loff_t *off)
{
      if (copy_from_user(&global_var, buf, sizeof(int))){//将用户空间的数据复制到内核空间的global_var
            return - EFAULT;
      } 
      printk("globalvar_write enter ,the data is %d\n",global_var);
      return sizeof(int);
}

//初始化字符设备驱动的file_operations结构体
struct file_operations globalvar_fops =
{
      //read: globalvar_read, write: globalvar_write,
      .write  = globalvar_write,
      .read =globalvar_read,
};

static int __init globalvar_init(void){
      int ret;
      
      ret = register_chrdev(MAJOR_NUM, "globalvar", &globalvar_fops); //注册设备驱动
      if (ret){
            printk("globalvar register failure");
      }
      else{
            printk("globalvar register success");
      }
      return ret;
}
//注销设备驱动
static void __exit globalvar_exit(void)
{
       unregister_chrdev(MAJOR_NUM, "globalvar");
}
module_init(globalvar_init);
module_exit(globalvar_exit);

对应的app：

#include <stdio.h>
#include <sys/stat.h>  //获得文件的属性，它可以返回一个结构，里面包含文件全部属性
#include <fcntl.h>        //设备驱动程序接口是由结构说明，它定义在fcntl.h中
#include <sys/types.h> //类型 clock_t,dev_t,off_t,ptrdiff,size_t,ssize_t,time_t

void main(void)
{
      int fd, num;
  
      fd = open("/dev/globalvar", O_RDWR, S_IRUSR | S_IWUSR); 
      if (fd != -1 ){

            read(fd, &num, sizeof(int));
            printf("The globalvar is %d\n", num);

            printf("Please input the num written to globalvar\n");
            scanf("%d", &num);
            write(fd, &num, sizeof(int));
     
            read(fd, &num, sizeof(int));
            printf("The globalvar is %d\n", num);
   
            close(fd);
      }else{
            printf("Device open failure\n");
      }
}

对应的加载脚本：

# !/bin/sh
insmod /home/project/ddr3/ddr3_globalvartest/drv/globalvar.ko
mknod /dev/globalvar c 1024 0
../app/app
dmesg -c

卸载脚本：

# !/bin/sh

rmmod globalvar
dmesg -c
#killall -9 app

原理既不多做作介绍了，很简单。