demo.c

Linux 2.6核下的字符驱动示例。以简单的代码表现Linux的驱动程序结构

*********************************************************************
//demo.c
/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 2007, 2010 fengGuojin([e-mail])
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/cdev.h>
#include <linux/version.h>
#include <linux/vmalloc.h>
#include <linux/ctype.h>
#include <linux/pagemap.h>

#include "demo.h"

MODULE_AUTHOR("GuoSong");
MODULE_LICENSE("Dual BSD/GPL");

struct DEMO_dev *DEMO_devices;//申明自己定义的设备结构的指针
static unsigned char demo_inc=0;//计数 记录此设备被打开的次数
static char demoBuffer[256];  //模拟存储器
int DEMO_open(struct inode *inode, struct file *filp)
{
    struct DEMO_dev *dev;
    //只允许打开设备一次
    if(demo_inc>0)return -ERESTARTSYS;
    demo_inc++;
    /*container_of 宏 通过结构中的某个变量获取结构本身的指针*/
    dev = container_of(inode->i_cdev, struct DEMO_dev, cdev);
    filp->private_data = dev;
    return 0;
}

int DEMO_release(struct inode *inode, struct file *filp)
{
    demo_inc--;
    return 0;
}

ssize_t DEMO_read(struct file *filp, char __user *buf, size_t count,loff_t *f_pos)
{
    int result;
    if (copy_to_user(buf,demoBuffer+*f_pos,count))
    {
       return -EFAULT; /* 把数据写到应用程序空间 */
    }
    
    *f_pos = pos; /* 改变文件的读写位置 */
    return count;
}

ssize_t DEMO_write(struct file *filp, const char __user *buf, size_t count,loff_t *f_pos)
{
    ssize_t retval = -ENOMEM; /* value used in "goto out" statements */
    if (copy_from_user(demoBuffer+*f_pos, buf, count)) {
       return  -EFAULT;;
    }
    *f_pos = pos;
    return count;
}

/* ioctl是用来控制设备的 ，unsigned int cmd就是发给设备的命令 
ioctl（）或许是Linux下最庞杂的函数*/
int DEMO_ioctl(struct inode *inode, struct file *filp,unsigned int cmd, unsigned long arg)
{
    if(cmd==COMMAND1)
    {
           printk("ioctl command1 successfully\n");
           return 0;
    }
    if(cmd==COMMAND2)
    {
           printk("ioctl command2 successfully\n");
           return 0;
    }
    
    printk("ioctl error\n");
          return -EFAULT;
}

//file_operations设备操作集 
struct file_operations DEMO_fops = {
    .owner =    THIS_MODULE,
    .read =     DEMO_read,
    .write =    DEMO_write,
    .ioctl =    DEMO_ioctl,
    .open =     DEMO_open,
    .release = DEMO_release,
};

/*******************************************************
                MODULE ROUTINE
*******************************************************/

void DEMO_cleanup_module(void)
{
    //通过主、次编号算出设备号
    dev_t devno = MKDEV(DEMO_MAJOR, DEMO_MINOR);

    if (DEMO_devices) 
    {
        cdev_del(&DEMO_devices->cdev);
        //内核下的内存操作函数还真怪异 习惯就好
        kfree(DEMO_devices);
    }
    //调用unregister_chrdev_region()函数释放分配的一系列设备号
    unregister_chrdev_region(devno,1);
}

int DEMO_init_module(void)
{
    int result;
    /* 在内核中，dev_t类型（在<linux/types.h>中定义）用来保存设备编号——包括主设备号和次设备号*/
    dev_t dev = 0;
    dev = MKDEV(DEMO_MAJOR, DEMO_MINOR);

   /*获取一个或多个设备编号来使用
   如果分配成功进行, register_chrdev_region 的返回值是 0. 出错的情况下, 返回一个负的错误码, 你不能存取请求的区域. */
    result = register_chrdev_region(dev, 1, "DEMO");
    if (result < 0) 
    {
        printk(KERN_WARNING "DEMO: can't get major %d\n", DEMO_MAJOR);
        return result;
    }
    //为自定义的设备结构申请空间
    DEMO_devices = kmalloc(sizeof(struct DEMO_dev), GFP_KERNEL);
    if (!DEMO_devices)
    {
        result = -ENOMEM;
        goto fail;
      }
    //为新申请的空间清零
    memset(DEMO_devices, 0, sizeof(struct DEMO_dev));
    //初始化一个字符驱动
    cdev_init(&DEMO_devices->cdev, &DEMO_fops);
    DEMO_devices->cdev.owner = THIS_MODULE;
    DEMO_devices->cdev.ops = &DEMO_fops;
    //在内核中添加字符驱动
    result = cdev_add (&DEMO_devices->cdev, dev, 1);
    if(result)
    {
        printk(KERN_NOTICE "Error %d adding DEMO\n", result);
        goto fail;
    }
    return 0;
fail:
    DEMO_cleanup_module();
    return result;
}