一个简单的Linux驱动示例

本文参考百度文库“linux驱动开发入门”点击打开链接和转载博文：点击打开链接。

一、基本知识

Linux设备驱动分为：字符设备、块设备和网络设备。原理图如下：



二、示例

示例主要转载自博客园的博客，见上。只是我采用的的Linux内核版本比那篇博文的新，有小许改动，粘贴代码如下：

内核版本：

ry@ubuntu:/$ uname -a

Linux ubuntu 3.16.0-30-generic #40~14.04.1-Ubuntu SMP Thu Jan 15 17:43:14 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

文件：hello_mod.c

/*
* =====================================================================================
*
*       Filename:  hello.c
*
*    Description:  hello_mod
*
*        Version:  1.0
*        Created:  01/28/2011 05:07:55 PM
*       Revision:  none
*       Compiler:  gcc
*
*         Author:  Tishion (shion), tishion@163.com
*        Company:  LIM
*
* =====================================================================================
*/

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/semaphore.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/ioctl.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/string.h>
#include "hello_mod_ioctl.h"

#define MAJOR_NUM 250
#define MINOR_NUM 0
#define IN_BUF_LEN 256
#define OUT_BUF_LEN 512

MODULE_AUTHOR("Tishion");
MODULE_DESCRIPTION("Hello_mod driver by tishion");

static struct class * hello_class;
static struct cdev hello_cdev;
static dev_t devnum = 0;
static char * modname = "hello_mod";
static char * devicename = "hello";
static char * classname = "hello_class";

static int open_count = 0;
static struct semaphore sem;
static DEFINE_SPINLOCK(spin);
static char * inbuffer = NULL;
static char * outbuffer = NULL;
static lang_t langtype;

static int hello_mod_open(struct inode *, struct file *);
static int hello_mod_release(struct inode *, struct file *);
static ssize_t hello_mod_read(struct file *, char *, size_t, loff_t *);
static ssize_t hello_mod_write(struct file *, const char *, size_t, loff_t *);
static long hello_mod_ioctl(struct file *, unsigned int, unsigned long);

struct file_operations hello_mod_fops =
{
.owner = THIS_MODULE,
.open = hello_mod_open,
.read = hello_mod_read,
.write = hello_mod_write,
.unlocked_ioctl = hello_mod_ioctl,
.release = hello_mod_release,
};

static int hello_mod_open(struct inode *inode, struct file *pfile)
{
printk("+hello_mod_open()!/n");
spin_lock(&spin);
if(open_count)
{
spin_unlock(&spin);
return -EBUSY;
}
open_count++;
spin_unlock(&spin);
printk("-hello_mod_open()!/n");
return 0;
}
static int hello_mod_release(struct inode *inode, struct file *pfile)
{
printk("+hello_mod_release()!/n");
open_count--;
printk("-hello_mod_release()!/n");
return 0;
}
static ssize_t hello_mod_read(struct file *pfile, char *user_buf, size_t len, loff_t *off)
{
printk("+hello_mod_read()!/n");

if(down_interruptible(&sem))
{
return -ERESTARTSYS;
}
memset(outbuffer, 0, OUT_BUF_LEN);
printk("    +switch()/n");
switch(langtype)
{
case english:
printk("        >in case: english/n");
sprintf(outbuffer, "Hello! %s.", inbuffer);
break;
case chinese:
printk("        >in case: chinese/n");
sprintf(outbuffer, "你好！ %s.", inbuffer);
break;
case pinyin:
printk("        >in case: pinyin/n");
sprintf(outbuffer, "ni hao! %s.", inbuffer);
break;
default:
printk("        >in case: default/n");
break;
}
printk("    -switch()/n");
if(copy_to_user(user_buf, outbuffer, len))
{
up(&sem);
return -EFAULT;
}
up(&sem);
printk("-hello_mod_read()!/n");
return 0;
}
static ssize_t hello_mod_write(struct file *pfile, const char *user_buf, size_t len, loff_t *off)
{
printk("+hello_mod_write()!/n");
if(down_interruptible(&sem))
{
return -ERESTARTSYS;
}
if(len > IN_BUF_LEN)
{
printk("Out of input buffer/n");
return -ERESTARTSYS;
}
if(copy_from_user(inbuffer, user_buf, len))
{
up(&sem);
return -EFAULT;
}
up(&sem);
printk("-hello_mod_write()!/n");
return 0;
}
static long hello_mod_ioctl(struct file *pfile, unsigned int cmd, unsigned long arg)
{
int err = 0;
printk("+hello_mod_ioctl()!/n");
printk("    +switch()/n");
switch(cmd)
{
case HELLO_IOCTL_RESETLANG:
printk("        >in case: HELLO_IOCTL_RESETLANG/n");
langtype = english;
break;
case HELLO_IOCTL_GETLANG:
printk("        >in case: HELLO_IOCTL_GETLANG/n");
err = copy_to_user((int *)arg, &langtype, sizeof(int));
break;
case HELLO_IOCTL_SETLANG:
printk("        >in case: HELLO_IOCTL_SETLANG/n");
err = copy_from_user(&langtype,(int *)arg, sizeof(int));
break;
default:
printk("        >in case: default/n");
err = ENOTSUPP;
break;
}
printk("    -switch()/n");
printk("-hello_mod_ioctl()!/n");
return err;
}
static int __init hello_mod_init(void)
{
int result;
printk("+hello_mod_init()!/n");
devnum = MKDEV(MAJOR_NUM, MINOR_NUM);
result = register_chrdev_region(devnum, 1, modname);

if(result < 0)
{
printk("hello_mod : can't get major number!/n");
return result;
}

cdev_init(&hello_cdev, &hello_mod_fops);
hello_cdev.owner = THIS_MODULE;
hello_cdev.ops = &hello_mod_fops;
result = cdev_add(&hello_cdev, devnum, 1);
if(result)
printk("Failed at cdev_add()");
hello_class = class_create(THIS_MODULE, classname);
if(IS_ERR(hello_class))
{
printk("Failed at class_create().Please exec [mknod] before operate the device/n");
}
else
{
device_create(hello_class, NULL, devnum,NULL, devicename);
}

open_count = 0;
langtype = english;
inbuffer = (char *)kmalloc(IN_BUF_LEN, GFP_KERNEL);
outbuffer = (char *)kmalloc(OUT_BUF_LEN, GFP_KERNEL);
sema_init(&sem, 1);
printk("-hello_mod_init()!/n");
return 0;
}

static void __exit hello_mod_exit(void)
{
printk("+hello_mod_exit!/n");
kfree(inbuffer);
kfree(outbuffer);
cdev_del(&hello_cdev);
device_destroy(hello_class, devnum);
class_destroy(hello_class);
unregister_chrdev_region(devnum, 1);
printk("-hello_mod_exit!/n");
return ;
}

module_init(hello_mod_init);
module_exit(hello_mod_exit);
MODULE_LICENSE("GPL");

头文件：hello_mod_ioctl.h

/*
* =====================================================================================
*
*       Filename:  hello_mod_ioctl.h
*
*    Description:  define the cmd supported by hello_mod
*
*        Version:  1.0
*        Created:  06/19/2011 10:24:20 PM
*       Revision:  none
*       Compiler:  gcc
*
*         Author:  Tishion (shion), tishion@163.com
*        Company:  LIM
*
* =====================================================================================
*/

#ifndef __HELLO_MOD_IOCTL_H__
#define __HELLO_MOD_IOCTL_H__

#define HELLO_MAGIC    12
#define HELLO_IOCTL_RESETLANG    _IO(HELLO_MAGIC,0)        //set langtype = english
#define HELLO_IOCTL_GETLANG        _IOR(HELLO_MAGIC,1,int)    //get langtype
#define HELLO_IOCTL_SETLANG        _IOW(HELLO_MAGIC,2,int)    //set langtype

typedef enum _lang_t
{
english, chinese, pinyin
}lang_t;

#endif

Makefile文件：（注意：Makefile的'M'要大写）

#**********************************************
# Makefile linux 2.6 Module
# This makefile is written for Ubuntu 10.10
# It may not perfomance without erros on the
# other version or distributions.
#**********************************************
#    BY:tishion
#    Mail:tishion@163.com
#    2011/06/19
#**********************************************
obj-m += hello_mod.o
CURRENT_PATH := $(shell pwd)
LINUX_KERNEL := $(shell uname -r)
LINUX_KERNEL_PATH := /usr/src/linux-headers-$(LINUX_KERNEL)
all:
make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) modules
clean:
make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) clean
install:
insmod hello_mod.ko
unistall:
rmmod hello_mod

以上三个文件即为驱动代码

另外，再给一个应用层测试代码，并共用驱动的头文件

hello_mod_test.c文件：

/*
* =====================================================================================
*
*       Filename:  hell_mod_test.c
*
*    Description:  hell_mod test app
*
*        Version:  1.0
*        Created:  06/20/2011 01:44:11 AM
*       Revision:  none
*       Compiler:  gcc
*
*         Author:  Tishion (shion), tishion@163.com
*        Company:  LIM
*
* =====================================================================================
*/

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/ioctl.h>
#include <string.h>
#include <errno.h>
#include "../hello_mod_ioctl.h"

int main()
{
char outbuf[512];
char * myname = "tishion";
lang_t langtype = english;
int fd = open("/dev/hello", O_RDWR, S_IRUSR|S_IWUSR);
if(fd != -1)
{
write(fd, myname, strlen(myname)+1);
langtype = chinese;
ioctl(fd, HELLO_IOCTL_SETLANG, &langtype);
read(fd, outbuf, 512);
printf("langtype=chinese:%s/n", outbuf);
memset(outbuf, 0, 512);
langtype = pinyin;
ioctl(fd, HELLO_IOCTL_SETLANG, &langtype);
read(fd, outbuf, 512);
printf("langtype=pinyin:%s/n", outbuf);
memset(outbuf, 0, 512);
ioctl(fd, HELLO_IOCTL_RESETLANG, &langtype);
read(fd, outbuf, 512);
printf("langtype=english:%s/n", outbuf);
}
else
{
perror("Failed at open():");
}
return 0;
}

最后，安装原博客编译和查看结果。

需要注意的是，需要到“/var/log/”目录下着“syslog”文件。