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头文件demo.h
#ifndef _DEMO_H_
#define _DEMO_H_
#include linux/ioctl.h> /* needed for the _IOW etc stuff used later */
/********************************************************
* Macros to help debugging
********************************************************/
#undef PDEBUG /* undef it, just in case */
#ifdef DEMO_DEBUG
#ifdef __KERNEL__
# define PDEBUG(fmt, args...) printk( KERN_DEBUG "DEMO: " fmt, ## args)
#else//usr space
# define PDEBUG(fmt, args...) fprintf(stderr, fmt, ## args)
#endif
#else
# define PDEBUG(fmt, args...) /* not debugging: nothing */
#endif
#undef PDEBUGG
#define PDEBUGG(fmt, args...) /* nothing: it's a placeholder */
//设备号
#define DEMO_MAJOR 50
#define DEMO_MINOR 0
#define COMMAND1 1
#define COMMAND2 2
//自己定义的设备结构
struct DEMO_dev
{
struct cdev cdev; /* Char device structure */
};
//函数申明 原来Linux驱动程序设计这么简单 只需要实现这么几个函数就可以了
int DEMO_open(struct inode *inode, struct file *filp)
ssize_t DEMO_read(struct file *filp, char __user *buf, size_t count,
loff_t *f_pos);
ssize_t DEMO_write(struct file *filp, const char __user *buf, size_t count,
loff_t *f_pos);
loff_t DEMO_llseek(struct file *filp, loff_t off, int whence);
int DEMO_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd, unsigned long arg);
int DEMO_release(struct inode *inode, struct file *filp)
#endif /* _DEMO_H_ */
源文件demo.c
#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("demo");
MODULE_LICENSE("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 u8 demoBuffer[256]; //8位无符号整型,相当于unsigned char
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++;
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;
loff_t pos= *f_pos; /* 文件的读写位置 */
if(pos>=256)
{
result=0;
goto out;
}
if(count>(256-pos))
{
count=256-pos;
}
pos += count;
if (copy_to_user(buf,demoBuffer+*f_pos,count))
{
count=-EFAULT; /* 把数据写到应用程序空间 */
goto out;
}
*f_pos = pos; /* 改变文件的读写位置 */
out:
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 */
loff_t pos= *f_pos;
if(pos>=256)
{
goto out;
}
//如果要写入的输入大于剩下的内存空间 就只写入剩下的空间数量 以防溢出
if(count>(256-pos))
{
count=256-pos;
}
pos += count;
//copy_from_user 将数据从用户空间复制到内核空间
if (copy_from_user(demoBuffer+*f_pos, buf, count)) {
retval = -EFAULT;
goto out;
}
*f_pos = pos;
return count;
out:
return retval;
}
/*ioctl的作用 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;
}
//llseek 实现随即存取 ,loff_t应该是一个无符号整型 记录文件指针偏移量的 这段代码参考用户态的seek()就不难理解
loff_t DEMO_llseek(struct file *filp, loff_t off, int whence)
{
loff_t pos;
pos = filp->f_pos;
switch (whence)
{
case 0:
pos = off;
break;
case 1:
pos += off;
break;
case 2:
default:
return -EINVAL;
}
if ((pos>256) || (pos0))
{
return -EINVAL;
}
return filp->f_pos=pos;
}
//file_operations这个结构体真是相当重要 需要搞清楚它的作用
struct file_operations DEMO_fops = {
.owner = THIS_MODULE,
.llseek = DEMO_llseek,
.read = DEMO_read,
.write = DEMO_write,
.ioctl = DEMO_ioctl,
.open = DEMO_open,
.release = DEMO_release,
};
/*******************************************************
MODULE ROUTINE
*******************************************************/
void DEMO_cleanup_module(void)
{
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)
{
/*
在内核中,dev_t类型(定义在中)用来保存设备编号——包括主设备号和次设备号。
在内核2.6.0中,dev_t是一个32位的数,其中12位表示主设备号,20位表示次设备号。
*/
int result;
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;
}
//将新申请的空间清零
memset(DEMO_devices, 0, sizeof(struct DEMO_dev));
//初始化一个字符驱动 结构
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:
//失败了
DEMO_cleanup_module();
return result;
}
//模块入口和出口
module_init(DEMO_init_module);
module_exit(DEMO_cleanup_module);
Makefile
obj-m := demo.o
KERNELDIR := /home/ydzhang/linux-2.6.19
PWD := $(shell pwd)
all:
$(MAKE) -C $(KERNELDIR) M=$(PWD)
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions
加载驱动,创建设备
加载驱动
# insmod demo.ko
然后使用lsmod 或 cat /proc/modules查看驱动是否加载
# mknod /dev/demo c 50 0 创建设备节点
测试代码 demo_test.c
#includesys/types.h>
#includeunistd.h>
#includefcntl.h>
#includelinux/rtc.h>
#includelinux/ioctl.h>
#includestdio.h>
#includestdlib.h>
#define COMMAND1 1
#define COMMAND2 2
int main()
{
int fd;
int i;
char data[256];
int retval;
fd=open("/dev/demo",O_RDWR);
if(fd==-1)
{
perror("error open\n");
exit(-1);
}
printf("open /dev/smbus successfully\n");
retval=ioctl(fd,COMMAND1,0);
if(retval==-1)
{
perror("ioctl error\n");
exit(-1);
}
printf("send command1 successfully\n");
retval=write(fd,"abc",3);
if(retval==-1)
{
perror("write error\n");
exit(-1);
}
retval=lseek(fd,0,0);
if(retval==-1)
{
perror("lseek error\n");
exit(-1);
}
retval=read(fd,data,3);
data[3] = 0;
printf("%s\n", data);
if(retval==-1)
{
perror("read error\n");
exit(-1);
}
printf("read successfully:%s\n",data);
close(fd);
return 0;
}
本文来自ChinaUnix博客,如果查看原文请点:http://blog.chinaunix.net/u2/87570/showart_2119245.html |
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