linux字符设备驱动学习笔记（一）：简单的字符设备驱动

linux字符设备驱动学习笔记（一）：简单的字符设备驱动

最近在鼓捣lnux字符设备驱动，在网上搜集的各种关于linux设备驱动的代码和注释，要么是针对2.4的，要么是错误百出，根本就不能运行成功，真希望大家在发博客的时候能认真核对下代码的正确性，特别是要把代码的运行环境和依赖条件列举出来，否则会对读者造成很大的误解。

以下代码的运行环境为：

操作系统:debian 6

内核版本:2.6.32(amd 64)

gcc版本：4.4.5

源代码如下所示(源代码确保编译可通过，运行无bug)：

#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/fs.h>
#include<linux/types.h>
#include<linux/cdev.h>
#include<asm/uaccess.h>
#include <linux/init.h> 

MODULE_LICENSE("GPL");


static int yang_open(struct inode*, struct file*);
static int yang_release(struct inode*, struct file*);

static ssize_t yang_read(struct file*, char *,size_t, loff_t*);
static ssize_t yang_write(struct file*,const char*, size_t,loff_t*);

loff_t yang_llseek(struct file *filp, loff_t off, int whence);

static int major;
static int device_open = 0;

static char *device_name = "myvar";

static dev_t devid;

static struct mydev *my_cdev;

struct mydev{
	char *data;
	struct cdev cdev;
	unsigned long size;
};


static struct file_operations fops = 
{
	.owner = THIS_MODULE,
	.read  = yang_read,
	.write = yang_write,
	.open  = yang_open,
	.release = yang_release,
	.llseek = yang_llseek
};

int init_yang_module(void)
{
	struct mydev *dev = (struct mydev *)kmalloc(sizeof(struct mydev),GFP_KERNEL);

	my_cdev = dev;//注册为全局变量，便于模块卸载

	memset(dev, 0, sizeof(struct mydev));

	dev->size = 10;
	
	int err;

	alloc_chrdev_region(&devid, 0, 1, "myvar");
	
	major = MAJOR(devid);
	
	cdev_init(&dev->cdev, &fops);

	err = cdev_add(&dev->cdev, devid, 1);

	if(err)
	{
		printk(KERN_INFO"I was major number %d.\n",major);
		return -1;
	}
	
	printk("major number is %d\n",MAJOR(devid));
	
	dev->data = (char*)kmalloc(dev->size * sizeof(char),GFP_KERNEL);

	memset(dev->data,0,dev->size * sizeof(char));
       
	return 0;
}

void cleanup_yang_module(void)
{
	cdev_del(&my_cdev->cdev);
	unregister_chrdev_region(devid, 1);
	printk("cleanup done\n");
}

loff_t yang_llseek(struct file *filp, loff_t off, int whence)
{
	struct mydev *dev = filp->private_data;

	loff_t newpos;
	switch(whence)
	{
		case SEEK_SET:
			newpos = off;
		case SEEK_CUR:
			newpos = filp->f_pos + off;
		case SEEK_END:
			newpos = dev->size + off;
	 		break;
		default:
	 		return -EINVAL;
	}
	if(newpos < 0) return -EINVAL;
	filp->f_pos = newpos;
	 return newpos;
}

static int yang_open(struct inode* inode, struct file* file)
{
	struct mydev *dev;

	dev = container_of(inode->i_cdev, struct mydev, cdev);

	file->private_data = dev;

	return 0;
}

static int yang_release(struct inode* inode, struct file* file)
{
	return 0;
}

static ssize_t yang_read(struct file* filp, char *buffer,size_t length, loff_t* off)
{
	struct mydev *dev = filp->private_data;

	if(*off >= dev->size)
	{
		return 0;
	}
	if(*off + length > dev->size)
	length = dev->size - *off;
	if(copy_to_user(buffer,dev->data + *off,length * sizeof(char)))
	{
		return -EFAULT;	
	}
	*off += length;

 	return length;
}
static ssize_t yang_write(struct file* filp,const char* buffer, size_t length,loff_t* off)
{
	struct mydev *dev = filp->private_data;

	if(length > dev->size)
	{
		return -EFAULT;
	}
	if(copy_from_user(dev->data,buffer,dev->size * sizeof(char)))
	{
		return -EFAULT;
	}
	*off += length;
	return dev->size;
}

module_init(init_yang_module);       
module_exit(cleanup_yang_module);        

以后有时间我再把注释加上，如果有兄弟刚刚学习linux设备驱动，这份源代码是最好的礼物。