rwbuf.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/uaccess.h>
#include <linux/init.h>

#define RWBUF_SIZE 2048
#define DEVICE_NAME "ChrDev"  
#define RWBUF_CLEAR 0x909090
#define RWBUF_LENGTH 0x808080
#define RWBUF_NUM 0x707070

static char rwbuf[RWBUF_SIZE]="13081070";  //buffer
static int inuse = 0; //only one process is permited once
static int rwlen = 8; //the current length of buffer
static int writenum = 0;  //the number of write 

static int rwbuf_open(struct inode *node, struct file *filep);
static int rwbuf_close(struct inode *node, struct file *filep);
static ssize_t rwbuf_write(struct file *filep, const char *buf, size_t count, loff_t *ppos);
static ssize_t rwbuf_read(struct file* filp, char *buf , size_t count, loff_t *ppos);
static int rwbuf_ioctl(struct inode *node, struct file * filep, unsigned int cmd, unsigned long arg);


static struct file_operations rwbuf_fops =
{
	read:  rwbuf_read,
	write: rwbuf_write,
	ioctl: rwbuf_ioctl,
	open:  rwbuf_open,
	release: rwbuf_close,
};


int init_module_rwbuf()
{
	register_chrdev(277,DEVICE_NAME,&rwbuf_fops);
	printk(KERN_ALERT "register ok\n");
	return 0;
}

void cleanup_module_rwbuf()
{
	unregister_chrdev(277,DEVICE_NAME);
	printk(KERN_ALERT "unreg ok\n");	
}

static int rwbuf_open(struct inode *node, struct file *filep)
{
	if(inuse==1)
		return -1;
	
	inuse=1;
	printk(KERN_ALERT "open ok\n");
	return 0;
}

static int rwbuf_close(struct inode *node, struct file *filep)
{
	inuse = 0;
	printk(KERN_ALERT "close ok\n");
	return 0;
}


static ssize_t rwbuf_write(struct file *filep, const char *buf, size_t count, loff_t *ppos)
{
	if(count<=1024)
	{
		writenum++;
		//printk(KERN_ALERT "write1\n");
		copy_from_user(rwbuf,buf,count);
		//printk(KERN_ALERT "write2\n");
		rwlen = count;
		//printk(KERN_ALERT "write ok\n");
		return rwlen;
	}
	else
	{
		writenum++;
		copy_from_user(rwbuf,buf,1024);
		rwlen = 1024;
		printk(KERN_ALERT "write overflow\n");
		return rwlen;
	}
}


static ssize_t rwbuf_read(struct file* filp, char *buf , size_t count, loff_t *ppos)
{
		printk(KERN_ALERT "read\n");
		count=rwlen;
		copy_to_user(buf,rwbuf,count);
		printk(KERN_ALERT "read ok\n");
		return count;
}


static int rwbuf_ioctl(struct inode *node, struct file * filep, unsigned int cmd, unsigned long arg)
{
	if(cmd==RWBUF_CLEAR)
	{
		rwlen = 0;
		printk(KERN_ALERT "rwbuf in kernel zero-ed\n");
		return 0;
	}
	else if(cmd==RWBUF_LENGTH)
	{
		printk(KERN_ALERT "length of buffer\n");
		return rwlen;
	}
	else if(cmd==RWBUF_NUM)
	{
		printk(KERN_ALERT "num of writing\n");
		return writenum;
	}
	return 0;
}


module_init(init_module_rwbuf);
module_exit(cleanup_module_rwbuf);