#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>

#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>

#define CHRMEM_SIZE 0x1000
#define MEM_CLEAR   0x1

static int chr_major;

struct chr_dev
{
	struct cdev cdev;
	unsigned char mem[CHRMEM_SIZE];
};

struct chr_dev* char_devp;

int chr_open(struct inode* inode, struct file* filp)
{
	filp->private_data = char_devp;
	return 0;
}

int chr_release(struct inode* inode, struct file* filp)
{
	return  0;
}

static int chr_ioctl(struct inode* inode, struct file* filp, unsigned int cmd, unsigned long arg)
{
	struct chr_dev* dev = filp->private_data;
	
	switch(cmd)
	{
		case MEM_CLEAR:
			memset(dev->mem, 0, CHRMEM_SIZE);
			break;
			
		default:
			return -EINVAL;
	}
	
	return 0;
}

static ssize_t chr_read(struct file* filp, char __user* buf, size_t size, loff_t* ppos)
{
	unsigned long p = *ppos;
	unsigned int count = size;
	int ret = 0;
	struct chr_dev* dev = filp->private_data;
	
	if(p >= CHRMEM_SIZE)
	{
		return 0;
	}
	
	if(count > CHRMEM_SIZE - p)
	{
		return 0;
	}
	
	if(copy_to_user(buf, (void*)(dev->mem + p), count))
	{
		return -EINVAL;
	}
	else
	{
		*ppos += count;
		ret = count;
	}
	
	return ret;
}

static ssize_t chr_write(struct file* filp, const char __user* buf, ssize_t size, loff_t *ppos)
{
	unsigned long p = *ppos;
	unsigned int count = size;
	int ret = 0;
	struct chr_dev* dev = filp->private_data;
	
	if(p >= CHRMEM_SIZE)
	{
		return 0;
	}
	
	if(count > CHRMEM_SIZE - p)
	{
		count = CHRMEM_SIZE - p;
	}
	
	if(copy_from_user(dev->mem + p, buf, count))
	{
		ret = -EINVAL;
	}
	else
	{
		*ppos += count;
		ret = count;
	}
	
	return ret;
}

static loff_t chr_llseek(struct file* filp, loff_t offset, int orig)
{
	loff_t ret = 0;
	
	/* orig can be SEEK_SET, SEEK_CUR, SEEK_END */
	switch(orig)
	{
		case 0:
			if(offset < 0)
			{
				ret = -EINVAL;