// Tap module, just for fun, Version 0.9
//
// Usage,
// Compile using
//	gcc -c tap.c -o tap.o -I/lib/modules/`uname -r`/build/include
//
// Use:
//
//	insmod ./tap.o
//	mknod /dev/water c 200 1
//	cat /dev/water
//
// Removal
//
//	rm /dev/water
//	rmmod tap
//
// Beau Kuiper Copyright (C) 2001
// Parts derived from devices/mm/mem.c from linux kernel

// Licensed under GPL 2.0

#define MODULE
#define __KERNEL__

#include <linux/config.h>
#include <linux/version.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/unistd.h>
#include <linux/types.h>
#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/raw.h>
#include <linux/file.h>
#include <linux/errno.h>

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

devfs_handle_t waterdev;
int water_pos;

#define WATER_MAJ 200
#define WATER_MIN 1

static loff_t water_lseek(struct file * file, loff_t offset, int orig)
{
	return file->f_pos = 0;
}

static size_t water_read(struct file * file, char * buf,
				size_t count, loff_t *ppos)
{
	unsigned long left, pos;
	
	if (!access_ok(VERIFY_WRITE, buf, count))
		return -EFAULT;
	
	left = count;
	pos = 0;
	
	while(pos < count)
	{
		strncpy(buf + pos, "WaterWater" + water_pos, min(left, (unsigned long)5));
		pos += min(left, (unsigned long)5);
		left -= 5;
	}
	
	water_pos += pos % 5;
	water_pos = water_pos % 5;
	
	return count;
}	

static size_t water_write(struct file * file, char * buf,
				size_t count, loff_t *ppos)
{
	return -EINVAL;
}

static struct file_operations water_fops = {
	llseek:		water_lseek,
	read:		water_read,
	write:		water_write,
};

static int water_open(struct inode * inode, struct file * filp)
{
	switch (MINOR(inode->i_rdev)) 
	{
		case WATER_MIN:
			filp->f_op = &water_fops;
			break;
		default:
			return -ENXIO;
	}
	return(0);
}

static struct file_operations water_meta_fops = {
	open:		water_open,
};

int init_module(void) 
{

	if (devfs_register_chrdev(WATER_MAJ ,"tap",&water_meta_fops))
	{
		printk("unable to get major %d for memory devs\n", WATER_MAJ);
		return -1;
	}
	
	waterdev = devfs_register(NULL, "water", DEVFS_FL_NONE, 
						 WATER_MAJ, WATER_MIN,
						 S_IRUGO | S_IWUGO | S_IFCHR,
						 &water_fops, NULL);
	water_pos = 0;
	return 0;
}

void cleanup_module(void)
{
	devfs_unregister_chrdev(WATER_MAJ, "tap");
	devfs_unregister(waterdev);
}