rickroll_module.c

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

#define DRIVER_AUTHOR "Dave B. <db@d1b.org>"
#define DRIVER_DESC "Rickroll ;)"
#define DEVICE_NAME "chardev"

MODULE_LICENSE("GPL");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);

int init_module(void);
void cleanup_module(void);
static int device_open(struct inode *, struct file *);
static ssize_t device_read(struct file *, char *, size_t, loff_t *);
static ssize_t device_write(struct file *, const char *, size_t, loff_t *);
static int device_release(struct inode * inode, struct file * );
static char * get_rickroll_line(void);

static int Major;
static int Device_Open;

static char *msg_Ptr; 

static struct file_operations fops = 
{
	.read = device_read,
	.write = device_write,
	.open = device_open,
	.release = device_release
};

int init_module(void)
{
	Major = register_chrdev(0, DEVICE_NAME, & fops);
	if (Major < 0)
	{
		printk(KERN_ALERT "Failed to register the rickroll device with %d\n", Major);
		return Major;
	}
	printk(KERN_INFO "Registered the rickroll device On major %d", Major);
	return 0;
}

void cleanup_module(void)
{
	unregister_chrdev(Major, DEVICE_NAME);
}

static int device_open(struct inode *inode, struct file * file)
{
	if (Device_Open)
	{
		return -EBUSY;
	}
	Device_Open++;
	msg_Ptr = get_rickroll_line();
	try_module_get(THIS_MODULE);
	return 0;
}

static int device_release(struct inode * inode, struct file * file)
{
	Device_Open--;
	module_put(THIS_MODULE);
	return 0;
}

static ssize_t device_read(struct file * filp, char * buffer, size_t length, loff_t * offset)
{
	int bytes_read = 0;
	char * newline = "\n\0";
	if (* msg_Ptr == 0)
	{
		return 0;
	}
	while (length && * msg_Ptr)
	{
		put_user(*(msg_Ptr++), buffer++);
		length--;
		bytes_read++;
	}
	put_user(*newline, buffer++);
	bytes_read++;
	return bytes_read;
}

static ssize_t device_write(struct file *filp, const char *buff, size_t len, loff_t * off)
{
	return -EINVAL;
}

char * get_rickroll_line(void)
{
	static int pos = 0;
	int value_of_pos;

	if (pos > 34)
	{
		pos = 0;
	}
	value_of_pos = pos;
	pos++;

	switch(value_of_pos)
	{
	case 0 :
		return "We're no strangers to love";
	case 1 :
		return "You know the rules and so do I";
	case 2 :
		return "A full commitment's what I'm thinking of";
	case 3 :
		return "You wouldn't get this from any other guy";
	case 4 :
		return "I just wanna tell you how I'm feeling";
	case 5 :
		return "Gotta make you understand";
	case 6 :
		return "Never gonna give you up";
	case 7 :
		return "Never gonna let you down";
	case 8 :
		return "Never gonna run around and desert you";
	case 9 :
		return "Never gonna make you cry";
	case 10 :
		return "Never gonna say goodbye";
	case 11 :
		return "Never gonna tell a lie and hurt you";
	case 12 :
		return "We've know each other for so long";
	case 13 :
		return "Your heart's been aching";
	case 14 :
		return "But you're too shy to say it";
	case 15 :
		return "Inside we both know what's been going on";
	case 16 :
		return "We know the game and we're gonna play it";
	case 17 :
		return "And if you ask me how I'm feeling";
	case 18 :
		return "Don't tell me you're too blind to see";
	case 19 :
		return "Never gonna give you up";
	case 20 :
		return "Never gonna let you down";
	case 21 :
		return "Never gonna run around and desert you";
	case 22 :
		return "Never gonna make you cry";
	case 23 :
		return "Never gonna say goodbye";
	case 24 :
		return "Never gonna tell a lie and hurt you";
	case 25 :
		return "(Repeat Chorus)";
	case 26 :
		return "Give you up, give you up";
	case 27 :
		return "Give you up, give you up";
	case 28 :
		return "Never gonna give,";
	case 29 :
		return "Never gonna give, give you up";
	case 30 :
		return "Never gonna give,";
	case 31 :
		return "Never gonna give, give you up";
	case 32 :
		return "(Last four lines repeat)";
	case 33 :
		return "I just wanna tell you how I'm feeling";
	case 34 :
		return "Gotta make you understand";
	}
	return "ERROR";
}