//-------------------------------------------------------------------
//	newcall.c
//
//	This module dynamically installs a new system-call, without
//	the need to modify and recompile the kernel's source files.
//	It is based on 'patching' an obsolete entry in the kernel's
//	'sys_call_table[]' array.  The address of that array can be
//	discovered, either in the 'System.map' file for the current
//	kernel (normally located in the '/boot' directory), or else
//	in the uncompressed kernel binary ELF file ('vmlinux') left
//	behind in the '/usr/src/linux' directory after compilation.
//
//	NOTE: Written and tested using Linux kernel version 2.4.17.
//
//	written on: 22 JUN 2004
//	revised on: 09 MAY 2005 -- for Linux kernel version 2.6.10
//-------------------------------------------------------------------

#include <linux/module.h>	// for init_module() 
#include <asm/uaccess.h>	// for copy_to/from_user()
#include <asm/unistd.h>		// for __NR_break

char modname[] = "newcall";
extern unsigned long *sys_call_table;
unsigned long save_old_syscall;

asmlinkage long my_syscall( int __user * num )
{
	int	val;

	if ( copy_from_user( &val, num, sizeof( int ) ) ) return -EFAULT;
	++val;
	if ( copy_to_user( num, &val, sizeof( int ) ) ) return -EFAULT; 

	return	0;  // SUCCESS
}	


int init_module( void )
{
	printk( "<1>\nInstalling \'%s\' module ", modname );
	printk( "(sys_call_table[] at %08X) \n", (int)sys_call_table );

	printk( "\nInstalling new function for system-call %d\n", __NR_break );

	save_old_syscall = sys_call_table[ __NR_break ];
	sys_call_table[ __NR_break ] = (unsigned long)my_syscall;
	return	0;  // SUCCESS
}

void cleanup_module( void )
{
	printk( "<1>Removing \'%s\' module\n", modname );
	sys_call_table[ __NR_break ] = save_old_syscall;
}

MODULE_LICENSE("GPL");