//-------------------------------------------------------------------
//	tcb.c
//
//	This module creates a read-only pseudo-file ("/proc/tcb")
//	which allows an application program to access the current
//	contents of its Task Control Block (i.e., 'task_struct').   
//
//	NOTE: Written and tested using Linux kernel version 2.4.26.
//
//	programmer: ALLAN CRUSE
//	written on: 18 SEP 2004
//-------------------------------------------------------------------

#include <linux/module.h>	// for init_module() 
#include <linux/proc_fs.h>	// for create_proc_entry() 
#include <asm/uaccess.h>	// for copy_to_user()

#define	PROC_DIR	NULL
#define	PROC_MODE	0444

static char modname[] = "tcb";
static loff_t tcbsize = sizeof( struct task_struct );

static ssize_t
my_read( struct file *file, char *buf, size_t count, loff_t *pos )
{
	struct task_struct	*tsk = current;
	int			nbytes = count;
	
	// we cannot read beyond the end of the task_struct
	if ( *pos >= tcbsize ) return 0;

	// maximum number of bytes to be transferred
	if ( *pos + nbytes > tcbsize ) nbytes = tcbsize - *pos;
	
	// perform the transfer, report error if unsuccessful
	if ( copy_to_user( buf, tsk, nbytes ) ) return -EFAULT;
		
	// report the number of bytes transferred
	return	nbytes;
}

static loff_t my_seek( struct file *file, loff_t offset, int whence )
{
	loff_t	newpos = -1;
	
	switch ( whence )
		{
		case 0:	newpos = offset; break;		// SEEK_SET
		case 1: newpos += offset; break;	// SEEK_CUR
		case 2: newpos = tcbsize + offset;	// SEEK_END
		}
	if (( newpos < 0 )||( newpos > tcbsize )) return -EINVAL;
	file->f_pos = newpos;
	return	newpos;
}	


static struct file_operations 
my_fops =	{
		owner:		THIS_MODULE,
		llseek:		my_seek,
		read:		my_read,
		};


int init_module( void )
{
	struct proc_dir_entry	*entry;

	entry = create_proc_entry( modname, PROC_MODE, PROC_DIR );
	entry->proc_fops = &my_fops;
	return	0;	// SUCCESS;
}


void cleanup_module( void )
{
	remove_proc_entry( modname, PROC_DIR );
}

MODULE_LICENSE("GPL");