//-------------------------------------------------------------------
//	channels.c
//
//	This module will install a set of kernel facilities for use 
//	by one process in posting a message to another process.  It
//	is currently under construction.
//
//	NOTE: This module expects our 'myexport.o' to be installed.
//
//	programmer: ALLAN CRUSE
//	date begun: 07 NOV 2004 -- implemented make operation
//	revised on: 10 NOV 2004 -- added open, post, and pend
//	completion:
//-------------------------------------------------------------------

#include <linux/module.h>	// for init_module() 
#include <linux/proc_fs.h>	// for create_proc_read_entry() 
#include <asm/uaccess.h>	// for copy_to/from_user()
#include "channels.h"		// for constants and functions

#define N_ELTS		16	// maximum number of channels

typedef struct	{
		pid_t		ownr;
		pid_t		user;
		void *		base;
		unsigned long	size;
		wait_queue_head_t rq;
		wait_queue_head_t wq;
		} CHANNEL;


static char modname[] = "channels";
static unsigned long save_old_syscall;
extern unsigned long * sys_call_table;
static CHANNEL channel[ N_ELTS ];

static int my_get_info( char *buf, char **start, off_t off, int count )
{
	int	i, len;

	len = sprintf( buf+len, "\n%s\n", modname );

	for (i = 0; i < N_ELTS; i++)
		{
		len += sprintf( buf+len, "%2d: ", i );
		len += sprintf( buf+len, "base=%08X ", channel[ i ].base );
		len += sprintf( buf+len, "size=%-8d ", channel[ i ].size );
		len += sprintf( buf+len, "ownr=%-5d ", channel[ i ].ownr );
		len += sprintf( buf+len, "user=%-5d ", channel[ i ].user );
		len += sprintf( buf+len, "\n" );
		}

	len += sprintf( buf+len, "\n" );
	return	len;
}

static asmlinkage long my_syscall( int cmd, int key, char *buf, int len )
{
	pid_t		pid = current->pid;
	int		idx, more;	
	void		*where;

	switch ( cmd )
		{
		case CHAN_MAKE:	
		for (idx = 0; idx < N_ELTS; idx++)
			if ( channel[ idx ].ownr == 0 ) break;
		if ( idx == N_ELTS ) return -ENOSPC;
		where = kmalloc( INFO_LENGTH, GFP_KERNEL );
		if ( !where ) return -ENOMEM;
		channel[ idx ].base = where;
		channel[ idx ].size = 0;
		channel[ idx ].user = 0;
		channel[ idx ].ownr = pid;
		return	idx;	
				
		case CHAN_OPEN:	
		if (( key < 0 )||(key >= N_ELTS )) return -EINVAL;
		if ( channel[ key ].ownr == 0 ) return -ENOTTY;
		if ( channel[ key ].user != 0 ) return -EBUSY;
		if ( channel[ key ].ownr == pid ) return -EPERM;
		channel[ key ].user = pid;
		return	0;	// <-- Is this what we want?

		case CHAN_SHUT:	break;
		case CHAN_POST:	
		if (( key < 0 )||(key >= N_ELTS )) return -EINVAL;
		if ( channel[ key].ownr != pid ) return -EPERM;
		while ( channel[ key ].size != 0 )
			{
			interruptible_sleep_on( &channel[ key ].wq );
			if ( signal_pending( current ) ) return -EINTR;
			}
		if ( len > INFO_LENGTH ) len = INFO_LENGTH;
		where = channel[ key ].base;
		more = copy_from_user( where, buf, len );
		if ( more ) return -EFAULT;
		channel[ key ].size = len;
		wake_up_interruptible( &channel[ key ].rq );
		return 	len;

		case CHAN_PEND: 
		if (( key < 0 )||(key >= N_ELTS )) return -EINVAL;
		if ( channel[ key].user != pid ) return -EPERM;
		while ( channel[ key ].size == 0 )
			{
			interruptible_sleep_on( &channel[ key ].rq );
			if ( signal_pending( current ) ) return -EINTR;
			}
		if ( len > channel[ key ].size ) len = channel[ key ].size;
		where = channel[ key ].base;
		more = copy_to_user( buf, where, len );
		if ( more ) return -EFAULT;
		channel[ key ].size = 0;
		wake_up_interruptible( &channel[ key ].wq );
		return 	len;

		case CHAN_KILL:	break;
		}

	return	-EINVAL;
}

int init_module( void )
{
	int	i;
	
	printk( "<1>\nInstalling \'%s\' module\n", modname );

	// initialize the stashes
	for (i = 0; i < N_ELTS; i++)
		{
		init_waitqueue_head( &channel[ i ].wq );
		init_waitqueue_head( &channel[ i ].rq );
		}

	// install the system-call
	save_old_syscall = sys_call_table[ OBSOLETE_ID ];
	sys_call_table[ OBSOLETE_ID ] = (unsigned long)my_syscall;
	
	// create the pseudo-file
	create_proc_info_entry( modname, 0, NULL, my_get_info );
	return	0;  // SUCCESS
}

void cleanup_module( void )
{
	int	i;
	
	// restore sys_call_table[]	
	sys_call_table[ OBSOLETE_ID ] = save_old_syscall;

	// remove the pseudo-file
	remove_proc_entry( modname, NULL );
	printk( "<1>Removing \'%s\' module\n", modname );
}

MODULE_LICENSE("GPL");