//-------------------------------------------------------------------
//	trynotif.c
//
//	This driver is intented to investigate the statement made by
//	John O'Gorman about the 'notifier' field in the task_struct.
//	"A device driver can set up this pointer to a function to be
//	called when any of the signals specified in 'notifier_mask'
//	is generated.  The driver can then decide whether to ignore
//	or handle this signal [Linux Process Manager, page 38]."  
//
//	Here is our plan for testing:
//	1) create some stopped processes (e.g. using 'loadonly.cpp') 
//	2) install this device-driver
//	3) this driver will install a pointer to a local function in
//	   the 'notifier' field of every stopped task's task_struct, 
//	   and initialize the 'notifier_mask' field for all signals
//	4) the 'kill' command will be issued by the user (to send a
//	   signal to one of the 'stopped' tasks)
//	5) check the log to see if our notifier-routine got called
//
//	NOTE: Written and tested using Linux kernel version 2.4.26.
//
//	programmer: ALLAN CRUSE
//	written on: 14 AUG 2004
//-------------------------------------------------------------------

#include <linux/module.h>	// for init_module() 
#include <linux/sched.h>	// for current
#include <linux/signal.h>	// for sigset_t

static char modname[] = "trynotif";
static sigset_t my_mask = { ~0LL }; 

static int my_notifier( void *priv )
{
	static int	rep = 0;
	printk( "NOTIFICATION #%d: pid=%d \n", ++rep, current->pid );
	return	~0;
}	

int init_module( void )
{
	// install notifier-function in all stopped processes
	struct task_struct	*tsk = current;
	while ( ( tsk = tsk->next_task ) != current )
		if ( tsk->state == TASK_STOPPED ) 
			{
			tsk->notifier = my_notifier;
			tsk->notifier_mask = &my_mask;
			printk( "pid=%5d %-16s \n", tsk->pid, tsk->comm );
			}	
	return	0;  // SUCCESS
}

void cleanup_module( void ) { }

MODULE_LICENSE("GPL");