//-------------------------------------------------------------------
//	freydemo.c
//
//	Demonstrates use of the 'keventd' daemon to start and stop
//	kernel threads, adapted from a demo-module by Martin Frey:
//
//	     http://www.scs.ch/~frey/linux/kernelthreads.html
//
//	NOTE: Developed and tested with Linux kernel version 2.4.4.
//
//	programmer: ALLAN CRUSE
//	written on: 15 MAR 2002
//	revised on: 15 NOV 2004 -- for Linux kernel version 2.4.26.
//-------------------------------------------------------------------

#include <linux/module.h>	// for init_module() 
#include <linux/sched.h>	// for schedule_task()
#include <asm/smplock.h>	// for lock_kernel()

#define NTHREADS 5		// number of kernel threads

typedef struct kthread_struct
	{
	struct task_struct	*thread;
	struct tq_struct	tq;
	void (*function)( struct kthread_struct *);
	struct semaphore	startstop_sem;
	wait_queue_head_t	wq;
	int			terminate;
	void			*arg;
	} kthread_t;


static char modname[] = "freydemo";
static pid_t keventd_pid;		// PID for 'keventd' daemon
static kthread_t example[ NTHREADS ]; 	// array of thread structures


static void kthread_launcher( void *data )
{
	kthread_t	*kthread = data;
	kernel_thread( (int (*)(void*))kthread->function, (void*)kthread, 0 ); 
}


void start_kthread( void (*func)( kthread_t *), kthread_t *kthread )
{
	static int	count = 0;

	init_MUTEX_LOCKED( &kthread->startstop_sem );

	kthread->function = func;
	kthread->arg = (void *)(++count);	

	kthread->tq.sync = 0;
	INIT_LIST_HEAD( &kthread->tq.list );
	kthread->tq.routine = kthread_launcher;
	kthread->tq.data = kthread;

	schedule_task( &kthread->tq );

	down( &kthread->startstop_sem );
}


void stop_kthread( kthread_t *kthread )
{
	if ( kthread->thread == NULL )
		{
		printk( "<1>  stop_kthread: killing nonexistent thread\n" );
		return;
		}

	lock_kernel();
	init_MUTEX_LOCKED( &kthread->startstop_sem );
	mb();
	kthread->terminate = 1;
	mb();
	kill_proc( kthread->thread->pid, SIGKILL, 1 );
	down( &kthread->startstop_sem );
	unlock_kernel();

	kill_proc( keventd_pid, SIGCHLD, 1 );
}


void init_kthread( kthread_t *kthread, const char *name )
{

	lock_kernel();
	kthread->thread = current;
	siginitsetinv( &current->blocked, 
		sigmask( SIGKILL )|sigmask( SIGINT )|sigmask( SIGTERM ) );
	init_waitqueue_head( &kthread->wq );
	kthread->terminate = 0;
	sprintf( &current->comm[0], "%s #%d", name, kthread->arg );
	unlock_kernel();

	up( &kthread->startstop_sem );
}


void exit_kthread( kthread_t *kthread )
{
	lock_kernel();
	kthread->thread = NULL;
	mb();
	up( &kthread->startstop_sem );
	unlock_kernel();	// <----???? Frey omits this
}


//-------------------------------------------------------------------


static void our_example_thread( kthread_t *kthread )
{
	init_kthread( kthread, "example thread" );
	printk( "<1>  Hi, I am kernel thread #%d\n", kthread->arg );
	
	for (;;)
		{
		interruptible_sleep_on_timeout( &kthread->wq, HZ );
		
		mb();
		if ( kthread->terminate ) break;
		
		printk( "<1>  thread #%d just woke up\n", kthread->arg );
		}

	exit_kthread( kthread );
}	


int init_module( void )
{
	struct task_struct	*tsk = &init_task;
	int	i;

	printk( "<1>\nInstalling \'%s\' module\n", modname );

	// determine the process-ID for the 'kevent' daemon
	while (  ( tsk = tsk->next_task ) != current )
		if ( strncmp( tsk->comm, "keventd", 7 ) == 0 ) 
			keventd_pid = tsk->pid;
	if ( !keventd_pid ) return -ESRCH;
	
	// start each one of our kernel threads
	for (i = 0; i < NTHREADS; i++)
		start_kthread( our_example_thread, &example[i] );
	return	0;  // SUCCESS
}


void cleanup_module( void )
{
	int	i;

	// stop each one of our kernel threads	
	for (i = 0; i < NTHREADS; i++) stop_kthread( &example[i] );
	printk( "<1>Removing \'%s\' module\n", modname );
}

MODULE_LICENSE("GPL");