//-------------------------------------------------------------------
//	timedfoo.c
//
//	This is an enhancement of our 'foo.c' device-driver.  It 
//	uses a kernel timer to curtail the frequency of calls to
//	its 'read()' function, by putting any task to sleep that
//	tries to reread from the device-file without waiting for
//	at least one-tenth of a second (as 'watchfoo.cpp' does).
//
//	programmer: ALLAN CRUSE
//	written on: 20 MAR 2005
//-------------------------------------------------------------------

#include <linux/module.h>	// for init_module() 
#include <linux/fs.h>		// for register_chrdev()
#include <asm/uaccess.h>	// for copy_to_user()
#include <linux/wait.h>		// for init_timer()

char modname[] = "foo";
int mymajor = 96;
struct timer_list mytimer;

struct foo_data	{ 
		int			ready;
		wait_queue_head_t	wq;
		} mydata;


void mytimeraction( unsigned long data )
{
	struct foo_data  *datap = (struct foo_data*)data;

	datap->ready = 1;
	wake_up_interruptible( &datap->wq );
}

ssize_t myread( struct file *file, char *buf, size_t count, loff_t *pos )
{
	void	*from = (void*)&jiffies_64;

	while ( !mydata.ready )
		{
		//printk( "going to sleep...  (ready=%d) \n", mydata.ready );
		if ( wait_event_interruptible( mydata.wq, mydata.ready ) )
			return 	-ERESTARTSYS;
		//printk( "awoke! (ready=%d) \n", mydata.ready );
		}
	mydata.ready = 0;
	
	if ( count > 8 ) count = 8;
	if ( copy_to_user( buf, from, count ) ) return -EFAULT;	

	mod_timer( &mytimer, jiffies + HZ / 10 );
	return	count;
}

struct file_operations myfops = {
				owner:		THIS_MODULE,
				read:		myread,
				};


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

	// initialize our timer-function's data-structure 
	mydata.ready = 1;
	init_waitqueue_head( &mydata.wq );

	// initialize our kernel-timer 
	init_timer( &mytimer );
	mytimer.function = mytimeraction;
	mytimer.data = (unsigned long)&mydata;
	mytimer.expires = jiffies + HZ * 2;

	// add our timer to the kernel's list of timers 
	add_timer( &mytimer );

	// register our device-driver with the kernel
	return	register_chrdev( mymajor, modname, &myfops );
}


void cleanup_module( void )
{
	printk( "<1>Removing \'%s\' module\n", modname );

	// unregister our device-driver 
	unregister_chrdev( mymajor, modname );

	// remove our timer from the kernel's list
	del_timer_sync( &mytimer );
}

MODULE_LICENSE("GPL");