//-------------------------------------------------------------------
//	howfast.cpp
//
//	This program shows how you can measure the rate at which the
//	kernel's 'jiffies' variable increments.  It makes use of the 
//	standard UNIX 'sleep()' function to create a 1-second delay,
//	and assumes our compiled 'jiffies.ko' module can be found in
//	the current directory.
//
//	programmer: ALLAN CRUSE
//	written on: 27 JAN 2005
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for system(), exit(), stroul() 
#include <unistd.h>	// for read(), sleep(), lseek(), close() 

#define BUFSZ	80

char filename[] = "/proc/jiffies";
char buffer[ BUFSZ ];

int main( int argc, char **argv )
{
	// install module that creates our pseudo-file
	system( "/sbin/insmod jiffies.ko" );

	// open the pseudo-file for reading	
	int	fd = open( filename, O_RDONLY );
	if ( fd < 0 ) { perror( filename ); exit(1); }

	// read the current value of jiffies
	if ( read( fd, buffer, BUFSZ ) < 0 ) { perror( "read 1" ); exit(1); }	
	unsigned long	first = strtoul( buffer+10, NULL, 10 );

	// delay for one second
	sleep( 1 );

	// now read the value of jiffies again
	lseek( fd, 0, SEEK_SET );
	if ( read( fd, buffer, BUFSZ ) < 0 ) { perror( "read 2" ); exit(1); }	
	unsigned long	final = strtoul( buffer+10, NULL, 10 );

	// calculate and display the number of jiffies-per-second
	printf( "%lu\n", first );
	printf( "%lu\n", final );
	printf( "difference = %lu \n", final - first );

	// close the pseudo-file and remove our kernel module
	close( fd );
	system( "/sbin/rmmod jiffies " );
}