//-------------------------------------------------------------------
//	nicasync.cpp
//
//	This demo illustrates the use of asynchronous notification 
//	to process packets received by the RealTek 8139 interface.
//	It relies upon a new version of our RealTek device-driver,
//	named 'nicasync.c', which implements the necessary support
//	for the asynchronous notification capability, as discussed
//	in the "Linux Device Drivers (3rd Ed)" book, in Chapter 6.  
//	You can run our 'trychat.cpp' program from another station
//	on the local network in order to test this demo.
//
//	       compile with: $ g++ nicasync.cpp -o nicasync
//
//	programmer: ALLAN CRUSE
//	written on: 27 APR 2005
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 
#include <string.h>	// for strlen()
#include <signal.h>	// for sigaction()
#include <sys/fcntl.h>	// for fcntl()
#include <sys/wait.h>	// for wait()
#include <sys/poll.h>	// for POLLIN, POLLOUT
#include <netinet/in.h>	// for htons()

#define CHAT_ID 0x0635	// identifies our packet-protocol

int done = 0;
char devname[] = "/dev/nic";

void my_sigaction( int signo, siginfo_t *info, void *data )
{
	if ( signo == SIGINT ) done = 1;  // <CONTROL>-C pressed
	else	if ( signo != SIGUSR1 ) return;

	// validate signal-information: data is ready to be read
	if ( info->si_code != 1 ) return;
	if ( (info->si_band & POLL_IN)==0 ) return;

	// read the new data from the network device
	unsigned char	msg[ 1536 ] = {0};	
	if ( read( info->si_fd, msg, sizeof( msg ) ) < 0 ) return; 

	// if it's a 'netchat' packet, then display its character
	if ( *(short*)(msg+12) == htons( CHAT_ID ) ) 
		{
		int	nbytes = *(short*)(msg+14);
		write( STDOUT_FILENO, msg+16, nbytes );
		}
}


int main( void )
{
	// install our signal-handler
	struct sigaction	oa, sa = {0};
	sigset_t		my_mask;
	sigemptyset( &my_mask );	// no blocked signals
	sa.sa_sigaction = my_sigaction;
	sa.sa_mask = my_mask;
	sa.sa_flags = SA_SIGINFO;	
	sigaction( SIGUSR1, &sa, &oa );
	sigaction( SIGINT, &sa, NULL );

	// open the device-file
	int	fd = open( devname, O_RDWR ); 
	if ( fd < 0 ) { perror( devname ); exit(1); }

	// set device-file's owner (for signal-delivery)
	fcntl( fd, F_SETOWN, getpid() );

	// specify which signal is to be delivered
	fcntl( fd, F_SETSIG, SIGUSR1 );

	// enable asynchronous notification
	int	flags = fcntl( fd, F_GETFL );
	fcntl( fd, F_SETFL, flags | FASYNC );

	// main loop to await <CONTROL>-C typed by user
	while ( !done ) pause();

	// restore the original signal-handler for SIGUSR1
	sigaction( SIGUSR1, &oa, NULL );

	// close the device-file and terminate this program
	close( fd );
	exit(0);
}