/*============= Give a user program IO access : lp_tty_start.c =============

  PURPOSE - show use of ioperm and exec to give a non-root program
            direct IO access to just lp0/1/2 and ttyS0/1/2/3.
            Priority is also adjusted.
	    
    USAGE - ./ioperm_start ./target_program_name  param1 param2 ...  

     NOTE - ioperm allows access to a limited range of IO between
            0 and 0x3FF and no access to interrupt disable/enable.
	  - the setgid, setuid removes root privileges.  
          - setpriority adjusts process scheduling priority.
	  - the command line minus the first parameter (the target
	    program name) is sent to the target program. 
*/
#include <iostream.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/io.h>
#include <sys/resource.h>

const int lp0  =  0x378; // lp (LPT) base addresses.
const int lp1  =  0x278;
const int lp2  =  0x3BC;
const int lp_length = 3;

const int ttyS0 = 0x3F8; // ttyS (COM) port base addresses.
const int ttyS1 = 0x2F8;
const int ttyS2 = 0x3E8;
const int ttyS3 = 0x2E8;
const int ttyS_length = 8;

int main( int argc, char *argv[] )
{
        // abort if no parameters:
        if ( argc < 2 ) {
                cerr << "usage: " << argv[ 0 ] << " program program-args...\n";
                exit( 1 );
        }
  
        // set process priority: see man setpriority
        // may need to sudo apt-get install manpages-dev to see it.
        const int priority = 0; // 0= normal, -20 highest, +20 lowest.
        const int this_process = 0;
        setpriority( PRIO_PROCESS, this_process, priority );

        /*--- Get access to the ports and remove root privileges.*/  
        if ( ioperm( lp0, lp_length, 1 ) ) 
                perror( "Failed ioperm lp0 on" ); 
        // if ( ioperm( lp1, lp_length, 1 ) ) 
        //   perror( "Failed ioperm lp1 on" ); 
        // if ( ioperm( lp2, lp_length, 1 ) ) 
        //   perror( "Failed ioperm lp2 on" ); 
        
        // if ( ioperm( ttyS0, ttyS_length, 1 ) ) 
        //   perror( "Failed ioperm ttyS0 on" ); 
        // if ( ioperm( ttyS1, ttyS_length, 1) ) 
        //   perror( "Failed ioperm ttyS1 on" ); 
        // if ( ioperm( ttyS2, ttyS_length, 1 ) ) 
        //   perror( "Failed ioperm ttyS2 on" ); 
        // if ( ioperm( ttyS3, ttyS_length, 1 ) ) 
        //   perror( "Failed ioperm ttyS3 on" ); 
        
        setgid( getgid() );
        setuid( getuid() );  
        
        /*--- do the exec to the target program, 
          use argv array from parameter 1 onward.*/
        execvp( argv[1], &argv[1] );
        /*    if get here exec must have failed.*/  
        perror( " execv failed" );
        cerr << "Target program was " << argv[ 1 ] << "\n";
        exit( 2 );
}