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

  PURPOSE - show use of iopl and exec to give a non-root program
            direct IO access, interrupt access, and set process priority.
            All forked and exec'ed programs inherit IO access.
	    
    USAGE - compile,  ensure the executable is owned by root,
            and do root SETUID with "chmod u+s iopl_start"
          - ./iopl_start ./target_program_name  param1 param2 ...  

     NOTE - iopl allows access to all IO ports 0-0xFFFF and the
            ability to enable or disable interrupts.
	  - the setgid, setuid removes root privileges.  
          - the setpriority can set process scheduling priority.
	  - the command line minus the first parameter (the target
	    program name) is sent to the target program. 
          - the ioperm method should be used instead unless interrupt control
            is required or forked processes also need IO privileges.
*/
#include <stdio.h>
#include <unistd.h>
#include <sys/io.h>
#include <sys/time.h>     /* for priority control.*/
#include <sys/resource.h> /* for priority control.*/

int main(int argc, char *argv[])
{ /*--- abort if no parameters.*/
    if ( argc < 2)
      {  fprintf(stderr, "   No target program name : aborting.\n") ;
         exit(-1) ;
      }
  
  /*--- set process priority, 0= normal, -20 highest, +20 lowest.*/
    setpriority( PRIO_PROCESS, -10, 0 ) ;

  /*--- Get access to the ports and remove root privileges.*/  
    if (iopl(3)) 
      { perror("   Failed iopl(3)"); 
        exit(-1);
      }      
    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") ;
    fprintf(stderr, "   Target program was %s.\n", argv[1]) ;
    exit( -1) ;
}