/*
 * Project:
 *  Explore the POSIX1003.1b Scheduling Interface.
 *
 * Author:
 *  (c) Till Christian Siering.
 *      
 * File:
 *  atprio1.c
 *      
 * Description:
 *  Runs a given Program with a given Priority using
 *  Scheduling-Fifo Scheduling.
 *      
 * Begin:
 *  I don't remember.
 *      
 * Changes:
 *  22.07.1997  added Comments.
 *      
 * To do:
 *  Probably the Scheduling Algorithm could be a Option, too.
 *      
 * References:
 *  Bill O. Gallmeister: POSIX.4, O'Reilly & Associates Inc.
 */

#include <stdio.h>
#include <errno.h>
#include <sched.h>

char *progname;

void
usage()
{
    fprintf(stderr,"Usage %s <priority> <command>\n", progname);
}

int
main(int argc, char **argv)
{

    int priority;
    int min_priority;
    int max_priority;
    struct sched_param cmd_sched_params;

    progname = argv[0];
    if(argc < 3) {
        usage();
        exit(1);
    }

    priority = atoi(argv[1]);
    if((min_priority = sched_get_priority_min(SCHED_FIFO)) == -1) {
        perror("sched_get_priority_min");
        exit(2);
    }
    if((max_priority = sched_get_priority_max(SCHED_FIFO)) == -1) {
        perror("sched_get_priority_max");
        exit(2);
    }
    if((priority < min_priority) || (priority > max_priority )) {
        fprintf(stderr,"Priority must be greater or equal %d and smaller or equal %d\n",
                min_priority, max_priority);
        exit(2);
    }

    cmd_sched_params.sched_priority = priority;

    /*
     * Set Scheduling-Fifo for this Process.
     */
    if(sched_setscheduler(0, SCHED_FIFO, &cmd_sched_params) < 0) {
        perror("sched_setscheduler");
        exit(2);
    }

    /*
     * Execute Command.
     */
    if(execvp(argv[2], &argv[2]) < 0) {
        perror("execvp");
        exit(3);
    }
}