/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (c) 1996 - 2000
 *      HD Associates, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by HD Associates, Inc
 * 4. Neither the name of the author nor the names of any co-contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY HD ASSOCIATES AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL HD ASSOCIATES OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

volatile int ticked;
#define CAN_USE_ALARMS

#ifdef CAN_USE_ALARMS
void tick(int arg)
{
        ticked = 1;
}
#endif

/* Fifo: Verify that fifo and round-robin scheduling seem to work.
 *
 * This tests:
 * 1. That sched_rr_get_interval seems to work;
 * 2. That FIFO scheduling doesn't seeem to be round-robin;
 * 3. That round-robin scheduling seems to work.
 * 
 */
static pid_t child;
static void tidyup(void)
{
        if (child)
                kill(child, SIGHUP);
}

static double
tvsub(const struct timeval *a, const struct timeval *b)
{
        long sdiff;
        long udiff;

        sdiff = a->tv_sec - b->tv_sec;
        udiff = a->tv_usec - b->tv_usec;

        return (double)(sdiff * 1000000 + udiff) / 1e6;
}

int fifo(int argc, char *argv[])
{
        int e = 0;
        volatile long *p, pid;
        int i;
        struct sched_param fifo_param;
        struct timespec interval;
#define MAX_RANAT 32
        struct timeval ranat[MAX_RANAT];

#ifdef CAN_USE_ALARMS
        static struct itimerval itimerval;
#endif

        /* What is the round robin interval?
         */

        if (sched_rr_get_interval(0, &interval) == -1) {
                perror("sched_rr_get_interval");
                exit(errno);
        }

#ifdef CAN_USE_ALARMS
        signal(SIGALRM, tick);
#endif

        fifo_param.sched_priority = 1;

        p = (long *)mmap(0, sizeof(*p),
        PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);

        if (p == (long *)-1)
                err(errno, "mmap");

        *p = 0;

        if (sched_setscheduler(0, SCHED_FIFO, &fifo_param) == -1)
        {
                perror("sched_setscheduler");
                return -1;
        }

        pid = getpid();

        if ((child = fork()) == 0)
        {
                /* Child process.  Just keep setting the pointer to our
                 * PID.  The parent will kill us when it wants to.
                 */

                pid = getpid();
                while (1)
                        *p = pid;
        }
        else
        {
                atexit(tidyup);
                *p = pid;


                ticked = 0;

#ifdef CAN_USE_ALARMS
                /* Set an alarm for 250 times the round-robin interval.
                 * Then we will verify that a similar priority process
                 * will not run when we are using the FIFO scheduler.
                 */
                itimerval.it_value.tv_usec = interval.tv_nsec / (1000 / 250);

                itimerval.it_value.tv_sec = itimerval.it_value.tv_usec / 1000000;
                itimerval.it_value.tv_usec %= 1000000;


                if (setitimer(ITIMER_REAL, &itimerval, 0) == -1) {
                        perror("setitimer");
                        exit(errno);
                }
#endif


                gettimeofday(ranat, 0);
                i = 1;
                while (!ticked && i < MAX_RANAT)
                        if (*p == child) {
                                gettimeofday(ranat + i, 0);
                                *p = 0;
                                e = -1;
                                i++;
                        }

                if (e) {
                        int j;

                        fprintf(stderr,
                        "SCHED_FIFO had erroneous context switches:\n");
                        for (j = 1; j < i; j++) {
                                fprintf(stderr, "%d %g\n", j,
                                        tvsub(ranat + j, ranat + j - 1));
                        }
                        return e;
                }

                /* Switch to the round robin scheduler and the child
                 * should run within twice the interval.
                 */
                if (sched_setscheduler(child, SCHED_RR, &fifo_param) == -1 ||
                sched_setscheduler(0, SCHED_RR, &fifo_param) == -1)
                {
                        perror("sched_setscheduler");
                        return -1;
                }

                e = -1;

                ticked = 0;

#ifdef CAN_USE_ALARMS

                /* Now we do want to see it run.  But only set
                 * the alarm for twice the interval:
                 */
                itimerval.it_value.tv_usec = interval.tv_nsec / 500;

                if (setitimer(ITIMER_REAL, &itimerval, 0) == -1) {
                        perror("setitimer");
                        exit(errno);
                }
#endif

                for (i = 0; !ticked; i++)
                        if (*p == child) {
                                e = 0;
                                break;
                        }

                if (e)
                        fprintf(stderr,"Child never ran when it should have.\n");
        }

        exit(e);
}

#ifdef STANDALONE_TESTS
int main(int argc, char *argv[]) { return fifo(argc, argv); }
#endif