/*      $OpenBSD: sigsuspend.c,v 1.1 2020/09/16 14:04:30 mpi Exp $      */
/*
 *      Written by Artur Grabowski <art@openbsd.org> 2005, Public domain.
 */

#include <stdlib.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#include <err.h>
#include <sys/types.h>
#include <sys/wait.h>

sig_atomic_t gotusr1;
sig_atomic_t gotusr2;

void
usr1handler(int signo)
{
        gotusr1 = 1;
}

void
usr2handler(int signo)
{
        gotusr2 = 1;
}

int
main()
{
        sigset_t set, oset;
        struct sigaction sa;
        pid_t pid, ppid;
        int status;

        ppid = getpid();

        memset(&sa, 0, sizeof(sa));
        sigemptyset(&sa.sa_mask);
        sa.sa_handler = usr1handler;
        if (sigaction(SIGUSR1, &sa, NULL))
                err(1, "sigaction(USR1)");

        sa.sa_handler = usr2handler;
        if (sigaction(SIGUSR2, &sa, NULL))
                err(1, "sigaction(USR2)");

        /*
         * Set the procmask to mask the early USR1 the child will send us.
         */
        sigemptyset(&set);
        sigaddset(&set, SIGUSR1);
        sigaddset(&set, SIGUSR2);
        if (sigprocmask(SIG_BLOCK, &set, &oset))
                err(1, "sigprocmask");

        switch((pid = fork())) {
        case 0:
                /*
                 * In the child. 
                 */

                kill(ppid, SIGUSR1);    /* Tell the parent we're ready. */

                sigemptyset(&set);
                sigaddset(&set, SIGUSR2);
                sigsuspend(&set);

                /*
                 * Check that sigsuspend didn't change the signal mask.
                 */
                if (sigprocmask(SIG_SETMASK, NULL, &oset))
                        err(1, "sigprocmask");
                if (!sigismember(&oset, SIGUSR1) ||
                    !sigismember(&oset, SIGUSR2))
                        errx(1, "sigprocmask is bad");

                /* Check that we got the sigusr1 that we expected. */
                if (!gotusr1)
                        errx(1, "didn't get usr1");
                if (gotusr2)
                        errx(1, "got incorrect usr2");
                
                sigemptyset(&set);
                sigaddset(&set, SIGUSR1);
                sigsuspend(&set);

                if (!gotusr2)
                        errx(1, "didn't get usr2");

                _exit(0);
        case -1:
                err(1, "fork");
        default:
                /*
                 * In the parent.
                 * Waiting for the initial USR1 that tells us the child
                 * is ready.
                 */
                while (gotusr1 == 0)
                        sigsuspend(&oset);

                /*
                 * Check that sigsuspend didn't change the signal mask.
                 */
                if (sigprocmask(SIG_SETMASK, NULL, &oset))
                        err(1, "sigprocmask");
                if (!sigismember(&oset, SIGUSR1) ||
                    !sigismember(&oset, SIGUSR2))
                        errx(1, "sigprocmask is bad");

                /*
                 * Deliberately send USR2 first to confuse.
                 */
                kill(pid, SIGUSR2);
                kill(pid, SIGUSR1);

                if (waitpid(pid, &status, 0) != pid)
                        err(1, "waitpid");

                if (WIFEXITED(status))
                        exit(WEXITSTATUS(status));
                exit(1);
        }
        /* NOTREACHED */
}