Zombie Screen

shotgun.c

#include <errno.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>

#if 0
#include <stdio.h>
#define print1 printf
#define print2 printf
#else
#define print1(a,b) do{}while(0)
#define print2(a,b,c) do{}while(0)
#endif

static pid_t child = -1, reaped;
static int i, code, status;

static void sig_forward(int sig) {
    print2("forwarding signal %d to pid %d\n", sig, child);
    kill(child, sig);
}
static struct sigaction sa = {
    .sa_mask = 0,
    .sa_flags = 0,
    .sa_handler = sig_forward,
};

static int loop() {
    sigaction(SIGHUP, &sa, NULL);
    sigaction(SIGINT, &sa, NULL);
    sigaction(SIGQUIT, &sa, NULL);
    sigaction(SIGTERM, &sa, NULL);
    sigaction(SIGUSR1, &sa, NULL);
    sigaction(SIGUSR2, &sa, NULL);
    do {
        reaped = wait(&status);
        print2("waited for pid %d, status %d\n", reaped, status);
        if (reaped == child) {
            if (WIFEXITED(status))
                code = WEXITSTATUS(status);
            else if (WIFSIGNALED(status))
                code = 128 + WTERMSIG(status);
            print1("child exitted, saving code %d\n", code);
        }
    } while(reaped != -1 || errno != ECHILD);
    return code;
}

int main(int argc, char *argv[]) {
    for (i = 0; i < argc; i++) {
        argv[i] = argv[i+1];
    }
    argv[argc-1] = NULL;
    if (argc == 1)
        return 1;
    child = fork();
    if (child < 0)
        return child;
    if (child == 0)
        return execvp(argv[0], argv);
    return loop();
}