问如何创建后台进程块，用于输入shell的`bg`命令？

EN

#include <unistd.h>

    sleep(600); /* triggering condition goes here */
    pid_t pgid = tcgetpgrp(0);
    pid_t pid;
    if ((pid = fork()) == 0) { /* Need to fork to safely create a new process group to bind to the terminal -- otherwise we might be in the same process group as we started in */
        pid_t npid = getpid();
        setpgid(npid, npid); /* create new process group and put us in it */
        pid_t pid2;
        if ((pid2 = fork() == 0) { /* what? another process */
            setpgid(getpid(), pgid);
            tcsetpgid(0, getpid()); /* set active process group */
            _exit(0);
        }
        if (pid2 > 0) {
            int junk;
            waitpid(pid2, &junk, 0);
        }
        struct termios savedattr;
        struct termios newattr;
        tcgetattr(0, &savedattr);
        newattr = savedattr;
        newattr.c_lflag |= ICANON | ECHO;
        tcsetattr(0, TCSANOW, &newattr); /* set sane terminal state */
        printf("\nHi there. I'm the background process and I want some input:");
        char buf[80];
        fgets(buf, 80, stdin);
        /* Do something with user input here */
        tcsetattr(0, TCSANOW, &savedattr); /* restore terminal state */
        tcsetpgrp(0, pgid); /* restore terminal owner -- only possible if the existing owner is a live process */
    } else {
        if (pid > 0) {
            int junk;
            waitpid(pid, &junk, 0);
        }
    }