第 64 章 伪终端 (Pseudoterminals)

#define _XOPEN_SOURCE 600
#include <stdlib.h>
#include <fcntl.h>
int posix_openpt(int flags);                    /* O_RDWR | O_NOCTTY */
int grantpt(int mfd);
int unlockpt(int mfd);
char *ptsname(int mfd);                         /* 静态缓存名 /dev/pts/N */

// 摘自《The Linux Programming Interface》 第 64 章 Listing 64-2
pid_t ptyFork(int *masterFd, char *slaveName, size_t snLen,
              const struct termios *slaveTermios, const struct winsize *slaveWS)
{
    int mfd, slaveFd, savedErrno;
    pid_t childPid;
    char slname[MAX_SNAME];
    mfd = ptyMasterOpen(slname, MAX_SNAME);
    if (mfd == -1) return -1;
    if (slaveName != NULL) {
        if (strlen(slname) < snLen) strncpy(slaveName, slname, snLen);
        else { close(mfd); errno = EOVERFLOW; return -1; }
    }
    childPid = fork();
    if (childPid == -1) { close(mfd); return -1; }

    if (childPid != 0) { /* Parent */
        *masterFd = mfd;
        return childPid;
    }

    /* Child: become session leader, acquire controlling tty on pty slave */
    if (setsid() == -1) errExit("setsid");
    close(mfd);
    slaveFd = open(slname, O_RDWR);
    if (slaveFd == -1) errExit("open-slave");
#ifdef TIOCSCTTY
    if (ioctl(slaveFd, TIOCSCTTY, 0) == -1) errExit("ioctl-TIOCSCTTY");
#endif
    if (slaveTermios != NULL)
        if (tcsetattr(slaveFd, TCSANOW, slaveTermios) == -1) errExit("tcsetattr");
    if (slaveWS != NULL)
        if (ioctl(slaveFd, TIOCSWINSZ, slaveWS) == -1) errExit("ioctl-TIOCSWINSZ");
    if (dup2(slaveFd, STDIN_FILENO) != STDIN_FILENO) errExit("dup2-STDIN");
    if (dup2(slaveFd, STDOUT_FILENO) != STDOUT_FILENO) errExit("dup2-STDOUT");
    if (dup2(slaveFd, STDERR_FILENO) != STDERR_FILENO) errExit("dup2-STDERR");
    if (slaveFd > STDERR_FILENO) close(slaveFd);
    return 0;
}

int arg = 1;
ioctl(mfd, TIOCPKT, &arg);   /* 启；0 关 */
/* 主循环：read → first byte 0 → 后面是 slave 写入数据 */
/*       first byte != 0 → 控制信息，丢弃 */
fd_set rfds, xfds;
FD_SET(mfd, &rfds);
FD_SET(mfd, &xfds);    /* 监听 packet 通知 */
select(mfd+1, &rfds, NULL, &xfds, NULL);
if (FD_ISSET(mfd, &xfds)) { /* poll()'s POLLPRI */
    /* 重新读 control byte */
}

// 摘自《The Linux Programming Interface》 第 64 章 Listing 64-3 (核心循环)
if (tcgetattr(STDIN_FILENO, &ttyOrig) == -1) errExit("tcgetattr");
if (ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) < 0) errExit("ioctl-TIOCGWINSZ");
childPid = ptyFork(&masterFd, slaveName, MAX_SNAME, &ttyOrig, &ws);
/* child */
/* execlp(shell, shell, (char*)NULL); */
/* parent */
scriptFd = open(argv[1] ? argv[1] : "typescript", O_WRONLY|O_CREAT|O_TRUNC, 0666);
ttySetRaw(STDIN_FILENO, &ttyOrig);   /* 关 term 处理 */
atexit(ttyReset);                     /* 退出恢复 */
for (;;) {
    FD_ZERO(&inFds);
    FD_SET(STDIN_FILENO, &inFds);
    FD_SET(masterFd, &inFds);
    select(masterFd + 1, &inFds, NULL, NULL, NULL);
    if (FD_ISSET(STDIN_FILENO, &inFds)) {
        numRead = read(STDIN_FILENO, buf, BUF_SIZE);
        if (numRead <= 0) exit(EXIT_SUCCESS);
        write(masterFd, buf, numRead);
    }
    if (FD_ISSET(masterFd, &inFds)) {
        numRead = read(masterFd, buf, BUF_SIZE);
        if (numRead <= 0) exit(EXIT_SUCCESS);
        write(STDOUT_FILENO, buf, numRead);
        write(scriptFd, buf, numRead);
    }
}

/* 父侦 SIGWINCH */
sa.sa_handler = sigwinch_handler;
sigaction(SIGWINCH, &sa, NULL);
/* handler 内：
   ioctl(STDIN_FILENO, TIOCGWINSZ, &ws);
   ioctl(masterFd, TIOCSWINSZ, &ws);  // 自动 propagate
*/

/* BSD 试探 */
for (x = "pqrstuvwxyzabcde"; *x; x++) {
    for (y = "0123456789abcdef"; *y; y++) {
        snprintf(name, sizeof(name), "/dev/pty%c%c", *x, *y);
        masterFd = open(name, O_RDWR);
        if (masterFd >= 0) goto found;
        if (errno == ENOENT) goto done;  /* 跑完 */
        /* EIO 等忽略继续 */
    }
}
found:
snprintf(slaveName, ..., "/dev/tty%c%c", *x, *y);