Question

我正在试图为代表 PTY 的文件描述符设定一个读过超时值。我将 VMIN = 0 和 VTIME = 10 的名词设置为名词。我期望当字符可用时返回, 或者在一秒钟后, 如果没有字符可用时返回。但是, 我的程序会永远在读取调用中。

PTY有什么特别之处使这个无效吗?有没有其他的 TERTIOS 设置使这个功能起作用?我在标准文件描述符上尝试过同样的配置,它和预期的一样有效。

#define _XOPEN_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <fcntl.h>

#define debug(...) fprintf (stderr, __VA_ARGS__)

static void set_term (int fd)
{
    struct termios termios;
    int res;

    res = tcgetattr (fd, &termios);
    if (res) {
        debug ("TERM get error
");
        return;
    }

    cfmakeraw (&termios);
    termios.c_lflag &= ~(ICANON);
    termios.c_cc[VMIN] = 0;
    termios.c_cc[VTIME] = 10;        /* One second */

    res = tcsetattr (fd, TCSANOW, &termios);
    if (res) {
        debug ("TERM set error
");
        return;
    }

}

int get_term (void)
{
    int fd;
    int res;
    char *name;

    fd = posix_openpt (O_RDWR);
    if (fd < 0) {
        debug ("Error opening PTY
");
        exit (1);
    }

    res = grantpt (fd);
    if (res) {
        debug ("Error granting PTY
");
        exit (1);
    }

    res = unlockpt (fd);
    if (res) {
        debug ("Error unlocking PTY
");
        exit (1);
    }

    name = ptsname (fd);
    debug ("Attach terminal on %s
", name);

    return fd;
}

int main (int argc, char **argv)
{
    int read_fd;
    int bytes;
    char c;

    read_fd = get_term ();

    set_term (read_fd);
    bytes = read (read_fd, &c, 1);
    debug ("Read returned
");

    return 0;
}

Answer 1

从linux < code>pty (7) manpage(维生素是我的):

A pseudoterminal (sometimes abbreviated "pty") is a pair of virtual character devices that provide a bidirectional communication channel. One end of the channel is called the master; the other end is called the slave. The slave end of the pseudoterminal provides an interface that behaves exactly like a classical terminal

然而,您的程序正在从主机主读取您的程序, 无法期望它的行为完全像终端设备。

如果您更改/扩展了 get_term 的最后几行,...

int slave_fd =  open (name, O_RDWR); /* now open the slave end..*/
if (slave_fd < 0) {
   debug ("Error opening slave PTY
");
   exit (1);
}

return slave_fd; /* ... and use it instead of the master..*/

...你的样板程序会像预期的一样有效

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