read(2)在哪里检查termios结构以确定它应该以(非)阻塞的方式读取STDIN?

read(2)在哪里检查termios结构以确定它应该以(非)阻塞的方式读取STDIN?

在Linux内核中TTY的实现。相关文件 https://docs.kernel.org/driver-api/tty/index.html .

首先,我们需要来自的宏 https://elixir.bootlin.com/linux/latest/source/include/linux/tty.h#L40 :

#define TIME_CHAR(tty) ((tty)->termios.c_cc[VTIME])
#define MIN_CHAR(tty) ((tty)->termios.c_cc[VMIN])

看起来这里使用了VMIN和VTIME https://elixir.bootlin.com/linux/latest/source/drivers/tty/n_tty.c#L2212 :

    minimum = time = 0;
    timeout = MAX_SCHEDULE_TIMEOUT;
    if (!ldata->icanon) {
        minimum = MIN_CHAR(tty);
        if (minimum) {
            time = (HZ / 10) * TIME_CHAR(tty);
        } else {
            timeout = (HZ / 10) * TIME_CHAR(tty);
            minimum = 1;
        }
    }
    ......
                timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
                        timeout);

    ......
    if (kb - kbuf >= minimum)
        break;
    if (time)
        timeout = time;