On Tue, 27 Nov 2007 13:53:21 -0500
Jeff Dike <[email protected]> wrote:
> tcsetattr(fd, TCSAFLUSH) will always return -EINTR on a pts device
> when O_ASYNC has been set. This is demonstrated by the test program
> below - just compile and follow the instructions. You'll get an
> infinite stream of SIGIOs and -EINTRs.
Cute. This appears to be entirely standards compliant but I agree its not
sane or expected behaviour.
> static void pty_unthrottle(struct tty_struct * tty)
> {
> ...
> tty_wakeup(o_tty);
> set_bit(TTY_THROTTLED, &tty->flags);
> }
My first thought would be to only do the tty_wakeup if there is data
pending.
> I'd love to get rid of the set_bit(TTY_THROTTLED, &tty->flags) in
> pty_unthrottle, but it's protected by this comment:
>
> /* For PTY's, the TTY_THROTTLED
> * flag is always set, to force the line discipline to always call the
> * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
> * characters in the queue. This is necessary since each time this
> * happens, we need to wake up any sleeping processes that could be
> * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
> * for the pty buffer to be drained.
> */
>
> Failing that, there should be a relevant state change in the device
> before it will deliver a SIGIO. I just have no idea where to put it.
Unfortunately neither am I. If the wakeup can be deferred if there is no
data pending then I think that will do the trick ?
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