linux-kernel - Re: tty: ctrl-c not always echoed, especially under load

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Message-ID: <20080807203716.4a9870f6@lxorguk.ukuu.org.uk>
Date:	Thu, 7 Aug 2008 20:37:16 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Joe Peterson <joe@...rush.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: tty: ctrl-c not always echoed, especially under load

On Wed, 06 Aug 2008 14:17:29 -0600
Joe Peterson <joe@...rush.com> wrote:

> Alan Cox wrote:
> > If the output buffer is full then echoed characters/^C etc will vanish the
> > way n_tty implements its buffering internally. It's always worked that
> > way.
> 
> One more observation:
> 
> In Linux, try this:
> 
> # cat > foo
> hi^Sthere^Q
> ^D
> 
> (in other words, during the cat into "foo", type "hi", hit ^S, then type
> "there", then hit ^Q, then, on the next line, ^D to end the file)
> 
> Note that the "there" does not appear after hitting ^Q, but it does
> appear in the file.  So the characters were accepted, but they were not
> echoed (not even saved for echo when the terminal is restarted).
> 
> This behavior differs from that of FreeBSD (just tried it for fun -
> haven't tried other Unix's yet).  I have noticed other times that the
> echo seems to get lost while the tty is stopped.  Not sure if all this
> is related, but something seems amiss.  Thoughts?

It should certainly occur if the output buffer is full but that shouldn't
be the case for a few bytes. Agreed the current behaviour is unexpected
and less than desirable so hack away.

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