Re: n_tty: Check the other end of pty pair before returning EAGAIN on a read()

From	Peter Hurley <peter@hurleysoftware.com>
Newsgroups	linux.kernel
Subject	Re: n_tty: Check the other end of pty pair before returning EAGAIN on a read()
Date	2015-12-18 17:50 +0100
Message-ID	<qH6oa-86R-15@gated-at.bofh.it> (permalink)
References	(2 earlier) <qEic9-3Yp-9@gated-at.bofh.it> <qEjrA-519-7@gated-at.bofh.it> <qEw5s-52w-23@gated-at.bofh.it> <qEwoO-5c5-15@gated-at.bofh.it> <qH4mo-6QB-81@gated-at.bofh.it>
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Hi Marc,

On 12/18/2015 06:26 AM, Marc Aurele La France wrote:
> On Fri, 11 Dec 2015, Peter Hurley wrote:
>> On 12/11/2015 05:37 AM, Marc Aurele La France wrote:
> 
>>> I am not asking to read data before it has been produced.  I am puzzled
>>> that despite knowing that the data exists, I can now be lied to when I
>>> try to retrieve it, when I wasn't before.  We are talking about what is
>>> essentially a two-way pipe, not some network or serial connection with
>>> transmission delays userland has long experience in dealing with.
> 
>>> These previously internal additional delays, that are now exposed to
>>> userland, are simply an implementation detail that userland did not,
>>> and should not, need to worry about.
>>
>> Your mental model is that pseudo-terminals are a synchronous pipe, which
>> is not true.
>>
>> But this argument is pointless because the regression needs to be fixed
>> regardless of the merits.
> 
> Fair enough.
> 
> Anything new on this?

It's on my todo list.

While considering this issue further, I was curious what ssh does
regarding the entire foreground process group and its output?

If ssh only knows that the child has terminated, how does it wait
for the rest of the foreground process group's output since those
processes may not yet have received their SIGHUP/SIGCONT signals
yet?

Regards,
Peter Hurley

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Thread

Re: n_tty: Check the other end of pty pair before returning EAGAIN  on a read() Marc Aurele La France <tsi@tuyoix.net> - 2015-12-18 15:40 +0100
  Re: n_tty: Check the other end of pty pair before returning EAGAIN on  a read() Peter Hurley <peter@hurleysoftware.com> - 2015-12-18 17:50 +0100
    Re: n_tty: Check the other end of pty pair before returning EAGAIN  on a read() Marc Aurele La France <tsi@tuyoix.net> - 2015-12-18 18:30 +0100

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