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

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Message-ID: <alpine.WNT.2.00.1512180723400.4908@CLUIJ>
Date:	Fri, 18 Dec 2015 07:26:24 -0700 (Mountain Standard Time)
From:	Marc Aurele La France <tsi@...oix.net>
To:	Peter Hurley <peter@...leysoftware.com>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
	Volth <openssh@...th.com>, Damien Miller <djm@...drot.org>
Subject: Re: n_tty: Check the other end of pty pair before returning EAGAIN
 on a read()

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?

Thanks.

Marc.
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