linux-kernel - Re: man termios

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Message-ID: <532C64A1.6090807@hurleysoftware.com>
Date:	Fri, 21 Mar 2014 12:11:13 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	mtk.manpages@...il.com
CC:	linux kernel <linux-kernel@...r.kernel.org>,
	linux-serial <linux-serial@...r.kernel.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Ivan <athlon_@...l.ru>
Subject: Re: man termios

On 03/21/2014 11:41 AM, Michael Kerrisk (man-pages) wrote:
>>> Peter, do you agree that Linux appears to differ from POSIX here? (Not
>>> sure if you tried my test program to verify...)
>>
>>
>> I did run the test program to validate that it's observed behavior is that
>> implemented by Linux, with which I'm very familiar.
>> I don't have a test setup for other *nixes.
>>
>> I would be interested to know the results of
>>
>>    ./noncanonical 0 5 3 0
>>    hello
>
> Solaris 10:
> read() completes when 5 bytes received.
> OpenBSD 5.4
> read() completes when 5 bytes received.

Ok, Linux does the same.

>> and
>>
>>    ./noncanonical 0 5 3 2
>>     hel
>
> Solaris
> read blocks()
> OpenBSD
> read blocks

If you type fast, Linux will complete this read() with 3 bytes.

> Plus my test case where Linux differs:
>
> ./noncanonical 100 5 3 0
>
> Linux: read() returns after 3 bytes input
>
> Solaris: read() returns only after 5 bytes input
> OpenBSD: read() returns only after 5 bytes input

Ok, thanks for testing.

>> on other platforms.
>>
>> With respect to POSIX compliance, it's hard to say. I'm not sure the
>> spec contemplates the degenerate case where max bytes < MIN. And
>
> Well, given the way the other implementations behave, I think it does
> contemplate it, because it carefull avoids talking about the number of
> bytes requested by read() in that case.

I agree that's certainly a valid interpretation.
I'll go back and see if this is a regression but I doubt it.

>> specifically
>> with regard to terminal i/o behavior, POSIX is essentially ex post facto,
>> and is really documenting existing behavior.
>>
>> Other than the degenerate case of max bytes < MIN, is there any other
>> variation between Solaris and Linux in non-canonical mode?
>
> The only one I've seen is the one I noted. I haven't tested too
> exhaustively though.

Thanks again. Please feel free to direct mail my way if you find other
variation.

Regards,
Peter Hurley

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