linux-kernel - Re: [PATCH man-pages] pty.7: clarify asynchronous nature of PTY IO.

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Date:	Wed, 06 May 2015 14:26:09 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	NeilBrown <neilb@...e.de>,
	Nic Percival <Nic.Percival@...rofocus.com>
CC:	mtk.manpages@...il.com, Michael Matz <matz@...e.de>,
	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH man-pages] pty.7: clarify asynchronous nature of PTY IO.

Hi Neil,

On 05/06/2015 12:59 AM, NeilBrown wrote:
> 
> A PTY is not like a pipe - there may be delayed between
> data being written at one end and it being available at the other.
> This became particularly apparent after
>  commit f95499c3030f ("n_tty: Don't wait for buffer work in read() loop")
> 
> in Linux 3.12
> 
> Signed-off-by: NeilBrown <neilb@...e.de>
> 
> ---

Thanks! Applied and tweaked a very little.

> Peter: does this seem reasonable and accurate to you?

I've got the patch sitting in a branch, in case Peter has suggestions for changes.

> MichaelK:  Would you prefer the commit ID in the man page.  It isn't so much
>    a deliberate change as a code improvement which caused problems for certain
>    use cases which depended on undefined behaviour.
>    Thread at https://lkml.org/lkml/2015/5/1/35

No, it's fine as is, thanks.

Cheers,

Michael


> diff --git a/man7/pty.7 b/man7/pty.7
> index 1332d11d9ca2..6c9ae182925c 100644
> --- a/man7/pty.7
> +++ b/man7/pty.7
> @@ -56,6 +56,12 @@ terminal emulators,
>  and
>  .BR expect (1).
>  
> +Data flow between master and slave is handle asynchronously, much like
> +data flow with a physical TTY.  Data written to the slave will be
> +available at the master promptly, but may not be available
> +immediately.  Similarly there may be a small processing delay between
> +a write to the master, and the effect being visible at the slave.
> +
>  Historically, two pseudoterminal APIs have evolved: BSD and System V.
>  SUSv1 standardized a pseudoterminal API based on the System V API,
>  and this API should be employed in all new programs that use
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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