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

Michael Kerrisk (man-pages)
2015-05-06T12:26:15Z

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@suse.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/