linux-kernel - Re: [PATCH v2 08/11] tty: splice

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Date: Wed, 3 Jan 2024 11:14:59 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Jiri Slaby <jirislaby@...nel.org>, Oliver Giles <ohw.giles@...il.com>
Cc: Ahelenia Ziemiańska <nabijaczleweli@...ijaczleweli.xyz>, 
	Jens Axboe <axboe@...nel.dk>, Christian Brauner <brauner@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org, 
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 08/11] tty: splice_read: disable

On Wed, 3 Jan 2024 at 03:36, Jiri Slaby <jirislaby@...nel.org> wrote:
>
> What are those "things" doing that "splice to tty", I don't recall and
> the commit message above ^^^ does not spell that out. Linus?

It's some annoying SSL VPN thing that splices to pppd:

   https://lore.kernel.org/all/C8KER7U60WXE.25UFD8RE6QZQK@oguc/

and I'd be happy to try to limit splice to tty's to maybe just the one
case that pppd uses.

So I don't think we should remove splice_write for tty's entirely, but
maybe we can limit it to only the case that the VPN thing used.

I never saw the original issue personally, and I think only Oliver
reported it, so cc'ing Oliver.

Maybe that VPN thing already has the pty in non-blocking mode, for
example, and we could make the tty splicing fail for any blocking op?

                Linus