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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 3 Jan 2024 11:14:59 -0800
Message-ID: <CAHk-=wgLZXULo7pg=nwUMFLsKNUe+1_X=Fk7+f-J0735Oir97w@mail.gmail.com>
Subject: Re: [PATCH v2 08/11] tty: splice_read: disable
To: Jiri Slaby <jirislaby@kernel.org>, Oliver Giles <ohw.giles@gmail.com>
Cc: =?UTF-8?Q?Ahelenia_Ziemia=C5=84ska?= <nabijaczleweli@nabijaczleweli.xyz>, 
	Jens Axboe <axboe@kernel.dk>, Christian Brauner <brauner@kernel.org>, 
	Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, linux-kernel@vger.kernel.org, 
	linux-serial@vger.kernel.org
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On Wed, 3 Jan 2024 at 03:36, Jiri Slaby <jirislaby@kernel.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