linux-kernel - tty splice branch (was "Re: Splicing to/from a tty")

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Date:   Wed, 20 Jan 2021 17:18:36 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Oliver Giles <ohw.giles@...il.com>,
        Robert Karszniewicz <r.karszniewicz@...tec.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jiri Slaby <jirislaby@...nel.org>
Subject: tty splice branch (was "Re: Splicing to/from a tty")

On Tue, Jan 19, 2021 at 8:44 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'll come back to this tomorrow and do the line-buffered icanon case
> too (unless pull requests pile up), and then I'll be happy with the
> tty changes, and I think I can submit this series for real to Greg.

Greg, I don't know how you want to handle this.

I have a branch with my tty splice patches at

    git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git tty-splice

and that now includes doing that "cookie continuation" thing even for
the N_TTY icanon modes.

It passes my local tests, and I did try a few rather odd things. And
Oliver tested an ealier version without that final commit on his load.
But...

That tty splice thing is clearly a regression, but it's not like we
have seen a lot of reports of it, so it's clearly a very special
thing.

End result: I'm leaving it to you to decide how you want to handle it.
You can tell me to just merge it myself as a regression fix, despite
it being fairly late in the 5.11 series.  Or you can pull it into your
tty tree for linux-next and 5.12. And we can just plan to backport it
(for 5.10 and 5.11) later when it has had more wide testing.

Another alternative is to do just that first patch immediately (the
"tty: implement write_iter" one), because that one should be the
simple case that gets sendfile() and splice() working when the
_destination_ is a tty. The "source is a tty" is the much more complex
case that the other patches deal with.

         Linus