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Date:   Thu, 21 Jan 2021 09:44:29 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Oliver Giles <ohw.giles@gmail.com>,
        Robert Karszniewicz <r.karszniewicz@phytec.de>,
        Christoph Hellwig <hch@lst.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jiri Slaby <jirislaby@kernel.org>
Subject: Re: tty splice branch (was "Re: Splicing to/from a tty")
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On Wed, Jan 20, 2021 at 05:18:36PM -0800, Linus Torvalds wrote:
> On Tue, Jan 19, 2021 at 8:44 PM Linus Torvalds
> <torvalds@linux-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.

Let me do this last thing.  I've taken your one patch into my
"tty-linus" branch and will go beat on it for a day and then ask you to
pull it in for the next 5.11-rc release, and I've taken your full series
into my "tty-next" branch so it will get much wider testing in
linux-next for a few weeks.  If it turns out that we get reports of the
"splice/sendfile from a tty", we can always merge them into 5.11 and
5.10 as needed.

Thanks for doing this work,

greg k-h