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Date:   Mon, 18 Jan 2021 19:54:00 +0000
From:   Al Viro <viro@zeniv-ca>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>,
        Johannes Berg <johannes@sipsolutions.net>,
        Oliver Giles <ohw.giles@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: Splicing to/from a tty
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On Mon, Jan 18, 2021 at 11:46:42AM -0800, Linus Torvalds wrote:
> On Mon, Jan 18, 2021 at 11:35 AM Al Viro <viro@zeniv-ca> wrote:
> >
> > I'd rather have sendfile(2) do what splice(2) does and handle pipes
> > directly.  Let me take a look,,,
> 
> It's not technically just the sendfile() thing. Some things do
> sendfile "internally" (ie they use do_splice_direct()).
> 
> Although maybe they always happen just on non-pipe destinations (ie
> file-to-file copy). I didn't check.
> 
> But particularly if it can be handled in do_splice_direct(), that
> would be a good thing.

FWIW, it might make sense to merge do_splice_direct() and do_splice();
interfaces are very similar and do_splice() is basically
	if both are pipes
		....
	else if input is pipe
		....
	else if output is pipe
		....
	else
		return -EINVAL
with do_splice_direct() being fairly close to the missing case.