linux-kernel - Re: Splicing to/from a tty

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Message-ID: <20210118195400.GC736435@zeniv-ca>
Date:   Mon, 18 Jan 2021 19:54:00 +0000
From:   Al Viro <viro@...iv-ca>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>,
        Johannes Berg <johannes@...solutions.net>,
        Oliver Giles <ohw.giles@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Splicing to/from a tty

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@...iv-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.