linux-kernel - Re: [RFC] extending splice for copy offloading

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Date:	Mon, 16 Sep 2013 14:44:53 -0500
From:	Rob Landley <rob@...dley.net>
To:	Eric Wong <normalperson@...t.net>
Cc:	Zach Brown <zab@...hat.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Bryan Schumaker <bjschuma@...app.com>,
	"Martin K. Petersen" <mkp@....net>, Jens Axboe <axboe@...nel.dk>,
	Mark Fasheh <mfasheh@...e.com>,
	Joel Becker <jlbec@...lplan.org>
Subject: Re: [RFC] extending splice for copy offloading

On 09/11/2013 04:17:23 PM, Eric Wong wrote:
> Zach Brown <zab@...hat.com> wrote:
> > Towards the end of that thread Eric Wong asked why we didn't just
> > extend splice.  I immediately replied with some dumb dismissive
> > answer.  Once I sat down and looked at it, though, it does make a
> > lot of sense.  So good job, Eric.  +10 Dummie points for me.
> 
> Thanks for revisiting that :>
> 
> > Some things to talk about:
> > - I really don't care about the naming here.  If you do, holler.
> 
> Exposing "DIRECT" to userspace now might confuse users into expecting
> O_DIRECT behavior.  I say this as an easily-confused user.
> 
> In the future, perhaps O_DIRECT behavior can become per-splice  
> (instead
> of just per-open) and can save SPLICE_F_DIRECT for that.
> 
> > - We might want different flags for file-to-file splicing and  
> acceleration
> > - We might want flags to require or forbid acceleration
> 
> > - We might want to provide all these flags to sendfile, too
> 
> Another syscall?  I prefer not.  Better to just maintain the sendfile
> API as-is for compatibility reasons and nudge users towards splice.
> 
> > Thoughts?  Objections?
> 
> I'll try to test/comment more in a week or two (not much time for
> computing until then).

Just a vague note that I've wanted to use splice implementing cp and  
patch and cat and so on in toybox, but couldn't because it needs a pipe.

So I'm quite interested in moves to lift this restriction...

Rob--
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