Re: [RFC] extending splice for copy offloading

Rob Landley
2013-09-17T04:42:51Z

On 09/11/2013 04:17:23 PM, Eric Wong wrote:
> Zach Brown <zab@redhat.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