Re: copy offload support in Linux - new system call needed?

["J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>]

On Wed, Dec 14, 2011 at 02:42:38PM -0500, Ric Wheeler wrote:
> On 12/14/2011 02:27 PM, Al Viro wrote:
> >On Wed, Dec 14, 2011 at 02:22:07PM -0500, Ric Wheeler wrote:
> >
> >>We had an active thread a couple of years back that came out of the
> >>reflink work and, at the time, there seemed to be moderately
> >>positive support for adding a new system call that would fit this
> >>use case (Joel Becker's copyfile()).
> >>
> >>Can we resurrect this effort? Is copyfile() still a good way to go,
> >>or should we look at other hooks?
> >copyfile(2) is probably a good way to go, provided that we do _not_
> >go baroque as it had happened the last time syscall had been discussed.
> >
> >IOW, to hell with progress reports, etc. - just a fastpath kind of
> >thing, in the same kind of relationship to cp(1) as rename(2) is to mv(1).
> >If it works - fine, if not - caller has to be ready to deal with handling
> >cross-device case anyway.
> 
> I think that this approach makes a lot of sense. Most of the
> devices/targets that support the copy offload, will do it in very
> reasonable amounts of time.

The current NFSv4.2 draft rolls both the "fast" and "slow" cases into
one operation:

	http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion2-06#section-2
 
Perhaps we should ask for separate operations for the two cases.  (Or at
least a "please don't bother if this is going to take 8 hours" flag....)

--b.

> 
> Let me see if I can dig up some of the presentations from the NetApp
> guys who presented overviews or the specifications from the IETF and
> T10....
> 
> Ric
> 
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