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

[Ric Wheeler <ricwheeler@gmail.com>]

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.

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