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

[Jeremy Allison <jra@samba.org>]

On Wed, Dec 14, 2011 at 02:22:07PM -0500, Ric Wheeler wrote:
> 
> Back at LinuxCon Prague, we talked about the new NFS and SCSI
> commands that let us offload copy operations to a storage device
> (like an NFS server or storage array).
> 
> This got new life in the virtual machine world where you might want
> to clone bulky guest files or ranges of blocks and was driven
> through the standards bodies by vmware, microsoft and some of the
> major storage vendors. Windows8 has this functionality fully coded
> and integrated in the GUI, I assume vmware also uses it and there
> are some vendors who announced support at the SNIA SDC conference.
> 
> 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?

Windows uses a COPYCHUNK call, which specifies the
following parameters:

Definition of a copy "chunk":

hyper source_off;
hyper target_off;
uint32 length;

and an array of these chunks which is passed
into their kernel.

This is what we have to implement in Samba.

Jeremy.