Re: New copyfile system call - discuss before LSF?

[Ric Wheeler]

On 02/21/2013 11:13 PM, Myklebust, Trond wrote:
> On Thu, 2013-02-21 at 23:05 +0100, Ric Wheeler wrote:
> > On 02/21/2013 09:00 PM, Paolo Bonzini wrote:
> > > Il 21/02/2013 15:57, Ric Wheeler ha scritto:
> > > > > sendfile64() pretty much already has the right arguments for a
> > > > > "copyfile", however it would be nice to add a 'flags' parameter: the
> > > > > NFSv4.2 version would use that to specify whether or not to copy file
> > > > > metadata.
> > > > That would seem to be enough to me and has the advantage that it is an
> > > > relatively obvious extension to something that is at least not totally
> > > > unknown to developers.
> > > >
> > > > Do we need more than that for non-NFS paths I wonder? What does reflink
> > > > need or the SCSI mechanism?
> > > For virt we would like to be able to specify arbitrary block ranges.
> > > Copying an entire file helps some copy operations like storage
> > > migration.  However, it is not enough to convert the guest's offloaded
> > > copies to host-side offloaded copies.
> > >
> > > Paolo
> > I don't think that the NFS protocol allows arbitrary ranges, but the SCSI
> > commands are ranged based.
> >
> > If I remember what the windows people said at a SNIA event a few years back,
> > they have a requirement that the target file be pre-allocated (at least for the
> > SCSI based copy). Not clear to me where they iterate over that target file to do
> > the block range copies, but I suspect it is in their kernel.
> The NFSv4.2 copy offload protocol _does_ allow the copying of arbitrary
> byte ranges. The main target for that functionality is indeed
> virtualisation and thin provisioning of virtual machines.

For background, here is a pointer to Fred Knight's SNIA talk on the SCSI support 
for offload:

https://snia.org/sites/default/files2/SDC2011/presentations/monday/FrederickKnight_Storage_Data_Movement_Offload.pdf

and a talk from Spencer Shepler that gives some detail on the NFS spec, 
including the "server side copy" bits:

https://snia.org/sites/default/files2/SDC2011/presentations/wednesday/SpencerShepler_IETF_NFSv4_Working_Group_v4.pdf

The talks both have references to the actual specs for the gory details.

Ric




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