Re: New copyfile system call - discuss before LSF?

From: Myklebust, Trond
Date: Thu Feb 21 2013 - 15:50:35 EST

On Thu, 2013-02-21 at 21:00 +0100, 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.

So how would a system call based on sendfile64() plus my flag parameter
prevent an underlying implementation from meeting your criterion?

Trond Myklebust
Linux NFS client maintainer

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