linux-kernel - Re: New copyfile system call

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Date:	Thu, 21 Feb 2013 20:50:27 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	Ric Wheeler <rwheeler@...hat.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Chris L. Mason" <clmason@...ionio.com>,
	Christoph Hellwig <hch@...radead.org>,
	Alexander Viro <aviro@...hat.com>,
	"Martin K. Petersen" <mkp@....net>, Hannes Reinecke <hare@...e.de>,
	"Joel Becker" <jlbec@...lplan.org>
Subject: Re: New copyfile system call - discuss before LSF?

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

NetApp
Trond.Myklebust@...app.com
www.netapp.com
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