linux-kernel - Re: New copyfile system call

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Message-ID: <51269A2B.7070000@redhat.com>
Date:	Thu, 21 Feb 2013 23:05:31 +0100
From:	Ric Wheeler <rwheeler@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	"Myklebust, Trond" <Trond.Myklebust@...app.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 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.

Ric

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