Re: New copyfile system call - discuss before LSF?

Ric Wheeler
2013-02-21T22:06:36Z

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