[libvirt] [RFC PATCH 0/5] Allow data upload/download to/from storage volumes

[Daniel P. Berrange]

On Tue, Mar 08, 2011 at 09:21:15AM -0500, Cole Robinson wrote:
> On 03/08/2011 04:31 AM, Daniel P. Berrange wrote:
> > On Mon, Mar 07, 2011 at 02:50:12PM -0500, Cole Robinson wrote:
> >> On 02/22/2011 08:23 AM, Daniel P. Berrange wrote:
> >>> This patch series introduces two new APIs to allow data upload/download
> >>> to/from storage volumes, using the streams APIs. Mostly I wrote this so
> >>> I had an easier way to test the streams handling in my RPC patch series
> >>> than using QEMU tunnelled migration code. Cole has expressed an interest
> >>> in this kind of functionality in the past to allow virt-manager to upload
> >>> kernel/initrd to remote hosts for provisioning guests.
> >>>
> >>> Most of the code here is pretty boring & trivial. The first patch is the
> >>> one that is remotely interesting. One might argue we should just spawn
> >>> 'dd' instead of this, but dd has some annoying aspects (you can't control
> >>> its write offset in units smaller than the block size) and this could be
> >>> useful more broadly.
> >>>
> >>
> >> Hmm doesn't look like any of the CreateUpload stuff is implemented? Dropped
> >> from an earlier patch or just not finished yet? If that was implemented, I
> >> think it would be all virt-manager would really need to facilitate URL
> >> installation on remote machines.
> > 
> > Yes, I was going to do a CreateUpload method, but then the actual impl
> > in the storage driver was going to touch quite alot of code. So I dropped
> > it for since, since you could do the same thing by just doing a CreateXML
> > followed by Upload operation. Provided you don't pre-allocate in the
> > CreatXML method it wouldn't have any negative performance hit todo the
> > two separate steps.
> > 
> 
> So just create a 1 byte raw volume, then upload, and it will grow as
> needed? Should be fine.

For portability you want to create a volume of the size you are planning
to upload, but set allocation==0, so it doesn't preallocate. This makes
it work if you want to upload to non-grow on demand volumes like LVM,
or block devices, or non-raw files

Regards,
Daniel
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