[libvirt] Block pull API QEMU progress update

[Daniel P. Berrange]

On Wed, Jun 22, 2011 at 03:20:09PM +0100, Stefan Hajnoczi wrote:
> I am sending this email as an update on the new image streaming for
> QEMU (aka block pull in libvirt).
> 
> Adam's libvirt virDomainBlockPull patches were recently merged to
> allow populating a disk image while the domain is running.  The QEMU
> side implementation is not merged into qemu.git yet because similarity
> with the live block copy feature has sparked discussion on how to
> unify the two.
> 
> The QEMU APIs for image streaming and live block copy may or may not
> be changed.  I think they should stay as they are because they provide
> good interfaces for those two features.  However, it is possible that
> unifying the implementations of the two features internally
> necessitates changes to the QEMU APIs.
> 
> If changes are made, the question becomes whether they require
> changing the libvirt block pull (and proposed live block copy) API.
> 
> Right now there is no proposal to change the QEMU APIs for the two
> features but I think it is useful for libvirt to be aware of the
> status on these features.  Perhaps a precautionary measure like not
> committing to the APIs until the QEMU patches are merged is
> worthwhile, just for safety.
> 
> Marcelo, Kevin, and I are working on unifying the QEMU side
> implementations of live block copy and image streaming.  Hopefully the
> specifics will be agreed soon and we can then enable these features in
> QEMU and libvirt.

With non-trivial risk of the QEMU interface being changed, then I
think it could be wise to temporarily revert the block pull API +
RPC additions in libvirt, for the 0.9.3 release, and re-add them
for 0.9.4 when the QEMU debate has settled.

Daniel
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