[libvirt] Block pull API QEMU progress update

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. Stefan