Re: [libvirt] [RFC PATCH REBASE 00/10] introduce push backups

Push backup is a backup when hypervisor itself copy backup data to destination in contrast to pull backup when hypervisor exports backup data thru some interface and mgmt itself make a copy. This patch series basically adds creating backup to API/remote/qemu/virsh and initial backup XML definition. Just like other blockjobs backup creation is asynchronous. That is creation is merely a backup start and client should track backup error/completion thru blockjob events. As backup is done transactionally all individual disk backup jobs will be aborted by qemu itself in case of error, client need not to do it manually. Client can cancel the backup by aborting blockjob on any disk being backed up. Backup xml desription is similar to snapshot one with some exceptions and is described in more details in definition patch [1]. I guess good client will track progress for every disk in backup to report progress and detect hangs so it don't need extra backup complete/error event that aggregate the overall backup result. However it looks like aborting backup can be implemented in libvirt as code will be common for all clients. We need to abort some of not yet completed per disk backups and retry if job to be aborted is completed meanwhile. Of coures this series is far from being complete. Incremental backups and backup persistent metadata is to be implemented. Let's just start work in this direction.