[libvirt] block-backup API for libvirt

[Eric Blake]

On 11/08/2013 01:56 PM, Ian Main wrote:
> 
> In qemu there will soon be drive-backup and block-backup commands that
> allow you to create backups or point-in-time snapshots of VM images.
> The original feature that drove this was to allow 'image fleecing',
> which involves creating a light weight mechanism to take a point in time
> snapshot of the running VM and access that remotely.
> 
> You can get a good idea of the API from this post:
> 
> http://lists.gnu.org/archive/html/qemu-devel/2013-10/msg02266.html
> 
> I would like to see this available via libvirt and wanted to start
> working on a suitable API.  I'm curious if anyone has any input on how
> they would like to see this done?  While I have done some work with and
> on libvirt I'm no expert on the design philosophy behind the APIs so
> some direction here before I get coding would be much appreciated.
> 
>>From what I can tell a volume based API that creates 'backups' and does
> the NBD export call could work but I'd like to hear if that's
> reasonable.

It seems to me that a new API virDomainBlockBackup(domain, disk,
destination, bandwidth, flags) is probably the right approach, as well
as enhancing the existing virDomainBlockJob* to report job status and/or
abort the job early.

For that matter, we need to overhaul the job support.  Right now,
virDomainBlockJob* assumes you can only have one outstanding job at a
time, which interferes with the notion of running fleecing from two
points in time.  Similarly, there can only be one virDomainGetJobInfo
active.  What we really need is a notion of a job id, a way to query the
job id most recently created by any existing job-related API, and a way
to query job status based on id rather than only the most-recently
started job.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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