[libvirt] [RFC v2] external (pull) backup API

[Eric Blake]

On 04/03/2018 07:01 AM, Nikolay Shirokovskiy wrote:
> Hi, all.                                                                                         
>                                                                                                  
> This is another RFC on pull backup API. This API provides means to read domain                   
> disks in a snapshotted state so that client can back them up as well as means                    
> to write domain disks to revert them to backed up state. The previous version                    
> of RFC is [1]. I'll also describe the API implementation details to shed light                   
> on misc qemu dirty bitmap commands usage.                                                        

Thanks for such a detailed message!  It's got enough that I want to
spend some time thinking about the implications, but this is an early
reply to let you know I'm at least working on it now.

The first thing that caught my eye:

> Here is a list of bitmap commands used in implementation but not yet in upstream (AFAIK).
> 
> x-vz-block-dirty-bitmap-remove
> x-vz-block-dirty-bitmap-merge
> x-vz-block-dirty-bitmap-disable
> x-vz-block-dirty-bitmap-enable (not in the examples; used when removing most recent checkpoint)
> x-vz-nbd-server-add-bitmap

How close are we to having upstream implementations of any of those
commands?  If not, what are their specifications?  Libvirt is very
hesitant to add code that depends on a qemu x-* command, but if we can
get the actual command into qemu.git without the x-* prefix, it is
easier to justify libvirt adding the API even if qemu 2.13 is not yet
released.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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