[libvirt] RFC: using a network device as a destination for a disk snapshot

[Eric Harney]

On 10/30/2013 10:44 AM, Eric Blake wrote:
> Here's the XML I think we need to add to domainsnapshot:
> 
> <domainsnapshot>
>   ...
>   <disks>
>     <disk name='vda' snapshot='external' type='network'>
>       <driver type='qcow2'/>
>       <source protocol='gluster' name='vol1/img2'>
>         <host name='red'/>
>       </source>
>     </disk>
> 
> that is, add an optional /disk at type attribute (if absent, it defaults to
> type='file'), and where if present, the <source> subelement then takes
> on alternate forms in the same manner in which //domain/devices/disk
> handles alternates (here, allowing a protocol, name, and host
> specification).
> 
> [Ultimately, we need to fix //domain/devices/disk to specify a full
> backing chain, but one step at a time...]
> 

This does match the XML that my (prototype) Nova code generated in hopes
that this would work, except that I didn't have a <driver> element.
(Makes sense, I can add this.)

<domainsnapshot>
  <disks>
    <disk name="vdb" snapshot="external" type="network">
      <source protocol="gluster"
name="gvol1/volume-931536e0-65a7-4bd9-85ed-48bdd0160642.f6e62e4c-17b9-49bd-8941-10e8d11a22ca">
        <host name="127.0.0.1"/>
      </source>
    </disk>
    <disk
name="/opt/stack/data/nova/instances/6ff2075e-7b23-492a-865a-e7f8269d95bb/disk"
snapshot="no"/>
  </disks>
</domainsnapshot>


$ qemu-img info
volume-931536e0-65a7-4bd9-85ed-48bdd0160642.f6e62e4c-17b9-49bd-8941-10e8d11a22ca

image:
volume-931536e0-65a7-4bd9-85ed-48bdd0160642.f6e62e4c-17b9-49bd-8941-10e8d11a22ca
file format: qcow2
virtual size: 1.0G (1073741824 bytes)
disk size: 193K
cluster_size: 65536
backing file: volume-931536e0-65a7-4bd9-85ed-48bdd0160642
backing file format: raw