[libvirt-users] Update on-disk XML after virsh snapshot-create-as

[Eric Blake]

On 04/14/2015 09:51 AM, Andrew Martin wrote:
>> There have been some bug fixes in newer libvirt; for example, commit
>> 9f97485 (v1.2.12) is relevant.  I'm not sure why your vendor is not
>> backporting these fixes to the build shipped in Ubuntu, but you can
>> manually run a newer libvirt to work around the problem.
> 
> I am unaware of a 3rd-party vendor that backports newer releases of libvirt
> for Ubuntu - is there one you would recommend? Currently, for 14.04 I am using
> the packages from the Ubuntu repository, and for 12.04 I built newer versions
> of libvirt myself in this PPA:
> https://launchpad.net/~xespackages/+archive/ubuntu/virtualization
> 
> Is there a better way to keep up-to-date with libvirt releases on Ubuntu LTS?

I don't use Ubuntu much myself, so ping Canonical again, and if they are
not providing timely backports, then self builds is all I can suggest.

>> Instead, if you are still suffering from a build of libvirt that fails
>> to update the files in /etc when taking a snapshot, do some other action
>> that DOES update /etc (such as changing the domain description), or at a
>> bare minimum use 'virsh define' instead of manually writing into /etc
>> yourself.
>>
> Thanks for this clarification. It looks like the following would update both
> the running and on-disk configs?
> virsh desc <domain> --config --live --new-desc "<new description here>"

Try it to make sure; it looks like in v1.2.0, that command sequence
would actually write the persistent definition, but forgot to write the
active definition out to disk (exact opposite problem of snapshot
creation writing the active definition out to disk but forgetting to
write the persistent definition).  I know that disk hotplug/hotunplug
worked that far back at writing both persistent and live definitions to
disk, but that's a bit heavyweight when it comes to trying to tweak the
domain just to ensure you hit a code path that properly flushes to disk.
 We've done better at auditing the code base in newer libvirt to ensure
that we flush to disk any time we modify the domain.

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

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