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Re: [libvirt] RFCv2: virDomainSnapshotCreateXML enhancements



Am 12.08.2011 09:18, schrieb Philipp Hahn:
> Hello Kevin, hello Eric,
> 
> On Thursday 11 August 2011 12:00:46 Kevin Wolf wrote:
>> Am 11.08.2011 00:08, schrieb Eric Blake:
>>> Libvirt currently has a bug in that it only saves <domain>/<uuid> rather
>>> than the full domain xml along with a checkpoint - if any devices are
>>> hot-plugged (or in the case of offline snapshots, if the domain
>>> configuration is changed) after a snapshot but before the revert, then
>>> things will most likely blow up due to the differences in devices in use
>>> by qemu vs. the devices expected by the snapshot.
>>
>> Offline snapshot means that it's only a disk snapshot, so I don't think
>> there is any problem with changing the hardware configuration before
>> restoring it.
>>
>> Or does libvirt try to provide something like offline checkpoints, where
>> restoring would not only restore the disk but also roll back the libvirt
>> configuration?
> 
> Try to load a VM state with the memory size changed in between and your VM is 
> busted; been there, experienced that :-( So it's nice to do a snapshot before 
> you play with your virtual hardware configuration and can go back there if 
> things go wrong.
> 
> For -loadvm to work you have to call kvm with the nearly same command line 
> arguments again; what may change you probably know better than me. For I 
> thinks it's essential to store the VM consiguration with the snapshot, which 
> would be the qemu command line arguments, which is equivalent to libvirts XML 
> description.

Yes, I understand this. I was talking about snapshots taken while the VM
is shut off, where it's not as clear. But for consistency it's probably
better to do the same with offline and online snapshots, so what libvirt
implements (or was it only Eric's plan?) is fine here.

Kevin


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