[libvirt] [RFC]: Snapshot API

[Chris Lalancette]

On 03/24/2010 10:40 AM, Paolo Bonzini wrote:
>> >  If you do not want to allow setting the parent, you can also add a
>> flag
>> >  --inactive to virsh snapshot-create that would create the snapshot
>> >  without making it active.  Then you would make<parent>  an
>> informational
>> >  field about which snapshot was*active*  when the new one was created.
>>
>> That's more or less what the<parent>  field is supposed to mean, although
>> I'm not sure I understand your proposal about --inactive.  How would you
>> go about doing that?
> 
> Say you were on snapshot A and the guest has a problem.  The easiest fix
> is reverting to snapshot A, but you want to investigate it anyway.  You
> create snapshot B with --inactive and, if you want, you can move the
> snapshot to another machine to activate it and look at it more calmly.
> 
> If the problem reproduces, you can create another inactive snapshot, and
> so on.
> 
> Alternatively, say the easiest fix is stopping and starting a daemon,
> but again you want to keep a snapshot to investigate it anyway.  You can
> create the inactive snapshot B and stop/start the daemon _while the
> system is live and running under snapshot A_, i.e. without manually
> shutting down and rebooting.
> 
> Is this clearer?

Much clearer, thank you.  So you are still snapshotting the *current*
image, but sort of storing it away for future reference.  That's where
my confusion was.

This seems like a good debugging aid; the only question is whether the
hypervisors can support this kind of thing.  I guess we can always emulate
it by taking a snapshot and then immediately reverting to the parent.

-- 
Chris Lalancette