[libvirt] snapshots += domain description?

[Philipp Hahn]

Hello,

I just encountered a problem with the current snapshot implementation for 
qemu/kvm: To revert back to a snapshot, the domain description must closely 
match the domain description when the snapshot was created. If the ram-size 
doesn't match or the VM now contains fewer CPUs or contains additional disks, 
kvm will either not load the snapshot or the machine will be broken 
afterwarts.
Is this a known problem?

Without looking into the implementation details I think saving the full domain 
description instead of just a reference to the domain uuid as part of the 
snapshot description would work better. Or am I supposed to save the domain 
description myself in addition the the data saved 
in /var/lib/libvirt/qemu/snapshot/$DOMAIN_NAME/$SNAPSHOT_NAME.xml. I think 
this is very important feature, because when you - for example - notice that 
you need additional disk space and would like to include an additional block 
device, this is your ideal time to take a snapshot you can revert to when you 
do something wrong.

Looking at VMware I see that reverting a VM there will not only revert the 
disks and ram back to the saved state, but also the description including 
name, ram size, etc.

Any comment or advise is appreciated.

Sincerely
Philipp Hahn
-- 
Philipp Hahn           Open Source Software Engineer      hahn at univention.de   
Univention GmbH        Linux for Your Business        fon: +49 421 22 232- 0
Mary-Somerville-Str.1  28359 Bremen                   fax: +49 421 22 232-99
                                                    http://www.univention.de
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