libvirt users - Nov 2014 - Re: some problem with snapshot by libvirt

Eric Blake <eblake@...> writes:
>
> On 05/27/2012 06:39 PM, xingxing gao wrote:
> > Hi,all,i am using libvirt to manage my vm,in these days i am testing
> > the libvirt snapshot ,but meet some problem:
> >
> > the snapshot was created from this command:
> > snapshot-create-as win7    --disk-only --diskspec
> > vda,snapshot=external  --diskspec hda,snapshot=no
> >
> > but when i tried to revert from the snapshot which created from the
> > above command ,i got error below:
> >
> > virsh # snapshot-revert win7 1338041515 --force
> > error: unsupported configuration: revert to external disk snapshot not
> > supported yet
>
> Yep.  You've run into a case where I haven't yet been able to code
> things.  The problem is that reverting to a disk image has a question -
> you are starting with two files (the snapshot backing file and the new
> qcow2 wrapper), but the moment you reload the backing file for
> modification, you invalidate the qcow2 wrapper.  There are two sane
> options - create yet another qcow2 wrapper around the same backing file,
> or delete the qcow2 wrapper as part of reverting to the snapshot, but we
> would probably need two new flags to the virDomainRevertToSnapshot API
> to select one of these two behaviors.  In the meantime, the only way to
> revert to a disk-only snapshot is to manually edit the domain XML to
> match what you want to do, possibly with manual qemu-img operations as
well.
>
> Help in writing the patches to improve the functionality would be welcome.
>
Has the issue ( revert to external disk snapshot ) been solved in later
versions of libvirt?

I am using:
Compiled against library: libvirt 1.2.2
Using library: libvirt 1.2.2
Using API: QEMU 1.2.2
Running hypervisor: QEMU 2.1.92

On trying to revert to an  external snapshot,
Getting the error: revert to external disk snapshot not supported yet

If not is there any alternate.

On 11/21/2014 12:56 PM, Payes Anand wrote:
>> Yep.  You've run into a case where I haven't yet been able to
code
>> things.
>>
>> Help in writing the patches to improve the functionality would be
welcome.
>>
> 
> Has the issue ( revert to external disk snapshot ) been solved in later
> versions of libvirt?
As of the latest 1.2.10 release, we are still awaiting someone to write
patches for reverting to external snapshots.
> If not is there any alternate.
You can do things manually, via qemu-img and editing domain xml.

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