[sheepdog] [libvirt] Why not add snapshot operations for Sheepdog storage driver in Libvirt

[Eric Blake]

On 02/08/2013 04:56 AM, harryxiyou wrote:
> Hi all,
> 
> Virsh has following operations about snapshot.
> 
>  Snapshot (help keyword 'snapshot')
>     snapshot-create                Create a snapshot from XML
>     snapshot-create-as             Create a snapshot from a set of args
>     snapshot-current               Get or set the current snapshot
>     snapshot-delete                Delete a domain snapshot
>     snapshot-dumpxml               Dump XML for a domain snapshot
>     snapshot-edit                  edit XML for a snapshot
>     snapshot-info                  snapshot information
>     snapshot-list                  List snapshots for a domain
>     snapshot-parent                Get the name of the parent of a snapshot
>     snapshot-revert                Revert a domain to a snapshot

These commands are related to domain snapshots.

> 
> But i cannot find relevant realization in Sheepdog storage driver in Libvirt.

That would be a storage volume snapshot, which is a different task.
Remember, a domain snapshot may include storage volume snapshots, and
may also include memory state snapshots, which makes it a more
comprehensive task; but also that some of the work of a domain snapshot
is offloaded to qemu, whereas storage volume snapshot manipulation would
have to be done in libvirt independently of qemu.  At one point I
proposed API for doing storage volume snapshot manipulation, but it
never became a pressing need, so no one has implemented it yet.
https://www.redhat.com/archives/libvir-list/2011-June/msg00761.html

> I am sure Sheepdog storage driver, now, cannot support snapshot operations
> in Libvirt. I wonder whether Sheepdog can realize snapshot operations
> in Libvirt?

Not just sheepdog, but qcow2 storage volume management would also
benefit from storage volume snapshot commands.

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

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