Re: [libvirt] New save/restore api proposal
On Monday 23 August 2010 14:51:51 you wrote:
On Thu, Aug 19, 2010 at 05:12:36PM +0200, Jean-Baptiste Rouault
wrote:
> Hello all,
>
> I'd like to add support for save and restore to the OpenVZ and VirtualBox
> drivers because I have to support these operations in the application I'm
> working on.
>
> However, the save/restore API in its current state doesn't fit well to
> our needs. The main problem is that the domain definition is included
> inside the save file. This is problematic because between the save and
> the restore operations, the names of the network interfaces on the host
> side are likely to have changed and we can't modify them before
> restoring the domain.
IMHO a more general approach is to set stable naming for the host
devices.
This is not possible for us because our application is distributed on multiple
servers. We have a huge nfs exported folder where we store all our guests'
disks and private folders. A saved guest which was running on one server can
be restored on another one so we can't set stable naming for the host side.
I really don't think we want to add yet more save/restore
functions
to the API. I'm not sure its even possible to implement those
proposals with VirtualBox, since it can't save state to an arbitrary
file.
The API in the VirtualBox SDK is IProgress IConsole::saveState().
This does a managed save internally to vbox. The next time the
guest is started, it will restore from this image. This maps
directly to libvirt's virDomainManagedSave() API. The OpenVZ docs
appear to explicitly forbid any change to the VM configugration
between time of save & restore. If it didn't forbid config changes,
then in theory you could call virDomainDefine() after calling
virDomainManagedSave() but before virDomainCreate() in order ot
change the config.
The problem of the managed save API for us is that it doesn't allow to set a
custom save path. We keep save states in each VM's folder so that any of our
servers is able to access them. Maybe a custom managed save path could be
specified in a domain's xml and then used instead of the default one ? This
isn't a problem for VirtualBox because there is the adoptSavedState API.
For other libvirt drivers I think this shouldn't be too difficult to implement.
As for OpenVZ, the vzctl chkpnt & vzctl restore commands look
like
they can map directly to both of the libvirt save/restore APis. The
original one taking a filename, and the new managed save ones.
Regards,
Daniel