[libvirt] New save/restore api proposal

[Jean-Baptiste Rouault]

On Monday 23 August 2010 17:27:46 Jean-Baptiste Rouault wrote:
> 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
> 
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Hi,

Sorry to dig up this old thread but I'd like to have some feedback
about adding the possibility to set a custom save path.

Regards,

Jean-Baptiste

-- 
Jean-Baptiste ROUAULT
Ingénieur R&D - Diateam : Architectes de l'information
Phone : +33 (0)9 53 16 02 70 Fax : +33 (0)2 98 050 051