[Libvir] Is it possible to add an interface to intercept the migration process?

[Richard W.M. Jones]

Meng Ran wrote:
> Hi All,
> 
> I'm thinking about if it possible to add an interface to let user 
> specified action to happen on destination during the migration, this 
> should be useful for migrating things that have different paths on 
> source and destination.
> 
> Allowing specified action(callback) to happen at a time point, e.g., 
> after the config file is transfered and before starting the vm, can 
> bring in a lot of flexibilities considering the migration of devices 
> which are shared but have different paths/views. Giving the dest a 
> chance to recognize these devices and update the config, and then start 
> the vm probably is helpful there.
> 
> Comment?

First of all this would have to be supported by a hypervisor (eg. Xen) 
before we could add it to libvirt.

In general I'm not sure how this could work for migration at all.  Live 
migration copies the memory image while the guest is still running, so 
there is no point where the user action could run.  Even offline 
migration only transfers the memory, not the disk, so if you need to 
reconfigure something on disk, you can just do it before starting the 
migration.

Perhaps you're thinking of shutting down the guest and copying its disk 
image to another machine and starting the guest up there?  In that case 
there should be ample opportunity to make changes to the disk by just 
mounting it on the host.  I think Platespin support this for their "V2V" 
migration.

If I've missed something about what you're trying to do, let me know.

Rich.

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