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

[Jack Meng]

Hi Richard,

Thanks for your reply.
Actually I'm thinking about how to recognize the same storage (probably 
external), not things on them. Sometimes storages are shared between 
hosts but have different paths to access, e.g., for fibre channel 
storages. So an update to the conf file is probably needed here to let 
the dest attach 'right' storages.

Mirroring/iSCSI is not the case I'm considering.

Best regards,
Jack

Richard W.M. Jones wrote:
> 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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