Re: [Qemu-devel] [RFC] Migration capability negotation

[Juan Quintela <quintela@redhat.com>]

Peter Lieven <pl@kamp.de> wrote:
> Hi,
>
> I was thinking that it would be great to have the source and
> destination during migration negoatiate
> migration capabilities e.g. something like this:
>
> User wants to use a feature e.g. 'zero_blocks'. He switches it to 'on'
> or maybe a new state 'auto' on the source VM.
>
> If the migration is started the source hypervisor sends a set of all
> desired features. The destination hypervisor
> answers with a subset of all features it supports and automatically
> enables them on its side. Depending on the returned
> subset the source disables all features the destination does not support.
>
> This would also allow us also to introduce new features which we would
> like to enable by default, but we cannot
> because we do not know if the destination will support it.
>
> Is there any way to add this without breaking backwards compability?
>
> Comments welcome.

As said by Eric,  comunications goes only in one direction (think that
we are migrating to a file,  A.K.A. savevm).  Anthony basically forbides
them.  You can do the equivalent thing from the management application.