[Qemu-devel] [RFC] Migration capability negotation

[Peter Lieven]

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.

Peter