libvirt users - Feb 2014 - Question about managing migration transfers

Hi folks,

As part of a project I am working on, I need to control every step of a 
migration, from when I establish the connection to the destination, to 
when I decide to move data blocks, its size, etc. As I can see in the 
documentation, tunnelled migration allows some kind of control, as the 
data goes through libvirt before leaving the host.

May someone put more light on the subject? Is there any possibility to 
achieve such control I am looking for, or libvirt hacking will be needed?

Thank you very much.