Re: [Qemu-devel] [PATCH v3 3/4] savevm: define new unambiguous migration format

[Paolo Bonzini]

On 08/12/2011 05:16 PM, Anthony Liguori wrote:
> > Because of the change we made for 0.15, this is no longer strictly
> > needed. It only matters if we add a subsection to a structure, right?

Yes.  We can also check the current migration format in the "needed" 
function for such subsections, if necessary.  This is what I plan to do 
for the floppy subsection, skipping it for old machine types that do not 
use the new migration format.

> I'm definitely not saying we shouldn't do this BTW.  But trying to
> understand whether we can position this as a strictly optional feature
> (iow, a capability) or whether this requires a hard break in the
> migration protocol.

This what? :)  Adding a subsection to a structure, or using the new 
migration format?  If you mean using the new format only when you have 
subsections in a structure, then you'll need quite a bit of new code to 
try all VMState handlers and see if they'll need a subsection.  I don't 
think it's worth it, also because we all hope this is a temporary 
solution until we have a serious format (e.g. ASN-1).

Paolo