[Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts

[Anthony Liguori]

Gleb Natapov wrote:
> > > > My problem implementing optional features/sections/... is not the
> > > > savevm/VMState bits.  At the end, implementing that is easy.  What is
> > > > more dificult is once that a device have 5 features, what are the valid
> > > > combinations.  i.e. if you have pci and msix features, msix requires
> > > > pci.  In this case, the dependency is trivial, but in others that
> > > > hasen't to be so obvious.
> > > >         
> > > It doesn't matter what device support and how it is configured. This can
> > > be handled by each device separately. i.e if destination detects that
> > > source had MSIX enabled for the device but destination hasn't it will
> > > signal an error.
> > >       
> > And guess what, with current code migration is going to "suceed" on the
> > source host and fail on the target host.
> >     
> Then current code is buggy. It should be possible to abort migration in
> the middle if device can't understand the data it received.
>   

It can, post_load() can error which will terminate the migration.  This 
can be used to validate fields beyond whether they fit into the type 
specified.

Regards,

Anthony Liguori
> --
>                         Gleb.
>