Re: [Qemu-devel] [PATCH v3 1/4] serial: reset thri_pending on IER writes with THRI=0

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> 
> 
> On 15/12/2014 14:30, Dr. David Alan Gilbert wrote:
> > Anyone who really cares about backwards migration compatibility would
> > probably have to guard the subsection with the machine-type to avoid
> > (e) ever happening (the heuristic from (c) might be useful to add).
> 
> Right.
> 
> > although if you do have to recut it, please clarify the text that says
> >  'and is enough to fix migration.' since it doesn't quite.
> 
> Ok, I'll clarify this, specifying which case remains broken by design.
> 
> > (This is an interesting example where with a migration format that allowed
> > 'optional' subsections you wouldn't break backwards migration if the
> > reader could ignore a section marked as such that it didn't recognise).
> 
> Right, the question is whether you really want to do this. :)

Well, it would solve this type of problem less painfully, your migration
would always succeed and destinations that knew what to do with it would
always do the right thing.  Of course you could also solve the problem
if the source knew the version of the destination, but you didn't like
that idea either.

Dave

> 
> Paolo
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK