[Qemu-devel] Re: The State of the SaveVM format

[Michael S. Tsirkin]

On Wed, Sep 09, 2009 at 11:22:50AM +0200, Juan Quintela wrote:
> "Michael S. Tsirkin" <address@hidden> wrote:
> > On Wed, Sep 09, 2009 at 10:47:27AM +0200, Juan Quintela wrote:
> >> More problems: Going from newer versions to old versions
> >> - I think that everybody thinks that this is a nice to have, but that it
> >>   will took a lot to make it work, and there are more urgent things to
> >>   do.
> >
> > It's actually easy if you make whatever is new in the new version an
> > optional feature.  Then to save in an old format, qemu is started with
> > the feature disabled.
> 
> That only works if invariants are maintained.  That is not true in
> general.  And furthermore, you are deciding that if you find a bug, and
> fix needs a new field -> just live with the bug.

Clarification: add an *option* to live with the bug, off by default.

> If you can recreate the state without the new field, then _why_ did
> you added it in the 1st place?
> 
> Later, Juan.