Re: [Qemu-devel] ping Re: [PATCH v7 03/16] migration: split common postcopy out of ram postcopy

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

* Kevin Wolf (kwolf@redhat.com) wrote:
> Am 25.09.2017 um 17:27 hat Dr. David Alan Gilbert geschrieben:
> > > > Whatever you think the preferred way to set up postcopy migration is: If
> > > > something worked before this patch and doesn't after it, that's a
> > > > regression and breaks backwards compatibility.
> > > > 
> > > > If we were talking about a graceful failure, maybe we could discuss
> > > > whether carefully and deliberately breaking compatibility could be
> > > > justified in this specific case. But the breakage is neither mentioned
> > > > in the commit message nor is it graceful, so I can only call it a bug.
> > > > 
> > > > Kevin
> > > 
> > > It's of course my fault, I don't mean "it's wrong test, so it's not my
> > > problem") And I've already sent a patch.
> > 
> > Why does this fail so badly, asserts etc - I was hoping for something
> > a bit more obvious from the migration code.
> > 
> > postcopy did originally work without the destination having the flag on
> > but setting the flag on the destination was always good practice because
> > it detected whether the host support was there early on.
> 
> So what does this mean for 2.11? Do you think it is acceptable breaking
> cases where the flag isn't set on the destination?

I think so, because we've always recommended setting it on the
destination for the early detection.

> If so, just changing the test case is enough. But if not, I'd rather
> keep the test case as it is and fix only the migration code.

I'd take the test case fix, but I also want to dig why it fails so
badly; it would be nice just to have a clean failure telling you
that postcopy was expected.

Dave

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