Re: [Qemu-devel] [PULL 8/9] static checker: e1000-82540em got aliased to e1000

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

* Amit Shah (amit.shah@redhat.com) wrote:
> On (Tue) 23 Feb 2016 [15:02:58], Jason Wang wrote:
> > >> This means that 2.5 cannot migrate 2.4 virtual machines, right?  Is that
> > >> something we want to rectify in 2.6 by making e1000-82540em an alias of
> > >> e1000 (instead of the other way round)?
> > > You're right; I misread it.  With that commit (8304402033):
> > >
> > > 2.4 with e1000-82540em will not migrate to 2.5 with e1000-82540em.
> > >
> > > This is despite they're aliased (so the cmdline is backward
> > > compatible), but the migration device name actually changed.
> > >
> > > Of course, 2.5->2.4 will also not work.
> > >
> > > Since 2.4 emits 'e1000-82540em' as the device name in the migration
> > > stream, and 2.5 emits just 'e1000', we have two different names for
> > > the same device in two versions.
> > >
> > > To fix this, we'll need a hack on the dest side to allow e1000 and
> > > e1000-82540em in the migration stream for the device, and this can be
> > > done for 2.6 and 2.5.stable.
> > >
> > > Jason, can you attempt this?
> > >
> > Sure, but just need to understand the "problem". If I understand this
> > correctly, the issue only happen for JSON description at the end of
> > migration stream, and it won't break migration in fact?
> 
> No, this does break migration.
> 
> The stream contained 'e1000-82540em' as the section header for the
> device earlier.  It now only has 'e1000'.  So a newer qemu will only
> accept 'e1000', but not 'e1000-82540em' (from an older release).

OK, so do we need to get this fixed for 2.6 - i.e. now.

Dave

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