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

[Amit Shah]

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).

                Amit