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

[Amit Shah <amit.shah@redhat.com>]

On (Wed) 06 Apr 2016 [09:48:19], Jason Wang wrote:
> 
> 
> On 04/05/2016 09:32 PM, Dr. David Alan Gilbert wrote:
> > * 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
> 
> Sorry for the late response.
> 
> Have a try with 2.4 -> 2.5 migration and it works. Looking at
> save_section_header(), it will save se->idstr which seems always be
> "e1000" even if e1000-82540em is used in cli, or is there anything I missed?

OK, sorry for the wrong alarm.

The VMStateDescription's 'name' field has remained the same; but the
section name has changed, which is fine (that isn't transmitted over
the wire).  So my initial reading was correct - and the whitelist I
added in 1483e0d74dcfd183ff46dd63cc57e1fe8b775bf8 is fine.

So nothing needed for the migration stream.

Thanks, Jason.

		Amit