Re: [Qemu-devel] [PATCH v2 5/6] e1000: Choose which set of props to migrate

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

* Jason Wang (jasowang@redhat.com) wrote:
> 
> 
> On 2018年03月29日 00:36, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > When we're using the subsection we migrate both
> > the 'props' and 'tso_props' data; when we're not using
> > the subsection (to migrate to 2.11 or old machine types) we've
> > got to choose what to migrate in the main structure.
> > 
> > If we're using the subsection migrate 'props' in the main structure.
> > If we're not using the subsection then migrate the last one
> > that changed, which gives behaviour similar to the old behaviour.
> > 
> > 
> 
> But only after migration. Why not simply switch back to the old behavior if
> migrate_tso_props if false?

Because:
  1) We know it's a broken behaviour so it's better not to unfix it
  2) The fix doesn't change guest visible behaviour other than actually
     sending the right packets; so there's no reason to make the fix
     itself dependent on the machine type.
  3) Gating the fix itself on the flag is actually more complex and
     would need checking the flag in lots of places that are already
     pretty complex, rather than what this does which is just check it
     in one place at migration.

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