Re: [Qemu-devel] fw cfg files cross-version migration races

[Gerd Hoffmann]

  Hi,

> > So, sorting entries (and the index assigned too) should fix this, right?
> > That looks easiest to me.
> 
> Presumably, anything happening before (and after) user-provided blobs
> are inserted will continue happening in the same order everywhere.

Which might change in the future though, in case the initialization
order changes for some reason.  It's not a problem we have at the
moment, so this stuff isn't urgent.  But we might face it in the future.

> So we really only have to sort the user provided blobs, so that if
> the same *set* is provided on both ends of the migration, things would
> work out OK.

I would simply sort everything (and do it for new machine types only,
for backward compatibility reasons).  Sorting user-provided blobs only
adds complexity for no reason.

> If a *different* set of blobs is specified on the migration origin vs.
> the migration destination, we lose by default and worrying about it is
> pointless -- did I get that right ?

Yes.  For migration to succeed you have to supply the same configuration
on both ends.  That includes user-provided fw_cfg blobs of course.

cheers,
  Gerd