On Thu, Apr 24, 2014 at 09:21:00AM +0100, Dr. David Alan Gilbert wrote: > * Markus Armbruster (arm...@redhat.com) wrote: > > "Dr. David Alan Gilbert" <dgilb...@redhat.com> writes: > > > > > * Eric Blake (ebl...@redhat.com) wrote: > > >> On 04/23/2014 10:37 AM, Dr. David Alan Gilbert (git) wrote: > > >> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > >> > > > >> > > >> > 4) At the moment you select BER output format by setting an > > >> > environment > > >> > variable ( export QEMUMIGFORMAT=BER ) , I need to put more > > >> > thought > > >> > in to the right way to do this, there are some harder questions > > >> > like > > >> > what happens to devices that are still using pre-vmstate > > >> > encodings > > >> > (that are currently sent as blobs) when they eventually convert > > >> > over > > >> > and thus how to keep compatibility with earlier BER output > > >> > versions > > >> > where they were blobs. > > >> > > >> I don't have good advice on how to address intra-version design (what > > >> happens when an old version of BER sends a blob but a new version on the > > >> receiving side expects formatted data instead of a blob), other than > > >> it's going to be similar to any other intra-version design that we > > >> already have to consider when upgrading from old to new qemu. > > >> > > >> But for how to select BER format, I _do_ have an idea: > > >> > > >> https://lists.gnu.org/archive/html/qemu-devel/2014-04/msg00782.html > > >> > > >> Basically, I think that the choice of migration format should be > > >> selected via a new extended capability added to > > >> migrate-set-capabilities. Setting the choice at the environment > > >> variable is too inflexible (it's locked down for the duration of the > > >> entire qemu process), whereas setting it via QMP is desirable (for > > >> example, it would let us choose at the time of migration whether we are > > >> migrating to an older host and want the old format, or migrating to a > > >> file for checkpointing reasons and want the new format). > > > > > > Yep, that would certainly be easy to do - and I can do that for > > > the next version. > > > It's more the intra-version I'm worried about, primarily because I don't > > > want to have to wait until every device is vmstate'd before moving this > > > code forward. > > > > > > The one thing that the environment variable does make nice and easy, > > > for dev, is using it with existing test setups - e.g. running virt-test > > > in BER mode or existing mode. > > > > Sounds like a useful hack to speed up development, but not so much like > > a useful permanent API :) > > Yep, I think what I'll do is go with Eric's suggestion of the > migration-capability, > but initialise it based on the environment variable; then I can take that > out once it all settles out. > > Dave
OK but for a new machine type, let's default to BER, right? I see no reason to keep supporting when non-BER when -M specifies 2.1 compatibility, do you? > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
