* 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 -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
