"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 :)
