Re: [Libguestfs] Having integration tests "test the future" with QEMU

On Wed, Mar 04, 2020 at 03:48:34PM +0100, Markus Armbruster wrote: > I understand libguestfs comes with integration tests. You might be > interested in something I'm developing for QEMU 5.0 to permit "testing > the future". I'd like to ensure it is actually useful before I > continue. Let me know what you think. > > = Motivation = > > When layers above QEMU somehow miss feature deprecation, things continue > to work until the deprecated interface goes away, at which point we have > an entirely avoidable regression. > > We've been trying to get better at communicating feature deprecation to > the layers above QEMU. An obvious first step was systematic > documentation. > > However, documentation is all too easy to miss. Even if you don't miss > it, you may need to continue using the deprecated feature with old > versions of QEMU, and that logic needs to be tested. > > I'm working on a way to run QEMU with the deprecated features disabled. > This permits "testing the future". > > From my cover letter: > > This series extends QMP introspection to cover deprecation. > Additionally, new option -compat lets you configure what to do when > deprecated interfaces get used. This is intended for testing users of > the management interfaces. It is experimental. > > -compat deprecated-input=<in-policy> configures what to do when > deprecated input is received. Available policies: > > * accept: Accept deprecated commands and arguments (default) > * reject: Reject them > * crash: Crash > > -compat deprecated-output=<out-policy> configures what to do when > deprecated output is sent. Available output policies: > > * accept: Emit deprecated command results and events (default) > * hide: Suppress them > > For now, -compat covers only deprecated syntactic aspects of QMP. We > may want to extend it to cover semantic aspects, CLI, and experimental > features. Yes we would add a -compat option when running qemu (only when running non-production builds of libguestfs) so that it would fail loudly when we use a deprecated feature. This is the best way I've heard of so far to get advanced warning of deprecated features.