Peter Maydell <peter.maydell@linaro.org> writes:
On Mon, 14 Sep 2020 at 09:55, Markus Armbruster <armbru@redhat.com> wrote:
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.
Some bikeshedding on option naming...
If this only covers QMP, should we make the argument to -compat have a name that expresses that? eg deprecated-qmp-input, deprecated-qmp-output ?
It's only implemented for QMP so far. But we really want it for all external interfaces for use by machines. Today, that's QMP and CLI. Naming the parameters deprecated-qmp-{input,output} leads to separate settings for QMP and CLI. Naming them just deprecated-{input,output} leads to a single set of settings common to all externeal interfaces, or to sugar for setting all the deprecated-*-{input,output} we may have. I don't think getting it wrong now would be a big deal. No excuse for getting it wrong unthinkingly :)
Also, it seems a bit repetitive to say 'deprecated' here all the time -- do you have a future use of -compat in mind which would be to adjust something that is *not* deprecated ? If not, maybe the 'deprecated' part should be in the option name rather than in every argument, eg
-deprecation-compat qmp-input=crash,qmp-output=hide,cli-option=reject
?
My cover letter hints at such future uses: "We may want to extend it to cover [...] experimental features." Something like -compat experimental-input=reject,experimental-output=hide