On Wed, 4 Jul 2018 17:14:02 +0100 Peter Maydell <peter.maydell@linaro.org> wrote:
On 4 July 2018 at 14:34, Kevin Wolf <kwolf@redhat.com> wrote:
Essentially, what is important to me isn't getting these options dropped exactly in 3.0, but not setting a bad precedence that deprecation isn't actually worth anything. We may easily end up with this deprecation process:
depreate a feature release QEMU version n + 1 release QEMU version n + 2 remove the feature while libvirt hasn't removed use of the feature: # ...and why should it when everything is still working? reinstate the feature release QEMU version n + x remove the feature
My take on the deprecation policy essentially is that it gives us a *minimum* bar for how soon we can drop something. We shouldn't be using it as an "always target this speed for dropping something" -- we ought to be pragmatic. We can drop stuff that's unused quickly, but should be slower for things that still have major users (or reconsider the deprecation entirely, potentially). There should be a balance between making our work as developers easier and inconveniencing our users.
What about the following? - put a feature on the "normal" deprecation list to remove after two releases Case (a): nobody complains, either within the deprecation period or when it is finally removed -> all is good Case (b): the feature turns out to be widely used, and/or it turns out that it offers value that currently can't be offered easily in another way -> remove from deprecation list; this obviously needs more thinking Case (c): the feature is used, the users are willing to move away from it, but they need a bit more time -> put it on a "deprecation watchlist", listing the users we are waiting for, and then remove after all are done (no +2) That way, we can still easily remove old cruft (case (a)), but still accommodate cases like this (case (c)). The obvious drawback is that we'd need someone to curate the deprecation watchlist, to poke the users we're waiting for, and probably remove anyway after some time if they don't get their act together.
In this particular case, reverting this deletion seems like a fairly easy call to me.
We should also definitely work on improving how we can let management-layer developers easily test that they're not accidentally relying on deprecated features, certainly (and also on better documentation for command line users of how to switch away from deprecated features -- for instance I am still using -redir in some of my scripts because the warning about it being deprecated is not precise about what exact command line option can be used instead, especially for the case where the ethernet device is builtin rather than created with -device...)
Yes, this as well.