On Thu, 10 Dec 2020, Christian Borntraeger wrote:
> > * However, the boilerplate to usefulness ratio doesn't look too good and I
> > wonder whether what we should do is adding a generic "misc" controller
> > which can host this sort of static hierarchical counting. I'll think more
> > on it.
>
> We first dicussed to have
> encryption_ids.stat
> encryption_ids.max
> encryption_ids.current
>
> and we added the sev in later, so that we can also have tdx, seid, sgx or whatever.
> Maybe also 2 or more things at the same time.
>
> Right now this code has
>
> encryption_ids.sev.stat
> encryption_ids.sev.max
> encryption_ids.sev.current
>
> And it would be trivial to extend it to have
> encryption_ids.seid.stat
> encryption_ids.seid.max
> encryption_ids.seid.current
> on s390 instead (for our secure guests).
>
> So in the end this is almost already a misc controller, the only thing that we
> need to change is the capability to also define things other than encryption.*.*
> And of course we would need to avoid adding lots of random garbage to such a thing.
>
> But if you feel ok with the burden to keep things kind of organized a misc
> controller would certainly work for the encryption ID usecase as well.
> So I would be fine with the thing as is or a misc controlĺer.
>
Yeah, I think generalization of this would come in the form of either (1)
the dumping ground of an actual "misc" controller, that you elude to, or
(2) a kernel abstraction so you can spin up your own generic controller
that has the {current, max, stat} support. In the case of the latter,
encryption IDs becomes a user of that abstraction.
Concern with a single misc controller would be that any subsystem that
wants to use it has to exactly fit this support: current, max, stat,
nothing more. The moment a controller needs some additional support, and
its controller is already implemented in previous kernel versionv as a
part of "misc," we face a problem.
On the other hand, a kernel abstraction that provides just the basic
{current, max, stat} support might be interesting if it can be extended by
the subsystem instance using it.
