Re: [PATCH v4 5/5] rust: devres: implement register_release()

[Danilo Krummrich <dakr@kernel.org>]

On Sat, Jun 28, 2025 at 02:13:08PM +0200, Benno Lossin wrote:
> On Sat Jun 28, 2025 at 11:58 AM CEST, Danilo Krummrich wrote:
> > On Sat, Jun 28, 2025 at 09:53:06AM +0200, Benno Lossin wrote:
> >> Hmm @Danilo, do you have any use-cases in mind or already done?
> >
> > There may be other use-cases, but the one that I could forsee is very specific:
> >
> > A Registration type that carries additional reference-counted data, where the
> > Registration should be released exactly when the device is unbound, independent
> > of the lifetime of the data.
> >
> > Obviously, this implies that the ForeignOwnable is an Arc.
> >
> > With KBox, Release and Drop are pretty much identical, so using
> > devres::release() instead, is much simpler and hence what we do for all simple
> > class device registrations.
> >
> > Besides that, the use-case described above can also be covered by Devres with
> > the pin-init rework, by having the Registration  embed a Devres<Inner>, which
> > is what irq::Registration does and I also do in the MiscDeviceRegistration
> > patches.
> >
> > Hence, I already considered dropping this patch -- and I think we should do this
> > for now.
> 
> Sounds good! We can always pick it up again when needed.

Exactly -- thanks Benno and Boqun! The discussion of the design of the Release
trait seems also relevant for other use-cases with ForeignOwnable types where we
require trait bounds for their target types.