linux-kernel - Re: [PATCH v4 5/5] rust: devres: implement register

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Message-ID: <aF_g1aspI_6GVRLC@pollux>
Date: Sat, 28 Jun 2025 14:32:21 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <lossin@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, gregkh@...uxfoundation.org,
	rafael@...nel.org, ojeda@...nel.org, alex.gaynor@...il.com,
	gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...nel.org,
	aliceryhl@...gle.com, tmgross@...ch.edu, david.m.ertman@...el.com,
	ira.weiny@...el.com, leon@...nel.org, kwilczynski@...nel.org,
	bhelgaas@...gle.com, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v4 5/5] rust: devres: implement register_release()

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.