linux-kernel - Re: [PATCH v3 4/4] rust: devres: implement register

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Message-ID: <aF0rzzlKgwopOVHV@pollux>
Date: Thu, 26 Jun 2025 13:15:27 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <lossin@...nel.org>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, ojeda@...nel.org,
	alex.gaynor@...il.com, boqun.feng@...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 v3 4/4] rust: devres: implement register_release()

On Thu, Jun 26, 2025 at 12:36:23PM +0200, Benno Lossin wrote:
> Or, we could change `Release` to be:
> 
>     pub trait Release {
>         type Ptr: ForeignOwnable;
> 
>         fn release(this: Self::Ptr);
>     }
> 
> and then `register_release` is:
> 
>     pub fn register_release<T: Release>(dev: &Device<Bound>, data: T::Ptr) -> Result
> 
> This way, one can store a `Box<T>` and get access to the `T` at the end.

I think this was also the case before? Well, it was P::Borrowed instead.

> Or if they store the value in an `Arc<T>`, they have the option to clone
> it and give it to somewhere else.

Anyways, I really like this proposal of implementing the Release trait.

> Related questions:
> 
> * should we implement `ForeignOwnable` for `&'static T`?

There's already a patch on the list doing this in the context of DebugFS [1].

[1] https://lore.kernel.org/lkml/20250624-debugfs-rust-v7-3-9c8835a7a20f@google.com/

> * should we require `'static` in `ForeignOwnable`? At the moment we only
>   have those kinds supported and it only makes sense, a foreign owned
>   object can be owned for any amount of time (so it must stay valid
>   indefinitely).

Sounds reasonable to me.