linux-kernel - Re: [PATCH] rust: types: add FOREIGN

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Message-ID: <CAH5fLggzYQcMhcscuODR7cu__LLKAXhZ0A-tsBGc7gGyAA6Ofg@mail.gmail.com>
Date: Tue, 10 Jun 2025 17:19:28 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Danilo Krummrich <dakr@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <lossin@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Tamir Duberstein <tamird@...il.com>, Viresh Kumar <viresh.kumar@...aro.org>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, Maíra Canal <mcanal@...lia.com>
Subject: Re: [PATCH] rust: types: add FOREIGN_ALIGN to ForeignOwnable

On Thu, Jun 5, 2025 at 10:00 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> The current implementation of `ForeignOwnable` is leaking the type of the
> opaque pointer to consumers of the API. This allows consumers of the opaque
> pointer to rely on the information that can be extracted from the pointer
> type.
>
> To prevent this, change the API to the version suggested by Maira
> Canal (link below): Remove `ForeignOwnable::PointedTo` in favor of a
> constant, which specifies the alignment of the pointers returned by
> `into_foreign`.
>
> Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
> Suggested-by: Maíra Canal <mcanal@...lia.com>
> Link: https://lore.kernel.org/r/20240309235927.168915-3-mcanal@igalia.com
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>

One nit below. With that and things other folks mentioned fixed, you may add:

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 22985b6f6982..025c619a2195 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -21,15 +21,11 @@
>  ///
>  /// # Safety
>  ///
> -/// Implementers must ensure that [`into_foreign`] returns a pointer which meets the alignment
> -/// requirements of [`PointedTo`].
> -///
> -/// [`into_foreign`]: Self::into_foreign
> -/// [`PointedTo`]: Self::PointedTo
> +/// Implementers must ensure that [`Self::into_foreign`] return pointers with alignment that is an
> +/// integer multiple of [`Self::FOREIGN_ALIGN`].

We should require non-null:

Implementers must ensure that [`Self::into_foreign`] returns pointers
that are non-null and with alignment that is an integer multiple of
[`Self::FOREIGN_ALIGN`].

Alice