linux-kernel - Re: [PATCH v10 1/2] rust: types: add `ForeignOwnable::PointedTo`

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Message-ID: <CAH5fLgjpE7a1jy+W-ZdscrR3D3FrO21iVNd1L-7WY0jGcwQ9mA@mail.gmail.com>
Date: Mon, 25 Nov 2024 15:49:40 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Tamir Duberstein <tamird@...il.com>
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 <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Maíra Canal <mcanal@...lia.com>, 
	Asahi Lina <lina@...hilina.net>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 1/2] rust: types: add `ForeignOwnable::PointedTo`

On Wed, Nov 20, 2024 at 12:48 PM Tamir Duberstein <tamird@...il.com> wrote:
>
> Allow implementors to specify the foreign pointer type; this exposes
> information about the pointed-to type such as its alignment.
>
> This requires the trait to be `unsafe` since it is now possible for
> implementors to break soundness by returning a misaligned pointer.
>
> Encoding the pointer type in the trait (and avoiding pointer casts)
> allows the compiler to check that implementors return the correct
> pointer type. This is preferable to directly encoding the alignment in
> the trait using a constant as the compiler would be unable to check it.
>
> Signed-off-by: Tamir Duberstein <tamird@...il.com>

I'm not super convinced by this way forward. It introduces more casts
to/from c_void in code using it, and forces us to expose internal
types such as ArcInner. Does anyone else have thoughts on this?

Alice