linux-kernel - Re: [PATCH v3 2/2] rust: types: require `ForeignOwnable::into

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Message-Id: <DAMHFC5U1496.25GQJSFU53PRD@kernel.org>
Date: Sat, 14 Jun 2025 20:53:34 +0200
From: "Benno Lossin" <lossin@...nel.org>
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>, "Alice Ryhl" <aliceryhl@...gle.com>, "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>
Subject: Re: [PATCH v3 2/2] rust: types: require
 `ForeignOwnable::into_foreign` return non-null

On Fri Jun 13, 2025 at 2:53 PM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@...nel.org> writes:
>
>> On Thu Jun 12, 2025 at 3:09 PM CEST, Andreas Hindborg wrote:
>>> The intended implementations of `ForeignOwnable` will not return null
>>> pointers from `into_foreign`, as this would render the implementation of
>>> `try_from_foreign` useless. Current users of `ForeignOwnable` rely on
>>> `into_foreign` returning non-null pointers. So require `into_foreign` to
>>> return non-null pointers.
>>>
>>> Suggested-by: Benno Lossin <lossin@...nel.org>
>>> Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
>>> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>>> ---
>>>  rust/kernel/types.rs | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
>>> index c156808a78d3..63a2559a545f 100644
>>> --- a/rust/kernel/types.rs
>>> +++ b/rust/kernel/types.rs
>>> @@ -43,6 +43,7 @@ pub unsafe trait ForeignOwnable: Sized {
>>>      /// # Guarantees
>>>      ///
>>>      /// - Minimum alignment of returned pointer is [`Self::FOREIGN_ALIGN`].
>>> +    /// - The returned pointer is not null.
>>
>> This also needs to be mentioned in the `Safety` section of this trait.
>> Alternatively you can put "Implementers must ensure the guarantees on
>> [`into_foreign`] are upheld." or similar.
>
> Which is exactly what I did :)

Ah didn't look at the first patch again, then it's fine :)

Reviewed-by: Benno Lossin <lossin@...nel.org>

---
Cheers,
Benno