linux-kernel - Re: [PATCH -next v7 1/2] rust: clist: Add support to interface with C linked lists

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Message-ID: <30888418-5ee0-4a09-9eed-c6cdad2761a5@nvidia.com>
Date: Fri, 6 Feb 2026 16:12:30 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: Gary Guo <gary@...yguo.net>, Daniel Almeida <daniel.almeida@...labora.com>
Cc: linux-kernel@...r.kernel.org,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Jonathan Corbet <corbet@....net>, Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, Huang Rui <ray.huang@....com>,
 Matthew Auld <matthew.auld@...el.com>,
 Matthew Brost <matthew.brost@...el.com>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 Helge Deller <deller@....de>, Danilo Krummrich <dakr@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
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 Philipp Stanner <phasta@...nel.org>, Elle Rhumsaa
 <elle@...thered-steel.dev>, joel@...lfernandes.org,
 nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
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Subject: Re: [PATCH -next v7 1/2] rust: clist: Add support to interface with C
 linked lists



On 2/6/2026 3:51 PM, Gary Guo wrote:
> On Fri Feb 6, 2026 at 8:46 PM GMT, Joel Fernandes wrote:
>> On 2/6/2026 12:49 PM, Daniel Almeida wrote:
>>>> +#[repr(transparent)]
>>>> +pub(crate) struct CList<T, const OFFSET: usize>(CListHead, PhantomData<T>);
>>>> +
>>>> +impl<T, const OFFSET: usize> CList<T, OFFSET> {
>>>> +    /// Create a typed [`CList`] reference from a raw sentinel `list_head` pointer.
>>>> +    ///
>>>> +    /// # Safety
>>>> +    ///
>>>> +    /// - `ptr` must be a valid pointer to an allocated and initialized `list_head` structure
>>>> +    ///   representing a list sentinel.
>>>> +    /// - `ptr` must remain valid and unmodified for the lifetime `'a`.
>>>> +    /// - The list must contain items where the `list_head` field is at byte offset `OFFSET`.
>>>> +    /// - `T` must be `#[repr(transparent)]` over the C struct.
>>>> +    #[inline]
>>>> +    pub(crate) unsafe fn from_raw<'a>(ptr: *mut bindings::list_head) -> &'a Self {
>>>> +        // SAFETY:
>>>> +        // - [`CList`] has same layout as [`CListHead`] due to repr(transparent).
>>>> +        // - Caller guarantees `ptr` is a valid, sentinel `list_head` object.
>>>> +        unsafe { &*ptr.cast() }
>>>> +    }
>>>> +
>>>> +    /// Check if the list is empty.
>>>> +    #[inline]
>>>> +    #[expect(dead_code)]
>>>> +    pub(crate) fn is_empty(&self) -> bool {
>>>
>>> Why can’t this be pub?
>>
>> I believe this was suggested by Gary. See the other thread where we are
>> discussing it (with Gary and Danilo) and let us discuss there.
> 
> I suggested the module to be `pub(crate)`. For the individual item it is not
> necessary if the module itself already have limited visibility.
> 
Sure, I can change it to module-level pub then, and drop the pub(crate) if
everyone agrees.

--
Joel Fernandes