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

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Message-Id: <DG86CJXCM7DB.1A4F4JTMSS9ZZ@garyguo.net>
Date: Fri, 06 Feb 2026 20:51:15 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Joel Fernandes" <joelagnelf@...dia.com>, "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>,
 "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>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Trevor Gross" <tmgross@...ch.edu>,
 "John Hubbard" <jhubbard@...dia.com>, "Alistair Popple"
 <apopple@...dia.com>, "Timur Tabi" <ttabi@...dia.com>, "Edwin Peer"
 <epeer@...dia.com>, "Alexandre Courbot" <acourbot@...dia.com>, "Andrea
 Righi" <arighi@...dia.com>, "Andy Ritger" <aritger@...dia.com>, "Zhi Wang"
 <zhiw@...dia.com>, "Balbir Singh" <balbirs@...dia.com>, "Philipp Stanner"
 <phasta@...nel.org>, "Elle Rhumsaa" <elle@...thered-steel.dev>,
 <joel@...lfernandes.org>, <nouveau@...ts.freedesktop.org>,
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 <intel-gfx@...ts.freedesktop.org>, <intel-xe@...ts.freedesktop.org>,
 <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH -next v7 1/2] rust: clist: Add support to interface with
 C linked lists

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.

Best,
Gary