linux-kernel - Re: [PATCH v3 06/14] rust: drm: gem: Add raw_dma

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Message-ID: <CAH5fLgjFePwYmyivpU-Vk2KbKtu7t5DJ1cZUJmEQ_Y+Dgynk9w@mail.gmail.com>
Date: Thu, 4 Sep 2025 15:09:51 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Lyude Paul <lyude@...hat.com>
Cc: dri-devel@...ts.freedesktop.org, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	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>, Danilo Krummrich <dakr@...nel.org>, 
	Sumit Semwal <sumit.semwal@...aro.org>, Christian König <christian.koenig@....com>, 
	Daniel Almeida <daniel.almeida@...labora.com>, Asahi Lina <lina+kernel@...hilina.net>, 
	"open list:DMA BUFFER SHARING FRAMEWORK:Keyword:bdma_(?:buf|fence|resv)b" <linux-media@...r.kernel.org>, 
	"moderated list:DMA BUFFER SHARING FRAMEWORK:Keyword:bdma_(?:buf|fence|resv)b" <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v3 06/14] rust: drm: gem: Add raw_dma_resv() function

On Sat, Aug 30, 2025 at 12:42 AM Lyude Paul <lyude@...hat.com> wrote:
>
> For retrieving a pointer to the struct dma_resv for a given GEM object. We
> also introduce it in a new trait, BaseObjectPrivate, which we automatically
> implement for all gem objects and don't expose to users outside of the
> crate.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
>  rust/kernel/drm/gem/mod.rs | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
> index ec36cd9ea69ed..f901d4263ee87 100644
> --- a/rust/kernel/drm/gem/mod.rs
> +++ b/rust/kernel/drm/gem/mod.rs
> @@ -186,6 +186,18 @@ fn create_mmap_offset(&self) -> Result<u64> {
>
>  impl<T: IntoGEMObject> BaseObject for T {}
>
> +/// Crate-private base operations shared by all GEM object classes.
> +#[expect(unused)]
> +pub(crate) trait BaseObjectPrivate: IntoGEMObject {
> +    /// Return a pointer to this object's dma_resv.
> +    fn raw_dma_resv(&self) -> *mut bindings::dma_resv {
> +        // SAFETY: `as_gem_obj()` always returns a valid pointer to the base DRM gem object
> +        unsafe { (*self.as_raw()).resv }
> +    }
> +}
> +
> +impl<T: IntoGEMObject> BaseObjectPrivate for T {}

I think this use of a trait is somewhat of an antipattern. I would
probably have suggested a standalone method instead.

Alice