linux-kernel - Re: [PATCH 4/4] rust: drm: don't pass the address of drm::Device to drm_dev

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Message-ID: <aIyFLDvb2kGoiWW9@google.com>
Date: Fri, 1 Aug 2025 09:13:16 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: lorenzo.stoakes@...cle.com, vbabka@...e.cz, Liam.Howlett@...cle.com, 
	urezki@...il.com, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	lossin@...nel.org, a.hindborg@...nel.org, tmgross@...ch.edu, 
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, 
	airlied@...il.com, simona@...ll.ch, rust-for-linux@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] rust: drm: don't pass the address of drm::Device to drm_dev_put()

On Thu, Jul 31, 2025 at 05:48:09PM +0200, Danilo Krummrich wrote:
> In drm_dev_put() call in AlwaysRefCounted::dec_ref() we rely on struct
> drm_device to be the first field in drm::Device, whereas everywhere
> else we correctly obtain the address of the actual struct drm_device.
> 
> Analogous to the from_drm_device() helper, provide the
> into_drm_device() helper in order to address this.
> 
> Fixes: 1e4b8896c0f3 ("rust: drm: add device abstraction")
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> +    /// # Safety
> +    ///
> +    /// `ptr` must be a valid pointer to `Self`.
> +    unsafe fn into_drm_device(ptr: NonNull<Self>) -> *mut bindings::drm_device {
> +        // SAFETY: By the safety requirements of this function, `ptr` is a valid pointer to `Self`.
> +        unsafe { &raw mut (*ptr.as_ptr()).dev }.cast()
> +    }

I think it would somewhat more consistent to use the naming raw_get() or
cast_into(), but I am ok with this naming too.

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

Alice