linux-kernel - Re: [PATCH v2 2/4] rust: device: implement bus_type

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Message-ID: <D8LGQ1BTPFBR.1P5LGD0LWP32W@proton.me>
Date: Thu, 20 Mar 2025 22:55:56 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Danilo Krummrich <dakr@...nel.org>, bhelgaas@...gle.com, gregkh@...uxfoundation.org, rafael@...nel.org, ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu
Cc: linux-pci@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] rust: device: implement bus_type_raw()

On Thu Mar 20, 2025 at 11:27 PM CET, Danilo Krummrich wrote:
> Implement bus_type_raw(), which returns a raw pointer to the device'
> struct bus_type.
>
> This is useful for bus devices, to implement the following trait.
>
> 	impl TryFrom<&Device> for &pci::Device
>
> With this a caller can try to get the bus specific device from a generic
> device in a safe way. try_from() will only succeed if the generic
> device' bus type pointer matches the pointer of the bus' type.
>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>

Reviewed-by: Benno Lossin <benno.lossin@...ton.me>

---
Cheers,
Benno

> ---
>  rust/kernel/device.rs | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
> index f6bdc2646028..1b554fdd93e9 100644
> --- a/rust/kernel/device.rs
> +++ b/rust/kernel/device.rs
> @@ -80,6 +80,16 @@ pub fn parent<'a>(&self) -> Option<&'a Self> {
>          }
>      }
>  
> +    /// Returns a raw pointer to the device' bus type.
> +    #[expect(unused)]
> +    pub(crate) fn bus_type_raw(&self) -> *const bindings::bus_type {
> +        // SAFETY:
> +        // - By the type invariants, `self.as_raw()` is a valid pointer to a `struct device`.
> +        // - `dev->bus` is a pointer to a `const struct bus_type`, which is only ever set at device
> +        //    creation.
> +        unsafe { (*self.as_raw()).bus }
> +    }
> +
>      /// Convert a raw C `struct device` pointer to a `&'a Device`.
>      ///
>      /// # Safety