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

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Message-ID: <Z9vTctFR7QAOa4tn@google.com>
Date: Thu, 20 Mar 2025 08:36:02 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: 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, benno.lossin@...ton.me, 
	a.hindborg@...nel.org, tmgross@...ch.edu, linux-pci@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] rust: device: implement bus_type_raw()

On Wed, Mar 19, 2025 at 09:30:26PM +0100, 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.
> 
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> ---
>  rust/kernel/device.rs | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
> index 76b341441f3f..e2de0efd4a27 100644
> --- a/rust/kernel/device.rs
> +++ b/rust/kernel/device.rs
> @@ -78,6 +78,13 @@ 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`.

Is this field immutable?

> +        unsafe { (*self.as_raw()).bus }
> +    }
> +
>      /// Convert a raw C `struct device` pointer to a `&'a Device`.
>      ///
>      /// # Safety
> -- 
> 2.48.1
>