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

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Message-ID: <Z9wDV7Y0-pwe_A-v@pollux>
Date: Thu, 20 Mar 2025 13:00:23 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
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 Thu, Mar 20, 2025 at 08:36:02AM +0000, Alice Ryhl wrote:
> 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?

dev->bus is a pointer to a const struct bus_type, yes.

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