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

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Message-ID: <Z9wedMSNOntie88F@google.com>
Date: Thu, 20 Mar 2025 13:56:04 +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 Thu, Mar 20, 2025 at 01:00:23PM +0100, Danilo Krummrich wrote:
> 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.

With that added to the SAFETY comment to justify reading the field is
data-race free, you may add:

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