Re: [PATCH net-next v2 3/6] rust: net::phy implement AsRef<kernel::device::Device> trait

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Jul 31, 2024 at 6:22 AM FUJITA Tomonori
<fujita.tomonori@gmail.com> wrote:
>
> Implement AsRef<kernel::device::Device> trait for Device. A PHY driver
> needs a reference to device::Device to call the firmware API.
>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> ---
>  rust/kernel/net/phy.rs | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/rust/kernel/net/phy.rs b/rust/kernel/net/phy.rs
> index 99a142348a34..561f0e357f31 100644
> --- a/rust/kernel/net/phy.rs
> +++ b/rust/kernel/net/phy.rs
> @@ -302,6 +302,15 @@ pub fn genphy_read_abilities(&mut self) -> Result {
>      }
>  }
>
> +impl AsRef<kernel::device::Device> for Device {
> +    fn as_ref(&self) -> &kernel::device::Device {
> +        let phydev = self.0.get();
> +        // SAFETY: The struct invariant ensures that we may access
> +        // this field without additional synchronization.
> +        unsafe { kernel::device::Device::as_ref(&mut (*phydev).mdio.dev) }

This is a case where I would recommend use of the `addr_of_mut!`
macro. The type of the mutable reference will be `&mut
bindings::device` without a `Opaque` wrapper around the referent, and
the lack of `Opaque` raises questions about uniqueness guarantees.
Using `addr_of_mut!` sidesteps those questions.

With `addr_of_mut!` and no intermediate mutable reference you may add:

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

Alice