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

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Message-ID: <CAH5fLggMWrDU2U81e4Cs5dV82VFdWC8+02sR8RTZisQGnFgNow@mail.gmail.com>
Date: Wed, 31 Jul 2024 10:38:11 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, andrew@...n.ch, 
	tmgross@...ch.edu, miguel.ojeda.sandonis@...il.com, benno.lossin@...ton.me
Subject: Re: [PATCH net-next v2 3/6] rust: net::phy implement
 AsRef<kernel::device::Device> trait

On Wed, Jul 31, 2024 at 6:22 AM FUJITA Tomonori
<fujita.tomonori@...il.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@...il.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@...gle.com>

Alice