Re: [PATCH net-next v4 3/6] rust: net::phy implement AsRef<kernel::device::Device> trait

[Benno Lossin <benno.lossin@proton.me>]

On 18.08.24 09:36, FUJITA Tomonori wrote:
> On Sun, 18 Aug 2024 06:01:27 +0000
> Benno Lossin <benno.lossin@proton.me> wrote:
>>>>> +        unsafe { kernel::device::Device::as_ref(addr_of_mut!((*phydev).mdio.dev)) }
>>>>> +    }
>>>>> +}
>>>
>>> SAFETY: A valid `phy_device` always have a valid `mdio.dev`.
>>>
>>> Better?
>>
>> It would be nice if you could add this on the invariants on
>> `phy::Device` (you will also have to extend the INVAIRANTS comment that
>> creates a `&'a mut Device`)
> 
> How about the followings?
> 
> diff --git a/rust/kernel/net/phy.rs b/rust/kernel/net/phy.rs
> index 5e8137a1972f..3e1d6c43ca33 100644
> --- a/rust/kernel/net/phy.rs
> +++ b/rust/kernel/net/phy.rs
> @@ -7,8 +7,7 @@
>  //! C headers: [`include/linux/phy.h`](srctree/include/linux/phy.h).
> 
>  use crate::{error::*, prelude::*, types::Opaque};
> -
> -use core::marker::PhantomData;
> +use core::{marker::PhantomData, ptr::addr_of_mut};
> 
>  /// PHY state machine states.
>  ///
> @@ -60,6 +59,7 @@ pub enum DuplexMode {
>  ///
>  /// Referencing a `phy_device` using this struct asserts that you are in
>  /// a context where all methods defined on this struct are safe to call.
> +/// This struct always has a valid `mdio.dev`.

Please turn this into a bullet point list.

>  ///
>  /// [`struct phy_device`]: srctree/include/linux/phy.h
>  // During the calls to most functions in [`Driver`], the C side (`PHYLIB`) holds a lock that is
> @@ -76,9 +76,9 @@ impl Device {
>      ///
>      /// # Safety
>      ///
> -    /// For the duration of 'a, the pointer must point at a valid `phy_device`,
> -    /// and the caller must be in a context where all methods defined on this struct
> -    /// are safe to call.
> +    /// For the duration of 'a, the pointer must point at a valid `phy_device` with
> +    /// a valid `mdio.dev`, and the caller must be in a context where all methods
> +    /// defined on this struct are safe to call.

Also here.

>      unsafe fn from_raw<'a>(ptr: *mut bindings::phy_device) -> &'a mut Self {
>          // CAST: `Self` is a `repr(transparent)` wrapper around `bindings::phy_device`.
>          let ptr = ptr.cast::<Self>();
> @@ -302,6 +302,14 @@ 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 `mdio.dev` is valid.
> +        unsafe { kernel::device::Device::as_ref(addr_of_mut!((*phydev).mdio.dev)) }
> +    }

Just to be sure: the `phydev.mdio.dev` struct is refcounted and
incrementing the refcount is fine, right?

---
Cheers,
Benno

> +}
> +
>  /// Defines certain other features this PHY supports (like interrupts).
>  ///
>  /// These flag values are used in [`Driver::FLAGS`].