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

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Message-Id: <20240818.112518.2098286584782950755.fujita.tomonori@gmail.com>
Date: Sun, 18 Aug 2024 11:25:18 +0000 (UTC)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: benno.lossin@...ton.me
Cc: fujita.tomonori@...il.com, netdev@...r.kernel.org,
 rust-for-linux@...r.kernel.org, andrew@...n.ch, tmgross@...ch.edu,
 miguel.ojeda.sandonis@...il.com, aliceryhl@...gle.com
Subject: Re: [PATCH net-next v4 3/6] rust: net::phy implement
 AsRef<kernel::device::Device> trait

On Sun, 18 Aug 2024 10:42:32 +0000
Benno Lossin <benno.lossin@...ton.me> wrote:

>> /// - 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`.
> 
> Hmm, I think `self.0.mdio.dev` would be clearer.

Sure, fixed.

>> /// # 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.
>> /// - 'mdio.dev' must be a valid.
> 
> Also here: `(*ptr).mdio.dev`.

Thanks, looks better.

Here's an updated patch.

diff --git a/rust/kernel/net/phy.rs b/rust/kernel/net/phy.rs
index 5e8137a1972f..ec337cbd391b 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.
 ///
@@ -58,8 +57,9 @@ pub enum DuplexMode {
 ///
 /// # Invariants
 ///
-/// 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.
+/// - 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 `self.0.mdio.dev`.
 ///
 /// [`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 +76,11 @@ 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`, and the caller
+    ///   must be in a context where all methods defined on this struct
+    ///   are safe to call.
+    /// - `(*ptr).mdio.dev` must be a valid.
     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 +304,14 @@ 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)) }
+    }
+}
+
 /// Defines certain other features this PHY supports (like interrupts).
 ///
 /// These flag values are used in [`Driver::FLAGS`].
-- 
2.34.1