netdev - Re: [PATCH net-next v10 1/4] rust: core abstractions for network PHY drivers

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Date: Tue, 12 Dec 2023 08:47:53 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: boqun.feng@...il.com
Cc: fujita.tomonori@...il.com, alice@...l.io, 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,
 wedsonaf@...il.com, aliceryhl@...gle.com
Subject: Re: [PATCH net-next v10 1/4] rust: core abstractions for network
 PHY drivers

On Mon, 11 Dec 2023 15:40:33 -0800
Boqun Feng <boqun.feng@...il.com> wrote:

> On Tue, Dec 12, 2023 at 08:15:05AM +0900, FUJITA Tomonori wrote:
> [...]
>> >> +    /// Reads a given C22 PHY register.
>> >> + // This function reads a hardware register and updates the stats so
>> >> takes `&mut self`.
>> >> +    pub fn read(&mut self, regnum: u16) -> Result<u16> {
>> >> +        let phydev = self.0.get();
>> >> + // SAFETY: `phydev` is pointing to a valid object by the type
>> >> invariant of `Self`.
>> >> +        // So an FFI call with a valid pointer.
>> > 
>> > This sentence also doesn't parse in my brain. Perhaps "So it's just an
>> > FFI call" or similar?
>> 
>> "So it's just an FFI call" looks good. I'll fix all the places that
>> use the same comment.
> 
> I would also mention that `(*phydev).mdio.addr` is smaller than
> PHY_MAX_ADDR (per C side invariants in mdio maybe), since otherwise
> mdiobus_read() would cause out-of-bound accesses at ->stats. The safety
> comments are supposed to describe why calling the C function won't cause
> memory safety issues..

(*phydev).mdio.addr is managed in the C side and Rust code doesn't
touch it (doesn't need to know anything about it). What safety comment
should be written here?