netdev - Re: [PATCH net-next v9 1/4] rust: core abstractions for network PHY drivers

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Date: Tue, 05 Dec 2023 12:23:20 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: boqun.feng@...il.com
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, benno.lossin@...ton.me,
 wedsonaf@...il.com, aliceryhl@...gle.com
Subject: Re: [PATCH net-next v9 1/4] rust: core abstractions for network
 PHY drivers

On Mon, 4 Dec 2023 18:00:15 -0800
Boqun Feng <boqun.feng@...il.com> wrote:

> On Tue, Dec 05, 2023 at 10:14:17AM +0900, FUJITA Tomonori wrote:
> [...]
>> +    /// Gets the current link state.
>> +    ///
>> +    /// It returns true if the link is up.
>> +    pub fn is_link_up(&self) -> bool {
>> +        const LINK_IS_UP: u64 = 1;
>> +        // TODO: the code to access to the bit field will be replaced with automatically
>> +        // generated code by bindgen when it becomes possible.
>> +        // SAFETY: The struct invariant ensures that we may access
>> +        // this field without additional synchronization.
>> +        let bit_field = unsafe { &(*self.0.get())._bitfield_1 };
>> +        bit_field.get(14, 1) == LINK_IS_UP
> 
> I made a mistake here [1], this should be:
> 
>     let bit_field = unsafe { &*(core::ptr::addr_of!((*self.0.get())._bitfield_1)) };
>     bit_field.get(14, 1) == LINK_IS_UP
> 
> without `core::ptr::add_of!`, `*(self.0.get())` would still create a
> temporary `&` to the underlying object I believe. `addr_of!` is the way
> to avoid create the temporary reference. Same for the other functions.

If so, how about functions to access to non bit field like phy_id()?

pub fn phy_id(&self) -> u32 {
    let phydev = self.0.get();
    unsafe { (*phydev).phy_id }
}