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

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Date: Mon, 4 Dec 2023 18:00:15 -0800
From: Boqun Feng <boqun.feng@...il.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, wedsonaf@...il.com, aliceryhl@...gle.com
Subject: Re: [PATCH net-next v9 1/4] rust: core abstractions for network PHY
 drivers

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.

[1]: https://lore.kernel.org/rust-for-linux/ZT6fzfV9GUQOZnlx@boqun-archlinux/

Regards,
Boqun

> +    }
> +
> +    /// Gets the current auto-negotiation configuration.
> +    ///
> +    /// It returns true if auto-negotiation is enabled.
> +    pub fn is_autoneg_enabled(&self) -> bool {
> +        // 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(13, 1) == bindings::AUTONEG_ENABLE as u64
> +    }
> +
> +    /// Gets the current auto-negotiation state.
> +    ///
> +    /// It returns true if auto-negotiation is completed.
> +    pub fn is_autoneg_completed(&self) -> bool {
> +        const AUTONEG_COMPLETED: 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(15, 1) == AUTONEG_COMPLETED
> +    }
> +
[...]