linux-kernel - Re: [PATCH 4/9] rust: list: add macro for implementing ListItem

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Date: Wed, 03 Apr 2024 10:42:06 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...sung.com>, Marco Elver <elver@...gle.com>, Kees Cook <keescook@...omium.org>, Coly Li <colyli@...e.de>, Paolo Abeni <pabeni@...hat.com>, Pierre Gondois <pierre.gondois@....com>, Ingo Molnar <mingo@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Wei Yang <richard.weiyang@...il.com>, Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 4/9] rust: list: add macro for implementing ListItem

On 02.04.24 14:17, Alice Ryhl wrote:
> +/// Declares that this type has a `ListLinks<ID>` field at a fixed offset.
> +///
> +/// This trait is only used to help implement `ListItem` safely. If `ListItem` is implemented
> +/// manually, then this trait is not needed.
> +///
> +/// # Safety
> +///
> +/// All values of this type must have a `ListLinks<ID>` field at the given offset.
> +pub unsafe trait HasListLinks<const ID: u64 = 0> {
> +    /// The offset of the `ListLinks` field.
> +    const OFFSET: usize;
> +
> +    /// Returns a pointer to the [`ListLinks<T, ID>`] field.
> +    ///
> +    /// # Safety
> +    ///
> +    /// The provided pointer must point at a valid struct of type `Self`.
> +    ///
> +    /// [`ListLinks<T, ID>`]: ListLinks
> +    // We don't really need this method, but it's necessary for the implementation of
> +    // `impl_has_work!` to be correct.
> +    #[inline]
> +    unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut ListLinks<ID> {
> +        // SAFETY: The caller promises that the pointer is valid.

The caller only provides a valid pointer, this also needs the
requirement from the trait that `OFFSET` is correct.

-- 
Cheers,
Benno

> +        unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut ListLinks<ID> }
> +    }
> +}