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Date: Wed, 03 Apr 2024 10:42:06 +0000
To: Alice Ryhl <aliceryhl@google.com>, Miguel Ojeda <ojeda@kernel.org>, Andrew Morton <akpm@linux-foundation.org>
From: Benno Lossin <benno.lossin@proton.me>
Cc: Alex Gaynor <alex.gaynor@gmail.com>, Wedson Almeida Filho <wedsonaf@gmail.com>, Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>, =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, Andreas Hindborg <a.hindborg@samsung.com>, Marco Elver <elver@google.com>, Kees Cook <keescook@chromium.org>, Coly Li <colyli@suse.de>, Paolo Abeni <pabeni@redhat.com>, Pierre Gondois <pierre.gondois@arm.com>, Ingo Molnar <mingo@kernel.org>, Jakub Kicinski <kuba@kernel.org>, Wei Yang <richard.weiyang@gmail.com>, Matthew Wilcox <willy@infradead.org>, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org
Subject: Re: [PATCH 4/9] rust: list: add macro for implementing ListItem
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References: <20240402-linked-list-v1-0-b1c59ba7ae3b@google.com> <20240402-linked-list-v1-4-b1c59ba7ae3b@google.com>
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On 02.04.24 14:17, Alice Ryhl wrote:
> +/// Declares that this type has a `ListLinks<ID>` field at a fixed offse=
t.
> +///
> +/// This trait is only used to help implement `ListItem` safely. If `Lis=
tItem` is implemented
> +/// manually, then this trait is not needed.
> +///
> +/// # Safety
> +///
> +/// All values of this type must have a `ListLinks<ID>` field at the giv=
en offset.
> +pub unsafe trait HasListLinks<const ID: u64 =3D 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 impl=
ementation 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.

--=20
Cheers,
Benno

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