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Mon, 31 Aug 2026 18:04:08 -0700 (PDT) From: alistair23@gmail.com X-Google-Original-From: alistair.francis@wdc.com To: linux-pci@vger.kernel.org, Jonathan.Cameron@huawei.com, djbw@kernel.org, rust-for-linux@vger.kernel.org, lukas@wunner.de, alistair@alistair23.me, jic23@kernel.org, linux-cxl@vger.kernel.org, bhelgaas@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Cc: gary@garyguo.net, ojeda@kernel.org, benno.lossin@proton.me, a.hindborg@kernel.org, wilfred.mallawa@wdc.com, tmgross@umich.edu, alistair23@gmail.com, boqun.feng@gmail.com, bjorn3_gh@protonmail.com, alex.gaynor@gmail.com, aliceryhl@google.com Subject: [PATCH v3 01/21] rust: transmute: add `cast_slice[_mut]` functions Date: Tue, 1 Sep 2026 11:03:27 +1000 Message-ID: <20260901010347.2614656-2-alistair.francis@wdc.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260901010347.2614656-1-alistair.francis@wdc.com> References: <20260901010347.2614656-1-alistair.francis@wdc.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Benno Lossin Add functions to make casting slices only one `unsafe` block. Signed-off-by: Benno Lossin Message-ID: <20250814124424.516191-2-lossin@kernel.org> --- rust/kernel/transmute.rs | 59 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs index 654b5ede2fe2..c1282fcc9e65 100644 --- a/rust/kernel/transmute.rs +++ b/rust/kernel/transmute.rs @@ -3,6 +3,7 @@ //! Traits for transmuting types. use core::mem::size_of; +use core::slice; /// Types for which any bit pattern is valid. /// @@ -227,3 +228,61 @@ macro_rules! impl_asbytes { {} [T], {} [T; N], } + +/// Casts the type of a slice to another. +/// +/// Also see [`cast_slice_mut`]. +/// +/// # Examples +/// +/// ```rust +/// # use kernel::transmute::cast_slice; +/// #[repr(transparent)] +/// #[derive(Debug)] +/// struct Container(T); +/// +/// let array = [0u32; 42]; +/// let slice = &array; +/// // SAFETY: `Container` transparently wraps a `u32`. +/// let container_slice = unsafe { cast_slice::>(slice) }; +/// pr_info!("{container_slice:?}"); +/// ``` +/// +/// # Safety +/// +/// - `T` and `U` must have the same layout. +pub unsafe fn cast_slice(slice: &[T]) -> &[U] { + // CAST: by the safety requirements, `T` and `U` have the same layout. + let ptr = slice.as_ptr().cast::(); + // SAFETY: `ptr` and `len` come from the same slice reference. + unsafe { slice::from_raw_parts(ptr, slice.len()) } +} + +/// Casts the type of a slice to another. +/// +/// Also see [`cast_slice`]. +/// +/// # Examples +/// +/// ```rust +/// # use kernel::transmute::cast_slice_mut; +/// #[repr(transparent)] +/// #[derive(Debug)] +/// struct Container(T); +/// +/// let mut array = [0u32; 42]; +/// let slice = &mut array; +/// // SAFETY: `Container` transparently wraps a `u32`. +/// let container_slice = unsafe { cast_slice_mut::>(slice) }; +/// pr_info!("{container_slice:?}"); +/// ``` +/// +/// # Safety +/// +/// - `T` and `U` must have the same layout. +pub unsafe fn cast_slice_mut(slice: &mut [T]) -> &mut [U] { + // CAST: by the safety requirements, `T` and `U` have the same layout. + let ptr = slice.as_mut_ptr().cast::(); + // SAFETY: `ptr` and `len` come from the same slice reference. + unsafe { slice::from_raw_parts_mut(ptr, slice.len()) } +} -- 2.55.0