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Message-Id: <20251029-gsp_boot-v7-8-34227afad347@nvidia.com>
Date: Wed, 29 Oct 2025 17:16:35 +0900
From: Alexandre Courbot <acourbot@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Benno Lossin <lossin@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>
Cc: John Hubbard <jhubbard@...dia.com>,
Alistair Popple <apopple@...dia.com>,
Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>,
Edwin Peer <epeer@...dia.com>, nouveau@...ts.freedesktop.org,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
rust-for-linux@...r.kernel.org, Alexandre Courbot <acourbot@...dia.com>
Subject: [PATCH v7 08/14] rust: enable slice_flatten feature and abstract
it through an extension trait
In Rust 1.80, the previously unstable `slice::flatten` family of methods
have been stabilized and renamed to `as_flattened`.
This creates an issue as we want to use `as_flattened`, but need to
support the MSRV (which at the moment is Rust 1.78) where it is named
`flatten`.
Solve this by enabling the `slice_flatten` feature, and abstracting
`as_flatten` behind an extension trait that calls the right method
depending on the Rust version.
This extension trait can be removed once the MSRV passes 1.80.
Suggested-by: Miguel Ojeda <ojeda@...nel.org>
Link: https://lore.kernel.org/all/CANiq72kK4pG=O35NwxPNoTO17oRcg1yfGcvr3==Fi4edr+sfmw@mail.gmail.com/
Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
---
init/Kconfig | 3 +++
rust/kernel/lib.rs | 4 ++++
rust/kernel/slice.rs | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++
scripts/Makefile.build | 3 ++-
4 files changed, 72 insertions(+), 1 deletion(-)
diff --git a/init/Kconfig b/init/Kconfig
index cab3ad28ca49..7da93c9cccc3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -147,6 +147,9 @@ config LD_CAN_USE_KEEP_IN_OVERLAY
# https://github.com/llvm/llvm-project/pull/130661
def_bool LD_IS_BFD || LLD_VERSION >= 210000
+config RUSTC_HAS_SLICE_AS_FLATTENED
+ def_bool RUSTC_VERSION >= 108000
+
config RUSTC_HAS_COERCE_POINTEE
def_bool RUSTC_VERSION >= 108400
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 3dd7bebe7888..2581a356d114 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -21,6 +21,9 @@
#![feature(inline_const)]
#![feature(pointer_is_aligned)]
//
+// Stable since Rust 1.80.0.
+#![feature(slice_flatten)]
+//
// Stable since Rust 1.81.0.
#![feature(lint_reasons)]
//
@@ -128,6 +131,7 @@
pub mod security;
pub mod seq_file;
pub mod sizes;
+pub mod slice;
mod static_assert;
#[doc(hidden)]
pub mod std_vendor;
diff --git a/rust/kernel/slice.rs b/rust/kernel/slice.rs
new file mode 100644
index 000000000000..7e837bec4bed
--- /dev/null
+++ b/rust/kernel/slice.rs
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Additional (and temporary) slice helpers.
+
+/// Extension trait providing a portable version of [`as_flattened`] and
+/// [`as_flattened_mut`].
+///
+/// In Rust 1.80, the previously unstable `slice::flatten` family of methods
+/// have been stabilized and renamed from `flatten` to `as_flattened`.
+///
+/// This creates an issue for as long as the MSRV is < 1.80, as the same functionality is provided
+/// by different methods depending on the compiler version.
+///
+/// This extension trait solves this by abstracting `as_flatten` and calling the correct method
+/// depending on the Rust version.
+///
+/// This trait can be removed once the MSRV passes 1.80.
+///
+/// [`as_flattened`]: slice::as_flattened
+/// [`as_flattened_mut`]: slice::as_flattened_mut
+pub trait AsFlattened<T> {
+ /// Takes an `&[[T; N]]` and flattens it to a `&[T]`.
+ ///
+ /// This is an portable layer on top of [`as_flattened`]; see its documentation for details.
+ ///
+ /// [`as_flattened`]: slice::as_flattened
+ fn as_flattened_slice(&self) -> &[T];
+
+ /// Takes an `&mut [[T; N]]` and flattens it to a `&mut [T]`.
+ ///
+ /// This is an portable layer on top of [`as_flattened_mut`]; see its documentation for details.
+ ///
+ /// [`as_flattened_mut`]: slice::as_flattened_mut
+ fn as_flattened_slice_mut(&mut self) -> &mut [T];
+}
+
+impl<T, const N: usize> AsFlattened<T> for [[T; N]] {
+ #[allow(clippy::incompatible_msrv)]
+ fn as_flattened_slice(&self) -> &[T] {
+ #[cfg(not(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED))]
+ {
+ self.flatten()
+ }
+
+ #[cfg(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED)]
+ {
+ self.as_flattened()
+ }
+ }
+
+ #[allow(clippy::incompatible_msrv)]
+ fn as_flattened_slice_mut(&mut self) -> &mut [T] {
+ #[cfg(not(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED))]
+ {
+ self.flatten_mut()
+ }
+
+ #[cfg(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED)]
+ {
+ self.as_flattened_mut()
+ }
+ }
+}
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index d0ee33a487be..a84b9e3171a3 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -308,6 +308,7 @@ $(obj)/%.lst: $(obj)/%.c FORCE
# The features in this list are the ones allowed for non-`rust/` code.
#
+# - Stable since Rust 1.80.0: `feature(slice_flatten)`.
# - Stable since Rust 1.81.0: `feature(lint_reasons)`.
# - Stable since Rust 1.82.0: `feature(asm_const)`,
# `feature(offset_of_nested)`, `feature(raw_ref_op)`.
@@ -317,7 +318,7 @@ $(obj)/%.lst: $(obj)/%.c FORCE
#
# Please see https://github.com/Rust-for-Linux/linux/issues/2 for details on
# the unstable features in use.
-rust_allowed_features := asm_const,asm_goto,arbitrary_self_types,lint_reasons,offset_of_nested,raw_ref_op,used_with_arg
+rust_allowed_features := asm_const,asm_goto,arbitrary_self_types,lint_reasons,offset_of_nested,raw_ref_op,slice_flatten,used_with_arg
# `--out-dir` is required to avoid temporaries being created by `rustc` in the
# current working directory, which may be not accessible in the out-of-tree
--
2.51.0
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