Conditional compilation in the kernel's Rust code is expressed with paired #[cfg(CONFIG_FOO)] / #[cfg(not(CONFIG_FOO))] attributes when selecting between two or more implementations of an item. This is verbose and easy to get out of sync.
The standard library gained core::cfg_select! for exactly this (stable since Rust 1.95.0): one macro that emits the first arm whose cfg predicate holds. The kernel's MSRV is 1.85.0, so it is not yet available. Patch 1 adds a macro_rules! backport under the same name and arm syntax, so call sites can be written today and switch to core::cfg_select! unchanged once the MSRV reaches 1.95.0. Patch 2 converts the existing paired #[cfg] selections in the kernel crate to it. One selection is deliberately left as #[cfg]: a #[macro_export] macro_rules! referred to by an absolute path ($crate::) cannot be wrapped in cfg_select! (rust-lang/rust#52234); see patch 2 for details. Testing: - KUnit: rust_kernel_cfg 14/14, rust_doctests_kernel 322/322 (x86_64). - clippy (CLIPPY=1) clean; rustfmt clean; checkpatch --strict: no errors (only the benign new-file MAINTAINERS warning). - Built x86_64 with CONFIG_DEBUG_FS=y and =n to cover both debugfs arms. - Other arches / CONFIG_64BIT=n arms not built locally; relying on CI. Link: https://github.com/Rust-for-Linux/linux/issues/1183 Signed-off-by: Nika Krasnova <[email protected]> --- Nika Krasnova (2): rust: kernel: add cfg_select! backport for config-based selection rust: kernel: migrate to cfg_select! for config-based selection rust/kernel/cfg.rs | 297 +++++++++++++++++++++++++++++++++++ rust/kernel/cpu.rs | 21 +-- rust/kernel/cpumask.rs | 42 ++--- rust/kernel/debugfs.rs | 145 +++++++++-------- rust/kernel/driver.rs | 44 +++--- rust/kernel/drm/device.rs | 53 ++++--- rust/kernel/error.rs | 47 +++--- rust/kernel/kunit.rs | 54 ++++--- rust/kernel/lib.rs | 78 ++++----- rust/kernel/mm.rs | 36 +++-- rust/kernel/prelude.rs | 1 + rust/kernel/sync/atomic.rs | 54 ++++--- rust/kernel/sync/atomic/predefine.rs | 35 +++-- rust/kernel/time.rs | 82 +++++----- 14 files changed, 665 insertions(+), 324 deletions(-) --- base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482 change-id: 20260629-backport-cfg_select-54f5e3d034ed -- Nika Krasnova
