Pull Rust updates from Miguel Ojeda:
"Toolchain and infrastructure:
- Add support for 'syn'.
Syn is a parsing library for parsing a stream of Rust tokens into a
syntax tree of Rust source code.
Currently this library is geared toward use in Rust procedural
macros, but contains some APIs that may be useful more generally.
'syn' allows us to greatly simplify writing complex macros such as
'pin-init' (Benno has already prepared the 'syn'-based version). We
will use it in the 'macros' crate too.
'syn' is the most downloaded Rust crate (according to crates.io),
and it is also used by the Rust compiler itself. While the amount
of code is substantial, there should not be many updates needed for
these crates, and even if there are, they should not be too big,
e.g. +7k -3k lines across the 3 crates in the last year.
'syn' requires two smaller dependencies: 'quote' and 'proc-macro2'.
I only modified their code to remove a third dependency
('unicode-ident') and to add the SPDX identifiers. The code can be
easily verified to exactly match upstream with the provided
scripts.
They are all licensed under "Apache-2.0 OR MIT", like the other
vendored 'alloc' crate we had for a while.
Please see the merge commit with the cover letter for more context.
- Allow 'unreachable_pub' and 'clippy::disallowed_names' for
doctests.
Examples (i.e. doctests) may want to do things like show public
items and use names such as 'foo'.
Nevertheless, we still try to keep examples as close to real code
as possible (this is part of why running Clippy on doctests is
important for us, e.g. for safety comments, which userspace Rust
does not support yet but we are stricter).
'kernel' crate:
- Replace our custom 'CStr' type with 'core::ffi::CStr'.
Using the standard library type reduces our custom code footprint,
and we retain needed custom functionality through an extension
trait and a new 'fmt!' macro which replaces the previous 'core'
import.
This started in 6.17 and continued in 6.18, and we finally land the
replacement now. This required quite some stamina from Tamir, who
split the changes in steps to prepare for the flag day change here.
- Replace 'kernel::c_str!' with C string literals.
C string literals were added in Rust 1.77, which produce '&CStr's
(the 'core' one), so now we can write:
c"hi"
instead of:
c_str!("hi")
- Add 'num' module for numerical features.
It includes the 'Integer' trait, implemented for all primitive
integer types.
It also includes the 'Bounded' integer wrapping type: an integer
value that requires only the 'N' least significant bits of the
wrapped type to be encoded:
// An unsigned 8-bit integer, of which only the 4 LSBs are used.
let v = Bounded::<u8, 4>::new::<15>();
assert_eq!(v.get(), 15);
'Bounded' is useful to e.g. enforce guarantees when working with
bitfields that have an arbitrary number of bits.
Values can also be constructed from simple non-constant expressions
or, for more complex ones, validated at runtime.
'Bounded' also comes with comparison and arithmetic operations
(with both their backing type and other 'Bounded's with a
compatible backing type), casts to change the backing type,
extending/shrinking and infallible/fallible conversions from/to
primitives as applicable.
- 'rbtree' module: add immutable cursor ('Cursor').
It enables to use just an immutable tree reference where
appropriate. The existing fully-featured mutable cursor is renamed
to 'CursorMut'.
kallsyms:
- Fix wrong "big" kernel symbol type read from procfs.
'pin-init' crate:
- A couple minor fixes (Benno asked me to pick these patches up for
him this cycle).
Documentation:
- Quick Start guide: add Debian 13 (Trixie).
Debian Stable is now able to build Linux, since Debian 13 (released
2025-08-09) packages Rust 1.85.0, which is recent enough.
We are planning to propose that the minimum supported Rust version
in Linux follows Debian Stable releases, with Debian 13 being the
first one we upgrade to, i.e. Rust 1.85.
MAINTAINERS:
- Add entry for the new 'num' module.
- Remove Alex as Rust maintainer: he hasn't had the time to
contribute for a few years now, so it is a no-op change in
practice.
And a few other cleanups and improvements"
* tag 'rust-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux: (53 commits)
rust: macros: support `proc-macro2`, `quote` and `syn`
rust: syn: enable support in kbuild
rust: syn: add `README.md`
rust: syn: remove `unicode-ident` dependency
rust: syn: add SPDX License Identifiers
rust: syn: import crate
rust: quote: enable support in kbuild
rust: quote: add `README.md`
rust: quote: add SPDX License Identifiers
rust: quote: import crate
rust: proc-macro2: enable support in kbuild
rust: proc-macro2: add `README.md`
rust: proc-macro2: remove `unicode_ident` dependency
rust: proc-macro2: add SPDX License Identifiers
rust: proc-macro2: import crate
rust: kbuild: support using libraries in `rustc_procmacro`
rust: kbuild: support skipping flags in `rustc_test_library`
rust: kbuild: add proc macro library support
rust: kbuild: simplify `--cfg` handling
rust: kbuild: introduce `core-flags` and `core-skip_flags`
...
`kernel::ffi::CStr` was introduced in commit d126d23801 ("rust: str:
add `CStr` type") in November 2022 as an upstreaming of earlier work
that was done in May 2021[0]. That earlier work, having predated the
inclusion of `CStr` in `core`, largely duplicated the implementation of
`std::ffi::CStr`.
`std::ffi::CStr` was moved to `core::ffi::CStr` in Rust 1.64 in
September 2022. Hence replace `kernel::str::CStr` with `core::ffi::CStr`
to reduce our custom code footprint, and retain needed custom
functionality through an extension trait.
Add `CStr` to `ffi` and the kernel prelude.
Link: faa3cbcca0 [0]
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Link: https://patch.msgid.link/20251018-cstr-core-v18-16-9378a54385f8@gmail.com
[ Removed assert that would now depend on the Rust version. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
