rust: completion: implement initial abstraction

Implement a minimal abstraction for the completion synchronization
primitive.

This initial abstraction only adds complete_all() and
wait_for_completi

rust: completion: implement initial abstraction

Implement a minimal abstraction for the completion synchronization
primitive.

This initial abstraction only adds complete_all() and
wait_for_completion(), since that is what is required for the subsequent
Devres patch.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20250612121817.1621-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

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Merge tag 'rust-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

Pull Rust updates from Miguel Ojeda:
"Toolchain and infrastructure:

- KUnit '#[test]'s:

- Support KUnit

Merge tag 'rust-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

Pull Rust updates from Miguel Ojeda:
"Toolchain and infrastructure:

- KUnit '#[test]'s:

- Support KUnit-mapped 'assert!' macros.

The support that landed last cycle was very basic, and the
'assert!' macros panicked since they were the standard library
ones. Now, they are mapped to the KUnit ones in a similar way to
how is done for doctests, reusing the infrastructure there.

With this, a failing test like:

#[test]
fn my_first_test() {
assert_eq!(42, 43);
}

will report:

# my_first_test: ASSERTION FAILED at rust/kernel/lib.rs:251
Expected 42 == 43 to be true, but is false
# my_first_test.speed: normal
not ok 1 my_first_test

- Support tests with checked 'Result' return types.

The return value of test functions that return a 'Result' will
be checked, thus one can now easily catch errors when e.g. using
the '?' operator in tests.

With this, a failing test like:

#[test]
fn my_test() -> Result {
f()?;
Ok(())
}

will report:

# my_test: ASSERTION FAILED at rust/kernel/lib.rs:321
Expected is_test_result_ok(my_test()) to be true, but is false
# my_test.speed: normal
not ok 1 my_test

- Add 'kunit_tests' to the prelude.

- Clarify the remaining language unstable features in use.

- Compile 'core' with edition 2024 for Rust >= 1.87.

- Workaround 'bindgen' issue with forward references to 'enum' types.

- objtool: relax slice condition to cover more 'noreturn' functions.

- Use absolute paths in macros referencing 'core' and 'kernel'
crates.

- Skip '-mno-fdpic' flag for bindgen in GCC 32-bit arm builds.

- Clean some 'doc_markdown' lint hits -- we may enable it later on.

'kernel' crate:

- 'alloc' module:

- 'Box': support for type coercion, e.g. 'Box<T>' to 'Box<dyn U>'
if 'T' implements 'U'.

- 'Vec': implement new methods (prerequisites for nova-core and
binder): 'truncate', 'resize', 'clear', 'pop',
'push_within_capacity' (with new error type 'PushError'),
'drain_all', 'retain', 'remove' (with new error type
'RemoveError'), insert_within_capacity' (with new error type
'InsertError').

In addition, simplify 'push' using 'spare_capacity_mut', split
'set_len' into 'inc_len' and 'dec_len', add type invariant 'len
<= capacity' and simplify 'truncate' using 'dec_len'.

- 'time' module:

- Morph the Rust hrtimer subsystem into the Rust timekeeping
subsystem, covering delay, sleep, timekeeping, timers. This new
subsystem has all the relevant timekeeping C maintainers listed
in the entry.

- Replace 'Ktime' with 'Delta' and 'Instant' types to represent a
duration of time and a point in time.

- Temporarily add 'Ktime' to 'hrtimer' module to allow 'hrtimer'
to delay converting to 'Instant' and 'Delta'.

- 'xarray' module:

- Add a Rust abstraction for the 'xarray' data structure. This
abstraction allows Rust code to leverage the 'xarray' to store
types that implement 'ForeignOwnable'. This support is a
dependency for memory backing feature of the Rust null block
driver, which is waiting to be merged.

- Set up an entry in 'MAINTAINERS' for the XArray Rust support.
Patches will go to the new Rust XArray tree and then via the
Rust subsystem tree for now.

- Allow 'ForeignOwnable' to carry information about the pointed-to
type. This helps asserting alignment requirements for the
pointer passed to the foreign language.

- 'container_of!': retain pointer mut-ness and add a compile-time
check of the type of the first parameter ('$field_ptr').

- Support optional message in 'static_assert!'.

- Add C FFI types (e.g. 'c_int') to the prelude.

- 'str' module: simplify KUnit tests 'format!' macro, convert
'rusttest' tests into KUnit, take advantage of the '-> Result'
support in KUnit '#[test]'s.

- 'list' module: add examples for 'List', fix path of
'assert_pinned!' (so far unused macro rule).

- 'workqueue' module: remove 'HasWork::OFFSET'.

- 'page' module: add 'inline' attribute.

'macros' crate:

- 'module' macro: place 'cleanup_module()' in '.exit.text' section.

'pin-init' crate:

- Add 'Wrapper<T>' trait for creating pin-initializers for wrapper
structs with a structurally pinned value such as 'UnsafeCell<T>' or
'MaybeUninit<T>'.

- Add 'MaybeZeroable' derive macro to try to derive 'Zeroable', but
not error if not all fields implement it. This is needed to derive
'Zeroable' for all bindgen-generated structs.

- Add 'unsafe fn cast_[pin_]init()' functions to unsafely change the
initialized type of an initializer. These are utilized by the
'Wrapper<T>' implementations.

- Add support for visibility in 'Zeroable' derive macro.

- Add support for 'union's in 'Zeroable' derive macro.

- Upstream dev news: streamline CI, fix some bugs. Add new workflows
to check if the user-space version and the one in the kernel tree
have diverged. Use the issues tab [1] to track them, which should
help folks report and diagnose issues w.r.t. 'pin-init' better.

[1] https://github.com/rust-for-linux/pin-init/issues

Documentation:

- Testing: add docs on the new KUnit '#[test]' tests.

- Coding guidelines: explain that '///' vs. '//' applies to private
items too. Add section on C FFI types.

- Quick Start guide: update Ubuntu instructions and split them into
"25.04" and "24.04 LTS and older".

And a few other cleanups and improvements"

* tag 'rust-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux: (78 commits)
rust: list: Fix typo `much` in arc.rs
rust: check type of `$ptr` in `container_of!`
rust: workqueue: remove HasWork::OFFSET
rust: retain pointer mut-ness in `container_of!`
Documentation: rust: testing: add docs on the new KUnit `#[test]` tests
Documentation: rust: rename `#[test]`s to "`rusttest` host tests"
rust: str: take advantage of the `-> Result` support in KUnit `#[test]`'s
rust: str: simplify KUnit tests `format!` macro
rust: str: convert `rusttest` tests into KUnit
rust: add `kunit_tests` to the prelude
rust: kunit: support checked `-> Result`s in KUnit `#[test]`s
rust: kunit: support KUnit-mapped `assert!` macros in `#[test]`s
rust: make section names plural
rust: list: fix path of `assert_pinned!`
rust: compile libcore with edition 2024 for 1.87+
rust: dma: add missing Markdown code span
rust: task: add missing Markdown code spans and intra-doc links
rust: pci: fix docs related to missing Markdown code spans
rust: alloc: add missing Markdown code span
rust: alloc: add missing Markdown code spans
...

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