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Burak Emir 11eca92a2c rust: add bitmap API. 
Provides an abstraction for C bitmap API and bitops operations.

This commit enables a Rust implementation of an Android Binder
data structure from commit 15d9da3f81 ("binder: use bitmap for faster
descriptor lookup"), which can be found in drivers/android/dbitmap.h.
It is a step towards upstreaming the Rust port of Android Binder driver.

We follow the C Bitmap API closely in naming and semantics, with
a few differences that take advantage of Rust language facilities
and idioms. The main types are `BitmapVec` for owned bitmaps and
`Bitmap` for references to C bitmaps.

  * We leverage Rust type system guarantees as follows:

    * all (non-atomic) mutating operations require a &mut reference which
      amounts to exclusive access.

    * the `BitmapVec` type implements Send. This enables transferring
      ownership between threads and is needed for Binder.

    * the `BitmapVec` type implements Sync, which enables passing shared
      references &Bitmap between threads. Atomic operations can be
      used to safely modify from multiple threads (interior
      mutability), though without ordering guarantees.

  * The Rust API uses `{set,clear}_bit` vs `{set,clear}_bit_atomic` as
    names for clarity, which differs from the C naming convention
    `set_bit` for atomic vs `__set_bit` for non-atomic.

  * we include enough operations for the API to be useful. Not all
    operations are exposed yet in order to avoid dead code. The missing
    ones can be added later.

  * We take a fine-grained approach to safety:

    * Low-level bit-ops get a safe API with bounds checks. Calling with
      an out-of-bounds arguments to {set,clear}_bit becomes a no-op and
      get logged as errors.

    * We also introduce a RUST_BITMAP_HARDENED config, which
      causes invocations with out-of-bounds arguments to panic.

    * methods correspond to find_* C methods tolerate out-of-bounds
      since the C implementation does. Also here, out-of-bounds
      arguments are logged as errors, or panic in RUST_BITMAP_HARDENED
      mode.

    * We add a way to "borrow" bitmaps from C in Rust, to make C bitmaps
      that were allocated in C directly usable in Rust code (`Bitmap`).

  * the Rust API is optimized to represent the bitmap inline if it would
    fit into a pointer. This saves allocations which is
    relevant in the Binder use case.

The underlying C bitmap is *not* exposed for raw access in Rust. Doing so
would permit bypassing the Rust API and lose static guarantees.

An alternative route of vendoring an existing Rust bitmap package was
considered but suboptimal overall. Reusing the C implementation is
preferable for a basic data structure like bitmaps. It enables Rust
code to be a lot more similar and predictable with respect to C code
that uses the same data structures and enables the use of code that
has been tried-and-tested in the kernel, with the same performance
characteristics whenever possible.

We use the `usize` type for sizes and indices into the bitmap,
because Rust generally always uses that type for indices and lengths
and it will be more convenient if the API accepts that type. This means
that we need to perform some casts to/from u32 and usize, since the C
headers use unsigned int instead of size_t/unsigned long for these
numbers in some places.

Adds new MAINTAINERS section BITMAP API [RUST].

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Burak Emir <bqe@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
2025-09-22 15:52:44 -04:00
arch arc: Fix __fls() const-foldability via __builtin_clzl() 2025-09-02 19:30:51 -04:00
block block: validate QoS before calling __rq_qos_done_bio() 2025-08-26 10:34:08 -06:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
Documentation sound fixes for 6.17-rc5 2025-09-02 13:38:07 -07:00
drivers phy: rockchip-pcie: switch to FIELD_PREP_WM16 macro 2025-09-22 15:52:44 -04:00
fs 17 hotfixes. 13 are cc:stable and the remainder address post-6.16 issues 2025-09-02 13:18:00 -07:00
include bitmap: introduce hardware-specific bitfield operations 2025-09-02 19:59:16 -04:00
init hardening: Require clang 20.1.0 for __counted_by 2025-08-29 12:04:53 -07:00
io_uring io_uring/kbuf: always use READ_ONCE() to read ring provided buffer lengths 2025-08-28 05:48:34 -06:00
ipc vfs-6.17-rc1.mmap_prepare 2025-07-28 13:43:25 -07:00
kernel - Fix a stall on the CPU offline path due to mis-counting a deadline server 2025-08-31 09:13:00 -07:00
lib hardening fixes for v6.17-rc4 2025-08-31 08:56:45 -07:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm 17 hotfixes. 13 are cc:stable and the remainder address post-6.16 issues 2025-09-02 13:18:00 -07:00
net net: ipv4: fix regression in local-broadcast routes 2025-08-28 10:52:30 +02:00
rust rust: add bitmap API. 2025-09-22 15:52:44 -04:00
samples Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
scripts kasan: fix GCC mem-intrinsic prefix with sw tags 2025-08-27 22:45:43 -07:00
security rust: add bitmap API. 2025-09-22 15:52:44 -04:00
sound ASoC: rockchip: i2s-tdm: switch to FIELD_PREP_WM16_CONST macro 2025-09-02 20:06:47 -04:00
tools 17 hotfixes. 13 are cc:stable and the remainder address post-6.16 issues 2025-09-02 13:18:00 -07:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge tag 'kvm-x86-no_assignment-6.17' of https://github.com/kvm-x86/linux into HEAD 2025-07-29 08:36:42 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore gitignore: allow .pylintrc to be tracked 2025-07-02 17:10:04 -06:00
.mailmap .mailmap: add entry for Easwar Hariharan 2025-08-19 16:35:55 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: retire Boris from TLS maintainers 2025-08-26 17:36:01 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS rust: add bitmap API. 2025-09-22 15:52:44 -04:00
Makefile Linux 6.17-rc4 2025-08-31 15:33:07 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.