* [PATCH v12 1/5] rust: add bindings for bitmap.h
2025-06-11 19:48 [PATCH v12 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
@ 2025-06-11 19:48 ` Burak Emir
2025-06-11 19:48 ` [PATCH v12 2/5] rust: add bindings for bitops.h Burak Emir
` (3 subsequent siblings)
4 siblings, 0 replies; 18+ messages in thread
From: Burak Emir @ 2025-06-11 19:48 UTC (permalink / raw)
To: Yury Norov, Kees Cook
Cc: Burak Emir, Rasmus Villemoes, Viresh Kumar, Miguel Ojeda,
Alex Gaynor, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
Makes the bitmap_copy_and_extend inline function available to Rust.
Adds F: to existing MAINTAINERS section BITMAP API BINDINGS [RUST].
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Burak Emir <bqe@google.com>
Acked-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
---
MAINTAINERS | 1 +
rust/bindings/bindings_helper.h | 1 +
rust/helpers/bitmap.c | 9 +++++++++
rust/helpers/helpers.c | 1 +
4 files changed, 12 insertions(+)
create mode 100644 rust/helpers/bitmap.c
diff --git a/MAINTAINERS b/MAINTAINERS
index d48dd6726fe6..86cae0ca5287 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4124,6 +4124,7 @@ F: tools/lib/find_bit.c
BITMAP API BINDINGS [RUST]
M: Yury Norov <yury.norov@gmail.com>
S: Maintained
+F: rust/helpers/bitmap.c
F: rust/helpers/cpumask.c
BITOPS API
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index ab37e1d35c70..b6bf3b039c1b 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -7,6 +7,7 @@
*/
#include <kunit/test.h>
+#include <linux/bitmap.h>
#include <linux/blk-mq.h>
#include <linux/blk_types.h>
#include <linux/blkdev.h>
diff --git a/rust/helpers/bitmap.c b/rust/helpers/bitmap.c
new file mode 100644
index 000000000000..a50e2f082e47
--- /dev/null
+++ b/rust/helpers/bitmap.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitmap.h>
+
+void rust_helper_bitmap_copy_and_extend(unsigned long *to, const unsigned long *from,
+ unsigned int count, unsigned int size)
+{
+ bitmap_copy_and_extend(to, from, count, size);
+}
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 1e7c84df7252..92721d165e35 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -7,6 +7,7 @@
* Sorted alphabetically.
*/
+#include "bitmap.c"
#include "blk.c"
#include "bug.c"
#include "build_assert.c"
--
2.50.0.rc1.591.g9c95f17f64-goog
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v12 2/5] rust: add bindings for bitops.h
2025-06-11 19:48 [PATCH v12 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
2025-06-11 19:48 ` [PATCH v12 1/5] rust: add bindings for bitmap.h Burak Emir
@ 2025-06-11 19:48 ` Burak Emir
2025-06-11 19:48 ` [PATCH v12 3/5] rust: add bitmap API Burak Emir
` (2 subsequent siblings)
4 siblings, 0 replies; 18+ messages in thread
From: Burak Emir @ 2025-06-11 19:48 UTC (permalink / raw)
To: Yury Norov, Kees Cook
Cc: Burak Emir, Rasmus Villemoes, Viresh Kumar, Miguel Ojeda,
Alex Gaynor, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
Makes atomic set_bit and clear_bit inline functions as well as the
non-atomic variants __set_bit and __clear_bit available to Rust.
Adds a new MAINTAINERS section BITOPS API BINDINGS [RUST].
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Burak Emir <bqe@google.com>
Acked-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
---
MAINTAINERS | 5 +++++
rust/helpers/bitops.c | 23 +++++++++++++++++++++++
rust/helpers/helpers.c | 1 +
3 files changed, 29 insertions(+)
create mode 100644 rust/helpers/bitops.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 86cae0ca5287..04d6727e944c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4141,6 +4141,11 @@ F: include/linux/bitops.h
F: lib/test_bitops.c
F: tools/*/bitops*
+BITOPS API BINDINGS [RUST]
+M: Yury Norov <yury.norov@gmail.com>
+S: Maintained
+F: rust/helpers/bitops.c
+
BLINKM RGB LED DRIVER
M: Jan-Simon Moeller <jansimon.moeller@gmx.de>
S: Maintained
diff --git a/rust/helpers/bitops.c b/rust/helpers/bitops.c
new file mode 100644
index 000000000000..5d0861d29d3f
--- /dev/null
+++ b/rust/helpers/bitops.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitops.h>
+
+void rust_helper___set_bit(unsigned long nr, unsigned long *addr)
+{
+ __set_bit(nr, addr);
+}
+
+void rust_helper___clear_bit(unsigned long nr, unsigned long *addr)
+{
+ __clear_bit(nr, addr);
+}
+
+void rust_helper_set_bit(unsigned long nr, volatile unsigned long *addr)
+{
+ set_bit(nr, addr);
+}
+
+void rust_helper_clear_bit(unsigned long nr, volatile unsigned long *addr)
+{
+ clear_bit(nr, addr);
+}
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 92721d165e35..4de8ac390241 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -8,6 +8,7 @@
*/
#include "bitmap.c"
+#include "bitops.c"
#include "blk.c"
#include "bug.c"
#include "build_assert.c"
--
2.50.0.rc1.591.g9c95f17f64-goog
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v12 3/5] rust: add bitmap API.
2025-06-11 19:48 [PATCH v12 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
2025-06-11 19:48 ` [PATCH v12 1/5] rust: add bindings for bitmap.h Burak Emir
2025-06-11 19:48 ` [PATCH v12 2/5] rust: add bindings for bitops.h Burak Emir
@ 2025-06-11 19:48 ` Burak Emir
2025-06-11 21:58 ` Alice Ryhl
2025-06-16 10:49 ` Alice Ryhl
2025-06-11 19:48 ` [PATCH v12 4/5] rust: add find_bit_benchmark_rust module Burak Emir
2025-06-11 19:48 ` [PATCH v12 5/5] rust: add dynamic ID pool abstraction for bitmap Burak Emir
4 siblings, 2 replies; 18+ messages in thread
From: Burak Emir @ 2025-06-11 19:48 UTC (permalink / raw)
To: Yury Norov, Kees Cook
Cc: Burak Emir, Rasmus Villemoes, Viresh Kumar, Miguel Ojeda,
Alex Gaynor, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
Provides an abstraction for C bitmap API and bitops operations.
This commit enables a Rust implementation of an Android Binder
data structure from commit 15d9da3f818c ("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:
* We leverage Rust type system guarantees as follows:
* all (non-atomic) mutating operations require a &mut reference which
amounts to exclusive access.
* the Bitmap type implements Send. This enables transferring
ownership between threads and is needed for Binder.
* the Bitmap 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, which differs from the C naming convention which uses
set_bit for atomic vs __set_bit for non-atomic.
* we include enough operations for the API to be useful, but not all
operations are exposed yet in order to avoid dead code. The missing
ones can be added later.
* We follow the C API closely with 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 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, we log out-of-bounds
arguments as errors and 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 (`CBitmap`).
* 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, and must never be exposed
(except in tests). Exposing the representation of the owned bitmap would
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>
---
MAINTAINERS | 7 +
rust/kernel/bitmap.rs | 582 +++++++++++++++++++++++++++++++++++++
rust/kernel/lib.rs | 1 +
security/Kconfig.hardening | 10 +
4 files changed, 600 insertions(+)
create mode 100644 rust/kernel/bitmap.rs
diff --git a/MAINTAINERS b/MAINTAINERS
index 04d6727e944c..565eaa015d9e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4127,6 +4127,13 @@ S: Maintained
F: rust/helpers/bitmap.c
F: rust/helpers/cpumask.c
+BITMAP API [RUST]
+M: Alice Ryhl <aliceryhl@google.com>
+M: Burak Emir <bqe@google.com>
+R: Yury Norov <yury.norov@gmail.com>
+S: Maintained
+F: rust/kernel/bitmap.rs
+
BITOPS API
M: Yury Norov <yury.norov@gmail.com>
R: Rasmus Villemoes <linux@rasmusvillemoes.dk>
diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
new file mode 100644
index 000000000000..1fe72ca980ac
--- /dev/null
+++ b/rust/kernel/bitmap.rs
@@ -0,0 +1,582 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Rust API for bitmap.
+//!
+//! C headers: [`include/linux/bitmap.h`](srctree/include/linux/bitmap.h).
+
+use crate::alloc::{AllocError, Flags};
+use crate::bindings;
+#[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
+use crate::pr_err;
+use core::ptr::NonNull;
+
+/// Represents a C bitmap. Wraps underlying C bitmap API.
+///
+/// # Invariants
+///
+/// Must reference a `[c_ulong]` long enough to fit `data.len()` bits.
+#[cfg_attr(CONFIG_64BIT, repr(align(8)))]
+#[cfg_attr(not(CONFIG_64BIT), repr(align(4)))]
+pub struct CBitmap {
+ data: [()],
+}
+
+/// SAFETY: All methods that take immutable references are either atomic or read-only.
+unsafe impl Sync for CBitmap {}
+
+impl CBitmap {
+ /// Borrows a C bitmap.
+ ///
+ /// # Safety
+ ///
+ /// * `ptr` holds a non-null address of an initialized array of `unsigned long`
+ /// that is large enough to hold `nbits` bits.
+ /// * the array must not be freed for the lifetime of this [`CBitmap`]
+ /// * concurrent access only happens through atomic operations
+ pub unsafe fn from_raw<'a>(ptr: *const usize, nbits: usize) -> &'a CBitmap {
+ let data: *const [()] = core::ptr::slice_from_raw_parts(ptr.cast(), nbits);
+ // INVARIANT: `data` references an initialized array that can hold `nbits` bits.
+ // SAFETY:
+ // The caller guarantees that `data` (derived from `ptr` and `nbits`)
+ // points to a valid, initialized, and appropriately sized memory region
+ // that will not be freed for the lifetime 'a.
+ // We are casting `*const [()]` to `*const CBitmap`. The `CBitmap`
+ // struct is a ZST with a `data: [()]` field. This means its layout
+ // is compatible with a slice of `()`, and effectively it's a "thin pointer"
+ // (its size is 0 and alignment is 1). The `slice_from_raw_parts`
+ // function correctly encodes the length (number of bits, not elements)
+ // into the metadata of the fat pointer. Therefore, dereferencing this
+ // pointer as `&CBitmap` is safe given the caller's guarantees.
+ unsafe { &*(data as *const CBitmap) }
+ }
+
+ /// Borrows a C bitmap exclusively.
+ ///
+ /// # Safety
+ ///
+ /// * `ptr` holds a non-null address of an initialized array of `unsigned long`
+ /// that is large enough to hold `nbits` bits.
+ /// * the array must not be freed for the lifetime of this [`CBitmap`]
+ /// * no concurrent access may happen.
+ pub unsafe fn from_raw_mut<'a>(ptr: *mut usize, nbits: usize) -> &'a mut CBitmap {
+ let data: *mut [()] = core::ptr::slice_from_raw_parts_mut(ptr.cast(), nbits);
+ // INVARIANT: `data` references an initialized array that can hold `nbits` bits.
+ // SAFETY:
+ // The caller guarantees that `data` (derived from `ptr` and `nbits`)
+ // points to a valid, initialized, and appropriately sized memory region
+ // that will not be freed for the lifetime 'a.
+ // Furthermore, the caller guarantees no concurrent access will happen,
+ // which upholds the exclusivity requirement for a mutable reference.
+ // Similar to `from_raw`, casting `*mut [()]` to `*mut CBitmap` is
+ // safe because `CBitmap` is a ZST with a `data: [()]` field,
+ // making its layout compatible with a slice of `()`.
+ unsafe { &mut *(data as *mut CBitmap) }
+ }
+
+ /// Returns a raw pointer to the backing [`Bitmap`].
+ pub fn as_ptr(&self) -> *const usize {
+ self as *const CBitmap as *const usize
+ }
+
+ /// Returns a mutable raw pointer to the backing [`Bitmap`].
+ pub fn as_mut_ptr(&mut self) -> *mut usize {
+ self as *mut CBitmap as *mut usize
+ }
+
+ /// Returns length of this [`CBitmap`].
+ #[expect(clippy::len_without_is_empty)]
+ pub fn len(&self) -> usize {
+ self.data.len()
+ }
+}
+
+/// Holds either a pointer to array of `unsigned long` or a small bitmap.
+#[repr(C)]
+union BitmapRepr {
+ bitmap: usize,
+ ptr: NonNull<usize>,
+}
+
+macro_rules! bitmap_assert {
+ ($cond:expr, $($arg:tt)+) => {
+ #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
+ assert!($cond, $($arg)*);
+ }
+}
+
+macro_rules! bitmap_assert_return {
+ ($cond:expr, $($arg:tt)+) => {
+ #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
+ assert!($cond, $($arg)*);
+
+ #[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
+ if !($cond) {
+ pr_err!($($arg)*);
+ return
+ }
+ }
+}
+
+/// Represents an owned bitmap.
+///
+/// Wraps underlying C bitmap API. See [`CBitmap`] for available
+/// methods.
+///
+/// # Examples
+///
+/// Basic usage
+///
+/// ```
+/// use kernel::alloc::flags::GFP_KERNEL;
+/// use kernel::bitmap::Bitmap;
+///
+/// let mut b = Bitmap::new(16, GFP_KERNEL)?;
+///
+/// assert_eq!(16, b.len());
+/// for i in 0..16 {
+/// if i % 4 == 0 {
+/// b.set_bit(i);
+/// }
+/// }
+/// assert_eq!(Some(0), b.next_bit(0));
+/// assert_eq!(Some(1), b.next_zero_bit(0));
+/// assert_eq!(Some(4), b.next_bit(1));
+/// assert_eq!(Some(5), b.next_zero_bit(4));
+/// assert_eq!(Some(12), b.last_bit());
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// # Invariants
+///
+/// * `nbits` is `<= i32::MAX` and never changes.
+/// * if `nbits <= bindings::BITS_PER_LONG`, then `repr` is a `usize`.
+/// * otherwise, `repr` holds a non-null pointer to an initialized
+/// array of `unsigned long` that is large enough to hold `nbits` bits.
+pub struct Bitmap {
+ /// Representation of bitmap.
+ repr: BitmapRepr,
+ /// Length of this bitmap. Must be `<= i32::MAX`.
+ nbits: usize,
+}
+
+impl core::ops::Deref for Bitmap {
+ type Target = CBitmap;
+
+ fn deref(&self) -> &CBitmap {
+ let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
+ // SAFETY: Bitmap is represented inline.
+ unsafe { core::ptr::addr_of!(self.repr.bitmap) }
+ } else {
+ // SAFETY: Bitmap is represented as array of `unsigned long`.
+ unsafe { self.repr.ptr.as_ptr() }
+ };
+
+ // SAFETY: We got the right pointer and invariants of [`Bitmap`] hold.
+ // An inline bitmap is treated like an array with single element.
+ unsafe { CBitmap::from_raw(ptr, self.nbits) }
+ }
+}
+
+impl core::ops::DerefMut for Bitmap {
+ fn deref_mut(&mut self) -> &mut CBitmap {
+ let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
+ // SAFETY: Bitmap is represented inline.
+ unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
+ } else {
+ // SAFETY: Bitmap is represented as array of `unsigned long`.
+ unsafe { self.repr.ptr.as_mut() }
+ };
+
+ // SAFETY: We got the right pointer and invariants of [`Bitmap`] hold.
+ // An inline bitmap is treated like an array with single element.
+ unsafe { CBitmap::from_raw_mut(ptr, self.nbits) }
+ }
+}
+
+/// Enable ownership transfer to other threads.
+///
+/// SAFETY: We own the underlying bitmap representation.
+unsafe impl Send for Bitmap {}
+
+/// Enable unsynchronized concurrent access to [`Bitmap`] through shared references.
+///
+/// SAFETY: `deref()` will return a reference to a [`CBitmap`] which is Sync. Its methods
+/// that take immutable references are either atomic or read-only.
+unsafe impl Sync for Bitmap {}
+
+impl Drop for Bitmap {
+ fn drop(&mut self) {
+ if self.nbits <= bindings::BITS_PER_LONG as _ {
+ return;
+ }
+ // SAFETY: `self.ptr` was returned by the C `bitmap_zalloc`.
+ //
+ // INVARIANT: there is no other use of the `self.ptr` after this
+ // call and the value is being dropped so the broken invariant is
+ // not observable on function exit.
+ unsafe { bindings::bitmap_free(self.repr.ptr.as_ptr()) };
+ }
+}
+
+impl Bitmap {
+ /// Constructs a new [`Bitmap`].
+ ///
+ /// Fails with [`AllocError`] when the [`Bitmap`] could not be allocated. This
+ /// includes the case when `nbits` is greater than `i32::MAX`.
+ #[inline]
+ pub fn new(nbits: usize, flags: Flags) -> Result<Self, AllocError> {
+ if nbits <= bindings::BITS_PER_LONG as _ {
+ return Ok(Bitmap {
+ repr: BitmapRepr { bitmap: 0 },
+ nbits,
+ });
+ }
+ if nbits > i32::MAX.try_into().unwrap() {
+ return Err(AllocError);
+ }
+ let nbits_u32 = u32::try_from(nbits).unwrap();
+ // SAFETY: `bindings::BITS_PER_LONG < nbits` and `nbits <= i32::MAX`.
+ let ptr = unsafe { bindings::bitmap_zalloc(nbits_u32, flags.as_raw()) };
+ let ptr = NonNull::new(ptr).ok_or(AllocError)?;
+ // INVARIANT: `ptr` returned by C `bitmap_zalloc` and `nbits` checked.
+ Ok(Bitmap {
+ repr: BitmapRepr { ptr },
+ nbits,
+ })
+ }
+
+ /// Returns length of this [`Bitmap`].
+ #[allow(clippy::len_without_is_empty)]
+ #[inline]
+ pub fn len(&self) -> usize {
+ self.nbits
+ }
+}
+
+impl CBitmap {
+ /// Set bit with index `index`.
+ ///
+ /// ATTENTION: `set_bit` is non-atomic, which differs from the naming
+ /// convention in C code. The corresponding C function is `__set_bit`.
+ ///
+ /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
+ /// or equal to `self.nbits`, does nothing.
+ ///
+ /// # Panics
+ ///
+ /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
+ /// or equal to `self.nbits`.
+ #[inline]
+ pub fn set_bit(&mut self, index: usize) {
+ bitmap_assert_return!(
+ index < self.len(),
+ "Bit `index` must be < {}, was {}",
+ self.len(),
+ index
+ );
+ // SAFETY: Bit `index` is within bounds.
+ unsafe { bindings::__set_bit(index, self.as_mut_ptr()) };
+ }
+
+ /// Set bit with index `index`, atomically.
+ ///
+ /// This is a relaxed atomic operation (no implied memory barriers).
+ ///
+ /// ATTENTION: The naming convention differs from C, where the corresponding
+ /// function is called `set_bit`.
+ ///
+ /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
+ /// or equal to `self.len()`, does nothing.
+ ///
+ /// # Panics
+ ///
+ /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
+ /// or equal to `self.len()`.
+ #[inline]
+ pub fn set_bit_atomic(&self, index: usize) {
+ bitmap_assert_return!(
+ index < self.len(),
+ "Bit `index` must be < {}, was {}",
+ self.len(),
+ index
+ );
+ // SAFETY: `index` is within bounds and the caller has ensured that
+ // there is no mix of non-atomic and atomic operations.
+ unsafe { bindings::set_bit(index, self.as_ptr() as *mut usize) };
+ }
+
+ /// Clear `index` bit.
+ ///
+ /// ATTENTION: `clear_bit` is non-atomic, which differs from the naming
+ /// convention in C code. The corresponding C function is `__clear_bit`.
+ ///
+ /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
+ /// or equal to `self.len()`, does nothing.
+ ///
+ /// # Panics
+ ///
+ /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
+ /// or equal to `self.len()`.
+ #[inline]
+ pub fn clear_bit(&mut self, index: usize) {
+ bitmap_assert_return!(
+ index < self.len(),
+ "Bit `index` must be < {}, was {}",
+ self.len(),
+ index
+ );
+ // SAFETY: `index` is within bounds.
+ unsafe { bindings::__clear_bit(index, self.as_mut_ptr()) };
+ }
+
+ /// Clear `index` bit, atomically.
+ ///
+ /// This is a relaxed atomic operation (no implied memory barriers).
+ ///
+ /// ATTENTION: The naming convention differs from C, where the corresponding
+ /// function is called `clear_bit`.
+ ///
+ /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
+ /// or equal to `self.len()`, does nothing.
+ ///
+ /// # Panics
+ ///
+ /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
+ /// or equal to `self.len()`.
+ #[inline]
+ pub fn clear_bit_atomic(&self, index: usize) {
+ bitmap_assert_return!(
+ index < self.len(),
+ "Bit `index` must be < {}, was {}",
+ self.len(),
+ index
+ );
+ // SAFETY: `index` is within bounds and the caller has ensured that
+ // there is no mix of non-atomic and atomic operations.
+ unsafe { bindings::clear_bit(index, self.as_ptr() as *mut usize) };
+ }
+
+ /// Copy `src` into this [`Bitmap`] and set any remaining bits to zero.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
+ /// use kernel::bitmap::Bitmap;
+ ///
+ /// let mut long_bitmap = Bitmap::new(256, GFP_KERNEL)?;
+ //
+ /// assert_eq!(None, long_bitmap.last_bit());
+ //
+ /// let mut short_bitmap = Bitmap::new(16, GFP_KERNEL)?;
+ //
+ /// short_bitmap.set_bit(7);
+ /// long_bitmap.copy_and_extend(&short_bitmap);
+ /// assert_eq!(Some(7), long_bitmap.last_bit());
+ ///
+ /// # Ok::<(), AllocError>(())
+ /// ```
+ #[inline]
+ pub fn copy_and_extend(&mut self, src: &Bitmap) {
+ let len = core::cmp::min(src.nbits, self.len());
+ // SAFETY: access to `self` and `src` is within bounds.
+ unsafe {
+ bindings::bitmap_copy_and_extend(
+ self.as_mut_ptr(),
+ src.as_ptr(),
+ len as u32,
+ self.len() as u32,
+ )
+ };
+ }
+
+ /// Finds last set bit.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
+ /// use kernel::bitmap::Bitmap;
+ ///
+ /// let bitmap = Bitmap::new(64, GFP_KERNEL)?;
+ ///
+ /// match bitmap.last_bit() {
+ /// Some(idx) => {
+ /// pr_info!("The last bit has index {idx}.\n");
+ /// }
+ /// None => {
+ /// pr_info!("All bits in this bitmap are 0.\n");
+ /// }
+ /// }
+ /// # Ok::<(), AllocError>(())
+ /// ```
+ #[inline]
+ pub fn last_bit(&self) -> Option<usize> {
+ // SAFETY: `_find_next_bit` access is within bounds due to invariant.
+ let index = unsafe { bindings::_find_last_bit(self.as_ptr(), self.len()) };
+ if index >= self.len() {
+ None
+ } else {
+ Some(index)
+ }
+ }
+
+ /// Finds next set bit, starting from `start`.
+ /// Returns `None` if `start` is greater of equal than `self.nbits`.
+ #[inline]
+ pub fn next_bit(&self, start: usize) -> Option<usize> {
+ bitmap_assert!(
+ start < self.len(),
+ "`start` must be < {} was {}",
+ self.len(),
+ start
+ );
+ // SAFETY: `_find_next_bit` tolerates out-of-bounds arguments and returns a
+ // value larger than or equal to `self.len()` in that case.
+ let index = unsafe { bindings::_find_next_bit(self.as_ptr(), self.len(), start) };
+ if index >= self.len() {
+ None
+ } else {
+ Some(index)
+ }
+ }
+
+ /// Finds next zero bit, starting from `start`.
+ /// Returns `None` if `start` is greater than or equal to `self.len()`.
+ #[inline]
+ pub fn next_zero_bit(&self, start: usize) -> Option<usize> {
+ bitmap_assert!(
+ start < self.len(),
+ "`start` must be < {} was {}",
+ self.len(),
+ start
+ );
+ // SAFETY: `_find_next_zero_bit` tolerates out-of-bounds arguments and returns a
+ // value larger than or equal to `self.len()` in that case.
+ let index = unsafe { bindings::_find_next_zero_bit(self.as_ptr(), self.len(), start) };
+ if index >= self.len() {
+ None
+ } else {
+ Some(index)
+ }
+ }
+}
+
+use macros::kunit_tests;
+
+#[kunit_tests(rust_kernel_bitmap)]
+mod tests {
+ use super::*;
+ use kernel::alloc::flags::GFP_KERNEL;
+
+ #[test]
+ fn cbitmap_borrow() {
+ let fake_c_bitmap: [usize; 2] = [0, 0];
+ // SAFETY: `fake_c_bitmap` is an array of expected length.
+ let b = unsafe {
+ CBitmap::from_raw(
+ core::ptr::addr_of!(fake_c_bitmap) as *const usize,
+ 2 * bindings::BITS_PER_LONG as usize,
+ )
+ };
+ assert_eq!(2 * bindings::BITS_PER_LONG as usize, b.len());
+ assert_eq!(None, b.next_bit(0));
+ }
+
+ #[test]
+ fn cbitmap_copy() {
+ let fake_c_bitmap: usize = 0xFF;
+ // SAFETY: `fake_c_bitmap` can be used as one-element array of expected length.
+ let b = unsafe { CBitmap::from_raw(core::ptr::addr_of!(fake_c_bitmap), 8) };
+ assert_eq!(8, b.len());
+ assert_eq!(None, b.next_zero_bit(0));
+ }
+
+ #[test]
+ fn bitmap_new() {
+ let b = Bitmap::new(0, GFP_KERNEL).unwrap();
+ assert_eq!(0, b.len());
+
+ let b = Bitmap::new(3, GFP_KERNEL).unwrap();
+ assert_eq!(3, b.len());
+
+ let b = Bitmap::new(1024, GFP_KERNEL).unwrap();
+ assert_eq!(1024, b.len());
+
+ // Requesting too large values results in [`AllocError`].
+ let b = Bitmap::new(1 << 31, GFP_KERNEL);
+ assert!(b.is_err());
+ }
+
+ #[test]
+ fn bitmap_set_clear_find() {
+ let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
+
+ // Zero-initialized
+ assert_eq!(None, b.next_bit(0));
+ assert_eq!(Some(0), b.next_zero_bit(0));
+ assert_eq!(None, b.last_bit());
+
+ b.set_bit(17);
+
+ assert_eq!(Some(17), b.next_bit(0));
+ assert_eq!(Some(17), b.next_bit(17));
+ assert_eq!(None, b.next_bit(18));
+ assert_eq!(Some(17), b.last_bit());
+
+ b.set_bit(107);
+
+ assert_eq!(Some(17), b.next_bit(0));
+ assert_eq!(Some(17), b.next_bit(17));
+ assert_eq!(Some(107), b.next_bit(18));
+ assert_eq!(Some(107), b.last_bit());
+
+ b.clear_bit(17);
+
+ assert_eq!(Some(107), b.next_bit(0));
+ assert_eq!(Some(107), b.last_bit());
+ }
+
+ #[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
+ #[test]
+ fn bitmap_out_of_bounds() {
+ let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
+
+ b.set_bit(2048);
+ b.set_bit_atomic(2048);
+ b.clear_bit(2048);
+ b.clear_bit_atomic(2048);
+ assert_eq!(None, b.next_bit(2048));
+ assert_eq!(None, b.next_zero_bit(2048));
+ assert_eq!(None, b.last_bit());
+ }
+
+ #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
+ #[test]
+ #[should_panic]
+ fn bitmap_out_of_bounds() {
+ let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
+
+ b.set_bit(2048);
+ }
+
+ #[test]
+ fn bitmap_copy_and_extend() {
+ let mut long_bitmap = Bitmap::new(256, GFP_KERNEL).unwrap();
+
+ long_bitmap.set_bit(3);
+ long_bitmap.set_bit(200);
+
+ let mut short_bitmap = Bitmap::new(32, GFP_KERNEL).unwrap();
+
+ short_bitmap.set_bit(17);
+
+ long_bitmap.copy_and_extend(&short_bitmap);
+
+ // Previous bits have been cleared.
+ assert_eq!(Some(17), long_bitmap.next_bit(0));
+ assert_eq!(Some(17), long_bitmap.last_bit());
+ }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index de07aadd1ff5..8c4161cd82ac 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -38,6 +38,7 @@
pub use ffi;
pub mod alloc;
+pub mod bitmap;
#[cfg(CONFIG_BLOCK)]
pub mod block;
#[doc(hidden)]
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index 3fe9d7b945c4..d77a39aef554 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -324,6 +324,16 @@ config LIST_HARDENED
If unsure, say N.
+config RUST_BITMAP_HARDENED
+ bool "Check integrity of bitmap Rust API"
+ depends on RUST
+ help
+ Enables additional assertions in the Rust Bitmap API to catch
+ arguments that are not guaranteed to result in an immediate access
+ fault.
+
+ If unsure, say N.
+
config BUG_ON_DATA_CORRUPTION
bool "Trigger a BUG when data corruption is detected"
select LIST_HARDENED
--
2.50.0.rc1.591.g9c95f17f64-goog
^ permalink raw reply related [flat|nested] 18+ messages in thread* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-11 19:48 ` [PATCH v12 3/5] rust: add bitmap API Burak Emir
@ 2025-06-11 21:58 ` Alice Ryhl
2025-06-12 8:46 ` Burak Emir
2025-06-16 10:49 ` Alice Ryhl
1 sibling, 1 reply; 18+ messages in thread
From: Alice Ryhl @ 2025-06-11 21:58 UTC (permalink / raw)
To: Burak Emir
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Wed, Jun 11, 2025 at 9:48 PM Burak Emir <bqe@google.com> wrote:
>
> Provides an abstraction for C bitmap API and bitops operations.
>
> This commit enables a Rust implementation of an Android Binder
> data structure from commit 15d9da3f818c ("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:
>
> * We leverage Rust type system guarantees as follows:
>
> * all (non-atomic) mutating operations require a &mut reference which
> amounts to exclusive access.
>
> * the Bitmap type implements Send. This enables transferring
> ownership between threads and is needed for Binder.
>
> * the Bitmap 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, which differs from the C naming convention which uses
> set_bit for atomic vs __set_bit for non-atomic.
>
> * we include enough operations for the API to be useful, but not all
> operations are exposed yet in order to avoid dead code. The missing
> ones can be added later.
>
> * We follow the C API closely with 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 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, we log out-of-bounds
> arguments as errors and 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 (`CBitmap`).
>
> * 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, and must never be exposed
> (except in tests). Exposing the representation of the owned bitmap would
> 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>
> ---
> MAINTAINERS | 7 +
> rust/kernel/bitmap.rs | 582 +++++++++++++++++++++++++++++++++++++
> rust/kernel/lib.rs | 1 +
> security/Kconfig.hardening | 10 +
> 4 files changed, 600 insertions(+)
> create mode 100644 rust/kernel/bitmap.rs
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 04d6727e944c..565eaa015d9e 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4127,6 +4127,13 @@ S: Maintained
> F: rust/helpers/bitmap.c
> F: rust/helpers/cpumask.c
>
> +BITMAP API [RUST]
> +M: Alice Ryhl <aliceryhl@google.com>
> +M: Burak Emir <bqe@google.com>
> +R: Yury Norov <yury.norov@gmail.com>
> +S: Maintained
> +F: rust/kernel/bitmap.rs
> +
> BITOPS API
> M: Yury Norov <yury.norov@gmail.com>
> R: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
> new file mode 100644
> index 000000000000..1fe72ca980ac
> --- /dev/null
> +++ b/rust/kernel/bitmap.rs
> @@ -0,0 +1,582 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2025 Google LLC.
> +
> +//! Rust API for bitmap.
> +//!
> +//! C headers: [`include/linux/bitmap.h`](srctree/include/linux/bitmap.h).
> +
> +use crate::alloc::{AllocError, Flags};
> +use crate::bindings;
> +#[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> +use crate::pr_err;
> +use core::ptr::NonNull;
> +
> +/// Represents a C bitmap. Wraps underlying C bitmap API.
> +///
> +/// # Invariants
> +///
> +/// Must reference a `[c_ulong]` long enough to fit `data.len()` bits.
> +#[cfg_attr(CONFIG_64BIT, repr(align(8)))]
> +#[cfg_attr(not(CONFIG_64BIT), repr(align(4)))]
> +pub struct CBitmap {
> + data: [()],
> +}
I wonder if we should just call this type Bitmap?
> +
> +/// SAFETY: All methods that take immutable references are either atomic or read-only.
> +unsafe impl Sync for CBitmap {}
You don't have any fields wrapping C types anymore, so this has no effect.
> +
> +impl CBitmap {
> + /// Borrows a C bitmap.
> + ///
> + /// # Safety
> + ///
> + /// * `ptr` holds a non-null address of an initialized array of `unsigned long`
> + /// that is large enough to hold `nbits` bits.
> + /// * the array must not be freed for the lifetime of this [`CBitmap`]
> + /// * concurrent access only happens through atomic operations
> + pub unsafe fn from_raw<'a>(ptr: *const usize, nbits: usize) -> &'a CBitmap {
> + let data: *const [()] = core::ptr::slice_from_raw_parts(ptr.cast(), nbits);
> + // INVARIANT: `data` references an initialized array that can hold `nbits` bits.
> + // SAFETY:
> + // The caller guarantees that `data` (derived from `ptr` and `nbits`)
> + // points to a valid, initialized, and appropriately sized memory region
> + // that will not be freed for the lifetime 'a.
> + // We are casting `*const [()]` to `*const CBitmap`. The `CBitmap`
> + // struct is a ZST with a `data: [()]` field. This means its layout
> + // is compatible with a slice of `()`, and effectively it's a "thin pointer"
> + // (its size is 0 and alignment is 1). The `slice_from_raw_parts`
> + // function correctly encodes the length (number of bits, not elements)
> + // into the metadata of the fat pointer. Therefore, dereferencing this
> + // pointer as `&CBitmap` is safe given the caller's guarantees.
> + unsafe { &*(data as *const CBitmap) }
> + }
> +
> + /// Borrows a C bitmap exclusively.
> + ///
> + /// # Safety
> + ///
> + /// * `ptr` holds a non-null address of an initialized array of `unsigned long`
> + /// that is large enough to hold `nbits` bits.
> + /// * the array must not be freed for the lifetime of this [`CBitmap`]
> + /// * no concurrent access may happen.
> + pub unsafe fn from_raw_mut<'a>(ptr: *mut usize, nbits: usize) -> &'a mut CBitmap {
> + let data: *mut [()] = core::ptr::slice_from_raw_parts_mut(ptr.cast(), nbits);
> + // INVARIANT: `data` references an initialized array that can hold `nbits` bits.
> + // SAFETY:
> + // The caller guarantees that `data` (derived from `ptr` and `nbits`)
> + // points to a valid, initialized, and appropriately sized memory region
> + // that will not be freed for the lifetime 'a.
> + // Furthermore, the caller guarantees no concurrent access will happen,
> + // which upholds the exclusivity requirement for a mutable reference.
> + // Similar to `from_raw`, casting `*mut [()]` to `*mut CBitmap` is
> + // safe because `CBitmap` is a ZST with a `data: [()]` field,
> + // making its layout compatible with a slice of `()`.
> + unsafe { &mut *(data as *mut CBitmap) }
> + }
> +
> + /// Returns a raw pointer to the backing [`Bitmap`].
> + pub fn as_ptr(&self) -> *const usize {
> + self as *const CBitmap as *const usize
> + }
> +
> + /// Returns a mutable raw pointer to the backing [`Bitmap`].
> + pub fn as_mut_ptr(&mut self) -> *mut usize {
> + self as *mut CBitmap as *mut usize
> + }
> +
> + /// Returns length of this [`CBitmap`].
> + #[expect(clippy::len_without_is_empty)]
> + pub fn len(&self) -> usize {
> + self.data.len()
> + }
> +}
> +
> +/// Holds either a pointer to array of `unsigned long` or a small bitmap.
> +#[repr(C)]
> +union BitmapRepr {
> + bitmap: usize,
> + ptr: NonNull<usize>,
> +}
> +
> +macro_rules! bitmap_assert {
> + ($cond:expr, $($arg:tt)+) => {
> + #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
> + assert!($cond, $($arg)*);
> + }
> +}
> +
> +macro_rules! bitmap_assert_return {
> + ($cond:expr, $($arg:tt)+) => {
> + #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
> + assert!($cond, $($arg)*);
> +
> + #[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> + if !($cond) {
> + pr_err!($($arg)*);
> + return
> + }
> + }
> +}
> +
> +/// Represents an owned bitmap.
> +///
> +/// Wraps underlying C bitmap API. See [`CBitmap`] for available
> +/// methods.
> +///
> +/// # Examples
> +///
> +/// Basic usage
> +///
> +/// ```
> +/// use kernel::alloc::flags::GFP_KERNEL;
> +/// use kernel::bitmap::Bitmap;
> +///
> +/// let mut b = Bitmap::new(16, GFP_KERNEL)?;
> +///
> +/// assert_eq!(16, b.len());
> +/// for i in 0..16 {
> +/// if i % 4 == 0 {
> +/// b.set_bit(i);
> +/// }
> +/// }
> +/// assert_eq!(Some(0), b.next_bit(0));
> +/// assert_eq!(Some(1), b.next_zero_bit(0));
> +/// assert_eq!(Some(4), b.next_bit(1));
> +/// assert_eq!(Some(5), b.next_zero_bit(4));
> +/// assert_eq!(Some(12), b.last_bit());
> +/// # Ok::<(), Error>(())
> +/// ```
> +///
> +/// # Invariants
> +///
> +/// * `nbits` is `<= i32::MAX` and never changes.
> +/// * if `nbits <= bindings::BITS_PER_LONG`, then `repr` is a `usize`.
> +/// * otherwise, `repr` holds a non-null pointer to an initialized
> +/// array of `unsigned long` that is large enough to hold `nbits` bits.
> +pub struct Bitmap {
> + /// Representation of bitmap.
> + repr: BitmapRepr,
> + /// Length of this bitmap. Must be `<= i32::MAX`.
> + nbits: usize,
> +}
> +
> +impl core::ops::Deref for Bitmap {
> + type Target = CBitmap;
> +
> + fn deref(&self) -> &CBitmap {
> + let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
You can define a local constant with the right size to avoid these casts:
const BITS_PER_LONG: usize = bindings::BITS_PER_LONG as usize;
> + // SAFETY: Bitmap is represented inline.
> + unsafe { core::ptr::addr_of!(self.repr.bitmap) }
> + } else {
> + // SAFETY: Bitmap is represented as array of `unsigned long`.
> + unsafe { self.repr.ptr.as_ptr() }
> + };
> +
> + // SAFETY: We got the right pointer and invariants of [`Bitmap`] hold.
> + // An inline bitmap is treated like an array with single element.
> + unsafe { CBitmap::from_raw(ptr, self.nbits) }
> + }
> +}
> +
> +impl core::ops::DerefMut for Bitmap {
> + fn deref_mut(&mut self) -> &mut CBitmap {
> + let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
> + // SAFETY: Bitmap is represented inline.
> + unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
> + } else {
> + // SAFETY: Bitmap is represented as array of `unsigned long`.
> + unsafe { self.repr.ptr.as_mut() }
> + };
> +
> + // SAFETY: We got the right pointer and invariants of [`Bitmap`] hold.
> + // An inline bitmap is treated like an array with single element.
> + unsafe { CBitmap::from_raw_mut(ptr, self.nbits) }
> + }
> +}
> +
> +/// Enable ownership transfer to other threads.
> +///
> +/// SAFETY: We own the underlying bitmap representation.
> +unsafe impl Send for Bitmap {}
> +
> +/// Enable unsynchronized concurrent access to [`Bitmap`] through shared references.
> +///
> +/// SAFETY: `deref()` will return a reference to a [`CBitmap`] which is Sync. Its methods
> +/// that take immutable references are either atomic or read-only.
> +unsafe impl Sync for Bitmap {}
> +
> +impl Drop for Bitmap {
> + fn drop(&mut self) {
> + if self.nbits <= bindings::BITS_PER_LONG as _ {
> + return;
> + }
> + // SAFETY: `self.ptr` was returned by the C `bitmap_zalloc`.
> + //
> + // INVARIANT: there is no other use of the `self.ptr` after this
> + // call and the value is being dropped so the broken invariant is
> + // not observable on function exit.
> + unsafe { bindings::bitmap_free(self.repr.ptr.as_ptr()) };
> + }
> +}
> +
> +impl Bitmap {
> + /// Constructs a new [`Bitmap`].
> + ///
> + /// Fails with [`AllocError`] when the [`Bitmap`] could not be allocated. This
> + /// includes the case when `nbits` is greater than `i32::MAX`.
> + #[inline]
> + pub fn new(nbits: usize, flags: Flags) -> Result<Self, AllocError> {
> + if nbits <= bindings::BITS_PER_LONG as _ {
> + return Ok(Bitmap {
> + repr: BitmapRepr { bitmap: 0 },
> + nbits,
> + });
> + }
> + if nbits > i32::MAX.try_into().unwrap() {
> + return Err(AllocError);
> + }
> + let nbits_u32 = u32::try_from(nbits).unwrap();
> + // SAFETY: `bindings::BITS_PER_LONG < nbits` and `nbits <= i32::MAX`.
> + let ptr = unsafe { bindings::bitmap_zalloc(nbits_u32, flags.as_raw()) };
> + let ptr = NonNull::new(ptr).ok_or(AllocError)?;
> + // INVARIANT: `ptr` returned by C `bitmap_zalloc` and `nbits` checked.
> + Ok(Bitmap {
> + repr: BitmapRepr { ptr },
> + nbits,
> + })
> + }
> +
> + /// Returns length of this [`Bitmap`].
> + #[allow(clippy::len_without_is_empty)]
> + #[inline]
> + pub fn len(&self) -> usize {
> + self.nbits
> + }
> +}
> +
> +impl CBitmap {
> + /// Set bit with index `index`.
> + ///
> + /// ATTENTION: `set_bit` is non-atomic, which differs from the naming
> + /// convention in C code. The corresponding C function is `__set_bit`.
> + ///
> + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> + /// or equal to `self.nbits`, does nothing.
> + ///
> + /// # Panics
> + ///
> + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> + /// or equal to `self.nbits`.
> + #[inline]
> + pub fn set_bit(&mut self, index: usize) {
> + bitmap_assert_return!(
> + index < self.len(),
> + "Bit `index` must be < {}, was {}",
> + self.len(),
> + index
> + );
> + // SAFETY: Bit `index` is within bounds.
> + unsafe { bindings::__set_bit(index, self.as_mut_ptr()) };
> + }
> +
> + /// Set bit with index `index`, atomically.
> + ///
> + /// This is a relaxed atomic operation (no implied memory barriers).
> + ///
> + /// ATTENTION: The naming convention differs from C, where the corresponding
> + /// function is called `set_bit`.
> + ///
> + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> + /// or equal to `self.len()`, does nothing.
> + ///
> + /// # Panics
> + ///
> + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> + /// or equal to `self.len()`.
> + #[inline]
> + pub fn set_bit_atomic(&self, index: usize) {
> + bitmap_assert_return!(
> + index < self.len(),
> + "Bit `index` must be < {}, was {}",
> + self.len(),
> + index
> + );
> + // SAFETY: `index` is within bounds and the caller has ensured that
> + // there is no mix of non-atomic and atomic operations.
> + unsafe { bindings::set_bit(index, self.as_ptr() as *mut usize) };
> + }
> +
> + /// Clear `index` bit.
> + ///
> + /// ATTENTION: `clear_bit` is non-atomic, which differs from the naming
> + /// convention in C code. The corresponding C function is `__clear_bit`.
> + ///
> + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> + /// or equal to `self.len()`, does nothing.
> + ///
> + /// # Panics
> + ///
> + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> + /// or equal to `self.len()`.
> + #[inline]
> + pub fn clear_bit(&mut self, index: usize) {
> + bitmap_assert_return!(
> + index < self.len(),
> + "Bit `index` must be < {}, was {}",
> + self.len(),
> + index
> + );
> + // SAFETY: `index` is within bounds.
> + unsafe { bindings::__clear_bit(index, self.as_mut_ptr()) };
> + }
> +
> + /// Clear `index` bit, atomically.
> + ///
> + /// This is a relaxed atomic operation (no implied memory barriers).
> + ///
> + /// ATTENTION: The naming convention differs from C, where the corresponding
> + /// function is called `clear_bit`.
> + ///
> + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> + /// or equal to `self.len()`, does nothing.
> + ///
> + /// # Panics
> + ///
> + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> + /// or equal to `self.len()`.
> + #[inline]
> + pub fn clear_bit_atomic(&self, index: usize) {
> + bitmap_assert_return!(
> + index < self.len(),
> + "Bit `index` must be < {}, was {}",
> + self.len(),
> + index
> + );
> + // SAFETY: `index` is within bounds and the caller has ensured that
> + // there is no mix of non-atomic and atomic operations.
> + unsafe { bindings::clear_bit(index, self.as_ptr() as *mut usize) };
> + }
> +
> + /// Copy `src` into this [`Bitmap`] and set any remaining bits to zero.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> + /// use kernel::bitmap::Bitmap;
> + ///
> + /// let mut long_bitmap = Bitmap::new(256, GFP_KERNEL)?;
> + //
> + /// assert_eq!(None, long_bitmap.last_bit());
> + //
> + /// let mut short_bitmap = Bitmap::new(16, GFP_KERNEL)?;
> + //
> + /// short_bitmap.set_bit(7);
> + /// long_bitmap.copy_and_extend(&short_bitmap);
> + /// assert_eq!(Some(7), long_bitmap.last_bit());
> + ///
> + /// # Ok::<(), AllocError>(())
> + /// ```
> + #[inline]
> + pub fn copy_and_extend(&mut self, src: &Bitmap) {
> + let len = core::cmp::min(src.nbits, self.len());
> + // SAFETY: access to `self` and `src` is within bounds.
> + unsafe {
> + bindings::bitmap_copy_and_extend(
> + self.as_mut_ptr(),
> + src.as_ptr(),
> + len as u32,
> + self.len() as u32,
> + )
> + };
> + }
> +
> + /// Finds last set bit.
> + ///
> + /// # Examples
> + ///
> + /// ```
> + /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> + /// use kernel::bitmap::Bitmap;
> + ///
> + /// let bitmap = Bitmap::new(64, GFP_KERNEL)?;
> + ///
> + /// match bitmap.last_bit() {
> + /// Some(idx) => {
> + /// pr_info!("The last bit has index {idx}.\n");
> + /// }
> + /// None => {
> + /// pr_info!("All bits in this bitmap are 0.\n");
> + /// }
> + /// }
> + /// # Ok::<(), AllocError>(())
> + /// ```
> + #[inline]
> + pub fn last_bit(&self) -> Option<usize> {
> + // SAFETY: `_find_next_bit` access is within bounds due to invariant.
> + let index = unsafe { bindings::_find_last_bit(self.as_ptr(), self.len()) };
> + if index >= self.len() {
> + None
> + } else {
> + Some(index)
> + }
> + }
> +
> + /// Finds next set bit, starting from `start`.
> + /// Returns `None` if `start` is greater of equal than `self.nbits`.
> + #[inline]
The html docs look better if you include a newline:
/// Finds next set bit, starting from `start`.
///
/// Returns `None` if `start` is greater of equal than `self.nbits`.
> + pub fn next_bit(&self, start: usize) -> Option<usize> {
> + bitmap_assert!(
> + start < self.len(),
> + "`start` must be < {} was {}",
> + self.len(),
> + start
> + );
> + // SAFETY: `_find_next_bit` tolerates out-of-bounds arguments and returns a
> + // value larger than or equal to `self.len()` in that case.
> + let index = unsafe { bindings::_find_next_bit(self.as_ptr(), self.len(), start) };
> + if index >= self.len() {
> + None
> + } else {
> + Some(index)
> + }
> + }
> +
> + /// Finds next zero bit, starting from `start`.
> + /// Returns `None` if `start` is greater than or equal to `self.len()`.
> + #[inline]
> + pub fn next_zero_bit(&self, start: usize) -> Option<usize> {
> + bitmap_assert!(
> + start < self.len(),
> + "`start` must be < {} was {}",
> + self.len(),
> + start
> + );
> + // SAFETY: `_find_next_zero_bit` tolerates out-of-bounds arguments and returns a
> + // value larger than or equal to `self.len()` in that case.
> + let index = unsafe { bindings::_find_next_zero_bit(self.as_ptr(), self.len(), start) };
> + if index >= self.len() {
> + None
> + } else {
> + Some(index)
> + }
> + }
> +}
> +
> +use macros::kunit_tests;
> +
> +#[kunit_tests(rust_kernel_bitmap)]
> +mod tests {
> + use super::*;
> + use kernel::alloc::flags::GFP_KERNEL;
> +
> + #[test]
> + fn cbitmap_borrow() {
> + let fake_c_bitmap: [usize; 2] = [0, 0];
> + // SAFETY: `fake_c_bitmap` is an array of expected length.
> + let b = unsafe {
> + CBitmap::from_raw(
> + core::ptr::addr_of!(fake_c_bitmap) as *const usize,
You can just do fake_c_bitmap.as_ptr()
> + 2 * bindings::BITS_PER_LONG as usize,
> + )
> + };
> + assert_eq!(2 * bindings::BITS_PER_LONG as usize, b.len());
> + assert_eq!(None, b.next_bit(0));
> + }
> +
> + #[test]
> + fn cbitmap_copy() {
> + let fake_c_bitmap: usize = 0xFF;
> + // SAFETY: `fake_c_bitmap` can be used as one-element array of expected length.
> + let b = unsafe { CBitmap::from_raw(core::ptr::addr_of!(fake_c_bitmap), 8) };
> + assert_eq!(8, b.len());
> + assert_eq!(None, b.next_zero_bit(0));
> + }
> +
> + #[test]
> + fn bitmap_new() {
> + let b = Bitmap::new(0, GFP_KERNEL).unwrap();
> + assert_eq!(0, b.len());
> +
> + let b = Bitmap::new(3, GFP_KERNEL).unwrap();
> + assert_eq!(3, b.len());
> +
> + let b = Bitmap::new(1024, GFP_KERNEL).unwrap();
> + assert_eq!(1024, b.len());
> +
> + // Requesting too large values results in [`AllocError`].
> + let b = Bitmap::new(1 << 31, GFP_KERNEL);
> + assert!(b.is_err());
> + }
> +
> + #[test]
> + fn bitmap_set_clear_find() {
> + let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
> +
> + // Zero-initialized
> + assert_eq!(None, b.next_bit(0));
> + assert_eq!(Some(0), b.next_zero_bit(0));
> + assert_eq!(None, b.last_bit());
> +
> + b.set_bit(17);
> +
> + assert_eq!(Some(17), b.next_bit(0));
> + assert_eq!(Some(17), b.next_bit(17));
> + assert_eq!(None, b.next_bit(18));
> + assert_eq!(Some(17), b.last_bit());
> +
> + b.set_bit(107);
> +
> + assert_eq!(Some(17), b.next_bit(0));
> + assert_eq!(Some(17), b.next_bit(17));
> + assert_eq!(Some(107), b.next_bit(18));
> + assert_eq!(Some(107), b.last_bit());
> +
> + b.clear_bit(17);
> +
> + assert_eq!(Some(107), b.next_bit(0));
> + assert_eq!(Some(107), b.last_bit());
> + }
> +
> + #[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> + #[test]
> + fn bitmap_out_of_bounds() {
> + let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
> +
> + b.set_bit(2048);
> + b.set_bit_atomic(2048);
> + b.clear_bit(2048);
> + b.clear_bit_atomic(2048);
> + assert_eq!(None, b.next_bit(2048));
> + assert_eq!(None, b.next_zero_bit(2048));
> + assert_eq!(None, b.last_bit());
> + }
> +
> + #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
> + #[test]
> + #[should_panic]
> + fn bitmap_out_of_bounds() {
I don't think we have #[should_panic] support in Rust KUnit yet.
> + let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
> +
> + b.set_bit(2048);
> + }
> +
> + #[test]
> + fn bitmap_copy_and_extend() {
> + let mut long_bitmap = Bitmap::new(256, GFP_KERNEL).unwrap();
> +
> + long_bitmap.set_bit(3);
> + long_bitmap.set_bit(200);
> +
> + let mut short_bitmap = Bitmap::new(32, GFP_KERNEL).unwrap();
> +
> + short_bitmap.set_bit(17);
> +
> + long_bitmap.copy_and_extend(&short_bitmap);
> +
> + // Previous bits have been cleared.
> + assert_eq!(Some(17), long_bitmap.next_bit(0));
> + assert_eq!(Some(17), long_bitmap.last_bit());
> + }
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index de07aadd1ff5..8c4161cd82ac 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -38,6 +38,7 @@
> pub use ffi;
>
> pub mod alloc;
> +pub mod bitmap;
> #[cfg(CONFIG_BLOCK)]
> pub mod block;
> #[doc(hidden)]
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 3fe9d7b945c4..d77a39aef554 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -324,6 +324,16 @@ config LIST_HARDENED
>
> If unsure, say N.
>
> +config RUST_BITMAP_HARDENED
> + bool "Check integrity of bitmap Rust API"
> + depends on RUST
> + help
> + Enables additional assertions in the Rust Bitmap API to catch
> + arguments that are not guaranteed to result in an immediate access
> + fault.
> +
> + If unsure, say N.
> +
> config BUG_ON_DATA_CORRUPTION
> bool "Trigger a BUG when data corruption is detected"
> select LIST_HARDENED
> --
> 2.50.0.rc1.591.g9c95f17f64-goog
>
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-11 21:58 ` Alice Ryhl
@ 2025-06-12 8:46 ` Burak Emir
2025-06-12 8:49 ` Alice Ryhl
2025-06-12 9:52 ` Miguel Ojeda
0 siblings, 2 replies; 18+ messages in thread
From: Burak Emir @ 2025-06-12 8:46 UTC (permalink / raw)
To: Alice Ryhl
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Wed, Jun 11, 2025 at 11:58 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
> On Wed, Jun 11, 2025 at 9:48 PM Burak Emir <bqe@google.com> wrote:
[...]
> > diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
> > new file mode 100644
> > index 000000000000..1fe72ca980ac
> > --- /dev/null
> > +++ b/rust/kernel/bitmap.rs
> > @@ -0,0 +1,582 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +// Copyright (C) 2025 Google LLC.
> > +
> > +//! Rust API for bitmap.
> > +//!
> > +//! C headers: [`include/linux/bitmap.h`](srctree/include/linux/bitmap.h).
> > +
> > +use crate::alloc::{AllocError, Flags};
> > +use crate::bindings;
> > +#[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> > +use crate::pr_err;
> > +use core::ptr::NonNull;
> > +
> > +/// Represents a C bitmap. Wraps underlying C bitmap API.
> > +///
> > +/// # Invariants
> > +///
> > +/// Must reference a `[c_ulong]` long enough to fit `data.len()` bits.
> > +#[cfg_attr(CONFIG_64BIT, repr(align(8)))]
> > +#[cfg_attr(not(CONFIG_64BIT), repr(align(4)))]
> > +pub struct CBitmap {
> > + data: [()],
> > +}
>
> I wonder if we should just call this type Bitmap?
>
OK. I am renaming the other type to OwnedBitmap then.
> > +
> > +/// SAFETY: All methods that take immutable references are either atomic or read-only.
> > +unsafe impl Sync for CBitmap {}
>
> You don't have any fields wrapping C types anymore, so this has no effect.
Removing.
> > +
> > +impl CBitmap {
> > + /// Borrows a C bitmap.
> > + ///
> > + /// # Safety
> > + ///
> > + /// * `ptr` holds a non-null address of an initialized array of `unsigned long`
> > + /// that is large enough to hold `nbits` bits.
> > + /// * the array must not be freed for the lifetime of this [`CBitmap`]
> > + /// * concurrent access only happens through atomic operations
> > + pub unsafe fn from_raw<'a>(ptr: *const usize, nbits: usize) -> &'a CBitmap {
> > + let data: *const [()] = core::ptr::slice_from_raw_parts(ptr.cast(), nbits);
> > + // INVARIANT: `data` references an initialized array that can hold `nbits` bits.
> > + // SAFETY:
> > + // The caller guarantees that `data` (derived from `ptr` and `nbits`)
> > + // points to a valid, initialized, and appropriately sized memory region
> > + // that will not be freed for the lifetime 'a.
> > + // We are casting `*const [()]` to `*const CBitmap`. The `CBitmap`
> > + // struct is a ZST with a `data: [()]` field. This means its layout
> > + // is compatible with a slice of `()`, and effectively it's a "thin pointer"
> > + // (its size is 0 and alignment is 1). The `slice_from_raw_parts`
> > + // function correctly encodes the length (number of bits, not elements)
> > + // into the metadata of the fat pointer. Therefore, dereferencing this
> > + // pointer as `&CBitmap` is safe given the caller's guarantees.
> > + unsafe { &*(data as *const CBitmap) }
> > + }
> > +
> > + /// Borrows a C bitmap exclusively.
> > + ///
> > + /// # Safety
> > + ///
> > + /// * `ptr` holds a non-null address of an initialized array of `unsigned long`
> > + /// that is large enough to hold `nbits` bits.
> > + /// * the array must not be freed for the lifetime of this [`CBitmap`]
> > + /// * no concurrent access may happen.
> > + pub unsafe fn from_raw_mut<'a>(ptr: *mut usize, nbits: usize) -> &'a mut CBitmap {
> > + let data: *mut [()] = core::ptr::slice_from_raw_parts_mut(ptr.cast(), nbits);
> > + // INVARIANT: `data` references an initialized array that can hold `nbits` bits.
> > + // SAFETY:
> > + // The caller guarantees that `data` (derived from `ptr` and `nbits`)
> > + // points to a valid, initialized, and appropriately sized memory region
> > + // that will not be freed for the lifetime 'a.
> > + // Furthermore, the caller guarantees no concurrent access will happen,
> > + // which upholds the exclusivity requirement for a mutable reference.
> > + // Similar to `from_raw`, casting `*mut [()]` to `*mut CBitmap` is
> > + // safe because `CBitmap` is a ZST with a `data: [()]` field,
> > + // making its layout compatible with a slice of `()`.
> > + unsafe { &mut *(data as *mut CBitmap) }
> > + }
> > +
> > + /// Returns a raw pointer to the backing [`Bitmap`].
> > + pub fn as_ptr(&self) -> *const usize {
> > + self as *const CBitmap as *const usize
> > + }
> > +
> > + /// Returns a mutable raw pointer to the backing [`Bitmap`].
> > + pub fn as_mut_ptr(&mut self) -> *mut usize {
> > + self as *mut CBitmap as *mut usize
> > + }
> > +
> > + /// Returns length of this [`CBitmap`].
> > + #[expect(clippy::len_without_is_empty)]
> > + pub fn len(&self) -> usize {
> > + self.data.len()
> > + }
> > +}
> > +
> > +/// Holds either a pointer to array of `unsigned long` or a small bitmap.
> > +#[repr(C)]
> > +union BitmapRepr {
> > + bitmap: usize,
> > + ptr: NonNull<usize>,
> > +}
> > +
> > +macro_rules! bitmap_assert {
> > + ($cond:expr, $($arg:tt)+) => {
> > + #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
> > + assert!($cond, $($arg)*);
> > + }
> > +}
> > +
> > +macro_rules! bitmap_assert_return {
> > + ($cond:expr, $($arg:tt)+) => {
> > + #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
> > + assert!($cond, $($arg)*);
> > +
> > + #[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> > + if !($cond) {
> > + pr_err!($($arg)*);
> > + return
> > + }
> > + }
> > +}
> > +
> > +/// Represents an owned bitmap.
> > +///
> > +/// Wraps underlying C bitmap API. See [`CBitmap`] for available
> > +/// methods.
> > +///
> > +/// # Examples
> > +///
> > +/// Basic usage
> > +///
> > +/// ```
> > +/// use kernel::alloc::flags::GFP_KERNEL;
> > +/// use kernel::bitmap::Bitmap;
> > +///
> > +/// let mut b = Bitmap::new(16, GFP_KERNEL)?;
> > +///
> > +/// assert_eq!(16, b.len());
> > +/// for i in 0..16 {
> > +/// if i % 4 == 0 {
> > +/// b.set_bit(i);
> > +/// }
> > +/// }
> > +/// assert_eq!(Some(0), b.next_bit(0));
> > +/// assert_eq!(Some(1), b.next_zero_bit(0));
> > +/// assert_eq!(Some(4), b.next_bit(1));
> > +/// assert_eq!(Some(5), b.next_zero_bit(4));
> > +/// assert_eq!(Some(12), b.last_bit());
> > +/// # Ok::<(), Error>(())
> > +/// ```
> > +///
> > +/// # Invariants
> > +///
> > +/// * `nbits` is `<= i32::MAX` and never changes.
> > +/// * if `nbits <= bindings::BITS_PER_LONG`, then `repr` is a `usize`.
> > +/// * otherwise, `repr` holds a non-null pointer to an initialized
> > +/// array of `unsigned long` that is large enough to hold `nbits` bits.
> > +pub struct Bitmap {
> > + /// Representation of bitmap.
> > + repr: BitmapRepr,
> > + /// Length of this bitmap. Must be `<= i32::MAX`.
> > + nbits: usize,
> > +}
> > +
> > +impl core::ops::Deref for Bitmap {
> > + type Target = CBitmap;
> > +
> > + fn deref(&self) -> &CBitmap {
> > + let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
>
> You can define a local constant with the right size to avoid these casts:
> const BITS_PER_LONG: usize = bindings::BITS_PER_LONG as usize;
Done.
> > + // SAFETY: Bitmap is represented inline.
> > + unsafe { core::ptr::addr_of!(self.repr.bitmap) }
> > + } else {
> > + // SAFETY: Bitmap is represented as array of `unsigned long`.
> > + unsafe { self.repr.ptr.as_ptr() }
> > + };
> > +
> > + // SAFETY: We got the right pointer and invariants of [`Bitmap`] hold.
> > + // An inline bitmap is treated like an array with single element.
> > + unsafe { CBitmap::from_raw(ptr, self.nbits) }
> > + }
> > +}
> > +
> > +impl core::ops::DerefMut for Bitmap {
> > + fn deref_mut(&mut self) -> &mut CBitmap {
> > + let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
> > + // SAFETY: Bitmap is represented inline.
> > + unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
> > + } else {
> > + // SAFETY: Bitmap is represented as array of `unsigned long`.
> > + unsafe { self.repr.ptr.as_mut() }
> > + };
> > +
> > + // SAFETY: We got the right pointer and invariants of [`Bitmap`] hold.
> > + // An inline bitmap is treated like an array with single element.
> > + unsafe { CBitmap::from_raw_mut(ptr, self.nbits) }
> > + }
> > +}
> > +
> > +/// Enable ownership transfer to other threads.
> > +///
> > +/// SAFETY: We own the underlying bitmap representation.
> > +unsafe impl Send for Bitmap {}
> > +
> > +/// Enable unsynchronized concurrent access to [`Bitmap`] through shared references.
> > +///
> > +/// SAFETY: `deref()` will return a reference to a [`CBitmap`] which is Sync. Its methods
> > +/// that take immutable references are either atomic or read-only.
> > +unsafe impl Sync for Bitmap {}
> > +
> > +impl Drop for Bitmap {
> > + fn drop(&mut self) {
> > + if self.nbits <= bindings::BITS_PER_LONG as _ {
> > + return;
> > + }
> > + // SAFETY: `self.ptr` was returned by the C `bitmap_zalloc`.
> > + //
> > + // INVARIANT: there is no other use of the `self.ptr` after this
> > + // call and the value is being dropped so the broken invariant is
> > + // not observable on function exit.
> > + unsafe { bindings::bitmap_free(self.repr.ptr.as_ptr()) };
> > + }
> > +}
> > +
> > +impl Bitmap {
> > + /// Constructs a new [`Bitmap`].
> > + ///
> > + /// Fails with [`AllocError`] when the [`Bitmap`] could not be allocated. This
> > + /// includes the case when `nbits` is greater than `i32::MAX`.
> > + #[inline]
> > + pub fn new(nbits: usize, flags: Flags) -> Result<Self, AllocError> {
> > + if nbits <= bindings::BITS_PER_LONG as _ {
> > + return Ok(Bitmap {
> > + repr: BitmapRepr { bitmap: 0 },
> > + nbits,
> > + });
> > + }
> > + if nbits > i32::MAX.try_into().unwrap() {
> > + return Err(AllocError);
> > + }
> > + let nbits_u32 = u32::try_from(nbits).unwrap();
> > + // SAFETY: `bindings::BITS_PER_LONG < nbits` and `nbits <= i32::MAX`.
> > + let ptr = unsafe { bindings::bitmap_zalloc(nbits_u32, flags.as_raw()) };
> > + let ptr = NonNull::new(ptr).ok_or(AllocError)?;
> > + // INVARIANT: `ptr` returned by C `bitmap_zalloc` and `nbits` checked.
> > + Ok(Bitmap {
> > + repr: BitmapRepr { ptr },
> > + nbits,
> > + })
> > + }
> > +
> > + /// Returns length of this [`Bitmap`].
> > + #[allow(clippy::len_without_is_empty)]
> > + #[inline]
> > + pub fn len(&self) -> usize {
> > + self.nbits
> > + }
> > +}
> > +
> > +impl CBitmap {
> > + /// Set bit with index `index`.
> > + ///
> > + /// ATTENTION: `set_bit` is non-atomic, which differs from the naming
> > + /// convention in C code. The corresponding C function is `__set_bit`.
> > + ///
> > + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> > + /// or equal to `self.nbits`, does nothing.
> > + ///
> > + /// # Panics
> > + ///
> > + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> > + /// or equal to `self.nbits`.
> > + #[inline]
> > + pub fn set_bit(&mut self, index: usize) {
> > + bitmap_assert_return!(
> > + index < self.len(),
> > + "Bit `index` must be < {}, was {}",
> > + self.len(),
> > + index
> > + );
> > + // SAFETY: Bit `index` is within bounds.
> > + unsafe { bindings::__set_bit(index, self.as_mut_ptr()) };
> > + }
> > +
> > + /// Set bit with index `index`, atomically.
> > + ///
> > + /// This is a relaxed atomic operation (no implied memory barriers).
> > + ///
> > + /// ATTENTION: The naming convention differs from C, where the corresponding
> > + /// function is called `set_bit`.
> > + ///
> > + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> > + /// or equal to `self.len()`, does nothing.
> > + ///
> > + /// # Panics
> > + ///
> > + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> > + /// or equal to `self.len()`.
> > + #[inline]
> > + pub fn set_bit_atomic(&self, index: usize) {
> > + bitmap_assert_return!(
> > + index < self.len(),
> > + "Bit `index` must be < {}, was {}",
> > + self.len(),
> > + index
> > + );
> > + // SAFETY: `index` is within bounds and the caller has ensured that
> > + // there is no mix of non-atomic and atomic operations.
> > + unsafe { bindings::set_bit(index, self.as_ptr() as *mut usize) };
> > + }
> > +
> > + /// Clear `index` bit.
> > + ///
> > + /// ATTENTION: `clear_bit` is non-atomic, which differs from the naming
> > + /// convention in C code. The corresponding C function is `__clear_bit`.
> > + ///
> > + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> > + /// or equal to `self.len()`, does nothing.
> > + ///
> > + /// # Panics
> > + ///
> > + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> > + /// or equal to `self.len()`.
> > + #[inline]
> > + pub fn clear_bit(&mut self, index: usize) {
> > + bitmap_assert_return!(
> > + index < self.len(),
> > + "Bit `index` must be < {}, was {}",
> > + self.len(),
> > + index
> > + );
> > + // SAFETY: `index` is within bounds.
> > + unsafe { bindings::__clear_bit(index, self.as_mut_ptr()) };
> > + }
> > +
> > + /// Clear `index` bit, atomically.
> > + ///
> > + /// This is a relaxed atomic operation (no implied memory barriers).
> > + ///
> > + /// ATTENTION: The naming convention differs from C, where the corresponding
> > + /// function is called `clear_bit`.
> > + ///
> > + /// If CONFIG_RUST_BITMAP_HARDENED is not enabled and `index` is greater than
> > + /// or equal to `self.len()`, does nothing.
> > + ///
> > + /// # Panics
> > + ///
> > + /// Panics if CONFIG_RUST_BITMAP_HARDENED is enabled and `index` is greater than
> > + /// or equal to `self.len()`.
> > + #[inline]
> > + pub fn clear_bit_atomic(&self, index: usize) {
> > + bitmap_assert_return!(
> > + index < self.len(),
> > + "Bit `index` must be < {}, was {}",
> > + self.len(),
> > + index
> > + );
> > + // SAFETY: `index` is within bounds and the caller has ensured that
> > + // there is no mix of non-atomic and atomic operations.
> > + unsafe { bindings::clear_bit(index, self.as_ptr() as *mut usize) };
> > + }
> > +
> > + /// Copy `src` into this [`Bitmap`] and set any remaining bits to zero.
> > + ///
> > + /// # Examples
> > + ///
> > + /// ```
> > + /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> > + /// use kernel::bitmap::Bitmap;
> > + ///
> > + /// let mut long_bitmap = Bitmap::new(256, GFP_KERNEL)?;
> > + //
> > + /// assert_eq!(None, long_bitmap.last_bit());
> > + //
> > + /// let mut short_bitmap = Bitmap::new(16, GFP_KERNEL)?;
> > + //
> > + /// short_bitmap.set_bit(7);
> > + /// long_bitmap.copy_and_extend(&short_bitmap);
> > + /// assert_eq!(Some(7), long_bitmap.last_bit());
> > + ///
> > + /// # Ok::<(), AllocError>(())
> > + /// ```
> > + #[inline]
> > + pub fn copy_and_extend(&mut self, src: &Bitmap) {
> > + let len = core::cmp::min(src.nbits, self.len());
> > + // SAFETY: access to `self` and `src` is within bounds.
> > + unsafe {
> > + bindings::bitmap_copy_and_extend(
> > + self.as_mut_ptr(),
> > + src.as_ptr(),
> > + len as u32,
> > + self.len() as u32,
> > + )
> > + };
> > + }
> > +
> > + /// Finds last set bit.
> > + ///
> > + /// # Examples
> > + ///
> > + /// ```
> > + /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> > + /// use kernel::bitmap::Bitmap;
> > + ///
> > + /// let bitmap = Bitmap::new(64, GFP_KERNEL)?;
> > + ///
> > + /// match bitmap.last_bit() {
> > + /// Some(idx) => {
> > + /// pr_info!("The last bit has index {idx}.\n");
> > + /// }
> > + /// None => {
> > + /// pr_info!("All bits in this bitmap are 0.\n");
> > + /// }
> > + /// }
> > + /// # Ok::<(), AllocError>(())
> > + /// ```
> > + #[inline]
> > + pub fn last_bit(&self) -> Option<usize> {
> > + // SAFETY: `_find_next_bit` access is within bounds due to invariant.
> > + let index = unsafe { bindings::_find_last_bit(self.as_ptr(), self.len()) };
> > + if index >= self.len() {
> > + None
> > + } else {
> > + Some(index)
> > + }
> > + }
> > +
> > + /// Finds next set bit, starting from `start`.
> > + /// Returns `None` if `start` is greater of equal than `self.nbits`.
> > + #[inline]
>
> The html docs look better if you include a newline:
>
> /// Finds next set bit, starting from `start`.
> ///
> /// Returns `None` if `start` is greater of equal than `self.nbits`.
Done
> > + pub fn next_bit(&self, start: usize) -> Option<usize> {
> > + bitmap_assert!(
> > + start < self.len(),
> > + "`start` must be < {} was {}",
> > + self.len(),
> > + start
> > + );
> > + // SAFETY: `_find_next_bit` tolerates out-of-bounds arguments and returns a
> > + // value larger than or equal to `self.len()` in that case.
> > + let index = unsafe { bindings::_find_next_bit(self.as_ptr(), self.len(), start) };
> > + if index >= self.len() {
> > + None
> > + } else {
> > + Some(index)
> > + }
> > + }
> > +
> > + /// Finds next zero bit, starting from `start`.
> > + /// Returns `None` if `start` is greater than or equal to `self.len()`.
> > + #[inline]
> > + pub fn next_zero_bit(&self, start: usize) -> Option<usize> {
> > + bitmap_assert!(
> > + start < self.len(),
> > + "`start` must be < {} was {}",
> > + self.len(),
> > + start
> > + );
> > + // SAFETY: `_find_next_zero_bit` tolerates out-of-bounds arguments and returns a
> > + // value larger than or equal to `self.len()` in that case.
> > + let index = unsafe { bindings::_find_next_zero_bit(self.as_ptr(), self.len(), start) };
> > + if index >= self.len() {
> > + None
> > + } else {
> > + Some(index)
> > + }
> > + }
> > +}
> > +
> > +use macros::kunit_tests;
> > +
> > +#[kunit_tests(rust_kernel_bitmap)]
> > +mod tests {
> > + use super::*;
> > + use kernel::alloc::flags::GFP_KERNEL;
> > +
> > + #[test]
> > + fn cbitmap_borrow() {
> > + let fake_c_bitmap: [usize; 2] = [0, 0];
> > + // SAFETY: `fake_c_bitmap` is an array of expected length.
> > + let b = unsafe {
> > + CBitmap::from_raw(
> > + core::ptr::addr_of!(fake_c_bitmap) as *const usize,
>
> You can just do fake_c_bitmap.as_ptr()
>
> > + 2 * bindings::BITS_PER_LONG as usize,
> > + )
> > + };
> > + assert_eq!(2 * bindings::BITS_PER_LONG as usize, b.len());
> > + assert_eq!(None, b.next_bit(0));
> > + }
> > +
> > + #[test]
> > + fn cbitmap_copy() {
> > + let fake_c_bitmap: usize = 0xFF;
> > + // SAFETY: `fake_c_bitmap` can be used as one-element array of expected length.
> > + let b = unsafe { CBitmap::from_raw(core::ptr::addr_of!(fake_c_bitmap), 8) };
> > + assert_eq!(8, b.len());
> > + assert_eq!(None, b.next_zero_bit(0));
> > + }
> > +
> > + #[test]
> > + fn bitmap_new() {
> > + let b = Bitmap::new(0, GFP_KERNEL).unwrap();
> > + assert_eq!(0, b.len());
> > +
> > + let b = Bitmap::new(3, GFP_KERNEL).unwrap();
> > + assert_eq!(3, b.len());
> > +
> > + let b = Bitmap::new(1024, GFP_KERNEL).unwrap();
> > + assert_eq!(1024, b.len());
> > +
> > + // Requesting too large values results in [`AllocError`].
> > + let b = Bitmap::new(1 << 31, GFP_KERNEL);
> > + assert!(b.is_err());
> > + }
> > +
> > + #[test]
> > + fn bitmap_set_clear_find() {
> > + let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
> > +
> > + // Zero-initialized
> > + assert_eq!(None, b.next_bit(0));
> > + assert_eq!(Some(0), b.next_zero_bit(0));
> > + assert_eq!(None, b.last_bit());
> > +
> > + b.set_bit(17);
> > +
> > + assert_eq!(Some(17), b.next_bit(0));
> > + assert_eq!(Some(17), b.next_bit(17));
> > + assert_eq!(None, b.next_bit(18));
> > + assert_eq!(Some(17), b.last_bit());
> > +
> > + b.set_bit(107);
> > +
> > + assert_eq!(Some(17), b.next_bit(0));
> > + assert_eq!(Some(17), b.next_bit(17));
> > + assert_eq!(Some(107), b.next_bit(18));
> > + assert_eq!(Some(107), b.last_bit());
> > +
> > + b.clear_bit(17);
> > +
> > + assert_eq!(Some(107), b.next_bit(0));
> > + assert_eq!(Some(107), b.last_bit());
> > + }
> > +
> > + #[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> > + #[test]
> > + fn bitmap_out_of_bounds() {
> > + let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
> > +
> > + b.set_bit(2048);
> > + b.set_bit_atomic(2048);
> > + b.clear_bit(2048);
> > + b.clear_bit_atomic(2048);
> > + assert_eq!(None, b.next_bit(2048));
> > + assert_eq!(None, b.next_zero_bit(2048));
> > + assert_eq!(None, b.last_bit());
> > + }
> > +
> > + #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
> > + #[test]
> > + #[should_panic]
> > + fn bitmap_out_of_bounds() {
>
> I don't think we have #[should_panic] support in Rust KUnit yet.
>
True, I observed the panic but the test is erroneously marked as failing.
I have commented it out and added TODO to enable it once
[should_panic] is supported.
> > + let mut b = Bitmap::new(128, GFP_KERNEL).unwrap();
> > +
> > + b.set_bit(2048);
> > + }
> > +
> > + #[test]
> > + fn bitmap_copy_and_extend() {
> > + let mut long_bitmap = Bitmap::new(256, GFP_KERNEL).unwrap();
> > +
> > + long_bitmap.set_bit(3);
> > + long_bitmap.set_bit(200);
> > +
> > + let mut short_bitmap = Bitmap::new(32, GFP_KERNEL).unwrap();
> > +
> > + short_bitmap.set_bit(17);
> > +
> > + long_bitmap.copy_and_extend(&short_bitmap);
> > +
> > + // Previous bits have been cleared.
> > + assert_eq!(Some(17), long_bitmap.next_bit(0));
> > + assert_eq!(Some(17), long_bitmap.last_bit());
> > + }
> > +}
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index de07aadd1ff5..8c4161cd82ac 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -38,6 +38,7 @@
> > pub use ffi;
> >
> > pub mod alloc;
> > +pub mod bitmap;
> > #[cfg(CONFIG_BLOCK)]
> > pub mod block;
> > #[doc(hidden)]
> > diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> > index 3fe9d7b945c4..d77a39aef554 100644
> > --- a/security/Kconfig.hardening
> > +++ b/security/Kconfig.hardening
> > @@ -324,6 +324,16 @@ config LIST_HARDENED
> >
> > If unsure, say N.
> >
> > +config RUST_BITMAP_HARDENED
> > + bool "Check integrity of bitmap Rust API"
> > + depends on RUST
> > + help
> > + Enables additional assertions in the Rust Bitmap API to catch
> > + arguments that are not guaranteed to result in an immediate access
> > + fault.
> > +
> > + If unsure, say N.
> > +
> > config BUG_ON_DATA_CORRUPTION
> > bool "Trigger a BUG when data corruption is detected"
> > select LIST_HARDENED
> > --
> > 2.50.0.rc1.591.g9c95f17f64-goog
> >
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-12 8:46 ` Burak Emir
@ 2025-06-12 8:49 ` Alice Ryhl
2025-06-12 9:04 ` Burak Emir
2025-06-12 9:52 ` Miguel Ojeda
1 sibling, 1 reply; 18+ messages in thread
From: Alice Ryhl @ 2025-06-12 8:49 UTC (permalink / raw)
To: Burak Emir
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Thu, Jun 12, 2025 at 10:47 AM Burak Emir <bqe@google.com> wrote:
>
> On Wed, Jun 11, 2025 at 11:58 PM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > On Wed, Jun 11, 2025 at 9:48 PM Burak Emir <bqe@google.com> wrote:
> [...]
> > > diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
> > > new file mode 100644
> > > index 000000000000..1fe72ca980ac
> > > --- /dev/null
> > > +++ b/rust/kernel/bitmap.rs
> > > @@ -0,0 +1,582 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +
> > > +// Copyright (C) 2025 Google LLC.
> > > +
> > > +//! Rust API for bitmap.
> > > +//!
> > > +//! C headers: [`include/linux/bitmap.h`](srctree/include/linux/bitmap.h).
> > > +
> > > +use crate::alloc::{AllocError, Flags};
> > > +use crate::bindings;
> > > +#[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> > > +use crate::pr_err;
> > > +use core::ptr::NonNull;
> > > +
> > > +/// Represents a C bitmap. Wraps underlying C bitmap API.
> > > +///
> > > +/// # Invariants
> > > +///
> > > +/// Must reference a `[c_ulong]` long enough to fit `data.len()` bits.
> > > +#[cfg_attr(CONFIG_64BIT, repr(align(8)))]
> > > +#[cfg_attr(not(CONFIG_64BIT), repr(align(4)))]
> > > +pub struct CBitmap {
> > > + data: [()],
> > > +}
> >
> > I wonder if we should just call this type Bitmap?
> >
>
> OK. I am renaming the other type to OwnedBitmap then.
Just thinking a bit more about naming ... how about calling it
BitmapVec? Rust generally uses the terminology "Vec" to refer to
arrays whose size is not known at compile-time, and "Array" when the
size is known. Then, if we eventually add another type for declaring
fixed-size bitmaps in Rust, that type can be BitmapArray (that's the
type you'll want in a global).
Alice
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-12 8:49 ` Alice Ryhl
@ 2025-06-12 9:04 ` Burak Emir
0 siblings, 0 replies; 18+ messages in thread
From: Burak Emir @ 2025-06-12 9:04 UTC (permalink / raw)
To: Alice Ryhl
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Thu, Jun 12, 2025 at 10:49 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> On Thu, Jun 12, 2025 at 10:47 AM Burak Emir <bqe@google.com> wrote:
> >
> > On Wed, Jun 11, 2025 at 11:58 PM Alice Ryhl <aliceryhl@google.com> wrote:
> > >
> > > On Wed, Jun 11, 2025 at 9:48 PM Burak Emir <bqe@google.com> wrote:
> > [...]
> > > > diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
> > > > new file mode 100644
> > > > index 000000000000..1fe72ca980ac
> > > > --- /dev/null
> > > > +++ b/rust/kernel/bitmap.rs
> > > > @@ -0,0 +1,582 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +
> > > > +// Copyright (C) 2025 Google LLC.
> > > > +
> > > > +//! Rust API for bitmap.
> > > > +//!
> > > > +//! C headers: [`include/linux/bitmap.h`](srctree/include/linux/bitmap.h).
> > > > +
> > > > +use crate::alloc::{AllocError, Flags};
> > > > +use crate::bindings;
> > > > +#[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
> > > > +use crate::pr_err;
> > > > +use core::ptr::NonNull;
> > > > +
> > > > +/// Represents a C bitmap. Wraps underlying C bitmap API.
> > > > +///
> > > > +/// # Invariants
> > > > +///
> > > > +/// Must reference a `[c_ulong]` long enough to fit `data.len()` bits.
> > > > +#[cfg_attr(CONFIG_64BIT, repr(align(8)))]
> > > > +#[cfg_attr(not(CONFIG_64BIT), repr(align(4)))]
> > > > +pub struct CBitmap {
> > > > + data: [()],
> > > > +}
> > >
> > > I wonder if we should just call this type Bitmap?
> > >
> >
> > OK. I am renaming the other type to OwnedBitmap then.
>
> Just thinking a bit more about naming ... how about calling it
> BitmapVec? Rust generally uses the terminology "Vec" to refer to
> arrays whose size is not known at compile-time, and "Array" when the
> size is known. Then, if we eventually add another type for declaring
> fixed-size bitmaps in Rust, that type can be BitmapArray (that's the
> type you'll want in a global).
It sounds good, better than OwnedBitmap.
My only hesitation is that BitmapVec does not support growing (or realloc).
On the other hand, we could support that in the future so it still makes sense.
cheers,
Burak
^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-12 8:46 ` Burak Emir
2025-06-12 8:49 ` Alice Ryhl
@ 2025-06-12 9:52 ` Miguel Ojeda
2025-06-19 9:32 ` Burak Emir
1 sibling, 1 reply; 18+ messages in thread
From: Miguel Ojeda @ 2025-06-12 9:52 UTC (permalink / raw)
To: Burak Emir
Cc: Alice Ryhl, Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Thu, Jun 12, 2025 at 10:47 AM Burak Emir <bqe@google.com> wrote:
>
> True, I observed the panic but the test is erroneously marked as failing.
> I have commented it out and added TODO to enable it once
> [should_panic] is supported.
No, please do not use `unwrap()`.
Instead, tests are supposed to be written as you would normally write
kernel code as much as possible, i.e. fallible.
We also have now support for tests that return `-> Result`, so you can
e.g. use the `?` operator.
Thanks!
Cheers,
Miguel
^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-12 9:52 ` Miguel Ojeda
@ 2025-06-19 9:32 ` Burak Emir
0 siblings, 0 replies; 18+ messages in thread
From: Burak Emir @ 2025-06-19 9:32 UTC (permalink / raw)
To: Miguel Ojeda
Cc: Alice Ryhl, Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Thu, Jun 12, 2025 at 11:53 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Thu, Jun 12, 2025 at 10:47 AM Burak Emir <bqe@google.com> wrote:
> >
> > True, I observed the panic but the test is erroneously marked as failing.
> > I have commented it out and added TODO to enable it once
> > [should_panic] is supported.
>
> No, please do not use `unwrap()`.
>
> Instead, tests are supposed to be written as you would normally write
> kernel code as much as possible, i.e. fallible.
>
> We also have now support for tests that return `-> Result`, so you can
> e.g. use the `?` operator.
Point taken about unwrap(), I will update all unit tests to return a result.
The lack for [should_panic] support remains
(CONFIG_RUST_BITMAP_HARDENED is intended to produce a panic which
would be nice to test), so I can only comment out the test.
Thanks,
Burak
^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-11 19:48 ` [PATCH v12 3/5] rust: add bitmap API Burak Emir
2025-06-11 21:58 ` Alice Ryhl
@ 2025-06-16 10:49 ` Alice Ryhl
2025-06-19 9:49 ` Burak Emir
1 sibling, 1 reply; 18+ messages in thread
From: Alice Ryhl @ 2025-06-16 10:49 UTC (permalink / raw)
To: Burak Emir
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Wed, Jun 11, 2025 at 9:48 PM Burak Emir <bqe@google.com> wrote:
> +impl core::ops::DerefMut for Bitmap {
> + fn deref_mut(&mut self) -> &mut CBitmap {
> + let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
> + // SAFETY: Bitmap is represented inline.
> + unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
> + } else {
> + // SAFETY: Bitmap is represented as array of `unsigned long`.
> + unsafe { self.repr.ptr.as_mut() }
Nit: You want NonNull::as_mut_ptr() here.
Alice
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-16 10:49 ` Alice Ryhl
@ 2025-06-19 9:49 ` Burak Emir
2025-06-19 10:50 ` Alice Ryhl
0 siblings, 1 reply; 18+ messages in thread
From: Burak Emir @ 2025-06-19 9:49 UTC (permalink / raw)
To: Alice Ryhl
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Mon, Jun 16, 2025 at 12:49 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
> On Wed, Jun 11, 2025 at 9:48 PM Burak Emir <bqe@google.com> wrote:
> > +impl core::ops::DerefMut for Bitmap {
> > + fn deref_mut(&mut self) -> &mut CBitmap {
> > + let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
> > + // SAFETY: Bitmap is represented inline.
> > + unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
> > + } else {
> > + // SAFETY: Bitmap is represented as array of `unsigned long`.
> > + unsafe { self.repr.ptr.as_mut() }
>
> Nit: You want NonNull::as_mut_ptr() here.
Can you explain? That seems to be an unstable method that exists so
one can get pointer to slice buffer.
The repr.ptr case is NonNull<usize>, not a slice - though "morally",
it is actually an owned C array.
Are you suggesting we could/should represent it as a Rust one?
However, we'd like it to use the C API to free etc.
Thanks,
Burak
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [PATCH v12 3/5] rust: add bitmap API.
2025-06-19 9:49 ` Burak Emir
@ 2025-06-19 10:50 ` Alice Ryhl
0 siblings, 0 replies; 18+ messages in thread
From: Alice Ryhl @ 2025-06-19 10:50 UTC (permalink / raw)
To: Burak Emir
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Thu, Jun 19, 2025 at 11:49 AM Burak Emir <bqe@google.com> wrote:
>
> On Mon, Jun 16, 2025 at 12:49 PM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > On Wed, Jun 11, 2025 at 9:48 PM Burak Emir <bqe@google.com> wrote:
> > > +impl core::ops::DerefMut for Bitmap {
> > > + fn deref_mut(&mut self) -> &mut CBitmap {
> > > + let ptr = if self.nbits <= bindings::BITS_PER_LONG as _ {
> > > + // SAFETY: Bitmap is represented inline.
> > > + unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
> > > + } else {
> > > + // SAFETY: Bitmap is represented as array of `unsigned long`.
> > > + unsafe { self.repr.ptr.as_mut() }
> >
> > Nit: You want NonNull::as_mut_ptr() here.
>
> Can you explain? That seems to be an unstable method that exists so
> one can get pointer to slice buffer.
>
> The repr.ptr case is NonNull<usize>, not a slice - though "morally",
> it is actually an owned C array.
> Are you suggesting we could/should represent it as a Rust one?
> However, we'd like it to use the C API to free etc.
Sorry I meant NonNull::as_ptr() which returns a mutable pointer:
https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.as_ptr
Alice
^ permalink raw reply [flat|nested] 18+ messages in thread
* [PATCH v12 4/5] rust: add find_bit_benchmark_rust module.
2025-06-11 19:48 [PATCH v12 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
` (2 preceding siblings ...)
2025-06-11 19:48 ` [PATCH v12 3/5] rust: add bitmap API Burak Emir
@ 2025-06-11 19:48 ` Burak Emir
2025-06-12 8:58 ` Alice Ryhl
2025-06-11 19:48 ` [PATCH v12 5/5] rust: add dynamic ID pool abstraction for bitmap Burak Emir
4 siblings, 1 reply; 18+ messages in thread
From: Burak Emir @ 2025-06-11 19:48 UTC (permalink / raw)
To: Yury Norov, Kees Cook
Cc: Burak Emir, Rasmus Villemoes, Viresh Kumar, Miguel Ojeda,
Alex Gaynor, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
Microbenchmark protected by a config FIND_BIT_BENCHMARK_RUST,
following `find_bit_benchmark.c` but testing the Rust Bitmap API.
We add a fill_random() method protected by the config in order to
maintain the abstraction.
The sample output from the benchmark, both C and Rust version:
find_bit_benchmark.c output:
```
Start testing find_bit() with random-filled bitmap
[ 438.101937] find_next_bit: 860188 ns, 163419 iterations
[ 438.109471] find_next_zero_bit: 912342 ns, 164262 iterations
[ 438.116820] find_last_bit: 726003 ns, 163419 iterations
[ 438.130509] find_nth_bit: 7056993 ns, 16269 iterations
[ 438.139099] find_first_bit: 1963272 ns, 16270 iterations
[ 438.173043] find_first_and_bit: 27314224 ns, 32654 iterations
[ 438.180065] find_next_and_bit: 398752 ns, 73705 iterations
[ 438.186689]
Start testing find_bit() with sparse bitmap
[ 438.193375] find_next_bit: 9675 ns, 656 iterations
[ 438.201765] find_next_zero_bit: 1766136 ns, 327025 iterations
[ 438.208429] find_last_bit: 9017 ns, 656 iterations
[ 438.217816] find_nth_bit: 2749742 ns, 655 iterations
[ 438.225168] find_first_bit: 721799 ns, 656 iterations
[ 438.231797] find_first_and_bit: 2819 ns, 1 iterations
[ 438.238441] find_next_and_bit: 3159 ns, 1 iterations
```
find_bit_benchmark_rust.rs output:
```
[ 451.182459] find_bit_benchmark_rust:
[ 451.186688] Start testing find_bit() Rust with random-filled bitmap
[ 451.194450] next_bit: 777950 ns, 163644 iterations
[ 451.201997] next_zero_bit: 918889 ns, 164036 iterations
[ 451.208642] Start testing find_bit() Rust with sparse bitmap
[ 451.214300] next_bit: 9181 ns, 654 iterations
[ 451.222806] next_zero_bit: 1855504 ns, 327026 iterations
```
Here are the results from 32 samples, with 95% confidence interval.
The microbenchmark was built with RUST_BITMAP_HARDENED=n and run on a
machine that did not execute other processes.
Random-filled bitmap:
+-----------+-------+-----------+--------------+-----------+-----------+
| Benchmark | Lang | Mean (ms) | Std Dev (ms) | 95% CI Lo | 95% CI Hi |
+-----------+-------+-----------+--------------+-----------+-----------+
| find_bit/ | C | 825.07 | 53.89 | 806.40 | 843.74 |
| next_bit | Rust | 870.91 | 46.29 | 854.88 | 886.95 |
+-----------+-------+-----------+--------------+-----------+-----------+
| find_zero/| C | 933.56 | 56.34 | 914.04 | 953.08 |
| next_zero | Rust | 945.85 | 60.44 | 924.91 | 966.79 |
+-----------+-------+-----------+--------------+-----------+-----------+
Rust appears 5.5% slower for next_bit, 1.3% slower for next_zero.
Sparse bitmap:
+-----------+-------+-----------+--------------+-----------+-----------+
| Benchmark | Lang | Mean (ms) | Std Dev (ms) | 95% CI Lo | 95% CI Hi |
+-----------+-------+-----------+--------------+-----------+-----------+
| find_bit/ | C | 13.17 | 6.21 | 11.01 | 15.32 |
| next_bit | Rust | 14.30 | 8.27 | 11.43 | 17.17 |
+-----------+-------+-----------+--------------+-----------+-----------+
| find_zero/| C | 1859.31 | 82.30 | 1830.80 | 1887.83 |
| next_zero | Rust | 1908.09 | 139.82 | 1859.65 | 1956.54 |
+-----------+-------+-----------+--------------+-----------+-----------+
Rust appears 8.5% slower for next_bit, 2.6% slower for next_zero.
In summary, taking the arithmetic mean of all slow-downs, we can say
the Rust API has a 4.5% slowdown.
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Suggested-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Reviewed-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Signed-off-by: Burak Emir <bqe@google.com>
---
MAINTAINERS | 1 +
lib/Kconfig.debug | 13 ++++
lib/Makefile | 1 +
lib/find_bit_benchmark_rust.rs | 103 ++++++++++++++++++++++++++++++++
rust/bindings/bindings_helper.h | 1 +
rust/kernel/bitmap.rs | 15 +++++
6 files changed, 134 insertions(+)
create mode 100644 lib/find_bit_benchmark_rust.rs
diff --git a/MAINTAINERS b/MAINTAINERS
index 565eaa015d9e..943d85ed1876 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4132,6 +4132,7 @@ M: Alice Ryhl <aliceryhl@google.com>
M: Burak Emir <bqe@google.com>
R: Yury Norov <yury.norov@gmail.com>
S: Maintained
+F: lib/find_bit_benchmark_rust.rs
F: rust/kernel/bitmap.rs
BITOPS API
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f9051ab610d5..d8ed53f35495 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2605,6 +2605,19 @@ config FIND_BIT_BENCHMARK
If unsure, say N.
+config FIND_BIT_BENCHMARK_RUST
+ tristate "Test find_bit functions in Rust"
+ depends on RUST
+ help
+ This builds the "find_bit_benchmark_rust" module. It is a micro
+ benchmark that measures the performance of Rust functions that
+ correspond to the find_*_bit() operations in C. It follows the
+ FIND_BIT_BENCHMARK closely but will in general not yield same
+ numbers due to extra bounds checks and overhead of foreign
+ function calls.
+
+ If unsure, say N.
+
config TEST_FIRMWARE
tristate "Test firmware loading via userspace interface"
depends on FW_LOADER
diff --git a/lib/Makefile b/lib/Makefile
index f07b24ce1b3f..99e49a8f5bf8 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -62,6 +62,7 @@ obj-y += hexdump.o
obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
obj-y += kstrtox.o
obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
+obj-$(CONFIG_FIND_BIT_BENCHMARK_RUST) += find_bit_benchmark_rust.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
test_dhry-objs := dhry_1.o dhry_2.o dhry_run.o
obj-$(CONFIG_TEST_DHRY) += test_dhry.o
diff --git a/lib/find_bit_benchmark_rust.rs b/lib/find_bit_benchmark_rust.rs
new file mode 100644
index 000000000000..29464c2a148b
--- /dev/null
+++ b/lib/find_bit_benchmark_rust.rs
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+//! Benchmark for find_bit-like methods in Bitmap Rust API.
+
+use kernel::alloc::flags::GFP_KERNEL;
+use kernel::bindings;
+use kernel::bitmap::Bitmap;
+use kernel::error::{code, Result};
+use kernel::prelude::module;
+use kernel::time::Ktime;
+use kernel::ThisModule;
+use kernel::{pr_cont, pr_err};
+
+const BITMAP_LEN: usize = 4096 * 8 * 10;
+// Reciprocal of the fraction of bits that are set in sparse bitmap.
+const SPARSENESS: usize = 500;
+
+/// Test module that benchmarks performance of traversing bitmaps.
+struct Benchmark();
+
+fn test_next_bit(bitmap: &Bitmap) {
+ let mut time = Ktime::ktime_get();
+ let mut cnt = 0;
+ let mut i = 0;
+
+ while let Some(index) = bitmap.next_bit(i) {
+ cnt += 1;
+ i = index + 1;
+ // CONFIG_RUST_BITMAP_HARDENED enforces strict bounds.
+ if i == BITMAP_LEN {
+ break;
+ }
+ }
+
+ time = Ktime::ktime_get() - time;
+ pr_cont!(
+ "next_bit: {:18} ns, {:6} iterations\n",
+ time.to_ns(),
+ cnt
+ );
+}
+
+fn test_next_zero_bit(bitmap: &Bitmap) {
+ let mut time = Ktime::ktime_get();
+ let mut cnt = 0;
+ let mut i = 0;
+
+ while let Some(index) = bitmap.next_zero_bit(i) {
+ cnt += 1;
+ i = index + 1;
+ // CONFIG_RUST_BITMAP_HARDENED enforces strict bounds.
+ if i == BITMAP_LEN {
+ break;
+ }
+ }
+
+ time = Ktime::ktime_get() - time;
+ pr_cont!(
+ "next_zero_bit: {:18} ns, {:6} iterations\n",
+ time.to_ns(),
+ cnt
+ );
+}
+
+fn find_bit_test() {
+ pr_err!("\n");
+ pr_cont!("Start testing find_bit() Rust with random-filled bitmap\n");
+
+ let mut bitmap = Bitmap::new(BITMAP_LEN, GFP_KERNEL).expect("alloc bitmap failed");
+ bitmap.fill_random();
+
+ test_next_bit(&bitmap);
+ test_next_zero_bit(&bitmap);
+
+ pr_cont!("Start testing find_bit() Rust with sparse bitmap\n");
+
+ let mut bitmap = Bitmap::new(BITMAP_LEN, GFP_KERNEL).expect("alloc sparse bitmap failed");
+ let nbits = BITMAP_LEN / SPARSENESS;
+ for _i in 0..nbits {
+ // SAFETY: BITMAP_LEN fits in 32 bits.
+ let bit: usize =
+ unsafe { bindings::__get_random_u32_below(BITMAP_LEN.try_into().unwrap()) as _ };
+ bitmap.set_bit(bit);
+ }
+
+ test_next_bit(&bitmap);
+ test_next_zero_bit(&bitmap);
+}
+
+impl kernel::Module for Benchmark {
+ fn init(_module: &'static ThisModule) -> Result<Self> {
+ find_bit_test();
+ // Return error so test module can be inserted again without rmmod.
+ Err(code::EINVAL)
+ }
+}
+
+module! {
+ type: Benchmark,
+ name: "find_bit_benchmark_rust",
+ authors: ["Burak Emir <bqe@google.com>"],
+ description: "Module with benchmark for bitmap Rust API",
+ license: "GPL v2",
+}
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index b6bf3b039c1b..f6ca7f1dd08b 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -31,6 +31,7 @@
#include <linux/platform_device.h>
#include <linux/poll.h>
#include <linux/property.h>
+#include <linux/random.h>
#include <linux/refcount.h>
#include <linux/sched.h>
#include <linux/security.h>
diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
index 1fe72ca980ac..f05a23e54fbf 100644
--- a/rust/kernel/bitmap.rs
+++ b/rust/kernel/bitmap.rs
@@ -253,6 +253,21 @@ pub fn new(nbits: usize, flags: Flags) -> Result<Self, AllocError> {
pub fn len(&self) -> usize {
self.nbits
}
+
+ /// Fills this `Bitmap` with random bits.
+ #[cfg(CONFIG_FIND_BIT_BENCHMARK_RUST)]
+ pub fn fill_random(&mut self) {
+ // SAFETY: `self.as_mut_ptr` points to either an array of the
+ // appropriate length or one usize.
+ unsafe {
+ bindings::get_random_bytes(
+ self.as_mut_ptr() as *mut ffi::c_void,
+ usize::div_ceil(self.nbits, bindings::BITS_PER_LONG as usize)
+ * bindings::BITS_PER_LONG as usize
+ / 8,
+ );
+ }
+ }
}
impl CBitmap {
--
2.50.0.rc1.591.g9c95f17f64-goog
^ permalink raw reply related [flat|nested] 18+ messages in thread* Re: [PATCH v12 4/5] rust: add find_bit_benchmark_rust module.
2025-06-11 19:48 ` [PATCH v12 4/5] rust: add find_bit_benchmark_rust module Burak Emir
@ 2025-06-12 8:58 ` Alice Ryhl
0 siblings, 0 replies; 18+ messages in thread
From: Alice Ryhl @ 2025-06-12 8:58 UTC (permalink / raw)
To: Burak Emir
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Wed, Jun 11, 2025 at 07:48:37PM +0000, Burak Emir wrote:
> + let mut bitmap = Bitmap::new(BITMAP_LEN, GFP_KERNEL).expect("alloc sparse bitmap failed");
> + let nbits = BITMAP_LEN / SPARSENESS;
> + for _i in 0..nbits {
> + // SAFETY: BITMAP_LEN fits in 32 bits.
> + let bit: usize =
> + unsafe { bindings::__get_random_u32_below(BITMAP_LEN.try_into().unwrap()) as _ };
This safety comment argues why the .unwrap() will not result in a panic,
but it should instead argue why the call to __get_random_u32_below() is
okay. I guess that it's because __get_random_u32_below() is always safe
to call?
I'm not a big fan of these .try_into().unwrap() conversions. I would
probably just have written `BITMAP_LEN as u32`. But I know that this is
a point of disagreement with other Rust maintainers.
Alice
^ permalink raw reply [flat|nested] 18+ messages in thread
* [PATCH v12 5/5] rust: add dynamic ID pool abstraction for bitmap
2025-06-11 19:48 [PATCH v12 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
` (3 preceding siblings ...)
2025-06-11 19:48 ` [PATCH v12 4/5] rust: add find_bit_benchmark_rust module Burak Emir
@ 2025-06-11 19:48 ` Burak Emir
2025-06-12 9:09 ` Alice Ryhl
4 siblings, 1 reply; 18+ messages in thread
From: Burak Emir @ 2025-06-11 19:48 UTC (permalink / raw)
To: Yury Norov, Kees Cook
Cc: Burak Emir, Rasmus Villemoes, Viresh Kumar, Miguel Ojeda,
Alex Gaynor, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
This is a port of the Binder data structure introduced in commit
15d9da3f818c ("binder: use bitmap for faster descriptor lookup") to
Rust.
Like drivers/android/dbitmap.h, the ID pool abstraction lets
clients acquire and release IDs. The implementation uses a bitmap to
know what IDs are in use, and gives clients fine-grained control over
the time of allocation. This fine-grained control is needed in the
Android Binder. We provide an example that release a spinlock for
allocation and unit tests (rustdoc examples).
The implementation does not permit shrinking below capacity below
BITS_PER_LONG.
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Burak Emir <bqe@google.com>
---
MAINTAINERS | 1 +
rust/kernel/id_pool.rs | 223 +++++++++++++++++++++++++++++++++++++++++
rust/kernel/lib.rs | 1 +
3 files changed, 225 insertions(+)
create mode 100644 rust/kernel/id_pool.rs
diff --git a/MAINTAINERS b/MAINTAINERS
index 943d85ed1876..bc95d98f266b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4134,6 +4134,7 @@ R: Yury Norov <yury.norov@gmail.com>
S: Maintained
F: lib/find_bit_benchmark_rust.rs
F: rust/kernel/bitmap.rs
+F: rust/kernel/id_pool.rs
BITOPS API
M: Yury Norov <yury.norov@gmail.com>
diff --git a/rust/kernel/id_pool.rs b/rust/kernel/id_pool.rs
new file mode 100644
index 000000000000..355a8ae93268
--- /dev/null
+++ b/rust/kernel/id_pool.rs
@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Rust API for an ID pool backed by a [`Bitmap`].
+
+use crate::alloc::{AllocError, Flags};
+use crate::bitmap::Bitmap;
+
+/// Represents a dynamic ID pool backed by a [`Bitmap`].
+///
+/// Clients acquire and release IDs from unset bits in a bitmap.
+///
+/// The capacity of the ID pool may be adjusted by users as
+/// needed. The API supports the scenario where users need precise control
+/// over the time of allocation of a new backing bitmap, which may require
+/// release of spinlock.
+/// Due to concurrent updates, all operations are re-verified to determine
+/// if the grow or shrink is sill valid.
+///
+/// # Examples
+///
+/// Basic usage
+///
+/// ```
+/// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
+/// use kernel::id_pool::IdPool;
+///
+/// let mut pool = IdPool::new(64, GFP_KERNEL)?;
+/// for i in 0..64 {
+/// assert_eq!(i, pool.acquire_next_id(i).ok_or(ENOSPC)?);
+/// }
+///
+/// pool.release_id(23);
+/// assert_eq!(23, pool.acquire_next_id(0).ok_or(ENOSPC)?);
+///
+/// assert_eq!(None, pool.acquire_next_id(0)); // time to realloc.
+/// let resizer = pool.grow_request().ok_or(ENOSPC)?.realloc(GFP_KERNEL)?;
+/// pool.grow(resizer);
+///
+/// assert_eq!(pool.acquire_next_id(0), Some(64));
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// Releasing spinlock to grow the pool
+///
+/// ```no_run
+/// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
+/// use kernel::sync::{new_spinlock, SpinLock};
+/// use kernel::id_pool::IdPool;
+///
+/// fn get_id_maybe_realloc(guarded_pool: &SpinLock<IdPool>) -> Result<usize, AllocError> {
+/// let mut pool = guarded_pool.lock();
+/// loop {
+/// match pool.acquire_next_id(0) {
+/// Some(index) => return Ok(index),
+/// None => {
+/// let alloc_request = pool.grow_request();
+/// drop(pool);
+/// let resizer = alloc_request.ok_or(AllocError)?.realloc(GFP_KERNEL)?;
+/// pool = guarded_pool.lock();
+/// pool.grow(resizer)
+/// }
+/// }
+/// }
+/// }
+/// ```
+pub struct IdPool {
+ map: Bitmap,
+}
+
+/// Indicates that an [`IdPool`] should change to a new target size.
+pub struct ReallocRequest {
+ num_ids: usize,
+}
+
+/// Contains a [`Bitmap`] of a size suitable for reallocating [`IdPool`].
+pub struct PoolResizer {
+ new: Bitmap,
+}
+
+impl ReallocRequest {
+ /// Allocates a new backing [`Bitmap`] for [`IdPool`].
+ ///
+ /// This method only prepares reallocation and does not complete it.
+ /// Reallocation will complete after passing the [`PoolResizer`] to the
+ /// [`IdPool::grow`] or [`IdPool::shrink`] operation, which will check
+ /// that reallocation still makes sense.
+ pub fn realloc(&self, flags: Flags) -> Result<PoolResizer, AllocError> {
+ let new = Bitmap::new(self.num_ids, flags)?;
+ Ok(PoolResizer { new })
+ }
+}
+
+impl IdPool {
+ /// Constructs a new [`IdPool`].
+ ///
+ /// [BITS_PER_LONG]: srctree/include/asm-generic/bitsperlong.h
+ /// A capacity below [`BITS_PER_LONG`][BITS_PER_LONG] is adjusted to
+ /// [`BITS_PER_LONG`][BITS_PER_LONG].
+ #[inline]
+ pub fn new(num_ids: usize, flags: Flags) -> Result<Self, AllocError> {
+ let num_ids = core::cmp::max(num_ids, bindings::BITS_PER_LONG as usize);
+ let map = Bitmap::new(num_ids, flags)?;
+ Ok(Self { map })
+ }
+
+ /// Returns how many IDs this pool can currently have.
+ #[expect(clippy::len_without_is_empty)]
+ #[inline]
+ pub fn len(&self) -> usize {
+ self.map.len()
+ }
+
+ /// Returns a [`ReallocRequest`] if the [`IdPool`] can be shrunk, [`None`] otherwise.
+ ///
+ /// [BITS_PER_LONG]: srctree/include/asm-generic/bitsperlong.h
+ /// The capacity of an [`IdPool`] cannot be shrunk below [`BITS_PER_LONG`][BITS_PER_LONG].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
+ /// use kernel::id_pool::{ReallocRequest, IdPool};
+ ///
+ /// let mut pool = IdPool::new(1024, GFP_KERNEL)?;
+ /// let alloc_request = pool.shrink_request().ok_or(AllocError)?;
+ /// let resizer = alloc_request.realloc(GFP_KERNEL)?;
+ /// pool.shrink(resizer);
+ /// assert_eq!(pool.len(), kernel::bindings::BITS_PER_LONG as usize);
+ /// # Ok::<(), AllocError>(())
+ /// ```
+ #[inline]
+ pub fn shrink_request(&self) -> Option<ReallocRequest> {
+ let len = self.map.len();
+ // Shrinking below [`BITS_PER_LONG`] is never possible.
+ if len <= bindings::BITS_PER_LONG as usize {
+ return None;
+ }
+ // Determine if the bitmap can shrink based on the position of
+ // its last set bit. If the bit is within the first quarter of
+ // the bitmap then shrinking is possible. In this case, the
+ // bitmap should shrink to half its current size.
+ let Some(bit) = self.map.last_bit() else {
+ return Some(ReallocRequest {
+ num_ids: bindings::BITS_PER_LONG as usize,
+ });
+ };
+ if bit >= (len / 4) {
+ return None;
+ }
+ let num_ids = core::cmp::max(bindings::BITS_PER_LONG as usize, len / 2);
+ Some(ReallocRequest { num_ids })
+ }
+
+ /// Shrinks pool by using a new [`Bitmap`], if still possible.
+ #[inline]
+ pub fn shrink(&mut self, mut resizer: PoolResizer) {
+ // Between request to shrink that led to allocation of `resizer` and now,
+ // bits may have changed.
+ // Verify that shrinking is still possible. In case shrinking to
+ // the size of `resizer` is no longer possible, do nothing,
+ // drop `resizer` and move on.
+ let Some(updated) = self.shrink_request() else {
+ return;
+ };
+ if updated.num_ids > resizer.new.len() {
+ return;
+ }
+
+ resizer.new.copy_and_extend(&self.map);
+ self.map = resizer.new;
+ }
+
+ /// Returns a [`ReallocRequest`] for growing this [`IdPool`], if possible.
+ ///
+ /// The capacity of an [`IdPool`] cannot be grown above [`i32::MAX`].
+ #[inline]
+ pub fn grow_request(&self) -> Option<ReallocRequest> {
+ let num_ids = self.map.len() * 2;
+ if num_ids > i32::MAX.try_into().unwrap() {
+ return None;
+ }
+ Some(ReallocRequest { num_ids })
+ }
+
+ /// Grows pool by using a new [`Bitmap`], if still necessary.
+ ///
+ /// The `resizer` arguments has to be obtained by calling [`Self::grow_request`]
+ /// on this object and performing a [`ReallocRequest::realloc`].
+ #[inline]
+ pub fn grow(&mut self, mut resizer: PoolResizer) {
+ // Between request to grow that led to allocation of `resizer` and now,
+ // another thread may have already grown the capacity.
+ // In this case, do nothing, drop `resizer` and move on.
+ if resizer.new.len() <= self.map.len() {
+ return;
+ }
+
+ resizer.new.copy_and_extend(&self.map);
+ self.map = resizer.new;
+ }
+
+ /// Acquires a new ID by finding and setting the next zero bit in the
+ /// bitmap.
+ ///
+ /// Upon success, returns its index. Otherwise, returns [`None`]
+ /// to indicate that a [`Self::grow_request`] is needed.
+ #[inline]
+ pub fn acquire_next_id(&mut self, offset: usize) -> Option<usize> {
+ let next_zero_bit = self.map.next_zero_bit(offset);
+ if let Some(nr) = next_zero_bit {
+ self.map.set_bit(nr);
+ }
+ next_zero_bit
+ }
+
+ /// Releases an ID.
+ #[inline]
+ pub fn release_id(&mut self, id: usize) {
+ self.map.clear_bit(id);
+ }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 8c4161cd82ac..d7def807900a 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -54,6 +54,7 @@
#[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
pub mod firmware;
pub mod fs;
+pub mod id_pool;
pub mod init;
pub mod io;
pub mod ioctl;
--
2.50.0.rc1.591.g9c95f17f64-goog
^ permalink raw reply related [flat|nested] 18+ messages in thread* Re: [PATCH v12 5/5] rust: add dynamic ID pool abstraction for bitmap
2025-06-11 19:48 ` [PATCH v12 5/5] rust: add dynamic ID pool abstraction for bitmap Burak Emir
@ 2025-06-12 9:09 ` Alice Ryhl
2025-06-20 8:27 ` Burak Emir
0 siblings, 1 reply; 18+ messages in thread
From: Alice Ryhl @ 2025-06-12 9:09 UTC (permalink / raw)
To: Burak Emir
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Wed, Jun 11, 2025 at 07:48:38PM +0000, Burak Emir wrote:
> This is a port of the Binder data structure introduced in commit
> 15d9da3f818c ("binder: use bitmap for faster descriptor lookup") to
> Rust.
>
> Like drivers/android/dbitmap.h, the ID pool abstraction lets
> clients acquire and release IDs. The implementation uses a bitmap to
> know what IDs are in use, and gives clients fine-grained control over
> the time of allocation. This fine-grained control is needed in the
> Android Binder. We provide an example that release a spinlock for
> allocation and unit tests (rustdoc examples).
>
> The implementation does not permit shrinking below capacity below
> BITS_PER_LONG.
>
> Suggested-by: Alice Ryhl <aliceryhl@google.com>
> Suggested-by: Yury Norov <yury.norov@gmail.com>
> Signed-off-by: Burak Emir <bqe@google.com>
> ---
> MAINTAINERS | 1 +
> rust/kernel/id_pool.rs | 223 +++++++++++++++++++++++++++++++++++++++++
> rust/kernel/lib.rs | 1 +
> 3 files changed, 225 insertions(+)
> create mode 100644 rust/kernel/id_pool.rs
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 943d85ed1876..bc95d98f266b 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4134,6 +4134,7 @@ R: Yury Norov <yury.norov@gmail.com>
> S: Maintained
> F: lib/find_bit_benchmark_rust.rs
> F: rust/kernel/bitmap.rs
> +F: rust/kernel/id_pool.rs
>
> BITOPS API
> M: Yury Norov <yury.norov@gmail.com>
> diff --git a/rust/kernel/id_pool.rs b/rust/kernel/id_pool.rs
> new file mode 100644
> index 000000000000..355a8ae93268
> --- /dev/null
> +++ b/rust/kernel/id_pool.rs
> @@ -0,0 +1,223 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2025 Google LLC.
> +
> +//! Rust API for an ID pool backed by a [`Bitmap`].
> +
> +use crate::alloc::{AllocError, Flags};
> +use crate::bitmap::Bitmap;
> +
> +/// Represents a dynamic ID pool backed by a [`Bitmap`].
> +///
> +/// Clients acquire and release IDs from unset bits in a bitmap.
> +///
> +/// The capacity of the ID pool may be adjusted by users as
> +/// needed. The API supports the scenario where users need precise control
> +/// over the time of allocation of a new backing bitmap, which may require
> +/// release of spinlock.
> +/// Due to concurrent updates, all operations are re-verified to determine
> +/// if the grow or shrink is sill valid.
> +///
> +/// # Examples
> +///
> +/// Basic usage
> +///
> +/// ```
> +/// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> +/// use kernel::id_pool::IdPool;
> +///
> +/// let mut pool = IdPool::new(64, GFP_KERNEL)?;
> +/// for i in 0..64 {
> +/// assert_eq!(i, pool.acquire_next_id(i).ok_or(ENOSPC)?);
> +/// }
> +///
> +/// pool.release_id(23);
> +/// assert_eq!(23, pool.acquire_next_id(0).ok_or(ENOSPC)?);
> +///
> +/// assert_eq!(None, pool.acquire_next_id(0)); // time to realloc.
> +/// let resizer = pool.grow_request().ok_or(ENOSPC)?.realloc(GFP_KERNEL)?;
> +/// pool.grow(resizer);
> +///
> +/// assert_eq!(pool.acquire_next_id(0), Some(64));
> +/// # Ok::<(), Error>(())
> +/// ```
> +///
> +/// Releasing spinlock to grow the pool
> +///
> +/// ```no_run
> +/// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> +/// use kernel::sync::{new_spinlock, SpinLock};
> +/// use kernel::id_pool::IdPool;
> +///
> +/// fn get_id_maybe_realloc(guarded_pool: &SpinLock<IdPool>) -> Result<usize, AllocError> {
> +/// let mut pool = guarded_pool.lock();
> +/// loop {
> +/// match pool.acquire_next_id(0) {
> +/// Some(index) => return Ok(index),
> +/// None => {
> +/// let alloc_request = pool.grow_request();
> +/// drop(pool);
> +/// let resizer = alloc_request.ok_or(AllocError)?.realloc(GFP_KERNEL)?;
> +/// pool = guarded_pool.lock();
> +/// pool.grow(resizer)
> +/// }
> +/// }
> +/// }
> +/// }
> +/// ```
These examples use two spaces for indentation, but in Rust we use four
spaces.
> +pub struct IdPool {
> + map: Bitmap,
> +}
> +
> +/// Indicates that an [`IdPool`] should change to a new target size.
> +pub struct ReallocRequest {
> + num_ids: usize,
> +}
> +
> +/// Contains a [`Bitmap`] of a size suitable for reallocating [`IdPool`].
> +pub struct PoolResizer {
> + new: Bitmap,
> +}
> +
> +impl ReallocRequest {
> + /// Allocates a new backing [`Bitmap`] for [`IdPool`].
> + ///
> + /// This method only prepares reallocation and does not complete it.
> + /// Reallocation will complete after passing the [`PoolResizer`] to the
> + /// [`IdPool::grow`] or [`IdPool::shrink`] operation, which will check
> + /// that reallocation still makes sense.
> + pub fn realloc(&self, flags: Flags) -> Result<PoolResizer, AllocError> {
> + let new = Bitmap::new(self.num_ids, flags)?;
> + Ok(PoolResizer { new })
> + }
> +}
> +
> +impl IdPool {
> + /// Constructs a new [`IdPool`].
> + ///
> + /// [BITS_PER_LONG]: srctree/include/asm-generic/bitsperlong.h
> + /// A capacity below [`BITS_PER_LONG`][BITS_PER_LONG] is adjusted to
> + /// [`BITS_PER_LONG`][BITS_PER_LONG].
I'm concerned that this might not render correctly in the html docs.
Markdown links are usually written below the text and with an empty
line:
/// A capacity below [`BITS_PER_LONG`][BITS_PER_LONG] is adjusted to
/// [`BITS_PER_LONG`][BITS_PER_LONG].
///
/// [BITS_PER_LONG]: srctree/include/asm-generic/bitsperlong.h
which can be further simplified to
/// A capacity below [`BITS_PER_LONG`] is adjusted to [`BITS_PER_LONG`].
///
/// [`BITS_PER_LONG`]: srctree/include/asm-generic/bitsperlong.h
Furthermore, if you declare a public BITS_PER_LONG constant on the Rust
side like I suggested in my reply to one of the other patches, then it
will automatically link to that if you've imported it with `use` and
don't specify a link target:
use kernel::bitmap::BITS_PER_LONG;
/// A capacity below [`BITS_PER_LONG`] is adjusted to [`BITS_PER_LONG`].
Same applies to other docs that link to this constant.
> + #[inline]
> + pub fn new(num_ids: usize, flags: Flags) -> Result<Self, AllocError> {
> + let num_ids = core::cmp::max(num_ids, bindings::BITS_PER_LONG as usize);
Nit: I like to write usize::max(...) instead of core::cmp::max(...),
which I think reads better.
> + let map = Bitmap::new(num_ids, flags)?;
> + Ok(Self { map })
> + }
> +
> + /// Returns how many IDs this pool can currently have.
> + #[expect(clippy::len_without_is_empty)]
> + #[inline]
> + pub fn len(&self) -> usize {
Maybe this should be called capacity() instead? Or maybe we just don't
have this method at all.
Alice
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [PATCH v12 5/5] rust: add dynamic ID pool abstraction for bitmap
2025-06-12 9:09 ` Alice Ryhl
@ 2025-06-20 8:27 ` Burak Emir
0 siblings, 0 replies; 18+ messages in thread
From: Burak Emir @ 2025-06-20 8:27 UTC (permalink / raw)
To: Alice Ryhl
Cc: Yury Norov, Kees Cook, Rasmus Villemoes, Viresh Kumar,
Miguel Ojeda, Alex Gaynor, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Trevor Gross, Gustavo A . R . Silva, Carlos LLama, Pekka Ristola,
rust-for-linux, linux-kernel, linux-hardening
On Thu, Jun 12, 2025 at 11:09 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> On Wed, Jun 11, 2025 at 07:48:38PM +0000, Burak Emir wrote:
> > This is a port of the Binder data structure introduced in commit
> > 15d9da3f818c ("binder: use bitmap for faster descriptor lookup") to
> > Rust.
> >
> > Like drivers/android/dbitmap.h, the ID pool abstraction lets
> > clients acquire and release IDs. The implementation uses a bitmap to
> > know what IDs are in use, and gives clients fine-grained control over
> > the time of allocation. This fine-grained control is needed in the
> > Android Binder. We provide an example that release a spinlock for
> > allocation and unit tests (rustdoc examples).
> >
> > The implementation does not permit shrinking below capacity below
> > BITS_PER_LONG.
> >
> > Suggested-by: Alice Ryhl <aliceryhl@google.com>
> > Suggested-by: Yury Norov <yury.norov@gmail.com>
> > Signed-off-by: Burak Emir <bqe@google.com>
> > ---
> > MAINTAINERS | 1 +
> > rust/kernel/id_pool.rs | 223 +++++++++++++++++++++++++++++++++++++++++
> > rust/kernel/lib.rs | 1 +
> > 3 files changed, 225 insertions(+)
> > create mode 100644 rust/kernel/id_pool.rs
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 943d85ed1876..bc95d98f266b 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -4134,6 +4134,7 @@ R: Yury Norov <yury.norov@gmail.com>
> > S: Maintained
> > F: lib/find_bit_benchmark_rust.rs
> > F: rust/kernel/bitmap.rs
> > +F: rust/kernel/id_pool.rs
> >
> > BITOPS API
> > M: Yury Norov <yury.norov@gmail.com>
> > diff --git a/rust/kernel/id_pool.rs b/rust/kernel/id_pool.rs
> > new file mode 100644
> > index 000000000000..355a8ae93268
> > --- /dev/null
> > +++ b/rust/kernel/id_pool.rs
> > @@ -0,0 +1,223 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +// Copyright (C) 2025 Google LLC.
> > +
> > +//! Rust API for an ID pool backed by a [`Bitmap`].
> > +
> > +use crate::alloc::{AllocError, Flags};
> > +use crate::bitmap::Bitmap;
> > +
> > +/// Represents a dynamic ID pool backed by a [`Bitmap`].
> > +///
> > +/// Clients acquire and release IDs from unset bits in a bitmap.
> > +///
> > +/// The capacity of the ID pool may be adjusted by users as
> > +/// needed. The API supports the scenario where users need precise control
> > +/// over the time of allocation of a new backing bitmap, which may require
> > +/// release of spinlock.
> > +/// Due to concurrent updates, all operations are re-verified to determine
> > +/// if the grow or shrink is sill valid.
> > +///
> > +/// # Examples
> > +///
> > +/// Basic usage
> > +///
> > +/// ```
> > +/// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> > +/// use kernel::id_pool::IdPool;
> > +///
> > +/// let mut pool = IdPool::new(64, GFP_KERNEL)?;
> > +/// for i in 0..64 {
> > +/// assert_eq!(i, pool.acquire_next_id(i).ok_or(ENOSPC)?);
> > +/// }
> > +///
> > +/// pool.release_id(23);
> > +/// assert_eq!(23, pool.acquire_next_id(0).ok_or(ENOSPC)?);
> > +///
> > +/// assert_eq!(None, pool.acquire_next_id(0)); // time to realloc.
> > +/// let resizer = pool.grow_request().ok_or(ENOSPC)?.realloc(GFP_KERNEL)?;
> > +/// pool.grow(resizer);
> > +///
> > +/// assert_eq!(pool.acquire_next_id(0), Some(64));
> > +/// # Ok::<(), Error>(())
> > +/// ```
> > +///
> > +/// Releasing spinlock to grow the pool
> > +///
> > +/// ```no_run
> > +/// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
> > +/// use kernel::sync::{new_spinlock, SpinLock};
> > +/// use kernel::id_pool::IdPool;
> > +///
> > +/// fn get_id_maybe_realloc(guarded_pool: &SpinLock<IdPool>) -> Result<usize, AllocError> {
> > +/// let mut pool = guarded_pool.lock();
> > +/// loop {
> > +/// match pool.acquire_next_id(0) {
> > +/// Some(index) => return Ok(index),
> > +/// None => {
> > +/// let alloc_request = pool.grow_request();
> > +/// drop(pool);
> > +/// let resizer = alloc_request.ok_or(AllocError)?.realloc(GFP_KERNEL)?;
> > +/// pool = guarded_pool.lock();
> > +/// pool.grow(resizer)
> > +/// }
> > +/// }
> > +/// }
> > +/// }
> > +/// ```
>
> These examples use two spaces for indentation, but in Rust we use four
> spaces.
>
> > +pub struct IdPool {
> > + map: Bitmap,
> > +}
> > +
> > +/// Indicates that an [`IdPool`] should change to a new target size.
> > +pub struct ReallocRequest {
> > + num_ids: usize,
> > +}
> > +
> > +/// Contains a [`Bitmap`] of a size suitable for reallocating [`IdPool`].
> > +pub struct PoolResizer {
> > + new: Bitmap,
> > +}
> > +
> > +impl ReallocRequest {
> > + /// Allocates a new backing [`Bitmap`] for [`IdPool`].
> > + ///
> > + /// This method only prepares reallocation and does not complete it.
> > + /// Reallocation will complete after passing the [`PoolResizer`] to the
> > + /// [`IdPool::grow`] or [`IdPool::shrink`] operation, which will check
> > + /// that reallocation still makes sense.
> > + pub fn realloc(&self, flags: Flags) -> Result<PoolResizer, AllocError> {
> > + let new = Bitmap::new(self.num_ids, flags)?;
> > + Ok(PoolResizer { new })
> > + }
> > +}
> > +
> > +impl IdPool {
> > + /// Constructs a new [`IdPool`].
> > + ///
> > + /// [BITS_PER_LONG]: srctree/include/asm-generic/bitsperlong.h
> > + /// A capacity below [`BITS_PER_LONG`][BITS_PER_LONG] is adjusted to
> > + /// [`BITS_PER_LONG`][BITS_PER_LONG].
>
> I'm concerned that this might not render correctly in the html docs.
> Markdown links are usually written below the text and with an empty
> line:
>
> /// A capacity below [`BITS_PER_LONG`][BITS_PER_LONG] is adjusted to
> /// [`BITS_PER_LONG`][BITS_PER_LONG].
> ///
> /// [BITS_PER_LONG]: srctree/include/asm-generic/bitsperlong.h
>
> which can be further simplified to
>
> /// A capacity below [`BITS_PER_LONG`] is adjusted to [`BITS_PER_LONG`].
> ///
> /// [`BITS_PER_LONG`]: srctree/include/asm-generic/bitsperlong.h
>
> Furthermore, if you declare a public BITS_PER_LONG constant on the Rust
> side like I suggested in my reply to one of the other patches, then it
> will automatically link to that if you've imported it with `use` and
> don't specify a link target:
>
> use kernel::bitmap::BITS_PER_LONG;
>
> /// A capacity below [`BITS_PER_LONG`] is adjusted to [`BITS_PER_LONG`].
>
> Same applies to other docs that link to this constant.
Previously, there was no BITS_PER_LONG in scope, so to make rustdoc work
I had resorted to clumsy way above. I had tried it locally, but was wondering
whether there is a better way.
In v13, I define a local BITS_PER_LONG usize const as you suggested on
the other file.
With that, it works and the code also reads better.
For a convenience const declaration, I think local redefinition is
better than linking elsewhere.
> > + #[inline]
> > + pub fn new(num_ids: usize, flags: Flags) -> Result<Self, AllocError> {
> > + let num_ids = core::cmp::max(num_ids, bindings::BITS_PER_LONG as usize);
>
> Nit: I like to write usize::max(...) instead of core::cmp::max(...),
> which I think reads better.
Done
> > + let map = Bitmap::new(num_ids, flags)?;
> > + Ok(Self { map })
> > + }
> > +
> > + /// Returns how many IDs this pool can currently have.
> > + #[expect(clippy::len_without_is_empty)]
> > + #[inline]
> > + pub fn len(&self) -> usize {
>
> Maybe this should be called capacity() instead? Or maybe we just don't
> have this method at all.
capacity sounds good. I think it is useful in helping readability.
Thanks,
Burak
^ permalink raw reply [flat|nested] 18+ messages in thread