* [PATCH v14 1/5] rust: add bindings for bitmap.h
2025-08-13 15:35 [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
@ 2025-08-13 15:35 ` Burak Emir
2025-08-13 15:35 ` [PATCH v14 2/5] rust: add bindings for bitops.h Burak Emir
` (5 subsequent siblings)
6 siblings, 0 replies; 13+ messages in thread
From: Burak Emir @ 2025-08-13 15:35 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>
Reviewed-by: Alice Ryhl <aliceryhl@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 fe168477caa4..3950f605dedb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4298,6 +4298,7 @@ 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 84d60635e8a9..7bb575043c86 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -36,6 +36,7 @@
#include <drm/drm_ioctl.h>
#include <kunit/test.h>
#include <linux/auxiliary_bus.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 7cf7fe95e41d..8437736fdf28 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -8,6 +8,7 @@
*/
#include "auxiliary.c"
+#include "bitmap.c"
#include "blk.c"
#include "bug.c"
#include "build_assert.c"
--
2.51.0.rc0.205.g4a044479a3-goog
^ permalink raw reply related [flat|nested] 13+ messages in thread* [PATCH v14 2/5] rust: add bindings for bitops.h
2025-08-13 15:35 [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
2025-08-13 15:35 ` [PATCH v14 1/5] rust: add bindings for bitmap.h Burak Emir
@ 2025-08-13 15:35 ` Burak Emir
2025-08-13 15:35 ` [PATCH v14 3/5] rust: add bitmap API Burak Emir
` (4 subsequent siblings)
6 siblings, 0 replies; 13+ messages in thread
From: Burak Emir @ 2025-08-13 15:35 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>
Reviewed-by: Alice Ryhl <aliceryhl@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 3950f605dedb..a9ebb2d49dea 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4315,6 +4315,11 @@ 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 8437736fdf28..abff1ef14d81 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -9,6 +9,7 @@
#include "auxiliary.c"
#include "bitmap.c"
+#include "bitops.c"
#include "blk.c"
#include "bug.c"
#include "build_assert.c"
--
2.51.0.rc0.205.g4a044479a3-goog
^ permalink raw reply related [flat|nested] 13+ messages in thread* [PATCH v14 3/5] rust: add bitmap API.
2025-08-13 15:35 [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
2025-08-13 15:35 ` [PATCH v14 1/5] rust: add bindings for bitmap.h Burak Emir
2025-08-13 15:35 ` [PATCH v14 2/5] rust: add bindings for bitops.h Burak Emir
@ 2025-08-13 15:35 ` Burak Emir
2025-08-13 15:35 ` [PATCH v14 4/5] rust: add find_bit_benchmark_rust module Burak Emir
` (3 subsequent siblings)
6 siblings, 0 replies; 13+ messages in thread
From: Burak Emir @ 2025-08-13 15:35 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. The main types are `BitmapVec` for owned bitmaps and
`Bitmap` for references to C bitmaps.
* We leverage Rust type system guarantees as follows:
* all (non-atomic) mutating operations require a &mut reference which
amounts to exclusive access.
* the `BitmapVec` type implements Send. This enables transferring
ownership between threads and is needed for Binder.
* the `BitmapVec` type implements Sync, which enables passing shared
references &Bitmap between threads. Atomic operations can be
used to safely modify from multiple threads (interior
mutability), though without ordering guarantees.
* The Rust API uses `{set,clear}_bit` vs `{set,clear}_bit_atomic` as
names for clarity, which differs from the C naming convention
`set_bit` for atomic vs `__set_bit` for non-atomic.
* we include enough operations for the API to be useful. Not all
operations are exposed yet in order to avoid dead code. The missing
ones can be added later.
* We take a fine-grained approach to safety:
* Low-level bit-ops get a safe API with bounds checks. Calling with
an out-of-bounds arguments to {set,clear}_bit becomes a no-op and
get logged as errors.
* We also introduce a RUST_BITMAP_HARDENED config, which
causes invocations with out-of-bounds arguments to panic.
* methods correspond to find_* C methods tolerate out-of-bounds
since the C implementation does. Also here, out-of-bounds
arguments are logged as errors, or panic in RUST_BITMAP_HARDENED
mode.
* We add a way to "borrow" bitmaps from C in Rust, to make C bitmaps
that were allocated in C directly usable in Rust code (`Bitmap`).
* the Rust API is optimized to represent the bitmap inline if it would
fit into a pointer. This saves allocations which is
relevant in the Binder use case.
The underlying C bitmap is *not* exposed for raw access in Rust. Doing so
would permit bypassing the Rust API and lose static guarantees.
An alternative route of vendoring an existing Rust bitmap package was
considered but suboptimal overall. Reusing the C implementation is
preferable for a basic data structure like bitmaps. It enables Rust
code to be a lot more similar and predictable with respect to C code
that uses the same data structures and enables the use of code that
has been tried-and-tested in the kernel, with the same performance
characteristics whenever possible.
We use the `usize` type for sizes and indices into the bitmap,
because Rust generally always uses that type for indices and lengths
and it will be more convenient if the API accepts that type. This means
that we need to perform some casts to/from u32 and usize, since the C
headers use unsigned int instead of size_t/unsigned long for these
numbers in some places.
Adds new MAINTAINERS section BITMAP API [RUST].
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Burak Emir <bqe@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
---
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 a9ebb2d49dea..1760df683cd2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4301,6 +4301,13 @@ 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..9235808dc03c
--- /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;
+
+const BITS_PER_LONG: usize = bindings::BITS_PER_LONG as usize;
+
+/// 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 Bitmap {
+ data: [()],
+}
+
+impl Bitmap {
+ /// 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 [`Bitmap`]
+ /// * concurrent access only happens through atomic operations
+ pub unsafe fn from_raw<'a>(ptr: *const usize, nbits: usize) -> &'a Bitmap {
+ 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 Bitmap`. The `Bitmap`
+ // 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 `&Bitmap` is safe given the caller's guarantees.
+ unsafe { &*(data as *const Bitmap) }
+ }
+
+ /// 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 [`Bitmap`]
+ /// * no concurrent access may happen.
+ pub unsafe fn from_raw_mut<'a>(ptr: *mut usize, nbits: usize) -> &'a mut Bitmap {
+ 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 Bitmap` is
+ // safe because `Bitmap` is a ZST with a `data: [()]` field,
+ // making its layout compatible with a slice of `()`.
+ unsafe { &mut *(data as *mut Bitmap) }
+ }
+
+ /// Returns a raw pointer to the backing [`Bitmap`].
+ pub fn as_ptr(&self) -> *const usize {
+ core::ptr::from_ref::<Bitmap>(self).cast::<usize>()
+ }
+
+ /// Returns a mutable raw pointer to the backing [`Bitmap`].
+ pub fn as_mut_ptr(&mut self) -> *mut usize {
+ core::ptr::from_mut::<Bitmap>(self).cast::<usize>()
+ }
+
+ /// Returns length of this [`Bitmap`].
+ #[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 [`Bitmap`] for available
+/// methods.
+///
+/// # Examples
+///
+/// Basic usage
+///
+/// ```
+/// use kernel::alloc::flags::GFP_KERNEL;
+/// use kernel::bitmap::BitmapVec;
+///
+/// let mut b = BitmapVec::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 BitmapVec {
+ /// Representation of bitmap.
+ repr: BitmapRepr,
+ /// Length of this bitmap. Must be `<= i32::MAX`.
+ nbits: usize,
+}
+
+impl core::ops::Deref for BitmapVec {
+ type Target = Bitmap;
+
+ fn deref(&self) -> &Bitmap {
+ let ptr = if self.nbits <= BITS_PER_LONG {
+ // 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 { Bitmap::from_raw(ptr, self.nbits) }
+ }
+}
+
+impl core::ops::DerefMut for BitmapVec {
+ fn deref_mut(&mut self) -> &mut Bitmap {
+ let ptr = if self.nbits <= BITS_PER_LONG {
+ // 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_ptr() }
+ };
+
+ // SAFETY: We got the right pointer and invariants of [`BitmapVec`] hold.
+ // An inline bitmap is treated like an array with single element.
+ unsafe { Bitmap::from_raw_mut(ptr, self.nbits) }
+ }
+}
+
+/// Enable ownership transfer to other threads.
+///
+/// SAFETY: We own the underlying bitmap representation.
+unsafe impl Send for BitmapVec {}
+
+/// Enable unsynchronized concurrent access to [`BitmapVec`] through shared references.
+///
+/// SAFETY: `deref()` will return a reference to a [`Bitmap`]. Its methods
+/// take immutable references are either atomic or read-only.
+unsafe impl Sync for BitmapVec {}
+
+impl Drop for BitmapVec {
+ fn drop(&mut self) {
+ if self.nbits <= BITS_PER_LONG {
+ 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 BitmapVec {
+ /// Constructs a new [`BitmapVec`].
+ ///
+ /// Fails with [`AllocError`] when the [`BitmapVec`] 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 <= BITS_PER_LONG {
+ return Ok(BitmapVec {
+ repr: BitmapRepr { bitmap: 0 },
+ nbits,
+ });
+ }
+ if nbits > i32::MAX.try_into().unwrap() {
+ return Err(AllocError);
+ }
+ let nbits_u32 = u32::try_from(nbits).unwrap();
+ // SAFETY: `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(BitmapVec {
+ repr: BitmapRepr { ptr },
+ nbits,
+ })
+ }
+
+ /// Returns length of this [`Bitmap`].
+ #[allow(clippy::len_without_is_empty)]
+ #[inline]
+ pub fn len(&self) -> usize {
+ self.nbits
+ }
+}
+
+impl Bitmap {
+ /// 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().cast_mut()) };
+ }
+
+ /// 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().cast_mut()) };
+ }
+
+ /// Copy `src` into this [`Bitmap`] and set any remaining bits to zero.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::alloc::{AllocError, flags::GFP_KERNEL};
+ /// use kernel::bitmap::BitmapVec;
+ ///
+ /// let mut long_bitmap = BitmapVec::new(256, GFP_KERNEL)?;
+ ///
+ /// assert_eq!(None, long_bitmap.last_bit());
+ ///
+ /// let mut short_bitmap = BitmapVec::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.len(), 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::BitmapVec;
+ ///
+ /// let bitmap = BitmapVec::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 or equal to `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 bitmap_borrow() {
+ let fake_bitmap: [usize; 2] = [0, 0];
+ // SAFETY: `fake_c_bitmap` is an array of expected length.
+ let b = unsafe { Bitmap::from_raw(fake_bitmap.as_ptr(), 2 * BITS_PER_LONG) };
+ assert_eq!(2 * BITS_PER_LONG, b.len());
+ assert_eq!(None, b.next_bit(0));
+ }
+
+ #[test]
+ fn bitmap_copy() {
+ let fake_bitmap: usize = 0xFF;
+ // SAFETY: `fake_c_bitmap` can be used as one-element array of expected length.
+ let b = unsafe { Bitmap::from_raw(core::ptr::addr_of!(fake_bitmap), 8) };
+ assert_eq!(8, b.len());
+ assert_eq!(None, b.next_zero_bit(0));
+ }
+
+ #[test]
+ fn bitmap_vec_new() -> Result<(), AllocError> {
+ let b = BitmapVec::new(0, GFP_KERNEL)?;
+ assert_eq!(0, b.len());
+
+ let b = BitmapVec::new(3, GFP_KERNEL)?;
+ assert_eq!(3, b.len());
+
+ let b = BitmapVec::new(1024, GFP_KERNEL)?;
+ assert_eq!(1024, b.len());
+
+ // Requesting too large values results in [`AllocError`].
+ let res = BitmapVec::new(1 << 31, GFP_KERNEL);
+ assert!(res.is_err());
+ Ok(())
+ }
+
+ #[test]
+ fn bitmap_set_clear_find() -> Result<(), AllocError> {
+ let mut b = BitmapVec::new(128, GFP_KERNEL)?;
+
+ // 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());
+ Ok(())
+ }
+
+ #[cfg(not(CONFIG_RUST_BITMAP_HARDENED))]
+ #[test]
+ fn owned_bitmap_out_of_bounds() -> Result<(), AllocError> {
+ let mut b = BitmapVec::new(128, GFP_KERNEL)?;
+
+ 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());
+ Ok(())
+ }
+
+ // TODO: uncomment once kunit supports [should_panic].
+ // #[cfg(CONFIG_RUST_BITMAP_HARDENED)]
+ // #[test]
+ // #[should_panic]
+ // fn owned_bitmap_out_of_bounds() -> Result<(), AllocError> {
+ // let mut b = BitmapVec::new(128, GFP_KERNEL)?;
+ //
+ // b.set_bit(2048);
+ // }
+
+ #[test]
+ fn bitmap_copy_and_extend() -> Result<(), AllocError> {
+ let mut long_bitmap = BitmapVec::new(256, GFP_KERNEL)?;
+
+ long_bitmap.set_bit(3);
+ long_bitmap.set_bit(200);
+
+ let mut short_bitmap = BitmapVec::new(32, GFP_KERNEL)?;
+
+ 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());
+ Ok(())
+ }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index ed53169e795c..586be7f246eb 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -62,6 +62,7 @@
pub mod alloc;
#[cfg(CONFIG_AUXILIARY_BUS)]
pub mod auxiliary;
+pub mod bitmap;
pub mod bits;
#[cfg(CONFIG_BLOCK)]
pub mod block;
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index b9a5bc3430aa..86f8768c63d4 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -255,6 +255,16 @@ 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
--
2.51.0.rc0.205.g4a044479a3-goog
^ permalink raw reply related [flat|nested] 13+ messages in thread* [PATCH v14 4/5] rust: add find_bit_benchmark_rust module.
2025-08-13 15:35 [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
` (2 preceding siblings ...)
2025-08-13 15:35 ` [PATCH v14 3/5] rust: add bitmap API Burak Emir
@ 2025-08-13 15:35 ` Burak Emir
2025-08-13 15:35 ` [PATCH v14 5/5] rust: add dynamic ID pool abstraction for bitmap Burak Emir
` (2 subsequent siblings)
6 siblings, 0 replies; 13+ messages in thread
From: Burak Emir @ 2025-08-13 15:35 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>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Burak Emir <bqe@google.com>
---
MAINTAINERS | 1 +
lib/Kconfig.debug | 13 ++++
lib/Makefile | 1 +
lib/find_bit_benchmark_rust.rs | 104 ++++++++++++++++++++++++++++++++
rust/bindings/bindings_helper.h | 1 +
rust/kernel/bitmap.rs | 15 +++++
6 files changed, 135 insertions(+)
create mode 100644 lib/find_bit_benchmark_rust.rs
diff --git a/MAINTAINERS b/MAINTAINERS
index 1760df683cd2..f99e7f4eb4ca 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4306,6 +4306,7 @@ 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 dc0e0c6ed075..386232d81a0e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2607,6 +2607,19 @@ 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 392ff808c9b9..96a83b937a60 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..6bdc51de2f30
--- /dev/null
+++ b/lib/find_bit_benchmark_rust.rs
@@ -0,0 +1,104 @@
+// 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::BitmapVec;
+use kernel::error::{code, Result};
+use kernel::prelude::module;
+use kernel::time::{Instant, Monotonic};
+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: &BitmapVec) {
+ let time = Instant::<Monotonic>::now();
+ 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;
+ }
+ }
+
+ let delta = time.elapsed();
+ pr_cont!(
+ "\nnext_bit: {:18} ns, {:6} iterations",
+ delta.as_nanos(),
+ cnt
+ );
+}
+
+fn test_next_zero_bit(bitmap: &BitmapVec) {
+ let time = Instant::<Monotonic>::now();
+ 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;
+ }
+ }
+
+ let delta = time.elapsed();
+ pr_cont!(
+ "\nnext_zero_bit: {:18} ns, {:6} iterations",
+ delta.as_nanos(),
+ cnt
+ );
+}
+
+fn find_bit_test() {
+ pr_err!("Benchmark");
+ pr_cont!("\nStart testing find_bit() Rust with random-filled bitmap");
+
+ let mut bitmap = BitmapVec::new(BITMAP_LEN, GFP_KERNEL).expect("alloc bitmap failed");
+ bitmap.fill_random();
+
+ test_next_bit(&bitmap);
+ test_next_zero_bit(&bitmap);
+
+ pr_cont!("\nStart testing find_bit() Rust with sparse bitmap");
+
+ let mut bitmap = BitmapVec::new(BITMAP_LEN, GFP_KERNEL).expect("alloc sparse bitmap failed");
+ let nbits = BITMAP_LEN / SPARSENESS;
+ for _i in 0..nbits {
+ // SAFETY: __get_random_u32_below is safe to call with any u32 argument.
+ let bit =
+ unsafe { bindings::__get_random_u32_below(BITMAP_LEN.try_into().unwrap()) as usize };
+ bitmap.set_bit(bit);
+ }
+
+ test_next_bit(&bitmap);
+ test_next_zero_bit(&bitmap);
+ pr_cont!("\n");
+}
+
+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 7bb575043c86..5d58316f871e 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -67,6 +67,7 @@
#include <linux/pm_opp.h>
#include <linux/poll.h>
#include <linux/property.h>
+#include <linux/random.h>
#include <linux/refcount.h>
#include <linux/regulator/consumer.h>
#include <linux/sched.h>
diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
index 9235808dc03c..6e0824579781 100644
--- a/rust/kernel/bitmap.rs
+++ b/rust/kernel/bitmap.rs
@@ -252,6 +252,21 @@ 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().cast::<ffi::c_void>(),
+ usize::div_ceil(self.nbits, bindings::BITS_PER_LONG as usize)
+ * bindings::BITS_PER_LONG as usize
+ / 8,
+ );
+ }
+ }
}
impl Bitmap {
--
2.51.0.rc0.205.g4a044479a3-goog
^ permalink raw reply related [flat|nested] 13+ messages in thread* [PATCH v14 5/5] rust: add dynamic ID pool abstraction for bitmap
2025-08-13 15:35 [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
` (3 preceding siblings ...)
2025-08-13 15:35 ` [PATCH v14 4/5] rust: add find_bit_benchmark_rust module Burak Emir
@ 2025-08-13 15:35 ` Burak Emir
2025-08-14 8:05 ` [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Alice Ryhl
2025-09-03 20:23 ` Yury Norov
6 siblings, 0 replies; 13+ messages in thread
From: Burak Emir @ 2025-08-13 15:35 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>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Burak Emir <bqe@google.com>
---
MAINTAINERS | 1 +
rust/kernel/id_pool.rs | 226 +++++++++++++++++++++++++++++++++++++++++
rust/kernel/lib.rs | 1 +
3 files changed, 228 insertions(+)
create mode 100644 rust/kernel/id_pool.rs
diff --git a/MAINTAINERS b/MAINTAINERS
index f99e7f4eb4ca..e62bebfffa9c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4308,6 +4308,7 @@ 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..a41a3404213c
--- /dev/null
+++ b/rust/kernel/id_pool.rs
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Rust API for an ID pool backed by a [`BitmapVec`].
+
+use crate::alloc::{AllocError, Flags};
+use crate::bitmap::BitmapVec;
+
+const BITS_PER_LONG: usize = bindings::BITS_PER_LONG as usize;
+
+/// Represents a dynamic ID pool backed by a [`BitmapVec`].
+///
+/// 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: BitmapVec,
+}
+
+/// Indicates that an [`IdPool`] should change to a new target size.
+pub struct ReallocRequest {
+ num_ids: usize,
+}
+
+/// Contains a [`BitmapVec`] of a size suitable for reallocating [`IdPool`].
+pub struct PoolResizer {
+ new: BitmapVec,
+}
+
+impl ReallocRequest {
+ /// Allocates a new backing [`BitmapVec`] 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 = BitmapVec::new(self.num_ids, flags)?;
+ Ok(PoolResizer { new })
+ }
+}
+
+impl IdPool {
+ /// Constructs a new [`IdPool`].
+ ///
+ /// A capacity below [`BITS_PER_LONG`] is adjusted to
+ /// [`BITS_PER_LONG`].
+ ///
+ /// [`BITS_PER_LONG`]: srctree/include/asm-generic/bitsperlong.h
+ #[inline]
+ pub fn new(num_ids: usize, flags: Flags) -> Result<Self, AllocError> {
+ let num_ids = core::cmp::max(num_ids, BITS_PER_LONG);
+ let map = BitmapVec::new(num_ids, flags)?;
+ Ok(Self { map })
+ }
+
+ /// Returns how many IDs this pool can currently have.
+ #[inline]
+ pub fn capacity(&self) -> usize {
+ self.map.len()
+ }
+
+ /// Returns a [`ReallocRequest`] if the [`IdPool`] can be shrunk, [`None`] otherwise.
+ ///
+ /// The capacity of an [`IdPool`] cannot be shrunk below [`BITS_PER_LONG`].
+ ///
+ /// [`BITS_PER_LONG`]: srctree/include/asm-generic/bitsperlong.h
+ ///
+ /// # 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.capacity(), kernel::bindings::BITS_PER_LONG as usize);
+ /// # Ok::<(), AllocError>(())
+ /// ```
+ #[inline]
+ pub fn shrink_request(&self) -> Option<ReallocRequest> {
+ let cap = self.capacity();
+ // Shrinking below [`BITS_PER_LONG`] is never possible.
+ if cap <= BITS_PER_LONG {
+ 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: BITS_PER_LONG,
+ });
+ };
+ if bit >= (cap / 4) {
+ return None;
+ }
+ let num_ids = usize::max(BITS_PER_LONG, cap / 2);
+ Some(ReallocRequest { num_ids })
+ }
+
+ /// Shrinks pool by using a new [`BitmapVec`], 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.capacity() * 2;
+ if num_ids > i32::MAX.try_into().unwrap() {
+ return None;
+ }
+ Some(ReallocRequest { num_ids })
+ }
+
+ /// Grows pool by using a new [`BitmapVec`], 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.capacity() {
+ 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 586be7f246eb..9b8a6c386c52 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -90,6 +90,7 @@
pub mod firmware;
pub mod fmt;
pub mod fs;
+pub mod id_pool;
pub mod init;
pub mod io;
pub mod ioctl;
--
2.51.0.rc0.205.g4a044479a3-goog
^ permalink raw reply related [flat|nested] 13+ messages in thread* Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings
2025-08-13 15:35 [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
` (4 preceding siblings ...)
2025-08-13 15:35 ` [PATCH v14 5/5] rust: add dynamic ID pool abstraction for bitmap Burak Emir
@ 2025-08-14 8:05 ` Alice Ryhl
2025-08-14 17:12 ` Yury Norov
2025-09-03 20:23 ` Yury Norov
6 siblings, 1 reply; 13+ messages in thread
From: Alice Ryhl @ 2025-08-14 8:05 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, Aug 13, 2025 at 03:35:41PM +0000, Burak Emir wrote:
> This series adds a Rust bitmap API for porting the approach from
> commit 15d9da3f818c ("binder: use bitmap for faster descriptor lookup")
> to Rust. The functionality in dbitmap.h makes use of bitmap and bitops.
>
> The Rust bitmap API provides a safe abstraction to underlying bitmap
> and bitops operations. For now, only includes method necessary for
> dbitmap.h, more can be added later. We perform bounds checks for
> hardening, violations are programmer errors that result in panics.
>
> We include set_bit_atomic and clear_bit_atomic operations. One has
> to avoid races with non-atomic operations, which is ensure by the
> Rust type system: either callers have shared references &bitmap in
> which case the mutations are atomic operations. Or there is a
> exclusive reference &mut bitmap, in which case there is no concurrent
> access.
>
> This series includes an optimization to represent the bitmap inline,
> as suggested by Yury.
>
> We ran a simple microbenchmark which shows that overall the Rust API
> can be expected to be about 4.5% slower than C API.
>
> We also introduce a Rust API in id_pool.rs that would replace
> dbitmap.h from the commit referenced above. This data structure is coupled
> with the bitmap API and adds support for growing and shrinking, along
> with fine-grained control over when allocation happens.
> The Binder code needs this since it holds a spinlock at the time it
> discovers that growing is necessary; this has to be release
> for performing a memory allocation with GFP_KERNEL that may cause
> sleep. We include example doctests that demonstrate this usage.
>
> Thanks everyone for all the helpful comments, this series has improved
> significantly as a result of your work.
Thanks a lot for doing this, Burak! I gave it a spin locally on
v6.17-rc1, and it seems to work.
Alice
^ permalink raw reply [flat|nested] 13+ messages in thread* Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings
2025-08-14 8:05 ` [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Alice Ryhl
@ 2025-08-14 17:12 ` Yury Norov
2025-08-15 7:36 ` Alice Ryhl
2025-08-26 13:58 ` Alice Ryhl
0 siblings, 2 replies; 13+ messages in thread
From: Yury Norov @ 2025-08-14 17:12 UTC (permalink / raw)
To: Alice Ryhl
Cc: Burak Emir, 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
> Thanks a lot for doing this, Burak! I gave it a spin locally on
> v6.17-rc1, and it seems to work.
Does this mean Tested-by?
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings
2025-08-14 17:12 ` Yury Norov
@ 2025-08-15 7:36 ` Alice Ryhl
2025-08-26 13:58 ` Alice Ryhl
1 sibling, 0 replies; 13+ messages in thread
From: Alice Ryhl @ 2025-08-15 7:36 UTC (permalink / raw)
To: Yury Norov
Cc: Burak Emir, 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, Aug 14, 2025 at 01:12:28PM -0400, Yury Norov wrote:
> > Thanks a lot for doing this, Burak! I gave it a spin locally on
> > v6.17-rc1, and it seems to work.
>
> Does this mean Tested-by?
Tested-by: Alice Ryhl <aliceryhl@google.com>
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings
2025-08-14 17:12 ` Yury Norov
2025-08-15 7:36 ` Alice Ryhl
@ 2025-08-26 13:58 ` Alice Ryhl
2025-08-26 23:58 ` Yury Norov
1 sibling, 1 reply; 13+ messages in thread
From: Alice Ryhl @ 2025-08-26 13:58 UTC (permalink / raw)
To: Yury Norov
Cc: Burak Emir, 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, Aug 14, 2025 at 7:12 PM Yury Norov <yury.norov@gmail.com> wrote:
>
> > Thanks a lot for doing this, Burak! I gave it a spin locally on
> > v6.17-rc1, and it seems to work.
>
> Does this mean Tested-by?
Just to confirm, is the plan that you will pick this up through your tree?
Alice
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings
2025-08-26 13:58 ` Alice Ryhl
@ 2025-08-26 23:58 ` Yury Norov
2025-08-27 6:34 ` Alice Ryhl
0 siblings, 1 reply; 13+ messages in thread
From: Yury Norov @ 2025-08-26 23:58 UTC (permalink / raw)
To: Alice Ryhl
Cc: Burak Emir, 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 Tue, Aug 26, 2025 at 03:58:01PM +0200, Alice Ryhl wrote:
> On Thu, Aug 14, 2025 at 7:12 PM Yury Norov <yury.norov@gmail.com> wrote:
> >
> > > Thanks a lot for doing this, Burak! I gave it a spin locally on
> > > v6.17-rc1, and it seems to work.
> >
> > Does this mean Tested-by?
>
> Just to confirm, is the plan that you will pick this up through your tree?
Yes I will.
This series is very related to bitmaps, so I think my branch is the right
place to move it. Let's wait for a few more weeks. If no any objections,
I'll apply it.
Everyone, please send your tags if you had chance to test and/or review
this series, especially the rust part.
Thanks,
Yury
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings
2025-08-26 23:58 ` Yury Norov
@ 2025-08-27 6:34 ` Alice Ryhl
0 siblings, 0 replies; 13+ messages in thread
From: Alice Ryhl @ 2025-08-27 6:34 UTC (permalink / raw)
To: Yury Norov
Cc: Burak Emir, 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, Aug 27, 2025 at 1:58 AM Yury Norov <yury.norov@gmail.com> wrote:
>
> On Tue, Aug 26, 2025 at 03:58:01PM +0200, Alice Ryhl wrote:
> > On Thu, Aug 14, 2025 at 7:12 PM Yury Norov <yury.norov@gmail.com> wrote:
> > >
> > > > Thanks a lot for doing this, Burak! I gave it a spin locally on
> > > > v6.17-rc1, and it seems to work.
> > >
> > > Does this mean Tested-by?
> >
> > Just to confirm, is the plan that you will pick this up through your tree?
>
> Yes I will.
>
> This series is very related to bitmaps, so I think my branch is the right
> place to move it. Let's wait for a few more weeks. If no any objections,
> I'll apply it.
I agree. Thanks a lot!
> Everyone, please send your tags if you had chance to test and/or review
> this series, especially the rust part.
>
> Thanks,
> Yury
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings
2025-08-13 15:35 [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Burak Emir
` (5 preceding siblings ...)
2025-08-14 8:05 ` [PATCH v14 0/5] rust: adds Bitmap API, ID pool and bindings Alice Ryhl
@ 2025-09-03 20:23 ` Yury Norov
6 siblings, 0 replies; 13+ messages in thread
From: Yury Norov @ 2025-09-03 20:23 UTC (permalink / raw)
To: Burak Emir
Cc: Kees Cook, 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
On Wed, Aug 13, 2025 at 03:35:41PM +0000, Burak Emir wrote:
> This series adds a Rust bitmap API for porting the approach from
> commit 15d9da3f818c ("binder: use bitmap for faster descriptor lookup")
> to Rust. The functionality in dbitmap.h makes use of bitmap and bitops.
Hi Burak,
I'm having hard times trying to merge the series in bitmap-for-next.
$ git am -3 v14_20250813_bqe_rust_adds_bitmap_api_id_pool_and_bindings.mbx
Applying: rust: add bindings for bitmap.h
Applying: rust: add bindings for bitops.h
Applying: rust: add bitmap API.
error: sha1 information is lacking or useless (MAINTAINERS).
error: could not build fake ancestor
Patch failed at 0003 rust: add bitmap API.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".
Can you please rebase and resend?
Thanks,
Yury
^ permalink raw reply [flat|nested] 13+ messages in thread