[PATCH v5 1/8] rust: cpumask: Add a `Cpumask` iterator

Mitchell Levy
2026-04-10T21:36:26Z

Add an iterator for `Cpumask` making use of C's `cpumask_next`.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
rust/helpers/cpumask.c | 6 ++++++
rust/kernel/cpumask.rs | 51 +++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/rust/helpers/cpumask.c b/rust/helpers/cpumask.c
index 5deced5b975e..76990e14dfdd 100644
--- a/rust/helpers/cpumask.c
+++ b/rust/helpers/cpumask.c
@@ -50,6 +50,12 @@ bool rust_helper_cpumask_full(struct cpumask *srcp)
return cpumask_full(srcp);
}

+__rust_helper
+unsigned int rust_helper_cpumask_next(int n, struct cpumask *srcp)
+{
+ return cpumask_next(n, srcp);
+}
+
__rust_helper
unsigned int rust_helper_cpumask_weight(struct cpumask *srcp)
{
diff --git a/rust/kernel/cpumask.rs b/rust/kernel/cpumask.rs
index 44bb36636ee3..b74a3fccf4b4 100644
--- a/rust/kernel/cpumask.rs
+++ b/rust/kernel/cpumask.rs
@@ -14,7 +14,10 @@
#[cfg(CONFIG_CPUMASK_OFFSTACK)]
use core::ptr::{self, NonNull};

-use core::ops::{Deref, DerefMut};
+use core::{
+ iter::FusedIterator,
+ ops::{Deref, DerefMut},
+};

/// A CPU Mask.
///
@@ -161,6 +164,52 @@ pub fn copy(&self, dstp: &mut Self) {
}
}

+/// Iterator for a `Cpumask`.
+pub struct CpumaskIter<'a> {
+ mask: &'a Cpumask,
+ /// [`None`] if no bits have been returned yet, or the index of the last bit returned by the
+ /// iterator. Equal to [`kernel::cpu::nr_cpu_ids()`] when the iterator has been exhausted.
+ last: Option<u32>,
+}
+
+impl<'a> CpumaskIter<'a> {
+ /// Creates a new `CpumaskIter` for the given `Cpumask`.
+ fn new(mask: &'a Cpumask) -> CpumaskIter<'a> {
+ Self { mask, last: None }
+ }
+}
+
+impl<'a> Iterator for CpumaskIter<'a> {
+ type Item = CpuId;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ // cpumask_next WARNs if the first argument is >= nr_cpu_ids when CONFIG_DEBUG_PER_CPU_MAPS
+ // is set. So, early out in that case
+ if let Some(last) = self.last {
+ if last >= kernel::cpu::nr_cpu_ids() {
+ return None;
+ }
+ }
+
+ // SAFETY: By the type invariant, `self.mask.as_raw` is a `struct cpumask *`.
+ let next = unsafe {
+ bindings::cpumask_next(self.last.map_or(-1, |l| l as i32), self.mask.as_raw())
+ };
+
+ self.last = Some(next);
+ CpuId::from_u32(next)
+ }
+}
+
+impl<'a> FusedIterator for CpumaskIter<'a> {}
+
+impl Cpumask {
+ /// Returns an iterator over the set bits in the cpumask.
+ pub fn iter(&self) -> CpumaskIter<'_> {
+ CpumaskIter::new(self)
+ }
+}
+
/// A CPU Mask pointer.
///
/// Rust abstraction for the C `struct cpumask_var_t`.

--
2.34.1