[PATCH v3 1/3] rust: add a wrapper for the `num_possible_cpus` C function

[Andreas Hindborg <a.hindborg@kernel.org>]

This function returns the maximum number of CPUs that can be online.

The wrapper is needed by the Rust null block driver.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/helpers/helpers.c  | 1 +
 rust/helpers/num_cpus.c | 8 ++++++++
 rust/kernel/cpu.rs      | 7 +++++++
 3 files changed, 16 insertions(+)

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 440fb7638e3c..89e38b08fd17 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -76,6 +76,7 @@
 #include "mm.c"
 #include "mutex.c"
 #include "net/genetlink.c"
+#include "num_cpus.c"
 #include "of.c"
 #include "page.c"
 #include "pci.c"
diff --git a/rust/helpers/num_cpus.c b/rust/helpers/num_cpus.c
new file mode 100644
index 000000000000..54e8bacb46c3
--- /dev/null
+++ b/rust/helpers/num_cpus.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/cpumask.h>
+
+__rust_helper unsigned int rust_helper_num_possible_cpus(void)
+{
+	return num_possible_cpus();
+}
diff --git a/rust/kernel/cpu.rs b/rust/kernel/cpu.rs
index cb6c0338ef5a..b38b6914b12e 100644
--- a/rust/kernel/cpu.rs
+++ b/rust/kernel/cpu.rs
@@ -6,6 +6,13 @@
 
 use crate::{bindings, device::Device, error::Result, prelude::ENODEV};
 
+/// Returns the maximum number of CPUs that may be online on the system.
+#[inline]
+pub fn num_possible_cpus() -> u32 {
+    // SAFETY: FFI call with no additional requirements.
+    unsafe { bindings::num_possible_cpus() }
+}
+
 /// Returns the maximum number of possible CPUs in the current system configuration.
 #[inline]
 pub fn nr_cpu_ids() -> u32 {

-- 
2.54.0