[PATCH 0/2] rust: add a few helpers

[PATCH 0/2] rust: add a few helpers

[Andreas Hindborg]

This series adds two helpers for obtaining information about the number
of numa domans and cpu count of the system.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
Andreas Hindborg (2):
      rust: add a wrapper for the `num_possible_cpus` C function
      rust: add a wrapper for the `nr_online_nodes` C function

 rust/helpers/helpers.c  |  1 +
 rust/helpers/num_cpus.c |  8 ++++++++
 rust/kernel/lib.rs      | 17 +++++++++++++++++
 3 files changed, 26 insertions(+)
---
base-commit: 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b
change-id: 20260215-cpu-helpers-08efb2572487

Best regards,
-- 
Andreas Hindborg <a.hindborg@kernel.org>

[PATCH 1/2] rust: add a wrapper for the `num_possible_cpus` C function

[Andreas Hindborg]

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

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/helpers/helpers.c  | 1 +
 rust/helpers/num_cpus.c | 8 ++++++++
 rust/kernel/lib.rs      | 6 ++++++
 3 files changed, 15 insertions(+)

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 79c72762ad9c4..a19d6562fcb3a 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -35,6 +35,7 @@
 #include "maple_tree.c"
 #include "mm.c"
 #include "mutex.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 0000000000000..daddacb0418d8
--- /dev/null
+++ b/rust/helpers/num_cpus.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/cpumask.h>
+
+unsigned int rust_helper_num_possible_cpus(void)
+{
+	return  num_possible_cpus();
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index f812cf1200428..7040e105dd3b9 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -366,3 +366,9 @@ pub fn file_from_location<'a>(loc: &'a core::panic::Location<'a>) -> &'a core::f
         c"<Location::file_as_c_str() not supported>"
     }
 }
+
+/// Returns maximum number of CPUs that may be online on the system.
+pub fn num_possible_cpus() -> u32 {
+    // SAFETY: FFI call with no additional requirements.
+    unsafe { bindings::num_possible_cpus() }
+}

-- 
2.51.2

[PATCH 2/2] rust: add a wrapper for the `nr_online_nodes` C function

[Andreas Hindborg]

This function returns the number of online numa nodes.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/lib.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 7040e105dd3b9..4e9f97f03adf2 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -372,3 +372,14 @@ pub fn num_possible_cpus() -> u32 {
     // SAFETY: FFI call with no additional requirements.
     unsafe { bindings::num_possible_cpus() }
 }
+
+/// Returns the number of online numa nodes.
+pub fn num_online_nodes() -> u32 {
+    // NOTE: In some configurations, we can read this variable without an unsafe block.
+    // SAFETY: When numa is enabled, this is a global mutable static. We do as C and just read it,
+    // even though it might race.
+    #[allow(unused_unsafe)]
+    unsafe {
+        bindings::nr_online_nodes
+    }
+}

-- 
2.51.2

Re: [PATCH 0/2] rust: add a few helpers

[Miguel Ojeda]

On Sun, Feb 15, 2026 at 9:10 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
>  rust/kernel/lib.rs      | 17 +++++++++++++++++

Please avoid adding things to the root of the crate.

Also, for both patches, please mention for what it will be used for.

Thanks!

Cheers,
Miguel

Re: [PATCH 0/2] rust: add a few helpers

[Andreas Hindborg]

"Miguel Ojeda" <miguel.ojeda.sandonis@gmail.com> writes:

> On Sun, Feb 15, 2026 at 9:10 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>
>>  rust/kernel/lib.rs      | 17 +++++++++++++++++
>
> Please avoid adding things to the root of the crate.

Ok, I'll move them.

>
> Also, for both patches, please mention for what it will be used for.

The are for rust null block. I have sent a few today already without
this mention. I can send a follow up email for each with the details.

Best regards,
Andreas Hindborg

Re: [PATCH 1/2] rust: add a wrapper for the `num_possible_cpus` C function

[Dirk Behme]

On 15.02.2026 21:10, Andreas Hindborg wrote:
> This function returns the max number of CPUs that can be online.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
>   rust/helpers/helpers.c  | 1 +
>   rust/helpers/num_cpus.c | 8 ++++++++
>   rust/kernel/lib.rs      | 6 ++++++
>   3 files changed, 15 insertions(+)
> 
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index 79c72762ad9c4..a19d6562fcb3a 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -35,6 +35,7 @@
>   #include "maple_tree.c"
>   #include "mm.c"
>   #include "mutex.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 0000000000000..daddacb0418d8
> --- /dev/null
> +++ b/rust/helpers/num_cpus.c
> @@ -0,0 +1,8 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/cpumask.h>
> +
> +unsigned int rust_helper_num_possible_cpus(void)

Should we add `__rust_helper` here?

Thanks

Dirk

Re: [PATCH 0/2] rust: add a few helpers

[Alice Ryhl]

On Sun, Feb 15, 2026 at 09:10:14PM +0100, Andreas Hindborg wrote:
> This series adds two helpers for obtaining information about the number
> of numa domans and cpu count of the system.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

I'd make both #[inline].

Alice