Re: [PATCH v3 4/7] rust: cpumask: Add getters for globally defined cpumasks

[Yury Norov <yury.norov@gmail.com>]

On Thu, Aug 28, 2025 at 12:00:11PM -0700, Mitchell Levy wrote:
> Add getters for the global cpumasks documented in
> `include/linux/cpumask.h`, specifically:
> - cpu_possible_mask
> - cpu_online_mask
> - cpu_enabled_mask
> - cpu_present_mask
> - cpu_active_mask
> 
> Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
> ---
>  rust/kernel/cpumask.rs | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/rust/kernel/cpumask.rs b/rust/kernel/cpumask.rs
> index b7401848f59e..ca9aa6875b4a 100644
> --- a/rust/kernel/cpumask.rs
> +++ b/rust/kernel/cpumask.rs
> @@ -77,6 +77,52 @@ pub unsafe fn as_ref<'a>(ptr: *const bindings::cpumask) -> &'a Self {
>          unsafe { &*ptr.cast() }
>      }
>  
> +    /// Get a CPU mask representing possible CPUs; has bit `cpu` set iff cpu is populatable
> +    #[inline]
> +    pub fn possible() -> &'static Self {
> +        // SAFETY: `__cpu_possible_mask` is a valid global provided by the kernel that lives
> +        // forever.
> +        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_possible_mask) }
> +    }

This function and the following look like returning a boolean.
Maybe possible_cpus()? 

The general rule is to keep the rust naming as close to C as
possible, but in this case Cpumask::cpu_possible_mask is, OK,
somewhat excessive.

Thanks,
Yury

> +
> +    /// Get a CPU mask representing online CPUs; has bit `cpu` set iff cpu available to the
> +    /// scheduler
> +    #[inline]
> +    pub fn online() -> &'static Self {
> +        // SAFETY: `__cpu_online_mask` is a valid global provided by the kernel that lives forever.
> +        // Since we wrap the returned pointer in an `Opaque`, it's ok that `__cpu_online_mask`
> +        // may change its value.
> +        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_online_mask) }
> +    }
> +
> +    /// Get a CPU mask representing enabled CPUs; has bit `cpu` set iff cpu can be brought online
> +    #[inline]
> +    pub fn enabled() -> &'static Self {
> +        // SAFETY: `__cpu_enabled_mask` is a valid global provided by the kernel that lives forever.
> +        // Since we wrap the returned pointer in an `Opaque`, it's ok that `__cpu_enabled_mask`
> +        // may change its value.
> +        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_enabled_mask) }
> +    }
> +
> +    /// Get a CPU mask representing present CPUs; has bit `cpu` set iff cpu is populated
> +    #[inline]
> +    pub fn present() -> &'static Self {
> +        // SAFETY: `__cpu_present_mask` is a valid global provided by the kernel that lives
> +        // forever. Since we wrap the returned pointer in an `Opaque`, it's ok that
> +        // `__cpu_present_mask` may change its value.
> +        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_present_mask) }
> +    }
> +
> +    /// Get a CPU mask representing active CPUs; has bit `cpu` set iff cpu is available to
> +    /// migration.
> +    #[inline]
> +    pub fn active() -> &'static Self {
> +        // SAFETY: `__cpu_active_mask` is a valid global provided by the kernel that lives forever.
> +        // Since we wrap the returned pointer in an `Opaque`, it's ok that `__cpu_active_mask`
> +        // may change its value.
> +        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_active_mask) }
> +    }
> +
>      /// Obtain the raw `struct cpumask` pointer.
>      pub fn as_raw(&self) -> *mut bindings::cpumask {
>          let this: *const Self = self;
> 
> -- 
> 2.34.1