[PATCH V2 1/2] rust: Add initial cpumask abstractions

[Viresh Kumar <viresh.kumar@linaro.org>]

Add initial Rust abstractions for struct cpumask, covering a subset of
its APIs. Additional APIs can be added as needed.

These abstractions will be used in upcoming Rust support for cpufreq and
OPP frameworks.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 rust/kernel/cpumask.rs | 209 +++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs     |   1 +
 2 files changed, 210 insertions(+)
 create mode 100644 rust/kernel/cpumask.rs

diff --git a/rust/kernel/cpumask.rs b/rust/kernel/cpumask.rs
new file mode 100644
index 000000000000..aa4919954c8c
--- /dev/null
+++ b/rust/kernel/cpumask.rs
@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! CPU mask abstractions.
+//!
+//! C header: [`include/linux/cpumask.h`](srctree/include/linux/cpumask.h)
+
+use crate::{
+    alloc::{AllocError, Flags},
+    bindings,
+    prelude::*,
+    types::Opaque,
+};
+#[cfg(CONFIG_CPUMASK_OFFSTACK)]
+use core::ptr::{self, NonNull};
+
+#[cfg(not(CONFIG_CPUMASK_OFFSTACK))]
+use core::mem::MaybeUninit;
+
+use core::ops::{Deref, DerefMut};
+
+/// This corresponds to the C type `struct cpumask`.
+#[repr(transparent)]
+pub struct Cpumask(Opaque<bindings::cpumask>);
+
+impl Cpumask {
+    /// Creates a mutable reference to an existing `struct cpumask` pointer.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` is valid for writing and remains valid for the lifetime
+    /// of the returned reference.
+    pub unsafe fn from_raw_mut<'a>(ptr: *mut bindings::cpumask) -> &'a mut Self {
+        // SAFETY: Guaranteed by the safety requirements of the function.
+        unsafe { &mut *ptr.cast() }
+    }
+
+    /// Creates a reference to an existing `struct cpumask` pointer.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` is valid for reading and remains valid for the lifetime
+    /// of the returned reference.
+    pub unsafe fn from_raw<'a>(ptr: *const bindings::cpumask) -> &'a Self {
+        // SAFETY: Guaranteed by the safety requirements of the function.
+        unsafe { &*ptr.cast() }
+    }
+
+    /// Obtain the raw `struct cpumask *`.
+    pub fn as_raw(&self) -> *mut bindings::cpumask {
+        self as *const Cpumask as *mut bindings::cpumask
+    }
+
+    /// Sets `cpu` in the cpumask.
+    pub fn set(&mut self, cpu: u32) {
+        // SAFETY: `mask` is guaranteed to be valid for the lifetime of `self`. And it is safe to
+        // call `cpumask_set_cpus()` for any CPU.
+        unsafe { bindings::cpumask_set_cpu(cpu, self.as_raw()) };
+    }
+
+    /// Clears `cpu` in the cpumask.
+    pub fn clear(&mut self, cpu: i32) {
+        // SAFETY: `mask` is guaranteed to be valid for the lifetime of `self`. And it is safe to
+        // call `cpumask_clear_cpu()` for any CPU.
+        unsafe { bindings::cpumask_clear_cpu(cpu, self.as_raw()) };
+    }
+
+    /// Sets all CPUs in the cpumask.
+    pub fn set_all(&mut self) {
+        // SAFETY: `mask` is guaranteed to be valid for the lifetime of `self`. And it is safe to
+        // call `cpumask_setall()`.
+        unsafe { bindings::cpumask_setall(self.as_raw()) };
+    }
+
+    /// Gets weight of the cpumask.
+    pub fn weight(&self) -> u32 {
+        // SAFETY: `mask` is guaranteed to be valid for the lifetime of `self`. And it is safe to
+        // call `cpumask_weight()`.
+        unsafe { bindings::cpumask_weight(self.as_raw()) }
+    }
+
+    /// Copies cpumask.
+    pub fn copy(&self, dstp: &mut Self) {
+        // SAFETY: `mask` is guaranteed to be valid for the lifetime of `self`. And it is safe to
+        // call `cpumask_copy()`.
+        unsafe { bindings::cpumask_copy(dstp.as_raw(), self.as_raw()) };
+    }
+}
+
+/// This corresponds to the C type alias `cpumask_var_t`.
+pub struct CpumaskBox {
+    #[cfg(CONFIG_CPUMASK_OFFSTACK)]
+    ptr: NonNull<Cpumask>,
+    #[cfg(not(CONFIG_CPUMASK_OFFSTACK))]
+    mask: Cpumask,
+}
+
+impl CpumaskBox {
+    /// Creates an initialized instance of the `CpumaskBox`.
+    pub fn new(_flags: Flags) -> Result<Self, AllocError> {
+        Ok(Self {
+            #[cfg(CONFIG_CPUMASK_OFFSTACK)]
+            ptr: {
+                let mut ptr: *mut bindings::cpumask = ptr::null_mut();
+
+                // SAFETY: Depending on the value of `_flags`, this call may sleep. Other than
+                // that, it is always safe to call this method.
+                unsafe { bindings::zalloc_cpumask_var(&mut ptr, _flags.as_raw()) };
+                NonNull::new(ptr.cast()).ok_or(AllocError)?
+            },
+
+            #[cfg(not(CONFIG_CPUMASK_OFFSTACK))]
+            // SAFETY: FFI type is valid to be zero-initialized.
+            mask: unsafe { core::mem::zeroed() },
+        })
+    }
+
+    /// Creates an uninitialized instance of the `CpumaskBox`.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that the returned `CpumaskBox` is properly initialized before
+    /// getting used.
+    unsafe fn new_uninit(_flags: Flags) -> Result<Self, AllocError> {
+        Ok(Self {
+            #[cfg(CONFIG_CPUMASK_OFFSTACK)]
+            ptr: {
+                let mut ptr: *mut bindings::cpumask = ptr::null_mut();
+
+                // SAFETY: Depending on the value of `_flags`, this call may sleep. Other than
+                // that, it is always safe to call this method.
+                unsafe { bindings::alloc_cpumask_var(&mut ptr, _flags.as_raw()) };
+                NonNull::new(ptr.cast()).ok_or(AllocError)?
+            },
+            #[cfg(not(CONFIG_CPUMASK_OFFSTACK))]
+            // SAFETY: Guaranteed by the safety requirements of the function.
+            mask: unsafe { MaybeUninit::uninit().assume_init() },
+        })
+    }
+
+    /// Creates a mutable reference to an existing `struct cpumask_var_t` pointer.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` is valid for writing and remains valid for the lifetime
+    /// of the returned reference.
+    pub unsafe fn from_raw_mut<'a>(ptr: *mut bindings::cpumask_var_t) -> &'a mut Self {
+        // SAFETY: Guaranteed by the safety requirements of the function.
+        unsafe { &mut *ptr.cast() }
+    }
+
+    /// Creates a reference to an existing `struct cpumask_var_t` pointer.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` is valid for reading and remains valid for the lifetime
+    /// of the returned reference.
+    pub unsafe fn from_raw<'a>(ptr: *const bindings::cpumask_var_t) -> &'a Self {
+        // SAFETY: Guaranteed by the safety requirements of the function.
+        unsafe { &*ptr.cast() }
+    }
+
+    /// Clones cpumask.
+    pub fn try_clone(cpumask: &Cpumask) -> Result<Self> {
+        // SAFETY: The returned cpumask_box is initialized right after this call.
+        let mut cpumask_box = unsafe { Self::new_uninit(GFP_KERNEL) }?;
+
+        cpumask.copy(&mut cpumask_box);
+        Ok(cpumask_box)
+    }
+}
+
+// Make CpumaskBox behave like a pointer to Cpumask.
+impl Deref for CpumaskBox {
+    type Target = Cpumask;
+
+    #[cfg(CONFIG_CPUMASK_OFFSTACK)]
+    fn deref(&self) -> &Cpumask {
+        // SAFETY: The caller owns CpumaskBox, so it is safe to deref the cpumask.
+        unsafe { &*self.ptr.as_ptr() }
+    }
+
+    #[cfg(not(CONFIG_CPUMASK_OFFSTACK))]
+    fn deref(&self) -> &Cpumask {
+        &self.mask
+    }
+}
+
+impl DerefMut for CpumaskBox {
+    #[cfg(CONFIG_CPUMASK_OFFSTACK)]
+    fn deref_mut(&mut self) -> &mut Cpumask {
+        // SAFETY: The caller owns CpumaskBox, so it is safe to deref the cpumask.
+        unsafe { self.ptr.as_mut() }
+    }
+
+    #[cfg(not(CONFIG_CPUMASK_OFFSTACK))]
+    fn deref_mut(&mut self) -> &mut Cpumask {
+        &mut self.mask
+    }
+}
+
+impl Drop for CpumaskBox {
+    fn drop(&mut self) {
+        #[cfg(CONFIG_CPUMASK_OFFSTACK)]
+        // SAFETY: It is safe to free the cpumask.
+        unsafe {
+            bindings::free_cpumask_var(self.as_raw())
+        };
+    }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 496ed32b0911..efbd7be98dab 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -40,6 +40,7 @@
 pub mod block;
 #[doc(hidden)]
 pub mod build_assert;
+pub mod cpumask;
 pub mod cred;
 pub mod device;
 pub mod device_id;
-- 
2.31.1.272.g89b43f80a514