[PATCH V3 1/2] rust: Add initial cpumask abstractions

[Viresh Kumar]

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@xxxxxxxxxx>
---
 rust/kernel/cpumask.rs | 301 +++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs     |   1 +
 2 files changed, 302 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..792210a77770
--- /dev/null
+++ b/rust/kernel/cpumask.rs
@@ -0,0 +1,301 @@
+// 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};
+
+/// A CPU Mask.
+///
+/// This represents the Rust abstraction for the C `struct cpumask`.
+///
+/// # Invariants
+///
+/// A [`Cpumask`] instance always corresponds to a valid C `struct cpumask`.
+///
+/// The callers must ensure that the `struct cpumask` is valid for access and remains valid for the
+/// lifetime of the returned reference.
+///
+/// ## Examples
+///
+/// The following example demonstrates how to update a [`Cpumask`].
+///
+/// ```
+/// use kernel::bindings;
+/// use kernel::cpumask::Cpumask;
+///
+/// fn set_clear_cpu(ptr: *mut bindings::cpumask, set_cpu: u32, clear_cpu: i32) {
+///     // SAFETY: The `ptr` is valid for writing and remains valid for the lifetime of the
+///     // returned reference.
+///     let mask = unsafe { Cpumask::from_raw_mut(ptr) };
+///     mask.set(set_cpu);
+///     mask.clear(clear_cpu);
+/// }
+/// ```
+#[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.
+        //
+        // INVARIANT: The caller ensures that `ptr` is valid for writing and remains valid for the
+        // lifetime of the returned reference.
+        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.
+        //
+        // INVARIANT: The caller ensures that `ptr` is valid for reading and remains valid for the
+        // lifetime of the returned reference.
+        unsafe { &*ptr.cast() }
+    }
+
+    /// Obtain the raw `struct cpumask` pointer.
+    pub fn as_raw(&self) -> *mut bindings::cpumask {
+        self as *const Cpumask as *mut bindings::cpumask
+    }
+
+    /// Set `cpu` in the cpumask.
+    ///
+    /// Equivalent to the kernel's `cpumask_set_cpu` API.
+    #[inline]
+    pub fn set(&mut self, cpu: u32) {
+        // SAFETY: By the type invariant, `self.as_raw` is a valid argument to `cpumask_set_cpus`.
+        unsafe { bindings::cpumask_set_cpu(cpu, self.as_raw()) };
+    }
+
+    /// Clear `cpu` in the cpumask.
+    ///
+    /// Equivalent to the kernel's `cpumask_clear_cpu` API.
+    #[inline]
+    pub fn clear(&mut self, cpu: i32) {
+        // SAFETY: By the type invariant, `self.as_raw` is a valid argument to `cpumask_clear_cpu`.
+        unsafe { bindings::cpumask_clear_cpu(cpu, self.as_raw()) };
+    }
+
+    /// Set all CPUs in the cpumask.
+    ///
+    /// Equivalent to the kernel's `cpumask_setall` API.
+    #[inline]
+    pub fn set_all(&mut self) {
+        // SAFETY: By the type invariant, `self.as_raw` is a valid argument to `cpumask_setall`.
+        unsafe { bindings::cpumask_setall(self.as_raw()) };
+    }
+
+    /// Get weight of the cpumask.
+    ///
+    /// Equivalent to the kernel's `cpumask_weight` API.
+    #[inline]
+    pub fn weight(&self) -> u32 {
+        // SAFETY: By the type invariant, `self.as_raw` is a valid argument to `cpumask_weight`.
+        unsafe { bindings::cpumask_weight(self.as_raw()) }
+    }
+
+    /// Copy cpumask.
+    ///
+    /// Equivalent to the kernel's `cpumask_copy` API.
+    #[inline]
+    pub fn copy(&self, dstp: &mut Self) {
+        // SAFETY: By the type invariant, `Self::as_raw` is a valid argument to `cpumask_copy`.
+        unsafe { bindings::cpumask_copy(dstp.as_raw(), self.as_raw()) };
+    }
+}
+
+/// A CPU Mask pointer.
+///
+/// This represents the Rust abstraction for the C `struct cpumask_var_t`.
+///
+/// # Invariants
+///
+/// A [`CpumaskBox`] instance always corresponds to a valid C `struct cpumask_var_t`.
+///
+/// The callers must ensure that the `struct cpumask_var_t` is valid for access and remains valid
+/// for the lifetime of [`CpumaskBox`].
+///
+/// ## Examples
+///
+/// The following example demonstrates how to create and update a [`CpumaskBox`].
+///
+/// ```
+/// use kernel::cpumask::CpumaskBox;
+/// use kernel::error::Result;
+///
+/// fn cpumask_foo() -> Result {
+///     let mut mask = CpumaskBox::new(GFP_KERNEL)?;
+///
+///     assert_eq!(mask.weight(), 0);
+///     mask.set(2);
+///     assert_eq!(mask.weight(), 1);
+///     mask.set(3);
+///     assert_eq!(mask.weight(), 2);
+///
+///     let mask2 = CpumaskBox::try_clone(&mask)?;
+///     assert_eq!(mask2.weight(), 2);
+///
+///     Ok(())
+/// }
+/// ```
+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.
+                //
+                // INVARIANT: The associated memory is freed when the `CpumaskBox` goes out of
+                // scope.
+                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.
+            //
+            // INVARIANT: The associated memory is freed when the `CpumaskBox` goes out of scope.
+            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.
+                //
+                // INVARIANT: The associated memory is freed when the `CpumaskBox` goes out of
+                // scope.
+                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.
+            //
+            // INVARIANT: The associated memory is freed when the `CpumaskBox` goes out of scope.
+            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.
+        //
+        // INVARIANT: The caller ensures that `ptr` is valid for writing and remains valid for the
+        // lifetime of the returned reference.
+        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.
+        //
+        // INVARIANT: The caller ensures that `ptr` is valid for reading and remains valid for the
+        // lifetime of the returned reference.
+        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: By the type invariant, `self.as_raw` is a valid argument to `free_cpumask_var`.
+        unsafe {
+            bindings::free_cpumask_var(self.as_raw())
+        };
+    }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 398242f92a96..dbed774ea9f7 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