cpumask: add functions similar to for_each_*_cpu

This commit adds three iterators which returns the CPU index. They are
PossibleCpusIndexIter, OnlineCpusIndexIter, and PresentCpusIndexIter
corresponding to C macros for_each_possible_cpu, for_each_online_cpu, and
for_each_present_cpu exclusively.

Signed-off-by: Li Hongyu <lihongyu1999@bupt.edu.cn>

rust/kernel/cpumask.rs

@@ -0,0 +1,201 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Cpumask variables and related functions.
+//!
+//! C header: [`include/linux/cpumask.h`](../../../../include/linux/cpumask.h).
+
+use crate::bindings;
+use core::iter::Iterator;
+
+/// A valid CPU index.
+///
+/// # Safety
+///
+/// - The 'ValidCpuIndex' should be used during the iteration of a CPU index iterator.
+pub struct ValidCpuIndex(u32);
+
+impl ValidCpuIndex {
+    /// Get the valid CPU index in u32.
+    pub fn get(&self) -> u32 {
+        self.0
+    }
+}
+
+/// An possible CPU index iterator.
+///
+/// This iterator has a similar abilitiy to the kernel's macro `for_each_possible_cpu`.
+pub struct PossibleCpusIndexIter {
+    index: i32,
+}
+
+/// An online CPU index iterator.
+///
+/// This iterator has a similar abilitiy to the kernel's macro `for_each_online_cpu`.
+pub struct OnlineCpusIndexIter {
+    index: i32,
+}
+
+/// An present CPU index iterator.
+///
+/// This iterator has a similar abilitiy to the kernel's macro `for_each_present_cpu`.
+pub struct PresentCpusIndexIter {
+    index: i32,
+}
+
+impl Iterator for PossibleCpusIndexIter {
+    type Item = ValidCpuIndex;
+
+    fn next(&mut self) -> Option<ValidCpuIndex> {
+        let next_cpu_id =
+            // SAFETY: Since [`bindings::__cpu_possible_mask`] will not change, there will not
+            // be data race in this part. When the last valid CPU index is found, this iterator
+            // will return `None`. Therefore, the index parameter is always valid.
+            unsafe { bindings::cpumask_next(self.index, &bindings::__cpu_possible_mask) };
+        // When [`bindings::cpumask_next`] can not find further CPUs set in the
+        // [`bindings::__cpu_possible_mask`], it returns a value >= [`bindings::nr_cpu_ids`].
+        //
+        // SAFETY: The [`bindings::nr_cpu_ids`] is fixed at the boot time.
+        if next_cpu_id >= unsafe { bindings::nr_cpu_ids } {
+            return None;
+        }
+        self.index = next_cpu_id as i32;
+        Some(ValidCpuIndex(next_cpu_id))
+    }
+}
+
+impl Iterator for OnlineCpusIndexIter {
+    type Item = ValidCpuIndex;
+
+    fn next(&mut self) -> Option<ValidCpuIndex> {
+        #[cfg(CONFIG_HOTPLUG_CPU)]
+        if self.index == -1 {
+            // The [`bindings::__cpu_online_mask`] and [`bindings::nr_cpu_ids`] may chanage if
+            // `CONFIG_HOTPLUG_CPU` is enabled. In case of race condition, a lock is needed
+            // here. If `CONFIG_HOTPLUG_CPU` is disabled, this function will not have any cost.
+            //
+            // SAFETY: FFI call, this is called once during iteration in case of dead lock.
+            unsafe { bindings::cpus_read_lock() };
+        }
+        let next_cpu_id =
+            // SAFETY: The [`bindings::cpus_read_lock`] prevents the data race. When the last 
+            // valid CPU index is found, this iterator will return `None`. Therefore, the 
+            // index parameter is always valid.
+            unsafe { bindings::cpumask_next(self.index, &bindings::__cpu_online_mask) };
+        // When [`bindings::cpumask_next`] can not find further CPUs set in the
+        // [`bindings::__cpu_online_mask`], it returns a value >= [`bindings::nr_cpu_ids`].
+        //
+        // SAFETY: The [`bindings::nr_cpu_ids`] is fixed at the boot time.
+        if next_cpu_id >= unsafe { bindings::nr_cpu_ids } {
+            // Unlock after finishing iteration.
+            //
+            // SAFETY: FFI call.
+            #[cfg(CONFIG_HOTPLUG_CPU)]
+            unsafe {
+                bindings::cpus_read_unlock()
+            };
+            return None;
+        }
+        self.index = next_cpu_id as i32;
+        Some(ValidCpuIndex(next_cpu_id))
+    }
+}
+
+impl Iterator for PresentCpusIndexIter {
+    type Item = ValidCpuIndex;
+
+    fn next(&mut self) -> Option<ValidCpuIndex> {
+        #[cfg(CONFIG_HOTPLUG_CPU)]
+        if self.index == -1 {
+            // The [`bindings::__cpu_present_mask`] and [`bindings::nr_cpu_ids`] may chanage
+            // if `CONFIG_HOTPLUG_CPU` is enabled. In case of race condition, a lock is needed
+            // here. If `CONFIG_HOTPLUG_CPU` is disabled, this function will not have any cost.
+            //
+            // SAFETY: FFI call, this is called once during iteration in case of dead lock.
+            unsafe { bindings::cpus_read_lock() };
+        }
+        let next_cpu_id =
+            // SAFETY: The [`bindings::cpus_read_lock`] prevents the data race. When the last 
+            // valid CPU index is found, this iterator will return `None`. Therefore, the 
+            // index parameter is always valid.
+            unsafe { bindings::cpumask_next(self.index, &bindings::__cpu_present_mask) };
+        // When [`bindings::cpumask_next`] can not find further CPUs set in the
+        // [`bindings::__cpu_present_mask`], it returns a value >= [`bindings::nr_cpu_ids`].
+        //
+        // SAFETY: The [`bindings::nr_cpu_ids`] is fixed at the boot time.
+        if next_cpu_id >= unsafe { bindings::nr_cpu_ids } {
+            // Unlock after finishing iteration.
+            //
+            // SAFETY: FFI call.
+            #[cfg(CONFIG_HOTPLUG_CPU)]
+            unsafe {
+                bindings::cpus_read_unlock()
+            };
+            return None;
+        }
+        self.index = next_cpu_id as i32;
+        Some(ValidCpuIndex(next_cpu_id))
+    }
+}
+
+/// Returns a [`PossibleCpusIndexIter`] that gives the possible CPU indexes.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::prelude::*;
+/// # use kernel::cpumask::possible_cpus;
+///
+/// fn example() {
+///     // This prints all the possible cpu indexes.
+///     for cpu in possible_cpus(){
+///         pr_info!("{}\n", cpu.get());
+///     }
+/// }
+/// ```
+pub fn possible_cpus() -> PossibleCpusIndexIter {
+    // Initial index is set to -1. Since [`bindings::cpumask_next`] return the next set bit in a
+    // [`bindings::__cpu_possible_mask`], the CPU index should begins from 0.
+    PossibleCpusIndexIter { index: -1 }
+}
+
+/// Returns a [`OnlineCpusIndexIter`] that gives the online CPU indexes.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::prelude::*;
+/// # use kernel::cpumask::online_cpus;
+///
+/// fn example() {
+///     // This prints all the online cpu indexes.
+///     for cpu in online_cpus(){
+///         pr_info!("{}\n", cpu.get());
+///     }
+/// }
+/// ```
+pub fn online_cpus() -> OnlineCpusIndexIter {
+    // Initial index is set to -1. Since [`bindings::cpumask_next`] return the next set bit in a
+    // [`bindings::__cpu_online_mask`], the CPU index should begins from 0.
+    OnlineCpusIndexIter { index: -1 }
+}
+
+/// Returns a [`PresentCpusIndexIter`] that gives the present CPU indexes.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::prelude::*;
+/// # use kernel::cpumask::present_cpus;
+///
+/// fn example() {
+///     // This prints all the present cpu indexes.
+///     for cpu in present_cpus(){
+///         pr_info!("{}\n", cpu.get());
+///     }
+/// }
+/// ```
+pub fn present_cpus() -> PresentCpusIndexIter {
+    // Initial index is set to -1. Since [`bindings::cpumask_next`] return the next set bit in a
+    // [`bindings::__cpu_present_mask`], the CPU index should begins from 0.
+    PresentCpusIndexIter { index: -1 }
+}

rust/kernel/lib.rs

@@ -93,6 +93,7 @@ pub mod platform;
 mod types;
 pub mod user_ptr;
 
+pub mod cpumask;
 #[doc(hidden)]
 pub use build_error::build_error;