diff options
Diffstat (limited to 'rust/kernel/sync/atomic.rs')
| -rw-r--r-- | rust/kernel/sync/atomic.rs | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 1bb1fc2be177..545a8d37ba78 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -577,6 +577,49 @@ where // SAFETY: `ret` comes from reading `self.0`, which is a valid `T` per type invariants. unsafe { from_repr(ret) } } + + /// Atomic fetch and subtract. + /// + /// Atomically updates `*self` to `(*self).wrapping_sub(v)`, and returns the value of `*self` + /// before the update. + /// + /// # Examples + /// + /// ``` + /// use kernel::sync::atomic::{Atomic, Acquire, Full, Relaxed}; + /// + /// let x = Atomic::new(42); + /// assert_eq!(42, x.load(Relaxed)); + /// assert_eq!(42, x.fetch_sub(12, Acquire)); + /// assert_eq!(30, x.load(Relaxed)); + /// + /// let x = Atomic::new(42); + /// assert_eq!(42, x.load(Relaxed)); + /// assert_eq!(42, x.fetch_sub(12, Full)); + /// assert_eq!(30, x.load(Relaxed)); + /// ``` + #[inline(always)] + pub fn fetch_sub<Rhs, Ordering: ordering::Ordering>(&self, v: Rhs, _: Ordering) -> T + where + // Types that support addition also support subtraction. + T: AtomicAdd<Rhs>, + { + let v = T::rhs_into_delta(v); + + // INVARIANT: `self.0` is a valid `T` after `atomic_fetch_sub*()` due to safety requirement + // of `AtomicAdd`. + let ret = { + match Ordering::TYPE { + OrderingType::Full => T::Repr::atomic_fetch_sub(&self.0, v), + OrderingType::Acquire => T::Repr::atomic_fetch_sub_acquire(&self.0, v), + OrderingType::Release => T::Repr::atomic_fetch_sub_release(&self.0, v), + OrderingType::Relaxed => T::Repr::atomic_fetch_sub_relaxed(&self.0, v), + } + }; + + // SAFETY: `ret` comes from reading `self.0`, which is a valid `T` per type invariants. + unsafe { from_repr(ret) } + } } #[cfg(any(CONFIG_X86_64, CONFIG_UML, CONFIG_ARM, CONFIG_ARM64))] |