// SPDX-License-Identifier: GPL-2.0 //! RCU support.//!//! C header: [`include/linux/rcupdate.h`](srctree/include/linux/rcupdate.h) use crate::{bindings, types::NotThreadSafe}; /// Evidence that the RCU read side lock is held on the current thread/CPU.////// The type is explicitly not `Send` because this property is per-thread/CPU.////// # Invariants////// The RCU read side lock is actually held while instances of this guard exist.pub struct Guard(NotThreadSafe); impl Guard {    /// Acquires the RCU read side lock and returns a guard.    #[inline]    pub fn new() -> Self {        // SAFETY: An FFI call with no additional requirements.        unsafe { bindings::rcu_read_lock() };        // INVARIANT: The RCU read side lock was just acquired above.        Self(NotThreadSafe)    }     /// Explicitly releases the RCU read side lock.    #[inline]    pub fn unlock(self) {}} impl Default for Guard {    #[inline]    fn default() -> Self {        Self::new()    }} impl Drop for Guard {    #[inline]    fn drop(&mut self) {        // SAFETY: By the type invariants, the RCU read side is locked, so it is ok to unlock it.        unsafe { bindings::rcu_read_unlock() };    }} /// Acquires the RCU read side lock.#[inline]pub fn read_lock() -> Guard {    Guard::new()}