1 files changed, 106 insertions, 0 deletions
diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs
new file mode 100644
index 000000000000..0ec985d560c8
--- /dev/null
+++ b/rust/kernel/sync/poll.rs
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024 Google LLC.
+
+//! Utilities for working with `struct poll_table`.
+
+use crate::{
+    bindings,
+    fs::File,
+    prelude::*,
+    sync::{CondVar, LockClassKey},
+};
+use core::{marker::PhantomData, ops::Deref};
+
+/// Creates a [`PollCondVar`] initialiser with the given name and a newly-created lock class.
+#[macro_export]
+macro_rules! new_poll_condvar {
+    ($($name:literal)?) => {
+        $crate::sync::poll::PollCondVar::new(
+            $crate::optional_name!($($name)?), $crate::static_lock_class!()
+        )
+    };
+}
+
+/// Wraps the kernel's `poll_table`.
+///
+/// # Invariants
+///
+/// The pointer must be null or reference a valid `poll_table`.
+#[repr(transparent)]
+pub struct PollTable<'a> {
+    table: *mut bindings::poll_table,
+    _lifetime: PhantomData<&'a bindings::poll_table>,
+}
+
+impl<'a> PollTable<'a> {
+    /// Creates a [`PollTable`] from a valid pointer.
+    ///
+    /// # Safety
+    ///
+    /// The pointer must be null or reference a valid `poll_table` for the duration of `'a`.
+    pub unsafe fn from_raw(table: *mut bindings::poll_table) -> Self {
+        // INVARIANTS: The safety requirements are the same as the struct invariants.
+        PollTable {
+            table,
+            _lifetime: PhantomData,
+        }
+    }
+
+    /// Register this [`PollTable`] with the provided [`PollCondVar`], so that it can be notified
+    /// using the condition variable.
+    pub fn register_wait(&self, file: &File, cv: &PollCondVar) {
+        // SAFETY:
+        // * `file.as_ptr()` references a valid file for the duration of this call.
+        // * `self.table` is null or references a valid poll_table for the duration of this call.
+        // * Since `PollCondVar` is pinned, its destructor is guaranteed to run before the memory
+        //   containing `cv.wait_queue_head` is invalidated. Since the destructor clears all
+        //   waiters and then waits for an rcu grace period, it's guaranteed that
+        //   `cv.wait_queue_head` remains valid for at least an rcu grace period after the removal
+        //   of the last waiter.
+        unsafe { bindings::poll_wait(file.as_ptr(), cv.wait_queue_head.get(), self.table) }
+    }
+}
+
+/// A wrapper around [`CondVar`] that makes it usable with [`PollTable`].
+///
+/// [`CondVar`]: crate::sync::CondVar
+#[pin_data(PinnedDrop)]
+pub struct PollCondVar {
+    #[pin]
+    inner: CondVar,
+}
+
+impl PollCondVar {
+    /// Constructs a new condvar initialiser.
+    pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
+        pin_init!(Self {
+            inner <- CondVar::new(name, key),
+        })
+    }
+}
+
+// Make the `CondVar` methods callable on `PollCondVar`.
+impl Deref for PollCondVar {
+    type Target = CondVar;
+
+    fn deref(&self) -> &CondVar {
+        &self.inner
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for PollCondVar {
+    #[inline]
+    fn drop(self: Pin<&mut Self>) {
+        // Clear anything registered using `register_wait`.
+        //
+        // SAFETY: The pointer points at a valid `wait_queue_head`.
+        unsafe { bindings::__wake_up_pollfree(self.inner.wait_queue_head.get()) };
+
+        // Wait for epoll items to be properly removed.
+        //
+        // SAFETY: Just an FFI call.
+        unsafe { bindings::synchronize_rcu() };
+    }
+}