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// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2024 Google LLC.
//! Utilities for working with `struct poll_table`.
use crate::{
alloc::AllocError,
bindings,
fs::File,
prelude::*,
sync::{
rcu::synchronize_rcu,
CondVar,
LockClassKey, //
}, //
types::Opaque, //
};
use core::{
marker::PhantomData,
mem::ManuallyDrop,
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)]
#[repr(transparent)]
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.
synchronize_rcu();
}
}
/// A [`KBox<PollCondVar>`] that uses `kfree_rcu`.
///
/// [`KBox<PollCondVar>`]: PollCondVar
pub struct PollCondVarBox {
inner: ManuallyDrop<Pin<KBox<PollCondVarBoxInner>>>,
}
#[pin_data]
#[repr(C)]
struct PollCondVarBoxInner {
#[pin]
inner: PollCondVar,
rcu: Opaque<bindings::kvfree_rcu_head>,
}
// SAFETY: PollCondVar is Send
unsafe impl Send for PollCondVarBoxInner {}
// SAFETY: PollCondVar is Sync
unsafe impl Sync for PollCondVarBoxInner {}
impl PollCondVarBox {
/// Constructs a new boxed [`PollCondVar`].
pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> Result<Self, AllocError> {
let b = KBox::pin_init(
pin_init!(PollCondVarBoxInner {
inner <- PollCondVar::new(name, key),
rcu: Opaque::uninit(),
}),
GFP_KERNEL,
)
.map_err(|_| AllocError)?;
Ok(PollCondVarBox {
inner: ManuallyDrop::new(b),
})
}
}
impl Deref for PollCondVarBox {
type Target = PollCondVar;
fn deref(&self) -> &PollCondVar {
&self.inner.inner
}
}
impl Drop for PollCondVarBox {
#[inline]
fn drop(&mut self) {
// SAFETY: ManuallyDrop::take ok because not already taken.
let boxed = unsafe { ManuallyDrop::take(&mut self.inner) };
// SAFETY: The code below frees the box without calling the actual destructor of the type,
// but it's okay because it re-implements the destructor using `kfree_rcu()` in place of
// `synchronize_rcu()`.
let ptr = KBox::into_raw(unsafe { Pin::into_inner_unchecked(boxed) });
// SAFETY: The pointer points at a valid `wait_queue_head`.
unsafe { bindings::__wake_up_pollfree((*ptr).inner.inner.wait_queue_head.get()) };
// SAFETY: This was allocated using `KBox::pin_init`, so it can be freed with `kvfree`.
unsafe { bindings::kvfree_call_rcu((*ptr).rcu.get(), ptr.cast::<ffi::c_void>()) };
}
}
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