From 6f907035a2456e2986905a3ae335fcbe98ef3ed6 Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Tue, 25 Apr 2023 13:57:10 +0200 Subject: [PATCH] rust: workqueue: add low-level workqueue bindings Define basic low-level bindings to a kernel workqueue. The API defined here can only be used unsafely. Later commits will provide safe wrappers. Signed-off-by: Alice Ryhl --- rust/kernel/lib.rs | 1 + rust/kernel/workqueue.rs | 99 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 100 insertions(+) create mode 100644 rust/kernel/workqueue.rs diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 676995d4e46038..c718524056a659 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -47,6 +47,7 @@ pub mod str; pub mod sync; pub mod task; pub mod types; +pub mod workqueue; #[doc(hidden)] pub use bindings; diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs new file mode 100644 index 00000000000000..e66b6b50dfae92 --- /dev/null +++ b/rust/kernel/workqueue.rs @@ -0,0 +1,99 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Work queues. +//! +//! C header: [`include/linux/workqueue.h`](../../../../include/linux/workqueue.h) + +use crate::{bindings, types::Opaque}; + +/// A kernel work queue. +/// +/// Wraps the kernel's C `struct workqueue_struct`. +/// +/// It allows work items to be queued to run on thread pools managed by the kernel. Several are +/// always available, for example, `system`, `system_highpri`, `system_long`, etc. +#[repr(transparent)] +pub struct Queue(Opaque); + +// SAFETY: Kernel workqueues are usable from any thread. +unsafe impl Send for Queue {} +unsafe impl Sync for Queue {} + +impl Queue { + /// Use the provided `struct workqueue_struct` with Rust. + /// + /// # Safety + /// + /// The caller must ensure that the provided raw pointer is not dangling, that it points at a + /// valid workqueue, and that it remains valid until the end of 'a. + pub unsafe fn from_raw<'a>(ptr: *const bindings::workqueue_struct) -> &'a Queue { + // SAFETY: The `Queue` type is `#[repr(transparent)]`, so the pointer cast is valid. The + // caller promises that the pointer is not dangling. + unsafe { &*(ptr as *const Queue) } + } + + /// Enqueues a work item. + /// + /// This may fail if the work item is already enqueued in a workqueue. + pub fn enqueue(&self, w: T) -> T::EnqueueOutput { + let queue_ptr = self.0.get(); + + // SAFETY: There are two cases. + // + // 1. If `queue_work_on` returns false, then we failed to push the work item to the queue. + // In this case, we don't touch the work item again. + // + // 2. If `queue_work_on` returns true, then we pushed the work item to the queue. The work + // queue will call the function pointer in the `work_struct` at some point in the + // future. We require `T` to be static, so the type has no lifetimes annotated on it. + // We require `T` to be send, so there are no thread-safety issues to take care of. + // + // In either case we follow the safety requirements of `__enqueue`. + unsafe { + w.__enqueue(move |work_ptr| { + bindings::queue_work_on(bindings::WORK_CPU_UNBOUND as _, queue_ptr, work_ptr) + }) + } + } +} + +/// A work item. +/// +/// This is the low-level trait that is designed for being as general as possible. +/// +/// # Safety +/// +/// Implementers must ensure that `__enqueue` behaves as documented. +pub unsafe trait WorkItem { + /// The return type of [`Queue::enqueue`]. + type EnqueueOutput; + + /// Enqueues this work item on a queue using the provided `queue_work_on` method. + /// + /// # Safety + /// + /// Calling this method guarantees that the provided closure will be called with a raw pointer + /// to a `struct work_struct`. The closure should behave in the following way: + /// + /// 1. If the `struct work_struct` cannot be pushed to a workqueue because its already in one, + /// then the closure should return `false`. It may not access the pointer after returning + /// `false`. + /// 2. If the `struct work_struct` is successfully added to a workqueue, then the closure + /// should return `true`. When the workqueue executes the work item, it will do so by + /// calling the function pointer stored in the `struct work_struct`. The work item ensures + /// that the raw pointer remains valid until that happens. + /// + /// This method may not have any other failure cases than the closure returning `false`. The + /// output type should reflect this, but it may also be an infallible type if the work item + /// statically ensures that pushing the `struct work_struct` will succeed. + /// + /// If the work item type is annotated with any lifetimes, then the workqueue must call the + /// function pointer before any such lifetime expires. (Or it may forget the work item and + /// never call the function pointer at all.) + /// + /// If the work item type is not [`Send`], then the work item must be executed on the same + /// thread as the call to `__enqueue`. + unsafe fn __enqueue(self, queue_work_on: F) -> Self::EnqueueOutput + where + F: FnOnce(*mut bindings::work_struct) -> bool; +}