Messages in this thread | | | Date | Sun, 11 Jun 2023 15:45:51 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH v2 1/8] rust: workqueue: add low-level workqueue bindings |
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On 01.06.23 15:49, Alice Ryhl wrote: > Define basic low-level bindings to a kernel workqueue. The API defined > here can only be used unsafely. Later commits will provide safe > wrappers. > > Co-developed-by: Gary Guo <gary@garyguo.net> > Signed-off-by: Gary Guo <gary@garyguo.net> > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
-- Cheers, Benno
> --- > rust/bindings/bindings_helper.h | 1 + > rust/kernel/lib.rs | 1 + > rust/kernel/workqueue.rs | 107 ++++++++++++++++++++++++++++++++ > 3 files changed, 109 insertions(+) > create mode 100644 rust/kernel/workqueue.rs > > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h > index 50e7a76d5455..ae2e8f018268 100644 > --- a/rust/bindings/bindings_helper.h > +++ b/rust/bindings/bindings_helper.h > @@ -10,6 +10,7 @@ > #include <linux/refcount.h> > #include <linux/wait.h> > #include <linux/sched.h> > +#include <linux/workqueue.h> > > /* `bindgen` gets confused at certain things. */ > const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL; > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > index 85b261209977..eaded02ffb01 100644 > --- a/rust/kernel/lib.rs > +++ b/rust/kernel/lib.rs > @@ -43,6 +43,7 @@ > 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 000000000000..9c630840039b > --- /dev/null > +++ b/rust/kernel/workqueue.rs > @@ -0,0 +1,107 @@ > +// 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<bindings::workqueue_struct>); > + > +// 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. > + /// > + /// The work item will be submitted using `WORK_CPU_UNBOUND`. > + pub fn enqueue<W, const ID: u64>(&self, w: W) -> W::EnqueueOutput > + where > + W: RawWorkItem<ID> + Send + 'static, > + { > + let queue_ptr = self.0.get(); > + > + // SAFETY: We only return `false` if the `work_struct` is already in a workqueue. The other > + // `__enqueue` requirements are not relevant since `W` is `Send` and static. > + // > + // The call to `bindings::queue_work_on` will dereference the provided raw pointer, which > + // is ok because `__enqueue` guarantees that the pointer is valid for the duration of this > + // closure. > + // > + // Furthermore, if the C workqueue code accesses the pointer after this call to > + // `__enqueue`, then the work item was successfully enqueued, and `bindings::queue_work_on` > + // will have returned true. In this case, `__enqueue` promises that the raw pointer will > + // stay valid until we call the function pointer in the `work_struct`, so the access is ok. > + unsafe { > + w.__enqueue(move |work_ptr| { > + bindings::queue_work_on(bindings::WORK_CPU_UNBOUND as _, queue_ptr, work_ptr) > + }) > + } > + } > +} > + > +/// A raw work item. > +/// > +/// This is the low-level trait that is designed for being as general as possible. > +/// > +/// The `ID` parameter to this trait exists so that a single type can provide multiple > +/// implementations of this trait. For example, if a struct has multiple `work_struct` fields, then > +/// you will implement this trait once for each field, using a different id for each field. The > +/// actual value of the id is not important as long as you use different ids for different fields > +/// of the same struct. (Fields of different structs need not use different ids.) > +/// > +/// Note that the id is used only to select the right method to call during compilation. It wont be > +/// part of the final executable. > +/// > +/// # Safety > +/// > +/// Implementers must ensure that any pointers passed to a `queue_work_on` closure by `__enqueue` > +/// remain valid for the duration specified in the documentation for `__enqueue`. > +pub unsafe trait RawWorkItem<const ID: u64> { > + /// The return type of [`Queue::enqueue`]. > + type EnqueueOutput; > + > + /// Enqueues this work item on a queue using the provided `queue_work_on` method. > + /// > + /// # Guarantees > + /// > + /// If this method calls the provided closure, then the raw pointer is guaranteed to point at a > + /// valid `work_struct` for the duration of the call to the closure. If the closure returns > + /// true, then it is further guaranteed that the pointer remains valid until someone calls the > + /// function pointer stored in the `work_struct`. > + /// > + /// # Safety > + /// > + /// The provided closure may only return `false` if the `work_struct` is already in a workqueue. > + /// > + /// If the work item type is annotated with any lifetimes, then you must not call the function > + /// pointer after any such lifetime expires. (Never calling the function pointer is okay.) > + /// > + /// If the work item type is not [`Send`], then the function pointer must be called on the same > + /// thread as the call to `__enqueue`. > + unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput > + where > + F: FnOnce(*mut bindings::work_struct) -> bool; > +} > -- > 2.41.0.rc0.172.g3f132b7071-goog >
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