rust: workqueue: add helper for defining work_struct fields
The main challenge with defining `work_struct` fields is making sure
that the function pointer stored in the `work_struct` is appropriate for
the work item type it is embedded in. It needs to know the offset of the
`work_struct` field being used (even if there are several!) so that it
can do a `container_of`, and it needs to know the type of the work item
so that it can call into the right user-provided code. All of this needs
to happen in a way that provides a safe API to the user, so that users
of the workqueue cannot mix up the function pointers.
There are three important pieces that are relevant when doing this:
* The pointer type.
* The work item struct. This is what the pointer points at.
* The `work_struct` field. This is a field of the work item struct.
This patch introduces a separate trait for each piece. The pointer type
is given a `WorkItemPointer` trait, which pointer types need to
implement to be usable with the workqueue. This trait will be
implemented for `Arc` and `Box` in a later patch in this patchset.
Implementing this trait is unsafe because this is where the
`container_of` operation happens, but user-code will not need to
implement it themselves.
The work item struct should then implement the `WorkItem` trait. This
trait is where user-code specifies what they want to happen when a work
item is executed. It also specifies what the correct pointer type is.
Finally, to make the work item struct know the offset of its
`work_struct` field, we use a trait called `HasWork<T, ID>`. If a type
implements this trait, then the type declares that, at the given offset,
there is a field of type `Work<T, ID>`. The trait is marked unsafe
because the OFFSET constant must be correct, but we provide an
`impl_has_work!` macro that can safely implement `HasWork<T>` on a type.
The macro expands to something that only compiles if the specified field
really has the type `Work<T>`. It is used like this:
```
struct MyWorkItem {
work_field: Work<MyWorkItem, 1>,
}
impl_has_work! {
impl HasWork<MyWorkItem, 1> for MyWorkItem { self.work_field }
}
```
Note that since the `Work` type is annotated with an id, you can have
several `work_struct` fields by using a different id for each one.
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>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Alice Ryhl
Tejun Heo
parent
0339413074
commit
7324b88975
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@ -30,6 +30,7 @@
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#include <linux/sched/signal.h>
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#include <linux/spinlock.h>
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#include <linux/wait.h>
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#include <linux/workqueue.h>
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__noreturn void rust_helper_BUG(void)
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{
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@ -144,6 +145,18 @@ struct kunit *rust_helper_kunit_get_current_test(void)
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}
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EXPORT_SYMBOL_GPL(rust_helper_kunit_get_current_test);
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void rust_helper_init_work_with_key(struct work_struct *work, work_func_t func,
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bool onstack, const char *name,
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struct lock_class_key *key)
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{
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__init_work(work, onstack);
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work->data = (atomic_long_t)WORK_DATA_INIT();
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lockdep_init_map(&work->lockdep_map, name, key, 0);
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INIT_LIST_HEAD(&work->entry);
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work->func = func;
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}
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EXPORT_SYMBOL_GPL(rust_helper_init_work_with_key);
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/*
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* `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can
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* use it in contexts where Rust expects a `usize` like slice (array) indices.
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@ -16,6 +16,7 @@
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#![feature(coerce_unsized)]
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#![feature(dispatch_from_dyn)]
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#![feature(new_uninit)]
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#![feature(offset_of)]
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#![feature(ptr_metadata)]
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#![feature(receiver_trait)]
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#![feature(unsize)]
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@ -2,9 +2,42 @@
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//! Work queues.
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//!
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//! This file has two components: The raw work item API, and the safe work item API.
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//!
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//! One pattern that is used in both APIs is the `ID` const generic, which exists to allow a single
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//! type to define multiple `work_struct` fields. This is done by choosing an id for each field,
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//! and using that id to specify which field you wish to use. (The actual value doesn't matter, as
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//! long as you use different values for different fields of the same struct.) Since these IDs are
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//! generic, they are used only at compile-time, so they shouldn't exist in the final binary.
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//!
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//! # The raw API
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//!
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//! The raw API consists of the `RawWorkItem` trait, where the work item needs to provide an
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//! arbitrary function that knows how to enqueue the work item. It should usually not be used
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//! directly, but if you want to, you can use it without using the pieces from the safe API.
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//!
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//! # The safe API
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//!
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//! The safe API is used via the `Work` struct and `WorkItem` traits. Furthermore, it also includes
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//! a trait called `WorkItemPointer`, which is usually not used directly by the user.
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//!
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//! * The `Work` struct is the Rust wrapper for the C `work_struct` type.
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//! * The `WorkItem` trait is implemented for structs that can be enqueued to a workqueue.
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//! * The `WorkItemPointer` trait is implemented for the pointer type that points at a something
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//! that implements `WorkItem`.
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//!
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//! C header: [`include/linux/workqueue.h`](../../../../include/linux/workqueue.h)
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use crate::{bindings, types::Opaque};
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use crate::{bindings, prelude::*, sync::LockClassKey, types::Opaque};
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use core::marker::PhantomData;
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/// Creates a [`Work`] initialiser with the given name and a newly-created lock class.
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#[macro_export]
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macro_rules! new_work {
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($($name:literal)?) => {
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$crate::workqueue::Work::new($crate::optional_name!($($name)?), $crate::static_lock_class!())
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};
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}
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/// A kernel work queue.
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///
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@ -108,6 +141,228 @@ pub unsafe trait RawWorkItem<const ID: u64> {
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F: FnOnce(*mut bindings::work_struct) -> bool;
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}
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/// Defines the method that should be called directly when a work item is executed.
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///
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/// This trait is implemented by `Pin<Box<T>>` and `Arc<T>`, and is mainly intended to be
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/// implemented for smart pointer types. For your own structs, you would implement [`WorkItem`]
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/// instead. The `run` method on this trait will usually just perform the appropriate
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/// `container_of` translation and then call into the `run` method from the [`WorkItem`] trait.
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///
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/// This trait is used when the `work_struct` field is defined using the [`Work`] helper.
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///
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/// # Safety
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///
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/// Implementers must ensure that [`__enqueue`] uses a `work_struct` initialized with the [`run`]
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/// method of this trait as the function pointer.
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///
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/// [`__enqueue`]: RawWorkItem::__enqueue
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/// [`run`]: WorkItemPointer::run
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pub unsafe trait WorkItemPointer<const ID: u64>: RawWorkItem<ID> {
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/// Run this work item.
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///
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/// # Safety
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///
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/// The provided `work_struct` pointer must originate from a previous call to `__enqueue` where
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/// the `queue_work_on` closure returned true, and the pointer must still be valid.
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unsafe extern "C" fn run(ptr: *mut bindings::work_struct);
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}
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/// Defines the method that should be called when this work item is executed.
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///
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/// This trait is used when the `work_struct` field is defined using the [`Work`] helper.
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pub trait WorkItem<const ID: u64 = 0> {
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/// The pointer type that this struct is wrapped in. This will typically be `Arc<Self>` or
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/// `Pin<Box<Self>>`.
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type Pointer: WorkItemPointer<ID>;
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/// The method that should be called when this work item is executed.
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fn run(this: Self::Pointer);
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}
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/// Links for a work item.
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///
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/// This struct contains a function pointer to the `run` function from the [`WorkItemPointer`]
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/// trait, and defines the linked list pointers necessary to enqueue a work item in a workqueue.
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///
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/// Wraps the kernel's C `struct work_struct`.
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///
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/// This is a helper type used to associate a `work_struct` with the [`WorkItem`] that uses it.
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#[repr(transparent)]
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pub struct Work<T: ?Sized, const ID: u64 = 0> {
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work: Opaque<bindings::work_struct>,
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_inner: PhantomData<T>,
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}
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// SAFETY: Kernel work items are usable from any thread.
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//
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// We do not need to constrain `T` since the work item does not actually contain a `T`.
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unsafe impl<T: ?Sized, const ID: u64> Send for Work<T, ID> {}
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// SAFETY: Kernel work items are usable from any thread.
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//
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// We do not need to constrain `T` since the work item does not actually contain a `T`.
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unsafe impl<T: ?Sized, const ID: u64> Sync for Work<T, ID> {}
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impl<T: ?Sized, const ID: u64> Work<T, ID> {
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/// Creates a new instance of [`Work`].
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#[inline]
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#[allow(clippy::new_ret_no_self)]
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pub fn new(name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self>
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where
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T: WorkItem<ID>,
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{
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// SAFETY: The `WorkItemPointer` implementation promises that `run` can be used as the work
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// item function.
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unsafe {
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kernel::init::pin_init_from_closure(move |slot| {
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let slot = Self::raw_get(slot);
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bindings::init_work_with_key(
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slot,
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Some(T::Pointer::run),
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false,
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name.as_char_ptr(),
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key.as_ptr(),
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);
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Ok(())
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})
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}
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}
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/// Get a pointer to the inner `work_struct`.
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///
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/// # Safety
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///
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/// The provided pointer must not be dangling and must be properly aligned. (But the memory
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/// need not be initialized.)
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#[inline]
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pub unsafe fn raw_get(ptr: *const Self) -> *mut bindings::work_struct {
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// SAFETY: The caller promises that the pointer is aligned and not dangling.
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//
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// A pointer cast would also be ok due to `#[repr(transparent)]`. We use `addr_of!` so that
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// the compiler does not complain that the `work` field is unused.
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unsafe { Opaque::raw_get(core::ptr::addr_of!((*ptr).work)) }
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}
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}
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/// Declares that a type has a [`Work<T, ID>`] field.
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///
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/// The intended way of using this trait is via the [`impl_has_work!`] macro. You can use the macro
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/// like this:
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///
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/// ```no_run
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/// use kernel::impl_has_work;
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/// use kernel::prelude::*;
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/// use kernel::workqueue::Work;
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///
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/// struct MyWorkItem {
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/// work_field: Work<MyWorkItem, 1>,
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/// }
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///
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/// impl_has_work! {
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/// impl HasWork<MyWorkItem, 1> for MyWorkItem { self.work_field }
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/// }
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/// ```
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///
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/// Note that since the `Work` type is annotated with an id, you can have several `work_struct`
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/// fields by using a different id for each one.
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///
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/// # Safety
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///
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/// The [`OFFSET`] constant must be the offset of a field in Self of type [`Work<T, ID>`]. The methods on
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/// this trait must have exactly the behavior that the definitions given below have.
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///
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/// [`Work<T, ID>`]: Work
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/// [`impl_has_work!`]: crate::impl_has_work
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/// [`OFFSET`]: HasWork::OFFSET
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pub unsafe trait HasWork<T, const ID: u64 = 0> {
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/// The offset of the [`Work<T, ID>`] field.
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///
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/// [`Work<T, ID>`]: Work
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const OFFSET: usize;
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/// Returns the offset of the [`Work<T, ID>`] field.
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///
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/// This method exists because the [`OFFSET`] constant cannot be accessed if the type is not Sized.
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///
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/// [`Work<T, ID>`]: Work
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/// [`OFFSET`]: HasWork::OFFSET
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#[inline]
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fn get_work_offset(&self) -> usize {
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Self::OFFSET
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}
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/// Returns a pointer to the [`Work<T, ID>`] field.
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///
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/// # Safety
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///
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/// The provided pointer must point at a valid struct of type `Self`.
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///
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/// [`Work<T, ID>`]: Work
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#[inline]
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unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID> {
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// SAFETY: The caller promises that the pointer is valid.
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unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut Work<T, ID> }
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}
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/// Returns a pointer to the struct containing the [`Work<T, ID>`] field.
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///
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/// # Safety
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///
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/// The pointer must point at a [`Work<T, ID>`] field in a struct of type `Self`.
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///
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/// [`Work<T, ID>`]: Work
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#[inline]
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unsafe fn work_container_of(ptr: *mut Work<T, ID>) -> *mut Self
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where
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Self: Sized,
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{
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// SAFETY: The caller promises that the pointer points at a field of the right type in the
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// right kind of struct.
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unsafe { (ptr as *mut u8).sub(Self::OFFSET) as *mut Self }
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}
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}
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/// Used to safely implement the [`HasWork<T, ID>`] trait.
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///
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/// # Examples
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///
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/// ```
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/// use kernel::impl_has_work;
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/// use kernel::sync::Arc;
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/// use kernel::workqueue::{self, Work};
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///
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/// struct MyStruct {
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/// work_field: Work<MyStruct, 17>,
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/// }
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///
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/// impl_has_work! {
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/// impl HasWork<MyStruct, 17> for MyStruct { self.work_field }
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/// }
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/// ```
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///
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/// [`HasWork<T, ID>`]: HasWork
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#[macro_export]
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macro_rules! impl_has_work {
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($(impl$(<$($implarg:ident),*>)?
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HasWork<$work_type:ty $(, $id:tt)?>
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for $self:ident $(<$($selfarg:ident),*>)?
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{ self.$field:ident }
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)*) => {$(
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// SAFETY: The implementation of `raw_get_work` only compiles if the field has the right
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// type.
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unsafe impl$(<$($implarg),*>)? $crate::workqueue::HasWork<$work_type $(, $id)?> for $self $(<$($selfarg),*>)? {
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const OFFSET: usize = ::core::mem::offset_of!(Self, $field) as usize;
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#[inline]
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unsafe fn raw_get_work(ptr: *mut Self) -> *mut $crate::workqueue::Work<$work_type $(, $id)?> {
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// SAFETY: The caller promises that the pointer is not dangling.
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unsafe {
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::core::ptr::addr_of_mut!((*ptr).$field)
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}
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}
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}
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)*};
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}
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/// Returns the system work queue (`system_wq`).
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///
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/// It is the one used by `schedule[_delayed]_work[_on]()`. Multi-CPU multi-threaded. There are
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@ -262,7 +262,7 @@ $(obj)/%.lst: $(src)/%.c FORCE
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# Compile Rust sources (.rs)
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# ---------------------------------------------------------------------------
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rust_allowed_features := new_uninit
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rust_allowed_features := new_uninit,offset_of
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# `--out-dir` is required to avoid temporaries being created by `rustc` in the
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# current working directory, which may be not accessible in the out-of-tree
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