diff options
author | Wedson Almeida Filho <walmeida@microsoft.com> | 2023-04-11 02:45:40 -0300 |
---|---|---|
committer | Miguel Ojeda <ojeda@kernel.org> | 2023-04-22 00:20:00 +0200 |
commit | 8da7a2b7432e8f043f04515895687f72cdb3e0a8 (patch) | |
tree | 8dd15c2ad5e49e92aba260bed3a9a49b7759ebc5 | |
parent | 313c4281bc9dfa98d76a71b16a684af1c52e7751 (diff) |
rust: introduce `current`
This allows Rust code to get a reference to the current task without
having to increment the refcount, but still guaranteeing memory safety.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230411054543.21278-10-wedsonaf@gmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
-rw-r--r-- | rust/helpers.c | 6 | ||||
-rw-r--r-- | rust/kernel/prelude.rs | 2 | ||||
-rw-r--r-- | rust/kernel/task.rs | 82 |
3 files changed, 89 insertions, 1 deletions
diff --git a/rust/helpers.c b/rust/helpers.c index 6e5b2c953d36..2cb7b82053d8 100644 --- a/rust/helpers.c +++ b/rust/helpers.c @@ -103,6 +103,12 @@ long rust_helper_PTR_ERR(__force const void *ptr) } EXPORT_SYMBOL_GPL(rust_helper_PTR_ERR); +struct task_struct *rust_helper_get_current(void) +{ + return current; +} +EXPORT_SYMBOL_GPL(rust_helper_get_current); + void rust_helper_get_task_struct(struct task_struct *t) { get_task_struct(t); diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs index fcdc511d2ce8..c28587d68ebc 100644 --- a/rust/kernel/prelude.rs +++ b/rust/kernel/prelude.rs @@ -36,3 +36,5 @@ pub use super::error::{code::*, Error, Result}; pub use super::{str::CStr, ThisModule}; pub use super::init::{InPlaceInit, Init, PinInit}; + +pub use super::current; diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs index d70cad131956..526d29a0ae27 100644 --- a/rust/kernel/task.rs +++ b/rust/kernel/task.rs @@ -5,7 +5,17 @@ //! C header: [`include/linux/sched.h`](../../../../include/linux/sched.h). use crate::{bindings, types::Opaque}; -use core::ptr; +use core::{marker::PhantomData, ops::Deref, ptr}; + +/// Returns the currently running task. +#[macro_export] +macro_rules! current { + () => { + // SAFETY: Deref + addr-of below create a temporary `TaskRef` that cannot outlive the + // caller. + unsafe { &*$crate::task::Task::current() } + }; +} /// Wraps the kernel's `struct task_struct`. /// @@ -15,6 +25,42 @@ use core::ptr; /// /// Instances of this type are always ref-counted, that is, a call to `get_task_struct` ensures /// that the allocation remains valid at least until the matching call to `put_task_struct`. +/// +/// # Examples +/// +/// The following is an example of getting the PID of the current thread with zero additional cost +/// when compared to the C version: +/// +/// ``` +/// let pid = current!().pid(); +/// ``` +/// +/// Getting the PID of the current process, also zero additional cost: +/// +/// ``` +/// let pid = current!().group_leader().pid(); +/// ``` +/// +/// Getting the current task and storing it in some struct. The reference count is automatically +/// incremented when creating `State` and decremented when it is dropped: +/// +/// ``` +/// use kernel::{task::Task, types::ARef}; +/// +/// struct State { +/// creator: ARef<Task>, +/// index: u32, +/// } +/// +/// impl State { +/// fn new() -> Self { +/// Self { +/// creator: current!().into(), +/// index: 0, +/// } +/// } +/// } +/// ``` #[repr(transparent)] pub struct Task(pub(crate) Opaque<bindings::task_struct>); @@ -27,6 +73,40 @@ unsafe impl Sync for Task {} type Pid = bindings::pid_t; impl Task { + /// Returns a task reference for the currently executing task/thread. + /// + /// The recommended way to get the current task/thread is to use the + /// [`current`](crate::current) macro because it is safe. + /// + /// # Safety + /// + /// Callers must ensure that the returned object doesn't outlive the current task/thread. + pub unsafe fn current() -> impl Deref<Target = Task> { + struct TaskRef<'a> { + task: &'a Task, + _not_send: PhantomData<*mut ()>, + } + + impl Deref for TaskRef<'_> { + type Target = Task; + + fn deref(&self) -> &Self::Target { + self.task + } + } + + // SAFETY: Just an FFI call with no additional safety requirements. + let ptr = unsafe { bindings::get_current() }; + + TaskRef { + // SAFETY: If the current thread is still running, the current task is valid. Given + // that `TaskRef` is not `Send`, we know it cannot be transferred to another thread + // (where it could potentially outlive the caller). + task: unsafe { &*ptr.cast() }, + _not_send: PhantomData, + } + } + /// Returns the group leader of the given task. pub fn group_leader(&self) -> &Task { // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always |