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authorWedson Almeida Filho <walmeida@microsoft.com>2023-04-11 02:45:40 -0300
committerMiguel Ojeda <ojeda@kernel.org>2023-04-22 00:20:00 +0200
commit8da7a2b7432e8f043f04515895687f72cdb3e0a8 (patch)
tree8dd15c2ad5e49e92aba260bed3a9a49b7759ebc5 /rust
parent313c4281bc9dfa98d76a71b16a684af1c52e7751 (diff)
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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>
Diffstat (limited to 'rust')
-rw-r--r--rust/helpers.c6
-rw-r--r--rust/kernel/prelude.rs2
-rw-r--r--rust/kernel/task.rs82
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