[PATCH v4 2/9] rust: task: add `Task::current_raw`

Alice Ryhl
2024-02-02T10:55:53Z

Introduces a safe function for getting a raw pointer to the current
task.

When writing bindings that need to access the current task, it is often
more convenient to call a method that directly returns a raw pointer
than to use the existing `Task::current` method. However, the only way
to do that is `bindings::get_current()` which is unsafe since it calls
into C. By introducing `Task::current_raw()`, it becomes possible to
obtain a pointer to the current task without using unsafe.

Link: https://lore.kernel.org/all/CAH5fLgjT48X-zYtidv31mox3C4_Ogoo_2cBOCmX0Ang3tAgGHA@mail.gmail.com/
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
rust/kernel/task.rs | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 148a4f4eb7a8..b579367fb923 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -97,6 +97,15 @@ unsafe impl Sync for Task {}
type Pid = bindings::pid_t;

impl Task {
+ /// Returns a raw pointer to the current task.
+ ///
+ /// It is up to the user to use the pointer correctly.
+ #[inline]
+ pub fn current_raw() -> *mut bindings::task_struct {
+ // SAFETY: Getting the current pointer is always safe.
+ unsafe { bindings::get_current() }
+ }
+
/// Returns a task reference for the currently executing task/thread.
///
/// The recommended way to get the current task/thread is to use the
@@ -119,14 +128,12 @@ pub unsafe fn current() -> impl Deref<Target = Task> {
}
}

- // SAFETY: Just an FFI call with no additional safety requirements.
- let ptr = unsafe { bindings::get_current() };
-
+ let current = Task::current_raw();
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() },
+ task: unsafe { &*current.cast() },
_not_send: NotThreadSafe,
}
}
--
2.43.0.594.gd9cf4e227d-goog