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

[Alice Ryhl <aliceryhl@google.com>]

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