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Date: Fri,  2 Feb 2024 10:55:36 +0000
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Subject: [PATCH v4 2/9] rust: task: add `Task::current_raw`
From: Alice Ryhl <aliceryhl@google.com>
To: Miguel Ojeda <ojeda@kernel.org>, Alex Gaynor <alex.gaynor@gmail.com>, 
	Wedson Almeida Filho <wedsonaf@gmail.com>, Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>, 
	"=?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?=" <bjorn3_gh@protonmail.com>, Benno Lossin <benno.lossin@proton.me>, 
	Andreas Hindborg <a.hindborg@samsung.com>, Peter Zijlstra <peterz@infradead.org>, 
	Alexander Viro <viro@zeniv.linux.org.uk>, Christian Brauner <brauner@kernel.org>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, 
	"=?UTF-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?=" <arve@android.com>, Todd Kjos <tkjos@android.com>, Martijn Coenen <maco@android.com>, 
	Joel Fernandes <joel@joelfernandes.org>, Carlos Llamas <cmllamas@google.com>, 
	Suren Baghdasaryan <surenb@google.com>, Dan Williams <dan.j.williams@intel.com>, 
	Kees Cook <keescook@chromium.org>, Matthew Wilcox <willy@infradead.org>, 
	Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Xu <dxu@dxuuu.xyz>, Alice Ryhl <aliceryhl@google.com>, linux-kernel@vger.kernel.org, 
	rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org
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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