[[PATCH]] rust: kernel: add SAFETY comments in aref doc example

[Christopher Joshy]

Replace TODO safety comments with proper explanations in the
`ARef::into_raw` doc example.

For the `unsafe impl AlwaysRefCounted`, explain that the empty
implementation is trivially sound since `Empty` has no data.

For the `ARef::from_raw` call, explain that the pointer is valid
because it is derived from a valid reference.

Link: https://github.com/Rust-for-Linux/linux/issues/351
Signed-off-by: Christopher Joshy <christopherjoshy4@xxxxxxxxx>
---
 rust/kernel/sync/aref.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
index b721b2e00..932343799 100644
--- a/rust/kernel/sync/aref.rs
+++ b/rust/kernel/sync/aref.rs
@@ -124,7 +124,8 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
     ///
     /// struct Empty {}
     ///
-    /// # // SAFETY: TODO.
+    /// # // SAFETY: `Empty` has no data, so `inc_ref` and `dec_ref` being no-ops is trivially
+    /// # // sound.
     /// unsafe impl AlwaysRefCounted for Empty {
     ///     fn inc_ref(&self) {}
     ///     unsafe fn dec_ref(_obj: NonNull<Self>) {}
@@ -132,7 +133,8 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
     ///
     /// let mut data = Empty {};
     /// let ptr = NonNull::<Empty>::new(&mut data).unwrap();
-    /// # // SAFETY: TODO.
+    /// # // SAFETY: `ptr` is derived from a valid reference and is therefore non-null, properly
+    /// # // aligned, and points to a valid `Empty` instance.
     /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };
     /// let raw_ptr: NonNull<Empty> = ARef::into_raw(data_ref);
     ///
-- 
2.43.0