[PATCH] rust: print: Document SAFETY invariants in rust_fmt_argument and call_printk

[Ali Zain]

Replace remaining "SAFETY: TODO" comments with proper explanations.

Document why the raw pointer cast to `fmt::Arguments` is valid
and clarify the invariants required when calling `_printk`
through FFI.

This does not change behaviour.

v2:
  - Fix rustfmt formatting issue reported by 0-day CI.
  - Remove extra blank line before unsafe block.

Signed-off-by: Ali Zain <alizainuimx@xxxxxxxxx>
---
 rust/kernel/list.rs  | 2 ++
 rust/kernel/print.rs | 1 -
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs
index 0d8a201f2..65d33957e 100644
--- a/rust/kernel/list.rs
+++ b/rust/kernel/list.rs
@@ -589,6 +589,8 @@ pub unsafe fn remove(&mut self, item: &T) -> Option<ListArc<T, ID>> {
         //   or in this list (with the same `ID`).
         // - We hold `&mut self`, so there is no concurrent mutation of
         //   the link fields.
+        // - `T::view_links(item)` returns the embedded link fields for this
+        //   object, which remain valid for the lifetime of `item`.
 
         let mut item = unsafe { ListLinks::fields(T::view_links(item)) };
         // SAFETY: The user provided a reference, and reference are never dangling.
diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
index 2ae7b4ce9..c3edc0ab3 100644
--- a/rust/kernel/print.rs
+++ b/rust/kernel/print.rs
@@ -112,7 +112,6 @@ pub unsafe fn call_printk(
     // at compile time, a null-terminated module name, and a pointer to
     // `fmt::Arguments` obtained via `core::ptr::from_ref`. All pointers
     // are valid for the duration of the call and respect the C ABI.
-
     unsafe {
         bindings::_printk(
             format_string.as_ptr(),
-- 
2.53.0