[PATCH 2/2] rust: alloc: add missing invariant in Vec::set_len()

[Danilo Krummrich <dakr@kernel.org>]

When setting a new length, we have to justify that the set length
represents the exact number of elements stored in the vector.

Fixes: 2aac4cd7dae3 ("rust: alloc: implement kernel `Vec` type")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc/kvec.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index 8540d9e2b717..0a4681ad4ce9 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -195,6 +195,9 @@ pub fn len(&self) -> usize {
     #[inline]
     pub unsafe fn set_len(&mut self, new_len: usize) {
         debug_assert!(new_len <= self.capacity());
+
+        // INVARIANT: By the safety requirements of this method `new_len` represents the exact
+        // number of elements stored within `self`.
         self.len = new_len;
     }
 
-- 
2.48.1