rust: alloc: add missing invariant in Vec::set_len()

Danilo Krummrich · Danilo Krummrich · commit fb1bf1067de9 · 2025-04-07T14:02:56.000+02:00
When setting a new length, we have to justify that the set length represents the exact number of elements stored in the vector. Reviewed-by: Benno Lossin <benno.lossin@proton.me> Reported-by: Alice Ryhl <aliceryhl@google.com> Closes: https://lore.kernel.org/rust-for-linux/20250311-iov-iter-v1-4-f6c9134ea824@google.com Fixes: 2aac4cd ("rust: alloc: implement kernel `Vec` type") Link: https://lore.kernel.org/r/20250315154436.65065-2-dakr@kernel.org Signed-off-by: Danilo Krummrich <dakr@kernel.org>
diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
@@ -193,6 +193,9 @@ where
     #[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;
     }
 

Original file line number	Diff line number	Diff line change
`@@ -193,6 +193,9 @@ where`
`193`	`193`	`#[inline]`
`194`	`194`	`pub unsafe fn set_len(&mut self, new_len: usize) {`
`195`	`195`	`debug_assert!(new_len <= self.capacity());`
	`196`	`+`
	`197`	+ // INVARIANT: By the safety requirements of this method `new_len` represents the exact
	`198`	+ // number of elements stored within `self`.
`196`	`199`	`self.len = new_len;`
`197`	`200`	`}`
`198`	`201`