Re: [PATCH 1/2] rust: alloc: extend safety requirements of Vec::set_len()

[Benno Lossin <benno.lossin@proton.me>]

On Sat Mar 15, 2025 at 4:43 PM CET, Danilo Krummrich wrote:
> Extend the safety requirements of set_len() to consider the case when
> the new length is smaller than the old length.
>
> Fixes: 2aac4cd7dae3 ("rust: alloc: implement kernel `Vec` type")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  rust/kernel/alloc/kvec.rs | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index ae9d072741ce..8540d9e2b717 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -189,7 +189,9 @@ pub fn len(&self) -> usize {
>      ///
>      /// - `new_len` must be less than or equal to [`Self::capacity`].
>      /// - If `new_len` is greater than `self.len`, all elements within the interval
> -    ///   [`self.len`,`new_len`) must be initialized.
> +    ///   [`self.len`,`new_len`) must be initialized,
> +    /// - if `new_len` is smaller than `self.len`, all elements within the interval
> +    ///   [`new_len`, `self.len`) must either be dropped or copied and taken ownership of.

What is meant by "copied"? I agree with Tamir, this can probably just be
"taken ownership of".

With that change:

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

---
Cheers,
Benno

>      #[inline]
>      pub unsafe fn set_len(&mut self, new_len: usize) {
>          debug_assert!(new_len <= self.capacity());
>
> base-commit: 80e54e84911a923c40d7bee33a34c1b4be148d7a