linux-kernel - Re: [PATCH 1/2] rust: alloc: replace `Vec::set_len` with `inc

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Message-ID: <Z9f-Z15bSh8MA1wJ@google.com>
Date: Mon, 17 Mar 2025 10:50:15 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Tamir Duberstein <tamird@...il.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Andrew Ballance <andrewjballance@...il.com>, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] rust: alloc: replace `Vec::set_len` with `inc_len`

On Sun, Mar 16, 2025 at 06:32:00PM -0400, Tamir Duberstein wrote:
> Rename `set_len` to `inc_len` and simplify its safety contract.

You're missing a Signed-off-by tag.

>  rust/kernel/alloc/kvec.rs | 19 +++++++++----------
>  rust/kernel/str.rs        |  2 +-
>  rust/kernel/uaccess.rs    |  2 +-
>  3 files changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index ae9d072741ce..d43a1d609434 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -183,17 +183,16 @@ pub fn len(&self) -> usize {
>          self.len
>      }
>  
> -    /// Forcefully sets `self.len` to `new_len`.
> +    /// Increments `self.len` by `additional`.
>      ///
>      /// # Safety
>      ///
> -    /// - `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 + additional` must be less than or equal to [`Self::capacity`].
> +    /// - All elements within the interval [`self.len`,`self.len + additional`) must be initialized.
>      #[inline]
> -    pub unsafe fn set_len(&mut self, new_len: usize) {
> -        debug_assert!(new_len <= self.capacity());
> -        self.len = new_len;
> +    pub unsafe fn inc_len(&mut self, additional: usize) {
> +        debug_assert!(self.len() + additional <= self.capacity());
> +        self.len += additional;

I guess we could use an INVARIANT: comment here.

Alice