linux-kernel - Re: [PATCH 2/2] rust: alloc: add `Vec::dec

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Message-ID: <CAJ-ks9=1MO0rZJ=5=-G5PCR6wPGBk8v_PWt9sy5dXNup25iqfg@mail.gmail.com>
Date: Sun, 16 Mar 2025 18:35:35 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Danilo Krummrich <dakr@...nel.org>, Andrew Ballance <andrewjballance@...il.com>, 
	Alice Ryhl <aliceryhl@...gle.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>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: alloc: add `Vec::dec_len`

On Sun, Mar 16, 2025 at 6:32 PM Tamir Duberstein <tamird@...il.com> wrote:
>
> Add `Vec::dec_len` that reduces the length of the receiver. This method
> is intended to be used from methods that remove elements from `Vec` such
> as `truncate`, `pop`, `remove`, and others. This method is intentionally
> not `pub`.
>
> Signed-off-by: Tamir Duberstein <tamird@...il.com>
> ---
>  rust/kernel/alloc/kvec.rs | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index d43a1d609434..5d604e04b9a5 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -195,6 +195,21 @@ pub unsafe fn inc_len(&mut self, additional: usize) {
>          self.len += additional;
>      }
>
> +    /// Decreases `self.len` by `count`.
> +    ///
> +    /// Returns a mutable reference to the removed elements.
> +    ///
> +    /// # Safety
> +    ///
> +    /// - `count` must be less than or equal to `self.len`.
> +    unsafe fn dec_len(&mut self, count: usize) -> &mut [T] {
> +        debug_assert!(count <= self.len());
> +        self.len -= count;
> +        // SAFETY: The memory between `self.len` and `self.len + count` is guaranteed to contain
> +        // `self.len` initialized elements of type `T`.

Oops, this should be

>        // SAFETY: The memory after `self.len()` is guaranteed to contain `count` initialized
>        // elements of type `T`.

Let me know if I should respin or if this can be changed when applied.



> +        unsafe { slice::from_raw_parts_mut(self.as_mut_ptr().add(self.len), count) }
> +    }
> +
>      /// Returns a slice of the entire vector.
>      #[inline]
>      pub fn as_slice(&self) -> &[T] {
>
> --
> 2.48.1
>