On Fri, Mar 14, 2025 at 09:42:33PM -0500, Andrew Ballance wrote:
> implements the equivalent to the std's Vec::truncate
> on the kernel's Vec type.
>
> Signed-off-by: Andrew Ballance <andrewjballance@xxxxxxxxx>
> ---
> rust/kernel/alloc/kvec.rs | 36 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index ae9d072741ce..75e9feebb81f 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -452,6 +452,42 @@ pub fn reserve(&mut self, additional: usize, flags: Flags) -> Result<(), AllocEr
>
> Ok(())
> }
> +
> + /// Shortens the vector, setting the length to `len` and drops the removed values.
> + /// If `len` is greater than or equal to the current length, this does nothing.
> + ///
> + /// This has no effect on the capacity and will not allocate.
Nit: Please also add an empty line here.
> + /// # Examples
> + /// ```
> + /// let mut v = kernel::kvec![1, 2, 3]?;
> + /// v.truncate(1);
> + /// assert_eq!(v.len(), 1);
> + /// assert_eq!(&v, &[1]);
> + ///
> + /// # Ok::<(), Error>(())
> + /// ```
> + pub fn truncate(&mut self, len: usize) {
> + if len >= self.len() {
> + return;
> + }
> +
> + // [new_len, len) is guaranteed to be valid because [0, len) is guaranteed to be valid
We typically use markdown for comments.
> + let drop_range = len..self.len();
> +
> + // SAFETY:
> + // we can safely ignore the bounds check because we already did our own check
> + let ptr: *mut [T] = unsafe { self.get_unchecked_mut(drop_range) };
> +
> + // SAFETY:
> + // it is safe to shrink the length because the new length is
> + // guaranteed to be less than the old length
> + unsafe { self.set_len(len) };
I just sent out a fix [1] for the safety requirements of set_len() in [1], which
I think would be good to consider.
[1] https://lore.kernel.org/rust-for-linux/20250315154436.65065-1-dakr@xxxxxxxxxx/
