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. + /// # 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 + 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) }; + + // SAFETY: + // - the dropped values are valid `T`s + // - we are allowed to invalidate [new_len, old_len) because we just changed the len + unsafe { ptr::drop_in_place(ptr) }; + } } impl<T: Clone, A: Allocator> Vec<T, A> { -- 2.48.1