implement 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..18bcc59f0b38 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; + } + + let drop_range = len..self.len(); + + // SAFETY: `drop_range` is a subrange of `[0, len)` by the bounds check above. + let ptr: *mut [T] = unsafe { self.get_unchecked_mut(drop_range) }; + + // SAFETY: + // - this will always shrink the vector because of the above bounds check + // - [`new_len`, `self.len`) will be dropped through the call to `drop_in_place` below + unsafe { self.set_len(len) }; + + // SAFETY: + // - the dropped values are valid `T`s by the type invariant + // - we are allowed to invalidate [`new_len`, `old_len`) because we just changed the + // len, therefore we have exclusive access to [`new_len`, `old_len`) + unsafe { ptr::drop_in_place(ptr) }; + } } impl<T: Clone, A: Allocator> Vec<T, A> { -- 2.48.1