On Sat Mar 15, 2025 at 3:42 AM CET, 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. > + /// # 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) }; What's this `get_unchecked_mut` method, I don't see it in `rust-next` or `alloc-next`. > + > + // SAFETY: > + // it is safe to shrink the length because the new length is > + // guaranteed to be less than the old length Please take a look at the documentation of `set_len`, in the safety section you'll find what you need to justify here. > + unsafe { self.set_len(len) }; > + > + // SAFETY: A couple points missing: - why is the pointer valid? > + // - the dropped values are valid `T`s > + // - we are allowed to invalidate [new_len, old_len) because we just changed the len This should justify why the value will never be accessed again. --- Cheers, Benno > + unsafe { ptr::drop_in_place(ptr) }; > + } > } > > impl<T: Clone, A: Allocator> Vec<T, A> {