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
