[PATCH v5 2/7] rust: alloc: add Vec::pop

Alice Ryhl
2025-05-02T13:19:45Z

This introduces a basic method that our custom Vec is missing. I expect
that it will be used in many places, but at the time of writing, Rust
Binder has six calls to Vec::pop.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
rust/kernel/alloc/kvec.rs | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index 412a2fe3ce79a0681175bf358e8e0f628e77e875..ebca0cfd31c67f3ce13c4825d7039e34bb54f4d4 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -320,6 +320,37 @@ pub fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError> {
Ok(())
}

+ /// Removes the last element from a vector and returns it, or `None` if it is empty.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut v = KVec::new();
+ /// v.push(1, GFP_KERNEL)?;
+ /// v.push(2, GFP_KERNEL)?;
+ /// assert_eq!(&v, &[1, 2]);
+ ///
+ /// assert_eq!(v.pop(), Some(2));
+ /// assert_eq!(v.pop(), Some(1));
+ /// assert_eq!(v.pop(), None);
+ /// # Ok::<(), Error>(())
+ /// ```
+ pub fn pop(&mut self) -> Option<T> {
+ if self.is_empty() {
+ return None;
+ }
+
+ let removed: *mut T = {
+ // SAFETY: We just checked that the length is at least one.
+ let slice = unsafe { self.dec_len(1) };
+ // SAFETY: The argument to `dec_len` was 1 so this returns a slice of length 1.
+ unsafe { slice.get_unchecked_mut(0) }
+ };
+
+ // SAFETY: The guarantees of `dec_len` allow us to take ownership of this value.
+ Some(unsafe { removed.read() })
+ }
+
/// Creates a new [`Vec`] instance with at least the given capacity.
///
/// # Examples

--
2.49.0.967.g6a0df3ecc3-goog