Commit ab309b6e authored by Miguel Ojeda's avatar Miguel Ojeda
Browse files

rust: avoid `box_uninit_write` feature 

Like commit 0903b9e2 ("rust: alloc: eschew
`Box<MaybeUninit<T>>::write`"), but for the new `rbtree` and `alloc` code.

That is, `feature(new_uninit)` [1] got partially stabilized [2]
for Rust 1.82.0 (expected to be released on 2024-10-17), but it
did not include `Box<MaybeUninit<T>>::write`, which got split into
`feature(box_uninit_write)` [3].

To avoid relying on a new unstable feature, rewrite the `write` +
`assume_init` pair manually.

Link: https://github.com/rust-lang/rust/issues/63291 [1]
Link: https://github.com/rust-lang/rust/pull/129401 [2]
Link: https://github.com/rust-lang/rust/issues/129397

 [3]
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Reviewed-by: default avatarMatt Gilbride <mattgilbride@google.com>
Link: https://lore.kernel.org/r/20240904144229.18592-1-ojeda@kernel.org


Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 68d3b6aa

rust/kernel/alloc/box_ext.rs

+4 −2
Original line number Diff line number Diff line
@@ -26,9 +26,11 @@ pub trait BoxExt<T>: Sized { 
    /// use kernel::alloc::{flags, box_ext::BoxExt};

    /// let value = Box::new([0; 32], flags::GFP_KERNEL)?;

    /// assert_eq!(*value, [0; 32]);

    /// let value = Box::drop_contents(value);

    /// let mut value = Box::drop_contents(value);

    /// // Now we can re-use `value`:

    /// let value = Box::write(value, [1; 32]);

    /// value.write([1; 32]);

    /// // SAFETY: We just wrote to it.

    /// let value = unsafe { value.assume_init() };

    /// assert_eq!(*value, [1; 32]);

    /// # Ok::<(), Error>(())

    /// ```

rust/kernel/rbtree.rs

+8 −9
Original line number Diff line number Diff line
@@ -1059,15 +1059,14 @@ impl<K, V> RBTreeNodeReservation<K, V> { 
    /// Initialises a node reservation.

    ///

    /// It then becomes an [`RBTreeNode`] that can be inserted into a tree.

    pub fn into_node(self, key: K, value: V) -> RBTreeNode<K, V> {

        let node = Box::write(

            self.node,

            Node {

    pub fn into_node(mut self, key: K, value: V) -> RBTreeNode<K, V> {

        self.node.write(Node {

            key,

            value,

            links: bindings::rb_node::default(),

            },

        );

        });

        // SAFETY: We just wrote to it.

        let node = unsafe { self.node.assume_init() };

        RBTreeNode { node }

    }

}