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    Subject[PATCH v2 3/6] rust: rbtree: add `RBTreeIterator`
    From
    From: Wedson Almeida Filho <wedsonaf@gmail.com>

    - Add Iterator implementation (`RBTreeIterator`) for `RBTree`, allowing
    iteration over (key, value) pairs in key order.
    - Add individual `keys()` and `values()` functions to iterate over keys
    or values alone.
    - Update doctests to use iteration instead of explicitly getting items.

    Iteration is needed by the binder driver to enumerate all values in a
    tree for oneway spam detection [1].

    Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-17-08ba9197f637@google.com/ [1]
    Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
    Reviewed-by: Alice Ryhl <aliceryhl@google.com>
    Tested-by: Alice Ryhl <aliceryhl@google.com>
    Signed-off-by: Matt Gilbride <mattgilbride@google.com>
    ---
    rust/kernel/rbtree.rs | 125 ++++++++++++++++++++++++++++++++++++++++++--------
    1 file changed, 107 insertions(+), 18 deletions(-)

    diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
    index a72e9f57e660..b1faac831cfc 100644
    --- a/rust/kernel/rbtree.rs
    +++ b/rust/kernel/rbtree.rs
    @@ -54,14 +54,30 @@ struct Node<K, V> {
    /// assert_eq!(tree.get(&30).unwrap(), &300);
    /// }
    ///
    +/// // Iterate over the nodes we just inserted.
    +/// {
    +/// let mut iter = tree.iter();
    +/// assert_eq!(iter.next().unwrap(), (&10, &100));
    +/// assert_eq!(iter.next().unwrap(), (&20, &200));
    +/// assert_eq!(iter.next().unwrap(), (&30, &300));
    +/// assert!(iter.next().is_none());
    +/// }
    +///
    +/// // Print all elements.
    +/// for (key, value) in &tree {
    +/// pr_info!("{} = {}\n", key, value);
    +/// }
    +///
    /// // Replace one of the elements.
    /// tree.try_create_and_insert(10, 1000)?;
    ///
    /// // Check that the tree reflects the replacement.
    /// {
    -/// assert_eq!(tree.get(&10).unwrap(), &1000);
    -/// assert_eq!(tree.get(&20).unwrap(), &200);
    -/// assert_eq!(tree.get(&30).unwrap(), &300);
    +/// let mut iter = tree.iter();
    +/// assert_eq!(iter.next().unwrap(), (&10, &1000));
    +/// assert_eq!(iter.next().unwrap(), (&20, &200));
    +/// assert_eq!(iter.next().unwrap(), (&30, &300));
    +/// assert!(iter.next().is_none());
    /// }
    ///
    /// // Change the value of one of the elements.
    @@ -69,9 +85,11 @@ struct Node<K, V> {
    ///
    /// // Check that the tree reflects the update.
    /// {
    -/// assert_eq!(tree.get(&10).unwrap(), &1000);
    -/// assert_eq!(tree.get(&20).unwrap(), &200);
    -/// assert_eq!(tree.get(&30).unwrap(), &3000);
    +/// let mut iter = tree.iter();
    +/// assert_eq!(iter.next().unwrap(), (&10, &1000));
    +/// assert_eq!(iter.next().unwrap(), (&20, &200));
    +/// assert_eq!(iter.next().unwrap(), (&30, &3000));
    +/// assert!(iter.next().is_none());
    /// }
    ///
    /// // Remove an element.
    @@ -79,9 +97,10 @@ struct Node<K, V> {
    ///
    /// // Check that the tree reflects the removal.
    /// {
    -/// assert_eq!(tree.get(&10), None);
    -/// assert_eq!(tree.get(&20).unwrap(), &200);
    -/// assert_eq!(tree.get(&30).unwrap(), &3000);
    +/// let mut iter = tree.iter();
    +/// assert_eq!(iter.next().unwrap(), (&20, &200));
    +/// assert_eq!(iter.next().unwrap(), (&30, &3000));
    +/// assert!(iter.next().is_none());
    /// }
    ///
    /// # Ok::<(), Error>(())
    @@ -121,9 +140,11 @@ struct Node<K, V> {
    ///
    /// // Check the nodes we just inserted.
    /// {
    -/// assert_eq!(tree.get(&10).unwrap(), &100);
    -/// assert_eq!(tree.get(&20).unwrap(), &200);
    -/// assert_eq!(tree.get(&30).unwrap(), &300);
    +/// let mut iter = tree.iter();
    +/// assert_eq!(iter.next().unwrap(), (&10, &100));
    +/// assert_eq!(iter.next().unwrap(), (&20, &200));
    +/// assert_eq!(iter.next().unwrap(), (&30, &300));
    +/// assert!(iter.next().is_none());
    /// }
    ///
    /// // Remove a node, getting back ownership of it.
    @@ -131,9 +152,10 @@ struct Node<K, V> {
    ///
    /// // Check that the tree reflects the removal.
    /// {
    -/// assert_eq!(tree.get(&10).unwrap(), &100);
    -/// assert_eq!(tree.get(&20).unwrap(), &200);
    -/// assert_eq!(tree.get(&30), None);
    +/// let mut iter = tree.iter();
    +/// assert_eq!(iter.next().unwrap(), (&10, &100));
    +/// assert_eq!(iter.next().unwrap(), (&20, &200));
    +/// assert!(iter.next().is_none());
    /// }
    ///
    /// // Turn the node into a reservation so that we can reuse it with a different key/value.
    @@ -145,9 +167,11 @@ struct Node<K, V> {
    ///
    /// // Check that the tree reflect the new insertion.
    /// {
    -/// assert_eq!(tree.get(&10).unwrap(), &100);
    -/// assert_eq!(tree.get(&15).unwrap(), &150);
    -/// assert_eq!(tree.get(&20).unwrap(), &200);
    +/// let mut iter = tree.iter();
    +/// assert_eq!(iter.next().unwrap(), (&10, &100));
    +/// assert_eq!(iter.next().unwrap(), (&15, &150));
    +/// assert_eq!(iter.next().unwrap(), (&20, &200));
    +/// assert!(iter.next().is_none());
    /// }
    ///
    /// # Ok::<(), Error>(())
    @@ -188,6 +212,25 @@ pub fn try_reserve_node() -> Result<RBTreeNodeReservation<K, V>> {
    pub fn try_allocate_node(key: K, value: V) -> Result<RBTreeNode<K, V>> {
    Ok(Self::try_reserve_node()?.into_node(key, value))
    }
    +
    + /// Returns an iterator over the tree nodes, sorted by key.
    + pub fn iter(&self) -> RBTreeIterator<'_, K, V> {
    + RBTreeIterator {
    + _tree: PhantomData,
    + // SAFETY: `root` is valid as it's embedded in `self` and we have a valid `self`.
    + next: unsafe { bindings::rb_first(&self.root) },
    + }
    + }
    +
    + /// Returns an iterator over the keys of the nodes in the tree, in sorted order.
    + pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
    + self.iter().map(|(k, _)| k)
    + }
    +
    + /// Returns an iterator over the values of the nodes in the tree, sorted by key.
    + pub fn values(&self) -> impl Iterator<Item = &'_ V> {
    + self.iter().map(|(_, v)| v)
    + }
    }

    impl<K, V> RBTree<K, V>
    @@ -350,6 +393,52 @@ fn drop(&mut self) {
    }
    }

    +impl<'a, K, V> IntoIterator for &'a RBTree<K, V> {
    + type Item = (&'a K, &'a V);
    + type IntoIter = RBTreeIterator<'a, K, V>;
    +
    + fn into_iter(self) -> Self::IntoIter {
    + self.iter()
    + }
    +}
    +
    +/// An iterator over the nodes of a [`RBTree`].
    +///
    +/// Instances are created by calling [`RBTree::iter`].
    +pub struct RBTreeIterator<'a, K, V> {
    + _tree: PhantomData<&'a RBTree<K, V>>,
    + next: *mut bindings::rb_node,
    +}
    +
    +// SAFETY: An [`RBTree`] allows the same kinds of access to its values that a struct allows to its
    +// fields, so we use the same Send condition as would be used for a struct with K and V fields.
    +unsafe impl<'a, K: Send, V: Send> Send for RBTreeIterator<'a, K, V> {}
    +
    +// SAFETY: An [`RBTree`] allows the same kinds of access to its values that a struct allows to its
    +// fields, so we use the same Sync condition as would be used for a struct with K and V fields.
    +unsafe impl<'a, K: Sync, V: Sync> Sync for RBTreeIterator<'a, K, V> {}
    +
    +impl<'a, K, V> Iterator for RBTreeIterator<'a, K, V> {
    + type Item = (&'a K, &'a V);
    +
    + fn next(&mut self) -> Option<Self::Item> {
    + if self.next.is_null() {
    + return None;
    + }
    +
    + // SAFETY: All links fields we create are in a `Node<K, V>`.
    + let cur = unsafe { crate::container_of!(self.next, Node<K, V>, links) };
    +
    + // SAFETY: The reference to the tree used to create the iterator outlives the iterator, so
    + // the tree cannot change. By the tree invariant, all nodes are valid.
    + self.next = unsafe { bindings::rb_next(self.next) };
    +
    + // SAFETY: By the same reasoning above, it is safe to dereference the node. Additionally,
    + // it is ok to return a reference to members because the iterator must outlive it.
    + Some(unsafe { (&(*cur).key, &(*cur).value) })
    + }
    +}
    +
    /// A memory reservation for a red-black tree node.
    ///
    /// It contains the memory needed to hold a node that can be inserted into a red-black tree. One
    --
    2.44.0.rc0.258.g7320e95886-goog


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