rust/kernel/rbtree.rs | 238 ++++++++++++++++++++++++++++++++++-------- 1 file changed, 195 insertions(+), 43 deletions(-)
Sometimes we may need to iterate over, or find an element in a read
only (or read mostly) red-black tree, and in that case we don't need a
mutable reference to the tree, which we'll however have to take to be
able to use the current (mutable) cursor implementation.
This patch adds a simple immutable cursor implementation to RBTree,
which enables us to use an immutable tree reference. The existing
(fully featured) cursor implementation is renamed to CursorMut,
while retaining its functionality.
Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.se>
---
Changelog:
---------
v1 -> v2:
* corrected grammar hiccups
* logic for cursor_lower_bound[_mut] variants put into a separate
* function
* to_key_value_raw() removed from the immutable cursor implementation
v2 -> v3:
* find_best_match() modified to directly return links
* safety comments corrected for Send/Sync
v3 -> v4:
* &raw is used instead of addr_mut!
rust/kernel/rbtree.rs | 238 ++++++++++++++++++++++++++++++++++--------
1 file changed, 195 insertions(+), 43 deletions(-)
diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index b8fe6be6fcc4..10f4df081889 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -243,34 +243,64 @@ pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
}
/// Returns a cursor over the tree nodes, starting with the smallest key.
- pub fn cursor_front(&mut self) -> Option<Cursor<'_, K, V>> {
+ pub fn cursor_front_mut(&mut self) -> Option<CursorMut<'_, K, V>> {
let root = addr_of_mut!(self.root);
// SAFETY: `self.root` is always a valid root node
let current = unsafe { bindings::rb_first(root) };
NonNull::new(current).map(|current| {
// INVARIANT:
// - `current` is a valid node in the [`RBTree`] pointed to by `self`.
- Cursor {
+ CursorMut {
current,
tree: self,
}
})
}
+ /// Returns an immutable cursor over the tree nodes, starting with the smallest key.
+ pub fn cursor_front(&self) -> Option<Cursor<'_, K, V>> {
+ let root = &raw const self.root;
+ // SAFETY: `self.root` is always a valid root node
+ let current = unsafe { bindings::rb_first(root) };
+ NonNull::new(current).map(|current| {
+ // INVARIANT:
+ // - `current` is a valid node in the [`RBTree`] pointed to by `self`.
+ Cursor {
+ current,
+ _tree: PhantomData,
+ }
+ })
+ }
+
/// Returns a cursor over the tree nodes, starting with the largest key.
- pub fn cursor_back(&mut self) -> Option<Cursor<'_, K, V>> {
+ pub fn cursor_back_mut(&mut self) -> Option<CursorMut<'_, K, V>> {
let root = addr_of_mut!(self.root);
// SAFETY: `self.root` is always a valid root node
let current = unsafe { bindings::rb_last(root) };
NonNull::new(current).map(|current| {
// INVARIANT:
// - `current` is a valid node in the [`RBTree`] pointed to by `self`.
- Cursor {
+ CursorMut {
current,
tree: self,
}
})
}
+
+ /// Returns a cursor over the tree nodes, starting with the largest key.
+ pub fn cursor_back(&self) -> Option<Cursor<'_, K, V>> {
+ let root = &raw const self.root;
+ // SAFETY: `self.root` is always a valid root node
+ let current = unsafe { bindings::rb_last(root) };
+ NonNull::new(current).map(|current| {
+ // INVARIANT:
+ // - `current` is a valid node in the [`RBTree`] pointed to by `self`.
+ Cursor {
+ current,
+ _tree: PhantomData,
+ }
+ })
+ }
}
impl<K, V> RBTree<K, V>
@@ -421,12 +451,47 @@ pub fn remove(&mut self, key: &K) -> Option<V> {
/// If the given key exists, the cursor starts there.
/// Otherwise it starts with the first larger key in sort order.
/// If there is no larger key, it returns [`None`].
- pub fn cursor_lower_bound(&mut self, key: &K) -> Option<Cursor<'_, K, V>>
+ pub fn cursor_lower_bound_mut(&mut self, key: &K) -> Option<CursorMut<'_, K, V>>
+ where
+ K: Ord,
+ {
+ let best = self.find_best_match(key)?;
+
+ NonNull::new(best.as_ptr()).map(|current| {
+ // INVARIANT:
+ // - `current` is a valid node in the [`RBTree`] pointed to by `self`.
+ CursorMut {
+ current,
+ tree: self,
+ }
+ })
+ }
+
+ /// Returns a cursor over the tree nodes based on the given key.
+ ///
+ /// If the given key exists, the cursor starts there.
+ /// Otherwise it starts with the first larger key in sort order.
+ /// If there is no larger key, it returns [`None`].
+ pub fn cursor_lower_bound(&self, key: &K) -> Option<Cursor<'_, K, V>>
where
K: Ord,
{
+ let best = self.find_best_match(key)?;
+
+ NonNull::new(best.as_ptr()).map(|current| {
+ // INVARIANT:
+ // - `current` is a valid node in the [`RBTree`] pointed to by `self`.
+ Cursor {
+ current,
+ _tree: PhantomData,
+ }
+ })
+ }
+
+ fn find_best_match(&self, key: &K) -> Option<NonNull<bindings::rb_node>> {
let mut node = self.root.rb_node;
- let mut best_match: Option<NonNull<Node<K, V>>> = None;
+ let mut best_key: Option<&K> = None;
+ let mut best_links: Option<NonNull<bindings::rb_node>> = None;
while !node.is_null() {
// SAFETY: By the type invariant of `Self`, all non-null `rb_node` pointers stored in `self`
// point to the links field of `Node<K, V>` objects.
@@ -439,42 +504,30 @@ pub fn cursor_lower_bound(&mut self, key: &K) -> Option<Cursor<'_, K, V>>
let right_child = unsafe { (*node).rb_right };
match key.cmp(this_key) {
Ordering::Equal => {
- best_match = NonNull::new(this);
+ // SAFETY: `this` is a non-null node so it is valid by the type invariants.
+ best_links = Some(unsafe { NonNull::new_unchecked(&mut (*this).links) });
break;
}
Ordering::Greater => {
node = right_child;
}
Ordering::Less => {
- let is_better_match = match best_match {
+ let is_better_match = match best_key {
None => true,
Some(best) => {
- // SAFETY: `best` is a non-null node so it is valid by the type invariants.
- let best_key = unsafe { &(*best.as_ptr()).key };
- best_key > this_key
+ best > this_key
}
};
if is_better_match {
- best_match = NonNull::new(this);
+ best_key = Some(this_key);
+ // SAFETY: `this` is a non-null node so it is valid by the type invariants.
+ best_links = Some(unsafe { NonNull::new_unchecked(&mut (*this).links) });
}
node = left_child;
}
};
}
-
- let best = best_match?;
-
- // SAFETY: `best` is a non-null node so it is valid by the type invariants.
- let links = unsafe { addr_of_mut!((*best.as_ptr()).links) };
-
- NonNull::new(links).map(|current| {
- // INVARIANT:
- // - `current` is a valid node in the [`RBTree`] pointed to by `self`.
- Cursor {
- current,
- tree: self,
- }
- })
+ best_links
}
}
@@ -507,7 +560,7 @@ fn drop(&mut self) {
}
}
-/// A bidirectional cursor over the tree nodes, sorted by key.
+/// A bidirectional mutable cursor over the tree nodes, sorted by key.
///
/// # Examples
///
@@ -526,7 +579,7 @@ fn drop(&mut self) {
/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
///
/// // Get a cursor to the first element.
-/// let mut cursor = tree.cursor_front().unwrap();
+/// let mut cursor = tree.cursor_front_mut().unwrap();
/// let mut current = cursor.current();
/// assert_eq!(current, (&10, &100));
///
@@ -564,7 +617,7 @@ fn drop(&mut self) {
/// tree.try_create_and_insert(20, 200, flags::GFP_KERNEL)?;
/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
///
-/// let mut cursor = tree.cursor_back().unwrap();
+/// let mut cursor = tree.cursor_back_mut().unwrap();
/// let current = cursor.current();
/// assert_eq!(current, (&30, &300));
///
@@ -577,7 +630,7 @@ fn drop(&mut self) {
/// use kernel::rbtree::RBTree;
///
/// let mut tree: RBTree<u16, u16> = RBTree::new();
-/// assert!(tree.cursor_front().is_none());
+/// assert!(tree.cursor_front_mut().is_none());
///
/// # Ok::<(), Error>(())
/// ```
@@ -628,7 +681,7 @@ fn drop(&mut self) {
/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
///
/// // Retrieve a cursor.
-/// let mut cursor = tree.cursor_front().unwrap();
+/// let mut cursor = tree.cursor_front_mut().unwrap();
///
/// // Get a mutable reference to the current value.
/// let (k, v) = cursor.current_mut();
@@ -655,7 +708,7 @@ fn drop(&mut self) {
/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
///
/// // Remove the first element.
-/// let mut cursor = tree.cursor_front().unwrap();
+/// let mut cursor = tree.cursor_front_mut().unwrap();
/// let mut current = cursor.current();
/// assert_eq!(current, (&10, &100));
/// cursor = cursor.remove_current().0.unwrap();
@@ -665,7 +718,7 @@ fn drop(&mut self) {
/// assert_eq!(current, (&20, &200));
///
/// // Get a cursor to the last element, and remove it.
-/// cursor = tree.cursor_back().unwrap();
+/// cursor = tree.cursor_back_mut().unwrap();
/// current = cursor.current();
/// assert_eq!(current, (&30, &300));
///
@@ -694,7 +747,7 @@ fn drop(&mut self) {
/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
///
/// // Get a cursor to the first element.
-/// let mut cursor = tree.cursor_front().unwrap();
+/// let mut cursor = tree.cursor_front_mut().unwrap();
/// let mut current = cursor.current();
/// assert_eq!(current, (&10, &100));
///
@@ -702,7 +755,7 @@ fn drop(&mut self) {
/// assert!(cursor.remove_prev().is_none());
///
/// // Get a cursor to the last element.
-/// cursor = tree.cursor_back().unwrap();
+/// cursor = tree.cursor_back_mut().unwrap();
/// current = cursor.current();
/// assert_eq!(current, (&30, &300));
///
@@ -726,18 +779,47 @@ fn drop(&mut self) {
///
/// # Invariants
/// - `current` points to a node that is in the same [`RBTree`] as `tree`.
-pub struct Cursor<'a, K, V> {
+pub struct CursorMut<'a, K, V> {
tree: &'a mut RBTree<K, V>,
current: NonNull<bindings::rb_node>,
}
-// SAFETY: The [`Cursor`] has exclusive access to both `K` and `V`, so it is sufficient to require them to be `Send`.
-// The cursor only gives out immutable references to the keys, but since it has excusive access to those same
-// keys, `Send` is sufficient. `Sync` would be okay, but it is more restrictive to the user.
-unsafe impl<'a, K: Send, V: Send> Send for Cursor<'a, K, V> {}
+/// A bidirectional immutable cursor over the tree nodes, sorted by key. This is a simpler
+/// variant of CursorMut that is basically providing read only access.
+///
+/// # Examples
+///
+/// In the following example, we obtain a cursor to the first element in the tree.
+/// The cursor allows us to iterate bidirectionally over key/value pairs in the tree.
+///
+/// ```
+/// use kernel::{alloc::flags, rbtree::RBTree};
+///
+/// // Create a new tree.
+/// let mut tree = RBTree::new();
+///
+/// // Insert three elements.
+/// tree.try_create_and_insert(10, 100, flags::GFP_KERNEL)?;
+/// tree.try_create_and_insert(20, 200, flags::GFP_KERNEL)?;
+/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
+///
+/// // Get a cursor to the first element.
+/// let cursor = tree.cursor_front().unwrap();
+/// let current = cursor.current();
+/// assert_eq!(current, (&10, &100));
+///
+/// # Ok::<(), Error>(())
+pub struct Cursor<'a, K, V> {
+ _tree: PhantomData<&'a RBTree<K, V>>,
+ current: NonNull<bindings::rb_node>,
+}
-// SAFETY: The [`Cursor`] gives out immutable references to K and mutable references to V,
-// so it has the same thread safety requirements as mutable references.
+// SAFETY: The immutable cursor gives out shared access to `K` and `V` so if `K` and `V` can be
+// shared across threads, then it's safe to share the cursor.
+unsafe impl<'a, K: Sync, V: Sync> Send for Cursor<'a, K, V> {}
+
+// SAFETY: The immutable cursor gives out shared access to `K` and `V` so if `K` and `V` can be
+// shared across threads, then it's safe to share the cursor.
unsafe impl<'a, K: Sync, V: Sync> Sync for Cursor<'a, K, V> {}
impl<'a, K, V> Cursor<'a, K, V> {
@@ -749,6 +831,76 @@ pub fn current(&self) -> (&K, &V) {
unsafe { Self::to_key_value(self.current) }
}
+ /// # Safety
+ ///
+ /// - `node` must be a valid pointer to a node in an [`RBTree`].
+ /// - The caller has immutable access to `node` for the duration of `'b`.
+ unsafe fn to_key_value<'b>(node: NonNull<bindings::rb_node>) -> (&'b K, &'b V) {
+ // SAFETY: By the type invariant of `Self`, all non-null `rb_node` pointers stored in `self`
+ // point to the links field of `Node<K, V>` objects.
+ let this = unsafe { container_of!(node.as_ptr(), Node<K, V>, links) };
+ // SAFETY: The passed `node` is the current node or a non-null neighbor,
+ // thus `this` is valid by the type invariants.
+ let k = unsafe { &(*this).key };
+ // SAFETY: The passed `node` is the current node or a non-null neighbor,
+ // thus `this` is valid by the type invariants.
+ let v = unsafe { &(*this).value };
+ (k, v)
+ }
+
+ /// Access the previous node without moving the cursor.
+ pub fn peek_prev(&self) -> Option<(&K, &V)> {
+ self.peek(Direction::Prev)
+ }
+
+ /// Access the previous node without moving the cursor.
+ pub fn peek_next(&self) -> Option<(&K, &V)> {
+ self.peek(Direction::Next)
+ }
+
+ fn peek(&self, direction: Direction) -> Option<(&K, &V)> {
+ self.get_neighbor_raw(direction).map(|neighbor| {
+ // SAFETY:
+ // - `neighbor` is a valid tree node.
+ // - By the function signature, we have an immutable reference to `self`.
+ unsafe { Self::to_key_value(neighbor) }
+ })
+ }
+
+ fn get_neighbor_raw(&self, direction: Direction) -> Option<NonNull<bindings::rb_node>> {
+ // SAFETY: `self.current` is valid by the type invariants.
+ let neighbor = unsafe {
+ match direction {
+ Direction::Prev => bindings::rb_prev(self.current.as_ptr()),
+ Direction::Next => bindings::rb_next(self.current.as_ptr()),
+ }
+ };
+
+ NonNull::new(neighbor)
+ }
+}
+
+// SAFETY: The [`CursorMut`] has exclusive access to both `K` and `V`, so it is sufficient to
+// require them to be `Send`.
+// The cursor only gives out immutable references to the keys, but since it has excusive access to
+// those same keys, `Send` is sufficient. `Sync` would be okay, but it is more restrictive to the
+// user.
+unsafe impl<'a, K: Send, V: Send> Send for CursorMut<'a, K, V> {}
+
+// SAFETY: The [`CursorMut`] gives out immutable references to K and mutable references to V,
+// so it has the same thread safety requirements as mutable references.
+unsafe impl<'a, K: Sync, V: Sync> Sync for CursorMut<'a, K, V> {}
+
+
+impl<'a, K, V> CursorMut<'a, K, V> {
+ /// The current node
+ pub fn current(&self) -> (&K, &V) {
+ // SAFETY:
+ // - `self.current` is a valid node by the type invariants.
+ // - We have an immutable reference by the function signature.
+ unsafe { Self::to_key_value(self.current) }
+ }
+
/// The current node, with a mutable value
pub fn current_mut(&mut self) -> (&K, &mut V) {
// SAFETY:
@@ -920,7 +1072,7 @@ unsafe fn to_key_value_raw<'b>(node: NonNull<bindings::rb_node>) -> (&'b K, *mut
}
}
-/// Direction for [`Cursor`] operations.
+/// Direction for [`Cursor`] and [`CursorMut`] operations.
enum Direction {
/// the node immediately before, in sort order
Prev,
--
2.39.2© 2016 - 2025 Red Hat, Inc.