* [PATCH v10 1/5] rust: rbtree: add red-black tree implementation backed by the C version
2024-08-19 15:07 [PATCH v10 0/5] Red-black tree abstraction needed by Rust Binder Matt Gilbride
@ 2024-08-19 15:07 ` Matt Gilbride
2024-08-19 15:07 ` [PATCH v10 2/5] rust: rbtree: add iterator Matt Gilbride
` (3 subsequent siblings)
4 siblings, 0 replies; 9+ messages in thread
From: Matt Gilbride @ 2024-08-19 15:07 UTC (permalink / raw)
To: Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel, Matt Gilbride
From: Wedson Almeida Filho <wedsonaf@gmail.com>
The rust rbtree exposes a map-like interface over keys and values,
backed by the kernel red-black tree implementation. Values can be
inserted, deleted, and retrieved from a `RBTree` by key.
This base abstraction is used by binder to store key/value
pairs and perform lookups, for example the patch
"[PATCH RFC 03/20] rust_binder: add threading support"
in the binder RFC [1].
Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-3-08ba9197f637@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>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
---
rust/helpers/helpers.c | 1 +
rust/helpers/rbtree.c | 9 ++
rust/kernel/lib.rs | 1 +
rust/kernel/rbtree.rs | 432 +++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 443 insertions(+)
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 173533616c91..30f40149f3a9 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -15,6 +15,7 @@
#include "kunit.c"
#include "mutex.c"
#include "page.c"
+#include "rbtree.c"
#include "refcount.c"
#include "signal.c"
#include "slab.c"
diff --git a/rust/helpers/rbtree.c b/rust/helpers/rbtree.c
new file mode 100644
index 000000000000..6d404b84a9b5
--- /dev/null
+++ b/rust/helpers/rbtree.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/rbtree.h>
+
+void rust_helper_rb_link_node(struct rb_node *node, struct rb_node *parent,
+ struct rb_node **rb_link)
+{
+ rb_link_node(node, parent, rb_link);
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 274bdc1b0a82..80bdf2b1016d 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -43,6 +43,7 @@
pub mod page;
pub mod prelude;
pub mod print;
+pub mod rbtree;
mod static_assert;
#[doc(hidden)]
pub mod std_vendor;
diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
new file mode 100644
index 000000000000..51c53a25bc7d
--- /dev/null
+++ b/rust/kernel/rbtree.rs
@@ -0,0 +1,432 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Red-black trees.
+//!
+//! C header: [`include/linux/rbtree.h`](srctree/include/linux/rbtree.h)
+//!
+//! Reference: <https://www.kernel.org/doc/html/latest/core-api/rbtree.html>
+
+use crate::{alloc::Flags, bindings, container_of, error::Result, prelude::*};
+use alloc::boxed::Box;
+use core::{
+ cmp::{Ord, Ordering},
+ marker::PhantomData,
+ mem::MaybeUninit,
+ ptr::{addr_of_mut, NonNull},
+};
+
+/// A red-black tree with owned nodes.
+///
+/// It is backed by the kernel C red-black trees.
+///
+/// # Examples
+///
+/// In the example below we do several operations on a tree. We note that insertions may fail if
+/// the system is out of memory.
+///
+/// ```
+/// use kernel::{alloc::flags, rbtree::{RBTree, RBTreeNode, RBTreeNodeReservation}};
+///
+/// // Create a new tree.
+/// let mut tree = RBTree::new();
+///
+/// // Insert three elements.
+/// tree.try_create_and_insert(20, 200, flags::GFP_KERNEL)?;
+/// tree.try_create_and_insert(10, 100, flags::GFP_KERNEL)?;
+/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
+///
+/// // 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);
+/// }
+///
+/// // Replace one of the elements.
+/// tree.try_create_and_insert(10, 1000, flags::GFP_KERNEL)?;
+///
+/// // 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);
+/// }
+///
+/// // Change the value of one of the elements.
+/// *tree.get_mut(&30).unwrap() = 3000;
+///
+/// // 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);
+/// }
+///
+/// // Remove an element.
+/// tree.remove(&10);
+///
+/// // 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);
+/// }
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// In the example below, we first allocate a node, acquire a spinlock, then insert the node into
+/// the tree. This is useful when the insertion context does not allow sleeping, for example, when
+/// holding a spinlock.
+///
+/// ```
+/// use kernel::{alloc::flags, rbtree::{RBTree, RBTreeNode}, sync::SpinLock};
+///
+/// fn insert_test(tree: &SpinLock<RBTree<u32, u32>>) -> Result {
+/// // Pre-allocate node. This may fail (as it allocates memory).
+/// let node = RBTreeNode::new(10, 100, flags::GFP_KERNEL)?;
+///
+/// // Insert node while holding the lock. It is guaranteed to succeed with no allocation
+/// // attempts.
+/// let mut guard = tree.lock();
+/// guard.insert(node);
+/// Ok(())
+/// }
+/// ```
+///
+/// In the example below, we reuse an existing node allocation from an element we removed.
+///
+/// ```
+/// use kernel::{alloc::flags, rbtree::{RBTree, RBTreeNodeReservation}};
+///
+/// // Create a new tree.
+/// let mut tree = RBTree::new();
+///
+/// // Insert three elements.
+/// tree.try_create_and_insert(20, 200, flags::GFP_KERNEL)?;
+/// tree.try_create_and_insert(10, 100, flags::GFP_KERNEL)?;
+/// tree.try_create_and_insert(30, 300, flags::GFP_KERNEL)?;
+///
+/// // 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);
+/// }
+///
+/// // Remove a node, getting back ownership of it.
+/// let existing = tree.remove(&30).unwrap();
+///
+/// // 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);
+/// }
+///
+/// // Create a preallocated reservation that we can re-use later.
+/// let reservation = RBTreeNodeReservation::new(flags::GFP_KERNEL)?;
+///
+/// // Insert a new node into the tree, reusing the previous allocation. This is guaranteed to
+/// // succeed (no memory allocations).
+/// tree.insert(reservation.into_node(15, 150));
+///
+/// // 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);
+/// }
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// # Invariants
+///
+/// Non-null parent/children pointers stored in instances of the `rb_node` C struct are always
+/// valid, and pointing to a field of our internal representation of a node.
+pub struct RBTree<K, V> {
+ root: bindings::rb_root,
+ _p: PhantomData<Node<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 Send condition as would be used for a struct with K and V fields.
+unsafe impl<K: Send, V: Send> Send for RBTree<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<K: Sync, V: Sync> Sync for RBTree<K, V> {}
+
+impl<K, V> RBTree<K, V> {
+ /// Creates a new and empty tree.
+ pub fn new() -> Self {
+ Self {
+ // INVARIANT: There are no nodes in the tree, so the invariant holds vacuously.
+ root: bindings::rb_root::default(),
+ _p: PhantomData,
+ }
+ }
+}
+
+impl<K, V> RBTree<K, V>
+where
+ K: Ord,
+{
+ /// Tries to insert a new value into the tree.
+ ///
+ /// It overwrites a node if one already exists with the same key and returns it (containing the
+ /// key/value pair). Returns [`None`] if a node with the same key didn't already exist.
+ ///
+ /// Returns an error if it cannot allocate memory for the new node.
+ pub fn try_create_and_insert(
+ &mut self,
+ key: K,
+ value: V,
+ flags: Flags,
+ ) -> Result<Option<RBTreeNode<K, V>>> {
+ Ok(self.insert(RBTreeNode::new(key, value, flags)?))
+ }
+
+ /// Inserts a new node into the tree.
+ ///
+ /// It overwrites a node if one already exists with the same key and returns it (containing the
+ /// key/value pair). Returns [`None`] if a node with the same key didn't already exist.
+ ///
+ /// This function always succeeds.
+ pub fn insert(&mut self, RBTreeNode { node }: RBTreeNode<K, V>) -> Option<RBTreeNode<K, V>> {
+ let node = Box::into_raw(node);
+ // SAFETY: `node` is valid at least until we call `Box::from_raw`, which only happens when
+ // the node is removed or replaced.
+ let node_links = unsafe { addr_of_mut!((*node).links) };
+
+ // The parameters of `bindings::rb_link_node` are as follows:
+ // - `node`: A pointer to an uninitialized node being inserted.
+ // - `parent`: A pointer to an existing node in the tree. One of its child pointers must be
+ // null, and `node` will become a child of `parent` by replacing that child pointer
+ // with a pointer to `node`.
+ // - `rb_link`: A pointer to either the left-child or right-child field of `parent`. This
+ // specifies which child of `parent` should hold `node` after this call. The
+ // value of `*rb_link` must be null before the call to `rb_link_node`. If the
+ // red/black tree is empty, then it’s also possible for `parent` to be null. In
+ // this case, `rb_link` is a pointer to the `root` field of the red/black tree.
+ //
+ // We will traverse the tree looking for a node that has a null pointer as its child,
+ // representing an empty subtree where we can insert our new node. We need to make sure
+ // that we preserve the ordering of the nodes in the tree. In each iteration of the loop
+ // we store `parent` and `child_field_of_parent`, and the new `node` will go somewhere
+ // in the subtree of `parent` that `child_field_of_parent` points at. Once
+ // we find an empty subtree, we can insert the new node using `rb_link_node`.
+ let mut parent = core::ptr::null_mut();
+ let mut child_field_of_parent: &mut *mut bindings::rb_node = &mut self.root.rb_node;
+ while !child_field_of_parent.is_null() {
+ parent = *child_field_of_parent;
+
+ // We need to determine whether `node` should be the left or right child of `parent`,
+ // so we will compare with the `key` field of `parent` a.k.a. `this` below.
+ //
+ // 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!(parent, Node<K, V>, links) };
+
+ // SAFETY: `this` is a non-null node so it is valid by the type invariants. `node` is
+ // valid until the node is removed.
+ match unsafe { (*node).key.cmp(&(*this).key) } {
+ // We would like `node` to be the left child of `parent`. Move to this child to check
+ // whether we can use it, or continue searching, at the next iteration.
+ //
+ // SAFETY: `parent` is a non-null node so it is valid by the type invariants.
+ Ordering::Less => child_field_of_parent = unsafe { &mut (*parent).rb_left },
+ // We would like `node` to be the right child of `parent`. Move to this child to check
+ // whether we can use it, or continue searching, at the next iteration.
+ //
+ // SAFETY: `parent` is a non-null node so it is valid by the type invariants.
+ Ordering::Greater => child_field_of_parent = unsafe { &mut (*parent).rb_right },
+ Ordering::Equal => {
+ // There is an existing node in the tree with this key, and that node is
+ // `parent`. Thus, we are replacing parent with a new node.
+ //
+ // INVARIANT: We are replacing an existing node with a new one, which is valid.
+ // It remains valid because we "forgot" it with `Box::into_raw`.
+ // SAFETY: All pointers are non-null and valid.
+ unsafe { bindings::rb_replace_node(parent, node_links, &mut self.root) };
+
+ // INVARIANT: The node is being returned and the caller may free it, however,
+ // it was removed from the tree. So the invariants still hold.
+ return Some(RBTreeNode {
+ // SAFETY: `this` was a node in the tree, so it is valid.
+ node: unsafe { Box::from_raw(this.cast_mut()) },
+ });
+ }
+ }
+ }
+
+ // INVARIANT: We are linking in a new node, which is valid. It remains valid because we
+ // "forgot" it with `Box::into_raw`.
+ // SAFETY: All pointers are non-null and valid (`*child_field_of_parent` is null, but `child_field_of_parent` is a
+ // mutable reference).
+ unsafe { bindings::rb_link_node(node_links, parent, child_field_of_parent) };
+
+ // SAFETY: All pointers are valid. `node` has just been inserted into the tree.
+ unsafe { bindings::rb_insert_color(node_links, &mut self.root) };
+ None
+ }
+
+ /// Returns a node with the given key, if one exists.
+ fn find(&self, key: &K) -> Option<NonNull<Node<K, V>>> {
+ let mut node = self.root.rb_node;
+ 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.
+ let this = unsafe { container_of!(node, Node<K, V>, links) };
+ // SAFETY: `this` is a non-null node so it is valid by the type invariants.
+ node = match key.cmp(unsafe { &(*this).key }) {
+ // SAFETY: `node` is a non-null node so it is valid by the type invariants.
+ Ordering::Less => unsafe { (*node).rb_left },
+ // SAFETY: `node` is a non-null node so it is valid by the type invariants.
+ Ordering::Greater => unsafe { (*node).rb_right },
+ Ordering::Equal => return NonNull::new(this.cast_mut()),
+ }
+ }
+ None
+ }
+
+ /// Returns a reference to the value corresponding to the key.
+ pub fn get(&self, key: &K) -> Option<&V> {
+ // SAFETY: The `find` return value is a node in the tree, so it is valid.
+ self.find(key).map(|node| unsafe { &node.as_ref().value })
+ }
+
+ /// Returns a mutable reference to the value corresponding to the key.
+ pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
+ // SAFETY: The `find` return value is a node in the tree, so it is valid.
+ self.find(key)
+ .map(|mut node| unsafe { &mut node.as_mut().value })
+ }
+
+ /// Removes the node with the given key from the tree.
+ ///
+ /// It returns the node that was removed if one exists, or [`None`] otherwise.
+ fn remove_node(&mut self, key: &K) -> Option<RBTreeNode<K, V>> {
+ let mut node = self.find(key)?;
+
+ // SAFETY: The `find` return value is a node in the tree, so it is valid.
+ unsafe { bindings::rb_erase(&mut node.as_mut().links, &mut self.root) };
+
+ // INVARIANT: The node is being returned and the caller may free it, however, it was
+ // removed from the tree. So the invariants still hold.
+ Some(RBTreeNode {
+ // SAFETY: The `find` return value was a node in the tree, so it is valid.
+ node: unsafe { Box::from_raw(node.as_ptr()) },
+ })
+ }
+
+ /// Removes the node with the given key from the tree.
+ ///
+ /// It returns the value that was removed if one exists, or [`None`] otherwise.
+ pub fn remove(&mut self, key: &K) -> Option<V> {
+ self.remove_node(key).map(|node| node.node.value)
+ }
+}
+
+impl<K, V> Default for RBTree<K, V> {
+ fn default() -> Self {
+ Self::new()
+ }
+}
+
+impl<K, V> Drop for RBTree<K, V> {
+ fn drop(&mut self) {
+ // SAFETY: `root` is valid as it's embedded in `self` and we have a valid `self`.
+ let mut next = unsafe { bindings::rb_first_postorder(&self.root) };
+
+ // INVARIANT: The loop invariant is that all tree nodes from `next` in postorder are valid.
+ while !next.is_null() {
+ // SAFETY: All links fields we create are in a `Node<K, V>`.
+ let this = unsafe { container_of!(next, Node<K, V>, links) };
+
+ // Find out what the next node is before disposing of the current one.
+ // SAFETY: `next` and all nodes in postorder are still valid.
+ next = unsafe { bindings::rb_next_postorder(next) };
+
+ // INVARIANT: This is the destructor, so we break the type invariant during clean-up,
+ // but it is not observable. The loop invariant is still maintained.
+
+ // SAFETY: `this` is valid per the loop invariant.
+ unsafe { drop(Box::from_raw(this.cast_mut())) };
+ }
+ }
+}
+
+/// 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
+/// can be obtained by directly allocating it ([`RBTreeNodeReservation::new`]).
+pub struct RBTreeNodeReservation<K, V> {
+ node: Box<MaybeUninit<Node<K, V>>>,
+}
+
+impl<K, V> RBTreeNodeReservation<K, V> {
+ /// Allocates memory for a node to be eventually initialised and inserted into the tree via a
+ /// call to [`RBTree::insert`].
+ pub fn new(flags: Flags) -> Result<RBTreeNodeReservation<K, V>> {
+ Ok(RBTreeNodeReservation {
+ node: <Box<_> as BoxExt<_>>::new_uninit(flags)?,
+ })
+ }
+}
+
+// SAFETY: This doesn't actually contain K or V, and is just a memory allocation. Those can always
+// be moved across threads.
+unsafe impl<K, V> Send for RBTreeNodeReservation<K, V> {}
+
+// SAFETY: This doesn't actually contain K or V, and is just a memory allocation.
+unsafe impl<K, V> Sync for RBTreeNodeReservation<K, V> {}
+
+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 {
+ key,
+ value,
+ links: bindings::rb_node::default(),
+ },
+ );
+ RBTreeNode { node }
+ }
+}
+
+/// A red-black tree node.
+///
+/// The node is fully initialised (with key and value) and can be inserted into a tree without any
+/// extra allocations or failure paths.
+pub struct RBTreeNode<K, V> {
+ node: Box<Node<K, V>>,
+}
+
+impl<K, V> RBTreeNode<K, V> {
+ /// Allocates and initialises a node that can be inserted into the tree via
+ /// [`RBTree::insert`].
+ pub fn new(key: K, value: V, flags: Flags) -> Result<RBTreeNode<K, V>> {
+ Ok(RBTreeNodeReservation::new(flags)?.into_node(key, value))
+ }
+}
+
+// SAFETY: If K and V can be sent across threads, then it's also okay to send [`RBTreeNode`] across
+// threads.
+unsafe impl<K: Send, V: Send> Send for RBTreeNode<K, V> {}
+
+// SAFETY: If K and V can be accessed without synchronization, then it's also okay to access
+// [`RBTreeNode`] without synchronization.
+unsafe impl<K: Sync, V: Sync> Sync for RBTreeNode<K, V> {}
+
+struct Node<K, V> {
+ links: bindings::rb_node,
+ key: K,
+ value: V,
+}
--
2.46.0.184.g6999bdac58-goog
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH v10 2/5] rust: rbtree: add iterator
2024-08-19 15:07 [PATCH v10 0/5] Red-black tree abstraction needed by Rust Binder Matt Gilbride
2024-08-19 15:07 ` [PATCH v10 1/5] rust: rbtree: add red-black tree implementation backed by the C version Matt Gilbride
@ 2024-08-19 15:07 ` Matt Gilbride
2024-08-19 15:07 ` [PATCH v10 3/5] rust: rbtree: add mutable iterator Matt Gilbride
` (2 subsequent siblings)
4 siblings, 0 replies; 9+ messages in thread
From: Matt Gilbride @ 2024-08-19 15:07 UTC (permalink / raw)
To: Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel, Matt Gilbride
From: Wedson Almeida Filho <wedsonaf@gmail.com>
- Add Iterator implementation 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>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
---
rust/kernel/rbtree.rs | 130 +++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 112 insertions(+), 18 deletions(-)
diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index 51c53a25bc7d..29e7a0795266 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -42,14 +42,30 @@
/// 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, flags::GFP_KERNEL)?;
///
/// // 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.
@@ -57,9 +73,11 @@
///
/// // 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.
@@ -67,9 +85,10 @@
///
/// // 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>(())
@@ -109,9 +128,11 @@
///
/// // 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.
@@ -119,9 +140,10 @@
///
/// // 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());
/// }
///
/// // Create a preallocated reservation that we can re-use later.
@@ -133,9 +155,11 @@
///
/// // 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>(())
@@ -167,6 +191,26 @@ pub fn new() -> Self {
_p: PhantomData,
}
}
+
+ /// Returns an iterator over the tree nodes, sorted by key.
+ pub fn iter(&self) -> Iter<'_, K, V> {
+ // INVARIANT: `bindings::rb_first` returns a valid pointer to a tree node given a valid pointer to a tree root.
+ Iter {
+ _tree: PhantomData,
+ // SAFETY: `self.root` is a valid pointer to the tree root.
+ 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>
@@ -358,6 +402,56 @@ fn drop(&mut self) {
}
}
+impl<'a, K, V> IntoIterator for &'a RBTree<K, V> {
+ type Item = (&'a K, &'a V);
+ type IntoIter = Iter<'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`].
+///
+/// # Invariants
+/// - `self.next` is a valid pointer.
+/// - `self.next` points to a node stored inside of a valid `RBTree`.
+pub struct Iter<'a, K, V> {
+ _tree: PhantomData<&'a RBTree<K, V>>,
+ next: *mut bindings::rb_node,
+}
+
+// SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
+// thread safety requirements as immutable references.
+unsafe impl<'a, K: Sync, V: Sync> Send for Iter<'a, K, V> {}
+
+// SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
+// thread safety requirements as immutable references.
+unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
+
+impl<'a, K, V> Iterator for Iter<'a, K, V> {
+ type Item = (&'a K, &'a V);
+
+ fn next(&mut self) -> Option<Self::Item> {
+ if self.next.is_null() {
+ return None;
+ }
+
+ // SAFETY: By the type invariant of `Iter`, `self.next` is a valid node in an `RBTree`,
+ // and by the type invariant of `RBTree`, all nodes point to the links field of `Node<K, V>` objects.
+ let cur = unsafe { container_of!(self.next, Node<K, V>, links) };
+
+ // SAFETY: `self.next` is a valid tree node by the type invariants.
+ 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.
///
///
--
2.46.0.184.g6999bdac58-goog
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH v10 3/5] rust: rbtree: add mutable iterator
2024-08-19 15:07 [PATCH v10 0/5] Red-black tree abstraction needed by Rust Binder Matt Gilbride
2024-08-19 15:07 ` [PATCH v10 1/5] rust: rbtree: add red-black tree implementation backed by the C version Matt Gilbride
2024-08-19 15:07 ` [PATCH v10 2/5] rust: rbtree: add iterator Matt Gilbride
@ 2024-08-19 15:07 ` Matt Gilbride
2024-08-20 7:35 ` Benno Lossin
2024-08-19 15:07 ` [PATCH v10 4/5] rust: rbtree: add cursor Matt Gilbride
2024-08-19 15:07 ` [PATCH v10 5/5] rust: rbtree: add `RBTree::entry` Matt Gilbride
4 siblings, 1 reply; 9+ messages in thread
From: Matt Gilbride @ 2024-08-19 15:07 UTC (permalink / raw)
To: Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel, Matt Gilbride
From: Wedson Almeida Filho <wedsonaf@gmail.com>
Add mutable Iterator implementation for `RBTree`,
allowing iteration over (key, value) pairs in key order. Only values are
mutable, as mutating keys implies modifying a node's position in the tree.
Mutable iteration is used by the binder driver during shutdown to
clean up the tree maintained by the "range allocator" [1].
Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@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>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
---
rust/kernel/rbtree.rs | 104 +++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 90 insertions(+), 14 deletions(-)
diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index 29e7a0795266..6c9a8f0a00e6 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -12,7 +12,7 @@
cmp::{Ord, Ordering},
marker::PhantomData,
mem::MaybeUninit,
- ptr::{addr_of_mut, NonNull},
+ ptr::{addr_of_mut, from_mut, NonNull},
};
/// A red-black tree with owned nodes.
@@ -194,11 +194,31 @@ pub fn new() -> Self {
/// Returns an iterator over the tree nodes, sorted by key.
pub fn iter(&self) -> Iter<'_, K, V> {
- // INVARIANT: `bindings::rb_first` returns a valid pointer to a tree node given a valid pointer to a tree root.
Iter {
_tree: PhantomData,
- // SAFETY: `self.root` is a valid pointer to the tree root.
- next: unsafe { bindings::rb_first(&self.root) },
+ // INVARIANT:
+ // - `self.root` is a valid pointer to a tree root.
+ // - `bindings::rb_first` produces a valid pointer to a node given `root` is valid.
+ iter_raw: IterRaw {
+ // SAFETY: by the invariants, all pointers are valid.
+ next: unsafe { bindings::rb_first(&self.root) },
+ _phantom: PhantomData,
+ },
+ }
+ }
+
+ /// Returns a mutable iterator over the tree nodes, sorted by key.
+ pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
+ IterMut {
+ _tree: PhantomData,
+ // INVARIANT:
+ // - `self.root` is a valid pointer to a tree root.
+ // - `bindings::rb_first` produces a valid pointer to a node given `root` is valid.
+ iter_raw: IterRaw {
+ // SAFETY: by the invariants, all pointers are valid.
+ next: unsafe { bindings::rb_first(from_mut(&mut self.root)) },
+ _phantom: PhantomData,
+ },
}
}
@@ -211,6 +231,11 @@ pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
pub fn values(&self) -> impl Iterator<Item = &'_ V> {
self.iter().map(|(_, v)| v)
}
+
+ /// Returns a mutable iterator over the values of the nodes in the tree, sorted by key.
+ pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
+ self.iter_mut().map(|(_, v)| v)
+ }
}
impl<K, V> RBTree<K, V>
@@ -414,13 +439,9 @@ fn into_iter(self) -> Self::IntoIter {
/// An iterator over the nodes of a [`RBTree`].
///
/// Instances are created by calling [`RBTree::iter`].
-///
-/// # Invariants
-/// - `self.next` is a valid pointer.
-/// - `self.next` points to a node stored inside of a valid `RBTree`.
pub struct Iter<'a, K, V> {
_tree: PhantomData<&'a RBTree<K, V>>,
- next: *mut bindings::rb_node,
+ iter_raw: IterRaw<K, V>,
}
// SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
@@ -434,21 +455,76 @@ unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
impl<'a, K, V> Iterator for Iter<'a, K, V> {
type Item = (&'a K, &'a V);
+ fn next(&mut self) -> Option<Self::Item> {
+ // SAFETY: Due to `self._tree`, `k` and `v` are valid for the lifetime of `'a`.
+ self.iter_raw.next().map(|(k, v)| unsafe { (&*k, &*v) })
+ }
+}
+
+impl<'a, K, V> IntoIterator for &'a mut RBTree<K, V> {
+ type Item = (&'a K, &'a mut V);
+ type IntoIter = IterMut<'a, K, V>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ self.iter_mut()
+ }
+}
+
+/// A mutable iterator over the nodes of a [`RBTree`].
+///
+/// Instances are created by calling [`RBTree::iter_mut`].
+pub struct IterMut<'a, K, V> {
+ _tree: PhantomData<&'a mut RBTree<K, V>>,
+ iter_raw: IterRaw<K, V>,
+}
+
+// SAFETY: The [`IterMut`] has exclusive access to both `K` and `V`, so it is sufficient to require them to be `Send`.
+// The iterator only gives out immutable references to the keys, but since the iterator 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 IterMut<'a, K, V> {}
+
+// SAFETY: The [`IterMut`] 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 IterMut<'a, K, V> {}
+
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+ type Item = (&'a K, &'a mut V);
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.iter_raw.next().map(|(k, v)|
+ // SAFETY: Due to `&mut self`, we have exclusive access to `k` and `v`, for the lifetime of `'a`.
+ unsafe { (&*k, &mut *v) })
+ }
+}
+
+/// A raw iterator over the nodes of a [`RBTree`].
+///
+/// # Invariants
+/// - `self.next` is a valid pointer.
+/// - `self.next` points to a node stored inside of a valid `RBTree`.
+struct IterRaw<K, V> {
+ next: *mut bindings::rb_node,
+ _phantom: PhantomData<fn() -> (K, V)>,
+}
+
+impl<K, V> Iterator for IterRaw<K, V> {
+ type Item = (*mut K, *mut V);
+
fn next(&mut self) -> Option<Self::Item> {
if self.next.is_null() {
return None;
}
- // SAFETY: By the type invariant of `Iter`, `self.next` is a valid node in an `RBTree`,
+ // SAFETY: By the type invariant of `IterRaw`, `self.next` is a valid node in an `RBTree`,
// and by the type invariant of `RBTree`, all nodes point to the links field of `Node<K, V>` objects.
- let cur = unsafe { container_of!(self.next, Node<K, V>, links) };
+ let cur: *mut Node<K, V> =
+ unsafe { container_of!(self.next, Node<K, V>, links) }.cast_mut();
// SAFETY: `self.next` is a valid tree node by the type invariants.
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) })
+ // SAFETY: By the same reasoning above, it is safe to dereference the node.
+ Some(unsafe { (addr_of_mut!((*cur).key), addr_of_mut!((*cur).value)) })
}
}
--
2.46.0.184.g6999bdac58-goog
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH v10 3/5] rust: rbtree: add mutable iterator
2024-08-19 15:07 ` [PATCH v10 3/5] rust: rbtree: add mutable iterator Matt Gilbride
@ 2024-08-20 7:35 ` Benno Lossin
0 siblings, 0 replies; 9+ messages in thread
From: Benno Lossin @ 2024-08-20 7:35 UTC (permalink / raw)
To: Matt Gilbride, Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho,
Boqun Feng, Gary Guo, Björn Roy Baron, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel
On 19.08.24 17:07, Matt Gilbride wrote:
> From: Wedson Almeida Filho <wedsonaf@gmail.com>
>
> Add mutable Iterator implementation for `RBTree`,
> allowing iteration over (key, value) pairs in key order. Only values are
> mutable, as mutating keys implies modifying a node's position in the tree.
>
> Mutable iteration is used by the binder driver during shutdown to
> clean up the tree maintained by the "range allocator" [1].
>
> Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@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>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Matt Gilbride <mattgilbride@google.com>
> ---
I got one nit below, but it already looks good:
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> rust/kernel/rbtree.rs | 104 +++++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 90 insertions(+), 14 deletions(-)
[...]
> +impl<K, V> Iterator for IterRaw<K, V> {
> + type Item = (*mut K, *mut V);
> +
> fn next(&mut self) -> Option<Self::Item> {
> if self.next.is_null() {
> return None;
> }
>
> - // SAFETY: By the type invariant of `Iter`, `self.next` is a valid node in an `RBTree`,
> + // SAFETY: By the type invariant of `IterRaw`, `self.next` is a valid node in an `RBTree`,
> // and by the type invariant of `RBTree`, all nodes point to the links field of `Node<K, V>` objects.
> - let cur = unsafe { container_of!(self.next, Node<K, V>, links) };
> + let cur: *mut Node<K, V> =
Do you need to specify this type? If not then the line would fit on one.
---
Cheers,
Benno
> + unsafe { container_of!(self.next, Node<K, V>, links) }.cast_mut();
>
> // SAFETY: `self.next` is a valid tree node by the type invariants.
> 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) })
> + // SAFETY: By the same reasoning above, it is safe to dereference the node.
> + Some(unsafe { (addr_of_mut!((*cur).key), addr_of_mut!((*cur).value)) })
> }
> }
>
>
> --
> 2.46.0.184.g6999bdac58-goog
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH v10 4/5] rust: rbtree: add cursor
2024-08-19 15:07 [PATCH v10 0/5] Red-black tree abstraction needed by Rust Binder Matt Gilbride
` (2 preceding siblings ...)
2024-08-19 15:07 ` [PATCH v10 3/5] rust: rbtree: add mutable iterator Matt Gilbride
@ 2024-08-19 15:07 ` Matt Gilbride
2024-08-20 8:00 ` Benno Lossin
2024-08-19 15:07 ` [PATCH v10 5/5] rust: rbtree: add `RBTree::entry` Matt Gilbride
4 siblings, 1 reply; 9+ messages in thread
From: Matt Gilbride @ 2024-08-19 15:07 UTC (permalink / raw)
To: Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel, Matt Gilbride
Add a cursor interface to `RBTree`, supporting the following use cases:
- Inspect the current node pointed to by the cursor, inspect/move to
it's neighbors in sort order (bidirectionally).
- Mutate the tree itself by removing the current node pointed to by the
cursor, or one of its neighbors.
Add functions to obtain a cursor to the tree by key:
- The node with the smallest key
- The node with the largest key
- The node matching the given key, or the one with the next larger key
The cursor abstraction is needed by the binder driver to efficiently
search for nodes and (conditionally) modify them, as well as their
neighbors [1].
Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@google.com/ [1]
Co-developed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
---
rust/kernel/rbtree.rs | 541 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 541 insertions(+)
diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index 6c9a8f0a00e6..754af0db86b5 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -236,6 +236,40 @@ pub fn values(&self) -> impl Iterator<Item = &'_ V> {
pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
self.iter_mut().map(|(_, v)| v)
}
+
+ /// Returns a cursor over the tree nodes, starting with the smallest key.
+ pub fn cursor_front(&mut self) -> Option<Cursor<'_, 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`.
+ // - Due to the type signature of this function, the returned [`Cursor`]
+ // borrows mutably from `self`.
+ Cursor {
+ current,
+ tree: self,
+ }
+ })
+ }
+
+ /// Returns a cursor over the tree nodes, starting with the largest key.
+ pub fn cursor_back(&mut self) -> Option<Cursor<'_, 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`.
+ // - Due to the type signature of this function, the returned [`Cursor`]
+ // borrows mutably from `self`.
+ Cursor {
+ current,
+ tree: self,
+ }
+ })
+ }
}
impl<K, V> RBTree<K, V>
@@ -396,6 +430,75 @@ fn remove_node(&mut self, key: &K) -> Option<RBTreeNode<K, V>> {
pub fn remove(&mut self, key: &K) -> Option<V> {
self.remove_node(key).map(|node| node.node.value)
}
+
+ /// 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(&mut self, key: &K) -> Option<Cursor<'_, K, V>>
+ where
+ K: Ord,
+ {
+ let mut node = self.root.rb_node;
+ let mut best_match: Option<NonNull<Node<K, V>>> = 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.
+ let this = unsafe { container_of!(node, Node<K, V>, links) }.cast_mut();
+ // SAFETY: `this` is a non-null node so it is valid by the type invariants.
+ let this_key = unsafe { &(*this).key };
+ // SAFETY: `node` is a non-null node so it is valid by the type invariants.
+ let left_child = unsafe { (*node).rb_left };
+ // SAFETY: `node` is a non-null node so it is valid by the type invariants.
+ let right_child = unsafe { (*node).rb_right };
+ if key == this_key {
+ return NonNull::new(node).map(|current| {
+ // INVARIANT:
+ // - `node` is a valid node in the [`RBTree`] pointed to by `self`.
+ // - Due to the type signature of this function, the returned [`Cursor`]
+ // borrows mutably from `self`.
+ Cursor {
+ current,
+ tree: self,
+ }
+ });
+ } else {
+ node = if key > this_key {
+ right_child
+ } else {
+ let is_better_match = match best_match {
+ 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
+ }
+ };
+ if is_better_match {
+ best_match = NonNull::new(this);
+ }
+ 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`.
+ // - Due to the type signature of this function, the returned [`Cursor`]
+ // borrows mutably from `self`.
+ Cursor {
+ current,
+ tree: self,
+ }
+ })
+ }
}
impl<K, V> Default for RBTree<K, V> {
@@ -427,6 +530,439 @@ fn drop(&mut self) {
}
}
+/// A bidirectional cursor over the tree nodes, sorted by key.
+///
+/// # 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 mut cursor = tree.cursor_front().unwrap();
+/// let mut current = cursor.current();
+/// assert_eq!(current, (&10, &100));
+///
+/// // Move the cursor, updating it to the 2nd element.
+/// cursor = cursor.move_next().unwrap();
+/// current = cursor.current();
+/// assert_eq!(current, (&20, &200));
+///
+/// // Peek at the next element without impacting the cursor.
+/// let next = cursor.peek_next().unwrap();
+/// assert_eq!(next, (&30, &300));
+/// current = cursor.current();
+/// assert_eq!(current, (&20, &200));
+///
+/// // Moving past the last element causes the cursor to return [`None`].
+/// cursor = cursor.move_next().unwrap();
+/// current = cursor.current();
+/// assert_eq!(current, (&30, &300));
+/// let cursor = cursor.move_next();
+/// assert!(cursor.is_none());
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// A cursor can also be obtained at the last element 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)?;
+///
+/// let mut cursor = tree.cursor_back().unwrap();
+/// let current = cursor.current();
+/// assert_eq!(current, (&30, &300));
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// Obtaining a cursor returns [`None`] if the tree is empty.
+///
+/// ```
+/// use kernel::rbtree::RBTree;
+///
+/// let mut tree: RBTree<u16, u16> = RBTree::new();
+/// assert!(tree.cursor_front().is_none());
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// [`RBTree::cursor_lower_bound`] can be used to start at an arbitrary node in the tree.
+///
+/// ```
+/// use kernel::{alloc::flags, rbtree::RBTree};
+///
+/// // Create a new tree.
+/// let mut tree = RBTree::new();
+///
+/// // Insert five 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)?;
+/// tree.try_create_and_insert(40, 400, flags::GFP_KERNEL)?;
+/// tree.try_create_and_insert(50, 500, flags::GFP_KERNEL)?;
+///
+/// // If the provided key exists, a cursor to that key is returned.
+/// let cursor = tree.cursor_lower_bound(&20).unwrap();
+/// let current = cursor.current();
+/// assert_eq!(current, (&20, &200));
+///
+/// // If the provided key doesn't exist, a cursor to the first larger element in sort order is returned.
+/// let cursor = tree.cursor_lower_bound(&25).unwrap();
+/// let current = cursor.current();
+/// assert_eq!(current, (&30, &300));
+///
+/// // If there is no larger key, [`None`] is returned.
+/// let cursor = tree.cursor_lower_bound(&55);
+/// assert!(cursor.is_none());
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// The cursor allows mutation of values 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)?;
+///
+/// // Retrieve a cursor.
+/// let mut cursor = tree.cursor_front().unwrap();
+///
+/// // Get a mutable reference to the current value.
+/// let (k, v) = cursor.current_mut();
+/// *v = 1000;
+///
+/// // The updated value is reflected in the tree.
+/// let updated = tree.get(&10).unwrap();
+/// assert_eq!(updated, &1000);
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// It also allows node removal. The following examples demonstrate the behavior of removing the current node.
+///
+/// ```
+/// 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)?;
+///
+/// // Remove the first element.
+/// let mut cursor = tree.cursor_front().unwrap();
+/// let mut current = cursor.current();
+/// assert_eq!(current, (&10, &100));
+/// cursor = cursor.remove_current().0.unwrap();
+///
+/// // If a node exists after the current element, it is returned.
+/// current = cursor.current();
+/// assert_eq!(current, (&20, &200));
+///
+/// // Get a cursor to the last element, and remove it.
+/// cursor = tree.cursor_back().unwrap();
+/// current = cursor.current();
+/// assert_eq!(current, (&30, &300));
+///
+/// // Since there is no next node, the previous node is returned.
+/// cursor = cursor.remove_current().0.unwrap();
+/// current = cursor.current();
+/// assert_eq!(current, (&20, &200));
+///
+/// // Removing the last element in the tree returns [`None`].
+/// assert!(cursor.remove_current().0.is_none());
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// Nodes adjacent to the current node can also be removed.
+///
+/// ```
+/// 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 mut cursor = tree.cursor_front().unwrap();
+/// let mut current = cursor.current();
+/// assert_eq!(current, (&10, &100));
+///
+/// // Calling `remove_prev` from the first element returns [`None`].
+/// assert!(cursor.remove_prev().is_none());
+///
+/// // Get a cursor to the last element.
+/// cursor = tree.cursor_back().unwrap();
+/// current = cursor.current();
+/// assert_eq!(current, (&30, &300));
+///
+/// // Calling `remove_prev` removes and returns the middle element.
+/// assert_eq!(cursor.remove_prev().unwrap().to_key_value(), (20, 200));
+///
+/// // Calling `remove_next` from the last element returns [`None`].
+/// assert!(cursor.remove_next().is_none());
+///
+/// // Move to the first element
+/// cursor = cursor.move_prev().unwrap();
+/// current = cursor.current();
+/// assert_eq!(current, (&10, &100));
+///
+/// // Calling `remove_next` removes and returns the last element.
+/// assert_eq!(cursor.remove_next().unwrap().to_key_value(), (30, 300));
+///
+/// # Ok::<(), Error>(())
+///
+/// ```
+///
+/// # Invariants
+/// - `current` points to a node that is in the same [`RBTree`] as `tree`.
+pub struct Cursor<'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> {}
+
+// 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.
+unsafe impl<'a, K: Sync, V: Sync> Sync for Cursor<'a, K, V> {}
+
+impl<'a, K, V> Cursor<'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:
+ // - `self.current` is a valid node by the type invariants.
+ // - We have an mutable reference by the function signature.
+ unsafe { Self::to_key_value_mut(self.current) }
+ }
+
+ /// Remove the current node from the tree.
+ ///
+ /// Returns a tuple where the first element is a cursor to the next node, if it exists,
+ /// else the previous node, else [`None`] (if the tree becomes empty). The second element
+ /// is the removed node.
+ pub fn remove_current(self) -> (Option<Self>, RBTreeNode<K, V>) {
+ let prev = self.get_neighbor_raw(Direction::Prev);
+ let next = self.get_neighbor_raw(Direction::Next);
+ // 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!(self.current.as_ptr(), Node<K, V>, links) }.cast_mut();
+ // SAFETY: `this` is valid by the type invariants as described above.
+ let node = unsafe { Box::from_raw(this) };
+ let node = RBTreeNode { node };
+ // SAFETY: The reference to the tree used to create the cursor outlives the cursor, so
+ // the tree cannot change. By the tree invariant, all nodes are valid.
+ unsafe { bindings::rb_erase(&mut (*this).links, addr_of_mut!(self.tree.root)) };
+
+ let current = match (prev, next) {
+ (_, Some(next)) => next,
+ (Some(prev), None) => prev,
+ (None, None) => {
+ return (None, node);
+ }
+ };
+
+ (
+ // INVARIANT:
+ // - `current` is a valid node in the [`RBTree`] pointed to by `self.tree`.
+ // - Due to the function signature, `self` is an owned [`Cursor`],
+ // and [`Cursor`]s are only created via functions with a mutable reference
+ // to an [`RBTree`].
+ Some(Self {
+ current,
+ tree: self.tree,
+ }),
+ node,
+ )
+ }
+
+ /// Remove the previous node, returning it if it exists.
+ pub fn remove_prev(&mut self) -> Option<RBTreeNode<K, V>> {
+ self.remove_neighbor(Direction::Prev)
+ }
+
+ /// Remove the next node, returning it if it exists.
+ pub fn remove_next(&mut self) -> Option<RBTreeNode<K, V>> {
+ self.remove_neighbor(Direction::Next)
+ }
+
+ fn remove_neighbor(&mut self, direction: Direction) -> Option<RBTreeNode<K, V>> {
+ if let Some(neighbor) = self.get_neighbor_raw(direction) {
+ let neighbor = neighbor.as_ptr();
+ // SAFETY: The reference to the tree used to create the cursor outlives the cursor, so
+ // the tree cannot change. By the tree invariant, all nodes are valid.
+ unsafe { bindings::rb_erase(neighbor, addr_of_mut!(self.tree.root)) };
+ // 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!(neighbor, Node<K, V>, links) }.cast_mut();
+ // SAFETY: `this` is valid by the type invariants as described above.
+ let node = unsafe { Box::from_raw(this) };
+ return Some(RBTreeNode { node });
+ }
+ None
+ }
+
+ /// Move the cursor to the previous node, returning [`None`] if it doesn't exist.
+ pub fn move_prev(self) -> Option<Self> {
+ self.mv(Direction::Prev)
+ }
+
+ /// Move the cursor to the next node, returning [`None`] if it doesn't exist.
+ pub fn move_next(self) -> Option<Self> {
+ self.mv(Direction::Next)
+ }
+
+ fn mv(self, direction: Direction) -> Option<Self> {
+ // INVARIANT:
+ // - `neighbor` is a valid node in the [`RBTree`] pointed to by `self.tree`.
+ // - Due to the function signature, `self` is an owned [`Cursor`],
+ // and [`Cursor`]s are only created via functions with a mutable reference
+ // to an [`RBTree`].
+ self.get_neighbor_raw(direction).map(|neighbor| Self {
+ tree: self.tree,
+ current: neighbor,
+ })
+ }
+
+ /// 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) }
+ })
+ }
+
+ /// Access the previous node mutably without moving the cursor.
+ pub fn peek_prev_mut(&mut self) -> Option<(&K, &mut V)> {
+ self.peek_mut(Direction::Prev)
+ }
+
+ /// Access the next node mutably without moving the cursor.
+ pub fn peek_next_mut(&mut self) -> Option<(&K, &mut V)> {
+ self.peek_mut(Direction::Next)
+ }
+
+ fn peek_mut(&mut self, direction: Direction) -> Option<(&K, &mut V)> {
+ self.get_neighbor_raw(direction).map(|neighbor| {
+ // SAFETY:
+ // - `neighbor` is a valid tree node.
+ // - By the function signature, we have a mutable reference to `self`.
+ unsafe { Self::to_key_value_mut(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:
+ /// - `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: the caller guarantees that `node` is a valid pointer in an `RBTree`.
+ let (k, v) = unsafe { Self::to_key_value_raw(node) };
+ // SAFETY: the caller guarantees immutable access to `node`.
+ (k, unsafe { &*v })
+ }
+
+ /// SAFETY:
+ /// - `node` must be a valid pointer to a node in an [`RBTree`].
+ /// - The caller has mutable access to `node` for the duration of 'b.
+ unsafe fn to_key_value_mut<'b>(node: NonNull<bindings::rb_node>) -> (&'b K, &'b mut V) {
+ // SAFETY: the caller guarantees that `node` is a valid pointer in an `RBTree`.
+ let (k, v) = unsafe { Self::to_key_value_raw(node) };
+ // SAFETY: the caller guarantees mutable access to `node`.
+ (k, unsafe { &mut *v })
+ }
+
+ /// SAFETY:
+ /// - `node` must be a valid pointer to a node in an [`RBTree`].
+ /// - The caller has immutable access to the key for the duration of 'b.
+ unsafe fn to_key_value_raw<'b>(node: NonNull<bindings::rb_node>) -> (&'b K, *mut 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) }.cast_mut();
+ // 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 { addr_of_mut!((*this).value) };
+ (k, v)
+ }
+}
+
+/// Direction for [`Cursor`] operations.
+enum Direction {
+ /// the node immediately before, in sort order
+ Prev,
+ /// the node immediately after, in sort order
+ Next,
+}
+
impl<'a, K, V> IntoIterator for &'a RBTree<K, V> {
type Item = (&'a K, &'a V);
type IntoIter = Iter<'a, K, V>;
@@ -585,6 +1121,11 @@ impl<K, V> RBTreeNode<K, V> {
pub fn new(key: K, value: V, flags: Flags) -> Result<RBTreeNode<K, V>> {
Ok(RBTreeNodeReservation::new(flags)?.into_node(key, value))
}
+
+ /// Get the key and value from inside the node.
+ pub fn to_key_value(self) -> (K, V) {
+ (self.node.key, self.node.value)
+ }
}
// SAFETY: If K and V can be sent across threads, then it's also okay to send [`RBTreeNode`] across
--
2.46.0.184.g6999bdac58-goog
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH v10 4/5] rust: rbtree: add cursor
2024-08-19 15:07 ` [PATCH v10 4/5] rust: rbtree: add cursor Matt Gilbride
@ 2024-08-20 8:00 ` Benno Lossin
0 siblings, 0 replies; 9+ messages in thread
From: Benno Lossin @ 2024-08-20 8:00 UTC (permalink / raw)
To: Matt Gilbride, Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho,
Boqun Feng, Gary Guo, Björn Roy Baron, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel
On 19.08.24 17:07, Matt Gilbride wrote:
> Add a cursor interface to `RBTree`, supporting the following use cases:
> - Inspect the current node pointed to by the cursor, inspect/move to
> it's neighbors in sort order (bidirectionally).
> - Mutate the tree itself by removing the current node pointed to by the
> cursor, or one of its neighbors.
>
> Add functions to obtain a cursor to the tree by key:
> - The node with the smallest key
> - The node with the largest key
> - The node matching the given key, or the one with the next larger key
>
> The cursor abstraction is needed by the binder driver to efficiently
> search for nodes and (conditionally) modify them, as well as their
> neighbors [1].
>
> Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@google.com/ [1]
> Co-developed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Tested-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Matt Gilbride <mattgilbride@google.com>
> ---
> rust/kernel/rbtree.rs | 541 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 541 insertions(+)
>
> diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
> index 6c9a8f0a00e6..754af0db86b5 100644
> --- a/rust/kernel/rbtree.rs
> +++ b/rust/kernel/rbtree.rs
> @@ -236,6 +236,40 @@ pub fn values(&self) -> impl Iterator<Item = &'_ V> {
> pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
> self.iter_mut().map(|(_, v)| v)
> }
> +
> + /// Returns a cursor over the tree nodes, starting with the smallest key.
> + pub fn cursor_front(&mut self) -> Option<Cursor<'_, 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`.
> + // - Due to the type signature of this function, the returned [`Cursor`]
> + // borrows mutably from `self`.
This second invariant doesn't exist on `Cursor`, probably some stale
comment.
> + Cursor {
> + current,
> + tree: self,
> + }
> + })
> + }
> +
> + /// Returns a cursor over the tree nodes, starting with the largest key.
> + pub fn cursor_back(&mut self) -> Option<Cursor<'_, 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`.
> + // - Due to the type signature of this function, the returned [`Cursor`]
> + // borrows mutably from `self`.
Ditto.
> + Cursor {
> + current,
> + tree: self,
> + }
> + })
> + }
> }
>
> impl<K, V> RBTree<K, V>
> @@ -396,6 +430,75 @@ fn remove_node(&mut self, key: &K) -> Option<RBTreeNode<K, V>> {
> pub fn remove(&mut self, key: &K) -> Option<V> {
> self.remove_node(key).map(|node| node.node.value)
> }
> +
> + /// 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(&mut self, key: &K) -> Option<Cursor<'_, K, V>>
> + where
> + K: Ord,
> + {
> + let mut node = self.root.rb_node;
> + let mut best_match: Option<NonNull<Node<K, V>>> = 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.
> + let this = unsafe { container_of!(node, Node<K, V>, links) }.cast_mut();
> + // SAFETY: `this` is a non-null node so it is valid by the type invariants.
> + let this_key = unsafe { &(*this).key };
> + // SAFETY: `node` is a non-null node so it is valid by the type invariants.
> + let left_child = unsafe { (*node).rb_left };
> + // SAFETY: `node` is a non-null node so it is valid by the type invariants.
> + let right_child = unsafe { (*node).rb_right };
> + if key == this_key {
> + return NonNull::new(node).map(|current| {
> + // INVARIANT:
> + // - `node` is a valid node in the [`RBTree`] pointed to by `self`.
> + // - Due to the type signature of this function, the returned [`Cursor`]
> + // borrows mutably from `self`.
Here again the stale invariant.
> + Cursor {
> + current,
> + tree: self,
> + }
> + });
You could do this instead of returning here:
best_match = NonNull::new(this);
break;
Then we don't have two places constructing a `Cursor` and can avoid
having to duplicate the `INVARIANT` comment.
> + } else {
> + node = if key > this_key {
I don't know how much this cares about performance, but you can avoid
having to do two comparisons by doing `match key.cmp(this_key)`. Maybe
the compiler is already doing that optimization though.
> + right_child
> + } else {
> + let is_better_match = match best_match {
> + 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
> + }
> + };
> + if is_better_match {
> + best_match = NonNull::new(this);
> + }
> + 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`.
> + // - Due to the type signature of this function, the returned [`Cursor`]
> + // borrows mutably from `self`.
Stale invariant (more instances below).
---
Cheers,
Benno
> + Cursor {
> + current,
> + tree: self,
> + }
> + })
> + }
> }
>
> impl<K, V> Default for RBTree<K, V> {
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH v10 5/5] rust: rbtree: add `RBTree::entry`
2024-08-19 15:07 [PATCH v10 0/5] Red-black tree abstraction needed by Rust Binder Matt Gilbride
` (3 preceding siblings ...)
2024-08-19 15:07 ` [PATCH v10 4/5] rust: rbtree: add cursor Matt Gilbride
@ 2024-08-19 15:07 ` Matt Gilbride
2024-08-20 8:08 ` Benno Lossin
4 siblings, 1 reply; 9+ messages in thread
From: Matt Gilbride @ 2024-08-19 15:07 UTC (permalink / raw)
To: Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel, Matt Gilbride
From: Alice Ryhl <aliceryhl@google.com>
This mirrors the entry API [1] from the Rust standard library on
`RBTree`. This API can be used to access the entry at a specific key and
make modifications depending on whether the key is vacant or occupied.
This API is useful because it can often be used to avoid traversing the
tree multiple times.
This is used by binder to look up and conditionally access or insert a
value, depending on whether it is there or not [2].
Link: https://doc.rust-lang.org/stable/std/collections/btree_map/enum.Entry.html [1]
Link: https://android-review.googlesource.com/c/kernel/common/+/2849906 [2]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
---
rust/kernel/rbtree.rs | 310 ++++++++++++++++++++++++++++++++++++++------------
1 file changed, 235 insertions(+), 75 deletions(-)
diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index 754af0db86b5..db185b6b3c65 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -297,12 +297,19 @@ pub fn try_create_and_insert(
/// key/value pair). Returns [`None`] if a node with the same key didn't already exist.
///
/// This function always succeeds.
- pub fn insert(&mut self, RBTreeNode { node }: RBTreeNode<K, V>) -> Option<RBTreeNode<K, V>> {
- let node = Box::into_raw(node);
- // SAFETY: `node` is valid at least until we call `Box::from_raw`, which only happens when
- // the node is removed or replaced.
- let node_links = unsafe { addr_of_mut!((*node).links) };
+ pub fn insert(&mut self, node: RBTreeNode<K, V>) -> Option<RBTreeNode<K, V>> {
+ match self.raw_entry(&node.node.key) {
+ RawEntry::Occupied(entry) => Some(entry.replace(node)),
+ RawEntry::Vacant(entry) => {
+ entry.insert(node);
+ None
+ }
+ }
+ }
+ fn raw_entry(&mut self, key: &K) -> RawEntry<'_, K, V> {
+ let raw_self: *mut RBTree<K, V> = self;
+ // The returned `RawEntry` is used to call either `rb_link_node` or `rb_replace_node`.
// The parameters of `bindings::rb_link_node` are as follows:
// - `node`: A pointer to an uninitialized node being inserted.
// - `parent`: A pointer to an existing node in the tree. One of its child pointers must be
@@ -321,62 +328,56 @@ pub fn insert(&mut self, RBTreeNode { node }: RBTreeNode<K, V>) -> Option<RBTree
// in the subtree of `parent` that `child_field_of_parent` points at. Once
// we find an empty subtree, we can insert the new node using `rb_link_node`.
let mut parent = core::ptr::null_mut();
- let mut child_field_of_parent: &mut *mut bindings::rb_node = &mut self.root.rb_node;
- while !child_field_of_parent.is_null() {
- parent = *child_field_of_parent;
+ let mut child_field_of_parent: &mut *mut bindings::rb_node =
+ // SAFETY: `raw_self` is a valid pointer to the `RBTree` (created from `self` above).
+ unsafe { &mut (*raw_self).root.rb_node };
+ while !(*child_field_of_parent).is_null() {
+ let curr = *child_field_of_parent;
+ // SAFETY: All links fields we create are in a `Node<K, V>`.
+ let node = unsafe { container_of!(curr, Node<K, V>, links) };
- // We need to determine whether `node` should be the left or right child of `parent`,
- // so we will compare with the `key` field of `parent` a.k.a. `this` below.
- //
- // 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!(parent, Node<K, V>, links) };
-
- // SAFETY: `this` is a non-null node so it is valid by the type invariants. `node` is
- // valid until the node is removed.
- match unsafe { (*node).key.cmp(&(*this).key) } {
- // We would like `node` to be the left child of `parent`. Move to this child to check
- // whether we can use it, or continue searching, at the next iteration.
- //
- // SAFETY: `parent` is a non-null node so it is valid by the type invariants.
- Ordering::Less => child_field_of_parent = unsafe { &mut (*parent).rb_left },
- // We would like `node` to be the right child of `parent`. Move to this child to check
- // whether we can use it, or continue searching, at the next iteration.
- //
- // SAFETY: `parent` is a non-null node so it is valid by the type invariants.
- Ordering::Greater => child_field_of_parent = unsafe { &mut (*parent).rb_right },
+ // SAFETY: `node` is a non-null node so it is valid by the type invariants.
+ match key.cmp(unsafe { &(*node).key }) {
+ // SAFETY: `curr` is a non-null node so it is valid by the type invariants.
+ Ordering::Less => child_field_of_parent = unsafe { &mut (*curr).rb_left },
+ // SAFETY: `curr` is a non-null node so it is valid by the type invariants.
+ Ordering::Greater => child_field_of_parent = unsafe { &mut (*curr).rb_right },
Ordering::Equal => {
- // There is an existing node in the tree with this key, and that node is
- // `parent`. Thus, we are replacing parent with a new node.
- //
- // INVARIANT: We are replacing an existing node with a new one, which is valid.
- // It remains valid because we "forgot" it with `Box::into_raw`.
- // SAFETY: All pointers are non-null and valid.
- unsafe { bindings::rb_replace_node(parent, node_links, &mut self.root) };
-
- // INVARIANT: The node is being returned and the caller may free it, however,
- // it was removed from the tree. So the invariants still hold.
- return Some(RBTreeNode {
- // SAFETY: `this` was a node in the tree, so it is valid.
- node: unsafe { Box::from_raw(this.cast_mut()) },
- });
+ return RawEntry::Occupied(OccupiedEntry {
+ rbtree: self,
+ node_links: curr,
+ })
}
}
+ parent = curr;
}
- // INVARIANT: We are linking in a new node, which is valid. It remains valid because we
- // "forgot" it with `Box::into_raw`.
- // SAFETY: All pointers are non-null and valid (`*child_field_of_parent` is null, but `child_field_of_parent` is a
- // mutable reference).
- unsafe { bindings::rb_link_node(node_links, parent, child_field_of_parent) };
+ RawEntry::Vacant(RawVacantEntry {
+ rbtree: raw_self,
+ parent,
+ child_field_of_parent,
+ _phantom: PhantomData,
+ })
+ }
- // SAFETY: All pointers are valid. `node` has just been inserted into the tree.
- unsafe { bindings::rb_insert_color(node_links, &mut self.root) };
- None
+ /// Gets the given key's corresponding entry in the map for in-place manipulation.
+ pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
+ match self.raw_entry(&key) {
+ RawEntry::Occupied(entry) => Entry::Occupied(entry),
+ RawEntry::Vacant(entry) => Entry::Vacant(VacantEntry { raw: entry, key }),
+ }
}
- /// Returns a node with the given key, if one exists.
- fn find(&self, key: &K) -> Option<NonNull<Node<K, V>>> {
+ /// Used for accessing the given node, if it exists.
+ pub fn find_mut(&mut self, key: &K) -> Option<OccupiedEntry<'_, K, V>> {
+ match self.raw_entry(key) {
+ RawEntry::Occupied(entry) => Some(entry),
+ RawEntry::Vacant(_entry) => None,
+ }
+ }
+
+ /// Returns a reference to the value corresponding to the key.
+ pub fn get(&self, key: &K) -> Option<&V> {
let mut node = self.root.rb_node;
while !node.is_null() {
// SAFETY: By the type invariant of `Self`, all non-null `rb_node` pointers stored in `self`
@@ -388,47 +389,30 @@ fn find(&self, key: &K) -> Option<NonNull<Node<K, V>>> {
Ordering::Less => unsafe { (*node).rb_left },
// SAFETY: `node` is a non-null node so it is valid by the type invariants.
Ordering::Greater => unsafe { (*node).rb_right },
- Ordering::Equal => return NonNull::new(this.cast_mut()),
+ // SAFETY: `node` is a non-null node so it is valid by the type invariants.
+ Ordering::Equal => return Some(unsafe { &(*this).value }),
}
}
None
}
- /// Returns a reference to the value corresponding to the key.
- pub fn get(&self, key: &K) -> Option<&V> {
- // SAFETY: The `find` return value is a node in the tree, so it is valid.
- self.find(key).map(|node| unsafe { &node.as_ref().value })
- }
-
/// Returns a mutable reference to the value corresponding to the key.
pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
- // SAFETY: The `find` return value is a node in the tree, so it is valid.
- self.find(key)
- .map(|mut node| unsafe { &mut node.as_mut().value })
+ self.find_mut(key).map(|node| node.into_mut())
}
/// Removes the node with the given key from the tree.
///
/// It returns the node that was removed if one exists, or [`None`] otherwise.
- fn remove_node(&mut self, key: &K) -> Option<RBTreeNode<K, V>> {
- let mut node = self.find(key)?;
-
- // SAFETY: The `find` return value is a node in the tree, so it is valid.
- unsafe { bindings::rb_erase(&mut node.as_mut().links, &mut self.root) };
-
- // INVARIANT: The node is being returned and the caller may free it, however, it was
- // removed from the tree. So the invariants still hold.
- Some(RBTreeNode {
- // SAFETY: The `find` return value was a node in the tree, so it is valid.
- node: unsafe { Box::from_raw(node.as_ptr()) },
- })
+ pub fn remove_node(&mut self, key: &K) -> Option<RBTreeNode<K, V>> {
+ self.find_mut(key).map(OccupiedEntry::remove_node)
}
/// Removes the node with the given key from the tree.
///
/// It returns the value that was removed if one exists, or [`None`] otherwise.
pub fn remove(&mut self, key: &K) -> Option<V> {
- self.remove_node(key).map(|node| node.node.value)
+ self.find_mut(key).map(OccupiedEntry::remove)
}
/// Returns a cursor over the tree nodes based on the given key.
@@ -1136,6 +1120,182 @@ unsafe impl<K: Send, V: Send> Send for RBTreeNode<K, V> {}
// [`RBTreeNode`] without synchronization.
unsafe impl<K: Sync, V: Sync> Sync for RBTreeNode<K, V> {}
+impl<K, V> RBTreeNode<K, V> {
+ /// Drop the key and value, but keep the allocation.
+ ///
+ /// It then becomes a reservation that can be re-initialised into a different node (i.e., with
+ /// a different key and/or value).
+ ///
+ /// The existing key and value are dropped in-place as part of this operation, that is, memory
+ /// may be freed (but only for the key/value; memory for the node itself is kept for reuse).
+ pub fn into_reservation(self) -> RBTreeNodeReservation<K, V> {
+ RBTreeNodeReservation {
+ node: Box::drop_contents(self.node),
+ }
+ }
+}
+
+/// A view into a single entry in a map, which may either be vacant or occupied.
+///
+/// This enum is constructed from the [`RBTree::entry`].
+///
+/// [`entry`]: fn@RBTree::entry
+pub enum Entry<'a, K, V> {
+ /// This [`RBTree`] does not have a node with this key.
+ Vacant(VacantEntry<'a, K, V>),
+ /// This [`RBTree`] already has a node with this key.
+ Occupied(OccupiedEntry<'a, K, V>),
+}
+
+/// Like [`Entry`], except that it doesn't have ownership of the key.
+enum RawEntry<'a, K, V> {
+ Vacant(RawVacantEntry<'a, K, V>),
+ Occupied(OccupiedEntry<'a, K, V>),
+}
+
+/// A view into a vacant entry in a [`RBTree`]. It is part of the [`Entry`] enum.
+pub struct VacantEntry<'a, K, V> {
+ key: K,
+ raw: RawVacantEntry<'a, K, V>,
+}
+
+/// Like [`VacantEntry`], but doesn't hold on to the key.
+///
+/// # Invariants
+/// - `parent` may be null if the new node becomes the root.
+/// - `child_field_of_parent` is a valid pointer to the left-child or right-child of `parent`. If `parent` is
+/// null, it is a pointer to the root of the [`RBTree`].
+struct RawVacantEntry<'a, K, V> {
+ rbtree: *mut RBTree<K, V>,
+ /// The node that will become the parent of the new node if we insert one.
+ parent: *mut bindings::rb_node,
+ /// This points to the left-child or right-child field of `parent`, or `root` if `parent` is
+ /// null.
+ child_field_of_parent: *mut *mut bindings::rb_node,
+ _phantom: PhantomData<&'a mut RBTree<K, V>>,
+}
+
+impl<'a, K, V> RawVacantEntry<'a, K, V> {
+ /// Inserts the given node into the [`RBTree`] at this entry.
+ ///
+ /// The `node` must have a key such that inserting it here does not break the ordering of this
+ /// [`RBTree`].
+ fn insert(self, node: RBTreeNode<K, V>) -> &'a mut V {
+ let node = Box::into_raw(node.node);
+
+ // SAFETY: `node` is valid at least until we call `Box::from_raw`, which only happens when
+ // the node is removed or replaced.
+ let node_links = unsafe { addr_of_mut!((*node).links) };
+
+ // INVARIANT: We are linking in a new node, which is valid. It remains valid because we
+ // "forgot" it with `Box::into_raw`.
+ // SAFETY: The type invariants of `RawVacantEntry` are exactly the safety requirements of `rb_link_node`.
+ unsafe { bindings::rb_link_node(node_links, self.parent, self.child_field_of_parent) };
+
+ // SAFETY: All pointers are valid. `node` has just been inserted into the tree.
+ unsafe { bindings::rb_insert_color(node_links, addr_of_mut!((*self.rbtree).root)) };
+
+ // SAFETY: The node is valid until we remove it from the tree.
+ unsafe { &mut (*node).value }
+ }
+}
+
+impl<'a, K, V> VacantEntry<'a, K, V> {
+ /// Inserts the given node into the [`RBTree`] at this entry.
+ pub fn insert(self, value: V, reservation: RBTreeNodeReservation<K, V>) -> &'a mut V {
+ self.raw.insert(reservation.into_node(self.key, value))
+ }
+}
+
+/// A view into an occupied entry in a [`RBTree`]. It is part of the [`Entry`] enum.
+///
+/// # Invariants
+/// - `node_links` is a valid, non-null pointer to a tree node in `self.rbtree`
+pub struct OccupiedEntry<'a, K, V> {
+ rbtree: &'a mut RBTree<K, V>,
+ /// The node that this entry corresponds to.
+ node_links: *mut bindings::rb_node,
+}
+
+impl<'a, K, V> OccupiedEntry<'a, K, V> {
+ /// Gets a reference to the value in the entry.
+ pub fn get(&self) -> &V {
+ // SAFETY:
+ // - `self.node_links` is a valid pointer to a node in the tree.
+ // - We have shared access to the underlying tree, and can thus give out a shared reference.
+ unsafe { &(*container_of!(self.node_links, Node<K, V>, links)).value }
+ }
+
+ /// Gets a mutable reference to the value in the entry.
+ pub fn get_mut(&mut self) -> &mut V {
+ // SAFETY:
+ // - `self.node_links` is a valid pointer to a node in the tree.
+ // - We have exclusive access to the underlying tree, and can thus give out a mutable reference.
+ unsafe {
+ &mut (*(container_of!(self.node_links, Node<K, V>, links) as *mut Node<K, V>)).value
+ }
+ }
+
+ /// Converts the entry into a mutable reference to its value.
+ ///
+ /// If you need multiple references to the `OccupiedEntry`, see [`self#get_mut`].
+ pub fn into_mut(self) -> &'a mut V {
+ // SAFETY:
+ // - `self.node_links` is a valid pointer to a node in the tree.
+ // - This consumes the `&'a mut RBTree<K, V>`, therefore it can give out a mutable reference that lives for `'a`.
+ unsafe {
+ &mut (*(container_of!(self.node_links, Node<K, V>, links) as *mut Node<K, V>)).value
+ }
+ }
+
+ /// Remove this entry from the [`RBTree`].
+ pub fn remove_node(self) -> RBTreeNode<K, V> {
+ // SAFETY: The node is a node in the tree, so it is valid.
+ unsafe { bindings::rb_erase(self.node_links, &mut self.rbtree.root) };
+
+ // INVARIANT: The node is being returned and the caller may free it, however, it was
+ // removed from the tree. So the invariants still hold.
+ RBTreeNode {
+ // SAFETY: The node was a node in the tree, but we removed it, so we can convert it
+ // back into a box.
+ node: unsafe {
+ Box::from_raw(container_of!(self.node_links, Node<K, V>, links) as *mut Node<K, V>)
+ },
+ }
+ }
+
+ /// Takes the value of the entry out of the map, and returns it.
+ pub fn remove(self) -> V {
+ self.remove_node().node.value
+ }
+
+ /// Swap the current node for the provided node.
+ ///
+ /// The key of both nodes must be equal.
+ fn replace(self, node: RBTreeNode<K, V>) -> RBTreeNode<K, V> {
+ let node = Box::into_raw(node.node);
+
+ // SAFETY: `node` is valid at least until we call `Box::from_raw`, which only happens when
+ // the node is removed or replaced.
+ let new_node_links = unsafe { addr_of_mut!((*node).links) };
+
+ // SAFETY: This updates the pointers so that `new_node_links` is in the tree where
+ // `self.node_links` used to be.
+ unsafe {
+ bindings::rb_replace_node(self.node_links, new_node_links, &mut self.rbtree.root)
+ };
+
+ // SAFETY:
+ // - `self.node_ptr` produces a valid pointer to a node in the tree.
+ // - Now that we removed this entry from the tree, we can convert the node to a box.
+ let old_node = unsafe {
+ Box::from_raw(container_of!(self.node_links, Node<K, V>, links) as *mut Node<K, V>)
+ };
+
+ RBTreeNode { node: old_node }
+ }
+}
+
struct Node<K, V> {
links: bindings::rb_node,
key: K,
--
2.46.0.184.g6999bdac58-goog
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH v10 5/5] rust: rbtree: add `RBTree::entry`
2024-08-19 15:07 ` [PATCH v10 5/5] rust: rbtree: add `RBTree::entry` Matt Gilbride
@ 2024-08-20 8:08 ` Benno Lossin
0 siblings, 0 replies; 9+ messages in thread
From: Benno Lossin @ 2024-08-20 8:08 UTC (permalink / raw)
To: Matt Gilbride, Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho,
Boqun Feng, Gary Guo, Björn Roy Baron, Andreas Hindborg,
Alice Ryhl, Greg Kroah-Hartman, Arve Hjønnevåg,
Todd Kjos, Martijn Coenen, Joel Fernandes, Carlos Llamas,
Suren Baghdasaryan, Christian Brauner
Cc: Rob Landley, Davidlohr Bueso, Michel Lespinasse, rust-for-linux,
linux-kernel
On 19.08.24 17:07, Matt Gilbride wrote:
> From: Alice Ryhl <aliceryhl@google.com>
>
> This mirrors the entry API [1] from the Rust standard library on
> `RBTree`. This API can be used to access the entry at a specific key and
> make modifications depending on whether the key is vacant or occupied.
> This API is useful because it can often be used to avoid traversing the
> tree multiple times.
>
> This is used by binder to look up and conditionally access or insert a
> value, depending on whether it is there or not [2].
>
> Link: https://doc.rust-lang.org/stable/std/collections/btree_map/enum.Entry.html [1]
> Link: https://android-review.googlesource.com/c/kernel/common/+/2849906 [2]
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Tested-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Matt Gilbride <mattgilbride@google.com>
One nit below, but feel free to add if it doesn't work:
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> ---
> rust/kernel/rbtree.rs | 310 ++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 235 insertions(+), 75 deletions(-)
[...]
> + /// Gets a mutable reference to the value in the entry.
> + pub fn get_mut(&mut self) -> &mut V {
> + // SAFETY:
> + // - `self.node_links` is a valid pointer to a node in the tree.
> + // - We have exclusive access to the underlying tree, and can thus give out a mutable reference.
> + unsafe {
> + &mut (*(container_of!(self.node_links, Node<K, V>, links) as *mut Node<K, V>)).value
Does `.cast_mut()` work here instead of `as *mut Node<K, V>`? (also
below)
---
Cheers,
Benno
> + }
> + }
> +
> + /// Converts the entry into a mutable reference to its value.
> + ///
> + /// If you need multiple references to the `OccupiedEntry`, see [`self#get_mut`].
> + pub fn into_mut(self) -> &'a mut V {
> + // SAFETY:
> + // - `self.node_links` is a valid pointer to a node in the tree.
> + // - This consumes the `&'a mut RBTree<K, V>`, therefore it can give out a mutable reference that lives for `'a`.
> + unsafe {
> + &mut (*(container_of!(self.node_links, Node<K, V>, links) as *mut Node<K, V>)).value
> + }
> + }
^ permalink raw reply [flat|nested] 9+ messages in thread