1 files changed, 140 insertions, 0 deletions

diff --git a/rust/kernel/maple_tree.rs b/rust/kernel/maple_tree.rs
index 319772878b89..7acb8478d1d9 100644
--- a/rust/kernel/maple_tree.rs
+++ b/rust/kernel/maple_tree.rs
@@ -213,6 +213,23 @@ impl<T: ForeignOwnable> MapleTree<T> {
         unsafe { T::try_from_foreign(ret) }
     }
 
+    /// Lock the internal spinlock.
+    #[inline]
+    pub fn lock(&self) -> MapleGuard<'_, T> {
+        // SAFETY: It's safe to lock the spinlock in a maple tree.
+        unsafe { bindings::spin_lock(self.ma_lock()) };
+
+        // INVARIANT: We just took the spinlock.
+        MapleGuard(self)
+    }
+
+    #[inline]
+    fn ma_lock(&self) -> *mut bindings::spinlock_t {
+        // SAFETY: This pointer offset operation stays in-bounds.
+        let lock_ptr = unsafe { &raw mut (*self.tree.get()).__bindgen_anon_1.ma_lock };
+        lock_ptr.cast()
+    }
+
     /// Free all `T` instances in this tree.
     ///
     /// # Safety
@@ -256,6 +273,91 @@ impl<T: ForeignOwnable> PinnedDrop for MapleTree<T> {
     }
 }
 
+/// A reference to a [`MapleTree`] that owns the inner lock.
+///
+/// # Invariants
+///
+/// This guard owns the inner spinlock.
+#[must_use = "if unused, the lock will be immediately unlocked"]
+pub struct MapleGuard<'tree, T: ForeignOwnable>(&'tree MapleTree<T>);
+
+impl<'tree, T: ForeignOwnable> Drop for MapleGuard<'tree, T> {
+    #[inline]
+    fn drop(&mut self) {
+        // SAFETY: By the type invariants, we hold this spinlock.
+        unsafe { bindings::spin_unlock(self.0.ma_lock()) };
+    }
+}
+
+impl<'tree, T: ForeignOwnable> MapleGuard<'tree, T> {
+    /// Create a [`MaState`] protected by this lock guard.
+    pub fn ma_state(&mut self, first: usize, end: usize) -> MaState<'_, T> {
+        // SAFETY: The `MaState` borrows this `MapleGuard`, so it can also borrow the `MapleGuard`s
+        // read/write permissions to the maple tree.
+        unsafe { MaState::new_raw(self.0, first, end) }
+    }
+
+    /// Load the value at the given index.
+    ///
+    /// # Examples
+    ///
+    /// Read the value while holding the spinlock.
+    ///
+    /// ```
+    /// use kernel::maple_tree::MapleTree;
+    ///
+    /// let tree = KBox::pin_init(MapleTree::<KBox<i32>>::new(), GFP_KERNEL)?;
+    ///
+    /// let ten = KBox::new(10, GFP_KERNEL)?;
+    /// let twenty = KBox::new(20, GFP_KERNEL)?;
+    /// tree.insert(100, ten, GFP_KERNEL)?;
+    /// tree.insert(200, twenty, GFP_KERNEL)?;
+    ///
+    /// let mut lock = tree.lock();
+    /// assert_eq!(lock.load(100).map(|v| *v), Some(10));
+    /// assert_eq!(lock.load(200).map(|v| *v), Some(20));
+    /// assert_eq!(lock.load(300).map(|v| *v), None);
+    /// # Ok::<_, Error>(())
+    /// ```
+    ///
+    /// Increment refcount under the lock, to keep value alive afterwards.
+    ///
+    /// ```
+    /// use kernel::maple_tree::MapleTree;
+    /// use kernel::sync::Arc;
+    ///
+    /// let tree = KBox::pin_init(MapleTree::<Arc<i32>>::new(), GFP_KERNEL)?;
+    ///
+    /// let ten = Arc::new(10, GFP_KERNEL)?;
+    /// let twenty = Arc::new(20, GFP_KERNEL)?;
+    /// tree.insert(100, ten, GFP_KERNEL)?;
+    /// tree.insert(200, twenty, GFP_KERNEL)?;
+    ///
+    /// // Briefly take the lock to increment the refcount.
+    /// let value = tree.lock().load(100).map(Arc::from);
+    ///
+    /// // At this point, another thread might remove the value.
+    /// tree.erase(100);
+    ///
+    /// // But we can still access it because we took a refcount.
+    /// assert_eq!(value.map(|v| *v), Some(10));
+    /// # Ok::<_, Error>(())
+    /// ```
+    #[inline]
+    pub fn load(&mut self, index: usize) -> Option<T::BorrowedMut<'_>> {
+        // SAFETY: `self.tree` contains a valid maple tree.
+        let ret = unsafe { bindings::mtree_load(self.0.tree.get(), index) };
+        if ret.is_null() {
+            return None;
+        }
+
+        // SAFETY: If the pointer is not null, then it references a valid instance of `T`. It is
+        // safe to borrow the instance mutably because the signature of this function enforces that
+        // the mutable borrow is not used after the spinlock is dropped.
+        Some(unsafe { T::borrow_mut(ret) })
+    }
+}
+
 /// A helper type used for navigating a [`MapleTree`].
 ///
 /// # Invariants
@@ -309,6 +411,44 @@ impl<'tree, T: ForeignOwnable> MaState<'tree, T> {
         // to the tree.
         unsafe { bindings::mas_find(self.as_raw(), max) }
     }
+
+    /// Find the next entry in the maple tree.
+    ///
+    /// # Examples
+    ///
+    /// Iterate the maple tree.
+    ///
+    /// ```
+    /// use kernel::maple_tree::MapleTree;
+    /// use kernel::sync::Arc;
+    ///
+    /// let tree = KBox::pin_init(MapleTree::<Arc<i32>>::new(), GFP_KERNEL)?;
+    ///
+    /// let ten = Arc::new(10, GFP_KERNEL)?;
+    /// let twenty = Arc::new(20, GFP_KERNEL)?;
+    /// tree.insert(100, ten, GFP_KERNEL)?;
+    /// tree.insert(200, twenty, GFP_KERNEL)?;
+    ///
+    /// let mut ma_lock = tree.lock();
+    /// let mut iter = ma_lock.ma_state(0, usize::MAX);
+    ///
+    /// assert_eq!(iter.find(usize::MAX).map(|v| *v), Some(10));
+    /// assert_eq!(iter.find(usize::MAX).map(|v| *v), Some(20));
+    /// assert!(iter.find(usize::MAX).is_none());
+    /// # Ok::<_, Error>(())
+    /// ```
+    #[inline]
+    pub fn find(&mut self, max: usize) -> Option<T::BorrowedMut<'_>> {
+        let ret = self.mas_find_raw(max);
+        if ret.is_null() {
+            return None;
+        }
+
+        // SAFETY: If the pointer is not null, then it references a valid instance of `T`. It's
+        // safe to access it mutably as the returned reference borrows this `MaState`, and the
+        // `MaState` has read/write access to the maple tree.
+        Some(unsafe { T::borrow_mut(ret) })
+    }
 }
 
 /// Error type for failure to insert a new value.