[PATCH v3 07/10] rust: list: add iterators

Alice Ryhl
2024-07-23T08:23:13Z

Rust Binder has lists containing stuff such as all contexts or all
processes, and sometimes needs to iterate over them. This patch enables
Rust Binder to do that using a normal for loop.

The iterator returns the ArcBorrow type, so it is possible to grab a
refcount to values while iterating.

Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
rust/kernel/list.rs | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 102 insertions(+)

diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs
index d3f8e38d9ff4..e320da063c07 100644
--- a/rust/kernel/list.rs
+++ b/rust/kernel/list.rs
@@ -5,7 +5,9 @@
//! A linked list implementation.

use crate::init::PinInit;
+use crate::sync::ArcBorrow;
use crate::types::Opaque;
+use core::iter::{DoubleEndedIterator, FusedIterator};
use core::marker::PhantomData;
use core::ptr;

@@ -436,6 +438,17 @@ pub fn push_all_back(&mut self, other: &mut List<T, ID>) {
// INVARIANT: The other list is now empty, so update its pointer.
other.first = ptr::null_mut();
}
+
+ /// Creates an iterator over the list.
+ pub fn iter(&self) -> Iter<'_, T, ID> {
+ // INVARIANT: If the list is empty, both pointers are null. Otherwise, both pointers point
+ // at the first element of the same list.
+ Iter {
+ current: self.first,
+ stop: self.first,
+ _ty: PhantomData,
+ }
+ }
}

impl<T: ?Sized + ListItem<ID>, const ID: u64> Default for List<T, ID> {
@@ -451,3 +464,92 @@ fn drop(&mut self) {
}
}
}
+
+/// An iterator over a [`List`].
+///
+/// # Invariants
+///
+/// * There must be a [`List`] that is immutably borrowed for the duration of `'a`.
+/// * The `current` pointer is null or points at a value in that [`List`].
+/// * The `stop` pointer is equal to the `first` field of that [`List`].
+#[derive(Clone)]
+pub struct Iter<'a, T: ?Sized + ListItem<ID>, const ID: u64 = 0> {
+ current: *mut ListLinksFields,
+ stop: *mut ListLinksFields,
+ _ty: PhantomData<&'a ListArc<T, ID>>,
+}
+
+impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> Iterator for Iter<'a, T, ID> {
+ type Item = ArcBorrow<'a, T>;
+
+ fn next(&mut self) -> Option<ArcBorrow<'a, T>> {
+ if self.current.is_null() {
+ return None;
+ }
+
+ let current = self.current;
+
+ // SAFETY: We just checked that `current` is not null, so it is in a list, and hence not
+ // dangling. There's no race because the iterator holds an immutable borrow to the list.
+ let next = unsafe { (*current).next };
+ // INVARIANT: If `current` was the last element of the list, then this updates it to null.
+ // Otherwise, we update it to the next element.
+ self.current = if next != self.stop {
+ next
+ } else {
+ ptr::null_mut()
+ };
+
+ // SAFETY: The `current` pointer points at a value in the list.
+ let item = unsafe { T::view_value(ListLinks::from_fields(current)) };
+ // SAFETY:
+ // * All values in a list are stored in an `Arc`.
+ // * The value cannot be removed from the list for the duration of the lifetime annotated
+ // on the returned `ArcBorrow`, because removing it from the list would require mutable
+ // access to the list. However, the `ArcBorrow` is annotated with the iterator's
+ // lifetime, and the list is immutably borrowed for that lifetime.
+ // * Values in a list never have a `UniqueArc` reference.
+ Some(unsafe { ArcBorrow::from_raw(item) })
+ }
+}
+
+impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'a, T, ID> {}
+
+impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> IntoIterator for &'a List<T, ID> {
+ type IntoIter = Iter<'a, T, ID>;
+ type Item = ArcBorrow<'a, T>;
+
+ fn into_iter(self) -> Iter<'a, T, ID> {
+ self.iter()
+ }
+}
+
+/// An owning iterator into a [`List`].
+pub struct IntoIter<T: ?Sized + ListItem<ID>, const ID: u64 = 0> {
+ list: List<T, ID>,
+}
+
+impl<T: ?Sized + ListItem<ID>, const ID: u64> Iterator for IntoIter<T, ID> {
+ type Item = ListArc<T, ID>;
+
+ fn next(&mut self) -> Option<ListArc<T, ID>> {
+ self.list.pop_front()
+ }
+}
+
+impl<T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for IntoIter<T, ID> {}
+
+impl<T: ?Sized + ListItem<ID>, const ID: u64> DoubleEndedIterator for IntoIter<T, ID> {
+ fn next_back(&mut self) -> Option<ListArc<T, ID>> {
+ self.list.pop_back()
+ }
+}
+
+impl<T: ?Sized + ListItem<ID>, const ID: u64> IntoIterator for List<T, ID> {
+ type IntoIter = IntoIter<T, ID>;
+ type Item = ListArc<T, ID>;
+
+ fn into_iter(self) -> IntoIter<T, ID> {
+ IntoIter { list: self }
+ }
+}

--
2.45.2.1089.g2a221341d9-goog