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Date: Thu, 25 Apr 2024 21:45:54 +0000
To: Matt Gilbride <mattgilbride@google.com>, Miguel Ojeda <ojeda@kernel.org>, Alex Gaynor <alex.gaynor@gmail.com>, Wedson Almeida Filho <wedsonaf@gmail.com>, Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>, =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, Andreas Hindborg <a.hindborg@samsung.com>, Alice Ryhl <aliceryhl@google.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, =?utf-8?Q?Arve_Hj=C3=B8nnev=C3=A5g?= <arve@android.com>, Todd Kjos <tkjos@android.com>, Martijn Coenen <maco@android.com>, Joel Fernandes <joel@joelfernandes.org>, Carlos Llamas <cmllamas@google.com>, Suren Baghdasaryan <surenb@google.com>, Christian Brauner <brauner@kernel.org>
From: Benno Lossin <benno.lossin@proton.me>
Cc: Rob Landley <rob@landley.net>, Davidlohr Bueso <dave@stgolabs.net>, Michel Lespinasse <michel@lespinasse.org>, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/5] rust: rbtree: add `RBTreeIterator`
Message-ID: <ba946689-d10b-4752-989f-4c6404d7ee55@proton.me>
In-Reply-To: <20240418-b4-rbtree-v3-2-323e134390ce@google.com>
References: <20240418-b4-rbtree-v3-0-323e134390ce@google.com> <20240418-b4-rbtree-v3-2-323e134390ce@google.com>
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On 18.04.24 16:15, Matt Gilbride wrote:
> @@ -188,6 +212,25 @@ pub fn try_reserve_node() -> Result<RBTreeNodeReserv=
ation<K, V>> {
>      pub fn try_allocate_node(key: K, value: V) -> Result<RBTreeNode<K, V=
>> {
>          Ok(Self::try_reserve_node()?.into_node(key, value))
>      }
> +
> +    /// Returns an iterator over the tree nodes, sorted by key.
> +    pub fn iter(&self) -> RBTreeIterator<'_, K, V> {
> +        RBTreeIterator {

There is a missing `INVARIANT` comment here justifying the invariants of
`RBTreeIterator`.

> +            _tree: PhantomData,
> +            // SAFETY: `root` is valid as it's embedded in `self` and we=
 have a valid `self`.
> +            next: unsafe { bindings::rb_first(&self.root) },
> +        }
> +    }
> +
> +    /// Returns an iterator over the keys of the nodes in the tree, in s=
orted order.
> +    pub fn keys(&self) -> impl Iterator<Item =3D &'_ K> {
> +        self.iter().map(|(k, _)| k)
> +    }
> +
> +    /// Returns an iterator over the values of the nodes in the tree, so=
rted by key.
> +    pub fn values(&self) -> impl Iterator<Item =3D &'_ V> {
> +        self.iter().map(|(_, v)| v)
> +    }
>  }
>=20
>  impl<K, V> RBTree<K, V>
> @@ -373,6 +416,56 @@ fn drop(&mut self) {
>      }
>  }
>=20
> +impl<'a, K, V> IntoIterator for &'a RBTree<K, V> {
> +    type Item =3D (&'a K, &'a V);
> +    type IntoIter =3D RBTreeIterator<'a, K, V>;
> +
> +    fn into_iter(self) -> Self::IntoIter {
> +        self.iter()
> +    }
> +}
> +
> +/// An iterator over the nodes of a [`RBTree`].
> +///
> +/// Instances are created by calling [`RBTree::iter`].
> +///
> +/// # Invariants
> +/// - `self.next` is a valid pointer.
> +/// - `self.next` points to a node stored inside of a valid `RBTree`.
> +pub struct RBTreeIterator<'a, K, V> {
> +    _tree: PhantomData<&'a RBTree<K, V>>,
> +    next: *mut bindings::rb_node,
> +}
> +
> +// SAFETY: The [`RBTreeIterator`] gives out immutable references to K an=
d V, so it has the same
> +// thread safety requirements as immutable references.
> +unsafe impl<'a, K: Sync, V: Sync> Send for RBTreeIterator<'a, K, V> {}

The bounds on `K` and `V` look like typos to me. They should be `Send`
instead.

> +
> +// SAFETY: The [`RBTreeIterator`] gives out immutable references to K an=
d V, so it has the same
> +// thread safety requirements as immutable references.
> +unsafe impl<'a, K: Sync, V: Sync> Sync for RBTreeIterator<'a, K, V> {}
> +
> +impl<'a, K, V> Iterator for RBTreeIterator<'a, K, V> {
> +    type Item =3D (&'a K, &'a V);
> +
> +    fn next(&mut self) -> Option<Self::Item> {
> +        if self.next.is_null() {
> +            return None;
> +        }
> +
> +        // SAFETY: By the type invariant of `Self`, all non-null `rb_nod=
e` pointers stored in `self`

This is not an invariant of `Self`, but rather `RBTree` and `self`
should be "`RBtree`s".

--=20
Cheers,
Benno

> +        // point to the links field of `Node<K, V>` objects.
> +        let cur =3D unsafe { container_of!(self.next, Node<K, V>, links)=
 };
> +
> +        // SAFETY: `self.next` is a valid tree node by the type invarian=
ts.
> +        self.next =3D unsafe { bindings::rb_next(self.next) };
> +
> +        // SAFETY: By the same reasoning above, it is safe to dereferenc=
e the node. Additionally,
> +        // it is ok to return a reference to members because the iterato=
r must outlive it.
> +        Some(unsafe { (&(*cur).key, &(*cur).value) })
> +    }
> +}
> +
>  /// A memory reservation for a red-black tree node.
>  ///
>  /// It contains the memory needed to hold a node that can be inserted in=
to a red-black tree. One
>=20
> --
> 2.44.0.769.g3c40516874-goog
>=20