linux-kernel - Re: [PATCH v4 4/6] rust: rbtree: add mutable iterator

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Date: Mon, 3 Jun 2024 10:41:41 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Matt Gilbride <mattgilbride@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Carlos Llamas <cmllamas@...gle.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Christian Brauner <brauner@...nel.org>,
	Rob Landley <rob@...dley.net>, Davidlohr Bueso <dave@...olabs.net>,
	Michel Lespinasse <michel@...pinasse.org>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/6] rust: rbtree: add mutable iterator

On Mon, Jun 03, 2024 at 04:05:19PM +0000, Matt Gilbride wrote:
[...]
> +/// 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 [`RBTreeIterator`] gives out mutable references to K and V, so it has the same

s/RBTreeIterator/IterMut ?

Also `IterMut` doesn't give out mutable references to K, which makes
me think...

> +// thread safety requirements as mutable references.
> +unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
> +

we can lose the constrains to `K: Sync`, right?

Regards,
Boqun

> +// SAFETY: The [`RBTreeIterator`] gives out mutable references to K and 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) })
> +    }
> +}
> +
[...]