linux-kernel - Re: [PATCH 2/6] rust: rbtree: add red-black tree implementation backed by the C version

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Date: Fri,  9 Feb 2024 13:04:26 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: mattgilbride@...gle.com
Cc: a.hindborg@...sung.com, alex.gaynor@...il.com, aliceryhl@...gle.com, 
	arve@...roid.com, benno.lossin@...ton.me, bjorn3_gh@...tonmail.com, 
	boqun.feng@...il.com, brauner@...nel.org, cmllamas@...gle.com, 
	dave@...olabs.net, gary@...yguo.net, gregkh@...uxfoundation.org, 
	joel@...lfernandes.org, linux-kernel@...r.kernel.org, maco@...roid.com, 
	michel@...pinasse.org, ojeda@...nel.org, rob@...dley.net, 
	rust-for-linux@...r.kernel.org, surenb@...gle.com, tkjos@...roid.com, 
	wedsonaf@...il.com
Subject: Re: [PATCH 2/6] rust: rbtree: add red-black tree implementation
 backed by the C version

> From: Wedson Almeida Filho <wedsonaf@...il.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@...il.com>
> Signed-off-by: Matt Gilbride <mattgilbride@...gle.com>

I have looked at these bindings many times over the past year. They
look good to me, modulo a few nits included in this email.

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

These abstractions have been very heavily exercised by the Rust Binder
driver.

Tested-by: Alice Ryhl <aliceryhl@...gle.com>

> +//! Red-black trees.
> +//!
> +//! C header: [`include/linux/rbtree.h`](../../../../include/linux/rbtree.h)
> +//!
> +//! Reference: <https://www.kernel.org/doc/html/latest/core-api/rbtree.html>

We changed these links, so it should say this instead:

[`include/linux/rbtree.h`](srctree/include/linux/rbtree.h)

> +    /// Allocates memory for a node to be eventually initialised and inserted into the tree via a
> +    /// call to [`RBTree::insert`].
> +    pub fn try_reserve_node() -> Result<RBTreeNodeReservation<K, V>> {
> +        Ok(RBTreeNodeReservation {
> +            node: Box::try_new(MaybeUninit::uninit())?,
> +        })
> +    }

This can be:

	use crate::prelude::*;
	use core::convert::Infallible;
	
	Ok(RBTreeNodeReservation {
	    node: Box::init::<Infallible>(crate::init::uninit())?,
	})

It might be slightly more verbose, but guarantees that we don't allocate
space for the value on the stack.

Alice