linux-kernel - Re: [PATCH] rust: rbtree: simplify finding `current` in `remove

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Message-ID: <20250704181419.0a6a4d97@nimda.home>
Date: Fri, 4 Jul 2025 18:14:19 +0300
From: Onur <work@...rozkan.dev>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
 ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com,
 gary@...yguo.net, bjorn3_gh@...tonmail.com, lossin@...nel.org,
 a.hindborg@...nel.org, tmgross@...ch.edu, dakr@...nel.org,
 mattgilbride@...gle.com, wedsonaf@...il.com, daniel@...lak.dev,
 tamird@...il.com
Subject: Re: [PATCH] rust: rbtree: simplify finding `current` in
 `remove_current`

On Fri, 4 Jul 2025 07:36:16 +0000
Alice Ryhl <aliceryhl@...gle.com> wrote:

> On Fri, Jul 04, 2025 at 08:45:39AM +0300, Onur Özkan wrote:
> > The previous version used a verbose `match` to get
> > `current`, which may be slightly confusing at first
> > glance.
> > 
> > This change makes it shorter and more clearly expresses
> > the intent: prefer `next` if available, otherwise fall
> > back to `prev`.
> > 
> > Signed-off-by: Onur Özkan <work@...rozkan.dev>
> > ---
> >  rust/kernel/rbtree.rs | 14 +++-----------
> >  1 file changed, 3 insertions(+), 11 deletions(-)
> > 
> > diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
> > index 8d978c896747..8f1052552132 100644
> > --- a/rust/kernel/rbtree.rs
> > +++ b/rust/kernel/rbtree.rs
> > @@ -769,18 +769,10 @@ pub fn remove_current(self) -> (Option<Self>,
> > RBTreeNode<K, V>) { // the tree cannot change. By the tree
> > invariant, all nodes are valid. unsafe { bindings::rb_erase(&mut
> > (*this).links, addr_of_mut!(self.tree.root)) };
> > 
> > -        let current = match (prev, next) {
> > -            (_, Some(next)) => next,
> > -            (Some(prev), None) => prev,
> > -            (None, None) => {
> > -                return (None, node);
> > -            }
> > -        };
> > -
> >          (
> > -            // INVARIANT:
> > -            // - `current` is a valid node in the [`RBTree`]
> > pointed to by `self.tree`.
> > -            Some(Self {
> > +            next.or(prev).map(|current| Self {
> > +                // INVARIANT:
> > +                // - `current` is a valid node in the [`RBTree`]
> > pointed to by `self.tree`. current,
> >                  tree: self.tree,
> >              }),
> 
> I'm okay with this change, but the INVARIANT: comment usually goes
> before the `StructName {` declaration rather than on the field. For
> example, what about this?
> 
> 	// INVARIANT:
> 	// - `current` is a valid node in the [`RBTree`] pointed to
> by `self.tree`. let cursor = next.or(prev).map(|current| Self {
> 	    current,
> 	    tree: self.tree,
> 	});
> 	
> 	(cursor, node)

Looks nice. Do you want me to send v2 right away, or wait couple of days
to give sometime to other reviewers?

Regards,
Onur