From patchwork Mon Feb 5 15:50:05 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matt Gilbride X-Patchwork-Id: 196891 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a05:7301:168b:b0:106:860b:bbdd with SMTP id ma11csp966519dyb; Mon, 5 Feb 2024 07:58:56 -0800 (PST) X-Google-Smtp-Source: AGHT+IFjo3TyR+WyODoD5g2BYIM/ccqEsaoVXcj5bfdzF/Dpr+yyfS2le+PnAvLSW49TttrIEtYL X-Received: by 2002:a17:90a:6343:b0:296:b5f:edad with SMTP id v3-20020a17090a634300b002960b5fedadmr80467pjs.22.1707148736484; Mon, 05 Feb 2024 07:58:56 -0800 (PST) ARC-Seal: i=2; a=rsa-sha256; t=1707148736; cv=pass; d=google.com; s=arc-20160816; b=S1cxvkbhxn4+C3sxirms6wbEtNXPlRD4RRqXeLFp0yZgcJU7ZZ9+gznKITImN9UCW1 dXbNXJPezFc/IyeFsnMQutnTsBrGuhMLs/RGsdZXRMXnXca4Qh0UsZuqPoWVBFVV5o8x tzq04/9Ct8S4oUrpABRqaHTWdnD4FPmVmR7I7gNpdSwJ7aoAQTJEq7Mcz7Gdq4cwg+Fo 7hepZt7tOh53PsU8mEO+8QXlJ0walnt5QEk1ebDJUiI8EPLaCXuB0ghKhzYKFUbvYPve maWjI1Dn0Bp20eIJAelqW/2byhkDPRTrFfTjYFY03zmIbj1hXe450lb5+x3e0nRZRqz3 u9Ng== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=cc:to:from:subject:message-id:references:mime-version :list-unsubscribe:list-subscribe:list-id:precedence:in-reply-to:date :dkim-signature; bh=JtORM6z3n6Nx7zIdzVBRR85gUfsLFA4+3fHETUbUVdg=; fh=e6N4BLnRvR5jteTOjoMGHvjEseGqs8+mnu+2f8+TeoQ=; b=wUxqFRpKHeF6CW0NoayxbQg06vwF4JN8BLXfBW3xYDIqavSfOIhk+lBpPdESLMk005 nFaymCsG1jstW68FN2XW8K8qC2K8kX5ipnHFzczSZ7JauDsHEpOZJqW5RqLakm+OtTRw nWJtcXoRWCm71vWzdZDMdu9QBH60cj+EyViS7+ZRb8jo4UO5mxzZPsBzXWgkas87fOZx pV8vj4Tdx2GsKU/BmtPJVX9Ot7k4MAJEvicPsNOLmOzPkYGokdFm4FqWCdFv5g0bpllU rgbxmOHz0IFb84JpYq5Ko5uQYOl2pJoUsg1FTMlj9d0hbiXlwC0kCrT4ctP5RN7BA4eY 2ZjQ==; dara=google.com ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@google.com header.s=20230601 header.b=ECodOzTp; arc=pass (i=1 spf=pass spfdomain=flex--mattgilbride.bounces.google.com dkim=pass dkdomain=google.com dmarc=pass fromdomain=google.com); spf=pass (google.com: domain of linux-kernel+bounces-52954-ouuuleilei=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) smtp.mailfrom="linux-kernel+bounces-52954-ouuuleilei=gmail.com@vger.kernel.org"; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com X-Forwarded-Encrypted: i=1; AJvYcCVm7mzwDjWC7LxLAhJBi7c4iEjWGYh4F1ZOAnPzWQqMIOHzyMHikc9M9NmZdF5DY+BrKn531yAlmYjyBIFHhkogeH6JMQ== Received: from sv.mirrors.kernel.org (sv.mirrors.kernel.org. [139.178.88.99]) by mx.google.com with ESMTPS id hk7-20020a17090b224700b00296a6e34458si1215431pjb.76.2024.02.05.07.58.56 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Feb 2024 07:58:56 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel+bounces-52954-ouuuleilei=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20230601 header.b=ECodOzTp; arc=pass (i=1 spf=pass spfdomain=flex--mattgilbride.bounces.google.com dkim=pass dkdomain=google.com dmarc=pass fromdomain=google.com); spf=pass (google.com: domain of linux-kernel+bounces-52954-ouuuleilei=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) smtp.mailfrom="linux-kernel+bounces-52954-ouuuleilei=gmail.com@vger.kernel.org"; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: from smtp.subspace.kernel.org (wormhole.subspace.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sv.mirrors.kernel.org (Postfix) with ESMTPS id 751D628A94F for ; Mon, 5 Feb 2024 15:52:18 +0000 (UTC) Received: from localhost.localdomain (localhost.localdomain [127.0.0.1]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3680F3CF63; Mon, 5 Feb 2024 15:50:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ECodOzTp" Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5794B4595A for ; Mon, 5 Feb 2024 15:50:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707148214; cv=none; b=n/zPCrs0uMqNvipqSR7pZeUc0APT3VtOBYVi8ZyfmRtI4ZT+jo9kAX4UWxcdXj2Xx+/g8fgfv8p4vRqst9nDAqqj1KFYUKW2xh9J4+gtnzqiv30Bo7VrK1fEr6PDf4Q/J25Yw2XiRXXRQOw3c39MUfpGsiFgLAA1qvobSyM/SMs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707148214; c=relaxed/simple; bh=fEdkpQRAKxcK+Vq+Ej5tRRpaejTCMjdLRVmNroqCOfw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=gm68aH6pQrwxRzEC0OY3p+FytD2fhvGLJNnoJzMW+et0sMRiST/n0wKikUl3ekXrMWo8eyPrF3JUITUNjaHsDnkYOuIyx4f78kCHdnwyDPU351rk3iqLQFUNo2mg4NZvzX3GDyK5UUAxKyU9qglYhGyFQWGC3wImQraLXnGSeiw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--mattgilbride.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ECodOzTp; arc=none smtp.client-ip=209.85.128.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--mattgilbride.bounces.google.com Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-6041bb56dbfso62798797b3.2 for ; Mon, 05 Feb 2024 07:50:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1707148210; x=1707753010; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=JtORM6z3n6Nx7zIdzVBRR85gUfsLFA4+3fHETUbUVdg=; b=ECodOzTpDLuiK1B/JxpKMoBWzzAohfjIZoTaPXbUaFquLe4BQ2TSTgBw4puALcHz6P OhUgsUxh3ApkCDy5hngMt117MZld7tUKkbsoIVV8HB/UkCDws2rifg9SjeEMyovtqJkU Xow/+San3+ysBIYScMFujk7zV5o539QJiLFf8zsI3GLg0JUC4rq36MJDnWr5O7ZZwC5N Kz/pLltL2Qn59v8K3zg9tyn6E3V1K2YF0QUjZobPOXecbGLVAYMYhsT2mOafh3gvqb19 mM4KkF8Dhc+NGxSVjezDq/v1UIGPaD8vZTQ8G7uw1mi9A7a8bXzuikUmJ/lwG/96tvr6 ajEQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707148210; x=1707753010; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=JtORM6z3n6Nx7zIdzVBRR85gUfsLFA4+3fHETUbUVdg=; b=jHGb5oq2q3TUGVr0VIZBP3FBJy+9u5F70V2McPIIsjvFFJZEVJMQOZeAn/adiZAnWP meYgLvJQNOJTXB05sKhELaKz9iid+q7xIyDzLxmI1lUSp0/BgdgPGZE6E8YsD/dnLBb7 MlNcAYiRZKlGZLeyb75WLX54tCreMZfOUVXuUI2AlG4L0XLDIWXrv82hSyNLUsvNojpr 3geRMXq52qx15R24nltjZ8F1XThGIDjwVQ04PCuzDuhtKopplVHqqEfkZpknlx5bKa7Q yB0I1/umOyXXHm9S3IpU+CChHbvceHZR1RiPTMSbmWc6+Qm+VoCgEfTWbCtXTOajx7L7 mTjg== X-Gm-Message-State: AOJu0YyXIOX5PLfBSt2NlyJhYi9CtydzK7xiRsTx6kVrI/Y7QOueqaEg x+638pjWyX37JicaPA0X/ysuVcoc8q0LEniQGuMzA2SQcucOMNt53dzP5aMhFwtBKlvuH33aAQ5 Wv/i8AVwHL3JqIcrV3UmKyye/zA== X-Received: from mattgilbride.c.googlers.com ([fda3:e722:ac3:cc00:2b:7d90:c0a8:2ac5]) (user=mattgilbride job=sendgmr) by 2002:a25:b183:0:b0:dc6:ebd4:cca2 with SMTP id h3-20020a25b183000000b00dc6ebd4cca2mr327456ybj.11.1707148210290; Mon, 05 Feb 2024 07:50:10 -0800 (PST) Date: Mon, 05 Feb 2024 15:50:05 +0000 In-Reply-To: <20240205-b4-rbtree-v1-0-995e3eee38c0@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240205-b4-rbtree-v1-0-995e3eee38c0@google.com> X-Mailer: b4 0.12.3 Message-ID: <20240205-b4-rbtree-v1-5-995e3eee38c0@google.com> Subject: [PATCH 5/6] rust: rbtree: add `RBTreeCursor` From: mattgilbride@google.com To: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " , Benno Lossin , Andreas Hindborg , Alice Ryhl , Greg Kroah-Hartman , " =?utf-8?q?Arve_Hj=C3=B8n?= =?utf-8?q?nev=C3=A5g?= " , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Christian Brauner Cc: Rob Landley , Davidlohr Bueso , Michel Lespinasse , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Matt Gilbride X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1790075193129518552 X-GMAIL-MSGID: 1790075193129518552 Add a cursor interface to `RBTree`, supporting the following use cases: - Inspect the current node pointed to by the cursor, inspect/move to it's neighbors in sort order (bidirectionally). - Mutate the tree itself by removing the current node pointed to by the cursor, or one of its neighbors. Add functions to obtain a cursor to the tree by key: - The node with the smallest key - The node with the largest key - The node matching the given key, or the one with the next larger key The cursor abstraction is needed by the binder driver to efficiently search for nodes and (conditionally) modify them, as well as their neighbors [1]. Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-6-08ba9197f637@google.com/ [1] Co-developed-by: Alice Ryhl Signed-off-by: Alice Ryhl Signed-off-by: Matt Gilbride Reviewed-by: Alice Ryhl Tested-by: Alice Ryhl --- rust/kernel/rbtree.rs | 512 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 512 insertions(+) diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs index db17734b3fa1..0db6a584a9fc 100644 --- a/rust/kernel/rbtree.rs +++ b/rust/kernel/rbtree.rs @@ -244,6 +244,36 @@ pub fn values(&self) -> impl Iterator { pub fn values_mut(&mut self) -> impl Iterator { self.iter_mut().map(|(_, v)| v) } + + /// Returns a cursor over the tree nodes, starting with the smallest key. + pub fn cursor_front(&mut self) -> Option> { + let root = addr_of_mut!(self.root); + // SAFETY: `self.root` is always a valid root node + let current = unsafe { bindings::rb_first(root) }; + if current.is_null() { + return None; + } + Some(RBTreeCursor { + _tree: PhantomData, + root, + current, + }) + } + + /// Returns a cursor over the tree nodes, starting with the largest key. + pub fn cursor_back(&mut self) -> Option> { + let root = addr_of_mut!(self.root); + // SAFETY: `self.root` is always a valid root node + let current = unsafe { bindings::rb_last(root) }; + if current.is_null() { + return None; + } + Some(RBTreeCursor { + _tree: PhantomData, + root, + current, + }) + } } impl RBTree @@ -376,6 +406,59 @@ pub fn remove(&mut self, key: &K) -> Option { } = *node; Some(value) } + + /// Returns a cursor over the tree nodes based on the given key. + /// + /// If the given key exists, the cursor starts there. + /// Otherwise it starts with the first larger key in sort order. + /// If there is no larger key, it returns [`None`]. + pub fn cursor_lower_bound(&mut self, key: &K) -> Option> + where + K: Ord, + { + let mut node = self.root.rb_node; + let mut best_match: Option>> = None; + while !node.is_null() { + // SAFETY: All links fields we create are in a `Node`. + let this = unsafe { crate::container_of!(node, Node, links) }.cast_mut(); + // SAFETY: `this` is a non-null node so it is valid by the type invariants. + let this_key = unsafe { &(*this).key }; + // SAFETY: `node` is a non-null node so it is valid by the type invariants. + let left_child = unsafe { (*node).rb_left }; + // SAFETY: `node` is a non-null node so it is valid by the type invariants. + let right_child = unsafe { (*node).rb_right }; + if key == this_key { + return Some(RBTreeCursor { + _tree: PhantomData, + root: addr_of_mut!(self.root), + current: node, + }); + } else { + node = if key > this_key { + right_child + } else { + let is_better_match = match best_match { + None => true, + Some(best) => { + // SAFETY: `best` is a non-null node so it is valid by the type invariants. + let best_key = unsafe { &(*best.as_ptr()).key }; + best_key > this_key + } + }; + if is_better_match { + best_match = NonNull::new(this); + } + left_child + } + }; + } + best_match.map(|best| RBTreeCursor { + _tree: PhantomData, + root: addr_of_mut!(self.root), + // SAFETY: `best` is a non-null node so it is valid by the type invariants. + current: unsafe { addr_of_mut!((*best.as_ptr()).links) }, + }) + } } impl Default for RBTree { @@ -406,6 +489,435 @@ fn drop(&mut self) { } } +/// A bidirectional cursor over the tree nodes, sorted by key. +/// +/// # Invariants +/// +/// In instance of `RBTreeCursor` is only acquired from [`RBTree`]. +/// A reference to the tree used to create the cursor outlives the cursor, so +/// the tree cannot change. By the tree invariant, all nodes are valid. +/// +/// # Examples +/// +/// In the following example, we obtain a cursor to the first element in the tree. +/// The cursor allows us to iterate bidirectionally over key/value pairs in the tree. +/// +/// ``` +/// use kernel::rbtree::RBTree; +/// +/// // Create a new tree. +/// let mut tree = RBTree::new(); +/// +/// // Insert three elements. +/// tree.try_create_and_insert(10, 100)?; +/// tree.try_create_and_insert(20, 200)?; +/// tree.try_create_and_insert(30, 300)?; +/// +/// // Get a cursor to the first element. +/// let mut cursor = tree.cursor_front().unwrap(); +/// let mut current = cursor.current(); +/// assert_eq!(current, (&10, &100)); +/// +/// // Move the cursor, updating it to the 2nd element. +/// cursor = cursor.move_next().unwrap(); +/// current = cursor.current(); +/// assert_eq!(current, (&20, &200)); +/// +/// // Peek at the next element without impacting the cursor. +/// let next = cursor.peek_next().unwrap(); +/// assert_eq!(next, (&30, &300)); +/// current = cursor.current(); +/// assert_eq!(current, (&20, &200)); +/// +/// // Moving past the last element causes the cursor to return [`None`]. +/// cursor = cursor.move_next().unwrap(); +/// current = cursor.current(); +/// assert_eq!(current, (&30, &300)); +/// let cursor = cursor.move_next(); +/// assert!(cursor.is_none()); +/// +/// # Ok::<(), Error>(()) +/// ``` +/// +/// A cursor can also be obtained at the last element in the tree. +/// +/// ``` +/// use kernel::rbtree::RBTree; +/// +/// // Create a new tree. +/// let mut tree = RBTree::new(); +/// +/// // Insert three elements. +/// tree.try_create_and_insert(10, 100)?; +/// tree.try_create_and_insert(20, 200)?; +/// tree.try_create_and_insert(30, 300)?; +/// +/// let mut cursor = tree.cursor_back().unwrap(); +/// let current = cursor.current(); +/// assert_eq!(current, (&30, &300)); +/// +/// # Ok::<(), Error>(()) +/// ``` +/// +/// Obtaining a cursor returns [`None`] if the tree is empty. +/// +/// ``` +/// use kernel::rbtree::RBTree; +/// +/// let mut tree: RBTree = RBTree::new(); +/// assert!(tree.cursor_front().is_none()); +/// +/// # Ok::<(), Error>(()) +/// ``` +/// +/// [`RBTree::cursor_lower_bound`] can be used to start at an arbitrary node in the tree. +/// +/// ``` +/// use kernel::rbtree::RBTree; +/// +/// // Create a new tree. +/// let mut tree = RBTree::new(); +/// +/// // Insert five elements. +/// tree.try_create_and_insert(10, 100)?; +/// tree.try_create_and_insert(20, 200)?; +/// tree.try_create_and_insert(30, 300)?; +/// tree.try_create_and_insert(40, 400)?; +/// tree.try_create_and_insert(50, 500)?; +/// +/// // If the provided key exists, a cursor to that key is returned. +/// let cursor = tree.cursor_lower_bound(&20).unwrap(); +/// let current = cursor.current(); +/// assert_eq!(current, (&20, &200)); +/// +/// // If the provided key doesn't exist, a cursor to the first larger element in sort order is returned. +/// let cursor = tree.cursor_lower_bound(&25).unwrap(); +/// let current = cursor.current(); +/// assert_eq!(current, (&30, &300)); +/// +/// // If there is no larger key, [`None`] is returned. +/// let cursor = tree.cursor_lower_bound(&55); +/// assert!(cursor.is_none()); +/// +/// # Ok::<(), Error>(()) +/// ``` +/// +/// The cursor allows mutation of values in the tree. +/// +/// ``` +/// use kernel::rbtree::RBTree; +/// +/// // Create a new tree. +/// let mut tree = RBTree::new(); +/// +/// // Insert three elements. +/// tree.try_create_and_insert(10, 100)?; +/// tree.try_create_and_insert(20, 200)?; +/// tree.try_create_and_insert(30, 300)?; +/// +/// // Retrieve a cursor. +/// let mut cursor = tree.cursor_front().unwrap(); +/// +/// // Get a mutable reference to the current value. +/// let (k, v) = cursor.current_mut(); +/// *v = 1000; +/// +/// // The updated value is reflected in the tree. +/// let updated = tree.get(&10).unwrap(); +/// assert_eq!(updated, &1000); +/// +/// # Ok::<(), Error>(()) +/// ``` +/// +/// It also allows node removal. The following examples demonstrate the behavior of removing the current node. +/// +/// ``` +/// use kernel::rbtree::RBTree; +/// +/// // Create a new tree. +/// let mut tree = RBTree::new(); +/// +/// // Insert three elements. +/// tree.try_create_and_insert(10, 100)?; +/// tree.try_create_and_insert(20, 200)?; +/// tree.try_create_and_insert(30, 300)?; +/// +/// // Remove the first element. +/// let mut cursor = tree.cursor_front().unwrap(); +/// let mut current = cursor.current(); +/// assert_eq!(current, (&10, &100)); +/// cursor = cursor.remove_current().unwrap(); +/// +/// // If a node exists after the current element, it is returned. +/// current = cursor.current(); +/// assert_eq!(current, (&20, &200)); +/// +/// // Get a cursor to the last element, and remove it. +/// cursor = tree.cursor_back().unwrap(); +/// current = cursor.current(); +/// assert_eq!(current, (&30, &300)); +/// +/// // Since there is no next node, the previous node is returned. +/// cursor = cursor.remove_current().unwrap(); +/// current = cursor.current(); +/// assert_eq!(current, (&20, &200)); +/// +/// // Removing the last element in the tree returns [`None`]. +/// assert!(cursor.remove_current().is_none()); +/// +/// # Ok::<(), Error>(()) +/// ``` +/// +/// Nodes adjacent to the current node can also be removed. +/// +/// ``` +/// use kernel::rbtree::RBTree; +/// +/// // Create a new tree. +/// let mut tree = RBTree::new(); +/// +/// // Insert three elements. +/// tree.try_create_and_insert(10, 100)?; +/// tree.try_create_and_insert(20, 200)?; +/// tree.try_create_and_insert(30, 300)?; +/// +/// // Get a cursor to the first element. +/// let mut cursor = tree.cursor_front().unwrap(); +/// let mut current = cursor.current(); +/// assert_eq!(current, (&10, &100)); +/// +/// // Calling `remove_prev` from the first element returns [`None`]. +/// assert!(cursor.remove_prev().is_none()); +/// +/// // Get a cursor to the last element. +/// cursor = tree.cursor_back().unwrap(); +/// current = cursor.current(); +/// assert_eq!(current, (&30, &300)); +/// +/// // Calling `remove_prev` removes and returns the middle element. +/// assert_eq!(cursor.remove_prev().unwrap(), (20, 200)); +/// +/// // Calling `remove_next` from the last element returns [`None`]. +/// assert!(cursor.remove_next().is_none()); +/// +/// // Move to the first element +/// cursor = cursor.move_prev().unwrap(); +/// current = cursor.current(); +/// assert_eq!(current, (&10, &100)); +/// +/// // Calling `remove_next` removes and returns the last element. +/// assert_eq!(cursor.remove_next().unwrap(), (30, 300)); +/// +/// # Ok::<(), Error>(()) +/// ``` +pub struct RBTreeCursor<'a, K, V> { + _tree: PhantomData<&'a RBTree>, + root: *mut bindings::rb_root, + current: *mut bindings::rb_node, +} + +// SAFETY: An [`RBTree`] allows the same kinds of access to its values that a struct allows to its +// fields, so we use the same Send condition as would be used for a struct with K and V fields. +unsafe impl<'a, K: Send, V: Send> Send for RBTreeCursor<'a, K, V> {} + +// SAFETY: An [`RBTree`] allows the same kinds of access to its values that a struct allows to its +// fields, so we use the same Sync condition as would be used for a struct with K and V fields. +unsafe impl<'a, K: Sync, V: Sync> Sync for RBTreeCursor<'a, K, V> {} + +impl<'a, K, V> RBTreeCursor<'a, K, V> { + /// The current node + pub fn current(&self) -> (&K, &V) { + Self::to_key_value(self.current) + } + + /// The current node, with a mutable value + pub fn current_mut(&mut self) -> (&K, &mut V) { + Self::to_key_value_mut(self.current) + } + + /// Remove the current node from the tree. + /// + /// Returns a cursor to the next node, if it exists, + /// else the previous node. Returns [`None`] if the tree + /// becomes empty. + pub fn remove_current(mut self) -> Option { + let prev = self.get_neighbor_raw(Direction::Prev); + let next = self.get_neighbor_raw(Direction::Next); + // SAFETY: All links fields we create are in a `Node`. + let this = unsafe { crate::container_of!(self.current, Node, links) }.cast_mut(); + // SAFETY: The reference to the tree used to create the cursor outlives the cursor, so + // the tree cannot change. By the tree invariant, all nodes are valid. + unsafe { bindings::rb_erase(&mut (*this).links, self.root) }; + + let current = match (prev, next) { + (_, Some(next)) => next, + (Some(prev), None) => prev, + (None, None) => { + return None; + } + }; + + Some(Self { + current, + _tree: self._tree, + root: self.root, + }) + } + + /// Remove the previous node, returning it if it exists. + pub fn remove_prev(&mut self) -> Option<(K, V)> { + self.remove_neighbor(Direction::Prev) + } + + /// Remove the next node, returning it if it exists. + pub fn remove_next(&mut self) -> Option<(K, V)> { + self.remove_neighbor(Direction::Next) + } + + fn remove_neighbor(&mut self, direction: Direction) -> Option<(K, V)> { + if let Some(neighbor) = self.get_neighbor_raw(direction) { + // SAFETY: All links fields we create are in a `Node`. + let this = unsafe { crate::container_of!(neighbor, Node, links) }.cast_mut(); + // SAFETY: The reference to the tree used to create the cursor outlives the cursor, so + // the tree cannot change. By the tree invariant, all nodes are valid. + unsafe { bindings::rb_erase(&mut (*this).links, self.root) }; + return Some(Self::to_key_value_owned(neighbor)); + } + None + } + + /// Move the cursor to the previous node, returning [`None`] if it doesn't exist. + pub fn move_prev(self) -> Option { + self.mv(Direction::Prev) + } + + /// Move the cursor to the next node, returning [`None`] if it doesn't exist. + pub fn move_next(self) -> Option { + self.mv(Direction::Next) + } + + fn mv(mut self, direction: Direction) -> Option { + self.get_neighbor_raw(direction).map(|neighbor| Self { + _tree: self._tree, + root: self.root, + current: neighbor, + }) + } + + /// Access the previous node without moving the cursor. + pub fn peek_prev(&self) -> Option<(&K, &V)> { + self.peek(Direction::Prev) + } + + /// Access the previous node without moving the cursor. + pub fn peek_next(&self) -> Option<(&K, &V)> { + self.peek(Direction::Next) + } + + fn peek(&self, direction: Direction) -> Option<(&K, &V)> { + // SAFETY: `self.current` is valid by the type invariants. + let neighbor = unsafe { + match direction { + Direction::Prev => bindings::rb_prev(self.current), + Direction::Next => bindings::rb_next(self.current), + } + }; + + if neighbor.is_null() { + return None; + } + + Some(Self::to_key_value(neighbor)) + } + + /// Access the previous node mutably without moving the cursor. + pub fn peek_prev_mut(&mut self) -> Option<(&K, &mut V)> { + self.peek_mut(Direction::Prev) + } + + /// Access the next node mutably without moving the cursor. + pub fn peek_next_mut(&mut self) -> Option<(&K, &mut V)> { + self.peek_mut(Direction::Next) + } + + fn peek_mut(&mut self, direction: Direction) -> Option<(&K, &mut V)> { + // SAFETY: `self.current` is valid by the type invariants. + let neighbor = unsafe { + match direction { + Direction::Prev => bindings::rb_prev(self.current), + Direction::Next => bindings::rb_next(self.current), + } + }; + + if neighbor.is_null() { + return None; + } + + Some(Self::to_key_value_mut(neighbor)) + } + + fn get_neighbor_raw(&mut self, direction: Direction) -> Option<*mut bindings::rb_node> { + // SAFETY: `self.current` is valid by the type invariants. + let neighbor = unsafe { + match direction { + Direction::Prev => bindings::rb_prev(self.current), + Direction::Next => bindings::rb_next(self.current), + } + }; + + if neighbor.is_null() { + return None; + } + + Some(neighbor) + } + + // This internal method should *only* be called with a valid pointer to a node. + fn to_key_value(node: *mut bindings::rb_node) -> (&'a K, &'a V) { + // SAFETY: All links fields we create are in a `Node`. + let this = unsafe { crate::container_of!(node, Node, links) }; + // SAFETY: The passed `node` is the current node or a non-null neighbor, + // thus `this` is valid by the type invariants. + let k = unsafe { &(*this).key }; + // SAFETY: The passed `node` is the current node or a non-null neighbor, + // thus `this` is valid by the type invariants. + let v = unsafe { &(*this).value }; + (k, v) + } + + // This internal method should *only* be called with a valid pointer to a node. + fn to_key_value_mut(node: *mut bindings::rb_node) -> (&'a K, &'a mut V) { + // SAFETY: All links fields we create are in a `Node`. + let this = unsafe { crate::container_of!(node, Node, links) }.cast_mut(); + // SAFETY: The passed `node` is the current node or a non-null neighbor, + // thus `this` is valid by the type invariants. + let k = unsafe { &(*this).key }; + // SAFETY: The passed `node` is the current node or a non-null neighbor, + // thus `this` is valid by the type invariants. + let v = unsafe { &mut (*this).value }; + (k, v) + } + + // This internal method should *only* be called with a valid pointer to a node *that is being removed*. + fn to_key_value_owned(node: *mut bindings::rb_node) -> (K, V) { + // SAFETY: All links fields we create are in a `Node`. + let this = unsafe { crate::container_of!(node, Node, links) }.cast_mut(); + // SAFETY: The passed `node` is the current node or a non-null neighbor, + // thus `this` is valid by the type invariants. + let n = unsafe { Box::from_raw(this) }; + + (n.key, n.value) + } +} + +/// Direction for [`RBTreeCursor`] operations. +enum Direction { + /// the node immediately before, in sort order + Prev, + /// the node immediately after, in sort order + Next, +} + impl<'a, K, V> IntoIterator for &'a RBTree { type Item = (&'a K, &'a V); type IntoIter = RBTreeIterator<'a, K, V>;