From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB351C4321E for ; Fri, 2 Dec 2022 16:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234018AbiLBQSp (ORCPT ); Fri, 2 Dec 2022 11:18:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234070AbiLBQSL (ORCPT ); Fri, 2 Dec 2022 11:18:11 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DEB81DFB59; Fri, 2 Dec 2022 08:16:47 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7B1A362322; Fri, 2 Dec 2022 16:16:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6F3EC43470; Fri, 2 Dec 2022 16:16:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1669997806; bh=YyjXthwblgrT88DPLFu+XIPGLqjTiZLg+Xpj0PN4MaE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iUVfcvaGJdF/n2QAZNTbyYm5gbDZ+FvzXb1+V8Q7HwFKlarV3seVo1NnOevDs7f9A uxcx1Ce9O/9sI14ZMd98O5sFBiUUgCcucTb4+KI/zXlega/CNBZpzsuRiXAlpPUEux oPtm3kxnmuw1fAt/iUFshg9JMuKQZavSA/KJpFUAd8Rl2yUN8Hbu+6kOtRGKw3hyBp I3ZSh6nvGSQ6ddBxn2yHDHPvwNJKZDL8JoiLX3U6mkmv8zs1eWyZhXSzHNioAell2D 8+znw2S00T/44bGNXLEEUmiMlyC/YIDBT6y9MFZowF6EDXr+RVIhfRd0/qFm5ZqEUb wCkPYCWBYfpTA== From: ojeda@kernel.org To: Miguel Ojeda , Wedson Almeida Filho , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, patches@lists.linux.dev Subject: [PATCH v2 28/28] rust: types: add `Opaque` type Date: Fri, 2 Dec 2022 17:14:59 +0100 Message-Id: <20221202161502.385525-29-ojeda@kernel.org> In-Reply-To: <20221202161502.385525-1-ojeda@kernel.org> References: <20221202161502.385525-1-ojeda@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: rust-for-linux@vger.kernel.org From: Wedson Almeida Filho Add the `Opaque` type, which is meant to be used with FFI objects that are never interpreted by Rust code, e.g.: struct Waiter { completion: Opaque, next: *mut Waiter, } It has the advantage that the objects don't have to be zero-initialised before calling their init functions, making the code performance closer to C. Signed-off-by: Wedson Almeida Filho [Reworded, adapted for upstream and applied latest changes] Signed-off-by: Miguel Ojeda --- rust/kernel/types.rs | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 3b0c44769708..e84e51ec9716 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -2,6 +2,31 @@ //! Kernel types. +use core::{cell::UnsafeCell, mem::MaybeUninit}; + +/// Stores an opaque value. +/// +/// This is meant to be used with FFI objects that are never interpreted by Rust code. +#[repr(transparent)] +pub struct Opaque(MaybeUninit>); + +impl Opaque { + /// Creates a new opaque value. + pub const fn new(value: T) -> Self { + Self(MaybeUninit::new(UnsafeCell::new(value))) + } + + /// Creates an uninitialised value. + pub const fn uninit() -> Self { + Self(MaybeUninit::uninit()) + } + + /// Returns a raw pointer to the opaque data. + pub fn get(&self) -> *mut T { + UnsafeCell::raw_get(self.0.as_ptr()) + } +} + /// A sum type that always holds either a value of type `L` or `R`. pub enum Either { /// Constructs an instance of [`Either`] containing a value of type `L`. -- 2.38.1