From patchwork Thu Mar 30 04:39:49 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wedson Almeida Filho X-Patchwork-Id: 76886 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:b0ea:0:b0:3b6:4342:cba0 with SMTP id b10csp873374vqo; Wed, 29 Mar 2023 21:51:03 -0700 (PDT) X-Google-Smtp-Source: AKy350asF4upxx/FN/CuQYQGINprGZGYeRhCpvznnpFnAlvzIxyGiq+4NmaDgmvOJiS/qq8Dqv7j X-Received: by 2002:a05:6402:658:b0:4fb:6523:2b38 with SMTP id u24-20020a056402065800b004fb65232b38mr22905510edx.27.1680151863361; Wed, 29 Mar 2023 21:51:03 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1680151863; cv=none; d=google.com; s=arc-20160816; b=MqZ4ezrOyT/GcXDbmPa/vW/v4NYw4LdhnjV+7YCMyyP811Fn+CFWfXnXXpufuFw3PP OA7MmLmXEs+YBqjA/QiyDceC86ZbVffnQKnBUcXruYyglARWEaVXW8278Zh/HFr1+Yrs aJlEmHTKNCeOrJJd16HHXlMVWJe4p6uD+fX/IMcrVBUI+/jPn8B6Sr4Se2YPI15Gdvwh Wh2rbt0ZqmC8AA7G7Z1r+nK9bq0+jwxPB8QGnAix8p7itd8YtwNzQ09bz1mK8dm3M+YN EmNAxDnDpIvmYlHGx5NvkaqdyKi/YsZTmBiiOPDbLDC+X7flXK+xuMjYYN0/A8PKFdZN cBgQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=ZIKW7/0TFQl6GljEgB3wW2iOFuiG0GQhzQq6GUBT1ww=; b=nAw2v8i4ojNK6FUWNZwVK3cUnR3f1AzRiBF3a0DbmIUvGSuy5mQZ72IOqU4x4XxT6L ELCMJoGObG1Xb4Eh70pDs0g+0NZSgjpVKT5D9wcQ1egkn7R/dKfvyKJTHjEfqr6JbJJi oFcHwMFCrMPMJBiHx/y4ygjjBM5zBUpN5VE3f8tAX+yvcrmc/ewqW16uY99DOCZoQhU6 c9K56VVe7ZJ9bfzdLgyz/icJFOUc9ATTNobYlsg6qB+6qM93LvK4Kxw482TtWW7EwLXT gRObHMala2X5zlZOl+GCbUJF0rFdC4NCEUj4LoQu9ajI52lkfJB8Gx0D77QXrwnkHsZY EkSw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20210112 header.b=b9kU6CT3; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id d19-20020a50fb13000000b004fd2b13b203si1345379edq.550.2023.03.29.21.50.38; Wed, 29 Mar 2023 21:51:03 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20210112 header.b=b9kU6CT3; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229951AbjC3EmB (ORCPT + 99 others); Thu, 30 Mar 2023 00:42:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37032 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230004AbjC3Ele (ORCPT ); Thu, 30 Mar 2023 00:41:34 -0400 Received: from mail-oa1-x30.google.com (mail-oa1-x30.google.com [IPv6:2001:4860:4864:20::30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AFE8A6A58; Wed, 29 Mar 2023 21:41:16 -0700 (PDT) Received: by mail-oa1-x30.google.com with SMTP id 586e51a60fabf-17aeb49429eso18554849fac.6; Wed, 29 Mar 2023 21:41:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680151276; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=ZIKW7/0TFQl6GljEgB3wW2iOFuiG0GQhzQq6GUBT1ww=; b=b9kU6CT36DIeFiFv2cLFVYwALpVHAH/iM/S1SgYTEqa+2W1Bii+11r9TC0fQ7CJgS9 u9VrmW/kP9KJ589PWODX8gDnc6xNODs8+pBNrwRwR3eTjeSxA+eJTcTI4nHV7ItQuQ6s ofIMO8Nv9EB79Q2CEm3Ie5y2UK48BIXn93J+sipvKOQA3eDNTqKwOGotAVeggVLpgIA9 5ByiXTB17NqhXHWkIOXmsNR+2dqopd+1+jJqjYeNCmQBqs/wamOZ2zwcbJ1zou+iRtcy mn7z2SCQMmAH8anq6fp4mp0/8aI/R21LeM/RQWYw3itaPYgIunK5RQ4b+5Bxmv186TXR Oalw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680151276; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=ZIKW7/0TFQl6GljEgB3wW2iOFuiG0GQhzQq6GUBT1ww=; b=4/T0jIpILRVAcucezL4ibUZ2seRVVSBtjW4acVIMVRyEkz3Mn8QKWweN2tkVCook3H m8RDgHHz2nid1yAWpbNgBgZ3tZ7ICbjkr37HLacqdxD6gWypqoKedDyB4ED+b5e7q5FQ rmU7Pmh0dZBoZsaOYlbeZxDbNhY8hvVhFX4SpvQaMRXZYBfvCaH76oqO4sqATFJvYG8P py+Dy2rsWjHZqJxxWddgY6goRgLeLbR2RfPh0xKnACOIj2jCTD/Vj3pVbqfCVdmQYvKX NKnuSCsnPmhMzq5YPwFe9kJ75GY4IFS5K6aRQ8Gvo9exHzeuW+W3rqCEaEYDVtU7o/VL sRZA== X-Gm-Message-State: AO0yUKWEzD8fFOaTKS79xplKJDfwUlyoTtr8oM3SOaOkOoyKdaTxaSyo Dpsc3tBTK/4Z4XJfWJGqTmZzfBdg8nKzug== X-Received: by 2002:a05:6870:4581:b0:17e:a4d6:5e0c with SMTP id y1-20020a056870458100b0017ea4d65e0cmr14683787oao.23.1680151275756; Wed, 29 Mar 2023 21:41:15 -0700 (PDT) Received: from wedsonaf-dev.home.lan ([189.124.190.154]) by smtp.googlemail.com with ESMTPSA id ea43-20020a056870072b00b0017e0c13b29asm7518599oab.36.2023.03.29.21.41.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Mar 2023 21:41:15 -0700 (PDT) From: Wedson Almeida Filho To: rust-for-linux@vger.kernel.org Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?B?= =?utf-8?q?j=C3=B6rn_Roy_Baron?= , linux-kernel@vger.kernel.org, Wedson Almeida Filho Subject: [PATCH 08/13] rust: introduce `ARef` Date: Thu, 30 Mar 2023 01:39:49 -0300 Message-Id: <20230330043954.562237-8-wedsonaf@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230330043954.562237-1-wedsonaf@gmail.com> References: <20230330043954.562237-1-wedsonaf@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-0.2 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1761766920669332897?= X-GMAIL-MSGID: =?utf-8?q?1761766920669332897?= From: Wedson Almeida Filho This is an owned reference to an object that is always ref-counted. This is meant to be used in wrappers for C types that have their own ref counting functions, for example, tasks, files, inodes, dentries, etc. Signed-off-by: Wedson Almeida Filho Reviewed-by: Gary Guo --- rust/kernel/types.rs | 107 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 107 insertions(+) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index dbfae9bb97ce..b071730253c7 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -6,8 +6,10 @@ use crate::init::{self, PinInit}; use alloc::boxed::Box; use core::{ cell::UnsafeCell, + marker::PhantomData, mem::MaybeUninit, ops::{Deref, DerefMut}, + ptr::NonNull, }; /// Used to transfer ownership to and from foreign (non-Rust) languages. @@ -295,6 +297,111 @@ opaque_init_funcs! { "Rust" manual_init4(arg1: A1, arg2: A2, arg3: A3, arg4: A4); } +/// Types that are _always_ reference counted. +/// +/// It allows such types to define their own custom ref increment and decrement functions. +/// Additionally, it allows users to convert from a shared reference `&T` to an owned reference +/// [`ARef`]. +/// +/// This is usually implemented by wrappers to existing structures on the C side of the code. For +/// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted +/// instances of a type. +/// +/// # Safety +/// +/// Implementers must ensure that increments to the reference count keep the object alive in memory +/// at least until matching decrements are performed. +/// +/// Implementers must also ensure that all instances are reference-counted. (Otherwise they +/// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object +/// alive.) +pub unsafe trait AlwaysRefCounted { + /// Increments the reference count on the object. + fn inc_ref(&self); + + /// Decrements the reference count on the object. + /// + /// Frees the object when the count reaches zero. + /// + /// # Safety + /// + /// Callers must ensure that there was a previous matching increment to the reference count, + /// and that the object is no longer used after its reference count is decremented (as it may + /// result in the object being freed), unless the caller owns another increment on the refcount + /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls + /// [`AlwaysRefCounted::dec_ref`] once). + unsafe fn dec_ref(obj: NonNull); +} + +/// An owned reference to an always-reference-counted object. +/// +/// The object's reference count is automatically decremented when an instance of [`ARef`] is +/// dropped. It is also automatically incremented when a new instance is created via +/// [`ARef::clone`]. +/// +/// # Invariants +/// +/// The pointer stored in `ptr` is non-null and valid for the lifetime of the [`ARef`] instance. In +/// particular, the [`ARef`] instance owns an increment on the underlying object's reference count. +pub struct ARef { + ptr: NonNull, + _p: PhantomData, +} + +impl ARef { + /// Creates a new instance of [`ARef`]. + /// + /// It takes over an increment of the reference count on the underlying object. + /// + /// # Safety + /// + /// Callers must ensure that the reference count was incremented at least once, and that they + /// are properly relinquishing one increment. That is, if there is only one increment, callers + /// must not use the underlying object anymore -- it is only safe to do so via the newly + /// created [`ARef`]. + pub unsafe fn from_raw(ptr: NonNull) -> Self { + // INVARIANT: The safety requirements guarantee that the new instance now owns the + // increment on the refcount. + Self { + ptr, + _p: PhantomData, + } + } +} + +impl Clone for ARef { + fn clone(&self) -> Self { + self.inc_ref(); + // SAFETY: We just incremented the refcount above. + unsafe { Self::from_raw(self.ptr) } + } +} + +impl Deref for ARef { + type Target = T; + + fn deref(&self) -> &Self::Target { + // SAFETY: The type invariants guarantee that the object is valid. + unsafe { self.ptr.as_ref() } + } +} + +impl From<&T> for ARef { + fn from(b: &T) -> Self { + b.inc_ref(); + // SAFETY: We just incremented the refcount above. + unsafe { Self::from_raw(NonNull::from(b)) } + } +} + +impl Drop for ARef { + fn drop(&mut self) { + // SAFETY: The type invariants guarantee that the `ARef` owns the reference we're about to + // decrement. + unsafe { T::dec_ref(self.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`.