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[2620:137:e000::1:20]) by mx.google.com with ESMTP id gv3-20020a1709072bc300b00947bae8c71bsi4712730ejc.916.2023.04.08.00.58.14; Sat, 08 Apr 2023 00:58:38 -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=gJPOyjdI; 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 S230064AbjDHHy6 (ORCPT + 99 others); Sat, 8 Apr 2023 03:54:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230144AbjDHHyf (ORCPT ); Sat, 8 Apr 2023 03:54:35 -0400 Received: from mail-oi1-x236.google.com (mail-oi1-x236.google.com [IPv6:2607:f8b0:4864:20::236]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7842810271; Sat, 8 Apr 2023 00:54:17 -0700 (PDT) Received: by mail-oi1-x236.google.com with SMTP id f14so18831052oiw.10; Sat, 08 Apr 2023 00:54:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680940457; 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=S9xdueeJy7MgLea0ONmd9MZ1VHllI6hHaQJbmcDSqvw=; b=gJPOyjdIa5tq77ALNTMPC2MFBLNhcROzoktPdDzydEf5g6t1f171CYPi/W6bF+1MJA a7NXuCM6eOUDRd0+M6o9IbTb5d1+Ssh0ZyPyZOhZTATdSu0gI96WjxXek3wDqz426r0N BEVi2tBlRqofAlJGtL2hom7owEyLzCBRWf9nXyjfmnNZggAFYy1B5ON4uCvSkTV4QcnX WiweHjRDLZsMoexiXJ0Wu81iJvxLmeSud9t01K9xmEllmRb7Z69Rfl/cDqpmlDM6L+8W +nwO42Zzn23IcAXkzJKO87F4ge9Vi62WpmBykdaxoF3gnyFjTQ9aHrxOvPWhls9kQY+7 q6kw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680940457; 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=S9xdueeJy7MgLea0ONmd9MZ1VHllI6hHaQJbmcDSqvw=; b=j/fOvvVHSxF8HFbZ3Rd04MOq3ocrXJceYPLzy+gJ3k3h1MyAfRh5VWKjsY+q7i0AFk 4xJERmHnZ5Wl02gZBkTyLVq5kuXwyewDYNpQHyr3N9vPjmhkOccs4qaYzs+y+FG+LgG4 O6siY+XQJZV1YOytY9Pr8raDi5o1S+5w8Dz5oyGuq+B+jh2pB2yY0ViN9a2jmtNUOfDB +VRc7B8khbbB3qQnnnWNEUcbWdJuiLPpbVoGkCMufCT8PIT+w1cocvy0H2maj0aCR/Xj sytq7pQNJolomk5xwpkrsuz/M1395mVFpOkR2DIPovtD7tSPVcBRePZT6eptXS/f3/0U V2SQ== X-Gm-Message-State: AAQBX9dI68dO8vTUccKuxKKeYpblF/N94Necvm9AD6V1Wn0/Pzb0ePcP I5YCFJPCQ3V6VllaiS56xL+a9fJ3l8o= X-Received: by 2002:a05:6808:16a7:b0:386:9af9:96db with SMTP id bb39-20020a05680816a700b003869af996dbmr2027862oib.38.1680940457034; Sat, 08 Apr 2023 00:54:17 -0700 (PDT) Received: from wedsonaf-dev.home.lan ([189.124.190.154]) by smtp.googlemail.com with ESMTPSA id o6-20020a4a9586000000b0051ffe0fe11bsm2435175ooi.6.2023.04.08.00.54.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Apr 2023 00:54:16 -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 v3 08/13] rust: introduce `ARef` Date: Sat, 8 Apr 2023 04:53:35 -0300 Message-Id: <20230408075340.25237-8-wedsonaf@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230408075340.25237-1-wedsonaf@gmail.com> References: <20230408075340.25237-1-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?1762594094792763463?= X-GMAIL-MSGID: =?utf-8?q?1762594094792763463?= 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: Martin Rodriguez Reboredo --- v1 -> v2: No changes v2 -> v3: No changes rust/kernel/types.rs | 107 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 107 insertions(+) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 3a46ec1a00cd..73709ce1f0a1 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. @@ -268,6 +270,111 @@ impl Opaque { } } +/// 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`.