From nobody Fri Feb 13 15:39:34 2026 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 2E5EDCE7A89 for ; Sat, 23 Sep 2023 14:50:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231815AbjIWOuM (ORCPT ); Sat, 23 Sep 2023 10:50:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60400 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231831AbjIWOuI (ORCPT ); Sat, 23 Sep 2023 10:50:08 -0400 Received: from mail-pl1-x62c.google.com (mail-pl1-x62c.google.com [IPv6:2607:f8b0:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 54CB31B2; Sat, 23 Sep 2023 07:49:59 -0700 (PDT) Received: by mail-pl1-x62c.google.com with SMTP id d9443c01a7336-1c451541f23so29926235ad.2; Sat, 23 Sep 2023 07:49:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1695480599; x=1696085399; darn=vger.kernel.org; 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=nsfSTO1+ET/8ylN5Kt9YqyfDUerwnIWDWqcWtfepBcc=; b=Jy1XWIruO0qByZarEt84oOuEeatgnpyCEQ/aNZBKWfzybdurVzhnQKbx1Z78ODRy4C nrc/n06tkFNsPC6YOCdGzpoQ0z/lWeglJUcyzUpSq5PP58jKcsORwEsFkXeAn+03EBLp K60k8C4SSr6sLDMiARBCW+h/175LxcGw75ZIPGNDI4/cEA0NXQnEoivpHO4S+NvgMEdd mB/6TNc4CqlgcEDohmhCvREzBRAs5zdMJu9aGYNs6qgsg/gkPFJwodLmseYnsE8/RU6L 6+CyB2ahJDg/KD56fN6APdpFc+Bj5cX5WdlQCqDEcoryU+efqrVFHaQoQ8XgINZzP3xT eHBQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695480599; x=1696085399; 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=nsfSTO1+ET/8ylN5Kt9YqyfDUerwnIWDWqcWtfepBcc=; b=mEU4lxHFeb7tP/h/1aCoEqRF1pbEQ+qsXa981kWoAKdrIpvAcHWUialEQTvW0Ywjwq WCIMj3iuEIKcY82+J1Y639izmVom7a/C0Z5sMjuDF+fquiWlTX/ze2NRN9A5igS6zWww YvZnu5ASTcmyzgHcL9ZH2Ts0Zpwxz4DMSJ5MbYE4OFppo+Est4sAUa1I/KJBXdV6E9hw lLiywzTCaezMd8kYBAYEdxxf+1C+JDxexAPz3nRGAhr4b8eBIHRgog3fru90IS/cDYgY XK+bKv/OT47TxrgGfriT0O9A4UhR6RLIWhaNM7yUDKcI8dhSvMlKuPkr3FMAIrBm3sY+ E/ww== X-Gm-Message-State: AOJu0Yy+xnyv7BWzdg4kADU807stYHCwxFXXTkKDnLXsZtcXHR57JnM3 2R8OR4kFvZNmVpOHje1D2zjFvo6bPBM= X-Google-Smtp-Source: AGHT+IEmoL7mzUmPG1muY18OmtRDlc/SVru6EsLSmoTOWdFwiBNvzA0YXb3ZJcSzKyhQ6bsJ1SpSxQ== X-Received: by 2002:a17:902:ed8f:b0:1c5:7470:5658 with SMTP id e15-20020a170902ed8f00b001c574705658mr1502288plj.13.1695480598631; Sat, 23 Sep 2023 07:49:58 -0700 (PDT) Received: from wedsonaf-dev.home.lan ([189.124.190.154]) by smtp.googlemail.com with ESMTPSA id s3-20020a170902ea0300b001c42d4b3675sm5392806plg.309.2023.09.23.07.49.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 Sep 2023 07:49:58 -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?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , linux-kernel@vger.kernel.org, Wedson Almeida Filho Subject: [PATCH v2 2/2] rust: arc: remove `ArcBorrow` in favour of `WithRef` Date: Sat, 23 Sep 2023 11:49:38 -0300 Message-Id: <20230923144938.219517-3-wedsonaf@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230923144938.219517-1-wedsonaf@gmail.com> References: <20230923144938.219517-1-wedsonaf@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Wedson Almeida Filho With GATs, we don't need a separate type to represent a borrowed object with a refcount, we can just use Rust's regular shared borrowing. In this case, we use `&WithRef` instead of `ArcBorrow<'_, T>`. Co-developed-by: Boqun Feng Signed-off-by: Boqun Feng Signed-off-by: Wedson Almeida Filho Reviewed-by: Benno Lossin Reviewed-by: Martin Rodriguez Reboredo --- rust/kernel/sync.rs | 2 +- rust/kernel/sync/arc.rs | 134 ++++++++++++---------------------------- 2 files changed, 39 insertions(+), 97 deletions(-) diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs index d219ee518eff..083494884500 100644 --- a/rust/kernel/sync.rs +++ b/rust/kernel/sync.rs @@ -12,7 +12,7 @@ pub mod lock; mod locked_by; =20 -pub use arc::{Arc, ArcBorrow, UniqueArc}; +pub use arc::{Arc, UniqueArc, WithRef}; pub use condvar::CondVar; pub use lock::{mutex::Mutex, spinlock::SpinLock}; pub use locked_by::LockedBy; diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 86bff1e0002c..a1806e38c37f 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -105,14 +105,14 @@ /// Coercion from `Arc` to `Arc`: /// /// ``` -/// use kernel::sync::{Arc, ArcBorrow}; +/// use kernel::sync::{Arc, WithRef}; /// /// trait MyTrait { /// // Trait has a function whose `self` type is `Arc`. /// fn example1(self: Arc) {} /// -/// // Trait has a function whose `self` type is `ArcBorrow<'_, Self>`. -/// fn example2(self: ArcBorrow<'_, Self>) {} +/// // Trait has a function whose `self` type is `&WithRef`. +/// fn example2(self: &WithRef) {} /// } /// /// struct Example; @@ -130,13 +130,6 @@ pub struct Arc { _p: PhantomData>, } =20 -#[pin_data] -#[repr(C)] -struct WithRef { - refcount: Opaque, - data: T, -} - // This is to allow [`Arc`] (and variants) to be used as the type of `self= `. impl core::ops::Receiver for Arc {} =20 @@ -215,16 +208,16 @@ unsafe fn from_inner(inner: NonNull>) -> S= elf { } } =20 - /// Returns an [`ArcBorrow`] from the given [`Arc`]. + /// Returns a shared reference to a [`WithRef`] the given [`Arc`]. /// - /// This is useful when the argument of a function call is an [`ArcBor= row`] (e.g., in a method - /// receiver), but we have an [`Arc`] instead. Getting an [`ArcBorrow`= ] is free when optimised. + /// This is useful when the argument of a function call is a [`WithRef= `] (e.g., in a method + /// receiver), but we have an [`Arc`] instead. Getting a [`WithRef`] i= s free when optimised. #[inline] - pub fn as_arc_borrow(&self) -> ArcBorrow<'_, T> { + pub fn as_with_ref(&self) -> &WithRef { // SAFETY: The constraint that the lifetime of the shared referenc= e must outlive that of - // the returned `ArcBorrow` ensures that the object remains alive = and that no mutable + // the returned `WithRef` ensures that the object remains alive an= d that no mutable // reference can be created. - unsafe { ArcBorrow::new(self.ptr) } + unsafe { self.ptr.as_ref() } } =20 /// Compare whether two [`Arc`] pointers reference the same underlying= object. @@ -234,20 +227,17 @@ pub fn ptr_eq(this: &Self, other: &Self) -> bool { } =20 impl ForeignOwnable for Arc { - type Borrowed<'a> =3D ArcBorrow<'a, T>; + type Borrowed<'a> =3D &'a WithRef; =20 fn into_foreign(self) -> *const core::ffi::c_void { ManuallyDrop::new(self).ptr.as_ptr() as _ } =20 - unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T= > { + unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a WithRef { // SAFETY: By the safety requirement of this function, we know tha= t `ptr` came from - // a previous call to `Arc::into_foreign`. - let inner =3D NonNull::new(ptr as *mut WithRef).unwrap(); - - // SAFETY: The safety requirements of `from_foreign` ensure that t= he object remains alive - // for the lifetime of the returned value. - unsafe { ArcBorrow::new(inner) } + // a previous call to `Arc::into_foreign`. The safety requirements= of `from_foreign` ensure + // that the object remains alive for the lifetime of the returned = value. + unsafe { &*(ptr.cast::>()) } } =20 unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self { @@ -320,119 +310,71 @@ fn from(item: Pin>) -> Self { } } =20 -/// A borrowed reference to an [`Arc`] instance. -/// -/// For cases when one doesn't ever need to increment the refcount on the = allocation, it is simpler -/// to use just `&T`, which we can trivially get from an `Arc` instance. +/// An instance of `T` with an attached reference count. /// -/// However, when one may need to increment the refcount, it is preferable= to use an `ArcBorrow` -/// over `&Arc` because the latter results in a double-indirection: a p= ointer (shared reference) -/// to a pointer (`Arc`) to the object (`T`). An [`ArcBorrow`] eliminat= es this double -/// indirection while still allowing one to increment the refcount and get= ting an `Arc` when/if -/// needed. -/// -/// # Invariants -/// -/// There are no mutable references to the underlying [`Arc`], and it rema= ins valid for the -/// lifetime of the [`ArcBorrow`] instance. -/// -/// # Example +/// # Examples /// /// ``` -/// use kernel::sync::{Arc, ArcBorrow}; +/// use kernel::sync::{Arc, WithRef}; /// /// struct Example; /// -/// fn do_something(e: ArcBorrow<'_, Example>) -> Arc { +/// fn do_something(e: &WithRef) -> Arc { /// e.into() /// } /// /// let obj =3D Arc::try_new(Example)?; -/// let cloned =3D do_something(obj.as_arc_borrow()); +/// let cloned =3D do_something(obj.as_with_ref()); /// /// // Assert that both `obj` and `cloned` point to the same underlying ob= ject. /// assert!(core::ptr::eq(&*obj, &*cloned)); -/// # Ok::<(), Error>(()) /// ``` /// -/// Using `ArcBorrow` as the type of `self`: +/// Using `WithRef` as the type of `self`: /// /// ``` -/// use kernel::sync::{Arc, ArcBorrow}; +/// use kernel::sync::{Arc, WithRef}; /// /// struct Example { -/// a: u32, -/// b: u32, +/// _a: u32, +/// _b: u32, /// } /// /// impl Example { -/// fn use_reference(self: ArcBorrow<'_, Self>) { +/// fn use_reference(self: &WithRef) { /// // ... /// } /// } /// -/// let obj =3D Arc::try_new(Example { a: 10, b: 20 })?; -/// obj.as_arc_borrow().use_reference(); -/// # Ok::<(), Error>(()) +/// let obj =3D Arc::try_new(Example { _a: 10, _b: 20 })?; +/// obj.as_with_ref().use_reference(); /// ``` -pub struct ArcBorrow<'a, T: ?Sized + 'a> { - inner: NonNull>, - _p: PhantomData<&'a ()>, -} - -// This is to allow [`ArcBorrow`] (and variants) to be used as the type of= `self`. -impl core::ops::Receiver for ArcBorrow<'_, T> {} - -// This is to allow `ArcBorrow` to be dispatched on when `ArcBorrow`= can be coerced into -// `ArcBorrow`. -impl, U: ?Sized> core::ops::DispatchFromDyn> - for ArcBorrow<'_, T> -{ -} - -impl Clone for ArcBorrow<'_, T> { - fn clone(&self) -> Self { - *self - } +#[pin_data] +#[repr(C)] +pub struct WithRef { + refcount: Opaque, + data: T, } =20 -impl Copy for ArcBorrow<'_, T> {} - -impl ArcBorrow<'_, T> { - /// Creates a new [`ArcBorrow`] instance. - /// - /// # Safety - /// - /// Callers must ensure the following for the lifetime of the returned= [`ArcBorrow`] instance: - /// 1. That `inner` remains valid; - /// 2. That no mutable references to `inner` are created. - unsafe fn new(inner: NonNull>) -> Self { - // INVARIANT: The safety requirements guarantee the invariants. - Self { - inner, - _p: PhantomData, - } - } -} +// This is to allow [`WithRef`] (and variants) to be used as the type of `= self`. +impl core::ops::Receiver for WithRef {} =20 -impl From> for Arc { - fn from(b: ArcBorrow<'_, T>) -> Self { +impl From<&WithRef> for Arc { + fn from(b: &WithRef) -> Self { // SAFETY: The existence of `b` guarantees that the refcount is no= n-zero. `ManuallyDrop` // guarantees that `drop` isn't called, so it's ok that the tempor= ary `Arc` doesn't own the // increment. - ManuallyDrop::new(unsafe { Arc::from_inner(b.inner) }) + ManuallyDrop::new(unsafe { Arc::from_inner(b.into()) }) .deref() .clone() } } =20 -impl Deref for ArcBorrow<'_, T> { +impl Deref for WithRef { type Target =3D T; =20 fn deref(&self) -> &Self::Target { - // SAFETY: By the type invariant, the underlying object is still a= live with no mutable - // references to it, so it is safe to create a shared reference. - unsafe { &self.inner.as_ref().data } + &self.data } } =20 --=20 2.34.1