From nobody Sun Feb 8 02:56:08 2026 Received: from mail-10629.protonmail.ch (mail-10629.protonmail.ch [79.135.106.29]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A90622A1CB for ; Mon, 10 Mar 2025 10:57:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=79.135.106.29 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741604257; cv=none; b=Eb6XOekuUEI3GsEdeU4vSlc4bkx34wgkn6I997hCH421R7HyYZIcSdIf7xku7NK38Y7LJLceVzWqB3U2OFr9VsPQgSYfHBxhUenMUO8SNLTO/1lEciEMd0AsTr+GFUggp/wXmRo33XgMWUg2m/gSlZ95My4CziaETxAARJPCUY8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741604257; c=relaxed/simple; bh=G4g8+U+HLV4Gx1vaKDqvgQtTExOBv2TMnZblyvutss0=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Gyk27tVfPTgudkjhqENX8/N+5zYPdwVyeSlJvIfoD4IpbRcKjR8+EBM8+ljwnt0lpnJ7XZ/dKU1nYMLXL+RIK4rzK/l+ymDwNcnDcB/agrzxWWqq/z6jxlcctUao4oAmVJd7r9gO0Tsp8Wvx8Hs7mzVQpC135TZ7EBKUeh21uW0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me; spf=pass smtp.mailfrom=pm.me; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b=knASrLgj; arc=none smtp.client-ip=79.135.106.29 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pm.me Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b="knASrLgj" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail3; t=1741604251; x=1741863451; bh=lqhztZytrydlxEcGl7cfjWRcRjfcWBDgUsWbhxkDSEI=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: Feedback-ID:From:To:Cc:Date:Subject:Reply-To:Feedback-ID: Message-ID:BIMI-Selector:List-Unsubscribe:List-Unsubscribe-Post; b=knASrLgj1v8ROp3wXvA26lKrUi+NziM5cDZGRFksM8MQg1BhHL3PblArEbIYWxc/X +06FMgKiDFiW2v93uy/H6ciJ10JruwFguhpSd/8P0g/AD9hr1ROXmEzw8Nkyr33Udn NGyg5+4l7mmiJE6vqgEeiMGo12xIpoQIhrBN9eGNRxkOqsa6ulU5pytq7Sk4+BwSJ6 7FnVPwFHb25esTjh89l5rlZtoEPdLliATwGN9ytFyTXmWC2tcpRwcrAgdjT5gavKap 1gh+tM8d1t4sNTQkgwENyi87iA0O+WzCHoSb3b92eqLi20GKLxZMCvNTIrvca+kOoP Z8SRQcMBnKfew== Date: Mon, 10 Mar 2025 10:57:24 +0000 To: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Asahi Lina From: Oliver Mangold Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Oliver Mangold Subject: [PATCH v7 1/4] rust: types: Add Ownable/Owned types Message-ID: <20250310-unique-ref-v7-1-4caddb78aa05@pm.me> In-Reply-To: <20250310-unique-ref-v7-0-4caddb78aa05@pm.me> References: <20250310-unique-ref-v7-0-4caddb78aa05@pm.me> Feedback-ID: 31808448:user:proton X-Pm-Message-ID: dc6aa8198b4e735e3bc33238a886717b525866ae Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Asahi Lina By analogy to AlwaysRefCounted and ARef, an Ownable type is a (typically C FFI) type that *may* be owned by Rust, but need not be. Unlike AlwaysRefCounted, this mechanism expects the reference to be unique within Rust, and does not allow cloning. Conceptually, this is similar to a KBox, except that it delegates resource management to the T instead of using a generic allocator. Link: https://lore.kernel.org/all/20250202-rust-page-v1-1-e3170d7fe55e@asah= ilina.net/ Signed-off-by: Asahi Lina Co-developed-by: Oliver Mangold Signed-off-by: Oliver Mangold --- rust/kernel/types.rs | 109 +++++++++++++++++++++++++++++++++++++++++++++++= ++++ 1 file changed, 109 insertions(+) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 55ddd50e8aaa075ac33d5f1088a7f72df05f74f4..e0ce3646a4d3b70c069322a9b0f= 25c00265a2af8 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -551,6 +551,115 @@ fn drop(&mut self) { } } =20 +/// Types that may be owned by Rust code or borrowed, but have a lifetime = managed by C code. +/// +/// It allows such types to define their own custom destructor function to= be called when +/// a Rust-owned reference is dropped. +/// +/// This is usually implemented by wrappers to existing structures on the = C side of the code. +/// +/// # Safety +/// +/// Implementers must ensure that any objects borrowed directly as `&T` st= ay alive for the duration +/// of the lifetime, and that any objects owned by Rust as `Owned`) sta= y alive while that owned +/// reference exists, until the [`Ownable::release()`] trait method is cal= led. +pub unsafe trait Ownable { + /// Releases the object (frees it or returns it to foreign ownership). + /// + /// # Safety + /// + /// Callers must ensure that the object is no longer referenced after = this call. + unsafe fn release(this: NonNull); +} + +/// A subtrait of Ownable that asserts that an `Owned` Rust reference i= s not only unique +/// within Rust and keeps the `T` alive, but also guarantees that the C co= de follows the +/// usual mutable reference requirements. That is, the kernel will never m= utate the +/// `T` (excluding internal mutability that follows the usual rules) while= Rust owns it. +/// +/// When this type is implemented for an [`Ownable`] type, it allows `Owne= d` to be +/// dereferenced into a &mut T. +/// +/// # Safety +/// +/// Implementers must ensure that the kernel never mutates the underlying = type while +/// Rust owns it. +pub unsafe trait OwnableMut: Ownable {} + +/// An owned reference to an ownable kernel object. +/// +/// The object is automatically freed or released when an instance of [`Ow= ned`] is +/// dropped. +/// +/// # Invariants +/// +/// The pointer stored in `ptr` is non-null and valid for the lifetime of = the [`Owned`] instance. +pub struct Owned { + ptr: NonNull, + _p: PhantomData, +} + +// SAFETY: It is safe to send `Owned` to another thread when the underl= ying `T` is `Send` because +// it effectively means sending a unique `&mut T` pointer (which is safe b= ecause `T` is `Send`). +unsafe impl Send for Owned {} + +// SAFETY: It is safe to send `&Owned` to another thread when the under= lying `T` is `Sync` +// because it effectively means sharing `&T` (which is safe because `T` is= `Sync`). +unsafe impl Sync for Owned {} + +impl Owned { + /// Creates a new instance of [`Owned`]. + /// + /// It takes over ownership of the underlying object. + /// + /// # Safety + /// + /// Callers must ensure that the underlying object is acquired and can= be considered owned by + /// Rust. + pub unsafe fn from_raw(ptr: NonNull) -> Self { + // INVARIANT: The safety requirements guarantee that the new insta= nce now owns the + // reference. + Self { + ptr, + _p: PhantomData, + } + } + + /// Consumes the `Owned`, returning a raw pointer. + /// + /// This function does not actually relinquish ownership of the object. + /// After calling this function, the caller is responsible for ownersh= ip previously managed + /// by the `Owned`. + pub fn into_raw(me: Self) -> NonNull { + ManuallyDrop::new(me).ptr + } +} + +impl Deref for Owned { + type Target =3D T; + + fn deref(&self) -> &Self::Target { + // SAFETY: The type invariants guarantee that the object is valid. + unsafe { self.ptr.as_ref() } + } +} + +impl DerefMut for Owned { + fn deref_mut(&mut self) -> &mut Self::Target { + // SAFETY: The type invariants guarantee that the object is valid, + // and that we can safely return a mutable reference to it. + unsafe { self.ptr.as_mut() } + } +} + +impl Drop for Owned { + fn drop(&mut self) { + // SAFETY: The type invariants guarantee that the `Owned` owns the= object we're about to + // release. + unsafe { T::release(self.ptr) }; + } +} + /// A sum type that always holds either a value of type `L` or `R`. /// /// # Examples --=20 2.48.1 From nobody Sun Feb 8 02:56:08 2026 Received: from mail-4316.protonmail.ch (mail-4316.protonmail.ch [185.70.43.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7249D227E8A for ; Mon, 10 Mar 2025 10:57:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; 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charset="utf-8" AlwaysRefCounted will become a marker trait to indicate that it is allowed to obtain an ARef from a `&`, which cannot be allowed for types which are also Ownable. Signed-off-by: Oliver Mangold --- rust/kernel/block/mq/request.rs | 10 ++++++--- rust/kernel/cred.rs | 8 ++++++-- rust/kernel/device.rs | 8 ++++++-- rust/kernel/fs/file.rs | 10 ++++++--- rust/kernel/pid_namespace.rs | 8 ++++++-- rust/kernel/task.rs | 6 +++++- rust/kernel/types.rs | 45 ++++++++++++++++++++++++-------------= ---- 7 files changed, 64 insertions(+), 31 deletions(-) diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request= .rs index 2f2bb5a04709cc90ae8971da166fc83bb53fb86b..f6bee0932499e554f8890786199= 7f8b9d1ffd51a 100644 --- a/rust/kernel/block/mq/request.rs +++ b/rust/kernel/block/mq/request.rs @@ -9,7 +9,7 @@ block::mq::Operations, error::Result, sync::Refcount, - types::{ARef, AlwaysRefCounted, Opaque}, + types::{ARef, AlwaysRefCounted, Opaque, RefCounted}, }; use core::{ marker::PhantomData, @@ -209,10 +209,10 @@ unsafe impl Send for Request {} unsafe impl Sync for Request {} =20 // SAFETY: All instances of `Request` are reference counted. This -// implementation of `AlwaysRefCounted` ensure that increments to the ref = count +// implementation of `RefCounted` ensure that increments to the ref count // keeps the object alive in memory at least until a matching reference co= unt // decrement is executed. -unsafe impl AlwaysRefCounted for Request { +unsafe impl RefCounted for Request { fn inc_ref(&self) { self.wrapper_ref().refcount().inc(); } @@ -234,3 +234,7 @@ unsafe fn dec_ref(obj: core::ptr::NonNull) { } } } + +// SAFETY: we currently do not implement `Ownable`, thus it is okay to can= obtain an `ARef` +// from a `&Request` (but this will change in the future). +unsafe impl AlwaysRefCounted for Request {} diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs index 81d67789b16f243e7832ff3b2e5e479a1ab2bf9e..e04d1021130eb1ec46fe48feb08= 8959da7656d66 100644 --- a/rust/kernel/cred.rs +++ b/rust/kernel/cred.rs @@ -11,7 +11,7 @@ use crate::{ bindings, task::Kuid, - types::{AlwaysRefCounted, Opaque}, + types::{AlwaysRefCounted, Opaque, RefCounted}, }; =20 /// Wraps the kernel's `struct cred`. @@ -71,7 +71,7 @@ pub fn euid(&self) -> Kuid { } =20 // SAFETY: The type invariants guarantee that `Credential` is always ref-c= ounted. -unsafe impl AlwaysRefCounted for Credential { +unsafe impl RefCounted for Credential { fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. unsafe { bindings::get_cred(self.0.get()) }; @@ -83,3 +83,7 @@ unsafe fn dec_ref(obj: core::ptr::NonNull) { unsafe { bindings::put_cred(obj.cast().as_ptr()) }; } } + +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` from a +// `&Credential`. +unsafe impl AlwaysRefCounted for Credential {} diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs index db2d9658ba47d9c492bc813ce3eb2ff29703ca31..189298518dc184405b1d62404b1= 90d4c0b08b7ad 100644 --- a/rust/kernel/device.rs +++ b/rust/kernel/device.rs @@ -7,7 +7,7 @@ use crate::{ bindings, str::CStr, - types::{ARef, Opaque}, + types::{ARef, AlwaysRefCounted, Opaque, RefCounted}, }; use core::{fmt, ptr}; =20 @@ -190,7 +190,7 @@ pub fn property_present(&self, name: &CStr) -> bool { } =20 // SAFETY: Instances of `Device` are always reference-counted. -unsafe impl crate::types::AlwaysRefCounted for Device { +unsafe impl RefCounted for Device { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the= refcount is non-zero. unsafe { bindings::get_device(self.as_raw()) }; @@ -202,6 +202,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `Device` from a +// `&Device`. +unsafe impl AlwaysRefCounted for Device {} + // SAFETY: As by the type invariant `Device` can be sent to any thread. unsafe impl Send for Device {} =20 diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs index e03dbe14d62a566349c4100f2f78b17d4c79aab5..a7836cc754e7927b6addc3bd06c= fe8c8119f1d9f 100644 --- a/rust/kernel/fs/file.rs +++ b/rust/kernel/fs/file.rs @@ -11,7 +11,7 @@ bindings, cred::Credential, error::{code::*, Error, Result}, - types::{ARef, AlwaysRefCounted, NotThreadSafe, Opaque}, + types::{ARef, AlwaysRefCounted, NotThreadSafe, Opaque, RefCounted}, }; use core::ptr; =20 @@ -190,7 +190,7 @@ unsafe impl Sync for File {} =20 // SAFETY: The type invariants guarantee that `File` is always ref-counted= . This implementation // makes `ARef` own a normal refcount. -unsafe impl AlwaysRefCounted for File { +unsafe impl RefCounted for File { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. @@ -205,6 +205,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` from a +/// `&File`. +unsafe impl AlwaysRefCounted for File {} + /// Wraps the kernel's `struct file`. Not thread safe. /// /// This type represents a file that is not known to be safe to transfer a= cross thread boundaries. @@ -225,7 +229,7 @@ pub struct LocalFile { =20 // SAFETY: The type invariants guarantee that `LocalFile` is always ref-co= unted. This implementation // makes `ARef` own a normal refcount. -unsafe impl AlwaysRefCounted for LocalFile { +unsafe impl RefCounted for LocalFile { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. diff --git a/rust/kernel/pid_namespace.rs b/rust/kernel/pid_namespace.rs index 0e93808e4639b37dd77add5d79f64058dac7cb87..3e45e945b7509b9607266b2e0e6= ef130e7a1ed39 100644 --- a/rust/kernel/pid_namespace.rs +++ b/rust/kernel/pid_namespace.rs @@ -9,7 +9,7 @@ =20 use crate::{ bindings, - types::{AlwaysRefCounted, Opaque}, + types::{AlwaysRefCounted, RefCounted, Opaque}, }; use core::ptr; =20 @@ -44,7 +44,7 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::pid_name= space) -> &'a Self { } =20 // SAFETY: Instances of `PidNamespace` are always reference-counted. -unsafe impl AlwaysRefCounted for PidNamespace { +unsafe impl RefCounted for PidNamespace { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. @@ -58,6 +58,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` +// from a `&PidNamespace`. +unsafe impl AlwaysRefCounted for PidNamespace {} + // SAFETY: // - `PidNamespace::dec_ref` can be called from any thread. // - It is okay to send ownership of `PidNamespace` across thread boundari= es. diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs index 07bc22a7645c0c7d792a0a163dd55b8ff0fe5f92..1cc1b02cb7fada6703da8cad775= 49dee578fc08d 100644 --- a/rust/kernel/task.rs +++ b/rust/kernel/task.rs @@ -327,7 +327,7 @@ pub fn wake_up(&self) { } =20 // SAFETY: The type invariants guarantee that `Task` is always refcounted. -unsafe impl crate::types::AlwaysRefCounted for Task { +unsafe impl crate::types::RefCounted for Task { fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. unsafe { bindings::get_task_struct(self.as_ptr()) }; @@ -339,6 +339,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` from a +// `&Task`. +unsafe impl crate::types::AlwaysRefCounted for Task {} + impl Kuid { /// Get the current euid. #[inline] diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index e0ce3646a4d3b70c069322a9b0f25c00265a2af8..e6f3308f931d90718d405443c30= 34a216388e0af 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -402,11 +402,9 @@ pub const fn raw_get(this: *const Self) -> *mut T { } } =20 -/// Types that are _always_ reference counted. +/// Types that are internally reference counted. /// /// It allows such types to define their own custom ref increment and decr= ement 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 c= reate reference-counted @@ -418,9 +416,9 @@ pub const fn raw_get(this: *const Self) -> *mut T { /// 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_r= ef`] keep the object +/// won't be able to honour the requirement that [`RefCounted::inc_ref`] k= eep the object /// alive.) -pub unsafe trait AlwaysRefCounted { +pub unsafe trait RefCounted { /// Increments the reference count on the object. fn inc_ref(&self); =20 @@ -433,11 +431,22 @@ pub unsafe trait AlwaysRefCounted { /// Callers must ensure that there was a previous matching increment t= o 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). + /// (e.g., it calls [`RefCounted::inc_ref`] twice, then calls + /// [`RefCounted::dec_ref`] once). unsafe fn dec_ref(obj: NonNull); } =20 +/// An extension to RefCounted, which declares that it is allowed to conve= rt +/// from a shared reference `&T` to an owned reference [`ARef`]. +/// +/// # Safety +/// +/// Implementers must ensure that no safety invariants are violated by upg= rading an `&T` +/// to an [`ARef`]. In particular that implies [`AlwaysRefCounted`] and= [`Ownable`] +/// cannot be implemented for the same type, as this would allow to violat= e the uniqueness +/// guarantee of [`Owned`] by derefencing it into an `&T` and obtaining= an [`ARef`] from that. +pub unsafe trait AlwaysRefCounted: RefCounted {} + /// An owned reference to an always-reference-counted object. /// /// The object's reference count is automatically decremented when an inst= ance of [`ARef`] is @@ -448,7 +457,7 @@ pub unsafe trait AlwaysRefCounted { /// /// 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 { +pub struct ARef { ptr: NonNull, _p: PhantomData, } @@ -457,16 +466,16 @@ pub struct ARef { // it effectively means sharing `&T` (which is safe because `T` is `Sync`)= ; additionally, it needs // `T` to be `Send` because any thread that has an `ARef` may ultimatel= y access `T` using a // mutable reference, for example, when the reference count reaches zero a= nd `T` is dropped. -unsafe impl Send for ARef {} +unsafe impl Send for ARef {} =20 // SAFETY: It is safe to send `&ARef` to another thread when the underl= ying `T` is `Sync` // because it effectively means sharing `&T` (which is safe because `T` is= `Sync`); additionally, // it needs `T` to be `Send` because any thread that has a `&ARef` may = clone it and get an // `ARef` on that thread, so the thread may ultimately access `T` using= a mutable reference, for // example, when the reference count reaches zero and `T` is dropped. -unsafe impl Sync for ARef {} +unsafe impl Sync for ARef {} =20 -impl ARef { +impl ARef { /// Creates a new instance of [`ARef`]. /// /// It takes over an increment of the reference count on the underlyin= g object. @@ -495,12 +504,12 @@ pub unsafe fn from_raw(ptr: NonNull) -> Self { /// /// ``` /// use core::ptr::NonNull; - /// use kernel::types::{ARef, AlwaysRefCounted}; + /// use kernel::types::{ARef, RefCounted}; /// /// struct Empty {} /// /// # // SAFETY: TODO. - /// unsafe impl AlwaysRefCounted for Empty { + /// unsafe impl RefCounted for Empty { /// fn inc_ref(&self) {} /// unsafe fn dec_ref(_obj: NonNull) {} /// } @@ -518,7 +527,7 @@ pub fn into_raw(me: Self) -> NonNull { } } =20 -impl Clone for ARef { +impl Clone for ARef { fn clone(&self) -> Self { self.inc_ref(); // SAFETY: We just incremented the refcount above. @@ -526,7 +535,7 @@ fn clone(&self) -> Self { } } =20 -impl Deref for ARef { +impl Deref for ARef { type Target =3D T; =20 fn deref(&self) -> &Self::Target { @@ -543,10 +552,10 @@ fn from(b: &T) -> Self { } } =20 -impl Drop for ARef { +impl Drop for ARef { fn drop(&mut self) { - // SAFETY: The type invariants guarantee that the `ARef` owns the = reference we're about to - // decrement. + // SAFETY: The type invariants guarantee that the `ARef` owns the = reference + // we're about to decrement. unsafe { T::dec_ref(self.ptr) }; 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charset="utf-8" From: Miguel Ojeda Rust 1.85.0 (current stable version) stabilized [1] `#[diagnostic::do_not_recommend]` [2]. In order to use it across all supported Rust versions, introduce a new Kconfig symbol for it. This allows to perform conditional compilation based on it, e.g. on the use site to enable the attribute: #[cfg_attr(RUSTC_HAS_DO_NOT_RECOMMEND, diagnostic::do_not_recommend)] impl A for i32 {} An alternative would have been to `allow` the following warning: #![allow(unknown_or_malformed_diagnostic_attributes)] However, that would lose the checking for typos across all versions, which we do not want to lose. One can also use the Kconfig symbol to allow the warning in older compilers instead, to avoid repeating the `cfg_attr` line above in all use sites: #![cfg_attr( not(RUSTC_HAS_DO_NOT_RECOMMEND), expect(unknown_or_malformed_diagnostic_attributes) )] That still loses the checking for typos in older versions, but we still keep it in newer ones, thus we should still catch mistakes eventually. In this case we can promote it to `expect` as shown above, so that we do not forget to remove these lines if we stop using the attribute somewhere. Link: https://github.com/rust-lang/rust/pull/132056 [1] Link: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-d= iagnosticdo_not_recommend-attribute [2] Link: https://lore.kernel.org/rust-for-linux/CANiq72mYfhuRWkjomb1vOMMPOaxvd= S6qjfVLAwxUw6ecdqyh2A@mail.gmail.com/ Signed-off-by: Miguel Ojeda Signed-off-by: Oliver Mangold --- init/Kconfig | 3 +++ 1 file changed, 3 insertions(+) diff --git a/init/Kconfig b/init/Kconfig index 12b0847603b20fe1d8c70c4c57dabc924efe697b..ed1abb1beec0767f3696dbb6ac9= 844ba7e0610c9 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -147,6 +147,9 @@ config CC_HAS_COUNTED_BY config RUSTC_HAS_COERCE_POINTEE def_bool RUSTC_VERSION >=3D 108400 =20 +config RUSTC_HAS_DO_NOT_RECOMMEND + def_bool RUSTC_VERSION >=3D 108500 + config PAHOLE_VERSION int default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE)) --=20 2.48.1 From nobody Sun Feb 8 02:56:08 2026 Received: from mail-4316.protonmail.ch (mail-4316.protonmail.ch [185.70.43.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 01FE8227E93 for ; Mon, 10 Mar 2025 10:57:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.70.43.16 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741604280; cv=none; b=RbHVR7EyQgMW8yXvkRH1//eRlHCsPAv/gIQBaP7gMyf+aYUfzjROlLLUS8XHDiqnxuPN0gLVJh2aYNUEnENmSGNAtP9pU1e2xdnsA//3xnkmZXKNLmaASqLWA1j4wjTpOYB2I00CTCYNTXHDZIdja2snbxVgP9crzezZTQRfq9A= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741604280; c=relaxed/simple; bh=TJugW9qRmuA5oYe1TVo0wUzv7Efg6z9e8snaknO8MGs=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=i/g6r6iOCvLOzfrC2gMrKQ+iljugNJ8onBPhI5dnCy9JEWiFTW400zQdlB19bKdVTB+84AV80C1iA3eeWzuY+p/oCrQ8qoDo4fuB7FdVJ/4c1b1h6OoGVirKPgXNEgVjqrtvAzQ77kKC69Th4UAOp3w4QBILQw4CK/ZPiANxV20= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me; spf=pass smtp.mailfrom=pm.me; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b=sLYnl8SX; arc=none smtp.client-ip=185.70.43.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pm.me Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b="sLYnl8SX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail3; t=1741604274; x=1741863474; bh=2lDf8dq/WG7sVxkTl4G1A2xfuBb4q1lzSGrMrbLyXs8=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: Feedback-ID:From:To:Cc:Date:Subject:Reply-To:Feedback-ID: Message-ID:BIMI-Selector:List-Unsubscribe:List-Unsubscribe-Post; b=sLYnl8SXGBMT9Cl3dFLmQR7LGMUmEQa5bR+arMMPCUqXa+HKhWD4BlLmlQ6Sem1CH 5q50wKLl8Yz+Yy6AYIojHMzUjCRQLTIJ45Jbq5r+u53x5JwQfHvbC2HQfnMrlxiwIo 95+5YpzveROj+LGyuo7yffXv4q1mktBFZi/79bdbU6d5Ipzz25DnjEPLpBey54IoEf HSzu9QW2twy8///rUsFhO1kdpy4NU52XnL3JRjcWpC4Qfo2Rg6uHVIKdakvNrNsskG giex8A0OmZKlCkMdGT00hrPRGfWyAUVNXGTqWhqBm7ZgyKLZ42NjPsgLhT2fzGirCH KRbbese+h7bTQ== Date: Mon, 10 Mar 2025 10:57:47 +0000 To: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Asahi Lina From: Oliver Mangold Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Oliver Mangold Subject: [PATCH v7 4/4] rust: adding OwnableRefCounted and SimpleOwnableRefCounted Message-ID: <20250310-unique-ref-v7-4-4caddb78aa05@pm.me> In-Reply-To: <20250310-unique-ref-v7-0-4caddb78aa05@pm.me> References: <20250310-unique-ref-v7-0-4caddb78aa05@pm.me> Feedback-ID: 31808448:user:proton X-Pm-Message-ID: f81b6abac87746fd99aa4c9bc405baef6d8e08b0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Types implementing one of these traits can safely convert between an ARef and an Owned. Signed-off-by: Oliver Mangold --- rust/kernel/types.rs | 275 +++++++++++++++++++++++++++++++++++++++++++++++= ++++ 1 file changed, 275 insertions(+) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index e6f3308f931d90718d405443c3034a216388e0af..3e703701b2bccf1a440f4064b6d= d90afb204d937 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -552,6 +552,12 @@ fn from(b: &T) -> Self { } } =20 +impl From> for ARef { + fn from(b: Owned) -> Self { + T::into_shared(b) + } +} + impl Drop for ARef { fn drop(&mut self) { // SAFETY: The type invariants guarantee that the `ARef` owns the = reference @@ -669,6 +675,275 @@ fn drop(&mut self) { } } =20 +/// A trait for objects that can be wrapped in either one of the reference= types [`Owned`] and +/// [`ARef`]. +/// +/// # Safety +/// +/// Implementers must ensure that: +/// +/// - Both the safety requirements for [`Ownable`] and [`RefCounted`] are = fulfilled. +/// - The uniqueness invariant of [`Owned`] is upheld until dropped. +/// - [`try_from_shared()`](OwnableRefCounted::into_shared) only returns a= n [`Owned`] if exactly +/// one [`ARef`] exists. +/// - [`into_shared()`](OwnableRefCounted::into_shared) set the reference = count to the value which +/// the returned [`ARef`] expects for an object with a single reference +/// in existence. This implies that if [`into_shared()`](OwnableRefCount= ed::into_shared) is left +/// on the default implementation, which just rewraps the underlying obj= ect, the reference count +/// needs not to be modified when converting a [`Owned`] to an [`ARef`]. +/// +/// # Examples +/// +/// A minimal example implementation of [`OwnableRefCounted`], [`Ownable`]= and its usage with +/// [`ARef`] and [`Owned`] looks like this: +/// +/// ``` +/// # #![expect(clippy::disallowed_names)] +/// use core::cell::Cell; +/// use core::ptr::NonNull; +/// use kernel::alloc::{flags, kbox::KBox, AllocError}; +/// use kernel::types::{ +/// ARef, RefCounted, Owned, Ownable, OwnableRefCounted, +/// }; +/// +/// struct Foo { +/// refcount: Cell, +/// } +/// +/// impl Foo { +/// fn new() -> Result, AllocError> { +/// // Use a `KBox` to handle the actual allocation. +/// let result =3D KBox::new( +/// Foo { +/// refcount: Cell::new(1), +/// }, +/// flags::GFP_KERNEL, +/// )?; +/// let result =3D NonNull::new(KBox::into_raw(result)) +/// .expect("Raw pointer to newly allocation KBox is null, thi= s should never happen."); +/// // SAFETY: We just allocated the `Foo`, thus it is valid. +/// Ok(unsafe { Owned::from_raw(result) }) +/// } +/// } +/// +/// // SAFETY: We increment and decrement each time the respective functio= n is called and only free +/// // the `Foo` when the refcount reaches zero. +/// unsafe impl RefCounted for Foo { +/// fn inc_ref(&self) { +/// self.refcount.replace(self.refcount.get() + 1); +/// } +/// +/// unsafe fn dec_ref(this: NonNull) { +/// // SAFETY: The underlying object is always valid when the func= tion is called. +/// let refcount =3D unsafe { &this.as_ref().refcount }; +/// let new_refcount =3D refcount.get() - 1; +/// if new_refcount =3D=3D 0 { +/// // The `Foo` will be dropped when `KBox` goes out of scope. +/// // SAFETY: The `Box` is still alive as the old refcou= nt is 1. +/// unsafe { KBox::from_raw(this.as_ptr()) }; +/// } else { +/// refcount.replace(new_refcount); +/// } +/// } +/// } +/// +/// // SAFETY: We only convert into an `Owned` when the refcount is 1. +/// unsafe impl OwnableRefCounted for Foo { +/// fn try_from_shared(this: ARef) -> Result, ARef> { +/// if this.refcount.get() =3D=3D 1 { +/// // SAFETY: The `Foo` is still alive as the refcount is 1. +/// Ok(unsafe { Owned::from_raw(ARef::into_raw(this)) }) +/// } else { +/// Err(this) +/// } +/// } +/// } +/// +/// // SAFETY: We are not `AlwaysRefCounted`. +/// unsafe impl Ownable for Foo { +/// unsafe fn release(this: NonNull) { +/// // SAFETY: Using `dec_ref()` from `RefCounted` to release is o= kay, as the refcount is +/// // always 1 for an `Owned`. +/// unsafe{ Foo::dec_ref(this) }; +/// } +/// } +/// +/// let foo =3D Foo::new().unwrap(); +/// let mut foo =3D ARef::from(foo); +/// { +/// let bar =3D foo.clone(); +/// assert!(Owned::try_from(bar).is_err()); +/// } +/// assert!(Owned::try_from(foo).is_ok()); +/// ``` +pub unsafe trait OwnableRefCounted: RefCounted + Ownable + Sized { + /// Checks if the [`ARef`] is unique and convert it to an [`Owned`] it= that is that case. + /// Otherwise it returns again an [`ARef`] to the same underlying obje= ct. + fn try_from_shared(this: ARef) -> Result, ARef= >; + /// Converts the [`Owned`] into an [`ARef`]. + + fn into_shared(this: Owned) -> ARef { + // SAFETY: Safe by the requirements on implementing the trait. + unsafe { ARef::from_raw(Owned::into_raw(this)) } + } +} + +/// This trait allows to implement all of [`Ownable`], [`RefCounted`] and +/// [`OwnableRefCounted`] together in a simplified way, +/// only requiring to provide the methods [`inc_ref()`](SimpleOwnableRefCo= unted::inc_ref), +/// [`dec_ref()`](SimpleOwnableRefCounted::dec_ref), +/// and [`is_unique()`](SimpleOwnableRefCounted::is_unique). +/// +/// For non-standard cases where conversion between [`Ownable`] and [`RefC= ounted`] needs +/// or [`Ownable::release()`] and [`RefCounted::dec_ref()`] cannot be the = same method, +/// [`Ownable`], [`RefCounted`] and [`OwnableRefCounted`] should be implem= ented manually. +/// +/// # Safety +/// +/// Implementers must ensure that: +/// +/// - Both the safety requirements as for [`Ownable`] and [`RefCounted`] a= re fulfilled. +/// - [`is_unique`](SimpleOwnableRefCounted::is_unique) must only return `= true` in case only one +/// [`ARef`] exists and it is impossible for one to be obtained other th= an by cloning an existing +/// [`ARef`] or converting an [`Owned`] to an [`ARef`]. +/// - It is safe to convert an unique [`ARef`] into an [`Owned`] simply by= re-wrapping the +/// underlying object without modifying the refcount. +/// +/// # Examples +/// +/// A minimal example implementation of [`SimpleOwnableRefCounted`] +/// and its usage with [`ARef`] and [`Owned`] looks like this: +/// +/// ``` +/// # #![expect(clippy::disallowed_names)] +/// use core::cell::Cell; +/// use core::ptr::NonNull; +/// use kernel::alloc::{flags, kbox::KBox, AllocError}; +/// use kernel::types::{ +/// ARef, SimpleOwnableRefCounted, Owned, +/// }; +/// +/// struct Foo { +/// refcount: Cell, +/// } +/// +/// impl Foo { +/// fn new() -> Result, AllocError> { +/// // Use a KBox to handle the actual allocation. +/// let result =3D KBox::new( +/// Foo { +/// refcount: Cell::new(1), +/// }, +/// flags::GFP_KERNEL, +/// )?; +/// let result =3D NonNull::new(KBox::into_raw(result)) +/// .expect("Raw pointer to newly allocation KBox is null, thi= s should never happen."); +/// // SAFETY: We just allocated the `Foo`, thus it is valid. +/// Ok(unsafe { Owned::from_raw(result) }) +/// } +/// } +/// +/// // SAFETY: we ensure that: +/// // - The `Foo` is only dropped when the refcount is zero. +/// // - `is_unique()` only returns `true` when the refcount is 1. +/// unsafe impl SimpleOwnableRefCounted for Foo { +/// fn inc_ref(&self) { +/// self.refcount.replace(self.refcount.get() + 1); +/// } +/// +/// unsafe fn dec_ref(this: NonNull) { +/// // SAFETY: The underlying object is always valid when the func= tion is called. +/// let refcount =3D unsafe { &this.as_ref().refcount }; +/// let new_refcount =3D refcount.get() - 1; +/// if new_refcount =3D=3D 0 { +/// // The `Foo` will be dropped when KBox goes out of scope. +/// // SAFETY: The `Box` is still alive as the old refcou= nt is 1. +/// unsafe { KBox::from_raw(this.as_ptr()) }; +/// } else { +/// refcount.replace(new_refcount); +/// } +/// } +/// +/// fn is_unique(&self) -> bool { +/// self.refcount.get() =3D=3D 1 +/// } +/// } +/// +/// let foo =3D Foo::new().unwrap(); +/// let mut foo =3D ARef::from(foo); +/// { +/// let bar =3D foo.clone(); +/// assert!(Owned::try_from(bar).is_err()); +/// } +/// assert!(Owned::try_from(foo).is_ok()); +/// ``` +pub unsafe trait SimpleOwnableRefCounted { + /// Checks if exactly one [`ARef`] to the object exists. In case the o= bject is [`Sync`], the + /// check needs to be race-free. + fn is_unique(&self) -> bool; + + /// Increments the reference count on the object. + fn inc_ref(&self); + + /// Decrements the reference count on the object when the [`SimpleOwna= bleRefCounted`] is + /// dropped. + /// + /// Frees the object when the count reaches zero. + /// + /// # Safety + /// + /// The safety constraints for [`RefCounted::dec_ref`] and [`Ownable::= release`] both apply to + /// this method, as it will be used to implement both of these traits. + unsafe fn dec_ref(obj: NonNull); +} + +#[cfg_attr(RUSTC_HAS_DO_NOT_RECOMMEND, diagnostic::do_not_recommend)] +// SAFETY: Safe by the requirements on implementation of [`SimpleOwnableRe= fCounted`]. +unsafe impl OwnableRefCounted for T { + fn try_from_shared(this: ARef) -> Result, ARef= > { + if T::is_unique(&*this) { + // SAFETY: Safe by the requirements on implementation of [`Sim= pleOwnable`]. + Ok(unsafe { Owned::from_raw(ARef::into_raw(this)) }) + } else { + Err(this) + } + } +} + +#[cfg_attr(RUSTC_HAS_DO_NOT_RECOMMEND, diagnostic::do_not_recommend)] +// SAFETY: Safe by the requirements on implementation of [`SimpleOwnableRe= fCounted`]. +unsafe impl Ownable for T { + unsafe fn release(this: NonNull) { + // SAFETY: Safe by the requirements on implementation of + // [`SimpleOwnableRefCounted::dec_ref()`]. + unsafe { SimpleOwnableRefCounted::dec_ref(this) }; + } +} + +#[cfg_attr(RUSTC_HAS_DO_NOT_RECOMMEND, diagnostic::do_not_recommend)] +// SAFETY: Safe by the requirements on implementation of [`SimpleOwnableRe= fCounted`]. +unsafe impl RefCounted for T { + fn inc_ref(&self) { + SimpleOwnableRefCounted::inc_ref(self); + } + + unsafe fn dec_ref(this: NonNull) { + // SAFETY: Safe by the requirements on implementation of + // [`SimpleOwnableRefCounted::dec_ref()`]. + unsafe { SimpleOwnableRefCounted::dec_ref(this) }; + } +} + +impl TryFrom> for Owned { + type Error =3D ARef; + /// Tries to convert the [`ARef`] to an [`Owned`] by calling + /// [`try_from_shared()`](OwnableRefCounted::try_from_shared). In case= the [`ARef`] is not + /// unique, it returns again an [`ARef`] to the same underlying object. + fn try_from(b: ARef) -> Result, Self::Error> { + T::try_from_shared(b) + } +} + /// A sum type that always holds either a value of type `L` or `R`. /// /// # Examples --=20 2.48.1