From nobody Fri Dec 19 00:16:47 2025 Received: from mail-24416.protonmail.ch (mail-24416.protonmail.ch [109.224.244.16]) (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 55B5C256C82 for ; Tue, 25 Mar 2025 11:57:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=109.224.244.16 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742903823; cv=none; b=uHay3IYjAdFv0QsryPBS/Zh14mbHiEIi8ChZMBCUErx/mJcEsbZtUh4CBLyytUDprq60xKmsnN8olL3/RyapWG5VlY0MMvQb/vVW5wXLGS6QNJDFOlltNUgeew0HlCFtAQQZGnhhSLsCqrP6YMsMWJO+rvAS3bvaR8c1fxE+Lpg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742903823; c=relaxed/simple; bh=KCA2sIAGxHHkgBLyC+jPdzMRzvM7WkLP3HCzEJqfGaM=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=dCb7coWZK58ktgSYXVB0mil2157i9k00jI65aG5v6zphAFW8ZJCFCK6hsfFj6rfDOAfyn+l/dU3KlX3hagNA4m6vV03DRAIRKztXY35xpMxtX7IQWiyaJ3KOiPmfG0Q7bdIrzQH0xgVETemGMOzf8WaMFl+FHd7izZ49Vh/DcgU= 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=OcZtAOkv; arc=none smtp.client-ip=109.224.244.16 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="OcZtAOkv" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail3; t=1742903819; x=1743163019; bh=jAchpJYz/gFgXntQllfuI6BSuOQvP9/pEZ9/46jt7AE=; 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=OcZtAOkvPvTVbge2cb03RW9gbOpWpxnGCbm8+1Q3I+sRLqVLvvPW4hJoxSv4GNRBT Zf7wfuV9LABRkxeEdNvVshuDDC0EVSlJ086kaZRqaPp7YkNWsIYtoZEAuSbZpYr9mk y3zgLSK834rmgVEAK8FOcZw4u6Urs2OiIEyatsdeBsXM7aUlPRALF9t6zfHufYD+A0 gdwPHwy4uhe6bg2qUQ+v3NYezzl7jpGFwwt8dkP1shIUPB4keGNVxphL73f38NbDCZ Lfoxxiq3YZsnqW5wvSLOmympIRWzOkEaAJaKzp9aG2TEgSRPDuGDtAMKoHFEfecTf/ PkwuuBfrxXltA== Date: Tue, 25 Mar 2025 11:56:51 +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 v9 1/5] rust: types: Add Ownable/Owned types Message-ID: <20250325-unique-ref-v9-1-e91618c1de26@pm.me> In-Reply-To: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> References: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> Feedback-ID: 31808448:user:proton X-Pm-Message-ID: 8225556763920ffca83c7b02e84b7c83bfe74180 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 [ om: - split code into separate file and `pub use` it from types.rs - make from_raw() and into_raw() public - fixes to documentation ] Signed-off-by: Oliver Mangold Reviewed-by: Boqun Feng --- rust/kernel/lib.rs | 1 + rust/kernel/ownable.rs | 117 +++++++++++++++++++++++++++++++++++++++++++++= ++++ rust/kernel/types.rs | 2 + 3 files changed, 120 insertions(+) diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 7697c60b2d1a670c436246d422de3b22b1520956..52c294bbf8ded260540e0bc0749= 9257bce91383c 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -61,6 +61,7 @@ #[cfg(CONFIG_NET)] pub mod net; pub mod of; +pub mod ownable; pub mod page; #[cfg(CONFIG_PCI)] pub mod pci; diff --git a/rust/kernel/ownable.rs b/rust/kernel/ownable.rs new file mode 100644 index 0000000000000000000000000000000000000000..f4bebea23ce1d62f5597e35199c= a38ea07b293db --- /dev/null +++ b/rust/kernel/ownable.rs @@ -0,0 +1,117 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Owned reference types. + +use core::{ + marker::PhantomData, + mem::ManuallyDrop, + ops::{Deref, DerefMut}, + ptr::NonNull, +}; + +/// 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 owned by Rust as [`Owned`] stay alive while that owne= d reference exists (i.e. +/// until the [`release()`](Ownable::release) trait method is called). +/// - That the C code follows the usual mutable reference requirements. Th= at is, the kernel will +/// never mutate the [`Ownable`] (excluding internal mutability that fol= lows the usual rules) +/// while Rust owns it. +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`] or `&mut Owned= ` Rust reference +/// may be dereferenced into a `&mut T`. +/// +/// # Safety +/// +/// Implementers must ensure that access to a `&mut T` is safe, implying t= hat it is okay to call +/// [`core::mem::swap`] on the `Ownable`. This excludes pinned types (mean= ing: most kernel types). +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) }; + } +} diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 2bbaab83b9d65da667a07e85b3c89c7fa881b53c..2cddbd3a2873b601419f7628c38= 6431a63cb9692 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -11,6 +11,8 @@ ptr::NonNull, }; =20 +pub use crate::ownable::{Ownable, OwnableMut, Owned}; + /// Used to transfer ownership to and from foreign (non-Rust) languages. /// /// Ownership is transferred from Rust to a foreign language by calling [`= Self::into_foreign`] and --=20 2.49.0 From nobody Fri Dec 19 00:16:47 2025 Received: from mail-10631.protonmail.ch (mail-10631.protonmail.ch [79.135.106.31]) (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 350AD2566ED for ; 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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 Suggested-by: Alice Ryhl --- 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 | 41 ++++++++++++++++++++++++-------------= ---- 7 files changed, 61 insertions(+), 30 deletions(-) diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request= .rs index 7943f43b957532749f5a95eee5546bf4f2b6cc5a..f47a13de1e073d564ae224d2e0d= 5cfb875f04da6 100644 --- a/rust/kernel/block/mq/request.rs +++ b/rust/kernel/block/mq/request.rs @@ -8,7 +8,7 @@ bindings, block::mq::Operations, error::Result, - types::{ARef, AlwaysRefCounted, Opaque}, + types::{ARef, AlwaysRefCounted, Opaque, RefCounted}, }; use core::{ marker::PhantomData, @@ -227,10 +227,10 @@ fn atomic_relaxed_op_unless(target: &AtomicU64, op: i= mpl Fn(u64) -> u64, pred: u } =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) { let refcount =3D &self.wrapper_ref().refcount(); =20 @@ -260,3 +260,7 @@ 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 38da555a2bdbb71d698c671ad1a7a337e50c6600..5bdc0a348e6d549d66b002aa6b8= 92b61ce31214a 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 2cddbd3a2873b601419f7628c386431a63cb9692..c8b78bcad259132808cc38c56b9= f2bd525a0b755 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -388,11 +388,9 @@ 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 @@ -404,9 +402,8 @@ 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 -/// alive.) -pub unsafe trait AlwaysRefCounted { +/// won't be able to honour the requirement that [`RefCounted::inc_ref`] k= eep the object alive.) +pub unsafe trait RefCounted { /// Increments the reference count on the object. fn inc_ref(&self); =20 @@ -419,11 +416,21 @@ 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 [`RefCou= nted::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 @@ -434,7 +441,7 @@ 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, } @@ -443,16 +450,16 @@ 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. @@ -481,12 +488,12 @@ 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) {} /// } @@ -504,7 +511,7 @@ 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. @@ -512,7 +519,7 @@ fn clone(&self) -> Self { } } =20 -impl Deref for ARef { +impl Deref for ARef { type Target =3D T; =20 fn deref(&self) -> &Self::Target { @@ -529,7 +536,7 @@ 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. --=20 2.49.0 From nobody Fri Dec 19 00:16:47 2025 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 DCC64256C75; 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charset="utf-8" SAFETY comment in rustdoc example was just 'TODO'. Fixed. Signed-off-by: Oliver Mangold --- rust/kernel/types.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index c8b78bcad259132808cc38c56b9f2bd525a0b755..db29f7c725e631c11099fa91229= 01ec2b3f4a039 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -492,7 +492,7 @@ pub unsafe fn from_raw(ptr: NonNull) -> Self { /// /// struct Empty {} /// - /// # // SAFETY: TODO. + /// // SAFETY: We do not free anything. /// unsafe impl RefCounted for Empty { /// fn inc_ref(&self) {} /// unsafe fn dec_ref(_obj: NonNull) {} @@ -500,7 +500,7 @@ pub unsafe fn from_raw(ptr: NonNull) -> Self { /// /// let mut data =3D Empty {}; /// let ptr =3D NonNull::::new(&mut data).unwrap(); - /// # // SAFETY: TODO. + /// // SAFETY: We keep `data` around longer than the `ARef`. /// let data_ref: ARef =3D unsafe { ARef::from_raw(ptr) }; /// let raw_ptr: NonNull =3D ARef::into_raw(data_ref); /// --=20 2.49.0 From nobody Fri Dec 19 00:16:47 2025 Received: from mail-24417.protonmail.ch (mail-24417.protonmail.ch [109.224.244.17]) (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 AFE0C2566D0 for ; Tue, 25 Mar 2025 11:57:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=109.224.244.17 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742903849; cv=none; b=UghEryL4iGdLKs9Q1i/M0aWYi6GBuRNKOolIqy8su5O8vXrkbR/uLYQHkT/ASzXMxrb4FPV+S0ztOL9Juov7HH1YhGRF20k0yWONpePwuHvwp4BJlXNdFvx7n9TLLzhXk5zx4obfVC5zUxLR5PaBSFRTkBZkCbo6N6MyUaOeDBc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742903849; c=relaxed/simple; bh=rLQI/6fN0QaLeCKW9O3VtH5UCERFGDVomzdGR8mNhlg=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=YwbQO8GYu1513tRiIiNymulFc8tJIl5GJfJeZ1Zcy6ymUiGfo33TMxE69vebS1zTPXH0DodOvEiK8ish71myPyW0My3PTQ0+adZH/PA1Ea93LRXCRYUaeNDM/F1/Ksjf7JB0BCQNGHcoOLaPIkPVmNMs2ZvL0c6zyisHjJd4kFI= 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=c/Jlzl29; arc=none smtp.client-ip=109.224.244.17 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="c/Jlzl29" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail3; t=1742903845; x=1743163045; bh=taOLR4DIcs8sPK6pnTo5SoNNIDGeCkilbyXwLsZy6oY=; 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=c/Jlzl294w+/SCmJs0l8SvHDGDb+OHmpykVJ9uakEoHQQTmc9K28tl8Llqjk6z3S2 2JEdv8psLdsS8mEjhrANihwCZUP4JXxIM26Q2kPEZJVRU7mggwCiIlGyHFbqR0S6zv jOwrr+QsWDJVwhd/TFaGlwpsYx0ePD5oQz+l4pZRnPDpzPWYJ1WZ/OZJUQOa1j6/mD abdNNo2EvLzKTiXK4jKLnDqrUL8iPRLptWvDGcGlcs9I+QbJ0G1YbUiLoJvzaRYs+d NQDVyAYEU5ml4LJXk/za/5/032B0ip4fCpSnbqHK/tQmlGRPot3UGtQ3MDFUU+1chX TqWCF+BG7RTJg== Date: Tue, 25 Mar 2025 11:57:19 +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 v9 4/5] rust: kbuild: provide `RUSTC_HAS_DO_NOT_RECOMMEND` symbol Message-ID: <20250325-unique-ref-v9-4-e91618c1de26@pm.me> In-Reply-To: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> References: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> Feedback-ID: 31808448:user:proton X-Pm-Message-ID: 494c905c3523f6e9620cce5c54fd3b8a18a34a23 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: 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 Reviewed-by: Andreas Hindborg --- init/Kconfig | 3 +++ 1 file changed, 3 insertions(+) diff --git a/init/Kconfig b/init/Kconfig index 324c2886b2ea31e84d6ff221338a1effa06298f2..6dd58788636ef26e017f704b2c0= 088401f28943c 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -132,6 +132,9 @@ 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 2.49.0 From nobody Fri Dec 19 00:16:47 2025 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 072D42566E7 for ; Tue, 25 Mar 2025 11:57:39 +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=1742903862; cv=none; b=if+2ZAddc8QMjS5ELczPpVVHI2eok1rcqBfs7OtTpZAEt0F3vGdlS40cZRo6lnxfgv2BCz5LApjT9PXAwc5TpSLBb5kagQdkUKrqA7Psm+J9ckM5cOM6k8w5RhmiMkG8jGuXaeM+6sOB7479ifCAvdhkXlW3gtvi5JnVexqCC9I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742903862; c=relaxed/simple; bh=FCbgwHJZe4cWFJob/cAvjCUXF1bIozzOffqO5dJ9ico=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=hudfphfI7caMiRDetBNHew//ARGlEWPhKWFZ5rB1qfN9FFoSCIEKUr+z1h5fftwRd+tRmdpxwj7phaVBFeSqQuGFNv96Tm0rjhLlNJ8Voh3Jv6iFOcLnTwEnhfTjq/QbMtqc7Hww0dd8pAikkR24rjtxYxXPqFQtS+kdhhLlsGo= 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=B4BfehnR; 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="B4BfehnR" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail3; t=1742903857; x=1743163057; bh=WXmiEWKhOTusWAn23N7UpMfR2VOHEW2xDiAsXVNYT/A=; 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=B4BfehnRq0CHgWOwzaPQ5wmfwnaqwUiaXcMffqzsIaGo7kk0/HYfMU0eRQWj1VWiv MUmBJEG3g7tW4zuqHhN6eFSp+/HB1QZ2zQFD/OtZ+IjE95w5hdnukaitKxmqTqeNXy HpNGR+fmDRuB0WZANR70XWa1g5w9OhIhOuis+ZfWg855kS2HFHmenKUNp0Z0SDNMt6 KGNntGIwSNGHMCUwfZ6nbaMLfb2kMtZjJtS8YLxIGdFjg4AUbb+3KHYJhSSlpnDmOg ezv+WmlFRXZnC+bpI5xpmTrNAEEAsPc4DDaC28hxbIsPHBw3/+oW77L2Ty1se8dntu kyGyqV2oQsknQ== Date: Tue, 25 Mar 2025 11:57:29 +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 v9 5/5] rust: Add OwnableRefCounted and SimpleOwnableRefCounted Message-ID: <20250325-unique-ref-v9-5-e91618c1de26@pm.me> In-Reply-To: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> References: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> Feedback-ID: 31808448:user:proton X-Pm-Message-ID: b9f696edfcc726e05327cc0867db057a223f8010 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. This is useful for types which generally are access through an ARef but have methods which can only safely called when the reference is unique, like e.g. `block::mq::Request::end_ok()`. Signed-off-by: Oliver Mangold Reviewed-by: Andreas Hindborg --- rust/kernel/ownable.rs | 244 +++++++++++++++++++++++++++++++++++++++++++++= ++++ rust/kernel/types.rs | 8 +- 2 files changed, 251 insertions(+), 1 deletion(-) diff --git a/rust/kernel/ownable.rs b/rust/kernel/ownable.rs index f4bebea23ce1d62f5597e35199ca38ea07b293db..59f84a838bbc4e80fc86dd8dc91= f1672fc649403 100644 --- a/rust/kernel/ownable.rs +++ b/rust/kernel/ownable.rs @@ -2,6 +2,7 @@ =20 //! Owned reference types. =20 +use crate::types::{ARef, RefCounted}; use core::{ marker::PhantomData, mem::ManuallyDrop, @@ -115,3 +116,246 @@ fn drop(&mut self) { unsafe { T::release(self.ptr) }; } } + +/// 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. +/// - [`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 [`Ownable`] and [`OwnableRefCounted`] t= ogether in a simplified +/// way, only requiring to implement [`RefCounted`] and providing the meth= od +/// [`is_unique()`](SimpleOwnableRefCounted::is_unique). +/// +/// For non-standard cases where conversion between [`Ownable`] and [`RefC= ounted`] does not allow +/// [`Ownable::release()`] and [`RefCounted::dec_ref()`] to be the same me= thod, [`Ownable`] +/// and [`OwnableRefCounted`] should be implemented separately. +/// +/// # Safety +/// +/// Implementers must ensure that: +/// +/// - The safety requirements for [`Ownable`] are fulfilled and [`RefCount= ed::dec_ref()`] can +/// be used for [`Ownable::release()`]. +/// - [`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 [`RefCounted`] and [`SimpleOwnable= RefCounted`] +/// 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, Owned, RefCounted, SimpleOwnableRefCounted, +/// }; +/// +/// 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 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 ensure that: +/// // - `is_unique()` only returns `true` when the refcount is 1. +/// unsafe impl SimpleOwnableRefCounted for Foo { +/// 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: RefCounted { + /// 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; +} + +#[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 { RefCounted::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) + } +} diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index db29f7c725e631c11099fa9122901ec2b3f4a039..a72ac86befc4923ee0bbbc1eea7= 33a245189706a 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -11,7 +11,7 @@ ptr::NonNull, }; =20 -pub use crate::ownable::{Ownable, OwnableMut, Owned}; +pub use crate::ownable::{Ownable, OwnableMut, OwnableRefCounted, Owned, Si= mpleOwnableRefCounted}; =20 /// Used to transfer ownership to and from foreign (non-Rust) languages. /// @@ -536,6 +536,12 @@ 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 we're about to --=20 2.49.0