From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 B7ADC40F75D; Mon, 24 Aug 2026 11:20:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787570403; cv=none; b=h5CAKBXNoA0BB1vKkNUSCIR9I5VC0nj27PfkltCAev6/J+hqRZVW9ktoa4a+C2ZbUQlw4pk+9a2Duaz+Lym/Y1Tcvf6zt0jN7vDn6biViebw2x0L5W7tHM+1th8gjeCLLwxqioECbumUZ3RQGO2AGblg+xQQou4smS2u7sBEUyw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787570403; c=relaxed/simple; bh=TzIAIwSsIR9R0rqS8Uk6Of8uwDIlBqJKvjolimTvkP8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=UJPch/Kf89Cb36c2/+JO3rfpIcnEtmbVnHTsHkdULGCCywReo3SH0h6/omNwfMwfBGBzqD025cWjnAM448ERGNyr+V74f9eaipEYjEN2chvUZTULHLzPlYEHC58oD049GcWvScO5cT0m+eGD+JCVYXZZp7Zpg1j3QbADDoAN478= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=k9Ss1Imm; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="k9Ss1Imm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 46F4E1F000E9; Mon, 24 Aug 2026 11:19:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787570401; bh=nW0Gvd41fIKfum8lv47xbr88JVN0R0Y3bAVxdgTJ0C0=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=k9Ss1ImmnTp+BNiJNQZZ1ogLaSj2TK3mGrEp+cfMzZa4dLWPVFQQuxdLWtQufl3t/ c97tCZshgvAk+N3/c7q4EFEW3QVe9BZAnEDz6SdSCW46ca8AnlglvoKt0wapYtiY5n FDAqcwST7FZOUw3rYYksuz1dvdeaBy7fIQMZ4chh3vfK/XQyURqRS1nPnR3w+zpG+a URubS/a5Qt3Uz2vcweFTiRSnrPW1Z0Ns/f3sbZtrNRHxUvfV1VrzB3fbu4Zgcsu695 2lwjWs/5Fd1nBPLSqmLNLCPyQv6QvXFtBIrGZVh3KK7LBZhDLM0uVOwmx+Puz1/9D/ +Zvpf4i+pVn7g== From: Andreas Hindborg Date: Mon, 24 Aug 2026 13:17:54 +0200 Subject: [PATCH v20 2/8] rust: types: Add Ownable/Owned types Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260824-unique-ref-v20-2-490735672187@kernel.org> References: <20260824-unique-ref-v20-0-490735672187@kernel.org> In-Reply-To: <20260824-unique-ref-v20-0-490735672187@kernel.org> To: Danilo Krummrich , Lorenzo Stoakes , Vlastimil Babka , "Liam R. Howlett" , Uladzislau Rezki , Miguel Ojeda , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Alice Ryhl , Trevor Gross , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , =?utf-8?q?Onur_=C3=96zkan?= , Lyude Paul , Greg Kroah-Hartman , =?utf-8?q?Arve_Hj=C3=B8nnev=C3=A5g?= , Todd Kjos , Christian Brauner , Carlos Llamas , "Rafael J. Wysocki" , Dave Ertman , Leon Romanovsky , Paul Moore , Serge Hallyn , David Airlie , Simona Vetter , Alexander Viro , Jan Kara , Igor Korotin , Viresh Kumar , Nishanth Menon , Stephen Boyd , Bjorn Helgaas , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= , Pavel Tikhomirov , Michal Wilczynski , Ira Weiny , Ira Weiny Cc: Andreas Hindborg , Philipp Stanner , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, driver-core@lists.linux.dev, linux-block@vger.kernel.org, linux-security-module@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fsdevel@vger.kernel.org, linux-pm@vger.kernel.org, linux-pci@vger.kernel.org, linux-pwm@vger.kernel.org, linux-usb@vger.kernel.org, Asahi Lina , Oliver Mangold , Boqun Feng X-Mailer: b4 0.16-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=10621; i=a.hindborg@kernel.org; h=from:subject:message-id; bh=GO++Qeu4a7kF68yEw+Vn2C+P9gU67mXjb8+4Ea2xpsk=; b=owEBbQKS/ZANAwAKAfpQKQiqxb3QAcsmYgBqjCiBdMlT+SR0TYzYvvg6VCUOxiI5R9GJUJyUK HV55E54nEGJAjMEAAEKAB0WIQRXitnI2WZ2JirAaob6UCkIqsW90AUCaowogQAKCRD6UCkIqsW9 0O0+D/9qBRK1TCio6k/0Tta5g889WaW728AnR/eO41sejRdpQpqDaI3a0o+Y1GFvN+pRg0WKTrZ R54Yp2LuDujUdHqQ8Syzo2oqWCXFq/eahqpkuZOYzuXrOdkgaw9K2vtVdKHV1YB38ry8X0gwfGy PovKTCmGojSGX/T9zv7y9JNH1aqGNB/VDObHwWbFAGNTiwZvuCOMq9sw3UsZC/JAyw9xW1bfUT7 Yhrls48eNxQ7lXUvT3ScVCQp6rADcg1fpR2QMdR72J36osQv4/yVTlqOH2ncZ03bp7Vj6RQPMdE t0ZcqPpTno5JultwD0VnueS3mR4bzbc9ZKfd3ParNPokfnmb7UONiTTYHukeB926IY1yl/WJeA+ 9v0V37erUsVUJQSWpaXZmDSkRxiyR6qBGG22LGljugJd+kIMOzRFmMWf1g8VzkYy4StbMU2bnJi s6axtmCIBrIl4rxAHwtZ1YG+Kij//5I2r4h4wMFNvON7YQRH0N89d0ccf8K3x948UMp1bfJTlvW FBNp5JqhH24rzGY1i6e1kIBDKSd7ea2mQmbXqMwgX3mP7z586EWo6GqtuA3Z0wmLCgyWsZUR3iv w6/GfvX5jwnyDCttAHEaXPvtuvW27YHe0WLGHE4NEh8BNuvw/uAB8PXRsDV0MkZdzApTt0QO0Ra y+xRkgSiP1RBm0A== X-Developer-Key: i=a.hindborg@kernel.org; a=openpgp; fpr=3108C10F46872E248D1FB221376EB100563EF7A7 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. [ om: - Split code into separate file and `pub use` it from types.rs. - Make from_raw() and into_raw() public. - Remove OwnableMut, and make DerefMut dependent on Unpin instead. - Usage example/doctest for Ownable/Owned. - Fixes to documentation and commit message. ] Link: https://lore.kernel.org/all/20250202-rust-page-v1-1-e3170d7fe55e@asahilina.net/ Signed-off-by: Asahi Lina Co-developed-by: Oliver Mangold Signed-off-by: Oliver Mangold Reviewed-by: Boqun Feng Reviewed-by: Daniel Almeida Reviewed-by: Gary Guo Reviewed-by: Alice Ryhl [ Andreas: Updated documentation, examples, and formatting. Change safety requirements, safety comments. ] Co-developed-by: Andreas Hindborg Signed-off-by: Andreas Hindborg --- rust/kernel/lib.rs | 1 + rust/kernel/owned.rs | 188 +++++++++++++++++++++++++++++++++++++++++++++++ rust/kernel/sync/aref.rs | 5 ++ rust/kernel/types.rs | 5 ++ 4 files changed, 199 insertions(+) diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 9512af7156df2..eb5256204a174 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -101,6 +101,7 @@ pub mod of; #[cfg(CONFIG_PM_OPP)] pub mod opp; +pub mod owned; pub mod page; #[cfg(CONFIG_PCI)] pub mod pci; diff --git a/rust/kernel/owned.rs b/rust/kernel/owned.rs new file mode 100644 index 0000000000000..7fe9ec3e55126 --- /dev/null +++ b/rust/kernel/owned.rs @@ -0,0 +1,188 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Unique owned pointer types for objects with custom drop logic. +//! +//! These pointer types are useful for C-allocated objects which by API-contract +//! are owned by Rust, but need to be freed through the C API. + +use core::{ + mem::ManuallyDrop, + ops::{ + Deref, + DerefMut, // + }, + pin::Pin, + ptr::NonNull, // +}; + +/// Types that specify their own way of performing allocation and destruction. Typically, this trait +/// is implemented on types from the C side. +/// +/// Implementing this trait allows types to be referenced via the [`Owned`] pointer type. This +/// is useful when it is desirable to tie the lifetime of the reference to an owned object, rather +/// than pass around a bare reference. [`Ownable`] types can define custom drop logic that is +/// executed when the owned reference [`Owned`] pointing to the object is dropped. +/// +/// Note: The underlying object is not required to provide internal reference counting, because it +/// represents a unique, owned reference. If reference counting (on the Rust side) is required, +/// [`AlwaysRefCounted`](crate::sync::aref::AlwaysRefCounted) should be implemented. +/// +/// # Examples +/// +/// A minimal example implementation of [`Ownable`] and its usage with [`Owned`] looks like +/// this: +/// +/// ``` +/// # #![expect(clippy::disallowed_names)] +/// # use core::cell::Cell; +/// # use core::ptr::NonNull; +/// # use kernel::sync::global_lock; +/// # use kernel::alloc::{flags, kbox::KBox, AllocError}; +/// # use kernel::types::{Owned, Ownable}; +/// +/// // Let's count the allocations to see if freeing works. +/// kernel::sync::global_lock! { +/// // SAFETY: we call `init()` right below, before doing anything else. +/// unsafe(uninit) static FOO_ALLOC_COUNT: Mutex = 0; +/// } +/// // SAFETY: We call `init()` only once, here. +/// unsafe { FOO_ALLOC_COUNT.init() }; +/// +/// struct Foo; +/// +/// impl Foo { +/// fn new() -> Result> { +/// // We are just using a `KBox` here to handle the actual allocation, as our `Foo` is +/// // not actually a C-allocated object. +/// let result = KBox::new( +/// Foo {}, +/// flags::GFP_KERNEL, +/// )?; +/// let result = KBox::into_non_null(result); +/// // Count new allocation +/// *FOO_ALLOC_COUNT.lock() += 1; +/// // SAFETY: +/// // - We just allocated the `Self`, thus it is valid and we own it. +/// // - We can transfer this ownership to the `from_raw` method. +/// Ok(unsafe { Owned::from_raw(result) }) +/// } +/// } +/// +/// impl Ownable for Foo { +/// unsafe fn release(this: NonNull) { +/// // SAFETY: The [`KBox`] is still alive. We can pass ownership to the [`KBox`], as +/// // by requirement on calling this function. +/// drop(unsafe { KBox::from_raw(this.as_ptr()) }); +/// // Count released allocation +/// *FOO_ALLOC_COUNT.lock() -= 1; +/// } +/// } +/// +/// { +/// let foo = Foo::new()?; +/// assert!(*FOO_ALLOC_COUNT.lock() == 1); +/// } +/// // `foo` is out of scope now, so we expect no live allocations. +/// assert!(*FOO_ALLOC_COUNT.lock() == 0); +/// # Ok::<(), Error>(()) +/// ``` +pub trait Ownable { + /// Tear down this `Ownable`. + /// + /// Implementers of `Ownable` can use this function to clean up the use of `Self`. This can + /// include freeing the underlying object. + /// + /// # Safety + /// + /// Callers must ensure that they have exclusive ownership of the `Self` pointed to by `this`, + /// and that this ownership is transferred to the `release` method. `this` must not be used + /// after calling this method, as the underlying object may have been freed. + unsafe fn release(this: NonNull); +} + +/// A mutable reference to an owned `T`. +/// +/// The [`Ownable`] is automatically freed or released when an instance of [`Owned`] is +/// dropped. +/// +/// # Invariants +/// +/// - Until `T::release` is called, this `Owned` exclusively owns the underlying `T`. +/// - The `T` value is pinned. +pub struct Owned { + ptr: NonNull, +} + +impl Owned { + /// Creates a new instance of [`Owned`]. + /// + /// This function takes over ownership of the underlying object. + /// + /// # Safety + /// + /// Callers must ensure that: + /// - `ptr` points to a valid instance of `T`. + /// - Until `T::release` is called, the returned `Owned` exclusively owns the underlying `T`. + #[inline] + pub unsafe fn from_raw(ptr: NonNull) -> Self { + // INVARIANT: By function safety requirement we satisfy the first invariant of `Self`. + // We treat `T` as pinned from now on. + Self { ptr } + } + + /// Consumes the [`Owned`], returning a raw pointer. + /// + /// This function does not drop the underlying `T`. When this function returns, ownership of the + /// underlying `T` is with the caller. + #[inline] + pub fn into_raw(me: Self) -> NonNull { + ManuallyDrop::new(me).ptr + } + + /// Get a pinned mutable reference to the data owned by this `Owned`. + #[inline] + pub fn as_pin_mut(&mut self) -> Pin<&mut T> { + // SAFETY: The type invariants guarantee that the object is valid, and that we can safely + // return a mutable reference to it. + let unpinned = unsafe { self.ptr.as_mut() }; + + // SAFETY: By type invariant `T` is pinned. + unsafe { Pin::new_unchecked(unpinned) } + } +} + +// SAFETY: It is safe to send an [`Owned`] to another thread when the underlying `T` is [`Send`], +// because of the ownership invariant. Sending an [`Owned`] is equivalent to sending the `T`. +unsafe impl Send for Owned {} + +// SAFETY: It is safe to send [`&Owned`] to another thread when the underlying `T` is [`Sync`], +// because of the ownership invariant. Sending an [`&Owned`] is equivalent to sending the `&T`. +unsafe impl Sync for Owned {} + +impl Deref for Owned { + type Target = T; + + #[inline] + fn deref(&self) -> &Self::Target { + // SAFETY: The type invariants guarantee that the object is valid. + unsafe { self.ptr.as_ref() } + } +} + +impl DerefMut for Owned { + #[inline] + 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 { + #[inline] + fn drop(&mut self) { + // SAFETY: By existence of `&mut self` we exclusively own `self` and the underlying `T`. As + // we are dropping `self`, we can transfer ownership of the `T` to the `release` method. + unsafe { T::release(self.ptr) }; + } +} diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs index b721b2e00b986..3bd5eb8a1a526 100644 --- a/rust/kernel/sync/aref.rs +++ b/rust/kernel/sync/aref.rs @@ -34,6 +34,11 @@ /// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted /// instances of a type. /// +/// Note: Implementing this trait allows types to be wrapped in an [`ARef`]. It requires an +/// internal reference count and provides only shared references. If unique references are required +/// [`Ownable`](crate::types::Ownable) should be implemented which allows types to be wrapped in an +/// [`Owned`](crate::types::Owned). +/// /// # Safety /// /// Implementers must ensure that increments to the reference count keep the object alive in memory diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index ac316fd7b538f..c41eab0ec983c 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -15,6 +15,11 @@ pub mod for_lt; pub use for_lt::ForLt; +pub use crate::owned::{ + Ownable, + 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 -- 2.51.2