From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 61A56238C15; Fri, 2 May 2025 09:57:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746179870; cv=none; b=HDXUO6ISFSGutqgpxrKnke66KOL+735mycbMicVwXADve8gklBIKwbxMtlIpaTYYCYiRi1/E2fh+TAAt0VRISHAS6k3WRQq4N9TPfL9FXhgsBm5HAP2jECB2JgAX0H+WijzM0KnFpk1ITr8iaklyApZtPUOuPY8DaPxlkB9NUFs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746179870; c=relaxed/simple; bh=pW1H8xXE21A+n17a+0P5k7+tQf/Aa0cTWaK+S948R4s=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=sjeLUENcct5CbUwBA73LMw9fbtCx0ZLEhJM5TOR1VM2R9BkE67X8FtXcEvYEVoz1k9R5FZht7aT6KacEl1w2MPxsHlWAMmqrd5epmCFQuN2cqXwo481iod0S+Zm6pbCbfl6jHdtVp9KED6ku2qTo0L26cdP5G+oIuN7iwR3oPo4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NDPm6fIN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NDPm6fIN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBF68C4CEED; Fri, 2 May 2025 09:57:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746179869; bh=pW1H8xXE21A+n17a+0P5k7+tQf/Aa0cTWaK+S948R4s=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=NDPm6fINYnhGBeSfvFNgqO/AnV4iA4AnGFqqrk5aE+5rqVTjGTwRhpP7iMrILQr/P DdILNeLXVmqJltLISpeZ6yEwnzgiG1b69h3l9aJG9+XRZ+wqowTXiKPFdXy9YpG/iy 3QBrNBcC9MorTP4JZH3m+MkQrafRgEAUd9PAhYNgrQEwnuFPFum42zYaOB0z+RoN7S di/ilaVBvsXnEM886gxQapzZz00wFLowQRp0bv1P5Fz2+gkK6b23JaJ2hNifMb4oLy FlcTh5Gqs+KULhcCTop+tz/xHkd6urhWFmGdzyc8sKVryJMbA4kEF8D1Umwv07/OAi b6B9CJ6avteJA== From: Andreas Hindborg To: "Oliver Mangold" Cc: "Miguel Ojeda" , "Alex Gaynor" , "Boqun Feng" , "Gary Guo" , =?utf-8?Q?Bj=C3=B6rn?= Roy Baron , "Benno Lossin" , "Alice Ryhl" , "Trevor Gross" , "Asahi Lina" , , Subject: Re: [PATCH v10 1/5] rust: types: Add Ownable/Owned types In-Reply-To: <20250502-unique-ref-v10-1-25de64c0307f@pm.me> (Oliver Mangold's message of "Fri, 02 May 2025 09:02:29 +0000") References: <20250502-unique-ref-v10-0-25de64c0307f@pm.me> <20250502-unique-ref-v10-1-25de64c0307f@pm.me> User-Agent: mu4e 1.12.7; emacs 30.1 Date: Fri, 02 May 2025 11:57:30 +0200 Message-ID: <87zffvz65x.fsf@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain "Oliver Mangold" writes: > 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@asahilina.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/types.rs | 3 ++ > rust/kernel/types/ownable.rs | 117 +++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 120 insertions(+) > > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index 9d0471afc9648f2973235488b441eb109069adb1..5d8a99dcba4bf733107635bf3f0c15840ec33e4c 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -11,6 +11,9 @@ > }; > use pin_init::{PinInit, Zeroable}; > > +pub mod ownable; > +pub use 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 > diff --git a/rust/kernel/types/ownable.rs b/rust/kernel/types/ownable.rs > new file mode 100644 > index 0000000000000000000000000000000000000000..52e7a69019f1e2bbbe3cf715651b67a5a5c7c13d > --- /dev/null > +++ b/rust/kernel/types/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 owned reference exists (i.e. > +/// until the [`release()`](Ownable::release) trait method is called). > +/// - That the C code follows the usual mutable reference requirements. That is, the kernel will > +/// never mutate the [`Ownable`] (excluding internal mutability that follows 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 that it is okay to call > +/// [`core::mem::swap`] on the `Ownable`. This excludes pinned types (meaning: 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 [`Owned`] is > +/// dropped. > +/// > +/// # Invariants > +/// > +/// The pointer stored in `ptr` is 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 underlying `T` is `Send` because > +// it effectively means sending a `&mut T` (which is safe because `T` is `Send`). > +unsafe impl Send for Owned {} > + > +// SAFETY: It is safe to send `&Owned` to another thread when the underlying `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. This part "the underlying object is acquired" is unclear to me. How about: Callers must ensure that *ownership of* the underlying object has been acquired. That is, the object can be considered owned by the caller. Best regards, Andreas Hindborg