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 451DD39022A; Fri, 11 Sep 2026 13:25:59 +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=1789133161; cv=none; b=mQXd5tHqC+2DaCWiT7UoXiF37PWZF4EDMK7E82RIarYGywgLbtJtfEeg6HJO2qojAWaM99zF0kchPcxtikodkckEEGM3/PY/bqjEGX/LuWiaM4JSdluc6kAkscS3sl1W9nRMvpTWQmGBuwiDOXjkMBii2WTq/bIBiqve+SKO6sQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789133161; c=relaxed/simple; bh=zFyyWzdhfFZMVM5stqf613uCaXnIeVSxmc31g5HKUZA=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=ldRG3ptfGA+efkj+hq8IbutQrj6EoFKmZYy4TUQPd3CbJaINrnr0X1GUejTi4MkQ8kVJAqaeshedy37fE2dJ0A3GtB74pNrR9SPJwAunrvBKkEcbhKjz9yuk6m38UgVgPU/ZuduFa35nQv5zZK8UnZro6CkKN63rK+wvVDmMi3Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VXtn1fiY; 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="VXtn1fiY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34FF51F00898; Fri, 11 Sep 2026 13:25:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789133159; bh=b8hBkIDR5gbaIa/OcVZo7VYHM8DXFaO8ihp5gcV65Tc=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=VXtn1fiY2o5DXMdoNaf8ZzLgSZsGCdT7ZwNY6FB4pdySVmjeQIqo+jTZLfm3/q33+ LnCbzK/A0d6W3mHy5MlGsh+dOBxN4T+7UuC7if51SC4Y4WOsawT4loI6z4f/cPPsPb LEHZm4NM/UiYfaaDB2e8nAEDA/bUbIeD89ffVwAWP5YoZyzbml/CvceH29+Tq6pfbc 5OiH8ODldkyB5xaiz0JQc+5SkYuDaxk8ZB5CaqnQ1olk+xod9sHadlEIgKFs0bPhqk mpWXADE1ONaJWHe+tK1DyeoOXHAnAcaBRnsz8NpG1Ysw760kl3cXOV1DCzOlIhHu25 jY4cewUPGE/7g== From: Andreas Hindborg To: Alice Ryhl Cc: 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 , Trevor Gross , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , Onur =?utf-8?Q?=C3=96zkan?= , Lyude Paul , Greg Kroah-Hartman , Arve =?utf-8?B?SGrDuG5uZXbDpWc=?= , 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 , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Pavel Tikhomirov , Michal Wilczynski , Ira Weiny , Matthew Brost , Thomas =?utf-8?Q?Hellstr=C3=B6m?= , 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, Oliver Mangold Subject: Re: [PATCH v21 6/9] rust: Add `OwnableRefCounted` In-Reply-To: References: <20260910-unique-ref-v21-0-e83257373062@kernel.org> <20260910-unique-ref-v21-6-e83257373062@kernel.org> Date: Fri, 11 Sep 2026 15:25:43 +0200 Message-ID: <87se3fvs14.fsf@kernel.org> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain "Alice Ryhl" writes: > On Thu, Sep 10, 2026 at 11:00:10AM +0200, Andreas Hindborg wrote: >> From: Oliver Mangold >> >> Types implementing one of these traits can safely convert between an >> `ARef` and an `Owned`. >> >> This is useful for types which generally are accessed through an `ARef` >> but have methods which can only safely be called when the reference is >> unique, like e.g. `block::mq::Request::end_ok()`. >> >> Signed-off-by: Oliver Mangold >> [ Andreas: Fix formatting, update documentation, fix error handling in >> examples. ] >> Assisted-by: LLM >> Co-developed-by: Andreas Hindborg >> Signed-off-by: Andreas Hindborg > >> /// 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. >> +/// 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 an object 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 >> +/// of type [`Owned<_>`] pointing to the object is dropped. > > This diff looks like it should be in the patch introducing Ownable. Yes, wrong target commit for the edit. > >> +/// # #![expect(clippy::disallowed_names)] >> +/// # use core::ptr::NonNull; >> +/// # use kernel::alloc::{flags, kbox::KBox, AllocError}; >> +/// # use kernel::sync::aref::{ARef, RefCounted}; >> +/// # use kernel::sync::atomic::Acquire; >> +/// # use kernel::sync::Refcount; >> +/// # use kernel::types::{Owned, Ownable, OwnableRefCounted}; >> +/// > > This newline will appear weirdly in generated docs because no content is > shown above it. Consider not hiding the imports. Will remove. > >> +pub trait OwnableRefCounted: RefCounted + Ownable + Sized { >> + /// Checks if the [`ARef`] is unique and converts it to an [`Owned`] if that is the case. >> + /// Otherwise it returns again an [`ARef`] to the same underlying object. >> + fn try_from_shared(this: ARef) -> Result, ARef>; >> + >> + /// Converts the [`Owned`] into an [`ARef`]. >> + fn into_shared(this: Owned) -> ARef; >> +} > > This trait provides two methods that have very different conditions for > existing, IMO. > > The into_shared() method is so likely to exist, that I would almost > consider placing it on the Ownable trait. > > pub trait Ownable { > unsafe fn release(this: NonNull); > > fn into_shared(this: Owned) -> ARef > where > Self: Refcounted; > } > > On the other hand, I think try_from_shared() is more likely to be a > tricky operation you cannot necessarily implement, and as such it can be > on its own separate trait like you have here. Ownable does not require RefCounted, so this method is not always implementable. > > At the very least, I can easily imagine that some types can never become > unique again after having been shared. It could make sense to split the capability in a separate trait. But perhaps we should wait with that till we need it and not introduce premature complexity? Best regards, Andreas Hindborg