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 EC80C36BCF2; Fri, 3 Jul 2026 07:32:03 +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=1783063925; cv=none; b=T4RSvyvgdwCug6IZMCxAskB66MWx6q3cIVvNtNk4Bo1+hMcjqdVlZfXCHV6MQWuX/q53onmpqYAnHSaUDPzPla43XyzBmbzj8jt8y2ajg/rcyPLPg8rOyNxTz4nwJnjyWB2nG+hUT4o4fWjS7S1VhVrDGEZn0hSqpPIlB/EFFm4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783063925; c=relaxed/simple; bh=8cHjGdlz/zSDfrf0QWx2gkGate7mdlZ5gQgrwEtnuT0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FY0foJ72VDJGlk5NU4ZvLnAuIRT21XPPWdufMD+omj5Xcoa5PTUAxqjaUlXXU3wgfJgRPy9hlVxXTjfCLfwAMW7isiR+tO2JzzG3CpTe3UCU/W+DBuyX4dfkr3w5vnGFu7FtasgRS70wKjbQC9L1+TpsKvBCtzD0Va0YviZ+GR8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=H+zF7IeP; 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="H+zF7IeP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E72CA1F00A3A; Fri, 3 Jul 2026 07:31:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783063923; bh=W0cm6V1SNatAYCiqUyWncuJR0N/zPSN18fPyAUJ6v+c=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=H+zF7IeP0YH4a2qhwK5CXkyAuahXhRTNYffTPeDhn8gTPFBJ/EMwovRyMtjHTfcAt wTKoM1wMa+RprgJmGwvnKthSKBLkPrIGcs4AFsbA+gAs1zvy/nByw5+dlUapsZSmpO j40kMJoEhtY95vb0mf7bUMjb/9KXq4x4FwjenBpQkvyZBIkOA5+S5KVMBT8jnitur9 pz5hT42R/5DhSXnljftTfh+900RWLLNBzatTfLFWeb2wUmNFvzL5S2JOb3onha9Gdr TtdPlai0ZRoOlK0wunkchFh+bUhfsZtzGUnhtZp1/XaU4+HjyjOVScXb9p7A7pVYti Ic4DJx87prOlg== From: Philipp Stanner To: Miguel Ojeda , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= , Philipp Stanner , Daniel Almeida , Greg Kroah-Hartman , Asahi Lina , Burak Emir , Lorenzo Stoakes , Joel Fernandes , Alexandre Courbot , Krishna Ketan Rai , Tamir Duberstein , Mirko Adzic , Alistair Francis , =?UTF-8?q?Onur=20=C3=96zkan?= , Shankari Anand Cc: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org Subject: [PATCH v5 1/5] rust: types: implement ForeignOwnable for ARef Date: Fri, 3 Jul 2026 09:31:37 +0200 Message-ID: <20260703073141.3962604-3-phasta@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260703073141.3962604-2-phasta@kernel.org> References: <20260703073141.3962604-2-phasta@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Danilo Krummrich Implement ForeignOwnable for ARef, making it possible for C code to own an ARef. Since ARef represents shared ownership, BorrowedMut is &T rather than &mut T, matching the semantics of the underlying reference-counted type. Signed-off-by: Danilo Krummrich Reviewed-by: Alice Ryhl --- rust/kernel/sync/aref.rs | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs index b721b2e00b98..540766613659 100644 --- a/rust/kernel/sync/aref.rs +++ b/rust/kernel/sync/aref.rs @@ -24,6 +24,11 @@ ptr::NonNull, // }; +use crate::{ + prelude::*, + types::ForeignOwnable, // +}; + /// Types that are _always_ reference counted. /// /// It allows such types to define their own custom ref increment and decrement functions. @@ -188,6 +193,41 @@ fn eq(&self, other: &ARef) -> bool { } impl Eq for ARef {} +// SAFETY: `into_foreign` returns a pointer from `NonNull::as_ptr`, so it's non-null. The +// `ARef` invariant guarantees that `ptr` points to a valid `T`, so it's aligned to `T`. +unsafe impl ForeignOwnable for ARef { + const FOREIGN_ALIGN: usize = core::mem::align_of::(); + + type Borrowed<'a> = &'a T; + type BorrowedMut<'a> = &'a T; + + fn into_foreign(self) -> *mut c_void { + ARef::into_raw(self).as_ptr().cast() + } + + unsafe fn from_foreign(ptr: *mut c_void) -> Self { + // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous + // call to `Self::into_foreign`. + let ptr = unsafe { NonNull::new_unchecked(ptr.cast()) }; + + // SAFETY: `ptr` came from `into_foreign`, which consumed an `ARef` without decrementing + // the refcount, so we can transfer the ownership to the new `ARef`. + unsafe { ARef::from_raw(ptr) } + } + + unsafe fn borrow<'a>(ptr: *mut c_void) -> &'a T { + // SAFETY: The safety requirements of this method ensure that the object remains alive and + // immutable for the duration of 'a. + unsafe { &*ptr.cast() } + } + + unsafe fn borrow_mut<'a>(ptr: *mut c_void) -> &'a T { + // SAFETY: The safety requirements for `borrow_mut` are a superset of the safety + // requirements for `borrow`. + unsafe { ::borrow(ptr) } + } +} + impl PartialEq<&'_ U> for ARef where T: AlwaysRefCounted + PartialEq, -- 2.54.0