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 8256B3B27C1; Thu, 18 Jun 2026 13:26:59 +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=1781789220; cv=none; b=booUe7ZVeWwZfqC1L1xf/y0LWxEvltXacGz8DUNO6PSlwOCqHk3/P5Wn3MR5dRL25DHG+n8W7PlsE/nk5flqaUVbwPOj3GAGPeWp75FdeNvdYSaX0nIbhUgW8m8kxlDCGsWAgljHulr2zUDcCd8yI9Xtes7/oP7jW/pHZQB05ZE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781789220; c=relaxed/simple; bh=iusRewpZ34TnQ5G2HLBSE7H0Lnu251CvtBRxV7HZGC0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YrRu66OJ4qTKLI67VBfqIErLp4h+jQ0+5s69EwaC0NIjvWxzAwjIGQdPEVpXaXQtL1hzY/SETs5/WE+QbNZ2iQKhwNUomYf1y8hzTq5XIv1bHrikUX5Gfht0MD5T+zKduK4Uz0sUFD2C2T3k4wYIf68fgS0WjPvDtKa+ocf/Uds= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=W/YIjnoD; 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="W/YIjnoD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD96A1F000E9; Thu, 18 Jun 2026 13:26:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781789219; bh=pDJyMWyNek1/CTCATK0JZj8GklloT+oL+OiV9mbnCoA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=W/YIjnoDJn9DZfacd5LPgniRpGXVFhZ9OYUQ2ivxpyHNYui3lN0BlVowyQ8/MiUh/ oQtZ+l2x7UFpadhXm0N6wahZ3r4vrjh4ra73GLhJONrfFth7SmrtjeVLZGT3BprSA3 i1fY6TwU+bAJ0uLZfI0r8Fa16vEspBWpKPOAHm2JY3yEE1VOrrNUJsRGfbHO8V0AYf MI1TtNhzVw+cangHJ1SoYH+HwYfcCu+j9byI8s/Vzzvf+R373m+rgHr4m8BXUiA64t uEhuwHiED8VUR2+lPnPg7NhZB2mKqkt+x8tVYt63BYus3L+vdhE80bHqa0t/bkQcGd BZPEy5XYqIc/w== 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 , Alexandre Courbot , Asahi Lina , Matthew Maurer , Lorenzo Stoakes , Joel Fernandes , Burak Emir , FUJITA Tomonori , Krishna Ketan Rai , Tamir Duberstein , =?UTF-8?q?Onur=20=C3=96zkan?= , Eliot Courtney , Mirko Adzic , Alistair Francis , 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 v3 1/4] rust: types: implement ForeignOwnable for ARef Date: Thu, 18 Jun 2026 15:26:24 +0200 Message-ID: <20260618132628.3811068-3-phasta@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260618132628.3811068-2-phasta@kernel.org> References: <20260618132628.3811068-2-phasta@kernel.org> Precedence: bulk X-Mailing-List: linux-media@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 --- rust/kernel/sync/aref.rs | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs index 9989f56d0605..82907383c44b 100644 --- a/rust/kernel/sync/aref.rs +++ b/rust/kernel/sync/aref.rs @@ -17,6 +17,10 @@ //! [`Arc`]: crate::sync::Arc //! [`Arc`]: crate::sync::Arc +use crate::{ + prelude::*, + types::ForeignOwnable, // +}; use core::{marker::PhantomData, mem::ManuallyDrop, ops::Deref, ptr::NonNull}; /// Types that are _always_ reference counted. @@ -183,6 +187,41 @@ 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