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McKenney" , "Frederic Weisbecker" , "Neeraj Upadhyay" , "Joel Fernandes" , "Josh Triplett" , "Uladzislau Rezki" , "Steven Rostedt" , "Mathieu Desnoyers" , "Lai Jiangshan" , "Zqiang" , "Daniel Almeida" , "Greg Kroah-Hartman" , "Igor Korotin" , "Lorenzo Stoakes" , "Alexandre Courbot" , "FUJITA Tomonori" , "Krishna Ketan Rai" , "Shankari Anand" , , "Boris Brezillon" , , , , , Subject: Re: [PATCH v2 5/6] rust: Add dma_fence abstractions From: "Gary Guo" To: , =?utf-8?q?Onur_=C3=96zkan?= X-Mailer: aerc 0.21.0 References: <20260616082819.2943886-2-phasta@kernel.org> <20260616082819.2943886-7-phasta@kernel.org> <20260616124755.460550-1-work@onurozkan.dev> In-Reply-To: X-ClientProxiedBy: LO3P123CA0033.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:388::11) To LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:488::16) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LOVP265MB8871:EE_|LO0P265MB6470:EE_ X-MS-Office365-Filtering-Correlation-Id: ec41858d-de02-424a-04e5-08decbbd22b5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|23010399003|376014|10070799003|1800799024|56012099006|4143699003|22082099003|18002099003; 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>>=20 >> Either the field ordering on the type or this code is wrong because the = first >> member of DriverFenceData is `rcu_head`. > > Yeah, that's a bug introduced in this revision. Thx for pointing it > out. Already fixed it downstream. > > I'm just wondering why my test did not blow up. > >> >=20 >> > +} >>=20 >> I am unsure whether it is safe to cast the pointer in Fence::from_raw wi= thout >> Fence being #[repr(transparent)] as the layout compatibility is not guar= anteed >> explicitly. > > Shouldn't #[repr(C)] do that trick, too? Do you need both? > > Who can answer that? You have `#[repr(C)]` for DriverFence, but not on `Fence`. `Fence::from_raw= ` does require layout equivalence between `Fence` and `bindings::dma_fence` a= nd this is done by adding `#[repr(transparent)]` on `Fence`. Best, Gary