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charset=UTF-8 Date: Wed, 29 Jul 2026 23:09:32 +0900 Message-Id: Cc: "Boqun Feng" , "Gary Guo" , "Lyude Paul" , "Daniel Almeida" , =?utf-8?q?Onur_=C3=96zkan?= , "Greg Kroah-Hartman" , "Carlos Llamas" , "Luis Chamberlain" , "Petr Pavlu" , "Daniel Gomez" , "Sami Tolvanen" , "Aaron Tomlin" , "Miguel Ojeda" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , "Danilo Krummrich" , "Tamir Duberstein" , , , Subject: Re: [PATCH 1/3] rust: sync: return `Result<&T, T>` from `SetOnce::populate()` From: "Alexandre Courbot" To: "Alice Ryhl" References: <20260722-setonce-populate-v1-0-fa7455c26c42@google.com> <20260722-setonce-populate-v1-1-fa7455c26c42@google.com> In-Reply-To: <20260722-setonce-populate-v1-1-fa7455c26c42@google.com> X-ClientProxiedBy: TYCP286CA0063.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:31a::12) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|LV1PR12MB999305:EE_ X-MS-Office365-Filtering-Correlation-Id: 1e92edad-9228-4b79-e70d-08deed7b0522 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|10070799003|1800799024|366016|23010399003|22082099003|18002099003|11063799006|4143699003|56012099006|10067099003; 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By returning &T in this case, such > infallible access methods become possible. > > Additionally, when `populate()` fails, the provided value is dropped. > This has two disadvantages: > > 1. If the caller holds a lock, the value is dropped under said lock. > 2. If the caller wishes to use the same value for something else, they > can't, because it's lost. > > Changing the return value to Result<&T, T> handles all of these cases. > > Rust Binder is updated to avoid a warning about an unused Result. Does the GEM shmem module also need to be updated for the same reason?