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charset=UTF-8 Date: Wed, 24 Jun 2026 23:49:19 +0900 Message-Id: Cc: , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v3 5/7] rust: devres: add DevresLt for ForLt-aware device resource access From: "Alexandre Courbot" To: "Danilo Krummrich" References: <20260618230834.812007-1-dakr@kernel.org> <20260618230834.812007-6-dakr@kernel.org> In-Reply-To: <20260618230834.812007-6-dakr@kernel.org> X-ClientProxiedBy: TYCP286CA0106.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:29c::13) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: driver-core@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|SJ2PR12MB8941:EE_ X-MS-Office365-Filtering-Correlation-Id: df1c4e4b-ec1a-45bf-9df9-08ded1ffc774 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|376014|7416014|366016|10070799003|6133799003|18002099003|22082099003|56012099006|4143699003|11063799006; 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For > lifetime-parameterized types like Bar<'a, SIZE> that are transmuted to > 'static for storage, this exposes the synthetic 'static lifetime to > callers -- any method on the stored type that returns a reference with > its lifetime parameter would yield a &'static reference, which is > unsound. > > Add DevresLt, a thin wrapper around Devres> > that shortens the stored 'static lifetime to the caller's borrow > lifetime in all access methods. > > DevresLt::new() is unsafe because the caller must guarantee that the > data remains valid for the device's full bound scope; the internal > transmute from F::Of<'a> to F::Of<'static> would otherwise allow > use-after-free. > > Two access patterns are provided: > > - CovariantForLt types get direct-reference accessors (access, > try_access) that return shortened references via > CovariantForLt::cast_ref. > > - Plain ForLt types use closure-based accessors (access_with, > try_access_with) whose universally quantified lifetime prevents > callers from smuggling in concrete short-lived references. > > Signed-off-by: Danilo Krummrich Reviewed-by: Alexandre Courbot