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charset=UTF-8 Date: Mon, 29 Jun 2026 16:17:35 +0900 Message-Id: Cc: , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Danilo Krummrich" , "Daniel Almeida" , "Tamir Duberstein" , =?utf-8?q?Onur_=C3=96zkan?= , "David Airlie" , "Simona Vetter" , , , , Subject: Re: [PATCH RFC 0/4] rust: dma: bridge zerocopy-derived types into the transmute byte-safety bound From: "Alexandre Courbot" To: "SeungJong Ha via B4 Relay" References: <20260628-dma-zerocopy-bridge-v1-0-9a2895ebe30d@gmail.com> In-Reply-To: <20260628-dma-zerocopy-bridge-v1-0-9a2895ebe30d@gmail.com> X-ClientProxiedBy: TY4P301CA0111.JPNP301.PROD.OUTLOOK.COM (2603:1096:405:37b::10) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: nova-gpu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|BL4PR12MB9533:EE_ X-MS-Office365-Filtering-Correlation-Id: 9de2e158-953a-409d-ae2c-08ded5ae80b2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|10070799003|376014|7416014|1800799024|366016|6133799003|56012099006|11063799006|22082099003|18002099003; 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This RFC > lets a type satisfy that bound by deriving zerocopy's byte-safety traits > instead of a hand-written unsafe impl. > > The bound cannot be switched to zerocopy wholesale (some DMA structs are > unions that IntoBytes cannot derive), and a blanket bridge impl is > rejected by coherence. So the series bridges the two per type: > > 1. add the bridge macro impl_transmute_via_zerocopy!, which emits the > transmute impls only for a zerocopy-derived type. > 2. re-export zerocopy::Immutable from the prelude. > 3-4. worked example: convert nova-core's GspMem and msgq POD types. Can you give more details about what the macro is for? My understanding is that it is a temporary fix for the generated bindings; if so, I'd prefer to apply a definitive solution (like using `#[derive(zerocopy_derive::most_traits)]`, or updating the bindings generator tool) rather than something that will be removed later. I also notice that the macro is in the Rust `transmute` module, but the only user is Nova; so it should have been either be Nova-local, or used by other Rust modules. But intuitively I'd say that we can (and should) probably do without this intermediate step. But please let me know if there is something I missed.