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Wysocki" , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: [PATCH v6 06/13] rust: uaccess: add UserSliceWriter::write_truncated() Date: Wed, 9 Sep 2026 16:44:59 +1000 Message-ID: <20260909064506.910162-7-apopple@nvidia.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260909064506.910162-1-apopple@nvidia.com> References: <20260909064506.910162-1-apopple@nvidia.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: SY8P282CA0021.AUSP282.PROD.OUTLOOK.COM (2603:10c6:10:29b::34) To MN0PR12MB5977.namprd12.prod.outlook.com (2603:10b6:208:37c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN0PR12MB5977:EE_|IA0PR12MB7697:EE_ X-MS-Office365-Filtering-Correlation-Id: ed2ba593-4d80-4b47-a2bc-08df0e3dfa92 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; ARA:13230040|366016|7416014|23010399003|376014|1800799024|56012099006|10067099003|11063799006|6133799003|22082099003|18002099003; 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This avoids requiring callers of versioned UAPIs to convert values to byte slices and truncate them manually. Signed-off-by: Alistair Popple Suggested-by: Danilo Krummrich --- rust/kernel/uaccess.rs | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs index 5f6c4d7a1a51..c63b91942631 100644 --- a/rust/kernel/uaccess.rs +++ b/rust/kernel/uaccess.rs @@ -624,6 +624,20 @@ pub fn write(&mut self, value: &T) -> Result { self.length -= len; Ok(()) } + + /// Writes as much of the provided value as fits in the remaining buffer. + /// + /// Copies `min(size_of::(), self.len())` bytes to userspace. Returns the number of bytes + /// actually written. This is useful for versioned structs where an older userspace may provide + /// a smaller buffer than the current kernel struct. + /// + /// Fails with [`EFAULT`] if the write happens on a bad address. This call may modify the + /// associated userspace slice even if it returns an error. + pub fn write_truncated(&mut self, value: &T) -> Result { + let len = self.length.min(size_of::()); + self.write_slice(&value.as_bytes()[..len])?; + Ok(len) + } } /// Reads a nul-terminated string into `dst` and returns the length. -- 2.54.0