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charset=UTF-8 Date: Fri, 24 Jul 2026 10:19:53 +0900 Message-Id: Cc: , "Danilo Krummrich" , "Abdiel Janulgue" , "Daniel Almeida" , "Robin Murphy" , "Andreas Hindborg" , "Miguel Ojeda" , "Boqun Feng" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Alice Ryhl" , "Trevor Gross" , "Tamir Duberstein" , =?utf-8?q?Onur_=C3=96zkan?= , "Timur Tabi" , , , Subject: Re: [PATCH] rust: dma: return zero for Coherent reads past EOF From: "Alexandre Courbot" To: "Gary Guo" References: <20260720-fix-dma-coherent-eof-v1-1-d92685db8da6@younes.io> In-Reply-To: X-ClientProxiedBy: TYCP286CA0110.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:29c::17) 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: MN2PR12MB3997:EE_|PH0PR12MB7815:EE_ X-MS-Office365-Filtering-Correlation-Id: 7f8ff116-c58f-46fa-29ee-08dee921ac76 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|366016|23010399003|376014|7416014|1800799024|22082099003|18002099003|10067099003|56012099006|4143699003|11063799006|5023799004|6133799003; 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The latter rejects offsets beyond the >>>> allocation even when the copy length is zero, so a debugfs read past E= OF >>>> returns -ERANGE. >>>> >>>> Return before calling write_dma() when the offset is at or beyond the >>>> allocation, matching simple_read_from_buffer() EOF semantics. >>>> >>>> Fixes: 016818513936 ("rust: dma: implement BinaryWriter for Coherent<[= u8]>") >>>> Signed-off-by: Younes Akhouayri >>>> --- >>>> rust/kernel/dma.rs | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs >>>> index 200def84fb69..36b72fb9ab46 100644 >>>> --- a/rust/kernel/dma.rs >>>> +++ b/rust/kernel/dma.rs >>>> @@ -1005,6 +1005,10 @@ fn write_to_slice( >>>> return Ok(0); >>>> }; >>>> =20 >>>> + if offset_val >=3D self.size() { >>>> + return Ok(0); >>>> + } >>>> + >>>> let count =3D self.size().saturating_sub(offset_val).min(writ= er.len()); >>> >>> This saturating_sub is redundant now and should just use -. >> >> Or even better, you could use `checked_sub` to perform the test and the >> subtraction in one go, while avoiding potentially panicking operands. > > I think the code is clearer with separate EOF check length calc. This als= o needs > to return `Ok` so it's not like that you can use `?`. Is it clearer? The `checked_sub` is efficient and makes it clear the code won't panic. And `ok_or` takes care of converting to the right error nicely.