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Wysocki" , "Miguel Ojeda" , "Boqun Feng" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , "Tamir Duberstein" , =?utf-8?q?Onur_=C3=96zkan?= , "Bjorn Helgaas" , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= , "Abdiel Janulgue" , "Robin Murphy" , "David Airlie" , "Simona Vetter" , "Michal Wilczynski" , =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= , "Danilo Krummrich" , , , , , , , Subject: Re: [PATCH v5 12/20] rust: io: move `Io` methods to extension trait From: "Gary Guo" To: "Alexandre Courbot" , "Gary Guo" X-Mailer: aerc 0.21.0 References: <20260626-io_projection-v5-0-d0961471ae50@garyguo.net> <20260626-io_projection-v5-12-d0961471ae50@garyguo.net> In-Reply-To: X-ClientProxiedBy: LO4P123CA0342.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:18c::23) To LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:488::16) Precedence: bulk X-Mailing-List: linux-pwm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LOVP265MB8871:EE_|LO2P265MB3038:EE_ X-MS-Office365-Filtering-Correlation-Id: 411b1d00-9edd-46fc-2978-08ded900a1a0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|10070799003|23010399003|366016|4143699003|3023799007|56012099006|22082099003|18002099003; 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Provided methods may want to rely on their implementations to n= ot >> be arbitrarily overridden by implementers for correctness or soundness. >> >> Thus, extract these methods to a new trait and provide a blanket >> implementation. This pattern is used extensively in userspace Rust >> libraries e.g. `tokio` where `AsyncRead` has minimum methods and >> `AsyncReadExt` is what users mostly interact with. >> >> To avoid changing all user imports, the base trait is renamed to `IoBase= ` >> and the newly added trait takes the existing `Io` name. >> >> A `size` method is added as an example of methods that users should not >> override. > > WDYM by "an example"? There are already all the I/O accessors that we > wish not to override; this looks more like a new method is just added. It wouldn't be incorrect if I/O accessors are overriden, it's just that we = don't anticipate these being overriden. On the other hand, `size` method can be e= asily relied upon by other methods (like patch 19 where you mentioned) and it can= lead to UB if it's overriden to something completely wrong. The `size` method is actually what motivated making this extension trait in the first place. Best, Gary > > Besides, it is not used until patch 19, so how about introducing it > there? > > <...> >> @@ -326,6 +323,21 @@ pub trait Io<'a>: Copy { >> =20 >> /// Return a view that covers the full region. >> fn as_view(self) -> ::View<'a, Self::Ta= rget>; >> +} >> + >> +/// Extension trait to provide I/O operation methods to types that impl= ement [`IoBase`]. >> +/// >> +/// This trait provides: >> +/// - Helper methods for offset validation and address calculation >> +/// - Fallible (runtime checked) accessors for different data widths >> +/// >> +/// Which I/O methods are available depends on the associated [`IoBacke= nd`] implementation. >> +pub trait Io<'a>: IoBase<'a> { >> + /// Returns the size of this I/O region. >> + #[inline] >> + fn size(self) -> usize { >> + KnownSize::size(Self::Backend::as_ptr(self.as_view())) > > nit: the documentation for `as_ptr` says that the pointer "should be > used for projection only". Technically we are not projecting here; maybe > the documentation should be updated to say the pointer must not be > dereferenced instead. > > In any case, > > Reviewed-by: Alexandre Courbot