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charset=UTF-8 Date: Tue, 25 Nov 2025 23:46:16 +0900 Message-Id: To: "Alice Ryhl" , "Alexandre Courbot" Cc: "Zhi Wang" , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v7 3/6] rust: io: factor common I/O helpers into Io trait From: "Alexandre Courbot" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20251119112117.116979-1-zhiw@nvidia.com> <20251119112117.116979-4-zhiw@nvidia.com> In-Reply-To: X-ClientProxiedBy: TYCP286CA0244.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:456::19) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|BL1PR12MB5946:EE_ X-MS-Office365-Filtering-Correlation-Id: 3f7b3b2c-368e-449a-93ed-08de2c31653a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014|10070799003; 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>> >> + if let Some(end) =3D offset.checked_add(type_size) { >> >> + end <=3D size && offset % type_size =3D=3D 0 >> >> + } else { >> >> + false >> >> } >> >> +} >> >> + >> >> +/// Represents a region of I/O space of a fixed size. >> >> +/// >> >> +/// Provides common helpers for offset validation and address >> >> +/// calculation on top of a base address and maximum size. >> >> +/// >> >> +pub trait Io { >> >> + /// Minimum usable size of this region. >> >> + const MIN_SIZE: usize; >> > >> > This associated constant should probably be part of `IoInfallible` - >> > otherwise what value should it take if some type only implement >> > `IoFallible`? >> > >> >> >> >> /// Returns the base address of this mapping. >> >> - #[inline] >> >> - pub fn addr(&self) -> usize { >> >> - self.0.addr() >> >> - } >> >> + fn addr(&self) -> usize; >> >> >> >> /// Returns the maximum size of this mapping. >> >> - #[inline] >> >> - pub fn maxsize(&self) -> usize { >> >> - self.0.maxsize() >> >> - } >> >> - >> >> - #[inline] >> >> - const fn offset_valid(offset: usize, size: usize) -> bool { >> >> - let type_size =3D core::mem::size_of::(); >> >> - if let Some(end) =3D offset.checked_add(type_size) { >> >> - end <=3D size && offset % type_size =3D=3D 0 >> >> - } else { >> >> - false >> >> - } >> >> - } >> >> + fn maxsize(&self) -> usize; >> >> >> >> + /// Returns the absolute I/O address for a given `offset`, >> >> + /// performing runtime bound checks. >> >> #[inline] >> >> fn io_addr(&self, offset: usize) -> Result { >> >> - if !Self::offset_valid::(offset, self.maxsize()) { >> >> + if !offset_valid::(offset, self.maxsize()) { >> >> return Err(EINVAL); >> >> } >> > >> > Similarly I cannot find any context where `maxsize` and `io_addr` are >> > used outside of `IoFallible`, hinting that these should be part of thi= s >> > trait. >> > >> >> >> >> @@ -239,50 +240,190 @@ fn io_addr(&self, offset: usize) -> Result<= usize> { >> >> self.addr().checked_add(offset).ok_or(EINVAL) >> >> } >> >> >> >> + /// Returns the absolute I/O address for a given `offset`, >> >> + /// performing compile-time bound checks. >> >> #[inline] >> >> fn io_addr_assert(&self, offset: usize) -> usize { >> >> - build_assert!(Self::offset_valid::(offset, SIZE)); >> >> + build_assert!(offset_valid::(offset, Self::MIN_SIZE)); >> >> >> >> self.addr() + offset >> >> } >> > >> > ... and `io_addr_assert` is only used from `IoFallible`. >> > >> > So if my gut feeling is correct, we can disband `Io` entirely and only >> >> ... except that we can't due to `addr`, unless we find a better way to >> provide this base. But even if we need to keep `Io`, the compile-time >> and runtime members should be moved to their respective traits. > > If you have IoInfallible depend on IoFallible, then you can place > `addr` on IoFallible. Indeed. Maybe we could even make `IoInfallible` automatically implemented, since it just needs to `unwrap_unchecked` the fallible implementation if the range is valid. > (And I still think you should rename IoFallible to Io and IoInfallible > to IoKnownSize.) Agreed, there are other reasons for I/O to fail than a bad index so this should not be part of the name of these traits.