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Message-Id: <3A86CF7A-C504-4870-A9DE-C44C1751F4E4@collabora.com>
Date: Tue, 25 Mar 2025 10:54:35 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Filipe Xavier <felipeaggger@...il.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...nel.org>,
Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>,
Danilo Krummrich <dakr@...nel.org>,
rust-for-linux@...r.kernel.org,
felipe_life@...e.com,
linux-kernel@...r.kernel.org,
Lyude Paul <lyude@...hat.com>
Subject: Re: [PATCH v2] rust: add new macro for common bitmap operations
Hi Filipe, just a few comments for now:
> On 25 Mar 2025, at 10:10, Filipe Xavier <felipeaggger@...il.com> wrote:
>
> We have seen a proliferation of mod_whatever::foo::Flags
> being defined with essentially the same implementation
> for BitAnd, BitOr, contains and etc.
>
> This macro aims to bring a solution for this,
> allowing to generate these methods for user-defined structs.
> With some use cases in KMS and VideoCodecs.
There is no one working on Rust support for video codecs as of today, please say
“upcoming GPU drivers” instead.
>
> Small use sample:
> `
> const READ: Permission = Permission(1 << 0);
> const WRITE: Permission = Permission(1 << 1);
>
> impl_flags!(Permissions, Permission, u32);
>
> let read_write = Permissions::from(READ) | WRITE;
> let read_only = read_write & READ;
> `
>
Not really sure we need this in the commit message as we already have
the examples section, which doubles as a kunit test.
At best, this will become stale and a source of errors.
> Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/We.20really.20need.20a.20common.20.60Flags.60.20type
> Signed-off-by: Filipe Xavier <felipeaggger@...il.com>
> Suggested-by: Daniel Almeida <daniel.almeida@...labora.com>
> Suggested-by: Lyude Paul <lyude@...hat.com>
> ---
> Changes in v2:
> - rename: change macro and file name to impl_flags.
> - negation sign: change char for negation to `!`.
> - transpose docs: add support to transpose user provided docs.
> - visibility: add support to use user defined visibility.
> - operations: add new operations for flag,
> to support use between bit and bitmap, eg: flag & flags.
> - code style: small fixes to remove warnings.
> - Link to v1: https://lore.kernel.org/r/20250304-feat-add-bitmask-macro-v1-1-1c2d2bcb476b@gmail.com
> ---
> rust/kernel/impl_flags.rs | 214 ++++++++++++++++++++++++++++++++++++++++++++++
> rust/kernel/lib.rs | 1 +
> rust/kernel/prelude.rs | 1 +
> 3 files changed, 216 insertions(+)
>
> diff --git a/rust/kernel/impl_flags.rs b/rust/kernel/impl_flags.rs
> new file mode 100644
> index 0000000000000000000000000000000000000000..e7cf00e14bdcd2acea47b8c158a984ac0206568b
> --- /dev/null
> +++ b/rust/kernel/impl_flags.rs
> @@ -0,0 +1,214 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! impl_flags utilities for working with flags.
> +
> +/// Declares a impl_flags type with its corresponding flag type.
> +///
> +/// This macro generates:
> +/// - Implementations of common bitmask operations ([`BitOr`], [`BitAnd`], etc.).
> +/// - Utility methods such as `.contains()` to check flags.
> +///
> +/// # Examples
> +///
> +/// Defining and using impl_flags:
> +///
> +/// ```
> +/// impl_flags!(
> +/// /// Represents multiple permissions.
> +/// pub Permissions,
> +/// /// Represents a single permission.
> +/// pub Permission,
> +/// u32
> +/// );
> +///
> +/// // Define some individual permissions.
> +/// const READ: Permission = Permission(1 << 0);
> +/// const WRITE: Permission = Permission(1 << 1);
> +/// const EXECUTE: Permission = Permission(1 << 2);
> +///
> +/// // Combine multiple permissions using operation OR (`|`).
> +/// let read_write = Permissions::from(READ) | WRITE;
We need to move away from this syntax. Can you please update the example? :)
> +///
> +/// assert!(read_write.contains(READ));
> +/// assert!(read_write.contains(WRITE));
> +/// assert!(!read_write.contains(EXECUTE));
> +///
> +/// // Removing a permission with operation AND (`&`).
> +/// let read_only = read_write & READ;
> +/// assert!(read_only.contains(READ));
> +/// assert!(!read_only.contains(WRITE));
> +///
> +/// // Toggling permissions with XOR (`^`).
> +/// let toggled = read_only ^ Permissions::from(READ);
> +/// assert!(!toggled.contains(READ));
> +///
> +/// // Inverting permissions with negation (`!`).
> +/// let negated = !read_only;
> +/// assert!(negated.contains(WRITE));
> +/// ```
> +#[macro_export]
> +macro_rules! impl_flags {
> + (
> + $(#[$outer_flags:meta])* $vis_flags:vis $flags:ident,
> + $(#[$outer_flag:meta])* $vis_flag:vis $flag:ident,
> + $ty:ty
> + ) => {
> + $(#[$outer_flags])*
> + #[repr(transparent)]
> + #[derive(Copy, Clone, Default, PartialEq, Eq)]
> + $vis_flags struct $flags($ty);
> +
> + $(#[$outer_flag])*
> + #[derive(Copy, Clone, PartialEq, Eq)]
> + $vis_flag struct $flag($ty);
> +
> + impl From<$flag> for $flags {
> + #[inline]
> + fn from(value: $flag) -> Self {
> + Self(value.0)
> + }
> + }
> +
> + impl From<$flags> for $ty {
> + #[inline]
> + fn from(value: $flags) -> Self {
> + value.0
> + }
> + }
> +
> + impl core::ops::BitOr for $flags {
> + type Output = Self;
> +
> + #[inline]
> + fn bitor(self, rhs: Self) -> Self::Output {
> + Self(self.0 | rhs.0)
> + }
> + }
> +
> + impl core::ops::BitOrAssign for $flags {
> + #[inline]
> + fn bitor_assign(&mut self, rhs: Self) {
> + *self = *self | rhs;
> + }
> + }
> +
> + impl core::ops::BitAnd for $flags {
> + type Output = Self;
> +
> + #[inline]
> + fn bitand(self, rhs: Self) -> Self::Output {
> + Self(self.0 & rhs.0)
> + }
> + }
> +
> + impl core::ops::BitAndAssign for $flags {
> + #[inline]
> + fn bitand_assign(&mut self, rhs: Self) {
> + *self = *self & rhs;
> + }
> + }
> +
> + impl core::ops::BitOr<$flag> for $flags {
> + type Output = Self;
> +
> + #[inline]
> + fn bitor(self, rhs: $flag) -> Self::Output {
> + self | Self::from(rhs)
> + }
> + }
> +
> + impl core::ops::BitOrAssign<$flag> for $flags {
> + #[inline]
> + fn bitor_assign(&mut self, rhs: $flag) {
> + *self = *self | rhs;
> + }
> + }
> +
> + impl core::ops::BitAnd<$flag> for $flags {
> + type Output = Self;
> +
> + #[inline]
> + fn bitand(self, rhs: $flag) -> Self::Output {
> + self & Self::from(rhs)
> + }
> + }
> +
> + impl core::ops::BitAndAssign<$flag> for $flags {
> + #[inline]
> + fn bitand_assign(&mut self, rhs: $flag) {
> + *self = *self & rhs;
> + }
> + }
> +
> + impl core::ops::BitXor for $flags {
> + type Output = Self;
> +
> + #[inline]
> + fn bitxor(self, rhs: Self) -> Self::Output {
> + Self(self.0 ^ rhs.0)
> + }
> + }
> +
> + impl core::ops::BitXorAssign for $flags {
> + #[inline]
> + fn bitxor_assign(&mut self, rhs: Self) {
> + *self = *self ^ rhs;
> + }
> + }
> +
> + impl core::ops::Not for $flags {
> + type Output = Self;
> +
> + #[inline]
> + fn not(self) -> Self::Output {
> + Self(!self.0)
> + }
> + }
> +
> + impl core::ops::BitOr for $flag {
> + type Output = $flags;
> + #[inline]
> + fn bitor(self, rhs: Self) -> Self::Output {
> + $flags(self.0 | rhs.0)
> + }
> + }
I see that you’ve already taken care of writing the code to make it work, so it’s just the
example that needs to be updated.
> +
> + impl core::ops::BitAnd for $flag {
> + type Output = $flags;
> + #[inline]
> + fn bitand(self, rhs: Self) -> Self::Output {
> + $flags(self.0 & rhs.0)
> + }
> + }
> +
> + impl core::ops::BitXor for $flag {
> + type Output = $flags;
> + #[inline]
> + fn bitxor(self, rhs: Self) -> Self::Output {
> + $flags(self.0 ^ rhs.0)
> + }
> + }
> +
> + impl core::ops::Not for $flag {
> + type Output = $flags;
> + #[inline]
> + fn not(self) -> Self::Output {
> + $flags(!self.0)
> + }
> + }
> +
> + impl $flags {
> + /// Returns an empty instance of `type` where no flags are set.
> + #[inline]
> + pub const fn empty() -> Self {
> + Self(0)
> + }
> +
> + /// Checks if a specific flag is set.
> + #[inline]
> + pub fn contains(self, flag: $flag) -> bool {
> + (self.0 & flag.0) == flag.0
> + }
> + }
> + };
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 496ed32b0911a9fdbce5d26738b9cf7ef910b269..7653485a456ae5aa51becbf04153ea54a7067d9e 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -49,6 +49,7 @@
> #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
> pub mod firmware;
> pub mod fs;
> +pub mod impl_flags;
> pub mod init;
> pub mod io;
> pub mod ioctl;
> diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
> index dde2e0649790ca24e6c347b29465ea0a1c3e503b..0f691dd2df71d821265fae01555ba50e6a76f372 100644
> --- a/rust/kernel/prelude.rs
> +++ b/rust/kernel/prelude.rs
> @@ -25,6 +25,7 @@
> #[doc(no_inline)]
> pub use super::dbg;
> pub use super::fmt;
> +pub use super::impl_flags;
> pub use super::{dev_alert, dev_crit, dev_dbg, dev_emerg, dev_err, dev_info, dev_notice, dev_warn};
> pub use super::{pr_alert, pr_crit, pr_debug, pr_emerg, pr_err, pr_info, pr_notice, pr_warn};
>
>
> ---
> base-commit: beeb78d46249cab8b2b8359a2ce8fa5376b5ad2d
> change-id: 20250304-feat-add-bitmask-macro-6424b1c317e2
>
> Best regards,
> --
> Filipe Xavier <felipeaggger@...il.com>
>
Give me a couple of days and I’ll test this.
— Daniel
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