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Message-ID: <8d38a00ffaad4fa33265dec7ae4191ed27c23a46.camel@redhat.com>
Date: Tue, 28 Oct 2025 18:02:20 -0400
From: Lyude Paul <lyude@...hat.com>
To: Filipe Xavier <felipeaggger@...il.com>, 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>
Cc: daniel.almeida@...labora.com, rust-for-linux@...r.kernel.org,
felipe_life@...e.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] rust: add new macro for common bitmap operations
This is almost perfect, there's one small thing we need to fix that I totally
forgot about: we're missing documentation for the impl_flags module itself, as
compilation complains about this when we run kunit. I don't think this needs
to be very verbose though since we've already got plenty of docs on impl_flags
itself. Something like "Macros for generating boilerplate for bitmask types."
would be good.
Also, some small docs fixes below:
On Sun, 2025-10-26 at 09:16 -0300, Filipe Xavier 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 upcoming GPU drivers.
>
> 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 v4:
> - Use enum: changed flag type from struct to enum.
> - Minor fix: airect casting (flag as $ty) instead of field access (.0).
> - Link to v3: https://lore.kernel.org/r/20250411-feat-add-bitmask-macro-v3-1-187bd3e4a03e@gmail.com
>
> Changes in v3:
> - New Feat: added support to declare flags inside macro use.
> - Minor fixes: used absolute paths to refer to items, fix rustdoc and fix example cases.
> - Link to v2: https://lore.kernel.org/r/20250325-feat-add-bitmask-macro-v2-1-d3beabdad90f@gmail.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 | 227 ++++++++++++++++++++++++++++++++++++++++++++++
> rust/kernel/lib.rs | 1 +
> rust/kernel/prelude.rs | 1 +
> 3 files changed, 229 insertions(+)
>
> diff --git a/rust/kernel/impl_flags.rs b/rust/kernel/impl_flags.rs
> new file mode 100644
> index 0000000000000000000000000000000000000000..15c8fc82e76254f927b7487379d8f0a2776a4010
> --- /dev/null
> +++ b/rust/kernel/impl_flags.rs
> @@ -0,0 +1,227 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/// Declares a impl_flags type with its corresponding flag type.
We probably want to be a bit more specific then "impl_flags type", maybe
"Common helper for declaring bitflag and bitmask types"
> +///
> +/// This macro generates:
> +/// - Implementations of common bitmap op. ([`::core::ops::BitOr`], [`::core::ops::BitAnd`], etc.).
> +/// - Utility methods such as `.contains()` to check flags.
We might want to expand on this a little bit:
This macro handles:
- A struct representing a bitmask, and an enumerator representing bitflags
which may be used in the aforementioned bitmask.
- Implementations of common bitmap ops…
etc.
Happy to give a r-b once this is fixed btw!
> +///
> +/// # Examples
> +///
> +/// Defining and using impl_flags:
> +///
> +/// ```
> +/// use kernel::impl_flags;
> +///
> +/// impl_flags!(
> +/// /// Represents multiple permissions.
> +/// #[derive(Debug, Clone, Default, Copy, PartialEq, Eq)]
> +/// pub struct Permissions(u32);
> +/// /// Represents a single permission.
> +/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
> +/// pub enum Permission {
> +/// Read = 1 << 0,
> +/// Write = 1 << 1,
> +/// Execute = 1 << 2,
> +/// }
> +/// );
> +///
> +/// // Combine multiple permissions using operation OR (`|`).
> +/// let read_write: Permissions = Permission::Read | Permission::Write;
> +///
> +/// assert!(read_write.contains(Permission::Read));
> +/// assert!(read_write.contains(Permission::Write));
> +/// assert!(!read_write.contains(Permission::Execute));
> +///
> +/// // Removing a permission with operation AND (`&`).
> +/// let read_only: Permissions = read_write & Permission::Read;
> +/// assert!(read_only.contains(Permission::Read));
> +/// assert!(!read_only.contains(Permission::Write));
> +///
> +/// // Toggling permissions with XOR (`^`).
> +/// let toggled: Permissions = read_only ^ Permission::Read;
> +/// assert!(!toggled.contains(Permission::Read));
> +///
> +/// // Inverting permissions with negation (`!`).
> +/// let negated = !read_only;
> +/// assert!(negated.contains(Permission::Write));
> +/// ```
> +#[macro_export]
> +macro_rules! impl_flags {
> + (
> + $(#[$outer_flags:meta])*
> + $vis_flags:vis struct $flags:ident($ty:ty);
> +
> + $(#[$outer_flag:meta])*
> + $vis_flag:vis enum $flag:ident {
> + $(
> + $(#[$inner_flag:meta])*
> + $name:ident = $value:expr
> + ),+ $( , )?
> + }
> + ) => {
> + $(#[$outer_flags])*
> + #[repr(transparent)]
> + $vis_flags struct $flags($ty);
> +
> + $(#[$outer_flag])*
> + #[repr($ty)]
> + $vis_flag enum $flag {
> + $(
> + $(#[$inner_flag])*
> + $name = $value
> + ),+
> + }
> +
> + impl ::core::convert::From<$flag> for $flags {
> + #[inline]
> + fn from(value: $flag) -> Self {
> + Self(value as $ty)
> + }
> + }
> +
> + impl ::core::convert::From<$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 as $ty | rhs as $ty)
> + }
> + }
> +
> + impl ::core::ops::BitAnd for $flag {
> + type Output = $flags;
> + #[inline]
> + fn bitand(self, rhs: Self) -> Self::Output {
> + $flags(self as $ty & rhs as $ty)
> + }
> + }
> +
> + impl ::core::ops::BitXor for $flag {
> + type Output = $flags;
> + #[inline]
> + fn bitxor(self, rhs: Self) -> Self::Output {
> + $flags(self as $ty ^ rhs as $ty)
> + }
> + }
> +
> + impl ::core::ops::Not for $flag {
> + type Output = $flags;
> + #[inline]
> + fn not(self) -> Self::Output {
> + $flags(!(self as $ty))
> + }
> + }
> +
> + impl ::core::ops::BitXor<$flag> for $flags {
> + type Output = Self;
> + #[inline]
> + fn bitxor(self, rhs: $flag) -> Self::Output {
> + self ^ Self::from(rhs)
> + }
> + }
> +
> + 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 as $ty) == flag as $ty
> + }
> + }
> + };
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 28007be98fbad0e875d7e5345e164e2af2c5da32..a315607629c321db377343ca678c9845ae69bb14 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -67,6 +67,7 @@
> #[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 baa774a351ceeb995a2a647f78a27b408d9f3834..085f23502544c80c2202eacd18ba190186a74f30 100644
> --- a/rust/kernel/prelude.rs
> +++ b/rust/kernel/prelude.rs
> @@ -27,6 +27,7 @@
> #[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: edc5e6e019c99b529b3d1f2801d5cce9924ae79b
> change-id: 20250304-feat-add-bitmask-macro-6424b1c317e2
>
> Best regards,
--
Cheers,
Lyude Paul (she/her)
Senior Software Engineer at Red Hat
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