[PATCH v5] rust: add new macro for common bitmap operations

[Filipe Xavier <felipeaggger@gmail.com>]

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@gmail.com>
Suggested-by: Daniel Almeida <daniel.almeida@collabora.com>
Suggested-by: Lyude Paul <lyude@redhat.com>
---
Changes in v5:
- Docs: improve macro documentation.
- Link to v4: https://lore.kernel.org/r/20251026-feat-add-bitmask-macro-v4-1-e1b59b4762bc@gmail.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 | 229 ++++++++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs        |   2 +
 rust/kernel/prelude.rs    |   1 +
 3 files changed, 232 insertions(+)

diff --git a/rust/kernel/impl_flags.rs b/rust/kernel/impl_flags.rs
new file mode 100644
index 0000000000000000000000000000000000000000..c1086677678408f46c4832e2110c761fab017055
--- /dev/null
+++ b/rust/kernel/impl_flags.rs
@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/// Common helper for declaring bitflag and bitmask types.
+///
+/// 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 op. ([`::core::ops::BitOr`], [`::core::ops::BitAnd`], etc.).
+/// - Utility methods such as `.contains()` to check flags.
+///
+/// # 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..57b789315deda3d2fa8961af79cad4462fff7fa8 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -67,6 +67,8 @@
 #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
 pub mod firmware;
 pub mod fs;
+#[doc(hidden)]
+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,
-- 
Filipe Xavier <felipeaggger@gmail.com>