[PATCH v15 0/7] rust: extend `module!` macro with integer parameter support

[PATCH v15 0/7] rust: extend `module!` macro with integer parameter support

[Andreas Hindborg]

Extend the `module!` macro with support module parameters. Also add some string
to integer parsing functions and updates `BStr` with a method to strip a string
prefix.

Based on code by Adam Bratschi-Kaye lifted from the original `rust` branch [1].

Link: https://github.com/Rust-for-Linux/linux/tree/bc22545f38d74473cfef3e9fd65432733435b79f [1]
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
Changes in v15:
- Rebase on v6.16-rc5.
- Dedent code in module macro for better formatting.
- Rename `OnceLock` to `SetOnce`.
- Use "being initialized" rather than "being mutably accessed" when
  describing initialization state of `OnceLock`.
- Use `Relaxed` ordering when transitioning to exclusive access in
  `OnceLock`.
- Add drop implementation for `OnceLock`.
- Re-export `OnceLock` from `kernel::sync` module.
- Improve indentation of in macro code. Prefix `cfg` to `::core::cfg` in
  macro code.
- Use `core::ptr::from_ref` rather than `as` casts.
- Hide `KernelParam` instances behind `const _: ()` blocks.
- Rename `ModuleParamAccess::get` to `ModuleParamAccess::value`.
- Rename `RacyKernelParam` to `KernelParam`.
- Remove `ModuleParam::Value`.
- Move `copy` implementation of `OnceLock`.
- Update safety comments and invariants of `OnceLock`.
- Link to v14: https://lore.kernel.org/r/20250702-module-params-v3-v14-0-5b1cc32311af@kernel.org

Note: This series now depends on the atomics series [1].

[1] https://lore.kernel.org/all/20250618164934.19817-1-boqun.feng@gmail.com

Changes in v14:
- Remove unnecessary `crate::` prefix from `module_param::set_param`.
- Make `FromStrRadix` safe again by moving unsafe blocks to macro implementation (thanks Benno).
- Use `core::ptr::write` in `set_param` and drop safety requirement regarding initialization.
- Add a TODO to use `SyncUnsafeCell` for `ModuleParamAccess` when available.
- Add a NOTE regarding `Copy` bound on `ModuleParam`.
- Remove `'static` lifetime qualifier from `ModuleParam::try_from_param_arg` argument.
- Fix a typo in the safety requirements for `set_param`.
- Remove unused `#[macro_export]` attribute.
- Remove obsolete documentation for `ModuleParam::try_from_param_arg`.
- Make `RacyKernelParam` tuple field private.
- Introduce `OnceLock` and use that to synchronize population of parameter values.
- Link to v13: https://lore.kernel.org/r/20250612-module-params-v3-v13-0-bc219cd1a3f8@kernel.org

Changes in v13:
- remove absolute path for `ffi` types.
- Split patch 2 into 4 separate patches.
- Overhaul safety framework for `set_param`.
- Remove generated docs for `kernel_param_ops`.
- Move `parse_int` to separate file.
- Rebase on v6.16-rc1
- Link to v12: https://lore.kernel.org/r/20250506-module-params-v3-v12-0-c04d80c8a2b1@kernel.org

Changes in v12:
- Assign through pointer rather than using `core::ptr::replace`.
- Prevent a potential use-after-free during module teardown.
- Link to v11: https://lore.kernel.org/r/20250502-module-params-v3-v11-0-6096875a2b78@kernel.org

Changes in v11:
- Apply a few nits from Miguel.
- Link to v10: https://lore.kernel.org/r/20250501-module-params-v3-v10-0-4da485d343d5@kernel.org

Changes in v10:
- Apply fixups from Miguel:
  - Add integer type suffixes to `assert!` in tests.
  - Fix links to docs.kernel.org.
  - Applyy markdown and intra-doc links where possible.
  - Change to `///` for `mod` docs.
  - Slightly reword a comment.
  - Pluralize "Examples" section name.
  - Hide `use`s in example.
  - Removed `#[expect]` for the `rusttest` target.
- Link to v9: https://lore.kernel.org/r/20250321-module-params-v3-v9-0-28b905f2e345@kernel.org

Changes in v9:
- Remove UB when parsing the minimum integer values.
- Make `FromStr` trait unsafe, since wrong implementations can cause UB.
- Drop patches that were applied to rust-next.
- Link to v8: https://lore.kernel.org/r/20250227-module-params-v3-v8-0-ceeee85d9347@kernel.org

Changes in v8:
- Change print statement in sample to better communicate parameter name.
- Use imperative mode in commit messages.
- Remove prefix path from `EINVAL`.
- Change `try_from_param_arg` to accept `&BStr` rather than `&[u8]`.
- Parse integers without 128 bit integer types.
- Seal trait `FromStrRadix`.
- Strengthen safety requirement of `set_param`.
- Remove comment about Display and `PAGE_SIZE`.
- Add note describing why `ModuleParamAccess` is pub.
- Typo and grammar fixes for documentation.
- Update MAINTAINERS with rust module files.
- Link to v7: https://lore.kernel.org/r/20250218-module-params-v3-v7-0-5e1afabcac1b@kernel.org

Changes in v7:
- Remove dependency on `pr_warn_once` patches, replace with TODO.
- Rework `ParseInt::from_str` to avoid allocating.
- Add a comment explaining how we parse "0".
- Change trait bound on `Index` impl for `BStr` to match std library approach.
- Link to v6: https://lore.kernel.org/r/20250211-module-params-v3-v6-0-24b297ddc43d@kernel.org

Changes in v6:
- Fix a bug that prevented parsing of negative default values for
  parameters in the `module!` macro.
- Fix a bug that prevented parsing zero in `strip_radix`. Also add a
  test case for this.
- Add `AsRef<BStr>` for `[u8]` and `BStr`.
- Use `impl AsRef<BStr>` as type of prefix in `BStr::strip_prefix`.
- Link to v5: https://lore.kernel.org/r/20250204-module-params-v3-v5-0-bf5ec2041625@kernel.org

Changes in v5:
- Fix a typo in a safety comment in `set_param`.
- Use a match statement in `parse_int::strip_radix`.
- Add an implementation of `Index` for `BStr`.
- Fix a logic inversion bug where parameters would not be parsed.
- Use `kernel::ffi::c_char` in `set_param` rather than the one in `core`.
- Use `kernel::c_str!` rather than `c"..."` literal in module macro.
- Rebase on v6.14-rc1.
- Link to v4: https://lore.kernel.org/r/20250109-module-params-v3-v4-0-c208bcfbe11f@kernel.org

Changes in v4:
- Add module maintainers to Cc list (sorry)
- Add a few missing [`doc_links`]
- Add panic section to `expect_string_field`
- Fix a typo in safety requirement of `module_params::free`
- Change `assert!` to `pr_warn_once!` in `module_params::set_param`
- Remove `module_params::get_param` and install null pointer instead
- Remove use of the unstable feature `sync_unsafe_cell`
- Link to v3: https://lore.kernel.org/r/20241213-module-params-v3-v3-0-485a015ac2cf@kernel.org

Changes in v3:
- use `SyncUnsafeCell` rather than `static mut` and simplify parameter access
- remove `Display` bound from `ModuleParam`
- automatically generate documentation for `PARAM_OPS_.*`
- remove `as *const _ as *mut_` phrasing
- inline parameter name in struct instantiation in  `emit_params`
- move `RacyKernelParam` out of macro template
- use C string literals rather than byte string literals with explicit null
- template out `__{name}_{param_name}` in `emit_param`
- indent template in `emit_params`
- use let-else expression in `emit_params` to get rid of an indentation level
- document `expect_string_field`
- move invication of `impl_int_module_param` to be closer to macro def
- move attributes after docs in `make_param_ops`
- rename `impl_module_param` to impl_int_module_param`
- use `ty` instead of `ident` in `impl_parse_int`
- use `BStr` instead of `&str` for string manipulation
- move string parsing functions to seperate patch and add examples, fix bugs
- degrade comment about future support from doc comment to regular comment
- remove std lib path from `Sized` marker
- update documentation for `trait ModuleParam`
- Link to v2: https://lore.kernel.org/all/20240819133345.3438739-1-nmi@metaspace.dk/

Changes in v2:
- Remove support for params without values (`NOARG_ALLOWED`).
- Improve documentation for `try_from_param_arg`.
- Use prelude import.
- Refactor `try_from_param_arg` to return `Result`.
- Refactor `ParseInt::from_str` to return `Result`.
- Move C callable functions out of `ModuleParam` trait.
- Rename literal string field parser to `expect_string_field`.
- Move parameter parsing from generation to parsing stage.
- Use absolute type paths in macro code.
- Inline `kparam`and `read_func` values.
- Resolve TODO regarding alignment attributes.
- Remove unnecessary unsafe blocks in macro code.
- Improve error message for unrecognized parameter types.
- Do not use `self` receiver when reading parameter value.
- Add parameter documentation to `module!` macro.
- Use empty `enum` for parameter type.
- Use `addr_of_mut` to get address of parameter value variable.
- Enabled building of docs for for `module_param` module.
- Link to v1: https://lore.kernel.org/rust-for-linux/20240705111455.142790-1-nmi@metaspace.dk/

---
Andreas Hindborg (7):
      rust: sync: add `SetOnce`
      rust: str: add radix prefixed integer parsing functions
      rust: introduce module_param module
      rust: module: use a reference in macros::module::module
      rust: module: update the module macro with module parameter support
      rust: samples: add a module parameter to the rust_minimal sample
      modules: add rust modules files to MAINTAINERS

 MAINTAINERS                  |   2 +
 rust/kernel/lib.rs           |   1 +
 rust/kernel/module_param.rs  | 181 +++++++++++++++++++++++++++++++++++++++
 rust/kernel/str.rs           |   2 +
 rust/kernel/str/parse_int.rs | 148 ++++++++++++++++++++++++++++++++
 rust/kernel/sync.rs          |   2 +
 rust/kernel/sync/set_once.rs | 125 +++++++++++++++++++++++++++
 rust/macros/helpers.rs       |  25 ++++++
 rust/macros/lib.rs           |  31 +++++++
 rust/macros/module.rs        | 198 ++++++++++++++++++++++++++++++++++++++-----
 samples/rust/rust_minimal.rs |  10 +++
 11 files changed, 705 insertions(+), 20 deletions(-)
---
base-commit: 47633099a672fc7bfe604ef454e4f116e2c954b1
change-id: 20241211-module-params-v3-ae7e5c8d8b5a
prerequisite-message-id: 20250618164934.19817-1-boqun.feng@gmail.com
prerequisite-patch-id: 997f74bd63d81dc66725d7f84ffcf5a3517da1eb
prerequisite-patch-id: 3e3f8bdada027406a356a2b35aebe13edbda0a94
prerequisite-patch-id: 468b093532aa503c23302142b8cfe7989e3cb8f1
prerequisite-patch-id: 96ca162a1e95a29d3aca2e748d600a31417b83e5
prerequisite-patch-id: 8f78abede975c0c9690ee0f4cf4e7af3cb145191
prerequisite-patch-id: a716ee7a51184d224ef60812ecfffadb51980153
prerequisite-patch-id: e54f74896a75147b66e509c1281804047d41f08b
prerequisite-patch-id: 3f77e2179901ae664a2d2e58965a9725ad13189e
prerequisite-patch-id: e964a9576f9c3970bb7a34b4d2891ffb92939d0e
prerequisite-patch-id: bba35ecdf783653e0fa46015bc289706508fac55

Best regards,
-- 
Andreas Hindborg <a.hindborg@kernel.org>

[PATCH v15 1/7] rust: sync: add `SetOnce`

[Andreas Hindborg]

Introduce the `SetOnce` type, a container that can only be written once.
The container uses an internal atomic to synchronize writes to the internal
value.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/sync.rs          |   2 +
 rust/kernel/sync/set_once.rs | 125 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 127 insertions(+)

diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 81e3a806e57e2..13e6bc7fa87ac 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -18,6 +18,7 @@
 mod locked_by;
 pub mod poll;
 pub mod rcu;
+mod set_once;
 
 pub use arc::{Arc, ArcBorrow, UniqueArc};
 pub use completion::Completion;
@@ -26,6 +27,7 @@
 pub use lock::mutex::{new_mutex, Mutex, MutexGuard};
 pub use lock::spinlock::{new_spinlock, SpinLock, SpinLockGuard};
 pub use locked_by::LockedBy;
+pub use set_once::SetOnce;
 
 /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
 #[repr(transparent)]
diff --git a/rust/kernel/sync/set_once.rs b/rust/kernel/sync/set_once.rs
new file mode 100644
index 0000000000000..e1e31f5faed09
--- /dev/null
+++ b/rust/kernel/sync/set_once.rs
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A container that can be initialized at most once.
+
+use super::atomic::ordering::Acquire;
+use super::atomic::ordering::Relaxed;
+use super::atomic::ordering::Release;
+use super::atomic::Atomic;
+use core::ptr::drop_in_place;
+use kernel::types::Opaque;
+
+/// A container that can be populated at most once. Thread safe.
+///
+/// Once the a [`SetOnce`] is populated, it remains populated by the same object for the
+/// lifetime `Self`.
+///
+/// # Invariants
+///
+/// - `init` may only increase in value.
+/// - `init` may only assume values in the range `0..=2`.
+/// - `init == 0` if and only if the container is empty.
+/// - `init == 1` if and only if being initialized.
+/// - `init == 2` if and only if the container is populated and valid for shared access.
+///
+/// # Example
+///
+/// ```
+/// # use kernel::sync::SetOnce;
+/// let value = SetOnce::new();
+/// assert_eq!(None, value.as_ref());
+///
+/// let status = value.populate(42u8);
+/// assert_eq!(true, status);
+/// assert_eq!(Some(&42u8), value.as_ref());
+/// assert_eq!(Some(42u8), value.copy());
+///
+/// let status = value.populate(101u8);
+/// assert_eq!(false, status);
+/// assert_eq!(Some(&42u8), value.as_ref());
+/// assert_eq!(Some(42u8), value.copy());
+/// ```
+pub struct SetOnce<T> {
+    init: Atomic<u32>,
+    value: Opaque<T>,
+}
+
+impl<T> Default for SetOnce<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+// TODO: change names
+
+impl<T> SetOnce<T> {
+    /// Create a new [`SetOnce`].
+    ///
+    /// The returned instance will be empty.
+    pub const fn new() -> Self {
+        // INVARIANT: The container is empty and we initialize `init` to `0`.
+        Self {
+            value: Opaque::uninit(),
+            init: Atomic::new(0),
+        }
+    }
+
+    /// Get a reference to the contained object.
+    ///
+    /// Returns [`None`] if this [`SetOnce`] is empty.
+    pub fn as_ref(&self) -> Option<&T> {
+        if self.init.load(Acquire) == 2 {
+            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
+            // contains a valid value.
+            Some(unsafe { &*self.value.get() })
+        } else {
+            None
+        }
+    }
+
+    /// Populate the [`SetOnce`].
+    ///
+    /// Returns `true` if the [`SetOnce`] was successfully populated.
+    pub fn populate(&self, value: T) -> bool {
+        // INVARIANT: If the swap succeeds:
+        //  - We increase `init`.
+        //  - We write the valid value `1` to `init`.
+        //  - Only one thread can succeed in this write, so we have exclusive access after the
+        //    write.
+        if let Ok(0) = self.init.cmpxchg(0, 1, Relaxed) {
+            // SAFETY: By the type invariants of `Self`, the fact that we succeeded in writing `1`
+            // to `self.init` means we obtained exclusive access to the contained object.
+            unsafe { core::ptr::write(self.value.get(), value) };
+            // INVARIANT:
+            //  - We increase `init`.
+            //  - We write the valid value `2` to `init`.
+            //  - We release our exclusive access to the contained object and the object is now
+            //    valid for shared access.
+            self.init.store(2, Release);
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Get a copy of the contained object.
+    ///
+    /// Returns [`None`] if the [`SetOnce`] is empty.
+    pub fn copy(&self) -> Option<T>
+    where
+        T: Copy,
+    {
+        self.as_ref().copied()
+    }
+}
+
+impl<T> Drop for SetOnce<T> {
+    fn drop(&mut self) {
+        if self.init.load(Acquire) == 2 {
+            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
+            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
+            // `self`.
+            unsafe { drop_in_place(self.value.get()) };
+        }
+    }
+}

-- 
2.47.2

[PATCH v15 2/7] rust: str: add radix prefixed integer parsing functions

[Andreas Hindborg]

Add the trait `ParseInt` for parsing string representations of integers
where the string representations are optionally prefixed by a radix
specifier. Implement the trait for the primitive integer types.

Tested-by: Daniel Gomez <da.gomez@samsung.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/str.rs           |   2 +
 rust/kernel/str/parse_int.rs | 148 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 150 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index a927db8e079c3..2b6c8b4a0ae4b 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -8,6 +8,8 @@
 
 use crate::prelude::*;
 
+pub mod parse_int;
+
 /// Byte string without UTF-8 validity guarantee.
 #[repr(transparent)]
 pub struct BStr([u8]);
diff --git a/rust/kernel/str/parse_int.rs b/rust/kernel/str/parse_int.rs
new file mode 100644
index 0000000000000..48eb4c202984c
--- /dev/null
+++ b/rust/kernel/str/parse_int.rs
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Integer parsing functions.
+//!
+//! Integer parsing functions for parsing signed and unsigned integers
+//! potentially prefixed with `0x`, `0o`, or `0b`.
+
+use crate::prelude::*;
+use crate::str::BStr;
+use core::ops::Deref;
+
+// Make `FromStrRadix` a public type with a private name. This seals
+// `ParseInt`, that is, prevents downstream users from implementing the
+// trait.
+mod private {
+    use crate::prelude::*;
+    use crate::str::BStr;
+
+    /// Trait that allows parsing a [`&BStr`] to an integer with a radix.
+    pub trait FromStrRadix: Sized {
+        /// Parse `src` to [`Self`] using radix `radix`.
+        fn from_str_radix(src: &BStr, radix: u32) -> Result<Self>;
+
+        /// Tries to convert `value` into [`Self`] and negates the resulting value.
+        fn from_u64_negated(value: u64) -> Result<Self>;
+    }
+}
+
+/// Extract the radix from an integer literal optionally prefixed with
+/// one of `0x`, `0X`, `0o`, `0O`, `0b`, `0B`, `0`.
+fn strip_radix(src: &BStr) -> (u32, &BStr) {
+    match src.deref() {
+        [b'0', b'x' | b'X', rest @ ..] => (16, rest.as_ref()),
+        [b'0', b'o' | b'O', rest @ ..] => (8, rest.as_ref()),
+        [b'0', b'b' | b'B', rest @ ..] => (2, rest.as_ref()),
+        // NOTE: We are including the leading zero to be able to parse
+        // literal `0` here. If we removed it as a radix prefix, we would
+        // not be able to parse `0`.
+        [b'0', ..] => (8, src),
+        _ => (10, src),
+    }
+}
+
+/// Trait for parsing string representations of integers.
+///
+/// Strings beginning with `0x`, `0o`, or `0b` are parsed as hex, octal, or
+/// binary respectively. Strings beginning with `0` otherwise are parsed as
+/// octal. Anything else is parsed as decimal. A leading `+` or `-` is also
+/// permitted. Any string parsed by [`kstrtol()`] or [`kstrtoul()`] will be
+/// successfully parsed.
+///
+/// [`kstrtol()`]: https://docs.kernel.org/core-api/kernel-api.html#c.kstrtol
+/// [`kstrtoul()`]: https://docs.kernel.org/core-api/kernel-api.html#c.kstrtoul
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::str::parse_int::ParseInt;
+/// # use kernel::b_str;
+///
+/// assert_eq!(Ok(0u8), u8::from_str(b_str!("0")));
+///
+/// assert_eq!(Ok(0xa2u8), u8::from_str(b_str!("0xa2")));
+/// assert_eq!(Ok(-0xa2i32), i32::from_str(b_str!("-0xa2")));
+///
+/// assert_eq!(Ok(-0o57i8), i8::from_str(b_str!("-0o57")));
+/// assert_eq!(Ok(0o57i8), i8::from_str(b_str!("057")));
+///
+/// assert_eq!(Ok(0b1001i16), i16::from_str(b_str!("0b1001")));
+/// assert_eq!(Ok(-0b1001i16), i16::from_str(b_str!("-0b1001")));
+///
+/// assert_eq!(Ok(127i8), i8::from_str(b_str!("127")));
+/// assert!(i8::from_str(b_str!("128")).is_err());
+/// assert_eq!(Ok(-128i8), i8::from_str(b_str!("-128")));
+/// assert!(i8::from_str(b_str!("-129")).is_err());
+/// assert_eq!(Ok(255u8), u8::from_str(b_str!("255")));
+/// assert!(u8::from_str(b_str!("256")).is_err());
+/// ```
+pub trait ParseInt: private::FromStrRadix + TryFrom<u64> {
+    /// Parse a string according to the description in [`Self`].
+    fn from_str(src: &BStr) -> Result<Self> {
+        match src.deref() {
+            [b'-', rest @ ..] => {
+                let (radix, digits) = strip_radix(rest.as_ref());
+                // 2's complement values range from -2^(b-1) to 2^(b-1)-1.
+                // So if we want to parse negative numbers as positive and
+                // later multiply by -1, we have to parse into a larger
+                // integer. We choose `u64` as sufficiently large.
+                //
+                // NOTE: 128 bit integers are not available on all
+                // platforms, hence the choice of 64 bits.
+                let val =
+                    u64::from_str_radix(core::str::from_utf8(digits).map_err(|_| EINVAL)?, radix)
+                        .map_err(|_| EINVAL)?;
+                Self::from_u64_negated(val)
+            }
+            _ => {
+                let (radix, digits) = strip_radix(src);
+                Self::from_str_radix(digits, radix).map_err(|_| EINVAL)
+            }
+        }
+    }
+}
+
+macro_rules! impl_parse_int {
+    ($($ty:ty),*) => {
+        $(
+            impl private::FromStrRadix for $ty {
+                fn from_str_radix(src: &BStr, radix: u32) -> Result<Self> {
+                    <$ty>::from_str_radix(core::str::from_utf8(src).map_err(|_| EINVAL)?, radix)
+                        .map_err(|_| EINVAL)
+                }
+
+                fn from_u64_negated(value: u64) -> Result<Self> {
+                    const ABS_MIN: u64 = {
+                        #[allow(unused_comparisons)]
+                        if <$ty>::MIN < 0 {
+                            1u64 << (<$ty>::BITS - 1)
+                        } else {
+                            0
+                        }
+                    };
+
+                    if value > ABS_MIN {
+                        return Err(EINVAL);
+                    }
+
+                    if value == ABS_MIN {
+                        return Ok(<$ty>::MIN);
+                    }
+
+                    // SAFETY: The above checks guarantee that `value` fits into `Self`:
+                    // - if `Self` is unsigned, then `ABS_MIN == 0` and thus we have returned above
+                    //   (either `EINVAL` or `MIN`).
+                    // - if `Self` is signed, then we have that `0 <= value < ABS_MIN`. And since
+                    //   `ABS_MIN - 1` fits into `Self` by construction, `value` also does.
+                    let value: Self = unsafe { value.try_into().unwrap_unchecked() };
+
+                    Ok((!value).wrapping_add(1))
+                }
+            }
+
+            impl ParseInt for $ty {}
+        )*
+    };
+}
+
+impl_parse_int![i8, u8, i16, u16, i32, u32, i64, u64, isize, usize];

-- 
2.47.2

[PATCH v15 3/7] rust: introduce module_param module

[Andreas Hindborg]

Add types and traits for interfacing the C moduleparam API.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/lib.rs          |   1 +
 rust/kernel/module_param.rs | 181 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 182 insertions(+)

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 6b4774b2b1c37..2b439ea061850 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -87,6 +87,7 @@
 pub mod list;
 pub mod miscdevice;
 pub mod mm;
+pub mod module_param;
 #[cfg(CONFIG_NET)]
 pub mod net;
 pub mod of;
diff --git a/rust/kernel/module_param.rs b/rust/kernel/module_param.rs
new file mode 100644
index 0000000000000..9b187ed1d3513
--- /dev/null
+++ b/rust/kernel/module_param.rs
@@ -0,0 +1,181 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Support for module parameters.
+//!
+//! C header: [`include/linux/moduleparam.h`](srctree/include/linux/moduleparam.h)
+
+use crate::prelude::*;
+use crate::str::BStr;
+use bindings;
+use kernel::sync::SetOnce;
+
+/// Newtype to make `bindings::kernel_param` [`Sync`].
+#[repr(transparent)]
+#[doc(hidden)]
+pub struct KernelParam(bindings::kernel_param);
+
+impl KernelParam {
+    #[doc(hidden)]
+    pub const fn new(val: bindings::kernel_param) -> Self {
+        Self(val)
+    }
+}
+
+// SAFETY: C kernel handles serializing access to this type. We never access it
+// from Rust module.
+unsafe impl Sync for KernelParam {}
+
+/// Types that can be used for module parameters.
+// NOTE: This trait is `Copy` because drop could produce unsoundness during teardown.
+pub trait ModuleParam: Sized + Copy {
+    /// Parse a parameter argument into the parameter value.
+    fn try_from_param_arg(arg: &BStr) -> Result<Self>;
+}
+
+/// Set the module parameter from a string.
+///
+/// Used to set the parameter value at kernel initialization, when loading
+/// the module or when set through `sysfs`.
+///
+/// See `struct kernel_param_ops.set`.
+///
+/// # Safety
+///
+/// - If `val` is non-null then it must point to a valid null-terminated string that must be valid
+///   for reads for the duration of the call.
+/// - `param` must be a pointer to a `bindings::kernel_param` initialized by the rust module macro.
+///   The pointee must be valid for reads for the duration of the call.
+///
+/// # Note
+///
+/// - The safety requirements are satisfied by C API contract when this function is invoked by the
+///   module subsystem C code.
+/// - Currently, we only support read-only parameters that are not readable from `sysfs`. Thus, this
+///   function is only called at kernel initialization time, or at module load time, and we have
+///   exclusive access to the parameter for the duration of the function.
+///
+/// [`module!`]: macros::module
+unsafe extern "C" fn set_param<T>(val: *const c_char, param: *const bindings::kernel_param) -> c_int
+where
+    T: ModuleParam,
+{
+    // NOTE: If we start supporting arguments without values, val _is_ allowed
+    // to be null here.
+    if val.is_null() {
+        // TODO: Use pr_warn_once available.
+        crate::pr_warn!("Null pointer passed to `module_param::set_param`");
+        return EINVAL.to_errno();
+    }
+
+    // SAFETY: By function safety requirement, val is non-null, null-terminated
+    // and valid for reads for the duration of this function.
+    let arg = unsafe { CStr::from_char_ptr(val) };
+
+    crate::error::from_result(|| {
+        let new_value = T::try_from_param_arg(arg)?;
+
+        // SAFETY: By function safety requirements, this access is safe.
+        let container = unsafe { &*((*param).__bindgen_anon_1.arg as *mut SetOnce<T>) };
+
+        container
+            .populate(new_value)
+            .then_some(0)
+            .ok_or(kernel::error::code::EEXIST)
+    })
+}
+
+macro_rules! impl_int_module_param {
+    ($ty:ident) => {
+        impl ModuleParam for $ty {
+            fn try_from_param_arg(arg: &BStr) -> Result<Self> {
+                <$ty as crate::str::parse_int::ParseInt>::from_str(arg)
+            }
+        }
+    };
+}
+
+impl_int_module_param!(i8);
+impl_int_module_param!(u8);
+impl_int_module_param!(i16);
+impl_int_module_param!(u16);
+impl_int_module_param!(i32);
+impl_int_module_param!(u32);
+impl_int_module_param!(i64);
+impl_int_module_param!(u64);
+impl_int_module_param!(isize);
+impl_int_module_param!(usize);
+
+/// A wrapper for kernel parameters.
+///
+/// This type is instantiated by the [`module!`] macro when module parameters are
+/// defined. You should never need to instantiate this type directly.
+///
+/// Note: This type is `pub` because it is used by module crates to access
+/// parameter values.
+pub struct ModuleParamAccess<T> {
+    value: SetOnce<T>,
+    default: T,
+}
+
+// SAFETY: We only create shared references to the contents of this container,
+// so if `T` is `Sync`, so is `ModuleParamAccess`.
+unsafe impl<T: Sync> Sync for ModuleParamAccess<T> {}
+
+impl<T> ModuleParamAccess<T> {
+    #[doc(hidden)]
+    pub const fn new(default: T) -> Self {
+        Self {
+            value: SetOnce::new(),
+            default,
+        }
+    }
+
+    /// Get a shared reference to the parameter value.
+    // Note: When sysfs access to parameters are enabled, we have to pass in a
+    // held lock guard here.
+    pub fn value(&self) -> &T {
+        self.value.as_ref().unwrap_or(&self.default)
+    }
+
+    /// Get a mutable pointer to `self`.
+    ///
+    /// NOTE: In most cases it is not safe deref the returned pointer.
+    pub const fn as_void_ptr(&self) -> *mut c_void {
+        core::ptr::from_ref(self).cast_mut().cast()
+    }
+}
+
+#[doc(hidden)]
+/// Generate a static [`kernel_param_ops`](srctree/include/linux/moduleparam.h) struct.
+///
+/// # Examples
+///
+/// ```ignore
+/// make_param_ops!(
+///     /// Documentation for new param ops.
+///     PARAM_OPS_MYTYPE, // Name for the static.
+///     MyType // A type which implements [`ModuleParam`].
+/// );
+/// ```
+macro_rules! make_param_ops {
+    ($ops:ident, $ty:ty) => {
+        #[doc(hidden)]
+        pub static $ops: $crate::bindings::kernel_param_ops = $crate::bindings::kernel_param_ops {
+            flags: 0,
+            set: Some(set_param::<$ty>),
+            get: None,
+            free: None,
+        };
+    };
+}
+
+make_param_ops!(PARAM_OPS_I8, i8);
+make_param_ops!(PARAM_OPS_U8, u8);
+make_param_ops!(PARAM_OPS_I16, i16);
+make_param_ops!(PARAM_OPS_U16, u16);
+make_param_ops!(PARAM_OPS_I32, i32);
+make_param_ops!(PARAM_OPS_U32, u32);
+make_param_ops!(PARAM_OPS_I64, i64);
+make_param_ops!(PARAM_OPS_U64, u64);
+make_param_ops!(PARAM_OPS_ISIZE, isize);
+make_param_ops!(PARAM_OPS_USIZE, usize);

-- 
2.47.2

[PATCH v15 4/7] rust: module: use a reference in macros::module::module

[Andreas Hindborg]

When we add parameter support to the module macro, we want to be able to
pass a reference to `ModuleInfo` to a helper function. That is not possible
when we move out of the local `modinfo`. So change the function to access
the local via reference rather than value.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/macros/module.rs | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/rust/macros/module.rs b/rust/macros/module.rs
index 2ddd2eeb28521..1a867a1e787ed 100644
--- a/rust/macros/module.rs
+++ b/rust/macros/module.rs
@@ -179,26 +179,26 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
     // Rust does not allow hyphens in identifiers, use underscore instead.
     let ident = info.name.replace('-', "_");
     let mut modinfo = ModInfoBuilder::new(ident.as_ref());
-    if let Some(author) = info.author {
-        modinfo.emit("author", &author);
+    if let Some(author) = &info.author {
+        modinfo.emit("author", author);
     }
-    if let Some(authors) = info.authors {
+    if let Some(authors) = &info.authors {
         for author in authors {
-            modinfo.emit("author", &author);
+            modinfo.emit("author", author);
         }
     }
-    if let Some(description) = info.description {
-        modinfo.emit("description", &description);
+    if let Some(description) = &info.description {
+        modinfo.emit("description", description);
     }
     modinfo.emit("license", &info.license);
-    if let Some(aliases) = info.alias {
+    if let Some(aliases) = &info.alias {
         for alias in aliases {
-            modinfo.emit("alias", &alias);
+            modinfo.emit("alias", alias);
         }
     }
-    if let Some(firmware) = info.firmware {
+    if let Some(firmware) = &info.firmware {
         for fw in firmware {
-            modinfo.emit("firmware", &fw);
+            modinfo.emit("firmware", fw);
         }
     }
 

-- 
2.47.2

[PATCH v15 5/7] rust: module: update the module macro with module parameter support

[Andreas Hindborg]

Allow module parameters to be declared in the rust `module!` macro.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/macros/helpers.rs |  25 +++++++
 rust/macros/lib.rs     |  31 +++++++++
 rust/macros/module.rs  | 178 ++++++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 224 insertions(+), 10 deletions(-)

diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
index e2602be402c10..365d7eb499c08 100644
--- a/rust/macros/helpers.rs
+++ b/rust/macros/helpers.rs
@@ -10,6 +10,17 @@ pub(crate) fn try_ident(it: &mut token_stream::IntoIter) -> Option<String> {
     }
 }
 
+pub(crate) fn try_sign(it: &mut token_stream::IntoIter) -> Option<char> {
+    let peek = it.clone().next();
+    match peek {
+        Some(TokenTree::Punct(punct)) if punct.as_char() == '-' => {
+            let _ = it.next();
+            Some(punct.as_char())
+        }
+        _ => None,
+    }
+}
+
 pub(crate) fn try_literal(it: &mut token_stream::IntoIter) -> Option<String> {
     if let Some(TokenTree::Literal(literal)) = it.next() {
         Some(literal.to_string())
@@ -103,3 +114,17 @@ pub(crate) fn file() -> String {
         proc_macro::Span::call_site().file()
     }
 }
+
+/// Parse a token stream of the form `expected_name: "value",` and return the
+/// string in the position of "value".
+///
+/// # Panics
+///
+/// - On parse error.
+pub(crate) fn expect_string_field(it: &mut token_stream::IntoIter, expected_name: &str) -> String {
+    assert_eq!(expect_ident(it), expected_name);
+    assert_eq!(expect_punct(it), ':');
+    let string = expect_string(it);
+    assert_eq!(expect_punct(it), ',');
+    string
+}
diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index fa847cf3a9b5f..2fb520dc930af 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -28,6 +28,30 @@
 /// The `type` argument should be a type which implements the [`Module`]
 /// trait. Also accepts various forms of kernel metadata.
 ///
+/// The `params` field describe module parameters. Each entry has the form
+///
+/// ```ignore
+/// parameter_name: type {
+///     default: default_value,
+///     description: "Description",
+/// }
+/// ```
+///
+/// `type` may be one of
+///
+/// - [`i8`]
+/// - [`u8`]
+/// - [`i8`]
+/// - [`u8`]
+/// - [`i16`]
+/// - [`u16`]
+/// - [`i32`]
+/// - [`u32`]
+/// - [`i64`]
+/// - [`u64`]
+/// - [`isize`]
+/// - [`usize`]
+///
 /// C header: [`include/linux/moduleparam.h`](srctree/include/linux/moduleparam.h)
 ///
 /// [`Module`]: ../kernel/trait.Module.html
@@ -44,6 +68,12 @@
 ///     description: "My very own kernel module!",
 ///     license: "GPL",
 ///     alias: ["alternate_module_name"],
+///     params: {
+///         my_parameter: i64 {
+///             default: 1,
+///             description: "This parameter has a default of 1",
+///         },
+///     },
 /// }
 ///
 /// struct MyModule(i32);
@@ -52,6 +82,7 @@
 ///     fn init(_module: &'static ThisModule) -> Result<Self> {
 ///         let foo: i32 = 42;
 ///         pr_info!("I contain:  {}\n", foo);
+///         pr_info!("i32 param is:  {}\n", module_parameters::my_parameter.read());
 ///         Ok(Self(foo))
 ///     }
 /// }
diff --git a/rust/macros/module.rs b/rust/macros/module.rs
index 1a867a1e787ed..c1400597774a5 100644
--- a/rust/macros/module.rs
+++ b/rust/macros/module.rs
@@ -26,6 +26,7 @@ struct ModInfoBuilder<'a> {
     module: &'a str,
     counter: usize,
     buffer: String,
+    param_buffer: String,
 }
 
 impl<'a> ModInfoBuilder<'a> {
@@ -34,10 +35,11 @@ fn new(module: &'a str) -> Self {
             module,
             counter: 0,
             buffer: String::new(),
+            param_buffer: String::new(),
         }
     }
 
-    fn emit_base(&mut self, field: &str, content: &str, builtin: bool) {
+    fn emit_base(&mut self, field: &str, content: &str, builtin: bool, param: bool) {
         let string = if builtin {
             // Built-in modules prefix their modinfo strings by `module.`.
             format!(
@@ -51,8 +53,14 @@ fn emit_base(&mut self, field: &str, content: &str, builtin: bool) {
             format!("{field}={content}\0")
         };
 
+        let buffer = if param {
+            &mut self.param_buffer
+        } else {
+            &mut self.buffer
+        };
+
         write!(
-            &mut self.buffer,
+            buffer,
             "
                 {cfg}
                 #[doc(hidden)]
@@ -75,20 +83,119 @@ fn emit_base(&mut self, field: &str, content: &str, builtin: bool) {
         self.counter += 1;
     }
 
-    fn emit_only_builtin(&mut self, field: &str, content: &str) {
-        self.emit_base(field, content, true)
+    fn emit_only_builtin(&mut self, field: &str, content: &str, param: bool) {
+        self.emit_base(field, content, true, param)
     }
 
-    fn emit_only_loadable(&mut self, field: &str, content: &str) {
-        self.emit_base(field, content, false)
+    fn emit_only_loadable(&mut self, field: &str, content: &str, param: bool) {
+        self.emit_base(field, content, false, param)
     }
 
     fn emit(&mut self, field: &str, content: &str) {
-        self.emit_only_builtin(field, content);
-        self.emit_only_loadable(field, content);
+        self.emit_internal(field, content, false);
+    }
+
+    fn emit_internal(&mut self, field: &str, content: &str, param: bool) {
+        self.emit_only_builtin(field, content, param);
+        self.emit_only_loadable(field, content, param);
+    }
+
+    fn emit_param(&mut self, field: &str, param: &str, content: &str) {
+        let content = format!("{param}:{content}", param = param, content = content);
+        self.emit_internal(field, &content, true);
+    }
+
+    fn emit_params(&mut self, info: &ModuleInfo) {
+        let Some(params) = &info.params else {
+            return;
+        };
+
+        for param in params {
+            let ops = param_ops_path(&param.ptype);
+
+            // Note: The spelling of these fields is dictated by the user space
+            // tool `modinfo`.
+            self.emit_param("parmtype", &param.name, &param.ptype);
+            self.emit_param("parm", &param.name, &param.description);
+
+            write!(
+                self.param_buffer,
+                "
+                pub(crate) static {param_name}:
+                    ::kernel::module_param::ModuleParamAccess<{param_type}> =
+                        ::kernel::module_param::ModuleParamAccess::new({param_default});
+
+                const _: () = {{
+                    #[link_section = \"__param\"]
+                    #[used]
+                    static __{module_name}_{param_name}_struct:
+                        ::kernel::module_param::KernelParam =
+                        ::kernel::module_param::KernelParam::new(
+                            ::kernel::bindings::kernel_param {{
+                                name: if ::core::cfg!(MODULE) {{
+                                    ::kernel::c_str!(\"{param_name}\").as_bytes_with_nul()
+                                }} else {{
+                                    ::kernel::c_str!(\"{module_name}.{param_name}\")
+                                        .as_bytes_with_nul()
+                                }}.as_ptr(),
+                                // SAFETY: `__this_module` is constructed by the kernel at load
+                                // time and will not be freed until the module is unloaded.
+                                #[cfg(MODULE)]
+                                mod_: unsafe {{
+                                    core::ptr::from_ref(&::kernel::bindings::__this_module)
+                                        .cast_mut()
+                                }},
+                                #[cfg(not(MODULE))]
+                                mod_: ::core::ptr::null_mut(),
+                                ops: core::ptr::from_ref(&{ops}),
+                                perm: 0, // Will not appear in sysfs
+                                level: -1,
+                                flags: 0,
+                                __bindgen_anon_1: ::kernel::bindings::kernel_param__bindgen_ty_1 {{
+                                    arg: {param_name}.as_void_ptr()
+                                }},
+                            }}
+                        );
+                }};
+                ",
+                module_name = info.name,
+                param_type = param.ptype,
+                param_default = param.default,
+                param_name = param.name,
+                ops = ops,
+            )
+            .unwrap();
+        }
+    }
+}
+
+fn param_ops_path(param_type: &str) -> &'static str {
+    match param_type {
+        "i8" => "::kernel::module_param::PARAM_OPS_I8",
+        "u8" => "::kernel::module_param::PARAM_OPS_U8",
+        "i16" => "::kernel::module_param::PARAM_OPS_I16",
+        "u16" => "::kernel::module_param::PARAM_OPS_U16",
+        "i32" => "::kernel::module_param::PARAM_OPS_I32",
+        "u32" => "::kernel::module_param::PARAM_OPS_U32",
+        "i64" => "::kernel::module_param::PARAM_OPS_I64",
+        "u64" => "::kernel::module_param::PARAM_OPS_U64",
+        "isize" => "::kernel::module_param::PARAM_OPS_ISIZE",
+        "usize" => "::kernel::module_param::PARAM_OPS_USIZE",
+        t => panic!("Unsupported parameter type {}", t),
     }
 }
 
+fn expect_param_default(param_it: &mut token_stream::IntoIter) -> String {
+    assert_eq!(expect_ident(param_it), "default");
+    assert_eq!(expect_punct(param_it), ':');
+    let sign = try_sign(param_it);
+    let default = try_literal(param_it).expect("Expected default param value");
+    assert_eq!(expect_punct(param_it), ',');
+    let mut value = sign.map(String::from).unwrap_or_default();
+    value.push_str(&default);
+    value
+}
+
 #[derive(Debug, Default)]
 struct ModuleInfo {
     type_: String,
@@ -99,6 +206,50 @@ struct ModuleInfo {
     description: Option<String>,
     alias: Option<Vec<String>>,
     firmware: Option<Vec<String>>,
+    params: Option<Vec<Parameter>>,
+}
+
+#[derive(Debug)]
+struct Parameter {
+    name: String,
+    ptype: String,
+    default: String,
+    description: String,
+}
+
+fn expect_params(it: &mut token_stream::IntoIter) -> Vec<Parameter> {
+    let params = expect_group(it);
+    assert_eq!(params.delimiter(), Delimiter::Brace);
+    let mut it = params.stream().into_iter();
+    let mut parsed = Vec::new();
+
+    loop {
+        let param_name = match it.next() {
+            Some(TokenTree::Ident(ident)) => ident.to_string(),
+            Some(_) => panic!("Expected Ident or end"),
+            None => break,
+        };
+
+        assert_eq!(expect_punct(&mut it), ':');
+        let param_type = expect_ident(&mut it);
+        let group = expect_group(&mut it);
+        assert_eq!(group.delimiter(), Delimiter::Brace);
+        assert_eq!(expect_punct(&mut it), ',');
+
+        let mut param_it = group.stream().into_iter();
+        let param_default = expect_param_default(&mut param_it);
+        let param_description = expect_string_field(&mut param_it, "description");
+        expect_end(&mut param_it);
+
+        parsed.push(Parameter {
+            name: param_name,
+            ptype: param_type,
+            default: param_default,
+            description: param_description,
+        })
+    }
+
+    parsed
 }
 
 impl ModuleInfo {
@@ -114,6 +265,7 @@ fn parse(it: &mut token_stream::IntoIter) -> Self {
             "license",
             "alias",
             "firmware",
+            "params",
         ];
         const REQUIRED_KEYS: &[&str] = &["type", "name", "license"];
         let mut seen_keys = Vec::new();
@@ -140,6 +292,7 @@ fn parse(it: &mut token_stream::IntoIter) -> Self {
                 "license" => info.license = expect_string_ascii(it),
                 "alias" => info.alias = Some(expect_string_array(it)),
                 "firmware" => info.firmware = Some(expect_string_array(it)),
+                "params" => info.params = Some(expect_params(it)),
                 _ => panic!("Unknown key \"{key}\". Valid keys are: {EXPECTED_KEYS:?}."),
             }
 
@@ -205,7 +358,9 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
     // Built-in modules also export the `file` modinfo string.
     let file =
         std::env::var("RUST_MODFILE").expect("Unable to fetch RUST_MODFILE environmental variable");
-    modinfo.emit_only_builtin("file", &file);
+    modinfo.emit_only_builtin("file", &file, false);
+
+    modinfo.emit_params(&info);
 
     format!(
         "
@@ -369,15 +524,18 @@ unsafe fn __exit() {{
                             __MOD.assume_init_drop();
                         }}
                     }}
-
                     {modinfo}
                 }}
             }}
+            mod module_parameters {{
+                {params}
+            }}
         ",
         type_ = info.type_,
         name = info.name,
         ident = ident,
         modinfo = modinfo.buffer,
+        params = modinfo.param_buffer,
         initcall_section = ".initcall6.init"
     )
     .parse()

-- 
2.47.2

[PATCH v15 6/7] rust: samples: add a module parameter to the rust_minimal sample

[Andreas Hindborg]

Showcase the rust module parameter support by adding a module parameter to
the `rust_minimal` sample.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 samples/rust/rust_minimal.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/samples/rust/rust_minimal.rs b/samples/rust/rust_minimal.rs
index 1fc7a1be6b6d7..8eb9583571d72 100644
--- a/samples/rust/rust_minimal.rs
+++ b/samples/rust/rust_minimal.rs
@@ -10,6 +10,12 @@
     authors: ["Rust for Linux Contributors"],
     description: "Rust minimal sample",
     license: "GPL",
+    params: {
+        test_parameter: i64 {
+            default: 1,
+            description: "This parameter has a default of 1",
+        },
+    },
 }
 
 struct RustMinimal {
@@ -20,6 +26,10 @@ impl kernel::Module for RustMinimal {
     fn init(_module: &'static ThisModule) -> Result<Self> {
         pr_info!("Rust minimal sample (init)\n");
         pr_info!("Am I built-in? {}\n", !cfg!(MODULE));
+        pr_info!(
+            "test_parameter: {}\n",
+            *module_parameters::test_parameter.value()
+        );
 
         let mut numbers = KVec::new();
         numbers.push(72, GFP_KERNEL)?;

-- 
2.47.2

[PATCH v15 7/7] modules: add rust modules files to MAINTAINERS

[Andreas Hindborg]

The module subsystem people agreed to maintain rust support for modules
[1]. Thus, add entries for relevant files to modules entry in MAINTAINERS.

Link: https://lore.kernel.org/all/0d9e596a-5316-4e00-862b-fd77552ae4b5@suse.com/ [1]

Acked-by: Daniel Gomez <da.gomez@samsung.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 MAINTAINERS | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index d431320ed3b2a..afa385ecc5c4c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16835,6 +16835,8 @@ F:	include/linux/module*.h
 F:	kernel/module/
 F:	lib/test_kmod.c
 F:	lib/tests/module/
+F:	rust/kernel/module_param.rs
+F:	rust/macros/module.rs
 F:	scripts/module*
 F:	tools/testing/selftests/kmod/
 F:	tools/testing/selftests/module/

-- 
2.47.2

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Andreas Hindborg]

Andreas Hindborg <a.hindborg@kernel.org> writes:

> Introduce the `SetOnce` type, a container that can only be written once.
> The container uses an internal atomic to synchronize writes to the internal
> value.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
>  rust/kernel/sync.rs          |   2 +
>  rust/kernel/sync/set_once.rs | 125 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 127 insertions(+)
>
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 81e3a806e57e2..13e6bc7fa87ac 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -18,6 +18,7 @@
>  mod locked_by;
>  pub mod poll;
>  pub mod rcu;
> +mod set_once;
>  
>  pub use arc::{Arc, ArcBorrow, UniqueArc};
>  pub use completion::Completion;
> @@ -26,6 +27,7 @@
>  pub use lock::mutex::{new_mutex, Mutex, MutexGuard};
>  pub use lock::spinlock::{new_spinlock, SpinLock, SpinLockGuard};
>  pub use locked_by::LockedBy;
> +pub use set_once::SetOnce;
>  
>  /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
>  #[repr(transparent)]
> diff --git a/rust/kernel/sync/set_once.rs b/rust/kernel/sync/set_once.rs
> new file mode 100644
> index 0000000000000..e1e31f5faed09
> --- /dev/null
> +++ b/rust/kernel/sync/set_once.rs
> @@ -0,0 +1,125 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! A container that can be initialized at most once.
> +
> +use super::atomic::ordering::Acquire;
> +use super::atomic::ordering::Relaxed;
> +use super::atomic::ordering::Release;
> +use super::atomic::Atomic;
> +use core::ptr::drop_in_place;
> +use kernel::types::Opaque;
> +
> +/// A container that can be populated at most once. Thread safe.
> +///
> +/// Once the a [`SetOnce`] is populated, it remains populated by the same object for the
> +/// lifetime `Self`.
> +///
> +/// # Invariants
> +///
> +/// - `init` may only increase in value.
> +/// - `init` may only assume values in the range `0..=2`.
> +/// - `init == 0` if and only if the container is empty.
> +/// - `init == 1` if and only if being initialized.
> +/// - `init == 2` if and only if the container is populated and valid for shared access.
> +///
> +/// # Example
> +///
> +/// ```
> +/// # use kernel::sync::SetOnce;
> +/// let value = SetOnce::new();
> +/// assert_eq!(None, value.as_ref());
> +///
> +/// let status = value.populate(42u8);
> +/// assert_eq!(true, status);
> +/// assert_eq!(Some(&42u8), value.as_ref());
> +/// assert_eq!(Some(42u8), value.copy());
> +///
> +/// let status = value.populate(101u8);
> +/// assert_eq!(false, status);
> +/// assert_eq!(Some(&42u8), value.as_ref());
> +/// assert_eq!(Some(42u8), value.copy());
> +/// ```
> +pub struct SetOnce<T> {
> +    init: Atomic<u32>,
> +    value: Opaque<T>,
> +}
> +
> +impl<T> Default for SetOnce<T> {
> +    fn default() -> Self {
> +        Self::new()
> +    }
> +}
> +
> +// TODO: change names

I just saw that this line decided to stick around, that was obviously
not intentional. Just disregard this line.


Best regards,
Andreas Hindborg

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Alice Ryhl]

On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> Introduce the `SetOnce` type, a container that can only be written once.
> The container uses an internal atomic to synchronize writes to the internal
> value.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

LGTM:
Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> +impl<T> Drop for SetOnce<T> {
> +    fn drop(&mut self) {
> +        if self.init.load(Acquire) == 2 {
> +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
> +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
> +            // `self`.
> +            unsafe { drop_in_place(self.value.get()) };

This load does not need to be Acquire. It can be a Relaxed load or
even an unsynchronized one since the access is exclusive.

Alice

Re: [PATCH v15 0/7] rust: extend `module!` macro with integer parameter support

[Miguel Ojeda]

On Mon, Jul 7, 2025 at 3:31 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> Based on code by Adam Bratschi-Kaye lifted from the original `rust` branch [1].

I would suggest adding this sort of note to the commit messages,
especially since the commits have no Co-developed-by/Link tags
otherwise.

From our discussion in Zulip: the code itself is older than that the
merge above. I think you wanted an example sentence for this --
something simple could be e.g.

    Based on the original module parameter support by Miguel [1],
later extended and generalized by Adam for more types [2][3].
Originally tracked at [4].

    Link: https://github.com/Rust-for-Linux/linux/pull/7 [1]
    Link: https://github.com/Rust-for-Linux/linux/pull/82 [2]
    Link: https://github.com/Rust-for-Linux/linux/pull/87 [3]
    Link: https://github.com/Rust-for-Linux/linux/issues/11 [4]

By the way, I guess you should inherit that issue in the last link :)
It had some details about things we may or may not want to support
etc. that I looked up back then. If you prefer that we close it or
that we create sub-issues, that is fine -- up to you!

Finally, if you end up adding strings, please link to Adam's
https://github.com/Rust-for-Linux/linux/pull/110.

Thanks!

Cheers,
Miguel

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Boqun Feng]

On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
> >
> > Introduce the `SetOnce` type, a container that can only be written once.
> > The container uses an internal atomic to synchronize writes to the internal
> > value.
> >
> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> 
> LGTM:
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> 
> > +impl<T> Drop for SetOnce<T> {
> > +    fn drop(&mut self) {
> > +        if self.init.load(Acquire) == 2 {
> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
> > +            // `self`.
> > +            unsafe { drop_in_place(self.value.get()) };
> 
> This load does not need to be Acquire. It can be a Relaxed load or
> even an unsynchronized one since the access is exclusive.

Right, I think we can do the similar as Revocable here:

        if *self.init.get_mut() == 2 { }

Further, with my following Benno's suggestion and making `Atomic<T>` an
`UnsafeCell<T>:

	https://lore.kernel.org/rust-for-linux/aGhh-TvNOWhkt0JG@Mac.home/

compiler can generate a noalias reference here, which allows further
optimization.

Regards,
Boqun

> 
> Alice

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Andreas Hindborg]

"Alice Ryhl" <aliceryhl@google.com> writes:

> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>
>> Introduce the `SetOnce` type, a container that can only be written once.
>> The container uses an internal atomic to synchronize writes to the internal
>> value.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>
> LGTM:
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>
>> +impl<T> Drop for SetOnce<T> {
>> +    fn drop(&mut self) {
>> +        if self.init.load(Acquire) == 2 {
>> +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>> +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
>> +            // `self`.
>> +            unsafe { drop_in_place(self.value.get()) };
>
> This load does not need to be Acquire. It can be a Relaxed load or
> even an unsynchronized one since the access is exclusive.

Right, that is actually very cool. My rationale was that if a reference
has been shared to another thread of execution, we would need to
synchronize here to see a possible initialization from that other
thread. But I guess it is impossible to end the lifetime of a reference
without doing a synchronization somewhere else.


Best regards,
Andreas Hindborg

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Andreas Hindborg]

"Boqun Feng" <boqun.feng@gmail.com> writes:

> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
>> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>> >
>> > Introduce the `SetOnce` type, a container that can only be written once.
>> > The container uses an internal atomic to synchronize writes to the internal
>> > value.
>> >
>> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>
>> LGTM:
>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>>
>> > +impl<T> Drop for SetOnce<T> {
>> > +    fn drop(&mut self) {
>> > +        if self.init.load(Acquire) == 2 {
>> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
>> > +            // `self`.
>> > +            unsafe { drop_in_place(self.value.get()) };
>>
>> This load does not need to be Acquire. It can be a Relaxed load or
>> even an unsynchronized one since the access is exclusive.
>
> Right, I think we can do the similar as Revocable here:
>
>         if *self.init.get_mut() == 2 { }
>
> Further, with my following Benno's suggestion and making `Atomic<T>` an
> `UnsafeCell<T>:
>
> 	https://lore.kernel.org/rust-for-linux/aGhh-TvNOWhkt0JG@Mac.home/
>
> compiler can generate a noalias reference here, which allows further
> optimization.
>

You would like to remove `PhantomPinned` to enable noalias? I guess that
makes sense in this case. I'll fix that for next spin.


Best regards,
Andreas Hindborg

Re: [PATCH v15 2/7] rust: str: add radix prefixed integer parsing functions

[Benno Lossin]

On Mon Jul 7, 2025 at 3:29 PM CEST, Andreas Hindborg wrote:
> Add the trait `ParseInt` for parsing string representations of integers
> where the string representations are optionally prefixed by a radix
> specifier. Implement the trait for the primitive integer types.
>
> Tested-by: Daniel Gomez <da.gomez@samsung.com>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Suggested-by: Benno Lossin <benno.lossin@proton.me>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

Reviewed-by: Benno Lossin <lossin@kernel.org>

---
Cheers,
Benno

> ---
>  rust/kernel/str.rs           |   2 +
>  rust/kernel/str/parse_int.rs | 148 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 150 insertions(+)

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Alice Ryhl]

On Tue, Jul 8, 2025 at 10:48 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> "Alice Ryhl" <aliceryhl@google.com> writes:
>
> > On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
> >>
> >> Introduce the `SetOnce` type, a container that can only be written once.
> >> The container uses an internal atomic to synchronize writes to the internal
> >> value.
> >>
> >> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> >
> > LGTM:
> > Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> >
> >> +impl<T> Drop for SetOnce<T> {
> >> +    fn drop(&mut self) {
> >> +        if self.init.load(Acquire) == 2 {
> >> +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
> >> +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
> >> +            // `self`.
> >> +            unsafe { drop_in_place(self.value.get()) };
> >
> > This load does not need to be Acquire. It can be a Relaxed load or
> > even an unsynchronized one since the access is exclusive.
>
> Right, that is actually very cool. My rationale was that if a reference
> has been shared to another thread of execution, we would need to
> synchronize here to see a possible initialization from that other
> thread. But I guess it is impossible to end the lifetime of a reference
> without doing a synchronization somewhere else.

Yup, a mutable reference generally implies synchronization.

Alice

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Benno Lossin]

On Mon Jul 7, 2025 at 3:29 PM CEST, Andreas Hindborg wrote:
> Introduce the `SetOnce` type, a container that can only be written once.
> The container uses an internal atomic to synchronize writes to the internal
> value.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

One nit and a safety comment fix below. (feel free to ignore the nit)
With the safety comment fixed:

Reviewed-by: Benno Lossin <lossin@kernel.org>

> ---
>  rust/kernel/sync.rs          |   2 +
>  rust/kernel/sync/set_once.rs | 125 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 127 insertions(+)
>
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 81e3a806e57e2..13e6bc7fa87ac 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -18,6 +18,7 @@
>  mod locked_by;
>  pub mod poll;
>  pub mod rcu;
> +mod set_once;

I would have named this `once`.

>  pub use arc::{Arc, ArcBorrow, UniqueArc};
>  pub use completion::Completion;

> +    /// Get a reference to the contained object.
> +    ///
> +    /// Returns [`None`] if this [`SetOnce`] is empty.
> +    pub fn as_ref(&self) -> Option<&T> {
> +        if self.init.load(Acquire) == 2 {
> +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
> +            // contains a valid value.

And the type invariants also ensure that the value of `self.init`
doesn't change.

So probably

    // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
    // contains a valid value. They also guarantee that `self.init` doesn't change.

If you come up with something better, feel free to use it.

---
Cheers,
Benno

> +            Some(unsafe { &*self.value.get() })
> +        } else {
> +            None
> +        }
> +    }

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Benno Lossin]

On Tue Jul 8, 2025 at 10:54 AM CEST, Andreas Hindborg wrote:
> "Boqun Feng" <boqun.feng@gmail.com> writes:
>
>> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
>>> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>> >
>>> > Introduce the `SetOnce` type, a container that can only be written once.
>>> > The container uses an internal atomic to synchronize writes to the internal
>>> > value.
>>> >
>>> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>>
>>> LGTM:
>>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>>>
>>> > +impl<T> Drop for SetOnce<T> {
>>> > +    fn drop(&mut self) {
>>> > +        if self.init.load(Acquire) == 2 {
>>> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>>> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
>>> > +            // `self`.
>>> > +            unsafe { drop_in_place(self.value.get()) };
>>>
>>> This load does not need to be Acquire. It can be a Relaxed load or
>>> even an unsynchronized one since the access is exclusive.
>>
>> Right, I think we can do the similar as Revocable here:
>>
>>         if *self.init.get_mut() == 2 { }
>>
>> Further, with my following Benno's suggestion and making `Atomic<T>` an
>> `UnsafeCell<T>:
>>
>> 	https://lore.kernel.org/rust-for-linux/aGhh-TvNOWhkt0JG@Mac.home/
>>
>> compiler can generate a noalias reference here, which allows further
>> optimization.
>>
>
> You would like to remove `PhantomPinned` to enable noalias? I guess that
> makes sense in this case. I'll fix that for next spin.

I think you two are talking about different things. Boqun is saying that
the `Atomic<T>` will use `UnsafeCell` rather than `Opaque`, which will
potentially allow more optimizations.

But you are talking about `SetOnce`, right? I think it makes more sense
for `SetOnce` to use `UnsafeCell<MaybeUninit<T>>` rather than `Opaque`
too. So feel free to change it in the next version.

---
Cheers,
Benno

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Andreas Hindborg]

"Benno Lossin" <lossin@kernel.org> writes:

> On Mon Jul 7, 2025 at 3:29 PM CEST, Andreas Hindborg wrote:
>> Introduce the `SetOnce` type, a container that can only be written once.
>> The container uses an internal atomic to synchronize writes to the internal
>> value.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>
> One nit and a safety comment fix below. (feel free to ignore the nit)
> With the safety comment fixed:
>
> Reviewed-by: Benno Lossin <lossin@kernel.org>
>
>> ---
>>  rust/kernel/sync.rs          |   2 +
>>  rust/kernel/sync/set_once.rs | 125 +++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 127 insertions(+)
>>
>> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
>> index 81e3a806e57e2..13e6bc7fa87ac 100644
>> --- a/rust/kernel/sync.rs
>> +++ b/rust/kernel/sync.rs
>> @@ -18,6 +18,7 @@
>>  mod locked_by;
>>  pub mod poll;
>>  pub mod rcu;
>> +mod set_once;
>
> I would have named this `once`.

So module `once` and struct `SetOnce`? Struct name `Once` would lead
thoughts to `std::sync::Once`, which is a different thing.

>
>>  pub use arc::{Arc, ArcBorrow, UniqueArc};
>>  pub use completion::Completion;
>
>> +    /// Get a reference to the contained object.
>> +    ///
>> +    /// Returns [`None`] if this [`SetOnce`] is empty.
>> +    pub fn as_ref(&self) -> Option<&T> {
>> +        if self.init.load(Acquire) == 2 {
>> +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>> +            // contains a valid value.
>
> And the type invariants also ensure that the value of `self.init`
> doesn't change.
>
> So probably
>
>     // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>     // contains a valid value. They also guarantee that `self.init` doesn't change.
>

Sure 👍


Best regards,
Andreas Hindborg

Re: [PATCH v15 0/7] rust: extend `module!` macro with integer parameter support

[Andreas Hindborg]

"Miguel Ojeda" <miguel.ojeda.sandonis@gmail.com> writes:

> On Mon, Jul 7, 2025 at 3:31 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>
>> Based on code by Adam Bratschi-Kaye lifted from the original `rust` branch [1].
>
> I would suggest adding this sort of note to the commit messages,
> especially since the commits have no Co-developed-by/Link tags
> otherwise.
>
> From our discussion in Zulip: the code itself is older than that the
> merge above. I think you wanted an example sentence for this --
> something simple could be e.g.
>
>     Based on the original module parameter support by Miguel [1],
> later extended and generalized by Adam for more types [2][3].
> Originally tracked at [4].
>
>     Link: https://github.com/Rust-for-Linux/linux/pull/7 [1]
>     Link: https://github.com/Rust-for-Linux/linux/pull/82 [2]
>     Link: https://github.com/Rust-for-Linux/linux/pull/87 [3]
>     Link: https://github.com/Rust-for-Linux/linux/issues/11 [4]
>
> By the way, I guess you should inherit that issue in the last link :)
> It had some details about things we may or may not want to support
> etc. that I looked up back then. If you prefer that we close it or
> that we create sub-issues, that is fine -- up to you!
>
> Finally, if you end up adding strings, please link to Adam's
> https://github.com/Rust-for-Linux/linux/pull/110.

Thanks, I'll add this!


Best regards,
Andreas Hindborg

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Benno Lossin]

On Tue Jul 8, 2025 at 3:06 PM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@kernel.org> writes:
>> On Mon Jul 7, 2025 at 3:29 PM CEST, Andreas Hindborg wrote:
>>> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
>>> index 81e3a806e57e2..13e6bc7fa87ac 100644
>>> --- a/rust/kernel/sync.rs
>>> +++ b/rust/kernel/sync.rs
>>> @@ -18,6 +18,7 @@
>>>  mod locked_by;
>>>  pub mod poll;
>>>  pub mod rcu;
>>> +mod set_once;
>>
>> I would have named this `once`.
>
> So module `once` and struct `SetOnce`? Struct name `Once` would lead
> thoughts to `std::sync::Once`, which is a different thing.

Hmm I thought that `Once` and `SetOnce` would live in the same module,
but if they don't then I think it's better to keep the `set_once`
module as-is.

---
Cheers,
Benno

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Andreas Hindborg]

"Benno Lossin" <lossin@kernel.org> writes:

> On Tue Jul 8, 2025 at 3:06 PM CEST, Andreas Hindborg wrote:
>> "Benno Lossin" <lossin@kernel.org> writes:
>>> On Mon Jul 7, 2025 at 3:29 PM CEST, Andreas Hindborg wrote:
>>>> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
>>>> index 81e3a806e57e2..13e6bc7fa87ac 100644
>>>> --- a/rust/kernel/sync.rs
>>>> +++ b/rust/kernel/sync.rs
>>>> @@ -18,6 +18,7 @@
>>>>  mod locked_by;
>>>>  pub mod poll;
>>>>  pub mod rcu;
>>>> +mod set_once;
>>>
>>> I would have named this `once`.
>>
>> So module `once` and struct `SetOnce`? Struct name `Once` would lead
>> thoughts to `std::sync::Once`, which is a different thing.
>
> Hmm I thought that `Once` and `SetOnce` would live in the same module,
> but if they don't then I think it's better to keep the `set_once`
> module as-is.

I guess they could live together. I was thinking a module for each. We
can always move it, the module name is not part of a public API.

Let's go with `set_once` for now and we can change it later, if we
decide it is for the better?


Best regards,
Andreas Hindborg

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Benno Lossin]

On Wed Jul 9, 2025 at 10:56 AM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@kernel.org> writes:
>
>> On Tue Jul 8, 2025 at 3:06 PM CEST, Andreas Hindborg wrote:
>>> "Benno Lossin" <lossin@kernel.org> writes:
>>>> On Mon Jul 7, 2025 at 3:29 PM CEST, Andreas Hindborg wrote:
>>>>> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
>>>>> index 81e3a806e57e2..13e6bc7fa87ac 100644
>>>>> --- a/rust/kernel/sync.rs
>>>>> +++ b/rust/kernel/sync.rs
>>>>> @@ -18,6 +18,7 @@
>>>>>  mod locked_by;
>>>>>  pub mod poll;
>>>>>  pub mod rcu;
>>>>> +mod set_once;
>>>>
>>>> I would have named this `once`.
>>>
>>> So module `once` and struct `SetOnce`? Struct name `Once` would lead
>>> thoughts to `std::sync::Once`, which is a different thing.
>>
>> Hmm I thought that `Once` and `SetOnce` would live in the same module,
>> but if they don't then I think it's better to keep the `set_once`
>> module as-is.
>
> I guess they could live together. I was thinking a module for each. We
> can always move it, the module name is not part of a public API.
>
> Let's go with `set_once` for now and we can change it later, if we
> decide it is for the better?

Sure.

---
Cheers,
Benno

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Andreas Hindborg]

"Benno Lossin" <lossin@kernel.org> writes:

> On Tue Jul 8, 2025 at 10:54 AM CEST, Andreas Hindborg wrote:
>> "Boqun Feng" <boqun.feng@gmail.com> writes:
>>
>>> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
>>>> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>>> >
>>>> > Introduce the `SetOnce` type, a container that can only be written once.
>>>> > The container uses an internal atomic to synchronize writes to the internal
>>>> > value.
>>>> >
>>>> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>>>
>>>> LGTM:
>>>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>>>>
>>>> > +impl<T> Drop for SetOnce<T> {
>>>> > +    fn drop(&mut self) {
>>>> > +        if self.init.load(Acquire) == 2 {
>>>> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>>>> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
>>>> > +            // `self`.
>>>> > +            unsafe { drop_in_place(self.value.get()) };
>>>>
>>>> This load does not need to be Acquire. It can be a Relaxed load or
>>>> even an unsynchronized one since the access is exclusive.
>>>
>>> Right, I think we can do the similar as Revocable here:
>>>
>>>         if *self.init.get_mut() == 2 { }

Ok, now I got it. You are saying I don't need to use the atomic load
method, because I have mutable access. Sounds good.

But I guess a relaxed load and access through a mutable reference should
result in the same code generation on most (all?) platforms?

>>>
>>> Further, with my following Benno's suggestion and making `Atomic<T>` an
>>> `UnsafeCell<T>:
>>>
>>> 	https://lore.kernel.org/rust-for-linux/aGhh-TvNOWhkt0JG@Mac.home/
>>>
>>> compiler can generate a noalias reference here, which allows further
>>> optimization.
>>>
>>
>> You would like to remove `PhantomPinned` to enable noalias? I guess that
>> makes sense in this case. I'll fix that for next spin.
>
> I think you two are talking about different things. Boqun is saying that
> the `Atomic<T>` will use `UnsafeCell` rather than `Opaque`, which will
> potentially allow more optimizations.
>
> But you are talking about `SetOnce`, right? I think it makes more sense
> for `SetOnce` to use `UnsafeCell<MaybeUninit<T>>` rather than `Opaque`
> too. So feel free to change it in the next version.

Exactly. We don't need `UnsafePinned` mechanics here.


Best regards,
Andreas Hindborg

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Benno Lossin]

On Wed Jul 9, 2025 at 12:34 PM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@kernel.org> writes:
>> On Tue Jul 8, 2025 at 10:54 AM CEST, Andreas Hindborg wrote:
>>> "Boqun Feng" <boqun.feng@gmail.com> writes:
>>>> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
>>>>> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>>>> >
>>>>> > Introduce the `SetOnce` type, a container that can only be written once.
>>>>> > The container uses an internal atomic to synchronize writes to the internal
>>>>> > value.
>>>>> >
>>>>> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>>>>
>>>>> LGTM:
>>>>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>>>>>
>>>>> > +impl<T> Drop for SetOnce<T> {
>>>>> > +    fn drop(&mut self) {
>>>>> > +        if self.init.load(Acquire) == 2 {
>>>>> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>>>>> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
>>>>> > +            // `self`.
>>>>> > +            unsafe { drop_in_place(self.value.get()) };
>>>>>
>>>>> This load does not need to be Acquire. It can be a Relaxed load or
>>>>> even an unsynchronized one since the access is exclusive.
>>>>
>>>> Right, I think we can do the similar as Revocable here:
>>>>
>>>>         if *self.init.get_mut() == 2 { }
>
> Ok, now I got it. You are saying I don't need to use the atomic load
> method, because I have mutable access. Sounds good.
>
> But I guess a relaxed load and access through a mutable reference should
> result in the same code generation on most (all?) platforms?

AFAIK it is not the same on arm.

---
Cheers,
Benno

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Boqun Feng]

On Wed, Jul 09, 2025 at 08:22:16PM +0200, Benno Lossin wrote:
> On Wed Jul 9, 2025 at 12:34 PM CEST, Andreas Hindborg wrote:
> > "Benno Lossin" <lossin@kernel.org> writes:
> >> On Tue Jul 8, 2025 at 10:54 AM CEST, Andreas Hindborg wrote:
> >>> "Boqun Feng" <boqun.feng@gmail.com> writes:
> >>>> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
> >>>>> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
> >>>>> >
> >>>>> > Introduce the `SetOnce` type, a container that can only be written once.
> >>>>> > The container uses an internal atomic to synchronize writes to the internal
> >>>>> > value.
> >>>>> >
> >>>>> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> >>>>>
> >>>>> LGTM:
> >>>>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> >>>>>
> >>>>> > +impl<T> Drop for SetOnce<T> {
> >>>>> > +    fn drop(&mut self) {
> >>>>> > +        if self.init.load(Acquire) == 2 {
> >>>>> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
> >>>>> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
> >>>>> > +            // `self`.
> >>>>> > +            unsafe { drop_in_place(self.value.get()) };
> >>>>>
> >>>>> This load does not need to be Acquire. It can be a Relaxed load or
> >>>>> even an unsynchronized one since the access is exclusive.
> >>>>
> >>>> Right, I think we can do the similar as Revocable here:
> >>>>
> >>>>         if *self.init.get_mut() == 2 { }
> >
> > Ok, now I got it. You are saying I don't need to use the atomic load
> > method, because I have mutable access. Sounds good.
> >
> > But I guess a relaxed load and access through a mutable reference should
> > result in the same code generation on most (all?) platforms?
> 
> AFAIK it is not the same on arm.
> 

Right, when LTO=y, arm64 use acquire load to implement
READ_ONCE()/atomic_read().

Regards,
Boqun

> ---
> Cheers,
> Benno
> 

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Benno Lossin]

On Wed Jul 9, 2025 at 10:12 PM CEST, Boqun Feng wrote:
> On Wed, Jul 09, 2025 at 08:22:16PM +0200, Benno Lossin wrote:
>> On Wed Jul 9, 2025 at 12:34 PM CEST, Andreas Hindborg wrote:
>> > "Benno Lossin" <lossin@kernel.org> writes:
>> >> On Tue Jul 8, 2025 at 10:54 AM CEST, Andreas Hindborg wrote:
>> >>> "Boqun Feng" <boqun.feng@gmail.com> writes:
>> >>>> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
>> >>>>> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>> >>>>> >
>> >>>>> > Introduce the `SetOnce` type, a container that can only be written once.
>> >>>>> > The container uses an internal atomic to synchronize writes to the internal
>> >>>>> > value.
>> >>>>> >
>> >>>>> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>> >>>>>
>> >>>>> LGTM:
>> >>>>> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>> >>>>>
>> >>>>> > +impl<T> Drop for SetOnce<T> {
>> >>>>> > +    fn drop(&mut self) {
>> >>>>> > +        if self.init.load(Acquire) == 2 {
>> >>>>> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>> >>>>> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
>> >>>>> > +            // `self`.
>> >>>>> > +            unsafe { drop_in_place(self.value.get()) };
>> >>>>>
>> >>>>> This load does not need to be Acquire. It can be a Relaxed load or
>> >>>>> even an unsynchronized one since the access is exclusive.
>> >>>>
>> >>>> Right, I think we can do the similar as Revocable here:
>> >>>>
>> >>>>         if *self.init.get_mut() == 2 { }
>> >
>> > Ok, now I got it. You are saying I don't need to use the atomic load
>> > method, because I have mutable access. Sounds good.
>> >
>> > But I guess a relaxed load and access through a mutable reference should
>> > result in the same code generation on most (all?) platforms?
>> 
>> AFAIK it is not the same on arm.
>> 
>
> Right, when LTO=y, arm64 use acquire load to implement
> READ_ONCE()/atomic_read().

But Andreas was talking about relaxed load vs mutable reference (=
normal unsynchronized write)?

---
Cheers,
Benno

Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

[Boqun Feng]

On Wed, Jul 09, 2025 at 10:22:04PM +0200, Benno Lossin wrote:
[...]
> >> >>>>> > +impl<T> Drop for SetOnce<T> {
> >> >>>>> > +    fn drop(&mut self) {
> >> >>>>> > +        if self.init.load(Acquire) == 2 {
> >> >>>>> > +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
> >> >>>>> > +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
> >> >>>>> > +            // `self`.
> >> >>>>> > +            unsafe { drop_in_place(self.value.get()) };
> >> >>>>>
> >> >>>>> This load does not need to be Acquire. It can be a Relaxed load or
> >> >>>>> even an unsynchronized one since the access is exclusive.
> >> >>>>
> >> >>>> Right, I think we can do the similar as Revocable here:
> >> >>>>
> >> >>>>         if *self.init.get_mut() == 2 { }
> >> >
> >> > Ok, now I got it. You are saying I don't need to use the atomic load
> >> > method, because I have mutable access. Sounds good.
> >> >
> >> > But I guess a relaxed load and access through a mutable reference should
> >> > result in the same code generation on most (all?) platforms?
> >> 
> >> AFAIK it is not the same on arm.
> >> 
> >
> > Right, when LTO=y, arm64 use acquire load to implement
> > READ_ONCE()/atomic_read().
> 
> But Andreas was talking about relaxed load vs mutable reference (=
> normal unsynchronized write)?
> 

No, I think it was a relaxed load (self.init.load(Relaxed)) vs a normal
unsynchronized *load* (*self.init.get_mut()). Yes, there is a mutable
reference, but we never use it for write.

Regards,
Boqun

> ---
> Cheers,
> Benno
>