Re: [PATCH 3/5] rust: add pr_*_ratelimit! macros for printing

["Gary Guo" <gary@garyguo.net>]

On Tue Jun 23, 2026 at 4:38 PM BST, Alice Ryhl wrote:
> Printing can be very expensive if it occurs often, so printing that can
> be triggered by userspace should be rate limited. For this purpose, add
> a Rust wrapper around `struct ratelimit_state` and use it in the new
> macros.
>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/helpers/helpers.c   |   1 +
>  rust/helpers/ratelimit.c |  14 ++++
>  rust/kernel/lib.rs       |   1 +
>  rust/kernel/prelude.rs   |   8 ++
>  rust/kernel/ratelimit.rs | 202 +++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 226 insertions(+)
>
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index d17eaec76450..2184b11c927f 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -80,6 +80,7 @@
>  #include "processor.c"
>  #include "property.c"
>  #include "pwm.c"
> +#include "ratelimit.c"
>  #include "rbtree.c"
>  #include "rcu.c"
>  #include "refcount.c"
> diff --git a/rust/helpers/ratelimit.c b/rust/helpers/ratelimit.c
> new file mode 100644
> index 000000000000..e5052f568b81
> --- /dev/null
> +++ b/rust/helpers/ratelimit.c
> @@ -0,0 +1,14 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/ratelimit.h>
> +
> +__rust_helper void rust_helper_ratelimit_state_init(struct ratelimit_state *rs,
> +						    int interval, int burst)
> +{
> +	ratelimit_state_init(rs, interval, burst);
> +}
> +
> +__rust_helper void rust_helper_ratelimit_state_exit(struct ratelimit_state *rs)
> +{
> +	ratelimit_state_exit(rs);
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index b72b2fbe046d..ba65ab4f0b8c 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -111,6 +111,7 @@
>  pub mod ptr;
>  #[cfg(CONFIG_RUST_PWM_ABSTRACTIONS)]
>  pub mod pwm;
> +pub mod ratelimit;
>  pub mod rbtree;
>  pub mod regulator;
>  pub mod revocable;
> diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
> index 44edf72a4a24..5a66028dd973 100644
> --- a/rust/kernel/prelude.rs
> +++ b/rust/kernel/prelude.rs
> @@ -89,13 +89,21 @@
>      },
>      init::InPlaceInit,
>      pr_alert,
> +    pr_alert_ratelimited,
>      pr_crit,
> +    pr_crit_ratelimited,
>      pr_debug,
> +    pr_debug_ratelimited,
>      pr_emerg,
> +    pr_emerg_ratelimited,
>      pr_err,
> +    pr_err_ratelimited,
>      pr_info,
> +    pr_info_ratelimited,
>      pr_notice,
> +    pr_notice_ratelimited,
>      pr_warn,
> +    pr_warn_ratelimited,
>      static_assert,
>      str::CStrExt as _,
>      try_init,
> diff --git a/rust/kernel/ratelimit.rs b/rust/kernel/ratelimit.rs
> new file mode 100644
> index 000000000000..da0a49412023
> --- /dev/null
> +++ b/rust/kernel/ratelimit.rs
> @@ -0,0 +1,202 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Rate limiting support.
> +//!
> +//! C header: [`include/linux/ratelimit.h`](srctree/include/linux/ratelimit.h)
> +
> +use crate::{
> +    bindings,
> +    prelude::*,
> +    types::Opaque, //
> +};
> +
> +/// Defines a `static` containing a [`Ratelimit`].
> +#[macro_export]
> +macro_rules! ratelimit_state_init {
> +    ($name:ident, $interval:expr, $burst:expr $(,)?) => {
> +        static $name: $crate::ratelimit::Ratelimit = {
> +            let init: $crate::bindings::ratelimit_state = $crate::bindings::ratelimit_state {
> +                lock: $crate::sync::lock::spinlock::raw_spin_lock_unlocked($crate::c_str!(
> +                    ::core::stringify!($name)
> +                )),
> +                interval: $interval,
> +                burst: $burst,
> +                // SAFETY: This type can be zeroed.
> +                ..unsafe { ::core::mem::zeroed() }
> +            };
> +            // SAFETY: This is a repr(transparent) wrapper, and the invariants are satisfied.
> +            unsafe { ::core::mem::transmute(init) }

Hmm, I don't see anything that prohibit this from being a const fn? What have  I
missed?

It looks like this type is move-initializable.

Best,
Gary

> +        };
> +    };
> +}
> +pub use ratelimit_state_init;
> +
> +/// Rate limiter state.
> +///
> +/// # Invariants
> +///
> +/// The `inner` field contains an initialized `struct ratelimit_state`.
> +#[pin_data(PinnedDrop)]
> +#[repr(transparent)]
> +pub struct Ratelimit {
> +    #[pin]
> +    inner: Opaque<bindings::ratelimit_state>,
> +}
> +
> +// SAFETY: `Ratelimit` is safe to be sent to any task.
> +unsafe impl Send for Ratelimit {}
> +
> +// SAFETY: `Ratelimit` is safe to be accessed concurrently as it is protected by an internal
> +// spinlock.
> +unsafe impl Sync for Ratelimit {}
> +
> +impl Ratelimit {
> +    /// Constructs a [`Ratelimit`] with the specified configuration.
> +    ///
> +    /// If `interval` is zero, then no rate limit is applied.
> +    #[inline]
> +    pub fn new(interval: i32, burst: i32) -> impl PinInit<Self> {
> +        // INVARIANT: This creates a `Ratelimit` containing an initialized `struct ratelimit_state`
> +        pin_init!(Self {
> +            inner <- Opaque::ffi_init(|slot: *mut bindings::ratelimit_state| {
> +                // SAFETY: `slot` is a valid pointer to an uninitialized `struct ratelimit_state`.
> +                // The memory is pinned so it remains valid until `ratelimit_state_exit` is called.
> +                unsafe { bindings::ratelimit_state_init(slot, interval, burst) };
> +            }),
> +        })
> +    }