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

[Alice Ryhl]

On Wed, Jul 1, 2026 at 6:20 PM Gary Guo <gary@xxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> > ---
> >  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.

I believe that the lock class key this implicitly creates is only
valid in static memory, and not for a Ratelimit stored anywhere else.

Alice