Re: [PATCH v3 2/2] rust: Add pr_*_once macros

[Gary Guo <gary@garyguo.net>]

On Mon, 17 Nov 2025 09:24:52 +0900
FUJITA Tomonori <fujita.tomonori@gmail.com> wrote:

> Add Rust version of pr_[emerg|alert|crit|err|warn|notic|info]_once
> macros, which print a message only once.
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>

A meta topic about this one.

I think we're adding too many macros with this. In C we had to do this
way because expressive power of mascros are more limited, but I wonder
if we should just add different flavours with macros.

For example, instead of

	pr_warn_once!("foo");

we could do

	pr_warn!(once, "foo");

If we are adding extra tunables, we could do something similar too.
Given all print macros start with a format string, doing this won't create
any ambiguity.

An added benefit is that now you only need to implement the functionality
once in `print_macro!` and all other macros gain the feature, too.

Best,
Gary

> ---
>  rust/kernel/print.rs | 70 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
> 
> diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
> index af32054be5a2..6fd84389a858 100644
> --- a/rust/kernel/print.rs
> +++ b/rust/kernel/print.rs
> @@ -506,3 +506,73 @@ macro_rules! do_once_lite {
>          ONCE.call_once(|| { $($e)* });
>      }};
>  }
> +
> +/// Prints an emergency-level message (level 0) only once.
> +///
> +/// Equivalent to the kernel's `pr_emerg_once` macro.
> +#[macro_export]
> +macro_rules! pr_emerg_once (
> +    ($($arg:tt)*) => (
> +        $crate::do_once_lite! { $crate::pr_emerg!($($arg)*) }
> +    )
> +);
> +
> +/// Prints an alert-level message (level 1) only once.
> +///
> +/// Equivalent to the kernel's `pr_alert_once` macro.
> +#[macro_export]
> +macro_rules! pr_alert_once (
> +    ($($arg:tt)*) => (
> +        $crate::do_once_lite! { $crate::pr_alert!($($arg)*) }
> +    )
> +);
> +
> +/// Prints a critical-level message (level 2) only once.
> +///
> +/// Equivalent to the kernel's `pr_crit_once` macro.
> +#[macro_export]
> +macro_rules! pr_crit_once (
> +    ($($arg:tt)*) => (
> +        $crate::do_once_lite! { $crate::pr_crit!($($arg)*) }
> +    )
> +);
> +
> +/// Prints an error-level message (level 3) only once.
> +///
> +/// Equivalent to the kernel's `pr_err_once` macro.
> +#[macro_export]
> +macro_rules! pr_err_once (
> +    ($($arg:tt)*) => (
> +        $crate::do_once_lite! { $crate::pr_err!($($arg)*) }
> +    )
> +);
> +
> +/// Prints a warning-level message (level 4) only once.
> +///
> +/// Equivalent to the kernel's `pr_warn_once` macro.
> +#[macro_export]
> +macro_rules! pr_warn_once (
> +    ($($arg:tt)*) => (
> +        $crate::do_once_lite! { $crate::pr_warn!($($arg)*) }
> +    )
> +);
> +
> +/// Prints a notice-level message (level 5) only once.
> +///
> +/// Equivalent to the kernel's `pr_notice_once` macro.
> +#[macro_export]
> +macro_rules! pr_notice_once (
> +    ($($arg:tt)*) => (
> +        $crate::do_once_lite! { $crate::pr_notice!($($arg)*) }
> +    )
> +);
> +
> +/// Prints an info-level message (level 6) only once.
> +///
> +/// Equivalent to the kernel's `pr_info_once` macro.
> +#[macro_export]
> +macro_rules! pr_info_once (
> +    ($($arg:tt)*) => (
> +        $crate::do_once_lite! { $crate::pr_info!($($arg)*) }
> +    )
> +);