Re: [PATCH v2 1/5] rust: add warn_on_err macro

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

On Fri Apr 24, 2026 at 3:35 PM BST, Alexandre Courbot wrote:
> On Thu Apr 23, 2026 at 8:34 PM JST, Gary Guo wrote:
>> On Tue Apr 21, 2026 at 7:16 AM BST, Alexandre Courbot wrote:
>>> While we already have the `warn_on` macro, a common usage pattern in
>>> Rust is to check whether a `Result` is an error. Add a helper macro that
>>> allows this.
>>>
>>> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
>>> ---
>>>  rust/kernel/bug.rs | 10 ++++++++++
>>>  1 file changed, 10 insertions(+)
>>>
>>> diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
>>> index ed943960f851..2fefc0aeef81 100644
>>> --- a/rust/kernel/bug.rs
>>> +++ b/rust/kernel/bug.rs
>>> @@ -130,3 +130,13 @@ macro_rules! warn_on {
>>>          cond
>>>      }};
>>>  }
>>> +
>>> +/// Report a warning if `res` is an error and return it unmodified.
>>> +#[macro_export]
>>> +macro_rules! warn_on_err {
>>> +    ($res:expr) => {{
>>> +        let res = $res;
>>> +        let _ = $crate::warn_on!(res.is_err());
>>> +        res
>>> +    }};
>>> +}
>>
>>
>> I think `warn_on_err` could just be expressed as
>>
>>     res.inspect_err(|_| warn_on!(true))
>
> This would turn the verbose error message into something like
>
>   [true] module.rs
>
> I.e. the expression passed as argument won't be printed.
>
> That being said, my version has the exact same problem and I don't see
> how we can fix this without splitting `warn_on` and making it more
> complex.
>
> Since this was done as a small convenience, I think I will just remove
> this from this patchset and revisit later as a separate series.

Something like this?

#[macro_export]
macro_rules! warn {
    () => {{
        const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);

        $crate::warn_flags!(file!(), WARN_ON_FLAGS);
    }}
    ($msg:expr) => {{
        #[cfg(CONFIG_DEBUG_BUGVERBOSE_DETAILED)]
        const _COND_STR: &str = concat!("[", $msg, "] ", file!());
        #[cfg(not(CONFIG_DEBUG_BUGVERBOSE_DETAILED))]
        const _COND_STR: &str = file!();

        const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);

        $crate::warn_flags!(_COND_STR, WARN_ON_FLAGS);
    }};
}

#[macro_export]
macro_rules! warn_on {
    ($cond:expr) => {{
        let cond = $cond;
        if cond {
            warn!(stringify!($cond));
        }
        cond
    }};
}

Then you can just use a `warn!()` with custom message.

Best,
Gary