Re: [PATCH] rust: time: implement `Display` for `Delta`

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

On Mon May 11, 2026 at 3:22 PM BST, Andreas Hindborg wrote:
> Alice Ryhl <aliceryhl@google.com> writes:
>
>> On Sun, Feb 15, 2026 at 09:14:05PM +0100, Andreas Hindborg wrote:
>>> Implement the `Display` trait for `Delta` so that it can be displayed by a
>>> formatter.
>>> 
>>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>> ---
>>>  rust/kernel/time.rs | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>> 
>>> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
>>> index 6ea98dfcd0278..e18fd17f38c5a 100644
>>> --- a/rust/kernel/time.rs
>>> +++ b/rust/kernel/time.rs
>>> @@ -474,3 +474,9 @@ pub fn rem_nanos(self, dividend: i32) -> Self {
>>>          }
>>>      }
>>>  }
>>> +
>>> +impl kernel::fmt::Display for Delta {
>>> +    fn fmt(&self, f: &mut kernel::fmt::Formatter<'_>) -> kernel::fmt::Result {
>>> +        f.write_fmt(kernel::prelude::fmt!("{}", self.as_nanos()))
>>
>> I think this can just be
>>
>> 	self.as_nanos().fmt(f)
>>
>> Though I think it would be nicer to include an 'ns' suffix here so it's
>> not just the number?
>
> I was planning to use this to format a delta to output via a configfs in
> rnull. The existing C driver does not include the "ns" suffix, which is
> why I did not either.
>
> I am not opposed to adding the suffix for this particular
> implementation, but that would mean my user for this code will no longer
> be a user, and I would drop the patch in favor of another solution at
> the call site.
>
> Please advise which of the following make most sense:
>
>  - Merge this patch without a suffix.
>  - Iterate on this patch and merge it without a user.
>  - Drop this patch for now.

Display is supposed to be user-facing and readable. So to me it's weird that the
"Display" impl would format "Delta" as nanoseconds without a suffix. I think if
you need to depend on its behaviour to be just nanosecond numbers, you should
perhaps just use `delta.as_nanos()` on the print side.

Best,
Gary