linux-kernel - Re: [PATCH net-next v3 4/8] rust: time: Implement addition of Ktime and Delta

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Message-ID: <ZxAZ36EUKapnp-Fk@Boquns-Mac-mini.local>
Date: Wed, 16 Oct 2024 12:54:07 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, andrew@...n.ch,
	hkallweit1@...il.com, tmgross@...ch.edu, ojeda@...nel.org,
	alex.gaynor@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me, a.hindborg@...sung.com,
	aliceryhl@...gle.com, anna-maria@...utronix.de, frederic@...nel.org,
	tglx@...utronix.de, arnd@...db.de, jstultz@...gle.com,
	sboyd@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 4/8] rust: time: Implement addition of Ktime
 and Delta

On Wed, Oct 16, 2024 at 12:52:09PM +0900, FUJITA Tomonori wrote:
> Implement Add<Delta> for Ktime to support the operation:
> 
> Ktime = Ktime + Delta
> 
> This is typically used to calculate the future time when the timeout
> will occur.
> 
> timeout Ktime = current Ktime (via ktime_get()) + Delta;
> // do something
> if (ktime_get() > timeout Ktime) {
>     // timed out
> }
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
> ---
>  rust/kernel/time.rs | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 8c00854db58c..9b0537b63cf7 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -155,3 +155,14 @@ pub fn as_secs(self) -> i64 {
>          self.nanos / NSEC_PER_SEC
>      }
>  }
> +
> +impl core::ops::Add<Delta> for Ktime {
> +    type Output = Ktime;
> +
> +    #[inline]
> +    fn add(self, delta: Delta) -> Ktime {
> +        Ktime {
> +            inner: self.inner + delta.as_nanos(),

What if overflow happens in this addition? Is the expectation that user
should avoid overflows? I asked because we have ktime_add_safe() which
saturate at KTIME_SEC_MAX.

Regards,
Boqun

> +        }
> +    }
> +}
> -- 
> 2.43.0
> 
>