linux-kernel - Re: [PATCH net-next v3 2/8] rust: time: Introduce Delta type

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Message-ID: <89854EA9-63AC-447C-807C-964BB61FF0D6@kloenk.dev>
Date: Thu, 17 Oct 2024 12:17:18 +0200
From: Fiona Behrens <me@...enk.dev>
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 2/8] rust: time: Introduce Delta type



On 16 Oct 2024, at 5:52, FUJITA Tomonori wrote:

> Introduce a type representing a span of time. Define our own type
> because `core::time::Duration` is large and could panic during
> creation.
>
> time::Ktime could be also used for time duration but timestamp and
> timedelta are different so better to use a new type.
>
> i64 is used instead of u64 to represent a span of time; some C drivers
> uses negative Deltas and i64 is more compatible with Ktime using i64
> too (e.g., ktime_[us|ms]_delta() APIs return i64 so we create Delta
> object without type conversion.
>
> Delta::from_[micro|millis|secs] APIs take i64. When a span of time
> overflows, i64::MAX is used.
>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
> ---
>  rust/kernel/time.rs | 74 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 74 insertions(+)
>
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 4a7c6037c256..38a70dc98083 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -8,9 +8,15 @@
>  //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
>  //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
>
> +/// The number of nanoseconds per microsecond.
> +pub const NSEC_PER_USEC: i64 = bindings::NSEC_PER_USEC as i64;
> +
>  /// The number of nanoseconds per millisecond.
>  pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64;
>
> +/// The number of nanoseconds per second.
> +pub const NSEC_PER_SEC: i64 = bindings::NSEC_PER_SEC as i64;
> +
>  /// The time unit of Linux kernel. One jiffy equals (1/HZ) second.
>  pub type Jiffies = core::ffi::c_ulong;
>
> @@ -81,3 +87,71 @@ fn sub(self, other: Ktime) -> Ktime {
>          }
>      }
>  }
> +
> +/// A span of time.
> +#[derive(Copy, Clone)]

Could we also derive PartialEq and Eq (maybe also PartialOrd and Ord)? Would need that to compare deltas in my LED driver.

> +pub struct Delta {
> +    nanos: i64,
> +}
> +

I think all this functions could be const (need from_millis as const for LED, but when at it we could probably make all those const?)

 - Fiona

> +impl Delta {
> +    /// Create a new `Delta` from a number of nanoseconds.
> +    #[inline]
> +    pub fn from_nanos(nanos: i64) -> Self {
> +        Self { nanos }
> +    }
> +
> +    /// Create a new `Delta` from a number of microseconds.
> +    #[inline]
> +    pub fn from_micros(micros: i64) -> Self {
> +        Self {
> +            nanos: micros.saturating_mul(NSEC_PER_USEC),
> +        }
> +    }
> +
> +    /// Create a new `Delta` from a number of milliseconds.
> +    #[inline]
> +    pub fn from_millis(millis: i64) -> Self {
> +        Self {
> +            nanos: millis.saturating_mul(NSEC_PER_MSEC),
> +        }
> +    }
> +
> +    /// Create a new `Delta` from a number of seconds.
> +    #[inline]
> +    pub fn from_secs(secs: i64) -> Self {
> +        Self {
> +            nanos: secs.saturating_mul(NSEC_PER_SEC),
> +        }
> +    }
> +
> +    /// Return `true` if the `Detla` spans no time.
> +    #[inline]
> +    pub fn is_zero(self) -> bool {
> +        self.nanos == 0
> +    }
> +
> +    /// Return the number of nanoseconds in the `Delta`.
> +    #[inline]
> +    pub fn as_nanos(self) -> i64 {
> +        self.nanos
> +    }
> +
> +    /// Return the number of microseconds in the `Delta`.
> +    #[inline]
> +    pub fn as_micros(self) -> i64 {
> +        self.nanos / NSEC_PER_USEC
> +    }
> +
> +    /// Return the number of milliseconds in the `Delta`.
> +    #[inline]
> +    pub fn as_millis(self) -> i64 {
> +        self.nanos / NSEC_PER_MSEC
> +    }
> +
> +    /// Return the number of seconds in the `Delta`.
> +    #[inline]
> +    pub fn as_secs(self) -> i64 {
> +        self.nanos / NSEC_PER_SEC
> +    }
> +}
> -- 
> 2.43.0