Re: [PATCH v9 6/7] rust: time: Add Instant::from_ktime()

[Alice Ryhl]

On Thu, Aug 21, 2025 at 9:34 PM Lyude Paul <lyude@xxxxxxxxxx> wrote:
>
> For implementing Rust bindings which can return a point in time.
>
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>

> V4:
> * Turn from_nanos() into an unsafe function in order to ensure that we
>   uphold the invariants of Instant
> V5:
> * Add debug_assert!() to from_nanos
> V8:
> * Change name of function from Instant::from_nanos() to
>   Instant::from_ktime()
> V9:
> * Fix outdated comments in from_ktime (nanos -> ktime)
>
>  rust/kernel/time.rs | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 64c8dcf548d63..874a1023dcdf9 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -200,6 +200,29 @@ pub fn elapsed(&self) -> Delta {
>      pub(crate) fn as_nanos(&self) -> i64 {
>          self.inner
>      }
> +
> +    /// Create an [`Instant`] from a `ktime_t` without checking if it is non-negative.
> +    ///
> +    /// # Panics
> +    ///
> +    /// On debug builds, this function will panic if `ktime` is not in the range from 0 to
> +    /// `KTIME_MAX`.
> +    ///
> +    /// # Safety
> +    ///
> +    /// The caller promises that `ktime` is in the range from 0 to `KTIME_MAX`.
> +    #[expect(unused)]

I would consider just making it pub to avoid the need for this expect.

> +    #[inline]
> +    pub(crate) unsafe fn from_ktime(ktime: bindings::ktime_t) -> Self {
> +        debug_assert!(ktime >= 0);

If you're going to have a debug assertion, perhaps it would make sense
to check both bounds?

Alice