Commit 22b65a40 authored by Lyude Paul's avatar Lyude Paul Committed by Andreas Hindborg
Browse files

rust: time: Implement Add<Delta>/Sub<Delta> for Instant 



In order to copy the behavior rust currently follows for basic arithmetic
operations and panic if the result of an addition or subtraction results in
a value that would violate the invariants of Instant, but only if the
kernel has overflow checking for rust enabled.

Signed-off-by: default avatarLyude Paul <lyude@redhat.com>
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Reviewed-by: default avatarFUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: default avatarDaniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250820203704.731588-2-lyude@redhat.com


Signed-off-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
parent 4b014749

rust/kernel/time.rs

+42 −1
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ 
//! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).



use core::marker::PhantomData;

use core::ops;



pub mod delay;

pub mod hrtimer;
@@ -224,7 +225,7 @@ pub(crate) unsafe fn from_ktime(ktime: bindings::ktime_t) -> Self { 
    }

}



impl<C: ClockSource> core::ops::Sub for Instant<C> {

impl<C: ClockSource> ops::Sub for Instant<C> {

    type Output = Delta;



    // By the type invariant, it never overflows.
@@ -236,6 +237,46 @@ fn sub(self, other: Instant<C>) -> Delta { 
    }

}



impl<T: ClockSource> ops::Add<Delta> for Instant<T> {

    type Output = Self;



    #[inline]

    fn add(self, rhs: Delta) -> Self::Output {

        // INVARIANT: With arithmetic over/underflow checks enabled, this will panic if we overflow

        // (e.g. go above `KTIME_MAX`)

        let res = self.inner + rhs.nanos;



        // INVARIANT: With overflow checks enabled, we verify here that the value is >= 0

        #[cfg(CONFIG_RUST_OVERFLOW_CHECKS)]

        assert!(res >= 0);



        Self {

            inner: res,

            _c: PhantomData,

        }

    }

}



impl<T: ClockSource> ops::Sub<Delta> for Instant<T> {

    type Output = Self;



    #[inline]

    fn sub(self, rhs: Delta) -> Self::Output {

        // INVARIANT: With arithmetic over/underflow checks enabled, this will panic if we overflow

        // (e.g. go above `KTIME_MAX`)

        let res = self.inner - rhs.nanos;



        // INVARIANT: With overflow checks enabled, we verify here that the value is >= 0

        #[cfg(CONFIG_RUST_OVERFLOW_CHECKS)]

        assert!(res >= 0);



        Self {

            inner: res,

            _c: PhantomData,

        }

    }

}



/// A span of time.

///

/// This struct represents a span of time, with its value stored as nanoseconds.