[PATCH v11 3/8] rust: time: Introduce Delta type

FUJITA Tomonori
2025-02-20T07:10:36Z

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.

i64 is used instead of bindings::ktime_t because when the ktime_t
type is used as timestamp, it represents values from 0 to
KTIME_MAX, which is different from Delta.

as_millis() method isn't used in this patchset. It's planned to be
used in Binder driver.

Tested-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Fiona Behrens <me@kloenk.dev>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
rust/kernel/time.rs | 88 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 88 insertions(+)

diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 48b71e6641ce..622cd01e24d7 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 = crate::ffi::c_ulong;

@@ -81,3 +87,85 @@ fn sub(self, other: Ktime) -> Ktime {
}
}
}
+
+/// A span of time.
+///
+/// This struct represents a span of time, with its value stored as nanoseconds.
+/// The value can represent any valid i64 value, including negative, zero, and
+/// positive numbers.
+#[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord, Debug)]
+pub struct Delta {
+ nanos: i64,
+}
+
+impl Delta {
+ /// A span of time equal to zero.
+ pub const ZERO: Self = Self { nanos: 0 };
+
+ /// Create a new [`Delta`] from a number of microseconds.
+ ///
+ /// The `micros` can range from -9_223_372_036_854_775 to 9_223_372_036_854_775.
+ /// If `micros` is outside this range, `i64::MIN` is used for negative values,
+ /// and `i64::MAX` is used for positive values due to saturation.
+ #[inline]
+ pub const fn from_micros(micros: i64) -> Self {
+ Self {
+ nanos: micros.saturating_mul(NSEC_PER_USEC),
+ }
+ }
+
+ /// Create a new [`Delta`] from a number of milliseconds.
+ ///
+ /// The `millis` can range from -9_223_372_036_854 to 9_223_372_036_854.
+ /// If `millis` is outside this range, `i64::MIN` is used for negative values,
+ /// and `i64::MAX` is used for positive values due to saturation.
+ #[inline]
+ pub const fn from_millis(millis: i64) -> Self {
+ Self {
+ nanos: millis.saturating_mul(NSEC_PER_MSEC),
+ }
+ }
+
+ /// Create a new [`Delta`] from a number of seconds.
+ ///
+ /// The `secs` can range from -9_223_372_036 to 9_223_372_036.
+ /// If `secs` is outside this range, `i64::MIN` is used for negative values,
+ /// and `i64::MAX` is used for positive values due to saturation.
+ #[inline]
+ pub const fn from_secs(secs: i64) -> Self {
+ Self {
+ nanos: secs.saturating_mul(NSEC_PER_SEC),
+ }
+ }
+
+ /// Return `true` if the [`Delta`] spans no time.
+ #[inline]
+ pub fn is_zero(self) -> bool {
+ self.as_nanos() == 0
+ }
+
+ /// Return `true` if the [`Delta`] spans a negative amount of time.
+ #[inline]
+ pub fn is_negative(self) -> bool {
+ self.as_nanos() < 0
+ }
+
+ /// Return the number of nanoseconds in the [`Delta`].
+ #[inline]
+ pub const fn as_nanos(self) -> i64 {
+ self.nanos
+ }
+
+ /// Return the smallest number of microseconds greater than or equal
+ /// to the value in the [`Delta`].
+ #[inline]
+ pub const fn as_micros_ceil(self) -> i64 {
+ self.as_nanos().saturating_add(NSEC_PER_USEC - 1) / NSEC_PER_USEC
+ }
+
+ /// Return the number of milliseconds in the [`Delta`].
+ #[inline]
+ pub const fn as_millis(self) -> i64 {
+ self.as_nanos() / NSEC_PER_MSEC
+ }
+}
--
2.43.0