kernel/
time.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! Time related primitives.
4//!
5//! This module contains the kernel APIs related to time and timers that
6//! have been ported or wrapped for usage by Rust code in the kernel.
7//!
8//! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
9//! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
10
11pub mod hrtimer;
12
13/// The number of nanoseconds per millisecond.
14pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64;
15
16/// The time unit of Linux kernel. One jiffy equals (1/HZ) second.
17pub type Jiffies = crate::ffi::c_ulong;
18
19/// The millisecond time unit.
20pub type Msecs = crate::ffi::c_uint;
21
22/// Converts milliseconds to jiffies.
23#[inline]
24pub fn msecs_to_jiffies(msecs: Msecs) -> Jiffies {
25    // SAFETY: The `__msecs_to_jiffies` function is always safe to call no
26    // matter what the argument is.
27    unsafe { bindings::__msecs_to_jiffies(msecs) }
28}
29
30/// A Rust wrapper around a `ktime_t`.
31#[repr(transparent)]
32#[derive(Copy, Clone)]
33pub struct Ktime {
34    inner: bindings::ktime_t,
35}
36
37impl Ktime {
38    /// Create a `Ktime` from a raw `ktime_t`.
39    #[inline]
40    pub fn from_raw(inner: bindings::ktime_t) -> Self {
41        Self { inner }
42    }
43
44    /// Get the current time using `CLOCK_MONOTONIC`.
45    #[inline]
46    pub fn ktime_get() -> Self {
47        // SAFETY: It is always safe to call `ktime_get` outside of NMI context.
48        Self::from_raw(unsafe { bindings::ktime_get() })
49    }
50
51    /// Divide the number of nanoseconds by a compile-time constant.
52    #[inline]
53    fn divns_constant<const DIV: i64>(self) -> i64 {
54        self.to_ns() / DIV
55    }
56
57    /// Returns the number of nanoseconds.
58    #[inline]
59    pub fn to_ns(self) -> i64 {
60        self.inner
61    }
62
63    /// Returns the number of milliseconds.
64    #[inline]
65    pub fn to_ms(self) -> i64 {
66        self.divns_constant::<NSEC_PER_MSEC>()
67    }
68}
69
70/// Returns the number of milliseconds between two ktimes.
71#[inline]
72pub fn ktime_ms_delta(later: Ktime, earlier: Ktime) -> i64 {
73    (later - earlier).to_ms()
74}
75
76impl core::ops::Sub for Ktime {
77    type Output = Ktime;
78
79    #[inline]
80    fn sub(self, other: Ktime) -> Ktime {
81        Self {
82            inner: self.inner - other.inner,
83        }
84    }
85}
86
87/// An identifier for a clock. Used when specifying clock sources.
88///
89///
90/// Selection of the clock depends on the use case. In some cases the usage of a
91/// particular clock is mandatory, e.g. in network protocols, filesystems.In other
92/// cases the user of the clock has to decide which clock is best suited for the
93/// purpose. In most scenarios clock [`ClockId::Monotonic`] is the best choice as it
94/// provides a accurate monotonic notion of time (leap second smearing ignored).
95#[derive(Clone, Copy, PartialEq, Eq, Debug)]
96#[repr(u32)]
97pub enum ClockId {
98    /// A settable system-wide clock that measures real (i.e., wall-clock) time.
99    ///
100    /// Setting this clock requires appropriate privileges. This clock is
101    /// affected by discontinuous jumps in the system time (e.g., if the system
102    /// administrator manually changes the clock), and by frequency adjustments
103    /// performed by NTP and similar applications via adjtime(3), adjtimex(2),
104    /// clock_adjtime(2), and ntp_adjtime(3). This clock normally counts the
105    /// number of seconds since 1970-01-01 00:00:00 Coordinated Universal Time
106    /// (UTC) except that it ignores leap seconds; near a leap second it may be
107    /// adjusted by leap second smearing to stay roughly in sync with UTC. Leap
108    /// second smearing applies frequency adjustments to the clock to speed up
109    /// or slow down the clock to account for the leap second without
110    /// discontinuities in the clock. If leap second smearing is not applied,
111    /// the clock will experience discontinuity around leap second adjustment.
112    RealTime = bindings::CLOCK_REALTIME,
113    /// A monotonically increasing clock.
114    ///
115    /// A nonsettable system-wide clock that represents monotonic time since—as
116    /// described by POSIX—"some unspecified point in the past". On Linux, that
117    /// point corresponds to the number of seconds that the system has been
118    /// running since it was booted.
119    ///
120    /// The CLOCK_MONOTONIC clock is not affected by discontinuous jumps in the
121    /// CLOCK_REAL (e.g., if the system administrator manually changes the
122    /// clock), but is affected by frequency adjustments. This clock does not
123    /// count time that the system is suspended.
124    Monotonic = bindings::CLOCK_MONOTONIC,
125    /// A monotonic that ticks while system is suspended.
126    ///
127    /// A nonsettable system-wide clock that is identical to CLOCK_MONOTONIC,
128    /// except that it also includes any time that the system is suspended. This
129    /// allows applications to get a suspend-aware monotonic clock without
130    /// having to deal with the complications of CLOCK_REALTIME, which may have
131    /// discontinuities if the time is changed using settimeofday(2) or similar.
132    BootTime = bindings::CLOCK_BOOTTIME,
133    /// International Atomic Time.
134    ///
135    /// A system-wide clock derived from wall-clock time but counting leap seconds.
136    ///
137    /// This clock is coupled to CLOCK_REALTIME and will be set when CLOCK_REALTIME is
138    /// set, or when the offset to CLOCK_REALTIME is changed via adjtimex(2). This
139    /// usually happens during boot and **should** not happen during normal operations.
140    /// However, if NTP or another application adjusts CLOCK_REALTIME by leap second
141    /// smearing, this clock will not be precise during leap second smearing.
142    ///
143    /// The acronym TAI refers to International Atomic Time.
144    TAI = bindings::CLOCK_TAI,
145}
146
147impl ClockId {
148    fn into_c(self) -> bindings::clockid_t {
149        self as bindings::clockid_t
150    }
151}
kernel/time.rs

kernel/
time.rs
