linux-kernel - [PATCH v3 3/3] rust: time: Add ktime

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Message-ID: <20250609010415.3302835-4-fujita.tomonori@gmail.com>
Date: Mon,  9 Jun 2025 10:04:13 +0900
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: a.hindborg@...nel.org,
	alex.gaynor@...il.com,
	ojeda@...nel.org
Cc: aliceryhl@...gle.com,
	anna-maria@...utronix.de,
	bjorn3_gh@...tonmail.com,
	boqun.feng@...il.com,
	dakr@...nel.org,
	frederic@...nel.org,
	gary@...yguo.net,
	jstultz@...gle.com,
	linux-kernel@...r.kernel.org,
	lossin@...nel.org,
	lyude@...hat.com,
	rust-for-linux@...r.kernel.org,
	sboyd@...nel.org,
	tglx@...utronix.de,
	tmgross@...ch.edu
Subject: [PATCH v3 3/3] rust: time: Add ktime_get() to ClockSource trait

Introduce the ktime_get() associated function to the ClockSource
trait, allowing each clock source to specify how it retrieves the
current time. This enables Instant::now() to be implemented
generically using the type-level ClockSource abstraction.

This change enhances the type safety and extensibility of timekeeping
by statically associating time retrieval mechanisms with their
respective clock types. It also reduces the reliance on hardcoded
clock logic within Instant.

Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
---
 rust/helpers/helpers.c |  1 +
 rust/helpers/time.c    | 18 ++++++++++++++++++
 rust/kernel/time.rs    | 32 ++++++++++++++++++++++++++++----
 3 files changed, 47 insertions(+), 4 deletions(-)
 create mode 100644 rust/helpers/time.c

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 0f1b5d115985..0613a849e05c 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -39,6 +39,7 @@
 #include "spinlock.c"
 #include "sync.c"
 #include "task.c"
+#include "time.c"
 #include "uaccess.c"
 #include "vmalloc.c"
 #include "wait.c"
diff --git a/rust/helpers/time.c b/rust/helpers/time.c
new file mode 100644
index 000000000000..9c296e93a560
--- /dev/null
+++ b/rust/helpers/time.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/timekeeping.h>
+
+ktime_t rust_helper_ktime_get_real(void)
+{
+	return ktime_get_with_offset(TK_OFFS_REAL);
+}
+
+ktime_t rust_helper_ktime_get_boottime(void)
+{
+	return ktime_get_with_offset(TK_OFFS_BOOT);
+}
+
+ktime_t rust_helper_ktime_get_clocktai(void)
+{
+	return ktime_get_with_offset(TK_OFFS_TAI);
+}
diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index bba62c7f37e4..9fd487276457 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -63,6 +63,11 @@ pub trait ClockSource {
     ///
     /// This constant corresponds to the C side `clockid_t` value.
     const ID: bindings::clockid_t;
+
+    /// Get the current time from the clock source.
+    ///
+    /// The function must return a value in the range from 0 to `KTIME_MAX`.
+    fn ktime_get() -> bindings::ktime_t;
 }
 
 /// A monotonically increasing clock.
@@ -80,6 +85,11 @@ pub trait ClockSource {
 
 impl ClockSource for Monotonic {
     const ID: bindings::clockid_t = bindings::CLOCK_MONOTONIC as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get()` outside of NMI context.
+        unsafe { bindings::ktime_get() }
+    }
 }
 
 /// A settable system-wide clock that measures real (i.e., wall-clock) time.
@@ -100,6 +110,11 @@ impl ClockSource for Monotonic {
 
 impl ClockSource for RealTime {
     const ID: bindings::clockid_t = bindings::CLOCK_REALTIME as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get_real()` outside of NMI context.
+        unsafe { bindings::ktime_get_real() }
+    }
 }
 
 /// A monotonic that ticks while system is suspended.
@@ -113,6 +128,11 @@ impl ClockSource for RealTime {
 
 impl ClockSource for BootTime {
     const ID: bindings::clockid_t = bindings::CLOCK_BOOTTIME as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get_boottime()` outside of NMI context.
+        unsafe { bindings::ktime_get_boottime() }
+    }
 }
 
 /// International Atomic Time.
@@ -130,6 +150,11 @@ impl ClockSource for BootTime {
 
 impl ClockSource for Tai {
     const ID: bindings::clockid_t = bindings::CLOCK_TAI as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get_tai()` outside of NMI context.
+        unsafe { bindings::ktime_get_clocktai() }
+    }
 }
 
 /// A specific point in time.
@@ -153,14 +178,13 @@ fn clone(&self) -> Self {
 impl<C: ClockSource> Copy for Instant<C> {}
 
 impl<C: ClockSource> Instant<C> {
-    /// Get the current time using `CLOCK_MONOTONIC`.
+    /// Get the current time from the clock source.
     #[inline]
     pub fn now() -> Self {
-        // INVARIANT: The `ktime_get()` function returns a value in the range
+        // INVARIANT: The `ClockSource::ktime_get()` function returns a value in the range
         // from 0 to `KTIME_MAX`.
         Self {
-            // SAFETY: It is always safe to call `ktime_get()` outside of NMI context.
-            inner: unsafe { bindings::ktime_get() },
+            inner: C::ktime_get(),
             _c: PhantomData,
         }
     }
-- 
2.43.0