linux-kernel - [PATCH v5 5/7] rust: time: Add Instant::from

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Message-ID: <20250613232754.451450-6-lyude@redhat.com>
Date: Fri, 13 Jun 2025 19:22:26 -0400
From: Lyude Paul <lyude@...hat.com>
To: rust-for-linux@...r.kernel.org,
	Andreas Hindborg <a.hindborg@...nel.org>,
	linux-kernel@...r.kernel.org
Cc: Boqun Feng <boqun.feng@...il.com>,
	FUJITA Tomonori <fujita.tomonori@...il.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	John Stultz <jstultz@...gle.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH v5 5/7] rust: time: Add Instant::from_nanos()

For implementing Rust bindings which can return a point in time.

Signed-off-by: Lyude Paul <lyude@...hat.com>

---
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

Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 rust/kernel/time.rs | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 70bd3be0facc0..eed77297d58a6 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -199,6 +199,28 @@ pub fn elapsed(&self) -> Delta {
     pub(crate) fn into_nanos(self) -> i64 {
         self.inner
     }
+
+    /// Create an [`Instant`] from a time duration specified in nano seconds.
+    ///
+    /// # Panics
+    ///
+    /// On debug builds, this function will panic if `nanos` violates our safety contract.
+    ///
+    /// # Safety
+    ///
+    /// The caller promises that `nanos` is in the range from 0 to `KTIME_MAX`.
+    #[expect(unused)]
+    #[inline]
+    pub(crate) unsafe fn from_nanos(nanos: i64) -> Self {
+        debug_assert!(nanos >= 0);
+
+        // INVARIANT: Our safety contract ensures that `nanos` is in the range from 0 to
+        // `KTIME_MAX`.
+        Self {
+            inner: nanos as bindings::ktime_t,
+            _c: PhantomData,
+        }
+    }
 }
 
 impl<C: ClockSource> core::ops::Sub for Instant<C> {
-- 
2.49.0