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[180.15.148.177]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-ad51ea79a47sm2877843a12.76.2025.02.07.05.31.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Feb 2025 05:31:56 -0800 (PST) From: FUJITA Tomonori To: linux-kernel@vger.kernel.org Cc: Boqun Feng , Gary Guo , Fiona Behrens , rust-for-linux@vger.kernel.org, netdev@vger.kernel.org, andrew@lunn.ch, hkallweit1@gmail.com, tmgross@umich.edu, ojeda@kernel.org, alex.gaynor@gmail.com, bjorn3_gh@protonmail.com, benno.lossin@proton.me, a.hindborg@samsung.com, aliceryhl@google.com, anna-maria@linutronix.de, frederic@kernel.org, tglx@linutronix.de, arnd@arndb.de, jstultz@google.com, sboyd@kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, tgunders@redhat.com Subject: [PATCH v10 4/8] rust: time: Introduce Instant type Date: Fri, 7 Feb 2025 22:26:19 +0900 Message-ID: <20250207132623.168854-5-fujita.tomonori@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250207132623.168854-1-fujita.tomonori@gmail.com> References: <20250207132623.168854-1-fujita.tomonori@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Introduce a type representing a specific point in time. We could use the Ktime type but C's ktime_t is used for both timestamp and timedelta. To avoid confusion, introduce a new Instant type for timestamp. Rename Ktime to Instant and modify their methods for timestamp. Implement the subtraction operator for Instant: Delta = Instant A - Instant B Reviewed-by: Boqun Feng Reviewed-by: Gary Guo Reviewed-by: Fiona Behrens Signed-off-by: FUJITA Tomonori --- rust/kernel/time.rs | 77 +++++++++++++++++++++++---------------------- 1 file changed, 39 insertions(+), 38 deletions(-) diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs index 622cd01e24d7..d64a05a4f4d1 100644 --- a/rust/kernel/time.rs +++ b/rust/kernel/time.rs @@ -5,6 +5,22 @@ //! This module contains the kernel APIs related to time and timers that //! have been ported or wrapped for usage by Rust code in the kernel. //! +//! There are two types in this module: +//! +//! - The [`Instant`] type represents a specific point in time. +//! - The [`Delta`] type represents a span of time. +//! +//! Note that the C side uses `ktime_t` type to represent both. However, timestamp +//! and timedelta are different. To avoid confusion, we use two different types. +//! +//! A [`Instant`] object can be created by calling the [`Instant::now()`] function. +//! It represents a point in time at which the object was created. +//! By calling the [`Instant::elapsed()`] method, a [`Delta`] object representing +//! the elapsed time can be created. The [`Delta`] object can also be created +//! by subtracting two [`Instant`] objects. +//! +//! A [`Delta`] type supports methods to retrieve the duration in various units. +//! //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h). //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h). @@ -31,59 +47,44 @@ pub fn msecs_to_jiffies(msecs: Msecs) -> Jiffies { unsafe { bindings::__msecs_to_jiffies(msecs) } } -/// A Rust wrapper around a `ktime_t`. +/// A specific point in time. +/// +/// # Invariants +/// +/// The `inner` value is in the range from 0 to `KTIME_MAX`. #[repr(transparent)] #[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord)] -pub struct Ktime { +pub struct Instant { inner: bindings::ktime_t, } -impl Ktime { - /// Create a `Ktime` from a raw `ktime_t`. - #[inline] - pub fn from_raw(inner: bindings::ktime_t) -> Self { - Self { inner } - } - +impl Instant { /// Get the current time using `CLOCK_MONOTONIC`. #[inline] - pub fn ktime_get() -> Self { - // SAFETY: It is always safe to call `ktime_get` outside of NMI context. - Self::from_raw(unsafe { bindings::ktime_get() }) - } - - /// Divide the number of nanoseconds by a compile-time constant. - #[inline] - fn divns_constant(self) -> i64 { - self.to_ns() / DIV - } - - /// Returns the number of nanoseconds. - #[inline] - pub fn to_ns(self) -> i64 { - self.inner + pub fn now() -> Self { + // INVARIANT: The `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() }, + } } - /// Returns the number of milliseconds. + /// Return the amount of time elapsed since the [`Instant`]. #[inline] - pub fn to_ms(self) -> i64 { - self.divns_constant::() + pub fn elapsed(&self) -> Delta { + Self::now() - *self } } -/// Returns the number of milliseconds between two ktimes. -#[inline] -pub fn ktime_ms_delta(later: Ktime, earlier: Ktime) -> i64 { - (later - earlier).to_ms() -} - -impl core::ops::Sub for Ktime { - type Output = Ktime; +impl core::ops::Sub for Instant { + type Output = Delta; + // By the type invariant, it never overflows. #[inline] - fn sub(self, other: Ktime) -> Ktime { - Self { - inner: self.inner - other.inner, + fn sub(self, other: Instant) -> Delta { + Delta { + nanos: self.inner - other.inner, } } }