Messages in this thread | | | Date | Wed, 27 Mar 2024 12:50:50 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH 3/5] rust: time: Introduce clock reading framework |
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On 26.03.24 20:19, Boqun Feng wrote: > On Tue, Mar 26, 2024 at 05:00:39PM +0000, Benno Lossin wrote: >> On 24.03.24 23:33, Boqun Feng wrote: >>> To make sure Rust code doesn't mix timestamps from different clocks, a >>> type safe clock reading framework is introduced. It includes: >>> >>> * A `Clock` trait that represents different clocks, to read a particular >>> clock, one needs implement the `Clock::now()` function. >>> >>> * A `Instant<Clock>` type that represents timestamps of different >>> clocks, whose implementation is just a `ktime_t`, so all the >>> calculation on `ktime_t` should apply to it as well. >>> >>> Co-developed-by: Heghedus Razvan <heghedus.razvan@protonmail.com> >>> Signed-off-by: Heghedus Razvan <heghedus.razvan@protonmail.com> >>> Co-developed-by: Asahi Lina <lina@asahilina.net> >>> Signed-off-by: Asahi Lina <lina@asahilina.net> >>> Signed-off-by: Boqun Feng <boqun.feng@gmail.com> >>> --- >>> rust/kernel/time.rs | 49 +++++++++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 49 insertions(+) >>> >>> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs >>> index b238b3a4e899..0f9f5605ed48 100644 >>> --- a/rust/kernel/time.rs >>> +++ b/rust/kernel/time.rs >>> @@ -6,6 +6,9 @@ >>> //! have been ported or wrapped for usage by Rust code in the kernel. >>> //! >>> //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h). >>> +//! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h). >>> + >>> +use core::marker::PhantomData; >>> >>> /// The number of nanoseconds per millisecond. >>> pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64; >>> @@ -64,3 +67,49 @@ pub fn to_ns(self) -> i64 { >>> self.inner >>> } >>> } >>> + >>> +/// Represents a clock, that is, a unique time source and it can be queried for the current time. >>> +pub trait Clock: Sized { >>> + /// Returns the current time for this clock. >>> + fn now() -> Instant<Self>; >>> +} >>> + >>> +/// Marker trait for clock sources that are guaranteed to be monotonic. >>> +pub trait Monotonic {} >> >> Why is this trait not an extension of `Clock`? >> > > This was carried over from the old version, for myself, it doesn't make > much difference between: > > trait A { .. } > trait B { .. } > > impl<T: A + B> ... > > vs > > trait A { .. } > trait B: A { .. } > > impl<T: B> ... > > hence I kept it as it is, but yes, it a `Monotonic` *`Clock`*, so I will > change it in the next version.
I think it would also make sense to rename it to `MonotonicClock`.
> >>> + >>> +/// A timestamp of a given [`Clock`] >> >> Missing '.'. >> > > Fixed locally. > >>> +#[repr(transparent)] >>> +#[derive(Debug)] >>> +pub struct Instant<T: Clock> { >>> + inner: bindings::ktime_t, >>> + clock: PhantomData<T>, >>> +} >>> + >>> +impl<T: Clock> Clone for Instant<T> { >>> + fn clone(&self) -> Self { >>> + *self >>> + } >>> +} >>> + >>> +impl<T: Clock> Copy for Instant<T> {} >>> + >>> +impl<T: Clock> Instant<T> { >>> + fn new(ktime: bindings::ktime_t) -> Self { >> >> When compiling, this function is marked as dead-code in this patch. >> > > Hmm... I cannot trigger any compile errors with this patch. If you see > an error, could you share the build command? It's not a `pub` function > though.
I created a fresh config using `menuconfig` and enabled CONFIG_RUST. Then I get this error:
error: associated function `new` is never used --> rust/kernel/time.rs:97:8 | 96 | impl<T: Clock> Instant<T> { | ------------------------- associated function in this implementation 97 | fn new(ktime: bindings::ktime_t) -> Self { | ^^^ | = note: `-D dead-code` implied by `-D warnings` = help: to override `-D warnings` add `#[allow(dead_code)]` error: aborting due to 1 previous error
Note that the error vanishes in the next patch, since there you do have a user for `new`.
-- Cheers, Benno
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