linux-kernel - Re: [PATCH 4/5] rust: time: Support reading CLOCK

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Date: Tue, 26 Mar 2024 17:03:41 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Boqun Feng <boqun.feng@...il.com>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...sung.com>, John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>, Valentin Obst <kernel@...entinobst.de>, Heghedus Razvan <heghedus.razvan@...tonmail.com>, Asahi Lina <lina@...hilina.net>
Subject: Re: [PATCH 4/5] rust: time: Support reading CLOCK_MONOTONIC

On 24.03.24 23:33, Boqun Feng wrote:
> Rust Binder will need to read CLOCK_MONOTONIC to compute how many
> milliseconds a transaction has been active for when dumping the current
> state of the Binder driver. This replicates the logic in C Binder [1].
> 
> For a usage example in Rust Binder, see [2].
> 
> Hence add the support for CLOCK_MONOTONIC read.
> 
> The `ktime_get` method cannot be safely called in NMI context. This
> requirement is not checked by these abstractions, but it is intended
> that klint [3] or a similar tool will be used to check it in the future.
> 
> Link: https://lore.kernel.org/lkml/5ac8c0d09392290be789423f0dd78a520b830fab.1682333709.git.zhangchuang3@xiaomi.com/ [1]
> Link: https://r.android.com/3004103 [2]
> Link: https://rust-for-linux.com/klint [3]
> Co-developed-by: Heghedus Razvan <heghedus.razvan@...tonmail.com>
> Signed-off-by: Heghedus Razvan <heghedus.razvan@...tonmail.com>
> Co-developed-by: Asahi Lina <lina@...hilina.net>
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> Co-developed-by: Alice Ryhl <aliceryhl@...gle.com>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>

With the nit fixed:

Reviewed-by: Benno Lossin <benno.lossin@...ton.me>

> ---
> @Alice, I still put the link to the usage of Android binder here, if you
> want to remove that, please let me know.
> 
>  rust/kernel/time.rs | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 0f9f5605ed48..5cd669cbea01 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -113,3 +113,22 @@ fn sub(self, other: Self) -> Self::Output {
>          Duration::new(self.inner.wrapping_sub(other.inner))
>      }
>  }
> +
> +/// Contains the various clock source types available to the kernel.
> +pub mod clock {
> +    use super::*;
> +
> +    /// A clock representing the default kernel time source (`CLOCK_MONOTONIC`).
> +    pub struct KernelTime;
> +
> +    /// `CLOCK_MONOTONIC` is monotonic.
> +    impl Monotonic for KernelTime {}
> +
> +    impl Clock for KernelTime {
> +        #[inline]
> +        fn now() -> Instant<Self> {
> +            // SAFETY: It is always safe to call `ktime_get` outside of NMI context.
> +            Instant::<Self>::new(unsafe { bindings::ktime_get() })

I don't think the turbofish syntax (the `::<Self>` part) is needed here.

-- 
Cheers,
Benno

> +        }
> +    }
> +}
> --
> 2.44.0
>