linux-kernel - Re: [PATCH] rust: time: New module for timekeeping functions

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Message-ID: <87zg96n12k.ffs@tglx>
Date:   Tue, 21 Feb 2023 22:46:59 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Josh Stone <jistone@...hat.com>, Asahi Lina <lina@...hilina.net>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
        asahi@...ts.linux.dev
Subject: Re: [PATCH] rust: time: New module for timekeeping functions

On Tue, Feb 21 2023 at 09:13, Josh Stone wrote:

> On 2/21/23 4:32 AM, Thomas Gleixner wrote:
>> Now the problem is that 'Instant' in it's specification is bound to
>> CLOCK_MONOTONIC and there is no way to express CLOCK_BOOTTIME, but
>> that's a shortcoming of the spec which ignores CLOCK_BOOTTIME
>> completely. IOW, that's also a problem for user space.
>
> That's not exactly *specified* -- it's meant to be opaque time. It is
> documented that this currently uses clock_gettime monotonic on unix
> targets, but "Disclaimer: These system calls might change over time."
> CLOCK_MONOTONIC isn't even consistent across unix targets whether that
> counts suspended time. It's been debated if we should switch to
> CLOCK_BOOTTIME on Linux, but for now we're sticking to monotonic:

You'll need both when you want to implement substantial parts of the low
level user space stack in Rust. Same for CLOCK_TAI.

Thanks,

        tglx