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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <7b93bf74-abdc-f8c1-9a12-7c7f080f9e19@asahilina.net>
Date:   Wed, 22 Feb 2023 01:31:28 +0900
From:   Asahi Lina <lina@...hilina.net>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     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>,
        John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>, 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 22/02/2023 01.02, Thomas Gleixner wrote:
> On Tue, Feb 21 2023 at 06:06, Boqun Feng wrote:
>> To me, there seems two options to provide Rust types for kernel time
>> management:
>>
>> *	Use KTime which maps to ktime_t, then we have the similar
>> 	semantics around it: sometimes it's a duration, sometimes it's
>> 	a point of time.. but I know "this is a safe language, you
>> 	should do more" ;-)
>>
>> *	Introduce kernel's own types, e.g. BootTime, RawTime, TAI,
>> 	RealTime, and make them play with Duration (actually I'd prefer
>> 	we have own Duration, because Rust core::time::Duration takes
>> 	more than u64), something like below:
>>
>>
>> 	pub struct BootTime {
>> 	    d: Duration
>> 	}
>>
>> 	impl BootTime {
>> 	    fn now() -> Self {
>> 	        unsafe { BootTime { d: ktime_to_duration(ktime_get_boottime())} }
>> 	    }
>> 	    fn add(self, d: Duration) -> Self {
>> 	        <Add a duration, similar to ktime_add>
>> 	    }
>> 	    fn sub(self, other: Self) -> Duration {
>> 	        ...
>> 	    }
> 
> I'm not rusty enough, but you really want two types:
> 
>     timestamp and timedelta
> 
> timestamp is an absolute time on a specific clock which is read via
> now() and you can add time deltas to it. The latter is required for
> arming an absolute timer on the clock.
> 
> timedelta is a relative time and completely independent of any
> clock. That's what you get when you subtract two timestamps, but you can
> also initialize it from a constant or some other source. timedelta can
> be used to arm a relative timer on any clock.

If all clocks end up as the same `timestamp` though, then this isn't
fully safe, because you could subtract `timestamp`s that came from
different clocks and the result would be meaningless. That's why the
Rust std Instant is specifically tied to one and only one system clock
on each platform.

~~ Lina