linux-kernel - Re: [Y2038][time namespaces] Question regarding CLOCK_REALTIME support plans in Linux time namespaces

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Message-ID: <20201030135816.GA1790@yuki.lan>
Date:   Fri, 30 Oct 2020 14:58:16 +0100
From:   Cyril Hrubis <chrubis@...e.cz>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     Andrei Vagin <avagin@...il.com>, Dmitry Safonov <dima@...sta.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        GNU C Library <libc-alpha@...rceware.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [Y2038][time namespaces] Question regarding CLOCK_REALTIME
 support plans in Linux time namespaces

Hi!
> I do have a question regarding the Linux time namespaces in respect of
> adding support for virtualizing the CLOCK_REALTIME.
> 
> According to patch description [1] and time_namespaces documentation
> [2] the CLOCK_REALTIME is not supported (for now?) to avoid complexity
> and overhead in the kernel.
> 
> Is there any plan to add support for it in a near future?
> 
> Why I'm asking? 
> 
> It looks like this kernel feature (with CLOCK_REALTIME support
> available) would be very helpful for testing Y2038 compliance for e.g.
> glibc 32 bit ports.
> 
> To be more specific - it would be possible to modify time after time_t
> 32 bit overflow (i.e. Y2038 bug) on the process running Y2038
> regression tests on the host system (64 bit one). By using Linux time
> namespaces the system time will not be affected in any way.

And what's exactly wrong with moving the system time forward for a
duration of the test?

-- 
Cyril Hrubis
chrubis@...e.cz