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

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Date:   Fri, 30 Oct 2020 16:10:26 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Zack Weinberg <zackw@...ix.com>, Cyril Hrubis <chrubis@...e.cz>
Cc:     Lukasz Majewski <lukma@...x.de>, Andrei Vagin <avagin@...il.com>,
        GNU C Library <libc-alpha@...rceware.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [Y2038][time namespaces] Question regarding CLOCK_REALTIME support plans in Linux time namespaces

On Fri, Oct 30 2020 at 10:02, Zack Weinberg wrote:
> On Fri, Oct 30, 2020 at 9:57 AM Cyril Hrubis <chrubis@...e.cz> wrote:
>> > 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.
> ...
>> > To be more specific - [if this were supported] 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?
>
> Interference with other processes on the same computer?  Some of us
> *do* like to run the glibc test suite on computers not entirely
> devoted to glibc CI.

That's what virtual machines are for.