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

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Message-ID: <871rhfoo7z.fsf@nanos.tec.linutronix.de>
Date:   Fri, 30 Oct 2020 14:08:48 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Lukasz Majewski <lukma@...x.de>, Andrei Vagin <avagin@...il.com>,
        Dmitry Safonov <dima@...sta.com>
Cc:     GNU C Library <libc-alpha@...rceware.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [Y2038][time namespaces] Question regarding CLOCK_REALTIME support plans in Linux time namespaces

Lukasz,

On Fri, Oct 30 2020 at 11:02, Lukasz Majewski wrote:
> 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?

Not really. Just having an offset on clock realtime would be incorrect
in a number of ways. Doing it correct is a massive trainwreck.

For a debug aid, which is what you are looking for, the correctness
would not really matter, but providing that is a really slippery
slope.

If at all we could hide it under a debug option which depends on
CONFIG_BROKEN and emitting a big fat warning in dmesg with a clear
statement that it _is_ broken, stays so forever and any attempt to "fix"
it results in a permanent ban from all kernel lists.

Preferrably we don't go there.

Thanks,

        tglx