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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Thomas Gleixner <tglx@linutronix.de>
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Date:   Wed, 03 Oct 2018 08:14:25 +0200
In-Reply-To: <alpine.DEB.2.21.1810030711520.1435@nanos.tec.linutronix.de>
        (Thomas Gleixner's message of "Wed, 3 Oct 2018 07:25:35 +0200 (CEST)")
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Subject: Re: Setting monotonic time?
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Thomas Gleixner <tglx@linutronix.de> writes:

> On Wed, 3 Oct 2018, Eric W. Biederman wrote:
>> Direct access to hardware/drivers and not through an abstraction like
>> the vfs (an abstraction over block devices) can legitimately be handled
>> by hotplug events.  I unplug one keyboard I plug in another.
>> 
>> I don't know if the input layer is more of a general abstraction
>> or more of a hardware device.  I have not dug into it but my guess
>> is abstraction from what I have heard.
>> 
>> The scary difficulty here is if after restart input is reporting times
>> in CLOCK_MONOTONIC and the applications in the namespace are talking
>> about times in CLOCK_MONOTONIC_SYNC.  Then there is an issue.  As even
>> with a fixed offset the times don't match up.
>> 
>> So a time namespace absolutely needs to do is figure out how to deal
>> with all of the kernel interfaces reporting times and figure out how to
>> report them in the current time namespace.
>
> So you want to talk to Arnd who is leading the y2038 effort. He knowns how
> many and which interfaces are involved aside of the obvious core timer
> ones. It's quite an amount and the problem is that you really need to do
> that at the interface level, because many of those time stamps are taken in
> contexts which are completely oblivious of name spaces. Ditto for timeouts
> and similar things which are handed in through these interfaces.

Yep.  That sounds right.

Eric