Re: [RFC 00/20] ns: Introduce Time Namespace

[Andrey Vagin]

On Thu, Sep 27, 2018 at 11:41:49PM +0200, Thomas Gleixner wrote:
> On Thu, 27 Sep 2018, Thomas Gleixner wrote:
> > Add time skew via NTP/PTP into the picture and you might have to adjust
> > timers as well, because you need to guarantee that they are not expiring
> > early.
> > 
> > I haven't looked through Dimitry's patches yet, but I don't see how this
> > can work at all without introducing subtle issues all over the place.
> 
> And just a quick scan tells me that this is broken. Timers will expire
> early or late. The latter is acceptible to some extent, but larger delays
> might come with surprise. Expiring early is an absolute nono.

Do you mean that we have to adjust all timers after changing offset for
CLOCK_MONOTONIC or CLOCK_BOOTTIME? Our idea is that offsets for
monotonic and boot times will be set immediately after creating a time
namespace before using any timers.

It is interesting to think what a use-case for changing these offsets
after creating timers. It may be useful for testing needs. A user sets a
timer in an hour and then change a clock offset forward and check that a
test application handles the timer properly.

> 
> Thanks,
> 
> 	tglx
>