Re: [chrony-dev] [PATCH] main: imply -x if time can't be set

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Thu, Mar 08, 2018 at 05:08:16PM +0100, Christian Ehrhardt wrote:
> 1. the option would not be default on, so "normal" users/installations
> would not be affected
> 2. cases that want the fallback behavior, but are unable to probe/detect at
> the time:
>    - so they can not decide to use normal -x
>    - also the environment might change on them withut reconfig
>    Both of the above would be solved by them dropping the new -x=fallback
> option for their case.

Does that include an assumption that if the clock cannot be
controlled, it's already synchronized by something else and if it can,
it's a separate time namespace?

> Our container folks will outline the CAP_SYS_TIME issue I mentioned before,
> so really the best test for my suggested SYS_IsTimeAdjustable would be (on
> top to what I have to check the Cap) a adjtime no-op.
> I tried via adjtimex cmdline and thought maybe "adjtimex -s 0" (in C from
> chrony eventually) would be a no-op check I'd think

The sys_linux initialization code resets the singleshot offset, which
could be used as an early check for adjtimex().

Ok, here are some suggestions for the implementation:
- change all SYS_*_Initialise() functions to return 1 and SYS_Initialise()
  to check the return code (with a LOG_FATAL message if it is 0)
- change reset_adjtime() and SYS_Linux_Initialise() to return 0 on failure
- change SYS_Initialise() to handle the failure if clock_control is -1
  and add (and document) -X option which sets clock_control to -1 in
  main.c

-- 
Miroslav Lichvar

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