Re: Suggested changes to util-linux for FHS compliance.

[Karel Zak <kzak@redhat.com>]

On Fri, Feb 19, 2021 at 12:30:12PM +0100, Karel Zak wrote:
> On Mon, Feb 15, 2021 at 10:16:30AM +0100, Karel Zak wrote:
> > On Fri, Feb 12, 2021 at 11:04:59AM -0600, Bruce Dubbs wrote:
> > > I don't recall if this has come up before, but I suggest a couple of changes
> > > to the default util-linux build configuuration:
> > > 
> > > 1. Change the default ADJTIME_PATH to be /var/lib/hwclock/adjtime
> > 
> > Good idea. I'll do that.
> 
> Hmm... I remembered now that we have in our TODO:
> 
>  hwclock
>  ------
>  - use /var/lib/hwclock/drift to store hw-clock drift numbers.
>  - use /etc/adjtime as read-only for UTC/LOCAL information only
>  - the /var/lib/hwclock/drift should be implemented backwardly compatible,
>    it means use the file only if exists, otherwise follow /etc/adjtime
> 
> so maybe the best would be to keep ADJTIME_PATH=/etc/adjtime and use
> it as read-only and use ${localstatedir}/lib/hwclock/drift for the
> rest.
> 
> Note that ADJTIME_PATH is used by more utils, like rtcwake or systemd,
> so move it is not so easy.

OK, I have implemented it, but frankly, I'm not sure about it ;-) 
I have added William to CC:, maybe he will come with comments.  
       
See https://github.com/karelzak/util-linux/tree/topic/hwclock-drift-file
branch.                                                    
       
The idea is to keep /etc/adjtime as a source for UTC/LOCAL flag, but   
hwclock drift info (which we need to update occasionally) move to    
/var/lib/hwclock/drift. The /etc/adjtime is de-facto standard and
move it means that 3rd party utils will have no way how to determine 
hwclock UTC/LOCAL mode.
       
Both files use "adjtime" file format to make it simple to convert
from one to another.                                         
       
The change should be backwardly compatible. If you do not have /var/lib/hwclock/drift 
then it falls back to /etc/adjtime.                                  
       
I'm not sure if this is not over-engineering. Maybe the current
solution is good enough, and all we need is to make it more
use-friendly to set ADJTIME_PATH for users like Bruce (although
maintain any status information in /etc (in the year 2021) is not
nice.


The another possibility is to make a real change. Introduce completely
new file in /etc (/etc/clockmode) with only UTC/LOCAL(, force all
applications to use it (I know about rtcwake and systemd), and keep
/var/lib/hwclock/drift as private hwclock(1) file in a private format.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com