[gpsd-dev] Clarifications needed for the time-service HOWTO

[Eric S. Raymond]

This thing is coming together nicely.  But, Gary, I need to extract
more information from your head (and from other founts of expertise
such as Hal and Harlan) before it will it will be anywhere near
complete.

Is it really true that most public NTP servers are Stratum 2, or
are there more layers in normal use?  When I look in my system's
config file, I see one server: ntp.ubuntu.com.  Stratum 2 or higher?
Is there any way I can tell? 

More generally: what can I discover about the quality of the chimers
I listen to?

How specific can we be about time jitter?  Is this a topic for the
HOWTO at all?

   Those hotplug devices will, however, may be able to use plain,
   non-kernel PPS. gpsd tries to automatically fall back to this when
   absence of root permissions makes KPPS unavailable. This fallback is
   complicated by the fact that gpsd needs to communicate to ntpd in
   a different way in root and non-root mode.  This complicates the
   configuration in ways beyond the scope of this document and is strongly
   discouraged in practice.

This paragraph troubles me. I'm not sure, but I think it may be
conflating two different issues and two sets of constraints. 

Which set of ntpd segments GPSD can use is constrained by whether
it started up as root or not.  But whether it can use KPPS is
controlled by whether it still has root *at the time the PPS source
is opened*. 

The following scenarios are possible:

1) GPSD started as root; device path passed on command line.  GPSD
will use privileged ntpd segments 0 and 1, KPPS will work. Best case.

2) GPSD started as root; device is hotplugged. GPSD
will use privileged ntpd segments 0 and 1, but KPPS will fail
(and fall back to plain PPS) because privileges were dropped 
before the device was opened.

3) GPSD started as non-root; device path either passed on command line
*or* hotplugged.  GPSD will use privileged ntpd segments 2 and 3; KPPS
will not work but plain PPS will.

The fallback to plain PPS has nothing to do with the ntpd
communication mode; this is shown by the fact that 1 and 2 aren't
the same case with the same outcome

I think everything after the first sentence in this 'graph should
be removed.  But maybe I'm missing something.
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>

[The disarming of citizens] has a double effect, it palsies the hand
and brutalizes the mind: a habitual disuse of physical forces totally
destroys the moral [force]; and men lose at once the power of
protecting themselves, and of discerning the cause of their
oppression.
        -- Joel Barlow, "Advice to the Privileged Orders", 1792-93