Soliciting opinions on desired "envstat -S" behavior

[Paul Goyette <paul%whooppee.com@localhost>]

Currently, the -S option for envstat(8) is documented to

    ...restore defaults to all devices registered with the framework.
    This will remove all properties that were set in the configuration
    file to the setting that the drivers use by default.

This was written this way long ago, before sysmon_envsys(9) learned how 
to import/export limit setting with hardware drivers.

As a result, the current behavior is sub-optimal, as it removes _ALL_ 
sensor limits, regardless of whether those limits were learned from the 
hardware driver or provided by the configuration file.  Even worse, the 
limits are removed from within the sysmon_envsys framework, but the 
hardware driver is not notified of the removal;  thus the hardware may 
still be checking the limits, and with the recent introduction of 
non-polled event delivery, the driver could actually report a limits 
event for a sensor with no limits!

I'm soliciting opinions on what the correct behavior should be, for each 
of the following sensor categories:

A. Sensors that have no hardware knowledge of limit values, and rely
   only on the sysmon_envsys(9) framework.

   I believe that the current behavior is correct - all knowledge of
   limit values is discarded.

B. Sensors that can provide initial limit values, but which cannnot
   handle changes to those values in hardware.  All limit processing is
   actually handled in the sysmon_envsys(9) framework and not in the
   driver or hardware.

   The current behavior works, but I believe that we should really
   "re-import" the initial values from the driver/hardware.  This is
   closest to the documented behavior.

C. Sensors that can actually process limit checking in the hardware (or
   in the driver) and that can accept new limit values to replace any
   initial (or factory default) values.

   I see at least three options here.

        C1. In addition to current behavior (removing all limits from
            the sysmon_envsys(9) framework), we should update the
            driver/hardware to let it remove its own limits.

   or   C2. Behave as proposed in (B) above, and simply reimport the
            current values from the hardware/driver after clearing
            the framework.

   or   C3. Remember the initial values from when the sensor was first
            registered, and after clearing the framework, reset both
            the hardware/driver and the framework to the remembered
            values.

I'd really appreciate comments/feedback/suggestions/etc.


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