BIND 10 #2037: remote config handler (python) always gets full config

[BIND 10 Development]

#2037: remote config handler (python) always gets full config
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            Reporter:  jinmei        |                        Owner:
                Type:  defect        |                       Status:  new
            Priority:  medium        |                    Milestone:  New
           Component:                |  Tasks
  configuration                      |                     Keywords:
           Sensitive:  0             |              Defect Severity:  N/A
         Sub-Project:  Core          |  Feature Depending on Ticket:
Estimated Difficulty:  0             |          Add Hours to Ticket:  0
         Total Hours:  0             |                    Internal?:  0
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 (I don't know if it's python specific.  I've not checked it with the
 C++ version)

 I've noticed if I specify a callback to add_remote_config() or
 add_remote_config_by_name(), the new_config parameter of the update
 always contains full configuration of the remote module, not just the
 latest update.

 One specific way to confirm this is:
 - configure zonemgr with some non default secondary_zones
 - run b10-ddns on trac2020 (or master when it's merged)
 - see the DDNS_SECONDARY_ZONES_UPDATE log message (it's for that non
   default config value for zonemgr)
 - tweak some other config value of zonemgr (e.g. lowerbound_retry) and
   commit it on bindctl
 - see the DDNS_SECONDARY_ZONES_UPDATE log message, even if
   secondary_zones is not updated.

 I don't know what's the expected behavior, but this seems to be
 suboptimal (b10-ddns expects to get only updates, although having
 redundant updates don't do harm except for the unnecessary overhead of
 updating).

 From a quick look at the code, one way to change this behavior would
 be to add remove_identical() for the remote config case in
 ccsession.py:check_command_without_recvmsg().  But I'm not sure if
 it's actually okay that cfgmgr sends the entire config, not only the
 update.  So, depending on that, we might rather fix cfgmgr.

 Further, if we make more fundamental cleanups to the config framework,
 maybe we should solve it as part of it.

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Ticket URL: <http://bind10.isc.org/ticket/2037>
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