BIND 10 #2851: extensions to ConfigurableClientList::getCachedZoneWriter

[BIND 10 Development]

#2851: extensions to ConfigurableClientList::getCachedZoneWriter
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |  jinmei
            Priority:  medium        |                       Status:
           Component:  data source   |  accepted
            Keywords:                |                    Milestone:
           Sensitive:  0             |  Sprint-20130514
         Sub-Project:  DNS           |                   Resolution:
Estimated Difficulty:  4             |                 CVSS Scoring:
         Total Hours:  0             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |  shared memory data source
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by jinmei):

 trac2851 is ready for review.

 It's based on a snapshot of trac2850, which is currently in review and
 may require more changes, but trac2851 should be mostly independent
 from those changes.  So I believe it's safe to start review.

 This branch is a sequence of small(-to-medium) changes, so it's
 probably easier to review it step by step:

 - in 31075ad and 73e1a3c, I removed an already-unused method from
   `ConfigurableClientList`.  see the commit logs.  changes to unit
   tests are a bit large, but it should be straightforward cleanup.
 - in 3e678f3 and 2d3ed73, I updated the behavior of
   `ConfigurableClientList::configure()`.  see commit log for 2d3ed73.
 - 74c2ed9 is the main change for this task.  Again, see the commit
   log.
 - 48c33c6 through 9377868 are another main change for this task (+ doc
   cleanup): ignoring read-only segment
 - finally, in 6dd9468 I introduced one extension that was not
   originally planned.  I believe this interface is more convenient
   (and intuitive) for #2856.

 I think we need a changelog entry as it has a subtle but some user
 visible effect (probably improvement):
 {{{
 611.?   [func]          jinmei
         datasrc: Error handling in loading zones into memory is now more
         consistent and convenient: data source configuration does not fail
         due to zones configured to be loaded into memory but not available
         in the data source, just like the case of missing zone file for
         the MasterFiles type of data source.  Also, zones that aren't
         loaded into memory due to errors can now be reloaded for b10-auth
         using the bindctl Auth loadzone command after fixing the error,
         without reconfiguring the entire data source.
         (Trac #2851, git TBD)
 }}}

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Ticket URL: <http://bind10.isc.org/ticket/2851#comment:8>
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