To minimize the effort required to set up IANA root zone mirroring,
define a default master server list for the root zone and use it when
that zone is to be mirrored and no master server list was explicitly
specified. Contents of that list are taken from RFC 7706 and are
subject to change in future releases.
Since the static get_masters_def() function in bin/named/config.c does
exactly what named_zone_configure() in bin/named/zoneconf.c needs to do,
make the former non-static and use it in the latter to prevent code
duplication.
Previous way of handling NOTIFY settings for mirror zones was a bit
tricky: any value of the "notify" option was accepted, but it was
subsequently overridden with dns_notifytype_explicit. Given the way
zone configuration is performed, this resulted in the following
behavior:
- if "notify yes;" was set explicitly at any configuration level or
inherited from default configuration, it was silently changed and so
only hosts specified in "also-notify", if any, were notified,
- if "notify no;" was set at any configuration level, it was
effectively honored since even though zone->notifytype was silently
set to dns_notifytype_explicit, the "also-notify" option was never
processed due to "notify no;" being set.
Effectively, this only allowed the hosts specified in "also-notify" to
be notified, when either "notify yes;" or "notify explicit;" was
explicitly set or inherited from default configuration.
Clean up handling of NOTIFY settings for mirror zones by:
- reporting a configuration error when anything else than "notify no;"
or "notify explicit;" is set for a mirror zone at the zone level,
- overriding inherited "notify yes;" setting with "notify explicit;"
for mirror zones,
- informing the user when the "notify" setting is overridden, unless
the setting in question was inherited from default configuration.
