[Samba] samba_upgradedns output

[Scott Goodwin]

When I run:
 # samba_upgradedns --dns-backend=BIND9_DLZ
I get the following:
lpcfg_load: refreshing parameters from /etc/samba/smb.conf
params.c:pm_process() - Processing configuration file "/etc/samba/smb.conf"
Reading domain information
lpcfg_load: refreshing parameters from /etc/samba/smb.conf
params.c:pm_process() - Processing configuration file "/etc/samba/smb.conf"
DNS accounts already exist
No zone file /var/lib/samba/private/dns/MYDOMAIN.COM.zone
DNS records will be automatically created
DNS partitions already exist
Adding dns-earl account
See /var/lib/samba/private/named.conf for an example configuration include
file for BIND
and /var/lib/samba/private/named.txt for further documentation required for
secure DNS updates
Finished upgrading DNS

What does the line "No zone file
/var/lib/samba/private/dns/MYDOMAIN.COM.zone" mean? Or rather, I know what
it means, but what is the file itself supposed to do?
In all the Samba4 documentation, I don't see any indication on where this
file is supposed to be created.  I even see references here:
https://wiki.samba.org/index.php/Dns-backend_bind#Interaction_with_AppArmor_or_SELinux
(the
SELinux settings) where this file is mentioned, but no other indication
anywhere on what its purpose is, or what should be in it. I mean,
obviously, it's a zone file, but for what? Aren't the zones kept in the tdb
files now?  Is this a relic from the BIND9_FLATFILE backend, and the
documentation hasn't been updated?

Any info appreciated.

Thanks