catalog: document and enforce 'unixtime' serial-policy for generated catalog zones

doc/man/knot.conf.5in

@@ -2110,10 +2110,12 @@ frequent updates), the serial is incremented instead.
 To avoid user confusion, use \fBdateserial\fP only if you expect at most
 100 updates per day per zone and \fBunixtime\fP only if you expect at most
 one update per second per zone.
+.sp
+Generated catalog zones use \fBunixtime\fP only.
 .UNINDENT
 .UNINDENT
 .sp
-\fIDefault:\fP increment
+\fIDefault:\fP increment (unixtime for generated catalog zones)
 .SS refresh\-min\-interval
 .sp
 Forced minimum zone refresh interval (in seconds) to avoid flooding primary server.

doc/reference.rst

@@ -2288,7 +2288,9 @@ Possible values:
    100 updates per day per zone and ``unixtime`` only if you expect at most
    one update per second per zone.
 
-*Default:* increment
+   Generated catalog zones use ``unixtime`` only.
+
+*Default:* increment (unixtime for generated catalog zones)
 
 .. _zone_refresh-min-interval:
 

src/knot/conf/tools.c

@@ -824,6 +824,8 @@ int check_zone(
 	                                           C_CATALOG_TPL, yp_dname(args->id));
 	conf_val_t catalog_zone = conf_zone_get_txn(args->extra->conf, args->extra->txn,
 	                                            C_CATALOG_ZONE, yp_dname(args->id));
+	conf_val_t catalog_serial = conf_zone_get_txn(args->extra->conf, args->extra->txn,
+	                                              C_SERIAL_POLICY, yp_dname(args->id));
 	if ((bool)(conf_opt(&catalog_role) == CATALOG_ROLE_INTERPRET) !=
 	    (bool)(catalog_tpl.code == KNOT_EOK)) {
 		args->err_str = "'catalog-role' must correspond to configured 'catalog-template'";
@@ -834,6 +836,12 @@ int check_zone(
 		args->err_str = "'catalog-role' must correspond to configured 'catalog-zone'";
 		return KNOT_EINVAL;
 	}
+	if (conf_opt(&catalog_role) == CATALOG_ROLE_GENERATE &&
+	    conf_opt(&catalog_serial) != SERIAL_POLICY_UNIXTIME && // Default doesn't harm.
+	    catalog_serial.code == KNOT_EOK) {
+		args->err_str = "'serial-policy' must be 'unixtime' for generated catalog zones";
+		return KNOT_EINVAL;
+	}
 
 	return KNOT_EOK;
 }