ntp: correct select behaviour; closes #818

o When servers are empty, show prefer and noselect as disabled.
o Tighten the config write by using the same code idiom as the
  frontend, which is the safer method.
o Untangle noselect and prefer, ntpd.conf will handle it.

src/etc/inc/system.inc

@@ -1608,14 +1608,17 @@ function system_ntp_configure($start_ntpd = true)
     }
     /* End GPS configuration */
 
+    $noselect = isset($config['ntpd']['noselect']) ? explode(' ', $config['ntpd']['noselect']) : array();
+    $prefer = isset($config['ntpd']['prefer']) ? explode(' ', $config['ntpd']['prefer']) : array();
+
     $ntpcfg .= "\n\n# Upstream Servers\n";
     /* foreach through ntp servers and write out to ntpd.conf */
     foreach (explode(' ', $config['system']['timeservers']) as $ts) {
         $ntpcfg .= "server {$ts} iburst maxpoll 9";
-        if (isset($config['ntpd']['prefer']) && substr_count($config['ntpd']['prefer'], $ts)) {
+        if (in_array($ts, $prefer)) {
             $ntpcfg .= ' prefer';
         }
-        if (isset($config['ntpd']['noselect']) && substr_count($config['ntpd']['noselect'], $ts)) {
+        if (in_array($ts, $noselect)) {
             $ntpcfg .= ' noselect';
         }
         $ntpcfg .= "\n";

src/www/services_ntpd.php

@@ -90,20 +90,8 @@ if ($_SERVER['REQUEST_METHOD'] === 'GET') {
         // list types
         $config['system']['timeservers'] = trim(implode(' ', $pconfig['timeservers_host']));
         $a_ntpd['noselect'] = !empty($pconfig['timeservers_noselect']) ? trim(implode(' ', $pconfig['timeservers_noselect'])) : null;
-        $a_ntpd['prefer'] = "";
-        if (!empty($pconfig['timeservers_prefer'])) {
-            foreach ($pconfig['timeservers_prefer'] as $timeserver) {
-                if (!is_array($pconfig['timeservers_noselect']) || !in_array($timeserver, $pconfig['timeservers_noselect'])) {
-                    // a timeserver can't be both preferred and disabled, don't set preferred when disabled
-                    $a_ntpd['prefer'] .= $timeserver . " ";
-                }
-            }
-        }
-        $a_ntpd['prefer'] = trim($a_ntpd['prefer']);
-
-        if (!empty($pconfig['interface'])) {
-            $a_ntpd['interface'] = implode(',', $pconfig['interface']);
-        }
+        $a_ntpd['prefer'] = !empty($pconfig['timeservers_prefer']) ? trim(implode(' ', $pconfig['timeservers_prefer'])) : null;
+        $a_ntpd['interface'] = !empty($pconfig['interface']) ? implode(',', $pconfig['interface']) : null;
 
         // unset empty
         foreach (array('noselect', 'prefer', 'interface') as $fieldname) {
@@ -258,8 +246,6 @@ include("head.inc");
 <?php
                         if (count($pconfig['timeservers_host']) == 0 ) {
                             $pconfig['timeservers_host'][] = "";
-                            $pconfig['timeservers_prefer'][] = false;
-                            $pconfig['timeservers_noselect'][] = false;
                         }
                         foreach($pconfig['timeservers_host'] as $item_idx => $timeserver):?>
                           <tr>