busybox: sysntpd - Support for NTP servers received via DHCP(v6)

The busybox ntpd utility currently uses ntp servers specified in uci.
This patch allows the ntpd utility to use NTP servers received via DHCP(v6)
Following uci parameters have been added:
    use_dhcp : enables NTP server config via DHCP(v6)
    dhcp_interface : use NTP servers received only on the specified DHCP(v6) interfaces; if empty all interfaces are considered

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>

package/utils/busybox/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=busybox
 PKG_VERSION:=1.24.2
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 PKG_FLAGS:=essential
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
@@ -42,7 +42,7 @@ define Package/busybox
   MAINTAINER:=Felix Fietkau <nbd@openwrt.org>
   TITLE:=Core utilities for embedded Linux
   URL:=http://busybox.net/
-  DEPENDS:=+BUSYBOX_USE_LIBRPC:librpc +BUSYBOX_CONFIG_PAM:libpam
+  DEPENDS:=+BUSYBOX_USE_LIBRPC:librpc +BUSYBOX_CONFIG_PAM:libpam +BUSYBOX_CONFIG_NTPD:jsonfilter
   MENU:=1
 endef
 

package/utils/busybox/files/sysntpd

@@ -7,13 +7,34 @@ USE_PROCD=1
 PROG=/usr/sbin/ntpd
 HOTPLUG_SCRIPT=/usr/sbin/ntpd-hotplug
 
+get_dhcp_ntp_servers() {
+	local interfaces="$1"
+	local filter="*"
+	local interface ntpservers ntpserver
+
+	for interface in $interfaces; do
+		[ "$filter" = "*" ] && filter="@.interface='$interface'" || filter="$filter,@.interface='$interface'"
+	done
+
+	ntpservers=$(ubus call network.interface dump | jsonfilter -e "@.interface[$filter]['data']['ntpserver']")
+
+	for ntpserver in $ntpservers; do
+		local duplicate=0
+		local entry
+		for entry in $server; do
+			[ "$ntpserver" = "$entry" ] && duplicate=1
+		done
+		[ "$duplicate" = 0 ] && server="$server $ntpserver"
+	done
+}
+
 validate_ntp_section() {
 	uci_validate_section system timeserver "${1}" \
-		'server:list(host)' 'enabled:bool:1' 'enable_server:bool:0'
+		'server:list(host)' 'enabled:bool:1' 'enable_server:bool:0' 'use_dhcp:bool:1' 'dhcp_interface:list(string)'
 }
 
 start_service() {
-	local server enabled enable_server peer
+	local server enabled enable_server use_dhcp dhcp_interface peer
 
 	validate_ntp_section ntp || {
 		echo "validation failed"
@@ -22,6 +43,8 @@ start_service() {
 
 	[ $enabled = 0 ] && return
 
+	[ $use_dhcp = 1 ] && get_dhcp_ntp_servers "$dhcp_interface"
+
 	[ -z "$server" ] && return
 
 	procd_open_instance
@@ -35,8 +58,32 @@ start_service() {
 	procd_close_instance
 }
 
-service_triggers()
-{
-	procd_add_reload_trigger "system"
+service_triggers() {
+	local script name use_dhcp
+
+	script=$(readlink -f "$initscript")
+	name=$(basename ${script:-$initscript})
+
+	procd_open_trigger
+	procd_add_config_trigger "config.change" "system" /etc/init.d/$name reload
+
+	config_load system
+	config_get use_dhcp ntp use_dhcp 1
+
+	[ $use_dhcp = 1 ] && {
+		local dhcp_interface
+		config_get dhcp_interface ntp dhcp_interface
+
+		if [ -n "$dhcp_interface" ]; then
+			for n in $dhcp_interface; do
+				procd_add_interface_trigger "interface.*" $n /etc/init.d/$name reload
+			done
+		else
+			procd_add_raw_trigger "interface.*" 1000 /etc/init.d/$name reload
+		fi
+	}
+
+	procd_close_trigger
+
 	procd_add_validation validate_ntp_section
 }