As pppd is mainly a link controller, move it's startup to pppd_pre_start and have pppd_start as a dummy function for old configs.

conf.d.Linux/net.example

@@ -622,9 +622,6 @@
 # You need to create the PPP net script yourself. Make it like so
 #ln -s net.lo /etc/init.d/net.ppp0
 #
-# We have to instruct ppp0 to actually use ppp
-#config_ppp0="ppp"
-#
 # Each PPP interface requires an interface to use as a "Link"
 #link_ppp0="/dev/ttyS0" 		# Most PPP links will use a serial port
 #link_ppp0="eth0"       		# PPPoE requires an ethernet interface

net.Linux/pppd.sh

@@ -16,29 +16,20 @@ requote() {
 	printf "'%s' " "$@"
 }
 
-pppd_start() {
+pppd_pre_start() {
 	${IN_BACKGROUND} && return 0
 
-	if [ "${IFACE%%[0-9]*}" != "ppp" ] ; then
-		eerror "PPP can only be invoked from net.ppp[0-9]"
-		return 1
-	fi
+	# Interface has to be called ppp
+	[ "${IFACE%%[0-9]*}" = "ppp" ] || return 0
 
 	local link= i= opts= unit="${IFACE#ppp}" mtu=
-	if [ -z "${unit}" ] ; then
-		eerror "PPP requires a unit - use net.ppp[0-9] instead of net.ppp"
-		return 1
-	fi
 	
 	# PPP requires a link to communicate over - normally a serial port
 	# PPPoE communicates over Ethernet
 	# PPPoA communicates over ATM
 	# In all cases, the link needs to be available before we start PPP
 	eval link=\$link_${IFVAR}
-	if [ -z "${link}" ] ; then
-		eerror "link_${IFVAR} has not been set in /etc/conf.d/net"
-		return 1
-	fi
+	[ -n "${link}" ] || return 0
 
 	case "${link}" in
 		/*)
@@ -50,6 +41,11 @@ pppd_start() {
 			;;
 	esac
 
+	if [ -z "${unit}" ] ; then
+		eerror "PPP requires a unit - use net.ppp[0-9] instead of net.ppp"
+		return 1
+	fi
+
 	eval $(_get_array "pppd_${IFVAR}")
 	opts="$@"
 
@@ -199,6 +195,11 @@ pppd_start() {
 	exit 0
 }
 
+# Dummy function for users that still have config_ppp0="ppp"
+pppd_start() {
+	return 0
+}
+
 pppd_stop() {
 	${IN_BACKGROUND} && return 0
 	local pidfile="/var/run/ppp-${IFACE}.pid"