netroot: Only start interface configuration if really needed

Currently network configuration is launched by udev as soon as it
discovers a driver. This isn't such a good idea since we don't know
if network configuration is actually required. Change this by writing
the udev rules on the fly if required.

modules.d/40network/60-net.rules

@@ -1,2 +0,0 @@
-ACTION=="add", SUBSYSTEM=="net", RUN+="/sbin/ifup $env{INTERFACE}"
-ACTION=="online", SUBSYSTEM=="net", RUN+="/sbin/netroot $env{INTERFACE}"

modules.d/40network/install

@@ -15,7 +15,7 @@ inst "$moddir/netroot" "/sbin/netroot"
 inst "$moddir/dhclient-script" "/sbin/dhclient-script"
 inst "$moddir/dhclient.conf" "/etc/dhclient.conf" 
 instmods ecb arc4
-inst_rules "$moddir/60-net.rules"
+inst_hook pre-udev 60 "$moddir/net-genrules.sh"
 inst_hook cmdline 91 "$moddir/dhcp-root.sh"
 inst_hook cmdline 99 "$moddir/parse-ip-opts.sh"
 inst_hook pre-pivot 10 "$moddir/kill-dhclient.sh"

modules.d/40network/net-genrules.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+# Don't continue if we don't need network
+[ -z "$netroot" ] && return;
+
+# Write udev rules
+{
+    printf 'ACTION=="add", SUBSYSTEM=="net", RUN+="/sbin/ifup $env{INTERFACE}"\n'
+    printf 'ACTION=="online", SUBSYSTEM=="net", RUN+="/sbin/netroot $env{INTERFACE}"\n'
+} > /etc/udev/rules.d/60-net.rules

modules.d/40network/parse-ip-opts.sh

@@ -26,6 +26,14 @@ ip_to_var() {
     esac
 }
 
+# Check if ip= lines should be used
+if getarg ip= >/dev/null ; then
+    if [ -z "$netroot" ] ; then
+	echo "Warning: No netboot configured, ignoring ip= lines"
+	return;
+    fi
+fi
+
 # Warn if defaulting to ip=dhcp
 if [ -n "$netroot" ] && [ -z "$(getarg ip=)" ] ; then
     warn "No ip= argument(s) for netroot provided, defaulting to DHCP"