Fix for mtu display (#2209)

images/01-base/Dockerfile

@@ -34,8 +34,9 @@ RUN rm /sbin/poweroff /sbin/reboot /sbin/halt && \
 COPY inputrc /etc/inputrc
 COPY growpart /usr/bin/growpart
 COPY start_ntp.sh /bin/start_ntp.sh
-COPY dhcpcd.enter-hook /etc/dhcpcd.enter-hook
+COPY dhcpcd/dhcpcd.enter-hook /etc/dhcpcd.enter-hook
-COPY dhcpcd.debug /usr/share/logrotate/logrotate.d/
+COPY dhcpcd/10-mtu /lib/dhcpcd/dhcpcd-hooks/
+COPY dhcpcd/dhcpcd.debug /usr/share/logrotate/logrotate.d/
 RUN sed -i s/"partx --update \"\$part\" \"\$dev\""/"partx --update --nr \"\$part\" \"\$dev\""/g /usr/bin/growpart && \
     sed -i -e 's/duid/clientid/g' /etc/dhcpcd.conf && \
     sed -i 1,10d /etc/rsyslog.conf && \

images/01-base/dhcpcd/10-mtu

@@ -0,0 +1,38 @@
+# Configure the MTU for the interface
+
+mtu_dir="$state_dir/mtu"
+
+set_mtu()
+{
+	local mtu=$1
+
+	if [ -w /sys/class/net/$interface/mtu ]; then
+		echo "$mtu" >/sys/class/net/$interface/mtu
+	else
+		ifconfig "$interface" mtu "$mtu"
+	fi
+}
+
+if [ "$reason" = PREINIT -a -e "$mtu_dir/$interface" ]; then
+	rm "$mtu_dir/$interface"
+elif [ -n "$new_interface_mtu" ] && $if_up; then
+	# The smalled MTU dhcpcd can work with is 576
+	if [ "$new_interface_mtu" -ge 576 ]; then
+		if set_mtu "$new_interface_mtu"; then
+			syslog info "MTU set to $new_interface_mtu"
+			# Save the MTU so we can restore it later
+			if [ ! -e "$mtu_dir/$interface" ]; then
+				mkdir -p "$mtu_dir"
+				echo "$ifmtu" > "$mtu_dir/$interface"
+			fi
+		fi
+	fi
+elif [ -e "$mtu_dir/$interface" ]; then
+	if $if_up || $if_down; then
+		# No MTU in this state, so restore the prior MTU
+		mtu=$(cat "$mtu_dir/$interface")
+		syslog info "MTU restored to $mtu"
+		set_mtu "$mtu"
+		rm "$mtu_dir/$interface"
+	fi
+fi