Add element to run DHCP on all network interfaces.

Ensures that all network interfaces are present in
/etc/network/interfaces. Any interface not already defined there
will be added and configured for DHCP.

Change-Id: I27e0902e62804e8d719acd7288109bd0e294fd16

elements/dhcp-all-interfaces/README.md

@@ -0,0 +1,14 @@
+Autodetect network interfaces during boot and configure them for DHCP
+
+The rationale for this is that we are likely to require multiple
+network interfaces for use cases such as baremetal and there is no way
+to know ahead of time which one is which, so we will simply run a
+DHCP client on all interfaces (except lo) that are visible on the first
+boot.
+
+The script /usr/local/sbin/generate-interfaces-file.sh will be called
+early in each boot and will scan available network interfaces and
+ensure they are all present in /etc/network/interfaces.
+
+Note that this element is only expected to be useful on Debian-derived
+distributions, currently.

elements/dhcp-all-interfaces/install.d/50-dhcp-all-interfaces

@@ -0,0 +1,9 @@
+#!/bin/sh -x
+
+# Prepare the target system for regenerating /etc/network/interfaces
+# on its first boot.
+
+SCRIPTDIR=$(dirname $0)
+
+install -D -g root -o root -m 0755 ${SCRIPTDIR}/generate-interfaces-file.sh /usr/local/sbin/generate-interfaces-file.sh
+install -D -g root -o root -m 0755 ${SCRIPTDIR}/dhcp-all-interfaces.conf /etc/init/dhcp-all-interfaces.conf

elements/dhcp-all-interfaces/install.d/dhcp-all-interfaces.conf

@@ -0,0 +1,10 @@
+# Call a script to generate an /etc/network/interfaces file to DHCP all available interfaces
+# Then remove this config file so the script is never run again
+
+description "DHCP any connected, but unconfigured network interfaces"
+
+start on starting network-interface
+
+task
+
+exec /usr/local/sbin/generate-interfaces-file.sh

elements/dhcp-all-interfaces/install.d/generate-interfaces-file.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+# Generate $INTERFACES_FILE on first boot
+# This will add any unconfigured network interfaces to /etc/network/interfaces
+#  and configure them for DHCP
+
+INTERFACES_FILE="/etc/network/interfaces"
+
+function get_if_link() {
+  cat /sys/class/net/${1}/carrier
+}
+
+for interface in $(ls /sys/class/net | grep -v ^lo$) ; do
+  echo -n "Inspecting interface: $interface..."
+  HAS_CONFIG=$(ifquery $interface >/dev/null 2>&1)
+  if [ "$HAS_CONFIG" == "" ]; then
+    ip link set dev $interface up >/dev/null 2>&1
+    HAS_LINK="$(get_if_link $interface)"
+
+    TRIES=3
+    while [ "$HAS_LINK" == "0" -a $TRIES -gt 0 ]; do
+      HAS_LINK="$(get_if_link $interface)"
+      if [ "$HAS_LINK" == "1" ]; then
+        break
+      else
+        sleep 1
+      fi
+      TRIES=$(( TRIES - 1 ))
+    done
+    if [ "$HAS_LINK" == "1" ] ; then
+      printf "auto $interface\r\niface $interface inet dhcp\r\n\r\n" >>$INTERFACES_FILE]
+      echo "Configured"
+    else
+      echo "No link detected, skipping"
+    fi
+  fi
+done