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

#!/bin/bash

ENI_FILE="/etc/network/interfaces"

if [ -d "/etc/network" ]; then
    CONF_TYPE="eni"
elif [ -d "/etc/sysconfig/network-scripts/" ]; then
    CONF_TYPE="netscripts"
else
    echo "Unsupported network configuration type!"
    exit 1
fi

if [ "$CONF_TYPE" == "eni" ]; then
    # Serialize runs so that we don't miss hot-add interfaces
    FLOCK=${1:-}
    if [ -z "$FLOCK" ] ; then
        exec flock -x $ENI_FILE $0 flocked
    fi
fi

function get_if_link() {
  cat /sys/class/net/${1}/carrier
}

function enable_interface() {
  local interface=$1

  if [ "$CONF_TYPE" == "eni" ]; then
      printf "auto $interface\niface $interface inet dhcp\n\n" >>$ENI_FILE
  elif [ "$CONF_TYPE" == "netscripts" ]; then
      printf "DEVICE=\"$interface\"\nBOOTPROTO=\"dhcp\"\nONBOOT=\"yes\"\nTYPE=\"Ethernet\"" >"/etc/sysconfig/network-scripts/ifcfg-$interface"
  fi
  echo "Configured $1"

}

function disable_interface() {
  local interface=$1

  if [ "$CONF_TYPE" == "netscripts" ]; then
      local IFCFG_FILE="/etc/sysconfig/network-scripts/ifcfg-$interface"
      if [ -f "$IFCFG_FILE" ]; then
          rm $IFCFG_FILE
      else
          echo "No link detected, skipping"
      fi
  else
      echo "No link detected, skipping"
  fi
}

for interface in $(ls /sys/class/net | grep -v ^lo$) ; do
  echo -n "Inspecting interface: $interface..."
  if ifquery $interface >/dev/null 2>&1 ; then
    echo "Has config, skipping."
  else
    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
      enable_interface "$interface"
    else
      disable_interface "$interface"
    fi
  fi
done