#!/bin/bash
#

# Copyright (C) 2014 Google Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.

# This script is a hook called to configure new TAP network interfaces
# used for instance communication, and it should be called whenever a
# new instance is started.
#
# This script configures the new interface but it also performs
# maintenance on the network interfaces that have been configured
# before, by checking whether those TAP interfaces still exist, etc.
#
# This script also controls the DHCP server that leases IP address for
# instances, i.e., the NICs inside the instances, not the TAP
# interfaces.  The DHCP server is started and restarted (or reHUPed)
# as necessary and always with up-to-date configuration files.
#
# This script expects the following environment variables
#
#   INTERFACE: network interface name to be configured
#   MODE: networking mode for 'INTERFACE' (must be 'routed')
#   MAC: MAC address for 'INTERFACE'
#   IP: IP address for 'INTERFACE'

source @PKGLIBDIR@/net-common

readonly NETMASK=255.255.255.255
readonly DNSMASQ_CONF=/var/run/ganeti/dnsmasq.conf
readonly DNSMASQ_HOSTS=/var/run/ganeti/dnsmasq.hosts
readonly DNSMASQ_PID=/var/run/ganeti/dnsmasq.pid

# join intercalates a sequence of arguments using the given separator
function join {
  local IFS="$1"
  shift
  echo "$*"
}

# restart_dnsmasq restarts the DHCP server dnsmasq with the (possibly
# up-to-date) configuration file.
#
# If all instances have been terminated, which means there are no more
# TAP network interfaces to monitor or IP addresses to lease, the DHCP
# server is terminated through 'SIGTERM'.
#
# If there are still instances running, then:
#  - if the DHCP server is running, a 'SIGHUP' will be sent to the
#    dnsmasq process which will cause the configuration file to be
#    re-read, while keeping the process running
#  - if the DHCP server is not running, it will be started, and the
#    configuration file will be passed it
function restart_dnsmasq {
  SIGNAL=

  if [ -z "$ALIVE_INTERFACES" -o -z "$ALIVE_LEASES" ]
  then
      SIGNAL=TERM
  else
      SIGNAL=HUP
  fi

  RUNNING=

  if [ -f "$DNSMASQ_PID" ]
  then
      PID=$(cat $DNSMASQ_PID)
      if [ -n "$PID" ] && ps -p "$PID"
      then
	  RUNNING=yes
      fi
  fi

  KILLED=

  if [ "$RUNNING" = yes ]
  then
      kill -$SIGNAL $PID

      if [ "$SIGNAL" = TERM ]
      then
	  KILLED=yes
      fi
  fi

  if [ "$KILLED" = yes ]
  then
      rm -f $DNSMASQ_PID
  fi

  if [ "$RUNNING" != yes -o "$KILLED" == yes ]
  then
      if [ -n "$ALIVE_INTERFACES" -a -n "$ALIVE_LEASES" ]
      then
	  dnsmasq -C $DNSMASQ_CONF
      fi
  fi

  return 0
}

# Check that environment variable 'INTERFACE' exists.
#
# This environment variable holds the TAP network interface that
# should be configured by this script.  Ganeti always passes it,
# but... :)
if [ -z "$INTERFACE" ]
then
  echo ifup-os: Failed to configure communication mechanism \
      interface because the \'INTERFACE\' environment variable was \
      not specified to the script
  exit 1
fi

# Check that environment variable 'MODE' exists.
#
# See comment about environment variable 'INTERFACE'.
if [ -z "$MODE" ]
then
  echo ifup-os: Failed to configure communication mechanism \
      interface because the \'MODE\' environment variable was \
      not specified to the script
  exit 1
fi

# Check whether the interface being configured has instance
# communication enabled, otherwise exit this script.
if ! is_instance_communication_tap; then exit 0; fi

# Check that environment variable 'MAC' exists.
#
# See comment about environment variable 'INTERFACE'.
if [ -z "$MAC" ]
then
  echo ifup-os: Failed to configure communication mechanism \
      interface because the \'MAC\' environment variable was \
      not specified to the script
  exit 1
fi

# Check that environment variable 'IP' exists.
#
# See comment about environment variable 'INTERFACE'.
if [ -z "$IP" ]
then
  echo ifup-os: Failed to configure communication mechanism \
      interface because the \'IP\' environment variable was \
      not specified to the script
  exit 1
fi

# Configure the TAP interface
#
# Ganeti defers the configuration of instance network interfaces to
# hooks, therefore, we must configure the interface's network address,
# netmask, and IP address.
#
# The TAP network interface, which is used by the instance
# communication, is part of the network 169.254.0.0/16 and has the IP
# 169.254.169.254.  Because all network interfaces used in the
# instance communication have the same IP, the routing table must also
# be configured, and that is done at a later step.
#
# Note the interface must be marked as up before configuring the
# routing table and before starting/restarting the DHCP server.
#
# Note also that we don't have to check whether the interface is
# already configured because reconfiguring the interface with the same
# parameters does not produce an error.
ifconfig $INTERFACE 169.254.169.254 netmask $NETMASK up

# There is a known bug where UDP packets comming from a host to a XEN
# guest are missing checksums. There are several ways how to tackle the
# issue, for example fixing the checksums using iptables (requires a
# newer version):
#
# iptables -A POSTROUTING -t mangle -p udp --dport bootpc -j CHECKSUM \
#   --checksum-fill
#
# The easiest one currently seems to be to just turn checksumming off
# for this direction:
ethtool -K $INTERFACE tx off || true

# Configure the routing table
#
# Given that all TAP network interfaces in the instance communication
# have the same IP address, the routing table must be configured in
# order to properly route traffic from the host to the guests.
#
# Note that we must first check if a duplicate routing rule has
# already been added to the routing table, as this operation will fail
# if we try to add a routing rule that already exists.
ACTIVE_IP=$(ip route | grep "dev $INTERFACE" | awk '{ print $1 }')

if [ -z "$ACTIVE_IP" -o "$ACTIVE_IP" != "$IP" ]
then
  route add -host $IP dev $INTERFACE
fi

# Ensure the DHCP server configuration files exist
touch $DNSMASQ_CONF
chmod 0644 $DNSMASQ_CONF

touch $DNSMASQ_HOSTS
chmod 0644 $DNSMASQ_HOSTS

# Determine dnsmasq operational mode.
#
# The DHCP server dnsmasq can run in different modes.  In this version
# of the script, only the mode 'bind-dynamic' is supported.  Please
# refer to the dnsmasq FAQ for a detailed of each mode.
#
# Note that dnsmasq might already be running, therefore, we don't need
# to determine which modes are supported by this DHCP server.
# Instead, we just read the current mode from the configuration file.
DNSMASQ_MODE=$(head -n 1 $DNSMASQ_CONF)

if [ -z "$DNSMASQ_MODE" ]
then
  BIND_DYNAMIC=$(dnsmasq --help | grep -e --bind-dynamic)

  if [ -z "$BIND_DYNAMIC" ]
  then
    echo ifup-os: dnsmasq mode \"bind-dynamic\" is not supported
    exit 1
  fi

  DNSMASQ_MODE=bind-dynamic
fi

# Determine the interfaces that should go in the configuration file.
#
# The TAP network interfaces used by the instance communication are
# named after the following pattern
#
#  gnt.com.%d
#
# where '%d' is a unique number within the host.  Fortunately, dnsmasq
# supports binding to specific network interfaces via a pattern.
ALIVE_INTERFACES=${GANETI_TAP}.*

# Determine which of the leases are not duplicated and should go in
# the new configuration file for the DHCP server.
#
# Given that instances come and go, it is possible that we offer more
# leases that necessary and, worse, that we have duplicate leases,
# that is, the same IP address for the same/different MAC addresses.
# Duplicate leases must be eliminated before being written to the
# configuration file.
CONF_LEASES=$(cat $DNSMASQ_HOSTS)
CONF_LEASES=$(join $'\n' $CONF_LEASES | sort -u)

ALIVE_LEASES=( $MAC,$IP )

for i in $CONF_LEASES
do
  LEASE_MAC=$(echo $i | cut -d "," -f 1)
  LEASE_IP=$(echo $i | cut -d "," -f 2)
  if [ "$LEASE_MAC" != "$MAC" -a "$LEASE_IP" != "$IP" ]
  then
      ALIVE_LEASES=( ${ALIVE_LEASES[@]} $i )
  fi
done

ALIVE_LEASES=$(echo ${ALIVE_LEASES[@]} | sort -u)

# Update dnsmasq configuration.
#
# Write the parameters we have collected before into the new dnsmasq
# configuration file.  Also, write the new leases into the new dnsmasq
# hosts file.  Finally, restart dnsmasq with the new configuration
# files.
cat > $DNSMASQ_CONF <<EOF
$DNSMASQ_MODE
dhcp-authoritative
dhcp-hostsfile=$DNSMASQ_HOSTS
dhcp-range=169.254.0.0,static,255.255.0.0
except-interface=eth*
except-interface=lo
leasefile-ro
no-hosts
no-ping
no-resolv
pid-file=$DNSMASQ_PID
port=0
strict-order
EOF
for i in $ALIVE_INTERFACES; do echo interface=$i >> $DNSMASQ_CONF; done

echo -n > $DNSMASQ_HOSTS
for i in $ALIVE_LEASES; do echo $i >> $DNSMASQ_HOSTS; done

restart_dnsmasq