#! /bin/sh

# SPDX-License-Identifier: GPL-2.0

CheckForwarding () {

  local sbase fwd

  sbase=/proc/sys/net/ipv4/conf

  fwd=0

  if [ -d $sbase ]; then

    for dir in $sbase/*/forwarding; do

      fwd=$(( fwd + $(cat "$dir") ))

    done

  else

    fwd=2

  fi

  return $fwd

}

RestartRDISC () {

  killall -HUP rdisc || rdisc -fs

}

ABCMaskLen () {

  local class;

  class=${1%%.*}

  if [ "$1" = "" -o $class -eq 0 -o $class -ge 224 ]; then return 0

  elif [ $class -ge 224 ]; then return 0

  elif [ $class -ge 192 ]; then return 24

  elif [ $class -ge 128 ]; then return 16

  else return 8; fi

}

label="label $1"

ldev="$1"

dev=${1%:*}

if [ "$dev" = "" -o "$1" = "help" ]; then

  echo "Usage: ifcfg DEV [[add|del [ADDR[/LEN]] [PEER] | stop]" 1>&2

  echo "       add - add new address" 1>&2

  echo "       del - delete address" 1>&2

  echo "       stop - completely disable IP" 1>&2

  exit 1

fi

shift

CheckForwarding

fwd=$?

if [ $fwd -ne 0 ]; then

  echo "Forwarding is ON or its state is unknown ($fwd). OK, No RDISC." 1>&2

fi

deleting=0

case "$1" in

add) shift ;;

stop)

  if [ "$ldev" != "$dev" ]; then

    echo "Cannot stop alias $ldev" 1>&2

    exit 1;

  fi

  ip -4 addr flush dev $dev $label || exit 1

  if [ $fwd -eq 0 ]; then RestartRDISC; fi

  exit 0 ;;

del*)

  deleting=1; shift ;;

*)

esac

ipaddr=

pfxlen=

if [ "$1" != "" ]; then

  ipaddr=${1%/*}

  if [ "$1" != "$ipaddr" ]; then

    pfxlen=${1#*/}

  fi

  if [ "$ipaddr" = "" ]; then

    echo "$1 is bad IP address." 1>&2

    exit 1

  fi

fi

shift

peer=$1

if [ "$peer" != "" ]; then

  if [ "$pfxlen" != "" -a "$pfxlen" != "32" ]; then

    echo "Peer address with non-trivial netmask." 1>&2

    exit 1

  fi

  pfx="$ipaddr peer $peer"

else

  if [ "$ipaddr" = "" ]; then

    echo "Missing IP address argument." 1>&2

    exit 1

  fi

  if [ "$pfxlen" = "" ]; then

    ABCMaskLen $ipaddr

    pfxlen=$?

  fi

  pfx="$ipaddr/$pfxlen"

fi

if [ "$ldev" = "$dev" -a "$ipaddr" != "" ]; then

  label=

fi

if [ $deleting -ne 0 ]; then

  ip addr del $pfx dev $dev $label || exit 1

  if [ $fwd -eq 0 ]; then RestartRDISC; fi

  exit 0

fi

if ! ip link set up dev $dev ; then

  echo "Error: cannot enable interface $dev." 1>&2

  exit 1

fi

if [ "$ipaddr" = "" ]; then exit 0; fi

if ! arping -q -c 2 -w 3 -D -I $dev $ipaddr ; then

  echo "Error: some host already uses address $ipaddr on $dev." 1>&2

  exit 1

fi

if ! ip address add $pfx brd + dev $dev $label; then

  echo "Error: failed to add $pfx on $dev." 1>&2

  exit 1

fi

arping -q -A -c 1 -I $dev $ipaddr

noarp=$?

( sleep 2 ;

  arping -q -U -c 1 -I $dev $ipaddr ) >/dev/null 2>&1 

ip route add unreachable 224.0.0.0/24 >/dev/null 2>&1

ip route add unreachable 255.255.255.255 >/dev/null 2>&1

if [ "`ip link ls $dev | grep -c MULTICAST`" -ge 1 ]; then

  ip route add 224.0.0.0/4 dev $dev scope global >/dev/null 2>&1

fi

if [ $fwd -eq 0 ]; then

  if [ $noarp -eq 0 ]; then

    ip ro append default dev $dev metric 30000 scope global

  elif [ "$peer" != "" ]; then

    if ping -q -c 2 -w 4 $peer ; then

      ip ro append default via $peer dev $dev metric 30001

    fi

  fi

  RestartRDISC

fi

exit 0