source: drbl-virt/conf/initrd_bin/network-bridge @ 186

#!/bin/bash
#============================================================================
# Default Xen network start/stop script.
# Xend calls a network script when it starts.
# The script name to use is defined in /etc/xen/xend-config.sxp
# in the network-script field.
#
# This script creates a bridge (default ${netdev}), adds a device
# (defaults to the device on the default gateway route) to it, copies
# the IP addresses from the device to the bridge and adjusts the routes
# accordingly.
#
# If all goes well, this should ensure that networking stays up.
# However, some configurations are upset by this, especially
# NFS roots. If the bridged setup does not meet your needs,
# configure a different script, for example using routing instead.
#
# Usage:
#
# network-bridge (start|stop|status) {VAR=VAL}*
#
# Vars:
#
# bridge     The bridge to use (default ${netdev}).
# netdev     The interface to add to the bridge (default gateway device).
# antispoof  Whether to use iptables to prevent spoofing (default no).
#
# Internal Vars:
# pdev="p${netdev}"
# tdev=tmpbridge
#
# start:
# Creates the bridge as tdev
# Copies the IP and MAC addresses from pdev to bridge
# Renames netdev to be pdev 
# Renames tdev to bridge
# Enslaves pdev to bridge
#
# stop:
# Removes pdev from the bridge
# Transfers addresses, routes from bridge to pdev
# Renames bridge to tdev
# Renames pdev to netdev 
# Deletes tdev
#
# status:
# Print addresses, interfaces, routes
#
#============================================================================


dir=/sbin
. "$dir/xen-script-common.sh"
. "$dir/xen-network-common.sh"

findCommand "$@"
evalVariables "$@"

modprobe netloop > /dev/null 2>&1 || true

is_network_root () {
    local rootfs=$(awk '{ if ($1 !~ /^[ \t]*#/ && $2 == "/") { print $3; }}' /etc/mtab)
    local rootopts=$(awk '{ if ($1 !~ /^[ \t]*#/ && $2 == "/") { print $4; }}' /etc/mtab)

    [[ "$rootfs" =~ "^nfs" ]] || [[ "$rootopts" =~ "_netdev" ]] && return 0 || return 1
}

find_alt_device () {
    local interf=$1
    local prefix=${interf%[[:digit:]]}
    local ifs=$(ip link show | grep " $prefix" |\
                gawk '{ printf ("%s",substr($2,1,length($2)-1)) }' |\
                sed s/$interf//)
    echo "$ifs"
}

netdev=${netdev:-$(ip route list 0.0.0.0/0  | \
                   sed 's/.*dev \([a-z]\+[0-9]\+\).*$/\1/')}
if is_network_root ; then
    altdevs=$(find_alt_device $netdev)
    for netdev in $altdevs; do break; done
    if [ -z "$netdev" ]; then
        [ -x /usr/bin/logger ] && /usr/bin/logger "network-bridge: bridging not supported on network root; not starting"
        exit
    fi
fi
netdev=${netdev:-eth0}
bridge=${bridge:-${netdev}}
antispoof=${antispoof:-no}

pdev="p${netdev}"
tdev=tmpbridge

get_ip_info() {
    addr_pfx=`ip addr show dev $1 | grep -E '^ *inet' | sed -e 's/ *inet //' -e 's/ .*//'`
    gateway=`ip route show dev $1 | fgrep default | sed 's/default via //'`
}
    
do_ifup() {
    if ! ifup $1 ; then
        if [ -n "$addr_pfx" ] ; then
            # use the info from get_ip_info()
            ip addr flush $1
            ip addr add ${addr_pfx} dev $1
            ip link set dev $1 up
            [ -n "$gateway" ] && ip route add default via ${gateway}
        fi
    fi
}

# Usage: transfer_addrs src dst
# Copy all IP addresses (including aliases) from device $src to device $dst.
transfer_addrs () {
    local src=$1
    local dst=$2
    # Don't bother if $dst already has IP addresses.
    if ip addr show dev ${dst} | grep -E -q '^ *inet ' ; then
        return
    fi
    # Address lines start with 'inet' and have the device in them.
    # Replace 'inet' with 'ip addr add' and change the device name $src
    # to 'dev $src'.
    ip addr show dev ${src} | grep -E '^ *inet ' | sed -e "
s/inet/ip addr add/
s@\([0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+/[0-9]\+\)@\1@
s/${src}/dev ${dst} label ${dst}/
s/secondary//
" | sh -e
    # Remove automatic routes on destination device
    ip route list | sed -ne "
/dev ${dst}\( \|$\)/ {
  s/^/ip route del /
  p
}" | sh -e
}

# Usage: transfer_routes src dst
# Get all IP routes to device $src, delete them, and
# add the same routes to device $dst.
# The original routes have to be deleted, otherwise adding them
# for $dst fails (duplicate routes).
transfer_routes () {
    local src=$1
    local dst=$2
    # List all routes and grep the ones with $src in.
    # Stick 'ip route del' on the front to delete.
    # Change $src to $dst and use 'ip route add' to add.
    ip route list | sed -ne "
/dev ${src}\( \|$\)/ {
  h
  s/^/ip route del /
  P
  g
  s/${src}/${dst}/
  s/^/ip route add /
  P
  d
}" | sh -e
}


##
# link_exists interface
#
# Returns 0 if the interface named exists (whether up or down), 1 otherwise.
#
link_exists()
{
    if ip link show "$1" >/dev/null 2>/dev/null
    then
        return 0
    else
        return 1
    fi
}

# Set the default forwarding policy for $dev to drop.
# Allow forwarding to the bridge.
antispoofing () {
    iptables -P FORWARD DROP
    iptables -F FORWARD
    iptables -A FORWARD -m physdev --physdev-in ${pdev} -j ACCEPT
}

# Usage: show_status dev bridge
# Print ifconfig and routes.
show_status () {
    local dev=$1
    local bridge=$2
    
    echo '============================================================'
    ip addr show ${dev}
    ip addr show ${bridge}
    echo ' '
    brctl show ${bridge}
    echo ' '
    ip route list
    echo ' '
    route -n
    echo '============================================================'
}

op_start () {
    if [ "${bridge}" = "null" ] ; then
  return
    fi

    if link_exists "$pdev"; then
        # The device is already up.
        return
    fi

    create_bridge ${tdev}

    preiftransfer ${netdev}
    transfer_addrs ${netdev} ${tdev}
    if ! ifdown ${netdev}; then
  # If ifdown fails, remember the IP details.
  get_ip_info ${netdev}
  ip link set ${netdev} down
  ip addr flush ${netdev}
    fi
    ip link set ${netdev} name ${pdev}
    ip link set ${tdev} name ${bridge}

    setup_bridge_port ${pdev}

    add_to_bridge2 ${bridge} ${pdev}
    do_ifup ${bridge}

    if [ ${antispoof} = 'yes' ] ; then
  antispoofing
    fi
}

op_stop () {
    if [ "${bridge}" = "null" ]; then
  return
    fi
    if ! link_exists "$bridge"; then
  return
    fi

    transfer_addrs ${bridge} ${pdev}
    if ! ifdown ${bridge}; then
  get_ip_info ${bridge}
    fi
    ip link set ${pdev} down
    ip addr flush ${bridge}

    brctl delif ${bridge} ${pdev}
    ip link set ${bridge} down

    ip link set ${bridge} name ${tdev}
    ip link set ${pdev} name ${netdev}
    do_ifup ${netdev}

    brctl delbr ${tdev}
}

# adds $dev to $bridge but waits for $dev to be in running state first
add_to_bridge2() {
    local bridge=$1
    local dev=$2
    local maxtries=10

    echo -n "Waiting for ${dev} to negotiate link."
    ip link set ${dev} up
    for i in `seq ${maxtries}` ; do
  if ifconfig ${dev} | grep -q RUNNING ; then
      break
  else
      echo -n '.'
      sleep 1
  fi
    done

    if [ ${i} -eq ${maxtries} ] ; then echo -n '(link isnt in running state)' ; fi
    echo

    add_to_bridge ${bridge} ${dev}
}

case "$command" in
    start)
  op_start
  ;;
    
    stop)
  op_stop
  ;;

    status)
  show_status ${netdev} ${bridge}
  ;;

    *)
  echo "Unknown command: $command" >&2
  echo 'Valid commands are: start, stop, status' >&2
  exit 1
esac