swap_to_bridge.sh

#!/bin/bash
#
# Usage:
# swap_to_bridge.sh [bridge_name]
#
set -x
#mount -o remount,exec /tmp
R=/tmp/root

INTERFACE="$(ip route | grep -v '^default' | grep -oP -m1 '(?<=dev )[^ ]*')"
BRIDGE="${1-br0}"
REPEAT=120 #2 minutes

# Wait for IP
while [ -z "$IPADDR" ]; do
  IPADDR="$(ip addr list $INTERFACE | grep -oP -m1 '(?<=inet )([0-9]+.){3}[0-9]+/[0-9]+')"
  sleep 1
    # Timeout check
    if [ "$REPEAT" -gt 0 ]; then
        ((REPEAT--))
    else
        exit 1
    fi
done
DEFROUTE="$(ip route | grep -oP '(?<=default via )([0-9]+.){3}[0-9]+')"

mkdir -p "$R/proc"
cp -r /bin /lib "$R"
mount -t proc none "$R/proc"
cat > "$R/script" <<EOF
echo brctl addbr "$BRIDGE"
brctl addbr "$BRIDGE"
echo brctl addif "$BRIDGE" "$INTERFACE"
brctl addif "$BRIDGE" "$INTERFACE"
echo ip link set "$BRIDGE" up
ip link set "$BRIDGE" up
echo ip addr flush "$INTERFACE"
ip addr flush "$INTERFACE"
echo ip addr add "$IPADDR" dev "$BRIDGE"
ip addr add "$IPADDR" dev "$BRIDGE"
echo ip route add "$DEFROUTE"
ip route add default via "$DEFROUTE" dev "$BRIDGE"
EOF
chroot "$R" busybox sh script
umount "$R/proc"
rm -rf "$R"