qemu-tap-helper.sh

#! /usr/bin/bash

# Author: Jakub Klinkovský (Lahwaacz)
# https://github.com/lahwaacz

########## Functions ##########

## Check if a string represents a network interface
# $1: potential interface name
function is_interface() {
    [[ -d "/sys/class/net/$1" ]]
}

## Create new TAP interface
# $1: name of the interface to create
function create_tap() {
    if ! is_interface "$1"; then
        echo "Creating TAP interface '$1'"
        ip tuntap add "$1" mode tap user "$username"
        ip link set dev "$1" up
    fi
}

## Delete TAP interface
# $1: name of the interface to delete
function del_tap() {
    echo "Deleting TAP interface '$1'"
    ip link set dev "$1" down
    ip tuntap del "$1" mode tap
}

## Check if the bridge has any interface
# $1: bridge interface name
function bridge_is_empty() {
    [[ $(ls "/sys/class/net/$1/brif" | wc -w) == "0" ]]
}

## Create bridge interface if it does not exist
# $1: bridge interface name
function create_br() {
    if is_interface "$1"; then
        if [[ ! -d "/sys/class/net/$1/brif" ]]; then
            echo "Interface '$1' already exists and is not a bridge"
            exit 1
        fi
    else
        echo "Creating bridge interface '$1'"
        ip link add name "$1" type bridge
        ip link set dev "$1" up

        # Xyne's excellent script to launch NAT
        echo "Starting NAT"
        nat-launch.sh "$wan_nic" "$1" up
    fi
}

## Delete bridge interface if it exists and has no interface
# $1: bridge interface name
function del_br() {
    if bridge_is_empty "$1"; then
        # Xyne's excellent script to launch NAT
        echo "Stopping NAT"
        nat-launch.sh "$wan_nic" "$1" down

        echo "Deleting bridge interface '$1'"
        ip link set dev "$1" down
        ip link delete "$1" type bridge
    fi
}

## Add interface to the bridge
# $1: bridge interface name
# $2: name of the interface to add
function br_add_iface() {
    echo "Adding interface '$2' to bridge '$1'"
    ip link set dev "$2" promisc on up
    ip addr flush dev "$2" scope host &>/dev/null
    ip addr flush dev "$2" scope site &>/dev/null
    ip addr flush dev "$2" scope global &>/dev/null
    ip link set dev "$2" master "$1"
    # skip forwarding delay
    bridge link set dev "$2" state 3
}

## Remove interface from the bridge
# $1: bridge interface name
# $2: name of the interface to remove
function br_rm_iface() {
    echo "Removing interface '$2' from bridge '$1'"
    ip link set "$2" promisc off down
    ip link set dev "$2" nomaster
}

########## Main ###############

function print_qemu_tap_helper_usage() {
    echo "usage: $0 <username> <TAP interface> <bridge interface> <WAN interface> <up|down>"
    echo "  <TAP interface> and <bridge interface> will be created,"
    echo "  NAT from <WAN interface> to <bridge interface> will be set up"
}

if [[ $EUID -ne 0 ]]; then
    echo "This script must be run as root." >&2
    exit 1
fi

if [[ -z $4 ]]; then
    print_qemu_tap_helper_usage
    exit 1
else
    username="$1"
    tap_nic="$2"
    br_nic="$3"
    wan_nic="$4"
    action="$5"
fi

# exit on errors
set -e

case "$action" in
    up)
        create_br "$br_nic"
        create_tap "$tap_nic"
        br_add_iface "$br_nic" "$tap_nic"
    ;;
    down)
        br_rm_iface "$br_nic" "$tap_nic"
        del_tap "$tap_nic"
        del_br "$br_nic"
    ;;
    *)
        print_qemu_tap_helper_usage
        exit 1
    ;;
esac