netris-nestri/build/etc/init.d/guest-net

#!/sbin/openrc-run

description="Configure the guest's network to match the host's tap"

# Overridden from /etc/conf.d/guest-net if present. These defaults match
# nesbox's own defaults; if you change the `network` section in the VM's
# JSON, change these to match.
: ${GUEST_IFACE:=eth0}
: ${GUEST_IP:=172.30.0.2}
: ${GUEST_PREFIX:=24}
: ${GUEST_GATEWAY:=172.30.0.1}

depend() {
    need localmount
    provide net
    keyword -shutdown
}

# Read one `nestri.<key>=<value>` from the kernel command line.
#
# The address has to come from somewhere per-boot, because the alternative --
# baking it into the image -- makes every guest built from that image the
# same host on the network. Two sandboxes then collide the moment they run
# together.
#
# `nestri.`-prefixed rather than the kernel's own `ip=`: that one needs
# CONFIG_IP_PNP and exists to configure NFS root, and the prefix makes it
# obvious whose parameter this is.
cmdline_value() {
    local key="$1" word
    for word in $(cat /proc/cmdline 2>/dev/null); do
        case "$word" in
            "nestri.${key}="*) printf '%s' "${word#nestri.${key}=}"; return 0 ;;
        esac
    done
    return 1
}

start() {
    ebegin "Bringing up loopback"
    ip link set lo up
    eend $?

    # The command line wins over conf.d when it says anything, and conf.d is
    # the fallback so a hand-written VM config with no parameters keeps
    # working -- which is how a guest gets debugged.
    local source="/etc/conf.d/guest-net"
    local cmdline_ip
    if cmdline_ip="$(cmdline_value ip)"; then
        # Accepts address/prefix; a bare address keeps the configured prefix
        # rather than guessing one.
        case "$cmdline_ip" in
            */*)
                GUEST_IP="${cmdline_ip%%/*}"
                GUEST_PREFIX="${cmdline_ip##*/}"
                ;;
            *)  GUEST_IP="$cmdline_ip" ;;
        esac
        source="kernel command line"
    fi

    local cmdline_gw
    if cmdline_gw="$(cmdline_value gw)"; then
        GUEST_GATEWAY="$cmdline_gw"
        source="kernel command line"
    fi

    # The VM may have been started with no network device at all, which is a
    # perfectly good configuration. Do not fail the boot over it.
    if [ ! -e "/sys/class/net/${GUEST_IFACE}" ]; then
        einfo "no ${GUEST_IFACE}: this VM has no network device"
        return 0
    fi

    # Says which source won, because "the address is wrong" and "the address
    # came from somewhere unexpected" look identical from inside the guest.
    ebegin "Configuring ${GUEST_IFACE} as ${GUEST_IP}/${GUEST_PREFIX} via ${GUEST_GATEWAY} (from ${source})"
    # `replace` rather than `add` so a restart is not an error.
    ip link set "${GUEST_IFACE}" up &&
        ip addr replace "${GUEST_IP}/${GUEST_PREFIX}" dev "${GUEST_IFACE}" &&
        ip route replace default via "${GUEST_GATEWAY}" dev "${GUEST_IFACE}"
    eend $? "could not configure ${GUEST_IFACE}"
}

stop() {
    if [ -e "/sys/class/net/${GUEST_IFACE}" ]; then
        ebegin "Bringing down ${GUEST_IFACE}"
        ip link set "${GUEST_IFACE}" down
        eend 0
    fi
    return 0
}