setup_host.sh

#!/usr/bin/env bash

# setup a debian/ubuntu host machine to provide internet for USB device connected
#   this should be run ONCE on the host machine

# all config lives in image_config.sh
source ./image_config.sh

# need to be root
if [ "$(id -u)" != "0" ]; then
    echo "Must be run as root"
    exit 1
fi

if [ "$(uname -s)" != "Linux" ]; then
    echo "Only works on Linux!"
    exit 1
fi

function remove_if_exists() {
    # remove a file if it exists
    FILEPATH="$1"
    if [ -f "$FILEPATH" ]; then
        echo "found ${FILEPATH}, removing"
        rm "$FILEPATH"
    fi
}

function append_if_missing() {
    # append string to file only if it does not already exist in the file
    STRING="$1"
    FILEPATH="$2"
    grep -q "$STRING" "$FILEPATH" || {
        echo "appending \"$STRING\" to $FILEPATH"
        echo "$STRING" >> "$FILEPATH"
        return 1
    }
    echo "Already found \"$STRING\" in $FILEPATH"
    return 0
}

function forward_port() {
    # usage: forward_port <host port> <superbird port>
    # forward a tcp port to access service on superbird via host
    #   if no superbird port is provided, same port number is used for both
    SOURCE="$1"
    DEST="$2"
    if [ -z "$DEST" ]; then
        DEST="$SOURCE"
    fi
    iptables -t nat -A PREROUTING -p tcp -i eth0 --dport "$SOURCE" -j DNAT --to-destination "${USBNET_PREFIX}.2:$DEST"
    iptables -t nat -A PREROUTING -p tcp -i wlan0 --dport "$SOURCE" -j DNAT --to-destination "${USBNET_PREFIX}.2:$DEST"
    iptables -A FORWARD -p tcp -d "${USBNET_PREFIX}.2" --dport "$DEST" -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
}

set -e  # bail on any errors

# install needed packages
#   NOTE: the flag "--break-system-packages" only exists on recent debian/ubuntu versions,
#   so we have to try with, and if there is an error try again without the flag
export DEBIAN_FRONTEND=noninteractive
apt install -y git htop build-essential cmake python3 python3-dev python3-pip iptables adb android-sdk-platform-tools-common iptables-persistent
python3 -m pip install --break-system-packages virtualenv nuitka ordered-set || {
    python3 -m pip install virtualenv nuitka ordered-set
}
python3 -m pip install --break-system-packages git+https://github.com/superna9999/pyamlboot || {
    python3 -m pip install git+https://github.com/superna9999/pyamlboot
}

# fix usb enumeration when connecting superbird in maskroom mode
echo '# Amlogic S905 series can be booted up in Maskrom Mode, and it needs a rule to show up correctly' > /etc/udev/rules.d/70-carthing-maskrom-mode.rules
echo 'SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTR{idVendor}=="1b8e", ATTR{idProduct}=="c003", MODE:="0666", SYMLINK+="worldcup"' >> /etc/udev/rules.d/70-carthing-maskrom-mode.rules

# prevent systemd / udev from renaming usb network devices by mac address
remove_if_exists /lib/systemd/network/73-usb-net-by-mac.link
remove_if_exists /lib/udev/rules.d/73-usb-net-by-mac.rules

#  allow IP forwarding
append_if_missing "net.ipv4.ip_forward = 1" /etc/sysctl.conf || {
    sysctl -p  # reload from conf
}

# forwarding rules
mkdir -p /etc/iptables

# clear all iptables rules
iptables -F
iptables -X
iptables -Z 
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -t raw -F
iptables -t raw -X

# rewrite iptables rules
iptables -P FORWARD ACCEPT
iptables -A FORWARD -o eth0 -i eth1 -s "${USBNET_PREFIX}.0/24" -m conntrack --ctstate NEW -j ACCEPT
iptables -A FORWARD -o eth0 -i eth1 -s "${USBNET_PREFIX}.0/24" -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A POSTROUTING -t nat -j MASQUERADE -s "${USBNET_PREFIX}.0/24"

# port forwards:
#   2022: ssh on superbird
#   5900: vnc on superbird
#   9222: chromium remote debugging on superbird

forward_port 2022 22
forward_port 5900
forward_port 9222

# persist rules to file
iptables-save > /etc/iptables/rules.v4

# write the usb network config
mkdir -p /etc/network/interfaces.d/

cat << EOF > /etc/network/interfaces.d/usb0
# generated by $0
allow-hotplug usb0
iface usb0 inet static
	address ${USBNET_PREFIX}.1
	netmask 255.255.255.0
EOF

# add superbird to /etc/hosts
append_if_missing "${USBNET_PREFIX}.2  ${HOST_NAME}"  "/etc/hosts"

echo "Need to reboot for all changes to take effect"