mktap

#!/usr/bin/env bash

cat <<'EOF'

This is where we get the `mknod` numbers from:
* /dev/net/tun - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/devices.txt#:~:text=%2Fdev%2Fnet%2Ftun
* /dev/tap0 = https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/devices.txt#:~:text=%2Fdev%2Ftap0

EOF

if [ ${UID:-1} -ne 0 ] && [ "x$USER" != "xroot" ]; then
    echo "You must run this script as root."
    exit 3
fi

nodtype=c
major=36
minor=16
_devpfx=/dev/tap
_dev=''
maxdev=15

for i in $(seq 0 $maxdev); do
    _dev=$_devpfx$i
    minor=$(expr $minor + $i)
    if [ ! -e $_dev ]; then
        declare -l _resp
        read -n 1 -r -t 30 -p "Create $_dev? [y/N]: " _resp
        echo
        if [ x$_resp = xy ]; then
            echo "Creating $_dev"
            _xt="$(shopt -op xtrace)"
            set -x
            mknod $_dev $nodtype $major $minor
            $_xt
            break
        else
            echo "Continuing..."
        fi
    else
        echo "$_dev already exists"
    fi
done

if [ -n $_dev ]; then
    if [ -e $_dev ]; then
        echo "Done."
        exit 0
    else
        echo "Already at max TAP devices."
        exit 1
    fi
else
    echo "Something went wrong."
    exit 2
fi