init script for teres with encrypted root

#!/bin/busybox sh

# Install busybox
/bin/busybox --install -s

# Mount the /proc and /sys filesystems.
mount -t proc none /proc
mount -t sysfs none /sys
mount -t devtmpfs none /dev

# turn off noise so we can see password prompt
echo "1 1 1 1" > /proc/sys/kernel/printk
# load display driver
modprobe disp

cmdline() {
        local value
        value=" $(cat /proc/cmdline) "
        value="${value##* $1=}"
        value="${value%% *}"
        [ "$value" != "" ] && echo "$value"
}

m_echo() {
    echo $1
    echo $1 > /dev/tty1
}

run_on_tty1() {
        setsid sh -c "exec $1 <>/dev/tty1 >&0 2>&1"
}

realboot() {
        m_echo "Unlocking rootfs: $1"

        run_on_tty1 "cryptsetup open --allow-discards $1 cryptroot"

        if [ ! -e /dev/mapper/cryptroot ]; then
                m_echo "Something went wrong: /dev/mapper/cryptroot does not exist"
        else
                m_echo "Encrypted root unlocked, mounting and booting..."

                mkdir -p /mnt/root
                mount -o rw /dev/mapper/cryptroot /mnt/root

                if [ -x /mnt/root/sbin/init -o -h /mnt/root/sbin/init ]; then
                        # Cleanup.
                        umount /proc
                        umount /sys
                        umount /dev

                        # Boot the real system.
                        exec switch_root /mnt/root /sbin/init
                else
                        umount /mnt/root
                fi
        fi
}

runshell() {
        m_echo "Dropping to a shell."
        m_echo
        setsid cttyhack /bin/sh
}

find_parition_by_value() {
        echo $(blkid | tr -d '"' | grep "$1" | cut -d ':' -f 1 | head -n 1)
}

boot() {
        m_echo "Kernel params: `cat /proc/cmdline`"
        local i=5
        local kernel_root_param=$(cmdline root)

        while [ "$i" -ge 1 ]; do
                m_echo "Waiting for root system $kernel_root_param, countdown : $i"

                local root=$(find_parition_by_value $kernel_root_param)
                if [ -e "$root" ]; then
                        realboot $root;
                fi;

                i=$(( $i - 1 ));
                sleep 5;
        done;

        # Default rootfs - sd partition 2
        realboot /dev/mmcblk0p2;
        run_on_tty1 "sh"
        runshell
}
boot;