Mount luks_root partition in RHCOS qcow2 image

coreos_image_mount_root.sh

#!/bin/bash

if [ x"$#" != x"2" ]; then
        echo "$0 image mountpoint"
        exit 1
fi

image=$1; shift
mountpoint=$1; shift
nbd=/dev/nbd0
LUKS_HEADER_OFFSET_SECTORS=32768

echo "=> qcow2-nbd --connect"
qemu-nbd --connect ${nbd} ${image}

echo "=> lsblk"
lsblk ${nbd}

echo "=> parted"
parted ${nbd} print
part_id=$(parted /dev/nbd0 print | awk '/luks_root/ {print $1}')
dev=${nbd}p${part_id}

echo "=> cryptsetup luksDump ${dev}"
cryptsetup luksDump ${dev}

cipher=$(cryptsetup luksDump ${dev} | awk '/cipher/{print$NF;exit}')
echo "* cipher: ${cipher}"

dev_size=$(($(blockdev --getsize ${dev}) - ${LUKS_HEADER_OFFSET_SECTORS}))
echo "* dev_size:  ${dev_size}"

echo "0 ${dev_size} linear ${dev} ${LUKS_HEADER_OFFSET_SECTORS}" | sudo dmsetup create coreos-luks-root-nocrypt

echo "=> ls -l /dev/mapper"
ls -l /dev/mapper

echo "=> mount"
mount /dev/mapper/coreos-luks-root-nocrypt ${mountpoint}

echo "=> df"
df -h

## for unmount...
# umount /mnt
# dmsetup remove coreos-luks-root-nocrypt
# qemu-nbd --disconnect ${nbd}