add-partition.sh

#!/usr/bin/env bash

# Add a FAT32 data partition to the end of the image.

set -o errexit
set -o nounset
set -o pipefail
set -o xtrace

IMG_FILE=$1

echo "IMG_FILE: $IMG_FILE"

# Size should be in MiB.
PART_SIZE=64
# Name will be converted to upper case.
PART_NAME=DATA
# Mount is relative to root of image.
PART_MOUNT=/data

# Currently only `FAT32` is supported.
PART_TYPE=fat32

# Use `parted` to print the partition table.
PARTED_OUT=$(parted -s "${IMG_FILE}" unit b print)
echo "PARTED OUTPUT: $PARTED_OUT"

# Find the end of the root partition. This assumes there are two partitions.
ROOT_END=$(echo "$PARTED_OUT" | grep -e '^ 2'| xargs echo -n \
| cut -d" " -f 3 | tr -d B)

# Determine where to start the new partition so that it is properly aligned to
# 4MiB erase blocks.
BLOCK=$((4 * 1024 * 1024))
PART_START=$((($ROOT_END + 1) / $BLOCK))
PART_START=$((($PART_START + 1) * $BLOCK))

# Work out how much to expand the image to fit the new partition.
# Convert `PART_SIZE` from MiB to B.
PART_EXPAND=$(($PART_SIZE * 1024 * 1024))
# Add the free space gap required between the end of the previous partition and
# the new one.
PART_EXPAND=$(($PART_EXPAND + ($PART_START - $ROOT_END)))
# Ensure the expansion aligns with 512B sector.
PART_EXPAND=$(($PART_EXPAND / 512))
PART_EXPAND=$((($PART_EXPAND + 1) * 512))
# Convert to MiB for quicker `dd`.
PART_EXPAND=$(($PART_EXPAND / (1024 * 1024)))

# Print values.
echo "ROOT_END: $ROOT_END"
echo "PART_START: $PART_START"
echo "PART_EXPAND: $PART_EXPAND"

# Expand the image with zeros using `dd`.
dd if=/dev/zero bs=1M count=$PART_EXPAND >> $IMG_FILE

# Use `parted` to print the partition table.
parted -s "${IMG_FILE}" unit b print free

# Create the partition in the new space.
parted -a none -s "${IMG_FILE}" mkpart primary "${PART_TYPE}" "${PART_START}B" 100%

# Use `parted` to print the partition table.
parted -s "${IMG_FILE}" unit b print free

# Check the partition is optimally aligned.
parted -s "${IMG_FILE}" align-check opt 3

# Mount the image using `mount.sh`.
source ./mount.sh $IMG_FILE
# This script must set `LOOP_DEV` and `ROOTFS_DIR`.

# Format the partition.
PART_NAME=$(echo $PART_NAME | tr a-z A-Z )
mkdosfs -n "${PART_NAME}" -F 32 -v "${LOOP_DEV}p3" > /dev/null

# Use `parted` to print the partition table.
parted -s "${IMG_FILE}" unit b print free

# Create the mount point and mount the new partition.
mkdir ${ROOTFS_DIR}/${PART_MOUNT}
mount -o rw ${LOOP_DEV}p3 ${ROOTFS_DIR}/${PART_MOUNT}

# Add the partition mount to `/etc/fstab`.
IMG_ID="$(dd if="${IMG_FILE}" skip=440 bs=1 count=4 2>/dev/null | xxd -e | cut -f 2 -d' ')"
echo "IMG_ID: $IMG_ID"
BOOT_PARTUUID="${IMG_ID}-01"
ROOT_PARTUUID="${IMG_ID}-02"
DATA_PARTUUID="${IMG_ID}-03"
sed -i "s/PARTUUID=[a-z0-9]*-01/PARTUUID=${BOOT_PARTUUID}/" "${ROOTFS_DIR}/etc/fstab"
sed -i "s/PARTUUID=[a-z0-9]*-02/PARTUUID=${ROOT_PARTUUID}/" "${ROOTFS_DIR}/etc/fstab"
echo "PARTUUID=${DATA_PARTUUID} ${PART_MOUNT} vfat defaults,umask=0000 0 0" >> "${ROOTFS_DIR}/etc/fstab"
echo "FSTAB:"
cat "${ROOTFS_DIR}/etc/fstab"

# Update `cmdline.txt` to use the new `PARTUUID`.
sed -i "s/PARTUUID=[a-z0-9]*-02/PARTUUID=${ROOT_PARTUUID}/" "${ROOTFS_DIR}/boot/cmdline.txt"
# Remove the existing `init` script used to expand the root file system as it
# can no longer be expanded with the new data partition in the way.
sed -i "s/init=.*//" "${ROOTFS_DIR}/boot/cmdline.txt"
echo "CMDLINE.TXT:"
cat "${ROOTFS_DIR}/boot/cmdline.txt"