# cat /usr/bin/resize_datafs.sh
#!/bin/bash
set -e

DATA_MOUNT="/data"

# Only run once
STAMP="/var/lib/resize-datafs.done"
[ -f "$STAMP" ] && exit 0

# Find device backing /data
DATA_DEV=$(findmnt -n -o SOURCE --target "$DATA_MOUNT")
[ -z "$DATA_DEV" ] && exit 0

# mmcblk1p3 -> mmcblk1
DISK="/dev/$(lsblk -no PKNAME "$DATA_DEV")"

# Partition number (3)
PARTNUM=$(echo "$DATA_DEV" | sed 's/.*p//')

# Unmount safely
umount "$DATA_MOUNT"

# Grow partition
echo ",+" | sfdisk -N "$PARTNUM" "$DISK" --no-reread

# Re-read partition table
partprobe "$DISK"
sleep 2

# Check filesystem
e2fsck -fy "$DATA_DEV" || true

# Resize filesystem
resize2fs "$DATA_DEV"

# Check filesystem after resize
e2fsck -fy "$DATA_DEV" || true

# Mount back
mount "$DATA_MOUNT"

# Mark done
mkdir -p /var/lib
touch "$STAMP"
sync

exit 0