root-subvol.sh

#!/bin/bash

BTRFS=      # /dev/sda2 or /dev/vda2

if [ -z "$BTRFS" ]; then
    read -r -p "Please choose BTRFS partiion: " BTRFS
fi

UUID=$(blkid "$BTRFS" | grep -oP '(?<=UUID=")([^"]+)' | head -n 1)

COW_PATHS=(
)

NOCOW_PATHS=(
    ".swap"
)

elem_in() {
    local e m="$1"; shift
    for e in "$@"; do [[ "$m" == "$e" ]] && return 0; done
    return 1
}

mount $BTRFS -o subvolid=5 /mnt

for vol in "${COW_PATHS[@]}" "${NOCOW_PATHS[@]}"
do
    orig_vol="$vol"

    mnt="${vol//\//_}"
    mnt="${mnt// /--}"

    mkdir -p "/$vol"
    btrfs sub cr "/mnt/@$mnt"

    if elem_in "$orig_vol" "${NOCOW_PATHS[@]}"; then
        chattr +C "/mnt/@$mnt"
    fi

    rsync -axX "/$vol/" "/mnt/@$mnt/"

    printf "\nUUID=$UUID\t/%s\tbtrfs\trw,noatime,compress=zstd:15,ssd,space_cache,subvolid=$(btrfs sub list / | grep "@$mnt" | grep -oP '(?<=ID )[0-9]+'),subvol=/@%s,discard=async\t0\t0\n" "${vol// /\\040}" "$mnt" >> /etc/fstab
done

umount /mnt
mount -a