#!/bin/sh

layer_dir=/home/d/sami
seed_file=debian-live-8.4.0-amd64-standard.btrfs
layer_file=debian-live-8.4.0-amd64-standard.layer.$$.btrfs
layer_size=1000
mountpoint=layer_dest.$$

disable_stdout() { exec 3>&1; exec >&2; }
enable_stdout() { exec >&3; }

with_stdout() { enable_stdout; "$@"; disable_stdout; }

create_layer_filesystem()
{
    [ ! -e "$layer_file" ] || return
    mkdir -p "$mountpoint"                                     &&
    dd if=/dev/zero of="$layer_file" bs=1M count="$layer_size" &&
    mount -o subvol=/,compress "$seed_file" "$mountpoint"      &&
    layer_dev=$(losetup -f --show "$layer_file")               &&
    btrfs device add "$layer_dev" "$mountpoint"                &&
    mount -o rw,remount "$mountpoint"
}

finish()
{
    umount "$mountpoint" &&
    btrfstune -S1 "$layer_file"
}

set -ex

cd "$layer_dir"                         &&
disable_stdout                          &&
create_layer_filesystem                 &&
with_stdout btrfs receive "$mountpoint" &&
finish