#!/bin/sh
# Snapper snapshots are read-only, and the system can't start from a read-only
# root. When GRUB boots a snapshot, mount it under an overlay whose writable
# layer lives in RAM. Changes made in that session are lost at shutdown.

[ "$(btrfs property get -ts "$NEWROOT" ro 2>/dev/null)" = "ro=true" ] || return 0

info "das-snapshot-overlay: read-only snapshot, adding a writable overlay"
lower=$(mktemp -d -p /)
ram=$(mktemp -d -p /)
mount --move "$NEWROOT" "$lower"
mount -t tmpfs -o mode=0755 das-overlay "$ram"
mkdir -p "$ram/upper" "$ram/work"
mount -t overlay -o "lowerdir=$lower,upperdir=$ram/upper,workdir=$ram/work" das-overlay "$NEWROOT"