#!/bin/sh
# Copyright 2015 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

if ! mountpoint -q /etc; then
  ETC=/tmp/etc_overlay
  mkdir ${ETC}
  if mount -t tmpfs tmpfs ${ETC} -o mode=755,nosuid,noexec,nodev ; then
    mkdir -p ${ETC}/etc ${ETC}/.work
    # Because /etc is read-only at the time systemd boots,
    # systemd saves machine-id in /run and then bind-mounts it
    # into /etc. A few services depend on /etc/machine-id, so we want
    # to make sure that there is no downtime on /etc/machine-id. Let's
    # keep the /etc/machine-id bind mount to make sure there is no downtime.
    # We also need to copy /etc/machine-id into the overlayfs upperdir before
    # mounting it to ensure no downtime after mounting the overlayfs.
    cp /run/machine-id "${ETC}/etc/machine-id"
    mount -o lowerdir=/etc,upperdir=${ETC}/etc,workdir=${ETC}/.work \
      -t overlay overlayfs /etc ||
      logger -t "$UPSTART_JOB" \
        "Cannot mount /etc overlay"
    umount ${ETC}
    rmdir ${ETC}
  else
    logger -t "$UPSTART_JOB" "Cannot mount tmpfs at ${ETC}"
  fi
fi