Symlink to backup dir until ephemeral storage available

Currently, when you call `register-state-path --leave-symlink /a`, a
symlink is left at /a pointing to /mnt/state/a. However, /mnt/state
doesn't point at ephemeral storage until the instance has booted. So if
another element tries to write through the symlink, it goes wrong.

This patch defers moving content (and leaving a symlink if required) to the
backup dir until finalise.d runs.

Change-Id: Id5bc25965db1fdf27f2bcb947c518f6f4566fd2f
Co-Author: Nicholas Randon

elements/use-ephemeral/bin/register-state-path

@@ -18,11 +18,11 @@
 set -eux
 set -o pipefail
 
-SCRIPT_NAME=$(basename $0)
-SCRIPT_HOME=$(dirname $0)
+SCRIPT_NAME=$(basename ${0})
+SCRIPT_HOME=$(dirname ${0})
 
 function show_options () {
-    echo "Usage: $SCRIPT_NAME [options] <path>"
+    echo "Usage: ${SCRIPT_NAME} [options] <path>"
     echo
     echo "Register <path> as a state path."
     echo
@@ -35,40 +35,34 @@ function show_options () {
     echo "Options:"
     echo "    --leave-symlink -- create a symlink from <path> to /mnt/state/<path>."
     echo
-    exit $1
+    exit ${1}
 }
 
 LEAVE_SYMLINK=""
 
-TEMP=`getopt -o h -l help,leave-symlink -n $SCRIPT_NAME -- "$@"`
+TEMP=`getopt -o h -l help,leave-symlink -n ${SCRIPT_NAME} -- "$@"`
 if [ $? != 0 ] ; then echo "Terminating..." >&2 ; exit 1 ; fi
 
-# Note the quotes around `$TEMP': they are essential!
-eval set -- "$TEMP"
+# Note the quotes around `${TEMP}': they are essential!
+eval set -- "${TEMP}"
 
 while true ; do
-    case "$1" in
+    case "${1}" in
         --leave-symlink) LEAVE_SYMLINK="true"; shift 1 ;;
         -h | --help) show_options 0;;
         --) shift ; break ;;
-        *) echo "Error: unsupported option $1." ; exit 1 ;;
+        *) echo "Error: unsupported option ${1}." ; exit 1 ;;
     esac
 done
 
 STATE_PATH=${1:-""}
 EXTRA=${2:-""}
 
-if [ -z "$STATE_PATH" -o -n "$EXTRA" ]; then
+if [ -z "${STATE_PATH}" -o -n "${EXTRA}" ]; then
     show_options 1
 fi
 
-mkdir -p /var/lib/use-ephemeral
-echo $STATE_PATH >> /var/lib/use-ephemeral/stateful-paths
-if [ -e "$STATE_PATH" -o -L "$STATE_PATH" ]; then
-    backup_dir=/var/lib/use-ephemeral/$(dirname "$STATE_PATH")
-    mkdir -p "$backup_dir"
-    mv "$STATE_PATH" "$backup_dir"
-fi
-if [ -n "$LEAVE_SYMLINK" ]; then
-    ln -s "/mnt/state/$STATE_PATH" "$STATE_PATH"
-fi
+backup="/var/lib/use-ephemeral"
+mkdir -p "${backup}"
+
+echo "${STATE_PATH};${LEAVE_SYMLINK}" >> "${backup}/stateful-paths"

elements/use-ephemeral/finalise.d/00-cleanup-stateful-paths

@@ -0,0 +1,40 @@
+#!/bin/bash
+#
+# Copyright 2013 Hewlett-Packard Development Company, L.P.
+# All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+set -eux
+set -o pipefail
+
+backup="/var/lib/use-ephemeral"
+paths="${backup}/stateful-paths"
+state="/mnt/state"
+
+[ -e "${paths}" ] || exit 0
+
+while read -r line; do
+    path="${line%;*}"
+
+    if [ -e "${path}" ]; then
+        backup_dir="${backup}$(dirname "${path}")"
+        mkdir -p "${backup_dir}"
+        mv "${path}" "${backup_dir}"
+    fi
+
+    if [ -n "${line##*;}" ]; then
+        ln -s "${state}${path}" "${path}"
+    fi
+done < "${paths}"
+

elements/use-ephemeral/os-refresh-config/pre-configure.d/01-setup-stateful-paths

@@ -26,11 +26,12 @@ state="/mnt/state"
 
 done="$(mktemp)"
 while read -r line; do
-    dst="${state}${line}"
+    path="${line%;*}"
+    dst="${state}${path}"
     dst_dir=$(dirname "${dst}")
 
     # stateful_paths may contain duplicates, don't copy any path twice
-    src="${backup}${line}"
+    src="${backup}${path}"
     [ -L "${src}" ] || src="$(readlink -f "${src}")"
     grep -qFx "${src}" "${done}" && continue
     echo "${src}" >> "${done}"