#!/bin/sh

# zfs-mount-generator - generates systemd mount units for zfs
# Copyright (c) 2017 Antonio Russo <antonio.e.russo@gmail.com>
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

set -ef

FSLIST="@sysconfdir@/zfs/zfs-list.cache"

[ -d "${FSLIST}" ] || exit 0

do_fail() {
  printf 'zfs-mount-generator.sh: %s\n' "$*" > /dev/kmsg
  exit 1
}

# see systemd.generator
if [ $# -eq 0 ] ; then
  dest_norm="/tmp"
elif [ $# -eq 3 ] ; then
  dest_norm="${1}"
else
  do_fail "zero or three arguments required"
fi

# For ZFSs marked "auto", a dependency is created for local-fs.target. To
# avoid regressions, this dependency is reduced to "wants" rather than
# "requires". **THIS MAY CHANGE**
req_dir="${dest_norm}/local-fs.target.wants/"
mkdir -p "${req_dir}"

# All needed information about each ZFS is available from
# zfs list -H -t filesystem -oname,mountpoint,canmount
# cached in $FSLIST, and each line is processed by the following function:

process_line() {

  # Check for canmount=off .
  if [ "${3}" = "off" ] ; then
    return
  elif [ "${3}" = "noauto" ] ; then
    # Don't let a noauto marked mountpoint block an "auto" market mountpoint
    return
  elif [ "${3}" = "on" ] ; then
    : # This is OK
  else
    do_fail "invalid canmount"
  fi

  # Check for legacy and blank mountpoints.
  if [ "${2}" = "legacy" ] ; then
    return
  elif [ "${2}" = "none" ] ; then
    return
  elif [ "${2%"${2#?}"}" != "/" ] ; then
    do_fail "invalid mountpoint $*"
  fi

  # Escape the mountpoint per systemd policy.
  mountfile="$(systemd-escape "${2#?}").mount"

  # If the mountpoint has already been created, give it precedence.
  if [ -e "${dest_norm}/${mountfile}" ] ; then
    printf 'zfs-mount-generator.sh: %s.mount already exists\n' "${2}" \
      >/dev/kmsg
    return
  fi

  # By ordering before zfs-mount.service, we avoid race conditions.
  cat > "${dest_norm}/${mountfile}" << EOF
# Automatically generated by zfs-mount-generator

[Unit]
SourcePath=${FSLIST}/${cachefile}
Documentation=man:zfs-mount-generator(8)
Before=local-fs.target zfs-mount.service
After=zfs-import.target
Wants=zfs-import.target

[Mount]
Where=${2}
What=${1}
Type=zfs
Options=zfsutil,auto
EOF

  # Finally, create the appropriate dependencies based on the ZFS properties.
  [ "$3" = "on" ] & ln -s "../${mountfile}" "${req_dir}"
}

# Feed each line into process_line
for cachefile in $(ls "${FSLIST}") ; do
  while read -r fs ; do
    process_line $fs
  done < "${FSLIST}/${cachefile}"
done