#!/bin/bash
# SPDX-License-Identifier: GPL-2.0-only

shopt -s extglob

m4_include(fstab-helpers)

write_source() {
  local src=$1 spec="" label="" uuid="" comment=()

  label=$(lsblk -rno LABEL "$1" 2>/dev/null)
  uuid=$(lsblk -rno UUID "$1" 2>/dev/null)

  # bind mounts do not have a UUID!

  case $bytag in
    '')
      [[ $uuid ]] && comment=("UUID=$uuid")
      [[ $label ]] && comment+=("LABEL=$(mangle "$label")")
      ;;
    LABEL)
      spec=$label
      [[ $uuid ]] && comment=("$src" "UUID=$uuid")
      ;;
    UUID)
      spec=$uuid
      comment=("$src")
      [[ $label ]] && comment+=("LABEL=$(mangle "$label")")
      ;;
    *)
      [[ $uuid ]] && comment=("$1" "UUID=$uuid")
      [[ $label ]] && comment+=("LABEL=$(mangle "$label")")
      [[ $bytag ]] && spec=$(lsblk -rno "$bytag" "$1" 2>/dev/null)
      ;;
  esac

  [[ -v comment ]] && printf '# %s\n' "${comment[*]}"

  if [[ $spec ]]; then
    printf '%-20s' "$bytag=$(mangle "$spec")"
  else
    printf '%-20s' "$(mangle "$src")"
  fi
}

optstring_apply_quirks() {
  local varname=$1 fstype=$2

  # SELinux displays a 'seclabel' option in /proc/self/mountinfo. We can't know
  # if the system we're generating the fstab for has any support for SELinux (as
  # one might install Arch from a Fedora environment), so let's remove it.
  optstring_remove_option "$varname" seclabel

  # Prune 'relatime' option for any pseudofs. This seems to be a rampant
  # default which the kernel often exports even if the underlying filesystem
  # doesn't support it. Example: https://bugs.archlinux.org/task/54554.
  if awk -v fstype="$fstype" '$1 == fstype { exit 1 }' /proc/filesystems; then
    optstring_remove_option "$varname" relatime
  fi

  case $fstype in
    btrfs)
      # Having only one of subvol= and subvolid= is enough for mounting a btrfs subvolume
      # And having subvolid= set prevents things like 'snapper rollback' to work, as it
      # updates the subvolume in-place, leaving subvol= unchanged with a different subvolid.
      if optstring_has_option "$varname" subvol; then
        optstring_remove_option "$varname" subvolid
      fi
      ;;
    f2fs)
      # These are build-time or runtime-unchangeable options for f2fs.
      # The former means that kernels supporting the options will only
      # provide the negative versions of these (e.g. noacl), and vice versa
      # for kernels without support.
      # The latter means that the options can only be specified/changed
      # during the initial mount but not remount.
      optstring_remove_option "$varname" noacl,acl,nouser_xattr,user_xattr,atgc
      ;;
    vfat)
      # Before Linux v3.8, "cp" is prepended to the value of the codepage.
      # shellcheck disable=SC2154 # codepage is implicitly declared through optstring_get_option
      if optstring_get_option "$varname" "codepage" && [[ "$codepage" = cp* ]]; then
        optstring_remove_option "$varname" "codepage"
        optstring_append_option "$varname" "codepage=${codepage#cp}"
      fi
      ;;
  esac
}

usage() {
  cat <<EOF
usage: ${0##*/} [options] root

  Options:
    -f <filter>    Restrict output to mountpoints matching the prefix FILTER
    -L             Use labels for source identifiers (shortcut for -t LABEL)
    -p             Exclude pseudofs mounts (default behavior)
    -P             Include pseudofs mounts
    -t <tag>       Use TAG for source identifiers (TAG should be one of: LABEL,
                      UUID, PARTLABEL, PARTUUID)
    -U             Use UUIDs for source identifiers (shortcut for -t UUID)

    -h             Print this help message

genfstab generates output suitable for addition to an fstab file based on the
devices mounted under the mountpoint specified by the given root.

EOF
}

if [[ -z $1 || $1 = @(-h|--help) ]]; then
  usage
  exit $(( $# ? 0 : 1 ))
fi

while getopts ':f:LPpt:U' flag; do
  case $flag in
    L)
      bytag=LABEL
      ;;
    U)
      bytag=UUID
      ;;
    f)
      prefixfilter=$OPTARG
      ;;
    P)
      pseudofs=1
      ;;
    p)
      pseudofs=0
      ;;
    t)
      bytag=${OPTARG^^}
      ;;
    :)
      die '%s: option requires an argument -- '\''%s'\' "${0##*/}" "$OPTARG"
      ;;
    ?)
      die '%s: invalid option -- '\''%s'\' "${0##*/}" "$OPTARG"
      ;;
  esac
done
shift $(( OPTIND - 1 ))

(( $# )) || die "No root directory specified"
root=$(realpath -mL "$1"); shift

if ! mountpoint -q "$root"; then
  die "$root is not a mountpoint"
fi

# handle block devices
cat <<EOF
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
EOF
printf "%-15s %-15s %-7s %-15s %-7s %s\n" '# <file system>' '<mount point>' '<type>' '<options>' '<dump>' '<pass>'
while read -r src target fstype opts fsroot; do
  if (( !pseudofs )) && fstype_is_pseudofs "$fstype"; then
    continue
  fi

  [[ $target = "$prefixfilter"* ]] || continue

  # default 5th and 6th columns
  dump=0 pass=2

  src=$(unmangle "$src")
  target=$(unmangle "$target")
  target=${target#"$root"}

  if (( !foundroot )) && findmnt "$src" "$root" >/dev/null; then
    # this is root. we can't possibly have more than one...
    pass=1 foundroot=1
  fi

  # if there's no fsck tool available, then only pass=0 makes sense.
  if ! fstype_has_fsck "$fstype"; then
    pass=0
  fi

  if [[ $fsroot != / && $fstype != btrfs ]]; then
    # it's a bind mount
    src=$(findmnt -funcevo TARGET "$src")$fsroot
    src="/${src#"${root}/"}"
    if [[ $src -ef $target ]]; then
      # hrmm, this is weird. we're probably looking at a file or directory
      # that was bound into a chroot from the host machine. Ignore it,
      # because this won't actually be a valid mount. Worst case, the user
      # just re-adds it.
      continue
    fi
    fstype=none
    opts+=,bind
    pass=0
  fi

  # filesystem quirks
  case $fstype in
    fuseblk)
      # well-behaved FUSE filesystems will report themselves as fuse.$fstype.
      # this is probably NTFS-3g, but let's just make sure.
      if ! newtype=$(lsblk -no FSTYPE "$src") || [[ -z $newtype ]]; then
        # avoid blanking out fstype, leading to an invalid fstab
        error 'Failed to derive real filesystem type for FUSE device on %s' "$target"
      else
        fstype=$newtype
      fi
      ;;
  esac

  optstring_apply_quirks "opts" "$fstype"

  # write one line
  write_source "$src"
  printf '\t%-10s' "/$(mangle "${target#/}")" "$fstype" "$opts"
  printf '\t%s %s' "$dump" "$pass"
  printf '\n\n'
done < <(findmnt -Recvruno SOURCE,TARGET,FSTYPE,OPTIONS,FSROOT "$root")

# handle swaps devices
{
  # ignore header
  read -r

  while read -r device type _ _ prio; do
    options=defaults
    if (( prio >= 0 )); then
      options+=,pri=$prio
    fi

    # skip files marked deleted by the kernel
    [[ $device = *'\040(deleted)' ]] && continue

    # skip devices not part of the prefix
    [[ $device = "$prefixfilter"* ]] || continue

    # skip zram devices
    [[ $device == *'zram'* ]] && continue

    if [[ $type = file ]]; then
      printf '%-20s' "${device#"${root%/}"}"
    elif [[ $device = /dev/dm-+([0-9]) ]]; then
      # device mapper doesn't allow characters we need to worry
      # about being mangled, and it does the escaping of dashes
      # for us in sysfs.
      write_source "$(dm_name_for_devnode "$device")"
    else
      write_source "$(unmangle "$device")"
    fi

    printf '\t%-10s\t%-10s\t%-10s\t0 0\n\n' 'none' 'swap' "$options"
  done
} </proc/swaps
