tweak-fstab

#!/bin/sh

myname=${0##*/}

# default compression 10
comp=10

# werether other filesystems than btrfs should get the noatime option
other_fs=0

show_usage () {
  printf '%s\n'   "Usage:"
  printf '\t%s\n' "${myname} [-o] [-c compression] [tweak] | [preview] | [help]"
}

show_help () {
  printf '%s\n'   "${myname}: tweak the mount options of btrfs file systems"
  show_usage
  printf '\n%s\n' "Options:"
  printf '%s\n'   "-o, --other-filesystem, other"
  printf '\t%s\n' "tweak the mount options for other filesystems than btrfs, defaults to noatime."
  printf '%s\n'   "-c N, --compression N, compression N, comp N"
  printf '\t%s\n' "where 'N' is the compression rate for btrfs."
  printf '%s\n'   "tweak"
  printf '\t%s\n' "run the fstab tweak, you need the permissions tho, so run as root or with sudo"
  printf '%s\n'   "preview"
  printf '\t%s\n' "show what the result changes to your fstab will be without writing anything"
  printf '%s\n'   "help"
  printf '\t%s\n' "show this message, '-h' '-help' '--help' are also supported"
  printf '\n%s\n' "Rationale:"
  printf '\t%s\n' "i am very opinionated with my fstab, i like to use btrfs for '/', '/home' and"
  printf '\t%s\n' "other storage drives mounted directly to my computer."
  printf '\t%s\n' "'noatime' improves performance by not registering access time for inodes and"
  printf '\t%s\n' "perhaps even reduces disc usage, maybe..."
  printf '\t%s\n' "'compress=zstd:10' btrfs is one of the filesystems that support compression"
  printf '\t%s\n' "it helps save space, which extra space or well more efficiently used space"
  printf '\t%s\n' "is never a bad idea, zstd may not be the best at speed or compression ratio"
  printf '\t%s\n' "but it hits a sweet spot where at compression level 10 it will try to save"
  printf '\t%s\n' "a lot of space without loosing much speed, is not the 'realtime' of levels"
  printf '\t%s\n' "1 to 5 buuuut considerably faster than 11 to 15."
}

fstab_awk () {
  awk -v cm="noatime,compress=zstd:${comp}" -v of="$other_fs" \
    '
    /btrfs/ { sub(/defaults/,cm)}
    { if (of==1) sub(/defaults/,"noatime") }
    { print $0 }
    ' "$1"
}

# usage: is_num "value"
is_num() {
    printf %d "$1" >/dev/null 2>&1
}

# input parsing
while [ "$#" -gt 0 ]; do
  case "$1" in
    -c|--compression|compression|comp)
      if is_num "$2"; then
        case "$2" in
          [1-9]|1[0-5])
            comp="$2"
            ;;
          *)
            printf '%s: argument for %s "%s" is not in range, using default value %s.\n' \
              "${myname}" "$1" "$2" "$comp" >&2
            ;;
        esac
      else
        printf '%s: argument for %s "%s" is not a number\n' "${myname}" "$1" "$2" >&2
        exit 1
      fi
      shift
      ;;
    -o|--other-filesystem|other) other_fs=1 ;;
    *) choice="$1" ;;
  esac
  shift
done


case "$choice" in
  preview)
    echo "fstab:"
    if [ -f /etc/old-fstab ]; then
      fstabfile=/etc/old-fstab
    else
      fstabfile=/etc/fstab
    fi
    fstab_awk "$fstabfile"
    ;;
  tweak)
    if [ ! -f /etc/old-fstab ]; then
      mv /etc/fstab /etc/old-fstab
    fi
    fstab_awk /etc/old-fstab > /etc/fstab
    ;;
  help|-h|-help|--help)
    show_help
    ;;
  *)
    printf '%s\n' "${myname}: does not recognize the argument ${choice}"
    show_usage
    exit 1
    ;;
esac