_backup_completion() {
  local options=(
    '-m[specify partition to mount for backup]:partition:($(_partitions))'
    '-b[specify backup directory]:backup directory:_files -/'
  )
  local curcontext="$curcontext" state line
  typeset -A opt_args

  _partitions() {
    lsblk -rno NAME | sed 's/^/\/dev\//'
  }

  _arguments -s $options
}

compdef _backup_completion backup