new_contents: #!/usr/bin/env python
  # Copyright (C) 2018 The Android Open Source Project
  #
  # 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.
  
  # Takes output of
  # adb shell 'find /data -print0 | xargs -0 ls -ldZ' | awk '{print $5 " " $9}'
  # in standard input and generates list of directories we need to scan to cover
  # the labels given on the command line.
  
  import sys
  import argparse
  
  class Node(object):
    def __init__(self, name, label=None):
      self.name = name
      self.label = label
      self.marked = False
      self.children = {}
  
    def Find(self, components):
      if not components:
        return self
  
      child = components[0]
      if child in self.children:
        return self.children[child].Find(components[1:])
  
      n = Node(child)
      self.children[child] = n
      return n
  
    def __iter__(self):
      for child in self.children.itervalues():
        yield self.name + '/' + child.name, child
        for p, ch in child:
          yield self.name + '/' + p, ch
  
    def Mark(self, labels):
      # Either incorrect label or already marked, we do not need to scan
      # this path.
      if self.marked or self.label not in labels:
        return False
  
      self.marked = True
  
      for child in self.children.itervalues():
        child.Mark(labels)
  
      return True
  
  
  def BuildTree(stream=sys.stdin):
    root = Node("")
  
    for line in stream:
      line = line.strip()
      if not line:
        continue
  
      label, path = line.split(' ', 1)
      #  u:object_r:system_data_file:s0  -> system_data_file.
      sanitized_label = label.split(':')[2]
      # Strip leading slash.
      components = path[1:].split('/')
  
      n = root.Find(components)
      n.label = sanitized_label
    return root
  
  
  def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('labels', metavar='L', type=str, nargs='+',
                        help='labels we want to find')
    args = parser.parse_args()
    root = BuildTree()
    for fullpath, elem in root:
      if elem.Mark(args.labels):
        print fullpath
  
  
  if __name__ == '__main__':
    main()
  
subject: Add tool to find scan roots.