old_contents: # -*- encoding: utf8 -*-
  #
  # The Qubes OS Project, http://www.qubes-os.org
  #
  # Copyright (C) 2017 Wojtek Porczyk <woju@invisiblethingslab.com>
  #
  # This program is free software; you can redistribute it and/or modify
  # it under the terms of the GNU General Public License as published by
  # the Free Software Foundation; either version 2 of the License, or
  # (at your option) any later version.
  #
  # This program is distributed in the hope that it will be useful,
  # but WITHOUT ANY WARRANTY; without even the implied warranty of
  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  # GNU General Public License for more details.
  #
  # You should have received a copy of the GNU General Public License along
  # with this program; if not, see <http://www.gnu.org/licenses/>.
  
  import qubes.api
  import qubes.ext
  
  class AdminExtension(qubes.ext.Extension):
      # pylint: disable=too-few-public-methods
      @qubes.ext.handler(
          'mgmt-permission:admin.vm.tag.Set',
          'mgmt-permission:admin.vm.tag.Remove')
      def on_tag_set_or_remove(self, vm, event, arg, **kwargs):
          '''Forbid changing specific tags'''
          # pylint: disable=no-self-use,unused-argument
          if arg.startswith('created-by-'):
              raise qubes.api.PermissionDenied()
  
      # TODO create that extension in the first place
  
new_contents: # -*- encoding: utf8 -*-
  #
  # The Qubes OS Project, http://www.qubes-os.org
  #
  # Copyright (C) 2017 Wojtek Porczyk <woju@invisiblethingslab.com>
  #
  # This program is free software; you can redistribute it and/or modify
  # it under the terms of the GNU General Public License as published by
  # the Free Software Foundation; either version 2 of the License, or
  # (at your option) any later version.
  #
  # This program is distributed in the hope that it will be useful,
  # but WITHOUT ANY WARRANTY; without even the implied warranty of
  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  # GNU General Public License for more details.
  #
  # You should have received a copy of the GNU General Public License along
  # with this program; if not, see <http://www.gnu.org/licenses/>.
  
  import qubes.api
  import qubes.ext
  
  class AdminExtension(qubes.ext.Extension):
      # pylint: disable=too-few-public-methods
      @qubes.ext.handler(
          'mgmt-permission:admin.vm.tag.Set',
          'mgmt-permission:admin.vm.tag.Remove')
      def on_tag_set_or_remove(self, vm, event, arg, **kwargs):
          '''Forbid changing specific tags'''
          # pylint: disable=no-self-use,unused-argument
          if arg.startswith('created-by-'):
              raise qubes.api.PermissionDenied(
                  'changing this tag is prohibited by {}.{}'.format(
                      __name__, type(self).__name__))
  
      # TODO create that tag here (need to figure out how to pass mgmtvm name)
  
subject: add explanation to PermissionDenied