..
      Copyright (c) 2013 OpenStack Foundation
      All Rights Reserved.

      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.

Guru Meditation Reports
=======================

Cinder contains a mechanism whereby developers and system administrators can
generate a report about the state of a running Cinder executable.
This report is called a *Guru Meditation Report* (*GMR* for short).

Generating a GMR
----------------

A *GMR* can be generated by sending the *USR2* signal to any Cinder process
with support (see below).
The *GMR* will then output to standard error for that particular process.

For example, suppose that ``cinder-api`` has process id ``8675``, and was run
with ``2>/var/log/cinder/cinder-api-err.log``.
Then, ``kill -USR2 8675`` will trigger the Guru Meditation report to be printed
to ``/var/log/cinder/cinder-api-err.log``.

There is other way to trigger a generation of report, user should add
a configuration in Cinder's conf file::

    [oslo_reports]
    file_event_handler=['The path to a file to watch for changes to trigger '
                        'the reports, instead of signals. Setting this option '
                        'disables the signal trigger for the reports.']
    file_event_handler_interval=['How many seconds to wait between polls when '
                                 'file_event_handler is set, default value '
                                 'is 1']

a *GMR* can be generated by "touch"ing the file which was specified in
file_event_handler. The *GMR* will then output to standard error for
that particular process.

For example, suppose that ``cinder-api`` was run with
``2>/var/log/cinder/cinder-api-err.log``, and the file path is
``/tmp/guru_report``.
Then, ``touch /tmp/guru_report`` will trigger the Guru Meditation report to be
printed to ``/var/log/cinder/cinder-api-err.log``.

Structure of a GMR
------------------

The *GMR* is designed to be extensible; any particular executable may add
its own sections.  However, the base *GMR* consists of several sections:

Package
  Shows information about the package to which this process belongs,
  including version information

Threads
  Shows stack traces and thread ids for each of the threads within this process

Green Threads
  Shows stack traces for each of the green threads within this process
  (green threads don't have thread ids)

Configuration
  Lists all the configuration options currently accessible via the CONF object
  for the current process

Adding Support for GMRs to New Executables
------------------------------------------

Adding support for a *GMR* to a given executable is fairly easy.

First import the module (currently residing in oslo-incubator), as well as the
Cinder version module:

.. code-block:: python

      from oslo_reports import guru_meditation_report as gmr
      from cinder import version

Then, register any additional sections (optional):

.. code-block:: python

      TextGuruMeditation.register_section('Some Special Section',
                                          some_section_generator)

Finally (under main), before running the "main loop" of the executable
(usually ``service.server(server)`` or something similar), register the *GMR*
hook:

.. code-block:: python

      TextGuruMeditation.setup_autorun(version)

Extending the GMR
-----------------

As mentioned above, additional sections can be added to the GMR for a
particular executable.  For more information, see the inline documentation
about oslo.reports:
`oslo.reports <http://docs.openstack.org/developer/oslo.reports/>`_
