Better workaround for policy file in PDF docs

Follow up to cinder change Ic752048b3a1f87 with a more elegant
solution.

Credit: Elod Illes <elod.illes@est.tech> on manila change
I4f22fe7b453940.

Change-Id: I58cf850543c862c57d51b225fa928f3000accda8

doc/source/configuration/block-storage/policy-config-HOWTO.rst

@@ -35,6 +35,12 @@ model Cinder employs and how it can be modified by adjusting policies.
   run Cinder with a custom policy configuration, however, you'll need to write
   your changes into a policy file.
 
+.. only:: html
+
+   * Elsewhere in this documentation, you can find a copy of the :doc:`sample
+     policy file <./samples/policy.yaml>` that contains all the default
+     settings.
+
 * Instructions for generating a sample ``policy.yaml`` file directly from the
   Cinder source code can be found in the file ``README-policy.generate.md``
   in the ``etc/cinder`` directory in the Cinder `source code repository

doc/source/configuration/block-storage/policy.rst

@@ -7,7 +7,9 @@ Policy configuration
 Configuration
 ~~~~~~~~~~~~~
 
-The following is an overview of all available policies in Cinder.
+The following is an overview of all available policies in Cinder.  For
+information on how to write a custom policy file to modify these policies,
+see :ref:`policy-file` in the Cinder configuration documentation.
 
 .. show-policy::
    :config-file: tools/config/cinder-policy-generator.conf

doc/source/configuration/block-storage/samples/index.rst

@@ -11,4 +11,5 @@ All the files in this section can be found in ``/etc/cinder``.
 
    cinder.conf.rst
    api-paste.ini.rst
+   policy.yaml.rst
    rootwrap.conf.rst

doc/source/configuration/block-storage/samples/policy.yaml.rst

@@ -0,0 +1,62 @@
+.. _policy-file:
+
+===========
+policy.yaml
+===========
+
+The ``policy.yaml`` file defines additional access controls that apply
+to the Block Storage service.
+
+Prior to Cinder 12.0.0 (the Queens release), a JSON policy file was required to
+run Cinder.  From the Queens release onward, the following hold:
+
+* It is possible to run Cinder safely without a policy file, as sensible
+  default values are defined in the code.
+
+* If you wish to run Cinder with policies different from the default, you may
+  write a policy file.
+
+  * Given that JSON does not allow comments, we recommend using YAML to write
+    a custom policy file.  (Also, see next item.)
+
+  * OpenStack has deprecated the use of a JSON policy file since the Wallaby
+    release (Cinder 18.0.0).  If you are still using the JSON format, there
+    is a `oslopolicy-convert-json-to-yaml`__ tool that will migrate your
+    existing JSON-formatted policy file to YAML in a backward-compatible way.
+
+    .. __: https://docs.openstack.org/oslo.policy/latest/cli/oslopolicy-convert-json-to-yaml.html
+
+* If you supply a custom policy file, you only need to supply entries for the
+  policies you wish to change from their default values.  For instance, if you
+  want to change the default value of "volume:create", you only need to keep
+  this single rule in your policy config file.
+
+* The default policy file location is ``/etc/cinder/policy.yaml``.  You may
+  override this by specifying a different file location as the value of the
+  ``policy_file`` configuration option in the ``[oslo_policy]`` section of the
+  the Cinder configuration file.
+
+* Instructions for generating a sample ``policy.yaml`` file directly from the
+  Cinder source code can be found in the file ``README-policy.generate.md``
+  in the ``etc/cinder`` directory in the Cinder `source code repository
+  <https://opendev.org/openstack/cinder>`_ (or its `github mirror
+  <https://github.com/openstack/cinder>`_).
+
+.. only:: html
+
+   The following provides a listing of the default policies. It is not
+   recommended to copy this file into ``/etc/cinder`` unless you are planning
+   on providing a different policy for an operation that is not the default.
+
+   The sample policy file can also be viewed in `file form
+   <../../../_static/cinder.policy.yaml.sample>`_.
+
+   .. literalinclude:: ../../../_static/cinder.policy.yaml.sample
+      :language: ini
+
+.. only:: latex
+
+   A sample policy file is available in the online version of this
+   documentation.  Make sure you are looking at the sample file for the
+   OpenStack release you are running as the available policy rules and
+   their default values may change from release to release.