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Ganesha Library
===============

The Ganesha Library provides base classes that can be used by drivers to
provision shares via NFS (NFSv3 and NFSv4), utilizing the NFS-Ganesha NFS
server.

Supported operations
--------------------

- Allow NFS Share access

  - Only IP access type is supported.

- Deny NFS Share access

Requirements
------------

`NFS-Ganesha <https://github.com/nfs-ganesha/nfs-ganesha/wiki>`__ 2.1 or newer.

NFS-Ganesha configuration
-------------------------

The library has just modest requirements against general NFS-Ganesha (in the
following: Ganesha) configuration; a best effort was made to remain agnostic
towards it as much as possible. This section describes the few requirements.

Note that Ganesha's concept of storage backend modules is called FSAL ("File
System Abstraction Layer"). The FSAL the driver intends to leverage needs to be
enabled in Ganesha config.

Beyond that (with default Manila config) the following line is needed to be
present in the Ganesha config file (that defaults to
/etc/ganesha/ganesha.conf):

``%include /etc/ganesha/export.d/INDEX.conf``

The above paths can be customized through Manila configuration as follows:

- `ganesha_config_dir` = toplevel directory for Ganesha configuration,
     defaults to /etc/ganesha
- `ganesha_config_path` = location of the Ganesha config file, defaults
    to ganesha.conf in `ganesha_config_dir`
- `ganesha_export_dir` = directory where Manila generated config bits are
    stored, defaults to `export.d` in `ganesha_config_dir`. The following
    line is required to be included (with value expanded) in the Ganesha
    config file (at `ganesha_config_path`):

    ``%include <ganesha_export_dir>/INDEX.conf``


Further Ganesha related Manila configuration
--------------------------------------------

There are further Ganesha related options in Manila (which affect the
behavior of Ganesha, but do not affect how to set up the Ganesha service
itself).

These are:

- `ganesha_service_name` = name of the system service representing Ganesha,
    defaults to ganesha.nfsd
- `ganesha_db_path` = location of on-disk database storing permanent Ganesha
    state
- `ganesha_export_template_dir` = directory from where Ganesha loads
    export customizations (cf. "Customizing Ganesha exports").

Using Ganesha Library in drivers
--------------------------------

A driver that wants to use the Ganesha Library has to inherit
from ``driver.GaneshaMixin``.

The driver has to contain a subclass of ``ganesha.GaneshaNASHelper``,
instantiate it along with the driver instance and delegate
``allow_access`` and ``deny_access`` methods to it (when appropriate,
ie. when ``access_proto`` is NFS).

In the following we explain what has to be implemented by the
``ganesha.GaneshaNASHelper`` subclass (to which we refer as "helper
class").

Ganesha exports are described by so-called *Ganesha export blocks*
(introduced in the 2.* release series), that is, snippets of Ganesha
config specifying key-pair values.

The Ganesha Library generates sane default export blocks for the
exports it manages, with one thing left blank, the so-called *FSAL
subblock*. The helper class has to implement the ``_fsal_hook``
method which returns the FSAL subblock (in Python represented as
a dict with string keys and values). It has one mandatory key,
``Name``, to which the value should be the name of the FSAL
(eg.: ``{"Name": "GLUSTER"}``). Further content of it is
optional and FSAL specific.

Customizing Ganesha exports
---------------------------

As noted, the Ganesha Library provides sane general defaults.

However, the driver is allowed to:

- customize defaults
- allow users to customize exports

The config format for Ganesha Library is called *export block
template*. They are syntactically either Ganesha export blocks,
(please consult the Ganesha documentation about the format),
or isomorphic JSON (as Ganesha export blocks are by-and-large
equivalent to arrayless JSON), with two special placeholders
for values: ``@config`` and ``@runtime``. ``@config`` means a
value that shall be filled from Manila config, and ``@runtime``
means a value that's filled at runtime with dynamic data.

As an example, we show the library's defaults in JSON format
(also valid Python literal):

  ::

    {
      "EXPORT": {
        "Export_Id": "@runtime",
        "Path": "@runtime",
        "FSAL": {
          "Name": "@config"
        },
        "Pseudo": "@runtime",
        "SecType": "sys",
        "Tag": "@runtime",
        "CLIENT": {
          "Clients": "@runtime",
          "Access_Type": "RW"
        },
        "Squash": "None"
      }
    }

The Ganesha Library takes these values from

*manila/share/drivers/ganesha/conf/00-base-export-template.conf*

where the same data is stored in Ganesha conf format (also supplied with
comments).

For customization, the driver has to extend the ``_default_config_hook``
method as follows:

-  take the result of the super method (a dict representing an export
   block template)
-  set up another export block dict that include your custom values,
   either by

   -  using a predefined export block dict stored in code
   -  loading a predefined export block from the Manila source tree
   -  loading an export block from an user exposed location (to allow
      user configuration)

-  merge the two export block dict using the ``ganesha_utils.patch``
   method
-  return the result

With respect to *loading export blocks*, that can be done through the
utility method ``_load_conf_dir``.

Known Restrictions
------------------

- The library does not support network segmented multi-tenancy model but
  instead works over a flat network, where the tenants share a network.

The :mod:`manila.share.drivers.ganesha` Module
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. automodule:: manila.share.drivers.ganesha
    :noindex:
    :members:
    :undoc-members:
    :show-inheritance:
