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+..
+.. SPDX-License-Identifier: GPL-2.0-or-later
+..
+.. June 19 2023, Christian Hopps <chopps@labn.net>
+..
+.. Copyright (c) 2023, LabN Consulting, L.L.C.
+..
+
+.. _mgmtd_dev:
+
+MGMTD Development
+=================
+
+Overview
+^^^^^^^^
+
+``mgmtd`` (Management Daemon) is a new centralized management daemon for FRR.
+
+Previously, ``vtysh`` was the only centralized management service provided.
+Internally ``vtysh`` connects to each daemon and sends CLI commands (both
+configuration and operational state queries) over a socket connection. This
+service only supports CLI which is no longer sufficient.
+
+An important next step was made with the addition of YANG support. A YANG
+infrastructure was added through a new development called *northbound*. This
+*northbound* interface added the capability of daemons to be configured and
+queried using YANG models. However, this interface was per daemon and not
+centralized, which is not sufficient.
+
+``mgmtd`` harnesses this new *northbound* interface to provide a centralized
+interface for all daemons. It utilizes the daemons YANG models to interact with
+each daemon. ``mgmtd`` currently provides the CLI interface for each daemon that
+has been converted to it, but in the future RESTCONF and NETCONF servers can
+easily be added as *front-ends* to mgmtd to support those protocols as well.
+
+
+Converting A Daemon to MGMTD
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+A daemon must first be transitioned to the new *northbound* interface if that
+has not already been done (see `this northbound conversion documentation
+<https://github.com/opensourcerouting/frr/wiki/Retrofitting-Configuration-Commands>`_
+for how to do this). Once this is done a few simple steps are all that is
+required move the daemon over to ``mgmtd`` control.
+
+Overview of Changes
+-------------------
+
+Adding support for a *northbound* converted daemon involves very little work. It
+requires enabling *frontend* (CLI and YANG) and *backend* (YANG) support.
+``mgmtd`` was designed to keep this as simple as possible.
+
+Front-End Interface:
+
+1. Add YANG module file to ``mgmtd/subdir.am`` (e.g., ``yang/frr-staticd.c``)
+2. Add YANG module description into array defined in ``mgmtd/mgmt_main.c``
+3. Add CLI handler file[s] to ``mgmtd/subdir.am`` (e.g., ``staticd/static_vty.c``)
+4. [if needed] Exclude (#ifndef) non-configuration CLI handlers from CLI source
+   file (e.g., inside ``staticd/static_vty.c``)
+
+Back-End Interface:
+
+5. Add XPATHs mappings to a couple arrays to direct ``mgmtd`` at your daemon in
+   ``mgmtd/mgmt_be_adapter.c``
+
+
+Add YANG and CLI into MGMTD
+---------------------------
+
+As an example here is the addition made to ``mgmtd/subdir.am`` for adding
+``staticd`` support.
+
+.. code-block:: make
+
+   if STATICD
+   nodist_mgmtd_mgmtd_SOURCES += \
+        yang/frr-staticd.yang.c \
+        yang/frr-bfdd.yang.c \
+        # end
+   nodist_mgmtd_libmgmt_be_nb_la_SOURCES += staticd/static_vty.c
+   endif
+
+An here is the addition to the modules array in ``mgmtd/mgmt_main.c``:
+
+.. code-block:: c
+
+   static const struct frr_yang_module_info *const mgmt_yang_modules[] = {
+           &frr_filter_info,
+           ...
+   #ifdef HAVE_STATICD
+           &(struct frr_yang_module_info){.name = "frr-staticd",
+				         .ignore_cbs = true},
+   #endif
+   }
+
+
+CLI Handlers
+------------
+
+The daemon's CLI handlers for configuration (which having been converted to
+*northbound* now simply generate YANG changes) will be linked directly into
+``mgmtd``.
+
+If the operational and debug CLI commands are kept in files separate from the
+daemon's configuration CLI commands then no extra work is required. Otherwise some
+CPP #ifndef's will be required.
+
+Currently ``mgmtd`` supports configuration CLI but not operational
+state so if both types of CLI handlers are present in a single file (e.g. a
+``xxx_vty.c`` or ``xxx_cli.c`` file ) then #ifndef will be used to exclude these
+non-configuration CLI handlers from ``mgmtd``. The same goes for *debug* CLI
+handlers. For example:
+
+.. code-block:: c
+
+  DEFPY(daemon_one_config, daemon_one_config_cmd,
+        "daemon one [optional-arg]"
+        ...
+  {
+        ...
+  }
+
+  #ifndef INCLUDE_MGMTD_CMDDEFS_ONLY
+  DEFPY(daemon_show_oepr, daemon_show_oepr_cmd,
+        "show daemon oper [all]"
+        ...
+  {
+        ...
+  }
+  #endif /* ifndef INCLUDE_MGMTD_CMDDEFS_ONLY */
+
+  void daemon_vty_init(void)
+  {
+	install_element(CONFIG_NODE, &daemon_one_config_cmd);
+        ...
+
+  #ifndef INCLUDE_MGMTD_CMDDEFS_ONLY
+          install_element(ENABLE_NODE, &daemon_show_oper_cmd);
+  #endif /* ifndef INCLUDE_MGMTD_CMDDEFS_ONLY */
+
+  }
+
+
+Add Back-End XPATH mappings
+---------------------------
+
+In order for ``mgmtd`` to direct configuration to your daemon you need to add
+some XPATH mappings to ``mgmtd/mgmt_be_adapter.c``. These XPATHs determine which
+configuration changes get sent over the *back-end* interface to your daemon.
+
+Below are the strings added for staticd support:
+
+.. code-block:: c
+
+   static const struct mgmt_be_xpath_map_init mgmt_xpath_map_init[] = {
+       {
+           .xpath_regexp = "/frr-vrf:lib/*",
+           .subscr_info =
+               {
+   #if HAVE_STATICD
+                   [MGMTD_BE_CLIENT_ID_STATICD] =
+                       MGMT_SUBSCR_VALIDATE_CFG |
+                       MGMT_SUBSCR_NOTIFY_CFG,
+   #endif
+               },
+       },
+       ...
+       {
+           .xpath_regexp =
+               "/frr-routing:routing/control-plane-protocols/control-plane-protocol/frr-staticd:staticd/*",
+           .subscr_info =
+               {
+   #if HAVE_STATICD
+                   [MGMTD_BE_CLIENT_ID_STATICD] =
+                       MGMT_SUBSCR_VALIDATE_CFG |
+                       MGMT_SUBSCR_NOTIFY_CFG,
+   #endif
+               },
+       },
+   };
+
+   #if HAVE_STATICD
+   static struct mgmt_be_client_xpath staticd_xpaths[] = {
+       {
+           .xpath = "/frr-vrf:lib/*",
+           .subscribed = MGMT_SUBSCR_VALIDATE_CFG | MGMT_SUBSCR_NOTIFY_CFG,
+       },
+       ...
+       {
+           .xpath =
+               "/frr-routing:routing/control-plane-protocols/control-plane-protocol/frr-staticd:staticd/*",
+           .subscribed = MGMT_SUBSCR_VALIDATE_CFG | MGMT_SUBSCR_NOTIFY_CFG,
+       },
+   };
+   #endif
+
+   static struct mgmt_be_client_xpath_map
+       mgmt_client_xpaths[MGMTD_BE_CLIENT_ID_MAX] = {
+   #ifdef HAVE_STATICD
+           [MGMTD_BE_CLIENT_ID_STATICD] = {staticd_xpaths,
+                           array_size(staticd_xpaths)},
+   #endif
+   };
+
+
+MGMTD Internals
+^^^^^^^^^^^^^^^
+
+This section will describe the internal functioning of ``mgmtd``, for now a
+couple diagrams are included to aide in source code perusal.
+
+
+The client side of a CLI change
+
+.. figure:: ../figures/cli-change-client.svg
+   :align: center
+
+
+The server (mgmtd) side of a CLI change
+
+.. figure:: ../figures/cli-change-mgmtd.svg
+   :align: center