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+.. _add_plugin:
+
+Adding a plugin
+===============
+
+.. toctree::
+
+Strategic Choices
+_________________
+
+Plugins may implement lightly-used, experimental, or test
+functionality. In such cases, please disable the plugin by default:
+
+.. code-block:: console
+
+ /* *INDENT-OFF* */
+ VLIB_PLUGIN_REGISTER () =
+ {
+ .version = VPP_BUILD_VER,
+ .description = "Plugin Disabled by Default...",
+ .default_disabled = 1,
+ };
+ /* *INDENT-ON* */
+
+Please do not create processes, or other dynamic data structures
+unless the plugin is configured by API or debug CLI.
+
+Specifically, please don't initialize bihash tables from
+VLIB_INIT_FUNCTIONS, *especially* if the bihash template involved
+doesn't #define BIHASH_LAZY_INSTANTIATE 1.
+
+.. code-block:: console
+
+ static clib_error_t * sample_init (vlib_main_t * vm)
+ {
+ <snip>
+ /* DONT DO THIS! */
+ BV(clib_bihash_init (h, ...))
+ <snip>
+ }
+ VLIB_INIT_FUNCTION (sample_init);
+
+Instead, please add a feature_init function:
+
+.. code-block:: console
+
+ static void
+ feature_init (my_main_t * mm)
+ {
+ if (mm->feature_initialized == 0)
+ {
+ BV(clib_bihash_init)(mm->hash_table, ...)
+ /* Create Other Things, e.g a periodic process */
+ mm->feature_initialized = 1;
+ }
+ }
+
+And call it from debug CLI and API message handlers any time the feature
+is enabled.
+
+How to create a new plugin
+__________________________
+
+This section shows how a VPP developer can create a new plugin, and
+add it to VPP. We assume that we are starting from the VPP <top-of-workspace>.
+
+As an example, we will use the **make-plugin.sh** tool found in
+**./extras/emacs**. make-plugin.sh is a simple wrapper for a comprehensive
+plugin generator constructed from a set of emacs-lisp skeletons.
+
+Change directory to **./src/plugins**, and run the plugin generator:
+
+.. code-block:: console
+
+ $ cd ./src/plugins
+ $ ../../extras/emacs/make-plugin.sh
+ <snip>
+ Loading /scratch/vpp-docs/extras/emacs/tunnel-c-skel.el (source)...
+ Loading /scratch/vpp-docs/extras/emacs/tunnel-decap-skel.el (source)...
+ Loading /scratch/vpp-docs/extras/emacs/tunnel-encap-skel.el (source)...
+ Loading /scratch/vpp-docs/extras/emacs/tunnel-h-skel.el (source)...
+ Loading /scratch/vpp-docs/extras/emacs/elog-4-int-skel.el (source)...
+ Loading /scratch/vpp-docs/extras/emacs/elog-4-int-track-skel.el (source)...
+ Loading /scratch/vpp-docs/extras/emacs/elog-enum-skel.el (source)...
+ Loading /scratch/vpp-docs/extras/emacs/elog-one-datum-skel.el (source)...
+ Plugin name: myplugin
+ Dispatch type [dual or qs]: dual
+ (Shell command succeeded with no output)
+
+ OK...
+
+The plugin generator script asks two questions: the name of the
+plugin, and which of two dispatch types to use. Since the plugin name
+finds its way into quite a number of places - filenames, typedef
+names, graph arc names - it pays to think for a moment.
+
+The dispatch type refers to the coding pattern used to construct
+**node.c**, the *pro forma* data-plane node. The **dual** option
+constructs a dual-single loop pair with speculative enqueueing. This
+is the traditional coding pattern for load-store intensive graph
+nodes.
+
+The **qs** option generates a quad-single loop pair which uses
+vlib_get_buffers(...) and vlib_buffer_enqueue_to_next(...). These
+operators make excellent use of available SIMD vector unit
+operations. It's very simple to change a quad-single loop-pair to a
+dual-single loop pair if you decide to do so later.
+
+Generated Files
+---------------
+
+Here are the generated files. We'll go through them in a moment.
+
+.. code-block:: console
+
+ $ cd ./myplugin
+ $ ls
+ CMakeLists.txt myplugin.api myplugin.c myplugin.h
+ myplugin_periodic.c myplugin_test.c node.c setup.pg
+
+Due to recent build system improvements, you **don't** need to touch
+any other files to integrate your new plugin into the vpp build. Simply
+rebuild your workspace from scratch, and the new plugin will appear.
+
+Rebuild your workspace
+----------------------
+
+This is the straightforward way to reconfigure and rebuild your workspace:
+
+.. code-block:: console
+
+ $ cd <top-of-workspace>
+ $ make rebuild [or rebuild-release]
+
+Thanks to ccache, this operation doesn't take an annoying amount of time.
+
+Sanity check: run vpp
+---------------------
+
+As a quick sanity check, run vpp and make sure that
+"myplugin_plugin.so" and "myplugin_test_plugin.so" are loaded:
+
+.. code-block:: console
+
+ $ cd <top-of-workspace>
+ $ make run
+ <snip>
+ load_one_plugin:189: Loaded plugin: myplugin_plugin.so (myplugin description goes here)
+ <snip>
+ load_one_vat_plugin:67: Loaded plugin: myplugin_test_plugin.so
+ <snip>
+ DBGvpp#
+
+If this simple test fails, please seek assistance.
+
+Generated Files in Detail
+_________________________
+
+This section discusses the generated files in some detail. It's fine to
+skim this section, and return later for more detail.
+
+CMakeLists.txt
+--------------
+
+This is the build system recipe for building your plugin. Please fix
+the copyright notice:
+
+.. code-block:: console
+
+ # Copyright (c) <current-year> <your-organization>
+
+The rest of the build recipe is pretty simple:
+
+.. code-block:: CMake
+
+ add_vpp_plugin (myplugin
+ SOURCES
+ myplugin.c
+ node.c
+ myplugin_periodic.c
+ myplugin.h
+
+ MULTIARCH_SOURCES
+ node.c
+
+ API_FILES
+ myplugin.api
+
+ API_TEST_SOURCES
+ myplugin_test.c
+ )
+
+As you can see, the build recipe consists of several lists of
+files. **SOURCES** is a list of C source files. **API_FILES** is a
+list of the plugin's binary API definition files [one such file is
+usually plenty], and so forth.
+
+**MULTIARCH_SOURCES** lists data plane graph node dispatch function
+source files considered to be performance-critical. Specific functions
+in these files are compiled multiple times, so that they can leverage
+CPU-specific features. More on this in a moment.
+
+If you add source files, simply add them to the indicated list(s).
+
+myplugin.h
+----------
+
+This is the primary #include file for the new plugin. Among other
+things, it defines the plugin's *main_t* data structure. This is the
+right place to add problem-specific data structures. Please **resist
+the temptation** to create a set of static or [worse yet] global
+variables in your plugin. Refereeing name-collisions between plugins
+is not anyone's idea of a good time.
+
+myplugin.c
+----------
+
+For want of a better way to describe it, myplugin.c is the vpp plugin
+equivalent of "main.c". Its job is to hook the plugin into the vpp
+binary API message dispatcher, and to add its messages to vpp's global
+"message-name_crc" hash table. See "myplugin_init (...")"
+
+Vpp itself uses dlsym(...) to track down the vlib_plugin_registration_t
+generated by the VLIB_PLUGIN_REGISTER macro:
+
+.. code-block:: C
+
+ VLIB_PLUGIN_REGISTER () =
+ {
+ .version = VPP_BUILD_VER,
+ .description = "myplugin plugin description goes here",
+ };
+
+Vpp only loads .so files from the plugin directory which contain an
+instance of this data structure.
+
+You can enable or disable specific vpp plugins from the command
+line. By default, plugins are loaded. To change that behavior, set
+default_disabled in the macro VLIB_PLUGIN_REGISTER:
+
+.. code-block:: C
+
+ VLIB_PLUGIN_REGISTER () =
+ {
+ .version = VPP_BUILD_VER,
+ .default_disabled = 1
+ .description = "myplugin plugin description goes here",
+ };
+
+The boilerplate generator places the graph node dispatch function
+onto the "device-input" feature arc. This may or may not be useful.
+
+.. code-block:: C
+
+ VNET_FEATURE_INIT (myplugin, static) =
+ {
+ .arc_name = "device-input",
+ .node_name = "myplugin",
+ .runs_before = VNET_FEATURES ("ethernet-input"),
+ };
+
+As given by the plugin generator, myplugin.c contains the binary API
+message handler for a generic "please enable my feature on such and
+such an interface" binary API message. As you'll see, setting up the
+vpp message API tables is simple. Big fat warning: the scheme is
+intolerant of minor mistakes. Example: forgetting to add
+mainp->msg_id_base can lead to very confusing failures.
+
+If you stick to modifying the generated boilerplate with care -
+instead of trying to build code from first principles - you'll save
+yourself a bunch of time and aggravation
+
+myplugin_test.c
+---------------
+
+This file contains binary API message **generation** code, which is
+compiled into a separate .so file. The "vpp_api_test" program loads
+these plugins, yielding immediate access to your plugin APIs for
+external client binary API testing.
+
+vpp itself loads test plugins, and makes the code available via the
+"binary-api" debug CLI. This is a favorite way to unit-test binary
+APIs prior to integration testing.
+
+node.c
+------
+
+This is the generated graph node dispatch function. You'll need to
+rewrite it to solve the problem at hand. It will save considerable
+time and aggravation to retain the **structure** of the node dispatch
+function.
+
+Even for an expert, it's a waste of time to reinvent the *loop
+structure*, enqueue patterns, and so forth. Simply tear out and
+replace the specimen 1x, 2x, 4x packet processing code with code
+relevant to the problem you're trying to solve.
+
+myplugin.api
+------------
+
+This contains the API message definition. Here we only have defined
+a single one named ``myplugin_enable_disable`` and an implicit
+``myplugin_enable_disable_reply`` containing only a return value due
+to the ``autoreply`` keyword.
+
+The syntax reference for ``.api`` files can be found at VPP API Language
+
+Addressing the binary API with this message will run the handler defined
+in ``myplugin.c`` as ``vl_api_myplugin_enable_disable_t_handler``.
+It will receive a message pointer ``*mp`` which is the struct defined
+in ``myplugin.api`` and should return another message pointer ``*rmp``,
+of the reply type. That's what ``REPLY_MACRO`` does.
+
+To be noted, all API messages are in net-endian and vpp is host-endian,
+so you will need to use :
+
+* ``u32 value = ntohl(mp->value);``
+* ``rmp->value = htonl(value);``
+
+You can now use this API with :ref:`GoLang bindings <add_plugin_goapi>`
+
+myplugin_periodic.c
+-------------------
+
+This defines a VPP process, a routine that will run indefinitely and
+be woken up intermittently, here to process plugin events.
+
+To be noted, vlib_processes aren't thread-safe, and data structures
+should be locked when shared between workers.
+
+Plugin "Friends with Benefits"
+------------------------------
+
+In vpp VLIB_INIT_FUNCTION functions, It's reasonably common to see a
+specific init function invoke other init functions:
+
+.. code-block:: C
+
+ if ((error = vlib_call_init_function (vm, some_other_init_function))
+ return error;
+
+In the case where one plugin needs to call a init function in another
+plugin, use the vlib_call_plugin_init_function macro:
+
+.. code-block:: C
+
+ if ((error = vlib_call_plugin_init_function (vm, "otherpluginname", some_init_function))
+ return error;
+
+This allows sequencing between plugin init functions.
+
+If you wish to obtain a pointer to a symbol in another plugin, use the
+vlib_plugin_get_symbol(...) API:
+
+.. code-block:: C
+
+ void *p = vlib_get_plugin_symbol ("plugin_name", "symbol");
+
+More Examples
+-------------
+
+For more information you can read many example plugins in the directory "./src/plugins".