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diff --git a/docs/developer/plugindoc/add_plugin.rst b/docs/developer/plugindoc/add_plugin.rst new file mode 100644 index 00000000000..cf771116095 --- /dev/null +++ b/docs/developer/plugindoc/add_plugin.rst @@ -0,0 +1,362 @@ +.. _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". |