Adding a plugin

Strategic Choices

Plugins may implement lightly-used, experimental, or test functionality. In such cases, please disable the plugin by default:

/* *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.

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:

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:

$ 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.

$ 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:

$ 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:

$ 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:

# Copyright (c) <current-year> <your-organization>

The rest of the build recipe is pretty simple:

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:

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:

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.

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 GoLang bindings

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:

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:

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:

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".