zebra: Add a sample dataplane plugin module

Add a dataplane plugin module as a sample or reference for
folks who might like to integrate with the zebra dataplane
subsystem. This isn't part of the FRR build or product; there
are some simple build and load-at-runtime instructions in
comments in the file.

Signed-off-by: Mark Stapp <mjs@voltanet.io>

zebra/sample_plugin.c

@@ -0,0 +1,134 @@
+/*
+ * Sample plugin for the FRR zebra dataplane.
+ *
+ * Copyright (c) 2019 Volta Networks, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; see the file COPYING; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/*
+ * Should be possible to build this plugin using this sort of command:
+ *
+ *    gcc -I ~/work/frr/ -I ~/work/frr/lib -I ~/work/frr/zebra \
+ *        -g -O0 -o sample_plugin.so -shared -fPIC sample_plugin.c
+ *
+ * where 'frr' is a configured and built frr sandbox.
+ *
+ * Run zebra with '-M /path/to/sample_plugin.so' to load the module.
+ */
+
+#include "config.h" /* Include this explicitly */
+#include "lib/zebra.h"
+#include "lib/libfrr.h"
+#include "zebra/zebra_dplane.h"
+#include "zebra/debug.h"
+
+static const char *plugin_name = "SAMPLE";
+
+static struct zebra_dplane_provider *prov_p;
+
+/*
+ * Startup/init callback, called from the dataplane.
+ */
+static int sample_start(struct zebra_dplane_provider *prov)
+{
+	/* Nothing special to do - we don't allocate anything. */
+	return 0;
+}
+
+
+/*
+ * Shutdown/cleanup callback, called from the dataplane pthread.
+ */
+static int sample_fini(struct zebra_dplane_provider *prov, bool early)
+{
+	/* Nothing special to do. */
+	return 0;
+}
+
+/*
+ * Callback from the dataplane to process incoming work; this runs in the
+ * dplane pthread.
+ */
+static int sample_process(struct zebra_dplane_provider *prov)
+{
+	int counter, limit;
+	struct zebra_dplane_ctx *ctx;
+
+	limit = dplane_provider_get_work_limit(prov_p);
+
+	/* Respect the configured limit on the amount of work to do in
+	 * any one call.
+	 */
+	for (counter = 0; counter < limit; counter++) {
+		ctx = dplane_provider_dequeue_in_ctx(prov_p);
+		if (!ctx)
+			break;
+
+		/* Just set 'success' status and return to the dataplane */
+		dplane_ctx_set_status(ctx, ZEBRA_DPLANE_REQUEST_SUCCESS);
+		dplane_provider_enqueue_out_ctx(prov_p, ctx);
+	}
+
+	return 0;
+}
+
+/*
+ * Init entry point called during zebra startup. This is registered during
+ * module init.
+ */
+static int init_sample_plugin(struct thread_master *tm)
+{
+	int ret;
+	struct zebra_dplane_provider *prov = NULL;
+
+	/* Note that we don't use or store the thread_master 'tm'. We
+	 * don't use the zebra main pthread: our plugin code will run in
+	 * the zebra dataplane pthread context.
+	 */
+
+	/* Register the plugin with the dataplane infrastructure. We
+	 * register to be called before the kernel, and we register
+	 * our init, process work, and shutdown callbacks.
+	 */
+	ret = dplane_provider_register(plugin_name, DPLANE_PRIO_PRE_KERNEL,
+				       DPLANE_PROV_FLAGS_DEFAULT,
+				       sample_start,
+				       sample_process,
+				       sample_fini,
+				       NULL,
+				       &prov_p);
+
+	if (IS_ZEBRA_DEBUG_DPLANE)
+		zlog_debug("sample plugin register => %d", ret);
+
+	return 0;
+}
+
+/*
+ * Base FRR loadable module info: basic info including module entry-point.
+ */
+static int module_init(void)
+{
+	hook_register(frr_late_init, init_sample_plugin);
+	return 0;
+}
+
+FRR_MODULE_SETUP(
+	.name = "dplane_sample",
+	.version = "0.0.1",
+	.description = "Dataplane Sample Plugin",
+	.init = module_init,
+	)