Add an example Khelp module, which will be referenced in the forthcoming Khelp

documentation.

Sponsored by:	FreeBSD Foundation
Discussed with:	David Hayes <dahayes at swin edu au>
MFC after:	5 weeks
X-MFC with:	r216615

share/examples/kld/Makefile

@@ -67,6 +67,6 @@
 #	$FreeBSD$
 #
 
-SUBDIR=	cdev dyn_sysctl firmware syscall
+SUBDIR=	cdev dyn_sysctl firmware khelp syscall
 
 .include <bsd.subdir.mk>

share/examples/kld/khelp/Makefile

@@ -0,0 +1,11 @@
+# $FreeBSD$
+
+.include <bsd.own.mk>
+
+# Change if the src tree you are compiling for is not in /usr/src
+#SYSDIR=/usr/src/sys
+
+KMOD=	h_example
+SRCS=	h_example.c
+
+.include <bsd.kmod.mk>

share/examples/kld/khelp/README

@@ -0,0 +1,6 @@
+$FreeBSD$
+
+An example Khelp module which uses the helper hook points available in the TCP
+stack to calculate a per-connection count of inbound and outbound packets when
+the connection is in the established state. The code is verbosely documented in
+an attempt to explain how everything fits together.

share/examples/kld/khelp/h_example.c

@@ -0,0 +1,154 @@
+/*-
+ * Copyright (c) 2010-2011 The FreeBSD Foundation
+ * All rights reserved.
+ *
+ * This software was developed at the Centre for Advanced Internet
+ * Architectures, Swinburne University of Technology, Melbourne, Australia by
+ * Lawrence Stewart under sponsorship from the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * This example Khelp module uses the helper hook points available in the TCP
+ * stack to calculate a per-connection count of inbound and outbound packets
+ * when the connection is in the established state. The code is verbosely
+ * documented in an attempt to explain how everything fits together.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/hhook.h>
+#include <sys/khelp.h>
+#include <sys/module.h>
+#include <sys/module_khelp.h>
+#include <sys/socket.h>
+#include <sys/socketvar.h>
+
+#include <netinet/tcp_var.h>
+
+#include <vm/uma.h>
+
+/*
+ * Function prototype for our helper hook (man 9 hhook) compatible hook
+ * function.
+ */
+static int example_hook(int hhook_type, int hhook_id, void *udata,
+    void *ctx_data, void *hdata, struct osd *hosd);
+
+/*
+ * Our per-connection persistent data storage struct.
+ */
+struct example {
+	uint32_t est_in_count;
+	uint32_t est_out_count;
+};
+
+/*
+ * Fill in the required bits of our module's struct helper (defined in
+ * <sys/module_khelp.h>).
+ *
+ * - Our helper will be storing persistent state for each TCP connection, so we
+ * request the use the Object Specific Data (OSD) feature from the framework by
+ * setting the HELPER_NEEDS_OSD flag.
+ *
+ * - Our helper is related to the TCP subsystem, so tell the Khelp framework
+ * this by setting an appropriate class for the module. When a new TCP
+ * connection is created, the Khelp framework takes care of associating helper
+ * modules of the appropriate class with the new connection.
+ */
+struct helper example_helper = {
+	.h_flags = HELPER_NEEDS_OSD,
+	.h_classes = HELPER_CLASS_TCP
+};
+
+/*
+ * Set which helper hook points our module wants to hook by creating an array of
+ * hookinfo structs (defined in <sys/hhook.h>). We hook the TCP established
+ * inbound/outbound hook points (TCP hhook points are defined in
+ * <netinet/tcp_var.h>) with our example_hook() function. We don't require a user
+ * data pointer to be passed to our hook function when called, so we set it to
+ * NULL.
+ */
+struct hookinfo example_hooks[] = {
+	{
+		.hook_type = HHOOK_TYPE_TCP,
+		.hook_id = HHOOK_TCP_EST_IN,
+		.hook_udata = NULL,
+		.hook_func = &example_hook
+	},
+	{
+		.hook_type = HHOOK_TYPE_TCP,
+		.hook_id = HHOOK_TCP_EST_OUT,
+		.hook_udata = NULL,
+		.hook_func = &example_hook
+	}
+};
+
+/*
+ * Very simple helper hook function. Here's a quick run through the arguments:
+ *
+ * - hhook_type and hhook_id are useful if you use a single function with many
+ * hook points and want to know which hook point called the function.
+ *
+ * - udata will be NULL, because we didn't elect to pass a pointer in either of
+ * the hookinfo structs we instantiated above in the example_hooks array.
+ *
+ * - ctx_data contains context specific data from the hook point call site. The
+ * data type passed is subsystem dependent. In the case of TCP, the hook points
+ * pass a pointer to a "struct tcp_hhook_data" (defined in <netinet/tcp_var.h>).
+ *
+ * - hdata is a pointer to the persistent per-object storage for our module. The
+ * pointer is allocated automagically by the Khelp framework when the connection
+ * is created, and comes from a dedicated UMA zone. It will never be NULL.
+ *
+ * - hosd can be used with the Khelp framework's khelp_get_osd() function to
+ * access data belonging to a different Khelp module.
+ */
+static int
+example_hook(int hhook_type, int hhook_id, void *udata, void *ctx_data,
+    void *hdata, struct osd *hosd)
+{
+	struct example *data;
+
+	data = hdata;
+
+	if (hhook_id == HHOOK_TCP_EST_IN)
+		data->est_in_count++;
+	else if (hhook_id == HHOOK_TCP_EST_OUT)
+		data->est_out_count++;
+
+	return (0);
+}
+
+/*
+ * We use a convenient macro which handles registering our module with the Khelp
+ * framework. Note that Khelp modules which set the HELPER_NEEDS_OSD flag (i.e.
+ * require persistent per-object storage) must use the KHELP_DECLARE_MOD_UMA()
+ * macro. If you don't require per-object storage, use the KHELP_DECLARE_MOD()
+ * macro instead.
+ */
+KHELP_DECLARE_MOD_UMA(example, &example_helper, example_hooks, 1,
+    sizeof(struct example), NULL, NULL);