2 * Copyright (c) 2010-2011 The FreeBSD Foundation
5 * This software was developed at the Centre for Advanced Internet
6 * Architectures, Swinburne University of Technology, Melbourne, Australia by
7 * Lawrence Stewart under sponsorship from the FreeBSD Foundation.
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
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21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * This example Khelp module uses the helper hook points available in the TCP
33 * stack to calculate a per-connection count of inbound and outbound packets
34 * when the connection is in the established state. The code is verbosely
35 * documented in an attempt to explain how everything fits together.
38 #include <sys/cdefs.h>
39 __FBSDID("$FreeBSD$");
41 #include <sys/param.h>
42 #include <sys/kernel.h>
43 #include <sys/hhook.h>
44 #include <sys/khelp.h>
45 #include <sys/module.h>
46 #include <sys/module_khelp.h>
47 #include <sys/socket.h>
48 #include <sys/socketvar.h>
50 #include <netinet/tcp_var.h>
55 * Function prototype for our helper hook (man 9 hhook) compatible hook
58 static int example_hook(int hhook_type, int hhook_id, void *udata,
59 void *ctx_data, void *hdata, struct osd *hosd);
62 * Our per-connection persistent data storage struct.
65 uint32_t est_in_count;
66 uint32_t est_out_count;
70 * Fill in the required bits of our module's struct helper (defined in
71 * <sys/module_khelp.h>).
73 * - Our helper will be storing persistent state for each TCP connection, so we
74 * request the use the Object Specific Data (OSD) feature from the framework by
75 * setting the HELPER_NEEDS_OSD flag.
77 * - Our helper is related to the TCP subsystem, so tell the Khelp framework
78 * this by setting an appropriate class for the module. When a new TCP
79 * connection is created, the Khelp framework takes care of associating helper
80 * modules of the appropriate class with the new connection.
82 struct helper example_helper = {
83 .h_flags = HELPER_NEEDS_OSD,
84 .h_classes = HELPER_CLASS_TCP
88 * Set which helper hook points our module wants to hook by creating an array of
89 * hookinfo structs (defined in <sys/hhook.h>). We hook the TCP established
90 * inbound/outbound hook points (TCP hhook points are defined in
91 * <netinet/tcp_var.h>) with our example_hook() function. We don't require a user
92 * data pointer to be passed to our hook function when called, so we set it to
95 struct hookinfo example_hooks[] = {
97 .hook_type = HHOOK_TYPE_TCP,
98 .hook_id = HHOOK_TCP_EST_IN,
100 .hook_func = &example_hook
103 .hook_type = HHOOK_TYPE_TCP,
104 .hook_id = HHOOK_TCP_EST_OUT,
106 .hook_func = &example_hook
111 * Very simple helper hook function. Here's a quick run through the arguments:
113 * - hhook_type and hhook_id are useful if you use a single function with many
114 * hook points and want to know which hook point called the function.
116 * - udata will be NULL, because we didn't elect to pass a pointer in either of
117 * the hookinfo structs we instantiated above in the example_hooks array.
119 * - ctx_data contains context specific data from the hook point call site. The
120 * data type passed is subsystem dependent. In the case of TCP, the hook points
121 * pass a pointer to a "struct tcp_hhook_data" (defined in <netinet/tcp_var.h>).
123 * - hdata is a pointer to the persistent per-object storage for our module. The
124 * pointer is allocated automagically by the Khelp framework when the connection
125 * is created, and comes from a dedicated UMA zone. It will never be NULL.
127 * - hosd can be used with the Khelp framework's khelp_get_osd() function to
128 * access data belonging to a different Khelp module.
131 example_hook(int hhook_type, int hhook_id, void *udata, void *ctx_data,
132 void *hdata, struct osd *hosd)
134 struct example *data;
138 if (hhook_id == HHOOK_TCP_EST_IN)
139 data->est_in_count++;
140 else if (hhook_id == HHOOK_TCP_EST_OUT)
141 data->est_out_count++;
147 * We use a convenient macro which handles registering our module with the Khelp
148 * framework. Note that Khelp modules which set the HELPER_NEEDS_OSD flag (i.e.
149 * require persistent per-object storage) must use the KHELP_DECLARE_MOD_UMA()
150 * macro. If you don't require per-object storage, use the KHELP_DECLARE_MOD()
153 KHELP_DECLARE_MOD_UMA(example, &example_helper, example_hooks, 1,
154 sizeof(struct example), NULL, NULL);