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30 .Nm snl_read_message ,
36 .Nm snl_parse_header ,
38 .Nm snl_parse_attrs_raw ,
39 .Nm snl_attr_get_flag ,
41 .Nm snl_attr_get_uint16 ,
42 .Nm snl_attr_get_uint32 ,
43 .Nm snl_attr_get_string ,
44 .Nm snl_attr_get_stringn ,
45 .Nm snl_attr_get_nla ,
46 .Nm snl_field_get_uint8 ,
47 .Nm snl_field_get_uint16 ,
48 .Nm snl_field_get_uint32
49 .Nd "simple netlink library"
51 .In netlink/netlink_snl.h
52 .In netlink/netlink_snl_route.h
54 .Fn snl_init "struct snl_state *ss" "int netlink_family"
55 .Fn snl_free "struct snl_state *ss"
56 .Ft "struct nlmsghdr *"
57 .Fn snl_read_message "struct snl_state *ss"
59 .Fn snl_send "struct snl_state *ss" "void *data" "int sz"
61 .Fn snl_get_seq "struct snl_state *ss"
63 .Fn snl_allocz "struct snl_state *ss" "int len"
64 .Fn snl_clear_lb "struct snl_state *ss"
66 .Fn snl_parse_nlmsg "struct snl_state *ss" "struct nlmsghdr *hdr" "const struct snl_hdr_parser *ps" "void *target"
68 .Fn snl_parse_header "struct snl_state *ss" "void *hdr" "int len" "const struct snl_hdr_parser *ps" "int pslen" "void *target"
70 .Fn snl_parse_attrs "struct snl_state *ss" "struct nlmsghdr *hdr" "int hdrlen" "const struct snl_attr_parser *ps" "int pslen" "void *target"
72 .Fn snl_parse_attrs_raw "struct snl_state *ss" "struct nlattr *nla_head" "int len" "const struct snl_attr_parser *ps" "int pslen" "void *target"
74 .Fn snl_attr_get_flag "struct snl_state *ss" "struct nlattr *nla" "void *target"
76 .Fn snl_attr_get_uint8 "struct snl_state *ss" "struct nlattr *nla" "void *target"
78 .Fn snl_attr_get_uint16 "struct snl_state *ss" "struct nlattr *nla" "void *target"
80 .Fn snl_attr_get_uint32 "struct snl_state *ss" "struct nlattr *nla" "void *target"
82 .Fn snl_attr_get_uint64 "struct snl_state *ss" "struct nlattr *nla" "void *target"
84 .Fn snl_attr_get_string "struct snl_state *ss" "struct nlattr *nla" "void *target"
86 .Fn snl_attr_get_stringn "struct snl_state *ss" "struct nlattr *nla" "void *target"
88 .Fn snl_attr_get_nla "struct snl_state *ss" "struct nlattr *nla" "void *target"
90 .Fn snl_attr_get_ip "struct snl_state *ss" "struct nlattr *nla" "void *target"
92 .Fn snl_attr_get_ipvia "struct snl_state *ss" "struct nlattr *nla" "void *target"
96 library provides an easy way of sending and receiving Netlink messages,
97 taking care of serialisation and deserialisation.
101 with a pointer to the
103 and the desired Netlink family to initialise the library instance.
104 To free the library instance, call
107 The library functions are NOT multithread-safe.
108 If multithreading is desired, consider initializing an instance
110 .Ss MEMORY ALLOCATION
111 The library uses pre-allocated extendable memory buffers to handle message parsing.
112 The typical usage pattern is to allocate the necessary data structures during the
113 message parsing or writing process via
115 and free all allocated data at once using
117 after handling the message.
118 .Ss COMPOSING AND SENDING MESSAGES
119 The library does not currently offer any wrappers for writing netlink messages.
120 Simple request messages can be composed by filling in all needed fields directly.
121 Example for constructing an interface dump request:
125 struct ifinfomsg ifmsg;
127 .hdr.nlmsg_type = RTM_GETLINK,
128 .hdr.nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST,
129 .hdr.nlmsg_seq = snl_get_seq(ss),
131 msg.hdr.nlmsg_len = sizeof(msg);
134 can be used to generate a unique message number.
135 To send the resulting message,
138 .Ss RECEIVING AND PARSING MESSAGES
139 To receive a message, use
140 .Fn snl_read_message .
141 Currently, this call is blocking.
143 The library provides an easy way to convert the message to the pre-defined C
145 For each message type, one needs to define rules, converting the protocol header
146 fields and the desired attributes to the specified structure.
147 It can be accomplished by using message parsers.
148 Each message parser consists of an array of attribute getters and an array of
149 header field getters.
150 The former array needs to be sorted by the attribute type.
152 .Fn SNL_VERIFY_PARSERS
153 macro to check if the order is correct.
154 .Fn SNL_DECLARE_PARSER "parser_name" "family header type" "struct snl_field_parser[]" "struct snl_attr_parser[]"
155 can be used to create a new parser.
156 .Fn SNL_DECLARE_ATTR_PARSER "parser_name" "struct snl_field_parser[]"
157 can be used to create an attribute-only message parser.
159 Each attribute getter needs to be embedded in the following structure:
161 typedef bool snl_parse_attr_f(struct snl_state *ss, struct nlattr *attr, const void *arg, void *target);
162 struct snl_attr_parser {
163 uint16_t type; /* Attribute type */
164 uint16_t off; /* field offset in the target structure */
165 snl_parse_attr_f *cb; /* getter function to call */
166 const void *arg; /* getter function custom argument */
169 The generic attribute getter has the following signature:
171 .Fn snl_attr_get_<type> "struct snl_state *ss" "struct nlattr *nla" "const void *arg" "void *target" .
172 nla contains the pointer of the attribute to use as the datasource.
173 The target field is the pointer to the field in the target structure.
174 It is up to the getter to know the type of the target field.
175 The getter must check the input attribute and return
176 false if the attribute is not formed correctly.
177 Otherwise, the getter fetches the attribute value and stores it in the target,
179 It is possible to use
181 to create the desired data structure .
182 A number of predefined getters for the common data types exist.
183 .Fn snl_attr_get_flag
184 converts a flag-type attribute to an uint8_t value of 1 or 0, depending on the
186 .Fn snl_attr_get_uint8
187 stores a uint8_t type attribute into the uint8_t target field.
188 .Fn snl_attr_get_uint16
189 stores a uint16_t type attribute into the uint16_t target field.
190 .Fn snl_attr_get_uint32
191 stores a uint32_t type attribute into the uint32_t target field.
192 .Fn snl_attr_get_uint64
193 stores a uint64_t type attribute into the uint64_t target field.
196 .Fn snl_attr_get_ipvia
197 stores a pointer to the sockaddr structure with the IPv4/IPv6 address contained
199 Sockaddr is allocated using
201 .Fn snl_attr_get_string
202 stores a pointer to the NULL-terminated string.
203 The string itself is allocated using
206 stores a pointer to the specified attribute.
207 .Fn snl_attr_get_stringn
208 stores a pointer to the non-NULL-terminated string.
210 Similarly, each family header getter needs to be embedded in the following structure:
212 typedef void snl_parse_field_f(struct snl_state *ss, void *hdr, void *target);
213 struct snl_field_parser {
214 uint16_t off_in; /* field offset in the input structure */
215 uint16_t off_out;/* field offset in the target structure */
216 snl_parse_field_f *cb; /* getter function to call */
219 The generic field getter has the following signature:
221 snl_field_get_<type> "struct snl_state *ss" "void *src" "void *target" .
222 A number of pre-defined getters for the common data types exist.
223 .Fn "snl_field_get_uint8"
224 fetches an uint8_t value and stores it in the target.
225 .Fn "snl_field_get_uint16"
226 fetches an uint8_t value and stores it in the target.
227 .Fn "snl_field_get_uint32"
228 fetches an uint32_t value and stores it in the target.
230 The following example demonstrates how to list all system interfaces
235 #include <netlink/netlink.h>
236 #include <netlink/netlink_route.h>
237 #include "netlink/netlink_snl.h"
238 #include "netlink/netlink_snl_route.h"
240 struct nl_parsed_link {
246 #define _IN(_field) offsetof(struct ifinfomsg, _field)
247 #define _OUT(_field) offsetof(struct nl_parsed_link, _field)
248 static const struct snl_attr_parser ap_link[] = {
249 { .type = IFLA_IFNAME, .off = _OUT(ifla_ifname), .cb = snl_attr_get_string },
250 { .type = IFLA_MTU, .off = _OUT(ifla_mtu), .cb = snl_attr_get_uint32 },
252 static const struct snl_field_parser fp_link[] = {
253 {.off_in = _IN(ifi_index), .off_out = _OUT(ifi_index), .cb = snl_field_get_uint32 },
257 SNL_DECLARE_PARSER(link_parser, struct ifinfomsg, fp_link, ap_link);
261 main(int ac, char *argv[])
265 if (!snl_init(&ss, NETLINK_ROUTE))
270 struct ifinfomsg ifmsg;
272 .hdr.nlmsg_type = RTM_GETLINK,
273 .hdr.nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST,
274 .hdr.nlmsg_seq = snl_get_seq(&ss),
276 msg.hdr.nlmsg_len = sizeof(msg);
278 if (!snl_send(&ss, &msg, sizeof(msg))) {
283 struct nlmsghdr *hdr;
284 while ((hdr = snl_read_message(&ss)) != NULL && hdr->nlmsg_type != NLMSG_DONE) {
285 if (hdr->nlmsg_seq != msg.hdr.nlmsg_seq)
288 struct nl_parsed_link link = {};
289 if (!snl_parse_nlmsg(&ss, hdr, &link_parser, &link))
291 printf("Link#%u %s mtu %u\n", link.ifi_index, link.ifla_ifname, link.ifla_mtu);
308 This library was implemented by
309 .An Alexander Chernikov Aq Mt melifaro@FreeBSD.org .