libnl  3.2.7
genl.c
1 /*
2  * lib/genl/genl.c Generic Netlink
3  *
4  * This library is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU Lesser General Public
6  * License as published by the Free Software Foundation version 2.1
7  * of the License.
8  *
9  * Copyright (c) 2003-2008 Thomas Graf <tgraf@suug.ch>
10  */
11 
12 /**
13  * @defgroup genl Generic Netlink
14  *
15  * @par Message Format
16  * @code
17  * <------- NLMSG_ALIGN(hlen) ------> <---- NLMSG_ALIGN(len) --->
18  * +----------------------------+- - -+- - - - - - - - - - -+- - -+
19  * | Header | Pad | Payload | Pad |
20  * | struct nlmsghdr | | | |
21  * +----------------------------+- - -+- - - - - - - - - - -+- - -+
22  * @endcode
23  * @code
24  * <-------- GENL_HDRLEN -------> <--- hdrlen -->
25  * <------- genlmsg_len(ghdr) ------>
26  * +------------------------+- - -+---------------+- - -+------------+
27  * | Generic Netlink Header | Pad | Family Header | Pad | Attributes |
28  * | struct genlmsghdr | | | | |
29  * +------------------------+- - -+---------------+- - -+------------+
30  * genlmsg_data(ghdr)--------------^ ^
31  * genlmsg_attrdata(ghdr, hdrlen)-------------------------
32  * @endcode
33  *
34  * @par Example
35  * @code
36  * #include <netlink/netlink.h>
37  * #include <netlink/genl/genl.h>
38  * #include <netlink/genl/ctrl.h>
39  *
40  * struct nl_sock *sock;
41  * struct nl_msg *msg;
42  * int family;
43  *
44  * // Allocate a new netlink socket
45  * sock = nl_socket_alloc();
46  *
47  * // Connect to generic netlink socket on kernel side
48  * genl_connect(sock);
49  *
50  * // Ask kernel to resolve family name to family id
51  * family = genl_ctrl_resolve(sock, "generic_netlink_family_name");
52  *
53  * // Construct a generic netlink by allocating a new message, fill in
54  * // the header and append a simple integer attribute.
55  * msg = nlmsg_alloc();
56  * genlmsg_put(msg, NL_AUTO_PID, NL_AUTO_SEQ, family, 0, NLM_F_ECHO,
57  * CMD_FOO_GET, FOO_VERSION);
58  * nla_put_u32(msg, ATTR_FOO, 123);
59  *
60  * // Send message over netlink socket
61  * nl_send_auto_complete(sock, msg);
62  *
63  * // Free message
64  * nlmsg_free(msg);
65  *
66  * // Prepare socket to receive the answer by specifying the callback
67  * // function to be called for valid messages.
68  * nl_socket_modify_cb(sock, NL_CB_VALID, NL_CB_CUSTOM, parse_cb, NULL);
69  *
70  * // Wait for the answer and receive it
71  * nl_recvmsgs_default(sock);
72  *
73  * static int parse_cb(struct nl_msg *msg, void *arg)
74  * {
75  * struct nlmsghdr *nlh = nlmsg_hdr(msg);
76  * struct nlattr *attrs[ATTR_MAX+1];
77  *
78  * // Validate message and parse attributes
79  * genlmsg_parse(nlh, 0, attrs, ATTR_MAX, policy);
80  *
81  * if (attrs[ATTR_FOO]) {
82  * uint32_t value = nla_get_u32(attrs[ATTR_FOO]);
83  * ...
84  * }
85  *
86  * return 0;
87  * }
88  * @endcode
89  * @{
90  */
91 
92 #include <netlink-generic.h>
93 #include <netlink/netlink.h>
94 #include <netlink/genl/genl.h>
95 #include <netlink/utils.h>
96 
97 /**
98  * @name Socket Creating
99  * @{
100  */
101 
102 int genl_connect(struct nl_sock *sk)
103 {
104  return nl_connect(sk, NETLINK_GENERIC);
105 }
106 
107 /** @} */
108 
109 /**
110  * @name Sending
111  * @{
112  */
113 
114 /**
115  * Send trivial generic netlink message
116  * @arg sk Netlink socket.
117  * @arg family Generic netlink family
118  * @arg cmd Command
119  * @arg version Version
120  * @arg flags Additional netlink message flags.
121  *
122  * Fills out a routing netlink request message and sends it out
123  * using nl_send_simple().
124  *
125  * @return 0 on success or a negative error code.
126  */
127 int genl_send_simple(struct nl_sock *sk, int family, int cmd,
128  int version, int flags)
129 {
130  struct genlmsghdr hdr = {
131  .cmd = cmd,
132  .version = version,
133  };
134 
135  return nl_send_simple(sk, family, flags, &hdr, sizeof(hdr));
136 }
137 
138 /** @} */
139 
140 
141 /**
142  * @name Message Parsing
143  * @{
144  */
145 
146 int genlmsg_valid_hdr(struct nlmsghdr *nlh, int hdrlen)
147 {
148  struct genlmsghdr *ghdr;
149 
150  if (!nlmsg_valid_hdr(nlh, GENL_HDRLEN))
151  return 0;
152 
153  ghdr = nlmsg_data(nlh);
154  if (genlmsg_len(ghdr) < NLMSG_ALIGN(hdrlen))
155  return 0;
156 
157  return 1;
158 }
159 
160 int genlmsg_validate(struct nlmsghdr *nlh, int hdrlen, int maxtype,
161  struct nla_policy *policy)
162 {
163  struct genlmsghdr *ghdr;
164 
165  if (!genlmsg_valid_hdr(nlh, hdrlen))
166  return -NLE_MSG_TOOSHORT;
167 
168  ghdr = nlmsg_data(nlh);
169  return nla_validate(genlmsg_attrdata(ghdr, hdrlen),
170  genlmsg_attrlen(ghdr, hdrlen), maxtype, policy);
171 }
172 
173 int genlmsg_parse(struct nlmsghdr *nlh, int hdrlen, struct nlattr *tb[],
174  int maxtype, struct nla_policy *policy)
175 {
176  struct genlmsghdr *ghdr;
177 
178  if (!genlmsg_valid_hdr(nlh, hdrlen))
179  return -NLE_MSG_TOOSHORT;
180 
181  ghdr = nlmsg_data(nlh);
182  return nla_parse(tb, maxtype, genlmsg_attrdata(ghdr, hdrlen),
183  genlmsg_attrlen(ghdr, hdrlen), policy);
184 }
185 
186 /**
187  * Get head of message payload
188  * @arg gnlh genetlink messsage header
189  */
190 void *genlmsg_data(const struct genlmsghdr *gnlh)
191 {
192  return ((unsigned char *) gnlh + GENL_HDRLEN);
193 }
194 
195 /**
196  * Get lenght of message payload
197  * @arg gnlh genetlink message header
198  */
199 int genlmsg_len(const struct genlmsghdr *gnlh)
200 {
201  struct nlmsghdr *nlh = (struct nlmsghdr *)((unsigned char *)gnlh -
202  NLMSG_HDRLEN);
203  return (nlh->nlmsg_len - GENL_HDRLEN - NLMSG_HDRLEN);
204 }
205 
206 /**
207  * Get head of attribute data
208  * @arg gnlh generic netlink message header
209  * @arg hdrlen length of family specific header
210  */
211 struct nlattr *genlmsg_attrdata(const struct genlmsghdr *gnlh, int hdrlen)
212 {
213  return genlmsg_data(gnlh) + NLMSG_ALIGN(hdrlen);
214 }
215 
216 /**
217  * Get length of attribute data
218  * @arg gnlh generic netlink message header
219  * @arg hdrlen length of family specific header
220  */
221 int genlmsg_attrlen(const struct genlmsghdr *gnlh, int hdrlen)
222 {
223  return genlmsg_len(gnlh) - NLMSG_ALIGN(hdrlen);
224 }
225 
226 /** @} */
227 
228 /**
229  * @name Message Building
230  * @{
231  */
232 
233 /**
234  * Add generic netlink header to netlink message
235  * @arg msg netlink message
236  * @arg pid netlink process id or NL_AUTO_PID
237  * @arg seq sequence number of message or NL_AUTO_SEQ
238  * @arg family generic netlink family
239  * @arg hdrlen length of user specific header
240  * @arg flags message flags
241  * @arg cmd generic netlink command
242  * @arg version protocol version
243  *
244  * Returns pointer to user specific header.
245  */
246 void *genlmsg_put(struct nl_msg *msg, uint32_t pid, uint32_t seq, int family,
247  int hdrlen, int flags, uint8_t cmd, uint8_t version)
248 {
249  struct nlmsghdr *nlh;
250  struct genlmsghdr hdr = {
251  .cmd = cmd,
252  .version = version,
253  };
254 
255  nlh = nlmsg_put(msg, pid, seq, family, GENL_HDRLEN + hdrlen, flags);
256  if (nlh == NULL)
257  return NULL;
258 
259  memcpy(nlmsg_data(nlh), &hdr, sizeof(hdr));
260  NL_DBG(2, "msg %p: Added generic netlink header cmd=%d version=%d\n",
261  msg, cmd, version);
262 
263  return nlmsg_data(nlh) + GENL_HDRLEN;
264 }
265 
266 /** @} */
267 
268 /** @} */