2 * lib/msg.c Netlink Messages Interface
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
9 * Copyright (c) 2003-2008 Thomas Graf <tgraf@suug.ch>
14 * @defgroup msg Messages
15 * Netlink Message Construction/Parsing Interface
17 * The following information is partly extracted from RFC3549
18 * (ftp://ftp.rfc-editor.org/in-notes/rfc3549.txt)
21 * Netlink messages consist of a byte stream with one or multiple
22 * Netlink headers and an associated payload. If the payload is too big
23 * to fit into a single message it, can be split over multiple Netlink
24 * messages, collectively called a multipart message. For multipart
25 * messages, the first and all following headers have the \c NLM_F_MULTI
26 * Netlink header flag set, except for the last header which has the
27 * Netlink header type \c NLMSG_DONE.
30 * The Netlink message header (\link nlmsghdr struct nlmsghdr\endlink) is shown below.
33 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
34 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
36 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
38 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
40 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
41 * | Process ID (PID) |
42 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
46 * The netlink message header and payload must be aligned properly:
48 * <------- NLMSG_ALIGN(hlen) ------> <---- NLMSG_ALIGN(len) --->
49 * +----------------------------+- - -+- - - - - - - - - - -+- - -+
50 * | Header | Pad | Payload | Pad |
51 * | struct nlmsghdr | | | |
52 * +----------------------------+- - -+- - - - - - - - - - -+- - -+
57 * <--- nlmsg_total_size(payload) --->
58 * <-- nlmsg_msg_size(payload) ->
59 * +----------+- - -+-------------+- - -+-------- - -
60 * | nlmsghdr | Pad | Payload | Pad | nlmsghdr
61 * +----------+- - -+-------------+- - -+-------- - -
62 * nlmsg_data(nlh)---^ ^
63 * nlmsg_next(nlh)-----------------------+
66 * The payload may consist of arbitary data but may have strict
67 * alignment and formatting rules depening on the specific netlink
71 * <---------------------- nlmsg_len(nlh) --------------------->
72 * <------ hdrlen ------> <- nlmsg_attrlen(nlh, hdrlen) ->
73 * +----------------------+- - -+--------------------------------+
74 * | Family Header | Pad | Attributes |
75 * +----------------------+- - -+--------------------------------+
76 * nlmsg_attrdata(nlh, hdrlen)---^
78 * @par The ACK Netlink Message
79 * This message is actually used to denote both an ACK and a NACK.
80 * Typically, the direction is from FEC to CPC (in response to an ACK
81 * request message). However, the CPC should be able to send ACKs back
82 * to FEC when requested.
85 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
86 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
87 * | Netlink message header |
88 * | type = NLMSG_ERROR |
89 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
91 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
92 * | OLD Netlink message header |
93 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
98 * // Various methods exist to create/allocate a new netlink
101 * // nlmsg_alloc() will allocate an empty netlink message with
102 * // a maximum payload size which defaults to the page size of
103 * // the system. This default size can be modified using the
104 * // function nlmsg_set_default_size().
105 * struct nl_msg *msg = nlmsg_alloc();
107 * // Very often, the message type and message flags are known
108 * // at allocation time while the other fields are auto generated:
109 * struct nl_msg *msg = nlmsg_alloc_simple(MY_TYPE, MY_FLAGS);
111 * // Alternatively an existing netlink message header can be used
112 * // to inherit the header values:
113 * struct nlmsghdr hdr = {
114 * .nlmsg_type = MY_TYPE,
115 * .nlmsg_flags = MY_FLAGS,
117 * struct nl_msg *msg = nlmsg_inherit(&hdr);
119 * // Last but not least, netlink messages received from netlink sockets
120 * // can be converted into nl_msg objects using nlmsg_convert(). This
121 * // will create a message with a maximum payload size which equals the
122 * // length of the existing netlink message, therefore no more data can
123 * // be appened without calling nlmsg_expand() first.
124 * struct nl_msg *msg = nlmsg_convert(nlh_from_nl_sock);
126 * // Payload may be added to the message via nlmsg_append(). The fourth
127 * // parameter specifies the number of alignment bytes the data should
128 * // be padding with at the end. Common values are 0 to disable it or
129 * // NLMSG_ALIGNTO to ensure proper netlink message padding.
130 * nlmsg_append(msg, &mydata, sizeof(mydata), 0);
132 * // Sometimes it may be necessary to reserve room for data but defer
133 * // the actual copying to a later point, nlmsg_reserve() can be used
134 * // for this purpose:
135 * void *data = nlmsg_reserve(msg, sizeof(mydata), NLMSG_ALIGNTO);
137 * // Attributes may be added using the attributes interface.
139 * // After successful use of the message, the memory must be freed
140 * // using nlmsg_free()
144 * @par 4) Parsing messages
147 * unsigned char *buf;
148 * struct nlmsghdr *hdr;
150 * n = nl_recv(handle, NULL, &buf);
152 * hdr = (struct nlmsghdr *) buf;
153 * while (nlmsg_ok(hdr, n)) {
154 * // Process message here...
155 * hdr = nlmsg_next(hdr, &n);
161 #include <netlink-local.h>
162 #include <netlink/netlink.h>
163 #include <netlink/utils.h>
164 #include <netlink/cache.h>
165 #include <netlink/attr.h>
166 #include <netlink/msg.h>
167 #include <linux/socket.h>
169 static size_t default_msg_size
= 4096;
172 * @name Attribute Access
179 * @name Message Parsing
184 * check if the netlink message fits into the remaining bytes
185 * @arg nlh netlink message header
186 * @arg remaining number of bytes remaining in message stream
188 int nlmsg_ok(const struct nlmsghdr
*nlh
, int remaining
)
190 return (remaining
>= sizeof(struct nlmsghdr
) &&
191 nlh
->nlmsg_len
>= sizeof(struct nlmsghdr
) &&
192 nlh
->nlmsg_len
<= remaining
);
196 * next netlink message in message stream
197 * @arg nlh netlink message header
198 * @arg remaining number of bytes remaining in message stream
200 * @returns the next netlink message in the message stream and
201 * decrements remaining by the size of the current message.
203 struct nlmsghdr
*nlmsg_next(struct nlmsghdr
*nlh
, int *remaining
)
205 int totlen
= NLMSG_ALIGN(nlh
->nlmsg_len
);
207 *remaining
-= totlen
;
209 return (struct nlmsghdr
*) ((unsigned char *) nlh
+ totlen
);
213 * parse attributes of a netlink message
214 * @arg nlh netlink message header
215 * @arg hdrlen length of family specific header
216 * @arg tb destination array with maxtype+1 elements
217 * @arg maxtype maximum attribute type to be expected
218 * @arg policy validation policy
222 int nlmsg_parse(struct nlmsghdr
*nlh
, int hdrlen
, struct nlattr
*tb
[],
223 int maxtype
, struct nla_policy
*policy
)
225 if (!nlmsg_valid_hdr(nlh
, hdrlen
))
226 return -NLE_MSG_TOOSHORT
;
228 return nla_parse(tb
, maxtype
, nlmsg_attrdata(nlh
, hdrlen
),
229 nlmsg_attrlen(nlh
, hdrlen
), policy
);
233 * nlmsg_validate - validate a netlink message including attributes
234 * @arg nlh netlinket message header
235 * @arg hdrlen length of familiy specific header
236 * @arg maxtype maximum attribute type to be expected
237 * @arg policy validation policy
239 int nlmsg_validate(struct nlmsghdr
*nlh
, int hdrlen
, int maxtype
,
240 struct nla_policy
*policy
)
242 if (!nlmsg_valid_hdr(nlh
, hdrlen
))
243 return -NLE_MSG_TOOSHORT
;
245 return nla_validate(nlmsg_attrdata(nlh
, hdrlen
),
246 nlmsg_attrlen(nlh
, hdrlen
), maxtype
, policy
);
252 * @name Message Building/Access
256 static struct nl_msg
*__nlmsg_alloc(size_t len
)
260 nm
= calloc(1, sizeof(*nm
));
266 nm
->nm_nlh
= malloc(len
);
270 memset(nm
->nm_nlh
, 0, sizeof(struct nlmsghdr
));
272 nm
->nm_protocol
= -1;
274 nm
->nm_nlh
->nlmsg_len
= nlmsg_total_size(0);
276 NL_DBG(2, "msg %p: Allocated new message, maxlen=%zu\n", nm
, len
);
285 * Allocate a new netlink message with the default maximum payload size.
287 * Allocates a new netlink message without any further payload. The
288 * maximum payload size defaults to PAGESIZE or as otherwise specified
289 * with nlmsg_set_default_size().
291 * @return Newly allocated netlink message or NULL.
293 struct nl_msg
*nlmsg_alloc(void)
295 return __nlmsg_alloc(default_msg_size
);
299 * Allocate a new netlink message with maximum payload size specified.
301 struct nl_msg
*nlmsg_alloc_size(size_t max
)
303 return __nlmsg_alloc(max
);
307 * Allocate a new netlink message and inherit netlink message header
308 * @arg hdr Netlink message header template
310 * Allocates a new netlink message and inherits the original message
311 * header. If \a hdr is not NULL it will be used as a template for
312 * the netlink message header, otherwise the header is left blank.
314 * @return Newly allocated netlink message or NULL
316 struct nl_msg
*nlmsg_inherit(struct nlmsghdr
*hdr
)
322 struct nlmsghdr
*new = nm
->nm_nlh
;
324 new->nlmsg_type
= hdr
->nlmsg_type
;
325 new->nlmsg_flags
= hdr
->nlmsg_flags
;
326 new->nlmsg_seq
= hdr
->nlmsg_seq
;
327 new->nlmsg_pid
= hdr
->nlmsg_pid
;
334 * Allocate a new netlink message
335 * @arg nlmsgtype Netlink message type
336 * @arg flags Message flags.
338 * @return Newly allocated netlink message or NULL.
340 struct nl_msg
*nlmsg_alloc_simple(int nlmsgtype
, int flags
)
343 struct nlmsghdr nlh
= {
344 .nlmsg_type
= nlmsgtype
,
345 .nlmsg_flags
= flags
,
348 msg
= nlmsg_inherit(&nlh
);
350 NL_DBG(2, "msg %p: Allocated new simple message\n", msg
);
356 * Set the default maximum message payload size for allocated messages
357 * @arg max Size of payload in bytes.
359 void nlmsg_set_default_size(size_t max
)
361 if (max
< nlmsg_total_size(0))
362 max
= nlmsg_total_size(0);
364 default_msg_size
= max
;
368 * Convert a netlink message received from a netlink socket to a nl_msg
369 * @arg hdr Netlink message received from netlink socket.
371 * Allocates a new netlink message and copies all of the data pointed to
372 * by \a hdr into the new message object.
374 * @return Newly allocated netlink message or NULL.
376 struct nl_msg
*nlmsg_convert(struct nlmsghdr
*hdr
)
380 nm
= __nlmsg_alloc(NLMSG_ALIGN(hdr
->nlmsg_len
));
384 memcpy(nm
->nm_nlh
, hdr
, hdr
->nlmsg_len
);
393 * Reserve room for additional data in a netlink message
394 * @arg n netlink message
395 * @arg len length of additional data to reserve room for
396 * @arg pad number of bytes to align data to
398 * Reserves room for additional data at the tail of the an
399 * existing netlink message. Eventual padding required will
402 * @return Pointer to start of additional data tailroom or NULL.
404 void *nlmsg_reserve(struct nl_msg
*n
, size_t len
, int pad
)
406 void *buf
= n
->nm_nlh
;
407 size_t nlmsg_len
= n
->nm_nlh
->nlmsg_len
;
410 tlen
= pad
? ((len
+ (pad
- 1)) & ~(pad
- 1)) : len
;
412 if ((tlen
+ nlmsg_len
) > n
->nm_size
)
416 n
->nm_nlh
->nlmsg_len
+= tlen
;
419 memset(buf
+ len
, 0, tlen
- len
);
421 NL_DBG(2, "msg %p: Reserved %zu bytes, pad=%d, nlmsg_len=%d\n",
422 n
, len
, pad
, n
->nm_nlh
->nlmsg_len
);
428 * Append data to tail of a netlink message
429 * @arg n netlink message
430 * @arg data data to add
431 * @arg len length of data
432 * @arg pad Number of bytes to align data to.
434 * Extends the netlink message as needed and appends the data of given
435 * length to the message.
437 * @return 0 on success or a negative error code
439 int nlmsg_append(struct nl_msg
*n
, void *data
, size_t len
, int pad
)
443 tmp
= nlmsg_reserve(n
, len
, pad
);
447 memcpy(tmp
, data
, len
);
448 NL_DBG(2, "msg %p: Appended %zu bytes with padding %d\n", n
, len
, pad
);
454 * Add a netlink message header to a netlink message
455 * @arg n netlink message
456 * @arg pid netlink process id or NL_AUTO_PID
457 * @arg seq sequence number of message or NL_AUTO_SEQ
458 * @arg type message type
459 * @arg payload length of message payload
460 * @arg flags message flags
462 * Adds or overwrites the netlink message header in an existing message
463 * object. If \a payload is greater-than zero additional room will be
464 * reserved, f.e. for family specific headers. It can be accesed via
467 * @return A pointer to the netlink message header or NULL.
469 struct nlmsghdr
*nlmsg_put(struct nl_msg
*n
, uint32_t pid
, uint32_t seq
,
470 int type
, int payload
, int flags
)
472 struct nlmsghdr
*nlh
;
474 if (n
->nm_nlh
->nlmsg_len
< NLMSG_HDRLEN
)
477 nlh
= (struct nlmsghdr
*) n
->nm_nlh
;
478 nlh
->nlmsg_type
= type
;
479 nlh
->nlmsg_flags
= flags
;
480 nlh
->nlmsg_pid
= pid
;
481 nlh
->nlmsg_seq
= seq
;
483 NL_DBG(2, "msg %p: Added netlink header type=%d, flags=%d, pid=%d, "
484 "seq=%d\n", n
, type
, flags
, pid
, seq
);
487 nlmsg_reserve(n
, payload
, NLMSG_ALIGNTO
) == NULL
)
494 * Release a reference from an netlink message
495 * @arg msg message to release reference from
497 * Frees memory after the last reference has been released.
499 void nlmsg_free(struct nl_msg
*msg
)
505 NL_DBG(4, "Returned message reference %p, %d remaining\n",
506 msg
, msg
->nm_refcnt
);
508 if (msg
->nm_refcnt
< 0)
511 if (msg
->nm_refcnt
<= 0) {
514 NL_DBG(2, "msg %p: Freed\n", msg
);
521 * @name Direct Parsing
527 void (*cb
)(struct nl_object
*, void *);
532 static int parse_cb(struct nl_object
*obj
, struct nl_parser_param
*p
)
534 struct dp_xdata
*x
= p
->pp_arg
;
540 int nl_msg_parse(struct nl_msg
*msg
, void (*cb
)(struct nl_object
*, void *),
543 struct nl_cache_ops
*ops
;
544 struct nl_parser_param p
= {
547 struct dp_xdata x
= {
552 ops
= nl_cache_ops_associate(nlmsg_get_proto(msg
),
553 nlmsg_hdr(msg
)->nlmsg_type
);
555 return -NLE_MSGTYPE_NOSUPPORT
;
558 return nl_cache_parse(ops
, NULL
, nlmsg_hdr(msg
), &p
);