1 /* 2 * lib/doc.c Documentation Purpose 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 (at) suug.ch> 10 */ 11 12 /** 13 * @mainpage 14 * 15 * @section intro Introduction 16 * 17 * libnl is a set of libraries to deal with the netlink protocol and some 18 * of the high level protocols implemented on top of it. Its goal is to 19 * simplify netlink protocol usage and to create an abstraction layer using 20 * object based interfaces for various netlink based subsystems.The library 21 * was developed and tested on the 2.6.x kernel releases but it may work with 22 * older kernel series. 23 * 24 * @section toc Table of Contents 25 * 26 * - \subpage core_doc 27 * - \subpage route_doc 28 * - \subpage genl_doc 29 * - \subpage nf_doc 30 * 31 * @section remarks Remarks 32 * 33 * @subsection cache_alloc Allocation of Caches 34 * 35 * Almost all subsystem provide a function to allocate a new cache 36 * of some form. The function usually looks like this: 37 * @code 38 * struct nl_cache *<object name>_alloc_cache(struct nl_sock *sk); 39 * @endcode 40 * 41 * These functions allocate a new cache for the own object type, 42 * initializes it properly and updates it to represent the current 43 * state of their master, e.g. a link cache would include all 44 * links currently configured in the kernel. 45 * 46 * Some of the allocation functions may take additional arguments 47 * to further specify what will be part of the cache. 48 * 49 * All such functions return a newly allocated cache or NULL 50 * in case of an error. 51 * 52 * @subsection addr Setting of Addresses 53 * @code 54 * int <object name>_set_addr(struct nl_object *, struct nl_addr *) 55 * @endcode 56 * 57 * All attribute functions avaiable for assigning addresses to objects 58 * take a struct nl_addr argument. The provided address object is 59 * validated against the address family of the object if known already. 60 * The assignment fails if the address families mismatch. In case the 61 * address family has not been specified yet, the address family of 62 * the new address is elected to be the new requirement. 63 * 64 * The function will acquire a new reference on the address object 65 * before assignment, the caller is NOT responsible for this. 66 * 67 * All functions return 0 on success or a negative error code. 68 * 69 * @subsection flags Flags to Character StringTranslations 70 * All functions converting a set of flags to a character string follow 71 * the same principles, therefore, the following information applies 72 * to all functions convertings flags to a character string and vice versa. 73 * 74 * @subsubsection flags2str Flags to Character String 75 * @code 76 * char *<object name>_flags2str(int flags, char *buf, size_t len) 77 * @endcode 78 * @arg flags Flags. 79 * @arg buf Destination buffer. 80 * @arg len Buffer length. 81 * 82 * Converts the specified flags to a character string separated by 83 * commas and stores it in the specified destination buffer. 84 * 85 * @return The destination buffer 86 * 87 * @subsubsection str2flags Character String to Flags 88 * @code 89 * int <object name>_str2flags(const char *name) 90 * @endcode 91 * @arg name Name of flag. 92 * 93 * Converts the provided character string specifying a flag 94 * to the corresponding numeric value. 95 * 96 * @return Link flag or a negative value if none was found. 97 * 98 * @subsubsection type2str Type to Character String 99 * @code 100 * char *<object name>_<type>2str(int type, char *buf, size_t len) 101 * @endcode 102 * @arg type Type as numeric value 103 * @arg buf Destination buffer. 104 * @arg len Buffer length. 105 * 106 * Converts an identifier (type) to a character string and stores 107 * it in the specified destination buffer. 108 * 109 * @return The destination buffer or the type encoded in hexidecimal 110 * form if the identifier is unknown. 111 * 112 * @subsubsection str2type Character String to Type 113 * @code 114 * int <object name>_str2<type>(const char *name) 115 * @endcode 116 * @arg name Name of identifier (type). 117 * 118 * Converts the provided character string specifying a identifier 119 * to the corresponding numeric value. 120 * 121 * @return Identifier as numeric value or a negative value if none was found. 122 * 123 * @page core_doc Core Library (-lnl) 124 * 125 * @section core_intro Introduction 126 * 127 * The core library contains the fundamentals required to communicate over 128 * netlink sockets. It deals with connecting and unconnecting of sockets, 129 * sending and receiving of data, provides a customizeable receiving state 130 * machine, and provides a abstract data type framework which eases the 131 * implementation of object based netlink protocols where objects are added, 132 * removed, or modified with the help of netlink messages. 133 * 134 * @section core_toc Table of Contents 135 * 136 * - \ref proto_fund 137 * - \ref sk_doc 138 * - \ref rxtx_doc 139 * - \ref cb_doc 140 * 141 * @section proto_fund Netlink Protocol Fundamentals 142 * 143 * The netlink protocol is a socket based IPC mechanism used for communication 144 * between userspace processes and the kernel. The netlink protocol uses the 145 * \c AF_NETLINK address family and defines a protocol type for each subsystem 146 * protocol (e.g. NETLINK_ROUTE, NETLINK_NETFILTER, etc). Its addressing 147 * schema is based on a 32 bit port number, formerly referred to as PID, which 148 * uniquely identifies each peer. 149 * 150 * The netlink protocol is based on messages each limited to the size of a 151 * memory page and consists of the netlink message header (struct nlmsghdr) 152 * plus the payload attached to it. The payload can consist of arbitary data 153 * but often contains a fixed sized family specifc header followed by a 154 * stream of \ref attr_doc. The use of attributes dramatically increases 155 * the flexibility of the protocol and allows for the protocol to be 156 * extended while maintaining backwards compatibility. 157 * 158 * The netlink message header (struct nlmsghdr): 159 * @code 160 * 0 1 2 3 161 * 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 1 162 * +-------------------------------------------------------------+ 163 * | Length | 164 * +------------------------------+------------------------------+ 165 * | Type | Flags | 166 * +------------------------------+------------------------------+ 167 * | Sequence Number | 168 * +-------------------------------------------------------------+ 169 * | Port (Address) | 170 * +-------------------------------------------------------------+ 171 * @endcode 172 * 173 * Netlink differs between requests, notifications, and replies. Requests 174 * are messages which have the \c NLM_F_REQUEST flag set and are meant to 175 * request an action from the receiver. A request is typically sent from 176 * a userspace process to the kernel. Every request should be assigned a 177 * sequence number which should be incremented for each request sent on the 178 * sending side. Depending on the nature of the request, the receiver may 179 * reply to the request with regular netlink messages which should contain 180 * the same sequence number as the request it relates to. Notifications are 181 * of informal nature and don't expect a reply, therefore the sequence number 182 * is typically set to 0. It should be noted that unlike in protocols such as 183 * TCP there is no strict enforcment of the sequence number. The sole purpose 184 * of sequence numbers is to assist a sender in relating replies to the 185 * corresponding requests. 186 * 187 * @msc 188 * A,B; 189 * A=>B [label="GET (seq=1, NLM_F_REQUEST)"]; 190 * A<=B [label="PUT (seq=1)"]; 191 * ...; 192 * A<=B [label="NOTIFY (seq=0)"]; 193 * @endmsc 194 * 195 * If the size of a reply exceeds the size of a memory page and thus exceeds 196 * the maximum message size, the reply can be split into a series of multipart 197 * messages. A multipart message has the \c flag NLM_F_MULTI set and the 198 * receiver is expected to continue parsing the reply until the special 199 * message type \c NLMSG_DONE is received. 200 * 201 * @msc 202 * A,B; 203 * A=>B [label="GET (seq=1, NLM_F_REQUEST)"]; 204 * A<=B [label="PUT (seq=1, NLM_F_MULTI)"]; 205 * ...; 206 * A<=B [label="PUT (seq=1, NLM_F_MULTI)"]; 207 * A<=B [label="NLMSG_DONE (seq=1)"]; 208 * @endmsc 209 * 210 * Errors can be reported using the standard message type \c NLMSG_ERROR which 211 * can carry an error code and the netlink mesage header of the request. 212 * Error messages should set their sequence number to the sequence number 213 * of the message which caused the error. 214 * 215 * @msc 216 * A,B; 217 * A=>B [label="GET (seq=1, NLM_F_REQUEST)"]; 218 * A<=B [label="NLMSG_ERROR code=EINVAL (seq=1)"]; 219 * @endmsc 220 * 221 * The \c NLMSG_ERROR message type is also used to send acknowledge messages. 222 * An acknowledge message can be requested by setting the \c NLM_F_ACK flag 223 * message except that the error code is set to 0. 224 * 225 * @msc 226 * A,B; 227 * A=>B [label="GET (seq=1, NLM_F_REQUEST | NLM_F_ACK)"]; 228 * A<=B [label="ACK (seq=1)"]; 229 * @endmsc 230 * 231 * @section sk_doc Dealing with Netlink Sockets 232 * 233 * In order to use the netlink protocol, a netlink socket is required. Each 234 * socket defines a completely independent context for sending and receiving 235 * of messages. The netlink socket and all its related attributes are 236 * represented by struct nl_sock. 237 * 238 * @code 239 * nl_socket_alloc() Allocate new socket structure. 240 * nl_socket_free(s) Free socket structure. 241 * @endcode 242 * 243 * @subsection local_port Local Port 244 * The local port number uniquely identifies the socket and is used to 245 * address it. A unique local port is generated automatically when the socket 246 * is allocated. It will consist of the Process ID (22 bits) and a random 247 * number (10 bits) to allow up to 1024 sockets per process. 248 * 249 * @code 250 * nl_socket_get_local_port(sk) Return the peer's port number. 251 * nl_socket_set_local_port(sk, port) Set the peer's port number. 252 * @endcode 253 * 254 * @subsection peer_port Peer Port 255 * A peer port can be assigned to the socket which will result in all unicast 256 * messages sent over the socket to be addresses to the corresponding peer. If 257 * no peer is specified, the kernel will try to automatically bind the socket 258 * to a kernel side socket of the same netlink protocol family. It is common 259 * practice not to bind the socket to a peer port as typically only one kernel 260 * side socket exists per netlink protocol family. 261 * 262 * @code 263 * nl_socket_get_peer_port(sk) Return the local port number. 264 * nl_socket_set_peer_port(sk, port) Set the local port number. 265 * @endcode 266 * 267 * @subsection sock_fd File Descriptor 268 * The file descriptor of the socket(2). 269 * 270 * @code 271 * nl_socket_get_fd(sk) Return file descriptor. 272 * nl_socket_set_buffer_size(sk, rx, tx) Set buffer size of socket. 273 * nl_socket_set_nonblocking(sk) Set socket to non-blocking state. 274 * @endcode 275 * 276 * @subsection group_sub Group Subscriptions 277 * Each socket can subscribe to multicast groups of the netlink protocol 278 * family it is bound to. The socket will then receive a copy of each 279 * message sent to any of the groups. Multicast groups are commonly used 280 * to implement event notifications. Prior to kernel 2.6.14 the group 281 * subscription was performed using a bitmask which limited the number of 282 * groups per protocol family to 32. This outdated interface can still be 283 * accessed via the function nl_join_groups even though it is not recommended 284 * for new code. Starting with 2.6.14 a new method was introduced which 285 * supports subscribing to an almost unlimited number of multicast groups. 286 * 287 * @code 288 * nl_socket_add_membership(sk, group) Become a member of a multicast group. 289 * nl_socket_drop_membership(sk, group) Drop multicast group membership. 290 * nl_join_groups(sk, groupmask) Join a multicast group (obsolete). 291 * @endcode 292 * 293 * @subsection seq_num Sequence Numbers 294 * The socket keeps track of the sequence numbers used. The library will 295 * automatically verify the sequence number of messages received unless 296 * the check was disabled using the function nl_socket_disable_seq_check(). 297 * When a message is sent using nl_send_auto_complete(), the sequence number 298 * is automatically filled in, and replies will be verified correctly. 299 * 300 * @code 301 * nl_socket_disable_seq_check(sk) Disable checking of sequece numbers. 302 * nl_socket_use_seq(sk) Use sequence number and bump to next. 303 * @endcode 304 * 305 * @subsection sock_cb Callback Configuration 306 * Every socket is associated a callback configuration which enables the 307 * applications to hook into various internal functions and control the 308 * receiving and sendings semantics. For more information, see section 309 * \ref cb_doc. 310 * 311 * @code 312 * nl_socket_alloc_cb(cb) Allocate socket based on callback set. 313 * nl_socket_get_cb(sk) Return callback configuration. 314 * nl_socket_set_cb(sk, cb) Replace callback configuration. 315 * nl_socket_modify_cb(sk, ...) Modify a specific callback function. 316 * @endcode 317 * 318 * @subsection sk_other Other Functions 319 * @code 320 * nl_socket_enable_auto_ack(sock) Enable automatic request of ACK. 321 * nl_socket_disable_auto_ack(sock) Disable automatic request of ACK. 322 * nl_socket_enable_msg_peek(sock) Enable message peeking. 323 * nl_socket_disable_msg_peek(sock) Disable message peeking. 324 * nl_socket_set_passcred(sk, state) Enable/disable credential passing. 325 * nl_socket_recv_pktinfo(sk, state) Enable/disable packet information. 326 * @endcode 327 * 328 * @section rxtx_doc Sending and Receiving of Data 329 * 330 * @subsection recv_semantisc Receiving Semantics 331 * @code 332 * nl_recvmsgs_default(set) 333 * | cb = nl_socket_get_cb(sk) 334 * v 335 * nl_recvmsgs(sk, cb) 336 * | [Application provides nl_recvmsgs() replacement] 337 * |- - - - - - - - - - - - - - - v 338 * | cb->cb_recvmsgs_ow() 339 * | 340 * | [Application provides nl_recv() replacement] 341 * +-------------->|- - - - - - - - - - - - - - - v 342 * | nl_recv() cb->cb_recv_ow() 343 * | +----------->|<- - - - - - - - - - - - - - -+ 344 * | | v 345 * | | Parse Message 346 * | | |- - - - - - - - - - - - - - - v 347 * | | | NL_CB_MSG_IN() 348 * | | |<- - - - - - - - - - - - - - -+ 349 * | | | 350 * | | |- - - - - - - - - - - - - - - v 351 * | | Sequence Check NL_CB_SEQ_CHECK() 352 * | | |<- - - - - - - - - - - - - - -+ 353 * | | | 354 * | | |- - - - - - - - - - - - - - - v [ NLM_F_ACK is set ] 355 * | | | NL_CB_SEND_ACK() 356 * | | |<- - - - - - - - - - - - - - -+ 357 * | | | 358 * | | +-----+------+--------------+----------------+--------------+ 359 * | | v v v v v 360 * | | Valid Message ACK NO-OP Message End of Multipart Error 361 * | | | | | | | 362 * | | v v v v v 363 * | |NL_CB_VALID() NL_CB_ACK() NL_CB_SKIPPED() NL_CB_FINISH() cb->cb_err() 364 * | | | | | | | 365 * | | +------------+--------------+----------------+ v 366 * | | | (FAILURE) 367 * | | | [Callback returned NL_SKIP] 368 * | | [More messages to be parsed] |<----------- 369 * | +----------------------------------| 370 * | | 371 * | [is Multipart message] | 372 * +-------------------------------------| [Callback returned NL_STOP] 373 * |<----------- 374 * v 375 * (SUCCESS) 376 * 377 * At any time: 378 * Message Format Error 379 * |- - - - - - - - - - - - v 380 * v NL_CB_INVALID() 381 * (FAILURE) 382 * 383 * Message Overrun (Kernel Lost Data) 384 * |- - - - - - - - - - - - v 385 * v NL_CB_OVERRUN() 386 * (FAILURE) 387 * 388 * Callback returned negative error code 389 * (FAILURE) 390 * @endcode 391 * 392 * @subsection send_semantics Sending Semantisc 393 * 394 * @code 395 * nl_send_auto_complete(sk, msg) 396 * | [Automatically completes netlink message header] 397 * | [(local port, sequence number) ] 398 * | 399 * | [Application provies nl_send() replacement] 400 * |- - - - - - - - - - - - - - - - - - - - v 401 * v cb->cb_send_ow() 402 * nl_send(sk, msg) 403 * | [If available, add peer port and credentials] 404 * v 405 * nl_sendmsg(sk, msg, msghdr) 406 * |- - - - - - - - - - - - - - - - - - - - v 407 * | NL_CB_MSG_OUT() 408 * |<- - - - - - - - - - - - - - - - - - - -+ 409 * v 410 * sendmsg() 411 * @endcode 412 * 413 * @section cb_doc Callback Configurations 414 * Callbacks and overwriting capabilities are provided to control various 415 * semantics of the library. All callback functions are packed together in 416 * struct nl_cb which is attached to a netlink socket or passed on to 417 * the respective functions directly. 418 * 419 * @subsection cb_ret_doc Callback Return Values 420 * Callback functions can control the flow of the calling layer by returning 421 * appropriate error codes: 422 * @code 423 * Action ID | Description 424 * -----------------+------------------------------------------------------- 425 * NL_OK | Proceed with whatever comes next. 426 * NL_SKIP | Skip message currently being processed and continue 427 * | with next message. 428 * NL_STOP | Stop parsing and discard all remaining messages in 429 * | this set of messages. 430 * @endcode 431 * 432 * All callbacks are optional and a default action is performed if no 433 * application specific implementation is provided: 434 * 435 * @code 436 * Callback ID | Default Return Value 437 * ------------------+---------------------- 438 * NL_CB_VALID | NL_OK 439 * NL_CB_FINISH | NL_STOP 440 * NL_CB_OVERRUN | NL_STOP 441 * NL_CB_SKIPPED | NL_SKIP 442 * NL_CB_ACK | NL_STOP 443 * NL_CB_MSG_IN | NL_OK 444 * NL_CB_MSG_OUT | NL_OK 445 * NL_CB_INVALID | NL_STOP 446 * NL_CB_SEQ_CHECK | NL_OK 447 * NL_CB_SEND_ACK | NL_OK 448 * | 449 * Error Callback | NL_STOP 450 * @endcode 451 * 452 * In order to simplify typical usages of the library, different sets of 453 * default callback implementations exist: 454 * @code 455 * NL_CB_DEFAULT: No additional actions 456 * NL_CB_VERBOSE: Automatically print warning and error messages to a file 457 * descriptor as appropriate. This is useful for CLI based 458 * applications. 459 * NL_CB_DEBUG: Print informal debugging information for each message 460 * received. This will result in every message beint sent or 461 * received to be printed to the screen in a decoded, 462 * human-readable format. 463 * @endcode 464 * 465 * @par 1) Setting up a callback set 466 * @code 467 * // Allocate a callback set and initialize it to the verbose default set 468 * struct nl_cb *cb = nl_cb_alloc(NL_CB_VERBOSE); 469 * 470 * // Modify the set to call my_func() for all valid messages 471 * nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, my_func, NULL); 472 * 473 * // Set the error message handler to the verbose default implementation 474 * // and direct it to print all errors to the given file descriptor. 475 * FILE *file = fopen(...); 476 * nl_cb_err(cb, NL_CB_VERBOSE, NULL, file); 477 * @endcode 478 * 479 * @page route_doc Routing Family 480 * 481 * @page genl_doc Generic Netlink Family 482 * 483 * @page nf_doc Netfilter Subsystem 484 */ 485
