nl.c

   1 /*
   2  * lib/nl.c             Core Netlink Interface
   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 core Core
  14  *
  15  * @details
  16  * @par 1) Connecting the socket
  17  * @code
  18  * // Bind and connect the socket to a protocol, NETLINK_ROUTE in this example.
  19  * nl_connect(sk, NETLINK_ROUTE);
  20  * @endcode
  21  *
  22  * @par 2) Sending data
  23  * @code
  24  * // The most rudimentary method is to use nl_sendto() simply pushing
  25  * // a piece of data to the other netlink peer. This method is not
  26  * // recommended.
  27  * const char buf[] = { 0x01, 0x02, 0x03, 0x04 };
  28  * nl_sendto(sk, buf, sizeof(buf));
  29  *
  30  * // A more comfortable interface is nl_send() taking a pointer to
  31  * // a netlink message.
  32  * struct nl_msg *msg = my_msg_builder();
  33  * nl_send(sk, nlmsg_hdr(msg));
  34  *
  35  * // nl_sendmsg() provides additional control over the sendmsg() message
  36  * // header in order to allow more specific addressing of multiple peers etc.
  37  * struct msghdr hdr = { ... };
  38  * nl_sendmsg(sk, nlmsg_hdr(msg), &hdr);
  39  *
  40  * // You're probably too lazy to fill out the netlink pid, sequence number
  41  * // and message flags all the time. nl_send_auto_complete() automatically
  42  * // extends your message header as needed with an appropriate sequence
  43  * // number, the netlink pid stored in the netlink socket and the message
  44  * // flags NLM_F_REQUEST and NLM_F_ACK (if not disabled in the socket)
  45  * nl_send_auto_complete(sk, nlmsg_hdr(msg));
  46  *
  47  * // Simple protocols don't require the complex message construction interface
  48  * // and may favour nl_send_simple() to easly send a bunch of payload
  49  * // encapsulated in a netlink message header.
  50  * nl_send_simple(sk, MY_MSG_TYPE, 0, buf, sizeof(buf));
  51  * @endcode
  52  *
  53  * @par 3) Receiving data
  54  * @code
  55  * // nl_recv() receives a single message allocating a buffer for the message
  56  * // content and gives back the pointer to you.
  57  * struct sockaddr_nl peer;
  58  * unsigned char *msg;
  59  * nl_recv(sk, &peer, &msg);
  60  *
  61  * // nl_recvmsgs() receives a bunch of messages until the callback system
  62  * // orders it to state, usually after receving a compolete multi part
  63  * // message series.
  64  * nl_recvmsgs(sk, my_callback_configuration);
  65  *
  66  * // nl_recvmsgs_default() acts just like nl_recvmsg() but uses the callback
  67  * // configuration stored in the socket.
  68  * nl_recvmsgs_default(sk);
  69  *
  70  * // In case you want to wait for the ACK to be recieved that you requested
  71  * // with your latest message, you can call nl_wait_for_ack()
  72  * nl_wait_for_ack(sk);
  73  * @endcode
  74  *
  75  * @par 4) Closing
  76  * @code
  77  * // Close the socket first to release kernel memory
  78  * nl_close(sk);
  79  * @endcode
  80  *
  81  * @{
  82  */
  83
  84 #include <netlink-local.h>
  85 #include <netlink/netlink.h>
  86 #include <netlink/utils.h>
  87 #include <netlink/handlers.h>
  88 #include <netlink/msg.h>
  89 #include <netlink/attr.h>
  90
  91 /**
  92  * @name Connection Management
  93  * @{
  94  */
  95
  96 /**
  97  * Create and connect netlink socket.
  98  * @arg sk              Netlink socket.
  99  * @arg protocol        Netlink protocol to use.
 100  *
 101  * Creates a netlink socket using the specified protocol, binds the socket
 102  * and issues a connection attempt.
 103  *
 104  * @return 0 on success or a negative error code.
 105  */
 106 int nl_connect(struct nl_sock *sk, int protocol)
 107 {
 108         int err;
 109         int flags = 0;
 110         socklen_t addrlen;
 111
 112 #ifdef SOCK_CLOEXEC
 113         flags = SOCK_CLOEXEC;
 114 #endif
 115
 116         sk->s_fd = socket(AF_NETLINK, SOCK_RAW | flags, protocol);
 117         if (sk->s_fd < 0) {
 118                 err = -nl_syserr2nlerr(errno);
 119                 goto errout;
 120         }
 121
 122         if (!(sk->s_flags & NL_SOCK_BUFSIZE_SET)) {
 123                 err = nl_socket_set_buffer_size(sk, 0, 0);
 124                 if (err < 0)
 125                         goto errout;
 126         }
 127
 128         err = bind(sk->s_fd, (struct sockaddr*) &sk->s_local,
 129                    sizeof(sk->s_local));
 130         if (err < 0) {
 131                 err = -nl_syserr2nlerr(errno);
 132                 goto errout;
 133         }
 134
 135         addrlen = sizeof(sk->s_local);
 136         err = getsockname(sk->s_fd, (struct sockaddr *) &sk->s_local,
 137                           &addrlen);
 138         if (err < 0) {
 139                 err = -nl_syserr2nlerr(errno);
 140                 goto errout;
 141         }
 142
 143         if (addrlen != sizeof(sk->s_local)) {
 144                 err = -NLE_NOADDR;
 145                 goto errout;
 146         }
 147
 148         if (sk->s_local.nl_family != AF_NETLINK) {
 149                 err = -NLE_AF_NOSUPPORT;
 150                 goto errout;
 151         }
 152
 153         sk->s_proto = protocol;
 154
 155         return 0;
 156 errout:
 157         close(sk->s_fd);
 158         sk->s_fd = -1;
 159
 160         return err;
 161 }
 162
 163 /**
 164  * Close/Disconnect netlink socket.
 165  * @arg sk              Netlink socket.
 166  */
 167 void nl_close(struct nl_sock *sk)
 168 {
 169         if (sk->s_fd >= 0) {
 170                 close(sk->s_fd);
 171                 sk->s_fd = -1;
 172         }
 173
 174         sk->s_proto = 0;
 175 }
 176
 177 /** @} */
 178
 179 /**
 180  * @name Send
 181  * @{
 182  */
 183
 184 /**
 185  * Send raw data over netlink socket.
 186  * @arg sk              Netlink socket.
 187  * @arg buf             Data buffer.
 188  * @arg size            Size of data buffer.
 189  * @return Number of characters written on success or a negative error code.
 190  */
 191 int nl_sendto(struct nl_sock *sk, void *buf, size_t size)
 192 {
 193         int ret;
 194
 195         ret = sendto(sk->s_fd, buf, size, 0, (struct sockaddr *)
 196                      &sk->s_peer, sizeof(sk->s_peer));
 197         if (ret < 0)
 198                 return -nl_syserr2nlerr(errno);
 199
 200         return ret;
 201 }
 202
 203 /**
 204  * Send netlink message with control over sendmsg() message header.
 205  * @arg sk              Netlink socket.
 206  * @arg msg             Netlink message to be sent.
 207  * @arg hdr             Sendmsg() message header.
 208  * @return Number of characters sent on sucess or a negative error code.
 209  */
 210 int nl_sendmsg(struct nl_sock *sk, struct nl_msg *msg, struct msghdr *hdr)
 211 {
 212         struct nl_cb *cb;
 213         int ret;
 214
 215         struct iovec iov = {
 216                 .iov_base = (void *) nlmsg_hdr(msg),
 217                 .iov_len = nlmsg_hdr(msg)->nlmsg_len,
 218         };
 219
 220         hdr->msg_iov = &iov;
 221         hdr->msg_iovlen = 1;
 222
 223         nlmsg_set_src(msg, &sk->s_local);
 224
 225         cb = sk->s_cb;
 226         if (cb->cb_set[NL_CB_MSG_OUT])
 227                 if (nl_cb_call(cb, NL_CB_MSG_OUT, msg) != NL_OK)
 228                         return 0;
 229
 230         ret = sendmsg(sk->s_fd, hdr, 0);
 231         if (ret < 0)
 232                 return -nl_syserr2nlerr(errno);
 233
 234         return ret;
 235 }
 236
 237
 238 /**
 239  * Send netlink message.
 240  * @arg sk              Netlink socket.
 241  * @arg msg             Netlink message to be sent.
 242  * @see nl_sendmsg()
 243  * @return Number of characters sent on success or a negative error code.
 244  */
 245 int nl_send(struct nl_sock *sk, struct nl_msg *msg)
 246 {
 247         struct sockaddr_nl *dst;
 248         struct ucred *creds;
 249
 250         struct msghdr hdr = {
 251                 .msg_name = (void *) &sk->s_peer,
 252                 .msg_namelen = sizeof(struct sockaddr_nl),
 253         };
 254
 255         /* Overwrite destination if specified in the message itself, defaults
 256          * to the peer address of the socket.
 257          */
 258         dst = nlmsg_get_dst(msg);
 259         if (dst->nl_family == AF_NETLINK)
 260                 hdr.msg_name = dst;
 261
 262         /* Add credentials if present. */
 263         creds = nlmsg_get_creds(msg);
 264         if (creds != NULL) {
 265                 char buf[CMSG_SPACE(sizeof(struct ucred))];
 266                 struct cmsghdr *cmsg;
 267
 268                 hdr.msg_control = buf;
 269                 hdr.msg_controllen = sizeof(buf);
 270
 271                 cmsg = CMSG_FIRSTHDR(&hdr);
 272                 cmsg->cmsg_level = SOL_SOCKET;
 273                 cmsg->cmsg_type = SCM_CREDENTIALS;
 274                 cmsg->cmsg_len = CMSG_LEN(sizeof(struct ucred));
 275                 memcpy(CMSG_DATA(cmsg), creds, sizeof(struct ucred));
 276         }
 277
 278         return nl_sendmsg(sk, msg, &hdr);
 279 }
 280
 281 /**
 282  * Send netlink message and check & extend header values as needed.
 283  * @arg sk              Netlink socket.
 284  * @arg msg             Netlink message to be sent.
 285  *
 286  * Checks the netlink message \c nlh for completness and extends it
 287  * as required before sending it out. Checked fields include pid,
 288  * sequence nr, and flags.
 289  *
 290  * @see nl_send()
 291  * @return Number of characters sent or a negative error code.
 292  */
 293 int nl_send_auto_complete(struct nl_sock *sk, struct nl_msg *msg)
 294 {
 295         struct nlmsghdr *nlh;
 296         struct nl_cb *cb = sk->s_cb;
 297
 298         nlh = nlmsg_hdr(msg);
 299         if (nlh->nlmsg_pid == 0)
 300                 nlh->nlmsg_pid = sk->s_local.nl_pid;
 301
 302         if (nlh->nlmsg_seq == 0)
 303                 nlh->nlmsg_seq = sk->s_seq_next++;
 304
 305         if (msg->nm_protocol == -1)
 306                 msg->nm_protocol = sk->s_proto;
 307
 308         nlh->nlmsg_flags |= NLM_F_REQUEST;
 309
 310         if (!(sk->s_flags & NL_NO_AUTO_ACK))
 311                 nlh->nlmsg_flags |= NLM_F_ACK;
 312
 313         if (cb->cb_send_ow)
 314                 return cb->cb_send_ow(sk, msg);
 315         else
 316                 return nl_send(sk, msg);
 317 }
 318
 319 /**
 320  * Send simple netlink message using nl_send_auto_complete()
 321  * @arg sk              Netlink socket.
 322  * @arg type            Netlink message type.
 323  * @arg flags           Netlink message flags.
 324  * @arg buf             Data buffer.
 325  * @arg size            Size of data buffer.
 326  *
 327  * Builds a netlink message with the specified type and flags and
 328  * appends the specified data as payload to the message.
 329  *
 330  * @see nl_send_auto_complete()
 331  * @return Number of characters sent on success or a negative error code.
 332  */
 333 int nl_send_simple(struct nl_sock *sk, int type, int flags, void *buf,
 334                    size_t size)
 335 {
 336         int err;
 337         struct nl_msg *msg;
 338
 339         msg = nlmsg_alloc_simple(type, flags);
 340         if (!msg)
 341                 return -NLE_NOMEM;
 342
 343         if (buf && size) {
 344                 err = nlmsg_append(msg, buf, size, NLMSG_ALIGNTO);
 345                 if (err < 0)
 346                         goto errout;
 347         }
 348
 349
 350         err = nl_send_auto_complete(sk, msg);
 351 errout:
 352         nlmsg_free(msg);
 353
 354         return err;
 355 }
 356
 357 /** @} */
 358
 359 /**
 360  * @name Receive
 361  * @{
 362  */
 363
 364 /**
 365  * Receive data from netlink socket
 366  * @arg sk              Netlink socket.
 367  * @arg nla             Destination pointer for peer's netlink address.
 368  * @arg buf             Destination pointer for message content.
 369  * @arg creds           Destination pointer for credentials.
 370  *
 371  * Receives a netlink message, allocates a buffer in \c *buf and
 372  * stores the message content. The peer's netlink address is stored
 373  * in \c *nla. The caller is responsible for freeing the buffer allocated
 374  * in \c *buf if a positive value is returned.  Interrupted system calls
 375  * are handled by repeating the read. The input buffer size is determined
 376  * by peeking before the actual read is done.
 377  *
 378  * A non-blocking sockets causes the function to return immediately with
 379  * a return value of 0 if no data is available.
 380  *
 381  * @return Number of octets read, 0 on EOF or a negative error code.
 382  */
 383 int nl_recv(struct nl_sock *sk, struct sockaddr_nl *nla,
 384             unsigned char **buf, struct ucred **creds)
 385 {
 386         int n;
 387         int flags = 0;
 388         static int page_size = 0;
 389         struct iovec iov;
 390         struct msghdr msg = {
 391                 .msg_name = (void *) nla,
 392                 .msg_namelen = sizeof(struct sockaddr_nl),
 393                 .msg_iov = &iov,
 394                 .msg_iovlen = 1,
 395                 .msg_control = NULL,
 396                 .msg_controllen = 0,
 397                 .msg_flags = 0,
 398         };
 399         struct cmsghdr *cmsg;
 400
 401         if (sk->s_flags & NL_MSG_PEEK)
 402                 flags |= MSG_PEEK;
 403
 404         if (page_size == 0)
 405                 page_size = getpagesize() * 4;
 406
 407         iov.iov_len = page_size;
 408         iov.iov_base = *buf = calloc(1, iov.iov_len);
 409         if (!*buf)
 410                 return -nl_syserr2nlerr(errno);
 411
 412         if (sk->s_flags & NL_SOCK_PASSCRED) {
 413                 msg.msg_controllen = CMSG_SPACE(sizeof(struct ucred));
 414                 msg.msg_control = calloc(1, msg.msg_controllen);
 415         }
 416 retry:
 417
 418         n = recvmsg(sk->s_fd, &msg, flags);
 419         if (!n)
 420                 goto abort;
 421         else if (n < 0) {
 422                 if (errno == EINTR) {
 423                         NL_DBG(3, "recvmsg() returned EINTR, retrying\n");
 424                         goto retry;
 425                 } else if (errno == EAGAIN) {
 426                         NL_DBG(3, "recvmsg() returned EAGAIN, aborting\n");
 427                         goto abort;
 428                 } else {
 429                         free(msg.msg_control);
 430                         free(*buf);
 431                         *buf = NULL;
 432                         return -nl_syserr2nlerr(errno);
 433                 }
 434         }
 435
 436         if (iov.iov_len < (size_t) n ||
 437             msg.msg_flags & MSG_TRUNC) {
 438                 /* Provided buffer is not long enough, enlarge it
 439                  * and try again. */
 440                 iov.iov_len *= 2;
 441                 iov.iov_base = *buf = realloc(*buf, iov.iov_len);
 442                 goto retry;
 443         } else if (msg.msg_flags & MSG_CTRUNC) {
 444                 msg.msg_controllen *= 2;
 445                 msg.msg_control = realloc(msg.msg_control, msg.msg_controllen);
 446                 goto retry;
 447         } else if (flags != 0) {
 448                 /* Buffer is big enough, do the actual reading */
 449                 flags = 0;
 450                 goto retry;
 451         }
 452
 453         if (msg.msg_namelen != sizeof(struct sockaddr_nl)) {
 454                 free(msg.msg_control);
 455                 free(*buf);
 456                 *buf = NULL;
 457                 return -NLE_NOADDR;
 458         }
 459
 460         for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
 461                 if (cmsg->cmsg_level == SOL_SOCKET &&
 462                     cmsg->cmsg_type == SCM_CREDENTIALS) {
 463                         *creds = calloc(1, sizeof(struct ucred));
 464                         memcpy(*creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 465                         break;
 466                 }
 467         }
 468
 469         free(msg.msg_control);
 470         return n;
 471
 472 abort:
 473         free(msg.msg_control);
 474         free(*buf);
 475         *buf = NULL;
 476         return 0;
 477 }
 478
 479 #define NL_CB_CALL(cb, type, msg) \
 480 do { \
 481         err = nl_cb_call(cb, type, msg); \
 482         switch (err) { \
 483         case NL_OK: \
 484                 err = 0; \
 485                 break; \
 486         case NL_SKIP: \
 487                 goto skip; \
 488         case NL_STOP: \
 489                 goto stop; \
 490         default: \
 491                 goto out; \
 492         } \
 493 } while (0)
 494
 495 static int recvmsgs(struct nl_sock *sk, struct nl_cb *cb)
 496 {
 497         int n, err = 0, multipart = 0;
 498         unsigned char *buf = NULL;
 499         struct nlmsghdr *hdr;
 500         struct sockaddr_nl nla = {0};
 501         struct nl_msg *msg = NULL;
 502         struct ucred *creds = NULL;
 503
 504 continue_reading:
 505         NL_DBG(3, "Attempting to read from %p\n", sk);
 506         if (cb->cb_recv_ow)
 507                 n = cb->cb_recv_ow(sk, &nla, &buf, &creds);
 508         else
 509                 n = nl_recv(sk, &nla, &buf, &creds);
 510
 511         if (n <= 0)
 512                 return n;
 513
 514         /* make clang analyzer happy */
 515         assert(n > 0 && buf);
 516
 517         NL_DBG(3, "recvmsgs(%p): Read %d bytes\n", sk, n);
 518
 519         hdr = (struct nlmsghdr *) buf;
 520         while (nlmsg_ok(hdr, n)) {
 521                 NL_DBG(3, "recgmsgs(%p): Processing valid message...\n", sk);
 522
 523                 nlmsg_free(msg);
 524                 msg = nlmsg_convert(hdr);
 525                 if (!msg) {
 526                         err = -NLE_NOMEM;
 527                         goto out;
 528                 }
 529
 530                 nlmsg_set_proto(msg, sk->s_proto);
 531                 nlmsg_set_src(msg, &nla);
 532                 if (creds)
 533                         nlmsg_set_creds(msg, creds);
 534
 535                 /* Raw callback is the first, it gives the most control
 536                  * to the user and he can do his very own parsing. */
 537                 if (cb->cb_set[NL_CB_MSG_IN])
 538                         NL_CB_CALL(cb, NL_CB_MSG_IN, msg);
 539
 540                 /* Sequence number checking. The check may be done by
 541                  * the user, otherwise a very simple check is applied
 542                  * enforcing strict ordering */
 543                 if (cb->cb_set[NL_CB_SEQ_CHECK])
 544                         NL_CB_CALL(cb, NL_CB_SEQ_CHECK, msg);
 545                 else if (hdr->nlmsg_seq != sk->s_seq_expect) {
 546                         if (cb->cb_set[NL_CB_INVALID])
 547                                 NL_CB_CALL(cb, NL_CB_INVALID, msg);
 548                         else {
 549                                 err = -NLE_SEQ_MISMATCH;
 550                                 goto out;
 551                         }
 552                 }
 553
 554                 if (hdr->nlmsg_type == NLMSG_DONE ||
 555                     hdr->nlmsg_type == NLMSG_ERROR ||
 556                     hdr->nlmsg_type == NLMSG_NOOP ||
 557                     hdr->nlmsg_type == NLMSG_OVERRUN) {
 558                         /* We can't check for !NLM_F_MULTI since some netlink
 559                          * users in the kernel are broken. */
 560                         sk->s_seq_expect++;
 561                         NL_DBG(3, "recvmsgs(%p): Increased expected " \
 562                                "sequence number to %d\n",
 563                                sk, sk->s_seq_expect);
 564                 }
 565
 566                 if (hdr->nlmsg_flags & NLM_F_MULTI)
 567                         multipart = 1;
 568
 569                 /* Other side wishes to see an ack for this message */
 570                 if (hdr->nlmsg_flags & NLM_F_ACK) {
 571                         if (cb->cb_set[NL_CB_SEND_ACK])
 572                                 NL_CB_CALL(cb, NL_CB_SEND_ACK, msg);
 573                         else {
 574                                 /* FIXME: implement */
 575                         }
 576                 }
 577
 578                 /* messages terminates a multpart message, this is
 579                  * usually the end of a message and therefore we slip
 580                  * out of the loop by default. the user may overrule
 581                  * this action by skipping this packet. */
 582                 if (hdr->nlmsg_type == NLMSG_DONE) {
 583                         multipart = 0;
 584                         if (cb->cb_set[NL_CB_FINISH])
 585                                 NL_CB_CALL(cb, NL_CB_FINISH, msg);
 586                 }
 587
 588                 /* Message to be ignored, the default action is to
 589                  * skip this message if no callback is specified. The
 590                  * user may overrule this action by returning
 591                  * NL_PROCEED. */
 592                 else if (hdr->nlmsg_type == NLMSG_NOOP) {
 593                         if (cb->cb_set[NL_CB_SKIPPED])
 594                                 NL_CB_CALL(cb, NL_CB_SKIPPED, msg);
 595                         else
 596                                 goto skip;
 597                 }
 598
 599                 /* Data got lost, report back to user. The default action is to
 600                  * quit parsing. The user may overrule this action by retuning
 601                  * NL_SKIP or NL_PROCEED (dangerous) */
 602                 else if (hdr->nlmsg_type == NLMSG_OVERRUN) {
 603                         if (cb->cb_set[NL_CB_OVERRUN])
 604                                 NL_CB_CALL(cb, NL_CB_OVERRUN, msg);
 605                         else {
 606                                 err = -NLE_MSG_OVERFLOW;
 607                                 goto out;
 608                         }
 609                 }
 610
 611                 /* Message carries a nlmsgerr */
 612                 else if (hdr->nlmsg_type == NLMSG_ERROR) {
 613                         struct nlmsgerr *e = nlmsg_data(hdr);
 614
 615                         if (hdr->nlmsg_len < (unsigned) nlmsg_msg_size(sizeof(*e))) {
 616                                 /* Truncated error message, the default action
 617                                  * is to stop parsing. The user may overrule
 618                                  * this action by returning NL_SKIP or
 619                                  * NL_PROCEED (dangerous) */
 620                                 if (cb->cb_set[NL_CB_INVALID])
 621                                         NL_CB_CALL(cb, NL_CB_INVALID, msg);
 622                                 else {
 623                                         err = -NLE_MSG_TRUNC;
 624                                         goto out;
 625                                 }
 626                         } else if (e->error) {
 627                                 /* Error message reported back from kernel. */
 628                                 if (cb->cb_err) {
 629                                         err = cb->cb_err(&nla, e,
 630                                                            cb->cb_err_arg);
 631                                         if (err < 0)
 632                                                 goto out;
 633                                         else if (err == NL_SKIP)
 634                                                 goto skip;
 635                                         else if (err == NL_STOP) {
 636                                                 err = -nl_syserr2nlerr(e->error);
 637                                                 goto out;
 638                                         }
 639                                 } else {
 640                                         err = -nl_syserr2nlerr(e->error);
 641                                         goto out;
 642                                 }
 643                         } else if (cb->cb_set[NL_CB_ACK])
 644                                 NL_CB_CALL(cb, NL_CB_ACK, msg);
 645                 } else {
 646                         /* Valid message (not checking for MULTIPART bit to
 647                          * get along with broken kernels. NL_SKIP has no
 648                          * effect on this.  */
 649                         if (cb->cb_set[NL_CB_VALID])
 650                                 NL_CB_CALL(cb, NL_CB_VALID, msg);
 651                 }
 652 skip:
 653                 hdr = nlmsg_next(hdr, &n);
 654         }
 655
 656         nlmsg_free(msg);
 657         free(buf);
 658         free(creds);
 659         buf = NULL;
 660         msg = NULL;
 661         creds = NULL;
 662
 663         if (multipart) {
 664                 /* Multipart message not yet complete, continue reading */
 665                 goto continue_reading;
 666         }
 667 stop:
 668         err = 0;
 669 out:
 670         nlmsg_free(msg);
 671         free(buf);
 672         free(creds);
 673
 674         return err;
 675 }
 676
 677 /**
 678  * Receive a set of messages from a netlink socket.
 679  * @arg sk              Netlink socket.
 680  * @arg cb              set of callbacks to control behaviour.
 681  *
 682  * Repeatedly calls nl_recv() or the respective replacement if provided
 683  * by the application (see nl_cb_overwrite_recv()) and parses the
 684  * received data as netlink messages. Stops reading if one of the
 685  * callbacks returns NL_STOP or nl_recv returns either 0 or a negative error code.
 686  *
 687  * A non-blocking sockets causes the function to return immediately if
 688  * no data is available.
 689  *
 690  * @return 0 on success or a negative error code from nl_recv().
 691  */
 692 int nl_recvmsgs(struct nl_sock *sk, struct nl_cb *cb)
 693 {
 694         if (cb->cb_recvmsgs_ow)
 695                 return cb->cb_recvmsgs_ow(sk, cb);
 696         else
 697                 return recvmsgs(sk, cb);
 698 }
 699
 700
 701 static int ack_wait_handler(struct nl_msg *msg, void *arg)
 702 {
 703         return NL_STOP;
 704 }
 705
 706 /**
 707  * Wait for ACK.
 708  * @arg sk              Netlink socket.
 709  * @pre The netlink socket must be in blocking state.
 710  *
 711  * Waits until an ACK is received for the latest not yet acknowledged
 712  * netlink message.
 713  */
 714 int nl_wait_for_ack(struct nl_sock *sk)
 715 {
 716         int err;
 717         struct nl_cb *cb;
 718
 719         cb = nl_cb_clone(sk->s_cb);
 720         if (cb == NULL)
 721                 return -NLE_NOMEM;
 722
 723         nl_cb_set(cb, NL_CB_ACK, NL_CB_CUSTOM, ack_wait_handler, NULL);
 724         err = nl_recvmsgs(sk, cb);
 725         nl_cb_put(cb);
 726
 727         return err;
 728 }
 729
 730 /** @} */
 731
 732 /** @} */