man7/sock_diag.7

   1 .\" Copyright (c) 2016 Pavel Emelyanov <xemul@virtuozzo.com>
   2 .\" Copyright (c) 2016 Dmitry V. Levin <ldv@altlinux.org>
   3 .\"
   4 .\" SPDX-License-Identifier: GPL-2.0-or-later
   5 .TH SOCK_DIAG 7 2021-03-22 "Linux man-pages (unreleased)"
   6 .SH NAME
   7 sock_diag \- obtaining information about sockets
   8 .SH SYNOPSIS
   9 .nf
  10 .B #include <sys/socket.h>
  11 .B #include <linux/sock_diag.h>
  12 .BR "#include <linux/unix_diag.h>" " /* for UNIX domain sockets */"
  13 .BR "#include <linux/inet_diag.h>" " /* for IPv4 and IPv6 sockets */"
  14 .PP
  15 .BI "diag_socket = socket(AF_NETLINK, " socket_type ", NETLINK_SOCK_DIAG);"
  16 .fi
  17 .SH DESCRIPTION
  18 The sock_diag netlink subsystem provides a mechanism for obtaining
  19 information about sockets of various address families from the kernel.
  20 This subsystem can be used to obtain information about individual
  21 sockets or request a list of sockets.
  22 .PP
  23 In the request, the caller can specify additional information it would
  24 like to obtain about the socket, for example, memory information or
  25 information specific to the address family.
  26 .PP
  27 When requesting a list of sockets, the caller can specify filters that
  28 would be applied by the kernel to select a subset of sockets to report.
  29 For now, there is only the ability to filter sockets by state (connected,
  30 listening, and so on.)
  31 .PP
  32 Note that sock_diag reports only those sockets that have a name;
  33 that is, either sockets bound explicitly with
  34 .BR bind (2)
  35 or sockets that were automatically bound to an address (e.g., by
  36 .BR connect (2)).
  37 This is the same set of sockets that is available via
  38 .IR /proc/net/unix ,
  39 .IR /proc/net/tcp ,
  40 .IR /proc/net/udp ,
  41 and so on.
  42 .\"
  43 .SS Request
  44 The request starts with a
  45 .I "struct nlmsghdr"
  46 header described in
  47 .BR netlink (7)
  48 with
  49 .I nlmsg_type
  50 field set to
  51 .BR SOCK_DIAG_BY_FAMILY .
  52 It is followed by a header specific to the address family that starts with
  53 a common part shared by all address families:
  54 .PP
  55 .in +4n
  56 .EX
  57 struct sock_diag_req {
  58     uint8_t  sdiag_family;
  59     uint8_t  sdiag_protocol;
  60 };
  61 .EE
  62 .in
  63 .PP
  64 The fields of this structure are as follows:
  65 .TP
  66 .I sdiag_family
  67 An address family.
  68 It should be set to the appropriate
  69 .B AF_*
  70 constant.
  71 .TP
  72 .I sdiag_protocol
  73 Depends on
  74 .IR sdiag_family .
  75 It should be set to the appropriate
  76 .B IPPROTO_*
  77 constant for
  78 .B AF_INET
  79 and
  80 .BR AF_INET6 ,
  81 and to 0 otherwise.
  82 .PP
  83 If the
  84 .I nlmsg_flags
  85 field of the
  86 .I "struct nlmsghdr"
  87 header has the
  88 .B NLM_F_DUMP
  89 flag set, it means that a list of sockets is being requested;
  90 otherwise it is a query about an individual socket.
  91 .\"
  92 .SS Response
  93 The response starts with a
  94 .I "struct nlmsghdr"
  95 header and is followed by an array of objects specific to the address family.
  96 The array is to be accessed with the standard
  97 .B NLMSG_*
  98 macros from the
  99 .BR netlink (3)
 100 API.
 101 .PP
 102 Each object is the NLA (netlink attributes) list that is to be accessed
 103 with the
 104 .B RTA_*
 105 macros from
 106 .BR rtnetlink (3)
 107 API.
 108 .\"
 109 .SS UNIX domain sockets
 110 For UNIX domain sockets the request is represented in the following structure:
 111 .PP
 112 .in +4n
 113 .EX
 114 struct unix_diag_req {
 115     uint8_t   sdiag_family;
 116     uint8_t   sdiag_protocol;
 117     uint16_t  pad;
 118     uint32_t  udiag_states;
 119     uint32_t  udiag_ino;
 120     uint32_t  udiag_show;
 121     uint32_t  udiag_cookie[2];
 122 };
 123 .EE
 124 .in
 125 .PP
 126 The fields of this structure are as follows:
 127 .TP
 128 .I sdiag_family
 129 The address family; it should be set to
 130 .BR AF_UNIX .
 131 .PP
 132 .I sdiag_protocol
 133 .PD 0
 134 .TP
 135 .PD
 136 .I pad
 137 These fields should be set to 0.
 138 .TP
 139 .I udiag_states
 140 This is a bit mask that defines a filter of sockets states.
 141 Only those sockets whose states are in this mask will be reported.
 142 Ignored when querying for an individual socket.
 143 Supported values are:
 144 .PP
 145 .RS 12
 146 1 <<
 147 .B TCP_ESTABLISHED
 148 .PP
 149 1 <<
 150 .B TCP_LISTEN
 151 .RE
 152 .TP
 153 .I udiag_ino
 154 This is an inode number when querying for an individual socket.
 155 Ignored when querying for a list of sockets.
 156 .TP
 157 .I udiag_show
 158 This is a set of flags defining what kind of information to report.
 159 Each requested kind of information is reported back as a netlink
 160 attribute as described below:
 161 .RS
 162 .TP
 163 .B UDIAG_SHOW_NAME
 164 The attribute reported in answer to this request is
 165 .BR UNIX_DIAG_NAME .
 166 The payload associated with this attribute is the pathname to which
 167 the socket was bound (a sequence of bytes up to
 168 .B UNIX_PATH_MAX
 169 length).
 170 .TP
 171 .B UDIAG_SHOW_VFS
 172 The attribute reported in answer to this request is
 173 .BR UNIX_DIAG_VFS .
 174 The payload associated with this attribute is represented in the following
 175 structure:
 176 .IP
 177 .in +4n
 178 .EX
 179 struct unix_diag_vfs {
 180     uint32_t udiag_vfs_dev;
 181     uint32_t udiag_vfs_ino;
 182 };
 183 .EE
 184 .in
 185 .IP
 186 The fields of this structure are as follows:
 187 .RS
 188 .TP
 189 .I udiag_vfs_dev
 190 The device number of the corresponding on-disk socket inode.
 191 .TP
 192 .I udiag_vfs_ino
 193 The inode number of the corresponding on-disk socket inode.
 194 .RE
 195 .TP
 196 .B UDIAG_SHOW_PEER
 197 The attribute reported in answer to this request is
 198 .BR UNIX_DIAG_PEER .
 199 The payload associated with this attribute is a
 200 .I uint32_t
 201 value
 202 which is the peer's inode number.
 203 This attribute is reported for connected sockets only.
 204 .TP
 205 .B UDIAG_SHOW_ICONS
 206 The attribute reported in answer to this request is
 207 .BR UNIX_DIAG_ICONS .
 208 The payload associated with this attribute is an array of
 209 .I uint32_t
 210 values
 211 which are inode numbers of sockets that has passed the
 212 .BR connect (2)
 213 call, but hasn't been processed with
 214 .BR accept (2)
 215 yet.
 216 This attribute is reported for listening sockets only.
 217 .TP
 218 .B UDIAG_SHOW_RQLEN
 219 The attribute reported in answer to this request is
 220 .BR UNIX_DIAG_RQLEN .
 221 The payload associated with this attribute is represented in the following
 222 structure:
 223 .IP
 224 .in +4n
 225 .EX
 226 struct unix_diag_rqlen {
 227     uint32_t  udiag_rqueue;
 228     uint32_t  udiag_wqueue;
 229 };
 230 .EE
 231 .in
 232 .IP
 233 The fields of this structure are as follows:
 234 .RS
 235 .TP
 236 .I udiag_rqueue
 237 For listening sockets:
 238 the number of pending connections.
 239 The length of the array associated with the
 240 .B UNIX_DIAG_ICONS
 241 response attribute is equal to this value.
 242 .IP
 243 For established sockets:
 244 the amount of data in incoming queue.
 245 .TP
 246 .I udiag_wqueue
 247 For listening sockets:
 248 the backlog length which equals to the value passed as the second argument to
 249 .BR listen (2).
 250 .IP
 251 For established sockets:
 252 the amount of memory available for sending.
 253 .RE
 254 .TP
 255 .B UDIAG_SHOW_MEMINFO
 256 The attribute reported in answer to this request is
 257 .BR UNIX_DIAG_MEMINFO .
 258 The payload associated with this attribute is an array of
 259 .I uint32_t
 260 values
 261 described below in the subsection "Socket memory information".
 262 .PP
 263 The following attributes are reported back without any specific request:
 264 .TP
 265 .B UNIX_DIAG_SHUTDOWN
 266 The payload associated with this attribute is
 267 .I uint8_t
 268 value which represents
 269 bits of
 270 .BR shutdown (2)
 271 state.
 272 .RE
 273 .TP
 274 .I udiag_cookie
 275 This is an array of opaque identifiers that could be used along with
 276 .I udiag_ino
 277 to specify an individual socket.
 278 It is ignored when querying for a list
 279 of sockets, as well as when all its elements are set to \-1.
 280 .PP
 281 The response to a query for UNIX domain sockets is represented as an array of
 282 .PP
 283 .in +4n
 284 .EX
 285 struct unix_diag_msg {
 286     uint8_t   udiag_family;
 287     uint8_t   udiag_type;
 288     uint8_t   udiag_state;
 289     uint8_t   pad;
 290     uint32_t  udiag_ino;
 291     uint32_t  udiag_cookie[2];
 292 };
 293 .EE
 294 .in
 295 .PP
 296 followed by netlink attributes.
 297 .PP
 298 The fields of this structure are as follows:
 299 .TP
 300 .I udiag_family
 301 This field has the same meaning as in
 302 .IR "struct unix_diag_req" .
 303 .TP
 304 .I udiag_type
 305 This is set to one of
 306 .BR SOCK_PACKET ,
 307 .BR SOCK_STREAM ,
 308 or
 309 .BR SOCK_SEQPACKET .
 310 .TP
 311 .I udiag_state
 312 This is set to one of
 313 .B TCP_LISTEN
 314 or
 315 .BR TCP_ESTABLISHED .
 316 .TP
 317 .I pad
 318 This field is set to 0.
 319 .TP
 320 .I udiag_ino
 321 This is the socket inode number.
 322 .TP
 323 .I udiag_cookie
 324 This is an array of opaque identifiers that could be used in subsequent
 325 queries.
 326 .\"
 327 .SS IPv4 and IPv6 sockets
 328 For IPv4 and IPv6 sockets,
 329 the request is represented in the following structure:
 330 .PP
 331 .in +4n
 332 .EX
 333 struct inet_diag_req_v2 {
 334     uint8_t   sdiag_family;
 335     uint8_t   sdiag_protocol;
 336     uint8_t   idiag_ext;
 337     uint8_t   pad;
 338     uint32_t  idiag_states;
 339     struct inet_diag_sockid id;
 340 };
 341 .EE
 342 .in
 343 .PP
 344 where
 345 .I "struct inet_diag_sockid"
 346 is defined as follows:
 347 .PP
 348 .in +4n
 349 .EX
 350 struct inet_diag_sockid {
 351     __be16    idiag_sport;
 352     __be16    idiag_dport;
 353     __be32    idiag_src[4];
 354     __be32    idiag_dst[4];
 355     uint32_t  idiag_if;
 356     uint32_t  idiag_cookie[2];
 357 };
 358 .EE
 359 .in
 360 .PP
 361 The fields of
 362 .I "struct inet_diag_req_v2"
 363 are as follows:
 364 .TP
 365 .I sdiag_family
 366 This should be set to either
 367 .B AF_INET
 368 or
 369 .B AF_INET6
 370 for IPv4 or IPv6 sockets respectively.
 371 .TP
 372 .I sdiag_protocol
 373 This should be set to one of
 374 .BR IPPROTO_TCP ,
 375 .BR IPPROTO_UDP ,
 376 or
 377 .BR IPPROTO_UDPLITE .
 378 .TP
 379 .I idiag_ext
 380 This is a set of flags defining what kind of extended information to report.
 381 Each requested kind of information is reported back as a netlink attribute
 382 as described below:
 383 .RS
 384 .TP
 385 .B INET_DIAG_TOS
 386 The payload associated with this attribute is a
 387 .I uint8_t
 388 value
 389 which is the TOS of the socket.
 390 .TP
 391 .B INET_DIAG_TCLASS
 392 The payload associated with this attribute is a
 393 .I uint8_t
 394 value
 395 which is the TClass of the socket.
 396 IPv6 sockets only.
 397 For LISTEN and CLOSE sockets, this is followed by
 398 .B INET_DIAG_SKV6ONLY
 399 attribute with associated
 400 .I uint8_t
 401 payload value meaning whether the socket
 402 is IPv6-only or not.
 403 .TP
 404 .B INET_DIAG_MEMINFO
 405 The payload associated with this attribute is represented in the following
 406 structure:
 407 .IP
 408 .in +4n
 409 .EX
 410 struct inet_diag_meminfo {
 411     uint32_t  idiag_rmem;
 412     uint32_t  idiag_wmem;
 413     uint32_t  idiag_fmem;
 414     uint32_t  idiag_tmem;
 415 };
 416 .EE
 417 .in
 418 .IP
 419 The fields of this structure are as follows:
 420 .RS
 421 .TP 12
 422 .I idiag_rmem
 423 The amount of data in the receive queue.
 424 .TP
 425 .I idiag_wmem
 426 The amount of data that is queued by TCP but not yet sent.
 427 .TP
 428 .I idiag_fmem
 429 The amount of memory scheduled for future use (TCP only).
 430 .TP
 431 .I idiag_tmem
 432 The amount of data in send queue.
 433 .RE
 434 .TP
 435 .B INET_DIAG_SKMEMINFO
 436 The payload associated with this attribute is an array of
 437 .I uint32_t
 438 values
 439 described below in the subsection "Socket memory information".
 440 .TP
 441 .B INET_DIAG_INFO
 442 The payload associated with this attribute is specific to the address family.
 443 For TCP sockets, it is an object of type
 444 .IR "struct tcp_info" .
 445 .TP
 446 .B INET_DIAG_CONG
 447 The payload associated with this attribute is a string that describes the
 448 congestion control algorithm used.
 449 For TCP sockets only.
 450 .RE
 451 .TP
 452 .I pad
 453 This should be set to 0.
 454 .TP
 455 .I idiag_states
 456 This is a bit mask that defines a filter of socket states.
 457 Only those sockets whose states are in this mask will be reported.
 458 Ignored when querying for an individual socket.
 459 .TP
 460 .I id
 461 This is a socket ID object that is used in dump requests, in queries
 462 about individual sockets, and is reported back in each response.
 463 Unlike UNIX domain sockets, IPv4 and IPv6 sockets are identified
 464 using addresses and ports.
 465 All values are in network byte order.
 466 .PP
 467 The fields of
 468 .I "struct inet_diag_sockid"
 469 are as follows:
 470 .TP
 471 .I idiag_sport
 472 The source port.
 473 .TP
 474 .I idiag_dport
 475 The destination port.
 476 .TP
 477 .I idiag_src
 478 The source address.
 479 .TP
 480 .I idiag_dst
 481 The destination address.
 482 .TP
 483 .I idiag_if
 484 The interface number the socket is bound to.
 485 .TP
 486 .I idiag_cookie
 487 This is an array of opaque identifiers that could be used along with
 488 other fields of this structure to specify an individual socket.
 489 It is ignored when querying for a list of sockets, as well as
 490 when all its elements are set to \-1.
 491 .PP
 492 The response to a query for IPv4 or IPv6 sockets is represented as an array of
 493 .PP
 494 .in +4n
 495 .EX
 496 struct inet_diag_msg {
 497     uint8_t   idiag_family;
 498     uint8_t   idiag_state;
 499     uint8_t   idiag_timer;
 500     uint8_t   idiag_retrans;
 501
 502     struct inet_diag_sockid id;
 503
 504     uint32_t  idiag_expires;
 505     uint32_t  idiag_rqueue;
 506     uint32_t  idiag_wqueue;
 507     uint32_t  idiag_uid;
 508     uint32_t  idiag_inode;
 509 };
 510 .EE
 511 .in
 512 .PP
 513 followed by netlink attributes.
 514 .PP
 515 The fields of this structure are as follows:
 516 .TP
 517 .I idiag_family
 518 This is the same field as in
 519 .IR "struct inet_diag_req_v2" .
 520 .TP
 521 .I idiag_state
 522 This denotes socket state as in
 523 .IR "struct inet_diag_req_v2" .
 524 .TP
 525 .I idiag_timer
 526 For TCP sockets, this field describes the type of timer that is currently
 527 active for the socket.
 528 It is set to one of the following constants:
 529 .IP
 530 .PD 0
 531 .RS 12
 532 .TP
 533 .B 0
 534 no timer is active
 535 .TP
 536 .B 1
 537 a retransmit timer
 538 .TP
 539 .B 2
 540 a keep-alive timer
 541 .TP
 542 .B 3
 543 a TIME_WAIT timer
 544 .TP
 545 .B 4
 546 a zero window probe timer
 547 .RE
 548 .PD
 549 .IP
 550 For non-TCP sockets, this field is set to 0.
 551 .TP
 552 .I idiag_retrans
 553 For
 554 .I idiag_timer
 555 values 1, 2, and 4, this field contains the number of retransmits.
 556 For other
 557 .I idiag_timer
 558 values, this field is set to 0.
 559 .TP
 560 .I idiag_expires
 561 For TCP sockets that have an active timer, this field describes its expiration
 562 time in milliseconds.
 563 For other sockets, this field is set to 0.
 564 .TP
 565 .I idiag_rqueue
 566 For listening sockets:
 567 the number of pending connections.
 568 .IP
 569 For other sockets:
 570 the amount of data in the incoming queue.
 571 .TP
 572 .I idiag_wqueue
 573 For listening sockets:
 574 the backlog length.
 575 .IP
 576 For other sockets:
 577 the amount of memory available for sending.
 578 .TP
 579 .I idiag_uid
 580 This is the socket owner UID.
 581 .TP
 582 .I idiag_inode
 583 This is the socket inode number.
 584 .\"
 585 .SS Socket memory information
 586 The payload associated with
 587 .B UNIX_DIAG_MEMINFO
 588 and
 589 .B INET_DIAG_SKMEMINFO
 590 netlink attributes is an array of the following
 591 .I uint32_t
 592 values:
 593 .TP
 594 .B SK_MEMINFO_RMEM_ALLOC
 595 The amount of data in receive queue.
 596 .TP
 597 .B SK_MEMINFO_RCVBUF
 598 The receive socket buffer as set by
 599 .BR SO_RCVBUF .
 600 .TP
 601 .B SK_MEMINFO_WMEM_ALLOC
 602 The amount of data in send queue.
 603 .TP
 604 .B SK_MEMINFO_SNDBUF
 605 The send socket buffer as set by
 606 .BR SO_SNDBUF .
 607 .TP
 608 .B SK_MEMINFO_FWD_ALLOC
 609 The amount of memory scheduled for future use (TCP only).
 610 .TP
 611 .B SK_MEMINFO_WMEM_QUEUED
 612 The amount of data queued by TCP, but not yet sent.
 613 .TP
 614 .B SK_MEMINFO_OPTMEM
 615 The amount of memory allocated for the socket's service needs (e.g., socket
 616 filter).
 617 .TP
 618 .B SK_MEMINFO_BACKLOG
 619 The amount of packets in the backlog (not yet processed).
 620 .SH VERSIONS
 621 .B NETLINK_INET_DIAG
 622 was introduced in Linux 2.6.14 and supported
 623 .B AF_INET
 624 and
 625 .B AF_INET6
 626 sockets only.
 627 In Linux 3.3, it was renamed to
 628 .B NETLINK_SOCK_DIAG
 629 and extended to support
 630 .B AF_UNIX
 631 sockets.
 632 .PP
 633 .B UNIX_DIAG_MEMINFO
 634 and
 635 .B INET_DIAG_SKMEMINFO
 636 were introduced in Linux 3.6.
 637 .SH STANDARDS
 638 The NETLINK_SOCK_DIAG API is Linux-specific.
 639 .SH EXAMPLES
 640 The following example program prints inode number, peer's inode number,
 641 and name of all UNIX domain sockets in the current namespace.
 642 .PP
 643 .EX
 644 #include <errno.h>
 645 #include <stdio.h>
 646 #include <string.h>
 647 #include <unistd.h>
 648 #include <sys/socket.h>
 649 #include <sys/un.h>
 650 #include <linux/netlink.h>
 651 #include <linux/rtnetlink.h>
 652 #include <linux/sock_diag.h>
 653 #include <linux/unix_diag.h>
 654
 655 static int
 656 send_query(int fd)
 657 {
 658     struct sockaddr_nl nladdr = {
 659         .nl_family = AF_NETLINK
 660     };
 661     struct
 662     {
 663         struct nlmsghdr nlh;
 664         struct unix_diag_req udr;
 665     } req = {
 666         .nlh = {
 667             .nlmsg_len = sizeof(req),
 668             .nlmsg_type = SOCK_DIAG_BY_FAMILY,
 669             .nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP
 670         },
 671         .udr = {
 672             .sdiag_family = AF_UNIX,
 673             .udiag_states = \-1,
 674             .udiag_show = UDIAG_SHOW_NAME | UDIAG_SHOW_PEER
 675         }
 676     };
 677     struct iovec iov = {
 678         .iov_base = &req,
 679         .iov_len = sizeof(req)
 680     };
 681     struct msghdr msg = {
 682         .msg_name = &nladdr,
 683         .msg_namelen = sizeof(nladdr),
 684         .msg_iov = &iov,
 685         .msg_iovlen = 1
 686     };
 687
 688     for (;;) {
 689         if (sendmsg(fd, &msg, 0) < 0) {
 690             if (errno == EINTR)
 691                 continue;
 692
 693             perror("sendmsg");
 694             return \-1;
 695         }
 696
 697         return 0;
 698     }
 699 }
 700
 701 static int
 702 print_diag(const struct unix_diag_msg *diag, unsigned int len)
 703 {
 704     if (len < NLMSG_LENGTH(sizeof(*diag))) {
 705         fputs("short response\en", stderr);
 706         return \-1;
 707     }
 708     if (diag\->udiag_family != AF_UNIX) {
 709         fprintf(stderr, "unexpected family %u\en", diag\->udiag_family);
 710         return \-1;
 711     }
 712
 713     unsigned int rta_len = len \- NLMSG_LENGTH(sizeof(*diag));
 714     unsigned int peer = 0;
 715     size_t path_len = 0;
 716     char path[sizeof(((struct sockaddr_un *) 0)\->sun_path) + 1];
 717
 718     for (struct rtattr *attr = (struct rtattr *) (diag + 1);
 719              RTA_OK(attr, rta_len); attr = RTA_NEXT(attr, rta_len)) {
 720         switch (attr\->rta_type) {
 721         case UNIX_DIAG_NAME:
 722             if (!path_len) {
 723                 path_len = RTA_PAYLOAD(attr);
 724                 if (path_len > sizeof(path) \- 1)
 725                     path_len = sizeof(path) \- 1;
 726                 memcpy(path, RTA_DATA(attr), path_len);
 727                 path[path_len] = \(aq\e0\(aq;
 728             }
 729             break;
 730
 731         case UNIX_DIAG_PEER:
 732             if (RTA_PAYLOAD(attr) >= sizeof(peer))
 733                 peer = *(unsigned int *) RTA_DATA(attr);
 734             break;
 735         }
 736     }
 737
 738     printf("inode=%u", diag\->udiag_ino);
 739
 740     if (peer)
 741         printf(", peer=%u", peer);
 742
 743     if (path_len)
 744         printf(", name=%s%s", *path ? "" : "@",
 745                 *path ? path : path + 1);
 746
 747     putchar(\(aq\en\(aq);
 748     return 0;
 749 }
 750
 751 static int
 752 receive_responses(int fd)
 753 {
 754     long buf[8192 / sizeof(long)];
 755     struct sockaddr_nl nladdr;
 756     struct iovec iov = {
 757         .iov_base = buf,
 758         .iov_len = sizeof(buf)
 759     };
 760     int flags = 0;
 761
 762     for (;;) {
 763         struct msghdr msg = {
 764             .msg_name = &nladdr,
 765             .msg_namelen = sizeof(nladdr),
 766             .msg_iov = &iov,
 767             .msg_iovlen = 1
 768         };
 769
 770         ssize_t ret = recvmsg(fd, &msg, flags);
 771
 772         if (ret < 0) {
 773             if (errno == EINTR)
 774                 continue;
 775
 776             perror("recvmsg");
 777             return \-1;
 778         }
 779         if (ret == 0)
 780             return 0;
 781
 782         if (nladdr.nl_family != AF_NETLINK) {
 783             fputs("!AF_NETLINK\en", stderr);
 784             return \-1;
 785         }
 786
 787         const struct nlmsghdr *h = (struct nlmsghdr *) buf;
 788
 789         if (!NLMSG_OK(h, ret)) {
 790             fputs("!NLMSG_OK\en", stderr);
 791             return \-1;
 792         }
 793
 794         for (; NLMSG_OK(h, ret); h = NLMSG_NEXT(h, ret)) {
 795             if (h\->nlmsg_type == NLMSG_DONE)
 796                 return 0;
 797
 798             if (h\->nlmsg_type == NLMSG_ERROR) {
 799                 const struct nlmsgerr *err = NLMSG_DATA(h);
 800
 801                 if (h\->nlmsg_len < NLMSG_LENGTH(sizeof(*err))) {
 802                     fputs("NLMSG_ERROR\en", stderr);
 803                 } else {
 804                     errno = \-err\->error;
 805                     perror("NLMSG_ERROR");
 806                 }
 807
 808                 return \-1;
 809             }
 810
 811             if (h\->nlmsg_type != SOCK_DIAG_BY_FAMILY) {
 812                 fprintf(stderr, "unexpected nlmsg_type %u\en",
 813                         (unsigned) h\->nlmsg_type);
 814                 return \-1;
 815             }
 816
 817             if (print_diag(NLMSG_DATA(h), h\->nlmsg_len))
 818                 return \-1;
 819         }
 820     }
 821 }
 822
 823 int
 824 main(void)
 825 {
 826     int fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG);
 827
 828     if (fd < 0) {
 829         perror("socket");
 830         return 1;
 831     }
 832
 833     int ret = send_query(fd) || receive_responses(fd);
 834
 835     close(fd);
 836     return ret;
 837 }
 838 .EE
 839 .SH SEE ALSO
 840 .BR netlink (3),
 841 .BR rtnetlink (3),
 842 .BR netlink (7),
 843 .BR tcp (7)