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NAME

       sock_diag - obtaining information about sockets

SYNOPSIS

       #include <sys/socket.h>
       #include <linux/sock_diag.h>
       #include <linux/unix_diag.h> /* for UNIX domain sockets */
       #include <linux/inet_diag.h> /* for IPv4 and IPv6 sockets */

       diag_socket = socket(AF_NETLINK, socket_type, NETLINK_SOCK_DIAG);

DESCRIPTION

       The  sock_diag  netlink  subsystem  provides  a  mechanism for obtaining information about
       sockets of various address families from the kernel.  This subsystem can be used to obtain
       information about individual sockets or request a list of sockets.

       In  the  request,  the  caller  can specify additional information it would like to obtain
       about the socket, for example, memory information or information specific to  the  address
       family.

       When requesting a list of sockets, the caller can specify filters that would be applied by
       the kernel to select a subset of sockets to report.  For now, there is only the ability to
       filter sockets by state (connected, listening, and so on.)

       Note  that  sock_diag reports only those sockets that have a name; that is, either sockets
       bound explicitly with bind(2) or sockets that  were  automatically  bound  to  an  address
       (e.g.,  by  connect(2)).   This  is  the  same  set  of  sockets  that  is  available  via
       /proc/net/unix, /proc/net/tcp, /proc/net/udp, and so on.

   Request
       The request starts with a struct nlmsghdr header described in netlink(7)  with  nlmsg_type
       field  set  to  SOCK_DIAG_BY_FAMILY.   It  is followed by a header specific to the address
       family that starts with a common part shared by all address families:

           struct sock_diag_req {
               __u8 sdiag_family;
               __u8 sdiag_protocol;
           };

       The fields of this structure are as follows:

       sdiag_family
              An address family.  It should be set to the appropriate AF_* constant.

       sdiag_protocol
              Depends on sdiag_family.  It should be set to the  appropriate  IPPROTO_*  constant
              for AF_INET and AF_INET6, and to 0 otherwise.

       If  the  nlmsg_flags  field  of the struct nlmsghdr header has the NLM_F_DUMP flag set, it
       means that a list of sockets is  being  requested;  otherwise  it  is  a  query  about  an
       individual socket.

   Response
       The  response  starts with a struct nlmsghdr header and is followed by an array of objects
       specific to the address family.  The array is to be accessed  with  the  standard  NLMSG_*
       macros from the netlink(3) API.

       Each  object  is  the  NLA (netlink attributes) list that is to be accessed with the RTA_*
       macros from rtnetlink(3) API.

   UNIX domain sockets
       For UNIX domain sockets the request is represented in the following structure:

           struct unix_diag_req {
               __u8    sdiag_family;
               __u8    sdiag_protocol;
               __u16   pad;
               __u32   udiag_states;
               __u32   udiag_ino;
               __u32   udiag_show;
               __u32   udiag_cookie[2];
           };

       The fields of this structure are as follows:

       sdiag_family
              The address family; it should be set to AF_UNIX.

       sdiag_protocol
       pad    These fields should be set to 0.

       udiag_states
              This is a bit mask that defines a filter of sockets  states.   Only  those  sockets
              whose  states  are  in  this  mask  will be reported.  Ignored when querying for an
              individual socket.  Supported values are:

                   1 << TCP_ESTABLISHED

                   1 << TCP_LISTEN

       udiag_ino
              This is an inode number when querying  for  an  individual  socket.   Ignored  when
              querying for a list of sockets.

       udiag_show
              This is a set of flags defining what kind of information to report.  Each requested
              kind of information is reported back as a netlink attribute as described below:

              UDIAG_SHOW_NAME
                     The attribute reported in answer to this  request  is  UNIX_DIAG_NAME.   The
                     payload  associated  with this attribute is the pathname to which the socket
                     was bound (a sequence of bytes up to UNIX_PATH_MAX length).

              UDIAG_SHOW_VFS
                     The attribute reported in answer to  this  request  is  UNIX_DIAG_VFS.   The
                     payload  associated  with  this  attribute  is  represented in the following
                     structure:

                         struct unix_diag_vfs {
                             __u32 udiag_vfs_dev;
                             __u32 udiag_vfs_ino;
                         };

                     The fields of this structure are as follows:

                     udiag_vfs_dev
                            The device number of the corresponding on-disk socket inode.

                     udiag_vfs_ino
                            The inode number of the corresponding on-disk socket inode.

              UDIAG_SHOW_PEER
                     The attribute reported in answer to this  request  is  UNIX_DIAG_PEER.   The
                     payload  associated with this attribute is a __u32 value which is the peer's
                     inode number.  This attribute is reported for connected sockets only.

              UDIAG_SHOW_ICONS
                     The attribute reported in answer to this request  is  UNIX_DIAG_ICONS.   The
                     payload associated with this attribute is an array of __u32 values which are
                     inode numbers of sockets that has passed the  connect(2)  call,  but  hasn't
                     been processed with accept(2) yet.  This attribute is reported for listening
                     sockets only.

              UDIAG_SHOW_RQLEN
                     The attribute reported in answer to this request  is  UNIX_DIAG_RQLEN.   The
                     payload  associated  with  this  attribute  is  represented in the following
                     structure:

                         struct unix_diag_rqlen {
                             __u32 udiag_rqueue;
                             __u32 udiag_wqueue;
                         };

                     The fields of this structure are as follows:

                     udiag_rqueue
                            For listening sockets: the number of pending connections.  The length
                            of  the  array associated with the UNIX_DIAG_ICONS response attribute
                            is equal to this value.

                            For established sockets: the amount of data in incoming queue.

                     udiag_wqueue
                            For listening sockets: the backlog length which equals to  the  value
                            passed as the second argument to listen(2).

                            For established sockets: the amount of memory available for sending.

              UDIAG_SHOW_MEMINFO
                     The  attribute reported in answer to this request is UNIX_DIAG_MEMINFO.  The
                     payload associated with this attribute is an array of __u32 values described
                     below in the subsection "Socket memory information".

              The following attributes are reported back without any specific request:

              UNIX_DIAG_SHUTDOWN
                     The  payload  associated  with this attribute is __u8 value which represents
                     bits of shutdown(2) state.

       udiag_cookie
              This is an array of opaque identifiers that could be used along with  udiag_ino  to
              specify  an  individual socket.  It is ignored when querying for a list of sockets,
              as well as when all its elements are set to -1.

       The response to a query for UNIX domain sockets is represented as an array of

           struct unix_diag_msg {
               __u8    udiag_family;
               __u8    udiag_type;
               __u8    udiag_state;
               __u8    pad;
               __u32   udiag_ino;
               __u32   udiag_cookie[2];
           };

       followed by netlink attributes.

       The fields of this structure are as follows:

       udiag_family
              This field has the same meaning as in struct unix_diag_req.

       udiag_type
              This is set to one of SOCK_PACKET, SOCK_STREAM, or SOCK_SEQPACKET.

       udiag_state
              This is set to one of TCP_LISTEN or TCP_ESTABLISHED.

       pad    This field is set to 0.

       udiag_ino
              This is the socket inode number.

       udiag_cookie
              This is an array of opaque identifiers that could be used in subsequent queries.

   IPv4 and IPv6 sockets
       For IPv4 and IPv6 sockets, the request is represented in the following structure:

           struct inet_diag_req_v2 {
               __u8    sdiag_family;
               __u8    sdiag_protocol;
               __u8    idiag_ext;
               __u8    pad;
               __u32   idiag_states;
               struct inet_diag_sockid id;
           };

       where struct inet_diag_sockid is defined as follows:

           struct inet_diag_sockid {
               __be16  idiag_sport;
               __be16  idiag_dport;
               __be32  idiag_src[4];
               __be32  idiag_dst[4];
               __u32   idiag_if;
               __u32   idiag_cookie[2];
           };

       The fields of struct inet_diag_req_v2 are as follows:

       sdiag_family
              This should be set  to  either  AF_INET  or  AF_INET6  for  IPv4  or  IPv6  sockets
              respectively.

       sdiag_protocol
              This should be set to one of IPPROTO_TCP, IPPROTO_UDP, or IPPROTO_UDPLITE.

       idiag_ext
              This  is a set of flags defining what kind of extended information to report.  Each
              requested kind of information is reported back as a netlink attribute as  described
              below:

              INET_DIAG_TOS
                     The  payload associated with this attribute is a __u8 value which is the TOS
                     of the socket.

              INET_DIAG_TCLASS
                     The payload associated with this attribute is a  __u8  value  which  is  the
                     TClass  of  the  socket.   IPv6 sockets only.  For LISTEN and CLOSE sockets,
                     this is  followed  by  INET_DIAG_SKV6ONLY  attribute  with  associated  __u8
                     payload value meaning whether the socket is IPv6-only or not.

              INET_DIAG_MEMINFO
                     The  payload  associated with this attribute is represented in the following
                     structure:

                         struct inet_diag_meminfo {
                             __u32 idiag_rmem;
                             __u32 idiag_wmem;
                             __u32 idiag_fmem;
                             __u32 idiag_tmem;
                         };

                     The fields of this structure are as follows:

                     idiag_rmem  The amount of data in the receive queue.

                     idiag_wmem  The amount of data that is queued by TCP but not yet sent.

                     idiag_fmem  The amount of memory scheduled for future use (TCP only).

                     idiag_tmem  The amount of data in send queue.

              INET_DIAG_SKMEMINFO
                     The payload associated with this attribute  is  an  array  of  __u32  values
                     described below in the subsection "Socket memory information".

              INET_DIAG_INFO
                     The  payload  associated  with  this  attribute  is  specific to the address
                     family.  For TCP sockets, it is an object of type struct tcp_info.

              INET_DIAG_CONG
                     The payload associated with this attribute is a string  that  describes  the
                     congestion control algorithm used.  For TCP sockets only.

       pad    This should be set to 0.

       idiag_states
              This  is  a  bit  mask  that defines a filter of socket states.  Only those sockets
              whose states are in this mask will be  reported.   Ignored  when  querying  for  an
              individual socket.

       id     This  is  a  socket  ID  object  that  is  used  in dump requests, in queries about
              individual sockets, and is reported back in  each  response.   Unlike  UNIX  domain
              sockets,  IPv4  and  IPv6  sockets  are  identified using addresses and ports.  All
              values are in network byte order.

       The fields of struct inet_diag_sockid are as follows:

       idiag_sport
              The source port.

       idiag_dport
              The destination port.

       idiag_src
              The source address.

       idiag_dst
              The destination address.

       idiag_if
              The interface number the socket is bound to.

       idiag_cookie
              This is an array of opaque identifiers that could be used along with  other  fields
              of this structure to specify an individual socket.  It is ignored when querying for
              a list of sockets, as well as when all its elements are set to -1.

       The response to a query for IPv4 or IPv6 sockets is represented as an array of

           struct inet_diag_msg {
               __u8    idiag_family;
               __u8    idiag_state;
               __u8    idiag_timer;
               __u8    idiag_retrans;

               struct inet_diag_sockid id;

               __u32   idiag_expires;
               __u32   idiag_rqueue;
               __u32   idiag_wqueue;
               __u32   idiag_uid;
               __u32   idiag_inode;
           };

       followed by netlink attributes.

       The fields of this structure are as follows:

       idiag_family
              This is the same field as in struct inet_diag_req_v2.

       idiag_state
              This denotes socket state as in struct inet_diag_req_v2.

       idiag_timer
              For TCP sockets, this field describes the type of timer that  is  currently  active
              for the socket.  It is set to one of the following constants:

                   0      no timer is active
                   1      a retransmit timer
                   2      a keep-alive timer
                   3      a TIME_WAIT timer
                   4      a zero window probe timer

              For non-TCP sockets, this field is set to 0.

       idiag_retrans
              For  idiag_timer values 1, 2, and 4, this field contains the number of retransmits.
              For other idiag_timer values, this field is set to 0.

       idiag_expires
              For TCP sockets that have an active timer, this field describes its expiration time
              in milliseconds.  For other sockets, this field is set to 0.

       idiag_rqueue
              For listening sockets: the number of pending connections.

              For other sockets: the amount of data in the incoming queue.

       idiag_wqueue
              For listening sockets: the backlog length.

              For other sockets: the amount of memory available for sending.

       idiag_uid
              This is the socket owner UID.

       idiag_inode
              This is the socket inode number.

   Socket memory information
       The  payload  associated with UNIX_DIAG_MEMINFO and INET_DIAG_SKMEMINFO netlink attributes
       is an array of the following __u32 values:

       SK_MEMINFO_RMEM_ALLOC
              The amount of data in receive queue.

       SK_MEMINFO_RCVBUF
              The receive socket buffer as set by SO_RCVBUF.

       SK_MEMINFO_WMEM_ALLOC
              The amount of data in send queue.

       SK_MEMINFO_SNDBUF
              The send socket buffer as set by SO_SNDBUF.

       SK_MEMINFO_FWD_ALLOC
              The amount of memory scheduled for future use (TCP only).

       SK_MEMINFO_WMEM_QUEUED
              The amount of data queued by TCP, but not yet sent.

       SK_MEMINFO_OPTMEM
              The amount of memory  allocated  for  the  socket's  service  needs  (e.g.,  socket
              filter).

       SK_MEMINFO_BACKLOG
              The amount of packets in the backlog (not yet processed).

VERSIONS

       NETLINK_INET_DIAG  was  introduced  in  Linux  2.6.14  and  supported AF_INET and AF_INET6
       sockets only.  In Linux 3.3, it was renamed to NETLINK_SOCK_DIAG and extended  to  support
       AF_UNIX sockets.

       UNIX_DIAG_MEMINFO and INET_DIAG_SKMEMINFO were introduced in Linux 3.6.

STANDARDS

       The NETLINK_SOCK_DIAG API is Linux-specific.

EXAMPLES

       The  following  example  program prints inode number, peer's inode number, and name of all
       UNIX domain sockets in the current namespace.

       #include <errno.h>
       #include <stdio.h>
       #include <string.h>
       #include <unistd.h>
       #include <sys/socket.h>
       #include <sys/un.h>
       #include <linux/netlink.h>
       #include <linux/rtnetlink.h>
       #include <linux/sock_diag.h>
       #include <linux/unix_diag.h>

       static int
       send_query(int fd)
       {
           struct sockaddr_nl nladdr = {
               .nl_family = AF_NETLINK
           };
           struct
           {
               struct nlmsghdr nlh;
               struct unix_diag_req udr;
           } req = {
               .nlh = {
                   .nlmsg_len = sizeof(req),
                   .nlmsg_type = SOCK_DIAG_BY_FAMILY,
                   .nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP
               },
               .udr = {
                   .sdiag_family = AF_UNIX,
                   .udiag_states = -1,
                   .udiag_show = UDIAG_SHOW_NAME | UDIAG_SHOW_PEER
               }
           };
           struct iovec iov = {
               .iov_base = &req,
               .iov_len = sizeof(req)
           };
           struct msghdr msg = {
               .msg_name = &nladdr,
               .msg_namelen = sizeof(nladdr),
               .msg_iov = &iov,
               .msg_iovlen = 1
           };

           for (;;) {
               if (sendmsg(fd, &msg, 0) < 0) {
                   if (errno == EINTR)
                       continue;

                   perror("sendmsg");
                   return -1;
               }

               return 0;
           }
       }

       static int
       print_diag(const struct unix_diag_msg *diag, unsigned int len)
       {
           if (len < NLMSG_LENGTH(sizeof(*diag))) {
               fputs("short response\n", stderr);
               return -1;
           }
           if (diag->udiag_family != AF_UNIX) {
               fprintf(stderr, "unexpected family %u\n", diag->udiag_family);
               return -1;
           }

           unsigned int rta_len = len - NLMSG_LENGTH(sizeof(*diag));
           unsigned int peer = 0;
           size_t path_len = 0;
           char path[sizeof(((struct sockaddr_un *) 0)->sun_path) + 1];

           for (struct rtattr *attr = (struct rtattr *) (diag + 1);
                    RTA_OK(attr, rta_len); attr = RTA_NEXT(attr, rta_len)) {
               switch (attr->rta_type) {
               case UNIX_DIAG_NAME:
                   if (!path_len) {
                       path_len = RTA_PAYLOAD(attr);
                       if (path_len > sizeof(path) - 1)
                           path_len = sizeof(path) - 1;
                       memcpy(path, RTA_DATA(attr), path_len);
                       path[path_len] = '\0';
                   }
                   break;

               case UNIX_DIAG_PEER:
                   if (RTA_PAYLOAD(attr) >= sizeof(peer))
                       peer = *(unsigned int *) RTA_DATA(attr);
                   break;
               }
           }

           printf("inode=%u", diag->udiag_ino);

           if (peer)
               printf(", peer=%u", peer);

           if (path_len)
               printf(", name=%s%s", *path ? "" : "@",
                       *path ? path : path + 1);

           putchar('\n');
           return 0;
       }

       static int
       receive_responses(int fd)
       {
           long buf[8192 / sizeof(long)];
           struct sockaddr_nl nladdr;
           struct iovec iov = {
               .iov_base = buf,
               .iov_len = sizeof(buf)
           };
           int flags = 0;

           for (;;) {
               struct msghdr msg = {
                   .msg_name = &nladdr,
                   .msg_namelen = sizeof(nladdr),
                   .msg_iov = &iov,
                   .msg_iovlen = 1
               };

               ssize_t ret = recvmsg(fd, &msg, flags);

               if (ret < 0) {
                   if (errno == EINTR)
                       continue;

                   perror("recvmsg");
                   return -1;
               }
               if (ret == 0)
                   return 0;

               if (nladdr.nl_family != AF_NETLINK) {
                   fputs("!AF_NETLINK\n", stderr);
                   return -1;
               }

               const struct nlmsghdr *h = (struct nlmsghdr *) buf;

               if (!NLMSG_OK(h, ret)) {
                   fputs("!NLMSG_OK\n", stderr);
                   return -1;
               }

               for (; NLMSG_OK(h, ret); h = NLMSG_NEXT(h, ret)) {
                   if (h->nlmsg_type == NLMSG_DONE)
                       return 0;

                   if (h->nlmsg_type == NLMSG_ERROR) {
                       const struct nlmsgerr *err = NLMSG_DATA(h);

                       if (h->nlmsg_len < NLMSG_LENGTH(sizeof(*err))) {
                           fputs("NLMSG_ERROR\n", stderr);
                       } else {
                           errno = -err->error;
                           perror("NLMSG_ERROR");
                       }

                       return -1;
                   }

                   if (h->nlmsg_type != SOCK_DIAG_BY_FAMILY) {
                       fprintf(stderr, "unexpected nlmsg_type %u\n",
                               (unsigned) h->nlmsg_type);
                       return -1;
                   }

                   if (print_diag(NLMSG_DATA(h), h->nlmsg_len))
                       return -1;
               }
           }
       }

       int
       main(void)
       {
           int fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG);

           if (fd < 0) {
               perror("socket");
               return 1;
           }

           int ret = send_query(fd) || receive_responses(fd);

           close(fd);
           return ret;
       }

SEE ALSO

       netlink(3), rtnetlink(3), netlink(7), tcp(7)