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NAME

     dtrace_tcp — a DTrace provider for tracing events related to the tcp(4) protocol

SYNOPSIS

     tcp:::accept-established(pktinfo_t *, csinfo_t *, ipinfo_t *, tcpsinfo_t *, tcpinfo_t *);

     tcp:::accept-refused(pktinfo_t *, csinfo_t *, ipinfo_t *, tcpsinfo_t *, tcpinfo_t *);

     tcp:::connect-established(pktinfo_t *, csinfo_t *, ipinfo_t *, tcpsinfo_t *, tcpinfo_t *);

     tcp:::connect-refused(pktinfo_t *, csinfo_t *, ipinfo_t *, tcpsinfo_t *, tcpinfo_t *);

     tcp:::connect-request(pktinfo_t *, csinfo_t *, ipinfo_t *, tcpsinfo_t *, tcpinfo_t *);

     tcp:::receive(pktinfo_t *, csinfo_t *, ipinfo_t *, tcpsinfo_t *, tcpinfo_t *);

     tcp:::send(pktinfo_t *, csinfo_t *, ipinfo_t *, tcpsinfo_t *, tcpinfo_t *);

     tcp:::state-change(void *, csinfo_t *, void *, tcpsinfo_t *, void *, tcplsinfo_t *);

DESCRIPTION

     The DTrace tcp provider allows users to trace events in the tcp(4) protocol implementation.
     This provider is similar to the dtrace_ip(4) and dtrace_udp(4) providers, but additionally
     contains probes corresponding to protocol events at a level higher than packet reception and
     transmission.  All tcp probes except for tcp:::state-change() have the same number and type
     of arguments.  The last three arguments are used to describe a TCP segment: the ipinfo_t
     argument exposes the version-agnostic fields of the IP header, while the tcpinfo_t argument
     exposes the TCP header, and the tcpsinfo_t argument describes details of the corresponding
     TCP connection state, if any.  Their fields are described in the ARGUMENTS section.

     The tcp:::accept-established() probe fires when a remotely-initiated active TCP open
     succeeds.  At this point the new connection is in the ESTABLISHED state, and the probe
     arguments expose the headers associated with the final ACK of the three-way handshake.  The
     tcp:::accept-refused() probe fires when a SYN arrives on a port without a listening socket.
     The probe arguments expose the headers associated with the RST to be transmitted to the
     remote host in response to the SYN segment.

     The tcp:::connect-established(), tcp:::connect-refused(), and tcp:::connect-request() probes
     are similar to the ‘accept’ probes, except that they correspond to locally-initiated TCP
     connections.  The tcp:::connect-established() probe fires when the SYN-ACK segment of a
     three-way handshake is received from the remote host and a final ACK is prepared for
     transmission.  This occurs immediately after the local connection state transitions from
     SYN-SENT to ESTABLISHED.  The probe arguments describe the headers associated with the
     received SYN-ACK segment.  The tcp:::connect-refused() probe fires when the local host
     receives a RST segment in response to a SYN segment, indicating that the remote host refused
     to open a connection.  The probe arguments describe the IP and TCP headers associated with
     the received RST segment.  The tcp:::connect-request() probe fires as the kernel prepares to
     transmit the initial SYN segment of a three-way handshake.

     The tcp:::send() and tcp:::receive() probes fire when the host sends or receives a TCP
     packet, respectively.  As with the dtrace_udp(4) provider, tcp probes fire only for packets
     sent by or to the local host; forwarded packets are handled in the IP layer and are only
     visible to the dtrace_ip(4) provider.

     The tcp:::state-change() probe fires upon local TCP connection state transitions.  Its
     first, third and fifth arguments are currently always NULL.  Its last argument describes the
     from-state in the transition, and the to-state can be obtained from args[3]->tcps_state.

ARGUMENTS

     The pktinfo_t argument is currently unimplemented and is included for compatibility with
     other implementations of this provider.  Its fields are:

           uinptr_t pkt_addr  Always set to 0.

     The csinfo_t argument is currently unimplemented and is included for compatibility with
     other implementations of this provider.  Its fields are:

           uintptr_t cs_addr  Always set to 0.

           uint64_t cs_cid    A pointer to the struct inpcb for this packet, or NULL.

           pid_t cs_pid       Always set to 0.

     The ipinfo_t type is a version-agnostic representation of fields from an IP header.  Its
     fields are described in the dtrace_ip(4) manual page.

     The tcpsinfo_t type is used to provide a stable representation of TCP connection state.
     Some tcp probes, such as tcp:::accept-refused(), fire in a context where there is no TCP
     connection; this argument is NULL in that case.  Its fields are:

           uintptr_t tcps_addr  The address of the corresponding TCP control block.  This is
                                currently a pointer to a struct tcpcb.

           int tcps_local       A boolean indicating whether the connection is local to the host.
                                Currently unimplemented and always set to -1.

           int tcps_active      A boolean indicating whether the connection was initiated by the
                                local host.  Currently unimplemented and always set to -1.

           uint16_t tcps_lport  Local TCP port.

           uint16_t tcps_rport  Remote TCP port.

           string tcps_laddr    Local address.

           string tcps_raddr    Remote address.

           int32_t tcps_state   Current TCP state.  The valid TCP state values are given by the
                                constants prefixed with ‘TCPS_’ in /usr/lib/dtrace/tcp.d.

           uint32_t tcps_iss    Initial send sequence number.

           uint32_t tcps_suna   Initial sequence number of sent but unacknowledged data.

           uint32_t tcps_snxt   Next sequence number for send.

           uint32_t tcps_rack   Sequence number of received and acknowledged data.

           uint32_t tcps_rnxt   Next expected sequence number for receive.

           u_long tcps_swnd     TCP send window size.

           int32_t tcps_snd_ws  Window scaling factor for the TCP send window.

           u_long tcps_rwnd     TCP receive window size.

           int32_t tcps_rcv_ws  Window scaling factor for the TCP receive window.

           u_long tcps_cwnd     TCP congestion window size.

           u_long tcps_cwnd_ssthresh
                                Congestion window threshold at which slow start ends and
                                congestion avoidance begins.

           uint32_t tcps_sack_fack
                                Last sequence number selectively acknowledged by the receiver.

           uint32_t tcps_sack_snxt
                                Next selectively acknowledge sequence number at which to begin
                                retransmitting.

           uint32_t tcps_rto    Round-trip timeout, in milliseconds.

           uint32_t tcps_mss    Maximum segment size.

           int tcps_retransmit  A boolean indicating that the local sender is retransmitting
                                data.

           int tcps_srtt        Smoothed round-trip time.

     The tcpinfo_t type exposes the fields in a TCP segment header in host order.  Its fields
     are:

           uint16_t tcp_sport      Source TCP port.

           uint16_t tcp_dport      Destination TCP port.

           uint32_t tcp_seq        Sequence number.

           uint32_t tcp_ack        Acknowledgement number.

           uint8_t tcp_offset      Data offset, in bytes.

           uint8_t tcp_flags       TCP flags.

           uint16_t tcp_window     TCP window size.

           uint16_t tcp_checksum   Checksum.

           uint16_t tcp_urgent     Urgent data pointer.

           struct tcphdr *tcp_hdr  A pointer to the raw TCP header.

     The tcplsinfo_t type is used by the tcp:::state-change() probe to provide the from-state of
     a transition.  Its fields are:

           int32_t tcps_state  A TCP state.  The valid TCP state values are given by the
                               constants prefixed with ‘TCPS_’ in /usr/lib/dtrace/tcp.d.

FILES

     /usr/lib/dtrace/tcp.d  DTrace type and translator definitions for the tcp provider.

EXAMPLES

     The following script logs TCP segments in real time:

           #pragma D option quiet
           #pragma D option switchrate=10hz

           dtrace:::BEGIN
           {
                   printf(" %3s %15s:%-5s      %15s:%-5s %6s  %s\n", "CPU",
                       "LADDR", "LPORT", "RADDR", "RPORT", "BYTES", "FLAGS");
           }

           tcp:::send
           {
                   this->length = args[2]->ip_plength - args[4]->tcp_offset;
                   printf(" %3d %16s:%-5d -> %16s:%-5d %6d  (", cpu, args[2]->ip_saddr,
                       args[4]->tcp_sport, args[2]->ip_daddr, args[4]->tcp_dport,
                       this->length);
                   printf("%s", args[4]->tcp_flags & TH_FIN ? "FIN|" : "");
                   printf("%s", args[4]->tcp_flags & TH_SYN ? "SYN|" : "");
                   printf("%s", args[4]->tcp_flags & TH_RST ? "RST|" : "");
                   printf("%s", args[4]->tcp_flags & TH_PUSH ? "PUSH|" : "");
                   printf("%s", args[4]->tcp_flags & TH_ACK ? "ACK|" : "");
                   printf("%s", args[4]->tcp_flags & TH_URG ? "URG|" : "");
                   printf("\s", args[4]->tcp_flags == 0 ? "null " : "");
                   printf("n;
           }               "

           tcp:::receive
           {
                   this->length = args[2]->ip_plength - args[4]->tcp_offset;
                   printf(" %3d %16s:%-5d <- %16s:%-5d %6d  (", cpu,
                       args[2]->ip_daddr, args[4]->tcp_dport, args[2]->ip_saddr,
                       args[4]->tcp_sport, this->length);
                   printf("%s", args[4]->tcp_flags & TH_FIN ? "FIN|" : "");
                   printf("%s", args[4]->tcp_flags & TH_SYN ? "SYN|" : "");
                   printf("%s", args[4]->tcp_flags & TH_RST ? "RST|" : "");
                   printf("%s", args[4]->tcp_flags & TH_PUSH ? "PUSH|" : "");
                   printf("%s", args[4]->tcp_flags & TH_ACK ? "ACK|" : "");
                   printf("%s", args[4]->tcp_flags & TH_URG ? "URG|" : "");
                   printf("\s", args[4]->tcp_flags == 0 ? "null " : "");
                   printf("n;
           }               "
     The following script logs TCP connection state changes as they occur:

           #pragma D option quiet
           #pragma D option switchrate=25hz

           int last[int];

           dtrace:::BEGIN
           {
                   printf("   %12s %-20s    %-20s %s\n",
                       "DELTA(us)", "OLD", "NEW", "TIMESTAMP");
           }

           tcp:::state-change
           {
                   this->elapsed = (timestamp - last[args[1]->cs_cid]) / 1000;
                   printf("   %12d %-20s -> %-20s %d\n", this->elapsed,
                       tcp_state_string[args[5]->tcps_state],
                       tcp_state_string[args[3]->tcps_state], timestamp);
                   last[args[1]->cs_cid] = timestamp;
           }

           tcp:::state-change
           /last[args[1]->cs_cid] == 0/
           {
                   printf("   %12s %-20s -> %-20s %d\n", "-",
                       tcp_state_string[args[5]->tcps_state],
                       tcp_state_string[args[3]->tcps_state], timestamp);
                   last[args[1]->cs_cid] = timestamp;
           }

COMPATIBILITY

     This provider is compatible with the tcp provider in Solaris.

SEE ALSO

     dtrace(1), dtrace_ip(4), dtrace_sctp(4), dtrace_udp(4), dtrace_udplite(4), tcp(4), SDT(9)

HISTORY

     The tcp provider first appeared in FreeBSD 10.0.

AUTHORS

     This manual page was written by Mark Johnston <markj@FreeBSD.org>.

BUGS

     The tcps_local and tcps_active fields of tcpsinfo_t are not filled in by the translator.