Provided by: freebsd-manpages_12.2-1_all 
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.