DTRACE_TCP(4) FreeBSD Kernel Interfaces Manual DTRACE_TCP(4)
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(";
}
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(";
}
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.
FreeBSD 13.1-RELEASE-p6 August 1, 2018 FreeBSD 13.1-RELEASE-p6
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