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:

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

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:

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

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

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(";
}

#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.