DTRACE_SCTP(4)

💖 NAME 💖

okay bestie, welcome to DTRACE_SCTP — she lives in section 4 of the Kernel Interfaces Manual, and she is literally a DTrace provider for tracing all the events related to the sctp(4) protocol 🦋✨

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🌸 SYNOPSIS 🌸

here's the whole cast of probes, no skips, no cuts 👑

sctp:cwnd::init(uint32_t, uint32_t, uintptr_t, int, int);

sctp:cwnd::ack(uint32_t, uint32_t, uintptr_t, int, int);

sctp:cwnd::rttvar(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t);

sctp:cwnd::rttstep(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t);

sctp:cwnd::fr(uint32_t, uint32_t, uintptr_t, int, int);

sctp:cwnd::to(uint32_t, uint32_t, uintptr_t, int, int);

sctp:cwnd::bl(uint32_t, uint32_t, uintptr_t, int, int);

sctp:cwnd::ecn(uint32_t, uint32_t, uintptr_t, int, int);

sctp:cwnd::pd(uint32_t, uint32_t, uintptr_t, int, int);

sctp:rwnd:assoc:val(uint32_t, uint32_t, int, int);

sctp:flightsize:net:val(uint32_t, uint32_t, uintptr_t, int, int);

sctp:flightsize:assoc:val(uint32_t, uint32_t, int, int);

sctp:::receive(pktinfo_t *, csinfo_t *, ipinfo_t *, sctpsinfo_t *,
    sctpinfo_t *);

sctp:::send(pktinfo_t *, csinfo_t *, ipinfo_t *, sctpsinfo_t *,
    sctpinfo_t *);

sctp:::state-change(void *, csinfo_t *, void *, sctpsinfo_t *, void *,
    sctplsinfo_t *);

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✨ DESCRIPTION ✨

so the DTrace sctp provider lets you trace events inside the sctp(4) protocol implementation 💅 she's giving very much the same energy as the dtrace_ip(4) and dtrace_udp(4) providers, except she also serves up probes for protocol events that happen at a level way above plain packet reception and transmission. main character behavior fr fr 👑

the sctp:cwnd::() probes track changes in the congestion window on a netp. the sctp:rwnd::() probes track changes in the receiver window for an assoc. the sctp:flightsize:net:val() probe tracks changes in the flight size on a net or assoc, and the sctp:flightsize:assoc:val() probe provides the total flight version 🛫

the arguments of all sctp probes except for sctp:cwnd::rtt*() and sctp::assoc:val() are: the Vtag for this end, the port number of the local side, the pointer to struct sctp_nets *changing, the old value of the cwnd, and the new value of the cwnd 🌈

the arguments of sctp:::val() are similar to the above, except the fourth argument is the up/down amount 📈📉

the sctp:cwnd::rtt*() probe arguments are:

• a bitmap of Vtag << 32 | localport << 16 | remoteport
• a bitmap of obw | nbw
• a bitmap of bwrtt | newrtt
• flight
• and a bitmap of (cwnd << 32) | point << 16 | retval(0/1)

the sctp:cwnd::init() probe fires when a remotely-initiated active SCTP open succeeds 🎉 at that point the new connection is in the ESTABLISHED state, and the probe arguments expose the headers associated with the final ACK of the four-way handshake 🤝

the sctp:::send() and sctp:::receive() probes fire when the host sends or receives an SCTP packet, respectively. and just like with the dtrace_udp(4) provider, sctp probes fire only for packets sent by or to the local host — forwarded packets get handled in the IP layer and are only visible to the dtrace_ip(4) provider, no cap 🙈

the sctp:::state-change() probe fires upon local SCTP association 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]->sctps_state 👀

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🎀 FILES 🎀

• /usr/lib/dtrace/sctp.d — DTrace type and translator definitions for the sctp provider 💾

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🍓 EXAMPLES 🍓

a script that logs SCTP packets in real time 🕐:

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

dtrace:::BEGIN
{
        printf(" %3s %15s:%-5s      %15s:%-5s0, "CPU",
            "LADDR", "LPORT", "RADDR", "RPORT");
}

sctp:::send
{
        printf(" %3d %16s:%-5d -> %16s:%-5d0, cpu,
            args[2]->ip_saddr, args[4]->sctp_sport,
            args[2]->ip_daddr, args[4]->sctp_dport);
}

sctp:::receive
{
        printf(" %3d %16s:%-5d <- %16s:%-5d0, cpu,
            args[2]->ip_daddr, args[4]->sctp_dport,
            args[2]->ip_saddr, args[4]->sctp_sport);
}

a script that logs SCTP association state changes as they occur 🦋:

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

int last[int];

dtrace:::BEGIN
{
        printf(" %3s %12s  %-25s    %-25s0,
            "CPU", "DELTA(us)", "OLD", "NEW");
}

sctp:::state-change
/ last[args[1]->cs_cid] /
{
        this->elapsed = (timestamp - last[args[1]->cs_cid]) / 1000;
        printf(" %3d %12d  %-25s -> %-25s0, cpu, this->elapsed,
            sctp_state_string[args[5]->sctps_state],
            sctp_state_string[args[3]->sctps_state]);
        last[args[1]->cs_cid] = timestamp;
}

sctp:::state-change
/ last[args[1]->cs_cid] == 0 /
{
        printf(" %3d %12s  %-25s -> %-25s0, cpu, "-",
            sctp_state_string[args[5]->sctps_state],
            sctp_state_string[args[3]->sctps_state]);
        last[args[1]->cs_cid] = timestamp;
}

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💅 COMPATIBILITY 💅

the sctp:::send(), sctp:::receive(), and sctp:::state-change() probes are compatible with the sctp provider in Solaris ✨ all the other probes are only available in FreeBSD 🧊

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👑 SEE ALSO 👑

dtrace(1), dtrace_ip(4), dtrace_udp(4), dtrace_udplite(4), sctp(4), SDT(9)

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🌈 AUTHORS 🌈

this manual page was written by Devin Teske <dteske@FreeBSD.org> 🫶

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and that's the whole page bestie, you ate that 💖 this one shipped from Debian, dated August 22, 2018 — go trace some packets, ily, periodt 🎀✨