tcpretrans.bt

#!/usr/bin/env bpftrace
/*
 * tcpretrans.bt Trace or count TCP retransmits
 *               For Linux, uses bpftrace and eBPF.
 *
 * USAGE: tcpretrans.bt
 *
 * This is a bpftrace version of the bcc tool of the same name.
 * It is limited to ipv4 addresses, and doesn't support tracking TLPs.
 *
 * This uses dynamic tracing of kernel functions, and will need to be updated
 * to match kernel changes.
 *
 * Copyright (c) 2018 Dale Hamel.
 * Licensed under the Apache License, Version 2.0 (the "License")
 *
 * 23-Nov-2018  Dale Hamel      created this.
 */

#ifndef BPFTRACE_HAVE_BTF
#include <linux/socket.h>
#include <net/sock.h>
#else
#include <sys/socket.h>
#endif

BEGIN
{
	printf("Tracing tcp retransmits. Hit Ctrl-C to end.\n");
	printf("%-8s %-8s %20s %21s %6s\n", "TIME", "PID", "LADDR:LPORT",
	    "RADDR:RPORT", "STATE");

	// See include/net/tcp_states.h:
	@tcp_states[1] = "ESTABLISHED";
	@tcp_states[2] = "SYN_SENT";
	@tcp_states[3] = "SYN_RECV";
	@tcp_states[4] = "FIN_WAIT1";
	@tcp_states[5] = "FIN_WAIT2";
	@tcp_states[6] = "TIME_WAIT";
	@tcp_states[7] = "CLOSE";
	@tcp_states[8] = "CLOSE_WAIT";
	@tcp_states[9] = "LAST_ACK";
	@tcp_states[10] = "LISTEN";
	@tcp_states[11] = "CLOSING";
	@tcp_states[12] = "NEW_SYN_RECV";
}

kprobe:tcp_retransmit_skb
{
	$sk = (struct sock *)arg0;
	$inet_family = $sk->__sk_common.skc_family;

	if ($inet_family == AF_INET || $inet_family == AF_INET6) {
		// initialize variable type:
		$daddr = ntop(0);
		$saddr = ntop(0);
		if ($inet_family == AF_INET) {
			$daddr = ntop($sk->__sk_common.skc_daddr);
			$saddr = ntop($sk->__sk_common.skc_rcv_saddr);
		} else {
			$daddr = ntop(
			    $sk->__sk_common.skc_v6_daddr.in6_u.u6_addr8);
			$saddr = ntop(
			    $sk->__sk_common.skc_v6_rcv_saddr.in6_u.u6_addr8);
		}
		$lport = $sk->__sk_common.skc_num;
		$dport = $sk->__sk_common.skc_dport;

		// Destination port is big endian, it must be flipped
		$dport = bswap($dport);

		$state = $sk->__sk_common.skc_state;
		$statestr = @tcp_states[$state];

		time("%H:%M:%S ");
		printf("%-8d %14s:%-6d %14s:%-6d %6s\n", pid, $saddr, $lport,
		    $daddr, $dport, $statestr);
	}
}

END
{
	clear(@tcp_states);
}