1/* Copyright (c) 2017 Facebook
2 *
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
6 *
7 * BPF program to set SYN and SYN-ACK RTOs to 10ms when using IPv6 addresses
8 * and the first 5.5 bytes of the IPv6 addresses are the same (in this example
9 * that means both hosts are in the same datacenter).
10 *
11 * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
12 */
13
14#include <uapi/linux/bpf.h>
15#include <uapi/linux/if_ether.h>
16#include <uapi/linux/if_packet.h>
17#include <uapi/linux/ip.h>
18#include <linux/socket.h>
19#include <bpf/bpf_helpers.h>
20#include <bpf/bpf_endian.h>
21
22#define DEBUG 1
23
24SEC("sockops")
25int bpf_synrto(struct bpf_sock_ops *skops)
26{
27	int rv = -1;
28	int op;
29
30	/* For testing purposes, only execute rest of BPF program
31	 * if neither port numberis 55601
32	 */
33	if (bpf_ntohl(skops->remote_port) != 55601 &&
34	    skops->local_port != 55601) {
35		skops->reply = -1;
36		return 1;
37	}
38
39	op = (int) skops->op;
40
41#ifdef DEBUG
42	bpf_printk("BPF command: %d\n", op);
43#endif
44
45	/* Check for TIMEOUT_INIT operation and IPv6 addresses */
46	if (op == BPF_SOCK_OPS_TIMEOUT_INIT &&
47		skops->family == AF_INET6) {
48
49		/* If the first 5.5 bytes of the IPv6 address are the same
50		 * then both hosts are in the same datacenter
51		 * so use an RTO of 10ms
52		 */
53		if (skops->local_ip6[0] == skops->remote_ip6[0] &&
54		    (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
55		    (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000))
56			rv = 10;
57	}
58#ifdef DEBUG
59	bpf_printk("Returning %d\n", rv);
60#endif
61	skops->reply = rv;
62	return 1;
63}
64char _license[] SEC("license") = "GPL";
65