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 congestion control to dctcp when both hosts are
8 * in the same datacenter (as deteremined by IPv6 prefix).
9 *
10 * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
11 */
12
13#include <uapi/linux/bpf.h>
14#include <uapi/linux/tcp.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_cong(struct bpf_sock_ops *skops)
26{
27	char cong[] = "dctcp";
28	int rv = 0;
29	int op;
30
31	/* For testing purposes, only execute rest of BPF program
32	 * if neither port numberis 55601
33	 */
34	if (bpf_ntohl(skops->remote_port) != 55601 &&
35	    skops->local_port != 55601) {
36		skops->reply = -1;
37		return 1;
38	}
39
40	op = (int) skops->op;
41
42#ifdef DEBUG
43	bpf_printk("BPF command: %d\n", op);
44#endif
45
46	/* Check if both hosts are in the same datacenter. For this
47	 * example they are if the 1st 5.5 bytes in the IPv6 address
48	 * are the same.
49	 */
50	if (skops->family == AF_INET6 &&
51	    skops->local_ip6[0] == skops->remote_ip6[0] &&
52	    (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
53	    (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
54		switch (op) {
55		case BPF_SOCK_OPS_NEEDS_ECN:
56			rv = 1;
57			break;
58		case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
59			rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
60					    cong, sizeof(cong));
61			break;
62		case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
63			rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
64					    cong, sizeof(cong));
65			break;
66		default:
67			rv = -1;
68		}
69	} else {
70		rv = -1;
71	}
72#ifdef DEBUG
73	bpf_printk("Returning %d\n", rv);
74#endif
75	skops->reply = rv;
76	return 1;
77}
78char _license[] SEC("license") = "GPL";
79