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 base_rtt to 80us when host is running TCP-NV and
8 * both hosts are in the same datacenter (as determined 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_helpers.h"
20 #include "bpf_endian.h"
21
22 #define DEBUG 1
23
24 SEC("sockops")
25 int bpf_basertt(struct bpf_sock_ops *skops)
26 {
27 char cong[20];
28 char nv[] = "nv";
29 int rv = 0, n;
30 int op;
31
32 op = (int) skops->op;
33
34 #ifdef DEBUG
35 bpf_printk("BPF command: %d\n", op);
36 #endif
37
38 /* Check if both hosts are in the same datacenter. For this
39 * example they are if the 1st 5.5 bytes in the IPv6 address
40 * are the same.
41 */
42 if (skops->family == AF_INET6 &&
43 skops->local_ip6[0] == skops->remote_ip6[0] &&
44 (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
45 (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
46 switch (op) {
47 case BPF_SOCK_OPS_BASE_RTT:
48 n = bpf_getsockopt(skops, SOL_TCP, TCP_CONGESTION,
49 cong, sizeof(cong));
50 if (!n && !__builtin_memcmp(cong, nv, sizeof(nv)+1)) {
51 /* Set base_rtt to 80us */
52 rv = 80;
53 } else if (n) {
54 rv = n;
55 } else {
56 rv = -1;
57 }
58 break;
59 default:
60 rv = -1;
61 }
62 } else {
63 rv = -1;
64 }
65 #ifdef DEBUG
66 bpf_printk("Returning %d\n", rv);
67 #endif
68 skops->reply = rv;
69 return 1;
70 }
71 char _license[] SEC("license") = "GPL";