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/bpf_helpers.h>
20 #include <bpf/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))) {
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";
72