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 initial receive window to 40 packets when using IPv6
8 * and the first 5.5 bytes of the IPv6 addresses are not the same (in this
9 * example that means both hosts are not 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_helpers.h"
20 #include "bpf_endian.h"
21
22 #define DEBUG 1
23
24 SEC("sockops")
25 int bpf_rwnd(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) !=
34 55601 && 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 RWND_INIT operation and IPv6 addresses */
46 if (op == BPF_SOCK_OPS_RWND_INIT &&
47 skops->family == AF_INET6) {
48
49 /* If the first 5.5 bytes of the IPv6 address are not the same
50 * then both hosts are not in the same datacenter
51 * so use a larger initial advertized window (40 packets)
52 */
53 if (skops->local_ip6[0] != skops->remote_ip6[0] ||
54 (bpf_ntohl(skops->local_ip6[1]) & 0xfffff000) !=
55 (bpf_ntohl(skops->remote_ip6[1]) & 0xfffff000))
56 rv = 40;
57 }
58 #ifdef DEBUG
59 bpf_printk("Returning %d\n", rv);
60 #endif
61 skops->reply = rv;
62 return 1;
63 }
64 char _license[] SEC("license") = "GPL";