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1/* Copyright (c) 2017 Facebook2 *3 * This program is free software; you can redistribute it and/or4 * modify it under the terms of version 2 of the GNU General Public5 * License as published by the Free Software Foundation.6 *7 * BPF program to set base_rtt to 80us when host is running TCP-NV and8 * 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 123 24SEC("sockops")25int 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 DEBUG35 bpf_printk("BPF command: %d\n", op);36#endif37 38 /* Check if both hosts are in the same datacenter. For this39 * example they are if the 1st 5.5 bytes in the IPv6 address40 * 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 DEBUG66 bpf_printk("Returning %d\n", rv);67#endif68 skops->reply = rv;69 return 1;70}71char _license[] SEC("license") = "GPL";72