/* Copyright (c) 2017 Facebook * * This program is free software; you can redistribute it and/or * modify it under the terms of version 2 of the GNU General Public * License as published by the Free Software Foundation. * * BPF program to set base_rtt to 80us when host is running TCP-NV and * both hosts are in the same datacenter (as determined by IPv6 prefix). * * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program. */ #include <uapi/linux/bpf.h> #include <uapi/linux/tcp.h> #include <uapi/linux/if_ether.h> #include <uapi/linux/if_packet.h> #include <uapi/linux/ip.h> #include <linux/socket.h> #include <bpf/bpf_helpers.h> #include <bpf/bpf_endian.h> #define DEBUG 1 SEC("sockops") int bpf_basertt(struct bpf_sock_ops *skops) { char cong[20]; char nv[] = "nv"; int rv = 0, n; int op; op = (int) skops->op; #ifdef DEBUG bpf_printk("BPF command: %d\n", op); #endif /* Check if both hosts are in the same datacenter. For this * example they are if the 1st 5.5 bytes in the IPv6 address * are the same. */ if (skops->family == AF_INET6 && skops->local_ip6[0] == skops->remote_ip6[0] && (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) == (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) { switch (op) { case BPF_SOCK_OPS_BASE_RTT: n = bpf_getsockopt(skops, SOL_TCP, TCP_CONGESTION, cong, sizeof(cong)); if (!n && !__builtin_memcmp(cong, nv, sizeof(nv))) { /* Set base_rtt to 80us */ rv = 80; } else if (n) { rv = n; } else { rv = -1; } break; default: rv = -1; } } else { rv = -1; } #ifdef DEBUG bpf_printk("Returning %d\n", rv); #endif skops->reply = rv; return 1; } char _license[] SEC("license") = "GPL";