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"; 72