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"; 65