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 load_sock_ops 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 #define bpf_printk(fmt, ...) \ 25 ({ \ 26 char ____fmt[] = fmt; \ 27 bpf_trace_printk(____fmt, sizeof(____fmt), \ 28 ##__VA_ARGS__); \ 29 }) 30 31 SEC("sockops") 32 int bpf_rwnd(struct bpf_sock_ops *skops) 33 { 34 int rv = -1; 35 int op; 36 37 /* For testing purposes, only execute rest of BPF program 38 * if neither port numberis 55601 39 */ 40 if (bpf_ntohl(skops->remote_port) != 41 55601 && skops->local_port != 55601) 42 return -1; 43 44 op = (int) skops->op; 45 46 #ifdef DEBUG 47 bpf_printk("BPF command: %d\n", op); 48 #endif 49 50 /* Check for RWND_INIT operation and IPv6 addresses */ 51 if (op == BPF_SOCK_OPS_RWND_INIT && 52 skops->family == AF_INET6) { 53 54 /* If the first 5.5 bytes of the IPv6 address are not the same 55 * then both hosts are not in the same datacenter 56 * so use a larger initial advertized window (40 packets) 57 */ 58 if (skops->local_ip6[0] != skops->remote_ip6[0] || 59 (bpf_ntohl(skops->local_ip6[1]) & 0xfffff000) != 60 (bpf_ntohl(skops->remote_ip6[1]) & 0xfffff000)) 61 rv = 40; 62 } 63 #ifdef DEBUG 64 bpf_printk("Returning %d\n", rv); 65 #endif 66 skops->reply = rv; 67 return 1; 68 } 69 char _license[] SEC("license") = "GPL"; 70