LXR linux/samples/bpf/tcp_rwnd

   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/bpf_helpers.h>
  20#include <bpf/bpf_endian.h>
  21
  22#define DEBUG 1
  23
  24SEC("sockops")
  25int 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}
  64char _license[] SEC("license") = "GPL";
  65