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_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
  31SEC("sockops")
  32int 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                skops->reply = -1;
  43                return 1;
  44        }
  45
  46        op = (int) skops->op;
  47
  48#ifdef DEBUG
  49        bpf_printk("BPF command: %d\n", op);
  50#endif
  51
  52        /* Check for RWND_INIT operation and IPv6 addresses */
  53        if (op == BPF_SOCK_OPS_RWND_INIT &&
  54                skops->family == AF_INET6) {
  55
  56                /* If the first 5.5 bytes of the IPv6 address are not the same
  57                 * then both hosts are not in the same datacenter
  58                 * so use a larger initial advertized window (40 packets)
  59                 */
  60                if (skops->local_ip6[0] != skops->remote_ip6[0] ||
  61                    (bpf_ntohl(skops->local_ip6[1]) & 0xfffff000) !=
  62                    (bpf_ntohl(skops->remote_ip6[1]) & 0xfffff000))
  63                        rv = 40;
  64        }
  65#ifdef DEBUG
  66        bpf_printk("Returning %d\n", rv);
  67#endif
  68        skops->reply = rv;
  69        return 1;
  70}
  71char _license[] SEC("license") = "GPL";
  72