samples/bpf/tcp_rwnd_kern.c

   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
  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";