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 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";