samples/bpf/tcp_basertt_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 base_rtt to 80us when host is running TCP-NV and
   8  * both hosts are in the same datacenter (as determined by IPv6 prefix).
   9  *
  10  * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
  11  */
  12
  13 #include <uapi/linux/bpf.h>
  14 #include <uapi/linux/tcp.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 SEC("sockops")
  25 int bpf_basertt(struct bpf_sock_ops *skops)
  26 {
  27         char cong[20];
  28         char nv[] = "nv";
  29         int rv = 0, n;
  30         int op;
  31
  32         op = (int) skops->op;
  33
  34 #ifdef DEBUG
  35         bpf_printk("BPF command: %d\n", op);
  36 #endif
  37
  38         /* Check if both hosts are in the same datacenter. For this
  39          * example they are if the 1st 5.5 bytes in the IPv6 address
  40          * are the same.
  41          */
  42         if (skops->family == AF_INET6 &&
  43             skops->local_ip6[0] == skops->remote_ip6[0] &&
  44             (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
  45             (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
  46                 switch (op) {
  47                 case BPF_SOCK_OPS_BASE_RTT:
  48                         n = bpf_getsockopt(skops, SOL_TCP, TCP_CONGESTION,
  49                                            cong, sizeof(cong));
  50                         if (!n && !__builtin_memcmp(cong, nv, sizeof(nv)+1)) {
  51                                 /* Set base_rtt to 80us */
  52                                 rv = 80;
  53                         } else if (n) {
  54                                 rv = n;
  55                         } else {
  56                                 rv = -1;
  57                         }
  58                         break;
  59                 default:
  60                         rv = -1;
  61                 }
  62         } else {
  63                 rv = -1;
  64         }
  65 #ifdef DEBUG
  66         bpf_printk("Returning %d\n", rv);
  67 #endif
  68         skops->reply = rv;
  69         return 1;
  70 }
  71 char _license[] SEC("license") = "GPL";