samples/bpf/tcp_cong_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 congestion control to dctcp when both hosts are
   8  * in the same datacenter (as deteremined 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/bpf_helpers.h>
  20 #include <bpf/bpf_endian.h>
  21
  22 #define DEBUG 1
  23
  24 SEC("sockops")
  25 int bpf_cong(struct bpf_sock_ops *skops)
  26 {
  27         char cong[] = "dctcp";
  28         int rv = 0;
  29         int op;
  30
  31         /* For testing purposes, only execute rest of BPF program
  32          * if neither port numberis 55601
  33          */
  34         if (bpf_ntohl(skops->remote_port) != 55601 &&
  35             skops->local_port != 55601) {
  36                 skops->reply = -1;
  37                 return 1;
  38         }
  39
  40         op = (int) skops->op;
  41
  42 #ifdef DEBUG
  43         bpf_printk("BPF command: %d\n", op);
  44 #endif
  45
  46         /* Check if both hosts are in the same datacenter. For this
  47          * example they are if the 1st 5.5 bytes in the IPv6 address
  48          * are the same.
  49          */
  50         if (skops->family == AF_INET6 &&
  51             skops->local_ip6[0] == skops->remote_ip6[0] &&
  52             (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
  53             (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
  54                 switch (op) {
  55                 case BPF_SOCK_OPS_NEEDS_ECN:
  56                         rv = 1;
  57                         break;
  58                 case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
  59                         rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
  60                                             cong, sizeof(cong));
  61                         break;
  62                 case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
  63                         rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
  64                                             cong, sizeof(cong));
  65                         break;
  66                 default:
  67                         rv = -1;
  68                 }
  69         } else {
  70                 rv = -1;
  71         }
  72 #ifdef DEBUG
  73         bpf_printk("Returning %d\n", rv);
  74 #endif
  75         skops->reply = rv;
  76         return 1;
  77 }
  78 char _license[] SEC("license") = "GPL";