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 load_sock_ops 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 #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_cong(struct bpf_sock_ops *skops)
  33 {
  34         char cong[] = "dctcp";
  35         int rv = 0;
  36         int op;
  37
  38         /* For testing purposes, only execute rest of BPF program
  39          * if neither port numberis 55601
  40          */
  41         if (bpf_ntohl(skops->remote_port) != 55601 &&
  42             skops->local_port != 55601)
  43                 return -1;
  44
  45         op = (int) skops->op;
  46
  47 #ifdef DEBUG
  48         bpf_printk("BPF command: %d\n", op);
  49 #endif
  50
  51         /* Check if both hosts are in the same datacenter. For this
  52          * example they are if the 1st 5.5 bytes in the IPv6 address
  53          * are the same.
  54          */
  55         if (skops->family == AF_INET6 &&
  56             skops->local_ip6[0] == skops->remote_ip6[0] &&
  57             (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
  58             (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
  59                 switch (op) {
  60                 case BPF_SOCK_OPS_NEEDS_ECN:
  61                         rv = 1;
  62                         break;
  63                 case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
  64                         rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
  65                                             cong, sizeof(cong));
  66                         break;
  67                 case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
  68                         rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
  69                                             cong, sizeof(cong));
  70                         break;
  71                 default:
  72                         rv = -1;
  73                 }
  74         } else {
  75                 rv = -1;
  76         }
  77 #ifdef DEBUG
  78         bpf_printk("Returning %d\n", rv);
  79 #endif
  80         skops->reply = rv;
  81         return 1;
  82 }
  83 char _license[] SEC("license") = "GPL";