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 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_basertt(struct bpf_sock_ops *skops)
  33 {
  34         char cong[20];
  35         char nv[] = "nv";
  36         int rv = 0, n;
  37         int op;
  38
  39         op = (int) skops->op;
  40
  41 #ifdef DEBUG
  42         bpf_printk("BPF command: %d\n", op);
  43 #endif
  44
  45         /* Check if both hosts are in the same datacenter. For this
  46          * example they are if the 1st 5.5 bytes in the IPv6 address
  47          * are the same.
  48          */
  49         if (skops->family == AF_INET6 &&
  50             skops->local_ip6[0] == skops->remote_ip6[0] &&
  51             (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
  52             (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
  53                 switch (op) {
  54                 case BPF_SOCK_OPS_BASE_RTT:
  55                         n = bpf_getsockopt(skops, SOL_TCP, TCP_CONGESTION,
  56                                            cong, sizeof(cong));
  57                         if (!n && !__builtin_memcmp(cong, nv, sizeof(nv)+1)) {
  58                                 /* Set base_rtt to 80us */
  59                                 rv = 80;
  60                         } else if (n) {
  61                                 rv = n;
  62                         } else {
  63                                 rv = -1;
  64                         }
  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";