LXR linux/tools/testing/selftests/bpf/progs/test_xdp_adjust_tail

   1// SPDX-License-Identifier: GPL-2.0
   2/* Copyright (c) 2018 Facebook
   3 *
   4 * This program is free software; you can redistribute it and/or
   5 * modify it under the terms of version 2 of the GNU General Public
   6 * License as published by the Free Software Foundation.
   7 */
   8#include <linux/bpf.h>
   9#include <linux/if_ether.h>
  10#include <bpf/bpf_helpers.h>
  11
  12int _version SEC("version") = 1;
  13
  14SEC("xdp_adjust_tail_shrink")
  15int _xdp_adjust_tail_shrink(struct xdp_md *xdp)
  16{
  17        void *data_end = (void *)(long)xdp->data_end;
  18        void *data = (void *)(long)xdp->data;
  19        int offset = 0;
  20
  21        if (data_end - data == 54) /* sizeof(pkt_v4) */
  22                offset = 256; /* shrink too much */
  23        else
  24                offset = 20;
  25        if (bpf_xdp_adjust_tail(xdp, 0 - offset))
  26                return XDP_DROP;
  27        return XDP_TX;
  28}
  29
  30char _license[] SEC("license") = "GPL";
  31