// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2018 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <bpf/bpf_helpers.h>

SEC("xdp")
int _xdp_adjust_tail_shrink(struct xdp_md *xdp)
{
        __u8 *data_end = (void *)(long)xdp->data_end;
        __u8 *data = (void *)(long)xdp->data;
        int offset = 0;

        switch (bpf_xdp_get_buff_len(xdp)) {
        case 54:
                /* sizeof(pkt_v4) */
                offset = 256; /* shrink too much */
                break;
        case 9000:
                /* non-linear buff test cases */
                if (data + 1 > data_end)
                        return XDP_DROP;

                switch (data[0]) {
                case 0:
                        offset = 10;
                        break;
                case 1:
                        offset = 4100;
                        break;
                case 2:
                        offset = 8200;
                        break;
                default:
                        return XDP_DROP;
                }
                break;
        default:
                offset = 20;
                break;
        }
        if (bpf_xdp_adjust_tail(xdp, 0 - offset))
                return XDP_DROP;
        return XDP_TX;
}

char _license[] SEC("license") = "GPL";