// SPDX-License-Identifier: GPL-2.0
/*
 * 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>

int _version SEC("version") = 1;

SEC("xdp.frags")
int xdp_adjust_frags(struct xdp_md *xdp)
{
        __u8 *data_end = (void *)(long)xdp->data_end;
        __u8 *data = (void *)(long)xdp->data;
        __u8 val[16] = {};
        __u32 offset;
        int err;

        if (data + sizeof(__u32) > data_end)
                return XDP_DROP;

        offset = *(__u32 *)data;
        err = bpf_xdp_load_bytes(xdp, offset, val, sizeof(val));
        if (err < 0)
                return XDP_DROP;

        if (val[0] != 0xaa || val[15] != 0xaa) /* marker */
                return XDP_DROP;

        val[0] = 0xbb; /* update the marker */
        val[15] = 0xbb;
        err = bpf_xdp_store_bytes(xdp, offset, val, sizeof(val));
        if (err < 0)
                return XDP_DROP;

        return XDP_PASS;
}

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