53 lines · c
1// SPDX-License-Identifier: GPL-2.02/* Copyright (c) 2018 Facebook3 *4 * This program is free software; you can redistribute it and/or5 * modify it under the terms of version 2 of the GNU General Public6 * 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 12SEC("xdp")13int _xdp_adjust_tail_shrink(struct xdp_md *xdp)14{15 __u8 *data_end = (void *)(long)xdp->data_end;16 __u8 *data = (void *)(long)xdp->data;17 int offset = 0;18 19 switch (bpf_xdp_get_buff_len(xdp)) {20 case 54:21 /* sizeof(pkt_v4) */22 offset = 256; /* shrink too much */23 break;24 case 9000:25 /* non-linear buff test cases */26 if (data + 1 > data_end)27 return XDP_DROP;28 29 switch (data[0]) {30 case 0:31 offset = 10;32 break;33 case 1:34 offset = 4100;35 break;36 case 2:37 offset = 8200;38 break;39 default:40 return XDP_DROP;41 }42 break;43 default:44 offset = 20;45 break;46 }47 if (bpf_xdp_adjust_tail(xdp, 0 - offset))48 return XDP_DROP;49 return XDP_TX;50}51 52char _license[] SEC("license") = "GPL";53