patches and low-level development discussion

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 /* SPDX-License-Identifier: (GPL-2.0-or-later OR BSD-2-clause) */
/* SPDX-FileCopyrightText: 2021 The xdp-tutorial Authors */
/* SPDX-FileCopyrightText: 2025 Yureka Lilian <yureka@cyberchaos.dev> */
/* Based on  https://github.com/xdp-project/xdp-tutorial/blob/main/common/parsing_helpers.h */

#ifndef __PARSING_HELPERS_H
#define __PARSING_HELPERS_H

#include <bpf/bpf_endian.h>

//#include <linux/if_ether.h>
#define ETH_P_8021Q     0x8100          /* 802.1Q VLAN Extended Header  */
#define ETH_P_8021AD    0x88A8          /* 802.1ad Service VLAN		*/

static __always_inline int proto_is_vlan(__u16 h_proto)
{
	return !!(h_proto == bpf_htons(ETH_P_8021Q) ||
	          h_proto == bpf_htons(ETH_P_8021AD));
}

static __always_inline int parse_ethhdr(struct xdp_md *ctx,
                                        struct ethhdr **ethhdr)
{
	void *data_end = (void *)(long)ctx->data_end;
	struct ethhdr *eth = (void *) (long) ctx->data;

	/* Byte-count bounds check; check if current pointer + size of header
	 * is after data_end.
	 */
	if ((void *) (eth + 1) > data_end)
		return -1;

	*ethhdr = eth;

	return eth->h_proto; /* network-byte-order */
}

#endif