#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/in.h>

	//Partie offset header en commentaire pour économiser les bytes sur la mémoire réservée pour le Kernel
	/*
	const unsigned short macLen = 6;	//2bytes
	const unsigned short macSrc = macLen;	//2bytes
	const unsigned short macDest = macLen;	//2bytes
	const unsigned short pktType =2;	//2bytes
	const unsigned short ethHead = macSrc+macDest+pktType; //=14

	//Partie offet IP
	const unsigned short iPVersionAndHeaderLen = 1;
	const unsigned short DSF = 1;
	const unsigned short totalLen = 2;
	const unsigned short id = 2;
	const unsigned short offsetIP = iPVersionAndHeaderLen + DSF + totalLen + id; //=6

	const unsigned short DF_offset = offsetIP + ethHead; //=20
	*/



SEC("xdp_udp")
int xdp_udp_func(struct xdp_md *ctx)
{
	void *data_end = (void *)(long)ctx->data_end;
	void *data = (void *)(long)ctx->data;

	struct ethhdr *eth = data; //structure ethernet from if_ether.h

	// Check that our packet ethernet headers is big enough, ie. at least the size of Ethernet's fixed headers
	if((void*)(eth + 1) > data_end) {
		return XDP_PASS;
	}

	// Check that the ethernet header declares an IPv4 packet
	if(eth->h_proto == bpf_htons(ETH_P_IP)) {
		struct iphdr *ip = (struct iphdr*)(eth + 1);
		// Check that the IP packet is big enough, ie. at least the size of IP's fixed headers
		if((void*)(ip + 1) > data_end) {
			return XDP_PASS;
		}

		if(ip->protocol == IPPROTO_UDP) {
			ip->frag_off |= 0x4000; //Set the DF flag to 1 -> 0b 0100 0000 0000 0000
		}
	}


	return XDP_PASS;
}