TripleCross/src/include/xdp/xdp_helper.h

#ifndef __XDP_HELPER_H__
#define __XDP_HELPER_H__

#include <bpf/bpf_helpers.h>

#include "packet/protocol/ip_helper.h"
#include "packet/protocol/tcp_helper.h"
#include "packet/packet_manager.h"

static struct expand_return{
    int code;
    struct xdp_md ret_md;
    void *data;
    void *data_end;
    struct ethhdr eth;
    struct iphdr ip;
    struct tcphdr tcp;
}expand_return;

/**
* Increases the packet payload reserved size by more_bytes bytes
* @param ctx XDP hook metadata
* @param eth start of ethernet header. Points inside ctx struct
* @param ip start of internet protocol header. Points inside ctx struct
* @param tcp start of tcp header. Points inside ctx struct
* @param more_bytes Number bytes to add
* @param
*/
static __always_inline struct expand_return expand_tcp_packet_payload(struct xdp_md *ctx, struct ethhdr *eth, struct iphdr *ip, struct tcphdr *tcp, int more_bytes){
    //We might be able to reuse some data from old headers,
    //but we will have to recompute checksums still
    struct ethhdr eth_copy;
    struct iphdr ip_copy;
    struct tcphdr tcp_copy;
    
    struct expand_return ret;

    //Copy the header for later before expanding ctx
    __builtin_memcpy(&eth_copy, eth, sizeof(struct ethhdr));
    __builtin_memcpy(&ip_copy, ip, sizeof(struct iphdr));
    __builtin_memcpy(&tcp_copy, tcp, sizeof(struct tcphdr));

    if (bpf_xdp_adjust_tail(ctx, (int)(sizeof(char)*more_bytes)) != 0)
    {
        //Failed to expand
        bpf_printk("Failed to expand a tcp packet reserved bytes by %i\n", more_bytes);
        ret.code = -1;//The rest is undefined
        return ret; 
    }

    //We now have to readjust the packet headers, checksums have changed
    //Note that we do not care about ctx->data_meta or any other extra field 
    //since we will not be using any communication here
    __builtin_memcpy(&(ret.eth), &eth_copy, sizeof(struct ethhdr));
    __builtin_memcpy(&(ret.ip), &ip_copy, sizeof(struct iphdr));
    __builtin_memcpy(&(ret.tcp), &tcp_copy, sizeof(struct tcphdr));  
    

    ret.ret_md = *ctx;
    ret.code = 0;
    ret.data = (void *)(long)ctx->data;
    ret.data_end = (void *)(long)ctx->data_end;
    return ret;
}

#endif