[lwip-users] network driver code for ethernetif.c

[V l]

I studied through my network interface driver and gained sufficient understanding of the network stack. 
I have ported lwip to the ARM device and now in stage of writing the ethernetif.c file to interface with my network driver . 
I know now that I have to just replace 

for(q = p; q != NULL; q = q->next) {
    /* Send the data from the pbuf to the interface, one pbuf at a
       time. The size of the data in each pbuf is kept in the ->len
       variable. */
    send data from(q->payload, q->len);
  }


send data from(q->payload, q->len); with my driver specific code to send the packet . Very nice ! But when I compile this code , its going to ask where this driver specific senddata is defined , the header file or library . 
How do I resolve this part of the riddle . Its a little newbie kind of question . But I have tried , I give up now. Plz help.
Regards
Sraddha