more questions on skbuff allocation

["bunty " <bunty123_4@rediffmail.com>]

hi,
         After reading some internet documents and kernel source code i am confused about following things on sk_buff structure:-
       1)I want to know where are actaully packet layer headers are stored by sk_buff structure? i got some diagrams that tells that area between data and tail contains compelete packet.then what is stored between skb->head and skb->data area?
        2) what exactly skb_put does?
        3) which functions very first takes data from application layer and store in skbuff?
        4) Is there any main alloc_skb call that allocates total length skb buffer for whole packet?

regards,
parag.