Name
skb_cow — 
     copy header of skb when it is required
 
Synopsis
| int skb_cow ( | struct sk_buff * skb, | 
|  | unsigned int headroom ); | 
 
Arguments
- skb
- 
     buffer to cow
     
- headroom
- 
     needed headroom
     
Description
   If the skb passed lacks sufficient headroom or its data part
   is shared, data is reallocated. If reallocation fails, an error
   is returned and original skb is not changed.
   
   The result is skb with writable area skb->head...skb->tail
   and at least headroom of space at head.