SKB_COW(9)

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.