Man page 9 : pskb_expand_head

pskb_expand_head - reallocate header of sk_buff

int pskb_expand_head(struct sk_buff *  skb , int  nhead , int  ntail , gfp_t  gfp_mask );

skb
    buffer to reallocate

nhead
    room to add at head

ntail
    room to add at tail

gfp_mask
    allocation priority

Expands (or creates identical copy, if nhead and ntail are zero) header of skb. sk_buff itself is not changed. sk_buff MUST have reference count of 1. Returns zero in the case of success or error, if expansion failed. In the last case, sk_buff is not changed.

All the pointers pointing into skb header may change and must be reloaded after call to this function.