struct sk_buff *alloc_skb (unsigned int size, int priority);
void skb_reserve (struct sk_buff *skb, unsigned int len);
int skb_headroom (const struct sk_buff *skb);
int skb_tailroom (const struct sk_buff *skb);

unsigned char *skb_put (struct sk_buff *skb, unsigned int len);
unsigned char *skb_push (struct sk_buff *skb, unsigned int len);

unsigned char *skb_pull (struct sk_buff *skb, unsigned int len);
void skb_trim (struct sk_buff *skb, unsigned int len);