MAX_PNPIPE_HEADER
skb = sock_alloc_send_skb(sk, MAX_PNPIPE_HEADER + len,
rskb = alloc_skb(MAX_PNPIPE_HEADER, GFP_ATOMIC);
struct sk_buff *skb = alloc_skb(MAX_PNPIPE_HEADER + len, priority);
skb_reserve(skb, MAX_PNPIPE_HEADER);