if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) return 0; 
static int udp_encap_rcv(struct sock * sk, struct sk_buff *skb){#ifndef CONFIG_XFRM	return 1; #else	struct udp_sock *up = udp_sk(sk);  	struct udphdr *uh = skb->h.uh;	struct iphdr *iph;	int iphlen, len;  	__u8 *udpdata = (__u8 *)uh + sizeof(struct udphdr);	__u32 *udpdata32 = (__u32 *)udpdata;	__u16 encap_type = up->encap_type;	/* if we're overly short, let UDP handle it */	if (udpdata > skb->tail)		return 1;	/* if this is not encapsulated socket, then just return now */	if (!encap_type)		return 1;	len = skb->tail - udpdata;	switch (encap_type) {	default:	case UDP_ENCAP_ESPINUDP:		/* Check if this is a keepalive packet.  If so, eat it. */		if (len == 1 && udpdata[0] == 0xff) {			return 0;		} else if (len > sizeof(struct ip_esp_hdr) && udpdata32[0] != 0 ) {			/* ESP Packet without Non-ESP header */			len = sizeof(struct udphdr);		} else			/* Must be an IKE packet.. pass it through */			return 1;		break;	case UDP_ENCAP_ESPINUDP_NON_IKE:		/* Check if this is a keepalive packet.  If so, eat it. */		if (len == 1 && udpdata[0] == 0xff) {			return 0;		} else if (len > 2 * sizeof(u32) + sizeof(struct ip_esp_hdr) &&			   udpdata32[0] == 0 && udpdata32[1] == 0) {						/* ESP Packet with Non-IKE marker */			len = sizeof(struct udphdr) + 2 * sizeof(u32);		} else			/* Must be an IKE packet.. pass it through */			return 1;		break;	}	/* At this point we are sure that this is an ESPinUDP packet,	 * so we need to remove 'len' bytes from the packet (the UDP	 * header and optional ESP marker bytes) and then modify the	 * protocol to ESP, and then call into the transform receiver.	 */	/* Now we can update and verify the packet length... */	iph = skb->nh.iph;	iphlen = iph->ihl << 2;	iph->tot_len = htons(ntohs(iph->tot_len) - len);	if (skb->len < iphlen + len) {		/* packet is too small!?! */		return 0;	}	/* pull the data buffer up to the ESP header and set the	 * transport header to point to ESP.  Keep UDP on the stack	 * for later.	 */	skb->h.raw = skb_pull(skb, len);	/* modify the protocol (it's ESP!) */	iph->protocol = IPPROTO_ESP;	/* and let the caller know to send this into the ESP processor... */	return -1;#endif}
4520	/local/tlutelli/issta_data/temp/c/2005_temp/2005/4520/4d78b6c78ae6d87e4c1c8072f42efa716f04afb9/udp.c/clean/net/ipv4/udp.c