text: /*
   *	Definitions for the UDP-Lite (RFC 3828) code.
   */
  #ifndef _UDPLITE_H
  #define _UDPLITE_H
  
  #include <net/ip6_checksum.h>
  
  /* UDP-Lite socket options */
  #define UDPLITE_SEND_CSCOV   10 /* sender partial coverage (as sent)      */
  #define UDPLITE_RECV_CSCOV   11 /* receiver partial coverage (threshold ) */
  
  extern struct proto 		udplite_prot;
  extern struct udp_table		udplite_table;
  
  /*
   *	Checksum computation is all in software, hence simpler getfrag.
   */
  static __inline__ int udplite_getfrag(void *from, char *to, int  offset,
  				      int len, int odd, struct sk_buff *skb)
  {
  	struct msghdr *msg = from;
  	return copy_from_iter_full(to, len, &msg->msg_iter) ? 0 : -EFAULT;
  }
  
  /* Designate sk as UDP-Lite socket */
  static inline int udplite_sk_init(struct sock *sk)
  {
  	udp_init_sock(sk);
  	udp_sk(sk)->pcflag = UDPLITE_BIT;
  	return 0;
  }
  
  /*
   * 	Checksumming routines
   */
  static inline int udplite_checksum_init(struct sk_buff *skb, struct udphdr *uh)
  {
  	u16 cscov;
  
          /* In UDPv4 a zero checksum means that the transmitter generated no
           * checksum. UDP-Lite (like IPv6) mandates checksums, hence packets
           * with a zero checksum field are illegal.                            */
  	if (uh->check == 0) {
  		net_dbg_ratelimited("UDPLite: zeroed checksum field\n");
  		return 1;
  	}
  
  	cscov = ntohs(uh->len);
  
  	if (cscov == 0)		 /* Indicates that full coverage is required. */
  		;
  	else if (cscov < 8  || cscov > skb->len) {
  		/*
  		 * Coverage length violates RFC 3828: log and discard silently.
  		 */
  		net_dbg_ratelimited("UDPLite: bad csum coverage %d/%d\n",
  				    cscov, skb->len);
  		return 1;
  
  	} else if (cscov < skb->len) {
          	UDP_SKB_CB(skb)->partial_cov = 1;
  		UDP_SKB_CB(skb)->cscov = cscov;
  		if (skb->ip_summed == CHECKSUM_COMPLETE)
  			skb->ip_summed = CHECKSUM_NONE;
          }
  
  	return 0;
  }
  
  /* Slow-path computation of checksum. Socket is locked. */
  static inline __wsum udplite_csum_outgoing(struct sock *sk, struct sk_buff *skb)
  {
  	const struct udp_sock *up = udp_sk(skb->sk);
  	int cscov = up->len;
  	__wsum csum = 0;
  
  	if (up->pcflag & UDPLITE_SEND_CC) {
  		/*
  		 * Sender has set `partial coverage' option on UDP-Lite socket.
  		 * The special case "up->pcslen == 0" signifies full coverage.
  		 */
  		if (up->pcslen < up->len) {
  			if (0 < up->pcslen)
  				cscov = up->pcslen;
  			udp_hdr(skb)->len = htons(up->pcslen);
  		}
  		/*
  		 * NOTE: Causes for the error case  `up->pcslen > up->len':
  		 *        (i)  Application error (will not be penalized).
  		 *       (ii)  Payload too big for send buffer: data is split
  		 *             into several packets, each with its own header.
  		 *             In this case (e.g. last segment), coverage may
  		 *             exceed packet length.
  		 *       Since packets with coverage length > packet length are
  		 *       illegal, we fall back to the defaults here.
  		 */
  	}
  
  	skb->ip_summed = CHECKSUM_NONE;     /* no HW support for checksumming */
  
  	skb_queue_walk(&sk->sk_write_queue, skb) {
  		const int off = skb_transport_offset(skb);
  		const int len = skb->len - off;
  
  		csum = skb_checksum(skb, off, (cscov > len)? len : cscov, csum);
  
  		if ((cscov -= len) <= 0)
  			break;
  	}
  	return csum;
  }
  
  /* Fast-path computation of checksum. Socket may not be locked. */
  static inline __wsum udplite_csum(struct sk_buff *skb)
  {
  	const struct udp_sock *up = udp_sk(skb->sk);
  	const int off = skb_transport_offset(skb);
  	int len = skb->len - off;
  
  	if ((up->pcflag & UDPLITE_SEND_CC) && up->pcslen < len) {
  		if (0 < up->pcslen)
  			len = up->pcslen;
  		udp_hdr(skb)->len = htons(up->pcslen);
  	}
  	skb->ip_summed = CHECKSUM_NONE;     /* no HW support for checksumming */
  
  	return skb_checksum(skb, off, len, 0);
  }
  
  void udplite4_register(void);
  int udplite_get_port(struct sock *sk, unsigned short snum,
  		     int (*scmp)(const struct sock *, const struct sock *));
  #endif	/* _UDPLITE_H */
  