udplite.h

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/*
 *  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)
{
    return memcpy_fromiovecend(to, (struct iovec *) from, offset, len);
}

/* Designate sk as UDP-Lite socket */
static inline int udplite_sk_init(struct 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) {
        LIMIT_NETDEBUG(KERN_DEBUG "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.
         */
        LIMIT_NETDEBUG(KERN_DEBUG "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);
}

extern void udplite4_register(void);
extern int  udplite_get_port(struct sock *sk, unsigned short snum,
            int (*scmp)(const struct sock *, const struct sock *));
#endif  /* _UDPLITE_H */