Function pim_register_prepare

freebsd/netinet/ip_mroute.c:2365–2408

* Return a copy of the data packet that is ready for PIM Register * encapsulation. * XXX: Note that in the returned copy the IP header is a valid one. */

 * XXX: Note that in the returned copy the IP header is a valid one.
 */
static struct mbuf *
pim_register_prepare(struct ip *ip, struct mbuf *m)
{
    struct mbuf *mb_copy = NULL;
    int mtu;

    /* Take care of delayed checksums */
    if (m->m_pkthdr.csum_flags & CSUM_DELAY_DATA) {
	in_delayed_cksum(m);
	m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA;
    }

    /*
     * Copy the old packet & pullup its IP header into the
     * new mbuf so we can modify it.
     */
    mb_copy = m_copypacket(m, M_NOWAIT);
    if (mb_copy == NULL)
	return NULL;
    mb_copy = m_pullup(mb_copy, ip->ip_hl << 2);
    if (mb_copy == NULL)
	return NULL;

    /* take care of the TTL */
    ip = mtod(mb_copy, struct ip *);
    --ip->ip_ttl;

    /* Compute the MTU after the PIM Register encapsulation */
    mtu = 0xffff - sizeof(pim_encap_iphdr) - sizeof(pim_encap_pimhdr);

    if (ntohs(ip->ip_len) <= mtu) {
	/* Turn the IP header into a valid one */
	ip->ip_sum = 0;
	ip->ip_sum = in_cksum(mb_copy, ip->ip_hl << 2);
    } else {
	/* Fragment the packet */
	mb_copy->m_pkthdr.csum_flags |= CSUM_IP;
	if (ip_fragment(ip, &mb_copy, mtu, 0) != 0) {
	    m_freem(mb_copy);
	    return NULL;
	}
    }
    return mb_copy;
}

/*
 * Send an upcall with the data packet to the user-level process.