Function in6_getmulti

freebsd/netinet6/in6_mcast.c:356–470

* Find and return a reference to an in6_multi record for (ifp, group), * and bump its reference count. * If one does not exist, try to allocate it, and update link-layer multicast * filters on ifp to listen for group. * Assumes the IN6_MULTI lock is held across the call. * Return 0 if successful, otherwise return an appropriate error code. */

 * Return 0 if successful, otherwise return an appropriate error code.
 */
static int
in6_getmulti(struct ifnet *ifp, const struct in6_addr *group,
    struct in6_multi **pinm)
{
	struct epoch_tracker	 et;
	struct sockaddr_in6	 gsin6;
	struct ifmultiaddr	*ifma;
	struct in6_multi	*inm;
	int			 error;

	error = 0;

	/*
	 * XXX: Accesses to ifma_protospec must be covered by IF_ADDR_LOCK;
	 * if_addmulti() takes this mutex itself, so we must drop and
	 * re-acquire around the call.
	 */
	IN6_MULTI_LOCK_ASSERT();
	IN6_MULTI_LIST_LOCK();
	IF_ADDR_WLOCK(ifp);
	NET_EPOCH_ENTER(et);
	inm = in6m_lookup_locked(ifp, group);
	NET_EPOCH_EXIT(et);

	if (inm != NULL) {
		/*
		 * If we already joined this group, just bump the
		 * refcount and return it.
		 */
		KASSERT(inm->in6m_refcount >= 1,
		    ("%s: bad refcount %d", __func__, inm->in6m_refcount));
		in6m_acquire_locked(inm);
		*pinm = inm;
		goto out_locked;
	}

	memset(&gsin6, 0, sizeof(gsin6));
	gsin6.sin6_family = AF_INET6;
	gsin6.sin6_len = sizeof(struct sockaddr_in6);
	gsin6.sin6_addr = *group;

	/*
	 * Check if a link-layer group is already associated
	 * with this network-layer group on the given ifnet.
	 */
	IN6_MULTI_LIST_UNLOCK();
	IF_ADDR_WUNLOCK(ifp);
	error = if_addmulti(ifp, (struct sockaddr *)&gsin6, &ifma);
	if (error != 0)
		return (error);
	IN6_MULTI_LIST_LOCK();
	IF_ADDR_WLOCK(ifp);

	/*
	 * If something other than netinet6 is occupying the link-layer
	 * group, print a meaningful error message and back out of
	 * the allocation.
	 * Otherwise, bump the refcount on the existing network-layer