int ip6_mc_source(int add, int omode, struct sock *sk,
	struct group_source_req *pgsr)
{
	struct in6_addr *source, *group;
	struct ipv6_mc_socklist *pmc;
	struct inet6_dev *idev;
	struct ipv6_pinfo *inet6 = inet6_sk(sk);
	struct ip6_sf_socklist *psl;
	struct net *net = sock_net(sk);
	int i, j, rv;
	int leavegroup = 0;
	int err;

	source = &((struct sockaddr_in6 *)&pgsr->gsr_source)->sin6_addr;
	group = &((struct sockaddr_in6 *)&pgsr->gsr_group)->sin6_addr;

	if (!ipv6_addr_is_multicast(group))
		return -EINVAL;

	idev = ip6_mc_find_dev_rtnl(net, group, pgsr->gsr_interface);
	if (!idev)
		return -ENODEV;

	err = -EADDRNOTAVAIL;

	mutex_lock(&idev->mc_lock);
	for_each_pmc_socklock(inet6, sk, pmc) {
		if (pgsr->gsr_interface && pmc->ifindex != pgsr->gsr_interface)
			continue;
		if (ipv6_addr_equal(&pmc->addr, group))
			break;
	}
	if (!pmc) {		/* must have a prior join */
		err = -EINVAL;
		goto done;
	}
	/* if a source filter was set, must be the same mode as before */
	if (rcu_access_pointer(pmc->sflist)) {
		if (pmc->sfmode != omode) {
			err = -EINVAL;
			goto done;
		}
	} else if (pmc->sfmode != omode) {
		/* allow mode switches for empty-set filters */
		ip6_mc_add_src(idev, group, omode, 0, NULL, 0);
		ip6_mc_del_src(idev, group, pmc->sfmode, 0, NULL, 0);
		pmc->sfmode = omode;
	}

	psl = sock_dereference(pmc->sflist, sk);
	if (!add) {
		if (!psl)
			goto done;	/* err = -EADDRNOTAVAIL */
		rv = !0;
		for (i = 0; i < psl->sl_count; i++) {
			rv = !ipv6_addr_equal(&psl->sl_addr[i], source);
			if (rv == 0)
				break;
		}
		if (rv)		/* source not found */
			goto done;	/* err = -EADDRNOTAVAIL */

		/* special case - (INCLUDE, empty) == LEAVE_GROUP */
		if (psl->sl_count == 1 && omode == MCAST_INCLUDE) {
			leavegroup = 1;
			goto done;
		}

		/* update the interface filter */
		ip6_mc_del_src(idev, group, omode, 1, source, 1);

		for (j = i+1; j < psl->sl_count; j++)
			psl->sl_addr[j-1] = psl->sl_addr[j];
		psl->sl_count--;
		err = 0;
		goto done;
	}
	/* else, add a new source to the filter */

	if (psl && psl->sl_count >= sysctl_mld_max_msf) {
		err = -ENOBUFS;
		goto done;
	}
	if (!psl || psl->sl_count == psl->sl_max) {
		struct ip6_sf_socklist *newpsl;
		int count = IP6_SFBLOCK;

		if (psl)
			count += psl->sl_max;
		newpsl = sock_kmalloc(sk, struct_size(newpsl, sl_addr, count),
				      GFP_KERNEL);
		if (!newpsl) {
			err = -ENOBUFS;
			goto done;
		}
		newpsl->sl_max = count;
		newpsl->sl_count = count - IP6_SFBLOCK;
		if (psl) {
			for (i = 0; i < psl->sl_count; i++)
				newpsl->sl_addr[i] = psl->sl_addr[i];
			atomic_sub(struct_size(psl, sl_addr, psl->sl_max),
				   &sk->sk_omem_alloc);
			kfree_rcu(psl, rcu);
		}
		psl = newpsl;
		rcu_assign_pointer(pmc->sflist, psl);
	}
	rv = 1;	/* > 0 for insert logic below if sl_count is 0 */
	for (i = 0; i < psl->sl_count; i++) {
		rv = !ipv6_addr_equal(&psl->sl_addr[i], source);
		if (rv == 0) /* There is an error in the address. */
			goto done;
	}
	for (j = psl->sl_count-1; j >= i; j--)
		psl->sl_addr[j+1] = psl->sl_addr[j];
	psl->sl_addr[i] = *source;
	psl->sl_count++;
	err = 0;
	/* update the interface list */
	ip6_mc_add_src(idev, group, omode, 1, source, 1);
done:
	mutex_unlock(&idev->mc_lock);
	if (leavegroup)
		err = ipv6_sock_mc_drop(sk, pgsr->gsr_interface, group);
	return err;
}