+/**
+ * netlink_change_ngroups - change number of multicast groups
+ *
+ * This changes the number of multicast groups that are available
+ * on a certain netlink family. Note that it is not possible to
+ * change the number of groups to below 32. Also note that it does
+ * not implicitly call netlink_clear_multicast_users() when the
+ * number of groups is reduced.
+ *
+ * @sk: The kernel netlink socket, as returned by netlink_kernel_create().
+ * @groups: The new number of groups.
+ */
+int netlink_change_ngroups(struct sock *sk, unsigned int groups)
+{
+ unsigned long *listeners, *old = NULL;
+ struct netlink_table *tbl = &nl_table[sk->sk_protocol];
+ int err = 0;
+
+ if (groups < 32)
+ groups = 32;
+
+ netlink_table_grab();
+ if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) {
+ listeners = kzalloc(NLGRPSZ(groups), GFP_ATOMIC);
+ if (!listeners) {
+ err = -ENOMEM;
+ goto out_ungrab;
+ }
+ old = tbl->listeners;
+ memcpy(listeners, old, NLGRPSZ(tbl->groups));
+ rcu_assign_pointer(tbl->listeners, listeners);
+ }
+ tbl->groups = groups;
+
+ out_ungrab:
+ netlink_table_ungrab();
+ synchronize_rcu();
+ kfree(old);
+ return err;
+}
+EXPORT_SYMBOL(netlink_change_ngroups);
+
+/**
+ * netlink_clear_multicast_users - kick off multicast listeners
+ *
+ * This function removes all listeners from the given group.
+ * @ksk: The kernel netlink socket, as returned by
+ * netlink_kernel_create().
+ * @group: The multicast group to clear.
+ */
+void netlink_clear_multicast_users(struct sock *ksk, unsigned int group)
+{
+ struct sock *sk;
+ struct hlist_node *node;
+ struct netlink_table *tbl = &nl_table[ksk->sk_protocol];
+
+ netlink_table_grab();
+
+ sk_for_each_bound(sk, node, &tbl->mc_list)
+ netlink_update_socket_mc(nlk_sk(sk), group, 0);
+
+ netlink_table_ungrab();
+}
+EXPORT_SYMBOL(netlink_clear_multicast_users);
+