+static struct genl_multicast_group notify_grp;
+
+/**
+ * genl_register_mc_group - register a multicast group
+ *
+ * Registers the specified multicast group and notifies userspace
+ * about the new group.
+ *
+ * Returns 0 on success or a negative error code.
+ *
+ * @family: The generic netlink family the group shall be registered for.
+ * @grp: The group to register, must have a name.
+ */
+int genl_register_mc_group(struct genl_family *family,
+ struct genl_multicast_group *grp)
+{
+ int id;
+ unsigned long *new_groups;
+ int err;
+
+ BUG_ON(grp->name[0] == '\0');
+
+ genl_lock();
+
+ /* special-case our own group */
+ if (grp == ¬ify_grp)
+ id = GENL_ID_CTRL;
+ else
+ id = find_first_zero_bit(mc_groups,
+ mc_groups_longs * BITS_PER_LONG);
+
+
+ if (id >= mc_groups_longs * BITS_PER_LONG) {
+ size_t nlen = (mc_groups_longs + 1) * sizeof(unsigned long);
+
+ if (mc_groups == &mc_group_start) {
+ new_groups = kzalloc(nlen, GFP_KERNEL);
+ if (!new_groups) {
+ err = -ENOMEM;
+ goto out;
+ }
+ mc_groups = new_groups;
+ *mc_groups = mc_group_start;
+ } else {
+ new_groups = krealloc(mc_groups, nlen, GFP_KERNEL);
+ if (!new_groups) {
+ err = -ENOMEM;
+ goto out;
+ }
+ mc_groups = new_groups;
+ mc_groups[mc_groups_longs] = 0;
+ }
+ mc_groups_longs++;
+ }
+
+ err = netlink_change_ngroups(genl_sock,
+ sizeof(unsigned long) * NETLINK_GENERIC);
+ if (err)
+ goto out;
+
+ grp->id = id;
+ set_bit(id, mc_groups);
+ list_add_tail(&grp->list, &family->mcast_groups);
+ grp->family = family;
+
+ genl_ctrl_event(CTRL_CMD_NEWMCAST_GRP, grp);
+ out:
+ genl_unlock();
+ return 0;
+}
+EXPORT_SYMBOL(genl_register_mc_group);
+
+/**
+ * genl_unregister_mc_group - unregister a multicast group
+ *
+ * Unregisters the specified multicast group and notifies userspace
+ * about it. All current listeners on the group are removed.
+ *
+ * Note: It is not necessary to unregister all multicast groups before
+ * unregistering the family, unregistering the family will cause
+ * all assigned multicast groups to be unregistered automatically.
+ *
+ * @family: Generic netlink family the group belongs to.
+ * @grp: The group to unregister, must have been registered successfully
+ * previously.
+ */
+void genl_unregister_mc_group(struct genl_family *family,
+ struct genl_multicast_group *grp)
+{
+ BUG_ON(grp->family != family);
+ genl_lock();
+ netlink_clear_multicast_users(genl_sock, grp->id);
+ clear_bit(grp->id, mc_groups);
+ list_del(&grp->list);
+ genl_ctrl_event(CTRL_CMD_DELMCAST_GRP, grp);
+ grp->id = 0;
+ grp->family = NULL;
+ genl_unlock();
+}
+
+static void genl_unregister_mc_groups(struct genl_family *family)
+{
+ struct genl_multicast_group *grp, *tmp;
+
+ list_for_each_entry_safe(grp, tmp, &family->mcast_groups, list)
+ genl_unregister_mc_group(family, grp);
+}
+