+/* Finds the multicast group called 'group_name' in genl family 'family_name'.
+ * When successful, writes its result to 'multicast_group' and returns 0.
+ * Otherwise, clears 'multicast_group' and returns a positive error code. */
+int
+nl_lookup_genl_mcgroup(const char *family_name, const char *group_name,
+ unsigned int *multicast_group)
+{
+ struct nlattr *family_attrs[ARRAY_SIZE(family_policy)];
+ struct ofpbuf all_mcs;
+ struct ofpbuf *reply;
+ struct nlattr *mc;
+ unsigned int left;
+ int error;
+
+ *multicast_group = 0;
+ error = do_lookup_genl_family(family_name, family_attrs, &reply);
+ if (error) {
+ return error;
+ }
+
+ nl_attr_get_nested(family_attrs[CTRL_ATTR_MCAST_GROUPS], &all_mcs);
+ NL_ATTR_FOR_EACH (mc, left, all_mcs.data, all_mcs.size) {
+ static const struct nl_policy mc_policy[] = {
+ [CTRL_ATTR_MCAST_GRP_ID] = {.type = NL_A_U32},
+ [CTRL_ATTR_MCAST_GRP_NAME] = {.type = NL_A_STRING},
+ };
+
+ struct nlattr *mc_attrs[ARRAY_SIZE(mc_policy)];
+ const char *mc_name;
+
+ if (!nl_parse_nested(mc, mc_policy, mc_attrs, ARRAY_SIZE(mc_policy))) {
+ error = EPROTO;
+ goto exit;
+ }
+
+ mc_name = nl_attr_get_string(mc_attrs[CTRL_ATTR_MCAST_GRP_NAME]);
+ if (!strcmp(group_name, mc_name)) {
+ *multicast_group =
+ nl_attr_get_u32(mc_attrs[CTRL_ATTR_MCAST_GRP_ID]);
+ error = 0;
+ goto exit;
+ }
+ }
+ error = EPROTO;
+
+exit:
+ ofpbuf_delete(reply);
+ return error;