mobile: assume IFF_NOARP when given a /32 prefix

Trying to ARP with no other machines in the broadcast domain
is pretty pointless, and in many cases doesn't work (ZTE MF691
/T-Mobile Rocket 2), so turn it off.

src/modem-manager/nm-modem.c

@@ -311,6 +311,27 @@ nm_modem_stage3_ip4_config_start (NMModem *self,
 	return ret;
 }
 
+void
+nm_modem_ip4_pre_commit (NMModem *modem,
+                         NMDevice *device,
+                         NMIP4Config *config)
+{
+	NMModemPrivate *priv = NM_MODEM_GET_PRIVATE (modem);
+
+	/* If the modem has an ethernet-type data interface (ie, not PPP and thus
+	 * not point-to-point) and IP config has a /32 prefix, then we assume that
+	 * ARP will be pointless and we turn it off.
+	 */
+	if (   priv->ip_method == MM_MODEM_IP_METHOD_STATIC
+	    || priv->ip_method == MM_MODEM_IP_METHOD_DHCP) {
+		NMIP4Address *addr = nm_ip4_config_get_address (config, 0);
+
+		g_assert (addr);
+		if (nm_ip4_address_get_prefix (addr) == 32)
+			nm_system_iface_set_arp (nm_device_get_ip_ifindex (device), FALSE);
+	}
+}
+
 /*****************************************************************************/
 
 NMActStageReturn

src/modem-manager/nm-modem.h

@@ -148,6 +148,8 @@ NMActStageReturn nm_modem_stage3_ip6_config_start (NMModem *modem,
                                                    NMDeviceClass *device_class,
                                                    NMDeviceStateReason *reason);
 
+void nm_modem_ip4_pre_commit (NMModem *modem, NMDevice *device, NMIP4Config *config);
+
 gboolean nm_modem_get_secrets (NMModem *modem,
                                const char *setting_name,
                                gboolean request_new,

src/nm-device-modem.c

@@ -309,6 +309,12 @@ act_stage3_ip4_config_start (NMDevice *device,
 	                                         reason);
 }
 
+static void
+ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
+{
+	nm_modem_ip4_pre_commit (NM_DEVICE_MODEM_GET_PRIVATE (device)->modem, device, config);
+}
+
 static NMActStageReturn
 act_stage3_ip6_config_start (NMDevice *device,
                              NMIP6Config **out_config,
@@ -509,6 +515,7 @@ nm_device_modem_class_init (NMDeviceModemClass *mclass)
 	device_class->act_stage2_config = act_stage2_config;
 	device_class->act_stage3_ip4_config_start = act_stage3_ip4_config_start;
 	device_class->act_stage3_ip6_config_start = act_stage3_ip6_config_start;
+	device_class->ip4_config_pre_commit = ip4_config_pre_commit;
 	device_class->get_enabled = get_enabled;
 	device_class->set_enabled = set_enabled;
 

src/nm-system.c

@@ -896,6 +896,50 @@ out:
 	return success;
 }
 
+/**
+ * nm_system_iface_set_arp:
+ * @ifindex: interface index
+ * @enable: %TRUE to enable ARP, or %FALSE to disable
+ *
+ * Sets a flag to indicate that ARP should or should not be used on the
+ * interface.  Point-to-point or IPv4 /32 interfaces often require that ARP
+ * be disabled.
+ *
+ * Returns: %TRUE on success, %FALSE on failure
+ **/
+gboolean
+nm_system_iface_set_arp (int ifindex, gboolean enable)
+{
+	struct rtnl_link *request = NULL, *old = NULL;
+	struct nl_sock *nlh;
+	gboolean success = FALSE;
+	int err;
+
+	g_return_val_if_fail (ifindex > 0, FALSE);
+
+	if (!(request = rtnl_link_alloc ()))
+		return FALSE;
+
+	if (enable)
+		rtnl_link_unset_flags (request, IFF_NOARP);
+	else
+		rtnl_link_set_flags (request, IFF_NOARP);
+
+	old = nm_netlink_index_to_rtnl_link (ifindex);
+	if (old) {
+		nlh = nm_netlink_get_default_handle ();
+		if (nlh) {
+			err = rtnl_link_change (nlh, old, request, 0);
+			if (err == 0)
+				success = TRUE;
+		}
+	}
+
+	rtnl_link_put (old);
+	rtnl_link_put (request);
+	return success;
+}
+
 static struct rtnl_route *
 add_ip4_route_to_gateway (int ifindex, guint32 gw, guint32 mss)
 {

src/nm-system.h

@@ -94,6 +94,8 @@ gboolean		nm_system_iface_set_mtu                 (int ifindex, guint32 mtu);
 
 gboolean		nm_system_iface_set_mac                 (int ifindex, const struct ether_addr *mac);
 
+gboolean        nm_system_iface_set_arp                 (int ifindex, gboolean arp);
+
 gboolean        nm_system_apply_bonding_config          (const char *iface,
                                                          NMSettingBond *s_bond);
 gboolean        nm_system_add_bonding_master            (const char *iface);