networkd: add support to configure NOARP/ARP for interface (#3854)

https://lists.freedesktop.org/archives/systemd-devel/2016-August/037268.html

man/systemd.network.xml

@@ -212,6 +212,17 @@
           below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.</para>
         </listitem>
       </varlistentry>
+      <varlistentry>
+        <term><varname>ARP=</varname></term>
+        <listitem>
+          <para> A boolean. Enables or disables the ARP (low-level Address Resolution Protocol)
+          for this interface. Defaults to unset, which means that the kernel default will be used.</para>
+          <para> For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual
+          interfaces atop a single lower-level physical interface, which will then only serve as a
+          link/"bridge" device aggregating traffic to the same physical link and not participate in
+          the network otherwise.</para>
+        </listitem>
+      </varlistentry>
     </variablelist>
   </refsect1>
 

src/network/networkd-link.c

@@ -1314,6 +1314,65 @@ int link_set_mtu(Link *link, uint32_t mtu) {
         return 0;
 }
 
+static int set_flags_handler(sd_netlink *rtnl, sd_netlink_message *m, void *userdata) {
+        _cleanup_link_unref_ Link *link = userdata;
+        int r;
+
+        assert(m);
+        assert(link);
+        assert(link->ifname);
+
+        if (IN_SET(link->state, LINK_STATE_FAILED, LINK_STATE_LINGER))
+                return 1;
+
+        r = sd_netlink_message_get_errno(m);
+        if (r < 0)
+                log_link_warning_errno(link, r, "Could not set link flags: %m");
+
+        return 1;
+}
+
+static int link_set_flags(Link *link) {
+        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *req = NULL;
+        unsigned ifi_change = 0;
+        unsigned ifi_flags = 0;
+        int r;
+
+        assert(link);
+        assert(link->manager);
+        assert(link->manager->rtnl);
+
+        if (link->flags & IFF_LOOPBACK)
+                return 0;
+
+        if (!link->network)
+                return 0;
+
+        if (link->network->arp < 0)
+                return 0;
+
+        r = sd_rtnl_message_new_link(link->manager->rtnl, &req, RTM_SETLINK, link->ifindex);
+        if (r < 0)
+                return log_link_error_errno(link, r, "Could not allocate RTM_SETLINK message: %m");
+
+        if (link->network->arp >= 0) {
+                ifi_change |= IFF_NOARP;
+                ifi_flags |= IFF_NOARP;
+        }
+
+        r = sd_rtnl_message_link_set_flags(req, ifi_flags, ifi_change);
+        if (r < 0)
+                return log_link_error_errno(link, r, "Could not set link flags: %m");
+
+        r = sd_netlink_call_async(link->manager->rtnl, req, set_flags_handler, link, 0, NULL);
+        if (r < 0)
+                return log_link_error_errno(link, r, "Could not send rtnetlink message: %m");
+
+        link_ref(link);
+
+        return 0;
+}
+
 static int link_set_bridge(Link *link) {
         _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *req = NULL;
         int r;
@@ -2411,6 +2470,10 @@ static int link_configure(Link *link) {
         if (r < 0)
                 return r;
 
+        r = link_set_flags(link);
+        if (r < 0)
+                return r;
+
         if (link_ipv4ll_enabled(link)) {
                 r = ipv4ll_configure(link);
                 if (r < 0)

src/network/networkd-network-gperf.gperf

@@ -28,6 +28,7 @@ Match.KernelCommandLine,                config_parse_net_condition,
 Match.Architecture,                     config_parse_net_condition,                     CONDITION_ARCHITECTURE,        offsetof(Network, match_arch)
 Link.MACAddress,                        config_parse_hwaddr,                            0,                             offsetof(Network, mac)
 Link.MTUBytes,                          config_parse_iec_size,                          0,                             offsetof(Network, mtu)
+Link.ARP,                               config_parse_tristate,                          0,                             offsetof(Network, arp)
 Network.Description,                    config_parse_string,                            0,                             offsetof(Network, description)
 Network.Bridge,                         config_parse_netdev,                            0,                             offsetof(Network, bridge)
 Network.Bond,                           config_parse_netdev,                            0,                             offsetof(Network, bond)

src/network/networkd-network.c

@@ -134,6 +134,7 @@ static int network_load_one(Manager *manager, const char *filename) {
         network->ipv6_hop_limit = -1;
         network->duid.type = _DUID_TYPE_INVALID;
         network->proxy_arp = -1;
+        network->arp = -1;
         network->ipv6_accept_ra_use_dns = true;
 
         r = config_parse(NULL, filename, file,

src/network/networkd-network.h

@@ -171,6 +171,7 @@ struct Network {
 
         struct ether_addr *mac;
         unsigned mtu;
+        int arp;
         uint32_t iaid;
         DUID duid;