networkd,resolved: add a per-interface mdns configuration option

src/libsystemd/sd-network/sd-network.c

@@ -139,6 +139,10 @@ _public_ int sd_network_link_get_llmnr(int ifindex, char **llmnr) {
         return network_link_get_string(ifindex, "LLMNR", llmnr);
 }
 
+_public_ int sd_network_link_get_mdns(int ifindex, char **mdns) {
+        return network_link_get_string(ifindex, "MDNS", mdns);
+}
+
 _public_ int sd_network_link_get_lldp(int ifindex, char **lldp) {
         _cleanup_free_ char *s = NULL, *p = NULL;
         size_t size;

src/network/networkd-link.c

@@ -2868,6 +2868,8 @@ int link_save(Link *link) {
 
                 fprintf(f, "LLMNR=%s\n",
                         resolve_support_to_string(link->network->llmnr));
+                fprintf(f, "MDNS=%s\n",
+                        resolve_support_to_string(link->network->mdns));
 
                 fputs("ADDRESSES=", f);
                 space = false;

src/network/networkd-network-gperf.gperf

@@ -46,6 +46,7 @@ Network.Gateway,                        config_parse_gateway,
 Network.Domains,                        config_parse_domains,                           0,                             offsetof(Network, domains)
 Network.DNS,                            config_parse_strv,                              0,                             offsetof(Network, dns)
 Network.LLMNR,                          config_parse_resolve_support,                   0,                             offsetof(Network, llmnr)
+Network.MulticastDNS,                   config_parse_resolve_support,                   0,                             offsetof(Network, mdns)
 Network.NTP,                            config_parse_strv,                              0,                             offsetof(Network, ntp)
 Network.IPForward,                      config_parse_address_family_boolean_with_kernel,0,                             offsetof(Network, ip_forward)
 Network.IPMasquerade,                   config_parse_bool,                              0,                             offsetof(Network, ip_masquerade)

src/network/networkd-network.c

@@ -121,6 +121,7 @@ static int network_load_one(Manager *manager, const char *filename) {
         network->unicast_flood = true;
 
         network->llmnr = RESOLVE_SUPPORT_YES;
+        network->mdns = RESOLVE_SUPPORT_NO;
 
         network->link_local = ADDRESS_FAMILY_IPV6;
 

src/network/networkd-network.h

@@ -145,6 +145,7 @@ struct Network {
         char **domains, **dns, **ntp, **bind_carrier;
 
         ResolveSupport llmnr;
+        ResolveSupport mdns;
 
         LIST_FIELDS(Network, networks);
 };

src/resolve/resolved-link.c

@@ -246,6 +246,33 @@ clear:
         return r;
 }
 
+static int link_update_mdns_support(Link *l) {
+        _cleanup_free_ char *b = NULL;
+        int r;
+
+        assert(l);
+
+        r = sd_network_link_get_mdns(l->ifindex, &b);
+        if (r == -ENODATA) {
+                r = 0;
+                goto clear;
+        }
+        if (r < 0)
+                goto clear;
+
+        l->mdns_support = resolve_support_from_string(b);
+        if (l->mdns_support < 0) {
+                r = -EINVAL;
+                goto clear;
+        }
+
+        return 0;
+
+clear:
+        l->mdns_support = RESOLVE_SUPPORT_NO;
+        return r;
+}
+
 static int link_update_search_domains(Link *l) {
         _cleanup_strv_free_ char **domains = NULL;
         char **i;
@@ -295,6 +322,7 @@ int link_update_monitor(Link *l) {
 
         link_update_dns_servers(l);
         link_update_llmnr_support(l);
+        link_update_mdns_support(l);
         link_allocate_scopes(l);
 
         r = link_update_search_domains(l);

src/systemd/sd-network.h

@@ -111,6 +111,13 @@ int sd_network_link_get_ntp(int ifindex, char ***addr);
  */
 int sd_network_link_get_llmnr(int ifindex, char **llmnr);
 
+/* Indicates whether or not MDNS should be enabled for the link
+ * Possible levels of support: yes, no, resolve
+ * Possible return codes:
+ *   -ENODATA: networkd is not aware of the link
+ */
+int sd_network_link_get_mdns(int ifindex, char **mdns);
+
 int sd_network_link_get_lldp(int ifindex, char **lldp);
 
 /* Get the DNS domain names for a given link. */