resolved: add bus API for configuring per-link DNS settings

This is useful for alternative network management solutions (such as NetworkManager) to push DNS configuration data
into resolved.

The calls will fail should networkd already have taken possesion of a link, so that the bus API is only available if
we don't get the data from networkd.

1 files changed, 77 insertions, 17 deletions

diff --git a/src/resolve/resolved-link.c b/src/resolve/resolved-link.c
index a5033e322a..6f37da46b0 100644
--- a/src/resolve/resolved-link.c
+++ b/src/resolve/resolved-link.c
@@ -63,15 +63,27 @@ int link_new(Manager *m, Link **ret, int ifindex) {
         return 0;
 }
 
+void link_flush_settings(Link *l) {
+        assert(l);
+
+        l->llmnr_support = RESOLVE_SUPPORT_YES;
+        l->mdns_support = RESOLVE_SUPPORT_NO;
+        l->dnssec_mode = _DNSSEC_MODE_INVALID;
+
+        dns_server_unlink_all(l->dns_servers);
+        dns_search_domain_unlink_all(l->search_domains);
+
+        l->dnssec_negative_trust_anchors = set_free_free(l->dnssec_negative_trust_anchors);
+}
+
 Link *link_free(Link *l) {
         if (!l)
                 return NULL;
 
-        dns_server_unlink_all(l->dns_servers);
-        dns_search_domain_unlink_all(l->search_domains);
+        link_flush_settings(l);
 
         while (l->addresses)
-                link_address_free(l->addresses);
+                (void) link_address_free(l->addresses);
 
         if (l->manager)
                 hashmap_remove(l->manager->links, INT_TO_PTR(l->ifindex));
@@ -82,13 +94,11 @@ Link *link_free(Link *l) {
         dns_scope_free(l->mdns_ipv4_scope);
         dns_scope_free(l->mdns_ipv6_scope);
 
-        set_free_free(l->dnssec_negative_trust_anchors);
-
         free(l);
         return NULL;
 }
 
-static void link_allocate_scopes(Link *l) {
+void link_allocate_scopes(Link *l) {
         int r;
 
         assert(l);
@@ -278,6 +288,26 @@ clear:
         return r;
 }
 
+void link_set_dnssec_mode(Link *l, DnssecMode mode) {
+
+        assert(l);
+
+        if (l->dnssec_mode == mode)
+                return;
+
+        if ((l->dnssec_mode == _DNSSEC_MODE_INVALID) ||
+            (l->dnssec_mode == DNSSEC_NO && mode != DNSSEC_NO) ||
+            (l->dnssec_mode == DNSSEC_ALLOW_DOWNGRADE && mode == DNSSEC_YES)) {
+
+                /* When switching from non-DNSSEC mode to DNSSEC mode, flush the cache. Also when switching from the
+                 * allow-downgrade mode to full DNSSEC mode, flush it too. */
+                if (l->unicast_scope)
+                        dns_cache_flush(&l->unicast_scope->cache);
+        }
+
+        l->dnssec_mode = mode;
+}
+
 static int link_update_dnssec_mode(Link *l) {
         _cleanup_free_ char *m = NULL;
         DnssecMode mode;
@@ -299,16 +329,7 @@ static int link_update_dnssec_mode(Link *l) {
                 goto clear;
         }
 
-        if ((l->dnssec_mode == DNSSEC_NO && mode != DNSSEC_NO) ||
-            (l->dnssec_mode == DNSSEC_ALLOW_DOWNGRADE && mode == DNSSEC_YES)) {
-
-                /* When switching from non-DNSSEC mode to DNSSEC mode, flush the cache. Also when switching from the
-                 * allow-downgrade mode to full DNSSEC mode, flush it too. */
-                if (l->unicast_scope)
-                        dns_cache_flush(&l->unicast_scope->cache);
-        }
-
-        l->dnssec_mode = mode;
+        link_set_dnssec_mode(l, mode);
 
         return 0;
 
@@ -396,11 +417,45 @@ clear:
         return r;
 }
 
-int link_update_monitor(Link *l) {
+static int link_is_unmanaged(Link *l) {
+        _cleanup_free_ char *state = NULL;
+        int r;
+
+        assert(l);
+
+        r = sd_network_link_get_setup_state(l->ifindex, &state);
+        if (r == -ENODATA)
+                return 1;
+        if (r < 0)
+                return r;
+
+        return STR_IN_SET(state, "pending", "unmanaged");
+}
+
+static void link_read_settings(Link *l) {
         int r;
 
         assert(l);
 
+        /* Read settings from networkd, except when networkd is not managing this interface. */
+
+        r = link_is_unmanaged(l);
+        if (r < 0) {
+                log_warning_errno(r, "Failed to determine whether interface %s is managed: %m", l->name);
+                return;
+        }
+        if (r > 0) {
+
+                /* If this link used to be managed, but is now unmanaged, flush all our settings -- but only once. */
+                if (l->is_managed)
+                        link_flush_settings(l);
+
+                l->is_managed = false;
+                return;
+        }
+
+        l->is_managed = true;
+
         r = link_update_dns_servers(l);
         if (r < 0)
                 log_warning_errno(r, "Failed to read DNS servers for interface %s, ignoring: %m", l->name);
@@ -424,7 +479,12 @@ int link_update_monitor(Link *l) {
         r = link_update_search_domains(l);
         if (r < 0)
                 log_warning_errno(r, "Failed to read search domains for interface %s, ignoring: %m", l->name);
+}
+
+int link_update_monitor(Link *l) {
+        assert(l);
 
+        link_read_settings(l);
         link_allocate_scopes(l);
         link_add_rrs(l, false);