resolved: also rewrite private /etc/resolv.conf when configuration is changed via bus calls

This also moves log message generation into manager_write_resolv_conf(), so
that it is shorter to invoke the function, given that we have to invoke it at a
couple of additional places now.

Fixes: #3225

src/resolve/resolved-link-bus.c

@@ -23,6 +23,7 @@
 #include "resolve-util.h"
 #include "resolved-bus.h"
 #include "resolved-link-bus.h"
+#include "resolved-resolv-conf.h"
 #include "strv.h"
 
 static BUS_DEFINE_PROPERTY_GET_ENUM(property_get_resolve_support, resolve_support, ResolveSupport);
@@ -232,6 +233,8 @@ int bus_link_method_set_dns_servers(sd_bus_message *message, void *userdata, sd_
         dns_server_unlink_marked(l->dns_servers);
         link_allocate_scopes(l);
 
+        (void) manager_write_resolv_conf(l->manager);
+
         return sd_bus_reply_method_return(message, NULL);
 
 clear:
@@ -306,6 +309,9 @@ int bus_link_method_set_domains(sd_bus_message *message, void *userdata, sd_bus_
                 goto clear;
 
         dns_search_domain_unlink_marked(l->search_domains);
+
+        (void) manager_write_resolv_conf(l->manager);
+
         return sd_bus_reply_method_return(message, NULL);
 
 clear:
@@ -444,6 +450,8 @@ int bus_link_method_revert(sd_bus_message *message, void *userdata, sd_bus_error
         link_allocate_scopes(l);
         link_add_rrs(l, false);
 
+        (void) manager_write_resolv_conf(l->manager);
+
         return sd_bus_reply_method_return(message, NULL);
 }
 

src/resolve/resolved-manager.c

@@ -284,9 +284,7 @@ static int on_network_event(sd_event_source *s, int fd, uint32_t revents, void *
                         log_warning_errno(r, "Failed to update monitor information for %i: %m", l->ifindex);
         }
 
-        r = manager_write_resolv_conf(m);
-        if (r < 0)
-                log_warning_errno(r, "Could not update "PRIVATE_RESOLV_CONF": %m");
+        (void) manager_write_resolv_conf(m);
 
         return 0;
 }

src/resolve/resolved-resolv-conf.c

@@ -225,29 +225,31 @@ int manager_write_resolv_conf(Manager *m) {
         assert(m);
 
         /* Read the system /etc/resolv.conf first */
-        manager_read_resolv_conf(m);
+        (void) manager_read_resolv_conf(m);
 
         /* Add the full list to a set, to filter out duplicates */
         r = manager_compile_dns_servers(m, &dns);
         if (r < 0)
-                return r;
+                return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
 
         r = manager_compile_search_domains(m, &domains);
         if (r < 0)
-                return r;
+                return log_warning_errno(r, "Failed to compile list of search domains: %m");
 
         r = fopen_temporary_label(PRIVATE_RESOLV_CONF, PRIVATE_RESOLV_CONF, &f, &temp_path);
         if (r < 0)
-                return r;
+                return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
 
-        fchmod(fileno(f), 0644);
+        (void) fchmod(fileno(f), 0644);
 
         r = write_resolv_conf_contents(f, dns, domains);
-        if (r < 0)
+        if (r < 0) {
+                log_error_errno(r, "Failed to write private resolv.conf contents: %m");
                 goto fail;
+        }
 
         if (rename(temp_path, PRIVATE_RESOLV_CONF) < 0) {
-                r = -errno;
+                r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
                 goto fail;
         }
 
@@ -256,5 +258,6 @@ int manager_write_resolv_conf(Manager *m) {
 fail:
         (void) unlink(PRIVATE_RESOLV_CONF);
         (void) unlink(temp_path);
+
         return r;
 }

src/resolve/resolved.c

@@ -85,11 +85,8 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
-        /* Write finish default resolv.conf to avoid a dangling
-         * symlink */
-        r = manager_write_resolv_conf(m);
-        if (r < 0)
-                log_warning_errno(r, "Could not create "PRIVATE_RESOLV_CONF": %m");
+        /* Write finish default resolv.conf to avoid a dangling symlink */
+        (void) manager_write_resolv_conf(m);
 
         sd_notify(false,
                   "READY=1\n"