network: make Reload bus method synchronous

Prompted by https://github.com/systemd/systemd/pull/30085#discussion_r1401534107.

Note, like Reconfigure bus method, even reconfiguration for an interface is
triggered by Reload method, the method only wait for the link enters
configuring state (or unmanaged state if no matching .network file exists).
Users still need to invoke systemd-networkd-wait-online if it is
necessary to wait for the interface enters configured state after Reload
medhod.

src/libsystemd/sd-bus/bus-common-errors.c

@@ -110,6 +110,7 @@ BUS_ERROR_MAP_ELF_REGISTER const sd_bus_error_map bus_common_errors[] = {
 
         SD_BUS_ERROR_MAP(BUS_ERROR_SPEED_METER_INACTIVE,         EOPNOTSUPP),
         SD_BUS_ERROR_MAP(BUS_ERROR_UNMANAGED_INTERFACE,          EOPNOTSUPP),
+        SD_BUS_ERROR_MAP(BUS_ERROR_NETWORK_ALREADY_RELOADING,    EBUSY),
 
         SD_BUS_ERROR_MAP(BUS_ERROR_NO_SUCH_HOME,                 EEXIST),
         SD_BUS_ERROR_MAP(BUS_ERROR_UID_IN_USE,                   EEXIST),

src/libsystemd/sd-bus/bus-common-errors.h

@@ -111,6 +111,7 @@
 
 #define BUS_ERROR_SPEED_METER_INACTIVE         "org.freedesktop.network1.SpeedMeterInactive"
 #define BUS_ERROR_UNMANAGED_INTERFACE          "org.freedesktop.network1.UnmanagedInterface"
+#define BUS_ERROR_NETWORK_ALREADY_RELOADING    "org.freedesktop.network1.AlreadyReloading"
 
 #define BUS_ERROR_NO_SUCH_HOME                 "org.freedesktop.home1.NoSuchHome"
 #define BUS_ERROR_UID_IN_USE                   "org.freedesktop.home1.UIDInUse"

src/network/networkd-link.c

@@ -1463,6 +1463,80 @@ int link_reconfigure(Link *link, bool force) {
         return 1; /* 1 means the interface will be reconfigured. */
 }
 
+typedef struct ReconfigureData {
+        Link *link;
+        Manager *manager;
+        sd_bus_message *message;
+} ReconfigureData;
+
+static void reconfigure_data_destroy_callback(ReconfigureData *data) {
+        int r;
+
+        assert(data);
+        assert(data->link);
+        assert(data->manager);
+        assert(data->manager->reloading > 0);
+        assert(data->message);
+
+        link_unref(data->link);
+
+        data->manager->reloading--;
+        if (data->manager->reloading <= 0) {
+                r = sd_bus_reply_method_return(data->message, NULL);
+                if (r < 0)
+                        log_warning_errno(r, "Failed to send reply for 'Reload' DBus method, ignoring: %m");
+        }
+
+        sd_bus_message_unref(data->message);
+        free(data);
+}
+
+static int reconfigure_handler_on_bus_method_reload(sd_netlink *rtnl, sd_netlink_message *m, ReconfigureData *data) {
+        assert(data);
+        assert(data->link);
+        return link_reconfigure_handler_internal(rtnl, m, data->link, /* force = */ false);
+}
+
+int link_reconfigure_on_bus_method_reload(Link *link, sd_bus_message *message) {
+        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *req = NULL;
+        _cleanup_free_ ReconfigureData *data = NULL;
+        int r;
+
+        assert(link);
+        assert(link->manager);
+        assert(link->manager->rtnl);
+        assert(message);
+
+        /* See comments in link_reconfigure() above. */
+        if (IN_SET(link->state, LINK_STATE_PENDING, LINK_STATE_INITIALIZED, LINK_STATE_LINGER))
+                return 0;
+
+        r = sd_rtnl_message_new_link(link->manager->rtnl, &req, RTM_GETLINK, link->ifindex);
+        if (r < 0)
+                return r;
+
+        data = new(ReconfigureData, 1);
+        if (!data)
+                return -ENOMEM;
+
+        r = netlink_call_async(link->manager->rtnl, NULL, req,
+                               reconfigure_handler_on_bus_method_reload,
+                               reconfigure_data_destroy_callback, data);
+        if (r < 0)
+                return r;
+
+        *data = (ReconfigureData) {
+                .link = link_ref(link),
+                .manager = link->manager,
+                .message = sd_bus_message_ref(message),
+        };
+
+        link->manager->reloading++;
+
+        TAKE_PTR(data);
+        return 0;
+}
+
 static int link_initialized_and_synced(Link *link) {
         int r;
 

src/network/networkd-link.h

@@ -252,6 +252,7 @@ LinkState link_state_from_string(const char *s) _pure_;
 
 int link_reconfigure_impl(Link *link, bool force);
 int link_reconfigure(Link *link, bool force);
+int link_reconfigure_on_bus_method_reload(Link *link, sd_bus_message *message);
 
 int manager_udev_process_link(Manager *m, sd_device *device, sd_device_action_t action);
 int manager_rtnl_process_link(sd_netlink *rtnl, sd_netlink_message *message, Manager *m);

src/network/networkd-manager-bus.c

@@ -198,9 +198,12 @@ static int bus_method_reconfigure_link(sd_bus_message *message, void *userdata,
 }
 
 static int bus_method_reload(sd_bus_message *message, void *userdata, sd_bus_error *error) {
-        Manager *manager = userdata;
+        Manager *manager = ASSERT_PTR(userdata);
         int r;
 
+        if (manager->reloading > 0)
+                return sd_bus_error_set(error, BUS_ERROR_NETWORK_ALREADY_RELOADING, "Already reloading.");
+
         r = bus_verify_polkit_async(
                         message,
                         "org.freedesktop.network1.reload",
@@ -212,10 +215,13 @@ static int bus_method_reload(sd_bus_message *message, void *userdata, sd_bus_err
         if (r == 0)
                 return 1; /* Polkit will call us back */
 
-        r = manager_reload(manager);
+        r = manager_reload(manager, message);
         if (r < 0)
                 return r;
 
+        if (manager->reloading > 0)
+                return 1; /* Will reply later. */
+
         return sd_bus_reply_method_return(message, NULL);
 }
 

src/network/networkd-manager.c

@@ -453,7 +453,7 @@ static int signal_restart_callback(sd_event_source *s, const struct signalfd_sig
 static int signal_reload_callback(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata) {
         Manager *m = ASSERT_PTR(userdata);
 
-        manager_reload(m);
+        (void) manager_reload(m, /* message = */ NULL);
 
         return 0;
 }
@@ -1085,7 +1085,7 @@ int manager_set_timezone(Manager *m, const char *tz) {
         return 0;
 }
 
-int manager_reload(Manager *m) {
+int manager_reload(Manager *m, sd_bus_message *message) {
         Link *link;
         int r;
 
@@ -1105,9 +1105,14 @@ int manager_reload(Manager *m) {
                 goto finish;
 
         HASHMAP_FOREACH(link, m->links_by_index) {
-                r = link_reconfigure(link, /* force = */ false);
-                if (r < 0)
-                        goto finish;
+                if (message)
+                        r = link_reconfigure_on_bus_method_reload(link, message);
+                else
+                        r = link_reconfigure(link, /* force = */ false);
+                if (r < 0) {
+                        log_link_warning_errno(link, r, "Failed to reconfigure the interface: %m");
+                        link_enter_failed(link);
+                }
         }
 
         r = 0;

src/network/networkd-manager.h

@@ -105,6 +105,8 @@ struct Manager {
         OrderedSet *remove_request_queue;
 
         Hashmap *tuntap_fds_by_name;
+
+        unsigned reloading;
 };
 
 int manager_new(Manager **ret, bool test_mode);
@@ -125,6 +127,6 @@ int manager_enumerate(Manager *m);
 int manager_set_hostname(Manager *m, const char *hostname);
 int manager_set_timezone(Manager *m, const char *timezone);
 
-int manager_reload(Manager *m);
+int manager_reload(Manager *m, sd_bus_message *message);
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(Manager*, manager_free);