udiskslinuxprovider: Move udev monitor in a separate thread

Traditionally the master uevent monitor was bound to a main thread.
However with most of the D-Bus object machinery, interface updates,
etc. being done in the same thread, lost uevents were spotted
on resource-constrained systems.

Better to dedicate a new thread for incoming uevents that are sent
to a probing thread right away, effectively acting as a storage queue.

src/udiskslinuxprovider.c

@@ -64,6 +64,9 @@ struct _UDisksLinuxProvider
  UDisksProvider parent_instance;
 
  GUdevClient *gudev_client;
+ GMainContext *uevent_monitor_context;
+ GMainLoop *uevent_monitor_loop;
+ GThread *uevent_monitor_thread;
  GAsyncQueue *probe_request_queue;
  GThread *probe_request_thread;
 
@@ -141,8 +144,6 @@ static void on_etc_udisks2_dir_monitor_changed (GFileMonitor *monitor,
  GFileMonitorEvent event_type,
  gpointer user_data);
 
-gpointer probe_request_thread_func (gpointer user_data);
-
 static void detach_module_interfaces (UDisksLinuxProvider *provider);
 static void ensure_modules (UDisksLinuxProvider *provider);
 
@@ -163,6 +164,12 @@ udisks_linux_provider_finalize (GObject *object)
  UDisksDaemon *daemon;
  UDisksModuleManager *module_manager;
 
+ /* stop the uevent monitor thread and wait for it */
+ g_main_loop_quit (provider->uevent_monitor_loop);
+ g_thread_join (provider->uevent_monitor_thread);
+ g_main_loop_unref (provider->uevent_monitor_loop);
+ g_main_context_unref (provider->uevent_monitor_context);
+
  /* stop the request thread and wait for it */
  g_async_queue_push (provider->probe_request_queue, (gpointer) 0xdeadbeef);
  g_thread_join (provider->probe_request_thread);
@@ -241,6 +248,7 @@ static gboolean
 on_idle_with_probed_uevent (gpointer user_data)
 {
  ProbeRequest *request = user_data;
+
  udisks_linux_provider_handle_uevent (request->provider,
  g_udev_device_get_action (request->udev_device),
  request->udisks_device);
@@ -279,7 +287,7 @@ uevent_is_spurious (GUdevDevice *dev)
  return FALSE;
 }
 
-gpointer
+static gpointer
 probe_request_thread_func (gpointer user_data)
 {
  UDisksLinuxProvider *provider = UDISKS_LINUX_PROVIDER (user_data);
@@ -308,11 +316,11 @@ probe_request_thread_func (gpointer user_data)
  *
  * */
  dev_initialized = g_udev_device_get_is_initialized (request->udev_device);
- for (n_tries=5; !dev_initialized && (n_tries > 0); n_tries--)
- {
- g_usleep (100000); /* microseconds */
- dev_initialized = g_udev_device_get_is_initialized (request->udev_device);
- }
+ for (n_tries = 5; !dev_initialized && (n_tries > 0); n_tries--)
+  {
+  g_usleep (100000); /* microseconds */
+  dev_initialized = g_udev_device_get_is_initialized (request->udev_device);
+  }
 
  /* ignore spurious uevents */
  if (!request->known_block && uevent_is_spurious (request->udev_device))
@@ -353,6 +361,34 @@ on_uevent (GUdevClient *client,
  g_async_queue_push (provider->probe_request_queue, request);
 }
 
+
+static const gchar *udev_subsystems[] = {"block", "iscsi_connection", "scsi", "nvme", NULL};
+
+static gpointer
+uevent_monitor_thread_func (gpointer user_data)
+{
+ UDisksLinuxProvider *provider = UDISKS_LINUX_PROVIDER (user_data);
+ GUdevClient *gudev_client;
+
+ g_main_context_push_thread_default (provider->uevent_monitor_context);
+
+ gudev_client = g_udev_client_new (udev_subsystems);
+ g_signal_connect (gudev_client,
+ "uevent",
+ G_CALLBACK (on_uevent),
+ provider);
+
+ g_main_loop_run (provider->uevent_monitor_loop);
+
+ g_signal_handlers_disconnect_by_func (gudev_client,
+ G_CALLBACK (on_uevent),
+ provider);
+ g_main_context_pop_thread_default (provider->uevent_monitor_context);
+ g_object_unref (gudev_client);
+
+ return NULL;
+}
+
 /* ---------------------------------------------------------------------------------------------------- */
 
 static void
@@ -363,7 +399,6 @@ udisks_linux_provider_init (UDisksLinuxProvider *provider)
 static void
 udisks_linux_provider_constructed (GObject *object)
 {
- const gchar *subsystems[] = {"block", "iscsi_connection", "scsi", "nvme", NULL};
  UDisksLinuxProvider *provider = UDISKS_LINUX_PROVIDER (object);
  UDisksDaemon *daemon;
  UDisksConfigManager *config_manager;
@@ -374,18 +409,19 @@ udisks_linux_provider_constructed (GObject *object)
  config_manager = udisks_daemon_get_config_manager (daemon);
 
  /* get ourselves an udev client */
- provider->gudev_client = g_udev_client_new (subsystems);
-
- g_signal_connect (provider->gudev_client,
- "uevent",
- G_CALLBACK (on_uevent),
- provider);
+ provider->gudev_client = g_udev_client_new (udev_subsystems);
 
  provider->probe_request_queue = g_async_queue_new ();
- provider->probe_request_thread = g_thread_new ("probing-thread",
+ provider->probe_request_thread = g_thread_new ("udisks-probing-thread",
  probe_request_thread_func,
  provider);
 
+ provider->uevent_monitor_context = g_main_context_new ();
+ provider->uevent_monitor_loop = g_main_loop_new (provider->uevent_monitor_context, FALSE);
+ provider->uevent_monitor_thread = g_thread_new ("udisks-uevent-monitor-thread",
+ uevent_monitor_thread_func,
+ provider);
+
  provider->mount_monitor = g_unix_mount_monitor_get ();
 
  provider->module_ifaces = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, g_object_unref);