[PATCH] config: if we can't connect to HAL, listen for a startup notification.

[Peter Hutterer]

If HAL isn't available when we try to connect, the registered NameOwnerChanged
signal handler waits until HAL is available. Once we connected to HAL, we
unregister the signal handler again.
This allows HAL to be started in parallel or after the server has started.

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
This is the version without the race condition. We register for the signal
immediately, then unregister on success. On failure, we just wait for the
signal to happen and add the devices then.

 config/hal.c |  111 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 105 insertions(+), 6 deletions(-)

diff --git a/config/hal.c b/config/hal.c
index 8dfbb07..36fa839 100644
--- a/config/hal.c
+++ b/config/hal.c
@@ -467,11 +467,10 @@ disconnect_hook(void *data)
     info->system_bus = NULL;
 }
 
-static void
-connect_hook(DBusConnection *connection, void *data)
+static BOOL
+connect_and_register(DBusConnection *connection, struct config_hal_info *info)
 {
     DBusError error;
-    struct config_hal_info *info = data;
     char **devices;
     int num_devices, i;
 
@@ -479,8 +478,10 @@ connect_hook(DBusConnection *connection, void *data)
 
     dbus_error_init(&error);
 
-    if (!info->hal_ctx)
-        info->hal_ctx = libhal_ctx_new();
+    if (info->hal_ctx)
+        return TRUE; /* already registered, pretend we did something */
+
+    info->hal_ctx = libhal_ctx_new();
     if (!info->hal_ctx) {
         LogMessage(X_ERROR, "config/hal: couldn't create HAL context\n");
         goto out_err;
@@ -512,7 +513,7 @@ connect_hook(DBusConnection *connection, void *data)
 
     dbus_error_free(&error);
 
-    return;
+    return TRUE;
 
 out_ctx2:
     if (!libhal_ctx_shutdown(info->hal_ctx, &error))
@@ -526,6 +527,104 @@ out_err:
     info->hal_ctx = NULL;
     info->system_bus = NULL;
 
+    return FALSE;
+}
+
+
+/**
+ * Handle NewOwnerChanged signals to deal with HAL startup at X server runtime.
+ *
+ * NewOwnerChanged is send once when HAL shuts down, and once again when it
+ * comes back up. Message has three arguments, first is the name
+ * (org.freedesktop.Hal), the second one is the old owner, third one is new
+ * owner.
+ */
+static DBusHandlerResult
+ownerchanged_handler(DBusConnection *connection, DBusMessage *message, void *data)
+{
+    int ret = DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+
+    if (dbus_message_is_signal(message,
+                               "org.freedesktop.DBus",
+                               "NameOwnerChanged")) {
+        DBusError error;
+        char *name, *old_owner, *new_owner;
+
+        dbus_error_init(&error);
+        dbus_message_get_args(message, &error,
+                              DBUS_TYPE_STRING, &name,
+                              DBUS_TYPE_STRING, &old_owner,
+                              DBUS_TYPE_STRING, &new_owner,
+                              DBUS_TYPE_INVALID);
+
+        if (dbus_error_is_set(&error)) {
+            ErrorF("[config/hal] failed to get NameOwnerChanged args: %s (%s)\n",
+                   error.name, error.message);
+        } else if (name && strcmp(name, "org.freedesktop.Hal") == 0) {
+
+            if (!old_owner || !strlen(old_owner)) {
+                DebugF("[config/hal] HAL startup detected.\n");
+                if (connect_and_register(connection, (struct config_hal_info*)data))
+                    dbus_connection_unregister_object_path(connection,
+                                                     "/org/freedesktop/DBus");
+                else
+                    ErrorF("[config/hal] Failed to connect to HAL bus.\n");
+            }
+
+            ret = DBUS_HANDLER_RESULT_HANDLED;
+        }
+        dbus_error_free(&error);
+    }
+
+    return ret;
+}
+
+/**
+ * Register a handler for the NameOwnerChanged signal.
+ */
+static BOOL
+listen_for_startup(DBusConnection *connection, void *data)
+{
+    DBusObjectPathVTable vtable = { .message_function = ownerchanged_handler, };
+    DBusError error;
+    const char MATCH_RULE[] = "sender='org.freedesktop.DBus',"
+                              "interface='org.freedesktop.DBus',"
+                              "type='signal',"
+                              "path='/org/freedesktop/DBus',"
+                              "member='NameOwnerChanged'";
+    int rc = FALSE;
+
+    dbus_error_init(&error);
+    dbus_bus_add_match(connection, MATCH_RULE, &error);
+    if (!dbus_error_is_set(&error)) {
+        if (dbus_connection_register_object_path(connection,
+                                                  "/org/freedesktop/DBus",
+                                                  &vtable,
+                                                  data))
+            rc = TRUE;
+        else
+            ErrorF("[config/hal] cannot register object path.\n");
+    } else {
+        ErrorF("[config/hal] couldn't add match rule: %s (%s)\n", error.name,
+                error.message);
+        ErrorF("[config/hal] cannot detect a HAL startup.\n");
+    }
+
+    dbus_error_free(&error);
+
+    return rc;
+}
+
+static void
+connect_hook(DBusConnection *connection, void *data)
+{
+    struct config_hal_info *info = data;
+
+    if (listen_for_startup(connection, data) &&
+        connect_and_register(connection, info))
+        dbus_connection_unregister_object_path(connection,
+                                               "/org/freedesktop/DBus");
+
     return;
 }
 
-- 
1.6.0.6