evdev: add a way for applications to tweak how devices are opened

In some cases, applications (or actually, wayland compositors)
don't have the required permissions to access evdev directly, but
can do so with an external helper like weston-launch.

Allow them to do so with a custom callback that replaces the regular
open() path.

https://bugzilla.gnome.org/show_bug.cgi?id=704269

2 files changed, 62 insertions, 4 deletions

diff --git a/clutter/evdev/clutter-device-manager-evdev.c b/clutter/evdev/clutter-device-manager-evdev.c
index bab4a8259..6c8399cba 100644
--- a/clutter/evdev/clutter-device-manager-evdev.c
+++ b/clutter/evdev/clutter-device-manager-evdev.c
@@ -73,6 +73,9 @@ G_DEFINE_TYPE_WITH_PRIVATE (ClutterDeviceManagerEvdev,
                             clutter_device_manager_evdev,
                             CLUTTER_TYPE_DEVICE_MANAGER)
 
+static ClutterOpenDeviceCallback open_callback;
+static gpointer                  open_callback_data;
+
 static const gchar *subsystems[] = { "input", NULL };
 
 /*
@@ -465,17 +468,33 @@ clutter_event_source_new (ClutterInputDeviceEvdev *input_device)
   ClutterInputDeviceType type;
   const gchar *node_path;
   gint fd;
+  GError *error;
 
   /* grab the udev input device node and open it */
   node_path = _clutter_input_device_evdev_get_device_path (input_device);
 
   CLUTTER_NOTE (EVENT, "Creating GSource for device %s", node_path);
 
-  fd = open (node_path, O_RDONLY | O_NONBLOCK);
-  if (fd < 0)
+  if (open_callback)
     {
-      g_warning ("Could not open device %s: %s", node_path, strerror (errno));
-      return NULL;
+      error = NULL;
+      fd = open_callback (node_path, O_RDONLY | O_NONBLOCK, open_callback_data, &error);
+
+      if (fd < 0)
+	{
+	  g_warning ("Could not open device %s: %s", node_path, error->message);
+	  g_error_free (error);
+	  return NULL;
+	}
+    }
+  else
+    {
+      fd = open (node_path, O_RDONLY | O_NONBLOCK);
+      if (fd < 0)
+	{
+	  g_warning ("Could not open device %s: %s", node_path, strerror (errno));
+	  return NULL;
+	}
     }
 
   /* setup the source */
@@ -1119,3 +1138,25 @@ clutter_evdev_reclaim_devices (void)
   priv->released = FALSE;
   clutter_device_manager_evdev_probe_devices (evdev_manager);
 }
+
+/**
+ * clutter_evdev_set_open_callback: (skip)
+ * @callback: the user replacement for open()
+ * @user_data: user data for @callback
+ *
+ * Through this function, the application can set a custom callback
+ * to invoked when Clutter is about to open an evdev device. It can do
+ * so if special handling is needed, for example to circumvent permission
+ * problems.
+ *
+ * Setting @callback to %NULL will reset the default behavior.
+ *
+ * For reliable effects, this function must be called before clutter_init().
+ */
+void
+clutter_evdev_set_open_callback (ClutterOpenDeviceCallback callback,
+                                 gpointer                  user_data)
+{
+  open_callback = callback;
+  open_callback_data = user_data;
+}
diff --git a/clutter/evdev/clutter-evdev.h b/clutter/evdev/clutter-evdev.h
index cc5e18edd..2b72951cb 100644
--- a/clutter/evdev/clutter-evdev.h
+++ b/clutter/evdev/clutter-evdev.h
@@ -30,6 +30,23 @@
 
 G_BEGIN_DECLS
 
+/**
+ * ClutterOpenDeviceCallback:
+ * @path: the device path
+ * @flags: flags to be passed to open
+ *
+ * This callback will be called when Clutter needs to access an input
+ * device. It should return an open file descriptor for the file at @path,
+ * or -1 if opening failed.
+ */
+typedef int (*ClutterOpenDeviceCallback) (const char  *path,
+					  int          flags,
+					  gpointer     user_data,
+					  GError     **error);
+
+void  clutter_evdev_set_open_callback (ClutterOpenDeviceCallback callback,
+				       gpointer                  user_data);
+
 void  clutter_evdev_release_devices (void);
 void  clutter_evdev_reclaim_devices (void);