Initial flatpak_get_gl_drivers() implementation

This is supposed to list all the currently loaded "non-standard" gl drivers.
If FLATPAK_GL_DRIVERS is set, then that is used, otherwise it looks
for an nvidia driver and if so, uses that, and always adding "default"
at the end which is meant to resolve to a stable mesa fallback build, as
well as "host" which can be used if you have a host-side driver
as an unmaintained extension.

common/flatpak-utils.c

@@ -359,6 +359,47 @@ flatpak_get_arches (void)
   return (const char **)arches;
 }
 
+const char **
+flatpak_get_gl_drivers (void)
+{
+  static gsize drivers = 0;
+  if (g_once_init_enter (&drivers))
+    {
+      gsize new_drivers;
+      char **new_drivers_c = 0;
+      const char *env = g_getenv ("FLATPAK_GL_DRIVERS");
+      if (env != NULL && *env != 0)
+        new_drivers_c = g_strsplit (env, ":", -1);
+      else
+        {
+          g_autofree char *nvidia_version = NULL;
+          char *dot;
+          GPtrArray *array = g_ptr_array_new ();
+
+          if (g_file_get_contents ("/sys/module/nvidia/version",
+                                   &nvidia_version, NULL, NULL))
+            {
+              g_strstrip (nvidia_version);
+              /* Convert dots to dashes */
+              while ((dot = strchr (nvidia_version, '.')) != NULL)
+                *dot = '-';
+              g_ptr_array_add (array, g_strconcat ("nvidia-", nvidia_version, NULL));
+            }
+
+          g_ptr_array_add (array, (char *)"default");
+          g_ptr_array_add (array, (char *)"host");
+
+          g_ptr_array_add (array, NULL);
+          new_drivers_c = (char **)g_ptr_array_free (array, FALSE);
+        }
+
+      new_drivers = (gsize)new_drivers_c;
+      g_once_init_leave (&drivers, new_drivers);
+    }
+
+  return (const char **)drivers;
+}
+
 gboolean
 flatpak_is_in_sandbox (void)
 {

common/flatpak-utils.h

@@ -64,6 +64,8 @@ gboolean flatpak_is_in_sandbox (void);
 const char * flatpak_get_arch (void);
 const char ** flatpak_get_arches (void);
 
+const char ** flatpak_get_gl_drivers (void);
+
 const char * flatpak_get_bwrap (void);
 
 char ** flatpak_get_current_locale_subpaths (void);