If the device if of type GDK_DEVICE_TYPE_MASTER, it will return the list of slave devices attached to it, otherwise it will return NULL
the list of slave devices, or NULL. The list must be freed with g_list_free(), the contents of the list are owned by GTK+ and should not be freed. [transfer container][element-type GdkDevice]
See Implementation
If the device if of type GDK_DEVICE_TYPE_MASTER, it will return the list of slave devices attached to it, otherwise it will return NULL