title: Error: field ‘rwsem’ has incomplete type
body: <p>I have a module. It has a header file : circular_buffer.h </p>
  
  <pre><code>typedef struct _buffer_entry_{
         char data[1024];
         int size;
         struct rw_semaphore rwsem;
  }buffer_entry;
  </code></pre>
  
  <p>when i compling. there are a error : rwsem has incomplete type?
  How can i fix it?</p>