> +/* > + * rchan_callback wrappers. Call the callbacks if available, otherwise fall back > + * to default behaviour. > + */ This adds an overly long line. That being said this behavior is pretty normal for kernel APIs, so I'm not even sure we need it at all. > + > +/* > + * subbuf_start() callback. > + */ and this one is for sure completley useless. Same for all the other similar ones. But taking one step back: All instances implement create_buf_file and remove_buf_file, which makes sense as that is the prime aim of these methods. So there is no point in making those optional. subbuf_start_callback is overriden by two instances, so making that optional totally makes sense. buf_mapped and buf_unmapped are never overriden, so they should be removed entirely. More importantly there is no case that passes a NULL rchan_callbacks, which makes complete sense as it wouldn't even create a file. So remove that case as well and just replace it with a sanity check in relay_open(). Please also add a patch to mark all rchan_callbacks instances const while you're at it.
