STREAMS error returns

[Prabhu Venkatesh]

I had this problem with my STREAMS driver. At some point in the
driver, I was queueing a zero-size message to the stream head
read queue,
i.e. (mp->b_wptr - mp->b_rptr == 0).

Even with minpsz at 0, the stream head returned a u.u_error
of EBADF when I tried to read the device.

(1) Should an error be returned at all?
(2) Assuming yes to (1), isn't EBADF a poor choice?
(3) Am I missing something?

prabhu