illumos gate

Although read(2) isn't explicitly documented on illumos to return -1 with ETIMEDOUT, the man page has this bit:

        In addition, read() and readv() will fail if the stream head
        had  processed  an  asynchronous  error before the call.  In
        this case, the value of errno does not reflect the result of
        read()  or readv() but reflects the prior error. If a hangup
        occurs on the stream being read, read() continues to operate
        normally   until  the  stream  head  read  queue  is  empty.
        Thereafter, it returns 0.

It's not that clear if that part applies out of context, or only in the context of specific kinds of streams in specific modes. Also, the tcp(7p) man page says:

   DIAGNOSTICS
        A socket operation may fail if:
...
        ETIMEDOUT
                         A connection was dropped due  to  excessive
                         retransmissions.

Anyway, I've confirmed that read(2) does do this when TCP keep-alive drops the connection.

As a result of this, we should improve the documentation here to point users to the fact that they can see errors from the underlying network protocols when using sockets.