select() previously returned EINVAL only when nfds > FD_SETSIZE+1. The
right test is nfds > FD_SETSIZE, i.e., for nfds = FD_SETSIZE+1 this is also
an error.

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

It's just to painful to do this piecemeal.

Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

to do. However, it did several things wrong that this patch fixes. Thanks
to Paolo Bonzini for finding these problems (see issue #35).

1. When poll() returned a bare POLLHUP, without POLLIN, our select() didn't
return a read event. But nothing in the manpages guarantees that POLLHUP
is accompanied by POLLIN, and some special file implementations might
forget it. As an example, in Linux POLLHUP without POLLIN is common.
But POLLHUP on its own already means that there's nothing more to read,
so a read() will return immediately without blocking - and therefore
select() needs to turn on the readable bit for this fd.

2. Similarly, a bare POLLRDHUP should turn on the writable bit: The
reader on this file hug up, so a write will fail immediately.

3. Our poll() and select() confused what POLLERR means. POLLERR does not
mean poll() found a bad file descriptor - there is POLLNVAL for that.
So this patch fixes poll() to set POLLNVAL, not POLLERR, and select()
to return with errno=EBADF when it sees POLLNVAL, not POLLERR.

4. Rather, POLLERR means the file descriptor is in an error state, so every
read() or write() will return immediately (with an error). So when we see
it, we need to turn on both read and write bits in this case.

5. The meaning of "exceptfds" isn't clear in any manual page, and it
seems there're a lot of opinions on what it might mean. In this patch I
did what Paolo suggested, which is to set the except bit when POLLPRI.
(I don't set exceptfds on POLLERR, or any other case).

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>

Added Cloudius copyright statement to core/*.

poll.cc already had a BSD copyright statement, I believe this is a mistake
(I think Guy wrote this code from scratch), but not wanting to rush to a
conclusion I'm leaving both copyright statements and we should address this
issue later.

add simple select() implementation on top of poll(), been tested by
running netperf/iperf3 which is using select() for waiting for reads
and setting timeouts.

haven't been thourougly tested.