main-loop: switch POSIX glib integration to Poller

Convert glib file descriptor polling from rfds/wfds/xfds to Poller.

The Windows code still needs poll_fds[] and n_poll_fds but they can now
become local variables.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
slirp: switch to Poller

Slirp uses rfds/wfds/xfds more extensively than other QEMU components.

The rarely-used out-of-band TCP data feature is used.  That means we
need the full table of select(2) to g_poll(3) events:

  rfds -> G_IO_IN | G_IO_HUP | G_IO_ERR
  wfds -> G_IO_OUT | G_IO_ERR
  xfds -> G_IO_PRI

I came up with this table by looking at Linux fs/select.c which maps
select(2) to poll(2) internally.

Another detail to watch out for are the global variables that reference
rfds/wfds/xfds during slirp_select_poll().  sofcantrcvmore() and
sofcantsendmore() use these globals to clear fd_set bits.  When
sofcantrcvmore() is called, the wfds bit is cleared so that the write
handler will no longer be run for this iteration of the event loop.

This actually seems buggy to me since TCP connections can be half-closed
and we'd still want to handle data in half-duplex fashion.  I think the
real intention is to avoid running the read/write handler when the
socket has been fully closed.  This is indicated with the SS_NOFDREF
state bit so we now check for it before invoking the TCP write handler.
Note that UDP/ICMP code paths don't care because they are
connectionless.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
iohandler: switch to Poller

Convert iohandler_select_fill() and iohandler_select_poll() to use
Poller instead of rfds/wfds/xfds.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
main-loop: drop rfds/wfds/xfds for good

Now that all *_fill() and *_poll() functions use Poller we no longer
need rfds/wfds/xfds or poller_from_select()/poller_to_select().

From now on everything uses GPollFD.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
aio: extract aio_dispatch() from aio_poll()

We will need to loop over AioHandlers calling ->io_read()/->io_write()
when aio_poll() is converted from select(2) to g_poll(2).

Luckily the code for this already exists, extract it into the new
aio_dispatch() function.

Two small changes:

 * aio_poll() checks !node->deleted to avoid calling handlers that have
   been deleted.

 * Fix typo 'then' -> 'them' in aio_poll() comment.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
aio: convert aio_poll() to g_poll(3)

AioHandler already has a GPollFD so we can directly use its
events/revents.

Add the int poller_idx field to AioContext so we can map g_poll(3)
results back to AioHandlers.

Reuse aio_dispatch() to invoke handlers after g_poll(3).

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
aio: support G_IO_HUP and G_IO_ERR

aio-posix.c could not take advantage of G_IO_HUP and G_IO_ERR because
select(2) does not have equivalent events.  Now that g_poll(3) is used
we can support G_IO_HUP and G_IO_ERR.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>