In commit 7868e26e
("qemu-ga: add initial win32 support") support was added for qemu-ga on
Windows using virtio-serial.  Other channel methods (ISA serial and UNIX
domain socket) are not supported on Windows.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

In the function ga_channel_write(), the handle ov.hEvent is created
by the call to CreateEvent(). However, the handle is not closed
prior to the function return.

This patch closes the handle before the return of the function.

Kudos to Paolo Bonzini for spotting this bug.
Signed-off-by: NJeff Cody <jcody@redhat.com>
Acked-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

This adds a win32 channel implementation that makes qemu-ga functional
on Windows using virtio-serial (unix-listen/isa-serial not currently
implemented). Unlike with the posix implementation, we do not use
GIOChannel for the following reasons:

 - glib calls stat() on an fd to check whether S_IFCHR is set, which is
   the case for virtio-serial on win32. Because of that, a one-time
   check to determine whether the channel is readable is done by making
   a call to PeekConsoleInput(), which reports the underlying handle is
   not a valid console handle, and thus we can never read from the
   channel.

 - if one goes as far as to "trick" glib into thinking it is a normal
   file descripter, the buffering is done in such a way that data
   written to the output stream will subsequently result in that same
   data being read back as if it were input, causing an error loop.
   furthermore, a forced flush of the channel only moves the data into a
   secondary buffer managed by glib, so there's no way to prevent output
   from getting read back as input.

The implementation here ties into the glib main loop by implementing a
custom GSource that continually submits asynchronous/overlapped I/O to
fill an GAChannel-managed read buffer, and tells glib to poll the
corresponding event handle for a completion whenever there is no
data/RPC in the read buffer to notify the main application about.