qemu-ga: add initial win32 support

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.

1 files changed, 1 insertions, 1 deletions

diff --git a/Makefile.objs b/Makefile.objs
index 39c7f4ef74..67deac8067 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -426,7 +426,7 @@ common-obj-y += qmp.o hmp.o
 
 qga-nested-y = commands.o guest-agent-command-state.o
 qga-nested-$(CONFIG_POSIX) += commands-posix.o channel-posix.o
-qga-nested-$(CONFIG_WIN32) += commands-win32.o
+qga-nested-$(CONFIG_WIN32) += commands-win32.o channel-win32.o
 qga-obj-y = $(addprefix qga/, $(qga-nested-y))
 qga-obj-y += qemu-ga.o module.o
 qga-obj-$(CONFIG_WIN32) += oslib-win32.o