[libvirt] [PATCH glib] Fix event loop implementation on win32

Daniel P. Berrange berrange at redhat.com
Fri Jan 24 17:04:31 UTC 2014

Libvirt uses gnulib for making winsock look like POSIX
sockets. This means that in the libvirt event handle
callbacks the application will be given a file descriptor
rather than a winsock HANDLE object. The g_io_channel_unix_new
method will detect that it is an FD and delegate to the
g_io_channel_win32_new_fd method. Unfortunately the glib Win32
event loop impl is not very good at dealing with FD objects,
simulating poll() by doing a read() on the FD :-(

The API docs for g_io_channel_win32_new_fd say

 "All reads from the file descriptor should be done by
  this internal GLib thread. Your code should call only

This isn't going to fly for libvirt, since it has zero
knowledge of glib at all, so is just doing normal read().

Fortunately we can work around this problem by turning
the FD we get from libvirt back into a HANDLE using the
_get_osfhandle() method.

Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
 libvirt-glib/libvirt-glib-event.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libvirt-glib/libvirt-glib-event.c b/libvirt-glib/libvirt-glib-event.c
index 87019b5..826db2d 100644
--- a/libvirt-glib/libvirt-glib-event.c
+++ b/libvirt-glib/libvirt-glib-event.c
@@ -31,6 +31,10 @@
 #include "libvirt-glib/libvirt-glib.h"
+#ifdef G_OS_WIN32
+#include <io.h>
  * SECTION:libvirt-glib-event
  * @short_description: Integrate libvirt with the GMain event framework
@@ -164,7 +168,7 @@ gvir_event_handle_add(int fd,
     data->events = events;
     data->cb = cb;
     data->opaque = opaque;
-    data->channel = g_io_channel_unix_new(fd);
+    data->channel = g_io_channel_unix_new(_get_osfhandle(fd));
     data->ff = ff;
     g_debug("Add handle %p %d %d %d %p\n", data, data->watch, data->fd, events, data->opaque);

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