AioContext: introduce aio_prepare

This will be used to implement socket polling on Windows.
On Windows, select() and g_poll() are completely different;
sockets are polled with select() before calling g_poll,
and the g_poll must be nonblocking if select() says a
socket is ready.

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

4 files changed, 23 insertions, 1 deletions

diff --git a/aio-posix.c b/aio-posix.c
index 0936b4ff9d..d3ac06e238 100644
--- a/aio-posix.c
+++ b/aio-posix.c
@@ -100,6 +100,11 @@ void aio_set_event_notifier(AioContext *ctx,
                        (IOHandler *)io_read, NULL, notifier);
 }
 
+bool aio_prepare(AioContext *ctx)
+{
+    return false;
+}
+
 bool aio_pending(AioContext *ctx)
 {
     AioHandler *node;
diff --git a/aio-win32.c b/aio-win32.c
index fd526864be..45422704a4 100644
--- a/aio-win32.c
+++ b/aio-win32.c
@@ -76,6 +76,11 @@ void aio_set_event_notifier(AioContext *ctx,
     aio_notify(ctx);
 }
 
+bool aio_prepare(AioContext *ctx)
+{
+    return false;
+}
+
 bool aio_pending(AioContext *ctx)
 {
     AioHandler *node;
diff --git a/async.c b/async.c
index 293a52a0a7..a99e7f639a 100644
--- a/async.c
+++ b/async.c
@@ -188,6 +188,11 @@ aio_ctx_prepare(GSource *source, gint    *timeout)
 
     /* We assume there is no timeout already supplied */
     *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
+
+    if (aio_prepare(ctx)) {
+        *timeout = 0;
+    }
+
     return *timeout == 0;
 }
 
diff --git a/include/block/aio.h b/include/block/aio.h
index 7ba3e9675b..ef4197b861 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -205,7 +205,14 @@ void qemu_bh_cancel(QEMUBH *bh);
 void qemu_bh_delete(QEMUBH *bh);
 
 /* Return whether there are any pending callbacks from the GSource
- * attached to the AioContext.
+ * attached to the AioContext, before g_poll is invoked.
+ *
+ * This is used internally in the implementation of the GSource.
+ */
+bool aio_prepare(AioContext *ctx);
+
+/* Return whether there are any pending callbacks from the GSource
+ * attached to the AioContext, after g_poll is invoked.
  *
  * This is used internally in the implementation of the GSource.
  */