aio: add aio_notify

With this change async.c does not rely anymore on any service from
main-loop.c, i.e. it is completely self-contained.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

async.c

@@ -30,6 +30,7 @@
 /* bottom halves (can be seen as timers which expire ASAP) */
 
 struct QEMUBH {
+    AioContext *ctx;
     QEMUBHFunc *cb;
     void *opaque;
     QEMUBH *next;
@@ -42,6 +43,7 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
 {
     QEMUBH *bh;
     bh = g_malloc0(sizeof(QEMUBH));
+    bh->ctx = ctx;
     bh->cb = cb;
     bh->opaque = opaque;
     bh->next = ctx->first_bh;
@@ -101,8 +103,7 @@ void qemu_bh_schedule(QEMUBH *bh)
         return;
     bh->scheduled = 1;
     bh->idle = 0;
-    /* stop the currently executing CPU to execute the BH ASAP */
-    qemu_notify_event();
+    aio_notify(bh->ctx);
 }
 
 void qemu_bh_cancel(QEMUBH *bh)
@@ -177,11 +178,20 @@ aio_ctx_dispatch(GSource     *source,
     return true;
 }
 
+static void
+aio_ctx_finalize(GSource     *source)
+{
+    AioContext *ctx = (AioContext *) source;
+
+    aio_set_event_notifier(ctx, &ctx->notifier, NULL, NULL);
+    event_notifier_cleanup(&ctx->notifier);
+}
+
 static GSourceFuncs aio_source_funcs = {
     aio_ctx_prepare,
     aio_ctx_check,
     aio_ctx_dispatch,
-    NULL
+    aio_ctx_finalize
 };
 
 GSource *aio_get_g_source(AioContext *ctx)
@@ -190,9 +200,21 @@ GSource *aio_get_g_source(AioContext *ctx)
     return &ctx->source;
 }
 
+void aio_notify(AioContext *ctx)
+{
+    event_notifier_set(&ctx->notifier);
+}
+
 AioContext *aio_context_new(void)
 {
-    return (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
+    AioContext *ctx;
+    ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
+    event_notifier_init(&ctx->notifier, false);
+    aio_set_event_notifier(ctx, &ctx->notifier, 
+                           (EventNotifierHandler *)
+                           event_notifier_test_and_clear, NULL);
+
+    return ctx;
 }
 
 void aio_context_ref(AioContext *ctx)

qemu-aio.h

@@ -62,6 +62,9 @@ typedef struct AioContext {
      * no callbacks are removed while we're walking and dispatching callbacks.
      */
     int walking_bh;
+
+    /* Used for aio_notify.  */
+    EventNotifier notifier;
 } AioContext;
 
 /* Returns 1 if there are still outstanding AIO requests; 0 otherwise */
@@ -101,6 +104,21 @@ void aio_context_unref(AioContext *ctx);
  */
 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
 
+/**
+ * aio_notify: Force processing of pending events.
+ *
+ * Similar to signaling a condition variable, aio_notify forces
+ * aio_wait to exit, so that the next call will re-examine pending events.
+ * The caller of aio_notify will usually call aio_wait again very soon,
+ * or go through another iteration of the GLib main loop.  Hence, aio_notify
+ * also has the side effect of recalculating the sets of file descriptors
+ * that the main loop waits for.
+ *
+ * Calling aio_notify is rarely necessary, because for example scheduling
+ * a bottom half calls it already.
+ */
+void aio_notify(AioContext *ctx);
+
 /**
  * aio_bh_poll: Poll bottom halves for an AioContext.
  *