aio / timers: aio_ctx_prepare sets timeout from AioContext timers

Calculate the timeout in aio_ctx_prepare taking into account
the timers attached to the AioContext.

Alter aio_ctx_check similarly.
Signed-off-by: NAlex Bligh <alex@alex.org.uk>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

async.c

@@ -150,7 +150,10 @@ aio_ctx_prepare(GSource *source, gint    *timeout)
 {
     AioContext *ctx = (AioContext *) source;
     QEMUBH *bh;
+    int deadline;
 
+    /* We assume there is no timeout already supplied */
+    *timeout = -1;
     for (bh = ctx->first_bh; bh; bh = bh->next) {
         if (!bh->deleted && bh->scheduled) {
             if (bh->idle) {
@@ -166,6 +169,14 @@ aio_ctx_prepare(GSource *source, gint    *timeout)
         }
     }
 
+    deadline = qemu_timeout_ns_to_ms(timerlistgroup_deadline_ns(&ctx->tlg));
+    if (deadline == 0) {
+        *timeout = 0;
+        return true;
+    } else {
+        *timeout = qemu_soonest_timeout(*timeout, deadline);
+    }
+
     return false;
 }
 
@@ -180,7 +191,7 @@ aio_ctx_check(GSource *source)
             return true;
 	}
     }
-    return aio_pending(ctx);
+    return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 }
 
 static gboolean