diff --git a/async.c b/async.c
new file mode 100644
index 0000000..60c1cb3
--- /dev/null
+++ b/async.c
@@ -0,0 +1,130 @@
+/*
+ * QEMU System Emulator
+ *
+ * Copyright (c) 2003-2008 Fabrice Bellard
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu-common.h"
+
+/***********************************************************/
+/* bottom halves (can be seen as timers which expire ASAP) */
+
+struct QEMUBH {
+    QEMUBHFunc *cb;
+    void *opaque;
+    int scheduled;
+    int idle;
+    int deleted;
+    QEMUBH *next;
+};
+
+static QEMUBH *first_bh = NULL;
+
+QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
+{
+    QEMUBH *bh;
+    bh = qemu_mallocz(sizeof(QEMUBH));
+    bh->cb = cb;
+    bh->opaque = opaque;
+    bh->next = first_bh;
+    first_bh = bh;
+    return bh;
+}
+
+int qemu_bh_poll(void)
+{
+    QEMUBH *bh, **bhp;
+    int ret;
+
+    ret = 0;
+    for (bh = first_bh; bh; bh = bh->next) {
+        if (!bh->deleted && bh->scheduled) {
+            bh->scheduled = 0;
+            if (!bh->idle)
+                ret = 1;
+            bh->idle = 0;
+            bh->cb(bh->opaque);
+        }
+    }
+
+    /* remove deleted bhs */
+    bhp = &first_bh;
+    while (*bhp) {
+        bh = *bhp;
+        if (bh->deleted) {
+            *bhp = bh->next;
+            qemu_free(bh);
+        } else
+            bhp = &bh->next;
+    }
+
+    return ret;
+}
+
+void qemu_bh_schedule_idle(QEMUBH *bh)
+{
+    if (bh->scheduled)
+        return;
+    bh->scheduled = 1;
+    bh->idle = 1;
+}
+
+void qemu_bh_schedule(QEMUBH *bh)
+{
+    if (bh->scheduled)
+        return;
+    bh->scheduled = 1;
+    bh->idle = 0;
+    /* stop the currently executing CPU to execute the BH ASAP */
+    qemu_notify_event();
+}
+
+void qemu_bh_cancel(QEMUBH *bh)
+{
+    bh->scheduled = 0;
+}
+
+void qemu_bh_delete(QEMUBH *bh)
+{
+    bh->scheduled = 0;
+    bh->deleted = 1;
+}
+
+void qemu_bh_update_timeout(int *timeout)
+{
+    QEMUBH *bh;
+
+    for (bh = first_bh; bh; bh = bh->next) {
+        if (!bh->deleted && bh->scheduled) {
+            if (bh->idle) {
+                /* idle bottom halves will be polled at least
+                 * every 10ms */
+                *timeout = MIN(10, *timeout);
+            } else {
+                /* non-idle bottom halves will be executed
+                 * immediately */
+                *timeout = 0;
+                break;
+            }
+        }
+    }
+}
+