qed: Use a coroutine for need_check_timer

This fixes the last place where we degraded from AIO to actual blocking
synchronous I/O requests. Putting it into a coroutine means that instead
of blocking, the coroutine simply yields while doing I/O.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

block/qed.c

@@ -264,11 +264,23 @@ static void qed_unplug_allocating_write_reqs(BDRVQEDState *s)
     qemu_co_enter_next(&s->allocating_write_reqs);
 }
 
-static void qed_clear_need_check(void *opaque, int ret)
+static void qed_need_check_timer_entry(void *opaque)
 {
     BDRVQEDState *s = opaque;
+    int ret;
 
-    if (ret) {
+    /* The timer should only fire when allocating writes have drained */
+    assert(!s->allocating_acb);
+
+    trace_qed_need_check_timer_cb(s);
+
+    qed_acquire(s);
+    qed_plug_allocating_write_reqs(s);
+
+    /* Ensure writes are on disk before clearing flag */
+    ret = bdrv_co_flush(s->bs->file->bs);
+    qed_release(s);
+    if (ret < 0) {
         qed_unplug_allocating_write_reqs(s);
         return;
     }
@@ -279,25 +291,14 @@ static void qed_clear_need_check(void *opaque, int ret)
 
     qed_unplug_allocating_write_reqs(s);
 
-    ret = bdrv_flush(s->bs);
+    ret = bdrv_co_flush(s->bs);
     (void) ret;
 }
 
 static void qed_need_check_timer_cb(void *opaque)
 {
-    BDRVQEDState *s = opaque;
-
-    /* The timer should only fire when allocating writes have drained */
-    assert(!s->allocating_acb);
-
-    trace_qed_need_check_timer_cb(s);
-
-    qed_acquire(s);
-    qed_plug_allocating_write_reqs(s);
-
-    /* Ensure writes are on disk before clearing flag */
-    bdrv_aio_flush(s->bs->file->bs, qed_clear_need_check, s);
-    qed_release(s);
+    Coroutine *co = qemu_coroutine_create(qed_need_check_timer_entry, opaque);
+    qemu_coroutine_enter(co);
 }
 
 void qed_acquire(BDRVQEDState *s)