block: Pause block jobs in bdrv_drain_all

This is necessary to suppress more IO requests from being generated from
block job coroutines.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 1428069921-2957-3-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -2040,6 +2040,16 @@ void bdrv_drain_all(void)
     bool busy = true;
     BlockDriverState *bs;
 
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
+        if (bs->job) {
+            block_job_pause(bs->job);
+        }
+        aio_context_release(aio_context);
+    }
+
     while (busy) {
         busy = false;
 
@@ -2051,6 +2061,16 @@ void bdrv_drain_all(void)
             aio_context_release(aio_context);
         }
     }
+
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
+        if (bs->job) {
+            block_job_resume(bs->job);
+        }
+        aio_context_release(aio_context);
+    }
 }
 
 /* make a BlockDriverState anonymous by removing from bdrv_state and