The tails of the "vhost_user_set_vring_addr" and "vhost_user_set_u64"
functions are now byte-for-byte identical. Factor the common tail out to a
new function called "vhost_user_write_sync".

This is purely refactoring -- no observable change.

Cc: "Michael S. Tsirkin" <mst@redhat.com> (supporter:vhost)
Cc: Eugenio Perez Martin <eperezma@redhat.com>
Cc: German Maglione <gmaglione@redhat.com>
Cc: Liu Jiang <gerry@linux.alibaba.com>
Cc: Sergio Lopez Pascual <slp@redhat.com>
Cc: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Tested-by: Albert Esteve <aesteve@redhat.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
---

Notes:
    v3:
    
    - pick up R-b from Eugenio, T-b from Albert
    
    v2:
    
    - pick up R-b's from Phil and Stefano
    
    - rename "vhost_user_write_msg" to "vhost_user_write_sync" (in code and
      commit message) [Stefano]

 hw/virtio/vhost-user.c | 66 +++++++++-----------
 1 file changed, 28 insertions(+), 38 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 64eac317bfb2..1476b36f0a6e 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -1320,10 +1320,35 @@ static int enforce_reply(struct vhost_dev *dev,
     return vhost_user_get_features(dev, &dummy);
 }
 
+/* Note: "msg->hdr.flags" may be modified. */
+static int vhost_user_write_sync(struct vhost_dev *dev, VhostUserMsg *msg,
+                                 bool wait_for_reply)
+{
+    int ret;
+
+    if (wait_for_reply) {
+        bool reply_supported = virtio_has_feature(dev->protocol_features,
+                                          VHOST_USER_PROTOCOL_F_REPLY_ACK);
+        if (reply_supported) {
+            msg->hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
+        }
+    }
+
+    ret = vhost_user_write(dev, msg, NULL, 0);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (wait_for_reply) {
+        return enforce_reply(dev, msg);
+    }
+
+    return 0;
+}
+
 static int vhost_user_set_vring_addr(struct vhost_dev *dev,
                                      struct vhost_vring_addr *addr)
 {
-    int ret;
     VhostUserMsg msg = {
         .hdr.request = VHOST_USER_SET_VRING_ADDR,
         .hdr.flags = VHOST_USER_VERSION,
@@ -1337,24 +1362,7 @@ static int vhost_user_set_vring_addr(struct vhost_dev *dev,
      */
     bool wait_for_reply = addr->flags & (1 << VHOST_VRING_F_LOG);
 
-    if (wait_for_reply) {
-        bool reply_supported = virtio_has_feature(dev->protocol_features,
-                                          VHOST_USER_PROTOCOL_F_REPLY_ACK);
-        if (reply_supported) {
-            msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
-        }
-    }
-
-    ret = vhost_user_write(dev, &msg, NULL, 0);
-    if (ret < 0) {
-        return ret;
-    }
-
-    if (wait_for_reply) {
-        return enforce_reply(dev, &msg);
-    }
-
-    return 0;
+    return vhost_user_write_sync(dev, &msg, wait_for_reply);
 }
 
 static int vhost_user_set_u64(struct vhost_dev *dev, int request, uint64_t u64,
@@ -1366,26 +1374,8 @@ static int vhost_user_set_u64(struct vhost_dev *dev, int request, uint64_t u64,
         .payload.u64 = u64,
         .hdr.size = sizeof(msg.payload.u64),
     };
-    int ret;
 
-    if (wait_for_reply) {
-        bool reply_supported = virtio_has_feature(dev->protocol_features,
-                                          VHOST_USER_PROTOCOL_F_REPLY_ACK);
-        if (reply_supported) {
-            msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
-        }
-    }
-
-    ret = vhost_user_write(dev, &msg, NULL, 0);
-    if (ret < 0) {
-        return ret;
-    }
-
-    if (wait_for_reply) {
-        return enforce_reply(dev, &msg);
-    }
-
-    return 0;
+    return vhost_user_write_sync(dev, &msg, wait_for_reply);
 }
 
 static int vhost_user_set_status(struct vhost_dev *dev, uint8_t status)