[PATCH v4 1/2] vhost: Change the sequence of device start

[Yajun Wu]

This patch is part of adding vhost-user vhost_dev_start support. The
motivation is to improve backend configuration speed and reduce live
migration VM downtime.

Moving the device start routines after finishing all the necessary device
and VQ configuration, further aligning to the virtio specification for
"device initialization sequence".

Following patch will add vhost-user vhost_dev_start support.

Signed-off-by: Yajun Wu <yaj...@nvidia.com>
Acked-by: Parav Pandit <pa...@nvidia.com>

---
 hw/block/vhost-user-blk.c | 18 +++++++++++-------
 hw/net/vhost_net.c        | 14 ++++++++------
 2 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index 13bf5cc47a..28409c90f7 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -168,13 +168,6 @@ static int vhost_user_blk_start(VirtIODevice *vdev, Error 
**errp)
         goto err_guest_notifiers;
     }
 
-    ret = vhost_dev_start(&s->dev, vdev);
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "Error starting vhost");
-        goto err_guest_notifiers;
-    }
-    s->started_vu = true;
-
     /* guest_notifier_mask/pending not used yet, so just unmask
      * everything here. virtio-pci will do the right thing by
      * enabling/disabling irqfd.
@@ -183,9 +176,20 @@ static int vhost_user_blk_start(VirtIODevice *vdev, Error 
**errp)
         vhost_virtqueue_mask(&s->dev, vdev, i, false);
     }
 
+    s->dev.vq_index_end = s->dev.nvqs;
+    ret = vhost_dev_start(&s->dev, vdev);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Error starting vhost");
+        goto err_guest_notifiers;
+    }
+    s->started_vu = true;
+
     return ret;
 
 err_guest_notifiers:
+    for (i = 0; i < s->dev.nvqs; i++) {
+        vhost_virtqueue_mask(&s->dev, vdev, i, true);
+    }
     k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false);
 err_host_notifiers:
     vhost_dev_disable_notifiers(&s->dev, vdev);
diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index d28f8b974b..0fe71ed309 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -387,21 +387,23 @@ int vhost_net_start(VirtIODevice *dev, NetClientState 
*ncs,
         } else {
             peer = qemu_get_peer(ncs, n->max_queue_pairs);
         }
-        r = vhost_net_start_one(get_vhost_net(peer), dev);
-
-        if (r < 0) {
-            goto err_start;
-        }
 
         if (peer->vring_enable) {
             /* restore vring enable state */
             r = vhost_set_vring_enable(peer, peer->vring_enable);
 
             if (r < 0) {
-                vhost_net_stop_one(get_vhost_net(peer), dev);
                 goto err_start;
             }
         }
+
+        r = vhost_net_start_one(get_vhost_net(peer), dev);
+        if (r < 0) {
+            if (peer->vring_enable) {
+                vhost_set_vring_enable(peer, false);
+            }
+            goto err_start;
+        }
     }
 
     return 0;
-- 
2.27.0