[PATCH v0] vhost: make SET_VRING_ADDR, SET_[PROTOCOL_]FEATEURES send replies

[Denis Plotnikov <den-plotnikov@yandex-team.ru>]

On vhost-user-blk migration, qemu normally sends a number of commands
to enable logging if VHOST_USER_PROTOCOL_F_LOG_SHMFD is negotiated.
Qemu sends VHOST_USER_SET_FEATURES to enable buffers logging and
VHOST_USER_SET_FEATURES per each started ring to enable "used ring"
data logging.
The issue is that qemu doesn't wait for reply from the vhost daemon
for these commands which may result in races between qemu expectation
of logging starting and actual login starting in vhost daemon.
To resolve this issue, this patch makes qemu wait for the commands result
explicilty if VHOST_USER_PROTOCOL_F_REPLY_ACK is negotiated.
Also, this patch adds the reply waiting for VHOST_USER_SET_PROTOCOL_FEATURES
command to make the features setting functions work similary.

Signed-off-by: Denis Plotnikov <den-plotnikov@yandex-team.ru>
---
 hw/virtio/vhost-user.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index ee57abe04526..e47b82adab00 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -1105,10 +1105,20 @@ static int vhost_user_set_vring_addr(struct vhost_dev *dev,
         .hdr.size = sizeof(msg.payload.addr),
     };
 
+    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;
+    }
+
     if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
         return -1;
     }
 
+    if (reply_supported) {
+        return process_message_reply(dev, &msg);
+    }
+
     return 0;
 }
 
@@ -1297,10 +1307,20 @@ static int vhost_user_set_u64(struct vhost_dev *dev, int request, uint64_t u64)
         .hdr.size = sizeof(msg.payload.u64),
     };
 
+    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;
+    }
+
     if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
         return -1;
     }
 
+    if (reply_supported) {
+        return process_message_reply(dev, &msg);
+    }
+
     return 0;
 }
 
-- 
2.25.1