[PATCH v5 1/6] libvhost-user: implement VHOST_USER_PROTOCOL_F_REPLY_ACK

[Johannes Berg <johannes@sipsolutions.net>]

From: Johannes Berg <johannes.berg@intel.com>

This is really simple, since we know whether a response is
already requested or not, so we can just send a (successful)
response when there isn't one already.

Given that, it's not all _that_ useful but the master can at
least be sure the message was processed, and we can exercise
more code paths using the example code.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 contrib/libvhost-user/libvhost-user.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index ec27b78ff108..8cc3054fd510 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -1168,7 +1168,8 @@ vu_get_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
                         1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD |
                         1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ |
                         1ULL << VHOST_USER_PROTOCOL_F_HOST_NOTIFIER |
-                        1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD;
+                        1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD |
+                        1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK;
 
     if (have_userfault()) {
         features |= 1ULL << VHOST_USER_PROTOCOL_F_PAGEFAULT;
@@ -1550,13 +1551,20 @@ vu_dispatch(VuDev *dev)
 {
     VhostUserMsg vmsg = { 0, };
     int reply_requested;
-    bool success = false;
+    bool need_reply, success = false;
 
     if (!vu_message_read(dev, dev->sock, &vmsg)) {
         goto end;
     }
 
+    need_reply = vmsg.flags & VHOST_USER_NEED_REPLY_MASK;
+
     reply_requested = vu_process_message(dev, &vmsg);
+    if (!reply_requested && need_reply) {
+        vmsg_set_reply_u64(&vmsg, 0);
+        reply_requested = 1;
+    }
+
     if (!reply_requested) {
         success = true;
         goto end;
-- 
2.24.1