vhost: clarify reply-ack in case a reply was already sent

For messages that require a reply, a second ack should not be
sent when reply-ack protocol feature is negotiated, even if
the corresponding flag is set in the message.

The code is compliant with the spec but it isn't clear it is,
so this patch adds a comment to make it explicit.

Suggested-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 09a90a2..a772999 100644 (file)
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -1783,6 +1783,11 @@ skip_to_reply:
        if (unlock_required)
                vhost_user_unlock_all_queue_pairs(dev);
 
+       /*
+        * If the request required a reply that was already sent,
+        * this optional reply-ack won't be sent as the
+        * VHOST_USER_NEED_REPLY was cleared in send_vhost_reply().
+        */
        if (msg.flags & VHOST_USER_NEED_REPLY) {
                msg.payload.u64 = ret == VH_RESULT_ERR;
                msg.size = sizeof(msg.payload.u64);