vhost-user: support cross-endian vnet headers

vhost-user already has a way to communicate the endianness of the guest
via the vring endianness messages.  The vring endianness always matches
the vnet header endianness so there is no need to do anything else in
the backend.
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <1543851204-41186-9-git-send-email-pbonzini@redhat.com>
Message-Id: <1550165756-21617-5-git-send-email-pbonzini@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

net/vhost-user.c

@@ -172,6 +172,17 @@ static void net_vhost_user_cleanup(NetClientState *nc)
     qemu_purge_queued_packets(nc);
 }
 
+static int vhost_user_set_vnet_endianness(NetClientState *nc,
+                                          bool enable)
+{
+    /* Nothing to do.  If the server supports
+     * VHOST_USER_PROTOCOL_F_CROSS_ENDIAN, it will get the
+     * vnet header endianness from there.  If it doesn't, negotiation
+     * fails.
+     */
+    return 0;
+}
+
 static bool vhost_user_has_vnet_hdr(NetClientState *nc)
 {
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);
@@ -193,6 +204,8 @@ static NetClientInfo net_vhost_user_info = {
         .cleanup = net_vhost_user_cleanup,
         .has_vnet_hdr = vhost_user_has_vnet_hdr,
         .has_ufo = vhost_user_has_ufo,
+        .set_vnet_be = vhost_user_set_vnet_endianness,
+        .set_vnet_le = vhost_user_set_vnet_endianness,
 };
 
 static gboolean net_vhost_user_watch(GIOChannel *chan, GIOCondition cond,