vhost-user-backend: Correct error handling in run

The error handling here to trigger break epoll seems not correct,
epoll will be ended once one event is handled, no matter successfully
or failed. Fix it.

Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>

vhost_user_backend/src/lib.rs

@@ -40,8 +40,6 @@ pub enum Error {
     WaitDaemon(std::boxed::Box<dyn std::any::Any + std::marker::Send>),
     /// Failed handling a vhost-user request.
     HandleRequest(VhostUserError),
-    /// Failed to handle the event.
-    HandleEvent(io::Error),
     /// Failed to process queue.
     ProcessQueue(VringEpollHandlerError),
     /// Failed to register listener.
@@ -439,13 +437,11 @@ impl<S: VhostUserBackend> VringWorker<S> {
 
                 let ev_type = event.data as u16;
 
-                if self
+                if let Err(e) = self.handler.write().unwrap().handle_event(ev_type, evset) {
-                    .handler
+                    println!(
-                    .write()
+                        "vring handler handle event {} with error {:?}\n",
-                    .unwrap()
+                        ev_type, e
-                    .handle_event(ev_type, evset)
+                    );
-                    .map_err(VringWorkerError::HandleEvent)?
-                {
                     break 'epoll;
                 }
             }