Better handle unknown state.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/server/events.go

@@ -333,6 +333,12 @@ func handleContainerExit(ctx context.Context, e *eventtypes.TaskExit, cntr conta
 		status.Pid = 0
 		status.FinishedAt = e.ExitedAt.UnixNano()
 		status.ExitCode = int32(e.ExitStatus)
+		// Unknown state can only transit to EXITED state, so we need
+		// to handle unknown state here.
+		if status.Unknown {
+			logrus.Debugf("Container %q transited from UNKNOWN to EXITED", cntr.ID)
+			status.Unknown = false
+		}
 		return status, nil
 	})
 	if err != nil {

pkg/server/helpers.go

@@ -359,6 +359,7 @@ func unknownContainerStatus() containerstore.Status {
 		FinishedAt: 0,
 		ExitCode:   unknownExitCode,
 		Reason:     unknownExitReason,
+		Unknown:    true,
 	}
 }
 

pkg/server/restart.go

@@ -308,7 +308,9 @@ func (c *criService) loadContainer(ctx context.Context, cntr containerd.Containe
 	}()
 	if err != nil {
 		log.G(ctx).WithError(err).Errorf("Failed to load container status for %q", id)
-		status = unknownContainerStatus()
+		// Only set the unknown field in this case, because other fields may
+		// contain useful information loaded from the checkpoint.
+		status.Unknown = true
 	}
 	opts := []containerstore.Opts{
 		containerstore.WithStatus(status, containerDir),