Nice automatic updates up to a point, then renice if necessary.

utils.cc

 // Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "update_engine/utils.h"
 
 #include <sys/mount.h>
+#include <sys/resource.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
@@ skipping 419 matching lines @@
   vector<string> command;
   command.push_back("/sbin/shutdown");
   command.push_back("-r");
   command.push_back("now");
   int rc = 0;
   Subprocess::SynchronousExec(command, &rc);
   TEST_AND_RETURN_FALSE(rc == 0);
   return true;
 }
 
+bool SetProcessPriority(ProcessPriority priority) {
+  int prio = static_cast<int>(priority);
+  LOG(INFO) << "Setting process priority to " << prio;
+  TEST_AND_RETURN_FALSE(setpriority(PRIO_PROCESS, 0, prio) == 0);
+  return true;
+}
+
+int ComparePriorities(ProcessPriority priority_lhs,
+                      ProcessPriority priority_rhs) {
+  return static_cast<int>(priority_rhs) - static_cast<int>(priority_lhs);
+}
+
 const char* const kStatefulPartition = "/mnt/stateful_partition";
 
 }  // namespace utils
 
 }  // namespace chromeos_update_engine