AU: Don't mark booted kernel good if we've applied an update.

main.cc

 // Copyright (c) 2010 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 <string>
 #include <tr1/memory>
 #include <vector>
 
 #include <base/at_exit.h>
 #include <base/command_line.h>
@@ skipping 22 matching lines @@
 DEFINE_bool(foreground, false,
             "Don't daemon()ize; run in foreground.");
 
 using std::string;
 using std::tr1::shared_ptr;
 using std::vector;
 
 namespace chromeos_update_engine {
 
 gboolean UpdateBootFlags(void* arg) {
-  // This purely best effort. Failures should be logged by Subprocess.
+  UpdateAttempter* attempter = reinterpret_cast<UpdateAttempter*>(arg);
+  if (attempter->status() == UPDATE_STATUS_UPDATED_NEED_REBOOT) {
+    // Don't update the flags if there's an update that's just been applied and
+    // we're waiting for reboot because we may end up reverting the update.
+    return FALSE;  // Don't call this callback again.
+  }
+  if (attempter->status() != UPDATE_STATUS_IDLE) {

[adlr, 2010/10/22 00:45:28]

since it's single threaded, and this and postinst are synchronous, I think it's
okay to go ahead and call setgoodkernel when status != NEED_REBOOT or
FINALIZING, but your version makes fewer requirements about things being
synchronous, which is good.

+    // To avoid races (e.g., setting a good kernel right after post-install but
+    // before the status changes), update the boot flag only if the attempter is
+    // idle.
+    return TRUE;  // Call this callback again.
+  }
+  // This is purely best effort. Failures should be logged by Subprocess.
   int unused = 0;
   vector<string> cmd(1, "/usr/sbin/chromeos-setgoodkernel");
   Subprocess::SynchronousExec(cmd, &unused);
   return FALSE;  // Don't call this callback again
 }
 
 namespace {
 
 void SetupDbusService(UpdateEngineService* service) {
   DBusGConnection *bus;
@@ skipping 81 matching lines @@
   UpdateEngineService* service =
       UPDATE_ENGINE_SERVICE(g_object_new(UPDATE_ENGINE_TYPE_SERVICE, NULL));
   service->update_attempter_ = &update_attempter;
   update_attempter.set_dbus_service(service);
   chromeos_update_engine::SetupDbusService(service);
 
   // Schedule periodic update checks.
   chromeos_update_engine::UpdateCheckScheduler scheduler(&update_attempter);
   scheduler.Run();
 
-  // Update boot flags after 45 seconds
-  g_timeout_add_seconds(45, &chromeos_update_engine::UpdateBootFlags, NULL);
+  // Update boot flags after 45 seconds.
+  g_timeout_add_seconds(45,
+                        &chromeos_update_engine::UpdateBootFlags,
+                        &update_attempter);
 
   // Run the main loop until exit time:
   g_main_loop_run(loop);
 
   // Cleanup:
   g_main_loop_unref(loop);
   update_attempter.set_dbus_service(NULL);
   g_object_unref(G_OBJECT(service));
 
   LOG(INFO) << "Chrome OS Update Engine terminating";
   return 0;
 }