diff --git a/common/constants.cc b/common/constants.cc
index 793ce97..25aa9a8 100644
--- a/common/constants.cc
+++ b/common/constants.cc
@@ -18,8 +18,7 @@
 
 namespace chromeos_update_engine {
 
-// TODO(andrewlassalle): Move this to the prefs directory.
-const char kDlcMetadataRootpath[] = "/var/lib/dlc/";
+const char kDlcPrefsSubDir[] = "dlc";
 
 const char kPowerwashSafePrefsSubDirectory[] = "update_engine/prefs";
 
diff --git a/common/constants.h b/common/constants.h
index 44b20b0..67519bd 100644
--- a/common/constants.h
+++ b/common/constants.h
@@ -19,9 +19,8 @@
 
 namespace chromeos_update_engine {
 
-// The root path of all DLC modules metadata.
-// Keep this in sync with the one in dlcservice.
-extern const char kDlcMetadataRootpath[];
+// The root path of all DLC metadata.
+extern const char kDlcPrefsSubDir[];
 
 // Directory for AU prefs that are preserved across powerwash.
 extern const char kPowerwashSafePrefsSubDirectory[];
diff --git a/common/prefs.cc b/common/prefs.cc
index 6d86a50..6a33037 100644
--- a/common/prefs.cc
+++ b/common/prefs.cc
@@ -18,9 +18,11 @@
 
 #include <algorithm>
 
+#include <base/files/file_enumerator.h>
 #include <base/files/file_util.h>
 #include <base/logging.h>
 #include <base/strings/string_number_conversions.h>
+#include <base/strings/string_split.h>
 #include <base/strings/string_util.h>
 
 #include "update_engine/common/utils.h"
@@ -29,6 +31,8 @@
 
 namespace chromeos_update_engine {
 
+const char kKeySeparator = '/';
+
 bool PrefsBase::GetString(const string& key, string* value) const {
   return storage_->GetKey(key, value);
 }
@@ -104,6 +108,13 @@
     observers_for_key.erase(observer_it);
 }
 
+string PrefsInterface::CreateSubKey(const string& name_space,
+                                    const string& sub_pref,
+                                    const string& key) {
+  return base::JoinString({name_space, sub_pref, key},
+                          string(1, kKeySeparator));
+}
+
 // Prefs
 
 bool Prefs::Init(const base::FilePath& prefs_dir) {
@@ -112,6 +123,24 @@
 
 bool Prefs::FileStorage::Init(const base::FilePath& prefs_dir) {
   prefs_dir_ = prefs_dir;
+  // Delete empty directories. Ignore errors when deleting empty directories.
+  base::FileEnumerator namespace_enum(
+      prefs_dir_, false /* recursive */, base::FileEnumerator::DIRECTORIES);
+  for (base::FilePath namespace_path = namespace_enum.Next();
+       !namespace_path.empty();
+       namespace_path = namespace_enum.Next()) {
+    base::FileEnumerator sub_pref_enum(namespace_path,
+                                       false /* recursive */,
+                                       base::FileEnumerator::DIRECTORIES);
+    for (base::FilePath sub_pref_path = sub_pref_enum.Next();
+         !sub_pref_path.empty();
+         sub_pref_path = sub_pref_enum.Next()) {
+      if (base::IsDirectoryEmpty(sub_pref_path))
+        base::DeleteFile(sub_pref_path, false);
+    }
+    if (base::IsDirectoryEmpty(namespace_path))
+      base::DeleteFile(namespace_path, false);
+  }
   return true;
 }
 
@@ -146,7 +175,7 @@
 bool Prefs::FileStorage::DeleteKey(const string& key) {
   base::FilePath filename;
   TEST_AND_RETURN_FALSE(GetFileNameForKey(key, &filename));
-  TEST_AND_RETURN_FALSE(base::DeleteFile(filename, false));
+  TEST_AND_RETURN_FALSE(base::DeleteFile(filename, true));
   return true;
 }
 
@@ -157,7 +186,7 @@
   for (size_t i = 0; i < key.size(); ++i) {
     char c = key.at(i);
     TEST_AND_RETURN_FALSE(base::IsAsciiAlpha(c) || base::IsAsciiDigit(c) ||
-                          c == '_' || c == '-');
+                          c == '_' || c == '-' || c == kKeySeparator);
   }
   *filename = prefs_dir_.Append(key);
   return true;
diff --git a/common/prefs_interface.h b/common/prefs_interface.h
index 03ae3ec..b559697 100644
--- a/common/prefs_interface.h
+++ b/common/prefs_interface.h
@@ -79,6 +79,11 @@
   // this key. Calling with non-existent keys does nothing.
   virtual bool Delete(const std::string& key) = 0;
 
+  // Creates a key which is part of a sub preference.
+  static std::string CreateSubKey(const std::string& name_space,
+                                  const std::string& sub_pref,
+                                  const std::string& key);
+
   // Add an observer to watch whenever the given |key| is modified. The
   // OnPrefSet() and OnPrefDelete() methods will be called whenever any of the
   // Set*() methods or the Delete() method are called on the given key,
diff --git a/common/prefs_unittest.cc b/common/prefs_unittest.cc
index 3f29319..f226949 100644
--- a/common/prefs_unittest.cc
+++ b/common/prefs_unittest.cc
@@ -31,6 +31,7 @@
 
 using std::string;
 using testing::_;
+using testing::ElementsAre;
 using testing::Eq;
 
 namespace {
@@ -59,6 +60,21 @@
   Prefs prefs_;
 };
 
+TEST(Prefs, Init) {
+  Prefs prefs;
+  const string name_space = "ns";
+  const string sub_pref = "sp";
+
+  base::ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  base::FilePath namespace_path = temp_dir.GetPath().Append(name_space);
+
+  EXPECT_TRUE(base::CreateDirectory(namespace_path.Append(sub_pref)));
+  EXPECT_TRUE(base::PathExists(namespace_path.Append(sub_pref)));
+  ASSERT_TRUE(prefs.Init(temp_dir.GetPath()));
+  EXPECT_FALSE(base::PathExists(namespace_path));
+}
+
 TEST_F(PrefsTest, GetFileNameForKey) {
   const char kAllvalidCharsKey[] =
       "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_-";
@@ -77,6 +93,18 @@
   EXPECT_FALSE(prefs_.file_storage_.GetFileNameForKey("", &path));
 }
 
+TEST_F(PrefsTest, CreateSubKey) {
+  const string name_space = "ns";
+  const string sub_pref1 = "sp1";
+  const string sub_pref2 = "sp2";
+  const string sub_key = "sk";
+
+  EXPECT_EQ(PrefsInterface::CreateSubKey(name_space, sub_pref1, sub_key),
+            "ns/sp1/sk");
+  EXPECT_EQ(PrefsInterface::CreateSubKey(name_space, sub_pref2, sub_key),
+            "ns/sp2/sk");
+}
+
 TEST_F(PrefsTest, GetString) {
   const string test_data = "test data";
   ASSERT_TRUE(SetValue(kKey, test_data));
@@ -279,6 +307,29 @@
   EXPECT_FALSE(prefs_.Exists(kKey));
 }
 
+TEST_F(PrefsTest, SetDeleteSubKey) {
+  const string name_space = "ns";
+  const string sub_pref = "sp";
+  const string sub_key1 = "sk1";
+  const string sub_key2 = "sk2";
+  auto key1 = prefs_.CreateSubKey(name_space, sub_pref, sub_key1);
+  auto key2 = prefs_.CreateSubKey(name_space, sub_pref, sub_key2);
+  base::FilePath sub_pref_path = prefs_dir_.Append(name_space).Append(sub_pref);
+
+  ASSERT_TRUE(prefs_.SetInt64(key1, 0));
+  ASSERT_TRUE(prefs_.SetInt64(key2, 0));
+  EXPECT_TRUE(base::PathExists(sub_pref_path.Append(sub_key1)));
+  EXPECT_TRUE(base::PathExists(sub_pref_path.Append(sub_key2)));
+
+  ASSERT_TRUE(prefs_.Delete(key1));
+  EXPECT_FALSE(base::PathExists(sub_pref_path.Append(sub_key1)));
+  EXPECT_TRUE(base::PathExists(sub_pref_path.Append(sub_key2)));
+  ASSERT_TRUE(prefs_.Delete(key2));
+  EXPECT_FALSE(base::PathExists(sub_pref_path.Append(sub_key2)));
+  prefs_.Init(prefs_dir_);
+  EXPECT_FALSE(base::PathExists(prefs_dir_.Append(name_space)));
+}
+
 class MockPrefsObserver : public PrefsInterface::ObserverInterface {
  public:
   MOCK_METHOD1(OnPrefSet, void(const string&));
@@ -299,6 +350,19 @@
   prefs_.Delete(kKey);
   testing::Mock::VerifyAndClearExpectations(&mock_obserser);
 
+  auto key1 = prefs_.CreateSubKey("ns", "sp1", "key1");
+  prefs_.AddObserver(key1, &mock_obserser);
+
+  EXPECT_CALL(mock_obserser, OnPrefSet(key1));
+  EXPECT_CALL(mock_obserser, OnPrefDeleted(_)).Times(0);
+  prefs_.SetString(key1, "value");
+  testing::Mock::VerifyAndClearExpectations(&mock_obserser);
+
+  EXPECT_CALL(mock_obserser, OnPrefSet(_)).Times(0);
+  EXPECT_CALL(mock_obserser, OnPrefDeleted(Eq(key1)));
+  prefs_.Delete(key1);
+  testing::Mock::VerifyAndClearExpectations(&mock_obserser);
+
   prefs_.RemoveObserver(kKey, &mock_obserser);
 }
 
@@ -359,6 +423,11 @@
   EXPECT_TRUE(prefs_.Delete(kKey));
   EXPECT_FALSE(prefs_.Exists(kKey));
   EXPECT_TRUE(prefs_.Delete(kKey));
+
+  auto key = prefs_.CreateSubKey("ns", "sp", "sk");
+  ASSERT_TRUE(prefs_.SetInt64(key, 0));
+  EXPECT_TRUE(prefs_.Exists(key));
+  EXPECT_TRUE(prefs_.Delete(kKey));
 }
 
 }  // namespace chromeos_update_engine
diff --git a/omaha_request_action.cc b/omaha_request_action.cc
index 81abb3e..c9b8aa0 100644
--- a/omaha_request_action.cc
+++ b/omaha_request_action.cc
@@ -413,37 +413,33 @@
       continue;
 
     const OmahaRequestParams::AppParams& dlc_params = it->second;
-
+    const string& dlc_id = dlc_params.name;
     // Skip if the ping for this DLC was not sent.
     if (!dlc_params.send_ping)
       continue;
 
-    base::FilePath metadata_path =
-        base::FilePath(params_->dlc_prefs_root()).Append(dlc_params.name);
-
-    Prefs prefs;
-    if (!base::CreateDirectory(metadata_path) || !prefs.Init(metadata_path)) {
-      LOG(ERROR) << "Failed to initialize the preferences path:"
-                 << metadata_path.value() << ".";
-      continue;
-    }
+    PrefsInterface* prefs = system_state_->prefs();
     // Reset the active metadata value to |kPingInactiveValue|.
-    if (!prefs.SetInt64(kPrefsPingActive, kPingInactiveValue))
-      LOG(ERROR) << "Failed to set the value of ping metadata '"
-                 << kPrefsPingActive << "'.";
+    auto active_key =
+        prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingActive);
+    if (!prefs->SetInt64(active_key, kPingInactiveValue))
+      LOG(ERROR) << "Failed to set the value of ping metadata '" << active_key
+                 << "'.";
 
-    if (!prefs.SetString(kPrefsPingLastRollcall,
-                         parser_data.daystart_elapsed_days))
+    auto last_rollcall_key =
+        prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingLastRollcall);
+    if (!prefs->SetString(last_rollcall_key, parser_data.daystart_elapsed_days))
       LOG(ERROR) << "Failed to set the value of ping metadata '"
-                 << kPrefsPingLastRollcall << "'.";
+                 << last_rollcall_key << "'.";
 
     if (dlc_params.ping_active) {
       // Write the value of elapsed_days into |kPrefsPingLastActive| only if
       // the previous ping was an active one.
-      if (!prefs.SetString(kPrefsPingLastActive,
-                           parser_data.daystart_elapsed_days))
+      auto last_active_key =
+          prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingLastActive);
+      if (!prefs->SetString(last_active_key, parser_data.daystart_elapsed_days))
         LOG(ERROR) << "Failed to set the value of ping metadata '"
-                   << kPrefsPingLastActive << "'.";
+                   << last_active_key << "'.";
     }
   }
 }
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index 2528f7b..e1f5ef9 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -429,12 +429,6 @@
                bool expected_allow_p2p_for_sharing,
                const string& expected_p2p_url);
 
-  // Helper function used to test the Ping request.
-  // Create the test directory and setup the Omaha response.
-  void SetUpStorePingReply(const string& dlc_id,
-                           base::FilePath* metadata_path_dlc,
-                           base::ScopedTempDir* tempdir);
-
   FakeSystemState fake_system_state_;
   FakeUpdateResponse fake_update_response_;
   // Used by all tests.
@@ -453,6 +447,36 @@
   string post_str;
 };
 
+class OmahaRequestActionDlcPingTest : public OmahaRequestActionTest {
+ protected:
+  void SetUp() override {
+    OmahaRequestActionTest::SetUp();
+    dlc_id_ = "dlc0";
+    active_key_ = PrefsInterface::CreateSubKey(
+        kDlcPrefsSubDir, dlc_id_, kPrefsPingActive);
+    last_active_key_ = PrefsInterface::CreateSubKey(
+        kDlcPrefsSubDir, dlc_id_, kPrefsPingLastActive);
+    last_rollcall_key_ = PrefsInterface::CreateSubKey(
+        kDlcPrefsSubDir, dlc_id_, kPrefsPingLastRollcall);
+
+    tuc_params_.http_response =
+        "<?xml version=\"1.0\" encoding=\"UTF-8\"?><response "
+        "protocol=\"3.0\"><daystart elapsed_days=\"4763\" "
+        "elapsed_seconds=\"36540\"/><app appid=\"test-app-id\" status=\"ok\">\""
+        "<updatecheck status=\"noupdate\"/></app><app "
+        "appid=\"test-app-id_dlc0\" "
+        "status=\"ok\"><ping status=\"ok\"/><updatecheck status=\"noupdate\"/>"
+        "</app></response>";
+    tuc_params_.expected_check_result =
+        metrics::CheckResult::kNoUpdateAvailable;
+    tuc_params_.expected_check_reaction = metrics::CheckReaction::kUnset;
+  }
+
+  std::string dlc_id_;
+  std::string active_key_;
+  std::string last_active_key_;
+  std::string last_rollcall_key_;
+};
 bool OmahaRequestActionTest::TestUpdateCheck() {
   brillo::FakeMessageLoop loop(nullptr);
   loop.SetAsCurrent();
@@ -2904,106 +2928,67 @@
   EXPECT_EQ(kEolDateInvalid, StringToEolDate(eol_date));
 }
 
-void OmahaRequestActionTest::SetUpStorePingReply(
-    const string& dlc_id,
-    base::FilePath* metadata_path_dlc,
-    base::ScopedTempDir* tempdir) {
-  // Create a uniquely named test directory.
-  ASSERT_TRUE(tempdir->CreateUniqueTempDir());
-  request_params_.set_root(tempdir->GetPath().value());
-  *metadata_path_dlc =
-      base::FilePath(request_params_.dlc_prefs_root()).Append(dlc_id);
-  ASSERT_TRUE(base::CreateDirectory(*metadata_path_dlc));
-
-  tuc_params_.http_response =
-      "<?xml version=\"1.0\" encoding=\"UTF-8\"?><response "
-      "protocol=\"3.0\"><daystart elapsed_days=\"4763\" "
-      "elapsed_seconds=\"36540\"/><app appid=\"test-app-id\" status=\"ok\">\""
-      "<updatecheck status=\"noupdate\"/></app><app appid=\"test-app-id_dlc0\" "
-      "status=\"ok\"><ping status=\"ok\"/><updatecheck status=\"noupdate\"/>"
-      "</app></response>";
-  tuc_params_.expected_check_result = metrics::CheckResult::kNoUpdateAvailable;
-  tuc_params_.expected_check_reaction = metrics::CheckReaction::kUnset;
-}
-
-TEST_F(OmahaRequestActionTest, StorePingReplyNoPing) {
-  string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0;
-  base::ScopedTempDir tempdir;
-  SetUpStorePingReply(dlc_id, &metadata_path_dlc0, &tempdir);
-  int64_t temp_int;
-  Prefs prefs;
-  ASSERT_TRUE(prefs.Init(metadata_path_dlc0));
-
-  OmahaRequestParams::AppParams app_param = {.name = dlc_id};
+TEST_F(OmahaRequestActionDlcPingTest, StorePingReplyNoPing) {
+  OmahaRequestParams::AppParams app_param = {.name = dlc_id_};
   request_params_.set_dlc_apps_params(
-      {{request_params_.GetDlcAppId(dlc_id), app_param}});
+      {{request_params_.GetDlcAppId(dlc_id_), app_param}});
 
   ASSERT_TRUE(TestUpdateCheck());
+
+  int64_t temp_int;
   // If there was no ping, the metadata files shouldn't exist yet.
-  EXPECT_FALSE(prefs.GetInt64(kPrefsPingActive, &temp_int));
-  EXPECT_FALSE(prefs.GetInt64(kPrefsPingLastActive, &temp_int));
-  EXPECT_FALSE(prefs.GetInt64(kPrefsPingLastRollcall, &temp_int));
+  EXPECT_FALSE(fake_prefs_.GetInt64(active_key_, &temp_int));
+  EXPECT_FALSE(fake_prefs_.GetInt64(last_active_key_, &temp_int));
+  EXPECT_FALSE(fake_prefs_.GetInt64(last_rollcall_key_, &temp_int));
 }
 
-TEST_F(OmahaRequestActionTest, StorePingReplyActiveTest) {
-  string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0;
-  base::ScopedTempDir tempdir;
-  SetUpStorePingReply(dlc_id, &metadata_path_dlc0, &tempdir);
-  int64_t temp_int;
-  Prefs prefs;
-  ASSERT_TRUE(prefs.Init(metadata_path_dlc0));
+TEST_F(OmahaRequestActionDlcPingTest, StorePingReplyActiveTest) {
   // Create Active value
-  prefs.SetInt64(kPrefsPingActive, 0);
+  fake_prefs_.SetInt64(active_key_, 0);
 
   OmahaRequestParams::AppParams app_param = {
       .active_counting_type = OmahaRequestParams::kDateBased,
-      .name = dlc_id,
+      .name = dlc_id_,
       .ping_active = 1,
       .send_ping = true};
   request_params_.set_dlc_apps_params(
-      {{request_params_.GetDlcAppId(dlc_id), app_param}});
+      {{request_params_.GetDlcAppId(dlc_id_), app_param}});
 
+  int64_t temp_int;
+  string temp_str;
   ASSERT_TRUE(TestUpdateCheck());
-  EXPECT_TRUE(prefs.GetInt64(kPrefsPingActive, &temp_int));
+  EXPECT_TRUE(fake_prefs_.GetInt64(active_key_, &temp_int));
   EXPECT_EQ(temp_int, kPingInactiveValue);
-  EXPECT_TRUE(prefs.GetInt64(kPrefsPingLastActive, &temp_int));
-  EXPECT_EQ(temp_int, 4763);
-  EXPECT_TRUE(prefs.GetInt64(kPrefsPingLastRollcall, &temp_int));
-  EXPECT_EQ(temp_int, 4763);
+  EXPECT_TRUE(fake_prefs_.GetString(last_active_key_, &temp_str));
+  EXPECT_EQ(temp_str, "4763");
+  EXPECT_TRUE(fake_prefs_.GetString(last_rollcall_key_, &temp_str));
+  EXPECT_EQ(temp_str, "4763");
 }
 
-TEST_F(OmahaRequestActionTest, StorePingReplyInactiveTest) {
-  string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0;
-  base::ScopedTempDir tempdir;
-  SetUpStorePingReply(dlc_id, &metadata_path_dlc0, &tempdir);
-  int64_t temp_int;
-  Prefs prefs;
-  ASSERT_TRUE(prefs.Init(metadata_path_dlc0));
+TEST_F(OmahaRequestActionDlcPingTest, StorePingReplyInactiveTest) {
   // Create Active value
-  prefs.SetInt64(kPrefsPingActive, 0);
+  fake_prefs_.SetInt64(active_key_, 0);
 
   OmahaRequestParams::AppParams app_param = {
       .active_counting_type = OmahaRequestParams::kDateBased,
-      .name = dlc_id,
+      .name = dlc_id_,
       .ping_active = 0,
       .send_ping = true};
   request_params_.set_dlc_apps_params(
-      {{request_params_.GetDlcAppId(dlc_id), app_param}});
+      {{request_params_.GetDlcAppId(dlc_id_), app_param}});
 
   // Set the previous active value to an older value than 4763.
-  prefs.SetInt64(kPrefsPingLastActive, 555);
+  fake_prefs_.SetString(last_active_key_, "555");
 
+  int64_t temp_int;
   ASSERT_TRUE(TestUpdateCheck());
-  ASSERT_TRUE(prefs.Init(metadata_path_dlc0));
-  EXPECT_TRUE(prefs.GetInt64(kPrefsPingActive, &temp_int));
+  EXPECT_TRUE(fake_prefs_.GetInt64(active_key_, &temp_int));
   EXPECT_EQ(temp_int, kPingInactiveValue);
-  EXPECT_TRUE(prefs.GetInt64(kPrefsPingLastActive, &temp_int));
-  EXPECT_EQ(temp_int, 555);
-  EXPECT_TRUE(prefs.GetInt64(kPrefsPingLastRollcall, &temp_int));
-  EXPECT_EQ(temp_int, 4763);
+  string temp_str;
+  EXPECT_TRUE(fake_prefs_.GetString(last_active_key_, &temp_str));
+  EXPECT_EQ(temp_str, "555");
+  EXPECT_TRUE(fake_prefs_.GetString(last_rollcall_key_, &temp_str));
+  EXPECT_EQ(temp_str, "4763");
 }
 
 }  // namespace chromeos_update_engine
diff --git a/omaha_request_params.cc b/omaha_request_params.cc
index 5267598..d4b8d64 100644
--- a/omaha_request_params.cc
+++ b/omaha_request_params.cc
@@ -214,7 +214,6 @@
 void OmahaRequestParams::set_root(const string& root) {
   root_ = root;
   test::SetImagePropertiesRootPrefix(root_.c_str());
-  dlc_prefs_root_ = root + kDlcMetadataRootpath;
 }
 
 int OmahaRequestParams::GetChannelIndex(const string& channel) const {
diff --git a/omaha_request_params.h b/omaha_request_params.h
index b33d0b1..d29ce70 100644
--- a/omaha_request_params.h
+++ b/omaha_request_params.h
@@ -58,7 +58,6 @@
         update_check_count_wait_enabled_(false),
         min_update_checks_needed_(kDefaultMinUpdateChecks),
         max_update_checks_allowed_(kDefaultMaxUpdateChecks),
-        dlc_prefs_root_(kDlcMetadataRootpath),
         is_install_(false) {}
 
   virtual ~OmahaRequestParams();
@@ -222,8 +221,6 @@
     return autoupdate_token_;
   }
 
-  inline std::string dlc_prefs_root() const { return dlc_prefs_root_; }
-
   // Returns the App ID corresponding to the current value of the
   // download channel.
   virtual std::string GetAppId() const;
@@ -410,9 +407,6 @@
   // When reading files, prepend root_ to the paths. Useful for testing.
   std::string root_;
 
-  // The metadata/prefs root path for DLCs.
-  std::string dlc_prefs_root_;
-
   // A list of DLC modules to install. A mapping from DLC App ID to |AppParams|.
   std::map<std::string, AppParams> dlc_apps_params_;
 
diff --git a/update_attempter.cc b/update_attempter.cc
index ae7f71e..0ead18a 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -28,7 +28,6 @@
 
 #include <base/bind.h>
 #include <base/compiler_specific.h>
-#include <base/files/file_enumerator.h>
 #include <base/files/file_util.h>
 #include <base/logging.h>
 #include <base/rand_util.h>
@@ -85,6 +84,7 @@
 using chromeos_update_manager::Policy;
 using chromeos_update_manager::StagingCase;
 using chromeos_update_manager::UpdateCheckParams;
+using std::map;
 using std::string;
 using std::vector;
 using update_engine::UpdateAttemptFlags;
@@ -658,6 +658,22 @@
   }
 }
 
+bool UpdateAttempter::ResetDlcPrefs(const string& dlc_id) {
+  vector<string> failures;
+  PrefsInterface* prefs = system_state_->prefs();
+  for (auto& sub_key :
+       {kPrefsPingActive, kPrefsPingLastActive, kPrefsPingLastRollcall}) {
+    auto key = prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, sub_key);
+    if (!prefs->Delete(key))
+      failures.emplace_back(sub_key);
+  }
+  if (failures.size() != 0)
+    PLOG(ERROR) << "Failed to delete prefs (" << base::JoinString(failures, ",")
+                << " for DLC (" << dlc_id << ").";
+
+  return failures.size() == 0;
+}
+
 bool UpdateAttempter::SetDlcActiveValue(bool is_active, const string& dlc_id) {
   if (dlc_id.empty()) {
     LOG(ERROR) << "Empty DLC ID passed.";
@@ -665,50 +681,30 @@
   }
   LOG(INFO) << "Set DLC (" << dlc_id << ") to "
             << (is_active ? "Active" : "Inactive");
-  // TODO(andrewlassalle): Should dlc_prefs_root be in systemstate instead of
-  //  omaha_request_params_?
-  base::FilePath metadata_path =
-      base::FilePath(omaha_request_params_->dlc_prefs_root()).Append(dlc_id);
+  PrefsInterface* prefs = system_state_->prefs();
   if (is_active) {
-    base::File::Error error;
-    if (!base::CreateDirectoryAndGetError(metadata_path, &error)) {
-      PLOG(ERROR) << "Failed to create metadata directory for DLC (" << dlc_id
-                  << "). Error:" << error;
-      return false;
-    }
-
-    Prefs prefs;
-    if (!prefs.Init(metadata_path)) {
-      LOG(ERROR) << "Failed to initialize the preferences path:"
-                 << metadata_path.value() << ".";
-      return false;
-    }
-
-    if (!prefs.SetInt64(kPrefsPingActive, kPingActiveValue)) {
+    auto ping_active_key =
+        prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingActive);
+    if (!prefs->SetInt64(ping_active_key, kPingActiveValue)) {
       LOG(ERROR) << "Failed to set the value of ping metadata '"
                  << kPrefsPingActive << "'.";
       return false;
     }
   } else {
-    if (!base::DeleteFile(metadata_path, true)) {
-      PLOG(ERROR) << "Failed to delete metadata directory("
-                  << metadata_path.value() << ") for DLC (" << dlc_id << ").";
-      return false;
-    }
+    return ResetDlcPrefs(dlc_id);
   }
   return true;
 }
 
-int64_t UpdateAttempter::GetPingMetadata(
-    const PrefsInterface& prefs, const std::string& metadata_name) const {
+int64_t UpdateAttempter::GetPingMetadata(const string& metadata_key) const {
   // The first time a ping is sent, the metadata files containing the values
   // sent back by the server still don't exist. A value of -1 is used to
   // indicate this.
-  if (!prefs.Exists(metadata_name))
+  if (!system_state_->prefs()->Exists(metadata_key))
     return kPingNeverPinged;
 
   int64_t value;
-  if (prefs.GetInt64(metadata_name, &value))
+  if (system_state_->prefs()->GetInt64(metadata_key, &value))
     return value;
 
   // Return -2 when the file exists and there is a problem reading from it, or
@@ -724,49 +720,41 @@
     LOG(INFO) << "Failed to retrieve DLC module IDs from dlcservice. Check the "
                  "state of dlcservice, will not update DLC modules.";
   }
-  base::FilePath metadata_root_path =
-      base::FilePath(omaha_request_params_->dlc_prefs_root());
-  // Cleanup any leftover metadata for DLCs which don't exist.
-  base::FileEnumerator dir_enum(metadata_root_path,
-                                false /* recursive */,
-                                base::FileEnumerator::DIRECTORIES);
-  std::unordered_set<string> dlc_ids(dlc_ids_.begin(), dlc_ids_.end());
-  for (base::FilePath name = dir_enum.Next(); !name.empty();
-       name = dir_enum.Next()) {
-    string id = name.BaseName().value();
-    if (dlc_ids.find(id) == dlc_ids.end()) {
-      LOG(INFO) << "Deleting stale metadata for DLC:" << id;
-      if (!base::DeleteFile(name, true))
-        PLOG(WARNING) << "Failed to delete DLC prefs path:" << name.value();
-    }
-  }
-  std::map<std::string, OmahaRequestParams::AppParams> dlc_apps_params;
+  PrefsInterface* prefs = system_state_->prefs();
+  map<string, OmahaRequestParams::AppParams> dlc_apps_params;
   for (const auto& dlc_id : dlc_ids_) {
     OmahaRequestParams::AppParams dlc_params{
         .active_counting_type = OmahaRequestParams::kDateBased,
         .name = dlc_id,
         .send_ping = false};
-    // Only send the ping when the request is to update DLCs. When installing
-    // DLCs, we don't want to send the ping yet, since the DLCs might fail to
-    // install or might not really be active yet.
-    if (!is_install_) {
-      base::FilePath metadata_path = metadata_root_path.Append(dlc_id);
-      Prefs prefs;
-      if (!base::CreateDirectory(metadata_path) || !prefs.Init(metadata_path)) {
-        LOG(ERROR) << "Failed to initialize the preferences path:"
-                   << metadata_path.value() << ".";
-      } else {
-        dlc_params.ping_active = kPingActiveValue;
-        if (!prefs.GetInt64(kPrefsPingActive, &dlc_params.ping_active) ||
-            dlc_params.ping_active != kPingActiveValue) {
-          dlc_params.ping_active = kPingInactiveValue;
-        }
-        dlc_params.ping_date_last_active =
-            GetPingMetadata(prefs, kPrefsPingLastActive);
-        dlc_params.ping_date_last_rollcall =
-            GetPingMetadata(prefs, kPrefsPingLastRollcall);
-        dlc_params.send_ping = true;
+    if (is_install_) {
+      // In some cases, |SetDlcActiveValue| might fail to reset the DLC prefs
+      // when a DLC is uninstalled. To avoid having stale values from that
+      // scenario, we reset the metadata values on a new install request.
+      // Ignore failure to delete stale prefs.
+      ResetDlcPrefs(dlc_id);
+      SetDlcActiveValue(true, dlc_id);
+    } else {
+      // Only send the ping when the request is to update DLCs. When installing
+      // DLCs, we don't want to send the ping yet, since the DLCs might fail to
+      // install or might not really be active yet.
+      dlc_params.ping_active = kPingActiveValue;
+      auto ping_active_key =
+          prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingActive);
+      if (!prefs->GetInt64(ping_active_key, &dlc_params.ping_active) ||
+          dlc_params.ping_active != kPingActiveValue) {
+        dlc_params.ping_active = kPingInactiveValue;
       }
+      auto ping_last_active_key =
+          prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingLastActive);
+      dlc_params.ping_date_last_active = GetPingMetadata(ping_last_active_key);
+
+      auto ping_last_rollcall_key =
+          prefs->CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingLastRollcall);
+      dlc_params.ping_date_last_rollcall =
+          GetPingMetadata(ping_last_rollcall_key);
+
+      dlc_params.send_ping = true;
     }
     dlc_apps_params[omaha_request_params_->GetDlcAppId(dlc_id)] = dlc_params;
   }
diff --git a/update_attempter.h b/update_attempter.h
index 9e48179..e270b59 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -439,13 +439,15 @@
   // Resets interactivity and forced update flags.
   void ResetInteractivityFlags();
 
-  // Get the integer values from the metadata directory set in |prefs| for
-  // |kPrefsPingLastActive| or |kPrefsPingLastRollcall|.
+  // Resets all the DLC prefs.
+  bool ResetDlcPrefs(const std::string& dlc_id);
+
+  // Get the integer values from the DLC metadata for |kPrefsPingLastActive|
+  // or |kPrefsPingLastRollcall|.
   // The value is equal to -2 when the value cannot be read or is not numeric.
   // The value is equal to -1 the first time it is being sent, which is
   // when the metadata file doesn't exist.
-  int64_t GetPingMetadata(const PrefsInterface& prefs,
-                          const std::string& metadata_name) const;
+  int64_t GetPingMetadata(const std::string& metadata_key) const;
 
   // Calculates the update parameters for DLCs. Sets the |dlc_ids_|
   // parameter on the |omaha_request_params_| object.
diff --git a/update_attempter_unittest.cc b/update_attempter_unittest.cc
index 56665ad..5a6a23e 100644
--- a/update_attempter_unittest.cc
+++ b/update_attempter_unittest.cc
@@ -72,6 +72,7 @@
 using std::unordered_set;
 using std::vector;
 using testing::_;
+using testing::Contains;
 using testing::DoAll;
 using testing::ElementsAre;
 using testing::Field;
@@ -2349,16 +2350,9 @@
 }
 
 TEST_F(UpdateAttempterTest, CalculateDlcParamsInstallTest) {
-  // Create a uniquely named test directory.
-  base::ScopedTempDir tempdir;
-  ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  fake_system_state_.request_params()->set_root(tempdir.GetPath().value());
   string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0 =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append(dlc_id);
-
-  ASSERT_TRUE(base::CreateDirectory(metadata_path_dlc0));
+  FakePrefs fake_prefs;
+  fake_system_state_.set_prefs(&fake_prefs);
   attempter_.is_install_ = true;
   attempter_.dlc_ids_ = {dlc_id};
   attempter_.CalculateDlcParams();
@@ -2371,22 +2365,18 @@
   EXPECT_EQ(false, dlc_app_params.send_ping);
   // When the DLC gets installed, a ping is not sent, therefore we don't store
   // the values sent by Omaha.
-  EXPECT_FALSE(
-      base::PathExists(metadata_path_dlc0.Append(kPrefsPingLastActive)));
-  EXPECT_FALSE(
-      base::PathExists(metadata_path_dlc0.Append(kPrefsPingLastRollcall)));
+  auto last_active_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastActive);
+  EXPECT_FALSE(fake_system_state_.prefs()->Exists(last_active_key));
+  auto last_rollcall_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastRollcall);
+  EXPECT_FALSE(fake_system_state_.prefs()->Exists(last_rollcall_key));
 }
 
 TEST_F(UpdateAttempterTest, CalculateDlcParamsNoPrefFilesTest) {
-  // Create a uniquely named test directory.
-  base::ScopedTempDir tempdir;
-  ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  fake_system_state_.request_params()->set_root(tempdir.GetPath().value());
   string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0 =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append(dlc_id);
-  ASSERT_TRUE(base::CreateDirectory(metadata_path_dlc0));
+  FakePrefs fake_prefs;
+  fake_system_state_.set_prefs(&fake_prefs);
   EXPECT_CALL(mock_dlcservice_, GetDlcsToUpdate(_))
       .WillOnce(
           DoAll(SetArgPointee<0>(std::vector<string>({dlc_id})), Return(true)));
@@ -2407,23 +2397,23 @@
 }
 
 TEST_F(UpdateAttempterTest, CalculateDlcParamsNonParseableValuesTest) {
-  // Create a uniquely named test directory.
-  base::ScopedTempDir tempdir;
-  ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  fake_system_state_.request_params()->set_root(tempdir.GetPath().value());
   string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0 =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append(dlc_id);
-  ASSERT_TRUE(base::CreateDirectory(metadata_path_dlc0));
+  MemoryPrefs prefs;
+  fake_system_state_.set_prefs(&prefs);
   EXPECT_CALL(mock_dlcservice_, GetDlcsToUpdate(_))
       .WillOnce(
           DoAll(SetArgPointee<0>(std::vector<string>({dlc_id})), Return(true)));
 
   // Write non numeric values in the metadata files.
-  base::WriteFile(metadata_path_dlc0.Append(kPrefsPingActive), "z2yz", 4);
-  base::WriteFile(metadata_path_dlc0.Append(kPrefsPingLastActive), "z2yz", 4);
-  base::WriteFile(metadata_path_dlc0.Append(kPrefsPingLastRollcall), "z2yz", 4);
+  auto active_key =
+      PrefsInterface::CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingActive);
+  auto last_active_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastActive);
+  auto last_rollcall_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastRollcall);
+  fake_system_state_.prefs()->SetString(active_key, "z2yz");
+  fake_system_state_.prefs()->SetString(last_active_key, "z2yz");
+  fake_system_state_.prefs()->SetString(last_rollcall_key, "z2yz");
   attempter_.is_install_ = false;
   attempter_.CalculateDlcParams();
 
@@ -2440,23 +2430,24 @@
 }
 
 TEST_F(UpdateAttempterTest, CalculateDlcParamsValidValuesTest) {
-  // Create a uniquely named test directory.
-  base::ScopedTempDir tempdir;
-  ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  fake_system_state_.request_params()->set_root(tempdir.GetPath().value());
   string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0 =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append(dlc_id);
-  ASSERT_TRUE(base::CreateDirectory(metadata_path_dlc0));
+  MemoryPrefs fake_prefs;
+  fake_system_state_.set_prefs(&fake_prefs);
   EXPECT_CALL(mock_dlcservice_, GetDlcsToUpdate(_))
       .WillOnce(
           DoAll(SetArgPointee<0>(std::vector<string>({dlc_id})), Return(true)));
 
   // Write numeric values in the metadata files.
-  base::WriteFile(metadata_path_dlc0.Append(kPrefsPingActive), "1", 1);
-  base::WriteFile(metadata_path_dlc0.Append(kPrefsPingLastActive), "78", 2);
-  base::WriteFile(metadata_path_dlc0.Append(kPrefsPingLastRollcall), "99", 2);
+  auto active_key =
+      PrefsInterface::CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingActive);
+  auto last_active_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastActive);
+  auto last_rollcall_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastRollcall);
+
+  fake_system_state_.prefs()->SetInt64(active_key, 1);
+  fake_system_state_.prefs()->SetInt64(last_active_key, 78);
+  fake_system_state_.prefs()->SetInt64(last_rollcall_key, 99);
   attempter_.is_install_ = false;
   attempter_.CalculateDlcParams();
 
@@ -2473,58 +2464,64 @@
 }
 
 TEST_F(UpdateAttempterTest, CalculateDlcParamsRemoveStaleMetadata) {
-  base::ScopedTempDir tempdir;
-  ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  fake_system_state_.request_params()->set_root(tempdir.GetPath().value());
   string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0 =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append(dlc_id);
-  ASSERT_TRUE(base::CreateDirectory(metadata_path_dlc0));
-  base::FilePath metadata_path_dlc_stale =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append("stale");
-  ASSERT_TRUE(base::CreateDirectory(metadata_path_dlc_stale));
-  EXPECT_CALL(mock_dlcservice_, GetDlcsToUpdate(_))
-      .WillOnce(
-          DoAll(SetArgPointee<0>(std::vector<string>({dlc_id})), Return(true)));
+  FakePrefs fake_prefs;
+  fake_system_state_.set_prefs(&fake_prefs);
+  auto active_key =
+      PrefsInterface::CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingActive);
+  auto last_active_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastActive);
+  auto last_rollcall_key = PrefsInterface::CreateSubKey(
+      kDlcPrefsSubDir, dlc_id, kPrefsPingLastRollcall);
+  fake_system_state_.prefs()->SetInt64(active_key, kPingInactiveValue);
+  fake_system_state_.prefs()->SetInt64(last_active_key, 0);
+  fake_system_state_.prefs()->SetInt64(last_rollcall_key, 0);
+  EXPECT_TRUE(fake_system_state_.prefs()->Exists(active_key));
+  EXPECT_TRUE(fake_system_state_.prefs()->Exists(last_active_key));
+  EXPECT_TRUE(fake_system_state_.prefs()->Exists(last_rollcall_key));
 
-  attempter_.is_install_ = false;
+  attempter_.dlc_ids_ = {dlc_id};
+  attempter_.is_install_ = true;
   attempter_.CalculateDlcParams();
 
-  EXPECT_TRUE(base::PathExists(metadata_path_dlc0));
-  EXPECT_FALSE(base::PathExists(metadata_path_dlc_stale));
+  EXPECT_FALSE(fake_system_state_.prefs()->Exists(last_active_key));
+  EXPECT_FALSE(fake_system_state_.prefs()->Exists(last_rollcall_key));
+  // Active key is set on install.
+  EXPECT_TRUE(fake_system_state_.prefs()->Exists(active_key));
+  int64_t temp_int;
+  EXPECT_TRUE(fake_system_state_.prefs()->GetInt64(active_key, &temp_int));
+  EXPECT_EQ(temp_int, kPingActiveValue);
 }
 
 TEST_F(UpdateAttempterTest, SetDlcActiveValue) {
-  base::ScopedTempDir tempdir;
-  ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  fake_system_state_.request_params()->set_root(tempdir.GetPath().value());
   string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0 =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append(dlc_id);
+  FakePrefs fake_prefs;
+  fake_system_state_.set_prefs(&fake_prefs);
   attempter_.SetDlcActiveValue(true, dlc_id);
-  Prefs prefs;
-  ASSERT_TRUE(base::PathExists(metadata_path_dlc0));
-  ASSERT_TRUE(prefs.Init(metadata_path_dlc0));
   int64_t temp_int;
-  EXPECT_TRUE(prefs.GetInt64(kPrefsPingActive, &temp_int));
+  auto active_key =
+      PrefsInterface::CreateSubKey(kDlcPrefsSubDir, dlc_id, kPrefsPingActive);
+  EXPECT_TRUE(fake_system_state_.prefs()->Exists(active_key));
+  EXPECT_TRUE(fake_system_state_.prefs()->GetInt64(active_key, &temp_int));
   EXPECT_EQ(temp_int, kPingActiveValue);
 }
 
 TEST_F(UpdateAttempterTest, SetDlcInactive) {
-  base::ScopedTempDir tempdir;
-  ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  fake_system_state_.request_params()->set_root(tempdir.GetPath().value());
   string dlc_id = "dlc0";
-  base::FilePath metadata_path_dlc0 =
-      base::FilePath(fake_system_state_.request_params()->dlc_prefs_root())
-          .Append(dlc_id);
-  base::CreateDirectory(metadata_path_dlc0);
-  EXPECT_TRUE(base::PathExists(metadata_path_dlc0));
+  MemoryPrefs fake_prefs;
+  fake_system_state_.set_prefs(&fake_prefs);
+  auto sub_keys = {
+      kPrefsPingActive, kPrefsPingLastActive, kPrefsPingLastRollcall};
+  for (auto& sub_key : sub_keys) {
+    auto key = PrefsInterface::CreateSubKey(kDlcPrefsSubDir, dlc_id, sub_key);
+    fake_system_state_.prefs()->SetInt64(key, 1);
+    EXPECT_TRUE(fake_system_state_.prefs()->Exists(key));
+  }
   attempter_.SetDlcActiveValue(false, dlc_id);
-  EXPECT_FALSE(base::PathExists(metadata_path_dlc0));
+  for (auto& sub_key : sub_keys) {
+    auto key = PrefsInterface::CreateSubKey(kDlcPrefsSubDir, dlc_id, sub_key);
+    EXPECT_FALSE(fake_system_state_.prefs()->Exists(key));
+  }
 }
 
 TEST_F(UpdateAttempterTest, GetSuccessfulDlcIds) {