diff --git a/common/constants.h b/common/constants.h
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+//
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef UPDATE_ENGINE_COMMON_CONSTANTS_H_
+#define UPDATE_ENGINE_COMMON_CONSTANTS_H_
+
+namespace chromeos_update_engine {
+
+// The name of the marker file used to trigger powerwash when post-install
+// completes successfully so that the device is powerwashed on next reboot.
+extern const char kPowerwashMarkerFile[];
+
+// The contents of the powerwash marker file.
+extern const char kPowerwashCommand[];
+
+// Directory for AU prefs that are preserved across powerwash.
+extern const char kPowerwashSafePrefsSubDirectory[];
+
+// The location where we store the AU preferences (state etc).
+extern const char kPrefsSubDirectory[];
+
+// Path to the stateful partition on the root filesystem.
+extern const char kStatefulPartition[];
+
+// Constants related to preferences.
+extern const char kPrefsAttemptInProgress[];
+extern const char kPrefsBackoffExpiryTime[];
+extern const char kPrefsBootId[];
+extern const char kPrefsCertificateReportToSendDownload[];
+extern const char kPrefsCertificateReportToSendUpdate[];
+extern const char kPrefsCurrentBytesDownloaded[];
+extern const char kPrefsCurrentResponseSignature[];
+extern const char kPrefsCurrentUrlFailureCount[];
+extern const char kPrefsCurrentUrlIndex[];
+extern const char kPrefsDailyMetricsLastReportedAt[];
+extern const char kPrefsDeltaUpdateFailures[];
+extern const char kPrefsFullPayloadAttemptNumber[];
+extern const char kPrefsInstallDateDays[];
+extern const char kPrefsLastActivePingDay[];
+extern const char kPrefsLastRollCallPingDay[];
+extern const char kPrefsManifestMetadataSize[];
+extern const char kPrefsMetricsAttemptLastReportingTime[];
+extern const char kPrefsMetricsCheckLastReportingTime[];
+extern const char kPrefsNumReboots[];
+extern const char kPrefsNumResponsesSeen[];
+extern const char kPrefsOmahaCohort[];
+extern const char kPrefsOmahaCohortHint[];
+extern const char kPrefsOmahaCohortName[];
+extern const char kPrefsP2PEnabled[];
+extern const char kPrefsP2PFirstAttemptTimestamp[];
+extern const char kPrefsP2PNumAttempts[];
+extern const char kPrefsPayloadAttemptNumber[];
+extern const char kPrefsPreviousVersion[];
+extern const char kPrefsResumedUpdateFailures[];
+extern const char kPrefsRollbackVersion[];
+extern const char kPrefsChannelOnSlotPrefix[];
+extern const char kPrefsSystemUpdatedMarker[];
+extern const char kPrefsTargetVersionAttempt[];
+extern const char kPrefsTargetVersionInstalledFrom[];
+extern const char kPrefsTargetVersionUniqueId[];
+extern const char kPrefsTotalBytesDownloaded[];
+extern const char kPrefsUpdateCheckCount[];
+extern const char kPrefsUpdateCheckResponseHash[];
+extern const char kPrefsUpdateCompletedBootTime[];
+extern const char kPrefsUpdateCompletedOnBootId[];
+extern const char kPrefsUpdateDurationUptime[];
+extern const char kPrefsUpdateFirstSeenAt[];
+extern const char kPrefsUpdateOverCellularPermission[];
+extern const char kPrefsUpdateServerCertificate[];
+extern const char kPrefsUpdateStateNextDataLength[];
+extern const char kPrefsUpdateStateNextDataOffset[];
+extern const char kPrefsUpdateStateNextOperation[];
+extern const char kPrefsUpdateStateSHA256Context[];
+extern const char kPrefsUpdateStateSignatureBlob[];
+extern const char kPrefsUpdateStateSignedSHA256Context[];
+extern const char kPrefsUpdateTimestampStart[];
+extern const char kPrefsUrlSwitchCount[];
+extern const char kPrefsWallClockWaitPeriod[];
+
+// A download source is any combination of protocol and server (that's of
+// interest to us when looking at UMA metrics) using which we may download
+// the payload.
+typedef enum {
+  kDownloadSourceHttpsServer,  // UMA Binary representation: 0001
+  kDownloadSourceHttpServer,   // UMA Binary representation: 0010
+  kDownloadSourceHttpPeer,     // UMA Binary representation: 0100
+
+  // Note: Add new sources only above this line.
+  kNumDownloadSources
+} DownloadSource;
+
+// A payload can be a Full or Delta payload. In some cases, a Full payload is
+// used even when a Delta payload was available for the update, called here
+// ForcedFull. The PayloadType enum is only used to send UMA metrics about the
+// successfully applied payload.
+typedef enum {
+  kPayloadTypeFull,
+  kPayloadTypeDelta,
+  kPayloadTypeForcedFull,
+
+  // Note: Add new payload types only above this line.
+  kNumPayloadTypes
+} PayloadType;
+
+// Maximum number of times we'll allow using p2p for the same update payload.
+const int kMaxP2PAttempts = 10;
+
+// Maximum wallclock time we allow attempting to update using p2p for
+// the same update payload - five days.
+const int kMaxP2PAttemptTimeSeconds = 5 * 24 * 60 * 60;
+
+// The maximum amount of time to spend waiting for p2p-client(1) to
+// return while waiting in line to use the LAN - six hours.
+const int kMaxP2PNetworkWaitTimeSeconds = 6 * 60 * 60;
+
+// The maximum number of payload files to keep in /var/cache/p2p.
+const int kMaxP2PFilesToKeep = 3;
+
+// The maximum number of days to keep a p2p file;
+const int kMaxP2PFileAgeDays = 5;
+
+// The default number of UMA buckets for metrics.
+const int kNumDefaultUmaBuckets = 50;
+
+// General constants
+const int kNumBytesInOneMiB = 1024 * 1024;
+
+// Number of redirects allowed when downloading.
+const int kDownloadMaxRedirects = 10;
+
+// The minimum average speed that downloads must sustain...
+//
+// This is set low because some devices may have very poor
+// connectivity and we want to make as much forward progress as
+// possible. For p2p this is high (25 kB/second) since we can assume
+// high bandwidth (same LAN) and we want to fail fast.
+const int kDownloadLowSpeedLimitBps = 1;
+const int kDownloadP2PLowSpeedLimitBps = 25 * 1000;
+
+// ... measured over this period.
+//
+// For non-official builds (e.g. typically built on a developer's
+// workstation and served via devserver) bump this since it takes time
+// for the workstation to generate the payload. For p2p, make this
+// relatively low since we want to fail fast.
+const int kDownloadLowSpeedTimeSeconds = 90;
+const int kDownloadDevModeLowSpeedTimeSeconds = 180;
+const int kDownloadP2PLowSpeedTimeSeconds = 60;
+
+// The maximum amount of HTTP server reconnect attempts.
+//
+// This is set high in order to maximize the attempt's chance of
+// succeeding. When using p2p, this is low in order to fail fast.
+const int kDownloadMaxRetryCount = 20;
+const int kDownloadMaxRetryCountOobeNotComplete = 3;
+const int kDownloadP2PMaxRetryCount = 5;
+
+// The connect timeout, in seconds.
+//
+// This is set high because some devices may have very poor
+// connectivity and we may be using HTTPS which involves complicated
+// multi-roundtrip setup. For p2p, this is set low because we can
+// the server is on the same LAN and we want to fail fast.
+const int kDownloadConnectTimeoutSeconds = 30;
+const int kDownloadP2PConnectTimeoutSeconds = 5;
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_COMMON_CONSTANTS_H_