diff --git a/uncrypt/Android.mk b/uncrypt/Android.mk
index 6422cb2..09cfdfc 100644
--- a/uncrypt/Android.mk
+++ b/uncrypt/Android.mk
@@ -15,6 +15,15 @@
 LOCAL_PATH := $(call my-dir)
 
 include $(CLEAR_VARS)
+LOCAL_CLANG := true
+LOCAL_SRC_FILES := bootloader_message_writer.cpp
+LOCAL_MODULE := libbootloader_message_writer
+LOCAL_STATIC_LIBRARIES := libbase libfs_mgr
+LOCAL_C_INCLUDES := $(LOCAL_PATH)/..
+LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
+include $(BUILD_STATIC_LIBRARY)
+
+include $(CLEAR_VARS)
 
 LOCAL_CLANG := true
 
@@ -24,7 +33,8 @@
 
 LOCAL_MODULE := uncrypt
 
-LOCAL_STATIC_LIBRARIES := libbase liblog libfs_mgr libcutils
+LOCAL_STATIC_LIBRARIES := libbootloader_message_writer libbase \
+                          liblog libfs_mgr libcutils \
 
 LOCAL_INIT_RC := uncrypt.rc
 
diff --git a/uncrypt/bootloader_message_writer.cpp b/uncrypt/bootloader_message_writer.cpp
new file mode 100644
index 0000000..3bb106a
--- /dev/null
+++ b/uncrypt/bootloader_message_writer.cpp
@@ -0,0 +1,107 @@
+/*
+ * Copyright (C) 2016 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.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/system_properties.h>
+
+#include <string>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/stringprintf.h>
+#include <android-base/unique_fd.h>
+#include <fs_mgr.h>
+
+#include "bootloader.h"
+
+static struct fstab* read_fstab(std::string* err) {
+  // The fstab path is always "/fstab.${ro.hardware}".
+  std::string fstab_path = "/fstab.";
+  char value[PROP_VALUE_MAX];
+  if (__system_property_get("ro.hardware", value) == 0) {
+    *err = "failed to get ro.hardware";
+    return nullptr;
+  }
+  fstab_path += value;
+  struct fstab* fstab = fs_mgr_read_fstab(fstab_path.c_str());
+  if (fstab == nullptr) {
+    *err = "failed to read " + fstab_path;
+  }
+  return fstab;
+}
+
+static std::string get_misc_blk_device(std::string* err) {
+  struct fstab* fstab = read_fstab(err);
+  if (fstab == nullptr) {
+    return "";
+  }
+  fstab_rec* record = fs_mgr_get_entry_for_mount_point(fstab, "/misc");
+  if (record == nullptr) {
+    *err = "failed to find /misc partition";
+    return "";
+  }
+  return record->blk_device;
+}
+
+static bool write_bootloader_message(const bootloader_message& boot, std::string* err) {
+  std::string misc_blk_device = get_misc_blk_device(err);
+  if (misc_blk_device.empty()) {
+    return false;
+  }
+  android::base::unique_fd fd(open(misc_blk_device.c_str(), O_WRONLY | O_SYNC));
+  if (fd.get() == -1) {
+    *err = android::base::StringPrintf("failed to open %s: %s", misc_blk_device.c_str(),
+                                       strerror(errno));
+    return false;
+  }
+  if (!android::base::WriteFully(fd.get(), &boot, sizeof(boot))) {
+    *err = android::base::StringPrintf("failed to write %s: %s", misc_blk_device.c_str(),
+                                       strerror(errno));
+    return false;
+  }
+  // TODO: O_SYNC and fsync duplicates each other?
+  if (fsync(fd.get()) == -1) {
+    *err = android::base::StringPrintf("failed to fsync %s: %s", misc_blk_device.c_str(),
+                                       strerror(errno));
+    return false;
+  }
+  return true;
+}
+
+bool clear_bootloader_message(std::string* err) {
+  bootloader_message boot = {};
+  return write_bootloader_message(boot, err);
+}
+
+bool write_bootloader_message(const std::vector<std::string>& options, std::string* err) {
+  bootloader_message boot = {};
+  strlcpy(boot.command, "boot-recovery", sizeof(boot.command));
+  strlcpy(boot.recovery, "recovery\n", sizeof(boot.recovery));
+  for (const auto& s : options) {
+    strlcat(boot.recovery, s.c_str(), sizeof(boot.recovery));
+    if (s.back() != '\n') {
+      strlcat(boot.recovery, "\n", sizeof(boot.recovery));
+    }
+  }
+  return write_bootloader_message(boot, err);
+}
+
+extern "C" bool write_bootloader_message(const char* options) {
+  std::string err;
+  return write_bootloader_message({options}, &err);
+}
diff --git a/uncrypt/include/bootloader_message_writer.h b/uncrypt/include/bootloader_message_writer.h
new file mode 100644
index 0000000..e0ca3f4
--- /dev/null
+++ b/uncrypt/include/bootloader_message_writer.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2016 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 BOOTLOADER_MESSAGE_WRITER_H
+#define BOOTLOADER_MESSAGE_WRITER_H
+
+#ifdef __cplusplus
+#include <string>
+#include <vector>
+
+bool clear_bootloader_message(std::string* err);
+
+bool write_bootloader_message(const std::vector<std::string>& options, std::string* err);
+
+#else
+#include <stdbool.h>
+
+// C Interface.
+bool write_bootloader_message(const char* options);
+#endif
+
+#endif  // BOOTLOADER_MESSAGE_WRITER_H
diff --git a/uncrypt/uncrypt.cpp b/uncrypt/uncrypt.cpp
index 2ef0935..d7105a0 100644
--- a/uncrypt/uncrypt.cpp
+++ b/uncrypt/uncrypt.cpp
@@ -109,6 +109,7 @@
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
+#include <bootloader_message_writer.h>
 #include <cutils/android_reboot.h>
 #include <cutils/properties.h>
 #include <cutils/sockets.h>
@@ -117,7 +118,6 @@
 #define LOG_TAG "uncrypt"
 #include <log/log.h>
 
-#include "bootloader.h"
 #include "unique_fd.h"
 
 #define WINDOW_SIZE 5
@@ -414,40 +414,6 @@
     return 0;
 }
 
-static std::string get_misc_blk_device() {
-    if (fstab == nullptr) {
-        return "";
-    }
-    struct fstab_rec* rec = fs_mgr_get_entry_for_mount_point(fstab, "/misc");
-    if (rec != nullptr) {
-        return rec->blk_device;
-    }
-    return "";
-}
-
-static int write_bootloader_message(const bootloader_message* in) {
-    std::string misc_blk_device = get_misc_blk_device();
-    if (misc_blk_device.empty()) {
-        ALOGE("failed to find /misc partition.");
-        return -1;
-    }
-    unique_fd fd(open(misc_blk_device.c_str(), O_WRONLY | O_SYNC));
-    if (!fd) {
-        ALOGE("failed to open %s: %s", misc_blk_device.c_str(), strerror(errno));
-        return -1;
-    }
-    if (!android::base::WriteFully(fd.get(), in, sizeof(*in))) {
-        ALOGE("failed to write %s: %s", misc_blk_device.c_str(), strerror(errno));
-        return -1;
-    }
-    // TODO: O_SYNC and fsync() duplicates each other?
-    if (fsync(fd.get()) == -1) {
-        ALOGE("failed to fsync %s: %s", misc_blk_device.c_str(), strerror(errno));
-        return -1;
-    }
-    return 0;
-}
-
 static int uncrypt(const char* input_path, const char* map_file, const int socket) {
     ALOGI("update package is \"%s\"", input_path);
 
@@ -510,8 +476,9 @@
 }
 
 static bool clear_bcb(const int socket) {
-    bootloader_message boot = {};
-    if (write_bootloader_message(&boot) != 0) {
+    std::string err;
+    if (!clear_bootloader_message(&err)) {
+        ALOGE("failed to clear bootloader message: %s", err.c_str());
         write_status_to_socket(-1, socket);
         return false;
     }
@@ -538,12 +505,9 @@
     ALOGI("  received command: [%s] (%zu)", content.c_str(), content.size());
 
     // c8. setup the bcb command
-    bootloader_message boot = {};
-    strlcpy(boot.command, "boot-recovery", sizeof(boot.command));
-    strlcpy(boot.recovery, "recovery\n", sizeof(boot.recovery));
-    strlcat(boot.recovery, content.c_str(), sizeof(boot.recovery));
-    if (write_bootloader_message(&boot) != 0) {
-        ALOGE("failed to set bootloader message");
+    std::string err;
+    if (!write_bootloader_message({content}, &err)) {
+        ALOGE("failed to set bootloader message: %s", err.c_str());
         write_status_to_socket(-1, socket);
         return false;
     }