AU: delta compress the kernel partition

src/platform/update_engine/utils.cc

 // Copyright (c) 2009 The Chromium 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/stat.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>
@@ skipping 87 matching lines @@
 bool ReadFileToString(const std::string& path, std::string* out) {
   vector<char> data;
   bool success = ReadFile(path, &data);
   if (!success) {
     return false;
   }
   (*out) = string(&data[0], data.size());
   return true;
 }
 
+off_t FileSize(const string& path) {
+  struct stat stbuf;
+  int rc = stat(path.c_str(), &stbuf);
+  CHECK_EQ(rc, 0);
+  if (rc < 0)
+    return rc;
+  return stbuf.st_size;
+}
+
 void HexDumpArray(const unsigned char* const arr, const size_t length) {
   const unsigned char* const char_arr =
       reinterpret_cast<const unsigned char* const>(arr);
   LOG(INFO) << "Logging array of length: " << length;
   const unsigned int bytes_per_line = 16;
   for (uint32_t i = 0; i < length; i += bytes_per_line) {
     const unsigned int bytes_remaining = length - i;
     const unsigned int bytes_per_this_line = min(bytes_per_line,
                                                  bytes_remaining);
     char header[100];
@@ skipping 220 matching lines @@
     return "Unknown error.";
   return error->message;
 }
 
 const char* const kStatefulPartition = "/mnt/stateful_partition";
 
 }  // namespace utils
 
 }  // namespace chromeos_update_engine