AU: delta compress the kernel partition

src/platform/update_engine/utils.h

 // 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.
 
 #ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__
 
 #include <errno.h>
 #include <algorithm>
 #include <set>
@@ skipping 18 matching lines @@
 
 // Calls pread() repeatedly until count bytes are read, or EOF is reached.
 // Returns number of bytes read in *bytes_read. Returns true on success.
 bool PReadAll(int fd, void* buf, size_t count, off_t offset,
               ssize_t* out_bytes_read);
 
 // Returns the entire contents of the file at path. Returns true on success.
 bool ReadFile(const std::string& path, std::vector<char>* out);
 bool ReadFileToString(const std::string& path, std::string* out);
 
+// Returns the size of the file at path. If the file doesn't exist or some
+// error occurrs, -1 is returned.
+off_t FileSize(const std::string& path);
+
 std::string ErrnoNumberAsString(int err);
 
 // Strips duplicate slashes, and optionally removes all trailing slashes.
 // Does not compact /./ or /../.
 std::string NormalizePath(const std::string& path, bool strip_trailing_slash);
 
 // Returns true if the file exists for sure. Returns false if it doesn't exist,
 // or an error occurs.
 bool FileExists(const char* path);
 
@@ skipping 215 matching lines @@
     bool _success = (_x);                                                      \
     if (!_success) {                                                           \
       LOG(ERROR) << #_x " failed.";                                            \
       return;                                                                  \
     }                                                                          \
   } while (0)
 
 
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__