AU: When generating delta, use scratch off end of filesystem

delta_diff_generator.h

 // Copyright (c) 2010 The Chromium OS 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_DELTA_DIFF_GENERATOR_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_DELTA_DIFF_GENERATOR_H__
 
 #include <string>
 #include <vector>
 #include "base/basictypes.h"
@@ skipping 61 matching lines @@
                                       const std::string& private_key_path);
 
   // These functions are public so that the unit tests can access them:
 
   // Takes a graph, which is not a DAG, which represents the files just
   // read from disk, and converts it into a DAG by breaking all cycles
   // and finding temp space to resolve broken edges.
   // The final order of the nodes is given in |final_order|
   // Some files may need to be reread from disk, thus |fd| and
   // |data_file_size| are be passed.
+  // If |scratch_vertex| is not kInvalidIndex, removes it from
+  // |final_order| before returning.
   // Returns true on success.
   static bool ConvertGraphToDag(Graph* graph,
                                 const std::string& new_root,
                                 int fd,
                                 off_t* data_file_size,
-                                std::vector<Vertex::Index>* final_order);
+                                std::vector<Vertex::Index>* final_order,
+                                Vertex::Index scratch_vertex);
 
   // Reads old_filename (if it exists) and a new_filename and determines
   // the smallest way to encode this file for the diff. It stores
   // necessary data in out_data and fills in out_op.
   // If there's no change in old and new files, it creates a MOVE
   // operation. If there is a change, or the old file doesn't exist,
   // the smallest of REPLACE, REPLACE_BZ, or BSDIFF wins.
   // new_filename must contain at least one byte.
   // Returns true on success.
   static bool ReadFileToDiff(const std::string& old_filename,
                              const std::string& new_filename,
                              std::vector<char>* out_data,
                              DeltaArchiveManifest_InstallOperation* out_op,
                              bool gather_extents);
 
+  // Creates a dummy REPLACE_BZ node in the given vertex. This can be used

[petkov, 2010/12/02 05:04:06]

I assume there's no difference if it's REPLACE_BZ vs. REPLACE, the only point is
that it needs to be a write-only node?

Maybe change to "in the given |vertex|." and describe that the node writes
|num_blocks| blocks starting at |start_block|.

[adlr, 2010/12/02 19:21:41]

Correct.
Done.

+  // to provide scratch space. The node should be marked invalid before
+  // writing all nodes to the output file.
+  static void CreateScratchNode(uint64_t start_block,
+                                uint64_t num_blocks,
+                                Vertex* vertex);
+
   // Modifies blocks read by 'op' so that any blocks referred to by
   // 'remove_extents' are replaced with blocks from 'replace_extents'.
   // 'remove_extents' and 'replace_extents' must be the same number of blocks.
   // Blocks will be substituted in the order listed in the vectors.
   // E.g. if 'op' reads blocks 1, 2, 3, 4, 5, 6, 7, 8, remove_extents
   // contains blocks 6, 2, 3, 5, and replace blocks contains
   // 12, 13, 14, 15, then op will be changed to read from:
   // 1, 13, 14, 4, 15, 12, 7, 8
   static void SubstituteBlocks(Vertex* vertex,
                                const std::vector<Extent>& remove_extents,
@@ skipping 94 matching lines @@
   DISALLOW_IMPLICIT_CONSTRUCTORS(DeltaDiffGenerator);
 };
 
 extern const char* const kBsdiffPath;
 extern const char* const kBspatchPath;
 extern const char* const kDeltaMagic;
 
 };  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_DELTA_DIFF_GENERATOR_H__