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

delta_diff_generator.h

Index: delta_diff_generator.h
diff --git a/delta_diff_generator.h b/delta_diff_generator.h
index 53d3f87037468f1e23617a606b9a1a781727653d..853f2dd628eb1b01a04b3b3c55e73a3c09ad153a 100644
--- a/delta_diff_generator.h
+++ b/delta_diff_generator.h
@@ -79,12 +79,15 @@ class DeltaDiffGenerator {
   // 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
@@ -100,6 +103,13 @@ class DeltaDiffGenerator {
                              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.