Disk cache v3 ref2

net/disk_cache/disk_format_base.h

 // Copyright (c) 2011 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.
 
 // For a general description of the files used by the cache see file_format.h.
 //
 // A block file is a file designed to store blocks of data of a given size. It
 // is able to store data that spans from one to four consecutive "blocks", and
 // it grows as needed to store up to approximately 65000 blocks. It has a fixed
 // size header used for book keeping such as tracking free of blocks on the
@@ skipping 15 matching lines @@
 namespace disk_cache {
 
 typedef uint32 CacheAddr;
 
 const uint32 kBlockVersion2 = 0x20000;  // Version 2.0.
 const uint32 kBlockCurrentVersion = 0x30000;  // Version 3.0.
 
 const uint32 kBlockMagic = 0xC104CAC3;
 const int kBlockHeaderSize = 8192;  // Two pages: almost 64k entries
 const int kMaxBlocks = (kBlockHeaderSize - 80) * 8;
+const int kNumExtraBlocks = 1024;
 
 // Bitmap to track used blocks on a block-file.
 typedef uint32 AllocBitmap[kMaxBlocks / 32];
 
 // A block-file is the file used to store information in blocks (could be
 // EntryStore blocks, RankingsNode blocks or user-data blocks).
 // We store entries that can expand for up to 4 consecutive blocks, and keep
 // counters of the number of blocks available for each type of entry. For
 // instance, an entry of 3 blocks is an entry of type 3. We also keep track of
 // where did we find the last entry of that type (to avoid searching the bitmap
 // from the beginning every time).
+//
+// The only difference between versions 2 and 3 is that the latter stores the
+// header and allocation file in a dedicated file, and the data in another file,
+// instead of using a single file for both things (as does version 2).
 // This Structure is the header of a block-file:
-struct BlockFileHeader {
+struct NET_EXPORT_PRIVATE BlockFileHeader {
   uint32          magic;
   uint32          version;
   int16           this_file;    // Index of this file.
   int16           next_file;    // Next file when this one is full.
   int32           entry_size;   // Size of the blocks of this file.
   int32           num_entries;  // Number of stored entries.
   int32           max_entries;  // Current maximum number of entries.
   int32           empty[4];     // Counters of empty entries for each type.
   int32           hints[4];     // Last used position for each entry type.
   volatile int32  updating;     // Keep track of updates to the header.
@@ skipping 63 matching lines @@
 };
 
 // The number of blocks stored by a child entry.
 const int kNumSparseBits = 1024;
 COMPILE_ASSERT(sizeof(SparseData) == sizeof(SparseHeader) + kNumSparseBits / 8,
                Invalid_SparseData_bitmap);
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_DISK_FORMAT_BASE_H_