Disk cache: Reference CL for the implementation of file format version 3.

net/disk_cache/addr.h

 // Copyright (c) 2012 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.
 
 // This is an internal class that handles the address of a cache record.
 // See net/disk_cache/disk_cache.h for the public interface of the cache.
 
 #ifndef NET_DISK_CACHE_ADDR_H_
 #define NET_DISK_CACHE_ADDR_H_
 
 #include "net/base/net_export.h"
-#include "net/disk_cache/disk_format.h"
+#include "net/disk_cache/disk_format_base.h"
 
 namespace disk_cache {
 
 enum FileType {
   EXTERNAL = 0,
   RANKINGS = 1,
-  BLOCK_256,
-  BLOCK_1K,
-  BLOCK_4K,
+  BLOCK_256 = 2,
+  BLOCK_1K = 3,
+  BLOCK_4K = 4,
+  BLOCK_FILES = 5,
+  BLOCK_ENTRIES = 6,
+  BLOCK_EVICTED = 7
 };
 
 const int kMaxBlockSize = 4096 * 4;
 const int kMaxBlockFile = 255;
 const int kMaxNumBlocks = 4;
 const int kFirstAdditionalBlockFile = 4;
+const int kFirstAdditionalBlockFileV3 = 7;
 
 // Defines a storage address for a cache record
 //
 // Header:
 //   1000 0000 0000 0000 0000 0000 0000 0000 : initialized bit
 //   0111 0000 0000 0000 0000 0000 0000 0000 : file type
 //
 // File type values:
 //   0 = separate file on disk
 //   1 = rankings block file
 //   2 = 256 byte block file
 //   3 = 1k byte block file
 //   4 = 4k byte block file
+//   5 = external files block file
+//   6 = active entries block file
+//   7 = evicted entries block file
 //
 // If separate file:
 //   0000 1111 1111 1111 1111 1111 1111 1111 : file#  0 - 268,435,456 (2^28)
 //
 // If block file:
 //   0000 1100 0000 0000 0000 0000 0000 0000 : reserved bits
 //   0000 0011 0000 0000 0000 0000 0000 0000 : number of contiguous blocks 1-4
 //   0000 0000 1111 1111 0000 0000 0000 0000 : file selector 0 - 255
 //   0000 0000 0000 0000 1111 1111 1111 1111 : block#  0 - 65,535 (2^16)
+//
+// Note that an Addr can be used to "point" to a variety of different objects,
+// from a given type of entry to random blobs of data. Conceptually, an Addr is
+// just a number that someone can inspect to find out how to locate the desired
+// record. Most users will not care about the specific bits inside Addr, for
+// example, what parts of it point to a file number; only the code that has to
+// select a specific file would care about those specific bits.
+//
+// From a general point of view, an Addr has a total capacity of 2^24 entities,
+// in that it has 24 bits that can identify individual records. Note that the
+// address space is bigger for independent files (2^28), but that would not be
+// the general case.
 class NET_EXPORT_PRIVATE Addr {
  public:
   Addr() : value_(0) {}
   explicit Addr(CacheAddr address) : value_(address) {}
   Addr(FileType file_type, int max_blocks, int block_file, int index) {
     value_ = ((file_type << kFileTypeOffset) & kFileTypeMask) |
              (((max_blocks - 1) << kNumBlocksOffset) & kNumBlocksMask) |
              ((block_file << kFileSelectorOffset) & kFileSelectorMask) |
              (index  & kStartBlockMask) | kInitializedMask;
   }
@@ skipping 34 matching lines @@
   }
 
   bool operator==(Addr other) const {
     return value_ == other.value_;
   }
 
   bool operator!=(Addr other) const {
     return value_ != other.value_;
   }
 
+  // Conversions between the address of an external file and the address of the
+  // control block of that external file.
+  Addr AsExternal() const;
+  Addr AsBlockFile() const;
+
   static int BlockSizeForFileType(FileType file_type) {
     switch (file_type) {
       case RANKINGS:
         return 36;
       case BLOCK_256:
         return 256;
       case BLOCK_1K:
         return 1024;
       case BLOCK_4K:
         return 4096;
+      case BLOCK_FILES:
+        return 8;
+      case BLOCK_ENTRIES:
+        return 104;
+      case BLOCK_EVICTED:
+        return 48;
       default:
         return 0;
     }
   }
 
   static FileType RequiredFileType(int size) {
     if (size < 1024)
       return BLOCK_256;
     else if (size < 4096)
       return BLOCK_1K;
     else if (size <= 4096 * 4)
       return BLOCK_4K;
     else
       return EXTERNAL;
   }
 
+  static int RequiredBlocks(int size, FileType file_type) {
+    int block_size = BlockSizeForFileType(file_type);
+    return (size + block_size - 1) / block_size;
+  }
+
   // Returns true if this address looks like a valid one.
-  bool SanityCheck() const;
-  bool SanityCheckForEntry() const;
+  bool SanityCheckV2() const;
+  bool SanityCheckV3() const;
+  bool SanityCheckForEntryV2() const;
+  bool SanityCheckForEntryV3() const;
   bool SanityCheckForRankings() const;
 
  private:
+  uint32 reserved_bits() const {
+    return value_ & kReservedBitsMask;
+  }
+
+  void SetFileType(FileType type);
+
   static const uint32 kInitializedMask    = 0x80000000;
   static const uint32 kFileTypeMask       = 0x70000000;
   static const uint32 kFileTypeOffset     = 28;
+  static const uint32 kReservedBitsMask   = 0x0c000000;
   static const uint32 kNumBlocksMask      = 0x03000000;
   static const uint32 kNumBlocksOffset    = 24;
   static const uint32 kFileSelectorMask   = 0x00ff0000;
   static const uint32 kFileSelectorOffset = 16;
   static const uint32 kStartBlockMask     = 0x0000FFFF;
   static const uint32 kFileNameMask       = 0x0FFFFFFF;
 
   CacheAddr value_;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_ADDR_H_