net/disk_cache/blockfile/addr.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // This is an internal class that handles the address of a cache record.
   6 // See net/disk_cache/disk_cache.h for the public interface of the cache.
   7
   8 #ifndef NET_DISK_CACHE_BLOCKFILE_ADDR_H_
   9 #define NET_DISK_CACHE_BLOCKFILE_ADDR_H_
  10
  11 #include "net/base/net_export.h"
  12 #include "net/disk_cache/blockfile/disk_format_base.h"
  13
  14 namespace disk_cache {
  15
  16 enum FileType {
  17   EXTERNAL = 0,
  18   RANKINGS = 1,
  19   BLOCK_256 = 2,
  20   BLOCK_1K = 3,
  21   BLOCK_4K = 4,
  22   BLOCK_FILES = 5,
  23   BLOCK_ENTRIES = 6,
  24   BLOCK_EVICTED = 7
  25 };
  26
  27 const int kMaxBlockSize = 4096 * 4;
  28 const int kMaxBlockFile = 255;
  29 const int kMaxNumBlocks = 4;
  30 const int kFirstAdditionalBlockFile = 4;
  31 const int kFirstAdditionalBlockFileV3 = 7;
  32
  33 // Defines a storage address for a cache record
  34 //
  35 // Header:
  36 //   1000 0000 0000 0000 0000 0000 0000 0000 : initialized bit
  37 //   0111 0000 0000 0000 0000 0000 0000 0000 : file type
  38 //
  39 // File type values:
  40 //   0 = separate file on disk
  41 //   1 = rankings block file
  42 //   2 = 256 byte block file
  43 //   3 = 1k byte block file
  44 //   4 = 4k byte block file
  45 //   5 = external files block file
  46 //   6 = active entries block file
  47 //   7 = evicted entries block file
  48 //
  49 // If separate file:
  50 //   0000 1111 1111 1111 1111 1111 1111 1111 : file#  0 - 268,435,456 (2^28)
  51 //
  52 // If block file:
  53 //   0000 1100 0000 0000 0000 0000 0000 0000 : reserved bits
  54 //   0000 0011 0000 0000 0000 0000 0000 0000 : number of contiguous blocks 1-4
  55 //   0000 0000 1111 1111 0000 0000 0000 0000 : file selector 0 - 255
  56 //   0000 0000 0000 0000 1111 1111 1111 1111 : block#  0 - 65,535 (2^16)
  57 //
  58 // Note that an Addr can be used to "point" to a variety of different objects,
  59 // from a given type of entry to random blobs of data. Conceptually, an Addr is
  60 // just a number that someone can inspect to find out how to locate the desired
  61 // record. Most users will not care about the specific bits inside Addr, for
  62 // example, what parts of it point to a file number; only the code that has to
  63 // select a specific file would care about those specific bits.
  64 //
  65 // From a general point of view, an Addr has a total capacity of 2^24 entities,
  66 // in that it has 24 bits that can identify individual records. Note that the
  67 // address space is bigger for independent files (2^28), but that would not be
  68 // the general case.
  69 class NET_EXPORT_PRIVATE Addr {
  70  public:
  71   Addr() : value_(0) {}
  72   explicit Addr(CacheAddr address) : value_(address) {}
  73   Addr(FileType file_type, int max_blocks, int block_file, int index) {
  74     value_ = ((file_type << kFileTypeOffset) & kFileTypeMask) |
  75              (((max_blocks - 1) << kNumBlocksOffset) & kNumBlocksMask) |
  76              ((block_file << kFileSelectorOffset) & kFileSelectorMask) |
  77              (index  & kStartBlockMask) | kInitializedMask;
  78   }
  79
  80   CacheAddr value() const { return value_; }
  81   void set_value(CacheAddr address) {
  82     value_ = address;
  83   }
  84
  85   bool is_initialized() const {
  86     return (value_ & kInitializedMask) != 0;
  87   }
  88
  89   bool is_separate_file() const {
  90     return (value_ & kFileTypeMask) == 0;
  91   }
  92
  93   bool is_block_file() const {
  94     return !is_separate_file();
  95   }
  96
  97   FileType file_type() const {
  98     return static_cast<FileType>((value_ & kFileTypeMask) >> kFileTypeOffset);
  99   }
 100
 101   int FileNumber() const {
 102     if (is_separate_file())
 103       return value_ & kFileNameMask;
 104     else
 105       return ((value_ & kFileSelectorMask) >> kFileSelectorOffset);
 106   }
 107
 108   int start_block() const;
 109   int num_blocks() const;
 110   bool SetFileNumber(int file_number);
 111   int BlockSize() const {
 112     return BlockSizeForFileType(file_type());
 113   }
 114
 115   bool operator==(Addr other) const {
 116     return value_ == other.value_;
 117   }
 118
 119   bool operator!=(Addr other) const {
 120     return value_ != other.value_;
 121   }
 122
 123   static int BlockSizeForFileType(FileType file_type) {
 124     switch (file_type) {
 125       case RANKINGS:
 126         return 36;
 127       case BLOCK_256:
 128         return 256;
 129       case BLOCK_1K:
 130         return 1024;
 131       case BLOCK_4K:
 132         return 4096;
 133       case BLOCK_FILES:
 134         return 8;
 135       case BLOCK_ENTRIES:
 136         return 104;
 137       case BLOCK_EVICTED:
 138         return 48;
 139       default:
 140         return 0;
 141     }
 142   }
 143
 144   static FileType RequiredFileType(int size) {
 145     if (size < 1024)
 146       return BLOCK_256;
 147     else if (size < 4096)
 148       return BLOCK_1K;
 149     else if (size <= 4096 * 4)
 150       return BLOCK_4K;
 151     else
 152       return EXTERNAL;
 153   }
 154
 155   static int RequiredBlocks(int size, FileType file_type) {
 156     int block_size = BlockSizeForFileType(file_type);
 157     return (size + block_size - 1) / block_size;
 158   }
 159
 160   // Returns true if this address looks like a valid one.
 161   bool SanityCheckV2() const;
 162   bool SanityCheckV3() const;
 163   bool SanityCheckForEntryV2() const;
 164   bool SanityCheckForEntryV3() const;
 165   bool SanityCheckForRankings() const;
 166
 167  private:
 168   uint32 reserved_bits() const {
 169     return value_ & kReservedBitsMask;
 170   }
 171
 172   static const uint32 kInitializedMask    = 0x80000000;
 173   static const uint32 kFileTypeMask       = 0x70000000;
 174   static const uint32 kFileTypeOffset     = 28;
 175   static const uint32 kReservedBitsMask   = 0x0c000000;
 176   static const uint32 kNumBlocksMask      = 0x03000000;
 177   static const uint32 kNumBlocksOffset    = 24;
 178   static const uint32 kFileSelectorMask   = 0x00ff0000;
 179   static const uint32 kFileSelectorOffset = 16;
 180   static const uint32 kStartBlockMask     = 0x0000FFFF;
 181   static const uint32 kFileNameMask       = 0x0FFFFFFF;
 182
 183   CacheAddr value_;
 184 };
 185
 186 }  // namespace disk_cache
 187
 188 #endif  // NET_DISK_CACHE_BLOCKFILE_ADDR_H_