Disk cache: Add base files for implementation of file format version 3.

net/disk_cache/v3/disk_format_v3.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.
 
 // The cache is stored on disk as a collection of block-files, plus an index
 // file plus a collection of external files.
 //
 // Any data blob bigger than kMaxBlockSize (net/addr.h) will be stored on a
 // separate file named f_xxx where x is a hexadecimal number. Shorter data will
 // be stored as a series of blocks on a block-file. In any case, CacheAddr
@@ skipping 42 matching lines @@
 // previous run, so it is discarded.
 
 #ifndef NET_DISK_CACHE_DISK_FORMAT_H_
 #define NET_DISK_CACHE_DISK_FORMAT_H_
 
 #include "base/basictypes.h"
 #include "net/base/net_export.h"
 
 namespace disk_cache {
 
-typedef uint32 CacheAddr;
-
-const int kIndexTablesize = 0x10000;
-const uint32 kIndexMagic = 0xC103CAC3;
 const uint32 kCurrentVersion = 0x20000;  // Version 2.0.
 
-struct LruData {
-  int32     pad1[2];
-  int32     filled;          // Flag to tell when we filled the cache.
-  int32     sizes[5];
-  CacheAddr heads[5];
-  CacheAddr tails[5];
-  CacheAddr transaction;     // In-flight operation target.
-  int32     operation;       // Actual in-flight operation.
-  int32     operation_list;  // In-flight operation list.
-  int32     pad2[7];
-};
-
 // Header for the master index file.
 struct NET_EXPORT_PRIVATE IndexHeader {
   IndexHeader();
 
   uint32      magic;
   uint32      version;
   int32       num_entries;   // Number of entries currently stored.
   int32       num_bytes;     // Total size of the stored data.
   int32       last_file;     // Last external file created.
   int32       this_id;       // Id for all entries being changed (dirty flag).
   CacheAddr   stats;         // Storage for usage data.
   int32       table_len;     // Actual size of the table (0 == kIndexTablesize).
   int32       crash;         // Signals a previous crash.
   int32       experiment;    // Id of an ongoing test.
   uint64      create_time;   // Creation time for this set of files.
   int32       pad[52];
   LruData     lru;           // Eviction control data.
 };
 
 // The structure of the whole index file.
 struct Index {
   IndexHeader header;
   CacheAddr   table[kIndexTablesize];  // Default size. Actual size controlled
                                        // by header.table_len.
 };
 
+// Possible states for a given entry.
+enum EntryState {
+  ENTRY_NORMAL = 0,
+  ENTRY_EVICTED,    // The entry was recently evicted from the cache.
+  ENTRY_DOOMED      // The entry was doomed.
+};
+
+// Flags that can be applied to an entry.
+enum EntryFlags {
+  PARENT_ENTRY = 1,         // This entry has children (sparse) entries.
+  CHILD_ENTRY = 1 << 1      // Child entry that stores sparse data.
+};
+
 // Main structure for an entry on the backing storage. If the key is longer than
 // what can be stored on this structure, it will be extended on consecutive
 // blocks (adding 256 bytes each time), up to 4 blocks (1024 - 32 - 1 chars).
 // After that point, the whole key will be stored as a data block or external
 // file.
 struct EntryStore {
   uint32      hash;               // Full hash of the key.
   CacheAddr   next;               // Next entry with the same hash or bucket.
   CacheAddr   rankings_node;      // Rankings node for this entry.
   int32       reuse_count;        // How often is this entry used.
   int32       refetch_count;      // How often is this fetched from the net.
   int32       state;              // Current state.
   uint64      creation_time;
   int32       key_len;
   CacheAddr   long_key;           // Optional address of a long key.
   int32       data_size[4];       // We can store up to 4 data streams for each
   CacheAddr   data_addr[4];       // entry.
   uint32      flags;              // Any combination of EntryFlags.
   int32       pad[4];
   uint32      self_hash;          // The hash of EntryStore up to this point.
   char        key[256 - 24 * 4];  // null terminated
 };
 
 COMPILE_ASSERT(sizeof(EntryStore) == 256, bad_EntyStore);
 const int kMaxInternalKeyLength = 4 * sizeof(EntryStore) -
                                   offsetof(EntryStore, key) - 1;
 
-// Possible states for a given entry.
-enum EntryState {
-  ENTRY_NORMAL = 0,
-  ENTRY_EVICTED,    // The entry was recently evicted from the cache.
-  ENTRY_DOOMED      // The entry was doomed.
-};
-
-// Flags that can be applied to an entry.
-enum EntryFlags {
-  PARENT_ENTRY = 1,         // This entry has children (sparse) entries.
-  CHILD_ENTRY = 1 << 1      // Child entry that stores sparse data.
-};
-
-#pragma pack(push, 4)
-// Rankings information for a given entry.
-struct RankingsNode {
-  uint64      last_used;        // LRU info.
-  uint64      last_modified;    // LRU info.
-  CacheAddr   next;             // LRU list.
-  CacheAddr   prev;             // LRU list.
-  CacheAddr   contents;         // Address of the EntryStore.
-  int32       dirty;            // The entry is being modifyied.
-  uint32      self_hash;        // RankingsNode's hash.
-};
-#pragma pack(pop)
-
-COMPILE_ASSERT(sizeof(RankingsNode) == 36, bad_RankingsNode);
-
-const uint32 kBlockMagic = 0xC104CAC3;
-const int kBlockHeaderSize = 8192;  // Two pages: almost 64k entries
-const int kMaxBlocks = (kBlockHeaderSize - 80) * 8;
-
-// 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).
-// This Structure is the header of a block-file:
-struct NET_EXPORT_PRIVATE BlockFileHeader {
-  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.
-  int32           user[5];
-  AllocBitmap     allocation_map;
-};
-
-COMPILE_ASSERT(sizeof(BlockFileHeader) == kBlockHeaderSize, bad_header);
-
-// Sparse data support:
-// We keep a two level hierarchy to enable sparse data for an entry: the first
-// level consists of using separate "child" entries to store ranges of 1 MB,
-// and the second level stores blocks of 1 KB inside each child entry.
-//
-// Whenever we need to access a particular sparse offset, we first locate the
-// child entry that stores that offset, so we discard the 20 least significant
-// bits of the offset, and end up with the child id. For instance, the child id
-// to store the first megabyte is 0, and the child that should store offset
-// 0x410000 has an id of 4.
-//
-// The child entry is stored the same way as any other entry, so it also has a
-// name (key). The key includes a signature to be able to identify children
-// created for different generations of the same resource. In other words, given
-// that a given sparse entry can have a large number of child entries, and the
-// resource can be invalidated and replaced with a new version at any time, it
-// is important to be sure that a given child actually belongs to certain entry.
-//
-// The full name of a child entry is composed with a prefix ("Range_"), and two
-// hexadecimal 64-bit numbers at the end, separated by semicolons. The first
-// number is the signature of the parent key, and the second number is the child
-// id as described previously. The signature itself is also stored internally by
-// the child and the parent entries. For example, a sparse entry with a key of
-// "sparse entry name", and a signature of 0x052AF76, may have a child entry
-// named "Range_sparse entry name:052af76:4", which stores data in the range
-// 0x400000 to 0x4FFFFF.
-//
-// Each child entry keeps track of all the 1 KB blocks that have been written
-// to the entry, but being a regular entry, it will happily return zeros for any
-// read that spans data not written before. The actual sparse data is stored in
-// one of the data streams of the child entry (at index 1), while the control
-// information is stored in another stream (at index 2), both by parents and
-// the children.
-
-// This structure contains the control information for parent and child entries.
-// It is stored at offset 0 of the data stream with index 2.
-// It is possible to write to a child entry in a way that causes the last block
-// to be only partialy filled. In that case, last_block and last_block_len will
-// keep track of that block.
-struct SparseHeader {
-  int64 signature;          // The parent and children signature.
-  uint32 magic;             // Structure identifier (equal to kIndexMagic).
-  int32 parent_key_len;     // Key length for the parent entry.
-  int32 last_block;         // Index of the last written block.
-  int32 last_block_len;     // Lenght of the last written block.
-  int32 dummy[10];
-};
-
-// The SparseHeader will be followed by a bitmap, as described by this
-// structure.
-struct SparseData {
-  SparseHeader header;
-  uint32 bitmap[32];        // Bitmap representation of known children (if this
-                            // is a parent entry), or used blocks (for child
-                            // entries. The size is fixed for child entries but
-                            // not for parents; it can be as small as 4 bytes
-                            // and as large as 8 KB.
-};
-
-// 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_H_