net/disk_cache/blockfile/disk_format.h - platform/external/chromium_org - Git at Google

 // 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 (disk_cache/addr.h) will be stored in
 // 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
 // represents the address of the data inside the cache.
 //
 // The index file is just a simple hash table that maps a particular entry to
 // a CacheAddr value. Linking for a given hash bucket is handled internally
 // by the cache entry.
 //
 // The last element of the cache is the block-file. A block file is a file
 // designed to store blocks of data of a given size. For more details see
 // disk_cache/disk_format_base.h
 //
 // A new cache is initialized with four block files (named data_0 through
 // data_3), each one dedicated to store blocks of a given size. The number at
 // the end of the file name is the block file number (in decimal).
 //
 // There are two "special" types of blocks: an entry and a rankings node. An
 // entry keeps track of all the information related to the same cache entry,
 // such as the key, hash value, data pointers etc. A rankings node keeps track
 // of the information that is updated frequently for a given entry, such as its
 // location on the LRU lists, last access time etc.
 //
 // The files that store internal information for the cache (blocks and index)
 // are at least partially memory mapped. They have a location that is signaled
 // every time the internal structures are modified, so it is possible to detect
 // (most of the time) when the process dies in the middle of an update.
 //
 // In order to prevent dirty data to be used as valid (after a crash), every
 // cache entry has a dirty identifier. Each running instance of the cache keeps
 // a separate identifier (maintained on the "this_id" header field) that is used
 // to mark every entry that is created or modified. When the entry is closed,
 // and all the data can be trusted, the dirty flag is cleared from the entry.
 // When the cache encounters an entry whose identifier is different than the one
 // being currently used, it means that the entry was not properly closed on a
 // previous run, so it is discarded.

 #ifndef NET_DISK_CACHE_BLOCKFILE_DISK_FORMAT_H_
 #define NET_DISK_CACHE_BLOCKFILE_DISK_FORMAT_H_

 #include "base/basictypes.h"
 #include "net/base/net_export.h"
 #include "net/disk_cache/blockfile/disk_format_base.h"

 namespace disk_cache {

 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.
 };

 // 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);

 }  // namespace disk_cache

 #endif  // NET_DISK_CACHE_BLOCKFILE_DISK_FORMAT_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 (disk_cache/addr.h) will be stored in
	// 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
	// represents the address of the data inside the cache.
	//
	// The index file is just a simple hash table that maps a particular entry to
	// a CacheAddr value. Linking for a given hash bucket is handled internally
	// by the cache entry.
	//
	// The last element of the cache is the block-file. A block file is a file
	// designed to store blocks of data of a given size. For more details see
	// disk_cache/disk_format_base.h
	//
	// A new cache is initialized with four block files (named data_0 through
	// data_3), each one dedicated to store blocks of a given size. The number at
	// the end of the file name is the block file number (in decimal).
	//
	// There are two "special" types of blocks: an entry and a rankings node. An
	// entry keeps track of all the information related to the same cache entry,
	// such as the key, hash value, data pointers etc. A rankings node keeps track
	// of the information that is updated frequently for a given entry, such as its
	// location on the LRU lists, last access time etc.
	//
	// The files that store internal information for the cache (blocks and index)
	// are at least partially memory mapped. They have a location that is signaled
	// every time the internal structures are modified, so it is possible to detect
	// (most of the time) when the process dies in the middle of an update.
	//
	// In order to prevent dirty data to be used as valid (after a crash), every
	// cache entry has a dirty identifier. Each running instance of the cache keeps
	// a separate identifier (maintained on the "this_id" header field) that is used
	// to mark every entry that is created or modified. When the entry is closed,
	// and all the data can be trusted, the dirty flag is cleared from the entry.
	// When the cache encounters an entry whose identifier is different than the one
	// being currently used, it means that the entry was not properly closed on a
	// previous run, so it is discarded.

	#ifndef NET_DISK_CACHE_BLOCKFILE_DISK_FORMAT_H_
	#define NET_DISK_CACHE_BLOCKFILE_DISK_FORMAT_H_

	#include "base/basictypes.h"
	#include "net/base/net_export.h"
	#include "net/disk_cache/blockfile/disk_format_base.h"

	namespace disk_cache {

	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.
	};

	// 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);

	} // namespace disk_cache

	#endif // NET_DISK_CACHE_BLOCKFILE_DISK_FORMAT_H_