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

net/disk_cache/block_files.cc

 // 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.
 
 #include "net/disk_cache/block_files.h"
 
 #include "base/atomicops.h"
 #include "base/file_util.h"
 #include "base/metrics/histogram.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
 #include "base/threading/thread_checker.h"
 #include "base/time.h"
 #include "net/disk_cache/cache_util.h"
+#include "net/disk_cache/disk_format_base.h"
 #include "net/disk_cache/file_lock.h"
 #include "net/disk_cache/trace.h"
 
 using base::TimeTicks;
 
 namespace {
 
-const char* kBlockName = "data_";
+const char kBlockName[] = "data_";
+const char kBlockDataPostfix[] = "_d";
 
 // This array is used to perform a fast lookup of the nibble bit pattern to the
 // type of entry that can be stored there (number of consecutive blocks).
 const char s_types[16] = {4, 3, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0};
 
 // Returns the type of block (number of consecutive blocks that can be stored)
 // for a given nibble of the bitmap.
 inline int GetMapBlockType(uint8 value) {
   value &= 0xf;
   return s_types[value];
 }
 
-void FixAllocationCounters(disk_cache::BlockFileHeader* header);
+}  // namespace
 
-// Creates a new entry on the allocation map, updating the apropriate counters.
-// target is the type of block to use (number of empty blocks), and size is the
-// actual number of blocks to use.
-bool CreateMapBlock(int target, int size, disk_cache::BlockFileHeader* header,
-                    int* index) {
-  if (target <= 0 || target > disk_cache::kMaxNumBlocks ||
-      size <= 0 || size > disk_cache::kMaxNumBlocks) {
+namespace disk_cache {
+
+BlockHeader::BlockHeader() : header_(NULL) {
+}
+
+BlockHeader::BlockHeader(BlockFileHeader* header) : header_(header) {
+}
+
+BlockHeader::BlockHeader(MappedFile* file)
+    : header_(reinterpret_cast<BlockFileHeader*>(file->buffer())) {
+}
+
+BlockHeader::BlockHeader(const BlockHeader& other) : header_(other.header_) {
+}
+
+BlockHeader::~BlockHeader() {
+}
+
+bool BlockHeader::CreateMapBlock(int target, int size, int* index) {
+  if (target <= 0 || target > kMaxNumBlocks ||
+      size <= 0 || size > kMaxNumBlocks) {
     NOTREACHED();
     return false;
   }
 
   TimeTicks start = TimeTicks::Now();
   // We are going to process the map on 32-block chunks (32 bits), and on every
   // chunk, iterate through the 8 nibbles where the new block can be located.
-  int current = header->hints[target - 1];
-  for (int i = 0; i < header->max_entries / 32; i++, current++) {
-    if (current == header->max_entries / 32)
+  int current = header_->hints[target - 1];
+  for (int i = 0; i < header_->max_entries / 32; i++, current++) {
+    if (current == header_->max_entries / 32)
       current = 0;
-    uint32 map_block = header->allocation_map[current];
+    uint32 map_block = header_->allocation_map[current];
 
     for (int j = 0; j < 8; j++, map_block >>= 4) {
       if (GetMapBlockType(map_block) != target)
         continue;
 
-      disk_cache::FileLock lock(header);
+      disk_cache::FileLock lock(header_);
       int index_offset = j * 4 + 4 - target;
       *index = current * 32 + index_offset;
       DCHECK_EQ(*index / 4, (*index + size - 1) / 4);
       uint32 to_add = ((1 << size) - 1) << index_offset;
-      header->num_entries++;
+      header_->num_entries++;
 
       // Note that there is no race in the normal sense here, but if we enforce
       // the order of memory accesses between num_entries and allocation_map, we
       // can assert that even if we crash here, num_entries will never be less
       // than the actual number of used blocks.
       base::subtle::MemoryBarrier();
-      header->allocation_map[current] |= to_add;
+      header_->allocation_map[current] |= to_add;
 
-      header->hints[target - 1] = current;
-      header->empty[target - 1]--;
-      DCHECK_GE(header->empty[target - 1], 0);
+      header_->hints[target - 1] = current;
+      header_->empty[target - 1]--;
+      DCHECK_GE(header_->empty[target - 1], 0);
       if (target != size) {
-        header->empty[target - size - 1]++;
+        header_->empty[target - size - 1]++;
       }
       HISTOGRAM_TIMES("DiskCache.CreateBlock", TimeTicks::Now() - start);
       return true;
     }
   }
 
   // It is possible to have an undetected corruption (for example when the OS
   // crashes), fix it here.
   LOG(ERROR) << "Failing CreateMapBlock";
-  FixAllocationCounters(header);
+  FixAllocationCounters();
   return false;
 }
 
-// Deletes the block pointed by index from allocation_map, and updates the
-// relevant counters on the header.
-void DeleteMapBlock(int index, int size, disk_cache::BlockFileHeader* header) {
-  if (size < 0 || size > disk_cache::kMaxNumBlocks) {
+void BlockHeader::DeleteMapBlock(int index, int size) {
+  if (size < 0 || size > kMaxNumBlocks) {
     NOTREACHED();
     return;
   }
   TimeTicks start = TimeTicks::Now();
   int byte_index = index / 8;
-  uint8* byte_map = reinterpret_cast<uint8*>(header->allocation_map);
+  uint8* byte_map = reinterpret_cast<uint8*>(header_->allocation_map);
   uint8 map_block = byte_map[byte_index];
 
   if (index % 8 >= 4)
     map_block >>= 4;
 
-  // See what type of block will be availabe after we delete this one.
+  // See what type of block will be available after we delete this one.
   int bits_at_end = 4 - size - index % 4;
   uint8 end_mask = (0xf << (4 - bits_at_end)) & 0xf;
   bool update_counters = (map_block & end_mask) == 0;
   uint8 new_value = map_block & ~(((1 << size) - 1) << (index % 4));
   int new_type = GetMapBlockType(new_value);
 
-  disk_cache::FileLock lock(header);
+  disk_cache::FileLock lock(header_);
   DCHECK((((1 << size) - 1) << (index % 8)) < 0x100);
   uint8  to_clear = ((1 << size) - 1) << (index % 8);
   DCHECK((byte_map[byte_index] & to_clear) == to_clear);
   byte_map[byte_index] &= ~to_clear;
 
   if (update_counters) {
     if (bits_at_end)
-      header->empty[bits_at_end - 1]--;
-    header->empty[new_type - 1]++;
-    DCHECK_GE(header->empty[bits_at_end - 1], 0);
+      header_->empty[bits_at_end - 1]--;
+    header_->empty[new_type - 1]++;
+    DCHECK_GE(header_->empty[bits_at_end - 1], 0);
   }
   base::subtle::MemoryBarrier();
-  header->num_entries--;
-  DCHECK_GE(header->num_entries, 0);
+  header_->num_entries--;
+  DCHECK_GE(header_->num_entries, 0);
   HISTOGRAM_TIMES("DiskCache.DeleteBlock", TimeTicks::Now() - start);
 }
 
-#ifndef NDEBUG
-// Returns true if the specified block is used. Note that this is a simplified
-// version of DeleteMapBlock().
-bool UsedMapBlock(int index, int size, disk_cache::BlockFileHeader* header) {
-  if (size < 0 || size > disk_cache::kMaxNumBlocks) {
+// Note that this is a simplified version of DeleteMapBlock().
+bool BlockHeader::UsedMapBlock(int index, int size) {
+  if (size < 0 || size > kMaxNumBlocks) {
     NOTREACHED();
     return false;
   }
   int byte_index = index / 8;
-  uint8* byte_map = reinterpret_cast<uint8*>(header->allocation_map);
+  uint8* byte_map = reinterpret_cast<uint8*>(header_->allocation_map);
   uint8 map_block = byte_map[byte_index];
 
   if (index % 8 >= 4)
     map_block >>= 4;
 
   DCHECK((((1 << size) - 1) << (index % 8)) < 0x100);
   uint8  to_clear = ((1 << size) - 1) << (index % 8);
   return ((byte_map[byte_index] & to_clear) == to_clear);
 }
-#endif  // NDEBUG
 
-// Restores the "empty counters" and allocation hints.
-void FixAllocationCounters(disk_cache::BlockFileHeader* header) {
-  for (int i = 0; i < disk_cache::kMaxNumBlocks; i++) {
-    header->hints[i] = 0;
-    header->empty[i] = 0;
+void BlockHeader::FixAllocationCounters() {
+  for (int i = 0; i < kMaxNumBlocks; i++) {
+    header_->hints[i] = 0;
+    header_->empty[i] = 0;
   }
 
-  for (int i = 0; i < header->max_entries / 32; i++) {
-    uint32 map_block = header->allocation_map[i];
+  for (int i = 0; i < header_->max_entries / 32; i++) {
+    uint32 map_block = header_->allocation_map[i];
 
     for (int j = 0; j < 8; j++, map_block >>= 4) {
       int type = GetMapBlockType(map_block);
       if (type)
-        header->empty[type -1]++;
+        header_->empty[type -1]++;
     }
   }
 }
 
-// Returns true if the current block file should not be used as-is to store more
-// records. |block_count| is the number of blocks to allocate.
-bool NeedToGrowBlockFile(const disk_cache::BlockFileHeader* header,
-                         int block_count) {
+bool BlockHeader::NeedToGrowBlockFile(int block_count) {
   bool have_space = false;
   int empty_blocks = 0;
-  for (int i = 0; i < disk_cache::kMaxNumBlocks; i++) {
-    empty_blocks += header->empty[i] * (i + 1);
-    if (i >= block_count - 1 && header->empty[i])
+  for (int i = 0; i < kMaxNumBlocks; i++) {
+    empty_blocks += header_->empty[i] * (i + 1);
+    if (i >= block_count - 1 && header_->empty[i])
       have_space = true;
   }
 
-  if (header->next_file && (empty_blocks < disk_cache::kMaxBlocks / 10)) {
+  if (header_->next_file && (empty_blocks < kMaxBlocks / 10)) {
     // This file is almost full but we already created another one, don't use
     // this file yet so that it is easier to find empty blocks when we start
     // using this file again.
     return true;
   }
   return !have_space;
 }
 
-// Returns the number of empty blocks for this file.
-int EmptyBlocks(const disk_cache::BlockFileHeader* header) {
+bool BlockHeader::CanAllocate(int block_count) {
+  bool have_space = false;
+  int empty_blocks = 0;
+  for (int i = 0; i < kMaxNumBlocks; i++) {
+    empty_blocks += header_->empty[i] * (i + 1);
+    if (i >= block_count - 1 && header_->empty[i])
+      have_space = true;
+  }
+
+  return have_space;
+}
+
+int BlockHeader::EmptyBlocks() const {
   int empty_blocks = 0;
   for (int i = 0; i < disk_cache::kMaxNumBlocks; i++) {
-    empty_blocks += header->empty[i] * (i + 1);
-    if (header->empty[i] < 0)
-      return false;
+    empty_blocks += header_->empty[i] * (i + 1);
+    if (header_->empty[i] < 0)
+      return 0;
   }
   return empty_blocks;
 }
 
-// Returns true if the counters look OK.
-bool ValidateCounters(const disk_cache::BlockFileHeader* header) {
-  if (header->max_entries < 0 || header->max_entries > disk_cache::kMaxBlocks ||
-      header->num_entries < 0)
+bool BlockHeader::ValidateCounters() const {
+  if (header_->max_entries < 0 || header_->max_entries > kMaxBlocks ||
+      header_->num_entries < 0)
     return false;
 
-  int empty_blocks = EmptyBlocks(header);
-  if (empty_blocks + header->num_entries > header->max_entries)
+  int empty_blocks = EmptyBlocks();
+  if (empty_blocks + header_->num_entries > header_->max_entries)
     return false;
 
   return true;
 }
 
-}  // namespace
+int BlockHeader::Size() const {
+  return static_cast<int>(sizeof(*header_));
+}
 
-namespace disk_cache {
+// ------------------------------------------------------------------------
 
 BlockFiles::BlockFiles(const base::FilePath& path)
-    : init_(false), zero_buffer_(NULL), path_(path) {
+    : init_(false),
+      small_steps_(false),
+      data_offset_(0),
+      zero_buffer_(NULL),
+      path_(path) {
 }
 
 BlockFiles::~BlockFiles() {
   if (zero_buffer_)
     delete[] zero_buffer_;
   CloseFiles();
 }
 
-bool BlockFiles::Init(bool create_files) {
+bool BlockFiles::Init(bool create_files, int num_files) {
   DCHECK(!init_);
   if (init_)
     return false;
 
+  data_offset_ = num_files > kFirstAdditionalBlockFile ? 0 : kBlockHeaderSize;
   thread_checker_.reset(new base::ThreadChecker);
 
-  block_files_.resize(kFirstAdditionalBlockFile);
-  for (int i = 0; i < kFirstAdditionalBlockFile; i++) {
+  block_headers_.resize(num_files);
+  block_data_.resize(num_files);
+  for (int i = 0; i < num_files; i++) {
     if (create_files)
       if (!CreateBlockFile(i, static_cast<FileType>(i + 1), true))
         return false;
 
     if (!OpenBlockFile(i))
       return false;
 
     // Walk this chain of files removing empty ones.
     if (!RemoveEmptyFile(static_cast<FileType>(i + 1)))
       return false;
+
+    if (!data_offset_ && !PreallocateSpace(static_cast<FileType>(i + 1)))
+      return false;
   }
 
   init_ = true;
   return true;
 }
 
+void BlockFiles::GetBitmaps(int num_files, BlockFilesBitmaps* bitmaps) {
+  bitmaps->clear();
+  bitmaps->resize(num_files);
+
+  for (int i = 0; i < num_files; i++) {
+    // Only the block_file argument is relevant for what we want.
+    Addr address(BLOCK_256, 1, i, 0);
+    BlockHeader header(GetFileHeader(address));
+    (*bitmaps)[i] = header;
+  }
+}
+
 MappedFile* BlockFiles::GetFile(Addr address) {
-  DCHECK(thread_checker_->CalledOnValidThread());
-  DCHECK(block_files_.size() >= 4);
-  DCHECK(address.is_block_file() || !address.is_initialized());
-  if (!address.is_initialized())
+  int file_index = GetFileIndex(address);
+  if (file_index < 0)
     return NULL;
 
-  int file_index = address.FileNumber();
-  if (static_cast<unsigned int>(file_index) >= block_files_.size() ||
-      !block_files_[file_index]) {
-    // We need to open the file
-    if (!OpenBlockFile(file_index))
-      return NULL;
-  }
-  DCHECK(block_files_.size() >= static_cast<unsigned int>(file_index));
-  return block_files_[file_index];
+  if (data_offset_)
+    return block_headers_[file_index];
+
+  DCHECK(block_data_.size() >= static_cast<unsigned int>(file_index));
+  return block_data_[file_index];
 }
 
 bool BlockFiles::CreateBlock(FileType block_type, int block_count,
                              Addr* block_address) {
   DCHECK(thread_checker_->CalledOnValidThread());
   if (block_type < RANKINGS || block_type > BLOCK_4K ||
       block_count < 1 || block_count > 4)
     return false;
   if (!init_)
     return false;
 
   MappedFile* file = FileForNewBlock(block_type, block_count);
   if (!file)
     return false;
 
   ScopedFlush flush(file);
-  BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
+  BlockHeader header(file);
 
   int target_size = 0;
   for (int i = block_count; i <= 4; i++) {
     if (header->empty[i - 1]) {
       target_size = i;
       break;
     }
   }
 
   DCHECK(target_size);
   int index;
-  if (!CreateMapBlock(target_size, block_count, header, &index))
+  if (!header.CreateMapBlock(target_size, block_count, &index))
     return false;
 
   Addr address(block_type, block_count, header->this_file, index);
   block_address->set_value(address.value());
   Trace("CreateBlock 0x%x", address.value());
   return true;
 }
 
 void BlockFiles::DeleteBlock(Addr address, bool deep) {
   DCHECK(thread_checker_->CalledOnValidThread());
   if (!address.is_initialized() || address.is_separate_file())
     return;
 
   if (!zero_buffer_) {
     zero_buffer_ = new char[Addr::BlockSizeForFileType(BLOCK_4K) * 4];
     memset(zero_buffer_, 0, Addr::BlockSizeForFileType(BLOCK_4K) * 4);
   }
   MappedFile* file = GetFile(address);
   if (!file)
     return;
 
   Trace("DeleteBlock 0x%x", address.value());
 
   size_t size = address.BlockSize() * address.num_blocks();
-  size_t offset = address.start_block() * address.BlockSize() +
-                  kBlockHeaderSize;
+  size_t offset = address.start_block() * address.BlockSize() + data_offset_;
   if (deep)
     file->Write(zero_buffer_, size, offset);
 
-  BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
-  DeleteMapBlock(address.start_block(), address.num_blocks(), header);
+  BlockHeader header(GetFileHeader(address));
+  header.DeleteMapBlock(address.start_block(), address.num_blocks());
   file->Flush();
 
   if (!header->num_entries) {
     // This file is now empty. Let's try to delete it.
     FileType type = Addr::RequiredFileType(header->entry_size);
     if (Addr::BlockSizeForFileType(RANKINGS) == header->entry_size)
       type = RANKINGS;
     RemoveEmptyFile(type);  // Ignore failures.
   }
 }
 
 void BlockFiles::CloseFiles() {
   if (init_) {
     DCHECK(thread_checker_->CalledOnValidThread());
   }
   init_ = false;
-  for (unsigned int i = 0; i < block_files_.size(); i++) {
-    if (block_files_[i]) {
-      block_files_[i]->Release();
-      block_files_[i] = NULL;
+  for (unsigned int i = 0; i < block_headers_.size(); i++) {
+    if (block_headers_[i]) {
+      block_headers_[i]->Release();
+      block_headers_[i] = NULL;
     }
   }
-  block_files_.clear();
+  for (unsigned int i = 0; i < block_data_.size(); i++) {
+    if (block_data_[i]) {
+      block_data_[i]->Release();
+      block_data_[i] = NULL;
+    }
+  }
+  block_headers_.clear();
+  block_data_.clear();
 }
 
 void BlockFiles::ReportStats() {
   DCHECK(thread_checker_->CalledOnValidThread());
   int used_blocks[kFirstAdditionalBlockFile];
   int load[kFirstAdditionalBlockFile];
   for (int i = 0; i < kFirstAdditionalBlockFile; i++) {
     GetFileStats(i, &used_blocks[i], &load[i]);
   }
   UMA_HISTOGRAM_COUNTS("DiskCache.Blocks_0", used_blocks[0]);
   UMA_HISTOGRAM_COUNTS("DiskCache.Blocks_1", used_blocks[1]);
   UMA_HISTOGRAM_COUNTS("DiskCache.Blocks_2", used_blocks[2]);
   UMA_HISTOGRAM_COUNTS("DiskCache.Blocks_3", used_blocks[3]);
 
   UMA_HISTOGRAM_ENUMERATION("DiskCache.BlockLoad_0", load[0], 101);
   UMA_HISTOGRAM_ENUMERATION("DiskCache.BlockLoad_1", load[1], 101);
   UMA_HISTOGRAM_ENUMERATION("DiskCache.BlockLoad_2", load[2], 101);
   UMA_HISTOGRAM_ENUMERATION("DiskCache.BlockLoad_3", load[3], 101);
 }
 
 bool BlockFiles::IsValid(Addr address) {
 #ifdef NDEBUG
   return true;
 #else
   if (!address.is_initialized() || address.is_separate_file())
     return false;
 
-  MappedFile* file = GetFile(address);
+  MappedFile* file = GetFileHeader(address);
   if (!file)
     return false;
 
-  BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
-  bool rv = UsedMapBlock(address.start_block(), address.num_blocks(), header);
+  BlockHeader header(file);
+  bool rv = header.UsedMapBlock(address.start_block(), address.num_blocks());
   DCHECK(rv);
-
-  static bool read_contents = false;
-  if (read_contents) {
-    scoped_ptr<char[]> buffer;
-    buffer.reset(new char[Addr::BlockSizeForFileType(BLOCK_4K) * 4]);
-    size_t size = address.BlockSize() * address.num_blocks();
-    size_t offset = address.start_block() * address.BlockSize() +
-                    kBlockHeaderSize;
-    bool ok = file->Read(buffer.get(), size, offset);
-    DCHECK(ok);
-  }
-
   return rv;
 #endif
 }
 
 bool BlockFiles::CreateBlockFile(int index, FileType file_type, bool force) {
-  base::FilePath name = Name(index);
+  base::FilePath name = HeaderName(index);
   int flags =
       force ? base::PLATFORM_FILE_CREATE_ALWAYS : base::PLATFORM_FILE_CREATE;
   flags |= base::PLATFORM_FILE_WRITE | base::PLATFORM_FILE_EXCLUSIVE_WRITE;
 
   scoped_refptr<File> file(new File(
       base::CreatePlatformFile(name, flags, NULL, NULL)));
   if (!file->IsValid())
     return false;
 
   BlockFileHeader header;
+  memset(&header, 0, sizeof(header));
+  header.magic = kBlockMagic;
+  header.version = data_offset_ ? kBlockVersion2 : kBlockCurrentVersion;
   header.entry_size = Addr::BlockSizeForFileType(file_type);
   header.this_file = static_cast<int16>(index);
   DCHECK(index <= kint16max && index >= 0);
 
-  return file->Write(&header, sizeof(header), 0);
+  if (!file->Write(&header, sizeof(header), 0))
+    return false;
+
+  if (header.version == kBlockVersion2)
+    return true;
+
+  // Now create another file for the data itself.
+  name = DataName(index);
+  file = new File(base::CreatePlatformFile(name, flags, NULL, NULL));
+  return file->IsValid();
 }
 
 bool BlockFiles::OpenBlockFile(int index) {
-  if (block_files_.size() - 1 < static_cast<unsigned int>(index)) {
+  if (block_headers_.size() - 1 < static_cast<unsigned int>(index)) {
     DCHECK(index > 0);
-    int to_add = index - static_cast<int>(block_files_.size()) + 1;
-    block_files_.resize(block_files_.size() + to_add);
+    int to_add = index - static_cast<int>(block_headers_.size()) + 1;
+    block_headers_.resize(block_headers_.size() + to_add);
+    block_data_.resize(block_data_.size() + to_add);
   }
+  DCHECK_EQ(block_headers_.size(), block_data_.size());
+  DCHECK(!block_headers_[index]);
 
-  base::FilePath name = Name(index);
+  base::FilePath name = HeaderName(index);
   scoped_refptr<MappedFile> file(new MappedFile());
 
   if (!file->Init(name, kBlockHeaderSize)) {
     LOG(ERROR) << "Failed to open " << name.value();
     return false;
   }
 
   size_t file_len = file->GetLength();
   if (file_len < static_cast<size_t>(kBlockHeaderSize)) {
     LOG(ERROR) << "File too small " << name.value();
     return false;
   }
 
-  BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
-  if (kBlockMagic != header->magic || kCurrentVersion != header->version) {
+  BlockHeader header(file);
+  if (kBlockMagic != header->magic ||
+      (kBlockVersion2 != header->version &&
+       kBlockCurrentVersion != header->version)) {
     LOG(ERROR) << "Invalid file version or magic " << name.value();
     return false;
   }
 
-  if (header->updating || !ValidateCounters(header)) {
+  if ((kBlockCurrentVersion == header->version && data_offset_) ||
+      (kBlockVersion2 == header->version && !data_offset_)) {
+    LOG(ERROR) << "Unexpected file version" << name.value();
+    return false;
+  }
+
+  if (kBlockVersion2 == header->version) {
+    if (static_cast<int>(file_len) <
+        header->max_entries * header->entry_size + kBlockHeaderSize) {
+      LOG(ERROR) << "File too small " << name.value();
+      return false;
+    }
+
+    if (index == 0) {
+      // Load the links file into memory with a single read.
+      scoped_ptr<char[]> buf(new char[file_len]);
+      if (!file->Read(buf.get(), file_len, 0))
+        return false;
+    }
+
+    ScopedFlush flush(file);
+    file.swap(&block_headers_[index]);
+
+    if (header->updating || !header.ValidateCounters()) {
+      // Last instance was not properly shutdown, or counters are out of sync.
+      if (!FixBlockFileHeader(index)) {
+        LOG(ERROR) << "Unable to fix block file " << name.value();
+        file.swap(&block_headers_[index]);
+        return false;
+      }
+    }
+    return true;
+  }
+
+  DCHECK(!block_data_[index]);
+
+  // Open the data file.
+  name = DataName(index);
+  scoped_refptr<MappedFile> data_file(new MappedFile());
+  if (!data_file->InitNoMap(name)) {
+    LOG(ERROR) << "Failed to open " << name.value();
+    return false;
+  }
+
+  if (static_cast<int>(data_file->GetLength()) <
+      header->max_entries * header->entry_size) {
+    LOG(ERROR) << "File too small " << name.value();
+    return false;
+  }
+
+  file.swap(&block_headers_[index]);
+  data_file.swap(&block_data_[index]);
+
+  if (header->updating || !header.ValidateCounters()) {
     // Last instance was not properly shutdown, or counters are out of sync.
-    if (!FixBlockFileHeader(file)) {
+    if (!FixBlockFileHeader(index)) {
       LOG(ERROR) << "Unable to fix block file " << name.value();
+      file.swap(&block_headers_[index]);
+      data_file.swap(&block_data_[index]);
       return false;
     }
   }
 
-  if (static_cast<int>(file_len) <
-      header->max_entries * header->entry_size + kBlockHeaderSize) {
-    LOG(ERROR) << "File too small " << name.value();
-    return false;
-  }
-
-  if (index == 0) {
-    // Load the links file into memory with a single read.
-    scoped_ptr<char[]> buf(new char[file_len]);
-    if (!file->Read(buf.get(), file_len, 0))
-      return false;
-  }
-
-  ScopedFlush flush(file);
-  DCHECK(!block_files_[index]);
-  file.swap(&block_files_[index]);
   return true;
 }
 
-bool BlockFiles::GrowBlockFile(MappedFile* file, BlockFileHeader* header) {
+bool BlockFiles::GrowBlockFile(BlockFileHeader* header) {
   if (kMaxBlocks == header->max_entries)
     return false;
 
+  int file_index = header->this_file;
+  MappedFile* file = data_offset_ ? block_headers_[file_index] :
+                                    block_data_[file_index];
   ScopedFlush flush(file);
-  DCHECK(!header->empty[3]);
-  int new_size = header->max_entries + 1024;
+  if (data_offset_)
+    DCHECK(!header->empty[3]);
+
+  int step_size = small_steps_ ? 32 : kNumExtraBlocks;
+  int new_size = header->max_entries + step_size;
   if (new_size > kMaxBlocks)
     new_size = kMaxBlocks;
 
-  int new_size_bytes = new_size * header->entry_size + sizeof(*header);
+  int new_size_bytes = new_size * header->entry_size + data_offset_;
 
   if (!file->SetLength(new_size_bytes)) {
     // Most likely we are trying to truncate the file, so the header is wrong.
-    if (header->updating < 10 && !FixBlockFileHeader(file)) {
+    if (header->updating < 10 && !FixBlockFileHeader(file_index)) {
       // If we can't fix the file increase the lock guard so we'll pick it on
       // the next start and replace it.
       header->updating = 100;
       return false;
     }
     return (header->max_entries >= new_size);
   }
 
   FileLock lock(header);
-  header->empty[3] = (new_size - header->max_entries) / 4;  // 4 blocks entries
+  header->empty[3] += (new_size - header->max_entries) / 4;  // 4 blocks entries
   header->max_entries = new_size;
 
   return true;
 }
 
 MappedFile* BlockFiles::FileForNewBlock(FileType block_type, int block_count) {
   COMPILE_ASSERT(RANKINGS == 1, invalid_file_type);
-  MappedFile* file = block_files_[block_type - 1];
-  BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
+  MappedFile* file = block_headers_[block_type - 1];
+  BlockHeader header(file);
 
   TimeTicks start = TimeTicks::Now();
-  while (NeedToGrowBlockFile(header, block_count)) {
+  while (header.NeedToGrowBlockFile(block_count)) {
     if (kMaxBlocks == header->max_entries) {
       file = NextFile(file);
       if (!file)
         return NULL;
-      header = reinterpret_cast<BlockFileHeader*>(file->buffer());
+      header = BlockHeader(file);
       continue;
     }
 
-    if (!GrowBlockFile(file, header))
+    if (!GrowBlockFile(header.Get()))
       return NULL;
     break;
   }
   HISTOGRAM_TIMES("DiskCache.GetFileForNewBlock", TimeTicks::Now() - start);
   return file;
 }
 
 MappedFile* BlockFiles::NextFile(MappedFile* file) {
   ScopedFlush flush(file);
   BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
   int new_file = header->next_file;
   if (!new_file) {
     // RANKINGS is not reported as a type for small entries, but we may be
     // extending the rankings block file.
     FileType type = Addr::RequiredFileType(header->entry_size);
     if (header->entry_size == Addr::BlockSizeForFileType(RANKINGS))
       type = RANKINGS;
 
     new_file = CreateNextBlockFile(type);
     if (!new_file)
       return NULL;
 
     FileLock lock(header);
     header->next_file = new_file;
   }
 
   // Only the block_file argument is relevant for what we want.
   Addr address(BLOCK_256, 1, new_file, 0);
-  return GetFile(address);
+  return GetFileHeader(address);
+}
+
+int BlockFiles::GetFileIndex(Addr address) {
+  DCHECK(thread_checker_->CalledOnValidThread());
+  DCHECK(block_headers_.size() >= 4);
+  DCHECK(address.is_block_file() || !address.is_initialized());
+  if (!address.is_initialized())
+    return -1;
+
+  int file_index = address.FileNumber();
+  if (static_cast<unsigned int>(file_index) >= block_headers_.size() ||
+      !block_headers_[file_index]) {
+    // We need to open the file
+    if (!OpenBlockFile(file_index))
+      return -1;
+  }
+  DCHECK(block_headers_.size() >= static_cast<unsigned int>(file_index));
+  return file_index;
+}
+
+MappedFile* BlockFiles::GetFileHeader(Addr address) {
+  int file_index = GetFileIndex(address);
+  if (file_index < 0)
+    return NULL;
+
+  return block_headers_[file_index];
 }
 
 int BlockFiles::CreateNextBlockFile(FileType block_type) {
   for (int i = kFirstAdditionalBlockFile; i <= kMaxBlockFile; i++) {
     if (CreateBlockFile(i, block_type, false))
       return i;
   }
   return 0;
 }
 
 // We walk the list of files for this particular block type, deleting the ones
 // that are empty.
 bool BlockFiles::RemoveEmptyFile(FileType block_type) {
-  MappedFile* file = block_files_[block_type - 1];
+  MappedFile* file = block_headers_[block_type - 1];
   BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
 
   while (header->next_file) {
     // Only the block_file argument is relevant for what we want.
     Addr address(BLOCK_256, 1, header->next_file, 0);
-    MappedFile* next_file = GetFile(address);
+    MappedFile* next_file = GetFileHeader(address);
     if (!next_file)
       return false;
 
     BlockFileHeader* next_header =
         reinterpret_cast<BlockFileHeader*>(next_file->buffer());
     if (!next_header->num_entries) {
       DCHECK_EQ(next_header->entry_size, header->entry_size);
       // Delete next_file and remove it from the chain.
       int file_index = header->next_file;
       header->next_file = next_header->next_file;
-      DCHECK(block_files_.size() >= static_cast<unsigned int>(file_index));
+      DCHECK(block_headers_.size() >= static_cast<unsigned int>(file_index));
       file->Flush();
 
       // We get a new handle to the file and release the old one so that the
       // file gets unmmaped... so we can delete it.
-      base::FilePath name = Name(file_index);
+      base::FilePath name = HeaderName(file_index);
       scoped_refptr<File> this_file(new File(false));
       this_file->Init(name);
-      block_files_[file_index]->Release();
-      block_files_[file_index] = NULL;
+      block_headers_[file_index]->Release();
+      block_headers_[file_index] = NULL;
 
       int failure = DeleteCacheFile(name) ? 0 : 1;
-      UMA_HISTOGRAM_COUNTS("DiskCache.DeleteFailed2", failure);
       if (failure)
         LOG(ERROR) << "Failed to delete " << name.value() << " from the cache.";
+
+      if (!data_offset_) {
+        name = DataName(file_index);
+        if (!DeleteCacheFile(name)) {
+          failure = 1;
+          LOG(ERROR) << "Failed to delete " << name.value() <<
+                        " from the cache.";
+        }  
+        block_data_[file_index]->Release();
+        block_data_[file_index] = NULL;
+      }
+      UMA_HISTOGRAM_COUNTS("DiskCache.DeleteFailed2", failure);
       continue;
     }
 
     header = next_header;
     file = next_file;
   }
   return true;
 }
 
+bool BlockFiles::PreallocateSpace(FileType block_type) {
+  MappedFile* file = block_headers_[block_type - 1];
+  BlockHeader header(file);
+
+  int empty_blocks = header.EmptyBlocks();
+  while (header->next_file) {
+    // Only the block_file argument is relevant for what we want.
+    Addr address(BLOCK_256, 1, header->next_file, 0);
+    MappedFile* next_file = GetFileHeader(address);
+    if (!next_file)
+      return false;
+
+    BlockHeader next_header(next_file);
+    empty_blocks += next_header.EmptyBlocks();
+
+    header = next_header;
+    file = next_file;
+  }
+  if (empty_blocks > kNumExtraBlocks * 2 / 3)
+    return true;
+
+  // Restart the search.
+  file = block_headers_[block_type - 1];
+  header = BlockHeader(file);
+  while (kMaxBlocks == header->max_entries) {
+    file = NextFile(file);
+    if (!file)
+      return false;
+    header = BlockHeader(file);
+  }
+  return GrowBlockFile(header.Get());
+}
+
 // Note that we expect to be called outside of a FileLock... however, we cannot
 // DCHECK on header->updating because we may be fixing a crash.
-bool BlockFiles::FixBlockFileHeader(MappedFile* file) {
-  ScopedFlush flush(file);
-  BlockFileHeader* header = reinterpret_cast<BlockFileHeader*>(file->buffer());
-  int file_size = static_cast<int>(file->GetLength());
-  if (file_size < static_cast<int>(sizeof(*header)))
+bool BlockFiles::FixBlockFileHeader(int index) {
+  DCHECK_GE(block_headers_.size(), static_cast<unsigned int>(index));
+  MappedFile* header_file = block_headers_[index];
+  ScopedFlush flush(header_file);
+  BlockHeader header(header_file);
+
+  MappedFile* data_file = data_offset_ ? header_file : block_data_[index];
+  int file_size = static_cast<int>(data_file->GetLength());
+  if (file_size < data_offset_)
     return false;  // file_size > 2GB is also an error.
 
   const int kMinBlockSize = 36;
   const int kMaxBlockSize = 4096;
   if (header->entry_size < kMinBlockSize ||
       header->entry_size > kMaxBlockSize || header->num_entries < 0)
     return false;
 
   // Make sure that we survive crashes.
   header->updating = 1;
-  int expected = header->entry_size * header->max_entries + sizeof(*header);
+  int expected = header->entry_size * header->max_entries + data_offset_;
   if (file_size != expected) {
-    int max_expected = header->entry_size * kMaxBlocks + sizeof(*header);
+    int max_expected = header->entry_size * kMaxBlocks + data_offset_;
     if (file_size < expected || header->empty[3] || file_size > max_expected) {
       NOTREACHED();
       LOG(ERROR) << "Unexpected file size";
       return false;
     }
     // We were in the middle of growing the file.
-    int num_entries = (file_size - sizeof(*header)) / header->entry_size;
+    int num_entries = (file_size - data_offset_) / header->entry_size;
     header->max_entries = num_entries;
   }
 
-  FixAllocationCounters(header);
-  int empty_blocks = EmptyBlocks(header);
+  header.FixAllocationCounters();
+  int empty_blocks = header.EmptyBlocks();
   if (empty_blocks + header->num_entries > header->max_entries)
     header->num_entries = header->max_entries - empty_blocks;
 
-  if (!ValidateCounters(header))
+  if (!header.ValidateCounters())
     return false;
 
   header->updating = 0;
   return true;
 }
 
 // We are interested in the total number of blocks used by this file type, and
 // the max number of blocks that we can store (reported as the percentage of
 // used blocks). In order to find out the number of used blocks, we have to
 // substract the empty blocks from the total blocks for each file in the chain.
 void BlockFiles::GetFileStats(int index, int* used_count, int* load) {
   int max_blocks = 0;
   *used_count = 0;
   *load = 0;
   for (;;) {
-    if (!block_files_[index] && !OpenBlockFile(index))
+    if (!block_headers_[index] && !OpenBlockFile(index))
       return;
 
     BlockFileHeader* header =
-        reinterpret_cast<BlockFileHeader*>(block_files_[index]->buffer());
+        reinterpret_cast<BlockFileHeader*>(block_headers_[index]->buffer());
 
     max_blocks += header->max_entries;
     int used = header->max_entries;
     for (int i = 0; i < 4; i++) {
       used -= header->empty[i] * (i + 1);
       DCHECK_GE(used, 0);
     }
     *used_count += used;
 
     if (!header->next_file)
       break;
     index = header->next_file;
   }
   if (max_blocks)
     *load = *used_count * 100 / max_blocks;
 }
 
-base::FilePath BlockFiles::Name(int index) {
+base::FilePath BlockFiles::HeaderName(int index) {
   // The file format allows for 256 files.
   DCHECK(index < 256 || index >= 0);
   std::string tmp = base::StringPrintf("%s%d", kBlockName, index);
   return path_.AppendASCII(tmp);
 }
 
+base::FilePath BlockFiles::DataName(int index) {
+  // The file format allows for 256 files.
+  DCHECK(index < 256 || index >= 0);
+  std::string tmp = base::StringPrintf("%s%d_d", kBlockName, index);
+  return path_.AppendASCII(tmp);
+}
+
 }  // namespace disk_cache