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

net/disk_cache/v3/entry_impl_v3.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/v3/entry_impl_v3.h"
+
+#include "base/hash.h"
+#include "base/message_loop.h"
+#include "base/metrics/histogram.h"
+#include "base/string_util.h"
+#include "net/base/io_buffer.h"
+#include "net/base/net_errors.h"
+#include "net/disk_cache/bitmap.h"
+#include "net/disk_cache/cache_util.h"
+#include "net/disk_cache/histogram_macros.h"
+#include "net/disk_cache/net_log_parameters.h"
+#include "net/disk_cache/storage_block-inl.h"
+#include "net/disk_cache/v3/backend_impl_v3.h"
+#include "net/disk_cache/v3/disk_format_v3.h"
+#include "net/disk_cache/v3/sparse_control_v3.h"
+
+using base::Time;
+using base::TimeDelta;
+using base::TimeTicks;
+
+namespace {
+
+const int kMinBufferSize = disk_cache::kMaxBlockSize;
+const int kMaxBufferSize = 1024 * 1024;  // 1 MB.
+const int kKeyIndex = 0;
+
+}  // namespace
+
+namespace disk_cache {
+
+typedef StorageBlock<EntryRecord> CacheEntryBlockV3;
+typedef StorageBlock<ShortEntryRecord> CacheShortEntryBlock;
+
+// This class handles individual memory buffers that store data before it is
+// sent to disk. The buffer can start at any offset, but if we try to write to
+// anywhere in the first 16KB of the file (kMaxBlockSize), we set the offset to jaja
+// zero. The buffer grows up to a size determined by the backend, to keep the
+// total memory used under control.
+class EntryImplV3::UserBuffer {
+ public:
+  explicit UserBuffer(BackendImplV3* backend)
+      : backend_(backend->GetWeakPtr()),
+        offset_(0),
+        grow_allowed_(true),
+        force_size_(false) {
+    buffer_ = new net::GrowableIOBuffer();
+    buffer_->SetCapacity(kMinBufferSize);
+  }
+  ~UserBuffer() {
+    if (backend_)
+      backend_->BufferDeleted(capacity() - kMinBufferSize);
+  }
+
+  // Returns true if we can handle writing |len| bytes to |offset|.
+  bool PreWrite(int offset, int len);
+
+  // Truncates the buffer to |offset| bytes.
+  void Truncate(int offset);
+
+  // Writes |len| bytes from |buf| at the given |offset|.
+  void Write(int offset, IOBuffer* buf, int len);
+
+  // Returns true if we can read |len| bytes from |offset|, given that the
+  // actual file has |eof| bytes stored. Note that the number of bytes to read
+  // may be modified by this method even though it returns false: that means we
+  // should do a smaller read from disk.
+  bool PreRead(int eof, int offset, int* len);
+
+  // Read |len| bytes from |buf| at the given |offset|.
+  int Read(int offset, IOBuffer* buf, int len);
+
+  void Rebase();
+
+  void ForceSize(bool value);
+
+  net::IOBuffer* Get();
+  int Size() { return static_cast<int>(buffer_->offset()); }
+  int Start() { return offset_; }
+  int End() { return offset_ + Size(); }
+
+ private:
+  int capacity() { return buffer_->capacity(); }
+  bool GrowBuffer(int required, int limit);
+
+  base::WeakPtr<BackendImplV3> backend_;
+  int offset_;
+  scoped_refptr<net::GrowableIOBuffer> buffer_;
+  bool grow_allowed_;
+  bool force_size_;
+  DISALLOW_COPY_AND_ASSIGN(UserBuffer);
+};
+
+bool EntryImplV3::UserBuffer::PreWrite(int offset, int len) {
+  DCHECK_GE(offset, 0);
+  DCHECK_GE(len, 0);
+  DCHECK_GE(offset + len, 0);
+
+  // We don't want to write before our current start.
+  if (offset < offset_)
+    return false;
+
+  // Lets get the common case out of the way.
+  if (offset + len <= capacity())
+    return true;
+
+  if (!Size())
+    return GrowBuffer(len, kMaxBufferSize);
+
+  int required = offset - offset_ + len;
+  return GrowBuffer(required, kMaxBufferSize * 6 / 5);
+}
+
+void EntryImplV3::UserBuffer::Truncate(int offset) {
+  DCHECK_GE(offset, 0);
+  DCHECK_GE(offset, offset_);
+  DVLOG(3) << "Buffer truncate at " << offset << " current " << offset_;
+
+  offset -= offset_;
+  if (Size() >= offset)
+    buffer_->set_offset(offset);
+}
+
+void EntryImplV3::UserBuffer::Write(int offset, IOBuffer* buf, int len) {
+  DCHECK_GE(offset, 0);
+  DCHECK_GE(len, 0);
+  DCHECK_GE(offset + len, 0);
+  DCHECK_GE(offset, offset_);
+  DVLOG(3) << "Buffer write at " << offset << " current " << offset_;
+
+  if (!Size())
+    offset_ = offset;
+
+  offset -= offset_;
+
+  if (offset > Size()) {
+    memset(buffer_->data(), 0, offset - Size());
+    buffer_->set_offset(offset);
+  }
+
+  if (!len)
+    return;
+
+  char* buffer = buf->data();
+  int valid_len = Size() - offset;
+  int copy_len = std::min(valid_len, len);
+  if (copy_len) {
+    memcpy(buffer_->StartOfBuffer() + offset, buffer, copy_len);
+    len -= copy_len;
+    buffer += copy_len;
+  }
+  if (!len)
+    return;
+
+  memcpy(buffer_->data(), buffer, len);
+  buffer_->set_offset(buffer_->offset() + len);
+}
+
+bool EntryImplV3::UserBuffer::PreRead(int eof, int offset, int* len) {
+  DCHECK_GE(offset, 0);
+  DCHECK_GT(*len, 0);
+
+  if (offset < offset_) {
+    // We are reading before this buffer.
+    if (offset >= eof)
+      return true;
+
+    // If the read overlaps with the buffer, change its length so that there is
+    // no overlap.
+    *len = std::min(*len, offset_ - offset);
+    *len = std::min(*len, eof - offset);
+
+    // We should read from disk.
+    return false;
+  }
+
+  if (!Size())
+    return false;
+
+  // See if we can fulfill the first part of the operation.
+  return (offset - offset_ < Size());
+}
+
+int EntryImplV3::UserBuffer::Read(int offset, IOBuffer* buf, int len) {
+  DCHECK_GE(offset, 0);
+  DCHECK_GT(len, 0);
+  DCHECK(Size() || offset < offset_);
+
+  int clean_bytes = 0;
+  if (offset < offset_) {
+    // We don't have a file so lets fill the first part with 0.
+    clean_bytes = std::min(offset_ - offset, len);
+    memset(buf->data(), 0, clean_bytes);
+    if (len == clean_bytes)
+      return len;
+    offset = offset_;
+    len -= clean_bytes;
+  }
+
+  int start = offset - offset_;
+  int available = Size() - start;
+  DCHECK_GE(start, 0);
+  DCHECK_GE(available, 0);
+  len = std::min(len, available);
+  memcpy(buf->data() + clean_bytes, buffer_->StartOfBuffer() + start, len);
+  return len + clean_bytes;
+}
+
+void EntryImplV3::UserBuffer::Rebase() {
+  DCHECK(!Size());
+  DCHECK(offset_ < capacity());
+  memset(buffer_->data(), 0, offset_);
+  buffer_->set_offset(offset_);
+  offset_ = 0;
+}
+
+void EntryImplV3::UserBuffer::ForceSize(bool value) {
+  force_size_ = value;
+}
+
+net::IOBuffer* EntryImplV3::UserBuffer::Get() {
+  buffer_->set_offset(0);
+  return buffer_.get();
+}
+
+bool EntryImplV3::UserBuffer::GrowBuffer(int required, int limit) {
+  DCHECK_GE(required, 0);
+  int current_size = capacity();
+  if (required <= current_size)
+    return true;
+
+  if (required > limit)
+    return false;
+
+  if (!backend_)
+    return false;
+
+  int to_add = std::max(required - current_size, kMinBufferSize * 4);
+  to_add = std::max(current_size, to_add);
+  required = std::min(current_size + to_add, limit);
+
+  grow_allowed_ = backend_->IsAllocAllowed(current_size, required, force_size_);
+  force_size_ = false;
+  if (!grow_allowed_)
+    return false;
+
+  DVLOG(3) << "Buffer grow to " << required;
+
+  buffer_->SetCapacity(required);
+  return true;
+}
+
+// ------------------------------------------------------------------------
+
+EntryImplV3::EntryImplV3(BackendImplV3* backend, Addr address, bool read_only)
+    : backend_(backend->GetWeakPtr()),
+      address_(address),
+      num_handles_(0),
+      doomed_(false),
+      read_only_(read_only),
+      modified_(true),
+      callback_(base::Bind(&EntryImplV3::OnIOComplete,
+                           base::Unretained(this))) {
+  for (int i = 0; i < kNumStreams; i++) {
+    unreported_size_[i] = 0;
+  }
+}
+
+EntryImplV3::EntryImplV3(BackendImplV3* backend,
+                         Addr address,
+                         const std::string& key,
+                         scoped_ptr<EntryRecord> record)
+    : entry_(record.Pass()),
+      backend_(backend->GetWeakPtr()),
+      key_(key),
+      address_(address),
+      num_handles_(0),
+      doomed_(false),
+      read_only_(false),
+      modified_(false),
+      callback_(base::Bind(&EntryImplV3::OnIOComplete,
+                           base::Unretained(this))) {
+  for (int i = 0; i < kNumStreams; i++) {
+    unreported_size_[i] = 0;
+  }
+}
+
+EntryImplV3::EntryImplV3(BackendImplV3* backend,
+                         Addr address,
+                         const std::string& key,
+                         scoped_ptr<ShortEntryRecord> record)
+    : short_entry_(record.Pass()),
+      backend_(backend->GetWeakPtr()),
+      key_(key),
+      address_(address),
+      num_handles_(0),
+      doomed_(false),
+      read_only_(false),
+      modified_(false),
+      callback_(base::Bind(&EntryImplV3::OnIOComplete,
+                           base::Unretained(this))) {
+  for (int i = 0; i < kNumStreams; i++) {
+    unreported_size_[i] = 0;
+  }
+}
+
+void EntryImplV3::CreateEntry(const std::string& key, uint32 hash,
+                              ShortEntryRecord* old_info) {
+  Trace("Create entry In");
+
+  key_ = key;
+  entry_.reset(new EntryRecord);
+  memset(entry_.get(), 0, sizeof(*entry_.get()));
+  entry_->key_len = static_cast<int>(key.size());
+  entry_->hash = hash;
+  entry_->creation_time = backend_->GetCurrentTime().ToInternalValue();
+  entry_->last_access_time = entry_->creation_time;
+  entry_->last_modified_time = entry_->creation_time;
+  modified_ = true;
+  backend_->UpdateRank(this, true);
+
+  if (old_info) {
+    entry_->reuse_count = old_info->reuse_count;
+    entry_->refetch_count = old_info->refetch_count;
+  }
+
+  backend_->ModifyStorageSize(0, static_cast<int32>(key.size()));
+  CACHE_UMA(COUNTS, "KeySize", 0, static_cast<int32>(key.size()));
+
+  WriteKey();
+  num_handles_++;
+  Log("Create Entry ");
+}
+
+void EntryImplV3::OnOpenEntry() {
+  num_handles_++;
+}
+
+scoped_ptr<ShortEntryRecord> EntryImplV3::GetShortEntryRecord() {
+  return short_entry_.Pass();
+}
+
+uint32 EntryImplV3::GetHash() const {
+  return entry_->hash;
+}
+
+Addr EntryImplV3::GetAddress() const {
+  return address_;
+}
+
+int EntryImplV3::GetReuseCounter() const {
+  return entry_->reuse_count;
+}
+
+void EntryImplV3::SetReuseCounter(int counter) {
+  DCHECK_LT(counter, 256);
+  DCHECK_GE(counter, 0);
+  entry_->reuse_count = static_cast<uint8>(counter);
+  modified_ = true;
+}
+
+int EntryImplV3::GetRefetchCounter() const {
+  return entry_->refetch_count;
+}
+
+void EntryImplV3::SetRefetchCounter(int counter) {
+  DCHECK_LT(counter, 256);
+  DCHECK_GE(counter, 0);
+  entry_->refetch_count = static_cast<uint8>(counter);
+  modified_ = true;
+}
+
+bool EntryImplV3::IsSameEntry(const std::string& key, uint32 hash) {
+  if (entry_->hash != hash ||
+      static_cast<size_t>(entry_->key_len) != key.size())
+    return false;
+
+  return (key.compare(GetKey()) == 0);
+}
+
+void EntryImplV3::InternalDoom() {
+  DCHECK(!doomed_);
+  net_log_.AddEvent(net::NetLog::TYPE_ENTRY_DOOM);
+  doomed_ = true;
+  modified_ = true;
+}
+
+bool EntryImplV3::SanityCheck() {
+  DCHECK(BasicSanityCheck(*entry_.get()));
+
+  if (entry_->reuse_count < 0 || entry_->refetch_count < 0)
+    return false;
+
+  if (entry_->state > ENTRY_USED || entry_->state < ENTRY_NEW)
+    return false;
+
+  return true;
+}
+
+bool EntryImplV3::DataSanityCheck() {
+  if (entry_->hash != base::Hash(GetKey()))
+    return false;
+
+  for (int i = 0; i < kNumStreams; i++) {
+    Addr data_addr(entry_->data_addr[i]);
+    int data_size = entry_->data_size[i];
+    if (data_size < 0)
+      return false;
+    if (!data_size && data_addr.is_initialized())
+      return false;
+    if (!data_addr.SanityCheckV3())
+      return false;
+    if (!data_size)
+      continue;
+    if (data_size <= kMaxBlockSize && data_addr.is_separate_file())
+      return false;
+    if (data_size > kMaxBlockSize && data_addr.is_block_file())
+      return false;
+  }
+  return true;
+}
+
+// Static.
+bool EntryImplV3::BasicSanityCheck(const EntryRecord& record) {
+  CacheEntryBlockV3 entry_block;
+  entry_block.SetData(const_cast<EntryRecord*>(&record));
+  if (!entry_block.VerifyHash())
+    return false;
+
+  if (record.key_len <= 0 || record.data_size[0] < record.key_len)
+    return false;
+
+  Addr data_addr(record.data_addr[0]);
+  if (!data_addr.is_initialized() || !data_addr.SanityCheckV3())
+    return false;
+
+  if (record.data_size[0] <= kMaxBlockSize && data_addr.is_separate_file())
+    return false;
+
+  if (record.data_size[0] > kMaxBlockSize && data_addr.is_block_file())
+    return false;
+
+  return true;
+}
+
+// Static.
+bool EntryImplV3::DeletedSanityCheck(const ShortEntryRecord& record) {
+  CacheShortEntryBlock entry_block;
+  entry_block.SetData(const_cast<ShortEntryRecord*>(&record));
+  if (!entry_block.VerifyHash())
+    return false;
+
+  if (record.key_len <= 0)
+    return false;
+
+  return true;
+}
+
+void EntryImplV3::FixForDelete() {
+  //EntryStore* stored = entry_.Data();
+  //Addr key_addr(stored->long_key);
+
+  //if (!key_addr.is_initialized())
+  //  stored->key[stored->key_len] = '\0';
+
+  //for (int i = 0; i < kNumStreams; i++) {
+  //  Addr data_addr(stored->data_addr[i]);
+  //  int data_size = stored->data_size[i];
+  //  if (data_addr.is_initialized()) {
+  //    if ((data_size <= kMaxBlockSize && data_addr.is_separate_file()) ||
+  //        (data_size > kMaxBlockSize && data_addr.is_block_file()) ||
+  //        !data_addr.SanityCheck()) {
+  //      STRESS_NOTREACHED();
+  //      // The address is weird so don't attempt to delete it.
+  //      stored->data_addr[i] = 0;
+  //      // In general, trust the stored size as it should be in sync with the
+  //      // total size tracked by the backend.
+  //    }
+  //  }
+  //  if (data_size < 0)
+  //    stored->data_size[i] = 0;
+  //}
+  //entry_.Store();
+}
+
+void EntryImplV3::SetTimes(base::Time last_used, base::Time last_modified) {
+  entry_->last_access_time = last_used.ToInternalValue();
+  entry_->last_modified_time = last_modified.ToInternalValue();
+  modified_ = true;
+}
+
+void EntryImplV3::BeginLogging(net::NetLog* net_log, bool created) {
+  DCHECK(!net_log_.net_log());
+  net_log_ = net::BoundNetLog::Make(
+      net_log, net::NetLog::SOURCE_DISK_CACHE_ENTRY);
+  net_log_.BeginEvent(
+      net::NetLog::TYPE_DISK_CACHE_ENTRY_IMPL,
+      CreateNetLogEntryCreationCallback(this, created));
+}
+
+const net::BoundNetLog& EntryImplV3::net_log() const {
+  return net_log_;
+}
+
+void EntryImplV3::NotifyDestructionForTest(const CompletionCallback& callback) {
+  DCHECK(destruction_callback_.is_null());
+  destruction_callback_ = callback;
+}
+
+// ------------------------------------------------------------------------
+
+void EntryImplV3::Doom() {
+  if (doomed_ || !backend_)
+    return;
+
+  backend_->InternalDoomEntry(this);
+}
+
+void EntryImplV3::Close() {
+  num_handles_--;
+  if (!num_handles_) {
+    if (sparse_.get())
+        sparse_->Close();
+
+    if (!pending_operations_.empty()) {
+      PendingOperation op =
+          { PENDING_CLEANUP, 0, 0, NULL, 0, CompletionCallback(), false };
+      pending_operations_.push(op);
+    } else {
+      Cleanup();
+    }
+  }
+  Release();
+}
+
+std::string EntryImplV3::GetKey() const {
+  return key_;
+}
+
+Time EntryImplV3::GetLastUsed() const {
+  return Time::FromInternalValue(entry_->last_access_time);
+}
+
+Time EntryImplV3::GetLastModified() const {
+  return Time::FromInternalValue(entry_->last_modified_time);
+}
+
+int32 EntryImplV3::GetDataSize(int index) const {
+  if (index < 0 || index >= kNumStreams)
+    return 0;
+
+  return GetAdjustedSize(index, entry_->data_size[index]);
+}
+
+int32 EntryImplV3::GetAdjustedSize(int index, int real_size) const {
+  DCHECK_GE(index, 0);
+  DCHECK_LE(index, kNumStreams);
+
+  if (index == kKeyIndex)
+    return real_size - key_.size();
+
+  return real_size;
+}
+
+int EntryImplV3::ReadData(int index, int offset, IOBuffer* buf, int buf_len,
+                        const CompletionCallback& callback) {
+  if (index < 0 || index >= kNumStreams)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (buf_len < 0)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (!pending_operations_.empty()) {
+    PendingOperation op =
+        { PENDING_READ, index, offset, buf, buf_len, callback, false };
+    pending_operations_.push(op);
+    return net::ERR_IO_PENDING;
+  }
+  
+  if (net_log_.IsLoggingAllEvents()) {
+    net_log_.BeginEvent(
+        net::NetLog::TYPE_ENTRY_READ_DATA,
+        CreateNetLogReadWriteDataCallback(index, offset, buf_len, false));
+  }
+
+  int result = ReadDataImpl(index, offset, buf, buf_len, NULL, callback);
+
+  if (result != net::ERR_IO_PENDING && net_log_.IsLoggingAllEvents()) {
+    net_log_.EndEvent(
+        net::NetLog::TYPE_ENTRY_READ_DATA,
+        CreateNetLogReadWriteCompleteCallback(result));
+  }
+  return result;
+}
+
+int EntryImplV3::WriteData(int index, int offset, IOBuffer* buf, int buf_len,
+                         const CompletionCallback& callback, bool truncate) {
+  if (index < 0 || index >= kNumStreams)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (offset < 0 || buf_len < 0)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (!pending_operations_.empty()) {
+    PendingOperation op =
+        { PENDING_WRITE, index, offset, buf, buf_len, callback, truncate };
+    pending_operations_.push(op);
+    return net::ERR_IO_PENDING;
+  }
+
+  if (net_log_.IsLoggingAllEvents()) {
+    net_log_.BeginEvent(
+        net::NetLog::TYPE_ENTRY_WRITE_DATA,
+        CreateNetLogReadWriteDataCallback(index, offset, buf_len, truncate));
+  }
+
+  int result = WriteDataImpl(index, offset, buf, buf_len, NULL, callback,
+                             truncate);
+
+  if (result != net::ERR_IO_PENDING && net_log_.IsLoggingAllEvents()) {
+    net_log_.EndEvent(
+        net::NetLog::TYPE_ENTRY_WRITE_DATA,
+        CreateNetLogReadWriteCompleteCallback(result));
+  }
+  return result;
+}
+
+int EntryImplV3::ReadSparseData(int64 offset, IOBuffer* buf, int buf_len,
+                              const CompletionCallback& callback) {
+  if (!sparse_.get())
+     sparse_.reset(new SparseControlV3(this));
+
+  TimeTicks start = TimeTicks::Now();
+  int result = sparse_->StartIO(SparseControlV3::kReadOperation, offset, buf,
+                                buf_len, callback);
+  ReportIOTime(kSparseRead, start);
+  return result;
+}
+
+int EntryImplV3::WriteSparseData(int64 offset, IOBuffer* buf, int buf_len,
+                               const CompletionCallback& callback) {
+  if (!sparse_.get())
+     sparse_.reset(new SparseControlV3(this));
+
+  TimeTicks start = TimeTicks::Now();
+  int result = sparse_->StartIO(SparseControlV3::kWriteOperation, offset, buf,
+                                buf_len, callback);
+  ReportIOTime(kSparseWrite, start);
+  return result;
+}
+
+int EntryImplV3::GetAvailableRange(int64 offset, int len, int64* start,
+                                 const CompletionCallback& callback) {
+  if (!sparse_.get())
+     sparse_.reset(new SparseControlV3(this));
+
+  return sparse_->GetAvailableRange(offset, len, start, callback);
+}
+
+bool EntryImplV3::CouldBeSparse() const {
+  if (sparse_.get())
+    return sparse_->CouldBeSparse();
+
+  scoped_ptr<SparseControlV3> sparse;
+  sparse.reset(new SparseControlV3(const_cast<EntryImplV3*>(this)));
+  return sparse->CouldBeSparse();
+}
+
+void EntryImplV3::CancelSparseIO() {
+  if (!sparse_.get())
+    return;
+
+  sparse_->CancelIO();
+}
+
+int EntryImplV3::ReadyForSparseIO(const CompletionCallback& callback) {
+  if (!sparse_.get())
+    return net::OK;
+
+  return sparse_->ReadyToUse(callback);
+}
+
+// ------------------------------------------------------------------------
+
+// When an entry is deleted from the cache, we clean up all the data associated
+// with it for two reasons: to simplify the reuse of the block (we know that any
+// unused block is filled with zeros), and to simplify the handling of write /
+// read partial information from an entry (don't have to worry about returning
+// data related to a previous cache entry because the range was not fully
+// written before).
+EntryImplV3::~EntryImplV3() {
+  if (!backend_)
+    return;
+  Log("~EntryImplV3 in");
+
+  DCHECK(!modified_);
+
+  // Remove this entry from the list of open entries.
+  backend_->OnEntryDestroyBegin(address_);
+
+  Trace("~EntryImplV3 out 0x%p", reinterpret_cast<void*>(this));
+  net_log_.EndEvent(net::NetLog::TYPE_DISK_CACHE_ENTRY_IMPL);
+  backend_->OnEntryDestroyEnd();
+
+  if (!destruction_callback_.is_null())
+    destruction_callback_.Run(net::OK);
+}
+
+void EntryImplV3::Cleanup() {
+  if (!backend_ || !modified_)
+    return;
+
+  Log("Cleanup in");
+
+  if (doomed_) {
+    DeleteEntryData(true);
+  } else {
+#if defined(NET_BUILD_STRESS_CACHE)
+    SanityCheck();
+#endif
+    net_log_.AddEvent(net::NetLog::TYPE_ENTRY_CLOSE);
+    for (int index = 0; index < kNumStreams; index++) {
+      if (user_buffers_[index].get()) {
+        int rv = Flush(index, 0);
+        if (rv != net::OK) {
+          DCHECK_EQ(rv, net::ERR_IO_PENDING);
+          PendingOperation op =
+              { PENDING_DONE, 0, 0, NULL, 0, CompletionCallback(), false };
+          pending_operations_.push(op);
+        }
+      }
+      Addr address(entry_->data_addr[index]);
+      if (address.is_separate_file())
+        backend_->Close(this, address);
+      if (unreported_size_[index]) {
+        backend_->ModifyStorageSize(
+            entry_->data_size[index] - unreported_size_[index],
+            entry_->data_size[index]);
+      }
+    }
+
+    if (modified_) {
+      entry_->state = ENTRY_USED;
+      WriteEntryData();
+    }
+  }
+
+  modified_ = false;
+  Trace("~Cleanup out 0x%p", reinterpret_cast<void*>(this));
+}
+
+void EntryImplV3::WriteKey() {
+  DCHECK(!user_buffers_[kKeyIndex]);
+  DCHECK(!entry_->data_addr[kKeyIndex]);
+  DCHECK(!entry_->data_size[kKeyIndex]);
+
+  user_buffers_[kKeyIndex].reset(new UserBuffer(backend_));
+  scoped_refptr<net::IOBuffer> buffer(new net::WrappedIOBuffer(key_.data()));
+
+  user_buffers_[kKeyIndex]->ForceSize(true);
+  bool rv = user_buffers_[kKeyIndex]->PreWrite(0, key_.size() + 1024);
+  DCHECK(rv);
+  user_buffers_[kKeyIndex]->ForceSize(false);
+  user_buffers_[kKeyIndex]->Write(0, buffer, key_.size());
+  UpdateSize(kKeyIndex, 0,  key_.size());
+}
+
+int EntryImplV3::ReadDataImpl(int index, int offset,
+                              IOBuffer* buf, int buf_len,
+                              PendingOperation* operation,
+                              const CompletionCallback& callback) {
+  DVLOG(2) << "Read from " << index << " at " << offset << " : " << buf_len;
+  if (index < 0 || index >= kNumStreams)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (index == kKeyIndex)
+    offset += key_.size();
+
+  int entry_size = entry_->data_size[index];
+  if (offset >= entry_size || offset < 0 || !buf_len)
+    return 0;
+
+  if (buf_len < 0)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (!backend_)
+    return net::ERR_UNEXPECTED;
+
+  TimeTicks start = TimeTicks::Now();
+
+  if (offset + buf_len > entry_size)
+    buf_len = entry_size - offset;
+
+  if (!buf_len)
+    return 0;
+
+  UpdateRank(false);
+
+  backend_->OnEvent(Stats::READ_DATA);
+  backend_->OnRead(buf_len);
+
+  Addr address(entry_->data_addr[index]);
+  int eof = address.is_initialized() ? entry_size : 0;
+  if (user_buffers_[index].get() &&
+      user_buffers_[index]->PreRead(eof, offset, &buf_len)) {
+    // Complete the operation locally.
+    buf_len = user_buffers_[index]->Read(offset, buf, buf_len);
+    ReportIOTime(kRead, start);
+    return buf_len;
+  }
+
+  address.set_value(entry_->data_addr[index]);//? again?
+  DCHECK(address.is_initialized());
+  if (!address.is_initialized()) {
+    Doom();//?
+    return net::ERR_FAILED;
+  }
+
+  if (operation)
+    operation->action = PENDING_DONE;
+  backend_->ReadData(this, address, offset, buf, buf_len, callback);
+  return net::ERR_IO_PENDING;
+}
+
+int EntryImplV3::WriteDataImpl(int index, int offset,
+                               IOBuffer* buf, int buf_len,
+                               PendingOperation* operation,
+                               const CompletionCallback& callback,
+                               bool truncate) {
+  DVLOG(2) << "Write to " << index << " at " << offset << " : " << buf_len;
+  if (index < 0 || index >= kNumStreams)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (offset < 0 || buf_len < 0)
+    return net::ERR_INVALID_ARGUMENT;
+
+  if (!backend_)
+    return net::ERR_UNEXPECTED;
+
+  int max_file_size = backend_->MaxFileSize();
+
+  // offset or buf_len could be negative numbers.
+  if (offset > max_file_size || buf_len > max_file_size ||
+      offset + buf_len > max_file_size) {
+    int size = offset + buf_len;
+    if (size <= max_file_size)
+      size = kint32max;
+    backend_->TooMuchStorageRequested(size);
+    return net::ERR_FAILED;
+  }
+
+  int actual_offset = (index == kKeyIndex) ? offset + key_.size() : offset;
+  
+  TimeTicks start = TimeTicks::Now();
+
+  // Read the size at this point (it may change inside prepare).
+  int entry_size = entry_->data_size[index];
+  bool extending = entry_size < actual_offset + buf_len;
+  truncate = truncate && entry_size > actual_offset + buf_len;
+  Trace("To PrepareTarget 0x%x", address_.value());
+
+  int rv = PrepareTarget(index, actual_offset, buf_len, truncate);
+  if (rv == net::ERR_IO_PENDING) {   
+    if (operation) {
+      DCHECK_EQ(operation->action, PENDING_WRITE);
+      operation->action = PENDING_FLUSH;
+    } else {
+      PendingOperation op =
+          { PENDING_FLUSH, index, offset, buf, buf_len, callback, truncate };
+      pending_operations_.push(op);
+    }
+    return rv;
+  }
+
+  if (rv != net::OK)
+    return rv;
+
+  Trace("From PrepareTarget 0x%x", address_.value());
+  if (extending || truncate)
+    UpdateSize(index, entry_size, actual_offset + buf_len);
+
+  UpdateRank(true);
+  modified_ = true;
+
+  backend_->OnEvent(Stats::WRITE_DATA);
+  backend_->OnWrite(buf_len);
+
+  if (user_buffers_[index].get()) {
+    // Complete the operation locally.
+    user_buffers_[index]->Write(actual_offset, buf, buf_len);
+    ReportIOTime(kWrite, start);
+    return buf_len;
+  }
+
+  Addr address(entry_->data_addr[index]);
+  if (actual_offset + buf_len == 0) {
+    if (truncate) {
+      DCHECK(!address.is_initialized());
+    }
+    return 0;
+  }
+
+  if (address.is_separate_file() && (truncate || (extending && !buf_len)))
+    backend_->Truncate(this, address, actual_offset + buf_len);
+
+  if (!buf_len)
+    return 0;
+
+  if (operation)
+    operation->action = PENDING_DONE;
+  backend_->WriteData(this, address, actual_offset, buf, buf_len, callback);
+  return net::ERR_IO_PENDING;
+}
+
+// ------------------------------------------------------------------------
+
+bool EntryImplV3::CreateDataBlock(int index, int size) {
+  DCHECK(index >= 0 && index < kNumStreams);
+
+  Addr address(entry_->data_addr[index]);
+  if (!CreateBlock(size, &address))
+    return false;
+
+  entry_->data_addr[index] = address.value();
+  return true;
+}
+
+bool EntryImplV3::CreateBlock(int size, Addr* address) {
+  DCHECK(!address->is_initialized());
+  if (!backend_)
+    return false;
+
+  FileType file_type = Addr::RequiredFileType(size);
+  if (EXTERNAL != file_type) {
+    int num_blocks = (size + Addr::BlockSizeForFileType(file_type) - 1) /
+                     Addr::BlockSizeForFileType(file_type);
+
+    return backend_->CreateBlock(file_type, num_blocks, address);
+  }
+
+  if (size > backend_->MaxFileSize())
+    return false;
+
+  Addr block_address;
+  if (!backend_->CreateBlock(BLOCK_FILES, 1, &block_address))
+    return false;
+  *address = block_address.AsExternal();
+
+  scoped_refptr<net::IOBufferWithSize> buffer(
+    new net::IOBufferWithSize(2 * sizeof(uint32)));
+  memcpy(buffer->data(), &entry_->hash, buffer->size());
+
+  backend_->WriteData(this, block_address, 0, buffer, buffer->size(),
+                      CompletionCallback());
+  return true;
+}
+
+// Note that this method may end up modifying a block file so upon return the
+// involved block will be free, and could be reused for something else. If there
+// is a crash after that point (and maybe before returning to the caller), the
+// entry will be left dirty... and at some point it will be discarded; it is
+// important that the entry doesn't keep a reference to this address, or we'll
+// end up deleting the contents of |address| once again.
+void EntryImplV3::DeleteData(Addr address) {
+  DCHECK(backend_);
+  if (!address.is_initialized())
+    return;
+  backend_->Delete(this, address);
+}
+
+void EntryImplV3::UpdateRank(bool modified) {
+  if (!backend_)
+    return;
+
+  Time current = backend_->GetCurrentTime();
+  entry_->last_access_time = current.ToInternalValue();
+
+  if (modified)
+    entry_->last_modified_time = current.ToInternalValue();
+
+  if (!doomed_) {
+    backend_->UpdateRank(this, modified);
+    return;
+  }
+}
+
+void EntryImplV3::DeleteEntryData(bool everything) {
+  DCHECK(doomed_ || !everything);
+
+  if (GetEntryFlags() & PARENT_ENTRY) {
+    // We have some child entries that must go away.
+    SparseControlV3::DeleteChildren(this);
+  }
+
+  if (GetDataSize(0))
+    CACHE_UMA(COUNTS, "DeleteHeader", 0, GetDataSize(0));
+  if (GetDataSize(1))
+    CACHE_UMA(COUNTS, "DeleteData", 0, GetDataSize(1));
+  for (int index = 0; index < kNumStreams; index++) {
+    Addr address(entry_->data_addr[index]);
+    if (address.is_initialized()) {
+      backend_->ModifyStorageSize(entry_->data_size[index] -
+                                      unreported_size_[index], 0);
+      entry_->data_addr[index] = 0;
+      entry_->data_size[index] = 0;
+      modified_ = true;
+      //entry_.Store();
+      DeleteData(address);
+    }
+  }
+
+  if (!everything)
+    return;
+
+  // Note that at this point node_ and entry_ are just two blocks of data, and
+  // even if they reference each other, nobody should be referencing them.
+
+  backend_->Delete(this, address_);
+}
+
+// We keep a memory buffer for everything that ends up stored on a block file
+// (because we don't know yet the final data size), and for some of the data
+// that end up on external files. This function will initialize that memory
+// buffer and / or the files needed to store the data.
+//
+// In general, a buffer may overlap data already stored on disk, and in that
+// case, the contents of the buffer are the most accurate. It may also extend
+// the file, but we don't want to read from disk just to keep the buffer up to
+// date. This means that as soon as there is a chance to get confused about what
+// is the most recent version of some part of a file, we'll flush the buffer and
+// reuse it for the new data. Keep in mind that the normal use pattern is quite
+// simple (write sequentially from the beginning), so we optimize for handling
+// that case.
+int EntryImplV3::PrepareTarget(int index, int offset, int buf_len,
+                               bool truncate) {
+  if (truncate)
+    return HandleTruncation(index, offset, buf_len);
+
+  if (!offset && !buf_len)
+    return net::OK;
+
+  if (!IsSimpleWrite(index, offset, buf_len))
+    return HandleOldData(index, offset, buf_len);
+
+  if (!user_buffers_[index].get())
+    user_buffers_[index].reset(new UserBuffer(backend_));
+
+  return PrepareBuffer(index, offset, buf_len);
+}
+
+// We get to this function with some data already stored. If there is a
+// truncation that results on data stored internally, we'll explicitly
+// handle the case here.
+int EntryImplV3::HandleTruncation(int index, int offset, int buf_len) {
+  Addr address(entry_->data_addr[index]);
+
+  int current_size = entry_->data_size[index];
+  int new_size = offset + buf_len;
+  DCHECK_LT(new_size, current_size);
+
+  if (!new_size) {
+    // This is by far the most common scenario.
+    backend_->ModifyStorageSize(current_size - unreported_size_[index], 0);//updatesize()
+    entry_->data_addr[index] = 0;
+    entry_->data_size[index] = 0;
+    unreported_size_[index] = 0;
+    modified_ = true;
+    //entry_->Store();
+    DeleteData(address);
+
+    user_buffers_[index].reset();
+    return net::OK;
+  }
+
+  // We never postpone truncating a file, if there is one, but we may postpone
+  // telling the backend about the size reduction.
+  if (user_buffers_[index].get()) {
+    DCHECK_GE(current_size, user_buffers_[index]->Start());
+    if (!address.is_initialized()) {
+      // There is no overlap between the buffer and disk.
+      if (new_size > user_buffers_[index]->Start()) {
+        // Just truncate our buffer.
+        DCHECK_LT(new_size, user_buffers_[index]->End());
+        user_buffers_[index]->Truncate(new_size);
+        return net::OK;
+      }
+
+      // Just discard our buffer.
+      user_buffers_[index].reset();
+      return PrepareBuffer(index, offset, buf_len);
+    }
+
+    // There is some overlap or we need to extend the file before the
+    // truncation.
+    if (new_size > user_buffers_[index]->Start()) {
+      if (offset > user_buffers_[index]->Start())
+        user_buffers_[index]->Truncate(new_size);
+      UpdateSize(index, current_size, new_size);
+      int rv = Flush(index, 0);
+      if (rv != net::OK)
+        return rv;
+    }
+    user_buffers_[index].reset();
+  }
+
+  // We have data somewhere, and it is not in a buffer.
+  DCHECK(!user_buffers_[index].get());
+  DCHECK(address.is_initialized());
+
+  if (!IsSimpleWrite(index, offset, buf_len))
+    return net::OK;  // Let the operation go directly to disk.
+
+  if (address.is_separate_file())
+    backend_->Truncate(this, address, offset + buf_len);
+
+  if (!user_buffers_[index].get())
+    user_buffers_[index].reset(new UserBuffer(backend_));
+
+  return PrepareBuffer(index, offset, buf_len);
+}
+
+bool EntryImplV3::IsSimpleWrite(int index, int offset, int buf_len) {
+  Addr address(entry_->data_addr[index]);
+  if (!address.is_initialized())
+    return true;
+
+  if (address.is_block_file() && (offset + buf_len > kMaxBlockSize))// check limit
+    return false;
+
+  if (!user_buffers_[index].get())
+    return true;
+
+  if ((offset >= user_buffers_[index]->Start()) &&
+      (offset <= user_buffers_[index]->End())) {
+    return true;
+  }
+
+  return offset > entry_->data_size[index];
+}
+
+int EntryImplV3::HandleOldData(int index, int offset, int buf_len) {
+  Addr address(entry_->data_addr[index]);
+  DCHECK(address.is_initialized());
+
+  if (address.is_block_file() && (offset + buf_len > kMaxBlockSize)) {// check limit
+    if (!GetAdjustedSize(index, offset) || !GetDataSize(index)) {
+      // There's nothing to save from the old data.
+      user_buffers_[index].reset();
+      DCHECK(!user_buffers_[kKeyIndex]);
+      DeleteData(address);
+      entry_->data_addr[kKeyIndex] = 0;
+      entry_->data_size[kKeyIndex] = 0;
+      WriteKey();
+      return PrepareBuffer(index, offset, buf_len);
+    }
+    // We have to move the data to a new file.
+    Addr new_address;
+    if (!CreateBlock(kMaxBlockSize * 2, &new_address))
+      return net::ERR_FAILED;
+
+    backend_->MoveData(this, address, new_address, entry_->data_size[index],
+                        callback_);
+    entry_->data_addr[index] = new_address.value();
+    return net::ERR_IO_PENDING;
+  }
+
+  int rv = Flush(index, 0);
+  if (rv != net::OK)
+    return rv;
+
+  user_buffers_[index].reset();  // Don't use a local buffer.
+  return net::OK;
+}
+
+int EntryImplV3::PrepareBuffer(int index, int offset, int buf_len) {
+  DCHECK(user_buffers_[index].get());
+  int rv = net::OK;
+  if ((user_buffers_[index]->End() && offset > user_buffers_[index]->End()) ||
+      offset > entry_->data_size[index]) {
+    // We are about to extend the buffer or the file (with zeros), so make sure
+    // that we are not overwriting anything.
+    Addr address(entry_->data_addr[index]);
+    if (address.is_initialized() && address.is_separate_file()) {
+      rv = Flush(index, 0);
+      if (rv != net::OK)
+        return rv;
+      // There is an actual file already, and we don't want to keep track of
+      // its length so we let this operation go straight to disk.
+      // The only case when a buffer is allowed to extend the file (as in fill
+      // with zeros before the start) is when there is no file yet to extend.
+      user_buffers_[index].reset();
+      return rv;
+    }
+  }
+
+  if (!user_buffers_[index]->PreWrite(offset, buf_len)) {
+    rv = Flush(index, offset + buf_len);
+    if (rv != net::OK)
+      return rv;
+
+    // Lets try again.
+    if (offset > user_buffers_[index]->End() ||
+        !user_buffers_[index]->PreWrite(offset, buf_len)) {
+      // We cannot complete the operation with a buffer.
+      DCHECK(!user_buffers_[index]->Size());
+      DCHECK(!user_buffers_[index]->Start());
+      user_buffers_[index].reset();
+    }
+  }
+  return rv;
+}
+
+int EntryImplV3::Flush(int index, int min_len) {
+  Addr address(entry_->data_addr[index]);
+  if (!user_buffers_[index].get())
+    return net::OK;
+
+  //DCHECK(!address.is_initialized() || address.is_separate_file());
+  DVLOG(3) << "Flush";
+
+  int size = std::max(entry_->data_size[index], min_len);
+  if (size && !address.is_initialized() && !CreateDataBlock(index, size))
+    return net::ERR_FAILED;
+
+  if (!entry_->data_size[index]) {
+    DCHECK(!user_buffers_[index]->Size());
+    return net::OK;
+  }
+
+  address.set_value(entry_->data_addr[index]);
+
+  int len = user_buffers_[index]->Size();
+  int offset = user_buffers_[index]->Start();
+  if (!len && !offset)
+    return net::OK;
+
+  if (!len) {
+    if (address.is_separate_file()) {
+      backend_->Truncate(this, address, offset);
+      return net::OK;
+    }
+    user_buffers_[index]->Rebase();
+    len = offset;
+    offset = 0;
+  }
+
+  backend_->WriteData(this, address, offset, user_buffers_[index]->Get(),
+                      len, callback_);
+  user_buffers_[index].reset();
+  return net::ERR_IO_PENDING;
+}
+
+void EntryImplV3::UpdateSize(int index, int old_size, int new_size) {
+  if (entry_->data_size[index] == new_size)
+    return;
+
+  unreported_size_[index] += new_size - old_size;
+  entry_->data_size[index] = new_size;
+  modified_ = true;
+}
+
+void EntryImplV3::WriteEntryData() {
+  CacheEntryBlockV3 entry_block;
+  entry_block.SetData(entry_.get());
+  entry_block.UpdateHash();
+
+  scoped_refptr<net::IOBufferWithSize> buffer(
+      new net::IOBufferWithSize(sizeof(EntryRecord)));
+  memcpy(buffer->data(), entry_.get(), buffer->size());
+
+  backend_->WriteData(this, address_, 0, buffer, buffer->size(),
+                      CompletionCallback());
+}
+
+void EntryImplV3::SetEntryFlags(uint32 flags) {
+  entry_->flags |= flags;
+  modified_ = true;
+}
+
+uint32 EntryImplV3::GetEntryFlags() {
+  return entry_->flags;
+}
+
+void EntryImplV3::GetData(int index, scoped_refptr<IOBuffer>* buffer, Addr* address) {
+  DCHECK(backend_);
+  if (user_buffers_[index].get() && user_buffers_[index]->Size() &&
+      !user_buffers_[index]->Start()) {
+    // The data is already in memory, just copy it and we're done.
+    int data_len = entry_->data_size[index];
+    if (data_len <= user_buffers_[index]->Size()) {
+      DCHECK(!user_buffers_[index]->Start());
+      *buffer = user_buffers_[index]->Get();
+      return;
+    }
+  }
+
+  // Bad news: we'd have to read the info from disk so instead we'll just tell
+  // the caller where to read from.
+  *buffer = NULL;
+  address->set_value(entry_->data_addr[index]);
+  if (address->is_initialized()) {
+    // Prevent us from deleting the block from the backing store.
+    backend_->ModifyStorageSize(entry_->data_size[index] -
+                                    unreported_size_[index], 0);
+    entry_->data_addr[index] = 0;
+    entry_->data_size[index] = 0;
+  }
+}
+
+void EntryImplV3::ReportIOTime(Operation op, const base::TimeTicks& start) {
+  if (!backend_)
+    return;
+
+  switch (op) {
+    case kRead:
+      CACHE_UMA(AGE_MS, "ReadTime", 0, start);
+      break;
+    case kWrite:
+      CACHE_UMA(AGE_MS, "WriteTime", 0, start);
+      break;
+    case kSparseRead:
+      CACHE_UMA(AGE_MS, "SparseReadTime", 0, start);
+      break;
+    case kSparseWrite:
+      CACHE_UMA(AGE_MS, "SparseWriteTime", 0, start);
+      break;
+    case kAsyncIO:
+      CACHE_UMA(AGE_MS, "AsyncIOTime", 0, start);
+      break;
+    case kReadAsync1:
+      CACHE_UMA(AGE_MS, "AsyncReadDispatchTime", 0, start);
+      break;
+    case kWriteAsync1:
+      CACHE_UMA(AGE_MS, "AsyncWriteDispatchTime", 0, start);
+      break;
+    default:
+      NOTREACHED();
+  }
+}
+
+void EntryImplV3::Log(const char* msg) {
+  Trace("%s 0x%p 0x%x", msg, reinterpret_cast<void*>(this), address_);
+  Trace("  data: 0x%x 0x%x", entry_->data_addr[0], entry_->data_addr[1]);
+  Trace("  doomed: %d", doomed_);
+}
+
+void EntryImplV3::OnIOComplete(int result) {
+  DCHECK_NE(result, net::ERR_IO_PENDING);
+  DCHECK(!pending_operations_.empty());
+  while (result != net::ERR_IO_PENDING) {
+    bool finished = false;
+    PendingOperation& next = pending_operations_.front();
+    switch (next.action) {
+      case PENDING_FLUSH:
+        if (result < 0)
+          finished = true;
+        next.action = PENDING_WRITE;
+        break;
+      case PENDING_READ:
+        result = ReadDataImpl(next.index, next.offset, next.buf,
+                              next.buf_len, &next, callback_);
+        if (result != net::ERR_IO_PENDING)
+          finished = true;
+        break;
+      case PENDING_WRITE:
+        result = WriteDataImpl(next.index, next.offset, next.buf,
+                               next.buf_len, &next, callback_,
+                               next.truncate);
+        if (result != net::ERR_IO_PENDING)
+          finished = true;
+        break;
+      case PENDING_CLEANUP:
+        Cleanup();
+        finished = true;
+        break;
+      case PENDING_DONE:
+        finished = true;
+        break;
+      default: NOTREACHED();
+    }
+    if (finished) {
+      next.buf = NULL;
+      if (!next.callback.is_null())
+        next.callback.Run(result);
+      pending_operations_.pop();
+
+      if (pending_operations_.empty()) {
+        if (modified_ && HasOneRef()) {
+          // One of the pending operations modified this entry after the last
+          // Close... issue an extra cleanup.
+          Cleanup();
+        }
+        break;
+      }
+
+      // Cleanup may issue multiple flushes so there may be multiple pending
+      // callbacks already in flight. Make sure we wait for them.
+      next = pending_operations_.front();
+      DCHECK_NE(next.action, PENDING_FLUSH);
+      if (next.action == PENDING_DONE)
+        break;
+    }
+  }
+}
+
+}  // namespace disk_cache