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220 lines
8.5 KiB
C++
220 lines
8.5 KiB
C++
// Copyright 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "net/disk_cache/simple/simple_version_upgrade.h"
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#include <cstring>
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#include "base/files/file.h"
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#include "base/files/file_path.h"
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#include "base/files/file_util.h"
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#include "base/files/memory_mapped_file.h"
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#include "base/logging.h"
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#include "base/pickle.h"
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#include "net/disk_cache/simple/simple_backend_version.h"
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#include "net/disk_cache/simple/simple_entry_format_history.h"
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#include "third_party/zlib/zlib.h"
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namespace {
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// It is not possible to upgrade cache structures on disk that are of version
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// below this, the entire cache should be dropped for them.
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const uint32_t kMinVersionAbleToUpgrade = 5;
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const char kFakeIndexFileName[] = "index";
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const char kIndexFileName[] = "the-real-index";
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void LogMessageFailedUpgradeFromVersion(int version) {
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LOG(ERROR) << "Failed to upgrade Simple Cache from version: " << version;
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}
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bool WriteFakeIndexFile(const base::FilePath& file_name) {
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base::File file(file_name, base::File::FLAG_CREATE | base::File::FLAG_WRITE);
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if (!file.IsValid())
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return false;
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disk_cache::FakeIndexData file_contents;
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file_contents.initial_magic_number =
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disk_cache::simplecache_v5::kSimpleInitialMagicNumber;
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file_contents.version = disk_cache::kSimpleVersion;
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file_contents.zero = 0;
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file_contents.zero2 = 0;
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int bytes_written = file.Write(0, reinterpret_cast<char*>(&file_contents),
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sizeof(file_contents));
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if (bytes_written != sizeof(file_contents)) {
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LOG(ERROR) << "Failed to write fake index file: "
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<< file_name.LossyDisplayName();
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return false;
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}
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return true;
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}
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} // namespace
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namespace disk_cache {
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FakeIndexData::FakeIndexData() {
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// Make hashing repeatable: leave no padding bytes untouched.
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std::memset(this, 0, sizeof(*this));
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}
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// Migrates the cache directory from version 4 to version 5.
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// Returns true iff it succeeds.
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//
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// The V5 and V6 caches differ in the name of the index file (it moved to a
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// subdirectory) and in the file format (directory last-modified time observed
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// by the index writer has gotten appended to the pickled format).
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//
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// To keep complexity small this specific upgrade code *deletes* the old index
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// file. The directory for the new index file has to be created lazily anyway,
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// so it is not done in the upgrader.
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//
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// Below is the detailed description of index file format differences. It is for
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// reference purposes. This documentation would be useful to move closer to the
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// next index upgrader when the latter gets introduced.
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//
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// Path:
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// V5: $cachedir/the-real-index
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// V6: $cachedir/index-dir/the-real-index
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//
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// Pickled file format:
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// Both formats extend Pickle::Header by 32bit value of the CRC-32 of the
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// pickled data.
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// <v5-index> ::= <v5-index-metadata> <entry-info>*
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// <v5-index-metadata> ::= UInt64(kSimpleIndexMagicNumber)
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// UInt32(4)
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// UInt64(<number-of-entries>)
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// UInt64(<cache-size-in-bytes>)
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// <entry-info> ::= UInt64(<hash-of-the-key>)
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// Int64(<entry-last-used-time>)
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// UInt64(<entry-size-in-bytes>)
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// <v6-index> ::= <v6-index-metadata>
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// <entry-info>*
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// Int64(<cache-dir-mtime>)
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// <v6-index-metadata> ::= UInt64(kSimpleIndexMagicNumber)
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// UInt32(5)
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// UInt64(<number-of-entries>)
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// UInt64(<cache-size-in-bytes>)
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// Where:
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// <entry-size-in-bytes> is equal the sum of all file sizes of the entry.
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// <cache-dir-mtime> is the last modification time with nanosecond precision
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// of the directory, where all files for entries are stored.
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// <hash-of-the-key> represent the first 64 bits of a SHA-1 of the key.
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bool UpgradeIndexV5V6(const base::FilePath& cache_directory) {
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const base::FilePath old_index_file =
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cache_directory.AppendASCII(kIndexFileName);
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if (!base::DeleteFile(old_index_file, /* recursive = */ false))
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return false;
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return true;
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}
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// Some points about the Upgrade process are still not clear:
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// 1. if the upgrade path requires dropping cache it would be faster to just
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// return an initialization error here and proceed with asynchronous cache
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// cleanup in CacheCreator. Should this hack be considered valid? Some smart
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// tests may fail.
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// 2. Because Android process management allows for killing a process at any
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// time, the upgrade process may need to deal with a partially completed
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// previous upgrade. For example, while upgrading A -> A + 2 we are the
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// process gets killed and some parts are remaining at version A + 1. There
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// are currently no generic mechanisms to resolve this situation, co the
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// upgrade codes need to ensure they can continue after being stopped in the
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// middle. It also means that the "fake index" must be flushed in between the
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// upgrade steps. Atomicity of this is an interesting research topic. The
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// intermediate fake index flushing must be added as soon as we add more
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// upgrade steps.
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bool UpgradeSimpleCacheOnDisk(const base::FilePath& path) {
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// There is a convention among disk cache backends: looking at the magic in
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// the file "index" it should be sufficient to determine if the cache belongs
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// to the currently running backend. The Simple Backend stores its index in
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// the file "the-real-index" (see simple_index_file.cc) and the file "index"
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// only signifies presence of the implementation's magic and version. There
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// are two reasons for that:
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// 1. Absence of the index is itself not a fatal error in the Simple Backend
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// 2. The Simple Backend has pickled file format for the index making it hacky
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// to have the magic in the right place.
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const base::FilePath fake_index = path.AppendASCII(kFakeIndexFileName);
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base::File fake_index_file(fake_index,
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base::File::FLAG_OPEN | base::File::FLAG_READ);
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if (!fake_index_file.IsValid()) {
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if (fake_index_file.error_details() == base::File::FILE_ERROR_NOT_FOUND) {
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return WriteFakeIndexFile(fake_index);
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}
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return false;
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}
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FakeIndexData file_header;
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int bytes_read = fake_index_file.Read(0,
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reinterpret_cast<char*>(&file_header),
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sizeof(file_header));
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if (bytes_read != sizeof(file_header) ||
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file_header.initial_magic_number !=
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disk_cache::simplecache_v5::kSimpleInitialMagicNumber) {
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LOG(ERROR) << "File structure does not match the disk cache backend.";
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return false;
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}
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fake_index_file.Close();
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uint32_t version_from = file_header.version;
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if (version_from < kMinVersionAbleToUpgrade ||
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version_from > kSimpleVersion) {
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LOG(ERROR) << "Inconsistent cache version.";
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return false;
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}
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if (file_header.zero != 0 && file_header.zero2 != 0) {
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LOG(WARNING) << "Rebuilding cache due to experiment change";
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return false;
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}
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bool new_fake_index_needed = (version_from != kSimpleVersion);
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// There should be one upgrade routine here for each incremental upgrade
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// starting at kMinVersionAbleToUpgrade.
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static_assert(kMinVersionAbleToUpgrade == 5, "upgrade routines don't match");
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DCHECK_LE(5U, version_from);
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if (version_from == 5) {
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// Upgrade only the index for V5 -> V6 move.
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if (!UpgradeIndexV5V6(path)) {
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LogMessageFailedUpgradeFromVersion(file_header.version);
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return false;
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}
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version_from++;
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}
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DCHECK_LE(6U, version_from);
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if (version_from == 6) {
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// No upgrade from V6 -> V7, because the entry format has not changed and
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// the V7 index reader is backwards compatible.
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version_from++;
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}
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if (version_from == 7) {
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// Likewise, V7 -> V8 is handled entirely by the index reader.
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version_from++;
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}
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DCHECK_EQ(kSimpleVersion, version_from);
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if (!new_fake_index_needed)
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return true;
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const base::FilePath temp_fake_index = path.AppendASCII("upgrade-index");
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if (!WriteFakeIndexFile(temp_fake_index)) {
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base::DeleteFile(temp_fake_index, /* recursive = */ false);
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LOG(ERROR) << "Failed to write a new fake index.";
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LogMessageFailedUpgradeFromVersion(file_header.version);
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return false;
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}
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if (!base::ReplaceFile(temp_fake_index, fake_index, NULL)) {
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LOG(ERROR) << "Failed to replace the fake index.";
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LogMessageFailedUpgradeFromVersion(file_header.version);
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return false;
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}
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return true;
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}
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} // namespace disk_cache
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