drive: Delete unused ID entries from an already updated DB

chrome/browser/chromeos/drive/resource_metadata_storage.cc

 // Copyright 2013 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 "chrome/browser/chromeos/drive/resource_metadata_storage.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 267 matching lines @@
   std::string serialized_header;
   ResourceMetadataHeader header;
   if (!resource_map->Get(leveldb::ReadOptions(),
                          leveldb::Slice(GetHeaderDBKey()),
                          &serialized_header).ok() ||
       !header.ParseFromString(serialized_header))
     return false;
   UMA_HISTOGRAM_SPARSE_SLOWLY("Drive.MetadataDBVersionBeforeUpgradeCheck",
                               header.version());
 
-  if (header.version() == kDBVersion) {  // Nothing to do.
-    return true;
+  if (header.version() == kDBVersion) {
+    // Before r272134, UpgradeOldDB() was not deleting unused ID entries.
+    // Delete unused ID entries to fix crbug.com/374648.
+    std::set<std::string> used_ids;
+
+    scoped_ptr<leveldb::Iterator> it(
+        resource_map->NewIterator(leveldb::ReadOptions()));
+    it->Seek(leveldb::Slice(GetHeaderDBKey()));
+    it->Next();
+    for (; it->Valid(); it->Next()) {
+      if (IsCacheEntryKey(it->key())) {
+        used_ids.insert(GetIdFromCacheEntryKey(it->key()));
+      } else if (!IsChildEntryKey(it->key()) && !IsIdEntryKey(it->key())) {
+        used_ids.insert(it->key().ToString());
+      }
+    }
+    if (!it->status().ok())
+      return false;
+
+    leveldb::WriteBatch batch;
+    for (it->SeekToFirst(); it->Valid(); it->Next()) {
+      if (IsIdEntryKey(it->key()) && !used_ids.count(it->value().ToString()))
+        batch.Delete(it->key());
+    }
+    if (!it->status().ok())
+      return false;
+
+    return resource_map->Write(leveldb::WriteOptions(), &batch).ok();
   } else if (header.version() < 6) {  // Too old, nothing can be done.
     return false;
   } else if (header.version() < 11) {  // Cache entries can be reused.
     leveldb::ReadOptions options;
     options.verify_checksums = true;
     scoped_ptr<leveldb::Iterator> it(resource_map->NewIterator(options));
 
     leveldb::WriteBatch batch;
     for (it->SeekToFirst(); it->Valid(); it->Next()) {
       if (IsCacheEntryKey(it->key())) {
@@ skipping 626 matching lines @@
   if (!it->status().ok() || num_child_entries != num_entries_with_parent) {
     DLOG(ERROR) << "Error during checking resource map. status = "
                 << it->status().ToString();
     return false;
   }
   return true;
 }
 
 }  // namespace internal
 }  // namespace drive