[fsp] Improve performance for reading small chunks of data.

storage/browser/fileapi/file_system_backend.h

 // 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.
 
 #ifndef STORAGE_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_
 #define STORAGE_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_
 
+#include <limits>
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "storage/browser/fileapi/file_permission_policy.h"
 #include "storage/browser/fileapi/open_file_system_mode.h"
 #include "storage/browser/storage_browser_export.h"
@@ skipping 10 matching lines @@
 class FileStreamWriter;
 class FileSystemContext;
 class FileSystemFileUtil;
 class FileSystemOperation;
 class FileSystemQuotaUtil;
 class WatcherManager;
 
 // Callback to take GURL.
 typedef base::Callback<void(const GURL& url)> URLCallback;
 
+// Maximum numer of bytes to be read by FileStreamReader classes. Used in
+// FileSystemBackend::CreateFileStreamReader(), when it's not known how many
+// bytes will be fetched in total.
+const int64 kMaximumLength = std::numeric_limits<int64>::max();
+
 // An interface for defining a file system backend.
 //
 // NOTE: when you implement a new FileSystemBackend for your own
 // FileSystem module, please contact to kinuko@chromium.org.
 //
 class STORAGE_EXPORT FileSystemBackend {
  public:
   // Callback for InitializeFileSystem.
   typedef base::Callback<void(const GURL& root_url,
                               const std::string& name,
@@ skipping 53 matching lines @@
   // read/write implementation.
   virtual bool HasInplaceCopyImplementation(FileSystemType type) const = 0;
 
   // Creates a new file stream reader for a given filesystem URL |url| with an
   // offset |offset|. |expected_modification_time| specifies the expected last
   // modification if the value is non-null, the reader will check the underlying
   // file's actual modification time to see if the file has been modified, and
   // if it does any succeeding read operations should fail with
   // ERR_UPLOAD_FILE_CHANGED error.
   // This method itself does *not* check if the given path exists and is a
-  // regular file.
-  // The |length| argument says how many bytes are going to be read using the
-  // instance of the file stream reader. If unknown, then equal to -1.
+  // regular file. At most |max_bytes_to_read| can be fetched from the file
+  // stream reader.
   virtual scoped_ptr<storage::FileStreamReader> CreateFileStreamReader(
       const FileSystemURL& url,
       int64 offset,
+      int64 max_bytes_to_read,
       const base::Time& expected_modification_time,
       FileSystemContext* context) const = 0;
 
   // Creates a new file stream writer for a given filesystem URL |url| with an
   // offset |offset|.
   // This method itself does *not* check if the given path exists and is a
   // regular file.
   virtual scoped_ptr<FileStreamWriter> CreateFileStreamWriter(
       const FileSystemURL& url,
       int64 offset,
@@ skipping 33 matching lines @@
   // Gets a redirect URL for contents. e.g. Google Drive URL for hosted
   // documents. Returns empty URL if the entry does not have the redirect URL.
   virtual void GetRedirectURLForContents(
       const storage::FileSystemURL& url,
       const storage::URLCallback& callback) = 0;
 };
 
 }  // namespace storage
 
 #endif  // STORAGE_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_