mojo: Start building a leveldb service.

This service encapsulates just leveldb and exports an interface for
Get/Put/Write. Instead of writing directly to the filesystem, it instead
takes a mojo:filesystem DirectoryPtr where it stores its data, letting
leveldb be entirely sandboxed.

BUG=585587

Review URL: https://codereview.chromium.org/1682803004

Cr-Commit-Position: refs/heads/master@{#375949}

1 files changed, 45 insertions, 0 deletions

diff --git a/components/filesystem/lock_table.h b/components/filesystem/lock_table.h
new file mode 100644
index 0000000..9be4ca6
--- /dev/null
+++ b/components/filesystem/lock_table.h
@@ -0,0 +1,45 @@
+// Copyright 2016 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 COMPONENTS_FILESYSTEM_LOCK_TABLE_H_
+#define COMPONENTS_FILESYSTEM_LOCK_TABLE_H_
+
+#include <set>
+
+#include "base/files/file.h"
+
+namespace filesystem {
+
+class FileImpl;
+
+// A table of all locks held by this process. We have one global table owned by
+// the app, but accessible by everything just in case two connections from the
+// same origin try to lock the same file.
+class LockTable {
+ public:
+  LockTable();
+  ~LockTable();
+
+  // Locks a file.
+  base::File::Error LockFile(FileImpl* file);
+
+  // Releases a lock, if there is one.
+  base::File::Error UnlockFile(FileImpl* file);
+
+  // Removes a path from the list of |locked_files_|. This can be called on
+  // files that were never locked, as it is called on all file closes and
+  // FileImpl destruction.
+  void RemoveFromLockTable(const base::FilePath& path);
+
+ private:
+  // Open, locked files. We keep track of this so we quickly error when we try
+  // to double lock a file.
+  std::set<base::FilePath> locked_files_;
+
+  DISALLOW_COPY_AND_ASSIGN(LockTable);
+};
+
+}  // namespace filesystem
+
+#endif  // COMPONENTS_FILESYSTEM_LOCK_TABLE_H_