46   Status NewSequentialFile(const std::string& f,
49   Status NewRandomAccessFile(const std::string& f,
52   Status NewWritableFile(const std::string& f, std::unique_ptr<WritableFile>* r,
54   Status ReuseWritableFile(const std::string& fname,
58   virtual Status NewDirectory(const std::string& name,  in NewDirectory()
61     Status as = a_->NewDirectory(name, result);  in NewDirectory()
62     Status bs = b_->NewDirectory(name, &br);  in NewDirectory()
66   Status FileExists(const std::string& f) override {  in FileExists()
67     Status as = a_->FileExists(f);  in FileExists()
68     Status bs = b_->FileExists(f);  in FileExists()
77   Status GetChildren(const std::string& dir,  in GetChildren()
80     Status as = a_->GetChildren(dir, &ar);  in GetChildren()
81     Status bs = b_->GetChildren(dir, &br);  in GetChildren()
94   Status DeleteFile(const std::string& f) override {  in DeleteFile()
95     Status as = a_->DeleteFile(f);  in DeleteFile()
96     Status bs = b_->DeleteFile(f);  in DeleteFile()
100   Status CreateDir(const std::string& d) override {  in CreateDir()
101     Status as = a_->CreateDir(d);  in CreateDir()
102     Status bs = b_->CreateDir(d);  in CreateDir()
106   Status CreateDirIfMissing(const std::string& d) override {  in CreateDirIfMissing()
107     Status as = a_->CreateDirIfMissing(d);  in CreateDirIfMissing()
108     Status bs = b_->CreateDirIfMissing(d);  in CreateDirIfMissing()
112   Status DeleteDir(const std::string& d) override {  in DeleteDir()
113     Status as = a_->DeleteDir(d);  in DeleteDir()
114     Status bs = b_->DeleteDir(d);  in DeleteDir()
118   Status GetFileSize(const std::string& f, uint64_t* s) override {  in GetFileSize()
120     Status as = a_->GetFileSize(f, &asize);  in GetFileSize()
121     Status bs = b_->GetFileSize(f, &bsize);  in GetFileSize()
128   Status GetFileModificationTime(const std::string& fname,  in GetFileModificationTime()
131     Status as = a_->GetFileModificationTime(fname, &amtime);  in GetFileModificationTime()
132     Status bs = b_->GetFileModificationTime(fname, &bmtime);  in GetFileModificationTime()
139   Status RenameFile(const std::string& s, const std::string& t) override {  in RenameFile()
140     Status as = a_->RenameFile(s, t);  in RenameFile()
141     Status bs = b_->RenameFile(s, t);  in RenameFile()
146   Status LinkFile(const std::string& s, const std::string& t) override {  in LinkFile()
147     Status as = a_->LinkFile(s, t);  in LinkFile()
148     Status bs = b_->LinkFile(s, t);  in LinkFile()
159   Status LockFile(const std::string& f, FileLock** l) override {  in LockFile()
161     Status as = a_->LockFile(f, &al);  in LockFile()
162     Status bs = b_->LockFile(f, &bl);  in LockFile()
168   Status UnlockFile(FileLock* l) override {  in UnlockFile()
170     Status as = a_->UnlockFile(ml->a_);  in UnlockFile()
171     Status bs = b_->UnlockFile(ml->b_);  in UnlockFile()