To find the VFS inode of a file in the Virtual File System, VFS must resolve the name a directory at a time, looking up the VFS inode representing each of the intermediate directories in the name. Each directory lookup involves calling the file system specific lookup whose address is held in the VFS inode representing the parent directory. This works because we always have the VFS inode of the root of each file system available and pointed at by the VFS superblock for that system. Each time an inode is looked up by the real file system it checks the directory cache for the directory. If there is no entry in the directory cache, the real file system gets the VFS inode either from the underlying file system or from the inode cache.