### Dentry cache
	
	    dir SWHID → directory entries
	
	The dentry (directory entry) cache map SWHIDs of type `dir` to the directory
	entries they contain. Each entry comes with its name as well as file attributes
	(i.e., all its needed to perform a detailed directory listing).
	
	Additional attributes of each directory entry should be looked up on a entry by
	entry basis, possibly hitting the metadata cache.
	
	The dentry cache for a given dir is populated, at the latest, when the content
	of the directory is listed. More aggressive prefetching might happen. For
	instance, when first opening a dir a recursive listing of it can be retrieved
	from the remote backend and used to recursively populate the dentry cache for
	all (transitive) sub-directories.