I have a question about the Virtual File System:

Are there situations when the dentry cache is used for NEGATIVE ANSWERS when performing a lookup for a directory entry?
-------- or, equivalently ----------
Are there cases, that the filesystem figures out that when no directory entry with a given name is found in the dentry cache then no such entry exists at all (so that ENOENT is returned without performing real_lookup)?

Theoretically, a directory node can be "fully cached" (after a complete readdir) so that name non-existence can be fully determined by the cache.