d_drop -- drop a dentry
(struct dentry * dentry);
d_drop unhashes the entry from the parent
dentry hashes, so that it won't be found through
a VFS lookup any more. Note that this is different
from deleting the dentry - d_delete will try to
mark the dentry negative if possible, giving a
successful _negative_ lookup, while d_drop will
just make the cache lookup fail.
d_drop is used mainly for stuff that wants
to invalidate a dentry for some reason (NFS
timeouts or autofs deletes).