Provided by:
linux-doc-2.6.15_2.6.15-23.39_all 
NAME
__d_drop - drop a dentry
SYNOPSIS
void __d_drop (struct dentry * dentry);
ARGUMENTS
dentry dentry to drop
DESCRIPTION
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).
__d_drop requires dentry->d_lock.