fh_lock, fh_unlock: toggle fh_locked, get the inode semaphore,
set some attributes (fh_pre_* for fh_lock, fh_post_* for fh_unlock).

fh_locked called in:
	nfsd_lookup, iff not looking up up "." or "..".
	...

fh_unlocked called in:
	do_open_lookup, iff not doing a create, called after nfsd_lookup,
		after nfsd_lookup, iff not doing a create.  I suppose
		do_open_lookup shouldn't be called on directories, hence
		not on dotents, so the unlocks should match up.
	fh_put, if fh_dentry:
	...