rem: lookup_vnode(fs_id fsid, vnode_id vnid)
add: lookup_vnode(fs_id fsID, vnode_id vnodeID)
context: lookup_vnode(fs_id fsid, vnode_id vnid){	struct vnode_hash_key key;	key.fsid = fsid;	key.vnid = vnid;	return hash_lookup(vnode_table, &key);}