rem: key.fsid = fsid; key.vnid = vnid;
add: key.fs_id = fsID; key.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);}